Plant Gum Exudates of the World: Sources, Distribution, Properties, and Applications

PLANT GUM EXUDATES OF THE WORLD Sources, Distribution, Properties, and Applications

PLANT GUM EXUDATES OF THE WORLD Sources, Distribution, Properties, and Applications

Amos Nussinovitch

Boca Raton London New York

CRC Press is an imprint of the Taylor & Francis Group, an informa business

CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2010 by Taylor and Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works Printed in the United States of America on acid-free paper 10 9 8 7 6 5 4 3 2 1 International Standard Book Number: 978-1-4200-5223-7 (Hardback) This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint. Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www.copyright.com (http:// www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Library of Congress Cataloging-in-Publication Data Nussinovitch, A. Plant gum exudates of the world : sources, distribution, properties, and applications / Amos Nussinovitch. p. cm. Includes bibliographical references and index. ISBN 978-1-4200-5223-7 (hardcover : alk. paper) 1. Gums and resins. I. Title. TP978.N874 2010 668’.37--dc22 Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com

2009031459

In fond memory of my classmates from the “Ohel Shem” secondary school in Ramat Gan— Mordechai (Moti) Korb, Jacob (Jack) Sofer, and Mordechai Geller—who died at a tragically young age in the Yom Kippur War and never got the opportunity to live out their dreams

Contents Preface .......................................................................................................................................xix Acknowledgments....................................................................................................................xxiii The Author ..............................................................................................................................xxv

1.

Role and Sources of Exudate Gums ................................................................................. 1 1.1 Introduction............................................................................................................. 1 1.2 Definitions............................................................................................................... 3 1.3 Gum Yields .............................................................................................................. 8 1.4 Agricultural Issues ................................................................................................... 9 1.5 Physical Properties of Gums................................................................................... 12 1.5.1 Color......................................................................................................... 12 1.5.2 Size and shape ...........................................................................................13 1.5.3 Taste and smell...........................................................................................14 1.5.4 Hardness and density.................................................................................15 1.5.5 Polarization ................................................................................................16 1.5.6 Solubility....................................................................................................16 1.5.7 Viscosity and mouthfeel.............................................................................17 1.6 Chemical Properties................................................................................................19 1.7 Commercial Assessments of Gums..........................................................................19 1.8 Industrial and Other Uses.......................................................................................19 References ........................................................................................................................ 20

2.

Physiological Aspects of Polysaccharide Formation in Plants..................................... 23 2.1 Introduction........................................................................................................... 23 2.2 Stress Factors, Ethylene and Gummosis ................................................................. 23 2.3 Borers and Gum Formation ................................................................................... 30 2.4 Gum Ducts.............................................................................................................31 2.5 Gummosis in Fruit Trees . ..................................................................................... 32 2.6 Induced Inoculation and Gum Yield...................................................................... 34 References..........................................................................................................................35

3.

Major Plant Exudates of the World .............................................................................. 39 3.1 Introduction........................................................................................................... 39 3.2 Gum Arabic and Other Acacia Gums .................................................................... 39 vii

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3.3

3.2.1 Acacia Fabaceae (subfamily: Mimosoideae)........................................... 39 3.2.1.1 Taxon: Acacia senegal (L.) Willd ................................................ 39 3.2.1.2 Taxon: Acacia seyal Delile.......................................................... 42 3.2.1.3 Taxon: Acacia abyssinica Hochst. ex Benth. subsp. calophylla Brenan....................................................................... 43 3.2.1.4 Taxon: Acacia bakeri Maiden..................................................... 43 3.2.1.5 Taxon: Acacia benthamii Meisn ................................................. 43 3.2.1.6 Taxon: Acacia binervata DC...................................................... 43 3.2.1.7 Taxon: Acacia catechu (L. f.) Willd. ........................................... 43 3.2.1.8 Taxon: Acacia dealbata Link ......................................................45 3.2.1.9 Taxon: Acacia decurrens Willd....................................................45 3.2.1.10 Taxon: Acacia drepanolobium Harms ex Y. Sjöstedt................... 46 3.2.1.11 Taxon: Acacia elata A. Cunn. ex Benth. .................................... 46 3.2.1.12 Taxon: Acacia farnesiana (L.) Willd........................................... 46 3.2.1.13 Taxon: Acacia ferruginea DC......................................................47 3.2.1.14 Taxon: Acacia harpophylla F. Muell. ex Benth.............................47 3.2.1.15 Taxon: Acacia jacquemontii Benth. ............................................47 3.2.1.16 Taxon: Acacia karroo Hayne.......................................................47 3.2.1.17 Taxon: Acacia kirkii Oliv............................................................47 3.2.1.18 Taxon: Acacia laeta R. Br. ex Benth........................................... 48 3.2.1.19 Taxon: Acacia leiophylla Benth. . ............................................... 48 3.2.1.20 Taxon: Acacia leucophloea (Roxb.) Willd.................................... 48 3.2.1.21 Taxon: Acacia maidenii F. Muell................................................ 49 3.2.1.22 Taxon: Acacia mellifera (Vahl) Benth......................................... 49 3.2.1.23 Taxon: Acacia modesta Wall....................................................... 49 3.2.1.24 Taxon: Acacia oerfota (Forssk.) Schweinf.................................... 49 3.2.1.25 Taxon: Acacia oswaldii F. Muell................................................. 50 3.2.1.26 Taxon: Acacia pendula A. Cunn. ex G. Don.............................. 50 3.2.1.27 Taxon: Acacia penninervis Sieber ex DC. ................................... 50 3.2.1.28 Taxon: Acacia pycnantha Benth. .................................................51 3.2.1.29 Taxon: Acacia retinodes Schltdl...................................................51 3.2.1.30 Taxon: Acacia salicina Lindl........................................................51 3.2.1.31 Taxon: Acacia sieberiana DC......................................................51 3.2.1.32 Taxon: Acacia stuhlmanii Taub...................................................51 3.2.1.33 Taxon: Acacia verniciflua A. Cunn  .. ..........................................52 3.2.1.34 Taxon: Acacia xanthophloea Benth..............................................52 3.2.2 Faidherbia Fabaceae (subfamily: Mimosoideae) . ....................................52 3.2.2.1 Taxon: Faidherbia albida (Delile) A. Chev..................................52 Gum Tragacanth and Similar Gums.......................................................................52 3.3.1 Astragalus Fabaceae (subfamily: Faboideae) . .........................................52 3.3.1.1 Taxon: Astragalus gummifer Labill. .........................................52 3.3.1.2 Taxon: Astragalus brachycalyx Fisch ............................................55 3.3.1.3 Taxon: Astragalus heratensis Bunge ........................................... 56 3.3.1.4 Taxon: Astragalus kurdicus Boiss................................................ 56 3.3.1.5 Taxon: Astragalus microcephalus Willd. ......................................57 3.3.1.6 Taxon: Astragalus verus Olivier ..................................................57

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3.4

3.3.2 Sterculia Malvaceae (subfamily: Sterculioideae)..................................57 3.3.2.1 Taxon: Sterculia urens Roxb........................................................57 3.3.2.2 Taxon: Sterculia foetida L. ......................................................... 60 3.3.2.3 Taxon: Sterculia guttata Roxb.....................................................61 3.3.2.4 Taxon: Sterculia quadrifida R. Br. ............................................. 62 3.3.2.5 Taxon: Sterculia scaphigera Wall. ............................................... 62 3.3.2.6 Taxon: Sterculia setigera Delile .................................................. 63 3.3.2.7 Taxon: Sterculia tragacantha Lindl. ........................................... 64 3.3.2.8 Taxon: Sterculia villosa Roxb. .................................................... 64 3.3.3 Brachychiton Malvaceae (subfamily: Sterculioideae)........................... 64 3.3.3.1 Taxon: Brachychiton acerifolius (A. Cunn. ex G. Don) Macarthur................................................................................. 64 3.3.4 Firmiana Malvaceae (subfamily: Sterculioideae) . ..............................65 3.3.4.1 Taxon: Firmiana simplex (L.) W. Wight .....................................65 3.3.5 Hildegardia Malvaceae (subfamily: Sterculioideae) ............................65 3.3.5.1 Taxon: Hildegardia barteri (Mast.) Kosterm ..............................65 3.3.6 Cochlospermum Bixaceae ..........................................................................65 3.3.6.1 Taxon: Cochlospermum religiosum (L.) Alston.............................65 Important Indian or Asiatic Gums and Their Botanical Sources............................ 66 3.4.1 Aegle Rutaceae (subfamily: Aurantioideae) ........................................ 66 3.4.1.1 Taxon: Aegle marmelos (L.) Corrêa . .......................................... 66 3.4.2 Albizia Fabaceae (subfamily: Mimosoideae) . ....................................... 68 3.4.2.1 Taxon: Albizia lebbeck (L.) Benth. ........................................... 68 3.4.2.2 Taxon: Albizia odoratissima (L. f.) Benth................................... 69 3.4.2.3 Taxon: Albizia procera (Roxb.) Benth. ..................................... 69 3.4.2.4 Taxon: Albizia chinensis (Osbeck) Merr..................................... 71 3.4.2.5 Taxon: Albizia amara (Roxb.) Boivin . ..................................... 72 3.4.3 Aleurites Euphorbiaceae (subfamily: Crotonoideae) .......................... 73 3.4.3.1 Taxon: Aleurites moluccanus (L.) Willd...................................... 73 3.4.4 Anogeissus Combretaceae .........................................................................76 3.4.4.1 Taxon: Anogeissus latifolia (Roxb. ex DC.) Wall. ex Guill. & Perr.................................................................76 3.4.5 Bauhinia Fabaceae (subfamily: Caesalpinioideae) .............................. 79 3.4.5.1 Taxon: Bauhinia purpurea L...................................................... 79 3.4.5.2 Taxon: Bauhinia roxburghiana Voigt ......................................... 80 3.4.5.3 Taxon: Bauhinia variegata L.......................................................81 3.4.6 Buchanania Anacardiaceae .................................................................... 82 3.4.6.1 Taxon: Buchanania lanzan Spreng............................................. 82 3.4.6.2 Taxon: Buchanania latifolia Roxb.............................................. 82 3.4.7 Toona Meliaceae .................................................................................... 83 3.4.7.1 Taxon: Toona ciliata M. Roem. ................................................. 83 3.4.8 Chloroxylon Rutaceae .............................................................................. 84 3.4.8.1 Taxon: Chloroxylon swietenia DC.............................................. 84 3.4.9 Delonix Fabaceae (subfamily: Caesalpinioideae) ................................ 84 3.4.9.1 Taxon: Delonix regia (Bojer ex Hook.) Raf................................ 84 3.4.10 Elaeodendron Celastraceae (subfamily: Celastroideae)..................... 86 3.4.10.1 Taxon: Elaeodendron glaucum (Rottb.) Pers............................... 86

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3.5

3.4.11 Limonia Rutaceae (subfamily: Aurantioideae) ................................... 89 3.4.11.1 Taxon: Limonia acidissima L...................................................... 89 3.4.12 Mangifera Anacardiaceae ...................................................................... 90 3.4.12.1 Taxon: Mangifera indica L......................................................... 90 3.4.13 Azadirachta Meliaceae ........................................................................... 93 3.4.13.1 Taxon: Azadirachta indica A. Juss.............................................. 93 3.4.14 Prosopis Fabaceae (subfamily: Mimosoideae) . ...................................... 95 3.4.14.1 Taxon: Prosopis cineraria (L.) Druce.......................................... 95 3.4.14.2 Taxon: Prosopis juliflora (Sw.) DC. ............................................ 95 3.4.15 Sesbania Fabaceae (subfamily: Faboideae) ............................................ 98 3.4.15.1 Taxon: Sesbania grandiflora (L.) Pers. ........................................ 98 3.4.16 Spondias Anacardiaceae ........................................................................ 98 3.4.16.1 Taxon: Spondias dulcis Sol. ex Parkinson ................................... 98 3.4.16.2 Taxon: Spondias pinnata (J. Koenig ex L. f.) Kurz ................... 100 3.4.17 Terminalia Combretaceae......................................................................101 3.4.17.1 Taxon: Terminalia bellirica (Gaertn.) Roxb. . ...........................101 Gums of The New World .....................................................................................104 3.5.1 Anacardium Anacardiaceae ..................................................................104 3.5.1.1 Taxon: Anacardium humile A. St.-Hil.......................................104 3.5.1.2 Taxon: Anacardium nanum A. St.-Hil. .....................................104 3.5.1.3 Taxon: Anacardium occidentale L. ...........................................104 3.5.2 Anadenanthera Fabaceae (subfamily: Mimosoideae) ...........................105 3.5.2.1 Taxon: Anadenanthera colubrina (Vell.) Brenan var. cebil (Griseb.) Altschul .....................................................................105 3.5.2.2 Taxon: Anadenanthera colubrina (Vell.) Brenan var. colubrina ..................................................................................106 3.5.3 Caesalpinia Fabaceae (subfamily: Caesalpinioideae) ..........................106 3.5.3.1 Taxon: Caesalpinia coriaria (Jacq.) Willd..................................106 3.5.4 Parkinsonia Fabaceae (subfamily: Caesalpinioideae) .........................107 3.5.4.1 Taxon: Parkinsonia praecox (Ruiz & Pav.) J. A. Hawkins subsp. praecox ...........................................................................107 3.5.5 Parapiptadenia Fabaceae (subfamily: Mimosoideae)...........................108 3.5.5.1 Taxon: Parapiptadenia rigida (Benth.) Brenan .........................108 3.5.6 Puya Bromeliaceae ................................................................................108 3.5.6.1 Taxon: Puya chilensis Molina....................................................108 3.5.7 Theobroma Malvaceae (subfamily: Byttnerioideae) ..........................110 3.5.7.1 Taxon: Theobroma cacao L........................................................110 3.5.8 Laguncularia Combretaceae ..................................................................110 3.5.8.1 Taxon: Laguncularia racemosa (L.) C. F. Gaertn.......................110 3.5.9 Pithecellobium Fabaceae (subfamily: Mimosoideae) ............................ 111 3.5.9.1 Taxon: Pithecellobium dulce (Roxb.) Benth............................... 111 3.5.10 Samanea Fabaceae (subfamily: Mimosoideae) ..................................... 111 3.5.10.1 Taxon: Samanea saman (Jacq.) Merr......................................... 111 3.5.11 Enterolobium Fabaceae (subfamily: Mimosoideae) ..............................113 3.5.11.1 Taxon: Enterolobium cyclocarpum (Jacq.) Griseb.......................113 3.5.12 Chloroleucon Fabaceae (subfamily: Mimosoideae) ............................... 115 3.5.12.1 Taxon: Chloroleucon mangense (Jacq.) Britton & Rose.............. 115

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3.6

3.5.13 Leucaena Fabaceae (subfamily: Mimosoideae) .................................... 115 3.5.13.1 Taxon: Leucaena collinsii Britton & Rose . ............................... 115 3.5.14 Lysiloma Fabaceae (subfamily: Mimosoideae).......................................116 3.5.14.1 Taxon: Lysiloma acapulcense (Kunth) Benth..............................116 3.5.15 Inga Fabaceae (subfamily: Mimosoideae) ............................................116 3.5.15.1 Taxon: Inga stipularis DC.........................................................116 3.5.16 Rhizophora Rhizophoraceae .................................................................117 3.5.16.1 Taxon: Rhizophora mangle L. ...................................................117 3.5.17 Melicoccus Sapindaceae (subfamily: Sapindoideae) .............................117 3.5.17.1 Taxon: Melicoccus bijugatus Jacq...............................................117 3.5.18 Ceiba Malvaceae (subfamily: Bombacoideae)......................................118 3.5.18.1 Taxon: Ceiba speciosa (A. St.-Hil.) Ravenna..............................118 3.5.19 Thespesia Malvaceae (subfamily: Malvoideae).....................................118 3.5.19.1 Taxon: Thespesia populnea (L.) Sol. ex Corrêa ..........................118 3.5.20 Cylindropuntia Cactaceae (subfamily: Opuntioideae) ....................... 120 3.5.20.1 Taxon: Cylindropuntia fulgida (Engelm.) F. M. Knuth............ 120 3.5.21 Manilkara Sapotaceae ...........................................................................121 3.5.21.1 Taxon: Manilkara zapota (L.) P. Royen ....................................121 3.5.22 Larix Pinaceae....................................................................................... 122 3.5.22.1 Taxon: Larix occidentalis Nutt................................................. 122 Miscellaneous Asiatic, African, and Australian Gums.......................................... 123 3.6.1 Actinidia Actinidiaceae  ....................................................................... 123 3.6.1.1 Taxon: Actinidia deliciosa (A. Chev.) C. F. Liang & A. R. Ferguson .................................................................... 123 3.6.2 Araucaria Araucariaceae...................................................................... 123 3.6.2.1 Taxon: Araucaria heterophylla (Salisb.) Franco......................... 123 3.6.3 Balanites Zygophyllaceae (subfamily: Tribuloideae).........................125 3.6.3.1 Taxon: Balanites aegyptiacus (L.) Delile ..................................125 3.6.4 Brabejum Proteaceae ................................................................................125 3.6.4.1 Taxon: Brabejum stellatifolium L.................................................125 3.6.5 Butea Fabaceae (subfamily: Faboideae) .............................................. 126 3.6.5.1 Taxon: Butea monosperma (Lam.) Taub................................... 126 3.6.6 Cercis Fabaceae (subfamily: Caesalpinioideae) . ............................... 127 3.6.6.1 Taxon: Cercis siliquastrum L.................................................... 127 3.6.7 Cissus Vitaceae ...................................................................................... 127 3.6.7.1 Taxon: Cissus populnea Guill. & Perr. ..................................... 127 3.6.8 Commiphora Burseraceae .....................................................................129 3.6.8.1 Taxon: Commiphora mollis (Oliv) Engl. ...................................129 3.6.9 Diospyros Ebenaceae . ............................................................................ 130 3.6.9.1 Taxon: Diospyros mespiliformis Hochst. ex A. DC......................... 130 3.6.10 Dicorynia Fabaceae (subfamily: Caesalpinioideae) ........................... 130 3.6.10.1 Taxon: Dicorynia paraensis Benth............................................... 130 3.6.11 Entandrophragma Meliaceae ................................................................ 130 3.6.11.1 Taxon: Entandrophragma angolense (Welw.) C. DC................. 130 3.6.12 Fagarta Rutaceae......................................................................................131 3.6.12.1 Taxon: Zanthoxylum zanthoxyloides (Lam.) Zepern. & Timler .................................................................................131

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3.6.13 Ferula Apiaceae.......................................................................................131 3.6.13.1 Taxon: Ferula foetida (Bunge) Regel.........................................131 3.6.14 Grevillea Proteaceae .............................................................................132 3.6.14.1 Taxon: Grevillea robusta A. Cunn. ex R. Br..............................132 3.6.15 Lophira Ochnaceae ...............................................................................133 3.6.15.1 Taxon: Lophira alata Banks ex C. F. Gaertn.............................133 3.6.16 Madhuca Sapotaceae ............................................................................ 134 3.6.16.1 Taxon: Madhuca longifolia (L.) J. F. Macbr.............................. 134 3.6.17 Millettia Fabaceae (subfamily: Faboideae)........................................... 134 3.6.17.1 Taxon: Millettia pinnata (L.) Panigrahi................................... 134 3.6.18 Mystroxylon Celastraceae (subfamily: Celastroideae).......................135 3.6.18.1 Taxon: Mystroxylon aethiopicum (Thunb.) Loes.........................135 3.6.19 Parkia Fabaceae (subfamily: Mimosoideae) ....................................... 136 3.6.19.1 Taxon: Parkia bicolor A. Chev. ................................................ 136 3.6.20 Pereskia Cactaceae (subfamily: Pereskioideae).................................. 136 3.6.20.1 Taxon: Pereskia guamacho F.A.C. Weber ................................. 136 3.6.21 Phormium Hemerocallidaceae............................................................ 136 3.6.21.1 Taxon: Phormium tenax J. R. Forst. & G. Forst....................... 136 3.6.22 Piptadeniastrum Fabaceae (subfamily: Mimosoideae)...........................137 3.6.22.1 Taxon: Piptadeniastrum africanum (Hook. f.) Brenan...............137 3.6.23 Pittosporum Pittosporaceae...................................................................137 3.6.23.1 Taxon: Pittosporum phillyreoides DC.........................................137 3.6.24 Polyscias Araliaceae (subfamily: Aralioideae) ...................................137 3.6.24.1 Taxon: Polyscias sambucifolia (Sieber ex DC.) Harms................137 3.6.24.2 Taxon: Prunus avium (L.) L........................................................138 3.6.25 Prunus Rosaceae (subfamily: Spiraeoideae) . ......................................140 3.6.25.1 Taxon: Prunus armeniaca L. ....................................................140 3.6.25.2 Taxon: Prunus domestica L. subsp. domestica ...........................141 3.6.25.3 Taxon: Prunus persica (L.) Batsch var. persica...........................143 3.6.25.4 Taxon: Prunus spinosa L............................................................143 3.6.26 Pterocarpus Fabaceae (subfamily: Faboideae)........................................144 3.6.26.1 Taxon: Pterocarpus marsupium Roxb.........................................144 3.6.27 Sapindus Sapindaceae (subfamily: Sapindoideae) ...............................145 3.6.27.1 Taxon: Sapindus trifoliatus L.....................................................145 3.6.28 Stangeria Zamiaceae  ..............................................................................145 3.6.28.1 Taxon: Stangeria eriopus (Kunze) Baill. ....................................145 3.6.29 Symphonia Clusiaceae............................................................................146 3.6.29.1 Taxon: Symphonia globulifera L. f. ............................................146 3.6.30 Talisia Sapindaceae (subfamily: Sapindoideae) . .................................147 3.6.30.1 Taxon: Talisia oliviformis (Kunth) Radlk..................................147 3.6.30.2 Taxon: Watsonia versfeldii J. W. Mathews & L. Bolus ..............147 3.6.31 Welwitschia Welwitschiaceae ..............................................................148 3.6.31.1 Taxon: Welwitschia mirabilis Hook. f........................................148 3.6.32 Ziziphus Rhamnaceae.............................................................................148 3.6.32.1 Taxon: Ziziphus jujuba Mill......................................................148 References........................................................................................................................149

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4.

Minor Plant Exudates of the World .......................................................................... 163 4.1 Introduction..........................................................................................................163 4.2 Adansonia Malvaceae (subfamily: Bombacoideae)............................................163 4.2.1 Taxon: Adansonia digitata L. ...................................................................163 4.3 Adenanthera Fabaceae (subfamily: Mimosoideae).............................................168 4.3.1 Taxon: Adenanthera pavonina L. . ............................................................168 4.4 Afzelia Fabaceae (subfamily: Caesalpinioideae)...............................................170 4.4.1 Taxon: Afzelia africana Sm. ex Pers. ........................................................170 4.5 Albizia Fabaceae .................................................................................................172 4.6 Anogeissus Combretaceae ....................................................................................173 4.6.1 Taxon: Anogeissus leiocarpus (DC.) Guill. & Perr. ....................................173 4.7 Atalaya Sapindaceae (subfamily: Sapindoideae)...............................................174 4.7.1 Taxon: Atalaya hemiglauca (F. Muell.) F. Muell. ex Benth. ......................174 4.8 Balsamocitrus Rutaceae (subfamily: Aurantioideae)........................................174 4.8.1 Taxon: Balsamocitrus dawei Stapf ............................................................174 4.9 Bauhinia Fabaceae...............................................................................................175 4.9.1 Taxon: Bauhinia carronii F. Muell............................................................175 4.9.2 Taxon: Bauhinia thonningii Schumach. & Thonn. ..................................175 4.9.3 Taxon: Tylosema fassoglense (Kotschy ex Schweinf.) Torre & Hillc............176 4.10 Julbernardia Fabaceae (subfamily: Caesalpinioideae)......................................176 4.10.1 Taxon: Julbernardia globiflora (Benth.) Troupin.......................................176 4.11 Bombax Malvaceae (subfamily: Bombacoideae)...............................................177 4.11.1 Taxon: Bombax ceiba L. ...........................................................................177 4.11.2 Taxon: Bombax insigne Wall. ...................................................................180 4.12 Borassus Arecaceae (subfamily: Coryphoideae) ...............................................180 4.12.1 Taxon: Borassus flabellifer L. ....................................................................180 4.13 Bosistoa Rutaceae (subfamily: Toddalioideae) .................................................181 4.13.1 Taxon: Bosistoa pentacocca (F. Muell.) Bail. ..............................................181 4.14 Brachystegia Fabaceae (subfamily: Caesalpinioideae).......................................181 4.14.1 Taxon: Brachystegia spiciformis Benth. . ....................................................181 4.15 Burkea Fabaceae (subfamily: Caesalpinioideae)...............................................183 4.15.1 Taxon: Burkea africana Hook. .................................................................183 4.16 Capparis Capparaceae..........................................................................................184 4.16.1 Taxon: Capparis nobilis (Endl.) F. Muell. ex Benth...................................184 4.17 Careya Lecythidaceae (subfamily: Planchonioideae).....................................185 4.17.1 Taxon: Careya arborea Roxb. ...................................................................185 4.18 Cassia Fabaceae (subfamily: Caesalpinioideae)................................................186 4.18.1 Taxon: Cassia fistula L. ............................................................................186 4.18.2 Taxon: Cassia sieberiana DC.....................................................................187 4.19 Cedrela Meliaceae ..............................................................................................189 4.19.1 Taxon: Cedrela odorata L. ........................................................................189 4.20 Ceiba Malvaceae (subfamily: Bombacoideae)...................................................190 4.20.1 Taxon: Ceiba pentandra (L.) Gaertn.........................................................190 4.21 Ceratopetalum Cunoniaceae ...............................................................................190 4.21.1 Taxon: Ceratopetalum apetalum D. Don...................................................190 4.21.2 Taxon: Ceratopetalum gummiferum Sm. . .................................................191

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4.22 Chukrasia Meliaceae...........................................................................................191 4.22.1 Taxon: Chukrasia tabularis A. Juss............................................................191 4.23 Citrus Rutaceae........................................................................................................ 193 4.24 Cocos Arecaceae (subfamily: Arecoideae) ........................................................195 4.24.1 Taxon: Cocos nucifera L. ..........................................................................195 4.25 Cola Sterculiaceae.............................................................................................197 4.25.1 Taxon: Cola cordifolia (Cav.) R. Br. . ........................................................197 4.26 Combretum Combretaceae . ...............................................................................198 4.27 Cordia Boraginaceae (subfamily: Cordioideae)............................................. 200 4.27.1 Taxon: Cordia myxa L. ........................................................................... 200 4.28 Cordyla Fabaceae (subfamily: Faboideae)..........................................................201 4.28.1 Taxon: Cordyla africana Lour. .................................................................201 4.29 Corypha Arecaceae (subfamily: Coryphoideae).............................................. 202 4.29.1 Taxon: Corypha utan Lam. ..................................................................... 202 4.30 Crataeva Capparaceae........................................................................................ 202 4.30.1 Taxon: Crataeva adansonii DC. .............................................................. 202 4.31 Cussonia Araliaceae........................................................................................... 204 4.31.1 Taxon: Cussonia arborea Hochst. ex A. Rich. . ........................................ 204 4.32 Cycas Cycadaceae............................................................................................... 204 4.32.1 Taxon: Cycas lane-poolei C. A. Gardner .................................................. 204 4.32.2 Taxon: Cycas circinalis L......................................................................... 204 4.33 Dichrostachys Fabaceae (subfamily: Mimosoideae)........................................... 207 4.33.1 Taxon: Dichrostachys cinerea (L.) Wight & Arn. . .................................... 207 4.34 Echinocarpus Elaeocarpaceae ........................................................................... 208 4.34.1 Taxon: Echinocarpus australis Benth. (now synonym of sloanea australis F. Muell., see section 4.6.2.2)............ 208 4.35 Elaeocarpus Elaeocarpaceae.............................................................................. 208 4.35.1 Taxon: Elaeocarpus grandis F. Muell. ....................................................... 208 4.35.2 Taxon: Elaeocarpus obovatus G. Don ....................................................... 208 4.35.3 Taxon: Elaeocarpus reticulatus Sm............................................................ 208 4.36 Encephalartos Zamiaceae..................................................................................... 208 4.36.1 Taxon: Encephalartos hildebrandtii A. Braun & C. D. Bouché................. 208 4.37 Entada Fabaceae (subfamily: Mimosoideae)..................................................... 209 4.37.1 Taxon: Entada africana Guill. & Perr...................................................... 209 4.38 Erythrophleum Fabaceae (subfamily: Caesalpinioideae).................................. 209 4.38.1 Taxon: Erythrophleum africanum (Welw. ex Benth.) Harms ................... 209 4.39 Flindersia Rutaceae .............................................................................................210 4.39.1 Taxon: Flindersia maculosa (Lindl.) F. Muell. ..........................................210 4.39.2 Taxon: Flindersia australis R. Br. ..............................................................211 4.40 Garuga Burseraceae ...........................................................................................211 4.40.1 Taxon: Garuga pinnata Roxb. ..................................................................211 4.41 Geijera Rutaceae . ...............................................................................................212 4.41.1 Taxon: Geijera paniculata (F. Muell.) Druce.............................................212 4.42 Geodorum Orchidaceae......................................................................................212 4.42.1 Taxon: Geodorum nutans (C. Presl) Ames ................................................212 4.43 Hakea Proteaceae..............................................................................................213 4.43.1 Taxon: Hakea gibbosa (Sm.) Cav. . ............................................................213

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4.44 Khaya Meliaceae.................................................................................................214 4.44.1 Taxon: Khaya grandifoliola C. DC. ..........................................................214 4.44.2 Taxon: Khaya madagascariensis Jum. & H. Perrier....................................214 4.44.3 Taxon: Khaya senegalensis (Desr.) A. Juss. .................................................214 4.45 Lagerstroemia Lythraceae ...................................................................................217 4.45.1 Taxon: Lagerstroemia parviflora Roxb. . ....................................................217 4.46 Lannea Anacardiaceae .......................................................................................219 4.46.1 Taxon: Lannea coromandelica (Houtt.) Merr. ...........................................219 4.47 Macrozamia Zamiaceae .......................................................................................221 4.47.1 Taxon: Macrozamia spiralis (Salisb.) Miq..................................................221 4.48 Melia Meliaceae .................................................................................................221 4.48.1 Taxon: Melia azedarach L. .......................................................................221 4.49 Melicope Rutaceae ............................................................................................. 224 4.49.1 Taxon: Bouchardatia neurococca (F. Muell.) ............................................ 224 4.50 Moringa Moringaceae . ..................................................................................... 225 4.50.1 Taxon: Moringa oleifera Lam. ................................................................. 225 4.51 Owenia Meliaceae.............................................................................................. 228 4.51.1 Taxon: Owenia venosa F. Muell. ............................................................. 228 4.52 Panax (Tieghemopanax) Araliaceae ................................................................... 228 4.52.1 Taxon: Polyscias elegans (C. Moore & F. Muell.) Harms .......................... 228 4.52.2 Taxon: Neopanax colensoi (Hook. f.) Allan .............................................. 228 4.53 Saltera Penaeaceae ............................................................................................ 228 4.53.1 Taxon: Saltera sarcocolla (L.) Bullock . .................................................... 228 4.54 Pentaceras Rutaceae ........................................................................................... 229 4.54.1 Taxon: Pentaceras australis (F. Muell.) Benth .......................................... 229 4.55 Prunus Rosaceae................................................................................................. 229 4.55.1 Taxon: Prunus dulcis (Mill.) D. A. Webb ................................................ 229 4.56 Pseudocedrela Meliaceae..................................................................................... 230 4.56.1 Taxon: Pseudocedrela kotschyi (Schweinf.) Harms. . ................................. 230 4.57 Saccopetalum Annonaceae...................................................................................231 4.57.1 Taxon: Miliusa tomentosa (Roxb.) J. Sinclaiv.............................................231 4.58 Sarcostemma Asclepiadaceae . ............................................................................231 4.58.1 Taxon: Sarcostemma brevistigma Wight & Arn.........................................231 4.59 Schefflera Araliaceae................................................................................................ 231 4.59.1 Taxon: Schefflera volkensii Harms................................................................. 231 4.60 Sclerocarya Anacardiaceae................................................................................. 232 4.60.1 Taxon: Sclerocarya birrea (A. Rich.) Hochst. ........................................... 232 4.61 Semecarpus Anacardiaceae .................................................................................233 4.61.1 Taxon: Semecarpus anacardium L. f. ........................................................233 4.62 Sloanea Elaeocarpaceae .................................................................................... 234 4.62.1 Taxon: Sloanea woollsii F. Muell.............................................................. 234 4.62.2 Taxon: Sloanea australis F. Muell. . .............................................................234 4.63 Soymida Meliaceae .............................................................................................235 4.63.1 Taxon: Soymida febrifuga (Roxb.) A. Juss. ................................................235 4.64 Tamarindus Fabaceae (subfamily: Caesalpinioideae)...................................... 236 4.64.1 Taxon: Tamarindus indica L. .................................................................. 236

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4.65 Heritiera Malvaceae ........................................................................................... 238 4.65.1 Taxon: Heritiera trifoliolata (F. Muell.) Kosterm. . .................................. 238 4.66 Terminalia Combretaceae ................................................................................. 238 4.67 Thevetia Apocynaceae . ............................................................................................ 245 4.67.1 Taxon: Thevetia peruviana (Pers.) K. Schum. ...........................................245 4.68 Virgilia Fabaceae (subfamily: Faboideae) ......................................................... 246 4.68.1 Taxon: Virgilia oroboides (P. J. Bergius) T. M. Salter ............................... 246 References........................................................................................................................247

5.

Food Applications of Plant Exudates........................................................................ 257 5.1 Introduction..........................................................................................................257 5.2 Food Uses of Gum Exudates.................................................................................258 5.2.1 Confectionery...........................................................................................258 5.2.2 Salad dressings and sauces........................................................................261 5.2.3 Frozen products....................................................................................... 262 5.2.3.1 Frozen dough .......................................................................... 263 5.2.3.2 Frozen sugar solutions ............................................................ 263 5.2.3.3 Frozen dairy products, ice pops and sherbets........................... 264 5.2.4 Spray-drying ........................................................................................... 264 5.2.4.1 Spray-drying of juices.............................................................. 264 5.2.4.2 Miscellaneous spray-dried products......................................... 266 5.2.4.3 Encapsulation via spray-drying.................................................267 5.2.5 Drum-drying ...........................................................................................267 5.2.6 Wine ....................................................................................................... 268 5.2.7 Adhesives................................................................................................. 269 5.2.8 Bakery products ...................................................................................... 269 5.2.9 Flavor fixatives and emulsifiers................................................................ 269 5.2.10 Beverages..................................................................................................270 5.2.11 Meat products ..........................................................................................270 5.2.12 Miscellaneous...........................................................................................270 5.2.13 Microencapsulation .................................................................................271 5.2.13.1 Oleoresins ................................................................................271 5.2.13.2 Linoleic acid microencapsulation .............................................274 5.2.13.3 Procyanidins ............................................................................275 5.2.14 Coacervation............................................................................................276 5.2.15 Deep-fat frying.........................................................................................276 5.2.16 Emulsions................................................................................................ 277 5.2.17 Foam....................................................................................................... 279 5.3 Gum Exudates in Animal Food . ......................................................................... 280 5.3.1 Introduction............................................................................................ 280 5.3.2 Insects..................................................................................................... 280 5.3.3 Mammals and primates............................................................................281 5.4 Health-Related Aspects ....................................................................................... 284 5.4.1 Safety ..................................................................................................... 284 5.4.2 Nutrition ................................................................................................ 285 References ...................................................................................................................... 286

Contents  ◾  xvii

6.

Gum Exudates in Water-Based Adhesives ................................................................ 293 6.1 Introduction..........................................................................................................293 6.2 Gums as Adhesives............................................................................................... 294 6.3 Industrial Uses of Exudate Glues . ....................................................................... 294 6.3.1 General . ................................................................................................. 294 6.3.2 Paper....................................................................................................... 294 6.3.3 Wood and furniture ................................................................................ 294 6.4 Biological Applications: A General Approach....................................................... 296 6.4.1 Ostomy devices ....................................................................................... 296 6.4.2 Denture fixatives ..................................................................................... 297 6.4.3 Bioelectrodes........................................................................................... 298 6.4.4 Exudate patches for transdermal drug delivery ....................................... 298 6.5 Hydrocolloid Adhesion Tests . ............................................................................. 299 6.6 Exudates as Wet Glues ......................................................................................... 302 6.7 Adhesion Mechanisms of Hydrogels .................................................................... 306 References....................................................................................................................... 308

7.

Medical, Cosmetic and Biotechnological Uses of Gum Exudates............................. 311 7.1 Introduction .........................................................................................................311 7.2 Pharmacological Applications . .............................................................................311 7.2.1 Demulcent and emollient qualities...........................................................311 7.2.2 Suspending and emulsifying agents..........................................................312 7.2.3 Laxatives . ................................................................................................314 7.2.4 Antiseptic preparations and ophthalmic infections...................................314 7.2.5 Tablets and pills . .....................................................................................314 7.2.6 Hydrophobic drug delivery.......................................................................314 7.2.7 Lycopene ................................................................................................. 315 7.2.8 Gelatin- And chitosan-gum arabic coacervates......................................... 315 7.2.9 Various medical uses . ..............................................................................317 7.2.9.1 Intravenous injections . ...........................................................317 7.2.9.2 Activity against leishmania and fungi . ...................................317 7.3 Folk Medicine ......................................................................................................318 7.4 Cosmetics and Other Products............................................................................. 320 7.4.1 General . ................................................................................................. 320 7.4.2 Different cosmetic preparations................................................................321 7.4.3 Perfume ...................................................................................................321 7.4.4 Powdered abrasive cleaners...................................................................... 322 7.5 Biotechnological Applications ............................................................................. 322 7.5.1 Recombinant plant gum ......................................................................... 322 7.5.2 Intracellular delivery................................................................................ 323 References....................................................................................................................... 323

8.

Analysis and Identification of Gum Exudates .......................................................... 327 8.1 Introduction .........................................................................................................327 8.2 Industrial Gums....................................................................................................327 8.2.1 Water solubility .......................................................................................327 8.2.2 Alcohol precipitability .............................................................................329

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8.2.3 Microscopic identification........................................................................329 8.2.4 Identification of gums in specific foods ....................................................332 8.2.5 Antibodies for the identification of gum arabic and other polysaccharides ........................................................................333 8.3 Group Analysis and Identification Schemes . ....................................................... 334 8.3.1 Characteristic reactions of gums.............................................................. 334 8.3.2 Cetavlon group identification scheme ......................................................337 8.4 Additional Analytical Methods ............................................................................338 8.4.1 IR spectroscopy........................................................................................338 8.4.2 Chromatographic techniques to identify plant gums ...............................339 8.4.3 Fourier transform-Raman spectroscopy of gum exudates ....................... 340 8.4.4 Capillary electrophoresis ......................................................................... 341 8.4.5 Other methods ....................................................................................... 342 References....................................................................................................................... 342

9.

Miscellaneous Uses of Plant Exudates . ....................................................................347 9.1 Introduction......................................................................................................... 347 9.2 Paints, Pigments and Painting.............................................................................. 347 9.3 Inks.......................................................................................................................351 9.4 Lithography...........................................................................................................354 9.5 Textiles..................................................................................................................355 9.6 Corrosion Inhibition ............................................................................................357 9.7 Immersion Plating.................................................................................................358 9.8 Drilling Fluids.......................................................................................................359 9.9 Oil-Well Cement.................................................................................................. 360 9.10 Binders and Special Coatings................................................................................361 9.10.1 Glaze binders............................................................................................361 9.10.2 Binders for insecticides.............................................................................361 9.10.3 Non-glare coatings for windshields . ........................................................361 9.11 Paper and E-Paper.................................................................................................361 9.12 Explosives............................................................................................................. 362 9.13 Ceramics.............................................................................................................. 364 9.14 Miscellaneous........................................................................................................365 9.14.1 Varnishes..................................................................................................365 9.14.2 Car polishes............................................................................................. 366 9.14.3 Cross-linked polystyrene ........................................................................ 366 9.14.4 Photoelectric determinations................................................................... 366 9.14.5 Polarographic determinations ..................................................................367 9.14.6 Abdominal ultrasound imaging and soil analyses ....................................367 9.14.7 Vinyl resin emulsions . ............................................................................ 368 References....................................................................................................................... 368

Organism Name Index ....................................................................................................... 371 General Index.....................................................................................................................383

Preface Natural gums—which exude from trees and shrubs in tear-like, striated nodules or amorphous lumps, and then dry in the sun to form hard, glassy exudates in a variety of colors—have been used for centuries in many different ways. Their use in food applications—for emulsification, thickening and stabilization, among others—dates back many years. Their use as food is well documented in the Bible: the famous “manna from heaven” that sustained the Israelites during their escape from Egypt was probably a gum exudate related to gum arabic or gum acacia. Their non-food-related uses in pharmaceuticals, cosmetics, textiles and lithography, and minor forest products can also be traced back in history. They were recognized items of trade in Biblical times, and ancient inscriptions depict the use of gum arabic—called kami by the Egyptians—in textile glues, embalming fluids, and dye dispersions. Plant exudates, both gums and resins, have also served as the basis for the creation of many new and improved gluing materials. At the Hebrew University of Jerusalem in Israel, our team has been working for the last 10 years on adhesion in general, and hydrocolloid glues and patches in particular. Part of our research has involved a thorough search in nature and in the literature for less known sources of gum exudates. In the course of this quest, we discovered that in the last 60 years many new gum exudates have been mentioned, in passing or in detail, and that their number is much higher than that first described in 1949 by Howes in his classic comprehensive monograph: Vegetable Gums and Resins. That book was devoted in its entirety to plant exudates, be they gums or resins. Many other polysaccharide/hydrocolloid books contain chapters devoted to the chemistry and industrial applications of the more common or commonly used exudates. On the other hand, there are many exudates that have never been described, nor have their applications ever been reviewed, despite that awareness of these lesser-known natural raw materials has increased in the last few years. Some have been proposed as alternatives for gum arabic, karaya, tragacanth, and ghatti as sources for novel medicines and foods, and for lesser-known industrial aims. Hence the need for a new and up-to-date book exclusively devoted to gum exudates became clear to me, and I decided to undertake this project. This book is unique in that it provides a definitive classification of gum exudates. Most, if not all, books dealing with gum exudates classify them according to country or geographic location. However, many trees are not endemic; in fact, exudate-bearing trees are distributed all over the globe, covering at least a few continents. Moreover, some of these classifications are artificial or unjustified. Other classifications have been suggested on the basis of the sugar residues comprising the internal chains of the polysaccharides’ molecular structure. This type of classification, in which one group can contain polysaccharides of diverse origins on account of their similar backbones, is not always correct and is best avoided, especially when external macromolecular xix

xx  ◾  Preface

conformations of the side chains better explain the relationships between structural and physical properties. Added to the fact that current knowledge of the detailed structures of certain gum exudates is limited, an unambiguous structural classification simply becomes unrealistic. This volume strives to eliminate the deceptive classifications found in currently available books. Here the gums are classified according to their botanical taxonomy, that is, family, genus, and species. One problem that is often encountered in the literature involves botanical names that were correct at the time of entry, but then evolved into synonyms and are now outdated, and author names that were never standardized. To avoid this pitfall, almost all of the botanical names in this volume were checked against the U.S. Department of Agriculture’s Germplasm Resources Information Network (GRIN at http://www.ars-grin.gov/), a reliable listing of names for most economic plants in which the author names have been standardized. This book contains two main chapters (3 and 4) devoted to listing the major and minor exudates of the world. Each gum is supported (wherever this information was available) with the botanical name and synonyms of the tree or shrub from which the gum is exuded, as well as a list of common and vernacular names, and information on geographic distribution, present common names for the gum, a description of the exudate’s appearance and color, information on water solubility, chemical characteristics and structural features, physical and physicochemical properties, and commercial availability. Each gum’s industrial and food applications are also mentioned and described in more detail in other chapters. The commercial and functional uses of other parts of the tree from which the gum originates are also detailed. This book is also unique in its color photographs, designed to present many of the gum exudates in their natural state as well as the relevant trees, leaves, flowers, or other plant parts. Other distinctive aspects of this book include seven additional comprehensive chapters devoted exclusively to gum exudate identification, functionality, and applications. Chapter 1 gives an overview of the roles and sources of gum exudates. This introductory chapter begins by explaining the differences between resins, oleoresins, gum resins, kino, latex, and gums. It includes a general description of selected gum-yielding plant species, delineates the role of exudates in industry, provides the history and ancient uses of these materials, describes socioeconomic aspects, lists trade and markets, names physical and chemical properties (further reviewed in Chapters 3 and 4), describes botanical aspects (including taxonomy, anatomy, production systems, harvesting, genetic resources, and breeding), and provides a brief overview of these substances’ prospects. Chapter 2 deals with the physiological aspects of polysaccharide formation in plant exudates. Gum exudates can be part of the plant’s normal metabolism, but more often than not their exudation is attributed to pathological phenomena. An understanding of the factors affecting gum formation is of fundamental importance in finding a cure for the disorder in some fruit trees, and in inducing prolific gum production for commercial purposes. Pathological exudation, or gummosis, owes its origin to a number of unrelated factors such as tissue infections caused by disease, pathogens, and parasitic invasion by microorganisms, fungi, viruses and insects; physical injury; chemicals; stress, and various climatic conditions. The chapter attempts to clearly separate the different causes of gummosis and its role as a protective function; it also expounds on the involvement of the primary cell wall in the early stages of gum formation, the interference of ethylene in the balanced biosynthesis of cell-wall polysaccharides, the role of enzymes in the transformation of cellulose, hemicelluloses, starch or pectic substances into gums, the development and ultrastructure of gum ducts, the induction of gummosis by the ethylene generator ethephon for enhanced commercial gum production, and aspects of gummosis in fruit trees.

Preface  ◾  xxi

Chapter 3 covers the world’s major plant exudates, providing a highly comprehensive list of the common gum exudates. The gums in this chapter are arranged according to the botanical taxonomy of their sources. This extensive chapter (together with Chapter 4, which covers the world’s minor exudates) makes up the major part of this book. For each tree or shrub from which gum is exuded, all available information on botanical names and their authorities, synonyms, vernacular, and common plant names is provided. In addition, information is provided on geographical distribution and common names for the gum (in an attempt to avoid duplication where different names have been given to the same gum).  The chapter also includes descriptions of exudate appearance and color, water solubility and hydrocolloidal properties, chemical and structural features, physical and physicochemical properties, commercial aspects and availability, industrial and food applications, and general uses and applications of the plant. Unique applications are covered in Chapters 5, 6, 7, and 9. For each gum, an exhaustive list of references to the literature, from the 1890s to the present, is included for the interested reader. Chapter 4 deals with world’s minor plant exudates. In a format similar to that of Chapter 3, a full list of the lesser-known, unexplored, and not previously reviewed gum exudates is provided. In some cases, this book provides the first record of a particular exudate. Note that limited sources of information for some gums permit only partial descriptions. Chapter 5 deals with food applications of plant exudates. Following their listing in Chapters 3 and 4, common industrial applications of gum exudates as well as special local, ethnic, and tribal uses are explored. It should be borne in mind that many exudates have not been given Generally Recognized as Safe (GRAS) status. Many such gums contain tannins or other ingredients that can be health hazards, and this information is covered in previous chapters. Chapter 5 traces the changes in relative importance of the currently utilized gum exudates and explains how these are influenced by changes in their value, price, or ease of collection, or by climate or other global changes. Available information on these gums from nutritional and safety standpoints is also described. This chapter is also devoted to unique applications, especially those that have prehistoric roots and have evolved into their present-day uses, and that are expected to undergo further development. Although similar chapters devoted to food applications can be found in other books, this chapter emphasizes the old versus the new, taste (providing sweetness and sensory evaluations of edible exudates), local versus international aspects, and, finally, comprehensive nutritional information on these gums. Chapter 6 describes gum exudates in water-based adhesives. Information on this issue is on the one hand most important and on the other hand quite limited. This unique chapter includes information on gum exudates as adhesive materials in medicinal products, namely, mucoadhesives, bioelectrodes, denture fixatives, ostomies, and transdermal patches; adhesive materials in the food, paper, and wood industries; mechanisms controlling adhesion of polysaccharides; testing of adhesive joints; purposes and future prospects of gum exudates in water-based adhesives; and a comprehensive comparative analysis of the adhesion properties of various gum exudates that have never before been explored and are presented for the first time in this book. Chapter 7 describes medical, cosmetic, and biotechnological uses of gum exudates. Many applications of gum exudates have a profound tradition. However, there is no doubt that a promising future for these materials is based on their medicinal, cosmetic, and biotechnological uses. This chapter describes different applications of gums in these fields, such as in bulk laxatives; in treatments for warts, ulcers, and pressure sores; for the soothing of irritated mucous membranes; as carriers in controlled-release hydrophilic matrix systems; as constituents in medicines; as binding agents in cosmetic preparations; in perfumed cachous and lozenges; in different creams and ointments; in eye cosmetics; in cough syrups; as part of intravenous injections; and in blood substitutes.

xxii  ◾  Preface

Chapter 8 deals with the analysis and identification of gum exudates. Although the analysis and identification of commercial gums is of the utmost importance, very few books discuss this topic. Since food quality has become a major issue in many countries, this chapter discusses the treatment of commercial gum samples that are usually sold in powdered form for a variety of uses in foods. This chapter attempts to bring together all of the fragmented knowledge available for as many exudates as possible. These include water-solubility properties, alcohol-precipitation characteristics, microscopic identification, and flocculation values. In addition, the chapter describes how to identify exudates in specific food products. In a few cases, the reader is supported with information on group analyses and identification schemes. A very short description of additional analytical methods is provided, although this is not the main focus of the book. In addition, the chapter briefly describes the chemical reactivities and compatibilities of different exudates. Although such information is limited, its collection under one title is expected to be highly relevant for producers of many kinds of foods, pharmaceutical products, coacervates, and more. Chapter 9 deals with miscellaneous uses of plant exudates. Although Chapters 5, 6, and 7 cover the main applications of these fascinating materials, many other, less known but nevertheless important uses exist, related to paper, photography, inhibition of corrosion, immersion plating of metals, drilling, ceramics, and binders, among many others. This book was written over a two-year period. In addition to enumerating and describing the numerous gum exudates, it describes the many traditional as well as nontraditional uses of exudates that have been developed in many hydrocolloid research and development laboratories all over the world. My hope is that this book will assist all levels of readers. It is dedicated not only to the academic community but also to the wider population of industrialists and experimenters who will find this book to be not only a source of knowledge, but also an initiator of novel ideas and inventions. In particular, this book is expected to be of interest to personnel involved in food formulation, food scientists, food technologists, industrial chemists and engineers of textiles, pharmaceutical staff and medical doctors, and those who develop cosmetics or deal with drug delivery through adhesive patches. In addition, botanists, floral experts (both professional and amateur), exudate developers and collectors, farmers, agriculturalists, and those who work on the development of arid lands are also potential readers. Finally, it is hoped that this book will find a prominent place in the traditional university and research institute libraries where food science, chemistry, agriculture, botany, and other theoretical and practical industrial topics are taught and studied.

Acknowledgments This book has been in the writing stages for the last two years. It contains a description of the world’s plant gum exudates: their sources, distribution, properties, and applications. It also includes many traditional and nontraditional uses of exudates that have been developed in our laboratory and many other hydrocolloid research and development laboratories worldwide. My hope is that this manuscript will assist all levels of readers in their search for comprehensive knowledge on the fascinating field of exudates, as well as those seeking up-to-date information on the very different current and past uses and applications of exudates in many areas. Comments and questions from these readers will be very much appreciated. I thank the publishers for giving me the opportunity to write this book. Special thanks to Stephen Zollo and David Fausel for the efficient way in which they contributed to the formation and processing of this manuscript. I wish to thank my editor, Camille Vainstein, for working shoulderto-shoulder with me when time was getting short. The help of my colleague and friend Dr. Omri Ben-Zion, who supported me with literature research, references, and good advice, is very much appreciated. The efficient help of Hanna Ben-Or in finding and rectifying the many old or inaccurate references was above and beyond the call of duty. Ben-Zion’s contribution of pictures and specimens collected in Israel for the book is much appreciated, as are the specimens collected in India by Krystal Colloids. Special thanks to Dr. Mark Nesbitt from the Royal Botanic Gardens, Kew, for a thorough reading, many corrections of Chapters 3 and 4, and help with the taxonomical information in this volume. I am grateful to Julia Steele from the Royal Botanic Gardens, Kew, who was so efficient at organizing the photography of specimens at Kew, and was welcoming, enthusiastic, and encouraging. The permissions that we obtained from publishers are warmly acknowledged. Special thanks to Forest Starr and Kim Starr, who generously provided me with so many excellent pictures of gum-exuding trees and shrubs. The generosity of Dr. Kevin C. Nixon and Sherry Vance who gave me the permission to use images from Plantsystematics.org is very much appreciated, as is the help and friendship of Dr. Madoka Hirashima and her picture-taking efforts in Japan. This list would not be complete without extending my heartfelt thanks to the many who contributed to the Web sites of USDA–GRIN and other nonprofit organizations, which made the writing of the botanical section of this book so much easier. The pictures adapted from Wikipedia are acknowledged in their turn, but I feel that it is equally appropriate here to acknowledge the many who have contributed to this gigantic educational achievement. The love and patience of my family, Varda, Ya’ara, Eran, and Yoav, who were very supportive during these last few difficult years when we were under huge pressure from many different directions. Last but not least, I thank the Hebrew University of Jerusalem for being my home and refuge for the last 18 years of very extensive research and teaching. xxiii

The Author Professor Amos Nussinovitch was born in Kibbutz Megiddo, Israel. He is the son of Holocaust survivors. Nussinovitch served as a soldier in the Yom Kippur and Lebanon wars, and both his heritage and the horrors of war deeply influenced his life, thoughts, and attitudes. He studied chemistry at the University of Tel Aviv, and food engineering and biotechnology at the Technion-Israel Institute of Technology. He has worked as an engineer in several companies and has been involved in a number of research and development projects in the United States and Israel, focusing especially on the mechanical properties of liquids, semisolids, solids, and powders. He is currently in the Biochemistry and Food Science Department of the Robert H. Smith Faculty of Agriculture, Food and Environment at the Hebrew University of Jerusalem, where he leads a large group of researchers working on theoretical and practical aspects of hydrocolloids, including: coating of cells and foods; special glues and exudate patches; water-soluble polymer uses in paper; exudate preparations in cosmetics and medicine; hydrocolloid uses in explosives, ink, and special cellular solids; and biological carriers. Nussinovitch is the author of the books Hydrocolloid Applications: Gum Technology in the Food and Other Industries and Water-Soluble Polymer Applications in Foods. He is the author or coauthor of numerous papers on hydrocolloids, physical properties of foods, and recently, the use of exudates in pharmaceutics, and he has about 30 patent applications. This book is devoted specifically to plant gum exudates of the world, their sources, distribution, properties, and applications.

xxv

Chapter 1

Role and Sources of Exudate Gums 1.1 INTRODUCTION Exudate gums have been used for centuries in a variety of fields: they have retained their importance despite the many alternative gums, with similar typical performances, which have since come into existence. Natural gums exude from trees and shrubs in tear-like, striated nodules or amorphous lumps, and then dry in the sun, forming hard, glassy exudates of different colors, from white to pale amber for gum arabic, pale gray to dark brown for karaya gum, and white to dark brown for tragacanth. Gum production increases under high temperatures and limited moisture, and yields can be increased by making incisions in the bark or stripping it from the tree or shrub. Exudate gums have been used in food applications for many years, for emulsification, thickening and stabilization, among others (Table 1.1). Gums were known and used in Biblical times: their use as food is well documented in the Bible: the famous “manna from heaven” that sustained the Israelites in their escape from Egypt was probably a gum exudate related to gum arabic or gum acacia (Glicksman, 1969). Similar acacia exudates have also been used for food. For example, in Australia, the natives eat wattle gum (Fig. 1.1), which is the exudate of the species of acacia tree known as wattle tree, in combination with fish (Maiden, 1890). In India, similar gum exudates are also quite widespread and are sold in marketplaces. The local food “laddu” and other sweetmeats (Fig. 1.2), sherbets and syrups are prepared from these materials (Glicksman, 1969). In the Australia-New Zealand region, as a result of local knowledge and widespread use of gum exudates, many picturesque gum-related colloquialisms have become part of the local language. Examples are the term “gum-sucker”, which stems from the practice in small boys of eating and chewing gum from eucalyptus or acacia, and is used loosely to refer to the natives of the area (Glicksman, 1969). Another phrase “to be up a gum tree” is used to mean being in a predicament (Partridge, 1961). Gum arabic, gum tragacanth, gum karaya and gum ghatti are safe for human consumption based on a long history of usage as well as recent toxicological studies. Tree gum exudates are also used in non-food applications, such as: pharmaceuticals, cosmetics, textiles and lithography, and minor forest products (Wang and Anderson, 1994). Gums have also long been utilized 1

2  ◾  Plant Gum Exudates of the World Table 1.1  Food Applications of Gum Arabic, Ghatti, Karaya and Tragacanth† Food Application

Gum Arabic

Gum Ghatti

Gum Karaya

Gum Tragacanth

Ice cream stabilizer

+

−

+

+

Ice milk

+

−

+

+

Milk shake

−

−

−

+

Sherbet

+

−

+

+

Ice pops and water ices

+

−

+

+

Chocolate milk drink

+

−

−

+

Cooked puddings and custards

−

−

+

−

Neufchatel-type processed cheese

−

−

+

+

Cheese spread

−

−

+

+

Whipped cream

−

−

+

−

Packageable milk or cream

+

−

−

−

Soft drinks with fruit pulp

+

−

−

−

Soft drinks

+

−

−

−

Beer foam stabilizer

+

−

−

−

Fining wines, juices and vinegar

+

−

−

−

Dry beverage mixes

+

−

−

−

Artificially sweetened beverages

+

−

−

−

Bread doughs and mixes

+

−

−

−

Cake batters and mixes

+

−

−

−

Pie filling

−

−

+

−

Doughnut glaze

+

−

−

−

Flat icing

+

−

+

−

Dairy products

Beverages

Bakery products

Role and Sources of Exudate Gums  ◾  3 Table 1.1  (Continued) Food Application

Gum Arabic

Gum Ghatti

Gum Karaya

Gum Tragacanth

French dressing

−

−

+

+

Salad dressing

−

−

+

+

Syrups and toppings

−

+

−

+

Relish

−

−

−

+

White sauces and gravies

−

−

−

+

Catsup

+

−

−

+

Caramels, nougats, taffy

+

−

−

+

Cough drops and lozenges

+

−

−

+

Gum drops, jujubes, pastilles

+

−

+

+

Dietetic syrups

+

+

−

−

Salad dressing

−

−

−

+

Prepared cereals

−

−

+

−

Processed baby food

−

−

+

−

Flavor fixative

+

−

−

−

Frozen foods

+

−

−

−

Dressings and sauces

Confectionary

Dietetic foods

Miscellaneous

†

Adopted in part from Glicksman (1969).

for many non-food-related functions, such as being recognized items of trade in Biblical times. Ancient inscriptions depict the use of gum arabic—called “kami” by the Egyptians, in textile glues, embalming fluids, and dye dispersions (Glicksman, 1969).

1.2 DEFINITIONS Exudates are fluids that ooze out of wounds in injured tress and harden upon exposure to air. This designation includes all types of natural exudates, including many water-insoluble materials such as resins, latex, chicle, etc., which accounts for the erroneous use of the term gum for many of the water-insoluble resins used in the paint and chemical industry today (Glicksman, 1969). Injury can be either a result of tapping (the removal of bark and/or wood to cause exudation) or of accidental or natural causes, such as attack by insects, animals or pathogens, or damage from

4  ◾  Plant Gum Exudates of the World

Figure 1.1  Wattle gum (Acacia pycnantha) from South Australia. Its main uses are medical and veterinary (mag. 2x; courtesy of the Royal Botanic Gardens, Kew; Cat. No. 58483).

drought or storms (Boer and Ella, 2000). The role of resinous exudates as a defense mechanism is described in Chapter 2. Gums exhibit great differences in their physical and chemical properties but they are all readily distinguishable from resins, oleoresins, balsams and products of a rubbery nature. Gums are

Figure 1.2  Laddu or Laddoo (Hindi:   ; Urdu: ) is an Indian, Pakistani and Bengali sweet that is often prepared to celebrate festivals or household events such as weddings. It is made of flour and other ingredients formed into balls that are dipped in sugar syrup (adapted with changes from http://commons.wikimedia.org/wiki/Image:Laddu.JPG, courtesy of Belayet Hossain).

Role and Sources of Exudate Gums  ◾  5

miscible in water and insoluble in liquids that dissolve resins, such as benzene, chloroform, ether, turpentine and fixed oils (Howes, 1949). Natural gums are capable of causing a large increase in solution viscosity, often even at low concentrations. In the food industry, they are used as thickening agents, gelling agents, emulsifiers and stabilizers. Examples include: agar (E406), alginic acid (E400), carrageenan (E407), gellan gum (E418), glucomannan (E425), guar gum (E412), gum arabic (E414), gum tragacanth (E413), karaya gum (E416), locust bean gum (E410), sodium alginate (E401), tara gum (E417) and xanthan gum (E415), among others. [The E numbers are codes for food additives and are usually found on food labels throughout the EU. The numbering scheme follows that of the International Numbering System (INS) as determined by the Codex Alimentarius committee. Only a subset of the INS additives are approved for use in the EU, as denoted by the ‘E’ prefix, which stands for Europe (http://en.wikipedia.org/wiki/E_number).] Resin is a solid to soft-semisolid amorphous, fusible, flammable substance obtained as a plant exudate or extract (Boer and Ella, 2000). The Oxford dictionary defines resin as a hydrocarbon secretion of many plants, particularly coniferous trees, valued for its chemical constituents and uses, such as in varnishes and adhesives, as an important source of raw materials for organic synthesis, or in incense and perfume. Fossilized resins are the source of amber. Amber, which is often hundreds of millions of years old, is an ancient sticky tree resin that has hardened and polymerized over the eons (Santiago-Blay and Lambert, 2007). Today, modern tools and tests such as nuclear magnetic resonance (NMR) spectroscopy can be used for sample verification. Since not all amber is the same, NMR catalogs have been created for the many different kinds. Besides helping to discern true from spurious samples, such a library has the added advantage of potentially indicating the kind of tree the amber may have come from, giving us a better idea of the prehistoric landscape (Santiago-Blay and Lambert, 2007). The term resin is not easy to define precisely. Nevertheless, resins do have some common properties. They are insoluble in water but usually dissolve readily in alcohol, ether, carbon bisulfide and certain other solvents (Howes, 1949). Natural resins are of vegetable origin, except Lac and other similar insect exudations. Plant resins are widely distributed in the vegetable kingdom and may be present in almost any organ or tissue of the plant (Howes, 1949). One example is acaroid resin or “gum accroides”, which is the product of several species of Xanthorrhoea endemic to Australia (Fig. 1.3). The term resin is also used for synthetic substances with similar properties. The on-line medical dictionary defines gum resin as the dry exudate from a number of plants, consisting of a mixture of gum and resin, the former soluble in water but not alcohol, the latter soluble in alcohol but not water. Oleoresin is defined as a natural plant product consisting of a viscous mixture of essential oils and non-volatile solids (Boer and Ella, 2000). The copals include a large group of resins that are characterized by their hardness and their relatively high melting point. They are among the best natural resins for use in varnish and paint formulations (Howes, 1949). Copals are derived from a number of different plants, mainly forest trees of the family Leguminosae that occur in various parts of the world (Howes, 1949). The name copal is probably derived from the Nahuatl copalli, meaning “resin.” When hard, copal is lustrous, varying in hue from almost colorless and transparent to a bright yellowish brown. It dissolves in alcohol or other organic solvents upon heating and is used in making varnishes and printing ink (http://www.britannica.com). Zanzibar copal, the principal commercial copal, is the fossil yielded by Hymenaea Verrucosa Gaerth. (syn. Trachylobium verrucosum); it is found embedded in the earth on the western coast of Zanzibar in tracts where not a tree is now visible. South American copals are available from Hymenaea courbaril L. and other species of trees in Brazil, Colombia, and other South American countries (http://www.britannica.com/). Kino (also keenow) gum is defined as a gum obtained from various tropical plants, and used as an astringent and in tanning. East Indian and Malabar kino are a reddish or black juice or resin from certain trees of the genus Pterocarpus and are used in medicine and tanning (Howes, 1949). Another definition of kino is any of several dark red to black tannin-containing dried juices or

6  ◾  Plant Gum Exudates of the World

Figure 1.3  An Australian resin derived from the species Xanthorrhoea preissii Endl. Its common names are: black boy and gum accroides (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 36427).

extracts obtained from various tropical trees—especially the dried juice usually obtained from the trunk of an Indian and Sri Lankan tree (Pterocarpus marsupium) as brown or black fragments and used as an astringent in diarrhea; or it is a tree that produces kino (especially P. marsupium) (http://www.britannica.com). One example of kino is produced from Butea monosperma, which is a medium-size deciduous tree with a crooked trunk that is up to 5 m in length by 60 cm in diameter, native of India, Burma and Ceylon and introduced into a few tropical countries as an ornamental, for example, Nigeria. The very light wood is white or yellowish-brown. The common names of the tree and gum are flame of the forest and Bengal kino, respectively (Fig. 1.4). Natural rubber latex comes from a liquid in tropical rubber trees (Fig. 1.5). Sapodilla (Manilkara zapota) is a long-living, evergreen tree native to the New World tropics. It is a native of Mexico and was introduced to the Philippines during the Spanish colonization. Sapodilla grows to 30 or 40 m in height. It is wind-resistant and the bark is rich in a white, gummy latex (Fig. 1.6). This liquid is processed to make many of the following rubber products, used at home and at work: balloons, rubber toys, pacifiers and baby-bottle nipples, rubber bands, adhesive tape and bandages, diapers and sanitary pads, condoms. In addition, many medical and dental supplies contain the protein latex, including gloves, urinary catheters, dental dams and material used to fill root canals, as well as tourniquets and equipment for resuscitation. Non-latex substitutes can be found for all of these latex-containing items, because this protein can cause an allergic reaction in some people. The thin, stretchy latex rubber in gloves, condoms and balloons are high in this protein. It causes more allergic reactions than products made of hard rubber (such as tires). Moreover, because some latex gloves are coated with cornstarch powder, the latex particles stick to the cornstarch and fly into the air when the gloves are taken off. In places where gloves are being put on and removed frequently, the air may contain many latex particles.

Role and Sources of Exudate Gums  ◾  7

Figure 1.4  Bengal kino of Butea monosperma (Lam.) Taub. [family Leguminosae Papilionoideae] (mag. 1.7X; courtesy of the Royal Botanic Gardens, Kew; Cat. No. 58424).

Figure 1.5  The extraction of latex from a tree (http://en.wikipedia.org/wiki/File:Latexproduction.jpg; photo by Jan-Pieter Nap).

8  ◾  Plant Gum Exudates of the World

Figure 1.6  Air-dried latex of the sapodilla tree Manilkara zapota from the Dominican Republic (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 50872).

1.3 GUM YIELDS Many plants exude viscous, gummy liquids. Healthy Acacia tress grown under favorable climatic and soil conditions produce little or no gum. However, trees grown under adverse conditions of excessive heat, scarcity of moisture and high elevation, produce sizeable quantities of gum arabic (Fig. 1.7). The physiological aspects of polysaccharide formation in plant exudates are discussed in Chapter 2. Yields can also be increased by deliberately stripping away the bark or injuring the tree (Glicksman, 1969). It is not surprising that many studies have been aimed at examining parameters that influence yield and determining what causes plants to produce more or less exudates. A comparative study of gum arabic yield trends and peaks per tree in relation to stand management (by farmers and by researchers) and type (natural and planted) was conducted at two locations in North Kordofan, Sudan, over a 3-year period (Ballal et al., 2005a). In addition, 8-year yield trends in relation to rainfall were compared based on the 1993-2000 gum yield data from 1,440 trees. Although the gum arabic yield followed the same trend over time in all stands at both locations, the gum yield from farm stands, whether planted or natural, was 47 to 60% lower than that from research stands. Late tapping reduced the gum yield by 40 and 50% at the two different locations, respectively. Yield was highly affected by rainfall, correlating positively with annual rainfall in 6 of the 8 years of the study (Ballal et al., 2005a). It was concluded that the findings of this study should be used to improve gum arabic yield through management intervention and to predict yield in relation to stand type, management regime and rainfall. The causes of variability in gum arabic yield (from Acacia senegal) and yield trends as a basis for yield control, prediction and stability were also evaluated at an experimental site in Demokeya, Western Sudan. The effects on gum arabic yield of date and intensity of tapping, rainfall, and the

Role and Sources of Exudate Gums  ◾  9

Figure 1.7  ‘Tear drops’ of gum arabic, the dried, gummy exudate obtained from acacia trees.

minimum and maximum temperatures at tapping and gum collection were examined from 1992 to 2000 in a 12-year-old plantation (Ballal et al., 2005b). Tapping dates were found to produce roughly similar gum-production patterns across years. Yield was found to be positively correlated with tapping intensity, rainfall and the minimum and maximum temperatures at tapping time, and negatively correlated with tapping time and the minimum and maximum temperatures at gum collection (Ballal et al., 2005b). The time of tapping, tapping intensity, rainfall and maximum temperature at gum collection were found to explain 85% of the total variability in gum yield per unit area. Such studies can be helpful in understanding the causes of yield variability in gum arabic. Results can also help predict, to a certain extent, future gum yield (Ballal et al., 2005b). The question of whether inoculating mature A. senegal trees with Rhizobium has an effect on the yield of gum arabic is discussed in Chapter 2.

1.4 AGRICULTURAL ISSUES Agroforestry is an approach to land use based on the planned integration of trees with crop and/or livestock production systems (Fig. 1.8) (Young, 1989; Kang et al., 1999). It is an ancient practice, which has nevertheless benefited from methodical research and experimentation since the 1970s (ICRAF, 1997). Agroforestry can be productive, and more profitable and sustainable than other land-use systems (Kang et al., 1985; Nair, 1993), and it has the potential to offer rural households a large variety of products for trade and household use. Researchers and farmers throughout sub-Saharan Africa have developed new agroforestry practices (Franzel et al., 2001). Agroforestry manufacturing systems provide a large number of products and benefits (Huang and Xu, 1999). The net production of phytomass can be increased by the well-organized sharing of site resources among trees and other intercropping components, together with nitrogen fixation and microclimate modification (Sharrow and Ismail, 2004). About 40 years ago, a plantation of A. senegal

10  ◾  Plant Gum Exudates of the World

Figure 1.8  Maize crops growing together with Faidherbia albida (Acacia albida Delile) and palms (http://en.wikipedia.org/wiki/Image:Faidherbia_albida.JPG, photo by Marco Schmidt).

was reported to increase total nitrogen and organic carbon while having no effect on the texture, pH, available phosphorus or available potassium of a sand sheet soil. The higher nitrogen content in the topsoil may have been partially due to symbiotic fixation (Gerakis and Tsangarakis, 1970). Agroforestry can also potentially advance the water-use efficiency of systems by minimizing the non-productive part of the available soil water (Ong et al., 2002). In other words, agroforestry systems can considerably increase rainfall utilization as compared to annual cropping systems (Ong et al., 2002). Plant growth is dependent on the availability of light, water and nutrients, and manipulation of tree density in agroforestry systems can therefore modify the biomass production of component species (Eastham et al., 1990). Benefits in terms of biomass and grain yields can be expected if there is complementary resource sharing by agricultural crops and trees (Cannell et al., 1996). Tree density has a strong effect on the distribution and depth of the stand’s roots (Boswell et al., 1975). Agroforestry systems have been recognized as a tool for rehabilitating already degraded lands (Bandolin and Fisher, 1991). No less important is the fact that trees improve crop productivity by reducing wind flow, thereby reducing water loss through transpiration (Zinkhan and Mercer, 1996). Much work has already been done on studying tree-crop interactions under various tree-spacing regimes to improve the productivity of agroforestry systems (Gupta et al., 1998). The most important forest in the Sudan may be the gum arabic belt. The “belt” refers to a zone of approx. 520,000 km2 that expands across Central Sudan between latitudes 10° and 14° N, accounting for one-fifth of the country’s total area (IIED and IES, 1990). The belt accommodates ~20% of Sudan’s population and 66% of its livestock. It acts as a natural barrier, protecting over 40% of the total area of Sudan from desert encroachment, and it represents the site for most of the agriculture and animal production. This includes irrigated, mechanized rain-fed, and traditional rain-fed agriculture and forestry (Ballal, 2002). Until recently, the traditional A. senegal-based

Role and Sources of Exudate Gums  ◾  11

agroforestry system was considered one of the most successful forms of natural forest management in tropical drylands (Fries, 1990), and was regarded as sustainable in terms of its environmental, social and economic benefits (Ballal, 1991). Traditionally, the A. senegal tree is managed in temporal succession with agricultural crops such as sorghum, pearl millet, groundnut, sesame and karkadeh (Hibiscus sabdariffa L.). This agroforestry system allows a period of 10 to 15 years for reestablishment of the soil’s fertility after a short period of arable cultivation (Ballal, 2002). The cycle thus consists of a relatively short period of cultivation followed by a relatively long fallow period. The bush fallow sequence begins by clearing a 15- to 20-year-old gum garden for the cultivation of field crops. Trees are cut at 10 cm from the soil surface, and stumps are left to start vigorous coppice regrowth. The cleared area is cultivated for a period of 4 to 6 years, during which time the coppice shoot regrowth is removed to improve the establishment and growth of agricultural crops. However when the soil fertility declines, as reflected by low crop yield, crop growing ceases and the area is left fallow under A. senegal. The remaining trees are tapped for gum arabic until the age of 15 to 20 years, after which they are cleared again for crop cultivation. Therefore, the final tree stand is mainly the result of coppice regeneration, as well as some regeneration from seeds dispersed naturally or sometimes on purpose for enrichment planting (Ballal, 2002). The bush-fallow system of cultivation has proven to be a successful, sustainable farming system, particularly on the marginal lands of Kordofan. A. senegal supports the local population’s livelihood, since its gum represents a major cash crop, and in addition, fuel wood is obtained from this tree for household use and for sale (Sharawi, 1986). As an outcome of the development of a vegetable oil industry in North Kordofan in the 1940s, which strengthened the production of groundnut and sesame, there was a favorable response in terms of prices and productivity to oil seeds. However, this development occurred at the expense of the gum orchards, and the traditional rotational fallow-cultivation cycle was dramatically shortened or completely abandoned (Awouda, 1973). Consequently, the negative impact on soil and water has been considerable, to the extent that commercial agriculture is also beginning to face some problems (Ballal, 2002). Indications of system imbalance were noted decades ago and today, the area is experiencing a serious decline in fertility, as well as soil erosion and desertification. Moreover, sustainable management of the gum gardens is threatened because of severe droughts and indiscriminate clearing of A. senegal stands for firewood and charcoal production as a shortterm source of income (Elfadl et al., 1998). This has resulted in more degraded land. Accordingly, the removal of A. senegal trees and a general deterioration of the stands have resulted in a reduction in gum arabic production, by 30 to 70% between 1973 and 1984 (Bayoumi, 1996). The spread of desert-like conditions has also resulted from both physical conditions and misuse of resources (Ahlcrona, 1983; Suliman and Drag, 1983). A study of the recovery of biomass productivity in North Kordofan concluded that land degradation and the ecological imbalance associated with drought cycles and mismanagement could be reversed, if rational management practices were applied in accordance with water availability from rainfall (Yagoub et al., 1993). A. senegal is the most important component of traditional dryland agroforestry systems in the Sudan. The spatial arrangement of trees and the type of agricultural crop used influence the interaction between them (Raddad et al., 2006). The influence of different A. senegal agroforestry systems on soil water and crop yields in clay soils of the Blue Nile region in Sudan was studied (Raddade and Luukkanen, 2007). Trees were grown at 5 x 5 m or 10 x 10 m spacing, either alone or in a mixture with sorghum or sesame. Results demonstrated no significant variation in the soil water content under different agroforestry systems. Intercropping also resulted in a higher land equivalent ratio. No significant variation was found in the yields of sorghum or sesame when these crops were grown with or without trees. At an early stage of agroforestry system management,

12  ◾  Plant Gum Exudates of the World

A. senegal has no detrimental effect on agricultural crop yield. However, the pattern of resource capture by trees and crops can change as the system matures. There was little competition between trees and crops for water, suggesting that in A. senegal agroforestry systems with 4-year-old trees, the clay soil has enough water to support crop growth over a whole growing season up to maturation and harvest (Raddade and Luukkanen, 2007). In conclusion, policy has a potential role in influencing the poverty and land-degradation problems facing Africa. Both ‘good’ and ‘bad’ policies can affect the economic incentives determining poor rural households’ decisions to conserve or degrade their land (Barbier, 2000). Many plant gum exudates are known worldwide. Four of them (arabic, ghatti, karaya and tragacanth) are of importance to the food industry (Glicksman, 1969). Many other gums, which are listed and described in Chapters 3 and 4, are known and used in their local areas of availability. Sometimes these gums can serve as substitutes for others, especially if they have similar properties. In the search for gum arabic substitutes, natural gum exudations in seven South American species of Prosopis and the productivity of induced gum exudation were evaluated (Vilela and Ravetta, 2005). Prosopis is a genus of about 45 species of leguminous spiny trees and shrubs, located in subtropical and tropical regions of the Americas, Africa and southwest Asia. They often thrive in dry soil and are resistant to drought, sometimes developing extremely deep root systems. Their wood is usually hard, dense and durable. Their fruits (pods) may contain large amounts of sugar. Natural exudates were found in three species: P. flexuosa, P. chilensis and P. nigra. In the latter two, exudates were dark, liquid and bitter, while in P. flexuosa, up to 1.6 kg per tree of amber-clear gum was harvested (Vilela and Ravetta, 2005). High-productive trees were old, with very little vegetative growth, and were growing on sandy soils. To induce gum exudation, trees were wounded, and these wounds exuded plentifully for 7 months. Exudation increased during late summer and fall, after the fruits had ripened (Vilela and Ravetta, 2005).

1.5 PHYSICAL PROPERTIES OF GUMS The physical properties and appearance of natural gums are of greatest significance in determining their marketability and end use. These differ with different botanical sources. There is a considerable dissimilarity in gums from the same species collected from plants grown under different climatic conditions or even from the same plant in different seasons. Physical properties are also affected by the age of the exudate, and treatment of the gum after collection by, for example, washing, drying, sun-bleaching and storage temperatures (Glicksman, 1969).

1.5.1 Color Color is a perceptual phenomenon that depends on the observer and on the conditions under which it is observed. It is a characteristic of light, which is measurable in terms of intensity and wavelength. A material’s color only becomes visible when light from a luminous object or source illuminates or strikes the surface (Sahin and Sumnu, 2006). Color is of great importance in the commercial valuation of gums, with light-colored gums being preferred. More than 80 years ago, the claim was made that there are no completely colorless gums, but this is still open to question (Wiesner, 1927): for example, the color of the finest gum arabic in the Sudan has been described as colorless (Blunt, 1926). Commercial grades of A. senegal from Sudan include the best grade, i.e. the hand-picked, selected, cleanest and largest pieces, with the lightest color. The second-best grade includes that which remains after the hand-picked material and siftings have been removed. This grade comprises

Role and Sources of Exudate Gums  ◾  13

whole and broken lumps with a pale to dark amber color. The standard grade has a light to dark amber color (Islam et al., 1997). Another example of higher gum grades can be found with commercial gum karaya which contains less foreign matter and has a lighter color than the non-commercial gum (FAO, 1995). Gum colors depend on the plant species, climate and soil. In its solid state, gum colors vary from almost transparent white through various shades of yellow, amber and orange to dark brown. Certain gums possess a pink, red or greenish hue. Color is primarily due to the presence of impurities: it often only appears as the gum ages on the tree and may be due to substances that have washed onto the gum. There is no doubt that old trees give off a dark gum. In addition, scorching from bush or grass fires darkens gums, and tannin from the sap or tissues of the parent plant is also believed to account for some of the very dark gums yielded by certain trees (Howes, 1949).

1.5.2 Size and shape As seen or collected under natural conditions, gums are represented by a variety of shapes and forms (Howes, 1949). The fragments are generally irregularly round, drop- or pear-shaped, as is well-illustrated in the variety of commercial grades of gum arabic. Some gums are characterized by stalactitic shapes. Following collection and possible fracturing, irregular rod-shaped segments can appear, as demonstrated by cashew gum (Howes, 1949). Gum tragacanth’s name is derived from the two Greek words tragos (goat) and akantha (horn) and probably refers to the curved shape of the ribbons in the best grade of the commercial gum (Verbeken et al., 2003). The surface of most gums is perfectly smooth when fresh, but may quickly become rough or covered with minute cracks due to weathering (Howes, 1949). These fissures are not restricted to the surface, and therefore in some gums might serve to break a tear into smaller fragments. After collection, the gum is cleaned and graded. This is traditionally done by manual sorting according to the size of the lumps (FAO, 1995). The gum can be further processed into kibbled and powdered forms. Kibbling is a mechanical process which breaks up large lumps into smaller granules with a more uniform size distribution and facilitates dissolution of the gum in water. Better solubility can be obtained with powdered gum, which is usually produced by dissolving the gum in water, removing impurities and spray-drying (Verbeken et al., 2003). It is possible to specify the size of regular gum lumps, but for irregular pieces, the term size must be arbitrarily specified (McCabe et al., 1993). Size can be determined using the projected-area method: the longest dimension of the maximum projected area, the minimum diameter of the maximum projected area diameter and the shortest dimension of the minimum projected area are defined (Sahin and Sumnu, 2006). Shape can be expressed in terms of sphericity and aspect ratio. Sphericity is the volumetric ratio of the solid to a sphere that has a diameter equal to the major diameter of the object such that it can circumscribe the solid sample (Mohsenin, 1970). Sphericity was first defined ~70 years ago (Wadell, 1935). The sphericity, Ψ, of a particle is the ratio of the surface area of a sphere (with the same volume as the given particle) to the surface area of the particle:

Ψ = π 1/3 (6 Vp 2/3) / Ap

where Vp is the particle volume and Ap is its surface area. Sphericity has also been defined differently by other researchers (McCabe et al., 1993; Bayram, 2005). The aspect ratio is calculated using the length and width of a sample. It may be applied to two characteristic dimensions of a three-dimensional shape, such as the ratio of the longest to shortest axis, or for symmetrical objects that are described by just two measurements, such as the length and diameter of a rod (Maduako and Faborode, 1990). Such definitions should be entered into the shape field of the classification of collected exudates in order to render it less descriptive, and more scientific.

14  ◾  Plant Gum Exudates of the World

1.5.3 Taste and smell True gums are generally odorless, or nearly so (Howes, 1949). In contrast, resins and oleoresins have distinctive odors. For example, the gum resin opoponax is obtained by wounding the roots of opopanax chironium (L.) W.D.J. Koch (syn. Pastinaca opoponax), a native plant of the countries surrounding the Levant. It occurs in lumps that are reddish-yellow on the surface, but white within. It has a bitter and acrid taste, and a peculiar smell. Due to its exotic aroma, opoponax has long been used in perfumery. Its aroma has also been described as smooth and sweet, like a bit of toffee mixed with subtle myrrh (http://www.somaluna.com/prod/opoponax.asp). Another example is myrrh, which forms as reddish-yellow tears. It has a peculiar smell, and an aromatic bitter taste. In water, it forms a yellow opaque solution. It becomes opaque in an alcoholic solution when water is added, but there is no precipitate (Bache, 1819). In order to experience plant odors, a courtyard of senses was created in 1999 in the Montreal Botanical Garden, designed to give its visitors a whole new way of “seeing” the plant world. In the last area of the garden, one finds the common gums cistus, which is covered in a resinous secretion that sticks to the fingers, perovskia, which has a penetrating fragrance that takes the visitor by surprise if the leaves are rubbed, and the blue gum tree, which has a strong medicinal camphor smell (Turcotte, 2006). Gum resins (Fig. 1.9) denote a class of vegetable substances which are regarded by chemists as consisting of gum and resin. They are generally contained in the vessels of the plant, i.e. the root, stem, branch, leaves, flowers, or fruit. Gum resins, in their solid state, are brittle, and they generally have a strong smell, which is sometimes bitter and nauseating (Claudius, 1825). Gums may be tasteless or generally devoid of any characteristic taste (Howes, 1949). Another older reference also suggests that gum has no particular smell or taste (Lewis, 1791). Nevertheless there is evidence that some gums are slightly sweet or bitter according to their botanical origins. Some gums

Figure 1.9  Gum resin of the beef-wood tree (Grevillea striata R.Br.) collected in 1887 from New South Wales, Australia (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 44995).

Role and Sources of Exudate Gums  ◾  15

have a distinctly bitter, lingering aftertaste, and this should of course be considered when gums are used for foods (Howes, 1949).

1.5.4 Hardness and density The term hardness is widely used. Engineers and metallurgists perform hardness tests to assess the mechanical properties of metals and other engineering materials (Mohsenin, 1970). Most experts agree that hardness, as used in metals, means resistance to permanent deformation associated primarily with their plastic properties and only secondarily with their elastic properties (Mohsenin, 1970). Hardness can be measured on the Mohs scale or various other scales, and some of these, which are used for indentation hardness in engineering—Rockwell, Vickers, and Brinell—can be compared using practical conversion tables (Malzbender, 2003). The Mohs scale of mineral hardness, created in 1812 by the German mineralogist Friedrich Mohs, characterizes the resistance to scratching of various minerals based on the ability of a harder material to scratch a softer one. Attempts to classify gum hardness as with minerals in order to use hardness as a diagnostic character for gum identification have not proven at all satisfactory (Howes, 1949). Among many other things, hardness in gums depends on moisture content, which in general ranges between 12 and 16% (Howes, 1949). For example, the moisture content of the gum obtained from A. senegal ranges from 12.5 to 16.0% (Idris et al. 1998). Analytical data for exudates from the Turkish Astragalus species (Anderson and Bridgeman, 1985) demonstrate a loss upon drying of 12.7% and 9.9% weight for A. microcephalus (Fig. 1.10) and A. gummifer, respectively (Anderson and Bridgeman, 1985). Density also proves unpredictable, even in the same gum, as it depends in part on the quantity of air that may have been introduced during its formation.

Figure 1.10  A gum from Astragalus microcephalus Willd. The gum was collected in Lycia (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 60009).

16  ◾  Plant Gum Exudates of the World

1.5.5 Polarization Optical rotation or activity defines the rotation of linearly polarized light as it travels through certain materials: these can be solutions of chiral molecules, e.g. sucrose (sugar), solids with rotated crystal planes such as quartz, and spin-polarized gases of atoms or molecules. Polarization is used to measure syrup concentration, in optics to manipulate polarization, in chemistry to characterize substances in solution, and it is being developed as a method to measure blood sugar concentration in diabetics (http:// en.wikipedia.org/wiki/Optical_rotation). In aqueous solutions, gums are either levorotatory or dextrorotatory. For example, eight gum specimens from Pereskia guamacho (Cactaceae) are dextrorotatory acidic arabinogalactans and give very clear solutions of moderate viscosity (De Pinto et al., 1994). The gum from Hymenaea courbaril (Caesalpiniaceae) is soluble in water, dextrorotatory and less viscous than the gum from Cyamopsis tetragonolobus (guar gum) (Omaira et al., 2007). Samanea saman (Fig. 1.11) and Pithecellobium mangense exude clear yellow gums, both dextrorotatory (De Pinto et al., 1995). Venezuelan gum exudates from nine specimens of Parkinsonia praecox (Leguminosae) were examined. The samples, which were highly soluble in water and levorotatory, had viscosities comparable to that of gum arabic (from A. senegal) (De Pinto et al., 1993). The sugar composition and amino acid content of a gum solution influences whether gums are levorotatory or dextrorotatory. In Acacia seyal and A. senegal gums, the sugar composition and amino acids are identical but are present in different proportions, which is the main reason why A. seyal is dextrorotatory and A. senegal is levorotatory (Flindt et al., 2005).

1.5.6 Solubility A gum’s solubility may be influenced by age and the length of time it has been attached to the tree. Most gums yield a certain amount of insoluble residue when mixed with water and in general,

Figure 1.11  An exudate from Samanea saman (Jacq.) Benth. (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 59137).

Role and Sources of Exudate Gums  ◾  17

there is more of this residue with the dark-colored gums than with the pale or light-colored gums (Howes, 1949). For example, native gum karaya is insoluble and only swells in water, due to the presence of acetyl groups (Imeson, 1992). Based on their solubility in water, three fractions were distinguished in gum karaya (Le Cerf et al., 1990). Only 10% of the native gum solubilizes in cold water, but this fraction increases to 30% in hot water. After deacetylation, 90% of the native gum dissolves in water. Only lower-molecular-weight molecules are able to dissolve in cold water, while deacetylation leads to the solubilization of higher-molecular-weight material (Le Cerf et al., 1990). Better solubility can be achieved by breaking large lumps into smaller more uniform granules, and solubility can be further enhanced using spray-dried gum powder (Verbeken et al., 2003). Many macromolecules are made up of a hydrophobic portion that creates an “inside”, consisting of segments not in contact with the solvent, and an “outside”, consisting of the more hydrophilic groups that are in contact with the water (Whistler, 1973). Some electrolytes are able to stabilize macromolecular conformations in aqueous solutions (Whistler, 1973). The free energies of the macromolecule states are the sum of the individual group-solvent and group-group interactions. A change of a kilocalorie or less per mole in one of the stabilizing interactions engaged in maintaining the delicate balance is sufficient to generate a cooperative transition to a different conformation (Whistler, 1973).

1.5.7 Viscosity and mouthfeel “Viscosity” (or “absolute viscosity”) is frequently referred to as dynamic viscosity. It is the internal friction of a liquid or its tendency to resist flow (Bourne, 1982). In colloidal suspensions, viscosity is increased by the thickening of the liquid phase due to liquid absorption and resultant swelling of the dispersed colloid (Glicksman, 1969). This in turn, is accountable for functional effects such as suspension of solid particles, emulsification of oil and water phases, stabilization of liquid-solid-gas phases, and related phenomena (Glicksman, 1969). Selection of the proper hydrocolloid is crucial for an operation’s success and for the food system’s shelf stability. The viscosity of the hydrocolloid system depends on 10 factors: concentration, temperature, degree of dispersion, solvation, electrical charge, previous thermal treatment, previous mechanical treatment, presence or absence of other lyophilic colloids, age of the lyophilic sol and presence of both electrolytes and non-electrolytes (Ostwald, 1922). These factors are considered “the ten commandments of food preparation” (Lowe, 1955). Upon arrival in the importing country, the gum exudate is usually ground to a powder, with particle size varying according to the desired viscosity. Although gum arabic is highly branched, it has a compact structure (Nussinovitch, 1997). Gum arabic solutions are distinguished by their low viscosity (Table 1.2), enabling the use of high gum concentrations in various applications (Dziezak, 1991; Imeson, 1992). Solutions display Newtonian behavior at concentrations of up to 40% and become pseudoplastic at higher concentrations. Above ~30%, the hydrated molecules effectively overlap and steric interactions result in much higher solution viscosities and increasing pseudoplastic behavior (Nussinovitch, 1997). The pH of the solution is usually around 4.5 to 5.5, but maximal viscosity is found at pH 6.0 (extension of the molecule). At still higher pH, ionic strength of the solution increases until the repulsive electrostatic charges are masked, yielding a compact conformation with lower viscosity (Anderson et al., 1990; Williams et al., 1990a; Imeson, 1992). Due to gum arabic’s high water solubility, low viscosity, and emulsification properties, it is used in soups and dessert mixes (Glicksman and Farkas, 1975). The best gum tragacanth quality consists of high viscosity, good solution color and low microbial count (Nussinovitch, 1997). The viscosity of gum karaya dispersions depends on their grade (Weiping, 2000), and storage of the dry gum results in loss of viscosity (Dziezak, 1991). The viscosity of a 1% solution of gum karaya at

18  ◾  Plant Gum Exudates of the World Table 1.2  Effect of Concentration on Viscosities (cps) of Gum Exudates†‡ Exudate %

Gum Arabic

Gum Ghatti

0.5

‡

Gum Tragacanth

400

−

1.0

−

2

3,300

54

1.5

−

−

−

−

2.0

−

35

−

906

2.5

−

−

−

−

3.0

−

−

−

10,605

3.5

−

−

−

−

4.0

−

−

−

44,275

288

−

111,000

5.0

†

Gum Karaya

7.3

6.0

−

−

−

183,500

7.5

−

1,012

−

−

10.0

16.5

2,444

−

−

20.0

40.5

−

−

−

30.0

200.0

−

−

−

35.0

423.8

−

−

−

40.0

936.3

−

−

−

50.0

4162.5

−

−

−

Measured with a Brookfield Synchro-Lectric viscometer at 25°C. Results for gum arabic, karaya and tragacanth were adopted from Whistler (1973); and for gum karaya from Glicksman (1969) and Davidson (1980).

normal pH is approximately 3,300 cps (Table 1.2). Maximal viscosity is achieved at pH 8.5 (Meer Corporation, 1958). Boiling of the dispersion results in a permanently reduced viscosity (Whistler, 1973). Heating, predominantly via pressure, gives smooth, uniform, semi-transparent, colloidal dispersions, with concentrations as high as 20 to 25% being achievable in this method relative to the 3 or 4% maximal concentration obtained by non-heated water hydration (Glicksman, 1969). The viscosity of a 1% solution of the highest grade of gum tragacanth is ~3,400 cps. In cold preparations, the maximum viscosity is usually reached after 24 h, but this can be obtained in ~2 h by raising the temperature of the solution to ~50°C (Glicksman, 1969). Viscosity of food products is not necessarily correlated with their mouthfeel. For example, beverages of identical viscosity can be either slimy and coat the mouth or smooth and pleasant (Glicksman, 1969). A correlation between the organoleptic characteristics of hydrocolloid solutions and their rheological behavior has been established (Szczesniak and Farkas, 1962).

Role and Sources of Exudate Gums  ◾  19

Measurements of solution viscosities at various rates of shear showed a relationship between the shape of the curve and the degree of sliminess. This was confirmed in a work on gum-thickened sucrose solutions (Stone and Oliver, 1966). Various hydrocolloid solutions were grouped into three categories: slimy (pectin, methyl cellulose, carboxymethyl cellulose, sodium alginate, locust bean gum), slightly slimy (carrageenan, guar gum and the gum exudates karaya and tragacanth), and non-slimy (starch). This method makes it possible to select the best gums for a desired mouthfeel or texture.

1.6 CHEMICAL PROPERTIES Gums are composed of carbon, hydrogen, oxygen, small quantities of mineral matter and sometimes a little nitrogen (Howes, 1949). The pure gum may also contain small quantities of tannin. The chemical composition of the three main exudate gums is complex and varies to some extent, depending on their source and age. Therefore, it is not possible to provide defined structural formulas for these biopolymers (Verbeken et al., 2003). The chemical structures of gum arabic, gum tragacanth, gum karaya and gum ghatti are described in Chapter 3 and the structures of less known exudates are discussed, where information is available, in Chapter 4.

1.7 COMMERCIAL ASSESSMENTS OF GUMS Climatic and political constraints influence the production and provision of gums. Sudan dominates the production and trade of gum arabic, accounting for 80 to 90% of the world market (Chikamai et al., 1996). Nigeria is the world’s second largest producer and exporter of gum arabic. In recent years, production is Sudan has been estimated at ~40,000 to 50,000 ton/year (Williams et al., 1990b; Williams and Phillips, 2000). Today, prices are at about US $1,500/ton. Europe is the biggest importer of gum arabic, and the US is its second largest market. India is the largest producer and exporter of gum karaya. From the end of the 1960s to the mid-1980s, their annual export averaged 4,000 to 6,000 ton (FAO, 1995). Senegal is the biggest African producer of this gum and exports around 1,000 ton annually. Sudan exports only small amounts of gum karaya. Europe is the largest importer of gum karaya. The price of Indian gum karaya varies between US $2,250/ton and US $6,000/ton, depending on the grade. The world’s largest producer of gum tragacanth is Iran (Anderson and Grant, 1988). At present, the world market for gum tragacanth is estimated to be no more than 500 ton/year (FAO, 1995). The price of ribbons is US $3,000 to 4,000/ton for the lowest grade and up to US $22,000/ton for the highest grade.

1.8 INDUSTRIAL AND OTHER USES Exudate gums are among the oldest natural gums. About 5,000 years ago, they were already being used as thickening and stabilizing agents. The three major exudate gums are gum arabic, gum tragacanth, and gum karaya (Verbeken et al., 2003). They possess a unique range of functionalities (Phillips and Williams, 2001; and see Table 1.1 and Chapter 5). Exudate gums have been important items of international trade in the food, pharmaceutical, adhesive, paper, textile, and other industries for centuries. These are reviewed in Chapters 6, 7 and 9.

20  ◾  Plant Gum Exudates of the World

References Anderson, D. M. W., Douglas, D. M., Morrison, N. A. et al. 1990. Specifications for gum Arabic (Acacia Senegal): analytical data for samples collected between 1904 and 1989. Food Additives and Contaminants A 7:303-21. Anderson, D. M. W., and M. M. E. Bridgeman. 1985. The composition of the proteinaceous polysaccharides exuded by Astragalus microcephalus, A. gummifer and A. kurdicus—the sources of Turkish gum tragacanth. Phytochemistry 24:2301-4. Anderson, D. M. W., and D. A. D. Grant. 1988. The chemical characterization of some Astragalus gum exudates. Food Hydrocolloids 2:417-23. Awouda, H. M. 1973. Social and economic problems of the gum arabic industry. A thesis submitted for the degree of Bachelor of Letters, Oxford University. Ahlcrona, E. 1983. The impact of climate and man on land transformation in Central Sudan: Application of remote sensing. Lund, Sweden: Lund University Press. Ballal, M. E. 1991. Acacia senegal: A multi-purpose tree species for the arid and semi-arid tropics. M.Sc. thesis, University of Wales, UK. Ballal, M. E. 2002. Yield trends of gum Arabic from Acacia senegal as related to some environmental and managerial factors. PhD thesis, University of Khartoum. Ballal, M. E., El Siddig, E. A., Efadl M. A., and O. Luukkanen. 2005a. Gum arabic yield in differently managed Acacia senegal stands in western Sudan. Agroforestry Syst. 63:237-45. Ballal M. E., El Siddig, E. A., Elfadl, M. A., and O. Luukkanen. 2005b. Relationship between environmental factors, tapping dates, tapping intensity and gum arabic yield of an Acacia senegal plantation in western Sudan. J. Arid Environ. 63:379-89. Bandolin, T. H., and R. F. Fisher. 1991. Agroforestry systems in North America. Agroforestry Syst. 16:95-118. Barbier, E. B. 2000. The economic linkages between rural poverty and land degradation: Some evidence from Africa. Agri. Ecosyst. Environ. 82:355-70. Bayoumi, A. M. S. 1996. General protection of forests—Arabic version. Sudan: Khartoum University Press. Bayram, M. 2005. Determination of the sphericity of granular food materials. J. Food Eng. 68:385-90. Blunt, H. S. 1926. Gum Arabic, with special reference to its production in the Sudan. London: Oxford University Press. Boer, E., and A. B. Ella. 2000. Plant resources of South-East Asia No. 18: Plants producing exudates. Leiden: Backhuys Publishers. Boswell, S. B., McCarty, C. D., Hench, K. W., and L. N. Lewis. 1975. Effect of tree density on the first ten years of growth and production of Washington Navel orange trees. J. Am. Soc. Hort. Sci. 100:370-3. Bourne, M. C. 1982. Food texture and viscosity. New York: Academic Press. Cannell, J., Jackson, R. B., Ehleringer, J. R., Mooney, H. A., Sala, O. E., and E. D. Schulze. 1996. Maximum rooting depth of vegetation types at the global scale. Oecologia 108:583-95. Chikamai, B. N., Banks, W. B., Anderson, D. M. W., and W. Weiping. 1996. Processing of gum arabic and some new opportunities. Food Hydrocolloids 10:309-16. Claudius, J. L. 1825. An encyclopedia of agriculture. London: Longman, Hurst, Rees, Orme, Brown, and Green. Davidson, R. L. 1980. Handbook of water-soluble gums and resins. New York: McGraw-Hill Book Company. De Pinto, G. L., Demoncada, N. P., Martinez, M., Degotera, O. G., Rivas, C., and E. Ocando. 1994. Composition of Pereskia-Guamacho gum exudates. Biochem. Systematics Ecol. 22:291-5. De Pinto, G., Martinez, M., De Gutierrez, G. O., Vera, A., Rivas, C., and E. Ocando. 1995. Comparison of two Pithecellobium gum exudates. Biochem. Systematics Ecol. 23:849-53. De Pinto, G., Rodriguez, O., Martinez, M., and C. Rivas. 1993. Composition of Cercidium-Praecox gum exudates. Biochem. Systematics Ecol. 21:297-300. Dziezak, J. D. 1991. A focus on gums. Food Technol. 45:116-32. Eastham, J., Rose, C. W., Charles, E. D., Cameron, D. M., and P. Berliner. 1990. Planting density effect on water use efficiency of trees and pasture in an agroforestry experiment. New Zealand J. Forestry Sci. 20:39-53. Elfadl, M. A., Luukkanen, O., and V. Kaarakka. 1998. Environmental conservation and economic development in the Sudan: A case study of gum arabic. Conference paper presented for Finnish Society for Development Studies. Helsinki (unpublished).

Role and Sources of Exudate Gums  ◾  21 FAO. 1995. Gums, resins and latexes of plant origin (Non-wood forest products 6). Rome: FAO. Flindt, C., Al-Assaf, S., Phillips, G. O., and P. A. Williams. 2005. Studies on acacia exudate gums. Part V. Structural features of Acacia seyal. Food Hydrocolloids 19:687-701. Bache, F. 1819. System of chemistry for the use of students of medicine. Philadelphia: William Fry, Printer. Franzel, S., Coe, R., Cooper, P., Place, F., and S. J. Scherr. 2001. Assessing the adoption potential of agroforestry practices in sub-Saharan Africa. Agri. Syst. 69:37-62. Fries, J. 1990. Management of natural forests in the semi-arid areas of Africa: Present knowledge and research needs. Uppsala: IRDC, Swed. Univ. Agric. Sci. Gerakis, P. A., and C. Z. Tsangarakis. 1970. The influence of Acacia senegal on the fertility of a sand sheet (‘goz’) soil in the central Sudan. Plant Soil 33:81-6. Glicksman, M. 1969. Gum technology in the food industry. New York: Academic Press. Glicksman, M., and E. H. Farkas. 1975. Method of preventing gelation in canned gravy-based pet foods. US Patent Application 3,881,031. Gupta, G. N., Singh, G., and G. R. Kachwaha. 1998. Performance of Prosopis cineraria and associated crops under varying spacing regimes in the arid zone of India. Agroforestry Sys. 40:149-57. Howes, F. N. 1949. Vegetable gums and resins. Waltham, MA: Chronica Botanica Company. Huang, W., and Q. Xu. 1999. Overyield of Taxodium ascendens-intercrop systems. Forest Ecol. Manag. 116:33-8. ICRAF. 1997. Annual report of the International Center for Research in Agroforestry 1996, 179-92. Nairobi, Kenya: ICRAF. Idris, O. H. M., Williams, P. A., and G. O. Phillips. 1998. Characterization of gum from Acacia senegal trees of different age and location using multidetection gel permeation chromatography. Food Hydrocolloids 12:379-88 IIED & IES. 1990. Gum arabic belt rehabilitation in the republic of the Sudan: Stage 1 Report, Vol 1. London: International Institute for Environment and Development (IIED) and Institute of Environmental Studies (IES). Imeson, A. 1992. Exudate gums. In Thickening and gelling agents for food, ed. A. Imeson, 66-97. London: Chapman and Hall. Islam, A. M., Phillips, G. O., Sljivo, M. J., and P. A. Williams. 1997. A review of recent developments on the regulatory, structural and functional aspects of gum arabic. Food Hydrocolloids 11:493-505. Kang, B.T., Atta-Krah, A. N., and L. Reynolds. 1999. Alley farming. United Kingdom: Macmillan Education Ltd. Kang, B. T., Grimme, H., and T. L. Lawson. 1985. Alley cropping sequentially cropped maize and cowpea with Luecaena on a sandy soil in Southern Nigeria. Plant Soil 85:267-77. Le Cerf, D., Irinei, F., and G. Muller. 1990. Solution properties of gum exudates from Sterculia urens (karaya gum). Carbohydr. Polym.13:375-86. Lewis, W. 1791. An experimental history of the materia medica. 4th ed. London: Printed for J. Johnson in St. Paul’s Church-Yard; R. Baldwin in Pater-noster-Row; J. Sewell in Cornbill; and S. Hayes, in Oxford Street. Lowe, B. 1955. Experimental cookery from the chemical and physical standpoint. 4th ed., 16-18. New York: Wiley. Maduako, J. N., and M. O. Faborode. 1990. Some physical properties of cocoa pods in relation to primary processing. IFE J. Technol. 2:1-7. Maiden, J. H. 1890. The chemistry and commercial possibilities of wattle gum. Pharm. J. 20:869-71, 980-2. Malzbender, J. 2003. Comment on hardness definitions. J. Eur. Ceramics Soc. 1355. McCabe, W. L., Smith, J. C., and P. Harriot. 1993. Unit operations of chemical engineering, 5th ed. Singapore: McGraw-Hill. Meer Corporation. 1958. Brochure on water soluble gums. New York: Meer Corp. Mohsenin, N. N. 1970. Physical properties of plant and animal materials. New York: Gordon and Breach. Nair, P. K. R. 1993. An introduction to agroforestry. The Netherlands: Kluwer. Nussinovitch, A. 1997. Hydrocolloid applications: gum technology in the food and other industries, 125-39. London: Blackie Academic & Professional. Omaira, A., Gladys, L. D., Maritza, M., Omaira, G., and S. Lilian. 2007. Structural features of a xylogalactan isolated from Hymenaea courbaril gum. Food Hydrocolloids 21:1302-9. Ong, C. K., Wilson, J., Deans, J. D., Mulayta, J., Raussen, T., and N. Wajja-Musukwe. 2002. Tree-crop interactions: Manipulation of water use and root function. Agri. Water Manag. 53:171-86.

22  ◾  Plant Gum Exudates of the World Ostwald, W. 1922. Theoretical and applied colloid chemistry (translated by M. H. Fisher). New York: Wiley. Partridge, E. 1961. A dictionary of slang and unconventional English, 360. New York: MacMillan. Phillips, G. O., and P. A. Williams. 2001. Tree exudate gums: Natural and versatile food additives and ingredients. Food Ingred. Anal. Int. 23:26, 28. Raddade, E. Y., and O. Luukkanen. 2007. The influence of different Acacia senegal agroforestry systems on soil water and crop yields in clay soils of the Blue Nile region, Sudan. Agri. Water manag. 87:61-72. Raddad, E. Y., Luukkanen, O., Salih, A. A., Kaarakka, V., and M. A. Elfadl. 2006. Productivity and nutrient cycling in young Acacia senegal farming systems on Vertisol in the Blue Nile region, Sudan. Agroforestry Sys. 68:193-207. Sahin, S., and S. G. Sumnu. 2006. Physical properties of foods. New York: Springer. Santiago-Blay, J. A., and J. B. Lambert. 2007. Amber’s botanical origins revealed. American Scientist 95:150-7. Sharawi, H. A. 1986. Acacia senegal in the gum belt of Western Sudan: A cost benefit analysis. MSc. thesis, University College of North Wales, Bangor, UK. Sharrow, S. H., and S. Ismail. 2004. Carbon and nitrogen storage in agroforests, tree plantations, and pastures in western Oregon USA. Agroforestry Sys. 60:123-30. Stone, H., and S. Oliver. 1966. Effect of viscosity on the detection of relative sweetness intensity of sucrose solutions. J. Food Sci. 31:129-34. Suliman, M. M., and A. Drag. 1983. Desertification with special emphasis on carrying capacity and pastoral resources. In I.E.S. preassessment of natural resources in Sudan. University of Khartoum: IES. Szczesniak, A. S., and E. H. Farkas. 1962. Objective characterization of the mouthfeel of gum solutions. J. Food Sci. 27:381-5. Turcotte, D. 2006. A garden for visually impaired visitors. The nature of success: Success for nature, 1-3. Montreal Botanical Garden, Montreal, Canada. www.bgci.org/educationcongress/proceedings/ Verbeken, D., Dierckx, S., and K. Dewettinck. 2003. Exudate gums: occurrence, production, and applications. Applied Microbiology and Biotechnology 63:10-21. Vilela, A. E., and D. A. Ravetta. 2005. Gum exudation in South-American species of Prosopis L. (Mimosaceae). J. Arid Environ. 60:389-95. Wadell, H. 1935. Volume, shape and roundness of quartz particles. J. Geol. 43:250-80. Wang, W. P., and D. M. W. Anderson. 1994. Non-food applications of tree gum exudates. Chem. Ind. Forest Prod. 14:67-76. Weiping, W. 2000. Tragacanth and karaya. In Handbook of hydrocolloids, ed. G. O. Philips, and P. A. Williams, 155-68. Cambridge: Woodhead.  Whistler, R. L. 1973. Industrial gums, 2nd edition. New York: Academic Press. Wiesner, J. V. 1927. Die Rohstoffe des Pflanzenreichs (Leipzig, Engelmann). In Vegetable gums and resins, ed. F. N. Howes, 6. Waltham, MA: Chronica Botanica Company. Williams, P. A., and G. O. Phillips. 2000. Gum arabic. In Handbook of hydrocolloids, ed. G. O. Philips, and P. A. Williams, 155-68. Cambridge: Woodhead.  Williams, P. A., Phillips, G. O., and R. C. Randall. 1990a. Structure-function relationships of gum Arabic. In Gums and stabilizers for the food industry 5, ed. G. O. Phillips, D. J. Wedlock, and P. A. Williams, 25-36. Oxford: IRL Press at Oxford University Press. Williams, P. A., Phillips, G. O., and M. A. Stephen. 1990b. Spectroscopic and molecular comparison of three fractions from Acacia senegal gum. Food Hydrocolloids 4:305-11. Yagoub, A. M., Fadlalla, B., Abdalla, A., and M. A. Abdel Rahman. 1993. Indication of recovery in biomass productivity and soil organic matter of Sudan’s Sahel. A case study of northern Kordofan. National Workshop on Dry Land Husbandry in the Sudan. Adis Ababa. Young , A. 1989. Agroforestry for soil conservation. Oxon, UK: CAB and ICRAF. Zinkhan, F. C., and D. E. Mercer. 1996. An assessment of agroforestry systems in the Southern USA. Agroforestry Sys. 35:303-21.

Chapter 2

Physiological Aspects of Polysaccharide Formation in Plants 2.1 INTRODUCTION Gum exudates can be part of the plant’s normal metabolism, but in most cases they are attributed to pathological phenomena. An understanding of the factors affecting gum formation is of fundamental importance in finding a cure for the disorder in fruit trees, as well as in stimulating prolific gum production for commercial collection. Pathological exudation, or “gummosis”, owes its origin to a number of unrelated factors, such as tissue infections caused by disease, pathogens and parasitic invasion by microorganisms, fungi, viruses and insects, physical injury, chemicals, stress, and various climatic conditions. This chapter delineates the different causes of gummosis and its protective functions. It details the involvement of the primary cell wall in the early stages of gum formation, the interference of ethylene with the balanced biosynthesis of cell-wall polysaccharides, the development and ultrastructure of gum ducts, the induction of gummosis by the ethylene generator ‘ethephon’ for enhanced commercial gum production, and aspects of gummosis in fruit trees.

2.2 STRESS FACTORS, ETHYLENE AND GUMMOSIS Gummosis is the outcome of the metamorphosis of organized cell-wall materials into unrecognizable amorphous substances such as gums (polysaccharides) or resins (Fahn, 1979). Starch can also be a source for gum formation. Different views have been expressed as to the way in which gum is produced during gummosis. A number of reports credit gum formation to cellwall decomposition (Tschirch, 1889; Butler, 1911; Groom, 1926; Vander Mollen et al., 1977; Stosser, 1979). However, in Citrus and some other plants, gum production results from the activity of secretory cells, i.e. cells which eliminate the secreted substance from the cytoplasm 23

24  ◾  Plant Gum Exudates of the World

(Catesson et al., 1976; Moreau et al., 1978; Catesson and Moreau, 1985; Gedalovich and Fahn, 1985; Morrison and Polito, 1985). In extreme cases, gummosis leads to the formation of lysigenous (i.e. of or pertaining to the space formed following cell lysis) gum cavities or ducts (Butler, 1911). Gummosis can be the consequence of physiological disturbances, mechanical damage, insects or microorganisms. Resin and gum ducts develop normally in some plants, or in response to external stimuli, such as microorganisms or growth substances. Among the latter, ethylene is the most effective stimulus (Fahn, 1988). Carbohydrate mucilages and gums are synthesized by dictyosomes (also called Golgi apparatus, Golgi body or Golgi complex: this is an organelle found in most eukaryotic cells whose primary function is to process and package the macromolecules that are synthesized by the cell), but virtually every cell compartment has been suggested to play a role in the secretion of lipophilic substances (Fahn, 1988). Once eliminated from the secretory structures, the secreted materials do not normally re-enter the plant’s metabolism. Secretion may take place in specially formed cell complexes or in ordinary tissues (Fahn, 1979). The first type appears in some Prunoideae and Meliaceae species (Butler, 1911; Groom, 1926), where special groups of parenchyma cells (i.e. thin-walled ground-tissue cells that make up the bulk of most non-woody structures, although sometimes their cell walls can be lignified) are formed by the cambium (i.e. a layer or layers of tissue that are the source of cells for secondary growth), instead of the normal wood elements (Fahn, 1979). Immediately after formation of these special groups of parenchyma cells, gummosis begins in the center of these complexes and then proceeds to the periphery (Fahn, 1979). Disintegration of each cell’s walls initiates in the primary cell wall and proceeds towards the innermost lamella of the secondary cell wall (i.e. all cell walls contain two layers, the middle lamella and the primary cell wall, and many cells produce an additional layer, called the secondary wall. The middle lamella serves as a cementing layer between the primary walls of adjacent cells). The resultant cavity is filled with gum. Gummosis may also occur in the bark (i.e. the outermost layers of stems and roots of woody plants), as in the case of gum arabic of Acacia senegal and other Acacia species. In cherry, vessels (i.e. specialized cells for fluid transport) of otherwise normal wood are often filled with gum (Fahn, 1974), formed only by the lamellae of the secondary wall. When plant organs of Dianthus and Ulmus were experimentally infected with a pathogen, gum production was shown to be the result of secretion from vessel-associated parenchyma cells and not of wall lysis (Catesson et al., 1976). A particular type of traumatic duct forms kino resins. These are found in the wood of the genus Eucalyptus (Fig. 2.1). In contrast to gums, kino contains polyphenols. Kino veins are 1.5 to 5 mm in length; they are oriented longitudinally, and occur as isolated veins or in a dense anastomosing (i.e. coalescing) network (Fahn, 1979). Kino veins form in the cambial region as an outcome of injury and develop in the zone of traumatized parenchyma. At specific foci, assemblies of polyphenol-containing cells break down and form ducts into which the contents of these kino-producing cells are released. In parallel, the cells surrounding the future kino veins divide and form peripheral “cambium”. Derivatives of these latter cells grow, accumulate polyphenols, break down and enlarge the quantity of kino already present in the ducts. The final phase includes production of a layer of derivatives by the peripheral “cambium”, which in turn become suberized in the shape of a typical periderm (i.e. the innermost area of the bark, which in older stems is a living tissue) (Fahn, 1979; Skene, 1965). As stated, gummosis is the process of accumulation and exudation of gum from plants (Butler, 1911). In numerous plants, gum production represents a generalized ethylene-mediated response to aging, stress, wounding, and injury by insects and pathogens (Butler, 1911; Higgins, 1919; Smith and Montgomery, 1959; Esau, 1965; Talboys, 1968; Agrios, 1969; Martin and Nelson, 1969; Nelson, 1978; Saniewski et al., 2006). Cell lysis in immature secondary xylem and periderm

Physiological Aspects of Polysaccharide Formation in Plants  ◾  25

Figure 2.1  Kino veins in the wood of the genus Eucalyptus (courtesy of O. Ben-Zion).

of the stem can form lacunae (bearing in mind that in young stems, the tissues from the outside to the inside include: epidermis, periderm, cortex, primary phloem, secondary phloem, vascular cambium and then xylem). Lacunae are sites of gum synthesis and accumulation (Wilde and Edgerton, 1975; Stosser, 1978a,b,c; Bukovac, 1979). The plant protects itself from water loss and pathogen invasion by sealing the wounds and occluding the xylem vessels with the produced gum, while the xylem is responsible for the transport of water and soluble mineral nutrients from the roots throughout the plant. The gums frequently include phenolic compounds that may assist in plant protection (Talboys, 1968). The yellow or brown colors of the gum may be a result of the polymerization of phenolic substances to form polyphenols. Severe gummosis is associated with shoot dieback (Wilde and Edgerton, 1975). Extensive ethephon-induced gummosis and shoot dieback can occur, even when the ethephon is applied at the recommended rates, especially if trees are under stress or the ethephon application is followed by exposure to high temperature (Wilde and Edgerton, 1975; Olien and Bukovac, 1978). Material was found plugging the vessels in longitudinal sections of sweet cherry (Prunus avium L.) shoots (Fig. 2.2) in which gum production had been stimulated by treatment with ethephon (Stosser, 1978a). Gums are complexes of different substances, mostly polysaccharides with various structures. The composition of the gum polysaccharides differs from species to species and from cultivar to cultivar (Boothby, 1983; Saniewski et al., 2002, 2004a,b). However, the composition and chemical characteristics of gums are genotypic-specific (Dea, 1970; Smith and Montgomery, 1959; Keegstra

26  ◾  Plant Gum Exudates of the World

A

B

Figure 2.2  (A) Exudate of wild cherry. (B) Gummosis of sweet cherry (Prunus avium) tree. The gum from bark wounds is aromatic and can be chewed as a substitute for chewing gum (courtesy of O. Ben-Zion).

Physiological Aspects of Polysaccharide Formation in Plants  ◾  27 O Cl

P OH OH

Figure 2.3  Ethephon, a plant growth regulator. Upon metabolism by the plant, it is converted into ethylene, a potent regulator of plant growth and maturity (http://en.wikipedia.org/wiki/ Image:Ethephon.png, courtesy of Edgar 181).

et al., 1973). For example, sour cherry (Prunus cerasus L.) gum is a weakly acidic arabinogalactan (Smith and Montgomery, 1959), similar in structure to the hemicellulosic arabinogalactan of larch (Aspinall, 1969) and the pectic arabinogalactan of suspension-cultured sycamore cells (Keegstra et al., 1973). Ethylene or ethylene-releasing compounds such as ethephon (2-chloroethyl-dioxido-oxophosphorane, molar mass 142.48 g/mol, density 1.58 g/cm3, melting point 74°C) (Fig. 2.3) stimulate gum formation (Boothby, 1983) in trees and fruits of stone-fruit species of the Rosaceae family, such as almonds (Fig. 2.4) (Ryugo and Labavitch, 1978), apricots (Bradley et al., 1969), Japanese apricots (Li et al., 1995), cherries (Olien and Bukovac, 1982a,b), ornamental Japanese cherries

Figure 2.4  Exudate of the almond tree Pruaus dulcis (courtesy of O. Ben-Zion).

28  ◾  Plant Gum Exudates of the World A

B

Figure 2.5  (A) Exudate of the plum tree (Prunus domestica, the species of most “plums” and “prunes” sold as such). (B) Gummosis of plum tree (courtesy of O. Ben-Zion).

(Ueda et al., 2003), peaches (Buchanan and Biggs, 1969; Li et al., 1995) and plums (Fig. 2.5) (Bukovac et al., 1969). Ethylene is believed to be the main factor responsible for the induction of gummosis. In peaches and Japanese apricots, gummosis can also be caused by the fungi Botryosphaeria dothidea and Lasiodiplodia theobromae (syn. Botryodiplodia theobromae) (Okie and Reilly, 1983; Li et al., 1995; Beckman, 2003). In plum and cherry trees, gummosis can be caused by the bacterium Pseudomonas syringae or the fungus Chondrostereum purpureum (syn. Stereum purpureum (Boothby, 1983)). In apricot shoots, gum formation can be caused by Monilinia laxa, Monilinia fructigena, Valsaria insitiva (syn. Cytospora cincta), or by larvae of Grapholita molesta (Rosik et al., 1971, 1975). Gummosis of fungal origin significantly reduces tree growth and fruit yield in susceptible peach

Physiological Aspects of Polysaccharide Formation in Plants  ◾  29 O

O

O

Figure 2.6  Methyl jasmonate (MeJA) (http://en.wikipedia.org/wiki/File:Jasmonic_acid_structure. png, courtesy of Edgar 181).

cultivars (Beckman, 2003). This kind of gummosis is difficult to control with fungicides (Li et al., 1995, Beckman, 2003). In fact, breeding cultivars resistant to pathogens and insects may be the only effective way of limiting or eliminating gummosis. The effect of methyl jasmonate (MeJA; methyl (1R,2R)-3-oxo-2-(2Z)-2-pentenyl-cyclopentaneacetate, molecular formula C13H20O3, molar mass 224.3 g/mol, melting point <25°C, boiling point 88-90°C at 0.1 mm Hg) (Fig. 2.6) on gum induction was studied in relation to the action of ethylene in peach (Prunus persica Batsch cv. Benishimizu) shoots. Ethephon at 1 or 2% (w/w) in lanolin induced gum production and strongly enhanced the promotive effect of MeJA on gum formation. MeJA also induced anthocyanin (water-soluble vacuolar pigments that may appear red, purple, or blue according to pH) accumulation in concurrently growing shoots, but ethephon did not (Saniewski et al., 1998). Application of naphthalene acetic acid (NAA) (Fig. 2.7) in solution to peach trees can inhibit sprout formation, and severe gummosis is observed around the treated areas (Couvillon et al., 1977). Internal levels of free auxin may be correlated with the rate of ethylene formation. Regulation of auxin-induced ethylene biosynthesis has been found in higher plants. Indole-3-acetic acid (IAA) (Fig. 2.8) (the most important member of the auxin family, generating most of auxin’s effects in intact plants, and the most potent native auxin) stimulates ethylene production by inducing synthesis of 1-aminocyclopropane-1-carboxylic acid (ACC) from S-adenosylmethionine (SAM) (Yang and Hoffman, 1984). In peach trunks, gummosis induced by NAA is associated with ethylene production (Saniewski et al., 2004b).

O OH

Figure 2.7  α-Naphthalene acetic acid (α-NAA) (http://en.wikipedia.org/wiki/File:1-Naphthaleneacetic_acid.png, courtesy of Rune Welsh).

30  ◾  Plant Gum Exudates of the World O OH N H

Figure 2.8  Indole-3-acetic acid (IAA) (http://en.wikipedia.org/wiki/File:Indol-3-ylacetic_acid2. svg, courtesy of Photohound).

2.3 BORERS AND GUM FORMATION The infliction of ecological stress on plants has implications for the insects that feed on them: in some cases, stress renders the plants more suitable as hosts by elevating nutrient concentrations and/or reducing chemical defenses (e.g., Rhoades, 1979; Mattson and Haack, 1987a,b; Holtzer et al., 1988; White, 1993), while in others it reduces host quality (e.g., Price and Clancy 1986; Price et al. 1987a,b; Hanks and Denno, 1993). Insects that bore into the phloem and cambium of woody vegetation cull the most benefits from host-plant stress due to fire damage, lightening damage, attack by other insect species and water shortage (Haack and Slansky, 1987; Larsson, 1989; Waring and Cobb, 1992; Koricheva et al., 1998). In general, borers attack all kinds of trees, but they are only successful in trees that are under stress. Additional stresses include old age, soil deficiency, too much or too little water, discontinued air and water supply from the roots, soil compaction, and removing the tree from its natural surroundings (www.roystree.com/roystree). The cause of the stress must be determined in order to eliminate it before the borers kill the tree. There is no successful recommended chemical treatment for borers. The only way to battle them is to improve the tree’s health, so that it can resist the borers itself. When the tree is too far gone, the only option is to dig it up and plant another one (www.roystree.com). Bark beetles depend specifically on water stress to break down their coniferous hosts’ resistance (Coulson, 1979; Mattson and Haack, 1987a); for instance: drought stress predisposes eucalyptus to attack by the cerambycid beetle Phoracantha semipunctata (Coleoptera: Cerambycidae) (Chararas, 1969). Eucalyptus species (angiosperms) are attacked by the phloem-boring larvae of P. semipunctata. This beetle is hardly ever a nuisance in its native Australia; however, in areas of the world where eucalyptus has been artificially introduced, P. semipunctata can kill living and apparently vigorous eucalyptus trees (Hanks et al., 1995). The adult female P. semipunctata deposits eggs in batches under unfastened bark and the larvae break through the bark and dig along the cambium, establishing themselves in as little as 3 months (Hanks et al., 1993a). The natural defense mechanism of most trees against borers is the production of kino, gum, latex or resin. The adult female borer, be it a beetle, a moth or a weevil, lays its eggs in as many trees as it can. Some borers are host-specific and only attack particular trees. The eggs hatch into young larvae and begin eating the tree, usually in or beneath the bark. Although a healthy tree can harm the insects via the secretion of kino, gum, latex or resin, stressed trees do not have sufficient exudates, and the borers are free to invade them: thus borers are always a secondary problem (www.roystree.com/roystree). In numerous plants, resistance to cerambycid beetles has been credited to the excessive moisture content of their bark or sapwood, high bark turgor pressure, flow of sap or resin, and plant secondary chemicals (Hanks, 1999). Eucalyptus resistance to attack by P. semipunctata has long been attributed to kino, a dark exudate that is secreted upon damage to the bark (Hillis, 1978).

Physiological Aspects of Polysaccharide Formation in Plants  ◾  31

Nevertheless, in this particular case, empirical evidence suggests that resistance to colonization by neonate larvae is not consistently associated with kino production (Hanks et al., 1991), which seems an unlikely first line of defense because its induction may require several days, or even weeks (Tippett, 1986), while the larvae penetrate the bark and reach the cambium within 24 h (Hanks et al., 1999).

2.4 GUM DUCTS Many important natural chemicals that have been utilized by man through the ages are manufactured by the secretory tissues of vascular plants. These chemicals have a variety of functions in the plants themselves (Fahn, 1988). Secretory tissues are usually classified according to the substances they produce, and include hydathodes (a tissue that secretes water through pores in the epidermis or leaf margins, typically at the tip of a marginal tooth or serration), salt glands, nectaries (a multicellular glandular structure that secretes nectar, found in flowers and on vegetative parts in some species of plants, often forming projections, lobes, or disk-like structures), mucilagesecreting cells, trichomes (on plants these are epidermal outgrowths of various kinds), ducts and cavities, gum ducts, enzyme-secreting glands of carnivorous plants, myrosin cells (i.e. idioblasts containing the enzyme myrosinase), stinging trichomes, oil cells, oil-secreting trichomes, osmophores, oil cavities, resin ducts, flavonoid-secreting tissues and laticifers (a specialized cell or row of cells containg latex) (Fahn, 1979). Natural gums and resins are considered to be by-products or end products of certain metabolic changes. Gum formation protects an injured plant part by sealing the damaged region and eliminating infection and water loss. Gums are present either in the intercellular spaces (ducts or cavities) of plant parts or as exudates produced due to injury. The ducts or cavities formed due to injury are called traumatic ducts/cavities (Nair, 2005). The development of traumatic ducts has been studied in the bark and/or wood of several Indian plant species (Nair et al., 1980, 1983, 1985). Gum ducts occur frequently in the vegetative organs of angiosperms. Ducts lined with typical parenchyma cells, known as epithelial cells, are located in many genera of Asteraceae, Apiaceae, Anacardiaceae, Fabaceae and Rosaceae, among others (Fahn, 1979). Aside from the naturally occurring ducts, gum and gum-resin ducts can be induced in plants organs. Insects, microorganisms and mechanical injury are some of the factors that contribute to the creation of gum ducts in plants (Rajput et al., 2005). The formation of gum-resin ducts in response to certain chemicals, such as ethephon and paraquat [the trade name for N,N’-dimethyl-4,4’-bipyridinium dichloride, a viologen (derivative of 4,4’-bipyridyl) which is used as a quaternary ammonium herbicide and is extremely poisonous to humans if swallowed], in the bark and sapwood of Azadirachta indica has been studied (Nair et al., 1980, 1985). Formation of gum-resin ducts was observed with only a small quantity of gum exudation observed, while the trees treated with ethephon showed plentiful gum exudation for prolonged periods. The gum-resin ducts that develop in response to injury remain active for short periods while the gum-resin ducts formed during injury followed immediately by fungal infection are active for a longer time and form several tangential rows of ducts (Nair et al., 1980). The distribution, development and structure of gum ducts were studied in Lannea coromandelica, an important gum-yielding plant of the family Anacardiaceae. Gum ducts are present in leaves, stems and fruits and are most abundant in the stem bark (Venkaiah and Shah, 1984). There is an integrated ramified duct system in the bark of the trunk. Ducts are classified according to their position and arrangement as vertical, horizontal (radial and tangential) or irregular. The gum is formed in two stages: it is secreted from the epithelial cells into the duct lumen, and

32  ◾  Plant Gum Exudates of the World

disintegration of the epithelial and neighboring cells follows, i.e. gummosis occurs. Ducts develop schizogenously in the primary phloem, pith and xylem rays and lysigenously in the secondary phloem and phelloderm (Venkaiah and Shah, 1984). Duct initiation is indicated by the formation of an intercellular space among a group of densely stained procambial phloem cells. Duct formation starts with dissolution of the wall’s middle lamella. The consequent swelling and separation of the cells along their radial walls cause the duct to widen (Venkaiah, 1992). During separation of the radial walls, dictyosomes and paramural bodies (membranous structure located between the plasma membrane and cell wall of plant cells. If it contains internal membranes, it may be called a lomasome, if not, it may be termed a plasmalemmasome) are observed in the peripheral cytoplasm at the site of dissolution. Plasmodesmata occur in the radial and inner tangential walls of epithelial cells of developing gum ducts (Venkaiah, 1992). The epithelial cells have a dense cytoplasm and contain rough endoplasmic reticulum, ribosomes, polysomes, mitochondria with swollen cristae (internal compartments formed by the inner membrane of a mitochondrion), plastids with poorly developed membranes, dictyosomes and vesicles. Dictyosomes and rough endoplasmic reticulum seem to be involved in the gum’s secretion. The polysaccharide gum constituents appear to originate from the outer wall layers of the epithelial cells. Following gum secretion, the epithelial cells degenerate (Venkaiah, 1992).

2.5 GUMMOSIS IN FRUIT TREES By definition, a fruit tree is a tree that bears fruit—the structures formed by the ripened ovary of a flower containing one or more seeds. In horticultural parlance, the term applies to trees that provide fruit for human consumption. Due to their wide-ranging importance, fruit trees have been investigated or used as models in many studies dealing with gummosis, ducts, duct structure and mechanisms related to duct or gum formation. The following provides some examples illustrating the various aspects of gummosis in fruit trees. “Citrus” is both a common term and a genus of flowering plants in the family Rutaceae, originating in tropical and subtropical southeastern regions of the world. Fahn and Rachmilevitz (Fahn and Rachmilevitz, 1970; Rachmilevitz and Fahn, 1973) studied secretory-cell ultrastructure in Citrus nectaries at various developmental stages. Towards the secretion phase, they detected a pronounced increase in the amount of endoplasmic reticulum with cisternae (flattened membrane disks that make up the Golgi apparatus. They carry the Golgi enzymes that help or modify cargo proteins traveling through them to other parts of the cell), with concomitant dilation and association with numerous vesicles. Gum ducts developing as a result of injury or infection occur in Acacia species, members of the Prunoideae and Citrus species (Gedalovich and Fahn, 1985). Activity of secretory cells results in gum production in Citrus. When gum ducts develop in the cambial region of Citrus trees, many active polysaccharide-containing dictyosomes are observed in the epithelial cells. The gum is first secreted into the space between the plasmalemma and the cell wall facing the duct lumen, and then to the outside of the cell wall (Fahn, 1988). The well-known ‘brown rot’ gummosis of Citrus trees is caused by the fungus Phytophthora citrophthora. When Citrus trees were artificially infected with this fungus, gum ducts began to develop schizogenously in the cambium (Fig. 2.9). With the ongoing activity of the cambium and differentiation of the xylem, the gum ducts became set in the latter and epithelial cell activity ceased. The cell wall of numerous epithelial cells broke and the gum that was still present in the cells was released (Gedalovich and Fahn, 1985). When ethrel [1-amino-cyclopropan-l-carboxylic acid (ACC)] and auxins were applied to branches of Citrus trees, they affected the formation of

Physiological Aspects of Polysaccharide Formation in Plants  ◾  33

Figure 2.9  Gummosis of Citrus trees (courtesy of O. Ben-Zion).

gum ducts in a manner similar to that caused by the fungus P. citrophthora (Gedalovich and Fahn, 1985). Ethrel (0.05%) in water induced the formation of gum ducts of the same length as those formed after infection with the fungus, i.e. 3 to 5 cm above and below the infected or treated wound. Elevated concentrations of ethrel resulted in much longer gum ducts (up to 15 cm) (Gedalovich and Fahn, 1985). The rate of cambial activity at the time of application affected the response of the branches to ethrel and to a greater extent, their response to auxin. Stem segments artificially contaminated with the fungus were found to release ethylene. As gum ducts were also formed in response to ACC, which is a precursor of ethylene in higher plants and not in fungi, it appears that the production of ethylene by the infected stem tissue has a direct influence on gumduct production in Citrus trees (Gedalovich and Fahn, 1985). Another example of gummosis in fruit trees is cashew gummosis which is caused by Lasiodiplodia theobromae (Botryodiplodia theobromae). This is the most important disease of cashew in the semiarid conditions of northeastern Brazil. Severe epidemics have occurred there in recent years, due to predisposition by water stress and the predominant use of a vulnerable clone cultivar (Freire et al., 2002). The disease is distinguished by swollen cankers in the trunk or woody branches, which may crack and ooze a transparent resin-like gum (Freire et al., 2002). Damage from gummosis includes decreased water and nutrient transport, destruction of branches, reduction of

34  ◾  Plant Gum Exudates of the World

photosynthesis, dieback, and plant death (Bezerra et al., 2004). The causal agent of gummosis dissemination was isolated from non-symptomatic seeds and transplants. It is likely that those plantpropagating materials act as a primary source of inoculum (Freire et al., 1999). The root beetle, Marshallus bondari, has been proposed as both a vector and facilitator of infection (Freire et al., 2002). Disease symptoms can be observed as early as the first year after planting, even though it is only after the second year that severe damage occurs (Cardoso et al., 2004). Measures for controlling gummosis, such as surgical removal of cankers followed by a copper fungicide treatment, and managing the root beetle by aluminum sulfite gas and sanitation, have had little success (Cardoso et al., 1995). The search for genetic resistance has been successful in mango (Prakash and Raoof, 1989); in cashew, however, there have been no reports of resistance to L. theobromae. Therefore, selection and evaluation of cashew cultivars that exhibit resistance to gummosis appears to be crucial. Toward this aim, 28 genotypes were selected from an open-pollinated population of dwarf cashew, cloned by grafting, and screened in field experiments for yield, quality and gummosis tolerance under high disease pressure. After 3 years, four clones were selected and planted in a similar experiment with the best commercial clone as the control treatment. Most genotypes were observed to be susceptible to gummosis; only one clone (CAPC 42) exhibited consistent and stable resistance in both experiments (Cardoso et al., 2006). These results demonstrate the existence of genetic resistance to gummosis in dwarf cashew germplasm and the source of the resistance could potentially be used in future breeding programs, in genetics studies, and for the identification of molecular markers (Cardoso et al., 2006). Yet another example of gummosis in fruit trees is the well-known plum wilt, symptoms of which include sudden wilting of the leaves on a branch or on the whole tree in the spring or early summer. The base of the wilted segment reveals dark, dead bark. Frequently, this dead area extends along one side of the trunk all the way to ground surface. Within a year of first wilting, the whole tree may die (Hesler and Whetzel, 1917). Gum is exuded from those trees that wilt in the early summer. Later, beetles bore holes in the bark through which gum flows freely. Death of the tree follows in the fall and winter, and even if the tree does not die, no leaves are put out the next spring (Hesler and Whetzel, 1917). Plum wilt is due to the fungus Lasiodiplodia triflorae. The pathogen enters the tree through wounds, one-third of the infections occurring through borer wounds. Wounds resulting from the Black Spot pathogen Bacterium pruni are also common points of entry for the plum wilt fungus (Hesler and Whetzel, 1917). Once it infects the plum tree, the fungus spreads in the bark. The medullary rays and sap tubes are further invaded when the mycelium passes from one duct to another, through wall pits. The fungus spreads promptly through the ducts, and gum is produced during their invasion: a layer of gum-filled tissue can be found around the margin of the infected area, which sharply limits the fungus for a time. Eight- to ten-year-old trees develop gum more readily, but not enough of it to prevent the rapid spread of the mycelium. While gum stops the fungus temporarily, its deposit in the ducts injures the host. When the attack results in gum deposition throughout a cross-section of a trunk or limb, the affected member dies, apparently from lack of water (Hesler and Whetzel, 1917).

2.6 INDUCED INOCULATION AND GUM YIELD An understanding of the factors that affect gum formation is of fundamental importance to finding a cure for the disorder in fruit trees, as well as to enabling prolific gum collection for commercial purposes. The influence of inductive inoculation on gum arabic yield production was studied by inoculating mature A. senegal trees in Rotto (Senegal) with Rhizobium. Eighty similar

Physiological Aspects of Polysaccharide Formation in Plants  ◾  35

10-year-old trees, with 5 m distance between them, were chosen (Faye et al., 2006). Soil characteristics did not differ within the plantation. The plantation was divided into two sections: one was inoculated at the beginning of the rainy season, and subjected to tapping at the same intensity and at the same time (Faye et al., 2006). The other section represented non-inoculated controls. Under low rainfall (250 mm), results were not significantly different between the sections. The trees were then reinoculated before the second rainy season. Following this wetter (440 mm precipitation) rainy season, the gum arabic yield of inoculated trees was significantly higher than that of their non-inoculated counterparts. The researchers concluded that the inoculation of 10-year-old trees enhances gum arabic yield under certain natural conditions (Faye et al., 2006). Another study dealt with the dependence of gum yield on other factors. Gum production, and genetic variation in shoot growth and water-use efficiency were compared among eight A. senegal provenances originating from contrasting conditions in the gum arabic belt in central Sudan. The clay provenances were distinctly superior to the sand provenances in all traits studied, particularly in basal diameter and crown width, reflecting their adaptation to the environment. The variation in water use and gum production was greater between provenance groups than within them, suggesting that selection among, rather than within, provenances can result in a distinct genetic gain in gum yield (Raddad and Luukkanen, 2006).

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36  ◾  Plant Gum Exudates of the World Chararas, C. 1969. Biologie et écologie de Phoracantha semipunctata F. (Coleoptera Cerambycidae xylophage) ravageur des eucalyptus en Tunisie, et méthodes de protection des peuplements. Ann. Inst. Natl. Rech. Tunisie 2:1-37. Coulson, R. N. 1979. Population dynamics of bark beetles. Annu. Rev. Entomol. 24:217-46. Couvillon, G. A., Bass, S., Joslin, B. W. et al. 1977. NAA-induced sprout control and gummosis in peach. Hortscience 12:123-4. Dea, I. C. N. 1970. The polysaccharide gum exudate of Prunus avium var. Actiana. Phytochemistry 9:1299302. Esau, K. 1965. Plant anatomy, second edn, 46, 260-1. New York: John Wiley and Sons. Fahn, A. 1974. Plant anatomy. second edn. Oxford: Pergamon Press. Fahn, A. 1979. Secretory tissue in plants. London: Academic Press. Fahn, A. 1988. Tansley Review No. 14. Secretory tissues in vascular plants. New Phytol.108:229-57. Fahn, A., and T. Rachmilevitz. 1970. Ultrastructure and nectar secretion in Lonicera japonica. In New research in plant anatomy, ed. N. K. B. Robson, O. F. Cutler, and M. Gregory, 51-56. London: Academic Press. Faye, A., Sarr, A., and D. Lesueur. 2006. Effect of inoculation with rhizobia on the gum-arabic production of 10-year-old Acacia senegal trees. Arid Land Res. Manag. 20:79-85. Freire, F. C. O., Cardoso, J. E., Santos, A. A., and F. M. P. Viana. 2002. Diseases of cashew (Anacardium occidentale L.) in Brazil. Crop Prot. 21:489-94. Freire, F. C. O., Kozakiewicz, Z., and R. R. M. Paterson. 1999. Mycoflora and mycotoxins of Brazilian cashew kernels. Mycopathologia 145:95-103. Gedalovich, F., and A. Fahn. 1985. The development and ultrastrueture of gum ducts in Citrus plants formed as a result of brown-rot gummosis. Protoplasma 127:73-81. Groom, P. 1926. Excretory systems in secondary xylem of Meliaceae. Ann. Bot. 40:633-49. Haack, R. A., and F. Slansky Jr. 1987. Nutritional ecology of wood feeding Coleoptera, Lepidoptera, and Hymenoptera. In Nutritional ecology of insects, mites, spiders, and related invertebrates, ed. F. Slansky Jr, and J. G. Rodriguez, 449-56. New York: John Wiley. Hanks, L. M. 1999. Influence of the larval host plant on reproductive strategies of cerambycid beetles. Annu. Rev. Entomol. 44:483-505. Hanks, L. M., and R. F. Denno. 1993. Natural enemies and plant water relations influence the distribution of an armored scale insect. Ecology 74:1081-91. Hanks, L. M., McElfresh, J. S., Millar, J. G., and T. D. Paine. 1993a. Phoracantha semipunctata (Coleoptera: Cerambycidae), a serious pest of Eucalyptus in California: biology and laboratory rearing procedures. Ann. Entomol. Soc. Am. 86:96-102. Hanks, L.M., Paine, T. D., and J. G. Millar. 1991. Mechanisms of resistance in Eucalyptus against larvae of the eucalyptus longhorned borer (Coleoptera: Cerambycidae). Environ. Entomol. 20:1583-8. Hanks, L. M., Paine, T. D., Millar, J. G., Campbell, C. D., and U. K. Schuch. 1999. Water relations of host trees and resistance to the phloem-boring beetle Phoracantha semipunctata F. (Coleoptera: Cerambycidae). Oecologia 119:400-7. Hanks, L. M., Paine, T. D., Millar, J. G., and J. L. Hom. 1995. Variation among Eucalyptus species in resistance to eucalyptus long horned borer in California. Entomol. Exp. Appl. 74:185-94. Hesler, L. R., and H. H. Whetzel, 1917. Manual of fruit diseases. New York: The Macmillan Company. Higgins, B. B. 1919. Gum formation with special reference to cankers and decays of woody plants. GA Agric. Exp. Stn. Bull. No. 127. Hillis, W. E. 1978. Wood quality and utilization. In Eucalypts for wood production, ed. W. E. Hillis, and A. G. Brown, 259-89. Melbourne: CSIRO. Holtzer, T. O., Archer, T. L., and J. M. Norman. 1988. Host suitability in relation to water stress. In Plant stress-insect interactions, ed. E. A. Heinrichs, 111-37. New York: John Wiley. Keegstra, K., Talmadge, K. W., Bauer, W. D., and P. Albersheim. 1973. The structure of plant cell walls. III. A model of the walls of suspension-cultured sycamore cells based on the interconnections of the macromolecular components. Plant Physiol. 51:188-96. Koricheva, J., Larsson, S., and E. Haukioja. 1998. Insect performance on experimentally stressed woody plants: A meta-analysis. Annu. Rev. Entomol. 43:195-216.

Physiological Aspects of Polysaccharide Formation in Plants  ◾  37 Larsson, S. 1989. Stressful times for the plant stress-insect performance hypothesis. Oikos 56:277-83. Li, H.-Y., Cao, R.-B., and Y. T. Mu. 1995. In vitro inhibition of Botryosphaeria dothidea and Lasiodiplodia theobromae, and chemical control of gummosis disease of Japanese apricot and peach trees in Zhejiang Province, China. Crop Prot. 14:187-91. Martin, G. C., and M. Nelson. 1969. Peach thinning with ethylene. HortScience 4:328-9. Mattson, W. J., and R. A. Haack. 1987a. The role of drought stress in provoking outbreaks of phytophagous insects. In Insect outbreaks, ed. P. Barbosa, and J. C. Schultz, 365-407. San Diego: Academic Press. Mattson, W. J., and R. A. Haack. 1987b. The role of drought in outbreaks of plant-eating insects. BioScience 37:110-8. Moreau, M., Catesson, A. M., Peresse, M., and Y. Czaniski. 1978. Dynamique comparée des réactions cytologiques du xylème de l’oeillet en presence de parasites vasculaires. Phytopathologische Zeitschrift 91:289306. Morrison, J. C., and Y. S. Polito. 1985. Gum duct development in almond fruit, Prunus dulcis (Mill.) D. A. Webb. Bot. Gaz. 146:15-25. Nair, B. 2005. Sustainable utilization of gum and resin by imporoved tapping technique in some species. http://www.fao.org/DOCREP/005//005/Y4496E/Y4496E29. Nair, G. M., Patel, K. R., Shah, J. J., and R. C. Pandalai. 1980. Effect of ethephone (2-chloroethyl phosphonic acid) on gummosis in the bark of Azadirachta indica A. Juss. Indian J. Exp. Biol. 18:500-3. Nair G. M., Shah, J. J., and S. V. Subramanyam. 1983. Ultrastructure and histochemistry of traumatic gum ducts in the wood of Azadirachta indica A. Juss. IAWA Bulletin n.s. 4:103-12. Nair, M. N. B., Bhat, J. R., and J. J. Shah. 1985. Induction of traumatic gum cavities in sapwood of the Neem (Azadirachta indica A. Juss.) by ethephone and paraquat. Indian J. Exp. Biol. 23:60-4. Nelson, N. D. 1978. Xylem ethylene, phenol-oxidizing enzymes, and nitrogen and heartwood formation in walnut and cherry. Can. J. Bot. 56:626-34. Okie, W. R., and C. C. Reilly. 1983. Reaction of peach and nectarine cultivars and selections to infection by Botryosphaeria dothidea. J. Am. Soc. Hort. Sci. 108:176-9. Olien, W. C., and M. J. Bukovac. 1978. The effect of temperature on rate of ethylene evolution from ethephon and from ethephon-treated leaves of sour cherry. J. Am. Soc. Hort. Sci. 103:199-202. Olien, W. C., and M. J. Bukovac. 1982a. Ethephon-induced gummosis in sour cherry (Prunus cerasus L.) I. Effect of xylem function and shoot water status. Plant Physiol. 70:547-55. Olien, W. C., and M. J. Bukovac. 1982b. Ethephon-induced gummosis in sour cherry (Prunus cerasus L.). II. Flow characteristics of gum solutions. Plant Physiol. 70:556-9. Prakash, O., and M. A. Raoof. 1989. Dieback disease of mango (Mangifera indica) its distribution, incidence, cause and management. Fitopatol. Bras. 14:207-15. Price, P. W., and K. M. Clancy. 1986. Multiple effects of precipitation on Salix lasiolepis and populations of the stem-galling saw fly, Euura lasiolepis. Ecol. Res 1:1-14. Price, P. W., Roininen, H., and J. Tahvanainen. 1987a. Plant age and attack by the bud galler, Euura mucronata. Oecologia 73:334-7. Price, P. W., Roininen, H., and J. Tahvanainen. 1987b. Why does the bud-galling saw fly, Euura mucronata, attack long shoots? Oecologia 74:1-6. Rachmilevitz, T., and A. Fahn. 1973. Ultrastructure of nectaries of Vitica rosea L., Vinca major L. and Citrus sinemis Osbeck cv. Valencia and its relation to the mechanism of nectar secretion. Ann. Bot. 37:1-9. Raddad, E. Y., and O. Luukkanen. 2006. Adaptive genetic variation in water-use efficiency and gum yield in Acacia senegal provenances grown on clay soil in the Blue Nile region, Sudan. Forest Ecol. Manag. 226:219-9. Rajput, K. S., Rao, K. S., and H. P. Vyas. 2005. Formation of gum ducts in Azadirachta indica A. Juss. J. Sustainable Forestry 20:1-12. Rhoades, D. F. 1979. Evolution of plant chemical defense against herbivores. In Herbivores: their interaction with secondary plant metabolites, ed. G. A. Rosenthal, and D. H. Janzen, 3-54. New York: Academic Press. Rosik, J., Kubala, J., Kardošova, A., and P. Lacok. 1975. Amino acids and inorganic compounds in apricottree gum (Prunus armeniaca L.) and in the polysaccharides prepared from this gum. Biologia (Bratislava) 30:255-63.

38  ◾  Plant Gum Exudates of the World Rosik, J., Kubala, J., Stanova, M., and P. Lacok. 1971. Structural properties of apricot gum polysaccharides. IV. Observation on their changes during vegetative cycle after evoked gummosis by pathogens. Biologia (Bratislava) 26:13-8. Ryugo, K., and J. Labavitch. 1978. Gums and mucilages in hulls of almonds. J. Am. Soc. Hort. Sci. 103:568-70. Saniewski, M., Miyamoto, K., and J. Ueda 1998. Methyl jasmonate induces gums and stimulates anthocyanin accumulation in peach shoots. J. Plant Growth Regul. 17:121-4. Saniewski, M., Miyamoto, K., and J. Ueda. 2004a. Carbohydrate composition of gum, anthocyanin accumulation and leaf abscission in peach shoots induced by methyl jasmonate and/or ethylene. Zesz. Prob. Post. Nauk. Roln. 496:619-26. Saniewski, M., Miyamoto, K., and J. Ueda. 2004b. Gum induction by methyl jasmonate in fruits, stems and petioles of Prunus domestica L. Acta Hort. 636:151-8. Saniewski, M., Ueda, J., Horbowicz, M., Miyamoto, K., and J. Puchalski. 2002. Gum in apricot (Prunus armeniaca L.) shoots induced by methyl jasmonate. Acta Agrobot. 54:27-34. Saniewski, M., Ueda, J., Miyamoto, K., Horbowicz, M., and J. Puchalski. 2006. Hormonal control of Gummosis in Rosaceae. J. Fruit Ornamental Plant Res. 14:137-44. Skene, D. S. 1965. The development of kino veins in Eucalptus oblique L’Herit. Aust. J. Bot. 13:367-78. Smith, F., and R. Montgomery. 1959. The chemistry of plant gums and mucilages, 106, 166, 264-9. New York: Reinhold Publishing Co. Stosser, R. 1978a. Untersuchungen uber die Entstehung der Lakunen bei der Gummibildung des Steinobsts. Mitt. Klostereneuburg 28:119-25. Stosser, R. 1978b. Die autoradiographische Lokalisierung der 14 C-Aktivitat nach Applikation markierter Zucker. Gartenbauwissenschaft 43:231-5. Stosser, R. 1978c. Der histochemische Nachweis einiger Enzyme im Zusammenhang mit der Gummibildung bei Susskirschen. Angew. Bot. 52:363-9. Stosser, R. 1979. Investigations on gum duct formation in cherries using plastic embedding medium. Scientia Hort. 11:247-52. Talboys, P. W. 1968. Water deficits in vascular disease. In Water deficits and plant growth, Vol. II, ed. T. T. Kozlowski, 255-31. New York: Academic Press. Tippett, J. T. 1986. Formation and fate of kino veins in Eucalyptus. L’Herit. Internat. Assoc. Wood Anatomists Bull. 7:137-43. Tschirch, A. 1889. Angewandte pflanzenanatomie. Vienna: Urban and Schwarzenberg. Ueda, J., Miyamoto, K., and M. Saniewski. 2003. Gum formation and leaf abscission in ornamental Japanese cherry (Prunus yedoensis): A possible role of ethylene and jasmonates in these processes. In Biology and biotechnology of the plant hormone ethylene III, NATO Science Series, Series I: Life and Behavioural Sciences, ed. M. Vendrell, H. Klee, J. C. Pech, and F. Romojaro, 349:303-4. Amsterdam, Berlin, Oxford, Tokyo, Washington, DC: IOS Press. Vander Molen, G. E., Beckman, C. H., and K. Rodehorst. 1977. Vascular gelation, a general response phenomenon following infection. Physiol. Plant Pathol. 11:95-100. Venkaiah, K. 1992. Development, ultrastructure and secretion of gum ducts in Lannea coromandelica (Houtt.) Merrill (Anacardiaceae). Ann. Bot. 69:449-57. Venkaiah, K., and J. J. Shah. 1984. Distribution, development and structure of gum ducts in Lannea coromandelica (Houtt.) Merril. Ann. Bot. 54:175-86. Waring, G. L., and N. S. Cobb. 1992. The impact of plant stress on herbivore population dynamics. In Insectplant interactions, ed. E. Bernays, 167-225. Ann Arbor: CRC Press. White, T. C. R. 1993. The inadequate environment: nitrogen and the abundance of animals. Berlin, Heidelberg, New York: Springer. Wilde, M. H., and L. J. Edgerton. 1975. Histology of ethephon injury on Montmorency cherry branches. HortScience 10:79-81. Yang, S. F., and N. E. Hoffman. 1984. Ethylene biosynthesis and its regulation in higher plants. Annu. Rev. Plant Physiol. 35:155-89.

Chapter 3

Major Plant Exudates of the World 3.1 INTRODUCTION Exudate gums have been used for centuries in a variety of fields; they have retained their importance despite the more recent advent of many alternative gums, with similar typical performances. The gums exude from trees and shrubs in tear-like, striated nodules or amorphous lumps, and then dry in the sun, forming hard, glassy, different-colored exudates (Nussinovitch, 1997). Gum production increases under high temperatures and limited moisture, and yields can be increased by making incisions in the bark or stripping it from the tree or shrub. Exudate gums have been utilized in food applications for years, for emulsification, thickening and stabilization (Nussinovitch, 1997). Arabic, tragacanth and karaya gums are safe for human consumption based on a long and harm-free history of use as well as on recent toxicological studies. Tree gum exudates are also used in non-food applications, such as: pharmaceuticals, cosmetics, textiles, lithography and minor forest products (Weiping and Anderson, 1994, Glicksman, 1983b).

3.2 GUM ARABIC AND OTHER ACACIA GUMS 3.2.1 Acacia Fabaceae (subfamily: Mimosoideae) 3.2.1.1 Taxon: Acacia senegal (L.) Willd. Synonyms: Acacia verek Guill. & Perr.; Mimosa senegal L.; Senegalia senegal (L.) Britton Common names: gum arabic, gum arabic tree, kher, Senegal gum, Sudanese gum arabic, threethorn acacia,  acacia à gomme [French], gommier blanc [French], gummiarabikumbaum [German], Senegal akazie [German], acacia del Senegal [Spanish] (USDA, ARS, National Genetic Resources Program, 2008). Gum arabic is also called ‘hashab’ after the local name of the tree or ‘kordofan’ after the main production area in the Sudan (Imeson, 1992).

39

40  ◾  Plant Gum Exudates of the World

+2

A

+2

D

B

C E

+2

Figure 3.1  Acacia senegal. The source of Sudan gum arabic. Flowering branch (A); flower (B); mature pods (C); seed (D) (adapted from Paul Hermann Wilhelm Taubert’s Leguminosae. in Engelmann (ed.): Natürliche Pflanzenfamilien. Vol. III, 3, 1891).

Economic importance: Environmental: boundary, barrier, support, ornamental, soil improver. Fuels: charcoal. Materials: gum/resin. Medicine: folk medicine. Distributional range (native): AFRICA-Northeast Tropical Africa: Chad, Ethiopia, Somalia, Sudan; East Tropical Africa: Kenya, Tanzania, Uganda; West-Central Tropical Africa: Cameroon, Rwanda, Zaire; West Tropical Africa: Cote D’Ivoire, Gambia, Mali, Mauritania, Niger, Nigeria, Senegal; South Tropical Africa: Angola, Mozambique, Zambia, Zimbabwe; Southern Africa: Botswana, Namibia, South Africa - Natal, Transvaal, Swaziland. ASIA, TEMPERATE-Arabian Peninsula: Arabia. ASIA, TROPICAL-Indian Subcontinent: India, Pakistan (USDA, ARS, National Genetic Resources Program, 2008). Exudate production: Almost 90% of the world market supply of gum arabic comes from Sudan. A. senegal is native to the drier parts of Sudan and the northern Sahara and is found throughout the vast area from Senegal to the Red Sea and on to Eastern India (Fig. 3.1). A. senegal gum in Sudan is derived from both natural stands and plantations, and is collected by tapping the trees (Howes, 1949). After superficial injury of the bark, large nodules or tears of gum are formed along the strip or wound on the exposed surfaces and are left to dry and harden. The length of time required for the tears to form depends on the weather: hot, dry weather accelerates the process, and cold or wet conditions retard it (Howes, 1949). In practice, the first gum collection is performed after 5 weeks, with further collections from the same trees at approximately 15-day intervals until the end of February, up to five or six collections in total. This tapping method can only be applied to Acacia trees with a thin, fibrous type of bark and not to the fleshy-bark species. Yield per tree does not exceed

Major Plant Exudates of the World  ◾  41

∼300 g (Howes, 1949). Most Acacia gums are water-soluble. Indian acacia gums are markedly inferior to African A. senegal or A. seyal in adhesive properties (Howes, 1949). After collection, the gum is separated into two major grades: cleaned and hand-picked selected. Gum arabic can be sold as is, or after industrial handling, such as grinding, sieving, or granulating (Thevenet, 1988). Raw gum is pre-cleaned to remove the bark, sand and fines, and foreign matter that make up less than 0.5% of food-grade powdered gum. Processing, which involves sieving, decanting, centrifuging, concentrating, pasteurizing and atomizing followed by spray-drying, yields a product with no insoluble matter which hydrates more rapidly than its unprocessed counterpart (Williams et al., 1990). The drying temperature influences the gum’s functional behavior. Heat in general (either from spray-drying or rollerdrying) causes the gum solutions to be slightly turbid or opalescent (Anderson et al., 1991). Exudate properties: Gum arabic contains no pathogens and no more than 103 microorganisms per gram (Blake et al., 1988). Because of the high temperatures involved, spray-dried preparations contain no more than ∼40% of the usual microorganism count (∼4 x 102 microorganisms per gram). The number of viable bacteria contained in the gum can also be reduced by treatment with ethylene oxide (no longer permitted for food use), or propylene oxide (less efficacious). Heating carried out during manufacture to reduce the microflora can lead to precipitation of the arabinogalactan-protein complex (Anderson and McDougall, 1987), which promotes stabilization and emulsification in a range of food products (Randall et al., 1989). To eradicate microorganisms, gum was subjected to 10 kG of irradiation: a reduction in viscosity was observed but there was no measurable effect on emulsion stability (Blake et al., 1988). Gum chemical characteristics and applications: Gum arabic from A. senegal is made up of ∼3.8% ash, 0.34% nitrogen, 0.24% methoxyl, 17% uronic acid, and the following sugar constituents following hydrolysis: 45% galactose, 24% arabinose, 13% rhamnose, 16% glucuronic acid and 15% 4-O-methyl glucuronic acid (Anderson et al., 1990). The gum is to some extent an acidic complex polysaccharide produced as a mixture of calcium, magnesium and potassium salts. It has a molecular mass of ∼580,000 Daltons. Gums from dissimilar sources exhibit large differences in content, amino-acid composition, uronic-acid content and molecular weight. Three principal fractions have been identified by hydrophobic affinity chromatography: a low-molecular-weight arabinogalactan (AG), a very highmolecular-weight arabinogalactan-protein complex (AGP) and a low-molecular-weight glycoprotein (GI) (Anderson et al., 1990). These components represent 88%, 10% and 1% of the molecule, respectively, and they contain 20%, 50% and 30% of the polypeptides, respectively. The protein is located on the outside of the AGP unit. The overall conformation of the gum arabic molecule is described by the ‘wattle blossom’ model in which approx. five bulky AG blocks, ∼200,000 Daltons each, are arranged along the GI polypeptide chain which may contain up to 1,600 amino-acid residues (Connolly et al., 1987). Gum arabic is used in five main food areas: confections, beverages and emulsions, flavor encapsulation, baked goods and brewing (Imeson, 1992; Whistler and Smart, 1953a). Gum arabic is unique in the very high gum concentrations which can be used to prepare solutions. Thus, large amounts of gum can be used in a variety of food products (Nussinovitch, 1997). The gum’s stability in acid solutions is useful for the stabilization of citrus oil emulsions (Anderson et al., 1990; Williams et al., 1990; Nussinovitch, 1997). Combinations of gum tragacanth and gum arabic at a 4:1 ratio produce a minimum viscosity which chemically, commercially and practically produces a thin, pourable emulsion with good shelf-life stability (Imeson, 1992). Gum arabic is used to produce a wide variety of confections, from

42  ◾  Plant Gum Exudates of the World

soft lozenges and pastilles to hard gums (Wolff and Manhke, 1982; Best, 1990). More information on the use of gums in confectioneries and on confections based on gum arabic can be found elsewhere (Reidel, 1983, 1986). Gum arabic is also used as an encapsulating agent for flavors used in dry foods such as powdered soups, beverages, dessert mixes, etc. A typical formulation contains 7% oil-based flavor and 28% gum arabic, and results in 20% flavor in the dried material (Thevenet, 1988). Foamed sodium caseinate solutions were optimally stabilized with 0.3% sodium alginate and karaya gum at pH 7.0, 0.2% at pH 8.0. The addition of sodium alginate increased foam stability of the solution, but did not increase foaming ability. Surface tensions and solution turbidities were related to foaming ability, and specific viscosities were related to foam stability (Yang et al., 1993).

3.2.1.2 Taxon: Acacia seyal Delile Synonyms: Acacia fistula Schweinf. [≡ Acacia seyal var. fistula]; Acacia stenocarpa Hochst. ex A. Rich. [= Acacia seyal var. seyal] Subordinate taxa: Acacia seyal Delile var. fistula (Schweinf.) Oliv.; Acacia seyal Delile var. seyal Common names: shittimwood, talh, thirtythorn, whistling tree (Fig. 3.2). Economic importance: Fuels: fuelwood. Materials: gum/resin. Medicine: folk medicine. Distributional range (native): AFRICA-Northern Africa: Egypt; Northeast Tropical Africa: Chad, Ethiopia, Somalia, Sudan; East Tropical Africa: Kenya, Tanzania, Uganda; WestCentral Tropical Africa: Cameroon, Central African Republic; West Tropical Africa: Cote

Figure 3.2  Acacia seyal. Widespread in North Africa and the source of “tahl” gum [illustration from book; source: Leguminosae. In Engelmann (ed.): Natürliche Pflanzenfamilien. Vol. III, 3. 1891; Author: Paul Hermann Wilhelm Taubert (1862-1897)].

Major Plant Exudates of the World  ◾  43

D’Ivoire, Mali, Mauritania, Niger, Nigeria, Senegal; South Tropical Africa: Malawi, Mozambique, Zambia. ASIA, TEMPERATE-Arabian Peninsula: Saudi Arabia, Yemen (USDA, ARS, National Genetic Resources Program, 2008). Gum chemical characteristics: In comparison with A. senegal and depending on the source, the glycan components of A. seyal contain a greater proportion of L-arabinose relative to D-galactose. The gum from A. seyal also contains significantly more 4-O-methyl-Dglucuronic acid but less L-rhamnose and unsubstituted D-glucuronic acid than that from A. senegal.

3.2.1.3  Taxon: Acacia abyssinica Hochst. ex Benth. subsp. calophylla Brenan Conspecific taxa: Acacia abyssinica subsp. abyssinica Distributional range (native): AFRICA-Northeast Tropical Africa: Sudan; East Tropical Africa: Kenya, Tanzania, Uganda; West-Central Tropical Africa: Rowanda, Zaire; South Tropical Africa: Malawi, Mozambique, Zimbabwe (USDA, ARS, National Genetic Resources Program, 2008).

3.2.1.4 Taxon: Acacia bakeri Maiden Synonym: Racosperma bakeri (Maiden) Pedley Distributional range (native): AUSTRALASIA-Australia: Australia - New South Wales, Queensland (USDA, ARS, National Genetic Resources Program, 2008).

3.2.1.5  Taxon: Acacia benthamii Meisn. Distributional range (native): AUSTRALASIA-Australia: Australia - Western Australia (USDA, ARS, National Genetic Resources Program, 2008).

3.2.1.6 Taxon: Acacia binervata DC. Synonym: Racosperma binervatum (DC.) Pedley Common name: two-vein hickory (Fig. 3.3). Distributional range (native): AUSTRALASIA-Australia: Australia - New South Wales, Queensland (USDA, ARS, National Genetic Resources Program, 2008).

3.2.1.7 Taxon: Acacia catechu (L. f.) Willd. Synonyms: Acacia wallichiana DC.; Mimosa catechu L. f. Common names: black catechu, black cutch, catechu, cutchtree. Economic importance: In India, A. catechu is a multipurpose tree (Fig. 3.4), producing nitrogen-rich fodder and green manure, high-quality fuelwood and charcoal, strong durable poles and timber, and it is the main source for ‘cutch’ and ‘katha’ (tanning extracts). The different parts of the tree have a variety of medicinal uses. Other uses include flavoring materials, food additives and a source of tannin/dyestuff.

44  ◾  Plant Gum Exudates of the World

Figure 3.3  Acacia binervata (mag. 3x; courtesy of the Royal Botanic Gardens, Kew; Cat. No. 58514).

Distributional range (native): ASIA, TEMPERATE-China: China - Guangdong, Guangxi, Yunnan, Zhejiang. ASIA, TROPICAL-Indian Subcontinent: Bhutan, India, Nepal, Pakistan; Indo-China: Myanmar (USDA, ARS, National Genetic Resources Program, 2008). The exudate: A. catechu gum appears in tears as large as 2.5 cm in diameter and has a sweetish taste (Mantell, 1947; Howes, 1949; Smith and Montgomery, 1959).

Figure 3.4  Acacia catechu tree.

Major Plant Exudates of the World  ◾  45

Figure 3.5  Acacia dealbata exudate sample from New South Wales (mag. 2x; courtesy of the Royal Botanic Gardens, Kew; Cat. No. 58553).

3.2.1.8 Taxon: Acacia dealbata Link Synonyms: Acacia decurrens var. dealbata (Link) F. Muell.; Racosperma dealbatum (Link) Pedley Common names: mimosa, silver wattle (Fig. 3.5), silwerwattel [Afrikaans], mimose [German]. Economic importance: Category: bee plant. Environmental: boundary, barrier, support, erosion control, ornamental. Materials: essential oils. Weed. Distributional range (native): AUSTRALASIA-Australia: Australia - Austr. Capital Terr., New South Wales, Tasmania, Victoria. OTHER-naturalized in Europe, Africa, New Zealand, United States, Azores, Madagascar (USDA, ARS, National Genetic Resources Program, 2008).

3.2.1.9  Taxon: Acacia decurrens Willd. Synonyms: Acacia adenophora Spreng.; Acacia decurrens var. pauciglandulosa F. Muell. ex Benth.; Mimosa decurrens J. C. Wendl.; Racosperma decurrens (Willd.) Pedley Common names: green wattle, Sydney wattle, groenwattel [Afrikaans], acacia noir [French], schwarze akazie [German] (Fig. 3.6). Economic importance: Environmental: ornamental. Materials: tannin/dyestuff. Weed. Distributional range (native): AUSTRALASIA-Australia: Australia - New South Wales, Victoria. OTHER-naturalized in South Africa (USDA, ARS, National Genetic Resources Program, 2008).

46  ◾  Plant Gum Exudates of the World

Figure 3.6  Acacia decurrens exudate sample (mag. 2x; courtesy of the Royal Botanic Gardens, Kew; Cat. No. 58563).

3.2.1.10 Taxon: Acacia drepanolobium Harms ex Y. Sjöstedt Distributional range (native): AFRICA-Northeast Tropical Africa: Ethiopia, Somalia, Sudan; East Tropical Africa: Kenya, Tanzania, Uganda; West-Central Tropical Africa: Zaire (USDA, ARS, National Genetic Resources Program, 2008).

3.2.1.11 Taxon: Acacia elata A. Cunn. ex Benth. Synonyms: Acacia terminalis auct. pl.; Racosperma elatum (A. Cunn. ex Benth.) Pedley Common names: cedar wattle, pepper-tree wattle, peperboomwattel [Afrikaans]. Economic importance: Weed. Distributional range (native): AUSTRALASIA-Australia: Australia - New South Wales. OTHERnaturalized in South Africa. (USDA, ARS, National Genetic Resources Program, 2008).

3.2.1.12 Taxon: Acacia farnesiana (L.) Willd. Synonyms: Acacia minuta (M. E. Jones) R. M. Beauch.; Acacia smallii Isely; Mimosa farnesiana L. (basionym); Pithecellobium minutum M. E. Jones; Vachellia densiflora Alexander ex Small; Vachellia farnesiana (L.) Wight & Arn. Common names: cassie, huisache, opopanax, popinac, sweet acacia, cassie ancienne [French], illenakazie [German], gaggia [Italian], aromo [Spanish], bayahonda [Spanish], coromo [Spanish], espino blanco [Spanish].

Major Plant Exudates of the World  ◾  47

Economic importance: Category: bee plant. Food additives: flavoring. Environmental: ornamental, soil improver. Materials: essential oils, lipids. Medicine: folk medicine. Weed: also potential seed contaminant. Distributional range (native): NORTH AMERICA-United States: Southern United States Florida, Louisiana; South-Central United States - Texas; Southwestern United States - Arizona, California [San Diego County]; Mexico: Mexico. SOUTH AMERICA-Mesoamerica: Belize, Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua, Panama; Caribbean: Antigua and Barbuda, Barbados, Cuba, Dominica, Grenada, Guadeloupe, Martinique, Montserrat, Netherlands Antilles, Puerto Rico, St. Kitts and Nevis-St. Kitts, St. Lucia, St. Vincent and Grenadines; Northern South America: French Guiana, Guyana, Suriname, Venezuela; Brazil: Brazil; Western South America: Bolivia, Colombia, Peru. OTHER-widely cultivated and naturalized, exact native range obscure (USDA, ARS, National Genetic Resources Program, 2008).

3.2.1.13 Taxon: Acacia ferruginea DC. Synonym: Mimosa ferruginea Roxb. Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: India, Sri Lanka. (USDA, ARS, National Genetic Resources Program, 2008).

3.2.1.14 Taxon: Acacia harpophylla F. Muell. ex Benth. Distributional range (native): AUSTRALASIA-Australia: Australia - New South Wales, Queensland. (USDA, ARS, National Genetic Resources Program, 2008).

3.2.1.15 Taxon: Acacia jacquemontii Benth. Synonym: Racosperma harpophyllum (F. Muell. ex Benth.) Pedley Common name: brigalow. Economic importance: Vertebrate poisons: mammals. Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: India - Delhi, Gujarat, Haryana, Madhya Pradesh, Maharashtra, Punjab, Rajasthan, Uttar, Pradesh, Pakistan (USDA, ARS, National Genetic Resources Program, 2008).

3.2.1.16 Taxon: Acacia karroo Hayne Synonym: Acacia dekindtiana A. Chev. Common names: karroothorn, sweet-thorn, soetdoring [Afrikaans]. Economic importance: Animal food: forage. Fuels: fuelwood. Materials: fiber, gum/resin. Medicine: folk medicine. Distributional range (native): AFRICA-South Tropical Africa: Angola, Malawi, Mozambique, Zambia, Zimbabwe; Southern Africa: Botswana, Lesotho, Namibia, South Africa, Swaziland (USDA, ARS, National Genetic Resources Program, 2008).

3.2.1.17 Taxon: Acacia kirkii Oliv. Subordinate taxa: Acacia kirkii subsp. kirkii, Acacia kirkii subsp. mildbraedii Common name: flood-plain acacia.

48  ◾  Plant Gum Exudates of the World

Distributional range (native): AFRICA-East Tropical Africa: Kenya, Tanzania, Uganda; WestCentral Tropical Africa: Burundi, Rwanda, Zaire; West Tropical Africa: Guinea, Mali; South Tropical Africa: Angola, Zambia, Zimbabwe; Southern Africa: Botswana, Namibia (USDA, ARS, National Genetic Resources Program, 2008).

3.2.1.18 Taxon: Acacia laeta R. Br. ex Benth. Distributional range (native): AFRICA-Northern Africa: Egypt; Northeast Tropical Africa: Chad, Ethiopia, Somalia, Sudan; East Tropical Africa: Kenya, Tanzania; West Tropical Africa: Burkina Faso, Mali, Niger, Nigeria. ASIA, TEMPERATE-Arabian Peninsula: Oman, Saudi Arabia, Yemen (USDA, ARS, National Genetic Resources Program, 2008).

3.2.1.19 Taxon: Acacia leiophylla Benth. Distributional range (native): AUSTRALASIA-Australia: Australia - South Australia. (USDA, ARS, National Genetic Resources Program, 2008).

3.2.1.20 Taxon: Acacia leucophloea (Roxb.) Willd. Synonym: Mimosa leucophloea Roxb. (Fig. 3.7) Common names: distiller’s acacia, kikar [India]. Economic importance: Environmental: potential for agroforestry. Human food: beverage base. Animal food: potential as fodder. Medicine: folk medicine.

Figure 3.7  Acacia leucophloea exudate sample (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 57997).

Major Plant Exudates of the World  ◾  49

Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: India, Pakistan, Sri Lanka; Indo-China: Myanmar, Thailand, Vietnam; Malesia: Indonesia, Malaysia (USDA, ARS, National Genetic Resources Program, 2008).

3.2.1.21 Taxon: Acacia maidenii F. Muell. Synonym: Racosperma maidenii (F. Muell.) Pedley Distributional range (native): AUSTRALASIA-Australia: Australia - New South Wales, Queensland, Victoria. (USDA, ARS, National Genetic Resources Program, 2008).

3.2.1.22 Taxon: Acacia mellifera (Vahl) Benth. Synonyms: Acacia detinens Burch. [≡ Acacia mellifera subsp. detinens]; Mimosa mellifera Vahl [≡ Acacia mellifera subsp. mellifera] Subordinate taxa: Acacia mellifera (Vahl) Benth. subsp. detinens (Burch.) Brenan; Acacia mellifera (Vahl) Benth. subsp. mellifera Common names: hookthorn, swaarthaak [Afrikaans]. Economic importance: Materials: potential as gum/resin. Distributional range (native): AFRICA-Northern Africa: Egypt; Northeast Tropical Africa: Chad, Ethiopia, Somalia, Sudan; East Tropical Africa: Kenya, Tanzania, Uganda; South Tropical Africa: Angola, Mozambique, Zambia, Zimbabwe; Southern Africa: Botswana, Namibia, South Africa - Cape Province, Orange Free State, Transvaal. ASIA, TEMPERATE-Arabian Peninsula: Saudi Arabia, Yemen (USDA, ARS, National Genetic Resources Program, 2008).

3.2.1.23 Taxon: Acacia modesta Wall. Common names: amritsar-gum, black sally, blackwood, phulai paloz [India], pulahi [India]. Economic importance: Fuels: A. modesta is much used for firewood: some areas have been cut over to such an extent that only coppice wood remains. Medicine: folk medicine. Distributional range (native): ASIA, TEMPERATE-Western Asia: Afghanistan. ASIA, TROPICAL-Indian Subcontinent: Pakistan, India - Punjab, Uttar Pradesh (USDA, ARS, National Genetic Resources Program, 2008). The tree and the exudate: A. modesta is one of the characteristic trees of the Punjab. It occurs in the sub-Himalayan tract and outer Himalayas from Jumna westwards and also to the salt ranges (Howes, 1949). The translucent yellowish gum of A. modesta occurs mostly as small tears or angular fragments, sometimes vermiform (Mantell, 1947; Howes, 1949; Smith and Montgomery, 1959). When A. modesta is mixed with A. arabica it may be termed gum mamrah (Howes, 1949).

3.2.1.24 Taxon: Acacia oerfota (Forssk.) Schweinf. Synonyms: Acacia nubica Benth.; Mimosa oerfota Forssk. Economic importance: Human food: beverage base. Distributional range (native): AFRICA-Northern Africa: Egypt; Northeast Tropical Africa: Chad, Ethiopia, Sudan; East Tropical Africa: Kenya, Tanzania, Uganda. ASIA, TEMPERATE-Arabian Peninsula: Oman, Saudi Arabia, Yemen; Western Asia: Iran (USDA, ARS, National Genetic Resources Program, 2008).

50  ◾  Plant Gum Exudates of the World

3.2.1.25 Taxon: Acacia oswaldii F. Muell. Synonym: Racosperma oswaldii (F. Muell.) Pedley Common names: umbrella acacia, umbrella bush. Distributional range (native): AUSTRALASIA-Australia: Australia - New South Wales, Northern Territory, Queensland, South Australia, Victoria, Western Australia (USDA, ARS, National Genetic Resources Program, 2008).

3.2.1.26 Taxon: Acacia pendula A. Cunn. ex G. Don Synonym: Racosperma pendulum (A. Cunn. ex G. Don) Pedley Common names: myall acacia, weeping myall, boree [Afrikaans], treurwattel [Afrikaans]. Economic importance: Animal food: potential as fodder. Distributional range (native): AUSTRALASIA-Australia: Australia - New South Wales, Queensland, Victoria. (USDA, ARS, National Genetic Resources Program, 2008).

3.2.1.27  Taxon: Acacia penninervis Sieber ex DC. Synonym: Racosperma penninerve (Sieber ex DC.) Pedley Common names: blackwood, mountain-hickory (Fig. 3.8). Distributional range (native): AUSTRALASIA-Australia: Australia - New South Wales, Queensland, Victoria. (USDA, ARS, National Genetic Resources Program, 2008).

Figure 3.8  Acacia penninervis exudate (mag. 2x; courtesy of the Royal Botanic Gardens, Kew; Cat. No. 58701).

Major Plant Exudates of the World  ◾  51

3.2.1.28 Taxon: Acacia pycnantha Benth. Common names: broadleaf wattle, golden wattle, gouewattel [Afrikaans], acacia doré [French], Goldakazie [German]. Economic importance: Environmental: ornamental. Weed. Distributional range (native): AUSTRALASIA-Australia: Australia - New South Wales, South Australia, Victoria. OTHER-naturalized in South Africa, western United States (USDA, ARS, National Genetic Resources Program, 2008).

3.2.1.29 Taxon: Acacia retinodes Schltdl. Common name: wirilda. Distributional range (native): AUSTRALASIA-Australia: Australia - South Australia, Tasmania [Flinders Island], Victoria. (USDA, ARS, National Genetic Resources Program, 2008).

3.2.1.30 Taxon: Acacia salicina Lindl. Common names: cooba, willow acacia. Distributional range (native): AUSTRALASIA-Australia: Australia - New South Wales, Northern Territory, Queensland, South Australia, Victoria. (USDA, ARS, National Genetic Resources Program, 2008).

3.2.1.31 Taxon: Acacia sieberiana DC. Synonyms: Acacia sieberiana subsp. vermoesenii (De Wild.) Troupin [= Acacia sieberiana var. woodii]; Acacia sieberiana var. vermoesenii (De Wild.) Keay & Brenan [= Acacia sieberiana var. woodii]; Acacia vermoesenii De Wild. [= Acacia sieberiana var. woodii]; Acacia verugera Schweinf. [= Acacia sieberiana var. sieberiana]; Acacia woodii Burtt Davy [≡ Acacia sieberiana var. woodii] Common names: flat-top thorn, paperbarkthorn, umbrellathorn, papierbasdoring [Afrikaans]. Distributional range (native): AFRICA-Northeast Tropical Africa: Chad, Ethiopia, Sudan; East Tropical Africa: Tanzania, Uganda; West-Central Tropical Africa: Congo, Rwanda, Zaire; West Tropical Africa: Benin, Burkina Faso, Cote D’Ivoire, Ghana, Guinea-Bissau, Mali, Niger, Nigeria, Togo; South Tropical Africa: Angola, Malawi, Mozambique, Zimbabwe; Southern Africa: Botswana, Namibia, South Africa - Natal, Transvaal, Swaziland (USDA, ARS, National Genetic Resources Program, 2008).

3.2.1.32 Taxon: Acacia stuhlmanii Taub. Distributional range (native): AFRICA-Northeast Tropical Africa: Ethiopia, Somalia; East Tropical Africa: Kenya, Tanzania; South Tropical Africa: Zambia, Zimbabwe; Southern Africa: Botswana, South Africa - Transvaal (USDA, ARS, National Genetic Resources Program, 2008).

52  ◾  Plant Gum Exudates of the World

3.2.1.33 Taxon: Acacia verniciflua A. Cunn. Synonym: Racosperma vernicifluum (A. Cunn.) Pedley Distributional range (native): AUSTRALASIA-Australia: Australia - Austr. Capital Terr., New South Wales, Queensland, South Australia, Tasmania, Victoria. (USDA, ARS, National Genetic Resources Program, 2008).

3.2.1.34 Taxon: Acacia xanthophloea Benth. Common name: fevertree. Distributional range (native): AFRICA-East Tropical Africa: Kenya, Tanzania; West-Central Tropical Africa: Zaire; South Tropical Africa: Malawi, Mozambique, Zimbabwe; Southern Africa: South Africa - Natal, Transvaal, Swaziland (USDA, ARS, National Genetic Resources Program, 2008).

3.2.2 Faidherbia Fabaceae (subfamily: Mimosoideae) 3.2.2.1 Taxon: Faidherbia albida (Delile) A. Chev. Synonym: Acacia albida Delile Common names: anatree, whitethorn, winterthorn, arbre blanc  [French], anabaum [German], espinheiro-de-Angola [Portuguese] (USDA, ARS, National Genetic Resources Program, 2008). Economic importance: Environmental: agroforestry, soil improver. Animal food: potential as forage. Medicine: folk medicine. Distributional range (native): AFRICA-Northern Africa: Algeria, Egypt; Northeast Tropical Africa: Chad, Ethiopia, Sudan; East Tropical Africa: Kenya, Tanzania, Uganda; West-Central Tropical Africa: Zaire; West Tropical Africa: Benin, Cote D’Ivoire, Gambia, Ghana, GuineaBissau, Mali, Mauritania, Niger, Nigeria, Senegal, Togo; South Tropical Africa: Angola, Malawi, Mozambique, Zambia, Zimbabwe; Southern Africa: Botswana, Namibia, South Africa - Natal, Transvaal. ASIA, TEMPERATE-Arabian Peninsula: Saudi Arabia; Western Asia: Cyprus, Israel, Syria. OTHER-naturalized elsewhere (USDA, ARS, National Genetic Resources Program, 2008).

3.3 GUM TRAGACANTH AND SIMILAR GUMS 3.3.1 Astragalus Fabaceae (subfamily: Faboideae) 3.3.1.1 Taxon: Astragalus gummifer Labill. Synonyms: Astracantha gummifera (Labill.) Podlech; Astragalus adpressus Ehrenb. ex Walp. Common names: gum tragacanth, tragacanth, tragacanth milk-vetch, astragale à gomme [French], gummitragant  [German], tragant  [German], alquitira  [Spanish], tragacanto [Spanish]. The name tragacanth comes from the Greek tragos (goat) and akantha (horn) and refers to the shape of the gum (Beach, 1954). It is also known as bassora gum, hogg gum, goat’s horn, leaf gum (Fig. 3.9) (Gentry, 1957), Smyrna or Anatolian tragacanth (from A. gummifera), Syrian tragacanth (white leaf gum) (Mantell, 1947; Howes, 1949). Economic importance: Food additives: emulsifier, thickening agent. Materials: gum/resin. Medicines: folklore.

Major Plant Exudates of the World  ◾  53

Figure 3.9  Astragalus gummifer gum (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 58415).

Distributional range (native): ASIA, TEMPERATE-Western Asia: Iraq, Lebanon, Syria, Turkey (USDA, ARS, National Genetic Resources Program, 2008). Gum water solubility: The soluble constituent tragacanthin dissolves in water to give a colloidal hydrosol solution, while the insoluble constituent bassorin swells to a gel-like state (Mantell, 1947). With a small proportion of water, a soft, adhesive paste is formed (Ben-Zion and Nussinovitch, 1997). If agitated with additional water, the paste forms a homogeneous mixture; nevertheless, after 1 or 2 days, a large proportion separates out, leaving a smaller dissolved portion (Howes, 1949). The gum is completely insoluble in alcohol. The viscosity of the mucilage is reduced by adding acid or alkali, particularly when heated (Howes, 1949). Several methods can be employed to eliminate lump formation and achieve a homogeneous solution, namely: vigorous agitation with a high-speed mixer, adding the gum slowly or preferably pre-wetting the gum with a wetting agent such as glycerin, propylene glycol or alcohol (Imeson, 1992). Improved solubility has also been achieved by lyophilizing the gum. The freeze-dried gum was found to swell rapidly to higher initial viscosities than untreated gum (Levi, 1955). Gum chemical characteristics: The gum is a complex, acidic proteoglycan, with a molecular weight of ∼800,000. The gum consists of a soluble arabinogalactan portion and an insoluble but water-swellable portion called “bassorin”. The ratio of these components varies from 9:1 to 1:1. Hydrolysis yields arabinogalactan, xylose, fucose, galactose, rhamnose and galacturonic acid with traces of starch and cellulosic material. The soluble constituent tragacanthin consists of arabinogalactan containing L-arabinofuranose and 1-4-linked D-galalactopyranose (Howes, 1949). Bassorin appears to be a complex of polymethoxylated acids. Because more

54  ◾  Plant Gum Exudates of the World

than 20 different species are used for gum production, there is wide variation in composition and performance. The more viscous gum species contain high proportions of fucose, xylose, galacturonic acid and methoxyl groups and low proportions of arabinose and nitrogenous fractions (Howes, 1949). Low-viscosity products include extra arabinose and galactose but lower proportions of methoxyl and galacturonic acid. The variations in the tragacanthinto-bassorin ratio contribute to viscosity variations in commercial gum. Carboxyl groups on the galacturonic acid residues are present in their calcium, magnesium and potassium salt forms (Howes, 1949). Analysis of a representative sample of gum tragacanth (Ferri, 1959) yielded 70% tragacanthin, 10% soluble gum, 10% moisture, 4% cellulose, 3% starch and 3% ash. According to older documentation (Felter and Lloyd, 1898), the gum consists of 20% moisture, 60% tragacanthin, 8 to 10% soluble gum, 3% cellulose, 2 to 8% starch, 3% mineral matter and traces of nitrogenous matter. Other records have reported 18.9% moisture, 35.9% soluble gum, 2.7% ash and 42.4% insoluble gum: no starch was found, although its absence is very rare. The insoluble part of gum tragacanth is dissolved by strong alkalis, forming a yellow substance. The soluble portion presents the following differences from arabin in Acacia gums: it does not exhibit an acid reaction; it does not precipitate in a solution of borax or of ferric chloride; it is precipitated by both neutral and basic lead acetate, while acacia precipitates only in basic lead salt (Felter and Lloyd, 1898). Tragacanth is acidic in reactions and 1 g of the gum requires 0.9 ml alkali (10 N) for neutralization. Tragacanth contains hydroxyproline in its peptides, presumably involved in stabilizing the arabinogalactan structure. Studies on structural features of tragacanthic acid can be found elsewhere (Sybil and Smith, 1945a,b,c; Aspinall and Baillie, 1963a,b; Aspinall et al., 1967; Aspinall and Puvanesarajah, 1984; Anderson and Bridgeman, 1985). Gum physical properties: The viscosity of tragacanth solution is decreased by heating as well as by adding acid, alkali or sodium chloride (Mantell, 1947). Viscosity has been found to be maximal at pH 8, dropping sharply at pH below 4 or above 6. Its maximum stable viscosity has been found to be near pH 5 (Schwarz et al., 1958). Compared to other gums, tragacanth is reasonably stable over a wide pH range, down to extremely acidic conditions at about pH 2 (Levy and Schwarz, 1958a,b). The stability may be related to the backbone resistance of the gum and to the protection afforded by the arabinofuranose side chains (Stauffer, 1980). Tragacanth mucilage will show increased viscosity if boiled, as well as with ageing, but decreased viscosity if neutralized. Homogenizing tragacanth mucilage causes the viscosity to increase to a maximum (Mantell, 1947). Viscosities of 3,500 to 4,600 cP have been found for 1% pseudoplastic solutions (Anderson, 1989a). In a cold preparation, the maximum viscosity is usually reached after 24 h, but it can be reached in about 2 h by raising the temperature of the solution to around 50°C (Imeson, 1992). Gum tragacanth colloidal dispersions do not exhibit thixotropy (Mantell, 1947). Although tragacanth alone is of little value as an emulsifying agent, low amounts of the gum in water lower the latter’s surface tension to facilitate emulsification. In oil-water emulsions, interfacial tension is reduced to ∼190-230 μN/cm, depending on the kind of tragacanth added (high-viscosity tragacanth produces a smaller reduction in interfacial tension). Emulsions with tragacanth often include acacia gums. Whereas gum arabic prevents coalescence by forming a film around the oil globules, tragacanth delays coalescence of the globules by increasing the viscosity of the external phase and thus slowing down movement of the dispersed oil phase (Schaub, 1958). Nitrogen content and sequences (bound polypeptides) may also control viscosity, with soluble high-viscosity material containing ∼0.07% nitrogen, versus ∼1.87% for insoluble fractions. In turn, nitrogen content is related to emulsification properties (Stauffer, 1980; Anderson and Grant, 1989). High viscosity at low shear is related

Major Plant Exudates of the World  ◾  55

to charge repulsion from the galacturonic acid residues and contributes to the emulsion stabilization and suspension abilities of the gum (Nussinovitch, 1997). Tragacanth’s elongated molecular structure accounts for its high viscosity. Solutions are acidic in the pH range of 5 to 6 (Imeson, 1992). To reduce the counts of resistant spores from soil and airborne contaminants, an ethylene-oxide gas treatment is used on gum designated for pharmaceutical products, whereas only the less efficient propylene oxide is permitted for gum designated for food uses (Nussinovitch, 1997). Commercial availability of the gum and applications: Tragacanth is one of the oldest drugs in Materia Medica and its commercial use dates way back. It was known in the days of Theophrastus, who described it three centuries before the Christian era. It has been listed in every edition of the U.S. Pharmacopoeia since 1820. Due to its high price, it is sometimes adulterated with poorer gums and whitened with lead carbonate (Mantell, 1947). Tragacanth is used in many low-pH products, for instance salad dressings, condiments and relishes; it serves as a stabilizer and provides a creamy oral sensation via its surface-active properties (Nussinovitch, 1997). Tragacanth provides a broad spectrum of the properties needed for condiments, dressings and sauces. Usage levels are 0.4 to 0.8% of the weight of the aqueous phase and depend on the oil content, the use of other thickeners and the required consistency (Nussinovitch, 1997). In confections and icings, gum tragacanth is used as a water-binding agent, due to a high proportion of the water-swellable (insoluble) fraction. Chewy sweets are prepared with blends of tragacanth and gum arabic to yield a chewy texture, and blends of tragacanth and gelatin for a chewy and cohesive texture (Nussinovitch, 1997). Tragacanth is used as a binder in highly sweetened icings, which contain fats to provide some pliability and to reduce evaporative moisture losses. Flavored oil emulsions are stabilized with 0.8 to 1.2% tragacanth and its blends: their shelf life is extended while the required combination of thickening, emulsifying and mouthfeel properties is supplied. In frozen desserts, gum tragacanth (0.2-0.5%) is used to control ice-crystal growth, to reduce moisture migration and ice-crystal development during storage, and to prevent color and flavor migration during storage and consumption. In baked-good fillings, the acid stability of tragacanth is exploited to yield a creamy texture with good clarity and gloss. In a few applications, such as ready-to-spread icings, gum tragacanth cannot be successfully replaced by other gums or gum combinations (Nussinovitch, 1997). In its powdered form, it has been used as a vehicle for active solid medicines, and to confer cohesion and firmness to lozenges. It has also been used to form pastes for preparing sticky labels (Felter and Lloyd, 1898). Gum tragacanth is a variable commodity because commercial samples may legitimately be admixtures, in any relative proportions, of the exudates of different Asiatic Astragalus species (Anderson and Bridgeman, 1985).

3.3.1.2 Taxon: Astragalus brachycalyx Fisch. Synonyms: Astracantha adscendens (Boiss. & Hausskn.) Podlech; Astragalus adscendens Boiss. & Hausskn. Common names: manna, Persian manna. Economic importance: Human food: gum/mucilage (source of a gum tragacanth used to make confections). Medicine: folk medicine. Distributional range (native): ASIA, TEMPERATE-Western Asia: Iran, Iraq, Turkey (USDA, ARS, National Genetic Resources Program, 2008).

56  ◾  Plant Gum Exudates of the World

Figure 3.10  Astragalus heratensis (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 57821).

3.3.1.3 Taxon: Astragalus heratensis Bunge Synonym: Astracantha heratensis (Bunge) Podlech Economic importance: Materials: gum/resin (Fig. 3.10). Distributional range (native): ASIA, TEMPERATE-Western Asia Afghanistan (USDA, ARS, National Genetic Resources Program, 2008).

3.3.1.4 Taxon: Astragalus kurdicus Boiss. Synonym: Astracantha kurdica (Boiss.) Podlech Economic importance: Materials: gum/resin. Distributional range (native): ASIA, TEMPERATE-Western Asia: Iran, Iraq, Turkey (USDA, ARS, National Genetic Resources Program, 2008).

Major Plant Exudates of the World  ◾  57

3.3.1.5 Taxon: Astragalus microcephalus Willd. Synonym: Astracantha microcephala (Willd.) Podlech Economic importance: Materials: gum/resin. Distributional range (native): ASIA, TEMPERATE-Western Asia: Iran, Iraq, Turkey; Caucasus: Armenia, Azerbaijan, Georgia; Soviet Middle Asia: Turkmenistan (USDA, ARS, National Genetic Resources Program, 2008).

3.3.1.6 Taxon: Astragalus verus Olivier Economic importance: Materials: exudate (Fig. 3.11). Distributional range (native): ASIA, TEMPERATE-Western Asia: Iran (USDA, ARS, National Genetic Resources Program, 2008).

3.3.2  S terculia Malvaceae (subfamily: Sterculioideae) 3.3.2.1 Taxon: Sterculia urens Roxb. Common names: Indian tragacanth, karaya, mucara. Distributional range (native): ASIA,TROPICAL-Indian Subcontinent: India, Sri Lanka (USDA, ARS, National Genetic Resources Program, 2008). Geographic distribution: The genus Sterculia contains more than a hundred species disseminated across the warmer parts of the world. The S. urens tree is characteristic of dry rocky hills and plateaus and common in the dry deciduous forests of northern and central India.

Figure 3.11  Astragalus verus exudate (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 58417).

58  ◾  Plant Gum Exudates of the World

Figure 3.12  Sterculia urens exudation.

It also occurs on the west coast of India, and in the dry forests of Burma and Sri Lanka (Mantell, 1947; Howes, 1949; Jayasinghe, 1981). Exudate appearance: S. urens gum exudes naturally but most of it is produced by artificial stimulation through a special tapping procedure (Fig. 3.12). In this procedure, portions of the trunk are blazed or the bark is cut away. Gum exudes straightaway and continues to form for a few days, but exudation is greatest during the first 24 h after blazing. The crude gum is allowed to dry on the tree and after its removal, further gum formation is induced by scraping the wound to expose fresh surface. The tapping or collecting season is roughly from October to January, and April to June. As the weather becomes warmer, the gum yield increases. Early rains reduce the size of the crop by washing away much of the exudation before it can dry (Howes, 1949; Goldstein and Alter, 1959). The average tree can be tapped about five times during its lifetime, with 1 to 5 kg exudate formed per tree during a season. The collected gum is broken by mallets to form irregularly shaped pieces with a somewhat crystalline appearance, or broken glassy tears (Kesar, 1935; American Pharmaceutical Association, 1946; Howes, 1949; Verma and Kharakwal, 1977). Two types of tree are said to exist in some parts of India, red- and white-barked. The former is reputed to yield more gum, and it is also thought that trees on hill slopes supply more gum than others (Kesar, 1935). Ethephon was found to enhance karaya gum yield from S. urens. The ethephon treatment resulted in an average 20 times more gum than from non-treated trees: the total harvest from seven treated trees, each tapped once, was about 1.5 kg of high-quality gum. The maximum gum-exudation response was achieved with 768 mg of active ethephon (Babu and Menon, 1989; Nair et al., 1995). Histological and histochemical changes during the development of gum canals in S. urens have been studied (Shah and Setia, 1976a). Exudate color: The highest grades of S. urens gum are white, translucent and almost free of bark. The lower grades vary from light yellow to brown. In its powedered form, the gum is white to grayish-white. Water solubility: All Sterculia gums swell in water. The particle size influences the type of water dispersion. A coarse granulation (6-30 mesh) of S. urens gum yields a discontinuous grainy dispersion. The gum swells to 60 to 100 times its original volume; a finely powdered gum (150-200 mesh) yields an apparently homogeneous dispersion (Goldstein and Alter, 1959). Karaya gum contains about 40% uronic acid residues and up to ∼8% acetyl groups. It is

Major Plant Exudates of the World  ◾  59

because of these substituents that the gum does not fully dissolve in water, swelling instead. Via chemical deacetylation, the gum can be changed from a water-swellable to water-soluble material (Nussinovitch, 1997). Relative to other exudate gums, karaya gum contains the lowest level of proteinaceous material. After dispersion in water, the gum absorbs the water to form a viscous solution, and yield stresses of 60 and 100 mN/cm2 have been determined for 2 and 3% gum concentrations (Mills and Kokini, 1984). The smoothness of the gum solution is determined by its particle size, but it can be altered by prolonged stirring to achieve a smooth texture and reduced viscosity. Gum solubility can be increased by deacetylation, which gives the product a more expanded conformation. The solutions are cohesive and stringy or ropy. Heating changes the polymer conformation and solubility increases. Ropiness is accompanied by lower acetyl content. Since heating increases solubility and the reduction in viscosity is irreversible, solution concentrations can be increased to 15% (Nussinovitch, 1997). Gum chemical characteristics: S. urens gum occurs naturally as a complex, partially acetylated, branched polysaccharide. The gum has a molecular weight of approximately 9,500,000 (Kubal and Gralen, 1948). As already noted, it contains about 40% uronic acid residues and approximately 8% acetyl groups. The gum is a calcium and magnesium salt, with a central chain of D-galactose (13%), L-rhamnose (15%) and D-galacturonic acid units (43%), with some side chains containing D-glucuronic acid. Powdered karaya contains about 14 to 18% moisture, less than 1% acid-insoluble ash, and less than 3% insoluble matter or bark. It tends to evolve acetic acid upon exposure to moist air. Indian karaya differs from the African variety in its higher acid value and more pronounced acetic acid odor. The pH of a 1% karaya (of Indian origin) solution is is 4.4 to 4.7, 4.7 to 5.2 for the African karaya. Above pH 7, alkali irreversibly transforms the characteristic short-bodied karaya swollen in solution into ropy, stringy mucilage. This has been ascribed to deacetylation of the karaya molecules. Karaya gum contains a low level of proteinaceous material in comparison with other gum exudates. The molecular structure and other chemical features of S. urens gum have been based on many studies (Rao and Sharma, 1957; Aspinall and Nasir, 1965; Aspinall and Sanderson, 1970a,b; Raymond and Nagel, 1973; Aspinall et al., 1981; Aspinall et al., 1987; Edwards et al., 1998; Weiping and Branwell, 2000). A recent description of the molecular structure of gum karaya is given by Weiping and Branwell (2000). Commercial availability and applications: In the early part of the 20th century, gum karaya was sold as gum tragacanth or as an adulterant of gum tragacanth because of the large price differential between the two gums. With increasing experience and knowledge of the uses of gums, however, gum karaya was proven superior in certain specific applications to existing gums and found a market of its own (Whistler and Smart, 1953c; Goldstein and Alter, 1959). The gum is used worldwide in various applications, even though some of these have disappeared with the development of other synthetic, reduced-cost gums. It is used as a stabilizing agent in foods such as water ices, soft candy, meringues and cheese spreads (Meer, 1980; Glicksman, 1983a; Anderson, 1989b; Imeson, 1992; Nussinovitch, 1997); in bulk laxatives (Meer, 1980), denture adhesives (Meer, 1980; Collys et al., 1997), and as a skin barrier in ostomies (Sedgewick, 1983); in long-fiber lightweight paper (Goldstein and Alter, 1959; Meer, 1980), finishing textiles (Goldstein and Alter, 1959; Meer, 1980), bioelectrodes (Cartlidge and Rutter, 1987; Eggins, 1993); to treat decubitus ulcer (Rhodes et al., 1979; Lowthian and Barnett, 1985) and warts (Bart et al., 1989; Anon., 1994), in ointments (Chiba et al., 1996) and in alcohol wave-set concentrates (Meer, 1980), and for petroleum and gas recovery (Meer, 1980). It has also been evaluated as a sustaining material in tablet dosages (Baveja and Rao, 1989; Bhardwaj et al., 2000; Murali et al., 2002), as a carrier in the design of oral controlled-release hydrophilic matrix systems (Chen and Cyr, 1970;

60  ◾  Plant Gum Exudates of the World

Murali et al., 2001, 2002), as an adhesive in skin-contact electrodes for medical applications (Eggins, 1993), and for transdermal delivery patches (Mottaz et al., 1988; Oh et al., 1998). Commercial and functional uses for other parts of the tree: The wood of S. urens finds some use, although it is not classified as high-quality timber. It has been employed for making packing cases, match splints, pencils, picture frames and other miscellaneous items (Kumar et al., 1988). In India, the tender roots of S. urens are first cut into small pieces, then boiled and mixed with either spices or sugar.

3.3.2.2 Taxon: Sterculia foetida L. Common names: Indian almond, Java olive, arbre puant [French], jangli badam [India], kepoh [Indonesian], kalumpang [Philippines], anacagüita [Spanish] (Fig. 3.13). Economic importance: Environmental: ornamental, shade/shelter (Fig. 3.14). Materials: wood. Food: roasted seeds.

Figure 3.13  Sterculia foetida gum.

Major Plant Exudates of the World  ◾  61

Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: Bangladesh, India, Sri Lanka; Indo-China: Myanmar, Thailand; Malesia: Indonesia, Malaysia. AUSTRALASIAAustralia: Australia - Queensland. OTHER-cultivated elsewhere in the tropics (USDA, ARS, National Genetic Resources Program, 2008).

3.3.2.3 Taxon: Sterculia guttata Roxb. Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: India (USDA, ARS, National Genetic Resources Program, 2008).

A

B

Figure 3.14  Sterculia foetida tree (A); leaves (B); fruits (C); seeds (D) (courtesy of Forest & Kim Starr).

62  ◾  Plant Gum Exudates of the World

C

D

Figure 3.14  (Continued).

3.3.2.4 Taxon: Sterculia quadrifida R. Br. Common name: bottletree.

3.3.2.5 Taxon: Sterculia scaphigera Wall. Economic importance: Medicine: folk medicine. Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: Bangladesh; IndoChina: Myanmar; Malesia: Malaysia (USDA, ARS, National Genetic Resources Program, 2008). The gum: In S. scaphigera, the gum is exuded from the fruits. When macerated with water, the pericarp or outer shell increases enormously in volume, forming a gelatinous mass.

Major Plant Exudates of the World  ◾  63

3.3.2.6 Taxon: Sterculia setigera Delile Synonym: Sterculia tomentosa Guill. & Perr. Distributional range (native): AFRICA-West Tropical Africa: Benin, Cote D’Ivoire, Gambia, Ghana, Guinea, Mali, Nigeria, Senegal, Togo (USDA, ARS, National Genetic Resources Program, 2008). Exudate properties and uses: Among the Sterculia species found in Africa, S. setigera is the only one known to be exploited commercially for its gum. More than 1,000 tons are exported annually from Africa. The gum of S. setigera has been described as hard amorphous nodules (Smith and Montgomery, 1959), with the dimensions of the African Sterculia gums approaching approximately 5 cm in their largest proportions (Goldstein and Alter, 1959). The yield of S. setigera gum in the dry zone is very small, but trees on river banks can sometimes yield abundantly (Dalziel, 1936). S. setigera and S. tragacantha (Fig. 3.15) both yield pale gums. S. setigera has been found to be more water-soluble than S. villosa or S. urens (Anderson et al., 1982). The gum of S. setigera is similar to gum karaya of Indian origin. It occurs as a partially acetylated (15.5%) derivative of the inorganic salt of an acidic, highly branched polysaccharaide. After being deacetylated with sodium hydroxide and freed from ash, it has an equivalent weight of 370-400 (Smith and Montgomery, 1959). Because the gum is resistant to acid hydrolysis, quantitative analysis of its component sugars gives only an approximate result: D-galactose (5 parts), L-rhamnose (5 parts), D-tagatose (1 part) and D-galacturonic acid (8 parts). Traces of D-xylose and 6-deoxy-D-fructose are also indicated (Goldstein and Alter, 1959). Structural and chemical features of S. setigera have been

Figure 3.15  Sterculia tragacantha (mag. 2x; courtesy of the Royal Botanic Gardens, Kew; Cat. No. 65017).

64  ◾  Plant Gum Exudates of the World

described by Hirst et al. (1949a,b), Hough and Jones (1950), Aspinall et al. (1965b) and Anderson et al. (1982). In the Western Sudan, tribes put the gum of S. setigera in food in place of baobab leaf where the latter is unobtainable. It is also used to prepare indigo-dyed cloth, and sometimes in Europe for dressing fabrics.

3.3.2.7 Taxon: Sterculia tragacantha Lindl. Economic importance: Materials: wood. Distributional range (native): AFRICA-East Tropical Africa: Tanzania; West-Central Tropical Africa: Cameroon, Zaire; West Tropical Africa: Benin, Cote D’Ivoire, Ghana, Guinea, Guinea-Bissau, Liberia, Mali, Nigeria, Sierra Leone, Togo; South Tropical Africa: Angola, Zambia (USDA, ARS, National Genetic Resources Program, 2008). The exudate: The gum of S. tragacantha exudes naturally through the tree’s corky bark and it is sometimes found on the fruit follicles, when these have been punctured by insects. In the latter case, considerable quantities of the gum can be yielded (Howes, 1949). The gum is often of a pinkish color. The percentage of acyl groups for S. tragacantha has been reported to be 11.1 (Jefferies et al., 1977b).

3.3.2.8 Taxon: Sterculia villosa Roxb. Economic importance: Materials: fiber. Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: Bhutan, India, Nepal, Pakistan (USDA, ARS, National Genetic Resources Program, 2008). The tree: S. villosa is distributed in the sub-Himalayan tract. It is also found in Andaman and the Cocos Islands. In Uttar Pradesh, it is common in Siwalik and in Pilibhit, Oudh, Gorakhpur and the Bundelkhad region. In southern India, it is found in Maharashtra, North Kanara, Knokan, South Kanara and also Gujarat. It is common throughout deciduous forests in Assam (Verma and Kharakwal, 1977).

3.3.3 Brachychiton Malvaceae (subfamily: Sterculioideae) 3.3.3.1 Taxon: Brachychiton acerifolius (A. Cunn. ex G. Don) Macarthur Synonym: Sterculia acerifolia A. Cunn. ex G. Don Common names: Australian flametree, flame bottletree, flame kurrajongs, flametree, Illawara flametree, flammender flaschenbaum [German]. Economic importance: Environmental: ornamental. Distributional range (native): AUSTRALASIA-Australia: Australia - New South Wales, Queensland (USDA, ARS, National Genetic Resources Program, 2008). General: Several gum-yielding Australian trees formerly included in the genus Sterculia have now been placed in the genus Brachychiton (Fig. 3.16). The difference between the two genera is that the seeds in Sterculia are naked whereas in Brachychiton they are covered with fibers.

Major Plant Exudates of the World  ◾  65

Figure 3.16  Brachychiton gum (mag. 2x; courtesy of the Royal Botanic Gardens, Kew; Cat. No. 64997).

3.3.4 Firmiana Malvaceae (subfamily: Sterculioideae) 3.3.4.1 Taxon: Firmiana simplex (L.) W. Wight Synonyms: Firmiana platanifolia (L. f.) Marsili; Hibiscus simplex L.; Sterculia platanifolia L. f. Common names: Chinese parasol tree, Chinese bottletree, Japanese varnishtree, phoenix tree, aogiri [transcribed Japanese]. Economic importance: Environmental: ornamental. Distributional range (native): ASIA, TEMPERATE-China: China; Eastern Asia: Taiwan, Japan - Ryukyu Islands; ASIA, TROPICAL-Indo-China: Vietnam. OTHER-cultivated and naturalized elsewhere (USDA, ARS, National Genetic Resources Program, 2008).

3.3.5 Hildegardia Malvaceae (subfamily: Sterculioideae) 3.3.5.1 Taxon: Hildegardia barteri (Mast.) Kosterm Synonyms: Firmiana barteri (Mast.) K. Schum.; Sterculia barteri Mast.

3.3.6 Cochlospermum Bixaceae 3.3.6.1 Taxon: Cochlospermum religiosum (L.) Alston Synonyms: Bombax gossypium L.; Cochlospermum gossypium (L.) DC.; Maximilianea gossypium (L.) Kuntze Common names: cottontree, silk cottontree, galgal [India], katira [India], algodão da Índia [Portuguese (Brazil)], capoquero blanco [Spanish].

66  ◾  Plant Gum Exudates of the World

Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: India; Indo-China: Myanmar. OTHER-also cultivated (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance: The exudate appears as large, clear, rounded lumps of irregular shape which are often striated or twisted. The lumps show a tendency to split into flat scales or large flat pieces. The gum is more readily pulverized than gum tragacanth (Howes, 1949). Exudate color: White, pale buff, straw-colored or pinkish and semi-transparent (Howes, 1949). Gum water solubility: It is only partially soluble in water, swells very quickly to form a nearly transparent gel which, however, is so brittle that it can be pulverized by gentle rubbing into a very large number of minute angular particles. After rupture, these particles do not recoalesce (Mantell, 1947). Gum chemical characteristics: The gum yields 14% acetic acid upon distillation and loses 19 to 21% of its weight upon heating to 100oC (Mantell, 1947). Another report claims that it has 18.9% acetyl and contains equimolecular amounts of L-rhamnose, D-galactose and D-galacturonic acid, together with trace amounts of a labile ketohexose. D-xylose has also been reported (Smith and Montgomery, 1959). The basic constituent sugars are similar to that of gum karaya but the proportions of the individual sugars vary. C. religiosum gum has a higher content of uronic acid (glucuronic and galacturonic acid, 63%) than of neutral sugars (arabinose, rhamnose and galactose, 37%), which can lead to significant differences in the gum’s utility and functionality in comparison to karaya. The gum has the remarkable property, also possessed by karaya, of giving off acetic acid when exposed to moist air. C. religiosum gum has higher soluble fiber, protein, tannin, calcium and potassium contents than karaya gum (Hirst and Dunstan, 1953; Aspinall et al., 1962, 1965b; Janaki and Sashidhar, 1998). Similar gums: The gum resembles karaya gum from Sterculia urens and Sterculia setigera (Smith and Montgomery, 1959). Commercial availability of the gum (pure state): The gum is available commercially in northern India (Janaki and Sashidhar, 1998), sometimes mixed with karaya. In the past, it was exported as a substitute for true tragacanth, and it has been employed in the textile, cigar, ice cream and paper industries and as a laxative agent to treat stomach and urine disorders. As an emulsifying agent, it is a good substitute for tragacanth in some preparations, but its higher acidity is objectionable for certain purposes (Howes, 1949). Commercial and functional uses for other parts of the tree: Bark and root are used for medicinal purposes. Seeds are useful for stuffing pillows. The bark has been used as a local cordage fiber (Gamble, 1922).

3.4 IMPORTANT INDIAN OR ASIATIC GUMS AND THEIR BOTANICAL SOURCES 3.4.1 Aegle Rutaceae (subfamily: Aurantioideae) 3.4.1.1 Taxon: Aegle marmelos (L.) Corrêa Synonyms: Belou marmelos (L.) A. Lyons; Crateva marmelos L. Common names: bael, baeltree, bel fruit tree, Bengal quince, golden apple, Indian baelfruit, mu ju, bel indien [French], belbaum [German], beli [India], bela [Spanish], milva [Spanish] (USDA, ARS, National Genetic Resources Program, 2008) (Fig. 3.17).

Major Plant Exudates of the World  ◾  67

+2

B

C

+2 +3 D

F +3

+2

+4

H

E

A

G

2/ 3

Figure 3.17  Aegle marmelos, a well-known and important fruit tree throughout India [courtesy of © L.H. Bailey Hortorium, Cornell University (for reproduced image, not source)].

Economic importance: Human food: The fruits may be sliced and dried and are frequently seen in this form in bazaars. The fruit pulp is eaten, or is used in India for making a kind of sherbet or as preserves. Materials: The bael fruit gum is used to prepare adhesives, for water-proofing, and in oil-emulsion coatings (Roy et al., 1975). Due to its mucilaginous nature, it has been considered a substitute for quince seed, the origin of the name “Bengal quince”. It may be used alone as an adhesive, or mixed with lime as a sort of cement. The wood is used for furniture-making and in construction (Howes, 1949; Parmar and Kaushal, 1982; Morton, 1987a). Medicines: It is valued for its medicinal properties in diarrhea and dysentery. Bael fruit, and particularly bael fruit gum, are known for their anti-amoebic and antihistaminic actions, and are important in Indian Ayurvedic medicine (Kirticar and Basu, 1948). Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: India - Andhra Pradesh, Bihar, Himachal Pradesh, Jammu and Kashmir, Karnataka, Kerala, Madhya Pradesh, Maharashtra, Punjab, Rajasthan, Tamil Nadu, Uttar Pradesh, West Bengal, Nepal; North Indian Ocean: India - Andaman and Nicobar; Indo-China: Myanmar. OTHERcultivated in Malesia (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance: Exudes from wounded branches and hangs down in long strands, becoming gradually solid. It is sweet like honey at first taste and then irritating to the throat (Morton, 1987a). A gum can also be obtained from the gummy envelope around the seeds of unripe bael fruits (Roy et al., 1975). The exudate is yellowish. Gum water solubility: Two distinct types of ‘gummy’ substance are yielded by the tree. An ordinary gum from the trunk (Fig. 3.18), which is water-soluble, and a gummy substance produced from the pulp of the fruit. The latter is quite insoluble in water and can be obtained as a white powder by precipitation with alcohol (Parikh et al., 1958).

68  ◾  Plant Gum Exudates of the World

Figure 3.18  Aegle marmelos exudate (mag. 2x; courtesy of the Royal Botanic Gardens, Kew; Cat. No. 64997).

Gum chemical characteristics: The purified bael fruit gum polysaccharide contains D-galactose (71%), L-arabinose (12.5%), L-rhamnose (6.5%) and galacturonic acid (7%) (Roy et al., 1977).

3.4.2 Albizia Fabaceae (subfamily: Mimosoideae) 3.4.2.1 Taxon: Albizia lebbeck (L.) Benth. Synonyms: Acacia lebbek (L.) Willd.; Mimosa lebbeck L.; Mimosa sirissa Roxb. Common names: East Indian walnut, frywood, koko, lebbek, lebbektree, siristree, women’s tongue tree, lebbekboom [Afrikaans], ébano-oriental [Portuguese (Brazil)], coração de negro [Portuguese (Brazil)], língua de mulher [Portuguese (Brazil)], língua de sogra [Portuguese (Brazil)] (USDA, ARS, National Genetic Resources Program, 2008). Economic importance: After the drought in 1973-1974, the gum exudates of A. lebbeck and A. zygia were investigated as alternatives to Acacia as sources of natural food and pharmaceutical emulsifiers (Ashton et al., 1975; US National Academy of Sciences, 1979). The gum of A. lebbeck has been reported in Bombay markets in a pure state, unmixed with other gums. Gum shiraz and gum mamrah are considered to be mixtures of A. lebbeck and A. odoratissima gums. Albizia species are a source of tannins. Saponins and fish-stupefying, insecticidal and anthelmintic compounds can be extracted from the bark of certain species for local native medicinal and other uses (Allen and Allen, 1981). In India, Albizia species are an important source of timber and fuelwood, and they are used as ornamental trees, for shade in tea plantations. Various parts of the tree are used in traditional medicine. Albizia gums are also used locally in Africa for cosmetics and book binding (Mwamba, 1995).

Major Plant Exudates of the World  ◾  69

Distributional range: Cultivated in the tropics, probably native in tropical mainland Asia, naturalized in Africa, the southeastern United States, tropical South America, West Indies, Cape Verde Island, Melanesia, Polynesia, Hawaii. Exudate properties: At times, Albizia gums exude quite freely on the stem and branches (Howes, 1949). The gum is formed as round elongated tears of variable size (Mital and Adotey, 1971). The gum of A. lebbeck is exuded freely and dries in stalactiform masses. The exudate is usually red to brown. The gum varies in color from light yellow to deep reddish-brown (Howes, 1949) (Fig. 3.19). It is sometimes imperfectly soluble (Howes, 1949), as reported at 5 g in 100 ml water (Clamens et al., 1998). Other physical properties of Albizia solutions are described elsewhere (Ashton et al., 1975; Mital et al., 1978). No complete structure of Albizia gum has thus far been proposed. A partial structure (Drummond and Percival, 1961) was proposed to consist of a main chain of β(1-3) D-galactose units with some β(1-6)-linked D-galactose units (Anderson and Morrison, 1990). Further chemical and structural features of Albizia species were proposed by other researchers (Anderson et al., 1966; Anderson and Dea, 1969; de Paula et al., 2001; Mhinzi, 2002). The differentiation between Albizia gums and levorotatory Acacia gums (which are permitted for food use) is not as easy as that between Acacia and Combretum gums, in which the presence of galacturonic acid and acetyl groups provides additional characteristic markers (Anderson and Weiping. 1990b).

3.4.2.2 Taxon: Albizia odoratissima (L. f.) Benth. Synonym: Mimosa odoratissima L. f. Common name: Ceylon rosewood.  Economic importance: Materials: wood. Distributional range (native): ASIA, TEMPERATE-China: China - Fujian, Guangdong, Guangxi, Guizhou, Yunnan. ASIA, TROPICAL-Indian Subcontinent: Bhutan, India, Nepal, Sri Lanka; Indo-China: Laos, Myanmar, Thailand, Vietnam (USDA, ARS, National Genetic Resources Program, 2008). Gum properties: The gum of A. odoratissima generally appears as large, transparent, superficially fissured, amber-colored tears (Howes, 1949). It is imperfectly soluble (Howes, 1949) and is sometimes mixed with gums of Albizia chinensis (syn. A. stipulate) and Toona ciliata (syn. Cedrela toona) and sold as khota gum (Caius and Radha, 1939).

3.4.2.3 Taxon: Albizia procera (Roxb.) Benth. Synonym: Mimosa procera Roxb. Common names: black siris, false lebbeck, forest siris, tall albizia, white siristree, basterlebbeck. Economic importance: In Australia, A. procera is regarded as good-quality cattle feed and at the same time as a sign of good country for farming sugar cane. Potential uses of the tree are as fuel (charcoal), for wood production and as a weed. Distributional range (native): ASIA, TEMPERATE-China: China - Guangdong, Guangxi; Eastern Asia: Taiwan. ASIA, TROPICAL-Indian Subcontinent: Bhutan, India, Nepal; IndoChina: Cambodia, Laos, Myanmar, Thailand, Vietnam; Malesia: Indonesia - Celebes, Java, Lesser Sunda Islands, Moluccas, Papua New Guinea, Philippines. AUSTRALASIA-Australia: Australia - Queensland (USDA, ARS, National Genetic Resources Program, 2008).

70  ◾  Plant Gum Exudates of the World A

B

Figure 3.19  Albizia lebbeck tree (A); leaves, flowers and pods (B) (courtesy of Forest & Kim Starr); exudate (C).

Major Plant Exudates of the World  ◾  71

Figure 3.19  (Continued).

Gum properties: The gum of A. procera occasionally exudes in small transparent tears and vermiform pieces. It is polished in appearance when fresh, but becomes dark and opaque with age (Howes, 1949) (Fig. 3.20). The freshly exuded gum of A. procera is completely soluble, yielding a thick, slightly gelatinous mucilage, while the dark opaque gum is imperfectly soluble (Howes, 1949).

3.4.2.4 Taxon: Albizia chinensis (Osbeck) Merr. Synonyms: Acacia stipulata DC.; Albizia marginata (Lam.) Merr.; Albizia stipulata (DC.) Boivin; Mimosa chinensis Osbeck (basionym); Mimosa marginata Lam. Common names: Chinese albizia, silktree.

72  ◾  Plant Gum Exudates of the World

Economic importance: Environmental: revegetator, shade/shelter. Materials: wood, potential as fiber. The gum of A. chinensis has been reported to be used by the Nepalese for sizing their “Daphne” paper (Howes, 1949). Distributional range (native): ASIA, TEMPERATE-China: China - Fujian, Guangdong, Guangxi, Hunan, Xizang, Yunnan. ASIA, TROPICAL-Indian Subcontinent: Bhutan, India, Nepal, Sri Lanka; Indo-China: Cambodia, Laos, Myanmar, Thailand, Vietnam. Malesia: Indonesia (USDA, ARS, National Genetic Resources Program, 2008). Gum properties: The gum of A. chinensis is dark and imperfectly soluble (Howes, 1949).

3.4.2.5 Taxon: Albizia amara (Roxb.) Boivin Synonyms: Albizia sericocephala Benth. [≡ Albizia amara subsp. sericocephala]; Mimosa amara Roxb. [≡ Albizia amara subsp. amara] (Fig. 3.21). Distributional range (native): AFRICA-Northeast Tropical Africa: Chad, Ethiopia, Sudan; East Tropical Africa: Kenya, Tanzania, Uganda; West-Central Tropical Africa: Rwanda; South Tropical Africa: Malawi, Mozambique, Zambia, Zimbabwe; Southern Africa: Botswana, South Africa - Transvaal. ASIA, TROPICAL-Indian Subcontinent: India, Sri Lanka (USDA, ARS, National Genetic Resources Program, 2008).

A

Figure 3.20  Albizia procera tree oozing gum (A) and exudate (B).

Major Plant Exudates of the World  ◾  73

Figure 3.20  (Continued).

3.4.3  Aleurites Euphorbiaceae (subfamily: Crotonoideae) 3.4.3.1 Taxon: Aleurites moluccanus (L.) Willd. Synonyms: Aleurites javanicus Gand.; Aleurites pentaphyllus Wall. ex Langeron; Aleurites remyi Sherff; Aleurites trilobus J. R. Forst. & G. Forst.; Jatropha moluccana L. Common names: candleberry, candlenut, candlenut tree, Indian walnut, lumbangtree, varnishtree, noyer de bancoul [French], noyer des Moluques [French], lichtnußbaum [German], noz da Índia [Portuguese], nogueira brasileira [Portuguese (Brazil)], nogueira da Índia [Portuguese (Brazil)], nogueira de iguape [Portuguese (Brazil)], calumbán [Spanish], camirio [Spanish], lumbán [Spanish], mkaa [Swahili], kukui. Economic importance: In Hawaii, the gum is used for the traditional “tapa” (paper cloth) (http://www.thebeadsite.com). A. moluccanus oil and nuts are widely traded. All parts of the tree have medicinal uses. The tree is widely cultivated throughout the tropics as an ornamental (Fig. 3.22). Human food: flavoring and seeds. Materials: the tree is a source of

74  ◾  Plant Gum Exudates of the World

Figure 3.21  Albizia amara gum (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 58930).

A

Figure 3.22  Aleurites moluccanus tree (A); leaves and fruits (B); flotsam nuts (C) (courtesy of Forest & Kim Starr).

Major Plant Exudates of the World  ◾  75

B

C

Figure 3.22  (Continued).

beads, lipids (source of candelnut or lumbang oil with several applications). Medicine: folk medicine. Vertebrate poisons: mammals. Distributional range (native): ASIA, TEMPERATE-China: China; Eastern Asia: Taiwan. ASIA, TROPICAL-Indian Subcontinent: India - Assam, Karnataka, Kerala, Maharashtra, Orissa, Tamil Nadu, West Bengal, Sri Lanka; Indo-China: Cambodia, Myanmar, Thailand, Vietnam. Malesia: Indonesia, Malaysia, Papua New Guinea, Philippines. AUSTRALASIA-Australia: Australia Queensland. OTHER-widely cultivated and naturalized in tropics (e.g., Hawaii; Duke, 1983a), exact native range obscure (USDA, ARS, National Genetic Resources Program, 2008). Exudate properties: The tasteless and odorless gum frequently exudes from the trunk and is sometimes collected by natives. The tree also exudes a resin (Greenway, 1941). The exudate is light in color; the gum is partially insoluble and swells considerably in water (Howes, 1949).

76  ◾  Plant Gum Exudates of the World

3.4.4 Anogeissus Combretaceae 3.4.4.1 Taxon: Anogeissus latifolia (Roxb. ex DC.) Wall. ex Guill. & Perr. Synonym: Conocarpus latifolius Roxb. ex DC. Common names: buttontree, dindiga tree, ghattitree, gum ghatti, baklee [India], dhaura [India]. The term “ghatti gum” is generally used in European commerce for any highly viscous gum of Indian origin (Howes, 1949). In the old days, after being collected and sundried, the gum was transported to Bombay by land through mountain ghats or passes, hence the name ghatti (Fleischer, 1959). Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: India, Nepal, Pakistan, Sri Lanka (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance: Gum ghatti is collected in exactly the same geographic areas as karaya, and therefore the harvesting and grading methods are similar (Imeson, 1992). The gum is regularly gathered in April from tapped trees. It has shapeless or rounded tears (0.5-1 cm in diameter) or larger vermiform pieces with glassy fractures. The gum has a slight odor and an insipid taste. Gum left on the tree throughout the monsoon season is dark and agglutinated in masses (Mantel, 1947; Fleischer, 1959). The average conventionally tapped gum yield per tree in a season is 60 to 100 g, with exudation being higher in dry years. In A. latifolia, there is no natural pre-formed gum-producing tissue system in either the bark or the wood. Natural wounds such as the breaking of branches by wind cause exudation. Heavy tapping injures the cambium and curtails the lifespan of the tree as wound-healing becomes difficult. In India, an ∼450-fold increase in gum yield has been recorded in trees treated with 1,600 mg of ethephon during April-May, when the trees are leafless (Bhatt, 1987). Exudate color and solubility: The highest grade is pale tan and almost free of adhering bark. The lower grades vary from medium tan to dark brown (Fig. 3.23) and may contain as much as 7% insoluble impurities. Powdered gum has a gray to reddish-gray color. The gum of A. latifolia does not dissolve in water to give a clear solution but rather, over 90% of the gum forms a colloidal dispersion. The gum may be made soluble by means of an autoclave (Mantell, 1947). Chemical characteristics: Structural and chemical features of A. latifolia have been previously studied (Aspinall et al., 1955, 1958a,b, 1965a; Elworthy and George, 1963; Aspinall and Christensen, 1965). One of the main structural features of A. latifolia gum is a linear arrangement of (1-6)-linked D-galactopyranose. It is composed of L-arabinose, D-galactose, D-mannose, D-xylose and D-glucuronic acid in a molar ratio of 10:6:2:1:2, respectively, plus trace amounts (less than 1%) of 6-deoxyhexose. Upon graded hydrolysis, two aldobiuronic acids, 6-O-(β-Dglucopyranosyluronic acid)-D-galactose and 2-O-(β-D-glucopyranosyluronic acid)-D-mannose, are obtained. Also present are 50% pentose and 12% galactose or galacturonic acid. Partial acid hydrolysis affords two homologous series of oligosaccharides together with small amounts of 3-O-β-D-galactopyranosyl-D-galactose and 2-O-(β-D-glucopyranosyluronic acid)-D-mannose (Aspinall et al., 1955, 1958a,b). Acid-labile side chains are attached to the backbone through L-arabinofuranose residues. The soluble portion of the gum, which contains 0.72% nitrogen, consists of a mixture of calcium, magnesium, potassium and sodium salt of a polysaccharide acid. With respect to its constituent sugars, ghatti greatly resembles acacia, damson, cherry, egg plum and mesquite gums, all of which contain a high proportion of terminal L-arabofuranose units. Also of interest is the fact that one of the aldobiouronic acids obtained upon hydrolysis, 6-O-β-D-glucopyranosyluronic acid-D-galactose, is characteristic

Major Plant Exudates of the World  ◾  77

Figure 3.23  Anogeissus latifolia gum.

of gum arabic. Ghatti appears to differ from the above gums in possessing a (1-6)-linked galactose framework. It contains 10 to 12% moisture, and up to 3% acid-insoluble ash. Spraydried ghatti grades have all of their insolubles removed and are significantly lower in viscosity due to processing conditions and hydrolysis during preparation. The gum is not colored blue by iodine solution, indicating the absence of starch and dextrin. It is insoluble in alcohol (Hamnna and Shaw, 1941; Mantell, 1947; Fleischer, 1959; Smith and Montgomery, 1959; Edwards et al., 1998). Physical properties: The molecular weight of the soluble portion is about 12,000 (Mantell, 1947). Small amounts of acid or alkali do not affect ghatti dispersions, since the gum acts as a buffer and reverts to its normal pH (about 5.5). Large amounts of acid or alkali will overcome this buffering action. Ghatti solutions lose their viscosity at high pH values. When dispersed in water at high concentrations (over 10%), the gum forms a viscous, adhesive mucilage which is less viscous than that of karaya but more viscous than gum arabic. Its

78  ◾  Plant Gum Exudates of the World

Figure 3.24  Terminalia gums.

adhesive properties are not as strong as those of gum arabic (Fleischer, 1959; Ben-Zion and Nussinovitch, 1997). Other rheological properties of A. latifolia solutions are reviewed elsewhere (Fleischer, 1959; Jefferies et al., 1977a; Meer, 1980). Commercial availability of the gum and applications: Although Indian ghatti is largely obtained from A. latifolia, there is no doubt that gums from totally dissimilar botanical sources are frequently referred to as ghatti gum by Indian merchants and are exported under this name. Such substitutes are collected from Terminalia elliptica (syn. T. alata) Terminalia bellirica, Terminalia chebula var. tomentella (Fig. 3.24), Bauhinia variegata, Acacia catechu and Acacia arabica (Indian gum arabic). Ghatti should not be confused with either “Bassora gum” (i.e. gums of this class which somewhat resemble gum tragacanth in their gelling properties, but which are darker than tragacanth) or Sterculia gum, each of which is sometimes referred to as “Indian gum” (Mantel, 1947). The uses of ghatti gum are comparable to those of gum arabic: in foods (Imeson, 1992), for tablet binding

Major Plant Exudates of the World  ◾  79

(Jain and Dixit, 1988a,b) and for emulsification purposes (Jain and Dixit, 1988a,b). It was once used extensively in oil-well-drilling fluids to enhance their viscosity and thixotropy, and to minimize fluid loss. Other hydrocolloids, such as xanthan, are used today as substitutes for ghatti. Powdered ghatti has also been used in explosives to keep the ammonium nitrate dry in wet ground. The gum absorbs any water which seeps into the explosive cartridge and swells to form an insulating surface layer. It has also been employed in paints as a glaze or varnish, as a binder in coating compositions and in ceramics as a binder to enhance the wet strength of clay prior to firing (Fleischer, 1959). Commercial and functional uses for other parts of the tree: The wood is extensively used for axle handles, construction, agricultural implements, house posts, poles, fuel and charcoal. Leaves are used for tanning (Fleischer, 1959). The bark is useful in medicinal preparations.

3.4.5 Bauhinia Fabaceae (subfamily: Caesalpinioideae) 3.4.5.1 Taxon: Bauhinia purpurea L. Synonym: Bauhinia triandra Roxb. Common names: butterfly-orchid tree, butterfly tree, camel’s foot, orchid tree, purple bauhinia, skoenlapperorgideëboom [Afrikaans], khairwal [India], pie de cabra [Spanish]. Economic importance: Environmental: ornamental (Fig. 3.25). Gene sources: potential gene source for tribal pulses. Weed.

Figure 3.25  Bauhinia purpurea leaves and flower (courtesy of Forest & Kim Starr).

80  ◾  Plant Gum Exudates of the World

Figure 3.26  Bauhinia roxburghiana (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 59240).

Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: Bhutan, India, Nepal, Pakistan, Sri Lanka; Indo-China: Myanmar, Thailand. OTHER-cultivated throughout the tropics (USDA, ARS, National Genetic Resources Program, 2008).

3.4.5.2 Taxon: Bauhinia roxburghiana Voigt Synonyms: Bauhinia retusa Roxb. (Fig. 3.26); Bauhinia semla Wunderlin Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: Bangladesh, Nepal, Pakistan, India - Andhra Pradesh, Bihar, Haryana, Himachal Pradesh, Karnataka, Madhya Pradesh, Maharashtra, Orissa, Punjab, Rajasthan, Tamil Nadu, Uttar Pradesh, West Bengal (USDA, ARS, National Genetic Resources Program, 2008). Commercial availability, properties and uses of the gum: The gum exudes from January to April (http://www.fao.com). Bauhinia gums are usually clear and light-colored, e.g. the gum of B. carronii is said to be yellow and tasteless (Howes, 1949). Bauhinia gums are only partially soluble in water, forming a gelatinous mass. B. retusa resembles gum tragacanth in its hydrocolloidal behavior (Howes, 1949). The gum of B. retusa has been collected in India and adjoining regions (Howes, 1949) and in Bhutan. It is used to color sweets (http://www. fao.com). The gum of B. thonningii is used in Zambia for caulking boats (Mwamba, 1995). In nature, the gum of B. surinamensis is an important part of the feed and diet of Geoffroy’s marmoset monkey (Passamani and Rylands, 2000).

Major Plant Exudates of the World  ◾  81

3.4.5.3 Taxon: Bauhinia variegata L. Synonyms: Bauhinia alba hort.; Bauhinia variegata var. alboflava de Wit; Bauhinia variegata var. candida Voigt Common names: mountain ebony, orchidtree, orgideëboom [Afrikaans], arbre de Saint-Thomas [French], buntfarbene bauhinie [German], kachnar [India], árvore de São Thomaz [Portuguese]. Distributional range (native): ASIA, TEMPERATE-China: China. ASIA, TROPICALIndian Subcontinent: Bhutan, India, Nepal, Pakistan; Indo-China: Laos, Myanmar, Thailand, Vietnam (USDA, ARS, National Genetic Resources Program, 2008). Commercial availability of the gum and functional uses for other parts of the tree: The gum of B. variegata is commercially available in India and is sold as gum ghatti for edible purposes (Fig. 3.27). In Sri Lanka, it is now used as a substitute for kino from Eucalyptus. Bauhinia trees are mainly ornamental. The bark, root and flowers of B. variegata are used in folk medicine. The flesh of Bauhinia thonningii seeds, contained in the pods, is edible when dried. 

Figure 3.27  Bauhinia variegata gum.

82  ◾  Plant Gum Exudates of the World

3.4.6  Buchanania Anacardiaceae 3.4.6.1 Taxon: Buchanania lanzan Spreng. Common names: chirauli nut, chirauli-nut tree, almondette [French], cheronjee [India], chironji [India]. Economic importance: Human food: nut. Medicine: folk medicine. Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: India; Malesia: Indonesia, Malaysia (USDA, ARS, National Genetic Resources Program, 2008). Exudate properties: When tapped, the exudate appears as large, clear, vitreous (glassy) tears that are either pale or dark in color (Fig. 3.28) (Howes, 1949), and the gum is partially soluble (Howes, 1949). It is suitable for dressing textiles and is utilized in folk medicine to treat intercostal pain (Kirtikar and Basu, 1918). Commercial and functional uses for other parts of the tree: The kernels are edible, and the oil extracted from them is used as a substitute for almond oil in native medicinal preparations and confectionery. In the Jhansi district, the kernel is worked up into an ointment to be used in skin diseases. The fruit is an important food item. The seed is used in confectionery. The bark is used to heal wounds and cure skin diseases.

3.4.6.2 Taxon: Buchanania latifolia Roxb. Common names: chirauli nut, chirauli-nut-tree, Hamilton’s mombin. Economic importance: Human food: nut. Medicine: folk medicine.

Figure 3.28  Buchanania lanzan gum.

Major Plant Exudates of the World  ◾  83

Distributional range (native): ASIA, TEMPERATE-China: China - Hainan, Yunnan. ASIA, TROPICAL-Indian Subcontinent: India, Nepal; Indo-China: Laos, Myanmar, Thailand, Vietnam (USDA, ARS, National Genetic Resources Program, 2008).

3.4.7  Toona Meliaceae 3.4.7.1 Taxon: Toona ciliata M. Roem. Synonyms: Cedrela toona Roxb. ex Willd.; Cedrela velutina DC.; Toona australis (Kuntze) Harms Common names: Australian red cedar, Australian cedar, red cedar, toon, toontree, toonboom [Afrikaans], hong chun [Transcribed Chinese]. Distributional range (native): ASIA, TEMPERATE-Western Asia: Afghanistan; China: China - Guangdong, Hainan, Sichuan, Yunnan. ASIA, TROPICAL-Indian Subcontinent: Bangladesh, Bhutan, India, Nepal, Pakistan, Sri Lanka; Indo-China: Cambodia, Laos, Myanmar, Thailand; Malesia: Indonesia, Malaysia, Papua New Guinea, Philippines. AUSTRALASIA-Australia: Australia - New South Wales, Queensland. OTHER-also cultivated, naturalized in tropical and South Africa, tropical America, Seychelles, and Hawaii (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance: The exudate forms in thin, ca. 2.5-cm long tears that are smooth, transparent, stalactiform masses (Fig. 3.29) (Maiden, 1890; Howes, 1949). Trees that are wellexposed to the sun yield the most gum. The gum of the Australian tree has been described as almost resin-free, while the gum of the Indian tree has been said to include some aromatic resin (Maiden, 1890; Greenway, 1941). The gum is recorded as very pale yellow, almost colorless (Maiden, 1890), or yellow to yellowish-brown (Howes, 1949).

Figure 3.29  Toona ciliata gum (mag. 3x; courtesy of the Royal Botanic Gardens, Kew; Cat. No. 63088).

84  ◾  Plant Gum Exudates of the World

Gum water solubility: The gum is partially soluble. It swells a great deal in cold water, and is almost completely dissolved within 24 h, forming a colorless cloudy solution (Maiden, 1890). The insoluble portion increases with age (Felter and Lloyd, 1898; Howes, 1949). Gum chemical characteristics: Analysis of the gum yields 68.3% arabin (water-soluble fraction), 6.3% metarabin (water-swellable fraction), 19.5% moisture and 5.2% ash (Felter and Lloyd, 1898; Maiden, 1890), without any trace of resin (Maiden, 1901). Commercial availability of the gum: The gum is reported to be available in Bombay markets. In its non-pure form, it is sold as part of the local commercial Indian “gum khota” (Caius and Radha, 1939). It has been used in India as a febrifuge (Grennway, 1941). Commercial and functional uses for other parts of the tree: The trees are of environmental importance for their ornamental characteristic. They are also used for shade or shelter, as animal food and as a source of tannin and dyestuff. The reddish open-grained wood is much used for joinery, furniture and cabinetwork, decorative veneers, racing boats, musical instruments, and pattern-making (Chudnoff, 1984).

3.4.8  Chloroxylon Rutaceae 3.4.8.1 Taxon: Chloroxylon swietenia DC. Synonym: Swietenia chloroxylon Roxb. Common name: East Indian satinwood. Economic importance: Materials: wood (timber for furniture-making and carving). Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: India, Sri Lanka (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance: The gum exudes in amber or brownish tears or rod-shaped pieces (Fig. 3.30). Gum water solubility: Partial. The gum swells in water, forming a gelatinous mass. Commercial availability of the gum (pure state): Available from Bombay merchants according to old records (Howes, 1949). In its non-pure form, it is mixed with other gums (Anderson et al., 1986).

3.4.9 Delonix Fabaceae (subfamily: Caesalpinioideae) 3.4.9.1 Taxon: Delonix regia (Bojer ex Hook.) Raf. Synonym: Poinciana regia Bojer ex Hook. Common names: flamboyant, flametree, peacock flower, royal poinciana, flamboiã [Portuguese (Brazil)], árbol de fuego [Spanish], flamboyánb [Spanish]. Distributional range (native): AFRICA-Western Indian Ocean: Madagascar. OTHER- widely cultivated (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance and properties: The gum exudes in irregularly shaped tears (Fig. 3.31). It is mainly found in large flat lumps on cut branches. Its color is yellow or reddish-brown. The gum of D. regia is soluble in water and forms a thick opalescent mucilage, similar to gum arabic (Howes, 1949). Commercial and functional uses for other parts of the tree: Used as an ornamental tree lining streets and avenues (Fig. 3.32). Other uses are as beads and in folk medicine.

Major Plant Exudates of the World  ◾  85 A

J +15 K

+6

L +12

a +10

C

O +20 M

b

N

1

/2

+5

D

E

+10

+15 +20 P

A

B

+15 F

+12

+25

G

H

+3 Q

B

Figure 3.30  Chloroxylon swietenia plant (A) [courtesy of L.H. Bailey Hortorium ©, Cornell University (for reproduced image, not source)]; tree oozing gum (B) and exudate (C).

86  ◾  Plant Gum Exudates of the World

Figure 3.30  (Continued).

3.4.10  Elaeodendron Celastraceae (subfamily: Celastroideae) 3.4.10.1 Taxon: Elaeodendron glaucum (Rottb.) Pers. Synonyms: Cassine glauca (Rottb.) Kuntze; Mangifera glauca Rottb. Common name: Ceylon tea. Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: Bhutan, India, Nepal, Pakistan, Sri Lanka; Indo-China: Cambodia; Malesia: Indonesia (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance and properties: Large or small transparent to reddish-brown tears with a finely fissured surface. Gum water solubility: Readily soluble in water, forming a clear, strong adhesive and a tasteless mucilage. Commercial availability of the gum (pure state): Traded in the past as a high-quality gum.

Major Plant Exudates of the World  ◾  87

A

Figure 3.31  Delonix regia tree oozing gum (A) and exudate (B).

88  ◾  Plant Gum Exudates of the World

A

B

Figure 3.32  Delonix regia tree (A); leaves and flowers (B); pods and seeds (C) (courtesy of Forest & Kim Starr).

Major Plant Exudates of the World  ◾  89

Figure 3.32  (Continued).

3.4.11 Limonia Rutaceae (subfamily: Aurantioideae) 3.4.11.1 Taxon: Limonia acidissima L. Synonyms:Feronia elephantum Corrêa; Feronia limonia (L.) Swingle; Schinus limonia L. Common names: elephant apple, Indian wood apple, wood apple. Distributional range (native): ASIA, TEMPERATE-China: China. ASIA, TROPICALIndian Subcontinent: India, Pakistan, Sri Lanka; Indo-China: Indochina, Myanmar, Thailand. SOUTH AMERICA-Caribbean: Dominican Republic (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance and solubility: Small irregular, rounded tears or large and agglomerated into masses. Exudes naturally, especially after the rainy season, on trunks or branches (Howes, 1949; Morton, 1987a). Its color is transparent or white-yellow transparent to reddish-amber (Mantell, 1947; Howes, 1949) (Fig. 3.33). The gum is completely soluble in water. The paler samples form a thick, colorless, tasteless, mucilage (Howes, 1949). Gum chemical characteristics: The gum consists of L-arabinose (35.5%) and D-xylose, D-galactose (42.7%), and traces of L-rhamnose and glucuronic acid (Lemeland, 1905; Smith and Montgomery, 1959; Morton, 1987a). Similar gums: L. acidissima gum is put to similar uses as Acacia gums. It is more viscous than gum arabic and not inferior in adhesive properties (Howes, 1949; Smith and Montgomery, 1959). Commercial availability of the gum (pure state): It is often presented in “bavool” gum (mainly Acacia arabica) sold by Bombay gum merchants. It may also be sold as gum arabic (Caius and Radha, 1939). It is traditionally used in making artists’ watercolors, ink, dyes and varnish (Morton, 1987a). The powdered gum, mixed with honey, is given to children to treat dysentery and diarrhea. Commercial and functional uses for other parts of the tree: This is a widespread fruit tree (similar to Aegle marmelos) used for food and medicinal preparations. The fruit shell is fashioned into snuffboxes and other small containers. The wood is valued for construction, pattern-making, agricultural implements, rollers for mills, carving, rulers, and other products. It also serves as fuel. Leaves, bark, roots and fruit pulp are all used for medicinal purposes (Morton, 1987a).

90  ◾  Plant Gum Exudates of the World

Figure 3.33  Feronia limonia gum (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 63831).

3.4.12 Mangifera Anacardiaceae 3.4.12.1 Taxon: Mangifera indica L. Common names: mango, mangue [French], manguier [French], mango [German], mangobaum [German], mangopalme [German], mangueira [Portuguese], manga [Portuguese, Spanish]. Economic importance: The fruits are edible and can be used for beverage-based preparations (Fig. 3.34). In addition, it is an ornamental tree. The Negritos of the Philippines utilize the gum-resin of the tree mixed with coconut oil to apply directly to scabies and other parasitic diseases of the skin. The gum-resin is also used for curing aphthae and for healing sores caused by herpes and venereal diseases such as syphilis (Quisumbing, 1951). In addition to its medicinal uses, it can be used to prepare vertebrate poisons for mammals. Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: India - Assam; IndoChina: Myanmar. OTHER-widely cultivated in the tropics (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance and properties: M. indica exudes a gum-resin, naturally or through wounds made in the bark, in the form of small tears with dull fractures. Mango fruits secrete a gum-resin in special duct regions, the ultrastructure of which has been reported (Joel and Fahn, 1980a,b,c). The gum consists mainly of terpenes but it also contains phenols and protein-carbohydrate mucilage. The fruit gum-resin is a skin-irritant. The exudate is transparent, reddish-brown to black (Fig. 3.35), and is slightly soluble in water (Greenway, 1941). Gum chemical characteristics: The exudate contains 78% resin (terpenes and phenols) and 15% gum, in addition to tannic acid (Joel and Fahn, 1980b; http://www.rajans.com). Commercial availability of the gum (pure state): The gum is sold in Indian bazaars as a substitute for gum arabic and is probably used for edible purposes (Howes, 1949).

Major Plant Exudates of the World  ◾  91 A

B

Figure 3.34  Mangifera indica tree (A); leaves (B) and fruits (C) (courtesy of Forest & Kim Starr).

92  ◾  Plant Gum Exudates of the World

C

Figure 3.34  (Continued).

Figure 3.35  Mangifera indica gum (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 61933).

Major Plant Exudates of the World  ◾  93

3.4.13  Azadirachta Meliaceae 3.4.13.1 Taxon: Azadirachta indica A. Juss. Synonyms: Antelaea azadirachta (L.) Adelb.; Melia azadirachta L. Subordinate taxa: Azadirachta indica var. indica; Azadirachta indica var. siamensis Common names: Indian lilac, margosa, neem, nimtree, margosier [French]. Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: Bangladesh, India; Indo-China: Myanmar. OTHER-cultivated and naturalized in tropical Asia, exact native range obscure (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance: Gum is produced very freely by trees growing in dry areas. In wet climates, the gum is liable to be washed away or spoiled before it can be collected. It appears in large tears, nodules or vermiform pieces, usually in the vicinity of a wounded area. The gum is usually cracked on the surface (Fig. 3.36). The best-quality gum is found in dry areas (Howes, 1949). Gum cavities are associated with gum formation in young stems: gum forms in the cavity as a result of the breakdown of cells lining the cavity. Bacteria have also been found in these cavities (Setia, 1984).

A

Figure 3.36  Azadirachta indica oozing gum (A) and exudate (B).

94  ◾  Plant Gum Exudates of the World

Figure 3.36  (Continued).

Exudate properties: The color of the gum is clear, pale-yellow to amber or light brown. It may darken to brown with age (Howes, 1949; Mukherjee and Srivastava, 1955). The gum dissolves freely in water, giving a light-brown viscous solution (Mukherjee and Srivastava, 1955; Narayan and Pattabiraman, 1973). It is inferior to gum arabic in its adhesive properties (Howes, 1949). Gum chemical characteristics: The gum is a highly branched polysaccharide composed of L-arabinose, L-fucose, D-galactose, and D-glucuronic acid; the ratio of D-galactose to L-arabinose is 3:2 (Mukherjee and Srivastava, 1955). Other structural and chemical features have been studied (Lakshmi and Pattabiraman, 1967; Anderson and Hendrie, 1971; Narayan and Pattabiraman, 1973). Commercial availability of the gum (pure state): The gum is bought and sold in the Bombay markets (Caius and Radha, 1939). Sometimes it is mixed with other East Indian gums (Mantell, 1947) and from time to time, it is sold as gum arabic. Commercial and functional uses for other parts of the tree: The tree is used for ornamental purposes and for shade/shelter. The wood is used for fuel. Neem is the source of a wide variety

Major Plant Exudates of the World  ◾  95

of products including adhesives, beauty aids, fertilizers, herbs, lumber, pesticides (oil) and numerous pharmaceuticals. These products are variously derived from the bark, leaves and seeds. The leaves are also used as cattle feed. Cultivation of neem for firewood is limited. Neem also produces a small edible fruit (Tewari, 1992; Conrick, 1994). It has been in pharmaceutical use in India for many centuries (Smith and Montgomery, 1959). In Sri Lanka, it is used as an adhesive (http://www.fao.com). It is used as a dye in textiles and traditional medicines.

3.4.14  Prosopis Fabaceae (subfamily: Mimosoideae) 3.4.14.1 Taxon: Prosopis cineraria (L.) Druce Synonyms: Mimosa cineraria L.; Prosopis spicigera L. Common names: jand, jandi, ghaf [transliterated Arabic], janum-chettu [India], khejri [India]. Economic importance: The foliage and pods of P. cineraria provide nutritious fodder. The tree yields excellent firewood and produces high-quality charcoal. The flowers are valuable in honey production (Arya et al., 1991; http://fadr.msu.ru). Distributional range (native): ASIA, TEMPERATE-Arabian Peninsula: Oman, Saudi Arabia, United Arab Emirates; Western Asia: Afghanistan, Iran. ASIA, TROPICAL- Indian Subcontinent: India, Pakistan (USDA, ARS, National Genetic Resources Program, 2008). Exudate properties and uses: The gum of P. cineraria exudes from the stumps of cut stems and branches as well as from other wounds, in the form of small, round or spherical balls resembling tear drops or angular fragments (Fig. 3.37), sometimes in large, about 5 cm long ovoid tears (Howes, 1949). It sometimes has a frosted or candied appearance, with the external presence of numerous minute cracks which cause the tears to crumble under pressure (Howes, 1949). The gum is tasteless, yellowish, and from time to time has an internal amber color (Arya et al., 1991). In solution, P. cineraria can produce about the same viscosity as gum arabic (Howes, 1949); however, due to its highly branched and compact structure, gum arabic can be dissolved at much higher concentrations (Goycoolea et al., 1995; Vilela et al., 2009). The gum is used locally in India for leather tanning. It has been reported as a treatment for scorpion stings and snake bites (http://fadr.msu.ru). In view of the rising cost of gum arabic, coupled with its limitations and variable supply, some believe that mesquite gum will become an increasingly popular alternative in the above non-food applications (Saunders and Becker, 1989).

3.4.14.2 Taxon: Prosopis juliflora (Sw.) DC. Synonyms: Mimosa juliflora Sw. [≡ Prosopis juliflora var. juliflora]; Prosopis horrida Kunth [≡ Prosopis juliflora var. horrida]; Prosopis vidaliana Náves [= Prosopis juliflora var. juliflora]. Subordinate taxa: Prosopis juliflora (Sw.) DC. var. horrida (Kunth) Burkart; Prosopis juliflora (Sw.) DC. var. juliflora Common names: ironwood, mesquite, bayarone [French], mesquitebaum [German], algaroba [Portuguese (Brazil)], prosópis [Portuguese (Brazil)], algarroba [Spanish], algarrobo [Spanish], cují negro [Spanish]. Distributional range (native): NORTH AMERICA-Mexico: Northern Mexico - Sinaloa, Central Mexico - Colima, Guerrero, Jalisco, Michoacan, Nayarit, Oaxaca. SOUTH AMERICA-Mesoamerica: Costa Rica, El Salvador, Guatemala, Honduras, Mexico Chiapas, Nicaragua, Panama; Northern South America: Venezuela; Western South America:

96  ◾  Plant Gum Exudates of the World

Figure 3.37  Prosopis cineraria gum.

Colombia, Ecuador [incl. Galapagos], Peru. OTHER-cultivated and naturalized in tropical Africa, Asia, Australia, West Indies, Mascarenes and Hawaii (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance: The gum of P. juliflora exudes spontaneously throughout the summer months from the stems and branches in a semi-fluid, sticky, soft condition, and then hardens in a few short hours, forming tear drops in a variety of sizes and colors that whiten with exposure to sunlight—all ultimately becoming translucent and often filled with minute fissures (Whistler and Smart, 1953b). The resultant exudate is very brittle (Mantell, 1947). In the dry summer, some gum will be found on the ground underneath the tree. There are many areas in which, because of changing weather, the gum is seldom encountered. The plant heals the scars created by tapping and usually secretes gum along the edges of the old wounds. It is collected by hand from small trees. The gum has irritant properties. Its

Major Plant Exudates of the World  ◾  97

ingestion over long periods of time has been reported to result in the death of cattle (Lewis and Elvin-Lewis, 1977). Gum of P. juliflora has been reported to exude in irregular round or vermiform pieces weighing 5 to 25 g each (Whistler and Smart, 1953b). The gum of P. juliflora and other varieties with the same geographic distribution is commonly clear and yellowish or light amber to brown (Whistler and Smart, 1953b), but can also be distinctly red, its darkness increasing with age (Howes, 1949). Gum water solubility: This gum is of average quality and is not always completely soluble in water. The portion that is not readily soluble swells and forms a soft jelly (Mantell, 1947). The gum dissolves completely in an equal weight of water in 24 h, at a temperature of ∼21°C. It has been classified as equivalent in solubility to the medium or poorer grades of Sudan gum arabic (Howes, 1949). Gum chemical characteristics: Analytical and structural studies of prosopis gums have been reported (White, 1946, 1947a,b, 1948; Cunneen and Smith, 1948a,b; Smith, 1951; Akher et al., 1952; Dutton and Unrau, 1963; Aspinall and Whitehead, 1970a,b; Churms et al., 1981; Anderson et al., 1985a,b; Goycoolea et al., 1997). The gum of P. juliflora is the natural salt of a complex acidic polysaccharide. It contains 11% moisture, 0.7% protein and 2 to 4% ash. A small amount of protein may arise from the enzyme which is responsible for the gum’s formation, or from contact of the gum with proteinaceous material in the tree. The composition of the ash indicates that the gum is predominantly in the form of a calcium salt. It contains L-arabinose, D-galactose and 4-O-methyl-D-glucuronic acid, identified as the α and β anomers of methyl (4-O-methyl-D-glucoside) uronamide, in the molar ratio of 4:2:1. One of several proposed structures is three D-galactopyranose units in the main chain united by (1-3) linkages, and a side chain attached to the C6 of each of these units. As in the case of gum arabic, it is also possible for the three D-galactose units to be joined by (1-6) or (1-3) and (1-6) linkages. The free acid form has an equivalent weight of 1,350 and contains 2.9% methoxyl (Smith and Montgomery, 1959). Commercial availability of the gum and applications: The gum was gathered and marketed in Mexico, South America, and the southwestern United States from the 1940s to the 1960s. The relatively low viscosity of prosopis gum’s aqueous solutions made it a practical substitute for gum tahla and technological grades of gum arabic (Anderson and Farquhar, 1982; Anderson et al., 1989c). At the end of the 19th century, an average annual yield of 5,400 kg was reported from Texas alone (Foreb, 1895). Generally, it is no longer readily available, most likely due to eradication in areas in which mesquite was considered a thorny pest. Nevertheless, there may be agroforestry opportunities in areas where windbreaks or soil stabilization and enrichment are desirable (Felker and Bandurski, 1979). In the past, the gum has been used as a binder in tablet dosage forms, as an emulsifying agent to encapsulate citrus essential oils, to relieve sore throat and irritated eyes, and as an antidote to lice. In the last application, the boiled gum was often mixed with mud and plastered on the hair for a day or two. When the “pack” was removed, the hair was dyed black, and was glossy and free of lice (Balls, 1962). Due to the presence of tannins, mesquite gum is not permitted as a food additive in the United States (Anderson and Weiping, 1989). However, it is used in domestic cooking in the Sonora region of northwestern Mexico, to prepare a traditional dessert known as ‘capirotada’ (Goycoolea et al., 1995). Its main current uses are in the ink, textile, and glue industries (Goycoola et al., 1995). It is also used as an emulsifier in confectioneries (where approved) and for mending pottery. The Apache chewed the gum as a candy, and it is surprisingly sweet when

98  ◾  Plant Gum Exudates of the World

burned. Mesquite gum has been used as the raw material for the preparation of L-arabinose, as reported in some of the standard chemical methods. Other gums proposed for the same uses are cherry, peach and Australian black wattle gums (Mantell, 1947; White, 1951). Commercial and functional uses for other parts of the tree: Flour from the pods of P. juliflora and other varieties with the same geographic distribution is made into gruel, and sometimes fermented to make a mesquite wine. The wood is used for parquet floors, furniture, turnery items, fenceposts, pilings, and as a substrate for the production of single-cell proteins, but it main use is for fuel. Toasted seeds are added to coffee. Bark, rich in tannin, is used for roofing in Colombia. Pods, foliage and flowers are used in medicinal preparations.

3.4.15  Sesbania Fabaceae (subfamily: Faboideae) 3.4.15.1 Taxon: Sesbania grandiflora (L.) Pers. Synonyms: Aeschynomene grandiflora (L.) L.; Agati grandiflora (L.) Desv.; Robinia grandiflora L.; Sesban grandiflorus Poir. Common names: scarlet wistaria tree, vegetable hummingbird, West Indian pea, agathi [India], agati [India] (Fig. 3.38). Distributional range (native): ASIA, TROPICAL-Malesia: Indonesia [possible origin]. OTHERcultivated in the tropics (USDA, ARS, National Genetic Resources Program, 2008). Exudate properties: The gum of S. grandiflora exudes from cut or injured bark (Duke, 1983) and is very astringent (Evans and Rotar, 1987; Howes, 1949). The gum is red when fresh and dark purple or nearly black after exposure (Howes, 1949). It is partially soluble in water and in alcohol (Howes, 1949). Gum chemical characteristics: Sesbania gums have chemical similarities to Acacia seyal gum but not to that of Acacia senegal. The gum of S. grandifolia from Hawaii contains galactose, arabinose and rhamnose in a molar ratio of 53:38:trace amounts, respectively (Anderson and Weiping, 1990). In India, it has been described as resembling kino gum (Howes, 1949) and evaluated as an alternative to gum arabic (Anderson, 1989d; Anderson and Weiping. 1990a). Commercial availability of the gum: The gum is traditionally applied to fishing cord to make it more durable (Duke, 1983e). In the past, it has been in local commercial use in the Philippines as a substitute for gum arabic (West and Brown, 1920). Commercial and functional uses for other parts of the tree: The tender leaves, green fruit and flowers of S. grandiflora are used as food for both humans and animals. Bark, leaves, gums (from seeds and exudates) and flowers are considered to have medicinal value. The wood is used, like bamboo, in Asian construction. The tree is grown as an ornamental, for shade, and for reforestation. In Java, the tree is extensively used as a pulp source, and the dried and powdered bark is used for cosmetics (Duke, 1983e).

3.4.16 Spondias Anacardiaceae 3.4.16.1 Taxon: Spondias dulcis Sol. ex Parkinson Synonym: Spondias cytherea Sonn. Common names: golden apple, Jew plum, makopa, Otaheite apple, Polynesian plum, wi tree, yellow plum, casamangue [French], pomme cythère [French], prune cythère [French], goldpflaume [German], ambarella [Spanish], jobo de la India [Spanish].

Major Plant Exudates of the World  ◾  99 A

III

III. Sesbania grandiflora, Pers.

B

Figure 3.38  Sesbania grandiflora (A) plant [courtesy of © L.H. Bailey Hortorium, Cornell University (for reproduced image, not source)]; (B) leaves; (C) flowers (Courtesy of Forest & Kim Starr).

100  ◾  Plant Gum Exudates of the World

C

Figure 3.38  (Continued).

Distributional range: Cultivated throughout the tropics, its probable origin is tropical Asia or Oceania (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance and properties: S. dulcis is subject to gummosis and is consequently shortlived (Morton, 1987c). It exudes in the West Indies in the dry season. The gum is yellow when freshly exuded (De Pinto et al., 2000a,b). It is soluble in cold water (De Pinto et al., 2000b), and its gum solutions are light brown (De Pinto et al., 2000b). The gum has high viscosity relative to the other Spondias gums (De Pinto et al., 2000a,b). Commercial and functional uses for other parts of the tree: All spondias yield edible fruits. These can be used as a basis for beverages. The tree has ornamental value and the wood is used for carpentry and other industrial uses. Various parts of the tree are used in tanning, dyeing and medicinal applications (Morton, 1987a,b,c,d).

3.4.16.2 Taxon: Spondias pinnata (J. Koenig ex L. f.) Kurz Synonyms: Mangifera pinnata J. Koenig ex L. f. (=) Spondias mangifera Willd. Common name: mangopflaume [German]. Distributional range (native): ASIA, TEMPERATE-China: China - Guangxi, Hainan, Yunnan, Hong Kong. ASIA, TROPICAL-Indian Subcontinent: Bhutan, India, Nepal, Pakistan, Sri Lanka; Indo-China: Cambodia, Myanmar, Thailand, Vietnam; Malesia: Malaysia, Philippines, Indonesia - Celebes, Java, Moluccas (USDA, ARS, National Genetic Resources Program, 2008).

Major Plant Exudates of the World  ◾  101

Exudate appearance and properties: The gum of S. pinnata appears in smooth stalactiform or large irregular pieces (Howes, 1949). It is yellow or reddish-brown, and darkens with age (Fig. 3.39) (Howes, 1949; Ghosal and Thakur, 1981). The gum has been found to be very soluble in cold water (Perez et al., 1995). However, it forms a gelatinous mucilage with water and is not entirely soluble (Howes, 1949). The gum contains D-galactose (47%), L-arabinose (23%) and D-galacturonic acid (30%). It is assumed to have a (1-3)-linked galactan backbone (Ghosal and Thakur, 1981). Commercial availability of the gum (pure form): The gum of S. pinnata has some medicinal applications (Morton, 1987c).

3.4.17 Terminalia Combretaceae The genus Terminalia includes both major and minor gums. Information on the latter can be found in Chapter 4.

3.4.17.1 Taxon: Terminalia bellirica (Gaertn.) Roxb. Synonym: Myrobalanus bellirica Gaertn. Common names: beach almond, beleric myrobalan, belleric, myrobalan, bohera, myrobalan belleric [French], belerische myrobalane [German], bahera[India], bibhitaki [Sanskrit], belérico [Spanish]. Economic importance: Environmental: ornamental. Invertebrate food: silkworms. Materials: lipids, tannin/dyestuff, wood. Medicine: folk medicine. Distributional range (native): ASIA, TEMPERATE-China: China - Yunnan. ASIA, TROPICAL-Indian Subcontinent: Bangladesh, Bhutan, India, Nepal, Pakistan, Sri Lanka; Indo-China: Laos, Myanmar, Thailand, Vietnam; Malesia: Indonesia, Malaysia. OTHER-naturalized in Africa (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance: Indian Terminalia gums are tapped and exude in the form of large tears with a smooth surface that is free of cracks. Crystals of calcium oxalate originate from the bark and are sometimes present in the gum (Howes, 1949). Terminalia gums are yellowish to reddish (Mantell, 1947) and usually dark (Howes, 1949) (Fig. 3.40). They swell and form a tough, gelatinous mass, which is only slightly soluble (Howes, 1949). Terminalia gums are inferior in thickening or adhesive ability to ghatti, karaya and tragacanth gums (Mantell, 1947). Commercial availability of the gum (pure state): Terminalia gums are used as a drug in the northern part of India (as a demulcent) (http://www.aidsinfonyc.org). They are sometimes mixed with East Indian gums (Mantell, 1947). In India, the gum is reported to be eaten by Santals (Gammie, 1902; Setia, 1981). Some Terminalia species are sold as ghatti gum. Commercial and functional uses for other parts of the tree: The leaves, bark and fruit have medicinal properties. The wood is very hard and is used for house-building, making bullock carts, ploughs etc. It is also considered sacred for idols in temples (Hayward, 1990).

102  ◾  Plant Gum Exudates of the World

A

Figure 3.39  Spondias pinnata tree oozing gum (A); gum exudate (B).

Major Plant Exudates of the World  ◾  103

A

Figure 3.40  Terminalia bellirica tree oozing gum (A); and exudate (B).

104  ◾  Plant Gum Exudates of the World

3.5 GUMS OF THE NEW WORLD 3.5.1 Anacardium Anacardiaceae 3.5.1.1 Taxon: Anacardium humile A. St.-Hil. Synonym: Anacardium pumilum A. St.-Hil. ex Engl. Distributional range (native): SOUTH AMERICA-Brazil: Brazil - Goias, Mato Grosso, Mato Grosso do Sul, Parana, Rondonia; Western South America: Bolivia - Santa Cruz; Southern South America: Paraguay - Amambay, Caaguazu, Canendiyu, Concepcion (USDA, ARS, National Genetic Resources Program, 2008).

3.5.1.2 Taxon: Anacardium nanum A. St.-Hil. 3.5.1.3 Taxon: Anacardium occidentale L. Distributional range (native): SOUTH AMERICA-Brazil Brazil - Minas Gerais (USDA, ARS, National Genetic Resources Program, 2008). Common names: cashew, anacardier [French], acajubaum [German], kaschubaum [German], nierenbaum [German], cajú [Portuguese], cajueiro [Portuguese], anacardo [Spanish], marañón [Spanish], merey [Spanish]. Distributional range (native): SOUTH AMERICA-Northern South America: French Guiana, Guyana, Suriname, Venezuela; Brazil: Brazil; Western South America: Colombia. OTHERcultivated in the tropics (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance and properties: Big tears or stalactytic mass (Fig. 3.41) (Howes, 1949). The tree has been documented to produce ∼10 g/week per cut (Clamens et al., 1998). Nut

Figure 3.41  Anacardium occidentale exudate (mag. 2x; courtesy of the Royal Botanic Gardens, Kew; Cat. No. 61857).

Major Plant Exudates of the World  ◾  105

production in trees older than 25 years increases after gum extraction (Sarubbo et al., 2000). Formation of gum ducts in the primary phloem of the stem has been studied (Nair et al., 1983). The color of the exudate is pale yellow to reddish (Bose and Biswas, 1970). The gum is only partially soluble in cold water where it swells into a jelly-like mass but dissolves rapidly when heated (Bose and Biswas, 1970). It forms slightly turbid mucilage (Howes, 1949). The reported solubility is 50 g/100 ml water (Clamens et al., 1998). Physical and rheological properties have been studied by many researchers and can be located elsewhere (e.g. De Paula and Rodrigues, 1995; De Pinto et al., 1995a; Zakaria and Rahman, 1996; Mothe and Rao, 1999; Sarubbo et al., 2000; Paula et al., 2002). Gum chemical characteristics: The gum contains galactose in the main backbone linked by β(1-3) bonds and branched chains joined through β(1-6) linkages. The composition was found to be galactose (72%), arabinose (4.7%), rhamnose (3.2%), glucose (14%) and glucuronic acid (4.5%) (De Paula et al., 1998). It has little intra- and intermolecular interactions. The gum contains 6% polysaccharide-protein complex. A. occidentale gum from Brazilian plants has a higher galactose content and lower arabinose and rhamnose contents than those from India and Papua. The other constituents (glucose, mannose and glucuronic acid) are similarly distributed. The gum from a cashew tree growing in India is lacking units of 4-O-methylglucuronic acid. Other side-chain structures are α-D-Galp-(1 leads to 6)-DGalp and α-L-Araf-(1 leads to 6)-D-Galp (Menestrina et al., 1998). The polysaccharide molecular mass is ∼110,000 Daltons (Anderson, and Bell, 1975; Menestrina et al., 1998). Information on other structural and chemical features can be found elsewhere (Bose and Biswas; 1970; de Paula and Rodrigues, 1995). Commercial availability of the gum and applications: The gum is utilized by South American bookbinders, who wash their books with it to repel moths and/or ants. The cashew oil found in minute quantities within the gum might act as an insect repellent. The gum has adhesive properties in its hydrocolloidal form (Howes, 1949; Bose and Biswas, 1970), and finds application for many pharmaceutical purposes and as a substitute for gum arabic (Smith and Montgomery, 1959). In Sri Lanka, it is used locally as an adhesive (Sri Bharathie, 1994). The cashew gum has attracted much attention from academia due to its potential industrial uses. It may be a potential byproduct of the Brazilian cashew nut industry, processing 200,000 tons of nuts yearly with a turnover of around $150 million/ year (Paula et al., 2002). Commercial and functional uses for other parts of the tree: The cashew nut is edible. The pedicel is eaten and made into beverages. The nut shell contains cardol and anacardic acid, has medicinal uses and is used as a preservative against insects for woodwork, books, etc. The nutshell substances are also present in the gum (Duke, 1983b).

3.5.2  Anadenanthera Fabaceae (subfamily: Mimosoideae) 3.5.2.1 Taxon: Anadenanthera colubrina (Vell.) Brenan var. cebil (Griseb.) Altschul Synonyms: Acacia cebil Griseb.; Anadenanthera macrocarpa (Benth.) Brenan; Piptadenia cebil (Griseb.) Griseb.; Piptadenia macrocarpa Benth. Conspecific taxa: Anadenanthera colubrina; Anadenanthera colubrina var. colubrina Distributional range (native): SOUTH AMERICA-Brazil: Brazil; Western South America: Bolivia, Peru; Southern South America: Argentina, Paraguay, Uruguay (USDA, ARS, National Genetic Resources Program, 2008).

106  ◾  Plant Gum Exudates of the World

The exudate: The gum of A. colubrina exudes in large tears or angular pieces (4-10 g each). The tears are often dull or frosted externally owing to the presence of minute superficial fissures. Sometimes a tear consists of distinct parts: a dull superficial fissured layer which easily disintegrates, surrounding a hard or vitreous core in the center of which there may be a cavity. The gum is not easily pulverized. Both Parapiptadenia rigida and A. colubrina gums may be mixed with woody matter or bark fragments (Howes, 1949). Exudate color: Dark with impurities or yellow to reddish (Howes, 1949). Gum water solubility: Gum of A. colubrina is freely soluble in water and yields a tasteless and odorless mucilage. Gum chemical characteristics: Complex, high-arabinose (80%) polysaccharide. Structural and chemical features can be found elsewhere (Delgobo et al., 1998, 1999). Similar gums: Gum preparations of A. colubrina possess viscosity and adhesive properties comparable to those of gum arabic. Commercial availability of the gum (pure state) and applications: In the past, when supplies of gum arabic were cut off, the gum of A. colubrina was exported to Europe as “Brazilian gum arabic” (Smith and Montgomery, 1959). It has been used in Brazil as an adhesive and a constituent in medicines. Shipments of the gum have been introduced to the market as mixtures of true hydrophilic gum and water-insoluble resin because collection has not been coordinated with botanical knowledge (Mantell, 1947). The gum is used in Brazil to treat pulmonary disorders (Delgobo et al., 1998). It is also used for tanning. Commercial and functional uses for other parts of the tree: The wood is used for heavy construction and for fuel. The bark is a possible source of tannins (Delgobo et al., 1998).

3.5.2.2 Taxon: Anadenanthera colubrina (Vell.) Brenan var. colubrina Synonyms: Mimosa colubrina Vell.; Piptadenia colubrina (Vell.) Benth. Conspecific taxa: Anadenanthera colubrina; Anadenanthera colubrina var. cebil Distributional range (native): SOUTH AMERICA-Brazil: Brazil - Bahia, Parana, Rio de Janeiro, Sao Paulo; Southern South America: Argentina - Misiones (USDA, ARS, National Genetic Resources Program, 2008).

3.5.3  Caesalpinia Fabaceae (subfamily: Caesalpinioideae) 3.5.3.1 Taxon: Caesalpinia coriaria (Jacq.) Willd. Synonym: Poinciana coriaria Jacq. Common names: divi-divi, cascalote [Spanish], dibidibi [Spanish], guaracabuya [Spanish], guatapana [Spanish], nacascol [Spanish], nacascolote [Spanish]. Economic importance: Environmental: ornamental. Materials: tannin/dyestuff. Distributional range (native): NORTH AMERICA-Mexico: Northern Mexico - Sinaloa, Central Mexico - Colima, Guerrero, Jalisco, Michoacan, Oaxaca. SOUTH AMERICAMesoamerica: Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua, Panama, Mexico Chiapas; Caribbean: Anguilla, Antigua and Barbuda-Antigua, Bahamas, Barbados, Cuba, Dominica, Dominican Republic, Grenada, Haiti, Jamaica, Martinique, Netherlands Antilles, Puerto Rico, St. Vincent and Grenadines; Northern South America: Venezuela; Western South America: Colombia. OTHER-widely cultivated in the tropics (USDA, ARS, National Genetic Resources Program, 2008).

Major Plant Exudates of the World  ◾  107

3.5.4  Parkinsonia Fabaceae (subfamily: Caesalpinioideae) 3.5.4.1 Taxon: Parkinsonia praecox (Ruiz & Pav.) J. A. Hawkins subsp. praecox Synonyms: Caesalpinia praecox Ruiz & Pav.; Cercidium praecox (Ruiz & Pav.) Harms; Cercidium praecox subsp. praecox; Cercidium spinosum Tul.; Cercidium viride (H. Karst.) H. Karst.; Rhetinophloeum viride H. Karst. Conspecific taxa: Parkinsonia praecox Distributional range (native): NORTH AMERICA-Mexico: Northern Mexico - Baja Sur, Sinaloa, Sonora, Zacatecas, Central Mexico - Guerrero, Jalisco, Michoacan, Oaxaca, Puebla. SOUTH AMERICA-Northern South America: Venezuela; Western South America: Bolivia, Ecuador, Peru; Southern South America: Argentina - Catamarca, Chaco, Cordoba, Formosa, Jujuy, Salta, San Luis, Santiago del Estero, Tucuman, Paraguay (USDA, ARS, National Genetic Resources Program, 2008). Exudate properties: The gum forms gradually in wounds made in the bark of the trunk or main branches. It is obtainable in large quantities either as stalactiform, asymmetrically shaped pieces (8-15 cm long) which break with a conchoidal fracture, or as tears (2-5 cm in diameter). From time to time, the tears fuse together in masses mixed with pieces of bark. It is similar in appearance to acacia gums. Gum production is more abundant in the dry and hot months (September to December and March to May). Gum yield is higher in mature trees than in young trees. Under the most favorable conditions, an average of 0.5 to 2.5 kg per tree can be obtained every 12 to 15 days (De Cordemoy, 1911; Mantell, 1947; Howes, 1949; Cerezo et al., 1969; Garriga and Haas, 1997). Stalactiforms are usually reddish-yellow, bright and transparent. When the gum is freshly exuded and has not had time to solidify it is golden yellow with a sweetish taste. Once solidified, a pink or darker shade may develop and the gum becomes very hard and difficult to pulverize (Howes, 1949, De Cordemoy, 1911). The gum is completely soluble in water and forms viscous slightly acidic mucilage. The formed viscosity is comparable to that of Acacia senegal gum (Howes, 1949; De Cordemoy, 1911). Gum chemical characteristics: The chemical structure is comparable to that of gum arabic. In fact, they have four similar carbohydrate groups, and differ in only one of them, i.e. xylose in gum brea instead of galactose in gum arabic. Both gums have a pH of 5.5 and similar physical properties (Garriga and Haas, 1997). The results showed a (1-leading to 4)-xylan core. Some xylose residues are substituted at O-2 by α-D-glucuronic acid and 4-O-methyl-α-D-glucuronic acid residues. β-D-Glucuronic acid is present, probably as terminal residues. The arabinose is present as α-L-furanose and β-L-pyranose. The gum of P. praecox contains major amounts of galacturonic acid and xylose compared to Caesalpinia eriostachys. P. praecox gum has a high nitrogen content (De Pinto et al., 1994) and contains tannins (Mantell, 1947). Other structural and chemical features of the gum have been studied (and see Cerezo et al., 1969). Commercial availability of the gum (pure form): The gum is commonly used in Argentina as a substitute for gum arabic (Cerezo et al., 1969). The gum has various industrial and pharmaceutical applications, including paints and adhesives. In its powdered form, it is used locally in the food industry as an emulsifier, thickener and stabilizer. However, its use as a food additive is not yet permitted in Argentina since it is not authoritatively registered in the National Food Code. Market sale prices of the raw gum range from US$1.5-2 per kg in villages, to US$4- 6 per kg in Buenos Aires. Prices are also influenced by the quality of the gum, e.g. humidity or presence of impurities (Garriga and Haas, 1997).

108  ◾  Plant Gum Exudates of the World

Commercial and functional uses for other parts of the tree: The wood does not have any major commercial use except for fuel and charcoal. It is used as an ornamental for its abundant yellow flowers at the end of winter and in spring (Garriga and Haas, 1997).

3.5.5  Parapiptadenia Fabaceae (subfamily: Mimosoideae) 3.5.5.1 Taxon: Parapiptadenia rigida (Benth.) Brenan Synonym: Piptadenia rigida Benth. Exudate properties: The gum of P. rigida (Fig. 3.42) is soft, shaped as angular or globular fragments which appear in 5.0 to 7.5 cm diameter lumps. It breaks with a clean vitreous fracture and from time to time small air bubbles are found inside (Mantell, 1947; Howes, 1949). Its color is amber to dark red (Mantell, 1947; Howes, 1949). The gum is soluble in water and yields a tasteless and odorless mucilage. The gum solutions of P. rigida yield intermediate viscosity between that of Sudan and Senegal gum arabic. Both P. rigida and Anadenanthera colubrina gums may be mixed with woody matter or bark fragments (Howes, 1949).

3.5.6 Puya Bromeliaceae 3.5.6.1 Taxon: Puya chilensis Molina Synonym: Puya coarctata Fisch. Exudate properties: The exudate has a thick, mucilaginous consistency and is acidulous. The gum is produced as a result of damage by the larvae of Kastnia elegans (Hamilton et al., 1957). Fragments of hollow cylinders vary from 0.2 to 1.5 cm in diameter. Globular or stalactytic pieces also occur. It breaks with a conchoidal fracture and its hardness is about the same as that of gum arabic (Howes, 1949). The exudate color is clear yellow but may be dark. It is seldom opaque (Howes, 1949; Hamilton et al., 1957). The gum resembles gum tragacanth in its hydrocolloidal properties (Howes, 1949). Gum water solubility: The gum is about 75% soluble in water, but solubility varies with different samples. The insoluble portion swells to a clear jelly-like mass (Howes, 1949; Hamilton et al., 1957). Borax does not precipitate it from solution or thicken it, but precipitation may be effected with neutral lead acetate (Felter and Lloyd, 1898). After dissolution of the crude gum with alkali followed by acidification and precipitation with acetone, it is readily dissolved in water (Hamilton et al., 1957). Its solubilization is probably due to the removal of ester groups of acetyl residues. Gum chemical characteristics: The free acid form of the gum, chagualic acid, has an equivalent weight of 1,030. It is composed of L-arabinose (7%), D-xylose (31%), D-galactose (36%) and 2-O-(D-glucopyranosideuronic acid)-D-xylose (27%) (Hamilton et al., 1957). Commercial availability of the gum (pure form): The gum is available locally. Commercial and functional uses for other parts of the tree: P. chilensis from Chile is sometimes cultivated as an ornamental or stove plant in other countries. The soft stem material has been used for corks and bungs and the leaf spines as fish hooks (Howes, 1947).

Major Plant Exudates of the World  ◾  109

Figure 3.42  Parapiptadenia rigida gum (mag. 2x; courtesy of the Royal Botanic Gardens, Kew; Cat. No. 58087).

110  ◾  Plant Gum Exudates of the World

3.5.7 Theobroma Malvaceae (subfamily: Byttnerioideae) 3.5.7.1 Taxon: Theobroma cacao L. Synonyms: Theobroma leiocarpum Bernoulli; Theobroma cacao subsp. cacao forma leiocarpum; Theobroma pentagonum Bernoulli; Theobroma cacao subsp. cacao forma pentagonum; Theobroma sativum (Aubl.) Lign. & Le Bey; Theobroma sphaerocarpum A. Chev.; Theobroma cacao subsp. sphaerocarpum. Common names: cacao, cocoa, cacaoyer [French], cacaoeiro [Portuguese (Brazil)], cacau [Portuguese (Brazil)]. Economic importance: Medicine: folk medicine. Distributional range (native): SOUTH AMERICA-Mesoamerica: Belize, Guatemala, Mexico Chiapas, Tabasco; Northern South America: French Guiana, Guyana, Suriname, Brazil: Brazil; Western South America: Colombia, Peru. OTHER-widely cultivated (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance: In cacao, lysigenous cavities filled with mucilaginous substances occurring in roots, stems, flowers, and leaves (Brooks and Guard, 1952) yield an average 1.5% of fresh weight and 8.4% of dry weight for stem gum, and 0.8% of fresh weight and 9.1% of dry weight for pod husks. Extraction is performed by boiling in alcohol (Figueira et al., 1993, 1994). Gum water solubility: Cacao stem gum produces a much smaller increase in viscosity with increasing concentration than karaya gum (Figueira et al., 1994). Gum chemical characteristics: Cacao pod gum has been found to be closer in composition to gum karaya than cacao stem gum. Both cocoa gums contain the same monosaccharides as gum karaya but with greater proportions of rhamnose, galacturonic acid, and glucuronic acid, and the addition of arabinose. The major component of stem gum is glucose, not found in any appreciable amount in cacao pod gum or gum karaya. Sugar molar ratios of rhamnose, arabinose, galactose, glucose, xylose, mannose, galacturonic acid and glucuronic acid were found to be, respectively, 2.0, 1.7, 1.0, 2.8, 0.0, 0.0, 1.1 and 1.4 for cacao stem gum and 1.6, 0.0, 1.0, 0.1, 0.0, 0.0, 1.3 and 0.6 for gum karaya (Figueira et al., 1993, 1994). Commercial availability of the gum (pure state): Cocoa gums from pod husks and stems have been evaluated as a potential replacement for karaya gum or as a new commercial product (Figueira et al., 1992). Commercial and functional uses for other parts of the tree: The cacao “beans” are produced in large, angular capsules, up to 30 cm long and 10 cm in diameter. The beans, or seeds, about 2.5 cm across, range from 20 to 40 per capsule, and are embedded in an acid, fleshy pulp. After removal from the capsule, the beans are washed or fermented to remove the mucilagenous pulp. Chocolate is the sweetened or unsweetened product of the roasted and ground beans, with most of the fat retained. Commercial cocoa is the finely ground product, with most of the fat removed. Both forms are very widely used in confections, ice cream, cookery, and drinks. Cocoa butter is also used in the manufacture of tobacco, soap, and cosmetics. Cacao has many applications in folk medicine. Gum from the pod or fruit husk and seed pulp was evaluated as potential byproducts of cacao (Figueira et al., 1993).

3.5.8  Laguncularia Combretaceae 3.5.8.1 Taxon: Laguncularia racemosa (L.) C. F. Gaertn. Synonym: Conocarpus racemosus L. Common names: white buttonwood, white mangrove.

Major Plant Exudates of the World  ◾  111

Distributional range (native): AFRICA-Africa. NORTH AMERICA- United States: Southeastern United States - Florida; Mexico. SOUTH AMERICA-Mesoamerica: Central America; Caribbean: West Indies (Little, 1983; USDA, ARS, National Genetic Resources Program, 2008). Gum water solubility: Reported solubility is 6 g/100 ml water. Viscosity is 60-fold that of Anacardium occidentale (cashew gum) (Clamens et al., 1998). Gum chemical characteristics: The constituent sugars are galactose, arabinose, rhamnose, galacturonic acid, glucuronic acid and its 4-O-methyl ether. This composition is similar to that of many Combretum gums. The uronic acid residues are partly acetylated (De Pinto et al., 1994, 1998; Duke, 1983c). Commercial and functional uses for other parts of the tree: The hard heavy wood is used for carpentry, construction, posts and tool handles, as well as for fuel and charcoal. The bark is used for tanning and for dying fishermen’s nets.

3.5.9  Pithecellobium Fabaceae (subfamily: Mimosoideae) 3.5.9.1 Taxon: Pithecellobium dulce (Roxb.) Benth. Common names: blackbead, camachile,  guayamochil, Madras thorn, Manila tamarind, sweet inga, pois sucré  [French], camambilarinde  [German], opiuma [Hawaiian], guamúchil [Spanish], huamúchil [Spanish], madre de flecha [Spanish]. Economic importance: Environmental: agroforestry, ornamental, shade/shelter, soil improver (Fig. 3.43). Human food: fruit. Fuels: fuelwood. Materials: beads, wood. Medicine: folk medicine. Distributional range (native): NORTH AMERICA-Mexico: Northern Mexico - Baja California, San Luis Potosi, Sonora, Tamaulipas, Central Mexico - Colima, Hidalgo, Jalisco, Puebla, Queretaro, Veracruz. SOUTH AMERICA-Mesoamerica: El Salvador, Guatemala, Honduras, Nicaragua, Mexico - Chiapas, Yucatan; Northern South America: Venezuela; Western South America: Colombia. OTHER-naturalized elsewhere in the tropics (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance: P. dulce gum collected in India usually appears as spherical tears, about 1.3 cm in diameter, and it is usually a transparent dark brown (Howes, 1949). Gum water solubility: The gum of P. dulce is freely soluble in water (Howes, 1949; De Pinto et al., 2001). Commercial and functional uses for other parts of the tree: P. dulce is used as a shade tree. Heartwood can be used in house construction, pattern wood, paneling, interior trim, furniture components, veneer and boat-building. Other uses include food (the immature pods as a cooked vegetable, or the seeds toasted and ground), soap-making (using tannins from the pods and bark), and medicinal use of bark extracts for colds and bronchitis. The seeds are rich in protein, conferring the potential to combat protein malnutrition. The chemical and functional properties of quamachil seed flour were studied. Very good foaming capacity and foam stability were observed in defatted whole seed flour and dehulled-defatted seed flour (Rao et al., 2008).

3.5.10  Samanea Fabaceae (subfamily: Mimosoideae) 3.5.10.1 Taxon: Samanea saman (Jacq.) Merr. Synonyms: Albizia saman (Jacq.) F. Muell.; Inga saman (Jacq.) Willd.; Mimosa saman Jacq. (basionym); Pithecellobium saman (Jacq.) Benth.

112  ◾  Plant Gum Exudates of the World

A

Figure 3.43  Pithecellobium dulce tree oozing gum (A) and exudate (B).

Major Plant Exudates of the World  ◾  113

Common names: cow tamarind, French tamarind, monkeypod, raintree, arbre de pluie [French], samán [Spanish]. Economic importance: Environmental: agroforestry, ornamental, shade/shelter. Fuels: potential as fuelwood. Invertebrate food: lac/wax insects. Materials: wood. Distributional range (native): SOUTH AMERICA-Mesoamerica: Costa Rica, El Salvador, Nicaragua, Panama; Northern South America: Venezuela; Western South America: Colombia. OTHER-cultivated and naturalized elsewhere in tropics, exact native range in neotropics obscure (USDA, ARS, National Genetic Resources Program, 2008). Gum properties: Although S. saman is an introduced tree in India, its gum has been purchased in both a pure state and mixed with other gums in Bombay markets (Caius and Radha, 1939). Samples of tapped S. saman collected in Venezuela yield ∼11 g/week per cut (Clamens et al., 1998). The gum is usually a transparent dark brown (Fig. 3.44) (Howes, 1949). It is not freely soluble, swelling instead into a tough, cartilage-like mass (Howes, 1949). Reported solubility for S. saman is approximately 5 g/100 ml water (Clamens et al., 1998). Functional uses for other parts of the tree: Many studies have been performed to validate the use of plants in traditional medicine. One such example is the study of antimicrobial activity of an aqueous extract of S. saman against Escherichia coli, Staphylococcus aureus and Candida albicans. The plant extract exhibited inhibitory activity against all three. E. coli growth was inhibited by 5 mg/ml, but a higher concentration of 10 mg/ml was necessary to inhibit S. aureus and C. albicans. Phytochemical screening of the plant revealed the presence of tannins, flavonoids, saponins, steroids, cardiac glycosides and terpenoids (Prasad et al., 2008).

3.5.11  Enterolobium Fabaceae (subfamily: Mimosoideae) 3.5.11.1 Taxon: Enterolobium cyclocarpum (Jacq.) Griseb. Common names: devil’s ear, earpod tree, elephant’s ear, monkeysoap, bois tanniste rouge [French], oreille d’éléphant [French], affenseife [German], árbol de las orejas [Spanish], carita [Spanish], corotú [Spanish], guanacaste [Spanish], parota [Spanish]. Economic importance: Environmental: agroforestry, ornamental, shade/shelter, soil improver. Fuels: fuelwood. Materials: beads, wood. Medicine: folk medicine. Distributional range (native): NORTH AMERICA-Mexico. SOUTH AMERICAMesoamerica: Central America; Northern South America: Venezuela; Brazil: Brazil - Roraima; Western South America: Colombia [possibly]. OTHER-naturalized in the West Indies (USDA, ARS, National Genetic Resources Program, 2008). Exudate properties: E. cyclocarpum gum is usually a transparent dark brown (Howes, 1949). It is partially soluble (Howes, 1949), approximately 5 g/100 ml water reported (Clamens et al., 1998). The gum has been used in the past for pharmaceuticals of native manufacture (Mantell, 1947). The gum has also been reported in Sinaloa, Mexico as a remedy for bronchitis (Howes, 1949). A mixture of Acacia glomerosa, E. cyclocarpum and Hymenaea courbaril gums for stabilizing low-fat ice-cream preparations was reported. In comparison to a mixture of commercial gums, the tested mixture provided suitable viscosity to the ice-cream mix with the corresponding overrun and texture. It also gave better foaming properties and air incorporation (Rincon et al., 2008).

114  ◾  Plant Gum Exudates of the World

A

Figure 3.44  Samanea saman tree oozing gum (A) and exudate (B).

Major Plant Exudates of the World  ◾  115

3.5.12  Chloroleucon Fabaceae (subfamily: Mimosoideae) 3.5.12.1 Taxon: Chloroleucon mangense (Jacq.) Britton & Rose Synonyms: Chloroleucon leucospermum (Brandegee) Britton & Rose [≡ Chloroleucon mangense var. leucospermum]; Mimosa mangensis Jacq. [≡ Chloroleucon mangense var. mangense]; Pithecellobium caraboboense Harms [= Chloroleucon mangense var. vincentis]; Pithecellobium leucospermum Brandegee [≡ Chloroleucon mangense var. leucospermum]; Pithecellobium vincentis Benth. [≡ Chloroleucon mangense var. vincentis] Distributional range (native): NORTH AMERICA-Mexico: Northern Mexico - Baja Sur, Sinaloa, Sonora, Central Mexico - Colima, Guerrero, Jalisco, Michoacan, Nayarit, Oaxaca. SOUTH AMERICA-Mesoamerica: Honduras, Mexico - Chiapas, Yucatan, Nicaragua, Panama; Caribbean: Cuba, Haiti, Jamaica, Martinique, St. Vincent and Grenadines-St. Vincent, Virgin Islands (U.S.) - St. Croix; Northern South America: Venezuela - Aragua, Bolivar, Carabobo, Falcon, Guarico, Miranda, Monagas, Yaracuy; Brazil: Acre, Mato Grosso, Rondonia; Western South America: Bolivia - Beni, Santa Cruz, Colombia - Antioquia, Atlantico, Cordoba, Cundinamarca, Guajira, Huila, Magdalena, Sucre, Tolima, Ecuador - Loja, Peru Loreto, San Martin (USDA, ARS, National Genetic Resources Program, 2008).

3.5.13  Leucaena Fabaceae (subfamily: Mimosoideae) 3.5.13.1 Taxon: Leucaena collinsii Britton & Rose Gum (common name): Leucaena gum. Distributional range (native): SOUTH AMERICA-Mesoamerica: Guatemala, Mexico Chiapas. The Neotropical genus Leucaena comprises 22 species, 6 infraspecific taxa and 2 named hybrids. The greatest diversity of species is in Mexico (17 species, 10 endemic) and northern Central America (9 species, 4 endemic). The genus extends north into southern Texas in the United States, and sporadically across the Caribbean and into South America, as far south as Peru (Hughes, 1998). Exudate appearance: The gum is produced infrequently under stress. Gummosis was first observed in India following attack by Fusarium incarnatum (syn. Fusarium semitectum), and was later seen in Hawaii following attacks by Phytophthora drechsleri and wood-boring beetles. Gum production is sporadic, low-yielding, and often associated with wood dieback. The exudate is in the shape of balls or drippings from mature bark. It is heaviest in the dry season. L. leucocephala x L. pallida hybrid trees have been found to exude gum copiously, with no wood dieback. Nine hybrid trees of this pedigree were grown in Waimanalo, Hawaii for four years, during which time approximately one-third failed to produce gum, one-third exuded gums sporadically and the final third exuded gum heavily. These high gum yielders exceeded the mean annual per-tree gum production (250 g/tree) of gum arabic by Acacia senegal and may yield up to 1 kg/year (Brewbaker and Sorensson, 1990). Gummosis causes the formation of a dark gum with low solubility, whereas gum exudation in response to tapping operations on healthy trees, as practiced in commercial gum arabic production, is of good quality, with a pale color and high solubility (Anderson, 1984; Anderson and Douglas, 1988). Exudate color: Translucent tan gum (Brewbaker and Sorensson, 1990), pale to dark brown, typically dull and opaque (Anderson and Douglas, 1988).

116  ◾  Plant Gum Exudates of the World

Gum water solubility: The water solubility of Leucaena gums evaluated to date is highly inferior to that of gum arabic. Leucaena gums, which are not readily dissolved in water, form clear gels (Anderson and Douglas, 1988). The Leucaena gums (except for Leucaena lanceolata S. Watson var. sousae (Zárate) C. E. Hughes) tend to be more viscous and more acidic than gum arabic. Hawaiian Leucaena gums are not as water-soluble as the Indian Leucaena gums (Anderson and Douglas, 1988). Similar gums: Analysis of several Leucaena gums has revealed that they have strongly negative specific rotation, with sugar and amino acid compositions that are similar to commercial gum of Acacia senegal. Although toxicity and related studies are lacking, Leucaena gum may have potential for use as a substitute for gum arabic (Anderson 1986; Anderson and Douglas, 1988). Gum chemical characteristics: Chemical analysis of gums from L. leucocephala, L. pallida and their hybrids indicates distinct similarities to gum arabic (Anderson, 1986; Anderson and Douglas, 1988). Commercial availability of the gum: Increasingly widespread establishment of Leucaena plantations, with Leucaena trees growing more rapidly than Acacia senegal, might increase their use as a source of gum exudates closely similar in composition to gum arabic. Leucaena gums are not permitted as food additives, and without undertaking expensive toxicological testing, they can find applications in various other technological fields (Anderson, 1984; Anderson et al., 1983). Commercial and functional uses for other parts of the tree: Uses of Leucaena wood include fuelwood, lumber, pulpwood (paper, rayon), craftwood and charcoal. Uses of foliage include animal fodder, green manure and food (juvenile shoots). Uses of legumes and seeds include animal fodder, tea, medicines and food (juvenile beans). Trees are used as ornamentals, windbreaks, shade trees, sources of green manure, and as stabilizing hedges on hillslopes. Seeds are strung into leis and jewelry (Brewbaker, 1987; Brewbaker and Sorensson, 1990). Leucaena also contains seed gum, a unique galactomannan with potential medicinal uses (Raval et al., 1988).

3.5.14  L ysiloma Fabaceae (subfamily: Mimosoideae) 3.5.14.1 Taxon: Lysiloma acapulcense (Kunth) Benth. Synonym: Acacia acapulcensis Kunth Distributional range (native): NORTH AMERICA-Mexico: Northern Mexico - San Luis Potosi, Sinaloa, Tamaulipas, Central Mexico - Colima, Guanajuato, Guerrero, Hidalgo, Jalisco, Mexico City, Michoacan, Morelos, Nayarit, Oaxaca, Queretaro, Veracruz. SOUTH AMERICA-Mesoamerica: El Salvador, Honduras, Mexico - Chiapas, Tabasco (USDA, ARS, National Genetic Resources Program, 2008). Gum water solubility: Gum solutions are very viscous.

3.5.15 Inga Fabaceae (subfamily: Mimosoideae) 3.5.15.1 Taxon: Inga stipularis DC. Distributional range (native): SOUTH AMERICA-Northern South America: French Guiana, Guyana, Suriname, Venezuela - Amazonas; Brazil: Brazil - Amapa, Amazonas, Para (USDA, ARS, National Genetic Resources Program, 2008). Commercial availability of the gum (pure state): In nature, the gum is an important part of the feed and diet of the Geoffroy’s marmoset monkey (Passamani and Rylands, 2000).

Major Plant Exudates of the World  ◾  117

3.5.16  Rhizophora Rhizophoraceae 3.5.16.1 Taxon: Rhizophora mangle L. Common names: American mangrove, mangrove,  red mangrove,  mangue vermelho [Portuguese], mangle [Spanish], mangle colorado [Spanish], mangle rojo [Spanish]. Distributional range (native): AFRICA-West Tropical Africa: Guinea, Nigeria, Senegal, Sierra Leone. NORTH AMERICA-United States: Southeastern United States - Florida; Mexico: Northern Mexico - Baja California, Sonora, Tamaulipas, Central Mexico - Nayarit, Veracruz. SOUTH AMERICA-Mesoamerica: Belize, Costa Rica, Honduras, Nicaragua, Panama; Caribbean: Dominican Republic, Jamaica, Puerto Rico; Northern South America: French Guiana, Guyana, Suriname, Venezuela; Brazil: Brazil; Western South America: Colombia, Ecuador, Peru. OTHER-naturalized in Hawaii and Polynesia (Little, 1983; USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance: Fusicoccum anamorphs have been isolated from necrotic tissues of stem galls of R. mangle in south Florida (Rayachhetry, 1996). Gum formation in R. mangle is presumably due to gummosis disease caused by Fusicoccum, a relative of the fungus Botryosphaeria dothidea, which opportunistically attacks more than 100 genera of mostly woody plants in temperate and tropical areas (Gilbert and de Steven, 1996). The gum is dark red (Mantell, 1947) or brownish (Rao et al., 1971). Gum water solubility: It absorbs water in considerable amounts to form amber-colored jellies with a stiffnes similar to that of gelatin. Gum chemical characteristics: The gum contains D-galactose, L-rhamnose, L-arabinose, D-galacturonic acid and 4-O-methyl-D-glucuronic acid. It contains no acetyl groups (Rao et al., 1971). Commercial and functional uses for other parts of the tree: The wood is used for boat construction, general heavy construction, charcoal, railroad crossties and turnery. The bark has a high content of tannin/dyestuff and is used commercially. It is also used for folk medicines (Duke, 1983d).

3.5.17  Melicoccus Sapindaceae (subfamily: Sapindoideae) 3.5.17.1 Taxon: Melicoccus bijugatus Jacq. Synonym: Melicocca bijuga L. Common names: genip, honeyberry, Spanish lime, kenépier [French], quenette  [French], honigbeere [German], quenepa [German], mamoncillo [Spanish]. Distributional range (native): SOUTH AMERICA-Northern South America: Venezuela; Western South America: Colombia. OTHER-widely cultivated in the tropics. There are a few trees in Israel, although none flower before 10 years of age (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance: A clear gum (De Pinto et al., 1993). Gum water solubility: The gum readily dissolves in cold water (De Pinto et al., 1993). Gum chemical characteristics: The gum contains galactose (43%), arabinose (15%), rhamnose (17%) and uronic acid (25%). It consists mainly of a (1-3)-β-D-galactan core with (1-6)-βD-galactopyranosyl branches and side chains of α-L-arabinofuranosyl residues which are predominantly (1-2)-linked. β-D-glucuronic acid and α-4-methyl ether are probably linked to O-6 and O-4 of galactose, respectively (De Pinto et al., 1993).

118  ◾  Plant Gum Exudates of the World

Commercial and functional uses for other parts of the tree: Consumable juice from squeezed pulp also used for dye, edible pulp and edible roasted seeds. The seeds and leaves are used medicinally. The heartwood is used for construction (Morton, 1987e). Foods of plant origin provide the human diet with not only certain antioxidant vitamins, but also a complex mixture of polyphenols with antioxidant activity. Numerous studies have focused on the protective and preventive effects of antioxidant activity on certain degenerative illnesses, such as cardiovascular diseases, cancer, neurological diseases, cataracts and oxidative stress dysfunctions. The objective of one such work was to evaluate total polyphenol content and antioxidant activity of several seeds, nuts, or grains of Theobroma cacao, Campsiandra comosa Benth., Sorghum bicolor (L.) Moench and M. bijugatus. The reducing power of cacao beans was the highest, followed by C. comosa. Moreover, C. comosa and cacao seeds exhibited antioxidant activity comparable to that of butylhydroxyanisol, a synthetic antioxidant. Total polyphenol content showed a good correlation with antioxidant activity. Moreover, these seeds might have the same health-beneficial effects attributed to other fruits and vegetables (Padilla et al., 2008).

3.5.18 Ceiba Malvaceae (subfamily: Bombacoideae) 3.5.18.1 Taxon: Ceiba speciosa (A. St.-Hil.) Ravenna Synonym: Chorisia speciosa A. St.-Hil. Common name: floss silktree. Economic importance: Environmental: ornamental. Distributional range (native): SOUTH AMERICA-Brazil: Brazil - Bahia, Mato Grosso, Mato Grosso do Sul, Minas Gerais, Para, Parana, Rio de Janeiro, Rondonia, Santa Catarina, São Paulo; Western South America: Bolivia - Beni, Cochabamba, La Paz, Santa Cruz, Peru - Cuzco, Junin, San Martin; Southern South America: Argentina - Chaco, Corrientes, Misiones, Santa Fe, Paraguay - Alto Parana, Caaguazu (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance: The gum exudes in tears upon injury, apparently to heal the wound. Gum chemical characteristics: Quantitative analysis of the gum in mole ratio showed L-rhamnose (1.8), L-arabinose (0.9), D-mannose (1.0), D-galactose (7.8), D-glucuronic acid (2.8) and trace amounts of D-xylose.

3.5.19  Thespesia Malvaceae (subfamily: Malvoideae) 3.5.19.1 Taxon: Thespesia populnea (L.) Sol. ex Corrêa Synonyms: Hibiscus populneoides Roxb.; Hibiscus populneus L.; Thespesia macrophylla Blume; Thespesia populneoides (Roxb.) Kostel. Common names: bendytree, corktree, milo, Pacific rosewood, portia tree, seaside mahoe, tulip tree, tespésia [Portuguese (Brazil)]. Distributional range (native): AFRICA-Northeast Tropical Africa: Eritrea, Somalia; East Tropical Africa: Kenya, Tanzania; West Tropical Africa: Benin, Ghana, Nigeria, Senegal, Togo; South Tropical Africa: Mozambique; Western Indian Ocean: Comoros, Madagascar, Mauritius, Reunion, Seychelles. ASIA, TEMPERATE-China: China - Guangdong, Hainan;

Major Plant Exudates of the World  ◾  119

Figure 3.45  Thespesia populnea leaves and flowers.

Eastern Asia: Taiwan, Japan - Ryukyu Islands. ASIA, TROPICAL-Indian Subcontinent: India [coastal], Sri Lanka; North Indian Ocean: India - Andaman and Nicobar, Maldives; IndoChina: Cambodia, Myanmar, Thailand, Vietnam. Malesia: Indonesia, Malaysia, Papua New Guinea, Philippines. AUSTRALASIA-Australia: Australia - Northern Territory, Queensland, Western Australia. NORTH AMERICA-Mexico: Central Mexico - Veracruz. PACIFICNorthwestern Pacific: Micronesia; South-Central Pacific: French Polynesia; Southwestern Pacific: Fiji, Vanuatu. SOUTH AMERICA-Mesoamerica: Mexico - Quintana Roo, Yucatan, Costa Rica, Honduras, Nicaragua, Panama; Caribbean: Antigua and Barbuda, Bahamas, Barbados, Bermuda, Cayman Islands, Cuba, Dominica, Grenada, Guadeloupe, Hispaniola, Jamaica, Martinique, Montserrat, Netherland Antilles, Puerto Rico, St. Kitts and Nevis, St. Lucia, St. Vincent and Grenadines, Virgin Islands (British), Virgin Islands (US); Northern South America: Venezuela - Falcon; Western South America: Colombia. OTHER-widely cultivated in the tropics (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance: A brown shiny gum. Gum water solubility: The gum is only slightly soluble, but swells in water. Commercial and functional uses for other parts of the tree: The tree is used for erosion control, as an ornamental, and for shade/shelter. The fruits, flowers and young leaves are edible (Fig. 3.45). The timber is used for small constructions. The tough fibrous bark is made into rope. The bark is also used to caulk boats (Malay). Cork is made from the inner bark. A yellow dye is obtained from the flowers and fruits, a red dye from the bark and heartwood. Other products extracted from the plant include tannin and oil. In India, these trees are planted to provide shade for coffee and tea plantations. Bark, leaves, young fruit and roots are used medicinally. Recently, eight new sesquiterpenoids were isolated from dichloromethane extracts of the wood and dark heartwood of T. populnea, together with 11 known compounds. Their structures were determined on the basis of spectroscopic analysis. The cytotoxic activity of the isolated compounds was evaluated against four cancer cell lines. Two compounds showed significant activity. Their antibacterial properties against Bacillus subtilis, Staphylococcus aureus, and Enterococcus faecalis were also presented (Boonsri et al., 2008).

120  ◾  Plant Gum Exudates of the World

3.5.20  Cylindropuntia Cactaceae (subfamily: Opuntioideae) 3.5.20.1 Taxon: Cylindropuntia fulgida (Engelm.) F. M. Knuth Synonym: Opuntia fulgida Engelm. Common names: boxing-glove cactus,  boxing-glove cholla, brinkadora, chain-fruit cholla, club cactus, jumping cholla, smooth chain-fruit cholla, Sonoran jumping cholla, roseakaktus [Afrikaans]. Distributional range (native): NORTH AMERICA- United States: Southwestern United States - Arizona; Mexico: Northern Mexico - Baja California, Sinaloa, Sonora (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance: The formation of C. fulgid gum seems to be favored by prolonged hot dry spells and it presumably helps the plant resist desiccation in periods of drought (Brown et al., 1949a). Gum exudation occurs most frequently on large, old or diseased plants and is found in lumps weighing 50 to 100 g. Among the Cactaceae, mainly cactuses that have a woody stem or woody skeleton in the stem produce gum. The gum appears to be absent in the fleshy or non-woody Cactaceae, which generally have a thin watery sap. It does not appear to owe its origin to pathological causes or insects as is the case with many gums, but to be a natural physiological exudation (Howes, 1949). The gum has been reported as sticky when it first exudes (Brown et al., 1949a), and hard once it dries. In addition to the gum from the stem, clean mucilage with excellent adhesive properties may be obtained by cutting across the immature fruits of another cactus species, Opuntia ficus-indica (Krishnan, 1939). The gum exudates of Opuntia megacantha have been reported to appear on the leaves of the plant when they are ravaged by insect attack. The jelly-like gum is exuded into the formed cavities (Churms et al., 1973a). Opuntia gums resemble gum tragacanth in its lump form (Mantell, 1947). The gum is whitish or cream yellow to brown, commonly transparent with a characteristic odor (Brown et al., 1949b; Howes, 1949). Gum water solubility: The gum of C. fulgid is partially soluble (approx. 50%) in hot water. It swells, forming a creamy white opalescent jelly (Mantell, 1947). The gum of O. ficus-indica is mostly insoluble in water. It swells to a jelly-like mass and contains the remains of parenchyma cells (Howes, 1949). It is more soluble in aqueous alkali (Amin et al., 1970). Gum chemical characteristics: The composition of C. fulgid gum seems to vary. In early work, some of the exudates were found soluble in ether (Sands and Klaas, 1929). A probable structure of repeating units in the degraded gum was also reported. The proposed structure of the gum shows that the repeating unit is composed of a total of 36 sugar residues which are linked as follows: β-linked D-galactose (7 moles), α-linked D-galactose (2 moles), β-linked D-galacturonic acid (3 moles), α-linked L-rhamnose (1 mole), α-linked L-arabinose (18 moles), and β-linked D-xylopyranose (5 moles) (Parikhe and Jones, 1966). The gum is highly branched. This is supported by the isolation of 2-O-methyl-D-galacturonic acid from the cleavage fragments of a methylated gum which shows that the D-galacturonic acid units are joined through C1, C3 and C4. The D-galactose units, all of which are probably in the main chain, are linked through C1, C3 and C6, demonstrating that D-galactose units favor the (1-3) and (1-6) linkage that is typical of many gums (Smith and Montgomery, 1959). The gum of O. ficus-indica often shows crystals of calcium oxalate, tannin and colored matter (Howes, 1949). A comparison of the chemical properties of C. fuldiga, O. ficus-indica and O. megacantha gives galactose, arabinose, rhamnose, xylose, glucuronic acid and galacturonic acid in a ratio of 45:29:2:13:0:11, 36:37:12:15:0:0, and 46:30:11:trace:13:0, respectively

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(Churms et al., 1973a). Chemical analyses of C. fulgid gum have also been performed by other groups (Sands and Klaas, 1929; Brown et al., 1949b). Chemical analyses of O. ficusindica gum (Amin et al., 1970) and the analytical and structural features of O. megacantha can be found elsewhere (Churms et al., 1973b). Similar gums: The gum of O. ficus-indica resembles tragacanth in that it is mostly insoluble in water but swells to a jelly-like mass and contains the remains of parenchyma cells. Commercial availability of the gum (pure form): In Mexico, it has been used in the local textile business as a size and a cloth stiffener (Mantell, 1947). It is also mixed with other substances and used as a masticatory by the indigens or mixed with fat to make inexpensive candles that resemble those made from the more costly beeswax (Howes, 1949). Commercial and functional uses for other parts of the tree: The tree is used for ornamental purposes. Apart from the hardened gum, the gummy sap of Opuntia species, easily extracted by crushing the fleshy tissue of the stem, was formerly employed in popular medicine, concentrated over a fire and mixed with inert substances to form a type of chewing gum, or used as an adhesive of sorts for sticking together pieces of wood, etc. (Howes, 1949). There are commercial products on the market based on prickly pear opuntias which are used as functional foods.

3.5.21  Manilkara Sapotaceae 3.5.21.1 Taxon: Manilkara zapota (L.) P. Royen Synonyms: Achradelpha mammosa O. F. Cook; Achras mammosa L.; Achras zapota L.; Achras zapota var. zapotilla Jacq.; Achras zapotilla (Jacq.) Nutt.; Calocarpum mammosum Pierre; Lucuma mammosa C. F. Gaertn.; Manilkara achras (Mill.) Fosberg; Manilkara zapotilla (Jacq.) Gilly; Pouteria mammosa Cronquist; Sapota zapotilla (Jacq.) Coville Common names: Chicle, chico, sapote, naseberry, sapodilla, sapote, sapotier [French], sapotillier [French], breiapfelbaum [German], kaugummibaum [German], sapodillbaum [German], sapote [German], sabojira [transcribed Japanese], níspero [Spanish], zapote [Spanish], zapotillo [Spanish] (USDA, ARS, National Genetic Resources Program, 2008). Distributional range (native): NORTH AMERICA-Mexico. SOUTH AMERICAMesoamerica: Belize, El Salvador, Guatemala, Nicaragua. OTHER-widely cultivated in the tropics (Morton, 1987f; USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance: The gum forms slowly in wounds made in the sapodilla tree following the collection of chicle (White, 1953a), a gummy latex containing 15% rubber and 38% resin and used as a chewing-gum base. Chicle is tasteless and non-toxic and is obtained by repeated tapping of wild and cultivated trees in Yucatan, Belize and Guatemala (Morton, 1987f). Gum water solubility: The gum is soluble in water (White, 1953a). Gum chemical characteristics: Composed of D-xylose, L-arabinose, D-glucuronic acid and 4-Omethyl-D-glucuronic acid in a molar ratio of 2.2:1:0.42:0.58 (Lambert et al., 1968). Precipitation of the gum from an acidic aqueous solution with alcohol gives the free acid which has an equivalent weight of 679. The primary or main chain structure is based upon units of D-xylose (White, 1954). Structural investigations of the gum can be found elsewhere (White, 1953a,b). Commercial availability of the gum (pure state) and applications: The gum has been used as a sizing agent for cloth and felt, as glue, and has been tested as a beater additive in the

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manufacture of paper. The ether derivative of the gum forms remarkably tough, colorless, transparent films (White, 1953a). Commercial and functional uses for other parts of the tree: Chicle has been employed for many years as the chief ingredient in chewing gum but today it is diluted to a certain extent or has been replaced by latex from other species or by synthetic resins. The wood is used for construction and carpentry. The tannin-rich bark is used by fishermen in the Philippines to tint their sails and fishing lines. Leaves, fruits and seeds have medicinal uses (Morton, 1987f).

3.5.22  Larix Pinaceae 3.5.22.1 Taxon: Larix occidentalis Nutt. Common name: western larch.  Economic importance: Materials: wood. Medicine: folk medicine. Distributional range (native): NORTH AMERICA-Canada: Western Canada - British Columbia; United States: Northwestern United States - Idaho, Montana, Oregon, Washington (Imeson, 1992, Timell, 1978). Gum (common names): arabinogalactan, larch gum, stractan, wood gum, wood sugar (larix of North America). Exudate appearance: The gum accumulates in masses under the bark as a result of injury. The excrescence can be picked off by hand and is often 95% pure. The supply is limited and manual collection is difficult. This source cannot compete in volume or in price with methods based on extraction of the chipped heartwood (Stout, 1959). When the larch forests in Russia burn, a gum issues from the trees during their combustion, which is termed gummi orenbergense (Felter and Lloyd, 1898). Gum water solubility: Larch gum is readily soluble in water. A clear water solution of up to 75% arabinogalactan with a pH of 4 to 4.5 can be prepared. Solubility increases with increasing temperature. These highly concentrated solutions are unusual because of their Newtonian flow properties (Ben-Zion and Nussinovitch, 1997). Solutions can withstand the addition of as much as 70% of their own volume of absolute alcohol without precipitating out, if the alcohol is added slowly with continuous stirring (Imeson, 1992). Gum chemical characteristics: Highly branched copolymer of L-arabinose and D-galactose in a ratio of 1:6. It is composed of two fractions with average molecular weights of 16,000 and 100,000 (Borgin, 1949). Arabinogalactan contains 16% volatile pinene and limonene (Fowells, 1965). Extensive studies into the molecular structures of various arabinogalactans from Larix species have been published (Churms et al., 1978; Timell, 1978). Gum physical properties: Larch gum reduces the surface tension of water solutions and the interfacial tension existing in water-oil mixtures, and is therefore an effective emulsifying agent. As a result of these properties, larch gum has been used in foods and can serve as a substitute for gum arabic (Imeson, 1992). It has also been evaluated as a wet glue for skin applications (Ben-Zion and Nussinovitch, 1997). Commercial availability of the gum (pure state) and applications: An attempt to commercially exploit larch gum was made by International Chemical Products, Montana, in the early 1920s. Larch gum was extracted, hydrolyzed, and oxidized to mucic acid by treatment with nitric acid. The mucic acid was to be used as a baking powder ingredient and there was no intention to produce a gum that might compete with gum arabic. The venture failed, reportedly because the process was too expensive (Imeson, 1992). In the early 1960s, a

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countercurrent hot-water extraction system was developed, and the gum was produced commercially by the St. Regis Paper Co. under the trade name Stractan (Glicksman, 1963). The potential annual production capacity of this gum was 10,000 tons based on wood residues from the lumber industry. The product could not compete with gum arabic, and commercial production was limited to small batches for specific uses, such as offset lithography, food, pharmaceuticals, paint and ink (Fowells, 1965). The gum is approved in the United States by the FDA (21 CFR 172.610) as a food additive for use as an emulsifier, stabilizer, and binding or bodying agent. The best potential commercial source of the gum is the heartwood of L. occidentalis which contains 8 to 25% gum in the lower stem of the tree on a dry wood basis. Other Larix species may also yield commercial quantities of gum (Imeson, 1992). Commercial and functional uses for other parts of the tree: The wood is primarily used for construction lumber. It is also used in plywood manufacture and to make fine veneer. Oleoresin is also extracted from the wood to produce turpentine and related products.

3.6 MISCELLANEOUS ASIATIC, AFRICAN, AND AUSTRALIAN GUMS 3.6.1 Actinidia Actinidiaceae 3.6.1.1 Taxon: Actinidia deliciosa (A. Chev.) C. F. Liang & A. R. Ferguson Synonyms: Actinidia chinensis var. deliciosa (A. Chev.) A. Chev.; Actinidia chinensis var. hispida C. F. Liang; Actinidia latifolia var. deliciosa A. Chev. Common names: Chinese gooseberry, kiwi, kiwifruit, strawberry peach, groseille de Chine [French], kiwi de Chine [French], chinesische stachelbeere [German], kiwifrucht [German]. Distributional range (native): ASIA, TEMPERATE-China: China - Fujian, Hubei, Jiangxi, Sichuan, Zhejiang (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance: Botryosphaeria dothidea, which is usually recognized by its anamorph Fusicoccum aesculi, is known to opportunistically attack woody plants in temperate and tropical areas, including the kiwifruit (A. deliciosa) (Pennycook and Samuels, 1985). Evidence for polysaccharide exudation from the stem pith has been recorded (Redgwell, 1986; Needs and Selvendran, 1994). Gum chemical characteristics: Acidic polysaccharide containing a complex glucuromannan backbone of D-mannose, L-fucose, L-arabinose and D-galactose. Trace amounts of xylose are also present (Redgwell, 1986; Needs and Selvendran, 1994). Commercial and functional uses for other parts of the tree: The trees are cultivated as ornamentals and for their edible fruit, which is also used as a beverage base. Another use is in folk medicines.

3.6.2 Araucaria Araucariaceae 3.6.2.1 Taxon: Araucaria heterophylla (Salisb.) Franco Synonym: Eutassa heterophylla Salisb. Common name: Norfolk Island pine. Economic importance: Environmental: ornamental.

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Figure 3.46  Araucaria heterophylla gum.

Distributional range (native): AUSTRALASIA-Australia: Australia - Norfolk Island (USDA, ARS, National Genetic Resources Program, 2008). Geographic distribution: Endemic to lowland areas of Norfolk Island, about 1,500 km east of Australia (A. heterophylla), New Guinea (Araucaria hunsteinii), East Australia (Araucaria cunninghamii), mountains in southeast and northern Queensland (Araucaria bidwillii). It is endemic to New Caledonia (Araucaria cookie and Araucaria rulei) and Brazil (Araucaria angustifolia). Tree: The genus Araucaria contains approximately 14 species. Several are known to yield a gum-resin (Maiden, 1901; Howes, 1949; Churms et al., 1973b; Clamens et al., 1998). Exudate appearance: Unlike most conifers, Araucaria yields a gum-resin rather than a pure resin or oleo-resin. The gum of A. heterophylla (Fig. 3.46) naturally exudes in big, hard and brittle irregularly shaped yellowish-brown lumps or sometimes as curled thin filaments, which are sometimes white. The gum of A. angustifolia or A. hunsteinii may exude freely from old trees, especially after damage by beetles, and soon hardens in the air. The gum flows out from the borehole, sometimes with debris or dead beetles stuck to the exudates. Gum water solubility: The exudate includes an insoluble resin and water-soluble gum.

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Gum characteristics: Analytical studies of the gums of various Araucaria species have been published (Aspinall and Fairweather, 1965; Aspinall and McKenna, 1968; Anderson and Munro, 1969; Churms et al., 1973b). The gum-resin of A. bidwillii contains a higher proportion of gum (Greenway, 1941). Commercial and functional uses for other parts of the tree: Araucaria trees are used as ornamentals worldwide and as timber for construction.

3.6.3  Balanites Zygophyllaceae (subfamily: Tribuloideae) 3.6.3.1 Taxon: Balanites aegyptiacus (L.) Delile Synonym: Ximenia aegyptiaca L. Common names: desert date, soapberry tree, dattier du désert [French], dattier sauvage [French], héglik [French], zachunbaum [German], betu [India], hingotia [India], lalo [India], zachun [India], mirobalano de Egipto [Spanish]. Distributional range (native): AFRICA-Northern Africa: Algeria, Egypt, Libya; Northeast Tropical Africa: Chad, Eritrea, Ethiopia, Somalia, Sudan; East Tropical Africa: Kenya, Tanzania, Uganda; West-Central Tropical Africa: Rwanda; West Tropical Africa: Burkina Faso, Cote D’Ivoire, Ghana, Guinea, Mali, Mauritania, Niger, Nigeria, Senegal, Togo; South Tropical Africa: Angola, Mozambique, Zimbabwe; Southern Africa: Botswana. ASIA, TEMPERATE-Arabian Peninsula: Saudi Arabia, Yemen; Western Asia: Jordan (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance: The tree exudes a gum or resin (Fig. 3.47). Commercial availability of the gum (pure state): The gum of Acacia senegal is sometimes mixed with Acacia seyal and B. aegyptiacus. Commercial and functional uses for other parts of the tree: The wood is used for tool handles, firewood, and produces good charcoal. The thorny branches are used for fencing. The fruit are eaten like candy, and sold as “desert dates”. The bark and roots are used as laxatives and for colic. The bark is used for sore throats, and as a remedy for sterility, mental diseases, epilepsy, yellow fever, syphilis, and toothaches, and also has the potential for use against invertebrateborne diseases, bilharzia and Guinea-worm. The yellow oil obtained from the essential seeds in Sudan and Chad is used as a type of soap and is also edible (Ladipo, 1997).

3.6.4  Brabejum Proteaceae 3.6.4.1 Taxon: Brabejum stellatifolium L. Common names: bitteramandel [German], wild almond, wilde-amandel, ghoeboontjie, ghoekoffie. Geographic distribution: South Africa. The tree: B. stellatifolium is the only member of the genus Brabejum, sometimes incorrectly spelled Brabeium. This name is based on the word brabeion, which is Greek for sceptre and may refer to the inflorescence. However, a brabeion was also the prize awarded at the Pythian Games held in Delphi, a crown of bay or laurel leaves, so it could just as well refer to the vague resemblance between Brabejum leaves and those of the bay or laurel tree (http://www. plantzafrica.com). The specific name stellatifolium means that the leaves radiate like the points of a star, which they do. The vernacular names bitteramandel (bitter almond) and wild almond are derived from the fruit’s resemblance to the almond (http://www.plantzafrica.com).

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Figure 3.47  Balanites aegyptiacus gum (mag. 2x; courtesy of the Royal Botanic Gardens, Kew; Cat. No. 63546).

Gum chemical characteristics: The gum is composed of L-arabinose (52%), D-galactose (37%), D-xylose (7%), D-mannose (3%) and probably L-rhamnose (<1%) (Stephen and van der Bijl, 1971). Uses: The fruits are poisonous, mostly when fresh, but the poison can be leached out by soaking them in water for several days, then boiling and roasting them. The practice of soaking, boiling, roasting and grinding the fruits is used to make a coffee substitute. The bitter taste is due to the presence of cyanogenic glycosides that liberate prussic acid (the toxic principle) when eaten. The timber is red and reticulated, is hard to saw, and was once popular for ornamental work. It was also used to make bowls, the heels of Dutch clogs, and wagon felloes (wheel rims) and brake blocks. The bark has been used for tanning (http://www.plantzafrica.com).

3.6.5  Butea Fabaceae (subfamily: Faboideae) 3.6.5.1 Taxon: Butea monosperma (Lam.) Taub. Synonym: Butea frondosa Roxb. ex Willd. Common names: bastard teak, Bengal kino, dhak, flame of the forest, arbre à laque [French], kinobaum[German], lackbaum [German], palas [India], palash [India]. Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: India, Nepal, Pakistan, Sri Lanka; Indo-China: Cambodia, Laos, Myanmar, Thailand, Vietnam; Malesia: Malaysia, Indonesia - Java (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance: Naturally exudes from fissures in branches in irregular or angular tears. It frequently has adhering bark fibers. It is brittle when chewed, without adhering to the teeth, and tinges the saliva lake-red. (A Lake pigment is a pigment manufactured by precipitating

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a dye with an inert binder, usually a metallic salt). Its taste is very astringent (http://www. henriettesherbal.com/). It ordinarily contains some tannin (Mantell, 1947). The exudate is an intense garnet-red color (ruby) and transparent in thin pieces (Fig. 3.48). It becomes black after exposure to the sun (http://www.henriettesherbal.com/). Gum water solubility: Described as a hydrophilic colloid (Mantell, 1947), it is only partially soluble in water. Commercial availability of the gum (pure state) and applications: Used locally in tanning and in precipitating indigo (http://www.wkonline.com). On rare occasion in the past it has been exported to England; it has never been exported to America (http://www.henriettesherbal. com/). It is used as a substitute for kino gum from Pterocarpus species for medicinal preparations to treat Pterygeum and corneal opacity (http://www.lankactronicle.com). It is also used as a substitute for gum arabic from Acacia catechu at relatively smaller use levels. Commercial and functional uses for other parts of the tree: Its leaves and flowers (‘gulal’) are essential for various religious rituals in Hindu homes. They are also used as cheap plates and cups for rural feasts. In some parts of India, leaves are used for wrapping tobacco to make biddies. They are further used as packing material for parcels. The foliage is also used as cattle feed. The seeds, fruits and roots are used medicinally. The flowers, which are also called “tesu”, yield a safron dye for cotton yarns. In Thailand, root extracts of Butea superba are sold for vasodilation, especially in the penis where its effect is very similar to Viagra (http://www.thaipuerarian.com).

3.6.6  Cercis Fabaceae (subfamily: Caesalpinioideae) 3.6.6.1 Taxon: Cercis siliquastrum L. Synonym: Cercis siliquastrum var. alba Weston Common names: Judas tree, lovetree. Distributional range (native): ASIA, TEMPERATE-Western Asia: Iran, Iraq, Israel, Jordan, Lebanon, Syria, Turkey. EUROPE-Southeastern Europe: Albania, Bulgaria, former Yugoslavia, Greece [incl. Crete], Italy [incl. Sicily]; Southwestern Europe: France (USDA, ARS, National Genetic Resources Program, 2008). Exudate properties: Gum exudes naturally in tears which run down the stem, but also from wounds. The gum is yellow when fresh and becomes darker as it ages on the tree. The gum is water-soluble. Commercial and functional uses for other parts of the tree: Used as an ornamental tree.

3.6.7  Cissus Vitaceae 3.6.7.1 Taxon: Cissus populnea Guill. & Perr. Geographic distribution: Southern and middle-belt areas of Benue and Kogi states of Nigeria. Exudate appearance: The gum is extracted from highly viscous mucilage exudates from the stem (Iwe, 1996). Gum water solubility: Strongly swells (more than karaya and tragacanth gums) (Iwe, 1996). Similar gums: karaya and tragacanth (Iwe, 1996). Commercial availability of the gum (pure state): Has been found in the local market in Makurdi (Iwe, 1996). Culturally, it has found application in homes as a soup-thickening agent and is applied medically for the treatment of venereal diseases and indigestion

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A

Figure 3.48  Butea monosperma tree oozing gum (A); exudate (B); flowers (C).

Major Plant Exudates of the World  ◾  129

C

Figure 3.48  (Continued).

(Hutchinton and Dalziel, 1958), and as a potential binder as well as disintegrant in tablet formulations (Balami and Bangudu, 1991). A comparative study was carried out to investigate the binder effects of Cissus populnea and Acacia senegal gums on the mechanical properties of paracetamol tablets. At all binder concentrations, A. senegal gum produced harder and more consolidated tablets than that of C. populnea, as reflected by the higher tensile strength and packing fraction values, respectively (Eichie and Amalime, 2007). The study showed that A. senegal mucilage displays better tableting characteristics and better amelioration of capping tendency. Both mucilages showed potential as substitutes for the more expensive starches used as binders in tablet formulations (Eichie and Amalime, 2007). It is also used as a thirst quencher among traditional hunters of the Idomas and Igalas (Iwe, 1996).

3.6.8 Commiphora Burseraceae 3.6.8.1 Taxon: Commiphora mollis (Oliv.) Engl. Synonym: Commiphora irrigensis Engl. Geographic distribution: Tanzania. Exudate appearance: C. iringensis produces gum, unlike other Commiphora species that produce resin (Greenway, 1941).

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3.6.9  Diospyros Ebenaceae 3.6.9.1 Taxon: Diospyros mespiliformis Hochst. ex A. DC. Synonyms: Diospyros sabiensis Hiern; Diospyros senegalensis Perr. ex A. DC. Economic importance: Materials: wood. Distributional range (native): AFRICA-Northeast Tropical Africa: Eritrea, Ethiopia, Sudan; East Tropical Africa: Kenya, Tanzania, Uganda; West-Central Tropical Africa: Cameroon, Central African Republic, Zaire; West Tropical Africa: Benin, Cote D’Ivoire, Gambia, Ghana, Guinea, Mali, Niger, Nigeria, Senegal, Togo; South Tropical Africa: Angola, Malawi, Mozambique, Zambia, Zimbabwe; Southern Africa: Botswana, Namibia, South Africa Transvaal, Swaziland. ASIA, TEMPERATE-Arabian Peninsula: Yemen (USDA, ARS, National Genetic Resources Program, 2008). Geographic distribution: A woodland and savannah tree. It is widespread at medium to low altitudes in Tanzania. It is more abundant along river banks and near swamps in Miombo woodlands than in wooded grasslands and lowland rainforests. It is found in Tabora, Morogoro, Dodoma, Mbeya, and Kilimanjaro. Commercial and functional uses for other parts of the tree: Fruits can be eaten fresh or preserved. Dried fruits are sometimes ground into flour. Seeds are eaten as nuts. Fruits are often used to brew beer or are fermented for wine. Bark and roots are used medicinally as an antimicrobial, and as treatments for malaria, syphilis, and leprosy. The leaves are used to treat fever, as wound dressings, and as an antidote to poison. The wood is used for timber.

3.6.10 Dicorynia Fabaceae (subfamily: Caesalpinioideae) 3.6.10.1 Taxon: Dicorynia paraensis Benth. Common name: angelique. Economic importance: Materials: wood. Distributional range (native): SOUTH AMERICA-Northern South America: Venezuela Amazonas, Bolivar; Brazil: Brazil - Amazonas, Para, Roraima; Western South America: Colombia (USDA, ARS, National Genetic Resources Program, 2008). Exudate color: Reddish-brown to black. Gum water solubility: Swells slightly in water to form a jelly. Gum chemical characteristics: Contains tannins. Commercial and functional uses for other parts of the tree: The wood is used for marine and general heavy construction, railroad crossties, industrial flooring (Chudnoff, 1984).

3.6.11  Entandrophragma Meliaceae 3.6.11.1 Taxon: Entandrophragma angolense (Welw.) C. DC. Common names: edinam, gedunohor. Distributional range (native): AFRICA-Northeast Tropical Africa: Sudan; East Tropical Africa: Kenya, Uganda; West-Central Tropical Africa: Cameroon, Equatorial Guinea, Zaire; West Tropical Africa: Cote D’Ivoire, Ghana, Guinea, Liberia, Nigeria, Sierra Leone; South Tropical Africa: Angola (USDA, ARS, National Genetic Resources Program, 2008).

Major Plant Exudates of the World  ◾  131

Commercial and functional uses for other parts of the tree: The wood of some species is used for furniture and cabinetwork, joinery, decorative veneers and plywood, and boat construction. Active principles were discovered in the stem bark of E. angolense, when compounds isolated from a dichloromethane-methanol (1:1) extract of the stem bark were used in an antimalarial test against chloroquine-resistant strain W2 of the malaria parasite Plasmodium falciparum. Of all the components, only 7 α-obacunyl acetate and acycloartane derivatives exhibited strong activity (Bickii et al., 2007). Recently, three new mexicanolides were isolated from the root bark of E. angolense. The structure of these new compounds was elucidated spectroscopically and their antifeedant property was also studied (Kipassa, 2008).

3.6.12  Fagarta Rutaceae 3.6.12.1 Taxon: Zanthoxylum zanthoxyloides (Lam.) Zepern. & Timler Synonyms: Zanthoxylum senegalense DC.; Fagara zanthoxyloides Lam. The tree and its geographical distribution: A common plant in West Africa that exudes a clear yellow gum during the dry season. The exudate: The gum is partly acetylated and has significant methoxyl content. A single unpurified nodule gave, on analysis, acetyl groups (6.95%) and methoxyl groups (2.6%). The nodules dissolve with difficulty in water to give a viscous solution with a faintly acid reaction (Torto, 1957). Chemical properties: After drying in a partial vacuum at 30°C, the purified gum turns into a white amorphous powder; equivalent weight by direct titration—1,100; sulfated ash, 0.25%; nitrogen, 0.23%; acetyl groups, none; methoxyl groups, 2.6% (a polysaccharide of equivalent weight 1,100 containing monomethyl-hexuronic residues would have a methoxyl content of 2.8%). It gives a positive reaction in naphthoresorcinol test for uronic acid, and fails to reduce Fehling’s solution. Specimens prepared from nodules of different trees did not show any significant differences in optical rotation or equivalent weights, indicating the essential homogeneity of the gum (Torto, 1957).

3.6.13  Ferula Apiaceae 3.6.13.1 Taxon: Ferula foetida (Bunge) Regel Common names: asafetida, asafoetida, assa-foetida, kamol, kavrak, rochaek, sassyr, hing [India]. Economic importance: Food additives: flavoring. Medicine: folk medicine, veterinary. Distributional range (native): ASIA, TEMPERATE-Western Asia: Afghanistan, Iran; Former Soviet Middle Asia: Kyrgyzstan, Turkmenistan, Uzbekistan. ASIA, TROPICAL-Indian Subcontinent: Pakistan (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance: Oleogum resin, consists of a mixture of polysaccharide and aromatic substances. Gum water solubility: The purified polysaccharide portion of the oleogum resin is readily soluble in cold water, forming a solution. Gum chemical characteristics: The polysaccharide consists of D-galactose, L-arabinose, L-rhamnose, and D-glucuronic acid together with its 4-O-methyl derivative in a ratio of 5:3:trace:1. It is composed of a main chain of mainly (1-3)-linked-β-D-galactopyranose residues to which are attached D-galactopyranose, L-arabinofuranose, and L-arabinopyranose residues. The mode of linkage of the last sugar has not been identified. The side chains are

132  ◾  Plant Gum Exudates of the World

attached residues of D-glucuronic acid, its 4-O-methyl ether, L-rhamnose and D-galactose (all in the pyranose form). An unequivocal structure for the gum has not yet been proposed. The polysaccharide has a much smaller percentage of uronic acid residues than that in frankincense or myrrh. Commercial availability of the gum and applications: The oleogum resin is available commercially and is a valuable remedy for hysteria, nervous disorders, flatulence, flatulent colic, constipation and spasmodic affectations of the bowels. Its volatile oil has components that leave the body via the respiratory system and aid in the coughing up of congested mucus. It is also used as an expectorant in chronic bronchitis, whooping cough, pneumonia and asthma, and lowers blood pressure by thinning the blood.

3.6.14  Grevillea Proteaceae 3.6.14.1 Taxon: Grevillea robusta A. Cunn. ex R. Br. Common names: Australian silky oak, silky oak, Australiese selwereik [Afrikaans]. Distributional range (native): AUSTRALASIA-Australia: Australia - New South Wales, Queensland (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance: Upon injury, epithelial cells in the bark of the mature (6- to 10-year-old) G. robusta tree produce a gum that is exuded at the point of injury. The gum also exudes naturally. Average production per tree is estimated at 1 kg per annum and tapping can be carried out for about 10 months of the year. The gum generally exudes in the shape of a tear with a size of up to 3 cm in diameter. It is soft and sticky when fresh with a slight aromatic smell and dries gradually. It is likely that other Grevillea species also yield gums (Anderson and De Pinto, 1982). The gum of G. robusta is yellowish-brown when fresh and black when aged on the tree. Sometimes tears are bright red (Fig. 3.49), probably due to the presence of tannins or other impurities. Gum water solubility: Gums of G. robusta, G. agrifolia, G. candelabroides and G. striata readily dissolve in water. The gum of Grevillea wickhamii is only partially soluble and requires a mild treatment with sodium borohydride to facilitate dissolution (Anderson and De Pinto, 1982). Water solutions are highly viscous with a pH of ∼6.5. G. robusta gum is not soluble in either hot or cold ethanol or in benzene. Gum chemical characteristics: Partial acid hydrolysis of G. robusta gum, which removes most of the L-arabinose residues (∼44% of the total carbohydrate), yielded a polysaccharide containing galactose, arabinose, mannose, and uronic acid in the molar ratio 3:1:1:2, respectively (Churms and Stephen, 1987). The gum of G. robusta is the neutral calcium and magnesium salt of a complex polysaccharide acid composed of D-glucuronic acid attached to D-galactose and L-arabinose (Smith and Montgomery, 1959). The molecular weights found for the gums of G. robusta, G. agrifolia, G. striata and G. wickhamii were 8.8, 3.6, 0.88 and 3.6 million, respectively (Anderson and De Pinto, 1982). Commercial availability of the gum (pure state): Because of the widespread geographical distribution of Grevillea species, their tolerance to a wide range of climates, and their commercial/ecological properties, they may find potential as a commercial source for highly viscous gums. The gum has also been used as a wood adhesive (http://www.easternarc.org/ html/gumstudies.html). Commercial and functional uses for other parts of the tree: G. robusta is an ornamental tree. It has been planted extensively in India and Sri Lanka as a shade tree for tea plantations,

Major Plant Exudates of the World  ◾  133

Figure 3.49  Grevillea robusta exudate.

and to some extent in Hawaii, India, and Brazil as a shade tree for coffee plantations. It has also been widely introduced in East Africa. It is an important honey tree in India where it is also regarded as a good fuelwood producer. The wood is used for furniture, plywood and joinery (Devaraj et al., 1999). G. striata provides a hard and durable wood often used for boomerangs called egngal alonhdh. Recently, seven compounds were isolated from a MeOH extract of leaves of G. robusta (Yamashita et al., 2008), and information regarding secondary metabolites from G. robusta can be located elsewhere (Wang et al., 2008).

3.6.15  Lophira Ochnaceae 3.6.15.1 Taxon: Lophira alata Banks ex C. F. Gaertn. Synonym: Lophira procera A. Chev. Common names: ekki, ironwood.

134  ◾  Plant Gum Exudates of the World

Economic importance: Materials: wood. Distributional range (native): AFRICA-West-Central Tropical Africa: Cameroon, Equatorial Guinea, Gabon, Zaire; West Tropical Africa: Cote D’Ivoire, Ghana, Liberia, Nigeria, Sierra Leone.

3.6.16  Madhuca Sapotaceae 3.6.16.1  Taxon: Madhuca longifolia (L.) J. F. Macbr. Synonyms: Bassia latifolia Roxb. [≡ Madhuca longifolia var. latifolia]; Bassia longifolia L.; Illipe latifolia (Roxb.) F. Muell. [≡ Madhuca longifolia var. latifolia]; Madhuca indica J. F. Gmel. [= Madhuca longifolia var. latifolia]; Madhuca latifolia (Roxb.) J. F. Macbr. [≡ Madhuca longifolia var. latifolia] Common names: moatree, mowra buttertree, mahua [India]. Economic importance: Human food: beverage base, vegetable (flowers eaten and used in making distilled liquor). Materials: lipids. Medicine: folk medicine. Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: India, Nepal, Sri Lanka; Indo-China: Myanmar. Exudate appearance and availability: The gum is collected between April and June and is commercially available. Commercial and functional uses for other parts of the tree: Edible fruits and flowers. The seeds yield an oil known as ‘bassia oil’.

3.6.17 Millettia Fabaceae (subfamily: Faboideae) 3.6.17.1 Taxon: Millettia pinnata (L.) Panigrahi Synonyms: Cytisus pinnatus L.; Derris indica (Lam.) Bennet; Galedupa indica Lam.; Galedupa pinnata (L.) Taub.; Pongamia glabra Vent.; Pongamia mitis Kurz; Pongamia pinnata (L.) Pierre Common names: Indian beech, karanja, karumtree, pongam, poonga oil tree. Distributional range (native): AFRICA-Western Indian Ocean: Mauritius, Reunion. ASIA, TEMPERATE-China: China - Fujian, Guangdong; Eastern Asia: Japan - Kyushu, Ryukyu Islands, Taiwan. ASIA, TROPICAL-Indian Subcontinent: Bangladesh, India - Andhra Pradesh, Arunachal Pradesh, Assam, Bihar, Dadra and N. Haveli, Delhi, Goa, Gujarat, Haryana, Himachal Pradesh, Jammu and Kashmir, Karnataka, Kerala, Madhya Pradesh, Maharashtra, Manipur, Meghalaya, Mizoram, Nagaland, Orissa, Pondicherry, Punjab, Rajasthan, Sikkim, Tamil Nadu, Tripura, Uttar Pradesh, West Bengal, Sri Lanka; North Indian Ocean: India - Andaman and Nicobar; Indo-China: Myanmar, Thailand, Vietnam; Malesia: Brunei, Christmas Island, Indonesia - Irian Jaya, Java, Kalimantan, Lesser Sunda Islands, Sumatra, Malaysia, Papua New Guinea, Philippines, Singapore. AUSTRALASIAAustralia: Australia - Northern Territory, Queensland. PACIFIC-Northwestern Pacific: Micronesia; Southwestern Pacific: Fiji. OTHER-cultivated in east Africa (USDA, ARS, National Genetic Resources Program, 2008). Geographic distribution: The natural distribution is along coasts and river banks in India and Burma (Negi, 2000). Millettia is native to the Asian subcontinent. It has been introduced to humid tropical lowlands in the Philippines, Malaysia, Australia, the Seychelles, the US, and Indonesia.

Major Plant Exudates of the World  ◾  135

Exudate color: Light brown (Guha and Basu, 1990) or black (Duke, 1983f). Gum water solubility: The gum is sparingly soluble in water and has a slight tendency to form a gel (Guha and Basu, 1990). Gum chemical characteristics: The polysaccharide contains L-arabinose (43.9%), D-galactose (23.1%), and D-glucuronic acid (23.5%) (Guha and Basu, 1990). Commercial availability of the gum (pure form): It is used to treat wounds caused by poisonous fish (Duke, 1983f). Commercial and functional uses for other parts of the tree: It is cultivated as an ornamental tree and as a host plant for lac insects, mainly in coastal India and all of Polynesia. Decomposed flowers are used by gardeners as compost. In the Philippines, the bark is used for making string and rope. In wet areas of the tropics, the leaves serve as green manure and as fodder (Negi, 2000). The black malodorous roots contain a potent fish-stupefying principle. In primitive areas of Malaysia and India, root extracts are applied to abscesses. Other plant parts, especially crushed seeds and leaves, are regarded as having antiseptic properties (Negi, 2000). White spot syndrome virus is an extremely virulent, contagious, causative agent of white spot syndrome in shrimp, which causes high mortality and affects most commercially important cultured marine crustacean species worldwide. Pelletized feed impregnated with ethanolic extract and purified compound from the leaves of P. pinnata was fed to shrimp prior to and after white spot syndrome virus infection, at daily doses of 200 and 300 μg/g body weight. Survival rate for the infected shrimp that were fed the two doses was 40 and 80%, respectively. Oral administration inhibited pathogenesis and reduced mortality in infected shrimp (Rameshthangam and Ramasamy, 2007). It was also reported that acetic ether and n-butanol extracts from P. pinnata roots could significantly inhibit the gastric mucosal damage induced by absolute alcohol in rats and reserpine in mice. The acetic ether root extract had the most beneficial effect on experimental gastric ulcer (Liu et al., 2007). The seeds contain pongam oil which is used for tanning leather, soap, and as an illuminating oil which is also used for lubrication and indigenous medicine. Use of the wood is limited to cabinetmaking, cart wheels, posts, and fuel. Seeds are used to poison fish. The ash of the wood is used in dyeing. All parts of the tree are used in folk remedies (Negi, 2000).

3.6.18  Mystroxylon Celastraceae (subfamily: Celastroideae) 3.6.18.1 Taxon: Mystroxylon aethiopicum (Thunb.) Loes. Synonym: Cassine aethiopica Thunb. Distributional range (native): AFRICA-Northeast Tropical Africa: Ethiopia, Sudan; East Tropical Africa: Kenya, Tanzania, Uganda; West-Central Tropical Africa: Cameroon, Zaire; West Tropical Africa: Guinea; South Tropical Africa: Angola, Malawi, Mozambique, Zambia, Zimbabwe; Southern Africa: Botswana, Namibia, South Africa - Cape Province, Natal, Transvaal, Swaziland; Western Indian Ocean: Madagascar, Seychelles (USDA, ARS, National Genetic Resources Program, 2008). Gum water solubility: Readily dissolves in cold water. Gum chemical characteristics: Compared to other gums, it has very low nitrogen, rhamnose and methoxyl contents, and has fairly low hydroxyproline content. It has features which are comparable to those of Acacia seyal gum.

136  ◾  Plant Gum Exudates of the World

3.6.19  Parkia Fabaceae (subfamily: Mimosoideae) 3.6.19.1 Taxon: Parkia bicolor A. Chev. Common names: African locust bean, faux néré [French]. Economic importance: Environmental: potential for shade/shelter. Distributional range (native): AFRICA-West-Central Tropical Africa: Cameroon, Congo, Gabon, Zaire; West Tropical Africa: Benin, Cote D’Ivoire, Ghana, Guinea, Liberia, Nigeria, Sierra Leone; South Tropical Africa: Angola (USDA, ARS, National Genetic Resources Program, 2008). Gum water solubility: The gums are water-soluble. Gum chemical characteristics: P. bicolor contains galactose (74%), arabinose (9%), rhamnose (0%), glucuronic acid (9.5%) and 4-O-methylglucuronic acid (7.5%). Parkia biglobosa contains galactose (73%), arabinose (9%), rhamnose (0%), glucuronic acid (11.5%) and 4-Omethylglucuronic acid (6.5%). The two gums are proteinaceous and have highly similar physicochemical properties.

3.6.20  Pereskia Cactaceae (subfamily: Pereskioideae) 3.6.20.1 Taxon: Pereskia guamacho F.A.C. Weber Common names: goma de cardon [Spanish]; guamacho gum; goma de guamacho (Howes, 1949). Distributional range (native): SOUTH AMERICA-Northern South America: Venezuela (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance: The gum’s appearance and color, cream yellow to brown, is similar to Opuntia gums (Mantell, 1947). Gum water solubility: Gum specimens from P. guamacho are moderately soluble in cold water. The intrinsic viscosity of Pereskia gum solutions has been found to be comparable to that of Parkia gum but higher than that of Acacia gums (De Pinto et al., 1994c). Gum chemical characterists: P. guamacho gum contains galacturonic acid, glucuronic acid and its 4-O-methyl ether, galactose (32-41%), arabinose (12-24%), xylose (1-6%) and rhamnose (2-17%), in addition to high proportions of calcium, magnesium and sodium. Spectral analysis evidenced the presence of (1-3) and (1-6)-linked galactose residues (De Pinto et al., 1994c). Commercial availability of the gum (pure state) and applications: Similar to gum from Opuntia. Commercial and functional uses for other parts of the tree: Edible fruits. Pachycereus hollianus is used as a barrier plant on account of its easy culture and upright habit (Howes, 1949).

3.6.21  Phormium Hemerocallidaceae 3.6.21.1 Taxon: Phormium tenax J. R. Forst. & G. Forst. Common names: harakeke, korari, New Zealand flax, New Zealand hemp, lino de Nueva Zelanda [Spanish], lirio de espada [Spanish]. Economic importance: Environmental: ornamental. Materials: fiber. Distributional range (native): AUSTRALASIA-New Zealand: New Zealand. OTHERnaturalized in Australia (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance: The crude gum is exuded from the leaves of the plant. Purification of the gum is achieved by precipitation from filtered acidified hot aqueous solution with alcohol (McIlroy, 1944, 1951; Smith and Montgomery, 1959).

Major Plant Exudates of the World  ◾  137

Gum chemical characteristics: Neutral salt of a polysaccharide acid composed of D-xylose and D-glucuronic acid with (1-2)- or (1-4)-linkages, the latter, by analogy with xylan and hemicellulose, being more probable. The gum is reported to have an equivalent weight of 880 (McIlroy, 1951; Whistler and Smart, 1953c). Commercial availability of the gum (pure form): There is a small market for cut leaves for use in flower arrangements, but most arrangers use leaves from their own garden plants for this purpose. Commercial and functional uses for other parts of the tree: It is grown as a commercial crop in various places around the world. Years ago, it was an extremely useful plant for the Maori people. It was used to provide clothing, ropes and cords, fishing nets and lines, baskets, mats, wall-hangings and panels. New Zealand had a thriving flax fiber industry until the 1950s. Flax leaves and fibers are still being used today to make traditional Maori items, but they are also gaining favor as an artistic medium. The flowers can be eaten; leaves and roots are used in folk medicine (Hindmarsh, 1999).

3.6.22  Piptadeniastrum Fabaceae (subfamily: Mimosoideae) 3.6.22.1 Taxon: Piptadeniastrum africanum (Hook. f.) Brenan Synonym: Piptadenia africana Hook. f. Common names: African greenheart, agboin, dahoma, false sasswood, redwood, dabema [French]. Distributional range (native): AFRICA-Northeast Tropical Africa: Sudan; East Tropical Africa: Uganda; West-Central Tropical Africa: Cameroon, Central African Republic, Gabon, Zaire; West Tropical Africa: Cote D’Ivoire, Ghana, Guinea, Liberia, Nigeria, Senegal, Sierra Leone, Togo; South Tropical Africa: Angola. Commercial and functional uses for other parts of the tree: The wood is used for heavy construction, wharf decking, and flooring.

3.6.23  Pittosporum Pittosporaceae 3.6.23.1 Taxon: Pittosporum phillyreoides DC. Common names: desert willow, willow pittosporum, weiden-klebsame [German]. Distributional range (native): AUSTRALASIA-Australia: Australia - Western Australia. Gum water solubility: Soluble in water.

3.6.24  Polyscias Araliaceae (subfamily: Aralioideae) 3.6.24.1 Taxon: Polyscias sambucifolia (Sieber ex DC.) Harms Synonyms: Panax sambucifolius Sieber ex DC.; Tieghemopanax sambucifolius (Sieber ex DC.) R. Vig.; Tieghemopanax sambucifolius var. angustifolius Ewart Distributional range (native): AUSTRALASIA-Australia: Australia - New South Wales, Queensland, Tasmania, Victoria. Exudate appearance: Resembles gum arabic in appearance but may be scented.

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Gum water solubility: Partial. Commercial and functional uses for other parts of the tree/shrub: Its timber is used for carpentry.

3.6.24.2 Taxon: Prunus avium (L.) L. Synonyms: Cerasus avium (L.) Moench; Cerasus avium var. aspleniifolia G. Kirchn.; Prunus avium var. aspleniifolia (G. Kirchn.) H. Jaeger; Prunus cerasus var. avium L.; Prunus macrophylla Poir. Common names: bird cherry, gean, mazzard cherry, sweet cherry, ou zhou tian ying tao [transcribed Chinese], cerisier des oiseaux [French], merisier [French], herzkirsche [German], süßkirsche [German], süßkirschenbaum [German], vogelkirsche [German], seiyo-mizakura [transcribed Japanese], cerejeira [Portuguese], cerezo [Spanish]. Economic importance: Environmental: ornamental. Human food: fruit. Materials: wood. Medicine: folk medicine. Distributional range (native): ASIA, TEMPERATE-Western Asia: Afghanistan, Iran, Turkey; Caucasus: Armenia, Azerbaijan, Georgia, Russian Federation - Ciscaucasia, Dagestan. EUROPE-Northern Europe: Denmark, Ireland, Norway, Sweden, United Kingdom; Middle Europe: Austria, Belgium, Czechoslovakia, Germany, Hungary, Netherlands, Poland, Switzerland; East Europe: Belarus, Moldova, Ukraine; Southeastern Europe: Albania, Bulgaria, Former Yugoslavia, Greece, Italy [incl. Sardinia]; Southwestern Europe: France, Portugal, Spain. OTHER-cultivated and naturalized elsewhere (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance: Irregular semi-solid nodules or lumps (Fig. 3.50), very closely resembling damson gum (Jones, 1939; Smith and Montgomery, 1959). The wild cherry trees (P. avium L. subsp. avium) produce the gum to a lesser extent than the cultivated ones (Rosik et al., 1966c). Like other Prunus trees, several factors may cause gum formation (gummosis), namely, infections by fungi or bacteria, boring insects, grafting incompatibility or treatment with certain chemicals (Stosser, 1979, 1980; Boothby, 1983). Ethephon, an ethylene-generating compound, is commonly used for the promotion of cherry fruit abscission as an aid to machine harvesting (Bukovak, 1979). Extensive ethephon induces gummosis, especially if the trees are under stress or if high temperatures follow ethephon application. Severe gummosis is associated with shoot dieback (Olien and Bukovak, 1982a,b). Cherry trees are more prolific gum producers than plum trees (Boothby, 1983). Untreated cultivated cherry trees may yield gum in abundance, sometimes covering about 30% of the stem and big branches. Exudate color: Shiny reddish to brownish or translucent amber, resembling the more common types of gum arabic. Gum water solubility: Gums from cultivated trees dissolve fully in water whereas gums from wild cherry trees are only partially dissolved (14.5%), the remainder swelling to a jelly. The gum has been treated to improve color and solubility (Butler and Cretcher, 1931; Howes, 1949; Rosik et al., 1966c). Gum chemical characteristics: The gum of the P. avium tree is an acidic polysaccharide with an equivalent weight of 1,760 and a molecular weight of 250,000. It contains D-glucuronic acid, D-xylose, L-arabinose, D-galactose and D-mannose in a molar ratio of 1:6.3:3:0.5, as well as trace amounts of rhamnose. It contains a fundamental chain of D-galactopyranose units bound mostly by β(1-6) bonds and branched in position 6 by glucuronic acid units, in

Major Plant Exudates of the World  ◾  139

Figure 3.50  Prunus avium exudate.

position 3 by single D-xylopyranose units and by an up to four-membered chain of L-arabi­ nose (Rosik et al., 1966a). The gum of the wild cherry tree, P. avium subsp. avium, has an acidic polysaccharide containing D-glucuronic acid, D-galactose, D-mannose, L-arabinose and D-xylose in the molar ratio of 10:45:1:70:10 with trace amounts of L-rhamnose. It is assumed that the main chain of the polysaccharide is formed by the D-galactopyranose units joined together predominantly by the β(1-6) linkages. The side chains are formed by D-glucuronic acid and units of L-arabinose, D-xylose and D-galactose (Rosik et al., 1966c). A comparison of the gum exudates of five P. avium taxa, namely, subsp. avium, var. actiana, var. juliana, var. duracina and cv. Black Republican showed some quite large variations in sugar content and specific rotation. This is good support for the taxonomic view that the P. avium complex is highly varied. The differences in composition of the gums from the different varieties of P. avium are much greater than those found between gums from different varieties of the species in Acacia, and are almost as large as the differences found between

140  ◾  Plant Gum Exudates of the World

gums from species in different sections of this latter genus (Dea, 1970). P. cerasus gum contains an acidic polysaccharide of equivalent weight 2,090 and molecular weight 660,000. It consists of L-arabinose, D-xylose, D-galactose, L-rhamnose and D-mannose in a molar ratio of 6:1:5:0.5:0.5 and of D-glucuronic acid. It is assumed that the principal polysaccharide chain is formed by D-galactopyranose units bound mainly by β(1-6) bonds. D-glucuronic acid is attached to the main chain by a D-glucuronic acid-1 to 6-D-galactose bond. The side chains are formed by D-xylose and L-arabinose. Cultivated cherry trees can be grown as grafts on different stocks, and the latter’s type may determine the nature of the exuded gum (Rosik et al., 1966b). The gum of P. cerasus bears a great deal of chemical resemblance to damson gum. The gum of P. laurocerasus L. contains glucuronic acid, galactose, arabinose, xylose and rhamnose in the molar ratio: 1:5:3.4:2.2:1.3 (Pridham and Worth, 1968). Wild P. virginiana L. has an equivalent weight of 1,790 and is composed of D-galactose (6 moles), L-arabinose (8 moles), D-xylose (6 moles), D-mannose (3 moles) and D-glucuronic acid (2 moles), as well as very small amounts of rhamnose (Butler and Cretcher, 1931; Smith and Montgomery, 1959). Other analytical and structural studies on cherry gums can be found elsewhere (Butler and Cretcher, 1931; Jones, 1939, 1947, 1949; Aspinall et al., 1976). Cherry trees treated with ethephon showed no differences in sugar composition relative to non-treated trees (Olien and Bukovac, 1982a,b). As for other cultivated Prunus trees, it is not clear whether the chemical nature of the exuded gum is dependent upon the type of stock on which the cherry trees are grafted. Similar gums: Resembles tragacanth in gelling properties. It is more difficult to pulverize and is inferior in adhesive properties to gum arabic (Howes, 1949). Commercial availability of the gum (pure form): It has been collected and used in Europe for technical purposes for many centuries, but has been superceded by gum arabic (Howes, 1949). Supplies in the US and Europe are not constant. The gum is a byproduct of the fruit distribution business and is usually collected during the off season. It is applied in pharmaceuticals and cough syrups (Mantell, 1947). In the past, commercial cherry gum was usually contaminated with other fruit gums, such as from plum and apricot trees (Butler and Cretcher, 1931). Commercial and functional uses for other parts of the tree: The cherry fruits are edible.

3.6.25  Prunus Rosaceae (subfamily: Spiraeoideae) 3.6.25.1  Taxon: Prunus armeniaca L. Synonyms: Amygdalus armeniaca (L.) Dumort.; Armeniaca vulgaris Lam.; Prunus armeniaca var. vulgaris Zabel Common names: apricot, Siberian apricot, xing  [transcribed Chinese], abricotier [French], aprikose [German], aprikosenbaum [German], marille [German], damasqueiro [Portuguese], abricó [Portuguese (Brazil)], damasco [Portuguese, Spanish], albaricoque [Spanish], damasquino [Spanish]. Economic importance: Bee plants. Environmental: ornamental, revegetator. Human food: beverage base, fruit, seeds. Materials: essential oils. Medicine: folk medicine. Vertebrate poisons: mammals. Distributional range (native): ASIA, TEMPERATE-Soviet Middle Asia: Kyrgyzstan; China: China. OTHER-widely cultivated, exact native range is obscure (USDA, ARS, National Genetic Resources Program, 2008). Gum (common names): May be termed bassora gum or moussul gum in trade (Felter and Lloyd, 1898).

Major Plant Exudates of the World  ◾  141

Gum chemical characteristics: The gum exudates of P. armeniaca contain xylose, L-arabinose and D-galactose in the molar ratio 1:8:8, and mannose, D-glucuronic acid and 4-O-methylD-glucuronic acid. A structure has been suggested to contain a great number of D-galactose units bound by (1-6) bonds and carrying side chains in position 3. The gum exudates of P. armeniaca have also been studied by others (e.g. Stephen and Churms, 1986).

3.6.25.2 Taxon: Prunus domestica L. subsp. domestica Common names: European plum, gage, garden plum, plum,  prune plum, prunier [French], prunier commun [French], Pflaume [German], Pflaumenbaum [German], Zwetsche [German], Zwetschge [German], Zwispeln [German], Ameixoeira [Portuguese], Cirolero [Spanish], ciruelo [Spanish]. Economic importance: Food additives: flavoring. Human food: beverage base, fruit, oil/fat. Medicines: folklore. Distributional range: Widely cultivated and naturalized. Exudate color and solubility: P. domestica gum is brownish and gradually darkens on exposure to air. The gum is water-soluble. The gum of P. domestica (plum) usually exudes at the end of the summer, in August and September (Hirst and Jones, 1947). It exudes as a viscid mass, containing bark and other impurities (Hirst and Jones, 1938). Victoria plum trees produce more gum than some other cultivars (Boothby, 1983). Orchardists recognize this as evidence of a need for better pruning, elimination of dead wood and removal of sources of infection. Water-stressed peach trees in Georgia which were inoculated with B. dothidea were found to have higher numbers of gum-exudation sites and lesions, and a higher percentage of bark necrosis than non-stressed trees. Yet when the trees were inoculated and stressed simultaneously, infection rarely occurred. Repeated tests demonstrated that water stress at the time of inoculation was not related to disease development (Pusey, 1989). It is believed that the gum has a protective function in limiting the spread of fungal and bacterial pathogens by isolating the infected tissues. Because microorganisms are unable to pass through the gum barrier, the infection is contained and affected plants may recover. If for any reason gum formation is retarded or prevented, the pathogen is able to spread and extensive damage may result (Boothby, 1983). Gums obtained from several trees in the same area all had the same physical properties. The possibility remains, however, that the type of gum exuded by the tree may be dependent on the type of stock on which the tree is grafted rather than on the type of plum producer (Hirst and Jones, 1947). It has been found that ethylene production by tissues of Prunus species is stimulated by the conditions which lead to gummosis (Boothby, 1983). The gums of P. armeniaca, P. persica and P. domestica trees grown in the northern part of Israel were found in tears or vermiform pieces (up to 2 cm in diameter). Gums left on the trees for several months after exudation were hard and adhered strongly to the bark. Lopping of branches, a common practice in Prunus horticulture, is accompanied by smearing the stumped area with a sealing wax. This usually prevents the formation of gum exudation due to tissue wounding. Gum may also exude on the surface of or inside fruits. The latter form, although harmless, is commercially undesirable because the gum swells during the canning process and yields a gelatinous mass in the end product (Boothby, 1983). Gum chemical characteristics: P. domestica gum (Fig. 3.51), which appears to be a homogeneous substance, has an equivalent weight of 1,220. It consists of L-arabinose (3 parts),

142  ◾  Plant Gum Exudates of the World

Figure 3.51  Prunus domestica exudate.

D-xylose (1 part), D-galactose (3 parts) and D-glucuronic acid (1 part). The main chain of the gum consists of D-galactose units linked through C1 and C3, and C1, C3, and C6. L-arabinose side chains consist of more than two units. Other side chains contain 6-O(β-D-glucopyranosyluronic acid)-D-galactose with D-galactose or D-xylose linked through C4 of the D-glucuronic acid moiety (Hirst and Jones, 1947, 1948; Brown et al., 1949a; Smith and Montgomery, 1959). Analytical and structural features of the gum have also been studied (Hirst and Jones, 1938, 1939, 1946). Similar gums: Egg-plum gum (P. domestica) resembles gum arabic more closely than do damson or cherry gums (Hirst and Jones, 1947, 1948). Commercial availability of the gum (pure form): In India, plum gum is sometimes mixed with gums arabic, ghatti and tragacanth (Mantell, 1947). In Syria, plum gum is used locally in confectionery. Some attempts have been made to collect these materials, as in the case of the cherry gums, as byproducts of fruit packaging and marketing operations. Due to the similarity of Prunus gums to cherry gum, they have appeared in trade under the name of cherry gum (Howes, 1949).

Major Plant Exudates of the World  ◾  143

3.6.25.3 Taxon: Prunus persica (L.) Batsch var. persica Synonyms: Amygdalus persica L.; Persica vulgaris Mill. Common names: peach, brugnonier [French], pêcher [French], Pfirsich [German], Pfirsichbaum [German], momo [Transcribed Japanese], pessegueiro [Portuguese], abridor [Spanish], duraznero [Spanish], durazno [Spanish], melocotonero [Spanish]. Economic importance: Human food: beverage base, fruit. Medicines: folklore.    Distributional range: Widely cultivated, origin north China. Exudate color: P. persica gum is reddish. Exudate appearance: The gum of P. persica (peach) exudes from bruised branches in the form of hard or semi-solid nodules. The gum forms on old or diseased trees as a result of the boring of various insects (Mantell, 1947) or of the common twig fungus Botryosphaeria dothidea (gummosis). Gum chemical characteristics: Gum of P. persica consists of D-galactose (5 parts), L-arabinose (6 parts), D-xylose (2 parts), D-glucuronic acid (1 part) and L-rhamnose (∼2%). D-galactose and L-arabinose are assumed to make up the main chain and side chains, respectively (Jones, 1950). The main polysaccharide chain is formed of D-galactose units, bound by β(1-6) glycoside bonds (Kardošová et al., 1978a,b). Analytical and structural features of the gum have been previously studied (Rosik and Wilkie, 1975; Kardošová et al., 1979).

3.6.25.4 Taxon: Prunus spinosa L. Common names: blackthorn, Sloe, hei ci li   [Transcribed Chinese], épine noire [French], prunellier  [French], prunier  [French], gewöhnliche, Schlehe  [German], Schlehdorn  [German], Schlehe [German], Schwarzdorn   [German], prugnolo [Italian], spino nero   [Italian], abrunheiro [Portuguese], ciruelo silvestre  [Spanish], endrino [Spanish], espino negro [Spanish]. Distributional range (native) ASIA-TEMPERATE - Western Asia: Iran, Turkey; Caucasus: Armenia, Azerbaijan, Georgia, Russian Federation - Ciscaucasia, Dagestan. EUROPENorthern Europe: Denmark, Finland, Ireland, Norway, Sweden, United Kingdom; Middle Europe: Austria, Belgium, Czechoslovakia, Germany, Hungary, Netherlands, Poland, Switzerland; East Europe: Belarus, Estonia, Latvia, Lithuania, Moldova, Russian Federation - European part, Ukraine; Southeastern Europe: Albania, Bulgaria, Former Yugoslavia, Greece, Italy, Romania; Southwestern Europe: France, Portugal, Spain (USDA, ARS, National Genetic Resources Program, 2008). Economic importance: Environmental: boundary/barrier/support, graft stock, ornamental, revegetator. Human food: beverage base, fruit. Medicines: folklore. Vertebrate poisons: mammals. Gum chemical characteristics: The gum of P. spinosa contains an acidic polysaccharide whose equivalent weight is 1,290. Its molecular weight is 350,000. It is composed of D-glucuronic acid, 4-O-methyl-D-glucuronic acid, D-galactose, D-mannose, L-arabinose, and D-xylose. It also contains trace amounts of L-rhamnose. The main chain of the polysaccharide is formed by the D-galactopyranose units, linked predominantly by β(1-6) bonds. The nonreducing end groups of the degraded polysaccharide are composed of D-glucuronic acid, D-galactose and D-xylose. L-arabinose is present in the side chains of the original polysaccharide (Rosik et al., 1966d).

144  ◾  Plant Gum Exudates of the World

Figure 3.52  Pterocarpus marsupium exudate (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 61212).

3.6.26  Pterocarpus Fabaceae (subfamily: Faboideae) 3.6.26.1 Taxon: Pterocarpus marsupium Roxb. Common names: East Indian kino, gammalu, Indian kino, Indian kino tree, malabar kino, bijasal [Hindi] (Fig. 3.52). Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: India, Sri Lanka (USDA, ARS, National Genetic Resources Program, 2008). Geographic distribution: P. marsupium occurs in the highlands of India and Sri Lanka. Gums of different quality, obtained from the West Indies and South America, are slightly different in tint (http://medherb.com). Pterocarpus lucens occurs in Africa, mainly in Uganda (Greenway, 1941). Gum (common names): Malabar or East Indian kino is obtained from P. marsupium (http:// www.botanical.com). The name “kino gum” is also the name of another gum (Dragon’s blood), which is actually a resin from the eucalyptus citriodora (lemon gum eucalyptus) (http://www.botanical.com). P. lucens is said to be a gum, not kino. Exudate appearance: P. marsupium exudate is obtained by making incisions in the bark, catching the red sap, and drying it in the sun. It is sold in the market in small, angular, brittle, shiny pieces and is odorless (http://medherb.com/cook/cook.pdf). It sticks to the teeth when chewed and turns saliva a bright red. It has a highly astringent taste (http://www.botanical. com). The kino in the young stems of P. marsupium is produced in the cells of the cortex and pith. Its formation is indicated by the deposition of granular tanniferous, proteinaceous and carbohydrate materials, all constituents of kino gum (Shah and Setia, 1976b). Exudate color: P. marsupium gum is very dark brown to red or ruby colored (Shah and Setia, 1976; http://medherb.com/cook/cook.pdf). P. lucens gum is red (Greenway, 1941).

Major Plant Exudates of the World  ◾  145

Gum water solubility: Water dissolves the gum of P. marsupium almost completely, showing that it is not a pure resin. It is almost entirely soluble in alcohol and is completely soluble in ether. When dissolved in boiling water, it deposits a red substance upon cooling; a cold filtered solution does the same after long exposure to air. Alkalis increase its solubility, but destroy its astringency. Presumably, this so-called gum consists mainly of tannic and kinic acids, redcolored matter and a trace of resinous material (http://medherb.com/cook/cook.pdf). Gum chemical characteristics: P. marsupium gum contains 75% tannic acid; it also contains a non-glucosidal tannin, kinonin and kino-red, in addition to a small quantity of catechol (polycatechin), protocatechic acid, resin, pectin and gallic acid. Carpusin is also present. Phytosterols, alkaloids and sesquiterpenes have been detected (http://www.pioneerherbs. com). Commercial availability of the gum (pure state) and applications: P. marsupium is used for various medicinal purposes and is recognized in the US Pharmacopeia. The gum is used to dye cloths a dark purple color. It is used as an astringent, for severe diarrhea and dysentery (Shah and Setia, 1976b; http://www.winrock.org; http://www.ibiblio.org/herbmed/eclectic/ usdisp/pterocarpus.html). Commercial and functional uses for other parts of the tree: Bark and heartwood of P. marsupium are used for various medicinal applications. The grated root is mixed with tobacco and smoked in a pipe as a cough remedy (http://www.pioneerherbs.com).

3.6.27  Sapindus Sapindaceae (subfamily: Sapindoideae) 3.6.27.1 Taxon: Sapindus trifoliatus L. Synonym: Sapindus laurifolius Vahl. Common names: three-leaf soapberry, saboeira [Portuguese], árbol del jabón [Spanish]. Economic importance: Environmental: ornamental. Medicine: folk medicine. Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: India, Pakistan, Sri Lanka (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance: Often contaminated by other products from the tree (Mantell, 1947). Gum water solubility: It shows hydrophilic colloidal properties to a limited extent (Mantell, 1947). Commercial availability of the gum (pure state): In the past, it has been used in native art, but it has rarely entered international trade, except for some specialized pharmaceutical applications (Mantell, 1947). Commercial and functional uses for other parts of the tree: Fruits are used as soap. S. trifoliatus is considered to be the finest natural source of saponin of the 13 varieties of Sapindus from Asia and South America. The saponins are used in detergents, shampoos, textiles, foods, pharmaceuticals and the photographic film industry. Wood is used for rural building construction, oil and sugar presses and agricultural implements (http://www.haryana-online.com).

3.6.28  Stangeria Zamiaceae 3.6.28.1 Taxon: Stangeria eriopus (Kunze) Baill. Synonyms: Lomaria eriopus Kunze; Stangeria paradoxa T. Moore Economic importance: Environmental: ornamental.

146  ◾  Plant Gum Exudates of the World

Distributional range (native): AFRICA-South Tropical Africa: Mozambique; Southern Africa: South Africa - Cape Province, Natal (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance: Similar to the gum mucilage of Encephalartos (De Luca et al., 1982).

3.6.29  Symphonia Clusiaceae 3.6.29.1 Taxon: Symphonia globulifera L. f. Common names: boarwood, anani [Portuguese (Brazil)], guanandi [Portuguese (Brazil)], oanani [Portuguese (Brazil)], pitá de lagoa [Portuguese (Brazil)], uanani [Portuguese (Brazil)], mani [Spanish (Venezuela)], ojoru [Spanish (Venezuela)], peramán, [Spanish (Venezuela)]. Distributional range (native): AFRICA-East Tropical Africa: Uganda; West-Central Tropical Africa: Cameroon, Gabon, Sao Tome and Principe, Zaire; West Tropical Africa: Cote D’Ivoire, Ghana, Liberia, Nigeria, Sierra Leone; South Tropical Africa: Angola. SOUTH AMERICA-Mesoamerica: Belize, Costa Rica, Honduras, Nicaragua, Panama; Caribbean: Dominica, Guadeloupe, Hispaniola, Jamaica, St. Lucia; Northern South America: French Guiana, Guyana, Suriname, Venezuela; Brazil: Brazil; Western South America: Bolivia, Colombia, Ecuador (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance: Presumably a gum-resin which has been variously described as a hydrophilic gum (Mantell, 1947) or as a resin (Howes, 1949). It exudes from cuts in the bark. A fluid at first, it becomes hard and friable, resembling Burgundy pitch. It occurs in irregular fragments or tears (Fig. 3.53) (Felter and Lloyd, 1898).

Figure 3.53  Symphonia globulifera (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 66686).

Major Plant Exudates of the World  ◾  147

Exudate color: Yellow when fresh but blackens on exposure to air (Howes, 1949) or sometimes transparent and reddish in color, at other times opaque (Felter and Lloyd, 1898). Gum water solubility: Water only partially dissolves the gum. Commercial availability of the gum (pure form): The gum of S. globulifera has been used in local applications as a thickener for native textiles. It has been termed “pig gum” or “animal gum” in the past, inasmuch as it was collected from trees which had been bruised by rooting rodents or other animals (Mantell, 1947). The gum has been used medicinally by indigenous peoples. Boiling and drying the sap produces a wax used in tool manufacture and maintenance. The sap has also been used by Piaroa Amerindians (among many others) to caulk canoes and to attach fish bones to their arrows, or as a general-purpose glue. As it burns without smoke or odor, the resinous exudate is burned as a source of light (http://www2.fpl.fs.fed.us Menninger, 1962). Commercial and functional uses for other parts of the tree: Railroad crossties, general construction, cooperage, furniture components, flooring, utility plywood, suggested as a substitute for oak.

3.6.30 Talisia Sapindaceae (subfamily: Sapindoideae) 3.6.30.1 Taxon: Talisia oliviformis (Kunth) Radlk. Synonym: Melicocca oliviformis Kunth Distributional range (native): SOUTH AMERICA-Mesoamerica: Belize, Guatemala - Peten, Mexico - Chiapas, Quintana Roo, Yucatan; Caribbean: Trinidad and Tobago - Trinidad; Northern South America: Venezuela; Western South America: Colombia - Cesar, Guajira, Magdalena, Ecuador - Sucumbios (USDA, ARS, National Genetic Resources Program, 2008). Commercial and functional uses for other parts of the tree: Edible fruit and ornamental tree.

3.6.30.2 Taxon: Watsonia versfeldii J. W. Mathews & L. Bolus Ditributional range: Australia: Western Australia, New South Wales, Victoria. Alien to Australia, alien to Western Australia, naturalised. Native distribution: Cape Province, South Africa, where it is rare (http://florabase.calm.wa.gov.au/browse/profile/1569). Exudate: The exudate of the seed casing is a polysaccharide with molecular structural features similar to those of cercidium and sapote gums (Cerezo et al., 1969). Chemical structure: The polysaccharides from W. versfeldii and Watsonia borbonica (Pourr.) Goldblatt subsp. borbonica (= Watsonia pyramidata (Andrews) Klatt) show marked similarities in structure: the backbone of β(1-4) D-xylose residues, and the presence of 3-Oα-D-galactopyranosyl-L-arabinose as a component of the side chains. The short side chains have residues of D-galactopyranose and L-arabinofuranose as non-reducing end groups. Apparently, there is less substitution of the D-xylose backbone by side chains in the W. versfeldii exudate than in the W. borbonica subsp. borbonica polysaccharide. The presence of a significant proportion of uranic acid is consistent with this material’s being of the same general type (D-xylose residues in chains with short branches that may contain residues of L-arabinose, D-xylose, and D-glucuronic acid) as that exuded from certain other plants which are widely scattered throughout the plant kingdom. Some resemblance is to be seen, for example, to gums of plants in the orders Ebenales (Sapota aclzras) and Bromeliales (Puya chilensis), as well as Liliales (Shaw and Stephen, 1966).

148  ◾  Plant Gum Exudates of the World

3.6.31 Welwitschia Welwitschiaceae 3.6.31.1 Taxon: Welwitschia mirabilis Hook. f. Synonyms: Tumboa bainesii Hook. f., nom. inval.; Welwitschia bainesii Carrière Distributional range (native): AFRICA-South Tropical Africa: Angola; Southern Africa: Namibia (USDA, ARS, National Genetic Resources Program, 2008). Geographic distribution: A disjunctive distribution in southwestern Africa. The type locality is in the vicinity of Cabo Negro on the coast of Angola (latitude 15-16°S), while more widely dispersed populations are found from the coast to ca. 200 km inland in Namibia (latitude 20-24° S) (Rodin, 1953). Exudate appearance: The tree exudes a thick gum-resin.

3.6.32  Ziziphus Rhamnaceae 3.6.32.1 Taxon: Ziziphus jujuba Mill. Synonyms: Rhamnus zizyphus L.; Ziziphus jujuba var. spinosa (Bunge) Hu ex H. F. Chow Common names: Chinese jujube, Chinese date, common jujube, jujube, jujubier commun [French], brustbeerbaum[German], chinesische dattel [German], jujube [German], açofeifeira [Portuguese], azufaifo [Spanish]. Economic importance: Human food: fruit. Fuels: potential as fuelwood. Materials: beads, chemicals. Medicine: folk medicine. Distributional range: Cultivated and naturalized in Eurasia, probably originated in Asia (Fig. 3.54). Exudate appearance: A number of species in India are said to yield gum. There are no records for those found in East Africa.

Figure 3.54  Ziziphus jujuba leaves and fruit.

Major Plant Exudates of the World  ◾  149

Commercial and functional uses for other parts of the tree: The anticarcinogenic effects attributed to phytochemicals may be based on synergistic, additive, or antagonistic interactions of many compounds. The chloroform-extracted fraction of Zizyphus jujuba, which has anticancer activity in HepG2 cells, was combined with green tea extract, producing an enhanced cell-growth-inhibition effect (Huang et al., 2008).

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150  ◾  Plant Gum Exudates of the World Anderson, D. M. W., and N. A. Morrison. 1990. Identification of Albizia gum exudates which are not permitted food additives. Food Additives and Contaminants 7:175-80. Anderson, D. M. W., and A. C. Munro. 1969. An analytical study of gum exudates from the genus Araucaria Jussieu (Gymnospermae). Carbohydr. Res. 11:43-51. Anderson, D. M. W., and W. Weiping. 1989. The characterization of proteinaceous Prosopis (mesquite) gums which are not permitted food additives. Food Hydrocolloids 3:235-42. Anderson, D. M. W., and W. Weiping. 1990a. The composition of some Sesbania gum exudates. Biochem. Systematics Ecol. 18:43-4. Anderson, D. M. W., and W. Weiping. 1990b. Composition of the gum from Combretum paniculatum and four other gums which are not permitted food additives. Phytochemistry 29(4):1193-5. Anderson, D. M. W., Bell, P. C., Gill, M. C. L., McDougall, F. J., and C. G. A. McNab. 1986. The gum exudates from Chloroxylon swietenia, Sclerocarya caffra, Azadirachta indica and Moringa oleifera. Phytochemistry 25:247-9. Anderson, D. M. W., Bridgeman, M. M. E., Brown, E. I. G., and J. A. M. Anderson. 1983. Studies of uronic acid materials. The gum exudate from a cultivar of Leucaena leucocephala (Lam.) de Wit. Int. Tree Crops J. 2:291-5. Anderson, D. M. W., Cree, G. M., Marashall, J. J., and S. Rahman. 1966. Studies on uronic acid materials. Part XIII. The composition of gum exudates from Albizia sericocephala and Albizia glaberrima. Carbohydr. Res. 2:63-9. Anderson, D. M. W., Howlett, J. F., and C. G. A. McNab. 1985a. The amino acid composition of gum exudates from prosopis species. Phytochemistry 24:2718-20. Anderson, D. M. W., Howlett, J. F., and C. G. A. McNab. 1985b. The amino acid composition of gum tragacanth. Food Additives and Contaminants 2:231-5. Anderson, D. M. W., McNab, C. G. A., and C. G. Anderson. 1982. Studies of uronic acid materials, Part 58: gum exudates from the genus Sterculia (gum karaya). Int. Tree Crops J. 2:147-54. Anderson, D. M. W., Millar, J. R. A., and W. Weiping. 1991. Gum arabic (Acacia senegal): unambiguous identification by 13C-NMR spectroscopy as an adjunct to the revised JECFA specification, and the application of 13C-NMR spectra for regulatory/legislative purposes. Food Additives and Contaminants 8:405-21. Anderson, D. M. W., Weiping W., and G. P. Lewis. 1990. The composition and properties of eight gum exudates leguminosae of American origin. Biochem. Systematics Ecol. 18:39-42. Anon. 1994. Wart remover drug products for over-the-counter human use: amendment of the final monograph. Federal Register 59:60315-7. Arya, S., Tokyo, O. P., Bisht, R. P., and R. Tomar. 1991. Prosopis cineria. Promising multipurpose tree for arid lands. Agroforestry Today 3:13. Ashton, W. R., Jefferies, M., Morley, R. G., Pass, G., Phillips, G. O., and D. M. Power. 1975. Physical properties and applications of aqueous solutions of Albizia zygia gum. J. Sci. Food Agric. 26:697-704. Aspinall, G. O., and J. Baillie. 1963a. Gum tragacanth. Part I. Fractionation of the gum and the structure of tragacanthic acid. J. Chem. Soc. 1702-14. Aspinall, G. O., and J. Baillie. 1963b. Gum tragacanth. Part II. The arabinogalactan. J. Chem. Soc. 1714-20. Aspinall, G. O., and T. B. Christensen. 1965. Gum ghatti (Indian gum). Part IV. Acidic oligosaccharides from the gum. J. Chem. Soc. 1965: 2673-6. Aspinall, G. O., and R. M. Fairweather. 1965. Araucaria bidwilli gum. Carbohydr. Res. 1:83-92. Aspinall, G. O., and J. P. McKenna. 1968. Araucaria bidwillii gum. Part II. Further studies on the polysaccharide components. Carbohydr. Res. 7:244-54. Aspinall, G. O., and U. D. Nasir. 1965. Plant gums of the genus Sterculia. Part I. The main structural features of Sterculia urens gum. J. Chem. Soc. 1965: 2710-20. Aspinall, G. O., and V. Puvanesarajah. 1984. The hex-5-enose degradation: cleavage of 6-deoxy-6-iodo-α-Dgalactopyranoseidic linkages in modified carboxyl-reduced methylated tragacanthic acid. Can. J. Chem. 62: 2736-9. Aspinall, G. O., and G. R. Sanderson. 1970a. Plant gums of the genus Sterculia. IV. Oligosaccharides from acidic Sterculia urens gum. Journal of the Chemical Society 16: 2256-2258. Aspinall, G. O., and G. R. Sanderson. 1970b. Plant gums of the genus Sterculia. V. Degradation of carboxyreduced Sterculia urens gum. J. Chem. Soc. 16:2259-64.

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158  ◾  Plant Gum Exudates of the World Olien, W. C., and M. J. Bukovac. 1982b. Ethephon-induced gummosis in sour cherry (Prunus cerasus L.). II. Flow characteristics of gum solutions. Plant Physiol. 70:556-9. Padilla, F. C., Rincon A. M., and L. Bou-Rached. 2008. Polyphenol content and antioxidant activity of several seeds and nuts. Archivos Latinoamericanos de Nutricion 58:303-8. Parikh, V. M., and J. K. N. Jones. 1966. Cholla gum. II. Structure of the undegraded cholla gum. Can. J. Chem. 44:1531-9. Parikh, V. M., Ingle, T. R., and B. V. Bhide. 1958. Studies in carbohydrates. Part VII. Investigation of bael fruit (Aegle marmelos) mucilage. J. Indian Chem. Soc. 35:125-9. Parmar, C., and M. K. Kaushal. 1982. Aegle marmelos. In Wild fruits, 1-5. New Delhi, India: Kalyani Publishers. Passamani, M., and B. A. Rylands. 2000. Feeding behavior of Geoffroy’s marmoset (Callithrix geoffroyi) in an Atlantic forest fragment of south-eastern Brazil. Primates 41: 27-38. Paula, C. B. H., Gomes, J. S. F., and C. M. R. de Paula. 2002. Swelling studies of chitosan/cashew nut gum physical gels. Carbohydr. Polymers 48:313-8. Pennycook, S. R., and G. J. Samuels. 1985. Botryosphaeria and Fusicoccum species associated with ripe fruit rot of Actinidia deliciosa (kiwifruit) in New Zealand. Mycotaxon 4:445-58. Perez, G. R. M., Sanchez, A. J., Perez, S. G., and R. S. Vargas. 1995. An analytical study of gums from Leucaena glabrata and Spondias purpurea. J. Sci. Food Agric. 68:39-41. Prasad R. N., Viswanathan, S., Devi, J. R., Nayak, V., Swetha, V. C., Archana, B. R., Parathasarathy, N., and J. Rajkumar. 2008. Preliminary phytochemical screening and antimicrobial activity of Samanea saman. J. Medicinal Plant Res. 2:268-70. Pridham, J. B., and H. G. J. Worth. 1968. Gum exudates from the bark of cherry laurel. Chem. Industry, October:1403. Pusey, P. L. 1989. Influence of water stress on susceptibility of nonwounded peach bark to Botryosphaeria dothidea. Plant Dis. 73:1000-3. Quisumbing, E. 1951. Medicinal plants of the Philippines. Manila: Dept. of Agriculture and Natural Resources, Bureau of Printing. Rameshthangam, P., and P. Ramasamy. 2007. Antiviral activity of bis(2-methylheptyl)phthalate isolated from Pongamia pinnata leaves against white spot syndrome virus of Penaeus monodon fabricius. Virus Res. 126:38-44. Randall, R. C., Phillips, G. O., and P. A. Williams. 1989. Effect of heat on the emulsifying properties of gum arabic. In Food colloids, ed. R. D. Bee, P. J. Richmond and J. Mingins, 386-90. Cambridge: Royal Society of Chemistry. Rao, C. V., Heidelberger, M., and W. P. Grosvenor. 1971. Immunochemical studies of mangle gum (Rhizophora mangle L). Immunochemistry 8:657-63. Rao, N. G., Rao, D. G., and T. Jyothirmayi. 2008. Protein solubility and functional properties of Quamachil (Pithecellobium dulce L.) seed flour. J. Food Sci. Technol. 45:480-3. Rao, P. S., and R. K. Sharma. 1957. Indian plant gums: composition and graded hydrolysis of karaya gum (Sterculia urens). Proceedings of the Indian Academy of Sciences 45A:24-9. Raval, D. K., Patel, R. G., and V. S. Patel. 1988. Rheological properties of Leucaena glauca gum in aqueous solutions. Starch Staerke 40:214-8. Rayachhetry, M. B., Blakeslee, G. M., Webb, R. S., and J. W. Kimbrough. 1996. Characteristics of the Fusicoccum anamorph of Botryosphaeria ribis, a potential biological control agent for Melaleuca quinquenervia in South Florida. Mycologia 88:239-48. Raymond, W. R., and C. W. Nagel. 1973. Microbial degradation of gum karaya. Carbohydr. Res. 30:293-312. Redgwell, R. J. 1986. Structural features of the mucilage from the stem pith of Kiwifruit (Actinidia deliciosa): Part I. Structure of the inner core. Carbohydr. Res. 153:97-106. Reidel, H. 1983. The use of gums in confectionery. Confect. Prod. 49:612-3. Reidel, H. 1986. Confections based on gum arabic. Confect. Prod. 52:433-4, 437. Rhodes, B., Daltrey, D., and J. G. Chattwood. 1979. The treatment of pressure sores in geriatric patients: a trial of sterculia powder. Nursing Times 75:365-8. Rincon, F., Leon de Pinto G., Beltran, O., Clamens, C., and R. Guerrero. 2008. Functionality of a mixture of gums from Acacia glomerosa, Enterolobium cyclocarpum and Hymenea courbaril in the low fat ice-cream preparation. Revista Cientifca-Facultad de Ciencias Veterinarias 18:87-92.

Major Plant Exudates of the World  ◾  159 Rodin, R.J. 1953. Distribution of Welwitschia mirabilis. Am. J. Bot. 40:280-5. Rosik, J., and K. C. B. Wilkie. 1975. Quantitative estimation of sugar residues in acidic gums. Phytochemistry 14:1019-21. Rosik, J., Brutenicova-Soskova, M., Zitko, V., and J. Kubala. 1966d. Polysaccharide from the Blackthorn (Prunus spinosa L.). Collection of Czechoslovak Chemical Communications 31:3410-5. Rosik, J., Zitko, V., Bauer, S., and J. Kubala. 1966c. A polysaccharide from the wild cherry tree gum (Prunus avium L. subs. Avium). Collection of Czechoslovak Chemical Communications 31:3353-61. Rosik, J., Zitko, V., and J. Kubala. 1966a. The structural features of cherry-tree gum (Prunus avium L. var Juliana L.). Collection of Czechoslovak Chemical Communications 31:1072-8. Rosik, J., Zitko, V., and J. Kubala. 1966b. The structure of sour cherry-tree gum (Prunus ceraus L.). Collection of Czechoslovak Chemical Communications 31:1569-77. Roy, A., Mukherjee, A. K., and C. V. N, Rao. 1975. Graded-hydrolysis studies on bael (Aegle marmelos) gum. Carbohydr. Res. 41:219-26. Roy, A., Mukherjee, A. K., and C. V. N. Rao. 1977. The structure of bael (Aegle marmelos) gum. Carbohydr. Res. 54:115-24. Sands, L., and R. Klaas. 1929. The composition of Cholla gum. I. The isolation of L-arabinose, D-galactose and L-rhamnose. J. Am. Chem. Soc. 51:3441-6. Sarubbo, L. A., Oliveira, L. A., Porto, A. L. et al. 2000. New aqueous two-phase system based on cashew-nut tree gum and poly(ethylene glycol). J.Chromatography B—Biomed. Sci. Appl. 743:79-84. Saunders, R. N., and R. Becker, 1989. In New crops for food and industry, ed. G. E. Wickens, N. Haq, and P. Day, 288-302. London: Chapman and Hall. Schaub, K. 1958. Rheological standardization of tragacanth and the evaluation of the emulsifying powers of acacia. Pharmaceutica Acta Helvetica 33:797-851. Schwarz, T. W., Levy, G., and H. H. Kawagoe. 1958. Tragacanth solutions. III. The effect of pH on the stability. J. Am. Pharmaceutical Assoc.—Sci. Ed. 47:695-6. Sedgewick, M. L. 1983. Combination of karaya-based skin barrier and a closed-cell foam in pouching of urinary diversions. J. Enterostomal Ther. 10:188-9. Setia, R. C. 1981. Developmental and histochemical studies on gum ducts in Terminalia crenulata Roth. Flora Morphologie, Geobotanik, Oekophysiologie 171:86-94. Setia, R. C. 1984. Development, structure and histochemistry of gum cavities in Pterocarpus marsupium Roxb. and Azadirachta indica Juss. Flora Morphologie, Geobotanik, Oekophysiologie 175:329-37. Shah, J. J., and R. C. Setia. 1976a. Histological and histochemical changes during the development of gums canals in Sterculia urens. Phytomorphology 26:151-8. Shah, J. J., and R. C. Setia. 1976b. Histological and histochemical studies in gum formation in Pterocarpus marsupium Roxb. Indian Forester 102:161-7. Shaw, D. H., and A. M. Stephen. 1966. A polysaccharide found on the seed boxes of Watsonia versveldii. Carbohydr. Res. 1:414-6. Smith, F. 1951. The constitution of Mesquite gum. Part III. The structure of the monomethyl glucuronic acid component. J. Chem. Soc. 2646-52. Smith, F., and R. Montgomery. 1959. The chemistry of plant gums and mucilages. New York: Reinhold Publ. Corp. Sri Bharathie, K. P. 1994. Sri Lanka. In Non-wood forest products in Asia, ed. P. B. Durst, U. Ward, and M. Kashio. Bangkok: RAPA Publication, Food and Agriculture Organization of the United Nations. Stauffer, K. R. 1980. Gum tragacanth. In Handbook of water-soluble gums and resins, ed. R. L. Davidson, ch.11, 11.1-11.31. New York: McGraw-Hill. Stephen, A. M. and S. C. Churms. 1986. Smith degradation of gums from Prunus species: observations on the core structure of Prunus armeniaca (apricot-tree) gum. South Afr. J. Chem. 39:7-14. Stephen, A. M., and P. van der Bijl. 1971. Acid hydrolysis of the polysaccharide gum exudates from Brabeium stellatifolium. J. South Afr. Chem. Inst. 24:103-12. Stosser, R. 1979. Gum duct formation in cherries using a plastic embedding-medium. Sci. Hort. 11:247-52. Stosser, R. 1980. Gum formation in Prunus (Cherry, apricot). Acta Hort. 85:317-22. Stout, A. W. 1959. Larch arabinogalactan. In Industrial gums, ed. R. L. Whistler, 307-309. New York: Academic Press.

160  ◾  Plant Gum Exudates of the World Sybil, P. J., and F. Smith. 1945a. The chemistry of gum tragacanth. Part I. Tragacanthic acid. J. Chem. Soc. 739-46. Sybil, P. J., and F. Smith. 1945b. The chemistry of gum tragacanth. Part II. Derivatives of D- and L-fucose. J. Chem. Soc. 746-8. Sybil, P. J., and F. Smith. 1945c. The chemistry of gum tragacanth. Part III. J. Chem. Soc. 749-51. Tewari, D. N. 1992. Monograph on neem (Azadirachta indica A. Juss.). Dehra Dun, India: International Book Distributors. Thevenet, F. 1988. Acacia gums, stabilisers for flavor encapsulation. In Flavor encapsulation, ed. S. J. Risch, and G. A. Reineccius, chapt. 5, 37-44. Washington D.C.: American Chemical Society. Timell, T. E. 1978. Wood hemicelluloses: Part II. In Advances in botanical research, ed. H. W. Woolhouse, 410433. London: Academic Press. Torto, F. G. 1957. The gum of Fagara xanthoxyloide. Nature 180:864–5. USDA, ARS, National Genetic Resources Program. 2008. Germplasm resources information network (GRIN). [Online Database] National Germplasm Resources Laboratory, Beltsville, MD. Available: http://www. ars-grin.gov/cgi-bin/npgs/acc/display.pl. US National Academy of Sciences. 1979. Tropical legumes: resources for the future, 171-84, 284-6. Washington D.C.: National Academy of Sciences. Verma, V. P. S., and G. N. Kharakwal. 1977. Experimental tapping of Sterculia villosa Roxb. for gum karaya. Indian Forester 103:269-72. Vilela, A., Bolkovic, M. L., Carmanchahi, P., Cony, M., de Lamo, D., and D. Wassner. 2009. Past, present and potential uses of native flora and wildlife of the Monte Desert Journal of Arid Environments 73:238-43. Wang, H., Leach, D. N., Forster P. I., and P. G. Waterman. 2008. Secondary metabolites from Grevillea robusta. Biochem. Systematics Ecol. 36:452-3. Weiping, W., and D. M. W. Anderson. 1994. Non-food applications of tree gum exudates. Chemistry and Industry of Forest Products, 14:67-76. Weiping, W., and A. Branwell. 2000. Tragacanth and karaya. In Handbook of hydrocolloids, ed. G. O. Philips, and P. A. Williams, 231-246. Cambridge: Woodhead Publishing Ltd. West, A. P., and W. H. Brown. 1920. Philippine resins, gums, seed oils and essential oils. Bull. No. 20. Philippines: Department of Agriculture and Natural Resources, Bureau of Forestry. Whistler, R. L., and C. L. Smart. 1953a. Gum Arabic. In Polysaccharide chemistry, 319-322. New York: Academic Press. Whistler, R. L., and C. L. Smart. 1953b. In Polysaccharide chemistry, 324-325. New York: Academic Press. Whistler, R. L., and C. L. Smart. 1953c. In Polysaccharide chemistry, 325-326. New York: Academic Press. White, C. S. 1951. Improvements in the preparation of L-arabinose from Mesquite gum. J. Am. Chem. Soc. 73:4038-9. White, E. V. 1946. The constitution of mesquite gum. I. The methanolysis products of methylated mesquite gum. J. Am. Chem. Soc. 68:272-5. White, E. V. 1947a. The constitution of mesquite gum. II. Partial hydrolysis of mesquite gum. J. Am. Chem. Soc. 69:622-3. White, E. V. 1947b. The constitution of mesquite gum. III. Heamethyl-3-glucuronosido-methyl-galactoside methyl ester. J. Am. Chem. Soc. 69:2264-6. White, E. V. 1948. The constitution of mesquite gum. IV. 4-methoxy-D-glucuronic acid. J. Am. Chem. Soc. 70:367-9. White, E. V. 1953a. The constitution of sapote gum. II. Components of the methyl ether derivative. J. Am. Chem. Soc. 75:4692-4. White, E. V. 1953b. The constitution of sapote gum. I. Methanolysis of sapote gum methyl ether. J. Am. Chem. Soc. 75:257-9. White, E. V. 1954. The constitution of sapote gum. III. A structural evaluation. J. Am. Chem. Soc. 76:4906-9. Williams, P. A., Phillips, G. O., and R. C. Randall. 1990. Structure-function relationships of gum arabic. In Gums and stabilisers for the food industry 5, ed. G. O. Phillips, and D.J. Wedlock and P.A. Williams, 25-36. Oxford: IRL Press at the Oxford University Press.

Major Plant Exudates of the World  ◾  161 Wolff, M. M., and C. Manhke. 1982. Confiserie: la gomme arabique. Rev. Fabr. ABCD, 57:23-7. Yamashita, Y., Matsunami, K., Otsuka, H., Shinzato, T., and Y. Takeda. 2008. Grevillosides A-F: glucosides of 5-alkylresorcinol derivatives from leaves of Grevillea robusta. Phytochemistry 69:2749-52. Yang, S.T., Kim, M., Park, C. et al. 1993. Effects of sodium alginate, gum karaya and gum arabic on the foaming properties of sodium caseinate. Korean J. Food Sci. Technol. 25:109-17. Zakaria, M. B., and Z. A. Rahman. 1996. Rheological properties of cashew gum. Carbohydr. Polymers 29:25-7. http://www.winrock.org/forestry/factpub/FACTSH/Enterolob.html http://www2.fpl.fs.fed.us/TechSheets/Chudnoff/TropAmerican http://www.haryana-online.com/Flora/ritha.htm http://www.hort.purdue.edu/newcrop/duke_energy/Pongamia_pinnata.html http://www.winrock.org/fnrm/factnet/factpub/FACTSH/P_erinaceus.html http://www.pioneerherbs.com/pterocarpus_marsupium.htm http://medherb.com/cook/html/PTEROCARPUS_MARSUPIUM.htm scanned from: W. Cook, The Physiomedical Dispensatory, MD, 1869 http://www.botanical.com/botanical/mgmh/k/kinos-04.html http://www.botanical.com/botanical/mgmh/k/kinos-04.html http://www.henriettesherbal.com/ http://www.lankachronicle.com/health_medicine.html http://www.wkonline.com/d/Gum_butea.html http://www.thaipuerarian.com/index.php?keyword=butea&Itemid=1&option-com_virtuemart&page=shop. browse

Chapter 4

Minor Plant Exudates of the World 4.1 INTRODUCTION This chapter includes a list of the lesser known, unexplored gum exudates. These gums are of local use or interest in the countries in which they occur. Limited sources of information for some gums permit, in a few cases, only partial descriptions. The chapter also includes some brief remarks on the economic importance of the plant and its parts.

4.2 Adansonia Malvaceae (subfamily: Bombacoideae) 4.2.1 Taxon: Adansonia digitata L. Common names: baobab, dead rat tree, monkey-bread tree (this name is generally assumed to be derived from the fact that monkeys eat the baobab’s fruit), calebassier du Sénégal [French], pain de singe [French], affenbrotbaum [German], imbondeiro [Portuguese (Angola)], baobá [Portuguese (Brazil)] (USDA, ARS, National Genetic Resources Program, 2008). Distributional range (native): AFRICA-Macaronesia: Cape Verde; Northeast Tropical Africa: Chad, Ethiopia, Somalia, Sudan; East Tropical Africa: Kenya, Tanzania; West-Central Tropical Africa: Cameroon, Zaire; West Tropical Africa: Benin, Burkina Faso, Cote D’Ivoire, Ghana, Guinea, Mali, Niger, Senegal, Sierra Leone, Togo; South Tropical Africa: Angola, Malawi, Mozambique, Zambia, Zimbabwe; Southern Africa: Botswana, Namibia, South Africa Transvaal; Western Indian Ocean: Madagascar. ASIA, TEMPERATE-Arabian Peninsula: Oman, Yemen. OTHER-widely naturalized in the tropics (USDA, ARS, National Genetic Resources Program, 2008). The tree: A. digitata is a deciduous, very large, indeed, majestic tree that can grow to up to 25 m in height, and can live for hundreds of years (Fig. 4.1). It has thick, angular, widespreading branches and a short, stout trunk which can reach 10-14 m (and sometimes more) in girth and often becomes deeply fluted. The shape of the trunk varies. In young trees it 163

164  ◾  Plant Gum Exudates of the World

A

B

Figure 4.1  (A) The tree Adansonia digitata (courtesy of Philip Greenspun; http://philip. greenspun.com/copyright/). (B) A. digitata bark (courtesy of Forest & Kim Starr; http://www. hear.org/starr/plants/images/species/).

Minor Plant Exudates of the World  ◾  165

is conical; in mature trees it may be cylindrical, bottle-shaped, or tapering with branching near the base (Gebauer et al., 2002). The baobabs are comprised of eight species with large, spectacular, nocturnal flowers (Baum, 1995a,b). A. digitata occurs throughout the drier parts of Africa. A second species is restricted to northwestern Australia (Adansonia gibbosa (A. Cunn.) Guymer, formerly Adansonia gregorii F. Muell.), and the remaining six species are endemic to Madagascar (Baum et al., 1998). Exudate appearance and properties: A. digitata yields a semi-fluid odorless and tasteless gum when wounded (Howes, 1949). The gum of A. digitata is white when fresh and becomes reddish-brown with age (Greeway, 1941; Howes, 1949). The gum is insoluble in water (Greeway, 1941), has an acidic reaction and resembles tragacanth in its hydrocolloidal properties (Burkill, 1985). The allied Australian species A. gibbosa exudes a similar pale gum from the stem which is edible, as well as a dark red gum from the fruit (Howes, 1949). Indigenous Australians obtain water from the hollows in this tree. The white powder that fills the seed pods is used for food. Decorative paintings or carvings have been found on the outer surface of the fruits. The leaves are used medicinally (Boland et al., 1984). The gum of A. digitata is used locally for cleaning sores (Burkill, 1985; FAO, 1988). A. gibbosa also yields a semi-fluid, odorless and tasteless edible gum when the trunk is wounded. Commercial and functional uses for other parts of the tree: The baobab (A. digitata) is important to the survival of natives in arid zones (Becker, 1983). Its leaves, bark, fruit, kernels and seeds are of immense importance to village life, since they provide food, emergency water, medicine, cosmetics and toiletries (Mathieu and Meissa, 2007; National Research Council, 2008), as well as material for hunting and fishing (Venter and Venter, 1996). Tubers, twigs, fruits, seeds, leaves and flowers of this plant are used as common ingredients in traditional dishes (Nordeide et al., 1996). According to a recent survey, the easier the bark harvesting, the tastier the pulp and leaves; the slimier the pulp, the less tasty it is; the more closely longitudinally marked the fruit capsules, the tastier the pulp (Assogbadjo et al., 2008). The fruit pulp has very high vitamin C content (Sidibe et al., 1998). Extraction of A. digitata fruit pericarp in 80% methanol yields proanthocyanidins as the major compound (Shahat, 2006). The fruits of A. digitata (Fig. 4.2) contain many seeds in a whitish and floury pulp. The compounded leaves consist of five to seven digitate leaflets. The fruit consists of 14 to 28% pulp which has low moisture content and is acidic, starchy, and rich in vitamin C, calcium and magnesium. After separating out the seeds, the pulp is traditionally used as an ingredient in various preparations or to make beverages. Despite lysine deficiency and the presence of some factors that are not easily digested, the seeds are an interesting protein source. They also contain ∼15% lipids. After cooking or grilling, they are either consumed as is or used in powdered form as a thickener. Recently, 14 species of wild edible fruits from Burkina Faso were analyzed for their phenolic and flavonoid contents and their antioxidant activities. Data showed that the total phenolic and flavonoid levels were significantly higher in acetone vs. methanol extracts. Detarium microcarpum fruit had the highest phenolic and flavonoid contents, followed by the fruits of Adansonia digitata, Ziziphus mauritiana, Ximenia americana and Lannea microcarpa. Significant amounts of total phenolics were also detected in the following fruit species, in decreasing order: Tamarindus indica > Sclerocarya birrea > Dialium guineense > Gardenia erubescens > Diospyros mespiliformis > Parkia biglobosa > Ficus sycomorus > Vitellaria paradoxa (Lamien-Meda et al., 2008). The leaves (Fig. 4.3) are rich in vitamins (especially C and A) and iron, and contain mucilage. The youngest leaves can be consumed as vegetables, but they are often dried and

166  ◾  Plant Gum Exudates of the World

A

B

Figure 4.2  (A) Boabab hanging fruit. (B) Boabab fruit on the ground (courtesy of Forest & Kim Starr). (C) Halved fruit (http://en.wikipedia.org/wiki/Image:Baobab_Frucht.jpg; courtesy of Alex Antener).

Minor Plant Exudates of the World  ◾  167

C

Figure 4.2  (Continued).

pulverized (Diop et al., 2006). Fresh young leaves have a protein content of 4%, and they are rich in vitamins A and C. Baobab leaf is an excellent source of calcium, iron, potassium, magnesium, manganese, molybdenum, phosphorus, and zinc (Yazzie et al., 1994). The mineral contents and levels of vitamins B1 and B2 were determined in dried baobab leaves from 5-yearold trees of A. digitata, A. gibbosa, Adansonia rubrostipa and Adansonia perrieri. Leaf vitamin and crude protein contents were highest in the Madagascar species, especially A. rubrostipa

Figure 4.3  Boabab leaves (courtesy of Forest & Kim Starr).

168  ◾  Plant Gum Exudates of the World

(88 mg B1/100 g leaf, 187 mg B2/100 g), protein 20.7% (dry weight) (Maranz et al., 2008). A comprehensive review on the baobab as a multipurpose tree with a promising future can be found elsewhere (Gebauer et al. 2002; Wickens, 2008).

4.3 Adenanthera Fabaceae (subfamily: Mimosoideae) 4.3.1 Taxon: Adenanthera pavonina L. Common names: coralwood, red sandalwood tree, sandalwood tree, bois de condori [French], condoribaum [German], indischer korallenbaum [German], carolina [Portuguese], árbol del coral [Spanish] (USDA, ARS, National Genetic Resources Program, 2008). Distributional range (native): ASIA, TEMPERATE-China: China. ASIA, TROPICALIndian Subcontinent: India, Sri Lanka; Indo-China: Cambodia, Laos, Myanmar, Thailand, Vietnam; Malaysia: Indonesia, Malaysia, Papua New Guinea. AUSTRALASIA-Australia: Northern Territory. PACIFIC-Southwestern Pacific: Solomon Islands. OTHER-widely cultivated in the tropics; naturalized in tropical Africa, Asia, Southeast United States, West Indies, Seychelles, Pacific Islands (USDA, ARS, National Genetic Resources Program, 2008). The tree and its uses: A. pavonina can be located in residential areas (transplanted), villages, paddy fields, and secondary forests. The tree (Fig. 4.4) is much planted for its ornamental

TARS 1207 A Adenanthera pavonina Red Sandalwood Tree

Figure 4.4  The tree and fruit of Adenanthera pavonina (computer image taken by USDA-ARS TARS).

Minor Plant Exudates of the World  ◾  169

Figure 4.5  Adenanthera pavonina leaves and flowers.

value and for its brilliant red seeds, which are used for necklaces (Howes, 1949; Lewis et al., 2003). It is also valued as firewood. The tree sprouts new branches easily and so is not damaged by harvesting for firewood. A red dye is obtained from the wood and is used by the Brahmins to make religious markings on their foreheads (Greenway, 1941; Howes, 1949). Different parts of the tree are edible. The young leaf shoots and flowers are eaten fresh or parboiled (Fig. 4.5). The seed/fruit is roasted and eaten as a snack, but is toxic when raw (Setalaphruk and Price, 2007). Chitinases have been isolated from various species and various organs of the plant, including the seeds. Thermostable chitinase from seeds of A. pavonina has been purified and characterized. A protein similar to the isolated chitinase was detected in exudates from seeds, discharged during germination (Santos et al., 2004). The seeds (Fig. 4.6) are a potential source of oil and protein in times of shortage (Ezeagu and Gowda, 2006). Analysis has shown that the seeds of A. pavonina contain appreciable amounts of protein (∼29 g/100 g of seeds), crude fat (∼18 g/100 g), and minerals, comparable to commonly consumed staples. Total sugar is low (∼8 g/100 g) while starch (42 g/100 g) constitutes the major carbohydrate. Low levels of non-digestible substances were reported, and methionine and cysteine are the most deficient amino acids. Linoleic and oleic acids make up 71% of the total fatty acids (Ezeagu et al., 2004). The oil of A. pavonina seeds was analyzed by chromatographic and instrumental means. The oil was found to be rich in neutral lipids (86.2%), and low in polar lipids (13.8%). The neutral lipids consist mainly of triacylglycerols (64.2%). Unsaturated fatty acids were found at as high as 71%, while the percentage of saturated fatty acids was only 29%. GC and GC/MS analyses revealed linoleic, oleic and lignocerotic acids to be predominant among all fatty acids in the A. pavonina oil, whereas stigmasterol was the major steroid identified in that study (Zarnowski et al., 2004). Stable formulations of submicron oil-in-water emulsions from A. pavonina seed oil, stabilized with soybean lecithin, can be formed. Non-ionic-surfactant phospholipid-based emulsions containing this edible oil may be useful as an alternative formulation matrix for pharmaceutical, nutritional or cosmetic applications of otherwise membrane-active components (Jaromin et al., 2006).

170  ◾  Plant Gum Exudates of the World

A

B

1 cm

Figure 4.6  (A) Adenanthera pavonina seeds on the ground. (B) Seeds of A. pavonina from India. U.S. National Seed Herbarium image. [Photographed by Steve Hurst for USDA-NRCS PLANTS Database. URL: http://plants.usda.gov.]

4.4 Afzelia Fabaceae (subfamily: Caesalpinioideae) 4.4.1 Taxon: Afzelia africana Sm. ex Pers. Synonyms: Intsia africana (Sm. ex Pers.) Kuntze; Pahudia africana (Sm. ex Pers.) Prain. Common name: African mahogany (Rehm, 1994). Distributional range (native): AFRICA-Northeast Tropical Africa: Chad, Sudan; East Tropical Africa: Uganda; West-Central Tropical Africa: Cameroon, Central African Republic, Zaire; West Tropical Africa: Benin, Cote D’Ivoire, Ghana, Guinea, Guinea-Bissau, Mali, Niger, Nigeria, Senegal, Sierra Leone, Togo (Lewis et al., 2003; USDA, ARS, National Genetic Resources Program, 2008). Exudate properties: When four lesser known indigenous tropical legumes (A. africana, Brachystegia eurycoma, Detarium microcarpum and Mucuna flagellipes) were analyzed, A. africana showed

Minor Plant Exudates of the World  ◾  171

a significantly higher crude protein content of 27%, followed by M. flagellipes with a value of 20.4%. A. africana appears to have potential as a source of vegetable oil for domestic and industrial use, as it contains 32% fat (Onweluzo et al., 1994). A. africana showed about 33% total carbohydrates, about 34 to 50% of which was found to consist of a gum (water-dispersible polysaccharide). M. flagellipes gum solution showed the highest pseudoplasticity with a flow behavior index of 0.41, while in comparison to the other, lesser-known tropical legumes, A. africana was the least pseudoplastic (Onweluzo et al., 1994; Chanda et al., 1995). The gum that was extracted from A. africana was evaluated for some functional properties. At a constant shear rate, the apparent viscosity of the gum was directly proportional to the gum concentration. At 2% concentration, the gum dispersion showed an apparent viscosity of 41 cps, measured at 174 s-1 and 25°C. The gum was found to contain D-galactose as a major monosaccharide. In addition, the presence of L-rhamnose was indicated. A. africana showed significantly lower water-absorption capacity and gelation properties than D. microcarpum and M. flagellipes. The gum showed better emulsion properties at acidic vs. alkaline pH (Onweluzo et al., 1995). The tree: A. africana is a common tree in the savannah and in mixed deciduous forests that may yield gum. The tree reaches 12.2 to 18.3 m in height. It has a scaling bark and a large woody pod (Howes, 1949). Commercial and functional uses for other parts of the tree: The tree yields a valuable mahoganylike timber (Greenway, 1941; Howes, 1949; Boutelje, 1980). Afzelia species are used primarily for wood, though some species also have medicinal uses. The seeds are red and black (Fig. 4.7) and can be used as beads. The viability of seeds and the survival of seedlings under natural conditions are key factors for sexual regeneration of woody species. To grow well, the seedlings of A. africana need to be protected against fire, grazing and drought. When the seeds’ water content is about 8% (fresh weight basis), they can be stored under ambient conditions for at least 33 months after collection without significant reduction in germination rate (Bationo et al., 2001). Afzelia species are also used as cattle feed. The behavior of sheep, goats and cattle on a shrub and tree savannah in the sub-humid zone of West Africa was studied during dry, rainy and cool seasons. The plant species consumed at the highest frequency by cattle were

Figure 4.7  Afzelia africana seeds (http://commons.wikimedia.org/wiki/User:Jeffdelonge; photo by Jeffdelonge;).

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A. africana, Khaya senegalensis (Desr.) A. Juss., Pterocarpus erinaceus Poir. and Dichrostachys cinerea (L.) Wight & Arn. (Ouedraogo-Kone et al., 2006). A. africana is used in folklore remedies for the treatment of diarrhea, gastrointestinal disorders and gonorrhea, among other ailments. A crude extract of its stem bark, containing alkaloids, tannins, flavonoids and saponins, exhibited antimicrobial activity at a concentration of 25 mg/ml against 21 bacterial isolates, including both Gram-positive and Gram-negative strains. On the other hand, the extract did not show any activity against tested fungal species (Akinpelu et al., 2008).

4.5 Albizia Fabaceae A number of species of Albizia are known to yield gum. The Indian species are described in Chapter 3. Albizia gums (Fig. 4.8) can be exuded very freely, but are not of high quality: they are likely to be dark and only somewhat soluble (Howes, 1949). The generic name was misspelled as Albizzia for many years (Anderson and Morrison, 1990a). Albizia species are closely allied to, and often mistaken for

Figure 4.8  Albizia gum (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 58101).

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Acacia species and vice versa (Allen and Allen, 1981). The main diagnostic taxonomic differences involve the stipules and the stamens which, in Albizia, are usually longer than in Acacia and united at the base into a tube (Anderson and Morrison, 1990a). Albizia species are a source of tannins. Saponins and fish-stupefying, insecticidal and anthelmintic compounds can be extracted from the bark of certain species for local native medicinal and other uses (Allen and Allen, 1981; Rukunga et al. 2007). No complete structure of Albizia gum has so far been proposed. A partial structure consists of a main chain of β-(1-3) D-galactose units with some β-(1-6)-linked D-galactose units (Anderson and Morrison, 1990a). Other chemical and structural features of Albizia species have also been proposed (Anderson and Dea, 1969; Anderson et al., 1996; de Paula et al., 2001; Mhinzi, 2002).

4.6 Anogeissus Combretaceae 4.6.1 Taxon: Anogeissus leiocarpus (DC.) Guill. & Perr. Synonyms: Anogeissus leiocarpa (DC.) Guill. & Perr.; Anogeissus schimperi Hochst ex Hutch. & Dalz. Common names: marke (Hausa), kane. Geographic distribution: Northern Nigeria, eastern part of Sudan (Howes, 1949). Gum (common name): marike gum (Smith and Montgomery, 1959). Exudate properties: The yellow or light brown (Smith and Montgomery, 1959) gum exudes in large or small fragments with a glassy or weathered surface (Howes, 1949). It is only partially soluble in water, swelling to a mucilaginous mass of relatively high viscosity (Greeway, 1941; Smith and Montgomery, 1959). The gum is composed of L-arabinose, D-galactose and glucuronic acid. The hydrolyzed gum has an equivalent weight of approximately 343. It contains neither proteins nor methoxyl groups (Smith and Montgomery, 1959). Leiocarpan A, the major polysaccharide component of A. leiocarpus gum, contains a backbone with alternating 4-O-substituted β-D-glucuronic acid and 2-O-substituted α-D-mannopyranose residues with terminal D-xylopyranose and L-arabinofuranose residues attached variously to the mannose residues (Aspinall and Puvanesarajha, 1983). Structural features of A. leiocarpus have been studied by several researchers (McIlroy, 1952; Aspinall and Christensen, 1961; Aspinall and McNab, 1965; Aspinall et al., 1969; Aspinall and Chaudhari, 1975). Commercial availability of the gum (pure form): In northern Nigeria and the eastern Sudan, the gum of A. leiocarpus has been reported to be chewed and eaten by the natives. It is also used for ink (Howes, 1949). Anogeissus latifolia, the source of much of the Indian ghatti gum described in Chapter 3, and Anogeissus acuminata (Roxb. ex DC.) Guill. & Perr. (formerly Anogeissus pendula Edgew.) yield a good-quality gum in India. Commercial and functional uses for other parts of the tree: A. leiocarpus is one of the most frequently used woody plants to build homes (houses, tents or huts), structures for grain storage, sheds and fences (Ganaba et al., 2004). The powdered bark is applied to wounds, sores, boils, cysts, and diabetic ulcers. It has also been mixed with green clay and applied as an unusual face mask for serious acne vulgaris (Dalziel, 1936). Extracts of A. leiocarpus have antiplasmodial, antitrypanosomal and antifungal activities. The antiplasmodial activity of methanolic extracts of 16 medicinal plants was evaluated by fluorometric assay. The most active extracts were those from A. leiocarpus and Terminalia avicennoides Guill. & Perr. None of the extracts or isolated compounds affected the integrity of human erythrocyte membranes, however, adverse effects were manifested in a concentration-dependent fashion

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(Shuaibu et al., 2008a). The antitrypanosomal activity of methanolic extract of A. leiocarpus was evaluated against four strains of Trypanosoma species with a minimum inhibitory concentration range of 12.5 to 50 mg/ml. Appropriate chemical analysis revealed hydrolyzable tannins with a range of activity. On fibroblasts, the compound did not reveal any serious toxicity at moderate concentration, but again, the effect was concentration-dependent (Shuaibu et al., 2008a,b). Chloroform, ethanolic, methanolic, ethyl acetate and aqueous root extracts of A. leiocarpus were investigated for antifungal activities. The plant extract inhibited the growth of all test organisms. A. leiocarpus appears to be more effective as an antifungal agent than T. avicennoides. Ethanolic extracts of the two plant roots were more effective than the methanolic, chloroform, or aqueous extracts against all of the tested fungi (Mann et al., 2008). Another study dealt with five species of Combretaceae growing in Togo that were investigated for their antifungal activity against 20 pathogenic fungi. The five hydroethanolic extracts of Terminalia glaucescens Planch. ex Benth. and A. leiocarpus appeared to be the most active (Batawila et al., 2005). The safety and anthelmintic activity of the crude aqueous leaf extract of A. leiocarpus were investigated in sheep naturally infected with gastrointestinal nematodiasis using a fecal egg count reduction test and a controlled test. It was concluded that the crude aqueous leaf extract of A. leiocarpus could be tolerated by sheep and exhibited limited, dose-dependent anthelmintic activity (Agaie and Onyeyili, 2007).

4.7 Atalaya Sapindaceae (subfamily: Sapindoideae) 4.7.1 Taxon: Atalaya hemiglauca (F. Muell.) F. Muell. ex Benth. Synonym: Thouinia hemiglauca F. Muell. Common names: cattle brush, whitewood. Economic importance: Vertebrate poisons: mammals (Lazarides and Hince, 1993). Distributional range (native): AUSTRALASIA-Australia: Australia - New South Wales, Northern Territory, Queensland, South Australia, Western Australia (USDA, ARS, National Genetic Resources Program, 2008). Exudate properties: The exudate is pale, and readily dissolves in cold water (Anderson and Weiping, 1990). The gum is of chemical interest in that it has a negative specific rotation very similar to that of Acacia senegal gum, the latter regarded as having a specific rotation of -30. Care should therefore be taken to differentiate between these two gums, although Australian exudates are not usually exported. Nevertheless, clear distinctions can be made on the basis of the very low nitrogen and rhamnose contents and viscosity of Atalaya gum compared with Acacia gum, as well as the former’s low hydroxyproline and high aspartic acid and cysteine contents (Maiden, 1901; Anderson and Weiping, 1990).

4.8 Balsamocitrus Rutaceae (subfamily: Aurantioideae) 4.8.1 Taxon: Balsamocitrus dawei Stapf Common name: Uganda powder-flask fruit (Swingle and Reece, 1967). Distributional range (native): AFRICA-East Tropical Africa: Uganda (USDA, ARS, National Genetic Resources Program, 2008).

Minor Plant Exudates of the World  ◾  175

Exudate properties: The fruit of Balsamocitrus contains a gummy substance (Howes, 1949) that is quite soluble in water. This gum contains a volatile oil with a characteristic odor which prevents its use as a substitute for gum arabic (Howes, 1949). Agricultural issue: Commercially used Balsamocitrus rootstocks can all be seriously damaged by the larvae of the sugar cane root weevil, Diaprepes abbreviatus (L.), while at least seven species within the subfamily Aurantiodeae have been observed to be significantly more resistant. The species Balsamocitrus dawei was most resistant to weevil larvae, exhibiting less root damage than commonly used rootstock cultivars, as well as significantly depressed larval growth and survival (Bowman et al., 2001).

4.9 Bauhinia Fabaceae The genus is well represented in tropical and subtropical Africa (Howes, 1949). Gum-producing species with wide spreadability are Bauhinia thonningii and Bauhinia fassoglensis; however, the latter species has been reassigned to the genus Tylosema, as Tylosema fassoglense. Commercially, these gums are not important.

4.9.1 Taxon: Bauhinia carronii F. Muell. Synonym: Lysiphyllum carronii (F. Muell.) Pedley. Common names: northern bean tree, Queensland ebony, red bauhinia. Distributional range (native): AUSTRALASIA-Australia: Australia - Queensland (USDA, ARS, National Genetic Resources Program, 2008). The tree and the exudate: The endemic tree “Queensland ebony” is up to 10 m tall, commonly multistemmed, with branchlets that are usually spreading or pendulous. Its dark gray bark is furrowed and hard (Flora of Australia online; www.anbg.gov.au/abrs/abif/flora/). It is widespread in Queensland except the Cape York Peninsula, the southwest and the far southeast. It grows in sandy or rocky soil in cypress-ironbark woodland, on sandy river banks, on flood plains, in gray silty soil, in clay in Brigalow scrub and Gidgee scrub, on red clay-loam flats, and on steep slopes in vine thickets. It flowers from August to February, with fruits recorded in most months (Flora of Australia online; www.anbg.gov.au/abrs/abif/flora/). B. carronii yields a yellow, tastless gum with good tenacity (Maiden, 1901; Howes, 1949).

4.9.2 Taxon: Bauhinia thonningii Schumach. & Thonn. Synonym: Piliostigma thonningii (Schumach. & Thonn.) Milne-Redh. Common name: koa. Distributional range (native): AFRICA-Northeast Tropical Africa: Chad, Ethiopia, Sudan; East Tropical Africa: Kenya, Tanzania; West-Central Tropical Africa: Cameroon, Gabon, Zaire; West Tropical Africa: Benin, Burkina Faso, Cote D’Ivoire, Gambia, Ghana, Guinea, Guinea-Bissau, Mali, Nigeria, Senegal, Sierra Leone, Togo; South Tropical Africa: Angola, Malawi, Mozambique, Zambia, Zimbabwe; Southern Africa: Botswana, Namibia, South Africa. ASIA, TEMPERATEArabian Peninsula: Yemen (USDA, ARS, National Genetic Resources Program, 2008). The shrub, exudate, products and uses: B. thonningii is a tall shrub with a twisted branched stem. It has a smooth bark that is vertically cracked and fibrous on the inner side. The wood is reddish, becoming dirty brown after exposure. The wood is simple to work, but likely to

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have insect damage; it can be used for hut poles, handles and mortars. The shrub blossoms from December to June and the fruit remains on the tree for a long time. Fruits are long, wide, flat and slightly cracked pods, velvet in the premature stages. Bark fibers are used to make binding, ropes and “pagne” cloth (Baumer, 1983). The bark is rich in tannins and may be used for tanning skins. Infusions of leaves and bark are used against worms, dysentery, diarrhea and malaria (Muregi et al., 2007). They are also used against leprosy, blennorrhagoeia, hemoglobinuria, sore throat and aching gums (Baumer, 1983). Pounded, boiled and macerated bark and roots produce a red dye used for “pagne” fabric and wooden objects. A dark blue dye can be extracted from pods and seeds (Baumer, 1983). Pods and young leaves are consumed by livestock. In the Republic of Sudan, roasted seeds are consumed by humans. The inner part of the bark contains a gum, which swells in water and then hardens and is therefore used for caulking of African boats (Baumer, 1983).

4.9.3 Taxon: Tylosema fassoglense (Kotschy ex Schweinf.) Torre & Hillc. Synonyms: Bauhinia fassoglensis Kotschy ex Schweinf.; Bauhinia kirkii Oliv. Economic importance: Human food: potential as vegetable. Distributional range (native): AFRICA-Northeast Tropical Africa: Ethiopia, Sudan; East Tropical Africa: Kenya, Tanzania, Uganda; West-Central Tropical Africa: Burundi, Rwanda, Zaire; South Tropical Africa: Angola, Malawi, Mozambique, Zambia, Zimbabwe; Southern Africa: Namibia, South Africa - Natal, Transvaal, Swaziland (USDA, ARS, National Genetic Resources Program, 2008). The tree: The genus Tylosema was established in 1955 and belongs to the Leguminosae. Four species, all inhabitants of Africa, have been distinguished (Coetzer and Ross, 1977). They are stem-trailing, herbaceous geophytes, arising from a large underground tuber. T. fassoglense is widely distributed throughout East African countries from Ethiopia to the Transvaal and westward to Angola and northern Namibia. T. fassoglense develops like a tree. It is not an evergreen: during the autumn it assumes a yellow color. The adult species are large in size, reaching 17 m in height. Its beans are consumed by natives (Wilczek, 1952), and a high protein content (comparable to that of soybean) and oil level approaching that of peanuts have been reported (Malaisse and Parent, 1985): the seeds contain 240-300 g lipid/kg and 446 g protein/kg dry weight. Major fatty acids in the oil are linoleic (36-42% of the total fatty acids), oleic (32-35%) and palmitic (11.5-15.7%) acids. The proteins characteristically have high levels of lysine, proline and tyrosine. Due to their very low content, both methionine and cysteine appear to be the limiting amino acids. T. fassoglense defatted meal contains substantial amounts of trypsin inhibitors and phytates: 295 trypsin units inhibited (TUI) per mg and 35 g/kg dry weight, respectively (Dubois et al., 1995).

4.10 Julbernardia Fabaceae (subfamily: Caesalpinioideae) 4.10.1 Taxon: Julbernardia globiflora (Benth.) Troupin Synonyms: Brachystegia globiflora Benth. (USDA, ARS, National Genetic Resources Program, 2008); Berlinia eminii Taub.; Isoberlinia globiflora (Benth.) Hutch. ex Greenway (Hyde and Wursten, 2008). Common name: mnondo.

Minor Plant Exudates of the World  ◾  177

Distributional range (native): AFRICA-East Tropical Africa: Tanzania; West-Central Tropical Africa: Zaire; South Tropical Africa: Malawi, Mozambique, Zambia, Zimbabwe; Southern Africa: Botswana, Namibia (USDA, ARS, National Genetic Resources Program, 2008). The tree: J. globiflora is a deciduous tree. An important constituent of miombo woodland (i.e. miombo is the Swahili word for Julbernardia, a tree genus that comprises a large number of species), often growing with Brachystegia spiciformis Benth. Its altidude range is 760 to 1660 m and it flowers from January to May (Hyde and Wursten, 2008). The mnondo is a medium-sized tree. In the northern half of its range, it is generally 15 to 16 m high, but can grow up to 18 m in height. In the southern half, it is usually smaller (12-13 m is a large specimen). Mnondo pods are concentrated at the top and sides of the tree and are readily visible in late summer. The exudate: In East Africa, J. globiflora, found in dry forest areas, yields an insoluble type of gum which has been described as a mixture of gum and kino (Howes, 1949).

4.11 Bombax Malvaceae (subfamily: Bombacoideae) 4.11.1 Taxon: Bombax ceiba L. Synonyms: Bombax malabaricum DC.; Gossampinus malabaricus (DC.) Merr.; Salmalia malabarica (DC.) Schott & Endl. Common names: Indian kapok, red cotton tree, red silk-cotton, silk-cotton tree, simal, fromager [French], bombax [French, Spanish], indischer seidenwollbaum [German]. Distributional range (native): ASIA, TEMPERATE-China: China - Fujian, Guangdong, Guangxi, Guizhou, Jiangxi, Sichuan, Yunnan; Eastern Asia: Taiwan. ASIA, TROPICALIndian Subcontinent: Bhutan, India, Nepal, Sri Lanka; Indo-China: Cambodia, Laos, Myanmar, Thailand, Vietnam; Malesia: Indonesia, Malaysia, Papua New Guinea, Philippines. AUSTRALASIA-Australia: Australia - Northern Territory, Queensland, Western Australia. OTHER-cultivated elsewhere (USDA, ARS, National Genetic Resources Program, 2008). The tree, the exudate and their uses: B. ceiba is a medium-sized deciduous tree found throughout western and southern India (Chadha, 1972). The tropical tree (Fig. 4.9A) has a straight tall trunk. Its leaves are deciduous in winter. Red flowers (Fig. 4.9B) with five petals appear in the spring before the new foliage and are one reason that the tree is widely planted. The flower is used as a common ingredient in Chinese herb tea. It produces a capsule which, when ripe, contains white fibers, like cotton (Fig. 4.9C), which has been used as a substitute for cotton. Its trunk bears spikes to deter animal attacks. Although its stout trunk suggests that it is useful for timber, its wood is too soft to be very useful. In general, its uses are ornamental, as fiber and/or wood, and for folk medicines. Phytochemical studies of this species have resulted in the isolation of several sesquiterpenoids (Seshadri et al., 1971, 1973; Sankaram et al., 1981; Puckhaber and Stipanovic, 2001; Sreeramulu et al., 2001). A new sesquiterpene lactone, together with a known naphthoquinone, were isolated from the root bark of B. ceiba. The structures of these two compounds were established by extensive oneand two-dimensional (1D and 2D) NMR spectral studies (Reddy et al., 2003). The antioxidant activity of a methanolic extract of B. ceiba was evaluated using several antioxidant assays, which tested its ability to scavenge, its action against lipid peroxidation and its effect on myeloperoxidase activity. In addition to its biological activity, the extract showed very

178  ◾  Plant Gum Exudates of the World

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Figure 4.9  (A) Bombax ceiba tree and (B) flowers. (C) Silky seed parts (courtesy of Forest & Kim Starr). (D) B. ceiba exudate (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 65260).

Minor Plant Exudates of the World  ◾  179

C

Figure 4.9  (Continued).

low toxicity to Vero cells (Vieira et al., 2009). The tree yields a dark opaque gum or gumresin. The gum is whitish when first exuded, but darkens to a dark mahogany or black color (Fig. 4.9D) upon drying (Howes, 1949). The gum is used medicinally in India as an astringent in bowel complaints (Howes, 1949), and is widely used in folk medicine as a demulcent, diuretic, aphrodisiac, emetic and for curing impotence (Kirtikar and Basu, 1975).

180  ◾  Plant Gum Exudates of the World

4.11.2 Taxon: Bombax insigne Wall. Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: India; Indo-China: Laos, Myanmar, Vietnam (USDA, ARS, National Genetic Resources Program, 2008). The exudate: B. insigne is an Indian species that yields a brown gum (Howes, 1949).

4.12 Borassus Arecaceae (subfamily: Coryphoideae) 4.12.1 Taxon: Borassus flabellifer L. Common names: doub palm, palmyra palm, tala palm, toddy palm, wine palm, borasse, rônier, lontaro, palmyrapalme, broção, palmira, boraço, boraso, palma, palmira. Economic importance: Environmental: ornamental. Human food: beverage base, fruit, sugar. Materials: fiber, wood. Medicine: folk medicine (USDA, ARS, National Genetic Resources Program, 2008). Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: India, Sri Lanka; Indo-China: Indochina, Myanmar, Thailand; Malesia: Indonesia, Malaysia, Papua New Guinea (USDA, ARS, National Genetic Resources Program, 2008). The tree: The palmyra palm (B. flabellifer) is a multipurpose tree of immense usefulness (Fig. 4.10). It is found extensively in India and its fruit is exploited for food (Fig. 4.11), as are its tuberous

TARS 16294 Borassus flabellifer Palmyra Palm

Figure 4.10  Palmyra palm (Borassus flabellifer), a multipurpose tree of immense usefulness (computer image taken by USDA-ARS TARS).

Minor Plant Exudates of the World  ◾  181

TARS 16294 Borassus flabellifer Palmyra Palm

Figure 4.11  Palmyra palm (Borassus flabellifer) fruit (computer image taken by USDA-ARS TARS).

seedlings; beverage and sugar are obtained from the sap, and fiber is obtained from the leaf and leaf base for brushes, cordage, weaving, and plaiting; trunk wood is used for construction and fuel, and numerous minor products (Davis and Johnson, 1987). Increasing exploitation of the palmyra palm threatens the future supply of its raw materials, which are so important to rural populations. Integrated development of palmyra products for local and export markets, as well as management/conservation measures, are needed, both to maximize the economic value of the products and to assure sustained yield from native stands (Davis and Johnson, 1987). B. flabellifer has various other uses. Peeled seedlings are eaten fresh or sun-dried, raw or cooked in various ways. They also yield starch. A fermented sweet sap (toddy), obtained by tapping the tip of the inflorescence, is a popular beverage. Roots, spadix ash, bark and sap from the flower stalk all have medicinal uses. In India, it is planted as a windbreak on the plains (Morton, 1988). Exudate properties: The exudate of B. flabellifer is vitreous (Howes, 1949) and black (Greenway, 1941). The gum swells in water and is insoluble (Howes, 1949).

4.13 Bosistoa Rutaceae (subfamily: Toddalioideae) 4.13.1 Taxon: Bosistoa pentacocca (F. Muell.) Baill. Synonyms: Bosistoa sapindiformis F. Muell. ex Benth; Euodia pentacocca F. Muell. Geographic distribution: Mullumbimby, New South Wales. The tree: B. pentacocca is confined to the rain forests of eastern Australia. No chemical work has been carried out on this species; the only thing that is known about the chemistry of this genus is the occurrence of the triterpenes taraxerol and taraxerol methyl ether (Parsons et al., 1993). Exudate properties: The exudate is pale and transparent. It is not entirely soluble in water and it resembles other Australian rutaceous gums in its physical properties (Howes, 1949).

4.14 Brachystegia Fabaceae (subfamily: Caesalpinioideae) 4.14.1 Taxon: Brachystegia spiciformis Benth. Synonym: Brachystegia randii Baker f. Common name: zebrawood (Webster’s Dictionary, 1961).

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Figure 4.12  Brachystegia spiciformis (image at PlantSystematics.org; from: A. Engler. 1910. Vegetation der Erde. Vol 9. Band 1. Fig. 364; [courtesy of L.H. Bailey Hortorium ©, Cornell University (for reproduced image, not source)].

Distributional range (native): AFRICA-East Tropical Africa: Kenya, Tanzania; West-Central Tropical Africa: Zaire; South Tropical Africa: Angola, Malawi, Mozambique, Zambia, Zimbabwe (USDA, ARS, National Genetic Resources Program, 2008). The tree: B. spiciformis is a medium-sized African tree, ecologically dominant over large areas of central Africa (Fig. 4.12). Its colorful springtime foliage serves as a seasonal marker. The tree typically reaches a height of about 16 m (Dale and Greenway, 1961). It starts to lose its leaves in late May and by early August it is nearly bare. In late August (when temperatures rise again), new bright red leaves are produced. In different trees, they vary from almost purple to brownish. The color shifts to deep green over a period of 10 to 20 days. The flowers appear after the new leaves and these are followed by the pods in April. The pods split open with a loud noise and the flat seeds (∼2 cm across) (Fig. 4.13) are flung away (Dale and Greenway, 1961).

Minor Plant Exudates of the World  ◾  183

C

5 mm

A

B

Figure 4.13  Brachystegia spiciformis (A) seed, (B) embryo in situ, (C) transection of seed: drawn by Lynda E. Chandler or Karen Parker [scanned by Robert J. Gibbons & Kate O’Mara; from Gunn, C.R. & C.A. Ritchie. 1988. Identification of disseminules listed in the Federal Noxious Weed Act. U.S. Department of Agriculture Technical Bulletin 1719] (courtesy of U.S. National Seed Herbarium).

Exudate properties: Brachystegias are the dominant feature of woody vegetation in many parts of Tropical Africa. They often exude gum (Howes, 1949), which is generally dark (Howes, 1949). B. spiciformis produces a deep red gum (Greenway, 1941). The dark appearance and poor quality also applies to Brachystegia floribunda Benth. (formerly Brachystegia nchangensis Greenway) and Brachystegia longifolia Benth. in northern Zimbabwe (Howes, 1949). The gum has low solubility (Anderson et al., 1984). It is an acidic polysaccharide (Anderson and Stefani, 1979), containing glucuronic acid, 4-O-methylglucuronic acid and galacturonic acid, together with galactose, minor amounts of arabinose, and relatively high proportions of rhamnose. The bark also yields high amounts of tannin (Anderson et al., 1984). The fact that Brachystegia species can also yield water-soluble gum polysaccharides is of interest, particularly because genera within the Caesalpinioideae have been recorded as sources of tannin-rich kinos, copal and dammar-type resins (Greenway, 1941). Commercial and functional uses for other parts of the tree: The wood of B. spiciformis is used for fuel (as both charcoal and firewood), and sometimes for boats and general construction. It is used as a shade tree, and for beehives. Its roots are used for medicinal applications.

4.15 Burkea Fabaceae (subfamily: Caesalpinioideae) 4.15.1 Taxon: Burkea africana Hook. Distributional range (native): AFRICA-Northeast Tropical Africa: Chad, Sudan; East Tropical Africa: Tanzania, Uganda; West-Central Tropical Africa: Cameroon, Central African Republic, Zaire; West Tropical Africa: Benin, Burkina Faso, Cote D’Ivoire, Ghana, Guinea, Mali, Niger, Nigeria, Senegal, Togo; South Tropical Africa: Angola, Malawi, Mozambique, Zambia, Zimbabwe; Southern Africa: Botswana, Namibia, South Africa - Transvaal (USDA, ARS, National Genetic Resources Program, 2008). The tree: B. africana is a deciduous tree (Fig. 4.14) that occurs all over tropical Africa, chiefly in savannah forests, and extending into the Transvaal (Howes, 1949; Lewis et al., 2003). The bark is rich in tannins and alkaloids and is used for tanning leather. Due to its toxicity, pulverized bark is

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F A

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C

+4

G

+8

Figure 4.14  Burkea africana [image at PlantSystematics.org; from: A. Engler. 1910. Vegetation der Erde. Vol 9. Band 1. Fig. 371; courtesy of L.H. Bailey Hortorium ©, Cornell University (for reproduced image, not source)].

thrown into water to paralyze fish. The heartwood produces a dark brown to reddish-brown hardwearing, insect-resistant timber, used for parquet flooring and fine cabinet and furniture work. The gum: B. africana produces a pale yellow to reddish brown, semi-transparent, tear-like exudate (Howes, 1949).

4.16 Capparis Capparaceae 4.16.1 Taxon: Capparis nobilis (Endl.) F. Muell. ex Benth. Common names: wild lemon, devils guts, caper tree. Geographic distribution: Australia.

Minor Plant Exudates of the World  ◾  185

Exudate properties: The exudate forms small particles or vermiform tears with a horny texture. It is a semi-transparent partially soluble exudate that swells to an enormous extent in water. The exudate shows some general resemblance to gums of the Sterculiaceae. In addition to the gum, fruits of the C. nobilis tree have commercial and functional uses (Maiden and Smith, 1895; Maiden, 1901; Howes, 1949).

4.17 Careya Lecythidaceae (subfamily: Planchonioideae) 4.17.1 Taxon: Careya arborea Roxb. Common name: patana oak. Distributional range (native): ASIA, TEMPERATE-Western Asia: Afghanistan. ASIA, TROPICAL-Indian Subcontinent: India, Sri Lanka; Indo-China: Myanmar, Thailand (USDA, ARS, National Genetic Resources Program, 2008). The exudate: The exudate of C. arborea is an astringent gum (Howes, 1949). Functional uses: C. arborea (Fig. 4.15) has been used for religious and medicinal purposes since ancient times in India, but unique among the tribal and rural people of Orissa is its use for garments and for safe abortion of unwanted pregnancies (Mohanty and Rout, 1999). A methanol extract of C. arborea bark was tested for its antioxidant and hepatoprotective activities in mice with Ehrlich’s ascites carcinoma tumors (Rahman et al., 2003). Control animals inoculated with this carcinoma showed a significant alteration in antioxidant and hepatoprotective parameters. Oral administration of the extract caused a significant reversal of these biochemical changes back to normal levels in the serum, liver and kidney, indicating the

2

3 1

Figure 4.15  Careya arborea [image at PlantSystematics.org; from: Lindley, John. The Vegetable Kingdom; The Structure, Classification, and Uses of Plants. Third Edition, 1853. Fig. DIII; courtesy of L.H. Bailey Hortorium ©, Cornell University (for reproduced image, not source)].

186  ◾  Plant Gum Exudates of the World

potent antioxidant and hepatoprotective nature of the standardized extract (Senthilkumar et al., 2008). Oral administration of this extract was also reported to cause a significant reduction in percent increase in body weight, packed cell volume, and viable tumor cell count when compared to mice of the control tumor-bearing group (Natesan et al., 2007).

4.18 Cassia Fabaceae (subfamily: Caesalpinioideae) 4.18.1 Taxon: Cassia fistula L. Common names: golden shower, Indian-laburnum,  purging cassia,   bâton casse [French], canéficer [French], casse fistuleuse [French], Röhrenkassie [German], cássia fístula [Portuguese (Brazil)], cássia-imperial   [Portuguese (Brazil)], cana fístula   [Portuguese (Brazil)], chuvade-ouro  [Portuguese (Brazil)], cañafístula   [Spanish]. Geographic distribution: C. fistula (Fig. 4.16) is native to India, the Amazon and Sri-Lanka; Cassia grandis L.f. is native from Mexico to the north of South America.

Figure 4.16  Cassia fistula, the golden shower tree: flowers and pods.

Minor Plant Exudates of the World  ◾  187

Figure 4.17  Cassia fistula gum (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 59464).

Exudate properties and uses: C. fistula gum (Fig. 4.17) is dark (Howes, 1949), and slightly soluble in water (Howes, 1949). Senna nicaraguensis (Benth.) H. S. Irwin & Barneby (formerly Cassia nicaraguensis Benth.) gum solutions are said to be very viscous (Anderson et al., 1990). Cassia grandis gum is very acidic. It contains tannin and an unusually high proportion of glycine. It contains major amounts of galacturonic acid and xylose in comparison to gums from Enterolobium cyclocarpum, Lysiloma acapulcense and S. nicaraguensis (Anderson et al., 1990). C. fistula is popularly planted as an ornamental tree. The pulp of the fruit, seeds and roots is used for various medicinal applications (Duke, 1983). C. grandis is used as an ornamental tree. The fractionation of a dichloromethane extract of C. fistula fruits led to the isolation of an active isoflavone, biochanin A. This compound was effective against promastigotes of Leishmania. In addition, biochanin A exhibited activity against Trypanosoma cruzi. These results could contribute to the development of novel antiprotozoal compounds for future drug design studies (Sartorelli et al., 2009).

4.18.2 Taxon: Cassia sieberiana DC. Distributional range (native): AFRICA-Northeast Tropical Africa: Chad, Sudan; East Tropical Africa: Uganda; West-Central Tropical Africa: Cameroon, Central African Republic, Zaire; West Tropical Africa: Benin, Cote D’Ivoire, Gambia, Ghana, Guinea, Guinea-Bissau, Liberia, Mali, Mauritania, Nigeria, Senegal, Sierra Leone, Togo (USDA, ARS, National Genetic Resources Program, 2008). The exudate: C. sieberiana is common in savannah and open forest areas throughout West Africa and extends to the eastern Sudan, Uganda and East Africa (Howes, 1949). In West Africa, the gum of C. sieberiana is mixed with the pulverized pod and may be applied

188  ◾  Plant Gum Exudates of the World A

B

Figure 4.18  Cedrela odorata (West Indian cedar) habit (A) and plant (B) (courtesy of Forest & Kim Starr).

Minor Plant Exudates of the World  ◾  189

by natives to sores (Dalziel, 1936). Further information on the chemical constituents and antimicrobial activity of several plants from Ghana, including C. sieberiana, can be found elsewhere (Asase et al., 2008).

4.19 Cedrela Meliaceae 4.19.1 Taxon: Cedrela odorata L. Synonyms: Cedrela glaziovii C. DC.; Cedrela mexicana M. Roem. Common names: Barbados cedar, cigar-box cedar, Mexican cedar, Spanish cedar, West Indian cedar (Fig. 4.18), cèdre acajou [French], cèdre des barbares, westindische zeder [German], cedro colorado [Spanish], cedro real [Spanish]. Distributional range (native): NORTH AMERICA-Mexico; SOUTH AMERICAMesoamerica: Belize, Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua, Panama; Caribbean: Antigua and Barbuda, Barbados, Cayman Islands, Cuba, Dominica, Dominican Republic, Grenada, Guadeloupe, Haiti, Jamaica, Martinique, Netherlands Antilles-Curacao, Puerto Rico, St. Lucia, Trinidad and Tobago; Northern South America: French Guiana, Guyana, Suriname, Venezuela; Brazil: Brazil; Western South America: Bolivia, Ecuador, Peru; Southern South America: Argentina (USDA, ARS, National Genetic Resources Program, 2008). Gum (common names): goma de cedro [Spanish], cedro gum, cedar gum (Mantell, 1947). Exudate properties and uses: The gum is exuded in abnormally large tears (up to 15 cm in length and 5 cm in diameter; Howes, 1949). Its color is red to brown or dark amber (Mantell, 1947; Howes, 1949). The gum (Fig. 4.19) is partially soluble (25%) (Howes, 1949) and swells to form clear jellies (Mantell, 1947). In its pure form, it is used locally for cosmetics and pharmaceuticals

Figure 4.19  Cedrela odorata gum (mag. 0.75x courtesy of the Royal Botanic Gardens, Kew; Cat. No. 63005).

190  ◾  Plant Gum Exudates of the World

(Mantell, 1947). Aqueous dispersions of C. odorata gum demonstrate viscoelastic properties and may have interesting applications as stabilizers of emulsions and suspensions due to their rheological behavior (Rinchon et al., 2009). Other commercial and functional uses for other parts of the tree are in building furniture and cigar boxes. Gums are also yielded by Cedrela australis F. Muell., as well as by Toona ciliata M. Roem. (formerly Cedrela toona Roxb. ex Willd.) (Howes, 1949). C. australis also yields a gum without any trace of resin (Maiden, 1901).

4.20 Ceiba Malvaceae (subfamily: Bombacoideae) 4.20.1 Taxon: Ceiba pentandra (L.) Gaertn. Synonyms: Bombax pentandrum L.; Ceiba caribaea (DC.) A. Chev.; Ceiba casearia Medik.; Eriodendron anfractuosum DC. Common names: kapok, kapok tree, silk cottontree, white silk cottontree, capoc  [French], fromager [French], kapokier [French], kapokbaum [German], samauma [Portuguese (Brazil)], samauma-da-várzea [Portuguese (Brazil)], árbol capoc [Spanish], ceiba [Spanish], pochote [Spanish] (USDA, ARS, National Genetic Resources Program, 2008). Economic importance: Environmental: ornamental, shade/shelter. Materials: fiber, lipids (fiber for filling pillows, life preservers and mattresses, oil for soap); Medicine: folk medicine. Distributional range (native): AFRICA-Northeast Tropical Africa: Sudan; East Tropical Africa: Tanzania, Uganda; West-Central Tropical Africa: Burundi, Cameroon, Gabon, Rwanda, Zaire; West Tropical Africa: Benin, Cote D’Ivoire, Ghana, Guinea-Bissau, Mali, Nigeria, Senegal, Sierra Leone, Togo; South Tropical Africa: Angola, Malawi, Mozambique, Zambia. NORTH AMERICA-Mexico: Northern Mexico - San Luis Potosi, Sonora, Tamaulipas; Central Mexico - Colima, Guerrero, Jalisco, Nayarit, Veracruz. SOUTH AMERICA-Mesoamerica: Belize, Costa Rica, El Salvador, Guatemala, Honduras, Mexico-Chiapas, Yucatan, Nicaragua, Panama; Caribbean: Anguilla, Antigua and Barbuda, Barbados, Cuba, Dominica, Dominican Republic, Grenada, Guadeloupe, Haiti, Jamaica, Martinique, Montserrat, Netherlands AntillesCuracao, Puerto Rico, St. Lucia, St. Vincent and Grenadines, Virgin Islands (British)-Virgin Gorda; Northern South America: French Guiana, Guyana, Suriname, Venezuela; Brazil: Acre, Maranhao, Para, Roraima; Western South America: Bolivia - Santa Cruz, Colombia, Ecuador, Peru - Huanuco, Loreto, Pasco. OTHER-naturalized in tropical Asia, native range uncertain (USDA, ARS, National Genetic Resources Program, 2008). The exudate: C. pentandra exudes an astringent dark gum. It swells in water and aside from its color, bears a resemblance to the tragacanth gums. It has been used as a replacement for katira gum in India (Howes, 1949).

4.21 Ceratopetalum Cunoniaceae 4.21.1 Taxon: Ceratopetalum apetalum D. Don Common name: coachwood. Economic importance: Materials: wood. Distributional range (native): AUSTRALASIA-Australia: Australia - New South Wales, Queensland (USDA, ARS, National Genetic Resources Program, 2008).

Minor Plant Exudates of the World  ◾  191

Figure 4.20  Ceratopetalum gummiferum (New South Wales Christmas tree) Forest & Kim Starr).

(courtesy of

4.21.2 Taxon: Ceratopetalum gummiferum Sm. (Fig. 4.20). Common name: Christmas bush. Distributional range (native): AUSTRALASIA-Australia: Australia - New South Wales (USDA, ARS, National Genetic Resources Program, 2008). Exudate properties: The gum is astringent. It is partially soluble and chemically it is presumed to be a gum-resin (Fig. 4.21). Commercial and functional uses for other parts of the tree: The tree is often used for Christmas decoration.

4.22 Chukrasia Meliaceae 4.22.1 Taxon: Chukrasia tabularis A. Juss. Synonyms: Chukrasia velutina M. Roem.; Swietenia chikrassa Roxb. Common names: chittagong tree, surian batu, chickrassy, chittagong wood, Burma almondwood, cherana puteh, repoh, suntang puteh, yinma, tawyinma, voryong nhom, nhom hin, nhom khao, siat-ka. Geographic distribution: India, Pakistan, Burma, Sri-Lanka to Indo-Malesia (De Cordemoy, 1911; Kalinganire and Pinyopusarerk, 2000). Exudate properties: Sometimes the gum reaches the market as an admixture in Indian gums. Its color is reddish to amber and it is water-soluble (Mantell, 1947). Commercial and functional uses for other parts of the tree: Polyphenols and polyphenolrich fractions of plants have been reported to have protective effects against lipid peroxidation, most probably by serving as scavengers of free radicals and/or by chelating metal ions.

192  ◾  Plant Gum Exudates of the World

Figure 4.21  (A) Ceratopetalum apetalum exudate. (B) Ceratopetalum gummiferum exudate (mag. 3x; courtesy of the Royal Botanic Gardens, Kew; Cat. No. 56964 & 56968).

Different extracts/subfractions of C. tabularis exhibited high protective activity (Kaur et al., 2009). Another study demonstrated the antioxidant activity of C. tabularis leaves, and its correlation with the phenolic content in the different fractions (Kaur et al., 2008). The wood is used for furniture, decorative veneers, paneling, carving, turnery and cooperage (Kalinganire and Pinyopusarerk, 2000).

Minor Plant Exudates of the World  ◾  193

4.23  Citrus Rutaceae Quite a few of the trees that produce the widespread citrus fruit (Fig. 4.22) yield gums on occasion (Howes, 1949). However, these gums do not appear to be of any economic importance (Howes, 1949). Certain pathological conditions of citrus that are associated with gummosis are discussed in Chapter 2. Taxa: Citrus aurantiifolia (Christm.) Swingle; Citrus limonia Osbeck (syn: Citrus limonelloides Hayata; Citrus limunum Risso; Citrus medica L. var. limonum Hook f.); Citrus maxima (Burm.) Merr. (syn: Citrus grandis Osbeck; Citrus decumana L.); Citrus sinensis (L.) Osbeck (syn: Citrus aurantium L. var. dulcis L; Citrus aurantium Risso); Citrus medica L. (syn: Citrus medica L. var. cedrata Risso; Citrus medica L. var. medica; Citrus aurantium L. var. medica Wight & Arnott; Citrus crassa Hasskarl). Common names: Chinese lemon, medicinal lemon, Canton lemon, Cantonese lemon, lemandarin, Mandarin lemon, lime (Citrus aurantiifolia), Mandarin lime, Rangpur lime (Citrus limonia), pumelo or shaddock (Citrus maxima), sweet orange (Citrus sinensis), citron, citron melon, Corsican citron, diamante citron, esrog, ethrog, etrog, Leghorn citron, preserving melon, stock melon (Citrus medica). Economic importance: Food: fruits, food additives, flavoring. Environmental: graft stock, ornamental. Medicine: folk medicine. Geographic distribution: Native to Southeast Asia, occurring from northern India to China and south through Malaysia, the East Indies and the Philippines. The trees are widely cultivated worldwide. Gum (common names): citrus gums (lemon, pumelo and orange gums). The exudate: The pale-yellow exudate appears in lumps or as a thin, shiny, brittle, solid layer on the trunk and branches. It has a characteristic aromatic odor. Symptoms of gummosis are usually found in association with injured or dead branches and caused by species of the fungal genus Phytophthora. The wood beneath the infected tissue is pink to orange. Gum pockets develop beneath the bark. Stressful growing conditions, such as freeze damage, high water table, salt accumulation, and poor cultural practices predispose trees to the disease. Citrus gum, which is soluble in water, disappears after heavy rains but is persistent on the trunk under dry conditions. Lesions spread around the circumference of the trunk, slowly girdling the tree. Badly affected trees have pale green leaves with yellow veins, a typical effect of girdling. If the lesions cease to expand or the fungus dies, the affected area is surrounded by callus tissue. Nursery and young orchard trees with small trunk circumference can be rapidly girdled and killed. Large trees may also be killed, but typically the trunks are partially girdled and the tree canopy undergoes defoliation, twig dieback, and short growth flushes. In susceptible rootstocks, lesions may occur on the crown roots below the soil line and symptoms in the canopy develop without obvious damage to the aboveground trunk (Graham and Timmer, 1994). Ethylene and gum-duct formation in citrus have been previously studied (Gedalovitch and Fahn, 1985a,b), and this is discussed in Chapter 2. Gum chemical characteristics: C. limonia gum is variously described as being composed of L-arabinose (2 parts), D-galactose (2 parts) and a mono-O-methyl-D-glucuronic acid (1 part), or of L-arabinose (2 parts), D-galactose (5 parts) and D-glucuronic acid (2 parts). The L-arabinose residues are present in the gum as end groups and some are linked through C1 and C3 (or C2). The ash-free gum shows an equivalent weight of 770-800. Analysis shows that the gum contains 4% methoxyl (Anderson et al., 1936; Connell et al., 1950; Dutton, 1956).

194  ◾  Plant Gum Exudates of the World

A

B

Figure 4.22  (A) Lime fruit (Citrus aurantiifolia) and flowers. (B) Orange fruit (Citrus sinensis) and leaves (courtesy of Forest & Kim Starr).

Minor Plant Exudates of the World  ◾  195

C. limonia and C. maxima gums have the same general structural features. It is most probable that the gum also contains 4-O-methyl-D-glucuronic acid due to the presence of 5.2% ethereal methyl groups (Connell et al., 1950).

4.24 Cocos Arecaceae (subfamily: Arecoideae) 4.24.1 Taxon: Cocos nucifera L. Common names: coconut, coconut palm (Fig. 4.23), copra, nariyal, cocotier [French], kokospalme [German], khopar [India], coqueiro [Portuguese], coco-da-bahia, coco-da-praia, coqueiro-da-bahia, coqueiro-da-praia [Portuguese (Brazil)], cocotero [Spanish]. Geographic distribution: Native to eastern tropical regions. It is grown both throughout the Asian continent (India, Sri-Lanka, Indonesia) and in Central and South America (Mexico, Brazil). In Africa, the largest producing countries are Mozambique, Tanzania and Ghana. Exudate appearance, properties and uses: Tears (Fig. 4.24) are occasionally found on the trunk of the palm, especially when there has been some sort of injury such as when a palm falls and in so doing grazes the trunk of another. The exudate color ranges from yellow to

Figure 4.23  Cocos nucifera (coconut palm).

196  ◾  Plant Gum Exudates of the World

Figure 4.24  Cocos nucifera exudate (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 35457).

black. It is usually reddish-brown, clear and vitreous. The gum is mostly insoluble in water, swelling to a jelly instead. It has poor adhesive properties. Commercial and functional uses for other parts of the tree: Coconuts (Fig. 4.25) are used as whole fruits or in parts: mesocarp fibers, milk, kernel (or flesh), husk. Its leaves are used to make baskets, roofing, etc. An alcoholic drink known as a toddy or palm wine is extracted

Minor Plant Exudates of the World  ◾  197

Figure 4.25  Cocos nucifera coconuts (courtesy of Forest & Kim Starr).

from its sugar sap, tapped from the inflorescences by means of apposite cuttings (Duke, 1972). The development of anthelmintic resistance has made the search for alternative means of controlling gastrointestinal nematodes of small ruminants imperative. Among these alternatives are several medicinal plants traditionally used as anthelmintics. The efficacy of C. nucifera fruit extract on sheep gastrointestinal parasites was studied (Oliveira et al., 2009). An ethyl acetate extract was obtained from the liquid of green coconut husk fiber. The extract’s efficacy in egg hatching and larval development tests, at the highest concentrations tested, was 100% on egg hatching and 99.77% on larval development. The parameters evaluated in the controlled test were not statistically different, indicating that despite the significant results of the in-vitro tests, the ethyl acetate extract has no activity against sheep gastrointestinal nematodes (Oliveira et al., 2009).

4.25 Cola Sterculiaceae 4.25.1 Taxon: Cola cordifolia (Cav.) R. Br. Synonym: Sterculia cordifolia Cav. Common names: mandinka kola, mandingo kola, tabayer, cola ntaba (Bailleul) [French] (http://www.aluka.org/). Geographic distribution: West tropical Africa and forests of Uganda (Greenway, 1941), which are the areas in which the tree is known to yield gum (Howes, 1949). The tree: C. cordifolia is a forest tree that grows to 30 m in height. Its flowers are a uniformly dull creamy-white inside, darker yellowish tinged reddish outside, changing to orange, rich pink and red. Fruiting carpels are a light tawny brown outside, pinkish inside (http://www. aluka.org/).

198  ◾  Plant Gum Exudates of the World

4.26 Combretum Combretaceae This large genus consists of over 200 species and is well represented in Africa. There are approx. 180 different African species and about 30 different Asian species. Several of the African species are known as gum yielders (Jurasek and Phillips, 1993). Geographic distribution: West tropical Africa and East Africa, mainly in the dry forests and low rainfall areas. Other Combretum species, presumably gum yielders, are distributed in the tropics and subtrobics of both hemispheres, except for Australia and the Pacific Islands (Fig. 4.26). Gum (common names): chiriri gum (Combretum lecananthum Engl. & Diels), mumuye gum (Combretum molle R. Br. ex G. Don, formerly C. sokodense Engl., in northern Nigeria) (Howes, 1949). Exudate properties: Gum of C. molle often appears in opaque, tinged lumps, often clear and light-colored (Howes, 1949). The pale-colored nodules produced by some species are not easily distinguished from Acacia nodules if they are mixed either inadvertently or deliberately. Gums of some of the East African and Sudanese Combretum species tend to be lighter than those of West Africa (Anderson, 1978). Some Combretum gums are perfectly soluble in cold water, others only partially so. One of the least viscous Combretum gums, Combretum nigricans Lepr. ex Guill. & Perr., has a much higher viscosity than is typical for Acacia gums. The gums of Combretum adenogonium Steud. ex A. Rich. (formerly Combretum fragrans F. Hoffm.) and Combretum collinum Fresen. give high viscous solutions resembling those of karaya or tragacanth gum. These high viscosities are reflected in high molecular weights.

Figure 4.26  (A) Combretum erythrophyllum Cat. No. 56674 (mag. 2x). (B) Combretum zeyheri Sond. Cat. No. 56687 (mag. 2x). (C) Combretum glutinosum Cat. No. 56688 (mag. 3x) (courtesy of the Royal Botanic Gardens, Kew).

Minor Plant Exudates of the World  ◾  199

Figure 4.26  (Continued).

The molecular weight of C. collinum gum is 11.6 million, which is probably the highest observed for a gum exudate (Anderson and Bell, 1977). Gum chemical characteristics: The composition of Combretum gums is much more complex than that of Acacia species gums. Various Combretum gums have been found to vary in acetylation degree, reaching up to approximately 7% in Combretum psidioides Welw. (Anderson,

200  ◾  Plant Gum Exudates of the World

1978). Extensive differences in chemical and physical properties also occur within the genus Combretum (Anderson, 1978). NMR spectroscopy has shown that the rhamnose and uronic acid contents of gum combretum are located within internal polysaccharide chains. This explains the well-known difference in emulsification functionality between gum arabic, in which all rhamnose and uronic acid groups are chain-terminal, and gum combretum which is, in addition, markedly hygroscopic and characterized commercially by its tendency to ‘block up’ during transit and storage. Analytical and structural features of some Combretum gums have been widely studied (McIlroy, 1957; Anderson et al., 1959, 1986; Aspinall and Bhovanandan, 1965a,b; Anderson and Bell, 1976; Douglas et al., 1976; Anderson and Weiping, 1990; Anderson and Morrison, 1990b). Commercial availability of the gum (pure form): Poorer quality grades from different botanical sources tend to be mixed and offered for sale under a variety of names, e.g., gum Niger, Nigerian gum, West African gum or East African gum. They are also liable to be mixed with gum of Indian origin and sold as gum ghatti. This practice is more acceptable than an admixture of Combretum with Acacia gums because the main botanical source of ghatti, Anogeissus latifolia, is also a member of the Combretaceae (Anderson, 1978). Combretum adenogonium Steud. ex A. Rich. (formerly Combretum dalzielii Hutch.) has been said to provide much of the gum collected in the Niger basin, south of 14o N, although it is not tapped. Gum of Combretum nigricans var. elliotii (Engl. & Diels) Aubrév. (formerly Combretum elliotii Engl. & Diels) was believed to be the most abundant gum-yielding tree in Sokoto Province, Nigeria. The gum was used in food, by leather workers and in making ink. Gum of Combretum lecananthum has also been reported to be eaten by the natives in Nigeria, when it exudes freely in the hot season. Gum of Combretum collinum subsp. hypopilinum (Diels) Okafor (formerly Combretum hypopilinum Diels and Combretum verticillatum Engl. & Diels) is used by natives in Nigeria to plug carious teeth (Howes, 1949). The gum of Combretum nigricans has recently been suggested to be the major source of West African combretum gums (Anderson et al., 1991a). Commercial and functional uses for other parts of the tree: Combretum species are used as shade trees and to line avenues. Woods of some species are used in construction. Various parts of the tree are used for medicinal preparations.

4.27 Cordia Boraginaceae (subfamily: Cordioideae) 4.27.1 Taxon: Cordia myxa L. Common names: Assyrian plum, sapistan, sebesten plum, selu, Sudan teak. Geographic distribution: Native of tropical Asia and Africa. Found scattered throughout the mid-Himalayas up to elevations of 1,470 m. Exudate appearance, solubility and commercial availability: Records of gum exudation are from India (Howes, 1949; Khan et al., 2001). A sweet, mucilaginous, highly viscous polysaccharide from unripe fruit pulp of Cordia africana Lam. (formerly Cordia abyssinica R. Br.) was isolated from fruits from Southern Africa (Benhura and Katayi, 2000; Benhura and Chidewe, 2002). The viscosity and the solubility of the fruit gum in aqueous solution have been studied (Benhura and Chidewe, 2002). Gum of Cordia sinensis Lam. (formerly Cordia gharaf Ehrenb. ex Asch.) is astringent and in India, it has been used for gargling (Greenway, 1941). Cordia gum is used as glue because of its excellent adhesive properties

Minor Plant Exudates of the World  ◾  201

(Benhura and Chidewe, 2002). At low temperature and concentrations of at least 1.5%, the fruit gum of Cordia africana can form a gel in water (Benhura and Katayi, 2000). The fruit gum can be used beneficially in gonorrhoea (Parmar and Kaushal, 1982). Commercial and functional uses for other parts of the tree: The edible fruits have a few medicinal applications, but they are especially useful as an expectorant and are effective in treating diseases of the lungs and chronic fever. They can also be used for pasting sheets of paper, cardboard, etc. (Parmar and Kaushal, 1982). The fruit is not widely used for consumption by humans but serves as food for monkeys and other animals (Benhura and Chidewe, 2002). Leaves are useful as fodder.

4.28 Cordyla Fabaceae (subfamily: Faboideae) 4.28.1 Taxon: Cordyla africana Lour. Geographic distribution: Tropical Africa extending south to Natal. Gum (common names): chiraya gum, da gum (in Sudan) (Howes, 1949). Exudate appearance and commercial avaliability: C. africana exudes gum or resin (Fig. 4.27). Cordyla richardii Milne-Redh. exudes only gum (Greenway, 1941). The gum has been used to make a type of sizing or whitewash for houses in West Africa (Dalziel, 1936). Commercial and functional uses for other parts of the tree: The fruits are edible, and are used in sauces.

Figure 4.27  Cordyla africana exudate (mag. 2x; courtesy of the Royal Botanic Gardens, Kew; EBC No. 60171).

202  ◾  Plant Gum Exudates of the World

4.29 Corypha Arecaceae (subfamily: Coryphoideae) 4.29.1 Taxon: Corypha utan Lam. Synonyms: Corypha elata Roxb.; Corypha gebanga (Blume) Blume; Taliera gebanga Schult. & Schult. f. Common names: buri palm, gebang palm, buripalme [German]. Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: India; Indo-China: Myanmar; Malesia: Indonesia, Malaysia, Papua New Guinea, Philippines. AUSTRALASIAAustralia: Australia - Northern Territory, Queensland (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance, availability and functionality: The gum of C. utan has a sweet smell and is considered rare. Its color is brownish-black (Corypha umbraculifera L.), (Fig. 4.28), or reddish-brown (C. utan). The gum is used medicinally by the Javanese and the tree is used for ornamental purposes.

4.30 Crataeva Capparaceae 4.30.1 Taxon: Crataeva adansonii DC. Common name: Gum num. Economic importance: Environmental: ornamental. A

Figure 4.28  (A) Corypha umbraculifera tree and (B) exudate (courtesy of the Royal Botanic Gardens, Kew; Cat. No.: 35306).

Minor Plant Exudates of the World  ◾  203

Figure 4.28 (Continued). 

Distributional range (native): AFRICA-Northern Africa: Egypt; Northeast Tropical Africa: Chad, Eritrea, Ethiopia, Sudan; East Tropical Africa: Kenya, Tanzania, Uganda; West-Central Tropical Africa: Cameroon, Central African Republic, Congo, Gabon, Rwanda, Zaire; West Tropical Africa: Benin, Cote D’Ivoire, Gambia, Ghana, Guinea, Mali, Mauritania, Niger, Nigeria, Senegal; South Tropical Africa: Zimbabwe; Western Indian Ocean: Madagascar. ASIA, TEMPERATE-China: China; Eastern Asia: Taiwan. ASIA, TROPICAL-Indian Subcontinent: Bangladesh, India, Pakistan, Sri Lanka; Indo-China: Indochina, Myanmar, Thailand, Malesia, Philippines; OTHER-cultivated elsewhere (USDA, ARS, National Genetic Resources Program, 2008). The tree: The growth of C. adansonii is often stunted due to grass fires (Howes, 1949).

204  ◾  Plant Gum Exudates of the World

4.31 Cussonia Araliaceae 4.31.1 Taxon: Cussonia arborea Hochst. ex A. Rich. Synonyms: Cussonia barteri Seem.; Cussonia djalonensis A. Chev.; Cussonia nigerica Hutch.; Cussonia longissima Hutch. & Dalz.; Cussonia spicata Thunb. Common name: cabbage-wood tree. Geographic distribution: northern Nigeria (C. arborea); eastern Cape Province in South Africa and Zimbabwe (Cussonia spicata). Exudate properties: The gum of C. arborea exudes from wounded trunks and hangs in slender rods. It has a slightly irritant quality (Howes, 1949). C. spicata occasionally exudes gum from its cork-like bark (Churms and Stephen, 1971). The gum of C. arborea is clear and colorless (Howes, 1949). The gum of C. spicata is light brown (Churms and Stephen, 1971). The gum is partially water-soluble. The water-insoluble portion of the gum exudates of C. spicata may be solubilized by alkali (Churms and Stephen, 1971). In northern Nigeria, Cussonia nigerica yields a clear colorless gum when wounded, which hangs in slender pencils and is also believed to have a slightly irritant quality (Howes, 1949). Gum chemical characteristics: C. spicata gum consists of a mixture of polysaccharides that differ not only in molecular weight but also in composition. Evidence obtained for the gum exudates of C. spicata suggests a molecular core consisting of D-galactose residues, mainly β-D-(1 to 3)-linked, most of which carry a D-glucuronic acid residue, β-linked at C-6. The molecular-weight distribution pattern of the degraded polysaccharide obtained upon partial hydrolysis with acid indicates a possible repeating unit with a molecular weight of 1,200. L-arabinose residues occur as short branches, each attached to the galactan framework (at C-4), with α-L-(1 to 5)-linkages between consecutive L-arabinose units in some cases. L-rhamnopyranose end groups are also present (Churms and Stephen, 1971). Commercial and functional uses for other parts of the tree: In Zimbabwe, the bark is used in folk medicine.

4.32 Cycas Cycadaceae 4.32.1 Taxon: Cycas lane-poolei C. A. Gardner Distributional range (native): AUSTRALASIA-Australia: Australia - Western Australia. Exudate appearance: Similar to the gum mucilage of Encephalartos (De Luca et al., 1982).

4.32.2 Taxon: Cycas circinalis L. Synonym: Cycas undulata Desf. ex Gaudich. Common names: queen sago, false sago, fern palm. Geographic distribution: C. circinalis is native to equatorial Africa. The tree: C. circinalis looks like a palm tree with its featherlike leaves organized in a rosette that crowns a single trunk. It can grow up to approx. 6 m in height. The dark green pinnate leaves grow to 2.4 m in length with narrow ∼30-cm leaflets that curve gracefully downward. This species is dioecious, with male and female reproductive parts on separate plants (Fig. 4.29).

Minor Plant Exudates of the World  ◾  205

A

B

Figure 4.29  Cycas circinalis. (A) Sago palm habit. (B) Sago palm leaves. (C) Sago palm spiked stems, and (D) sago palm fruit (courtesy of Forest & Kim Starr).

206  ◾  Plant Gum Exudates of the World

C

D

Figure 4.29  (Continued).

Minor Plant Exudates of the World  ◾  207

Gum properties: Gum is produced by C. circinalis and Cycas rumphii Miq. C. circinalis gum is said to be insoluble in water but absorbing a considerable quantity of it, becomes mucilage. It is similar to tragacanth in its hydrocolloidal behavior (Greenway, 1941). Specimens of C. circinalis consist of large brown lumps (Howes, 1949). Commercial and functional uses for parts of the tree: Flour is obtained from the seeds, which must be carefully washed and processed to remove toxins. There is evidence that longterm use of this flour, even if properly prepared, can eventually result in paralysis and other neurological disorders.

4.33 Dichrostachys Fabaceae (subfamily: Mimosoideae) 4.33.1 Taxon: Dichrostachys cinerea (L.) Wight & Arn. Synonyms: Cailliea dichrostachys Guill. et al.; Cailliea nutans (Pers.) Skeels; Dichrostachys cinerea var. hirtipes Brenan & Brummitt [= Dichrostachys cinerea subsp. argillicola]; Dichrostachys cinerea subsp. lugardae (N. E. Br.) Brenan & Brummitt [= Dichrostachys cinerea subsp. africana]; Dichrostachys cinerea var. lugardiae Brenan & Brummitt [= Dichrostachys cinerea subsp. africana var. africana]; Dichrostachys forbesii Benth. [≡ Dichrostachys cinerea subsp. forbesii]; Dichrostachys glomerata (Forssk.) Chiov. [= Dichrostachys cinerea subsp. cinerea]; Dichrostachys nutans (Pers.) Benth. [= Dichrostachys cinerea subsp. cinerea]; Dichrostachys nutans var. setulosa Welw. ex Oliv. [≡ Dichrostachys cinerea subsp. africana var. setulosa]; Dichrostachys nyassana Taub. [≡ Dichrostachys cinerea subsp. nyassana]; Dichrostachys platycarpa Welw. ex W. Bull [≡ Dichrostachys cinerea subsp. platycarpa]; Mimosa cinerea L. [≡ Dichrostachys cinerea subsp. cinerea]; (=) Mimosa glomerata Forssk.; (=) Mimosa nutans Pers (USDA, ARS, National Genetic Resources Program, 2008). Common names: marabou thorn, marabou. Distributional range (native): AFRICA-Macaronesia: Cape Verde; Northeast Tropical Africa: Chad, Ethiopia, Somalia, Sudan; East Tropical Africa: Kenya, Tanzania, Uganda; WestCentral Tropical Africa: Burundi, Cameroon, Gabon, Rwanda, Zaire; West Tropical Africa: Benin, Cote D’Ivoire, Gambia, Ghana, Guinea, Guinea-Bissau, Liberia, Mali, Niger, Nigeria, Senegal, Sierra Leone, Togo; South Tropical Africa: Angola, Malawi, Mozambique, Zambia, Zimbabwe; Southern Africa: Botswana, Namibia, South Africa - Cape Province, Natal, Transvaal, Swaziland. ASIA, TEMPERATE-Arabian Peninsula: Oman, Saudi Arabia, Yemen. ASIA, TROPICAL-Indian Subcontinent: India, Sri Lanka; Indo-China: Myanmar; Malesia: Indonesia-Java, Lesser Sunda Islands. AUSTRALASIA-Australia: Australia - Northern Territory (USDA, ARS, National Genetic Resources Program, 2008). Similar gums: Presumably gum arabic (the plant is related to acacia). Commercial and functional uses for other parts of the tree: The D. cinerea tree is often a valued source of fuel. Various parts of the tree are used medicinally. Further information on additional medicinal properties of the aerial parts of D. cinerea can be found elsewhere (Abou Zeid et al., 2008).

208  ◾  Plant Gum Exudates of the World

4.34 Echinocarpus Elaeocarpaceae 4.34.1 Taxon: Echinocarpus australis Benth. (now synonym of Sloanea australis F. Muell., see section 4.6.2.2)

4.35 Elaeocarpus Elaeocarpaceae 4.35.1 Taxon: Elaeocarpus grandis F. Muell. Synonym: Elaeocarpus angustifolius Blume.

4.35.2 Taxon: Elaeocarpus obovatus G. Don Common names: blueberry ash, gray carobean, hard quandong. Economic importance: Materials: wood. Distributional range (native): AUSTRALASIA-Australia: Australia - New South Wales, Queensland.

4.35.3 Taxon: Elaeocarpus reticulatus Sm. Common name: blueberry ash. Economic importance: Environmental: ornamental. Distributional range (native): AUSTRALASIA-Australia: Australia - New South Wales, Queensland, Tasmania, Victoria. Exudate appearance: Exudes in small quantities, and the gum is pale in color. Commercial and functional uses for other parts of the tree: Aborigines make necklaces from the seeds after eating the fruit flesh.

4.36 Encephalartos Zamiaceae 4.36.1 Taxon: Encephalartos hildebrandtii A. Braun & C. D. Bouché Distributional range (native): AFRICA-East Tropical Africa: Kenya, Tanzania. Exudate appearance: The gum of Encephalartos species is found in abundance in ducts within the stem and on the surfaces of cones were it originates in the radial canals and makes its way, in aqueous solution, between the seeds to the periphery (Stephens and Stephen, 1988). Studies on the gum of Encephalartos friderici-guilielmi Lehm. describe its exudate from cones as hard, dry nodules in older plants or as soft exudates from trees following heavy rains (Vogt and Stephen, 1993b). The exudate of E. hildebrandtii has been described as rods and tears (Howes, 1949). Incisions made in the rachis stimulate the exudation of the gum (De Luca et al., 1982). Exudate color and gum properties: The exudate of E. hildebrandtii is a clear yellow or pale brown. The gummy exudates from cones of several species of Encephalartos resemble each other in their sugar and uronic acid constituents, though the proportions vary. They are

Minor Plant Exudates of the World  ◾  209

made up of a complex acidic polysaccharide. E. friderici-guilielmi gum was found to have a (1 to 3)-D-galactan with <20% of other residues (D-mannose, and some L-arabinose and L-rhamnose). A tentative formulation of the gum shows L-rhamnose and D-glucuronic acid residues exterior to a branched D-galactan framework. These structures are 3-linked to D-mannose, through D-galactopyranosyl or possibly L-arabinopyranosyl residues, within mannoglucuronoglycan chains. Other units occupy O-4 of D-mannose (Adinolfi et al., 1991; Vogt and Stephen, 1993b). Structural features of Encephalartos longifolium were studied by Stephen and de Bruyn (1967) and Vogt and Stephen (1993a). The amount of each monosaccharide obtained upon hydrolysis of the mucilage of E. longifolium was found to be constant in individual specimens, irrespective of age, sex or growth conditions (De Luca et al., 1982). Structural features of Encephalartos ghellinckii were studied by Stephens and Stephen (1988). Commercial and functional uses for other parts of the tree: E. hildebrandtii is well-represented internationally as a garden tree.

4.37 Entada Fabaceae (subfamily: Mimosoideae) 4.37.1 Taxon: Entada africana Guill. & Perr. Synonym: Entada sudanica Schweinf. Distributional range (native): AFRICA-Northeast Tropical Africa: Chad, Ethiopia, Sudan; East Tropical Africa: Uganda; West-Central Tropical Africa: Cameroon, Central African Republic, Zaire; West Tropical Africa: Benin, Cote D’Ivoire, Gambia, Ghana, Guinea-Bissau, Mali, Niger, Nigeria, Senegal, Togo (USDA, ARS, National Genetic Resources Program, 2008). Commercial and functional uses for other parts of the tree: The wood is used for construction. Leaves, bark and roots serve for a variety of medicinal uses. Leaves make good fodder. Some Nigerian medicinal plants, e.g. E. africana, Hymenocardia acida, Sterculia setigera and Stereospermum kunthianum, may be useful in the treatment of tuberculosis and other respiratory diseases. Phytochemical analysis showed terpenes and triterpenoid saponins to be the most prominent compounds in these plants’ extracts which can also be used as potential antimycobacterial agents (Mann et al., 2008).

4.38 Erythrophleum Fabaceae (subfamily: Caesalpinioideae) 4.38.1 Taxon: Erythrophleum africanum (Welw. ex Benth.) Harms Common name: African blackwood. Distributional range (native): AFRICA-Northeast Tropical Africa: Chad, Sudan; East Tropical Africa: Tanzania; West-Central Tropical Africa: Central African Republic, Rwanda, Zaire; West Tropical Africa: Benin, Cote D’Ivoire, Gambia, Ghana, Guinea, Guinea-Bissau, Mali, Nigeria, Senegal, Togo; South Tropical Africa: Angola, Mozambique, Zambia, Zimbabwe; Southern Africa: Botswana, Namibia (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance: E. africanum exudate gum (Fig. 4.30) is similar to gum arabic. Erythrophleum suaveolens (Guill. & Perr.) Brenan (formerly Erythrophleum guineense G. Don) exudes a gum or gum-resin (Greenway, 1949). The exudate color is amber (Howes, 1949).

210  ◾  Plant Gum Exudates of the World

Figure 4.30  Erythrophleum africanum gum (mag. 2x; courtesy of the Royal Botanic Gardens, Kew; Cat. No.: 57900).

Commercial and functional uses for other parts of the tree: The leaves of E. africanum are known in the arid lands of tropical Africa to possess toxicological properties. Phytochemical, acute and subacute evaluations of the possible toxicity risk of E. africanum aqueous leaf extracts have been reported (Hassan et al., 2007). The phytochemical constituents detected in the leaf extracts were saponins, cardiac glycosides, tannins, flavonoid glycosides, free flavonoids and alkaloids. The lethal dose (LD50) of the aqueous leaf extract was greater than 3000 mg/kg in albino rats (Hassan et al., 2007).

4.39 Flindersia Rutaceae Several species yield gum of fairly good quality in Australia (Howes, 1949).

4.39.1 Taxon: Flindersia maculosa (Lindl.) F. Muell. Synonym: Elaeodendron maculosum Lindl. Common names: leopard tree, leopardwood. Distributional range (native): AUSTRALASIA-Australia: Australia - New South Wales, Queensland. Exudate properties: The gum exudes from the stems and branches during the summer months, in masses “as large as a pigeon eggs” (Fig. 4.31). It has a pleasant taste and is eaten by the aborigines, and commonly employed by the Bushmen to treat diarrhea. It has been described as one of the best Australian gums. The exudate color is clear amber; it is partially soluble

Minor Plant Exudates of the World  ◾  211

Figure 4.31  Flindersia maculosa gum (mag. 4x; courtesy of the Royal Botanic Gardens, Kew; Cat. No. 63858).

and has good adhesive properties. The gum contains ∼80% arabin (water-soluble portion), but no metarabin (Maiden, 1889; Felter and Lloyd, 1898; Howes, 1949).

4.39.2 Taxon: Flindersia australis R. Br. Common names: Australian teak, crow’s ash. Economic importance: The wood of F. australis, is one of the most durable and valuable of the Australian timbers, suitable for various types of construction. Distributional range (native): AUSTRALASIA -Australia: Australia - New South Wales, Queensland.

4.40 Garuga Burseraceae 4.40.1 Taxon: Garuga pinnata Roxb. Distributional range (native): ASIA, TEMPERATE-China: China - Guangxi, Sichuan, Yunnan; ASIA, TROPICAL-Indian Subcontinent: Bangladesh, Bhutan, India, Nepal; Indo-China: Myanmar, Thailand, Vietnam; Malesia: Malaysia, Philippines (USDA, ARS, National Genetic Resources Program, 2008). Exudate properties: The tree produces a clear gum or gum-resin very freely. The exudate color is greenish-yellow (Howes, 1949). Commercial and functional uses for other parts of the tree: The leaves and fruits are edible (Fig. 4.32).

212  ◾  Plant Gum Exudates of the World XIII.

??

Garuga, pinnata, Roxb.

??

Figure 4.32  Garuga pinnata (http://commons.wikimedia.org/wiki/Image:Garuga_pinnata_Bra13. png; from: D. Brandis, Illustrations of the Forest Flora of North-West and Central India, 1874).

4.41 Geijera Rutaceae 4.41.1 Taxon: Geijera paniculata (F. Muell.) Druce Synonyms: Coatesia paniculata F. Muell.; Geijera muelleri Benth. Common names: axebreaker, capivi.  Distributional range (native): AUSTRALASIA- Australia: Australia - New South Wales, Queensland. Exudate properties: Large, light amber to lightish brown and transparent tears with a very bright fracture. The gum is rigid but pulverizes fairly well. It is partially soluble in water.

4.42 Geodorum Orchidaceae 4.42.1 Taxon: Geodorum nutans (C. Presl) Ames Synonym: Dendrobium nutans C. Presl. Common name: kula [Philippines]. Distributional range (native): ASIA, TEMPERATE-Eastern Asia: Taiwan. ASIA, TRO­ PICAL-Malesia: Philippines (USDA, ARS, National Genetic Resources Program, 2008).

Minor Plant Exudates of the World  ◾  213

Exudate properties: The gum exudes from the tuberous roots. It has been used as a glue for cementing together parts of wooden musical instruments such as mandolins and guitars (Howes, 1949). In preparing the glue, the rhizomes are first cooked and then finely grated. Several other Philippine orchids are used for the same purpose: Geodorum citrinum Jacks. from Peninsular Malaysia, and Geodorum purpureum R. Br. from Peninsular Malaysia and Java (Boer and Ella, 2000). Commercial and functional uses for other parts of the tree: The tree is used for ornamental purposes. The tuberous parts are used as an emollient poultice.

4.43 Hakea Proteaceae 4.43.1 Taxon: Hakea gibbosa (Sm.) Cav. Synonym: Banksia gibbosa Sm. Common names: rock hakea, harige hakea (Henderson, 2001). Distributional range (native): AUSTRALASIA-Australia: Australia - New South Wales. OTHER-naturalized in South Africa and New Zealand (USDA, ARS, National Genetic Resources Program, 2008). Exudate properties: The gum of Hakea sericea Schrad. & J. C. Wendl. occurs infrequently but, when it does, it may be found in very large quantities on a single shrub. The exuded gum is initially soft and dries to an intensely hard, horny mass. It is produced from damaged or injured bark on stem and branches. In H. sericea, this is often associated with the gummosis fungus Colletotrichum, and the amount of gum is a good indication of the degree of fungal attack. The fungus kills the bark around the lesions and, if the base of the main stem is infected, the fungus may girdle the stem, resulting in death of the shrub. Inoculating the Hakea shrub with gum containing antagonisitic fungal spores helps in biological control. The gum from H. gibbosa is certainly produced more frequently that that of H. sericea, but the cause of the secretion might be wind or human damage, rather than insect or fungal attack (Stephen, 1956). Initially, the gum is colorless; it may later become reddish-brown if contaminated by extracts from the bark (Stephen, 1956; http://aliens.csir.co.za). Fresh exudate material of H. sericea is soluble in water but the gum hardens with time, and its solubility decreases until it becomes completely insoluble (Stephen, 1956). The gum resembles Sterculia gums in physical properties. Gum chemical characteristics: Acid polysaccharide. Gum of H. sericea has an equivalent weight of 2,000. The gum yields on average: L-arabinose (19%), D-xylose (8%), D-galactose (58%), D-mannose (7%) and D-glucuronic acid (8%). Most of the L-arabinose in the gum appears to be present in the furanose form. The galactose-to-arabinose ratio may be higher for H. sericea than for H. gibbosa gum. The modes of linkage of the sugar units are typical of those present in plant polysaccharide exudates of the arabinogalactan type. The linkage of the peripheral sugar assemblies at O-3 of D-mannose forms the interior core. The gum contains O-acetyl groups (Stephen, 1956; Eagles et al., 1993). The molecular weight of H. gibbosa is 2 million (Eagles, 1992). Commercial availability of the gum (pure state) and applications: The gum of H. gibbosa has been evaluated as a mucoadhesive component of oral tablets for the sustained release of peptides, proteins (Alur et al., 1999a) and low-molecular-weight organic compounds (Alur et al., 1999b,c; Alur et al., 2001).

214  ◾  Plant Gum Exudates of the World

4.44 Khaya Meliaceae 4.44.1 Taxon: Khaya grandifoliola C. DC. Common names: benin mahogany, beninwood. Economic importance: Materials: wood. Distributional range (native): AFRICA-Northeast Tropical Africa: Sudan; East Tropical Africa: Uganda; West-Central Tropical Africa: Central African Republic, Zaire; West Tropical Africa: Benin, Cote D’Ivoire, Ghana, Guinea-Bissau, Nigeria, Togo (USDA, ARS, National Genetic Resources Program, 2008).

4.44.2 Taxon: Khaya madagascariensis Jum. & H. Perrier Common name: Madagascar mahogany. Economic importance: Materials: wood. Distributional range (native): AFRICA-Western Indian Ocean: Madagascar (USDA, ARS, National Genetic Resources Program, 2008).

4.44.3 Taxon: Khaya senegalensis (Desr.) A. Juss. Synonym: Swietenia senegalensis Desr. Common names: bisselon, dryzone mahogany (Fig. 4.33). Economic importance: Materials: wood.

K 20/ 1

1/ 1

F

E

+6

A

1/ 3

H

B

+8

G

C

+10

D +15

J

Figure 4.33  Khaya senegalensis [image at PlantSystematics.org; from A. Engler. 1910. Vegetation der Erde. Vol 9. Band 1. Fig. 257; courtesy of L.H. Bailey Hortorium ©, Cornell University (for reproduced image, not source)].

Minor Plant Exudates of the World  ◾  215

Distributional range (native): AFRICA-Northeast Tropical Africa: Chad, Sudan; East Tropical Africa: Uganda; West-Central Tropical Africa: Central African Republic; West Tropical Africa: Benin, Cote D’Ivoire, Gambia, Guinea, Guinea-Bissau, Mali, Niger, Nigeria, Senegal, Sierra Leone, Togo (USDA, ARS, National Genetic Resources Program, 2008). Gum (common name): khaya gum (Smith and Montgomery, 1959). Exudate properties: Khaya gums are tapped as conglomerates of vermiform fragments and dust. They are only collected in the dry season (Howes, 1949). The gum of Khaya madagascariensis is odorless (Gerard, 1912). Of all the other Khaya species mentioned, Khaya anthotheca (Welw.) C. DC. is the only one that exudes a gum-resin (Greenway, 1941). Khaya gums are pale greenishyellow to golden yellow (Howes, 1949). The gum-resin of K. anthotheca is yellow (Greenway, 1941). Khaya grandifoliola softens and swells in cold water to a mucilaginous mass, and dissolves with difficulty in hot water to give a clear neutral solution. However, after dissolution of the crude gum with alkali followed by acidification and precipitation with acetone, it is readily dissolved in water (McIlroy, 1952; Aspinall et al., 1956; Aslam et al., 1978). The solubilization is probably due to removal of the ester groups of the acetyl residues (Smith and Montgomery, 1959). Gum chemical characteristics: The gum of K. grandifoliola has been described as a branched polysaccharide, composed of D-galactose (3 parts), L-rhamnose (2 parts), D-galacturonic acid (4 parts), 4-O-methyl-D-glucuronic acid (1 part) and traces of L-arabinose. L-rhamnose residues constitue branch points (at C4) in the molecule. It is assumed to be the only gum exudate examined that contains two different uronic acids. The gum resembles gum tragacanth and pectic acid in that it contains large proportions of 1 leading to 4-linked galacturonic acid units, and like gum tragacanth, it contains 6-deoxyhexose. It also resembles the gums from Sterculia setigera (Fig. 4.34; see section 3.3.2.6) and Cochlospermum gossypium which likewise contain D-galactose, L-rhamnose, and D-galacturonic acid; and as with these two gums, the galactose units of khaya gum are joined by 1 leading to 4 bonds. In comparison, galactose units in

Figure 4.34  Sterculia setigera gum (mag. 2x; courtesy of the Royal Botanic Gardens, Kew; Cat. No. 65016).

216  ◾  Plant Gum Exudates of the World

acacia, cherry and damson gums are joined through C1 and C3 and C1 and C6, though in the case of gum arabic, it is more likely that the major proportion of the galactose units are joined through C3. In K. grandifoliola, the L-rhamnose units serve as branch points whereas in the Sterculia and Cochlospermum gums, the L-rhamnose units are joined through C1 and C2 and thus occur only in the chains, and not at branch points or as terminal units as in the case of gum arabic. Unlike S. setigera gum and gum tragacanth in which branching occurs at the galacturonic acid units, the D-galacturonic acid components of khaya gum do not form branch points in the molecule. The gum appears as partly acetylated (Aspinall et al., 1956; Smith and Montgomery, 1959), and a structure was proposed by Smith and Montgomery (1959). Analytical features of the gum have been previously studied by McIlroy (1952). The structural features of K. senegalensis gum (Fig. 4.35) were studied by Aspinall et al. (1965) and Aspinall and Bhattacharjee (1970b). This gum is composed of the same sugar residues as K. grandifoliola, but in different proportions. The gum contains two polysaccharide components, a major (Aspinall et al., 1960) and minor (Aspinall et al., 1965) one. This gum is also partly acetylated. The structural features of Khaya ivorensis were studied by Aspinall (Aspinall and Bhattacharjee, 1970a; Aspinall et al., 1988). The major portion of the polysaccharide may

Figure 4.35  Khaya senegalensis gum (mag. 2x; courtesy of the Royal Botanic Gardens, Kew; Cat. No. 63205).

Minor Plant Exudates of the World  ◾  217

Figure 4.36  Cochlospermum religiosum gum (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 67054).

be formulated as a backbone of alternating 4-linked α-D-galacturonic acid and 2-linked α-Lrhamnopyranose residues with side chains of β-D-galactopyranosyl or 4-O-(4-O-methyl-α-Dglucopyranosyl-uronic acid)-β-D-galactopyranosyl units attached to O-4 of rhamnose residues. Similar gums: This gum is used as a low-quality gum arabic and resembles karaya gum as well as those of S. setigera and C. religiosum. (Fig. 4.36; see section 3.3.6.1). Commercial availability of the gum (pure form): This gum has been reported to have healing qualities and has been evaluated as a binder in a paracetamol tablet formulation (Odeku and Itiola, 1998; Odeku and Itiola. 2002). Commercial and functional uses for other parts of the tree: K. senegalensis is one of the hardest African mahoganies and the hardest of the Khaya species. It is widely used on a commercial scale, particularly in West Africa. It is favored for furniture, elegant joinery, trim and boat building. The wood is also used locally for railroad ties, flooring, turnery and veneer. The leaves are used as fodder for cattle and camels. The bark is used in tanning and various medicinal applications. The seed oil is used in West Africa for cooking.

4.45 Lagerstroemia Lythraceae 4.45.1 Taxon: Lagerstroemia parviflora Roxb. Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: Bhutan, India, Nepal; Indo-China: Myanmar (USDA, ARS, National Genetic Resources Program, 2008). Tree and exudate properties: The plant and the twig are presented in (Fig 4.37). The exudate appears tear-shaped. The gum is sweet and edible, and its color can be light or dark (Howes, 1949).

218  ◾  Plant Gum Exudates of the World A

B

Figure 4.37  Lagerstroemia parviflora (A) plant and (B) twig.

Minor Plant Exudates of the World  ◾  219

Functional uses for other parts of the tree: A methanol extract of the flowers of L. parviflora was investigated for its effect on a cough model induced by sulfur dioxide gas in mice. The extract exhibited significant antitussive activity, in comparison to controls, which was found to be dose-dependent. At a dose of a few hundred milligrams per kilogram body weight, the extract showed maximum inhibition of the cough reflex at 90 min post-administration, and its antitussive activity was comparable to that of codeine phosphate, a standard antitussive agent (Mazumder et al., 2007).

4.46 Lannea Anacardiaceae 4.46.1 Taxon: Lannea coromandelica (Houtt.) Merr. Synonym: Dialium coromandelicum Houtt. Common name: jhingangummi [German]. Distributional range (native): ASIA, TEMPERATE-China: China - Guangdong, Guangxi, Yunnan. ASIA, TROPICAL-Indian Subcontinent: Bangladesh, Bhutan, India-Arunachal Pradesh, Assam, Bihar, Gujarat, Himachal Pradesh, Jammu and Kashmir, Karnataka, Kerala, Madhya Pradesh, Maharashtra, Meghalaya, Orissa, Rajasthan, Sikkim, Tamil Nadu, Tripura, Uttar Pradesh, West Bengal, Nepal, Pakistan, Sri Lanka; North Indian Ocean: India-Andaman and Nicobar; Indo-China: Cambodia, Laos, Myanmar, Thailand, Vietnam (USDA, ARS, National Genetic Resources Program, 2008). Gum (common names): jeol gum (Smith and Montgomery, 1959), jhingan gum (Soni, 1995), modal gum (Parikh et al., 1956a,b). Exudate properties: L. coromandelica gum occurs as a natural exudation or by tapping. The natural exudate contains considerable amounts of impurities which usually consist of bark and leaves, or in some cases soil matter (Mukherjee and Banerjee, 1948a). The gum can exude frequently as a result of boring larval insects, in which case it may be faulted by excreta from the insect’s tunnels (Gamble, 1922). It appears as irregular, rounded or angular pieces—sometimes large and brittle or friable due to the presence of numerous cracks. Tannin from the bark may contaminate the gum (Howes, 1949). The gum of L. coromandelica (Fig. 4.38) is initially white in color, changing to brownish-black with age (Parikh et al., 1956a). The gum swells in water but dissolves completely with time (Parikh et al., 1956a). Fresh gums of L. coromandelica are readily miscible in water, whereas old dry gum exudates are only slightly miscible (Mukherjee and Banerjee, 1948a); the latter, when kept in contact with water for several days, give a uniform solution (Mukherjee and Banerjee, 1948b). The gum forms a somewhat glairy, tasteless mucilage with good adhesive properties. Aqueous solutions of the gum are similar in their properties to solutions of gum arabic. Solubility decreases with age (Smith and Montgomery, 1959). Gum chemical characteristics: The gum of Lannea humilis (Oliv.) Engl. contains galactose (75%), arabinose (11%), rhamnose (2%) and uronic acids (12%) (Anderson and Hendrie, 1972). The gum of L. coromandelica contains D-galactose (70%), L-arabinose (11%), L-rhamnose (2%) and uronic acids (17%) (Anderson and Hendrie, 1973). It contains approx. 1% acyl groups (Jefferies et al., 1977). The molecules of both gums are very highly branched. Their galactan framework consists of short chains of β (1-3)-linked D-galactose residues, branched and interspersed with β (1-6) linkages. Either single D-galactose end groups of short side chains of D-galactose or L-arabinose residues and three aldobiouronic acids attach to positions 3 and 6 of this framework.

220  ◾  Plant Gum Exudates of the World

Figure 4.38  The gum of Lannea coromandelica (mag. 3x; courtesy of the Royal Botanic Gardens, Kew; Cat. No. 61901).

A possible structural fragment that shows these features was proposed by Anderson and Hendrie (1972, 1973). The weight-average molecular weight found for Lannea humilis gum was 257,000 (Anderson and Hendrie, 1972) and for L. coromandelica, 168,000 in one case (Bhattacharyya and Mukherjee, 1964) or 17.5 million (Chaudhuri and Mukherjee, 1967), an unusually high value for an acidic gum exudate. Previous analytical, structural and practical studies of Lannea gums (Fig. 4.39) have been published by: Chaudhuri and Mukherjee, (1969a); Chaudhuri et al., (1969b); Mukherjee (1948); Mukherjee and Chakravarti (1948); Mukherjee, (1953); Mukherjee et al. (1953); Mukherjee and Choudhury, (1953); Mukherjee and Rohatgi (1948a); Mukherjee and Rohatgi, (1948b); Mukherjee and Sinha (1953); Parikh et al. (1956a,b); Bhattacharyya and Mukherjee (1964); Bhattacharyya and Rao (1964); Chaudhuri and Mukherjee (1967); Ramachandran and Joshi (1968), and Anderson and Hendrie (1970). Commercial availability of the gum (pure state): The gum of L. coromandelica is a partial substitute for Machilus macrantha (Jigat) bark as an adhesive in the manufacture of agarbatti. It is also used medicinally in asthma and rheumatism (Parikh et al., 1956a). In India, it has been used in “Caligo” printing and as a paper size in Nepal (Howes, 1949; Whistler and Smart, 1953). It has been used in many parts of India as a nutritive food, especially following puerperal fever in women (Mukherjee and Banerjee, 1948a). It is used locally in Sri Lanka (http://www.fao.org/docrep/008/ af349e/af349e06.htm). The gum of Lannea acida is eaten by the natives (Dalziel, 1936). Commercial and functional uses for other parts of the tree: It is used as an avenue-lining tree in Java. Bark, leaves and fruits are useful in medicinal preparations. The bark yields a dye used for fish nets. The leaves are used as fodder for cattle. The tree is valued for its heartwood. Chlorophyll a, chlorophyll b and carotenoid can be located in leaves of L. coromandelica, Asparagus racemosus, Boswellia serrata, Dolichondrone falcata, Grewia tiliaefolia, Rhus

Minor Plant Exudates of the World  ◾  221

Figure 4.39  Lannea gum (mag. 1.5x; courtesy of the Royal Botanic Gardens, Kew; Cat. No. 61906).

mysurensis, Securinega virosa, Wrightia tinctoria and Zizyphus glabrata, all important medicinal plants. The highest amount of these compounds was observed in the leaves of S. virosa, in all seasons (Kadam et al., 2008).

4.47 Macrozamia Zamiaceae 4.47.1 Taxon: Macrozamia spiralis (Salisb.) Miq. Synonym: Zamia spiralis Salisb. Economic importance: Environmental: ornamental. Distributional range (native): AUSTRALASIA- Australia: Australia - New South Wales (USDA, ARS, National Genetic Resources Program, 2008). Exudate properties: Gum has been documented from several Australian species of Macrozamia. The exudate of M. spiralis (“burrawong”) is clear, dark brown and forms in small and large tears (Howes, 1949; Kennedy, 1996).

4.48 Melia Meliaceae 4.48.1 Taxon: Melia azedarach L. Synonyms: Melia azedarach var. japonica (G. Don) Makino; Melia toosendan Siebold & Zucc. Common names: chinaberry, Persian lilac, Sichuan pagoda-tree, syringa berrytree, bessieboom syringe [Afrikaans], maksering [Afrikaans], chuan liang zi [Transcribed Chinese], arbre à

222  ◾  Plant Gum Exudates of the World

chapelets [French], lilas des Indes  [French], indischer zedrachbaum [German], persischer flieder  [German], sendan [Transcribed Japanese], amargoseira-do-Himalaio [Portuguese], cinamomo [Portuguese (Brazil)], sabonete-de-soldado [Portuguese (Brazil)], melia [Spanish], paraíso [Spanish]. Economic importance: Environmental: ornamental. Materials: beads, wood. Medicine: folk medicine. Non-vertebrate poisons: potential for plant pest control. Vertebrate poisons: mammals. Weed: potential seed contaminant. Distributional  range (native): ASIA, TEMPERATE-China: China [tropical]; Eastern Asia: Japan-Kyushu, Ryukyu Islands, Shikoku. ASIA, TROPICAL-Indian Subcontinent: India, Sri Lanka; Malesia: Indonesia - Irian Jaya, Lesser Sunda Islands, Papua New Guinea. AUSTRALASIA-Australia: Australia [tropical]. PACIFIC-Southwestern Pacific: Solomon Islands. OTHER: naturalized in southern Europe, Africa, United States (including Hawaii), Mexico, tropical South America, West Indies, and Galapagos Islands (USDA, ARS, National Genetic Resources Program, 2008). Gum (common names): neem gum (Setia, 1984), kohomba gum (Sri Lanka) (http://www.fao. org/docrep/X5334e/x5334e0a.htm). Exudate properties: In trees (Fig. 4.40) growing in dry areas, the gum is produced very freely (Fig. 4.41). In wet climates, the gum is liable to be washed away or spoiled before it can be collected. It appears in large tears, nodules or vermiform pieces, generally around a wounded

Figure 4.40  Melia azedarach tree (courtesy of Forest & Kim Starr).

Minor Plant Exudates of the World  ◾  223

A

Figure 4.41  (A) Melia azedarach tree oozing gum. (B) M. azedarach exudate (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 63043).

224  ◾  Plant Gum Exudates of the World

area. The gum is usually cracked on the surface. The best-quality gum is found in dry areas (Howes, 1949). Gum cavities are associated with gum formation in the young stem. Gum is formed in a cavity as a result of the breakdown of cells lining the cavity. Bacteria have also been located in these cavities (Setia, 1984). The exudate is clear, pale-yellow to amber or light brown. It may darken to brown with age (Howes, 1949; Mukherjee and Srivastava, 1955). It dissolves freely in water, giving a light brown viscous solution (Mukherjee and Srivastava, 1955; Narayan and Pattabiraman, 1973). It is inferior to gum arabic in its adhesive properties (Howes, 1949). Gum chemical characteristics: The gum is a highly branched polysaccharide, composed of L-arabinose, L-fucose, D-galactose, and D-glucuronic acid, with the ratio of D-galactose to L-arabinose being 3:2 (Mukherjee and Srivastava, 1955). Other structural and chemical features have been studied by Lakshmi and Pattabiraman (1967), Anderson and Hendrie (1971), and Narayan and Pattabiraman (1973). Similar gums: gum arabic (Howes, 1949), gum ghatti (Mantell, 1947). Commercial availability of the gum (pure state): The gum of M. azedarach was once traded in the Bombay markets. It is sometimes mixed with other East Indian gums (Mantell, 1947) and sometimes sold as gum arabic. It has been in pharmaceutical use in India for many centuries (Smith and Montgomery, 1959). In Sri Lanka, it is used as an adhesive (http://www.fao.org/ docrep/X5334e/x5334e0a.htm). It is also used as a dye in textiles and traditional medicines. Commercial and functional uses for other parts of the tree: M. azedarach is the source of a wide variety of products including adhesives, beauty aids, fertilizers, herbs, lumber, pesticides (oil) and numerous pharmaceuticals. These products are variously derived from the bark, leaves and seeds. The leaves are also used as cattle feed. Its cultivation for firewood has been limited. The tree also produces small edible fruit (Tewari, 1992; Conrick, 1994). The antimicrobial activity of leaf and callus extracts of M. azedarach was tested on in-vitro shoot cultures of the peach rootstock ‘MRS 2/5’ (Prunus cerasifera x Prunus spinosa) that were heavily contaminated with Sphingomonas paucimobilis and Bacillus circulans (Marino et al., 2009). The undiluted leaf extract showed bactericidal activity on plated isolates. Furthermore, as a 10% supplement, it was the best treatment for ridding contaminated cultures of B. circulans, while 20% extract was needed to eliminate S. paucimobilis, and could induce higher growth and proliferation rates in surviving shoots than untreated cultures. The callus extract was ineffective. The bactericidal activity of the leaf extract appeared to be due to a synergistic effect of azadirachtin with other unidentified compounds present in the extract (Marino et al., 2009).

4.49 Melicope Rutaceae 4.49.1 Taxon: Bouchardatia neurococca (F. Muell.) Baill. Synonym: Melicope neurococca (F. Muell.) Benth. Geographic distribution: Found from the Hastings River, New South Wales, to Maryborough in Queensland. Exudate appearance: The gum exudes in large tears or globular masses. Similar gums: The gum of B. neurococca is said to closely resemble the gums of Geijera paniculata (F.Muell.) Druce (syn. Geijera muelleri Benth.) and Pentaceras australis (F. Muell.) Benth. (Howes, 1949; Maiden and Smith, 1895).

Minor Plant Exudates of the World  ◾  225

4.50 Moringa Moringaceae 4.50.1 Taxon: Moringa oleifera Lam. Synonyms: Guilandina moringa L.; Moringa moringa (L.) Small; Moringa pterygosperma Gaertn. Common names: ben oil tree, benzolive tree, drumstick tree (Fig. 4.42), horseradish tree, moringa, néverdié, West Indian ben, ben ailée [French], moringa ailée [French], mouroungue [French], pois quénique [French], meerrettichbaum [German], moringueiro [Portuguese], muringueiro [Portuguese], quiabo-da-quina [Portuguese (Brazil)], maranga [Spanish], paraíso [Spanish], paraíso blanco [Spanish]. Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: India, Pakistan. OTHER: cultivated elsewhere (USDA, ARS, National Genetic Resources Program, 2008). Gum (common names): moringa gum (Mantell, 1947), drumstick gum (Smith and Montgomery, 1959), sajna gum (Bhattacharya et al., 1982). Exudate properties: The gum (Fig. 4.43) is produced freely in tear form, especially as a result of insect attack (Howes, 1949; Ingle and Bhide, 1954). The exudate color is initially white and changes to mahogany, reddish-brown or brownish-black on the surface when exposed to air (Greenway, 1941; Howes, 1949; Ingle and Bhide, 1954; Smith and Montgomery, 1959). It is sparingly soluble in water, but swells enormously to give highly viscous solutions at low A

Figure 4.42  Moringa oleifera. (A) Drumstick tree habit, (B) flowers, (C) pods and seeds (courtesy of Forest & Kim Starr).

226  ◾  Plant Gum Exudates of the World

B

C

Figure 4.42  (Continued).

concentrations. The viscous solution gellifies when 10% of the following reagents are added to it: iodine in potassium iodine, mercuric chloride, ammonium molybdate, ferric chloride, and lead acetate (Ingle and Bhide, 1954). Gum chemical characteristics: The exudate is assumed to be a mixture of gum and resin. The gum consists of L-arabinose, D-galactose and D-glucuronic acid, L-rhamnose, D-mannose, and D-xylose in the molar ratios of ∼14.5:11.3:3:2:1:1. A tentative structure was assigned to the average repeating unit of the gum (Bhattacharya et al., 1982; Das and Banerji, 1982). No acetyl groups were found in the gum, although 2% sodium hydroxide solutions were found to significantly reduce its viscosity (Ingle and Bhide, 1954). Upon treatment with 10% sulfuric acid, the gum precipitated with a fibrous material (presumably cellulose), amounting to 5.3% of the gum (Smith and Montgomery, 1959).

Minor Plant Exudates of the World  ◾  227

Figure 4.43  Moringa oleifera gum.

Similar gums: Moringa gum resembles tragacanth in its hydrocolloidal properties (Howes, 1949; Dange and Nikore, 1970). Commercial availability of the gum (pure state) and applications: The gum has been used in calico printing (batik dyeing) (Mantell, 1947), as a bland-tasting condiment (http://www. echonet.org/shopsite_sc/store/html/MiracleTree.html), and mixed with sesame oil to relieve headaches. It is also poured into the ears for the relief of earache. In India, it is used for dental caries and to treat syphilis and rheumatism. In India and Senegal, it is considered useful in treating fevers, dysentery and asthma. It is used as an astringent and rubefacient (skin tonics). In Java, it is given for intestinal complaints (Kirtikar and Basu, 1935; http://www. churchworldservice.org/moringa/TMTmeds.html). Commercial and functional uses of other parts of the tree: Young roots are scraped and used by the natives as “horseradish”. Leaves are used in vegetable curries and in pickling. Unripe pods are used as a curry vegetable, boiled and sliced like beans. Flowers and bark

228  ◾  Plant Gum Exudates of the World

are used in native medicine. The seeds yield valuable oil for use in artist’s paints, salad oil and soap. They can be eaten boiled or fried when still green. The timber is suitable for pulp, cellophane or rayon. Isolation of bioactive compounds from the roots of M. oleifera, a traditional herb in southeast Asia, yielded a rare aurantiamide acetate compound and a 1,3-dibenzyl urea compound. These compounds were characterized and found to inhibit the production of TNF-alpha and IL-2. Furthermore, the 1,3-dibenzyl urea compound exhibited significant analgesic activity in a dose-dependent manner. These findings may help in understanding the mechanism controlling activated mast cells in inflammatory conditions such as arthritis, for which the crude extract has been used (Sashidhara et al., 2009).

4.51 Owenia Meliaceae 4.51.1 Taxon: Owenia venosa F. Muell. Common names: crow apple, rose almond. Geographic distribution: Endemic to Australia—New South Wales (Owenia cepiodora F. Muell.); from the New South Wales border to Rockhampton, Queensland. Locally found in Brisbane Forest Park and Brookfield (Owenia venosa F. Muell.). Commercial and functional uses for other parts of the shrub: O. venosa’s hard reddish timber is useful for floorboards and fancy turnery (Howes, 1949). The seeds of Owenia acidula and O. venosa were found to contain a simple limonoid and a derivative of the cyclopropane protolimonoid glabretal (Mulholland and Taylor, 1992).

4.52 Panax (Tieghemopanax) Araliaceae 4.52.1 Taxon: Polyscias elegans (C. Moore & F. Muell.) Harms Synonym: Panax elegans C. Moore & F. Muell.

4.52.2 Taxon: Neopanax colensoi (Hook. f.) Allan Synonym: Panax colensoi Hook. f. The exudates: The Australian gums of P. sambucifolia, P. elegans and Polyscias murrayi (F. Muell.) Harms generally bear a resemblance to gum arabic in appearance, but are not completely soluble and may be scented. N. colensoi in New Zealand also yields gum (Howes, 1949).

4.53 Saltera Penaeaceae 4.53.1 Taxon: Saltera sarcocolla (L.) Bullock Synonym: Penaea sarcocolla L. Common name: gum saracocolla (Howes, 1949). Geographic distribution: Central and South Africa.

Minor Plant Exudates of the World  ◾  229

Exudate properties: A gum-resin that exudes in rounded, sponge-like grains that are quite friable, and often found in agglutinated masses. Fine hairs are often found intermixed with it. It has no odor, except upon heating when it emits an odor of burning sugar, but it has an insipid and sweetish taste, followed by a bitter-like acidity. The taste has been compared to that of liquorice root (Felter and Lloyd, 1898). The exudate is yellowish, reddish or brownish. The gum is mostly water-soluble. In alcohol it is nearly wholly soluble, the residue consisting of impurities (Felter and Lloyd, 1898). Gum chemical characteristics: A resin portion is separated from the gum by extraction in ether. Sarcocollin (C13H23O6) is extracted by alcohol from the residual gum (Felter and Lloyd, 1898). Commercial availability of the gum (pure state): The sarcocollin extract is used for Sarcocolla. This drug is now used in medicine, but was formerly used to heal wounds, check otorrhoea, and as an application for scrofulous enlargements and chronic articular inflammations. It has also been extracted from gum tragacanth (Felter and Lloyd, 1898).

4.54 Pentaceras Rutaceae 4.54.1 Taxon: Pentaceras australis (F. Muell.) Benth. Common names: scrub hickory, crow’s ash. Geographic distribution: Australia. Exudate appearance: Large tears or globular masses. Similar gums: Gums of Geijera muelleri and Melicope neurococca.

4.55 Prunus Rosaceae 4.55.1 Taxon: Prunus dulcis (Mill.) D. A. Webb Synonyms: Amygdalus communis L.; Amygdalus dulcis Mill.; Prunus amygdalus Batsch; Prunus communis (L.) Arcang.; Prunus dulcis var. amara (DC.) Buchheim. Common names: almond, bitter almond, sweet almond, bian tao [Chinese], amandier [French], amandier commun [French], mandel [German], mandelbaum [German], bittermandelbaum [German], amendo [Japanese], amendoeira [Portuguese], amêndoa-amarga [Portuguese (Brazil)], amêndoa-doce [Portuguese (Brazil)], almendro [Spanish]. Economic importance: Food: additive, flavoring, bee plants. Human food: nut, materials, lipids. Medicine: folk medicine. Vertebrate poisons: mammals. Distributional range (native): ASIA, TEMPERATE-Arabian Peninsula: Saudi Arabia. Western Asia: Israel, Jordan, Lebanon, Syria, Turkey. OTHER-cultivated and naturalized in Mediterranean region and temperate Asia (USDA, ARS, National Genetic Resources Program, 2008). Exudate properties: Almond gum is colorless or pale yellow to amber-brown. The gum of Prunus dulcis is only 10% soluble in water (Smith and Montgomery, 1959). The gum of the wild almond Prunus eburnea (Spach) Aitch. is reported to be water-soluble (Howes, 1949). The gum exudes and is collected during the autumn from the trunk and larger branches of old almond trees and thus the harvest does not cause severe damage. The production of gum reduces the number of leaves and flowers (Smith and Montgomery, 1959). It exudes as small

230  ◾  Plant Gum Exudates of the World

tears agglomerated into larger masses (Butler, 1911). The fungus Botryosphaeria dothidea is known to attack P. dulcis trees, among many others. In studying the effects of the fungi on healthy plants, a variety of inoculation procedures were used, with differing results. B. dothidea was extremely virulent when almond branches were inoculated in spring, summer or fall, but only mildly virulent when inoculations were performed in winter. Interestingly, the almond varieties “Ne Plus Ultra” and “Mission” appear to have some resistance to the fungus (English et al., 1975). Almond gum resembles the gums exuded by other Prunus trees in physical properties and appearance. Studies on gum-duct development in the fruits of the almond tree can be found elsewhere (Morrison and Polito, 1985). Gum chemical characteristics: Almond gum is described as the salt of an acidic polysaccharide whose acid groups are neutralized with calcium, iron and potassium. Its molecular structure has not yet been fully characterized. Upon heating an aqueous solution of the gum acid, autohydrolysis is effected and all L-arabinose and D-xylose residues are liberated, leaving a degraded gum nucleus that is relatively stable to acid. Hydrolysis of the degraded gum yields D-galactose (2 moles) and 6-O-(β-D-glucopyranosyluronic acid)-D-galactose (1 mole). Isolation of the latter in high yields suggests that it is the only aldobiouronic acid present in the gum. Hydrolysis of the methylated gum has led to the identification of 2,3,5-tri-O-methyl-L-arabinose, indicating that L-arabofuranose residues are present as end groups (Smith and Montgomery, 1959). Commercial availability of the gum (pure form): In Syria, almond gum is used in the local confectionery industry in combination with plum gum exudates. It is sold as Syrian gum or Carmania. In India, almond gum is sometimes mixed with gum arabic, ghatti and tragacanth to form the irregular ‘East Indian gums’ (Mantell, 1947). In Iran, it is collected in the Zagross region as well as in southern Khorasan, Sistan and Baluchistan, where its main applications are in the manufacturing of industrial glues. Wild almond gum is the only gum in Iran whose harvest is not subjected to any form of legal restrictions or limitations and the harvesters’ work is not controlled. This gum is exported to European countries. In 1934, 540 tons of wild almond (P. eburnea) were exported from Iran (compared to 1,100 tons of gum tragacanth) (Manoochehri, 1995).

4.56 Pseudocedrela Meliaceae 4.56.1 Taxon: Pseudocedrela kotschyi (Schweinf.) Harms. Synonyms: Cedrela kotschyi Schweinf.; Pseudocedrela chevalieri C.DC.; Soymida roupalifolia Schweinf. (http://www.aluka.org/). Geographic distribution: Dry forests of West Africa. The tree: A large timber tree, commonly 6 to 9 m high, sometimes up to 18 m high and 1.8 m in girth, with a gray fissured bark, panicles of fragrant white flowers, silvery gray foliage when young, and erect fruits that often grow in clusters in heavy soils. Exudate properties: The exudate appears as pale yellow to yellowish-brown tears (Howes, 1949). The gum has good solubility, yielding an almost tasteless, yellowish-brown, somewhat turbid mucilage (Howes, 1949; Anderson and Weiping, 1990). Gum chemical characterisitics: The gum has very low arabinose and rhamnose contents and its amino acid composition is high in hydroxyproline and serine, which are more commonly associated with Acacia and other genera within the Leguminosae (Anderson and Weiping, 1990). Commercial availability of the gum (pure state): Medicinal use of the gum by natives in West Africa has been reported, as well as its use as a poison applied to arrows (Greenway,

Minor Plant Exudates of the World  ◾  231

1941). The antimicrobial activity of sequential n-hexane, acetone and 50% aqueous methanol extracts of leaves, stem bark and roots of four species of medicinal plants, Cassia sieberiana, Haematostaphis barteri, Mitragyna inermis and Pseudocedrela kotschyi from Ghana, were tested against Bacillus subtilis, Pseudomonas syringae and Cladosporium herbarum. Extracts of all four plant species gave positive results against at least one test organism. Preliminary chemical analysis revealed the presence of flavonoids, stilbenes and alkaloids (Asase et al., 2008).

4.57 Saccopetalum Annonaceae 4.57.1 Taxon: Miliusa tomentosa (Roxb.) J. Sinclair Synonym: Saccopetalum tomentosum (Roxb.) Hook. f. & Thomson Common names: umbia, humb (Indian name). Gum (common name): karee gum. Geographic distribution: Occurs in India, in Oudh and southwards throughout the peninsula. Exudate properties: The gum is pale yellow. Similar gums: M. tomentosa gum resembles gums such as tragacanth and the gum of Cochlospermum religiosum (Hogg gum) in its hydrocolloidal properties. Commercial and functional uses for other parts of the tree: The fruits are edible. The wood, though suited for heavy construction, is seldom used (http://ignca.nic.in/cd_07013.htm).

4.58 Sarcostemma Asclepiadaceae 4.58.1 Taxon: Sarcostemma brevistigma Wight & Arn. Common names: soma [Sanskrit], somlata [Hindi]. Geographic distribution: Various parts of India. It is found in dry rocky places in Bihar, Bengal, Konkan, Deccan, Tamil Nadu, Maharashtra, and Kerala. The shrub: This Asclepiad is a leafless, jointed and fleshy climbing plant. The gum: A clear pale yellow gum which has no recognized uses (Howes, 1949). Medicinal properties: S. brevistigma has been found to be active as an antirheumatic, antiallergen, antiemetic and bronchodilator. Phytochemical studies have revealed the presence of bergenin, brevine, brevinine, sarcogenin, sarcobiose and flavonoids (Oberai et al., 1985). The aerial parts of this plant are reported to contain pregnane glycosides with 2-deoxy sugars (Oberai et al., 1985). A fraction of this plant’s extract has been reported to have antiallergenic and anti-inflammatory activities. It also inhibits the contractions induced by acetylcholine and histamine on isolated guinea pig ileum, and has bronchospasmolytic activity (Kumar et al., 2007).

4.59 Schefflera Araliaceae 4.59.1 Taxon: Schefflera volkensii Harms Synonym: Heptaleurum volkensii Harms. Common name: schefflera. The generic name honors G. Scheffler, a German botanical collector in Tanzania, Rowanda and Burundi in around 1900.

232  ◾  Plant Gum Exudates of the World

Geographic distribution: Locally common in mountain evergreen forests in East Africa (Howes, 1949). Native: Burundi, Ethiopia, Kenya, Rwanda, Tanzania, Uganda. The tree: S. volkensii is a scandent or tall tree which can reach 24 to 30 m. From time to time, it can grow as an epiphyte on other trees. It can be used for erosion control since it protects the surrounding soil from water erosion. The tree provides light shade and its leaves provide good mulching material, effective at improving soils. S. volkensii has an impressive form and can therefore be used for ornamental purposes. It can be grown with crops since its high crown lets in sunlight (Lisanework and Mesfin, 1989). Commercial availability of the gum (pure form) and the tree: The gum is mixed with honey and used as a remedy in Kenya. The gum has been used by some tribes to treat colds, cough and lung troubles (Greenway, 1941). S. volkensii provides good-quality fuelwood, and its timber can be used for a number of general purposes.

4.60 Sclerocarya Anacardiaceae 4.60.1 Taxon: Sclerocarya birrea (A. Rich.) Hochst. Subordinate taxa: Sclerocarya birrea subsp. birrea, Sclerocarya birrea subsp. caffra Synonyms: Sclerocarya caffra Sond. [≡ Sclerocarya birrea subsp. caffra]; Spondias birrea A. Rich. [≡ Sclerocarya birrea subsp. birrea]. Geographic distribution: A common tree in many dry areas throughout tropical Africa. Native to Zaire, Ethiopia, Kenya, Tanzania, Angola, Malawi, Mozambique, Zambia, Zimbabwe, Botswana, Cape Province, Caprivi Strip, Namibia, Natal, Swaziland, Transvaal, Madagascar. Exudate properties: The clear and nearly colorless gum (Greenway, 1941) exudes from the stem and becomes brittle and friable when dry (Greenway, 1941), but is readily dissolved in cold water (Anderson and Weiping, 1990). Trees growing in Israel exude gum from unripe fruits. The gum exudes in small vermiform pieces of up to 0.5 cm in length. The exudation may occur due to stressful weather conditions, but also as a natural protection against flying insects that tend to adhere to the gum when it is moist and sticky. Gum chemical characteristics: It has very low arabinose and rhamnose contents and its amino acid composition is high in hydroxyproline and serine which are more commonly associated with Acacia and other genera within the Leguminosae (Anderson and Weiping, 1990). Commercial availability of the gum (pure state): It is used locally in West Africa to make ink by mixing with soot and water (Howes, 1949). The San people from the Kalahari desert in Namibia and Botswana use the gum to apply the poisonous larvae of a small beetle (Polyclada spp.) to the tips of their hunting arrows. Commercial and functional uses for other parts of the tree: The fruits are edible, and are also used for beverage liquer. The bark and leaves have medicinal and cosmetic uses. The antifungal activity of S. birrea, which is used in South African traditional medicine for the treatment of skin diseases, was evaluated against three yeasts: Candida parapsilosis, Cryptococcus albidus and Rhodoturula mucilaginosa. S. birrea bark was extracted with hexane, dichloromethane, chloroform, ethyl acetate, acetone, methanol and ethanol and tested against these three yeasts (Masoko et al., 2008). Results suggested that the plant be further explored for possible antifungal agents and provided preliminary scientific validation of the

Minor Plant Exudates of the World  ◾  233

traditional medicinal use of this plant (Masoko et al., 2008). Another study reported that an ethanolic extract of S. birrea stem bark modulates blood glucose, glomerular filtration rate and mean arterial blood pressure of induced diabetic rats (Gondwe et al., 2008).

4.61 Semecarpus Anacardiaceae 4.61.1 Taxon: Semecarpus anacardium L. f. Common names: marking nut tree (because it was used by washermen to make a water-insoluble mark on clothes before washing), phobi nut tree, varnishtree anacarde d’Orient [French], ostindischer tintenbaum [German] (USDA, ARS, National Genetic Resources Program, 2008). Economic importance: Environmental: ornamental. Medicine: folk medicine. Vertebrate poisons: mammals. Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: India, Nepal. OTHER-cultivated elsewhere (USDA, ARS, National Genetic Resources Program, 2008). The tree: S. anacardium is a deciduous tree. The nut is about 2.5 cm long, ovoid and a smooth, lustrous black color. Exudate properties: The tree exudes a dark or blackish gum (Fig. 4.44) or gum-resin (Howes, 1949). The gum-resin exuding from the bark is used to treat leprosy, venereal infections and nervous debility. It is also used as an abortifacient and a vermifuge (http://www.indmedplants kr.org/SEMECARPUS_ANACARDIUM.HTM).

Figure 4.44  Semecarpus anacardium gum (mag. 2x; courtesy of the Royal Botanic Gardens, Kew; Cat. No. 62163).

234  ◾  Plant Gum Exudates of the World

Commercial and functional uses for other parts of the tree: In Ayurveda, the fruit is considered a rasayana—a rejuvenating compound that imparts longevity, and it is processed before use as it is toxic in nature. Recent studies have shown the fruit to be a good anti-inflammatory agent and effective in various types of cancers (Puri, 2003). The Indian system of medicine makes use of several medicinal plants with proven beneficial claims towards hyperlipidemia, inflammation and obesity, which are all closely related to atherosclerosis. BHUx is a novel polyherbal formulation consisting of five medicinal plants, among them Terminalia arjuna and S. anacardium. The formulation was found to have antioxidant, anti-inflammatory, hypolipidemic and antiproliferative properties (Tripathi, 2009). Another study demonstrated the antioxidant activity of various extracts of S. anacardium nuts in vitro: petroleum ether and ethanol extracts showed the highest antioxidant activity among the nut extracts tested. The antioxidant activities of the extracts were found to be identical in magnitude and comparable to those of standard antioxidant compounds. The antioxidant activities of the extracts were concentration-dependent (Pal et al., 2008). The tree resembles the cashew nut tree in having edible nut kernels. Juice from the nut is used for various medicinal applications. The bruised nut, in addition to the gum, is used as an abortifacient and a vermifuge. The juice of the nutshell is known in the trade as Bhiloawan shell liquid, and is rich in phenols. The non-vesicant form of the juice is used in the paint industry and in waterproofing.

4.62 Sloanea Elaeocarpaceae 4.62.1 Taxon: Sloanea woollsii F. Muell. Synonym: Echinocarpus australis Benth. Common names: yellow carabeen, carribin, grey carrobean, carabeen. The tree: Large tree with plank buttresses sometimes extending 2 to 5 m up the trunk. The new foliage is light green with elliptic to lanceolate leaves. Peduncles are 2 to 3 cm long, petals are absent, and there are ca. 24 stamens. The capsule is ovoid, 10 to 20 mm long, prickly, woody, opening via two valves; there are one or two black seeds covered by a red aril (http:// plantnet.rbgsyd.nsw.gov.au/). Geographic distribution: New South Wales and Queensland. The gum: The large buttressed tree yields gum (Howes, 1949).

4.62.2 Taxon: Sloanea australis F. Muell. Common names: maiden’s blush, blush alder, blush carrabeen, blush carrobean, cudgerie. Geographic distribution: Occurs in New South Wales and Queensland. The tree: The tree is medium-sized, irregularly buttressed, crooked and often with coppice shoots near the base of the trunk; new foliage is often reddish. Leaves are obovate lamina, tapered at the base and then expanding towards the junction with the petiole; the base is more or less cordate, leaf margins are serrated, and both surfaces are glabrous; domatia are absent. The petiole is 5 to 30 mm long but usually short and thick (http://plantnet.rbgsyd. nsw.gov.au/). Exudate properties: On drying, the gum contracts, forming transverse cracks which break with a bright conchoidal fracture. The gum is tough and tasteless (Maiden, 1889). The crude gum swells in cold water to many times its original bulk, reminiscent of sterculia gums. The

Minor Plant Exudates of the World  ◾  235

swollen gum is slightly adhesive. Analysis of the gum shows that the soluble portion is ∼12% while the swelling portion is ∼60%. The rest is mainly moisture and ∼5% ash. This gum does not completely dissolve under continuous boiling (Maiden, 1889). Commercial uses: The gum of S. australis has been used in Australia for the stiffening of straw hats (Howes, 1949). Wood of S. australis is used for construction, and its flowers for decoration.

4.63 Soymida Meliaceae 4.63.1 Taxon: Soymida febrifuga (Roxb.) A. Juss. Synonym: Swietenia febrifuga Roxb. Common name: Indian redwood. Economic importance: Materials: fiber, tannin/dyestuff, wood. Medicine: folk medicine. Vertebrate poisons: mammals. Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: India - Andhra Pradesh, Bihar, Gujarat, Karnataka, Kerala, Madhya Pradesh, Maharashtra, Orissa, Rajasthan, Tamil Nadu, Uttar Pradesh, Sri Lanka (USDA, ARS, National Genetic Resources Program, 2008). The tree: S. febrifuga is an indigenous lofty deciduous medicinal tree, a monotypic genus endemic to India. Exudate properties: The exudate forms as large clear pale yellow to dark brown pieces (Fig. 4.45) (Howes, 1949). The gum forms an adhesive mucilage (Gamble, 1922). Commercial and functional uses for other parts of the tree: S. febrifuga has been used therapeutically for centuries in Indian traditional medicine for the treatment of diseases such as inflammation, diabetes, cancer and wound-healing in tribal communities (Diwan and Singh, 1992). One group claims antiplasmodial activity (Simonsen et al., 2001). The decoction of the bark contains a resinous bitter component that is well adapted for gargles, vaginal infections, enemata, rheumatic swellings, and stomach pain. The bark is said to be used as an anticancer remedy (Ambaye et al., 1971), for blood coagulation, wounds, dental diseases, uterine bleeding and hemorrhage (Yoganarasimhan, 1996) and as an acrid, refrigerant, antihelminthic, aphrodisiac, laxative; it is good for sore throats, removes “vata”, cures ‘tridosha’ fevers, cough and asthma, and acts as an anti-inflammatory (Diwan and Singh, 1992). Hexane, ethyl acetate and methanol extracts of S. febrifuga root callus were checked for their phytochemical constituents and antimicrobial activity. Ethyl acetate extract was found to be most effective. Silica-gel-column chromatography led to the separation and isolation of methyl angolensate (MA) and luteolin7-O-glucoside. These had an antibacterial effect against Bacillus subtilis and Salmonella typhimurium, respectively. In addition, MA exhibited antifungal activity towards Aspergillus niger while luteolin-7-O-glucoside inhibited Alternaria alternata (Chiruvella et al., 2007). Recently, the methanolic and aqueous extracts of the S. febrifuga leaf have been shown to exhibit higher antioxidant activity and total phenolic content than the hexane extract. The higher antioxidant activity of the former extract may be due to its higher total phenolic content. The extracts also showed antibacterial and antifungal activity but the hexane extracts showed little activity compared with the others. The extent of the extracts’ antimicrobial activity was lower than that of the standard antibiotics chloramphenicol and amphotericin B (Reddy et al., 2008). MA, a natural tetranortriterpenoid purified from S. febrifuga, was examined for its anticancer properties. MA was found to inhibit the growth of T-cell leukemia and chronic myelogenous leukemia cells in a time- and dose-dependent manner (Chiruvella et al., 2008).

236  ◾  Plant Gum Exudates of the World

Figure 4.45  Soymida febrifuga gum.

4.64 Tamarindus Fabaceae (subfamily: Caesalpinioideae) 4.64.1 Taxon: Tamarindus indica L. Common names: Indian tamarind, kilytree tamarind, tamarin [French], tamarindier [French], tamarinier [French], tamarinde [German], tamarindenbaum [German], tamarindeiro [Portuguese], tâmara-da-Índia [Portuguese (Brazil)], tamarinda [Portuguese (Brazil)], tamarindo-do-Egito [Portuguese (Brazil)], tamarino [Portuguese (Brazil)], tamarindo [Portuguese (Brazil), Spanish] (USDA, ARS, National Genetic Resources Program, 2008). Economic importance: Food: additive, flavoring. Environmental: ornamental, shade/shelter. Human food: beverage base, fruit. Fuels: charcoal. Materials: beads. Medicine: folk medicine (USDA, ARS, National Genetic Resources Program, 2008). The tree: The tamarind, T. indica, is widespread and renowned in the African and Asiatic tropics (Howes, 1949). T. indica is a medium to large tree inhabiting the dry African savannas but can also be found in the humid tropical plains where the dry season lasts 4 or 5 months. The trees (Fig. 4.46) require a strong dry season to bear fruit. The tree reaches 30 m in

Minor Plant Exudates of the World  ◾  237

A

B

Figure 4.46  Tamarindus indica. (A) Tamarind habit. (B) Tamarind leaves and fruit (courtesy of Forest & Kim Starr).

238  ◾  Plant Gum Exudates of the World

height and is reputed to stay productive for 150 to 200 years. It has a dome-shaped crown and it creates a fine windbreak. The clusters of pale yellow flowers yield curved, rust-colored pods (http://www.css.cornell.edu/ecf3/Web/new/AF/). Exudate properties: The gum is dark (Howes, 1949), and exhibits poor solubility. It swells enormously (Greenway, 1941). It is not regarded as having any special value (Howes, 1949). Commercial and functional uses for other parts of the tree: The fruit pulp is edible, as is the gum from the seeds. It is used as an ornamental shade tree and street-lining tree, and its wood is used for construction (Morton, 1987). Pulp contained within the pods can be utilized as an ingredient in sauces and juices. Each mature tree produces from 100 to 300 kg of pulp. There is large variability in production due to site quality, tree origin, and climate. The pulp contains 8 to 18% tartaric acid. Seed extracts exhibit antimicrobial activity against Escherichia coli and fungicide action due to tamarindineal (5-hydroxy-2-oxohexa-3,5-dienal) (Imbambi et al., 1992). Tamarind fruit pulp extract, which is traditionally used in spices, food components and juices, is rich in polyphenols which have demonstrated anti-atherosclerotic, antioxidant and immunomodulatory activities (Paula et al., 2009), as well as having the potential to modulate neutrophil-mediated inflammatory diseases (Paula et al., 2009). Seeds contain an adhesive or binding agent which may be utilized in paper and textiles. Tamarind xyloglucan, the main constituent of tamarind kernel powder, forms stiff gels and is employed for thickening, stabilizing and gelling in foods (Rao et al., 1999).

4.65 Heritiera Malvaceae This is a small genus of East Asian and Australian timber trees (http://www.onpedia.com/ dictionary/).

4.65.1 Taxon: Heritiera trifoliolata (F. Muell.) Kosterm. Synonym: Tarrietia argyrodendron Benth. Common names: silky elm, ironwood, silver tree. Geographic distribution: Found in New South Wales and Queensland. The gum: The gum of H. trifoliolata (‘Buyong’ or ‘Ironwood gum’ or ‘silky elm gum’) is said to be similar to Sterculia gum (Howes, 1949).

4.66 Terminalia Combretaceae The genus Terminalia is the largest in the sub-tribe Terminaliinae of the tribe Combreteae which belongs to the sub-family Combretoidea of the Combretaceae. It comprises approximately 150 species, some known to yield gum: Terminalia arjuna (Roxb.) Wight & Arn. (Fig. 4.47A); Terminalia bellirica Roxb. (see section 3.4.17.1); Terminalia catappa L.; Terminalia chebula Retz.; Terminalia alata Heyne ex Roth (Fig. 4.47B) (syn: Pentaptera tomentosa Roxb. ex DC.; Terminalia coriacea Wight & Arn.; Terminalia elliptica Willd.; Terminalia macrocarpa Steud; Terminalia tomentosa (Roxb. ex DC.) Wight & Arn.[Fig. 4.47C] (Mantell, 1947); Terminalia crenulata Roth. (Setia, 1981); Terminalia macroptera Guill. & Perr.; Terminalia stuhlmannii Engl., Terminalia superba Engl. & Diels (Limba) (syn: Terminalia altissima A. Chev.) (Howes, 1949); Terminalia sericea Burch. (Anderson, 1974).

Minor Plant Exudates of the World  ◾  239

Common names: arjun [Sanskrit, Bengali and Hindi], vellamatta marutae [Tamil], arjun sadada [Marathi], tellamaddi [Telugu], arjun (Terminalia arjuna), bahera tree (Terminalia bellirica), saja, saj, sea almond tree, tropical almond (Terminalia catappa) (Fig. 4.48) and (Fig. 4.49), myrobalans fruits, hirda fruits, haritaki [Sanskrit and Bengali], harad [Hindi],

Figure 4.47  Exudates of (A) Terminalia arjuna [mag. 2x; Cat. No. 56715], (B) Terminalia alata [mag. 3x; Cat. No. 56712], (C) Terminalia tomentosa [mag. 1.7x; Cat. No. 56771] (courtesy of the Royal Botanic Gardens, Kew).

240  ◾  Plant Gum Exudates of the World

Figure 4.47  (Continued).

karkchettu [Telugu], kadukkaya [Tamil], harade [Marathi] (Terminalia chebula), asan wood, Indian laurel, taukkyan (Burma), sadar, matti, asan, marda (India) (Terminalia alata); silver terminalia (Terminalia sericea), ofram, frake, afara, akom, limba korina (Terminalia superba), Indian almond (Terminalia catappa in Ghana). Geographic distribution: T. arjuna, T. bellirica (Fig. 4.50), T. catappa, T. chebula, T. alata and T. crenulata are widespread in the forests of India, Burma and Sri Lanka at the lower elevations. T. macroptera, T. stuhlmannii, T. superba and T. sericea occur in rain and savanna forests in Africa, and are favored plantation species in West Africa. Exudate properties: Indian Terminalia gums are tapped and exude in the form of large tears with a smooth surface that is free of cracks. They are yellowish to reddish (Mantell, 1947) and usually dark (Howes, 1949). Crystals of calcium oxalate, originating from the bark, are sometimes present in the gum (Howes, 1949). Terminalia gums swell and form a tough, gelatinous mass, with very little dissolution (Howes, 1949). The gums of T. sericea and T. superba are very viscous and dissolve readily to give pale solutions (Anderson and Bell, 1974). Developmental and histochemical studies on gum ducts in T. crenulata were performed by Setia (1981). In Africa, the gum is formed due to the presence of coleopteran larvae that live between the wood and the bark. Terminalia gums serve as food for the forkcrowned lemur (Dominique and Petter, 1980). Gum chemical characteristics: T. tomentosa contains galactose (30%), arabinose (21%), xylose (14.5%), rhamnose (1.5%) and glucuronic acid (33%). It is much more acidic than gums from T. sericea and T. superba (Anderson and Bell, 1974). The gum of T. sericea contains galactose (22%), arabinose (48%), rhamnose (6%), mannose (7%), xylose (6%), galacturonic

Minor Plant Exudates of the World  ◾  241

acid (2.1%), glucuronic acid (1.6%) and 4-O-methylglucuronic acid (7.2%). The gum of T. superba contains galactose (20%), arabinose (51%), rhamnose (5%), mannose (9%), xylose (4%), galacturonic acid (3.1%), glucuronic acid (5.2%) and 4-O-methylglucuronic acid (2.3%). Both gums contain determinable amounts of acetyl groups, but due to their minor A

B

Figure 4.48  Terminalia catappa (A) habit, (B) leaves and flowers. (C) Seeds and (D) trunk (courtesy of Forest & Kim Starr).

242  ◾  Plant Gum Exudates of the World

C

D

Figure 4.48  (Continued).

proportion, the gum solutions do not have a perceptible acetic acid odor (Anderson and Bell, 1974). Similar gums: Terminalia gums are inferior in thickening or adhesive ability to ghatti, karaya and tragacanth gums (Mantell, 1947). Commercial availability of the gum (pure state): Terminalia gums are used as a drug in the northern parts of India (as a demulcent) (http://www.aidsinfonyc.org). They are sometimes mixed with East Indian gums (Mantell, 1947). In India, the gum is eaten by the Santals

Minor Plant Exudates of the World  ◾  243

Figure 4.49  Terminalia catappa exudate (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 56737).

(Gammie, 1902; Setia, 1981). Some Terminalia species (such as T. alata) are sold as gum ghatti. In India, the gum of T. crenulata finds its usefulness as incense and in the preparation of cosmetics (Setia, 1981). The gum of T. sericea is used locally as a food by the Juoasi and Punguvlei tribes (http://www.sigridleger.de). The gum or gum-resin, known as ashanti gum on the Gold Coast is believed to have been largely the product of T. superba (Dalziel, 1936). The gum of T. catappa was evaluated as a commercial gum source in South-Central Ghana (Hayward, 1990). Commercial and functional uses for other parts of the tree: The leaves, bark and fruit have medicinal properties. The wood is very hard and is used to build houses, as well as bullock carts, ploughs etc. It is also considered sacred for making the idols found in temples. The nuts of Terminalia are edible. A recent report examined the effect of an aqueous extract of T. arjuna on the antioxidant defense system in lymphoma. The extract was found to downregulate anaerobic metabolism by inhibiting the activity of lactate dehydrogenase in lymphoma-bearing mice, which was elevated in non-treated cancerous mice (Verma and Vinayak, 2009). Thus, the antioxidant action of this T. arjuna extract may induce an anticarcinogenic effect by reducing oxidative stress concomitant with its inhibition of anaerobic metabolism (Verma and Vinayak, 2009). Ethanol extracts of T. bellirica and T. chebula have been reported to exhibit protective activity against photosensitization-induced oxidation of rat liver mitochondrial lipids. The extracts also afforded excellent protection against iron-mediated lipid peroxidation. The activities of the extracts were primarily due to their constituent phenolics (Bhattacharya et al., 2009).

244  ◾  Plant Gum Exudates of the World

A

Figure 4.50  Terminalia bellirica plant (A), and tree oozing gum (B).

Minor Plant Exudates of the World  ◾  245

4.67 Thevetia Apocynaceae 4.67.1 Taxon: Thevetia peruviana (Pers.) K. Schum. Synonyms: Cascabela peruviana (Pers.) Raf.; Cascabela thevetia (L.) Lippoid; Cerbera thevetia L.; Thevetia neriifolia Juss. ex Steud. Common names: be-still tree, foreigner’s tree, lucky nut, yellow oleander, oléandre jaune [French], nohomālie [Hawaiian], pua, venevene, venevene [Maori (Cook Islands)], adelfa amarilla, cabalonga, chirca, jacapa [Spanish], piti, piti, poupou [Tahitian] (http://www.hear. org/pier/species/Thevetia_peruviana.htm). Geographic distribution: Peru. Now widely cultivated as an ornamental tree in tropical and subtropical areas. The shrub: The scientific name is Thevetia, after André Thévet (1502-1590), French missionary who collected plants in South America (http://www.deserttropicals.com/Plants/Apocynaceae/ Thevetia_peruviana.html). It is an arborescent shrub, with leaves that are linear-lanceolate, acute or sub-obtuse, acute at the base, coriaceous, dark green and somewhat glossy above and paler on their underside. The petiole is very short (3 mm), the blade is 8 to 14 cm long and less than 1 cm wide, and glabrous. Cymes are many-flowered, the calyx is 1 to 1.3 cm long, lobes are acute-acuminate, and the corolla is 5 to 7 cm long, yellow (and rarely, light orange). The fruit is a juicy black drupe, 4 to 5.5 cm wide (http://www.hear.org/pier/species/) (Fig. 4.51). T. peruviana has a preference for fertile, well-drained soils, but can survive in most soils (Csurhes and Edwards, 1998), and can be invasive in dryer sites. Such arborescent shrubs can be located in Fiji freely naturalized in pastures, under coconuts (Smith, 1988), in Hawaii as an ornamental (Wagner et al., 1999) or in New Caledonia (MacKee, 1994), or the Galapagos Islands (McMullen, 1999). Exudate properties: The gum is tasteless, dark-colored, and swells in water. A

Figure 4.51  Thevetia nerifolia tree (A), fruits and heart-shaped seed (B) (courtesy of Shawn Sabrina Murray).

246  ◾  Plant Gum Exudates of the World B

Figure 4.51  (Continued).

Commercial and functional uses for other parts of the tree: T. peruviana is cultivated throughout the tropics as an ornamental shrub or street-lining tree (Howes, 1949). All parts of the plant, particularly the seeds, are poisonous owing to the presence of cardiac glycosides or cardiac toxins which act directly on the heart. Ingestion of these plant parts can lead to death. The whole plant exudes a milky juice which is very poisonous (Eddleston and Haggalla, 2008). In the years 2001 and 2002 at Batticaloa Teaching Hospital in Sri Lanka, 315 postmortems were performed on deaths due to injury: intentional self-harm was responsible for 48.6% of the cases, while T. peruviana was responsible for 33 deaths (Eddleston and Haggalla, 2008). Other cases of fatal self-poisoning with Cerbera manghas fruits were also reported (Eddleston and Haggalla, 2008). In another study, the toxic activities of solvent extract from T. peruviana was examined against larvae of Balanus albicostatus Pilsbry. The toxicity of fat-soluble extracts with non-polar organic solvents was found to be higher than that of polar-solvent extracts (Xiu-Yan and Chang-Yi, 2008).

4.68 Virgilia Fabaceae (subfamily: Faboideae) 4.68.1 Taxon: Virgilia oroboides (P. J. Bergius) T. M. Salter Synonyms: Sophora capensis L.; Sophora oroboides P. J. Bergius; Virgilia capensis (L.) Poir. (USDA, ARS, National Genetic Resources Program, 2008). Distributional range (native): AFRICA-Southern Africa: South Africa - Cape Province (USDA, ARS, National Genetic Resources Program, 2008). The tree: An ornamental tree with lilac (pink to purple) flowers, sometimes cultivated (Howes, 1949). Exudate appearance and uses: Large vitreous tears exude very freely from the bark (Howes, 1949). The exudate (Fig. 4.52) is employd by Bushwomen as a replacement for starch (Howes, 1949).

Minor Plant Exudates of the World  ◾  247

Figure 4.52  Virgilia oroboides exudate (mag. 2x; courtesy of the Royal Botanic Gardens, Kew; Cat. No. 61543).

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254  ◾  Plant Gum Exudates of the World Mukherjee, S. N., and K. K. Rohatgi. 1948b. Studies on gum Jeol (Lannea grandis, Engler). Part VI. Influence of neutral salts on some electrochemical and viscous properties. J. Indian Chem. Soc. 25:531-7. Mukherjee, S. N., and S. K. Sinha. 1953. Studies on gum Jeol (Lannea grandis, Engler). Part IX. Interaction of jeolic acid with non-electrolytes. J. Indian Chem. Soc. 30:647-51. Mukherjee, S., and H. C. Srivastava. 1955. The structure of neem gum. J. Am. Chem. Soc. 77:422. Mukherjee, S. N., Chakravarti, S. C., and R. N. R. Choudhury. 1953. Studies on gum Jeol (Lannea grandis Engler). Part X. The aldobionic acid. J. Indian Chem. Soc. 30:851-8. Mulholland, D. A., and D. A. H. Taylor. 1992. Limonoids from Australian members of the Meliaceae. Phytochemistry 31:4136-66. Muregi, F. W., Ishih, A., Miyase, T. et al. 2007. Antimalarial activity of methanolic extracts from plants used in Kenyan ethnomedicine and their interactions with chloroquine (CQ) against a CQ-tolerant rodent parasite, in mice. J. Ethnopharmacol. 111:190-5. Narayan, V. S., and T. N. Pattabiraman. 1973. Studies on plant gums: Part II – Separation of protein-rich & carbohydrate-rich components of neem (Azadirachta indica) gum. Indian J. Biochem. Biophys. 10:155. Natesan, S., Badami, S., Dongre, S. H., and A. Godavarthi. 2007. Antitumor activity and antioxidant status of the methanol extract of Careya arborea bark against Dalton’s lymphoma ascites-induced ascitic and solid tumor in mice. J. Pharmaceutical Sci. 103:12-23. National Research Council. 2008. Fruits. In Lost crops of Africa. 1996, vol. 3, 41-59. LOCATION: National Research Council. Nordeide, M. B., Hatloy, A., Folling, M., Lied, E., and A. Oshaug. 1996. Nutrient composition and nutritional importance of green leaves and wild food resources in an agricultural district, Koutiala, in Southern Mali. Int. J. Food Sci. Nutr. 47:455-68. Oberai, K., Khare, M. P., and A. Khare. 1985. A pregnane ester diglycoside from sarcostemma-brevistigma. Phytochemistry 24:1341-3. Odeku, O. A., and O. A. Itiola. 1998. Evaluation of khaya gum as a binder in a paracetamol tablet formulation. Pharmacy Pharmacol. Comm. 4:183-8. Odeku, O. A., and O. A. Itiola. 2002. Characterization of Khaya gum as a binder in a paracetamol tablet formulation. Drug Dev. Ind. Pharmacy 28:329-37. Oliveira, L. M. B., Bevilaqua, C. M. L., Costa, C. T. C. et al. 2009. Anthelmintic activity of Cocos nucifera L. against sheep gastrointestinal nematodes. Vet. Parasitol. 159:55-9. Onweluzo, J. C., Obanu, Z. A., and K. C. Onuoha. 1994. Composition of some lesser known tropical legumes. J. Food Sci. Technol.-Mysore 31:307-10. Onweluzo, J. C., Onuoha, K. C., and Z. A. Obanu. 1995. Certain functional properties of gums derived from some lesser known tropical legumes (Afzelia africana, Detarium microcarpum and Mucuna flagellipes. Plant Foods for Human Nutrition 48:55-63. Ouedraogo-Kone, S., Kabore-Zoungrana, C. Y., and I. Ledin. 2006. Behavior of goats, sheep and cattle on natural pasture in the sub-humid zone of West Africa. Livestock Sci. 105:244-52. Pal, D. K., Kumar, S., Chakrabarty, P., and M. Kumar. 2008. A study on the antioxidant activity of Semecarpus anacardium L.f. nuts. J. Natural Remedies 8:160-3. Parikh, V. M., Ingle, T. R., and B. V. Bhide. 1956a. Studies in carbohydrates. Part III. Investigation of modal gum (Lannea grandis). J. Indian Chem. Soc. 33:119-21. Parikh, V. M., Ingle, T. R., and B. V. Bhide. 1956b. Studies in carbohydrates. Part IV. Investigation of modal gum (Lannea grandis). Structure of the aldobionic acid. J. Indian Chem. Soc. 33:125-8. Parmar, C., and M. K. Kaushal. 1982. Cordia oblique. In Wild fruits, 19-22. New Delhi: Kalyani Publishers. Parsons, I. C., Gray, A. I., Waterman, P. G., and T. G. Hartley. 1993. New triterpenes and flavonoids from the leaves of Bosistoa brassii. J. Nat. Prod. 56:46-53. Paula, F. S., Kabeya, L. M., Kanashiro, A., de Figueiredo, A. S.., Azzolini, A. E., Uyemura, S. A., and Y. M. Lucisano-Valim. 2009. Modulation of human neutrophil oxidative metabolism and degranulation by extract of Tamarindus indica L. fruit pulp. Food Chem. Toxicol. 47:163-70. Puckhaber, L. S., and R. D. Stipanovic. 2001. Revised structure for a sesquiterpene lactone from Bombax malbaricum. J. Nat. Prod. 64:260-1. Puri, H. S. 2003. RASAYANA: Ayurvedic herbs for longevity and rejuvenation, 74-79. London: Taylor & Francis.

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256  ◾  Plant Gum Exudates of the World Smith, F., and R. Montgomery. 1959. The chemistry of plant gums and mucilages, 298, 305-6, 315-316. New York: Reinhold Pub. Corp. Soni, P. L. 1995. Some commercially important Indian gum exudates. Indian Forester 121:754-9. Sreeramulu, K., Rao, K. V., Venkata Rao C., and D. Gunasekar. 2001. A new naphthoquinone from Bombax malabaricum. J. Asian Nat. Prod. Res. 3:261-5. Stephen, A. M. 1956. The composition of Hakea acicularis gum. J. Chem. Soc. 4487-90. Stephen, A. M., and D.C. de Bruyn. 1967. The gum exudates of Encephalartos longifolius Lehm. (Female) (Family Cycadaceae). Carbohydr. Res. 5:256-5. Stephens, D. S., and A. M. Stephen. 1988. Exudates from Encephalartos cones as chemical taxonomic markers. South African J. Chem. 84:263-6. Swingle, W. T., and P. C. Reece. 1967. The botany of Citrus and its wild relatives. In The Citrus Industry Vol 1 (rev). Reuther W., Webber H.J. & Bachelor L.D. (eds), University of California Press, pp. 190-430. Tewari, D. N. 1992. Monograph on neem (Azadirachta indica A. Juss.). Dehra Dun, India: International Book Distributors. Tripathi, Y. B. 2009. BHUx: a patented polyherbal formulation to prevent hyperlipidemia and atherosclerosis. Recent Patents on Inflammation and Allergy Drug Discovery 3:49-57.  USDA, ARS, National Genetic Resources Program. 2008. Germplasm resources information network (GRIN). [Online Database] National Germplasm Resources Laboratory, Beltsville, MD. Available: http://www. ars-grin.gov/cgi-bin/npgs/acc/display.pl. Venter, F., and J.-A. Venter. 1996. Marking the most of indigenous trees. Singapore: Briza Publications. Verma, N., and M. Vinayak. 2009. Effect of Terminalia arjuna on antioxidant defense system in cancer. Mol. Biol. Rep. 36:159-64. Vieira, T. O., Said, A., Aboutabl, E., Azzam, M., and B. T. Creczynski-Pasa. 2009. Antioxidant activity of methanolic extract of Bombax ceiba. Redox Rep. 14:41-6. Vogt, D. C., and A. M. Stephen. 1993a. The gum exudate of Encephalartos longifolius Lehm. (female): Further hydrolytic studies. Carbohydr. Res. 238:249-60. Vogt, D. C., and A. M. Stephen. 1993b. The gum exudate of Encephalartos friderici-guilielmi. Carbohydr. Res. 241:217-26. Wagner, W. L., Herbst, D. R., and S. H. Sohmer. 1999. Manual of the flowering plants of Hawaii. Revised edition (two volumes). Bernice P. Bishop Museum special publication. Honolulu: University of Hawai‘i Press/Bishop Museum Press. Webster’s Dictionary. 1961. Webster’s third new international dictionary. Springfield Mass.: G. & C. Merriam Co. Whistler, R. L., and C. L. Smart. 1953. Polysaccharide chemistry. New York: Academic Press. Wickens, G. E. 2008. The Baobabs: Pachycauls of Africa, Madagascar and Australia. Netherlands: Kluwer Academic Publishers Group. Wilczek, R. 1952. Bauhinieae. In Flore du Congo belge et du Ruandu-Urundi, vol. 3 (Spermatophytes), 265-278. Brussels: INEAC. Xiu-Yan, L., and L. Chang-Yi. 2008. Toxicity comparison of extracts from six terrestrial plants to larvae of Balanus albicostatus. J Plant Res. Environ. 17:22-7. Yazzie, D., Vanderjagt, D. J., Pastuzyn, A., Okolo, A., and R. H. Glew. 1994. The amino acid and mineral content of baobab (Adansonia digitata L.) leaves. J. Food Composit. Anal. 7:189-93. Yoganarasimhan, S. N. 1996. Medicinal plants of India, vol.1. Banglore: Interline Publishing Pvt. Ltd. Zarnowski, R., Jaromin, A., Certik, M. et al. 2004. The oil of Adenanthera pavonina L. seeds and its emulsions. Zeitschrift fur Naturforschung C-A. J. BioSci. 59:321-6.

Chapter 5

Food Applications of Plant Exudates 5.1 INTRODUCTION Many plants exude viscous, gummy liquids that, upon exposure to air, form clear, dry, glassy masses. The colors and shapes of the natural exudates vary widely. Gum formation can be either a protective mechanism resulting from a pathological condition, or a part of the plant’s normal physiological metabolism. Its synthesis can be considered a result of microorganism infection and the plant’s effort to seal the infected area, or it can be attributed to fungal attack of the plant and the consequent release of enzymes that penetrate the vegetative tissues and transform the cellulosic materials of the plant’s cell wall into gum (Howes, 1949; Jones and Smith, 1949; Glicksman, 1969). Originally, the term “gum” referred to all types of natural plant exudates, including those that are not water-soluble such as chicle, latex and resins. This is the origin of the erroneous use of the word gum for resins that are used on a regular basis in the chemical and paint industries (Glicksmam, 1969). Many plant gum exudates are known all over the world; however only four of them (arabic, ghatti, karaya and tragacanth) are of real importance to the food industry. Many other locally known exudates are used to a limited extent, sometimes as substitutes for the four main exudates due to their analogous properties which render them suitable for similar applications (Glicksman, 1969). However, many of these exudates have not been granted generally recognized as safe (GRAS) status. GRAS is a US Food and Drug Administration (FDA) designation validating that a chemical or substance is considered safe as a food additive by experts. Many such unapproved exudates contain tannins or other ingredients that can be health hazards. The appearance and properties of the natural gums determine their commercial value and end use. Gum exudates can be used “in foods for human consumption” or “as food for animals”. Therefore, this chapter is divided into two main sections. The first deals with the question of what foods/preparations might benefit from exudates’ unique properties in improving texture, functionality or other features via their inclusion in a formulation. The second section discusses the use of gum exudates as foods by animals. 257

258  ◾  Plant Gum Exudates of the World

5.2 FOOD USES OF GUM EXUDATES 5.2.1 Confectionery The term confectionery refers to food items that are (or at least are perceived to be) rich in sugar. Confectioneries include sweets, lollipops, candy bars, chocolate, and other sweet snack foods. The term does not generally apply to cakes, biscuits, or puddings which require the use of cutlery, although there are exceptions (meringues, for example). American English classifies many confections as candy. Some of the categories and types of candy include: hard candy, lollipops, lemon drops, peppermint drops and disks, candy canes, rock candy, etc. Confections also include fudge, toffee, licorice candy, chocolates, gum/gelatin candies, lokum/turkish delight, jelly beans, marshmallow, marzipan, chewing gum, halva, alfajor and dragées, among others (Fig. 5.1). As a thickener and an agent that can prevent the crystallization of sugar, gum arabic plays a major role in the confectionery industry, especially in products in which sugar content is high and moisture content comparatively low, as in jujubes and pastilles (Whistler, 1973). Jujube refers to several types of candy, which vary on a regional basis. In the United States, Jujubes is the brand name of a particular type of candy, whereas in Canada the word is generic, and describes any of many similar confections. A pastille was originally a pill-shaped lump of compressed herbs which was burned to release its medicinal properties. Today, “pastille” can also refer to a medicinal pill or flavored candy, or to any kind of incense. A pastille is also known as a “troche”, or medicated lozenge, that dissolves like candy. To manufacture jujubes and pastilles, gum arabic is dissolved in water, the solution is filtered, and then mixed with sugar and boiled. Flavor is incorporated with minimal stirring to eliminate the formation of opaque spots or bubbles (Jacobs, 1949). The major use of gum arabic is in the food industry. As a colorless, odorless, non-toxic, tasteless and watersoluble food additive, it can influence both the viscosity and the texture of foods without affecting their color, flavor or odor (Whistler, 1973). It is therefore not surprising that gum arabic is used to produce a wide variety of confections, from soft lozenges to hard gums (Wolff and Manhke, 1982; Best, 1990). Gum arabic and other hydrocolloids may influence crystallization in three

Figure 5.1  A confection selection (http://en.wikipedia.org/wiki/Image:Saint-remy-de-pceconfiseries.jpg, courtesy of Greudin).

Food Applications of Plant Exudates  ◾  259

different ways (Shuman, 1960). The hydrocolloid can attach itself to a growing crystal surface and thus alter its normal growth pattern; the hydrocolloid and the crystal may compete for the same building blocks; the gum may combine with impurities that affect crystal growth (Shuman, 1960; Glicksman, 1969). Low levels of gum arabic (up to 2.0%) are included in chewy sweets based on gelatin to improve product adhesion, reduce elasticity and produce extra-fine sugar crystallization with a smooth texture. Chewy gels with desirable texture can be produced by creating special conditions of pH, protein concentration and heating, among others (Anson and Pader, 1958). More information on the use of gums in confectioneries and on confections based on gum arabic can be found elsewhere (Reidel, 1983, 1986). Natural gums are used to a great extent in the confectionery industry. At one time, agar was used for the production of jellies (candies) and marshmallows, and gum arabic was used in gumdrops. The gum within the formulation served to form the “jelly”, but an additional function was to prevent sugar crystallization and to emulsify fat, keeping it evenly distributed within the product (Klose and Glicksman, 1975). Glaze or glazing refers to a thin shiny coating, or the act of applying it. In non-food applications, it may refer to a transparent glazing material in a building; a vitreous coating for a ceramic material or a glaze in metallurgy. In painting, glaze can be a layer of paint that contributes to gloss but itself is often transparent. In food preparations, glaze is a coating of a glossy, often sweet mixture applied to the food surface and glazing agents are food additives that provide the food with a shiny appearance or a protective coating. Gum arabic can also be used for glaze production in candy products, or as a component in chewing gum, cough drops and candy lozenges (Whistler, 1973). A lozenge (◊) is a type of rhombus. It is an equilateral parallelogram whose acute angles are 45°. Sometimes, the 45° restriction is dropped, and the only requirement is that two opposite angles be acute and the other two, obtuse. A throat lozenge or cough drop is a small, medicated candy intended to be dissolved slowly in the mouth in order to lubricate and soothe irritated tissues of the throat (usually due to a sore throat), possibly from a common cold or influenza. Cough tablets took the name of “lozenge” based on their original shape. Gum arabic is required in the production of lozenges to bind the paste base (Williams, 1961). Lozenges are produced by fine mixing of powdered or ground sugar with the addition of gum arabic. Peppermint or fruit flavors are added and the mass is mixed to form a stiff dough that can be rolled into sheets and pressed (Jacobs, 1949). The term halva, originally derived from the Arabic root halwā (sweet), is used to describe many distinct types of sweet confections (Fig. 5.2). From a food technology point of view, halva can be regarded as an emulsion, and oil separation (emulsion instability) is therefore a major problem in this sweet that affects quality upon storage. The result is toughness, and contamination of packaging materials by the separated oil. The effectiveness of incorporating non-hydrogenated palm oil, glycerol, soy protein concentrate, gelatin, lecithin, pectin, gum arabic, sugar powder, or calcium chloride in improving halva quality was studied (Ereifej et al., 2005). Soy protein concentrate, gelatin, glycerol, and lecithin incorporation did not improve emulsion stability. However, gum arabic, pectin, calcium chloride and sugar powder minimized emulsion instability. Nonhydrogenated palm oil (1.0 or 2.5%) increased the viscosity of the oil phase and contributed to emulsion stability (Ereifej et al., 2005). Gum arabic is a very effective emulsifying agent because of its protective colloid functionality (Glicksman, 1969). In general, it produces stable emulsions with most oils over a wide range of pH values and in the presence of electrolytes. The gum may prevent the coalescence of oil globules by forming a film at the oil interface, and stabilize the emulsion by influencing its relative viscosity (Glicksman, 1969). Other exudates, such as apricot, prune and sweet cherry, also demonstrate effective emulsification abilities but their commercial availability is limited.

260  ◾  Plant Gum Exudates of the World

Figure 5.2  Balkan style tahini-based halva with pistachios (http://en.wikipedia.org/wiki/ Image:PistHalva.jpg, courtesy of Sjschen).

Another type of confectionery product is gummy candies. Their texture is achieved by using various gelling agents. Gums not only modify viscosity and consistency, they also often attenuate odor, taste and flavor intensities (Guichard et al., 1991). Gel texture can directly affect the release of flavor compounds (Carr et al., 1996). The presence of flavor in the vapor phase is a function of its diffusion in the solid phase. The diffusion of a solute is inversely proportional to its viscosity (Roberts et al., 1996). At very low water contents, as in fruit pastilles, viscosity and water activity can affect the diffusion, and therefore the release of aroma compounds (Hansson et al., 2001). The most important ingredients in gummy candies are sucrose, glucose and corn syrups. Their influence on flavor release and sensory perception of aroma compounds, such as 3-methyl-1-butanol, 2-phenyl ethanol and ethyl phenyl glycidate, from fruit pastille model systems, was studied. Significant sensory differences were detected among the flavor intensities of gels produced with different combinations of the sugar mixtures: sucrose+glucose, sucrose+glucose+corn syrup. Headspace analysis confirmed the sugars’ influence on flavor release, and gelation caused a decrease in flavor release. The presence of corn syrup DE40 in pastilles resulted in less flavor release than that from the sucrose+glucose gel (Lubbers and Guichard, 2003). As stated, the included hydrocolloid may influence the volatile release of the confectionery system. The chewing, swallowing and breath flow profiles of 35 subjects during the consumption of gum arabic- and carrageenan-based confectionery chews were studied by electromyography, electroglottography and turbine airflow technologies (Blissett et al., 2006). Simultaneous volatile-release measurements were obtained using atmospheric pressure chemical ionization mass spectrometry. Subgroups of subjects displaying different eating characteristics were identified for both products. Parameters accounting for the maximum variance (gum arabic, 42% and carrageenan, 52%) between the subgroups were chewing force, chewing rate, proportion of work and total number of chews (Blissett et al., 2006). It was concluded that volatile-release measurements were significantly different among the subgroups consuming the gum arabic product. The impact of the different eating characteristics on volatile release from the carrageenan product was less defined, and was postulated to be a result of

Food Applications of Plant Exudates  ◾  261

Figure 5.3  Salad platter (http://en.wikipedia.org/wiki/Image:Salad_platter02.jpg).

the contrasting textural properties. Manipulating the in-vivo breakdown of chewy confectionery products by texture modification may also influence volatile release and subsequently, consumer’s flavor perception (Blissett et al., 2006).

5.2.2 Salad dressings and sauces A salad is a mixture of foods, usually including vegetables or fruits, often with a dressing or sauce. Salad is often served as an appetizer before a larger main course (Fig. 5.3). Salad dressing is a confusing term since it refers to both a specific product and a general category for any type of seasoned dressing used on salads (Gates, 1987). The Kraft Cheese Company entered the salad dressing industry in 1925. The primary ingredient in salad dressing is oil—most commonly, soybean, canola, olive, peanut or sunflower oils. Other food ingredients that are incorporated into salad dressings include, but are not limited to, eggs, vinegar, salt, honey, sugar, spices and herbs, tomato, vegetable bits, sherry, and lemon or lime juice. A large sub-industry is involved in the processing of these ingredients. Different stabilizers and thickeners are incorporated into the formulation in order to maintain its stability and postpone or eliminate phase separation. Xanthan gum as a stabilizer (Fig. 5.4) and gum arabic or propylene glycol alginate as emulsifiers (in various combinations) were used to stabilize/emulsify an olive oil-lemon juice Greek salad dressing (Paraskevopoulou et al., 2005). Samples containing xanthan and gum arabic were more stable in terms of oil droplet coalescence and less stable in terms of creaming. The use of propylene glycol alginate in place of gum arabic resulted in emulsions with higher creaming stability (Paraskevopoulou et al., 2005). Lipid oxidation is a major cause of quality deterioration in salad dressings. Polysaccharides used to improve emulsion stability and texture may also affect lipid oxidation. The oxidative stability of an olive oil-lemon juice emulsion (50:50, v/v), stabilized with gum arabic or propylene glycol alginate in admixture with xanthan, was investigated (Paraskevopoulou et al., 2007). Emulsions were homogenized to form different particle sizes and stored at room temperature for 6 to 8 months. The formation of primary and secondary oxidation products was then measured, and shelf life was compared to that of bulk olive oil. The polysaccharides were found to have the ability to inhibit lipid oxidation, probably due

262  ◾  Plant Gum Exudates of the World CH2OH

CH2OH OH

O COOH H3C

H3C

6

R4

R

O O

OH

O OH

R4O

O

OH

O

O

OH

OH O OH

OH COOH

R6O

O

n

O

O

O

OH

Figure 5.4  Structure of xanthan gum (http://en.wikipedia.org/wiki/Image: Xanthan.svg, author: NEUROtiker).

to their amphiphilic character as well as their ability to increase viscosity (Paraskevopoulou et al., 2007). Olive oil-lemon juice emulsions were also assessed for consumer acceptance. The panelists were asked to smell the samples and rate them according to rancidity using a four-point (1 = no perception, 4 = extreme) intensity scale. The results were in accordance with those of the chemical analysis. Lipid oxidation was not affected by oil droplet size, as demonstrated by peroxide value measurements and sensory evaluation (Paraskevopoulou et al., 2007). Gum karaya can also be used in dressings as a stabilizer, sometimes in conjunction with gum arabic, which acts as a protective colloid (Whistler, 1973). Gum tragacanth can be used in the preparation of various salad dressings due to its acid resistance, and its ability to thicken the water phase of the emulsion at low gum concentrations (on the order of 0.4-0.75%). In some salad dressings and sauces, gum tragacanth was replaced with other stabilizers: the products became thin or showed poor performance and therefore gum tragacanth is still used widely in this field (Glicksmam, 1969). To eliminate lumping, the gum should be dispersed in the oil or some of the oil in the recipe and only then further mixed with the water phase, followed by heat treatment and homogenization (Whistler, 1973). The best way to use gum tragacanth is by adding the gum to the condiment at the end of the boiling phase, then rapidly cooling the mixture; the product should be prepared in two parts, by first mixing the ingredients, without the gum, with water and part of the sugar and then preparing a smooth mucilage consisting of gum, sugar and fluid to obtain a smooth consistency (Burrell, 1958). In low-calorie dressings, the oil content is decreased and a higher level of gum is required to deal with the higher water content. The inclusion of gum tragacanth in dressings yields creamier and more stable products. With condiments and sauces, gum additions of 0.4 to 0.8% of the total weight of the sauce or condiment contribute to emulsion stability and thickness when pH is low and the vinegar content high (Whistler, 1973).

5.2.3 Frozen products Freezing is a unit operation in which the temperature of a food is reduced below its freezing point and a proportion of the water undergoes a change in state to form ice crystals (Fellows, 2000).

Food Applications of Plant Exudates  ◾  263

Preservation is achieved by combining reduced water activity and low temperatures. The major groups of commercially frozen foods are: fruits (whole, pureed or as juice concentrates), vegetables (e.g. green beans, peas, spinach, etc.), fish fillets and seafood, meats and meat products, and baked goods and prepared foods (Fellows, 2000).

5.2.3.1 Frozen dough Flour is the basic ingredient in all baked products. Other ingredients may include, but are not restricted to, eggs, sweeteners (i.e. sucrose, honey, syrups, molasses and artificial sweeteners), fat, leavening agents, fluids (e.g. milk, fruit juices and flavor) and salt (Gates, 1987). Dough is a soft, thick mixture of dry ingredients, such as flour or meal, and liquid, such as water, that is kneaded, shaped, and baked, especially as bread or pastry. Conventional methods of dough development for bakery products produce doughs with very short storage lives. Freezing dough increases the storage life for different bakery products. Shelf life can be enhanced by the incorporation of different hydrocolloids in the flour, but there nevertheless remains a decreasing trend in the quality of the frozen dough bakery products with increasing storage periods (Asghar et al., 2007). When gum arabic and carboxymethylcellulose (CMC) were added to wheat flour destined for use in frozen dough pizzas, water absorption, arrival time, departure time, peak time and tolerance index were found to be higher in flours containing 3% CMC, whereas mixing time and peak height percentage were higher in the treatment with 3% gum arabic. The use of gum arabic and CMC, both at 3% on a flour weight basis, improved the quality of the frozen pizza dough. Frozen dough stabilizers have great potential for improving the overall baking quality of wheat flour which has been stored frozen (Asghar et al., 2007). Another study investigated the effect of gums on the starch and protein characteristics of frozen doughs: these were supplemented with three levels of gum arabic, CMC, κ-carrageenan, and locust bean gum. Scanning electron micrographs of unfrozen doughs showed starch granules securely embedded in the gluten matrix. After 8 and 16 weeks of frozen storage, the frozen control dough without gum additives clearly showed damage to the gluten network, and the starch granules appeared to be separated from the gluten. Doughs with locust bean gum and gum arabic showed better maintenance of the gluten network compared with the frozen control, evaluated after different periods of storage (Sharadanant and Khan, 2006). Doughs with gum arabic and CMC had the lowest amount of residual proteins, but still higher than the control doughs. Thus hydrophilic gums can improve the shelf-life stability of frozen doughs during long periods of frozen storage (Sharadanant and Khan, 2006).

5.2.3.2 Frozen sugar solutions Hydrocolloids are added to frozen desserts to produce a smooth texture and to protect the product during storage. High-pressure freezing techniques are also aimed at enhancing product quality (Fernandez et al., 2007). Sugar is used in frozen desserts, cakes and other baked products, to make most candies, and in frostings and icings, among many other products (Gates, 1987). Sugar solutions can therefore be used as model solutions for frozen foods (Gulseren and Coupland, 2007). To study the structure of complicated food systems under freezing, solutions containing sucrose, lactose, milk salts, protein from skim milk powder and hydrocolloids must be examined (Rogers et al., 2006). One example of such a study involved hydrocolloid addition and its effect on ice-crystal characteristics of frozen sucrose solutions. Freezing was effected by high-pressure assisted freezing (HPAF) at 100 MPa and by high-pressure shift freezing (HPSF) from 210 MPa to 0.1 and 100 MPa. Ice crystals were found to be smaller when a hydrocolloid mixture of locust bean and xanthan gums was added, irrespective of the freezing method (Fernandez et al., 2007). The influence of dextran, pullulan and gum arabic

264  ◾  Plant Gum Exudates of the World

on the physical properties of frozen sucrose solutions (added to 57.5 and 67.5%, w/w) was also studied. Addition of the different polysaccharides at 1%, regardless of their structure or molecular weight, did not have any influence on the viscosity of the solution (Lopez et al., 2005). At 10% addition, pullulan was the only polysaccharide that increased the viscosity of the sucrose solution. The viscoelastic behavior of the sucrose solutions was not modified by the presence of dextran, gum arabic or pullulan. These results were confirmed by differential scanning calorimetry (DSC) (Lopez et al., 2005).

5.2.3.3 Frozen dairy products, ice pops and sherbets The most common frozen dessert is ice cream. Such frozen desserts are most desirable when their ice crystals are small, enabling smooth sensory evaluation of the product (Gates, 1987). The main ingredients in frozen desserts include water from some source and sugar. Optional ingredients include gelatin, eggs, milk solids, emulsifiers and stabilizers. These ingredients can influence the consistency, texture and flavor of the frozen dessert. Commercial frozen desserts use gums to provide body and bind water (Gates, 1987). Gum arabic can be used as a stabilizer in ice creams and other frozen products. In such products, gum inclusion prevents the formation of ice crystals via water absorption. The water is held as hydration water and thus a smoother, finer texture is created. On the other hand, this inclusion changes the melting behavior of the product. In another process, gum arabic was mixed with milk or cream under mild heating and the fluid was poured into molds, cooled and packaged, producing products that are better kept under refrigeration and dissolve easily in hot beverages (Whistler, 1973). A concentration of 0.2 to 0.35% was needed when gum tragacanth was used as a stabilizer for ice cream mixtures. This gum is also beneficial in other frozen products, such as water ices, ice pops and sherbets, at a concentration of ∼0.5% for the prevention of syrup separation (Whistler, 1973). In the manufacture of ice pops and sherbets, gum karaya is used at concentrations of ∼0.2 to 0.4% both to eliminate the formation of large ice crystals and to prevent “bleeding” of free water, in addition to contributing to the water-holding capacity of the gum (Whistler, 1973).

5.2.4 Spray-drying Dehydration (or drying) is defined as the application of heat under controlled conditions to remove most of the water normally present in a food by evaporation (Fellows, 2002). In spray dryers, a dispersion containing ∼40 to 60% moisture is atomized to form fine droplets sprayed into a co- or counter-current flow of heated air at 150-300°C in a large drying chamber. Four kinds of atomizers can be used: centrifugal, pressure nozzle, two-fluid nozzle and ultrasonic. As a result of the large surface area of the droplets, rapid drying, on the order of 1 to 10 s, occurs (Fellows, 2000). A very large variety of food materials can be spray-dried (e.g. milk, coffee, cocoa, tea, potato, ice cream mix, butter, cream, yoghurt and cheese powder, coffee whitener, fruit juices, meat and yeast extract, encapsulated flavors, etc.; Heath, 1985). Spray dehydration is rapid; it involves large-scale continuous production, low labor costs and simple operation and maintenance. However, limitations include high capital costs, the need for high moisture content to permit the food’s atomization, high energy costs and higher volatile losses (Fellows, 2000).

5.2.4.1 Spray-drying of juices The juices of many fruits and some vegetables are used as beverages. Juices are available as fresh or pasteurized, for the production of nectars, as concentrated frozen or preserved products, and in dehydrated forms. Natural juices can serve as a source of different nutrients, including ascorbic acid (vitamin C), iron and potassium. Fruit juices might include pigments such as anthocyanin.

Food Applications of Plant Exudates  ◾  265

3' R7

7

R6

6

4'

R2

5'

O+

5

R1

R3 3

R4

R5

Figure 5.5  Anthocyanidin scaffold: the flavylium (2-phenylchromenylium) cation [http:// en.wikipedia.org/wiki/Image:Anthocyane.png, author: de Benutzer Thiesi].

Anthocyanins are glucosides of anthocyanidins, the basic chemical structure of which is shown here (Fig. 5.5), and anthoxanthin (Gates, 1987). There are a number of dehydration techniques/ methods that can be applied to juices (i.e. air, foam, vacuum, spray, drum and freeze dehydration). For economic reasons, most are based on some degree of juice concentration above single strength, generally as high as practical given the flow characteristics and mechanical properties of the concentrated juice and design features of the dryer (Bates et al., 2001). Fruit juices are not easy to dry. The high sugar content, consisting primarily of the reducing sugars glucose and fructose, presents a problem. At low moisture levels, the products are quite hygroscopic, readily picking up moisture from the air to become sticky and difficult to manipulate. Dried fruit products, especially juices, must be isolated from the atmosphere during and after drying. The dry product is then rapidly packed into a hermetically sealed moisture-barrier material, either a bulk container or the final package. Juice powder also presents a large surface area and is quite susceptible to oxidation without surface-bound water to protect the reactive sites (Bates et al., 2001). Another difficulty is the sticky point of the dried juices. Even with little remaining moisture at high temperatures (greater than ∼70°C), the product will be in a glassy syrupy state and stick to machinery, vastly complicating product handling. Low-dextrose equivalent (DE) corn syrups can reduce the sticky point, but then the juice powder is not pure. Means of overcoming these limitations are described for distinct types of drying. Nevertheless, equipment modifications and more demanding product-handling procedures are required to overcome stickiness and the hygroscopic nature of dehydrated juices (Bates et al., 2001). One of the food industry’s goals is to produce a powdered drink that tastes the same as real juice, and to make such a powdered drink from the juice of real fruits and vegetables. To date, attempts to produce powder from juice have been unsuccessful because traditional powder-rendering processes cause the juice to become a sticky (as already mentioned), non free-flowing product, rather than a powder. For example, merely freeze-drying or spray-drying the juice does not produce the sought-after powder because these processes do not pulverize the fructose in the juice (Palermiti, 1993). Nevertheless, freeze-dehydration has been shown to be effective at encapsulating limonene using a mixture of gum arabic and sucrose gelatin (Kaushik and Roos, 2007). One method of manufacturing a concentrate from juice that may be used to make a powder has been suggested. Reconstitution as a juice drink via the addition of water to the powder, or its use as a taffy-like solid that may be consumed without being reconstituted, and in which the juice is freeze- or spray-dried, requires the use of lubricants and/or dextran to improve the texture of the dried juice so that it may be packaged and stored for later consumption (Palermiti, 1993). Tropical juices are good candidates for spray-drying. For the success of such an operation, different ingredients, including maltodextrins, waxy starches and gum arabic, should be included in

266  ◾  Plant Gum Exudates of the World

Figure 5.6  Fruit and flower of acerola (Malpighia glabra) (http://commons.wikimedia.org/wiki/ Image:Flower_of_acerola.jpg, photo taken by Mateus Hidalgo).

the fluid before drying. For example, when immature acerola juice was dehydrated by spray-drying, maltodextrin DE25, gum arabic, or a mixture of both in different proportions were used as encapsulating materials. Acerola (Malpighia glabra), also known as Barbados cherry (Fig. 5.6), is a small tropical fruit-bearing tree in the family Malpighiaceae. The fruit is bright red, 1.5 to 2 cm in diameter, containing two to three hard seeds. It is juicy, often with a flavor that is both sweet and sour and very high in vitamin C and other nutrients (Righetto and Netto, 2005). With spray-drying, a constant ratio of 1:1 was kept between the juice solids and encapsulating material. The monolayer moisture of the encapsulated juices varied from 5.1 to 5.7 g H2O/100 g of solids (25°C). Stickiness was observed at temperatures close to Tg (glass transition temperature), and collapse occurred at temperatures of 20°C or more above the Tg. Maltodextrin DE25 and gum arabic contributed equally to the stability of the system (Righetto and Netto, 2005). Another example of tropical fruit juice spray-drying and inclusion of gums that might improve the final product is the production of dried mango juice. Maltodextrin, gum arabic and waxy starch at concentrations of 12% were added to mango juice (12°Bx) before spray-drying. Crystalline cellulose at a concentration of 0, 3, 6 or 9% was also added. Microstructure analyses showed that the powders of the mango juices obtained using carriers such as maltodextrin, gum arabic and waxy starch without the addition of cellulose presented surfaces of amorphous particles (Cano-Chauca et al., 2005). With the addition of cellulose, the particles showed half-crystalline surfaces. Stickiness decreased with increasing cellulose concentration. The functional property of solubility was affected when 9% cellulose was added, reaching values of 72, 71 and 31% for the carriers maltodextrin, gum arabic and waxy starch, respectively (Cano-Chauca et al., 2005).

5.2.4.2  Miscellaneous spray-dried products A special spray-drying method called ‘Leafflash’ was developed, wherein very hot air flows at very high velocity, enabling the drying of highly viscous liquids. An example of this used a mixture of two volatile products, citral and linalyl acetate (Bhandari et al., 1992). Citral (C10H16O) is a synthetic,

Food Applications of Plant Exudates  ◾  267

pale-yellow liquid flavoring that has a strong, lemon-like odor and characteristic bittersweet taste, originally found in lemongrass oil, among other sources. Linalyl acetate (C12H20O2) is a colorless synthetic flavoring with a bergamot-lavender odor and a persistent sweet-acrid taste (Nussinovitch, 2003). When these two volatile materials, in respective proportions of 80:20 (w/w), and blends of maltodextrin and gum arabic were included within the formulations, and emulsions were produced, atomized and dried at inlet air temperatures of 300 to 400°C, no adverse effect was observed on chemical properties. The use of maltodextrin (less expensive than gum arabic) for delicate flavor encapsulation is possible in an emulsion containing 60% total solids (Bhandari et al., 1992). Probiotic bacterial cultures are intended to assist in the reestablishment of the body’s naturally occurring gut flora. Claims have been made that probiotics strengthen the immune system, and combat allergies, excessive alcohol intake, stress, exposure to toxic substances, and other diseases (Nichols, 2007). Probiotic bacteria can be dried at low temperature in two steps, combining spraydrying and vacuum-drying, in order to enhance their survival during storage. A sufficient number of dried probiotics survived storage for more than 3 months at 30°C, if an appropriate combination of protein and carbohydrate was selected as the carrier and optimal storage conditions were maintained. The use of soy protein and maltodextrin, or skim milk and gum arabic resulted in the best survival rates of probiotics during storage. No evident difference was found between different spray-dryer configurations, although cocurrent flow was preferred (Chavez and Ledeboer, 2007).

5.2.4.3 Encapsulation via spray-drying Gum arabic is the most commonly used coating material for encapsulation via spray-drying. It is a natural emulsifier and is used as a flavor fixative in the production of powdered aroma concentrates (Pegg and Shahidi, 1999). Compared to maltodextrins, gum arabic (acacia) gives superior aroma retention during drying and storage. Maltodextrins and gum acacia mixtures are successfully used for the encapsulation of flavors that are stable against oxidation (Bhandari et al., 1992). Two types of lipids, both rich in arachidonic acid content, were encapsulated using various soluble soybean polysaccharides and gum arabic as the wall material. Microencapsulation effectively retarded their oxidation (Kikuchi et al., 2006). The capsule shape achieved by spray-drying depends on the wall materials. For example, microcapsules that contained short-chain fatty acids (SCFAs) and used gum arabic as the wall material had surface dents or invaginations. Microcapsules containing maltodextrin were spherical with few surface dents, and some of them had pores. The larger sizes were observed for microcapsules containing maltodextrin (Teixeira et al., 2004). Another previous report reviewed other materials’ properties for microencapsulation, such as karaya gum, tragacanth gum, acacia gums, gum arabic (structure, viscosity, acidity, surface tension), and gum arabic as an emulsifier and stabilizer (liquid emulsions, encapsulated by spray-drying, and microencapsulated by coacervation) (Balke, 1984).

5.2.5 Drum-drying Drum dryers are those dryers in which heat is supplied to the food by conduction. Drying can be performed in the absence of oxygen, and heat consumption is lower per kilogram of evaporated water (Fellows, 2000). In drum dryers, the food is spread over the outer surface of a rotating hollow steel drum. The drum rotates, and the food is applied to it as it rotates. The food remains on the drum surface for the greater part of the rotation, during which time drying takes place; it is then scraped off (Earle and Earle, 1983). Drum dryers are suitable for slurries and are used for the production of potato flakes, pre-cooked cereals, molasses, dried soups, fruit purees and whey, among other foods

268  ◾  Plant Gum Exudates of the World

Figure 5.7  Jackfruit (Kerala, India) [http://en.wikipedia.org/wiki/Image:Jackfruit1.JPG, courtesy of MANOJTV].

for humans or animals (Fellows, 2000). Good-quality double drum-dried jackfruit (Fig. 5.7) powder could be obtained by incorporating 2.7% soy lecithin and 10.3% gum arabic into the jackfruit puree (Pua et al., 2007). Gum arabic and maltodextrin were also used in vacuum-dried products (Gabas et al., 2007; and compare to section 5.2.4.1 where in order to obtain good-quality spray-dried tropical juices, gum arabic, maltodextrins and other ingredients, are included within the formulation).

5.2.6 Wine Gum arabic is used regularly in a variety of processes in the wine industry in incredibly variable proportions [20-1000 g per hl (i.e. per 100 l)]. A few manufacturers declare its use while others do not state this clearly on the label, arguing that it is totally natural or that such a declaration would create pointless alarm among consumers. Gum arabic is seen by wine-makers as a natural stabilizer used post-filtration, just prior to bottling. Its use has several aims: stabilization of red wine color in young wines, while increasing the perception of body or volume; reducing the perception of acidity and tannin harshness, while adding body. Due to the inclusion of gum arabic in wines, it is not surprising that a method for the identification and semi-quantitative determination of gum arabic in wines has been described (Gallina et al., 2004). Tests carried out on solutions spiked with known amounts of wine and gum arabic enable the definition of suitable conditions for their quantitative precipitation and size-exclusion analysis. GC-MS analyses of the different

Food Applications of Plant Exudates  ◾  269

recovered fractions allowed discriminating between gum arabic and wine polysaccharides through the identification of glucose and mannose, present only in wine polysaccharides. The proposed method was based on the wine polysaccharides’ free peak area obtained by size-exclusion chromatography (Gallina et al., 2004). Gum arabic was determined in a ratio of 1/10 (w/w) with wine polysaccharides, with a detection limit of 0.074 mg/ml, which is lower than the lowest gum arabic amount usually added to wines. It was concluded that the described procedure was suitable for semi-quantitative analysis, even though its accuracy allowed a quite reliable determination of the amount of gum arabic usually added to wine (Gallina et al., 2004).

5.2.7 Adhesives Gums (gum arabic and apple pectin), and sometimes mixtures of gums and aqueous sugar solutions, are not only used as adhesives and edible glues in the food industry; they can also contribute to viscosity and thickening, as well as to potential gelation acceleration (Mazurkiewicz et al., 1993). Gum arabic was used as part of a breadcrumb composition to permit better adhesion to moistened comestibles, such as chicken pieces, pork chops, fish fillets or vegetable strips, during coating and cooking, without the need for a batter coating. The formulation included breadcrumbs, whose particle size was such that most, if not all of the crumbs were retained on a 20-mesh US standard screen after passing through a 5-mesh US standard screen, and an edible adhesive, applied to the surface of the crumbs. The adhesive contained a protein at somewhat more than 1% by weight of the crumbs and (optionally) a starch and/or gum. An example of such a composition contained (g): bread crumbs (75), egg white solids (10), gum arabic (0.9), water (17.1) and a spice blend (10) (Rispoli and Shaw, 1981). Coatings based on wheat gluten, dextrin, modified starches and gum arabic have also been invented to improve the adherence of salt and flavorings to nuts (Daniels, 1973).

5.2.8 Bakery products Baking is a unit operation that uses heated air to alter the eating quality of foods. It is usually applied to flour-based items. A secondary purpose of baking is preservation, via the destruction of microorganisms and the reduction of water activity at the surface of the food. Baking involves simultaneous heat and mass transfer (Fellows, 2000). Baked products include pastries and pies, shortening cakes, sponge cakes, yeast and quick breads, among others (Gates, 1987). Baking is considered in two main areas, bread, and cakes and biscuits (Sutherland et al., 1986). As noted in section 5.2.1, in cooking, a glaze is a coating made up of a glossy, often sweet substance applied to foods. Egg whites and icing are both used as glazes. For example, doughnut glaze is made from a simple mixture of confectioner’s sugar and water. Glazes can also be made from fruit and are often applied to pastries. Gum arabic is used not only in glazes for confections but in glazes and toppings for bakery products, due to its inherent viscosity and adhesive properties. The glaze is applied warm and adheres firmly to the buns upon cooling. Moreover, gum arabic maintains the stability of the glaze (Whistler, 1973). Gum tragacanth is also used for the stabilization of bakery emulsions and fillings in which suspended fruit, fruit pieces, natural flavor extracts and other flavors are used (Whistler, 1973).

5.2.9 Flavor fixatives and emulsifiers Flavor is a combination of taste and smell. A flavor such as bitterness can be acceptable in one food (e.g. coffee) and not acceptable in another (e.g. milk). Unacceptable flavor will lead to rejection of food (Gates, 1987). A food’s flavor can be altered with natural or artificial flavorings. Due to the

270  ◾  Plant Gum Exudates of the World

high cost, or unavailability or instability of natural flavor extracts, most commercial flavorings are nature-identical, i.e. they are the chemical equivalent of natural flavors but chemically synthesized rather than extracted from the source materials. Certain artificial flavorings have an E number [i.e. number codes for food additives that are usually found on food labels throughout the European Union. The numbering scheme follows that of the International Numbering System (INS) as determined by the Codex Alimentarius committee], which may be included on food labels. Used as a flavor fixative, gum arabic is able, after spray-drying (see also section 5.2.4), to form a thin film around the flavoring, protecting it from oxidation, evaporation and absorption of moisture from the air. Many materials can be thusly encapsulated, including essential oils and imitation flavorings. Other colloids or colloid combinations can also be used (Whistler, 1973). Gum arabic serves in the preparation of many flavor emulsions. Possible blends include gum arabic and gum tragacanth. For citrus-oil emulsions, combinations of gum arabic and gum karaya are used (Whistler, 1973).

5.2.10 Beverages Beverages are liquid foods that are consumed by drinking. A few examples are juices (alone or in a cocktail or punch), milk (with or without additional ingredients), fruit-milk drinks, carbonated beverages, coffee, tea, cocoa and chocolate beverages (Gates, 1987). Juices as beverages and their spray-drying are discussed in section 5.2.4.1. The number of alcoholic beverages is vast, but they can be grouped into three basic types: beers, wines and ciders, and distilled products in which the alcohol content of the fermented liquor is increased by distillation. The use of gum arabic in the wine industry is discussed in section 5.2.6. Aside from its roles in stabilization, perceived increases in body and volume and perceived reduction in acidity and tannin harshness, gum arabic is also used as a foam stabilizer in beverages. Combinations of vegetable oil and gum arabic in spray-drying are also beneficial in the production of clouding agents (Whistler, 1973).

5.2.11 Meat products Meat is animal muscle tissue. It is composed of different proportions of water, protein and fat. Structural components of lean tissue include muscle fiber, connective tissue, fat tissue, bone and pigment. Ground meat is prepared only from skeletal meat, and must be labeled in accordance with its proportion of lean to fat (Gates, 1987). Minced (ground) meat is sometimes centrally prepared and transported to retail outlets in vacuum packs. Due to its shorter shelf life relative to whole joints (as a result of greater surface area and nutrient availability to microorganisms), meat in its bulk form is coarsely minced and a second mincing is performed before packaging for retail. In ground meat products, the addition of ∼0.25% gum karaya provides efficient water-holding ability, giving products such as bologna a smooth appearance (Whistler, 1973).

5.2.12 Miscellaneous Vitamins are essential nutrients that are required in small amounts for various roles in the human body. Vitamins are divided into water-soluble (B-complex and C) and fat-soluble (A, D, E and K). Gum ghatti can be used in the preparation of stable, powdered fat-soluble vitamins (Whistler, 1973). Gum arabic may help in reducing the degradation of water-soluble vitamins such as vitamin C. Kinetics studies on the degradation and non-enzymatic browning of green West Indian cherry juice and synthetic ascorbic acid, encapsulated in maltodextrin DE20 or a mixture of this with gum arabic, were carried out at different temperatures (15, 25, 35 and 45°C). Vitamin C degradation

Food Applications of Plant Exudates  ◾  271

followed a first-order and non-enzymatic browning a zero-order kinetics model. At higher storage temperatures, the formulation containing a mixture of maltodextrin and gum arabic (3:1) was the most effective for vitamin C protection (Righetto and Netto, 2006). Gum karaya at concentrations of ∼0.8% or less is used in cheese spreads. Gum arabic, and blends of amidated low-methoxy pectin and CMC were used as emulsion-stabilizing agents for reduced-fat fresh white cheese-like products obtained by multiple emulsions (Lobato-Calleros et al., 2006). The use of gum arabic or maltodextrins as “matrix-forming” materials improves the storage stability of spray-dried dairy and dairylike emulsions but compromises the emulsion’s droplet size after reconstitution (Vega and Roos, 2006). When mixtures of caseinate and gum arabic (protein-polymer conjugation) were incubated with transglutaminase, the elution times decreased markedly, indicating conjugation between the protein and the polysaccharide. The molecular masses of the conjugates increased to 950 and 1600 kDa, respectively. The produced conjugates exhibited unique functional properties. A whey protein-maltodextrin conjugate was found to be capable of producing fine emulsion droplets with either triglyceride oil or orange oil (Akhtar and Dickinson, 2007). Due to its binding properties, gum karaya can be used as a meringue stabilizer, and in addition, confers greater volume to the product. Other uses of gum tragancanth include its role in the stabilization of vitamin C in aqueous solutions, and in cream centers of candies that include natural fruit acids (Whistler, 1973).

5.2.13 Microencapsulation 5.2.13.1 Oleoresins Spices represent an important area of long-distance international trade. Oleoresins contain the aroma and flavor of the spice in a concentrated form, usually as a viscous liquid or semisolid material. Spice oleoresins can be derived through non-aqueous volatile solvent extraction of powdered and dried spices. These solvents are removed at the end of the process through evaporation. The demand for spice oleoresins is on the rise in the global market. Solvent-extracted oleoresins exhibit a flavor profile close to that of the freshly ground spice, which makes them an acceptable form of natural flavoring in a wide spectrum of food applications (Shaikh et al., 2006). Despite the solvent extraction, spice oleoresins have many advantages over ground spices, although their sensitivity to light, heat and oxygen is a disadvantage. One approach to overcoming this problem is microencapsulation (Shaikh et al., 2006). Black pepper is valued for its unique taste and spicy aroma. Oleoresin produced by solvent extraction of dried powdered pepper contains both the aroma and pungency components (Premi, 2000). Extraction yields of oleoresin have been reported to be in the range of 5 to 15% (Purseglove et al., 1980). The volatile oil, piperine, and the other non-volatile constituents cumulatively account for the quality of black pepper oleoresin. This oleoresin was microencapsulated by spray-drying, using gum arabic and modified starch as wall materials (Shaikh et al., 2006). The microcapsules were evaluated for the content and stability of the volatiles, non-volatiles, total piperine and entrapped piperine for 6 weeks. Piperine (Fig. 5.8; C17H19NO3) has a molar mass of 285.3 g/mol, a density of 1.193 g/cm3, a melting point of 130°C and it decomposes with boiling (Bhardwaj et al., 2002). Piperine is the alkaloid responsible in part for the pungency of black pepper. It was first discovered by Hans Christian Ørsted in 1819. Piperine inhibits different enzymes. By inhibiting drug metabolism, piperine may increase the bioavailability of various compounds (Atal et al., 1985). It was reported that gum arabic offers greater protection to the pepper oleoresin than modified starch, as seen from the t1/2, i.e. the time required for a constituent to be reduced to 50% of piperine initial value (Shaikh et al., 2006).

272  ◾  Plant Gum Exudates of the World A N O

O O

B

Figure 5.8  (A) Chemical structure of piperine (http://en.wikipedia.org/wiki/Image: Piperine1. png). (B) Piperine crystals extracted from black pepper (Piper nigrum) - recrystallized from acetone (http://en.wikipedia.org/wiki/Image:Piperine_crystals.jp; courtesy of impz).

Cardamom is the dried fruit of Elettaria cardamomum (Mathai, 1985). Its flavor is incorporated in bakery, confectionery and meat products, by using cardamom essential oil or the solventextracted cardamom oleoresin. The major compounds of the cardamom oleoresin are 1,8-cineole (C10H18O; colorless liquid; melting point: 2°C; boiling point: 176 - 177°C; specific gravity: 0.922; stable; flammable; incompatible with acids, bases, strong oxidizing agents), and α-terpinyl acetate [Synonym: (±)-2-(4-methyl-3 cyclohexenyl)isopropyl acetate; molecular formula C12H20O2; molecular weight 196.29; boiling point 220°C; density 0.953 g/ml at 25°C; flash point 100°C], which make up two-thirds of the total volatiles (Lewis et al., 1966). Possible oxidative degradation can be reduced by microencapsulation using starches and gums, which serve as the most common carrier/matrix materials (Reineccius, 1988, 1989). Microencapsulation of cardamom oleoresin by spray-drying using gum arabic, maltodextrin, and a commercially available modified starch as wall materials has been achieved (Krishnan et al., 2005). The microcapsules were evaluated for the content and stability of volatiles, non-volatiles, entrapped 1,8-cineole and entrapped α-terpinyl acetate for 6 weeks. Gum arabic offered greater protection to the oleoresin than maltodextrin or modified starch (Krishnan et al., 2005). Cumin is the dried seed of the herb Cuminum cyminum L., a member of the parsley family. Cumin seeds are used as a spice for their distinctive aroma, which is due to their essential oil content (Fig. 5.9). The main aroma constituent is cuminaldehyde (4-isopropylbenzaldehyde). Cumin can be used as an

Food Applications of Plant Exudates  ◾  273 A

B

Figure 5.9  (A) Cuminum cyminum (adapted from Koehler’s Medicinal-Plants 1887). (B) Close-up of cumin (C. cyminum) seeds [http://en.wikipedia.org/wiki/Image:Sa_cumin.jpg, courtesy of Sanjay Acharya].

274  ◾  Plant Gum Exudates of the World

ingredient in curry powder and is found in some cheeses, traditional breads, enchiladas, tacos, salsa and other related foods. C. cyminum oleoresin is obtained by solvent extraction of the seeds with subsequent removal of the solvent. This liquid has a dark color with the characteristic cumin odor and flavor. Its volatile oil content is 30 to 35 ml/100 g, and 1 kg of cumin oleoresin is equivalent in value to 15 to 20 kg of seeds. Gum arabic, maltodextrin, modified starch and their ternary blends were used for microencapsulations of cumin oleoresin by spray-drying, and their encapsulation efficiency and stability under storage were studied. The cumin oleoresin microcapsules were evaluated for the content and stability of volatiles, and total cuminaldehyde, γ-terpinene and p-cymene content for 6 weeks. In general, gum arabic offered greater protection than maltodextrin or modified starch, although the order of protection offered was volatiles > cuminaldehyde > p-cymene > γ-terpinene. A 4:1:1 blend of gum arabic/maltodextrin/modified starch offered better protection than gum arabic alone, as judged by the constitutents' t1/2. However, the protective effect of the ternary blend was not the same for all of the constituents, following the order: volatiles > p-cymene > cuminaldehyde > γ-terpinene (Kanakdande et al., 2007). Paprika oleoresin is extracted from the fruits of Capsicum annum L. by using organic solvents (mainly hexane) which are removed prior to use (Jarén-Galán et al., 1999). The oleoresin is composed of capsaicin (C18H27NO3, molar mass 305.4, melting point 62-65°C, boiling point 210-220°C), the main flavoring compound which gives pungency at higher concentrations, and capsanthin (C40H56O3, molecular weight 584.9 g/mol, appearance: red oil, soluble in water) and capsorubin, the main coloring compounds (among other carotenoids) (Pérez-Gálvez et al., 2003). The oleoresin and its components are used in formulating nutraceuticals, colorants and pharmaceuticals. The paprika oleoresin is microencapsulated by the traditional gelatin-gum arabic microcapsule (Fernandez-Trujillo, 2007).

5.2.13.2 Linoleic acid microencapsulation In nutrition, the term used for fats is lipids. A fatty acid is a component of the lipids in foods, usually as part of an acylglycerol (Gates, 1987). Lipid-oxidation rates can be predicted to some extent by some key factors, including the degree of fatty acid unsaturation, the distribution of fatty acids into different lipid classes, temperature, and the presence of oxygen, antioxidants, and oxidation catalysts (Lehtinen and Laakso, 2000). Saturated fatty acid is a fatty acid in which each of the carbons, except the terminal carbons, are bonded to two hydrogens (Gates, 1987). Linoleic acid is an unsaturated omega-6 fatty acid. n-6 fatty acids are a family of unsaturated fatty acids which all have a carbon-carbon double bond in the n-6 position, i.e., the sixth bond from the end of the fatty acid. The protein-rich fraction of oat reduces the oxidation rate of free linoleic acid by reducing the concentration of linoleic acid that can serve as a substrate for lipoxygenase (Lehtinen and Laakso, 2000). The mechanism underlying this behavior appears to be similar to the trapping of linoleic acid by cyclodextrin (Lopez-Nicolas et al., 1997). Another approach to reducing linoleic acid (Fig. 5.10) oxidation is microencapsulation with gum arabic using a spray-dryer with a centrifugal atomizer. The oxidation of encapsulated linoleic O HO 1

6 9

1

12

Figure 5.10  Chemical structure of linoleic acid (http://en.wikipedia. org/wiki/ Image: LAnumbering.png, courtesy of Edgar181).

Food Applications of Plant Exudates  ◾  275

acid was studied at various temperatures and at different relative humidities (Fang et al., 2005). The temperature of the dryer’s inlet air was found to have no significant effect on the moisture content of the microcapsules; hence, the oxidation process of encapsulated linoleic acid was unaffected by the inlet air temperature. However, the rotational speed of the atomizer did affect the size and moisture content of the microcapsules, which were found to be larger and higher, respectively, for microcapsules prepared at the lower rotational speed (Fang et al., 2005). Linoleic acid in a gum arabic-based microcapsule is more resistant to oxidation than that in a maltodextrinbased microcapsule. Although the size of the oil droplets in the emulsion with maltodextrin decreased and the emulsion stability improved by addition of a small-molecule emulsifier to linoleic acid, the oxidative stability of the encapsulated linoleic acid was not significantly improved. Encapsulated linoleic acid of small droplet size oxidized more slowly than that of large droplet size (Minemoto et al., 2002). The oxidation of linoleic acid in larger microcapsules proceeded more slowly. In addition, oxidation progressed more quickly at higher relative humidity, and it was suggested that the glass transition of the wall material might affect the progress of oxidation. Relative humidity was found to have little effect on the activation energy of oxidation during storage of the microcapsules (Fang et al., 2005). The oxidation processes of linoleic acid mixed with ferulic acid or the 1-pentyl, 1-hexyl and 1-heptyl ferulates, encapsulated with gum arabic or maltodextrin, were also studied. The alkyl ferulates had a higher antioxidative effect than ferulic acid, but there was no significant difference among the three alkyl ferulates (Fang et al., 2006). Suppression of oxidation by 1-hexyl ferulate or ferulic acid was more effective at higher additiveto-linoleic acid molar ratios. The suppressive effect of the alkyl ferulates was more pronounced for linoleic acid encapsulated with maltodextrin than for that encapsulated with gum arabic because of maltodextrin’s lack of antioxidative ability (Fang et al., 2006). Another approach that tackles both degradation of conjugated linoleic acid (CLA) and its acid degradation used the encapsulation of CLA in three different matrices: whey protein concentrate (WPC), gum arabic and a blend of WPC and maltodextrin 10 DE (1:1, w/w). Kinetics studies on the degradation of CLA and lipid oxidation of microcapsules were carried out at water activity values of 0.108 to 0.892, at 35 and 45°C. The highest values of CLA degradation and lipid oxidation were observed in the water-activity range of 0.103 to 0.429 for all matrices at 45°C, whereas the lowest CLA degradation and lipid oxidation were observed for WPC at a water activity of 0.743 and 35°C. WPC microcapsules exhibited the best morphology and encapsulation efficiency and the lowest CLA degradation (Jimenez et al., 2006).

5.2.13.3 Procyanidins Procyanidins, compounds commonly found in red wine, are thought to be good for our blood vessels. The endothelial cells lining our arteries are an important site of action for the vascularprotection effects of active polyphenols such as procyanidins (Corder et al., 2006). When wine is made in the traditional way, the grape fermentation period lasts 3 to 4 weeks, as opposed to the 1-week period in more modern methods. The traditional method allows for the full extraction of procyanidins from the skin and seeds. Procyanidins were extracted from grape-seed residues after oil removal. Microencapsulation of procyanidins was performed with gum arabic and maltodextrin as wall materials. After homogenization, spray-drying was used to prepare microcapsules. The microencapsulation efficiency was up to ∼89%. Analysis of the stable product showed that the procyanidin did not change during the processing and that the procyanidin microcapsule membrane was uninterrupted, maintaining fairly good integrity (Zhang et al., 2007).

276  ◾  Plant Gum Exudates of the World

5.2.14 Coacervation Coacervation is the separation of a colloid-rich layer from a lipophilic sol upon the addition of another substance (Aulton, 2002). This layer, which is present in the form of an amorphous liquid, constitutes the coacervate. Simple coacervation may be brought about by a ‘salting-out’ effect upon addition of an electrolyte or a non-solvent (Aulton, 2002). An important method of microencapsulation, employing complex coacervation, was developed by the National Cash Register Company. This method can produce capsules for use in controlled dry delivery, fragrance samplers, pesticides and cosmetic ingredients. In a complex coacervation process, gelatin with a high isoelectric point and gum arabic with many carboxyl groups are added to a core-containing suspension at relatively low pH above 35°C. The gelatin and gum arabic react to form microdroplets of polymer coacervate which separate. The wall around the core is hardened by the addition of formaldehyde or glutaraldehyde (Jason and Kalota, 1996). In the final steps, the suspension of microcapsules is cooled and the pH raised, after which the suspension is filtered leaving the microcapsules on the filter media (Jason and Kalota, 1996). Encapsulates having shells of cross-linked mixtures of proteins and polysaccharides are widely used in the food and pharmaceutical industries for controlled release of active and flavor compounds. Several analytical techniques were applied to characterize glutardialdehyde (GDA)-cross-linked encapsulates made of gelatin and gum arabic. Cross-linking occurred between GDA molecules and lysine and hydroxylysine ε-amino groups, and up to eight different types of cross-linked products could be identified. These included pyridinium ions and Schiff bases, as well as unreacted GDA condensation products (Fuquet et al., 2007). Many variations of complex coacervation are known, as well as polymer combinations. Complex coacervation is employed to encapsulate solids and liquids (Jason and Kalota, 1996). Another method of complex coacervation involves the formation of electrostatic complexes of gum arabic with chitosan. These polysaccharides are oppositely charged and optimum coacervate yield can be achieved at a gum arabic-to-chitosan ratio of 5, in a pH range of 3.5 to 5.0 (EspinosaAndrews et al., 2007). Coacervate yield was drastically decreased at pH values below 3.5 due to a low degree of ionization of gum arabic molecules, and at pH values above 5 due to low solubility of chitosan. Increasing ionic strength decreased coacervate yield due to shielding of ionized groups (Espinosa-Andrews et al., 2007). To avoid the participation of gelatin in the preparation of protein-gum arabic coacervates, complexes of pea globulin and α-gliadin proteins with gum arabic were prepared at different acidic pH values (Chourpa et al., 2006). Raman microspectrometry confirmed a higher content of β-sheets and random coils in pea globulin and dominating α-helical structures in α-gliadin. For protein-gum arabic complexes, Raman data supported the existence of specific pH conditions for optimal complex coacervation (pH 2.75 for globulin and pH 3.0 for gliadin), when pH-induced conformational perturbations of free protein structure are strongest and compensation of these perturbations by gum arabic is most pronounced (Chourpa et al., 2006).

5.2.15 Deep-fat frying Frying is a unit operation used mainly to alter the eating quality of foods (Fellows, 2000). Frying results in the thermal destruction of microorganisms and enzymes, as well as in reduced water activity at the food’s surface. During deep-fat frying, heat is transferred via convection within the hot oil and conduction to the interior of the food (Rispoli et al.,1987; Fellows, 2000). Throughout deep-fat frying, moisture loss is proportional to the square root of frying time and the oil absorption that occurs as moisture is removed from the food (Saguy and Pinthus, 1995). There are many

Food Applications of Plant Exudates  ◾  277

approaches for reducing the oil content of deep-fried foods including: pre-fry drying; blowing hot air against the freshly fried products and draining the excess oil from them; contacting the fried product with solvents such as difluorodichloromethane, and using certain additives (Annapure et al., 1999). Attempts to use hydrocolloid combinations with the goal of reducing oil content in fried foods have proven useful. Hydrocolloids at 0.25 to 2.00% (on the basis of chickpea flour weight) were screened for their ability to reduce oil uptake in a model deep-fat-fried product prepared from chickpea flour. Results indicated that the ability to reduce oil uptake in such a product decreases in the following order: gum arabic > carrageenan > gum karaya > guar gum > CMC > hydroxypropylmethyl cellulose (HPMC) (Annapure et al., 1999). Hydrocolloids such as xanthan, gum ghatti, gum tragacanth, and locust bean gum were found to be ineffective for this purpose (<10% reduction in oil content). Among all the hydrocolloids tested in this study, 2.0% gum arabic was the most useful: a 19% reduction in oil content with respect to the control was achieved (Annapure et al., 1999). It is possible that hydrocolloids are successful in such usages due to the formation of an oil-resistant barrier film or an alteration in surface hydrophobicity of the product being fried; in addition, a few hydrocolloids have thermal gelation capability. However, it should be noted that the presence of other food constituents can alter these properties. Hydrocolloids can be part of the recipe (as described above), or can be included in the batter, to reduce fat absorption during deep-fat frying (Sahin et al., 2005). One study consisted of investigating the effects of various gum types, i.e. HPMC, guar gum, xanthan gum and gum arabic, on the quality of deep-fat-fried chicken nuggets. Chicken samples which were 4 cm in diameter and 1.5 cm thick were taken from the breast portion and coated with batters composed of a 3:5 solidto-water ratio by immersion. The solid content of the batter formulations contained equal amounts of corn and wheat flours, 1.0% gum, 1.0% salt and 0.5% leavening agent. As a control, batter without gum addition was used. Samples were fried at 180°C for 3, 6, 9 and 12 min. The hardness and oil content of the chicken nuggets increased whereas the moisture content decreased during frying. HPMC and xanthan gums reduced oil absorption significantly compared with other gums and the control. When gum arabic was added to the batter formulation, the product exhibited the highest oil content and porosity (Sahin et al., 2005). Another report claimed that adding different hydrocolloids to batter formulations controlled moisture loss and oil uptake, resulting in crisp and porous products in a deep-fat-frying operation (Neslihan et al., 2006). Addition of gums not only helps reduce fat during frying, it also improves adhesion (Rispoli and Shaw, 1981). It may be that the protein, particularly gum arabic, contributes to the better batter adhesion.

5.2.16 Emulsions Emulsion is the dispersion of two immiscible liquids (Gates, 1987). Two types of liquid-liquid emulsions are: oil in water (o/w) (e.g. milk) or water in oil (w/o) (e.g. margarine) (Fellows, 2000). Emulsion stability depends on: type and quantity of the emulsifying agent, size of the globules in the dispersed phase, interfacial forces, viscosity of the continuous phase, and differences in the densities of the dispersed and continuous phases (Fellows, 2000). Homogenization is required to achieve stable emulsions. Homogenization consists of the size reduction (to 0.5-30 μm) of liquid or solid particles within the dispersed phase and emulsifying agents, by intense shearing forces (Fellows, 2000). A long list of selected emulsifying agents exist, including ionic and non-ionic emulsifiers and hydrocolloids. Emulsifying agents can be of natural origin or synthetic. The synthetic emulsifying agents are classified into polar and non-polar (Fellows, 2000). Hydrocolloids or gums also serve as stabilizers, due to their ability to induce long-term stability in systems consisting of water and oil. A partial list of hydrocolloids that can serve as emulsifying

278  ◾  Plant Gum Exudates of the World

agents in food processing includes: alginates, CMC, carrageenan, guar gum, gum arabic, locust bean gum, methylcellulose, pectin, gum tragacanth and xanthan. Gum arabic is known for its emulsification properties. Its surface activity was shown to be derived from the anchoring ability of the hydrophobic proteinaceous moieties (attached to the polysaccharide backbone) onto the oil phase (Garti and Leser, 2001). The role of the proteinaceous moiety in emulsification was also investigated using pectin from sugar beet as a model polysaccharide. Its important role in explaining emulsification properties has been proven, as in the case of gum arabic and soluble soy polysaccharides (Funami et al., 2007). Certain hydrophilic (anionic or non-ionic) polysaccharides, purified to close to protein-free levels, can exhibit surface activities and emulsification properties despite their rigid and hydrophilic nature. The adsorption isotherms of the surface-active biopolymers are similar to those of other macromolecular amphiphiles (Garti and Leser, 2001). Such gums include mainly those of the galactomannan family (locust bean gum, guar and fenugreek), as well as others from less known sources (Portulaca oleracea and Opuntia ficus-indica). Adsorption can be induced by a salting-out effect, resulting in semisolid interfacial layers. Hydrocolloids can form thick birefringent gel-like mechanical barriers at the oil-water interface of an emulsion’s oil droplets (Garti and Leser, 2001). Gum arabic has a unique combination of excellent emulsifying properties and low solution viscosity, making it very useful as a stabilizer of citrus oil emulsion concentrates in soft drinks and as a flavor encapsulator. Gum arabic is a mixture of principally polysaccharides and proteoglycans, the latter being arabinogalactan proteins (AGPs). It also contains trace levels of lipids (Yadav et al., 2007a). To test the hypothesis that lipids which are attached to the gum arabic AGPs as glycosylphosphatidylinositol (GPI) lipids make an important contribution to this gum’s emulsifying activity, gum arabic was treated with nitrous acid. This resulted in decreased emulsifying activity and loss of some glucosamine and nitrogen, but had very little effect on the principal carbohydrate composition. Treatment with 50% aqueous hydrogen fluoride at 0°C resulted in decreased emulsion properties but also a significant loss of arabinosyl residues (Yadav et al., 2007a). The approximately 1 to 3% subfraction of gum arabic components that adsorb to the surface of oil droplets has a higher abundance of GPI-linker components, much higher relative lipid and nitrogen contents, and somewhat higher emulsification activity than the whole gum. These results are consistent with roles of both lipids and proteins in the gum’s emulsification activity (Yadav et al., 2007a). Another manuscript added more information on the role of gum arabic in increasing emulsion stability. Stability was evaluated on the basis of oil-droplet size, creaming, viscosity, and protein-adsorption measurements. The addition of gum arabic caused a decrease in the amount of protein adsorbed at the interface. The addition of locust bean gum in some emulsions reduced the amount of protein adsorbed. Emulsion stability was affected by the nature of the polysaccharide (Makri and Doxastakis, 2006). Differences were also observed with respect to the nature of the protein, the method of its preparation and emulsion pH. All polysaccharides enhanced the emulsion’s viscosity, with xanthan and xanthan-locust bean gum exhibiting the highest values. The stability was enhanced by the increased viscosity of the continuous phase and the creation of a network, which prevented the oil droplets from coalescing (Makri and Doxastakis, 2006). As noted previously, gum arabic is used for the production of beverages and flavor concentrates. Therefore, it is not surprising to find a manuscript dealing with the effect of gum concentration, molecular parameters and homogenization conditions on the droplet size and stability of emulsions prepared using a conventional commercial Acacia senegal product and a series of A. senegal test gums prepared by controlled maturation process (Aoki et al., 2007). Pressure homogenization after vigorous stirring was found to produce the best results. The greater effectiveness of the matured gums was explained by the AGP complex’s unfolding as a result of pressure

Food Applications of Plant Exudates  ◾  279

homogenization and occupying a greater volume around the oil droplet, which in turn produced greater stabilization (Aoki et al., 2007). Another manuscript showed that it is possible to age emulsifier in a process comparable to that which occurs to the exudate gum as the age of the tree increases from 1 to 15 years. In this process, the molecular parameters of a “good” gum can be matched (Al-Assaf et al., 2007). Gum arabic can be replaced by other agents for the stabilization of o/w emulsions. For example, the emulsifying activities of two new glycoprotein emulsifiers from marine Halomonas species were comparable and, under certain conditions, superior to those produced by the commercial emulsifiers tested, i.e. xanthan gum, gum arabic and lecithin (Gutierrez et al., 2007b). Another new high-molecular-weight glycoprotein produced extracellularly by Antarctobacter sp. compared well with xanthan gum and gum arabic as an emulsion/stabilizing agent for a range of different food oils (Gutierrez et al., 2007a). The US food industry would benefit from a domestically produced gum with a dependable supply and consistent quality that can be used for preparing o/w emulsions, such as citrus oil emulsions for beverages. Corn fiber gum (CFG) is an arabinoxylan (hemicellulose) extracted from the corn kernel pericarp and/or endosperm fiber fractions that could potentially fulfill this need (Yadav et al., 2007b).

5.2.17 Foam The most general definition of a foam is a substance formed by trapping many gas bubbles in a liquid or solid. Another definition is that foams are two-phase systems which have gas bubbles dispersed in either a liquid or a solid, separated from each other by a thin film (Fellows, 2000). Stable foams can be produced by low vapor pressure in the bubbles to reduce evaporation and rupturing of the film; gelation or insolubilization of the film to increase rigidity of the foam as well as to decrease loss of entrapped gases; a low surface tension, to allow the bubbles to contain more air and avoiding their contraction (Fellows, 2000). Food foams are stabilized in different manners, for instance: ice cream is a foam whose structure is stabilized by freezing; marshmallow is stabilized by gelatin gelation, and meringues are stabilized by heat or by the addition of hydrocolloids. Foaming beverages, such as root beer and root beer floats prepared from vanilla ice cream and root beer, provide a drinkable product with a distinctive frothy foam head. The disadvantage of traditional floats is the inconvenience of preparation and the carbonation requirement for the foam preparation. A further drawback of traditional root beer is that it does not provide the thick, creamy mouth feel found in floats (Motts and Delease, 2008). Thus new foaming compositions are needed which will provide the desirable advantages of convenience, foam stability, and mouth feel. Another advantage might be a foaming composition prepared in a convenient form, which can be further formulated into a beverage concentrate, syrup, or final beverage. It was suggested that an excellent foam-creating property would be achieved by using a long list of gums, including the exudates gum arabic, gum ghatti, modified gum ghatti, tragacanth gum and/or a combination of these (Motts and Delease, 2008). Another invention relates to formulations for palatable foams with enhanced stability. The formulations include a base liquid (such as milk), a surfactant, a polysaccharide, and a polymer capable of molecular interaction with the polysaccharide. The polysaccharides that work best are high average molecular weight macromolecules, preferably with a high concentration of charged groups. In certain forms, the moieties capable of molecular interaction with the polysaccharide include one or more of the following: gum arabic, gum tragacanth, xanthan gum, alginic acid, alginate, chitin, beta-glucan, glycosaminoglycan, agar, carrageenan, guar gum, glucomannan, and any salt thereof (Soane et al., 2007).

280  ◾  Plant Gum Exudates of the World

A different approach to stabilizing foam is by combining protein isolates and hydrocolloids. For example, the foaming behavior of protein isolates from common bean (Phaseolus vulgaris L.) and scarlet runner bean (Phaseolus coccineus L.), prepared by isoelectric precipitation and ultrafiltration, was evaluated (Makri and Doxastakis, 2007). Gum arabic, locust bean gum (0.1% and 0.25% w/v), xanthan gum and a xanthan/locust bean gum mixture (0.1% w/v) had positive effects on foam creation. All polysaccharides increased foam stability, probably due to the increase in viscosity and to the creation of a network, which prevents the air droplets from coalescing. Isolates from P. coccineus and isolates obtained by ultrafiltration seemed to exhibit better foaming properties (Makri and Doxastakis, 2007).

5.3 GUM EXUDATES IN ANIMAL FOOD 5.3.1 Introduction The information in this chapter is mostly collected from manuscripts dealing with ecological studies of habitat and dietary requirements. A fundamental goal in ecology is to predict the outcome of competitive interactions. Ecological stoichiometry, which relates nutrient balance to ecological processes, provides a framework for identifying mechanistic links between macronutrient availability, nutritional physiology and competitive performance. Because carbohydrates serve as a principal metabolic fuel, carbohydrate scarcity may impinge upon behaviors related to aggression and activity (Grover et al., 2007).

5.3.2 Insects Insects are invertebrate animals of the class Insecta, phylum Arthropoda. Like other arthropods, an insect has an exoskeleton, a segmented body, and jointed legs. Adult insects typically have wings and are the only flying invertebrates. There are about 900,000 known insect species, with thousands of new ones described yearly. They are commonly grouped into 27 to 32 orders, depending upon the classification used. The largest order is that of the beetles. Next, in order of size, are the moths and butterflies; the wasps, ants, and bees; and the flies and mosquitoes. Other major orders are the true bugs; the cicadas, aphids, and scale insects; the grasshoppers and crickets; the cockroaches; and the mantids. Ants are any member of ∼10,000 species belonging to the social insect family Formicidae. They are found all over the world, but are particularly widespread in hot climates. Their length ranges from 2 to 25 mm and their color is regularly black, brown, yellow or red. Different species differ widely in their diets and may be carnivorous, herbivorous, or omnivorous. Some ants even “farm” fungi for food, cultivating them in their nests, or “milk” aphids. Harvester ants eat and store seeds. The army ants of the New World tropics and the driver ants of tropical Africa are carnivorous itinerant species. They travel like armies in long columns, overrunning and devouring animals that cannot flee their path; the African species even consume large mammals. It was assumed that for Argentine ants (Linepithema humile), a widespread and aggressively invasive species (Fig. 5.11), carbohydrate scarcity may affect behaviors involved in competitive dominance (e.g. aggression, activity) to a greater extent than deficiencies in protein or other nutrients used preferentially for growth (Grover et al., 2007). When this hypothesis was tested with a diet manipulation study involving laboratory colonies of ants, carbohydrate scarcity was shown to compromise aggression and activity in ants. Moreover, access to carbohydrate-rich resources (e.g. plant exudates, hernipteran honeydew) might influence behavioral investments that

Food Applications of Plant Exudates  ◾  281

Figure 5.11  Argentine ants accessing a commercial trap commonly available in the United States (http://en.wikipedia.org/wiki/Image:Argentine_ants_accessing_trap.JPG, author: Thmazing).

contribute to competitive performance. Such investments might be especially important for invasive ants, given their aggressiveness and tendency to interact with honeydew-producing Hemiptera (Grover et al., 2007).

5.3.3 Mammals and primates Gums (although not necessarily exudates) can serve as part of a mammal’s diet. A good example of this is seen in the squirrel glider (Petaurus norfolcensis), an inhabitant of the forests and woodlands of eastern Australia (Fig. 5.12). Homopterous insects are its primary food, consumed throughout the year. Arthropods, nectar and pollen, and Acacia gum make up the remainder of their diet (Holland et al., 2007). Another mammal which consumes gum exudates as part of its diet is the slow loris (Nycticebus coucang; Lorisidae) (Fig. 5.13). The dietary habit of the slow loris, an inhabitant of West Malaysian forests, was studied by direct observation of radio-tagged individuals and by analyzing their feces. Their diet was found to be composed of five distinct types of food: floral nectar and nectar-producing parts, phloem sap, fruits, plant gum exudates, and arthropods (Wiens et al., 2006). The largest amount of time spent feeding was on phloem sap (34.9%), floral nectar and nectar-producing parts (31.7%), and fruits (22.5%). The loris’ slow pace has been causally linked to a low intake rate of usable energy due to a diet that is generally low in energy, is periodically, but unpredictably scarce, and contains high amounts of toxins or digestion inhibitors (Wiens et al., 2006). Malagasy primates are characterized by a great variety of dietary habits: some of them are omnivores, folivores, frugivores, gumnivores, insectivores or even specialized hard-object feeders. All cheirogaleids feed on tree exudates, but whereas gum consumption is occasional or limited for Microcebus, Cheirogaleus and Mirza, gums are the dominant food source for Phaner and Allocebus (Viguier, 2004). A long-term ecological study of habitat and dietary requirements was performed for the pied bare-face tamarin (Saguinus bicolor bicolor). One group was studied for 11 months

282  ◾  Plant Gum Exudates of the World

Figure 5.12  The squirrel glider (Petaurus norfolcensis) (Source: John Gould, F.R.S., Mammals of Australia, Vol. I Plate 24, London 1863).

in an area of secondary forest in a suburb of Manaus, in Amazonas, Brazil. Three main types of vegetation were found inside the group’s home range: capoeira, older secondary forest and campinarana (white sand forest). The tamarins ate fruits (21 species), flowers (1 species), exudates (4 species), and arthropods (insects and spiders). Trees used for feeding were low and had small crown diameters. Three plant species (Protium aracouchinni, Myrcia cf. fallax, and Couma utilis) were used intensively during the three seasons covered by the study period (Egler, 1992). The concentrated use of three fruit species, each for an extended period (one fruiting species per season), provided the tamarins with a regular food supply. Tamarins consumed exudates from holes in the bark of trees of the families Anacardiaceae and Vochysiaceae, as well as gum exuded from seed pods of Mimosaceae. Exudates were exploited during the dry season and at the beginning of the wet season. Group travel was primarily based on routes connecting the exploited fruiting trees, with foraging for animal prey along the way. Tamarins searched for arthropods on trunks, branches and leaves and in trunk holes. The foraging and feeding tactics displayed by S. bicolor bicolor were closely linked to its morphological characteristics (small size and weight, claw-like

Food Applications of Plant Exudates  ◾  283

Figure 5.13  The slow loris (http://en.wikipedia.org/wiki/Image:Slow_Loris_Female.jpg, courtesy of Lionel Mauritson).

nails), which allowed access to energy-rich resources (arthropods and plant exudates) in different strata of the vegetation (Egler, 1992). A comprehensive study looked at the nutritional value and importance of gum exudates as feed for arboreal marsupials (Lindenmayer et al., 1994). Chemical analysis of the total sugar and nitrogen contents of Acacia dealbata, Acacia obliquinervia and Acacia frigescens gum exudates was performed. Values for sugar content ranged from 24 to 68% per sample and the significant difference depended on the Acacia species, forest location and forest type (Lindenmayer et al., 1994). Nitrogen content (from 0.2 to 0.7% per sample) of Acacia gum was significantly influenced by a combination of three interacting factors: Acacia species, tree diameter, and forest type. The findings of this study therefore indicated that the sugar and nitrogen contents of Acacia gum may vary among forest types and tree species. Acacia gum is an important source of food for several species of arboreal marsupials, and differences in their sugar and nitrogen contents could potentially influence the distribution and abundance of these animals (Lindenmayer et al., 1994). Two closely related primates—the common marmoset (Callithrix jacchus) (Fig. 5.14) and the cotton-top tamarin (Saguinus oedipus)—were studied for their decision-making abilities (choosing between small, short-term rewards and large, long-term rewards), and it was suggested that gum exudate consumption and foraging ecology might provide selective pressure for the evolution of self-control. All animals, humans included, discount future rewards—the present value of delayed rewards is viewed as less than the value of immediate rewards. Nevertheless, there exists considerable, albeit unexplained variation among species in their capacity to wait for rewards—that is, to exert patience or self-control (Stevens et al., 2005). The two primates faced a self-control paradigm in which individuals chose between taking an immediate small reward and waiting a variable amount of time for a large reward. Under these conditions, marmosets waited significantly longer for food than tamarins. Feeding ecology might explain this fact. Marmosets rely on gum, a food product acquired by waiting for exudate to flow from trees, whereas tamarins feed on insects, a food product that requires impulsive action (Stevens et al., 2005).

284  ◾  Plant Gum Exudates of the World

Figure 5.14  Common marmoset (http://en.wikipedia.org/wiki/Image:Marmoset_copy.jpg, courtesy of Carmem A. Busko).

5.4 HEALTH-RELATED ASPECTS 5.4.1 Safety Gum arabic is a GRAS food additive (FDA, 1974). It is neither mutagenic (JECFA, 1982; Sheu et al., 1986) nor teratogenic (JECFA, 1982; Collins et al., 1987), has no subchronic toxicity (Anderson et al., 1982; JECFA, 1982), chronic toxicity or carcinogenicity (National Toxicology Programme, 1982; Melnick et al., 1983). Moreover, its safety has been established in healthy volunteers (McLean Ross et al., 1983). The estimated acceptable daily intake (ADI) for humans was set as “not specified” in 1982, and this was confirmed in 1992 (JECFA, 1993; Dondain and Phillips, 1999). The safety of a new generation of gum arabic (SUPER GUM™), obtained by heating enhancement and accelerated maturation of conventional gum arabic, was also confirmed (Doi et al., 2006). During the latter study, the gum was administered to both sexes of F344 rats at dietary levels of 0 (control), 1.25%, 2.5%, and 5.0% (10 rats/sex per group). The treatment had no effects on clinical signs, survival, body weight or food and water consumption, or on urinalysis, ophthalmology, hematology, or blood biochemistry readings. Gross pathology

Food Applications of Plant Exudates  ◾  285

and histopathology exhibited no differences of toxicological significance between control and treatment groups (Doi et al., 2006). Gum arabic is used in tablet-coating plants and as such, pharmaceutical industry workers are exposed to its dust. Common complaints have included work-related shortness of breath, chest tightness, runny nose, itching and redness of the eyes. Thus, sensitization to gum arabic was investigated with respect to allergies to this substance compared with a control group (Sander et al., 2006). Allergy to gum arabic was shown by skin-prick test, presence of specific IgE and a positive bronchial challenge with gum arabic. Sensitization to gum arabic carbohydrate structures occurs causally in atopic patients with pollen sensitization without obvious exposure to gum arabic. This study suggests that allergy to gum arabic is mediated preferentially by IgE antibodies directed to the polypeptide chains of this gum (Sander et al., 2006).

5.4.2 Nutrition Food manufacturers use the term “dietary fiber” to describe their products or its contents, but there is no internationally accepted legal definition or approval system to support this practice. A physiological botanical description of “dietary fiber” is the remnants of plant components that are resistant to hydrolysis by human alimentary enzymes; this definition was soon extended to include all undigestible plant polysaccharides. Chemical materials such as resistant starch, oligosaccharides, lignin and associated plant substances, which are both soluble and insoluble, are now included. Gum arabic, like other food fiber materials, is universally recognized scientifically as a food additive but its regulatory status remains a matter of discussion and some uncertainty. The same uncertainty also relates to the regulatory status, as dietary fiber, of other soluble and insoluble plant/algal polysaccharides (Phillips et al., 2008). Upon its consumption, gum arabic is fermented by the intestinal bacteria to SCFAs, particularly propionate. Using an enrichment culture of pig cecal bacteria from a selected high-molecular-weight gum arabic (MW 1.77 x 106), it was observed that a Prevotella ruminicola-like bacterium, as the predominant bacterium, is most likely responsible for gum arabic fermentation to propionate (Kishimoto et al., 2006). On the one hand, dietary supplementation with gum arabic (SUPER GUMTM) increased serum butyrate, which at least in vitro has beneficial effects on renal profibrotic cytokine generation (Matsumoto et al., 2006). On the other hand, plant hydrocolloids can reduce protein digestibility and, consequently, modify the bioavailability of amino acids. In-vitro hydrolysis at 37°C of β-lactoglobulin in mixed dispersions containing gum arabic, low-methylated pectin or xylan was studied. β-lactoglobulin was almost totally resistant to pepsin digestion and the three plant hydrocolloids significantly inhibited β-lactoglobulin digestibility. The decrease in digestibility obtained with xylan was greater than that obtained with gum arabic or low-methylated pectin (Mouecoucou et al., 2003). The question of whether the efficiency of intestinal calcium (Ca) absorption is improved by concomitant ingestion of gum arabic in rats was also investigated. The Ussing Chamber method was utilized to clarify the effect of gum arabic on upper and lower small-intestinal absorption of Ca (Kawase et al., 2007). The Ussing Chamber is comprised of two separate parts, which come together to form a closed chamber. At the interface between the two parts, a layer of tissue, e.g., excised intestinal tissue, is mounted on pins, extending across the interface between the two parts of the chamber. Thus, the tissue separates the chamber into two halves, each of which contains a quantity of buffer solution in contact with the tissue layer. The buffer solution is circulated through each chamber half by an air-lift pump and temperature is maintained at a constant level by a temperature-controlled water jacket surrounding part of the buffer recirculation path. Transport across the membrane is typically

286  ◾  Plant Gum Exudates of the World

determined by using radioactive material as a tracer, but other analytical techniques can be used to measure transport. In addition, other tracers, such as fluorescent materials, can be used (Hidalgo et al., 1996). Increased in-vitro Ca permeation was observed in rats that ingested water with 7.5% gum arabic for 10 days. These results suggested that administration of gum arabic with Ca could increase the efficiency of oral Ca absorption (Kawase et al., 2007). Diarrhea is a common and deadly threat to millions of infants and children worldwide. Similarly, malabsorption can aggravate the health status of the chronically ill, particularly in the elderly population. Prompt recovery from intestinal dysfunction may have a substantial impact on many populations. The proabsorptive effects of gum arabic could directly reduce and ameliorate intestinal dysfunction. Natural proteoglycans, such as gum arabic, can reduce secretory effects induced by cathartics and, hence, are predictive of potential effectiveness in the context of diarrhea or malabsorption due to infectious or systemic causes (Codipilly et al., 2006). Stem exudates, seeds, leaves and the insides of pods are also used for skin diseases, as well as to control parasites in dogs and to treat diarrhea (Lans et al., 2000).

References Akhtar, M., and E. Dickinson. 2007. Whey protein-maltodextrin conjugates as emulsifying agents: An alternative to gum Arabic. Food Hydrocolloids 21:607-16. Al-Assaf, S., Phillips, G. O., Aoki, H., and Y. Sasaki. 2007. Characterization and properties of Acacia senegal (L.) Willd. var. senegal with enhanced properties (Acacia (sen) SUPER GUMTM): Part 1. Controlled maturation of Acacia senegal var. senegal to increase viscoelasticity, produce a hydrogel form and convert a poor into a good emulsifier. Food Hydrocolloids 21:319-28. Anderson, D. M. W., Ashby, P., Busuttil, A. et al. 1982. Subchronic effects of gum arabic (Acacia) in the rat. Toxicol. Lett. 14:221-27. Annapure, U. S., Singhal, R. S., and P. R. Kulkarni. 1999. Screening of hydrocolloids for reduction in oil uptake of a model deep fat fried product. Fett/Lipid 101(6):S217-21. Anson, M. L., and M. Pader. 1958. Method of making protein food product. US Patent 2,833,651. Aoki, H., Katayama, T., Ogasawara, T., Sasaki, Y., Al-Assaf, S., and G. O. Phillips. 2007. Characterization and properties of Acacia senegal (L.) Willd. var. senegal with enhanced properties (Acacia (sen) SUPER GUMTM): Part 5. Factors affecting the emulsification of Acacia senegal and Acacia (sen) SUPER GUMTM. Food Hydrocolloids 21:353-58. Asghar, A., Anjum, F. M., Butt, M. S., Tariq, M. W., and S. Hussain. 2007. Rheological and storage effect of hydrophilic gums on the quality of frozen dough pizza. Food Sci. Technol. Res. 13:96-102. Atal, C. K., Dubey, R.K., and J. Singh. 1985. Biochemical basis of enhanced drug bioavailability by piperine: Evidence that piperine is a potent inhibitor of drug metabolism. J. Pharmacol. Exp. Ther. 232:258-62. Aulton, M. E. 2002. Pharmaceutics, the science of dosage form design, 2nd edition. Edinbourg: Churchill Livingstone. Balke, W. J. 1984. The use of natural hydrocolloids as thickeners, stabilizers and emulsifiers. Special report, New York State Agricultural Experiment Station, No. 53, 31-4. Bates, R. P., Morris, J. R., and P. G. Crandall. 2001. Principles and practices of small- and medium-scale fruit juice processing. FAO Agricultural Services Bulletin #146. Best, E. T. 1990. In Gums and jellies, in sugar confectionary manufacture, ed E. B. Jackson, 190-217. Glasgow: Blackie. Bhandari, B. R., Dumoulin, E. D., Richard, H. M. J., Noleau, I., and A. M. Lebert. 1992. Flavor encapsulation by spray drying: Applications to citral and linalyl acetate. J. Food Sci. 57:217-21. Bhardwaj, R. K., Glaeser, H., Becquemont, L., Klotz, U., Gupta, S. K., and M. F. Fromm. 2002. Piperine, a major constituent of black pepper, inhibits human P-glycoprotein and CYP3A4. J. Pharmacol. Exp. Ther. 302:645-50.

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288  ◾  Plant Gum Exudates of the World Gabas, A. L., Telis, V. R. N., Sobral, P. J. A., and J. Telis-Romero. 2007. Effect of maltodextrin and arabic gum in water vapor sorption thermodynamic properties of vacuum dried pineapple pulp powder. J. Food Eng. 82:246-52. Gallina, A., Fiorese, E., Pastore, P., and F. Magno. 2004. Identification and semi quantitative determination of gum arabic in wines by GC-MS and size exclusion chromatography. Annali Di Chimica 94:177-84. Garti, N., and M. E. Leser. 2001. Emulsification properties of hydrocolloids. Polymers for Avanced Technologies 12:123-35. Gates, J. C. 1987. Basic foods, 3rd edition. New York: Holt, Rinehart and Winston, Inc. Glicksman, M. 1969. Gum technology in the food industry. New York: Academic Press. Grover, C. D., Kay, A. D., Monson, J. A., Marsh, T. C., and D. A. Holway. 2007. Linking nutrition and behavioral dominance: carbohydrate scarcity limits aggression and activity in Argentine ants. Proc. Royal Soc. B-Biol. Sci. 274:2951-7. Guichard, E., Issanchou, S., Descourvieres, A., and P. Etievant. 1991. Pectin concentration, molecular weight and degree of esterification: Influence on volatile composition and sensory characteristics of strawberry jam. J. Food Sci. 56:1621-7. Gulseren, I., and J. N. Coupland. 2007. Ultrasonic velocity measurements in frozen model food solutions. J. Food Eng. 79:1071-8. Gutierrez, T., Mulloy, B., Bavington, C., Black, K., Green, D. H., and H. David. 2007a. Partial purification and chemical characterization of a glycoprotein (putative hydrocolloid) emulsifier produced by a marine bacterium Antarctobacter. Appl. Microbiol. Biotechnol. 76:1017-26. Gutierrez, T., Mulloy, B., Black, K., and D. H. Green. 2007b. Glycoprotein emulsifiers from two marine Halomonas species: Chemical and physical characterization. J. Appl. Microbiol. 103:1716-27. Hansson, A., Andersson, J., and A. Leufven. 2001. The effect of sugars and pectin on flavour release from a soft drink-related model system. Food Chem. 72:363-8. Heath, H. B. 1985. The flavor trap. Food Flavor Ingredients 7:21-25. Hidalgo, I., Juvenal, R., Frederick, M. S., and L. Philip. 1996. Diffusion chamber system and method for transport studies. WO/1996/002627. Holland, G. J., Bennett, A. F., and R. van der Ree. 2007. Time-budget and feeding behaviour of the squirrel glider (Petaurus norfolcensis) in remnant linear habitat. Wildlife Res. 34:288-95. Howes, F. N. 1949. Vegetable gums and resins. Waltham, MA: Chronica Botanica. Jacobs, M. B. 1949. Candy flavorings. Am. Perfumer Essential Oil Rev. 54:54. Jarén-Galán, M., Nienaber, U., and S. J. Schwartz. 1999. Paprika (Capsicum annuum) oleoresin extraction with supercritical carbon dioxide. J. Agric. Food Chem. 47:3558-64. Jason, M. E., and D. J. Kalota. 1996. Microencapsulation process by coacervation. US Patent 5,540,927. JECFA. 1982. Toxicological evaluation of certain food additives, 526. Arabic gum (gum arabic). In Twentysixth Report of the Joints FAO/WHO Expert Committee on Food Additives, Food Additives Series 17, 22-7. Geneva: World Health Organization. JECFA. 1993. Toxicological evaluation of certain food additives and contaminants, 789. Carotenes from natural sources (algal and vegetable). Geneva: World Health Organization. Jimenez, M., Garcia, H. S., and C. I. Beristain. 2006. Spray-dried encapsulation of conjugated linoleic acid (CLA) with polymeric matrices. J.Sci. Food Agri. 86:2431-7. Jones, J. K. N., and F. Smith. 1949. Plant gums and mucilages. Adv. Carbohydrate Chem. 4:243-83. Kanakdande, D., Bhosale, R., and R. S. Singhal. 2007. Stability of cumin oleoresin microencapsulated in different combination of gum arabic, maltodextrin and modified starch. Carbohydrate Polymers 67:536-41. Kaushik, V., and Y. H. Roos. 2007. Limonene encapsulation in freeze-drying of gum Arabic-sucrose-gelatin systems. LWT-Food Sci. Technol. 40:1381-91. Kawase, A., Hirata, N., Tokunaga, M., Matsuda, H., and M. Iwaki. 2007. Gum arabic enhances intestinal calcium absorption in rats. J. Health Sci. 53:622-4. Kikuchi, S., Fang, X., Shima, M., Katano, K., Fukami, H., and S. Aiachi. 2006. Oxidation of arachidonoyl glycerols encapsulated with saccharides. Food Sci. Technol. Res. 12:247-51. Kishimoto, A., Ushida, K., Phillips, G. O., Ogasawara, T., and Y. Sasaki. 2006. Identification of intestinal bacteria responsible for fermentation of gum arabic in pig model. Curr. Microbiol. 53:173-7.

Food Applications of Plant Exudates  ◾  289 Klose, R.E. and M. Glicksman. 1975. Gums. In: Furia, T. E., Editor. Handbook of Food Additives (2nd Edition ed.), Cleveland: CRC Press. pp. 295–359. Krishnan, S., Kshirsagar, A. C., and R. S. Singhal. 2005. The use of gum arabic and modified starch in the microencapsulation of a food flavoring agent. Carbohydrate Polymers 62:309-15. Lans, C., Harper, T., Georges, K., and E. Bridgewater. 2000. Medicinal plants used for dogs in Trinidad and Tobago. Preventive Veterinary Medicine 45:201-20. Lewis, Y. S., Nambudiri, E. S., and T. Philip. 1966. Composition of cardamom oils. Perfumery and Essential Oil Record 57:623-8. Lindenmayer, D. B., Boyle, S., Burgman, M. A., McDonald, D., and B. Tomkins. 1994. The sugar and nitrogen-content of the Acacia species in the mountain ash and alpine ash forests of Central Victoria and its potential implications for exudivorous arboreal marsupials. Australian J. Ecol, 19:169-77. Lobato-Calleros, C., Rodriguez, E., Sandoval-Castilla, O., Vernon-Carter, E. J., and J. Alvarez-Ramirez. 2006. Reduced-fat white fresh cheese-like products obtained from W-1/O/W-2 multiple emulsions: Viscoelastic and high-resolution image analyses. Food Res. Int. 39:678-85. Lopez, E.C., Champion, D., Blond, G., and M. Le Meste. 2005. Influence of dextran, pullulan and gum arabic on the physical properties of frozen sucrose solutions. Carbohydrate Polymers 59:83-91. Lopez-Nicolas, J. M., Bru, R., and F. Garcia-Carmona. 1997. Enzymic oxidation of linoleic acid by lipoxygenase forming inclusion complexes with cyclodextrins as starch model molecules. J. Agric. Food Chem. 45:1144-8. Lubbers, S., and E. Guichard. 2003. The effects of sugars and pectin on flavour release from a fruit pastille model system. Food Chem. 81:269-73. Makri, E. A., and G. I. Doxastakis. 2006. Study of emulsions stabilized with Phaseolus vulgaris or Phaseolus coccineus with the addition of Arabic gum, locust bean gum and xanthan gum. Food Hydrocolloids 20:1141-52. Makri, E. A., and G. I. Doxastakis. 2007. Surface tension of Phaseolus vulgaris and coccineus proteins and effect of polysaccharides on their foaming properties. Food Chem. 101:37-48. Mathai, C.K. 1985. Quality evaluation of the ‘Agmark’ grades of cardamom Elleteria cardamomum. J. Sci. Food Agric. 36:450-2. Matsumoto, N., Riley, S., Fraser, D. et al. 2006. Butyrate modulates TGF-beta 1 generation and function: Potential renal benefit for Acacia(sen) SUPERGUMTM (gum arabic)? Kidney International 69:257-65. Mazurkiewicz, J., Zaleska, H., and J. Zaplotny. 1993. Studies in carbohydrate-based glues and thickeners for foodstuffs. I. Glucose-sucrose-apple pectin ternary system. Starch 45:175-7. McLean Ross A. H., Eastwood, M. A., Brydon, W. G., Anderson, J. A., and D. M. W. Anderson. 1983. The dietary effects of gum arabic (Acacia senegal) in humans. Am. J. Clin. Nutr. 37:368-75. Melnick, R. L., Huff, J., Haseman, J. K., Dieter, M. P., and C. K. Grieshaber. 1983. Chronic effects of agar, guar gum, gum arabic, locust-bean gum, or tara gum in F344 rats and B6C3F1 mice. Food Chem. Toxicol. 21:305-11. Minemoto, Y., Hakamata, K., Adachi, S., and R. Matsuno. 2002. Oxidation of linoleic acid encapsulated with gum arabic or maltodextrin by spray-drying. J. Microencapsulation 19:181-9. Motts, L. L. P., and P. Delease. 2008. Foam-creating compositions, foaming beverage compositions and methods of preparation thereof. WO/2008/008393. Mouecoucou, J., Sanchez, C., Villaume, C. et al. 2003. Effects of different levels of gum arabic, low methylated pectin and xylan on in vitro digestibility of beta-lactoglobulin. J. Dairy Sci. 86: 3857-65. Neslihan, A., Serpil, S., and S. Gulum. 2006. Functionality of batters containing different gums for deep-fat frying of carrot slices. J. Food Eng. 75:522-6. Nichols, A. W. 2007. Probiotics and athletic performance: A systematic review. Curr. Sports Medicine Rep. 6:269-73. National Toxicology Programme. 1982. Carcinogenesis bioassay of gum arabic (CAS no.9000–01–5) in F344 rats and B6C3F1 mice (feed study). Natl Toxicol. Program Tech. Rep. Ser. 227, 1–124. Nussinovitch, A. 2003. Water-soluble polymer applications in foods. Blackwell Publishing, UK: Oxford. Palermiti, F. M. 1993. Method of manufacturing a juice concentrate. US Patent 5,194,280. Paraskevopoulou, A., Boskou D., and V. Kiosseoglou. 2005. Stabilization of olive oil-lemon juice emulsion with polysaccharides. Food Chem. 90:627-34.

290  ◾  Plant Gum Exudates of the World Paraskevopoulou, D., Boskou, D., and A. Paraskevopoulou. 2007. Oxidative stability of olive oil-lemon juice salad dressings stabilized with polysaccharides. Food Chem. 101:1197-204. Pegg, R. B., and F. Shahidi. 1999. Encapsulation and controlled release in food preservation. In Handbook of food preservation, ed. M. Shafiur Rahman, pp. 611-67. New York and Basel: Marcel Dekker, Inc. Pekka Lehtinen, P., and S. Simo Laakso. 2000. Inhibition of linoleic acid oxidation by interaction with a protein-rich oat fraction. J. Agric. Food Chem. 48:5654-7. Pérez-Gálvez, A., Martin, H. D., Sies, H., and W. Stahl. 2003. Incorporation of carotenoids from paprika oleoresin into human chylomicrons. Br. J. Nutr. 89:787-93. Phillips, G. O., Ogasawara, T., and K. Ushida. 2008. The regulatory and scientific approach to defining gum arabic (Acacia senegal and Acacia seyal) as a dietary fibre. Food Hydrocolloids 22:24-35. Premi, B. P. 2000. Essential oils and oleoresins in India, Beverage and Food World 27:12-9. Pua, C. K., Abd Hamid, N. S., Rusul, G., and R. Abd Rahman. 2007. Production of drum-dried jackfruit (Artocarpus heterophyllus) powder with different concentration of soy lecithin and gum Arabic. J. Food Eng. 78:630-6. Purseglove, J. W., Brown, E. J., Green, C. L., and S. R. J. Robbins. 1980. Spices Vol. 1. New York: Longman Inc. Reidel, H. 1983. The use of gums in confectionery. Confect. Prod. 49:612-3. Reidel, H. 1986. Confections based on gum arabic. Confect. Prod. 52:433-7. Reineccius, G. A. 1988. Spray drying of food flavours. In Flavour encapsulation, ed. G. A. Reineccius, and S. J. Risch, 55-66. Washington, DC: American Chemical Society. Reineccius, G. A. 1989. Flavour encapsulation. Food Rev. Int. 5(2), 448. Righetto, A. M., and F. M. Netto. 2005. Effect of encapsulating materials on water sorption, glass transition and stability of juice from immature acerola. Int. J. Food Properties 8:337-46. Righetto, A. M., and F. M. Netto. 2006. Vitamin C stability in encapsulated green West Indian cherry juice and in encapsulated synthetic ascorbic acid. J. Sci. Food Agric. 86:1202-8. Rispoli, J. M., and J. R. Shaw. 1981. Self-sticking bread crumb composition and process. US Patent 4,260,637. Rispoli, J. M., Sergenian, H. H., Topalian, H., Rogers, M. A., and J. S. Swartley. 1987. Coating mix containing a fried component and process therefore. European Patent EP0110587B1. Roberts, D. D., Elmore, J. S., Langley, K. R., and J. Bakker. 1996. Effects of sucrose, guar gum, and carboxymethylcellulose on the release of volatile flavor compounds under dynamic conditions. J. Agric, Food Chem. 44:1321-6. Rogers, M. A., Roos, Y. H., and H. D. Goff. 2006. Structural heterogeneity and its effect on the glass transition in sucrose solutions containing protein and polysaccharide. Food Hydrocolloids 20:774-9. Saguy, I. S., and E. J. Pinthus. 1995. Oil uptake during deep-fat frying: Factors and mechanisms. Food Technol. 4, 142-5, 152. Sahin, S., Sumnu, G., and B. Altunakar. 2005. Effects of batters containing different gum types on the quality of deep-fat fried chicken nuggets. J. Sci. Food Agric. 85:2375-9. Sander, I., Raulf-Heimsoth, M., Wiemer, K., Kespohl, S., Bruning, T., and R. Merget. 2006. Sensitization due to gum arabic (Acacia senegal): The cause of occupational allergic asthma or crossreaction to carbohydrates? Int. Arch. Allergy Immunol. 141:51-6. Shaikh, J., Bhosale, R., and R. Singhal. 2006. Microencapsulation of black pepper oleoresin. Food Chem. 94:105-10. Sharadanant, R., and K. Khan. 2006. Effect of hydrophilic gums on the quality of frozen dough: Electron microscopy, protein solubility, and electrophoresis studies. Cereal Chem. 83:411-7. Sheu, C. W., Cain, K. T., Rushbrook, C. J., Jorgenson, T. A., and W. M. Generoso. 1986. Tests for mutagenic effects of ammoniated glycyrrhizin, butylated hydroxytoluene, and gum arabic in rodent germ cells, Environ. Mutagen. 8:357-67. Shuman, A. C. 1960. Theoretical aspects of hydrocolloids in controlling crystal structure in foods. Physical functions of hydrocolloids. Advan. Chem. Ser. 25:59-63. Soane, D., Berg, M. C., Mowers, W. A., and B. Walker. 2007. Stabilized edible foams. USPTO Applicaton 20070065555

Food Applications of Plant Exudates  ◾  291 Stevens J. R., Hallinan, E. V., and M. D. Hauser. 2005. The ecology and evolution of patience in two New World monkeys. Biol. Lett. 1:223-6. Sutherland, J. P., Varnam, A.H., and M. G. Evans. 1986. A color atlas of food quality control. A Wolf Science Book, Weert, The Netherlands. Teixeira, M. I., Andrade, L. R., Farina, M., and M. H. M. Rocha-Leao. 2004. Characterization of short chain fatty acid microcapsules produced by spray drying. Mater. Sci. Eng. C-Biometric and Supramolecular Systems 24:653-8. Vega, C., and Y. H. Roos. 2006. Invited review: Spray-dried dairy and dairy-like-emulsions—compositional considerations. J. Dairy Sci. 89:383-401. Whistler, R. L. 1973. Industrial gums, 2nd edition. New York: Academic Press. Viguier, B. 2004. Functional adaptations in the craniofacial morphology of Malagasy primates: Shape variations associated with gummivory in the family Cheirogaleidae. Annals of Anatomy-Anatomischer Anzeiger 186:495-501. Wiens, F., Zitzmann, A., and N. A. Hussein. 2006. Fast food for slow lorises: Is low metabolism related to secondary compounds in high-energy plant diet? J. Mammalogy 87:790-8. Williams, C. T. 1961. The function of gum acacia in sugar confectionery. Confect. Manuf. 6:299. Wolff, M. M., and C. Manhke. 1982. Confiserie: la gomme arabique. Rev. Fabr. ABCD, 57:23-7. Yadav M. P., Igartuburu J. M., Yan Y. C., and E. A. Nothnagel. 2007a. Chemical investigation of the structural basis of the emulsifying activity of gum Arabic. Food Hydrocolloids 21:297-308. Yadav, M. P., Johnston, D. B., Hotchkiss, A. T., and K. B. Hicks. 2007b. Corn fiber gum: A potential gum arabic replacer for beverage flavor emulsification. Food Hydrocolloids 21:1022-30. Zhang L. F., Mou D. H., and Y. S. Du. 2007. Procyanidins: Extraction and micro-encapsulation. J. of the Science of Food and Agriculture 87: 2192-7.

Chapter 6

Gum Exudates in Water-Based Adhesives 6.1 INTRODUCTION Although the use of adhesives can be traced back many centuries, their industrial production started only ∼300 years ago. Modern structural adhesives can be dated from about 1910, when phenol-formaldehyde resins were introduced (Bruno, 1970). In around 1930, water-based glues composed ∼90% of the adhesives market. From 1930 to 1986, this figure decreased to ∼60%. However, these glues have seen an average annual increase of a few percentage points in recent years, due to renewed interest from the packaging, construction and medicinal industries, indicating that nature-based products will continue to hold a certain percentage of the market (Hagquist et al., 1990; Darnay and Redd, 1994). Information on gum exudates in water-borne adhesives is very important, but limited. This chapter includes information on gum exudates as adhesive materials in medicinal products, namely mucoadhesives (Anders and Merkle, 1989), bioelectrodes, denture fixatives, ostomies and transdermal patches; adhesive materials in the paper and wood industries; mechanisms controlling adhesion of polysaccharides; testing of adhesive joints; purposes and future prospects of gum exudates in water-borne adhesives, and a comprehensive comparative analysis of the adhesion properties of various gum exudates (Nussinovitch, 2003). An adhesive is a substrate that can hold materials together by surface attachment. The joint is the site at which two adherends are held together by a layer of adhesive (ASTM, 1982), via attractive forces, physical interactions and mechanical interlocking (Patrick, 1966), the latter produced by the penetration of adhesive materials into microscopic pores and other surface irregularities. In analyzing interactions between an adhesive and an adherend, major attention should be paid to the zone between the bulk adhesive and bulk adherend, i.e. the “interphase”. The level of performance required from an adhesive depends on the strength of the adherend and the load that it is expected to carry (Bolger, 1983).

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6.2 GUMS AS ADHESIVES Many hydrocolloids (gums) have been known for centuries to have adhesive properties. In fact, the word ‘gum’ means a sticky substance. It was formerly defined as such by the Egyptian term qemai or kami, referring to the exudate of the acanthus plant and its adhesive capacity (Glicksman, 1982; Nussinovitch, 1997). In ancient times, mummies were wrapped in bandages glued with gum arabic (Lucas, 1962). Hydrocolloid glues are hydrophilic, non-toxic and non-flammable, and possess good wettability properties which improve their penetration into porous substrates. The development of synthetic hydrocolloids in the last century has broadened their uses with such commodities as paper, wood, textiles, leather, food, cosmetics and medicine (Nussinovitch, 1997).

6.3 INDUSTRIAL USES OF EXUDATE GLUES 6.3.1 General A large number of hydrocolloids have been mentioned in the literature as adhesive agents (Chen and Cyr, 1970; Bauman and Conner, 1994). They include gum talha (similar to gum arabic), gum ghatti, gum karaya, gum tragacanth, arabinogalactan, dextran, pectin, tapioca-dextrin, carboxymethyl cellulose (CMC), methyl cellulose (MC), hydroxypropyl cellulose (HPC), hydroxypropyl methyl cellulose (HPMC), carbopol, polyethylene oxide, polyvinyl pyrrolidone, polyvinyl alcohol, retene, pullulan, and chitosan. Some lesser-known water-soluble gums which possess wetadhesive bonding properties include: gum angaco, brea gum and psylium seed gum (Mantell, 1947), gum cashew (Howes, 1949), gum damson, jeol, myrrh (Smith and Montgomery, 1959) and scleroglucan (Glicksman, 1982).

6.3.2 Paper Paper is manufactured by pressing together moist fibers, typically cellulose pulp, and drying them into flexible sheets. It is mainly used to write or print on, and for packaging. Paper made from the papyrus plant was in use in Egypt in around 3500 BC. True paper is believed to have originated in China in the 2nd century AD, although there is some evidence for its use prior to this time. Use of hydrocolloids in the paper industry began in ancient Egypt when starch was used for adhering papyrus sheets (Lucas, 1962). Today, different gums and synthetic glues make up the major portion of the glue market for the paper industry, e.g. for paper lamination and cardboards, among many other uses (Torrey, 1980; Brief, 1990). For envelopes, stamps, wallpaper and similar products, special dry hydrocolloid glues that regain their adhesive properties upon wetting are used. They are based on gum arabic, among other hydrocolloids (Kirby, 1967; Sharkey, 1987). Tobacco is sometimes packaged in paper cylinders that are glued together with starch or gum tragacanth (Brief, 1990). Additional information on paper and the role of exudates in its manufacture can be found in Chapter 9 of this book.

6.3.3 Wood and furniture In ancient times, gum arabic and gelatin were used by the Egyptians in furniture manufacturing (Keimel, 1994). They utilized animal glues to adhere furniture, ivory, and papyrus. Over 1,500 years ago, some North American Indian tribes used collagen adhesives to make archery bows.

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Moving further back into history, evidence has been found indicating that glue-like materials were being used to attach handles to tools 36,000 years ago. Thus glue has been used to assemble items, among them furniture, since ancient times, and it is not hard to find glued pieces dating back hundreds of years (Barrett, 1998). The adhesives in these earlier times contained protein as their chemical backbone, and are termed natural adhesives. In World War II, a second category of adhesives was developed using synthetic resin adhesives—called “synthetic” because they were generated chemically. Both natural and synthetic glues can be used for furniture manufacturing. Adhesives can, when used correctly, make a joint that will be stronger than the wood itself. Thus the best adhesive is not necessarily the most expensive one. In choosing adhesives, cost and ease of application are often key factors. Other considerations involve the glue’s adhesive properties, moisture durability, heat/temperature sensitivity, flexibility, color and staining (http://www.woodweb.com/). Animal glues are applied hot to the adherends; as they cool, they lose their moisture and become quite hard. The wood must also be warm: cold wood can cool the adhesive too rapidly to produce a strong joint. The major drawback to these adhesives is their low moisture resistance: in the presence of moisture, the strength of the joint deteriorates. Heat and humidity cause hide glue to release its bond, making it a relatively simple matter to separate pieces without damaging them. This is why animal glues are useful for musical instruments, which often require disassembly to make repairs. Hide glue also cures slowly, so it can be a good option for difficult joints or constructions that take a long time to assemble. Other natural glues include starch glues, which can be applied hot or cold. They cure very slowly via moisture loss. Disadvantages include slight staining of the wood and poor moisture resistance. Casein, another popular natural adhesive that cures by water evaporation, is low-cost, easily applied, and has good gap-filling properties and moderate moisture resistance. Disadvantages include, but are not limited to the tendency to stain wood and a short working life. Nevertheless, recent improved formulations have eliminated these disadvantages. Glues made from soybean or blood are similar to vegetable and casein adhesives and are used primarily for veneer gluing. Blood glues are quite resistant to moisture due to natural phenolics (http://www.woodweb.com/). Another option for gluing wood and canvas is Terminalia bellirica (Bahera), a natural gum used as an additive in water-based natural rubber adhesive formulations. The lap-shear strength of joints with wood substrates increased with an increase in natural gum concentration up to 80 parts per 100 of rubber loading. Similarly, the peel strength of canvas-to-canvas joints increased with incorporation of this gum. The results were explained by the viscoelastic properties, morphology and surface chemistry of the rubber-gum mixtures (Saha et al., 2005). Yet another report described the effective bond strength of a natural gum adhesive in the wood industry. This gum was extracted from kendu (Diospyros montana Roxb.) (syn. D. cordifolia Roxb.) fruit and was studied with different interfaces such as general-purpose wood-wood, teakwood-teakwood, plywood-plywood, and others. The gum adhesive showed superior bond strength for wood-wood adhesion, comparable to that of synthetic adhesives (Parija et al., 1999). It is therefore clear that further research into the use of natural adhesives in the wood/furniture industry stands to be quite productive. The goal of most furniture manufacturing is to create something that can withstand exposure to heat and humidity, and today’s furniture maker has more options. These include the water-resistant epoxies, polyurethane glue which actually cures by exposure to moisture, and cross-linking polyvinyl-acetate adhesives (Barrett, 1998). Many other types of glue are also in use: polyamide, neoprene, polyvinyl acetate, urea-formaldehyde, phenolformaldehyde, melamine-urea-formaldehyde, recorcinol-phenol-formaldehyde, epoxy ethylene vinyl acetate, and others. Gelatin is still used, especially for gluing cloth to wood (Krage and

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Wootton, 1965), as the furniture industry uses glues not only for wood attachment. For example, in the furniture upholstery industry, the solvent-based glue that was being sprayed posed a health risk to workers through possible solvent exposure. The solvent-based glue was therefore substituted with a water-based one. A dense aerosol appeared during use of the water-based substitute, and therefore the amounts of fresh air and exhaust had to be adjusted. In the case of water-based glues, there is the possibility of exposure to natural resins that can sensitize the skin and respiratory tract. Therefore, an interdisciplinary approach to improvement of the workplace should receive more emphasis, whereby the effects of the different glues or their formulations will be taken into account (Schimberg and Sillanpaa, 1999).

6.4 BIOLOGICAL APPLICATIONS: A GENERAL APPROACH Bioadhesive applications of hydrocolloids in medicine and cosmetics have been widely explored. A few examples are adhesive biodelivery systems (Smart et al., 1984; Robinson et al., 1987; Bottenberg et al., 1991; Smart, 1991; Bouckaert and Remon, 1993; Irons and Robinson, 1994), adhesive bioelectrodes (Keusch and Essmyer, 1987), cosmetic preparations (Toulmin, 1956), pressure-sensitive adhesives (PSAs) (Piglowski and Kozlowski, 1985; KiyoShi et al., 1986), ostomy rings (Glicksman, 1982), adhesive ointments (Kanig and Manago-Ulgado, 1965), and dental adhesives (Shay, 1991). One of the earliest discussions on hydrocolloids’ ability to serve as glues in biological systems was published ∼40 years ago (Chen and Cyr, 1970). Almost 15 years later, Smart et al. (1984) examined the mean adhesive forces of many hydrocolloids to mucus. They found that gum tragacanth produces the least adhesive force in comparison with sodium CMC or carbopol (Robinson et al., 1987). Hydrocolloids are part of both biodelivery and the protective layers in biodelivery adhesive systems. The first layer is prepared, for example, from gum karaya, HPC, HPMC, propylene glycol alginate and the drug. The second is composed of ethyl cellulose, sodium CMC and HPC. Biological hydrocolloid glues for the vaginal area and eyes, and in sprays for the nose and other mucosal areas, have been developed (Nagai and Machida, 1993; Irons and Robinson, 1994), using gum tragacanth, chitosan, pullulan, HPC, starch or carbopol. Adhesive bioelectrodes have gum karaya, PVA (polyvinyl alcohol), hydroxyethyl methacrylate, agar, MC or CMC in their formulations (Keusch and Essmyer, 1987).

6.4.1 Ostomy devices Conventional ostomy devices consist of a collection bag or pouch attached to a skin-compatible medical-grade adhesive pad, also known as a label or faceplate. In some cases, the device is destined for one-time use and thus, the faceplate must be removed after a limited time. In other cases, the device is designed for several uses and the pouch or bag can be detached from the adhesive faceplate and emptied, or a fresh pouch attached to the faceplate several times before the faceplate itself has to be removed from the skin (Jensen, 1990). Gum karaya is utilized in the formulation of ostomy powders, pastes, rings, discs and sheets, and carries several advantages: it is soothing to the skin and it is resistant to the enzymatic breakdown of colonic bacteria. “Karaya washers” are widely sold for use in ostomy devices, and are produced by mixing karaya powder and glycerol and molding the mixture at about 120°C to produce a gelatinous ring. Since karaya gum is quite expensive and sometimes in short supply, there is a pressing need for acceptable or

Gum Exudates in Water-Based Adhesives   ◾  297

better alternatives to such washers for use with surgical appliances (Potaczek, 1982). In addition, karaya has been associated with some risk. The initial karaya ostomy bag is likely to be a source of Rhizopus infection, and prolonged exposure before the first ostomy bag change may precipitate infection in the susceptible individuals who use such bags. Karaya may contain opportunistic molds that also pose a risk of infection among susceptible persons (LeMaile-Williams et al., 2006). The production of substitutes has been suggested: at least one polyhydric alcohol and at least one material selected from a group of naturally occurring high-molecular-weight polysaccharide gums, other than gum karaya, are heated, and resins which are copolymers of vinyl ether and a second component selected from maleic anhydride and its corresponding free acid are added, all in the absence of solvent, to promote a chemical reaction between the components and to drive off water produced in the reaction, the reaction being carried substantially to completion (Potaczek, 1982).

6.4.2 Denture fixatives Dentures are removable devices that serve as a substitute for missing teeth and adjacent structures in the oral cavity. Denture fixatives are widely used to hold dentures in place, both while the mouth is at rest and during mastication. Denture fixative compositions need to perform their intended function without causing irritation to the mucosal denture surfaces (Sudo, 2007). Ideal compositions ensure that the dentures will remain fixed in place while functioning as intended. This is sometimes difficult to achieve, particularly when the dentures are not perfectly fitted or when their fit deteriorates over time, due to wear or to changes in the mucosal denture surfaces (Sudo, 2007). Denture fixatives work by reacting cream or powder with saliva in the mouth to develop adhesive properties. The key ingredients then work together to hold the dentures in place and provide a strong lasting hold (http://www.denture.co.uk/). Both synthetic and natural gums combined with various adhesives and other ingredients have been used alone or in combination to achieve improved denture fixative compositions. Early fixatives were formulated from vegetable gums such as acacia and tragacanth (Grasso, 2004). New and improved denture fixative compositions include at least one additional adhesive material selected from the group of natural and/or synthetic polymeric gums. The exudates gum karaya and gum tragacanth can be used, as well as other hydrocolloids such as guar gum, gelatin, algin, sodium alginate, chitosan, polyethylene glycol, acrylamide polymers, carboxyvinyl polymers, polyvinyl alcohol, polyvinyl pyrrolidone, cellulose derivatives and mixtures thereof. Such compositions do not cause oral mucosal irritation and may also be used to protect oral mucosal surfaces (Sudo, 2007). An extremely desirable characteristic in a denture fixative is that it quickly generate a tacky, uniform and viscous mucilage upon contact with saliva. It is also highly desirable that the mucilage spread over the denture-mucosa interface in order to effectively seal the denture in place, and that the mucilage possess sufficient cohesive strength to withstand the stresses of mastication which act to rupture the seal and thus dislodge the denture. Suitable hydrophilic polymers for this device can be synthetic gums such as cellulose derivatives, polyethylene oxide, and polyvinyl alcohol, or natural gums such as gum karaya, among others. Further improvement in adhesive properties appears to be due to the synergistic effect of combinations of ingredients (Chang and Zientek, 1985). A wide range of hydrocolloids, such as gum karaya, gum arabic, cellulose derivatives, polyox and others, are thus used in dentistry. Powdered gum karaya of suitable swelling, viscosity and particle size finds application in the manufacture of denture adhesives. Commercially available denture adhesives are found in either powdered or paste form. The swelling and moisture-absorbing

298  ◾  Plant Gum Exudates of the World

capacity of gum karaya help in absorbing saliva from the mouth and fixing the dentures firmly to the plate without any gap.

6.4.3 Bioelectrodes Bioelectrodes function as an interface between biological entities and electronic systems. Electrical activity/potentials within the biological system are either passively sensed (measured) or actively stimulated (induced). A conductive adhesive is useful to establish an electrical connection between human skin and the biomedical electrodes of an electromedical apparatus, such as a high-impedance electromyograph, electrocardiograph, electrical neurostimulator for pain relief, and the like (Engel, 1985). A common biomedical electrode makes use of gum karaya to secure the electrode to the skin. Gum karaya is combined with certain metallic cations, such as sodium, potassium, calcium, or magnesium. The gum does not dissolve but swells in water to a paste-like gel. Because natural polymers originate in nature where soil and climatic conditions are variable, and the conditions under which they are collected and processed are variable, there may be inconsistency in the physical and chemical properties of natural polymers and in the amount of impurities present. Such inconsistency could lead to variations in the electrical performance of biomedical electrodes that include these natural polymers. This variation in electrical performance is not desired in biomedical electrodes, where consistent electrical properties are important for signal reception. Furthermore, natural polymers may support undesirable microbial growth and have the potential to create adverse skin conditions including allergenic and antigenic reactions (Hymes, 1978). Therefore, an improved combination electrode for use in monitoring and stimulatory medical applications was provided, made up of an electrical current conductor including a connector plug and a skin-interfacing substrate material, this substrate consisting of, for example, a mixture of natural organic polysaccharide and hydric alcohol having tailored electrically conductive and adhesive properties (Hymes, 1978). Another patent deals with a bioelectrode which has a backing, an adjacent conductive layer, and a layer of conductive adhesive adjacent to that. This bioelectrode is designed to have two special configurations. It is originally manufactured with the backing forming a sealed protective enclosure for the layer of conductive adhesive. When a physician wishes to apply the electrode to a patient, the layer of conductive adhesive is readily exposed for contact and adherence to the patient’s skin (Netherly and Burton, 1998). A specialized body-contacting substance is needed to transfer the current. In recent years, this substance has generally consisted of a soft, conductive adhesive which can fill the dual role of transferring the current and adhering the electrode to the body. Thus, many of the best-known conductive adhesives are “hydrophilic”, tending to have or to absorb water. The packaging for bioelectrodes must therefore protect the conductive adhesive from physical damage or contamination, as well as from drying out (Netherly and Burton, 1998).

6.4.4  Exudate patches for transdermal drug delivery The long-known adhesive properties of some hydrocolloids have found various applications in the pharmaceutical (medicinal), cosmetic and food industries. Especially important is the creation of PSA patches for transdermal or topical drug delivery. PSAs are traditionally based on

Gum Exudates in Water-Based Adhesives   ◾  299

polyisobutylenes, silicones and acrylics. The disadvantages of synthetic PSAs are the need modify them by adding other resins and tackifiers, the adhesive residue they leave on the skin, and damage to the skin upon removal. Novel carriers are thus needed to improve patch-skin adhesion and biocompatibility. The objectives of a recent study were to: physically and chemically characterize tree gum exudates; formulate an adhesive-matrix patch based on a tree gum exudate for transdermal drug delivery; test the influence of exudate concentration on the patch’s adhesive and mechanical properties; study the adhesion of the manufactured patches to different substrates; study the influence of some drugs on the patch’s adhesive properties, and test the applicability of the patches for transdermal drug delivery (Nussinovitch, 2008). The following exudates: Sterculia foetida, Bauhinia variegata, Buchanania lanzan, Terminalia crenulata, Terminalia catappa, Terminalia bellirica and gum karaya were studied. Ground gum exudates were mixed with non-therapeutic substances to produce a paste which turns into an adhesive matrix upon gelation. Mechanical tests were performed in an Instron universal testing machine to check the patches’ compression, viscoelasticity, elasticity, peel and probe tack. The peel test was performed by positioning skin (porcine skin from the back, abdomen or ear, or a skinsurface model [SSM]) on a special sliding rack, connected to the Instron, designed to maintain a fixed angle during peeling. The probe-tack test was performed in a custom-made apparatus connected to the Instron, capable of measuring forces related to bond formation. Quantitative tack gives an indication of the potential ease and success of application when patches are brought into contact with skin. All skin substrates were characterized with a light microscope, roughness tester and gloss meter. Nicotine release was also measured using Franz diffusion cells with porcine ear skin (Nussinovitch, 2008). Patches were successfully produced from S. foetida, B. variegata and T. bellirica, all formulations exhibiting desirable tacky and elastic characteristics as well as structural integrity. The patches were very elastic and did not break, even at 85% deformation. In both adhesion tests, increasing the exudate concentration created a more adhesive patch, and in both tests, a higher adhesion force was obtained with porcine dorsal skin than with abdominal or ear skin. The same results were obtained with patches that contained drugs. Our topical patches, containing salicylic acid, were much more adhesive than a commercial patch for the treatment of warts. In fact, addition of salicylic acid increased patch adhesion. The results of this study support the potential applicability of such patches for transdermal or topical drug delivery. The patches exhibit improved patch-skin adhesion and biocompatibility. They are suitable for a broad range of drugs and can be applied at different pHs. The patches can serve as a drug-containing adhesive matrix or as an adhesive layer for multilayered patches (Nussinovitch, 2008).

6.5 HYDROCOLLOID ADHESION TESTS A fairly large number of tests have been proposed to evaluate adhesive-bonding strength. They include 90°-peeling, tensile-bond and lap-shear tests. Different forms of failure have been recognized: failure within the adhesive layer, termed cohesive failure; failure at the interface between the adherend and the adhesive—adhesive failure, and failure of the adherend itself. Following testing, the ratio between adhesive and cohesive failure is estimated. Samples in which failure occurs within the substrate are discarded, since they do not constitute a test of the adhesive material (Portelli, 1986; Fiszman and Damasio, 2000). The bond-strength value, measured by a specific test, is not just an inherently fundamental property of the type of adhesive; it also depends on

300  ◾  Plant Gum Exudates of the World

Figure 6.1  Specimen mounted on an Instron universal testing machine during the 90°-peel test.

other factors. Various experimental procedures, using biological or other hydrocolloid adhesives, have been carried out to test different important variables, such as crosshead speed at debonding (Smart, 1991), adhesive-layer thickness (Smart et al., 1984), water-holding capability of a sample (Kanig and Manago-Ulgado, 1965; Chen and Cyr, 1970), duration of contact (Chen and Cyr, 1970; Smart et al., 1984), the effect of molecular weight (Smart et al., 1984) and the type of adhesive (Chen and Cyr, 1970). Peel tests are used for both quality control and to compare adhesives. They are important for quantifying stripping or peeling forces. In peel tests, a bendable adherend that is adhesively bonded to another rigid or flexible adherend is stripped away (Fig. 6.1). Throughout this procedure, the distribution of the stress within the peel joints is complex, being influenced by the properties of the adherend and the joint geometry. The width of the adherend being peeled is an important factor in calculating the peel strength, generally in pounds per inch. The average load needed to maintain the peeling after initiation is used to estimate the peeling force. In tensile tests, tension is utilized to examine adhesive joints, bonds or design via the application of vertical forces on the adhesive layer. In shear tests, the structural adhesive within bonded structures is usually designed so that it will sustain shear loads most of the time, due to the strength of adhesives in shear, as compared to that under peel or tensile loads. When the adhesively bonded structure is considered to be under shear, applied loads are active in the plane of the adhesive

Gum Exudates in Water-Based Adhesives   ◾  301

Figure 6.2  Specimen mounted on an Instron universal testing machine during the lap-shear test.

layer. As a result of the loads, the adherends can slide, which in turn causes shearing or sliding of the adhesive. A certain length of overlap between adherends is typical when lap-shear tests are applied (Fig. 6.2). The layer between the overlapping areas consists of the structural adhesive, and tension-to-failure is used during the lap-shear test. The critical shear strength is calculated by dividing the load at failure by the area of the overlap (Portelli, 1986). Recently, a modified probe-tack test (Fig. 6.3) has been described which includes a special device that is capable of detecting first contact between the probe and a PSA and setting this contact as the initial dwell time (Ben-Zion and Nussinovitch, 2008). In tests using viscoelastic PSA materials (hydrogels), this modified device gives results which differ significantly from those obtained with conventional probe-tack testers. In particular, when tack values are plotted against dwell time, the modified tester reveals a sigmoidal pattern for low-energy tack, followed by a transition to the normal power-law curve of the high-energy tack. This transition behavior was studied as a function of crosshead velocity, compression pressure, adhesive rheology, and adherend surface roughness. The practical implication was that far more information can be obtained from this modified device than from conventional probe-tack testers. The modified machine and methodology should prove particularly valuable as an experimental tool and for quality-control tests in the manufacture of PSA products, particularly soft and tacky viscoelastic substances (Ben-Zion and Nussinovitch, 2008).

302  ◾  Plant Gum Exudates of the World

Figure 6.3  A modified probe-tack test in which a special device is capable of detecting the first contact between the probe and a pressure-sensitive adhesive and determining this contact as the initial dwell time.

6.6 EXUDATES AS WET GLUES Four exudates were studied for their ability to create very thick suspensions with “good” adhesive properties at predetermined gum concentrations ranging from 25 to 75% (w/w). The exudates were: gum talha, gum ghatti, gum karaya and gum tragacanth. The hydrocolloids at different concentrations were added in powdered form to double-distilled water and mixed with a standard dough mixer for at least 15 min, until a thick, uniform and smooth pasty wet glue was obtained (Ben Zion and Nussinovitch, 1996; Ben Zion and Nussinovitch, 1997). Preliminary tests revealed that the four exudates can serve as bioadhesives in hydrophilic systems. Wet glues were produced from these exudates and tested over a wide range of concentrations, and the color and pH of the exudate pastes were determined. Table 6.1 gives some of their physical properties. All preparations were tested immediately following their production. Paste temperature was taken at the end of mixing, and 5 min later it had risen by 0.97 + 0.14°C. The pH values of the wet exudate glues ranged from 3.52 with gum karaya to ∼4.61 with gum tragacanth. pH may be an important factor in the utilization of bioadhesive materials. Paste color may also be a factor in choosing a bioadhesive for a particular application. A variety of different colors could be found among the wet glues. Gum talha had the smallest L* values (dark brown) and gum tragacanth the highest (yellowish)

Gum Exudates in Water-Based Adhesives   ◾  303 Table 6.1  Physical Properties of Hydrocolloid Pastes

Hydrocolloid Gum talha

Gum karaya

Gum tragacanth

Gum ghatti

Color Parameters

Loading (g/100 g)

pH

L*

a*

b*

Hue

65

4.02

22.16

0.00

0.43

Dark brown

70

3.98

21.69

0.59

1.08

“

75

3.95

24.21

3.07

4.03

“

25

3.68

27.98

2.00

4.95

Light brown

35

3.61

29.17

2.09

4.82

“

45

3.52

26.94

2.51

5.40

“

25

4.65

43.94

–0.92

6.26

Yellowish

35

4.61

47.76

–0.34

8.73

“

45

4.56

52.51

–0.11

11.67

“

55

4.22

23.65

1.18

2.55

Dark brown

65

4.17

23.69

1.45

2.64

“

75

4.12

24.82

1.68

2.58

“

(the higher the L* value, the lighter the paste). The a* value spans the green-red axis of the color system and the b* value, the yellow-blue axis. For the four exudates, a* and b* values fluctuated between -0.92 and 11.7 and due to their relatively lower values, had less influence on the perception of color than L* (Table 6.1). The viscous exudate pastes were smeared homogeneously onto two different substrates: (a) a cellulose-acetate film normally used for dialysis, and (b) a SSM (Charkoudian, 1988, 1989), in order to test the adhesion of medical adhesives (Table 6.2). The water content in the SSM was on the order of 1% (Ben Zion and Nussinovitch, 1997). Gum ghatti and gum talha were chosen for the assessment of physical properties, as representatives of tree and shrub exudates, respectively (Ben Zion and Nussinovitch, 1997). A typical 90°-peeling curve for 70% gum talha is presented in Fig. 6.4A. The sample was pulled apart at a constant crosshead speed, and the measured force was constant after reaching a steady-state condition. For 65% gum ghatti, the experimental values of the tensile-bond and lap-shear strengths were 452.8 and 27.1 g force/cm2, respectively. For comparison, 35% carbopol had tensile-bond and lap-shear strengths of 1112.7 and 46.1 g force/ cm2, respectively. Fig. 6.4B shows the influence of deformation rate on the values of peel-bond strength for gum ghatti adhesive paste. The increase in adhesive strength paralleled that of the deformation rate, suggesting that the adhesive bond is of a viscoelastic nature, i.e. that a faster rate of stress application to the adhesive bond gives it less time to deform and flow (Smart, 1991). Fig. 6.4C represents the dependence of peel-bond strength on adhesive-layer thickness. Gum ghatti was chosen for this study since it is the easiest gum with which to produce various uniform thicknesses of wet glue with maximal accuracy. In addition, the peel-bond strength is relatively high, making it a worthwhile substance for experimentation. There was a reduction in peel-bond strength as the thickness of the wet glue decreased (Fig. 6.4C). When the wet glue was thicker than ∼3.8 mm, the peel-bond strength reached an asymptotic value of ∼ 7 g force/cm. This may be explained by a failure inside the glue layer, whereas for thicknesses of less than 3.8 mm, the failure was adhesive.

304  ◾  Plant Gum Exudates of the World Table 6.2  Peel-Bond-strength Values for Various Hydrocolloid Pastes, Tested on Cellulose-acetate Film and on SSM* Peel-bond Strength (g force/cm)†

Gum talha

Gum karaya

Gum tragacanth

Gum ghatti

*

Loading (g/100 g)

CelluloseAcetate Membrane

SSM

65

5.9 (1.1)

3.6 (0.4)

70

18.8 (1.6)

7.5 (0.6)

75

45.2 (2.5)

15.4 (1.3)

25

4.9 (0.7)

3.4 (0.5)

35

12.2 (0.7)

10.7 (0.8)

45

31.4 (2.4)

26.3 (2.1)

25

4.4 (0.6)

3.4(0.4)

35

11.9 (0.6)

9.4 (0.3)

45

30.9 (1.1)

23.2 (0.9)

55

7.1 (0.9)

6.0 (1.0)

65

22.0 (1.6)

11.5 (0.6)

75

62.6 (1.4)

0.0 (0.0)

SSM: skin-surface model. † Results are means ± standard deviation.

This observation is typical for gum ghatti, but not necessarily common to other gums. Data found in the literature for non-gummy materials (such as cured adhesives) provide evidence of different behaviors (Gardon, 1966). To study the influence of water absorbance on peel-bond strength, SSM films with different moisture contents were produced by immersing them in water for 0, 2, 5, 9 and 13 min. This operation produced films with water contents of ∼1, 31, 39, 46 and 56%, respectively. Fig. 6.4D shows the relationship between this parameter and 90°-peel bond strength. Gum ghatti exhibited decreases in peel-bond strength as the water content in the SSM increased. Hydrocolloids develop their wet adhesive properties at various degrees of hydration, reaching maximum adhesion at an optimum degree of hydration (Chen and Cyr, 1970). Some hydrocolloids exhibit wet adhesiveness in the presence of only very little water, whereas excessive water transforms it to a slippery, non-adhesive mucilage. A wet surface used as a substrate for adhesives is different from a dry one. The first state is not static and water diffuses from the surface of the wet substrate (SSM) into the hydrocolloid interface. The rate and capacity of the hydrocolloids’ water absorbance affect the amount of water present near the interface, between the adhesive and the substrate. These properties appear to be important in determining the time required for initial wet adhesion, hydration time and duration of adhesion. Rapid water absorption may shorten the duration of adhesion because erosion proceeds rapidly. An excessive amount of water at the interface causes overextension of the hydrogen bonds and other adhesive forces, leading to a weakening in adhesive bond strength (Chen and Cyr, 1970). Fig. 6.5 presents the relationship between peel-bond strength

Gum Exudates in Water-Based Adhesives   ◾  305 A

20

25

16

20

12

15

Peel-bond Strength (g force/cm)

8

10

4 0

5 0

0.5

1.0 1.5 Deformation (cm)

0

2.0

C

25

12

15

9

10

6

5

3 0

0

1 2 3 4 5 6 Thickness of Adhesive Layer (mm)

7

0

20 40 60 80 Crosshead Speed (mm/min)

100

D

15

20

0

B

30

0

10

20 40 50 30 Moisture Content (%)

60

Figure 6.4  (A) Typical curve for the 90°-peel test for 70% gum talha. (B) Influence of deformation rate on values of peel-bond strength for gum ghatti adhesive paste. (C) Peel-bond strength versus gum ghatti adhesive paste thickness. (D) Peel-bond strength versus water content of SSM films for gum ghatti (adapted with changes from Ben-Zion and Nussinovitch, 1997).

0.4

150 120

0.3

90

0.2

60

0.1

30 0

0

5

10 15 20 Drying Time (h)

25

Water No.

Peel-bond Strength (g force/cm)

and water number (amount of water evaporated from a standard sample) and the drying time of wet glues produced from gum ghatti. The wet glue served as an adhesive between the covering cellulose-acetate membrane and the SSM layer with ∼1% water content. For gum ghatti, the peelbond strength increased with time up to ∼8 h and then decreased, as a result of the gradual drying of the wet glues. The water number increased with drying time.

0

Figure 6.5  Relationship between contact time of the covering cellulose-acetate film adhered to the SSM substrate with 1% water content by hydrocolloid adhesive, and the 90° peel-bond strength effected by water loss from the paste, expressed as water number. The dashed line represents the water number; the solid line represents the peel-bond strength for 65% gum ghatti (adapted with changes from Ben-Zion and Nussinovitch, 1997).

306  ◾  Plant Gum Exudates of the World

6.7 ADHESION MECHANISMS OF HYDROGELS A major task for pharmaceutical formulators is to seek novel biocompatible adhesives for medical applications in general and topical uses in particular (Webster, 1997). As a result of the advantages of adhesive hydrogels over conventional PSAs, the former offer great potential for topical applications such as transdermal drug delivery (Eggins, 1993; Ferrari et al., 1996; Venkatraman and Gale, 1998). Studying hydrogel adhesion mechanisms is a key step in developing future PSA products in the fields of medicine and/or cosmetics. Although scientists have successfully studied the rheological and chemical behaviors of many hydrocolloid systems, their adhesion properties and mechanisms remain unclear. This may be due to the fact that adhesion is a very complex field, beyond the reach of any single global model theory. Given the large number of phenomena involved in the process, the variety of substances to be bonded, and the excessive number of bonding conditions, the search for a universal theory capable of explaining all of the experimental facts is a lost cause. Actually, quite a few adhesion mechanisms can be involved concurrently (Schultz and Nardin, 1994). Six main theories have been proposed to explain the interactions between adhesive and adherend which, taken together, can be seen as both complementary and contradictory. The theory of mechanical interlocking (Fig. 6.6) perceives mechanical keying (anchoring) of the adhesive to the cavities, pores and superficial asperities of the solid adherend as the most important factor controlling adhesive strength (McBain and Hopkins, 1925). Various studies have criticized this theory by stating that better adhesion does not necessarily result from the mechanical-interlocking mechanism; instead, surface roughness can raise the viscoelastic (or plastic) dissipated energy due to stress concentrations (Hine et al., 1984). The electrostatic model theory (Fig. 6.7) likens the adhesive-adherend system to a plate capacitor whose plates consist of the electrical double layer that occurs when two materials of differing character are brought into contact (Derjaguin and Landau, 1941). Throughout interfacial failure of this system, separating the capacitor plates leads to an increase in the potential difference until discharge occurs. The diffusion theory of adhesion has been suggested for identical compatible polymers. Accordingly, the adhesion strength of two macromolecules in intimate contact is due to mutual interdiffusion of the molecules across the interface, thus creating an interphase (Voyutskii and Margolina, 1949). Such a mechanism (Fig. 6.8) implies that the macromolecular chains or

Adhesive

Substrate

Figure 6.6  Demonstration of the mechanical interlocking that occurs when an adhesive penetrates into the pores, holes, crevices and other irregularities of the adhered surface of a substrate, and locks mechanically to the substrate.

Gum Exudates in Water-Based Adhesives   ◾  307

Adhesive

δ–

δ–

δ– δ–

δ– δ+

δ+

δ+

δ+

δ–

δ–

δ–

δ–

δ+ δ–

Substrate

Figure 6.7  Demonstration of the electrostatic theory of adhesion which is the outcome of the difference in electronegativities of adhering materials.

chain segments are sufficiently mobile and mutually soluble (Kinloch, 1980). Theoretically, diffusion has been described to occur predominantly at the ends of the macromolecular chains (De Gennes, 1982). The thermodynamic adsorption theory claims that adhesion occurs under conditions of adequate wetting (Shanahan, 1991). The rheological model claims that the failure energy of an adhered assembly can be expressed as the product of two terms, the first being the reversible energy of adhesion, and the second, a parameter that depends upon the separation rate and temperature (Gent and Schultz, 1972). The latter term accounts for energy dissipation resulting from the irreversible deformation of the viscoelastic solid adhesive during failure propagation and depends on the bulk properties of the adhesive. Adhesion can also be greatly improved by chemical bonds formed across the adhesive-adherend interface (Kinloch, 1980). The formation of chemical bonds depends upon the reactivities of both the adhesive and the adherend. These bonds are generally considered primary bonds (covalent, ionic), as opposed to secondary-force interactions (van der Waals, hydrogen bonds). Primary bonds correspond to high interaction energies of ∼60 to 700 kJ/mol, whereas secondary bonds do not exceed 50 kJ/mol (Fourche, 1995).

Adhesive

Substrate

Figure 6.8  Demonstration of the diffusion theory that attributes the adhesion of polymeric materials to the interpenetration of chains at the interface.

308  ◾  Plant Gum Exudates of the World

References Anders, R. and N. Merkle. 1989. Evaluation of laminated mucoadhesive patches for buccul drug delivery. Int. J. Pharm. 49:231-40. ASTM. 1982. Annual book of ASTM standards, part 22. Philadelphia, PA: American Society for Testing and Materials. Barrett, N. 1998. Woodworking guide: Wood glue. Popular Mechanics. Published in the November issue. Bauman, M. G. D. and A. H. Conner. 1994. Carbohydrate polymers as Adhesives. In: Handbook of Adhesive Technology (Ed. by A. Pizzi), pp. 299-313. New York: Marcel Dekker Inc. Ben-Zion, O. and A. Nussinovitch. 1996. Predicting the deformability modulus of multi-layered texturized fruits and gels. Lebensm. -Wiss. u. Technol., 29:129-34. Ben-Zion, O., and A. Nussinovitch. 1997. Hydrocolloid wet glues. Food Hydrocolloids 11:429-42. Ben-Zion, O., and A. Nussinovitch. 2008. A modified apparatus for testing the probe tack of pressuresensitive adhesive materials. J. Adhes. Sci. Technol. 22:205-16. Bolger, J. C. 1983. Structural adhesives: today’s state of the art. In Adhesives in manufacturing, ed. G. L. Schneberger, 133. New York: Marcel Dekker. Bottenberg, P., Cleymaet, R., de-Muynck, C., Remon, J. P., Coomans, D., Michotte, Y. & D. Slop. 1991. Development and testing of bioadhesive fluoride containing slow-release tablets for oral use. J. Pharm. Pharmacol. 43:457-64. Bouckaert, S., and J. P. Remon. 1993. In-vitro bioadhesion of a buccal, miconazole slow-release tablet. J. Pharm. Pharmacol. 45:504-7. Brief, A. 1990. The role of adhesives in the economy. In Handbook of adhesives, ed. I. Skeist, 21-38. New York: Van Nostrand Reinhold. Bruno, E. J. 1970. Adhesives in modern manufacturing. Dearborn, MI: Society for Manufacturing Engineers. Chang, T.-S., and L. J. Zientek. 1985. Denture fixative composition containing partially neutralized copolymers of maleic acid or anhydride and alkyl vinyl ethers which are optionally partially crosslinked. US Patent 4,521,551. Charkoudian, J. C. 1988. A model skin surface for testing adhesion to skin. J. Cosmet. Chem. 39:225-34. Charkoudian, J. C. 1989. Model human skin. US Patent 11,877,454. Chen, J. L., and G. N. Cyr. 1970. Compositions producing adhesion through hydration. In Adhesion in Biological Systems, ed. R. S. Manly, 163-81. New York: Academic Press. Darnay, A. J., and M. A. Redd. 1994. Adhesives and sealants. In Market share reporter, 232-3. Detroit, MI: Gale Research Inc. De Gennes, P. G. 1982. Mechanical and chemomechanical aspects of adhesion. In Microscopic aspects of adhesion and lubrication, ed. J. M. Georges, pp. 355-7. New York: Elsevier. Derjaguin, B. V., and L. Landau. 1941. Theory of the stability of strongly charged lyophobic sols and of the adhesion of strongly charged particles in solutions of electrolytes. Acta Physicochim. USSR 14:633-62. Eggins, B. R. 1993. Skin contact electrodes for medical applications. The Analyst 118:439-42. Engel, M. R. 1985. Conductive adhesive and biomedical electrode. US Patent 4,524,087. Ferrari, F., Bertoni, M., Rossi, S. et al. 1996. Comparative rheomechanical and adhesive properties of two hydrocolloid dressings: Dependence on the degree of hydration. Drug Development and Industrial Pharmacy 22:1223-30. Fiszman, S. M., and M. H. Damasio. 2000. Instrumental measurement of adhesiveness in solid and semisolid foods, a survey. J. Text. Studies 31:69-91. Fourche, G. 1995. An overview of the basic aspects of polymer adhesion. Part I: Fundamentals. Polym. Eng. Sci. 35:957-67. Gardon, J. L. 1966. Some destructive cohesion and adhesion tests. In Treatise on adhesion and adhesives, vol. 1, ed. R. L. Patrick, 286–323. New York: Marcel Dekker. Gent, A. N., and J. Schultz. 1972. Effect of wetting liquids on the strength of adhesion of viscoelastic materials. J. Adhes. 3:281-94. Glicksman, M. 1982. In Food Hydrocolloids, vol. 3, 176. Boca Raton, FL: CRC Press Inc. Grasso, J. 2004. Denture adhesives. Dental Clinics of North America 48:721-33.

Gum Exudates in Water-Based Adhesives   ◾  309 Hagquist, J., Meyer, K. F., and K. M. Sandra. 1990. Adhesives market and applications. In Adhesives and sealants, ed. C. A. Dostal, 87-8. London: ASM International. Hine, P. J., El Muddarris, S., and D. E. Packham. 1984. Surface pretreatment of zinc and its adhesion to epoxy-resins. J. Adhes.17:207-29. Howes, F. N. 1949. In Vegetable gums and resins, 56-8, 61-2. Waltham, MA: Chronica Botanica Comp. Hymes, A. C. 1978. Monitoring and stimulation electrode. US Patent 4,125,110. Irons, B. K. and J. R. Robinson. 1994. Bioadhesives in drug delivery. In Handbook of Adhesive Technology (Ed. by A Pizzi), pp. 615-27. New York: Marcel Dekker Inc. Jensen, O. R. 1990. Adhesive connecting rings for an ostomy device. US Patent 4,894,058. Kanig, J. L., and P. Manago-Ulgado. 1965. The in-vitro evaluation of orolingual adhesives. J. Oral Therap. Pharm. 4:413-20. Keimel, F. A. 1994. Historical development of adhesive binding. In Handbook of adhesive technology, ed. A. Pizzi, 3-15. New York: Marcel Dekker Inc. Keusch, P., and J. L. Essmyer. 1987. Adhesive polyethylene oxide hydrogel sheet and its production. US Patent 4,684,558. Kinloch, A. J. 1980. Review: The science of adhesion. I. Surface and interfacial aspects. J. Mater. Sci. 15:2141-66. Kirby, K W. 1967. Vegetable adhesives. In Adhesion and adhesives, ed. R. Howink, 167-85. Amsterdam: Elsevier Publ. Comp. Kragh, A. M. and J. Wootton. 1965. Chapter 2: Animal glue and related protein adhesives. In Adhesion and Adhesives. Edited by: R. Houwink and G. Salomon. pp. 141-166. Amsterdam: Elsevier. LeMaile-Williams, M., Burwell, L. A., Salisbury, D. et al. 2006. Outbreak of cutaneous Rhizopus arrhizus infection associated with karaya ostomy bags. Clin. Infect. Dis. 43:83-8. Lucas, A. 1962. Adhesives. In Ancient Egyptian materials and industries, by A. Lucas. 4th ed. Rev. and enl. by J.R. Harris, pp. 8-14. . London: Edward Arnold Publ. Ltd. Mantell, C. L. 1947. In Water-soluble gums, 48, 71, 72. New York: Reinhold Publ. Corp. Maloshuk, Yu. S., Raevskii, V. G. Semenikhina, A. A., and S. S. Voyutskii. 1965. Autoadhesion of technical elastromeric systems. In Autohesion of technical elastomeric systems, Mekhanika Polimerov (English translation) 1(2): 5–8. McBain, J. W., and D. G. Hopkins. 1925. On adhesives and adhesive action. J. Phys. Chem. 29:188-204. Nagai, T. and Y. Machida. 1993. Buccal delivery systems using hydrogels. Adv. Drug Delivery Rev. 11:179-81. Netherly, S. G., and S. A. Burton. 1998. Self-packaging bioelectrodes. US Patent 5,827,184. Nussinovitch, A. 1997. Hydrocolloid applications, gum technology in the food and other industries. London: Blackie Academic and Professional. Nussinovitch, A. 2003. Water-soluble polymer applications in foods. Oxford, UK: Blackwell Publishing. Nussinovitch, A. 2008. Exudate patches for transdermal and topical drug delivery. In IHC 2008, International Hydrocolloids Conference, 15-19 June, Rasa Sentosa Resort, Singapore, 80-81. Ono, K., Sakurai, Y., and Y. Kishimeto. 1986. Pressure-sensitive adhesive tape, sheet or label. Japanese patent JP61250050. Parija, S., Misra, M., Mohanty, A. K., and S. K. Nayak. 1999. Studies on effective bond strength of kendu fruit adhesive. Polymer-Plastics Technol. Eng. 38:1107-19. Patrick, R. L. 1966. In Treatise on adhesion and adhesives, vol. 1, ed. R. L. Patrick, 4. New York: Marcel Dekker. Piglowski, J., and M. Kozlowski. 1985. Rheological properties of pressure sensitive adhesives: polyisobutylene/sodium carboxymethylcellulose. Rheol. Acta 24:519-24. Portelli, G. B. 1986. In Structural adhesives chemistry and technology, ed. S. R. Hartshorn, 407-49. New York, London: Plenum Press. Potaczek, J. J. 1982. Gelatinous articles and compositions. US Patent 4,359,047. Robinson, J. R., Longer, M. A., and M. Veillard. 1987. Bioadhesive polymers for controlled drug delivery. In Controlled delivery of drugs, vol. 507, ed. R. L Juliano, 307-14. New York: Annals of the New York Academy of Sciences. Saha, S., Singha, N. K., Chattopadhyay, R. N., Ganguly, A., and A. K. Bhowmick (2005). Studies of Terminalia bellerica (Bahera), a natural gum, as an additive in a water-based adhesive composition. J. Adhes. Sci. Technol. 19:1349-61.

310  ◾  Plant Gum Exudates of the World Schimberg, R. W., and J. E. Sillanpaa. 1999. Glue spraying in the upholstered furniture industry: Presentation of a wholistic approach to improve work conditions. Gefahrstoffe Reinhaltung Der Luf. 59:381-5. Schultz, J., and M. Nardin. 1994. Theories and mechanisms of adhesion. In Handbook of adhesive technology, ed. A. Pizzi, Chapt. 2. New York: Marcel Dekker, Inc. Shanahan, M. E. R. 1991. Adhesion and wetting: Similarities and differences. Rubber World 205:28-36. Sharkey, J. B. 1987. Chemistry of stamps: Dyes, phosphors, adhesives. J. Chem. Educ. 64:195-200. Shay, K. 1991. Denture adhesives--choosing the right powders and pastes. J. Amer. Dent. Assoc., 122:70-6. Smart, J. D. 1991. An in-vitro assessment of some mucosa dosage forms. Int. J. Pharm. 73:69-74. Smart, J. D., Kellaway, I. W., and H. E. C. Orthington. 1984. An in-vitro investigation of mucosa-adhesive materials for use in controlled drug delivery. J. Pharm. Pharmacol. 36:295-9. Smith, F. and R. Montgomery. 1959. In The chemistry of plant gums and mucilages, 15-20, 199, 404-5. New York: Reinhold Publ. Corp. Sudo, A. P. 2007. Denture fixative composition. European Patent EP 1,803,788 A1. Torrey, S. 1980. In Adhesive technology developments since 1977, 197-200. Park Ridge, NJ: Noyes Data Corporation. Toulmin, H. A. 1956. Dextran compound coated body powder. US Patent 2,749,277. Venkatraman, S. and R. Gale. 1998. Skin adhesives and skin adhesion. 1. Transdermal drug delivery systems. Biomaterials 19:1119-36. Webster, I. 1997. Recent developments in pressure-sensitive adhesives for medical applications. Int. J. Adhesion Adhesives 17:69-73.

Chapter 7

Medical, Cosmetic and Biotechnological Uses of Gum Exudates 7.1 INTRODUCTION Many applications of gum exudates are steeped in tradition. However, there is no doubt that a promising future for these materials lies in their medical, cosmetic and biotechnological uses (Whistler, 1993). This chapter describes such applications, for example in bulk laxatives, in ulcer treatments, for the soothing of irritated mucous membranes, as a carrier in controlled-release matrix systems, as a constituent in medicines, as a binding agent in cosmetic preparations, in perfumed preparations, in different creams, in cosmetics and in cough syrups, as part of intravenous injections, in blood substitutes, and many other biotechnological applications (Verbeken et al., 2003).

7.2 PHARMACOLOGICAL APPLICATIONS 7.2.1 Demulcent and emollient qualities Pharmacology is the study of how substances interact with living organisms to produce a change in function. Pharmaceuticals are substances aimed at treating, curing, preventing, or recognizing disease and relieving pain through their application in the organism. It has been estimated that ∼5% of gum arabic production is used for pharmaceutical purposes (Whistler, 1973). Gum arabic has inherent emulsifying and stabilizing properties. In addition, its demulcent and emollient qualities are important in many pharmaceutical applications. A demulcent is an agent that relieves irritation in inflamed mucous membranes. Terminalia gums, which were sometimes mixed with East Indian gums, were once used as demulcents in northern India (Mantell, 1947). Emollients are substances that soften and soothe the skin. The soothing property of gum arabic makes it useful in many types of cough syrups and cough drops. Such syrups can mask the bitter acid taste of 311

312  ◾  Plant Gum Exudates of the World

Figure 7.1  Semal (Bombax ceiba) trunk of a young tree in Kolkata (http://en.wikipedia.org/ wiki/Image:Semal; Author: J.M. Garg).

medicines (i.e. agents used to treat, prevent or alleviate disease symptoms) via its protective colloid action (Whistler, 1973). Gum arabic in the form of a solution or mucilage is an agreeable lenitive for irritated and inflamed membranes, and it is frequently used for this purpose in medicinal preparations for coughs, colds, hoarseness, pharyngitis, gastric irritation and inflammation, diarrhea, dysentery, etc. Local anti-inflammatory effects on the small intestine have been achieved by administering a non-absorbable proteoglycan such as gum arabic (Wapnir et al., 2008). Semal (Fig. 7.1) is a fast-growing, buttressed tree that can reach up to 60 m in height. According to Ayurveda, semal bark is a demulcent and styptic. It exudes an edible gum which is a stimulant, tonic, demulcent, dysenteric and analgesic, and is useful in treating giardiasis and diarrhea (Jain, 2000).

7.2.2 Suspending and emulsifying agents A suspending agent helps reduce the sedimentation rate of particles in suspension. It works by increasing the viscosity of the liquid vehicle, thereby slowing down settling in accordance with Stokes Law. Gum arabic can be used as an efficient suspending agent in suspensions of insoluble drugs. Examples of these include calamine—a mixture of zinc oxide with about 0.5% Fe2O3, which is the main ingredient in calamine lotion (used as an anti-itching agent to treat sunburn, eczema, rashes, poison ivy, insect bites and stings), kaolin suspensions, cod liver emulsions and

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non-settling magnesia suspension (Jain and Dixit, 1998). Gum tragacanth can also be used as a suspending agent for many pharmaceutical products. Other uses for these gums are as a binder in tablets; in lotions for external applications; at high concentration as a base for jelly lubricants; in spermicidal jellies; in formulating stable oral suspensions; in medicinal oil emulsions; in various types of elixirs (i.e. a pharmaceutical preparation containing an active ingredient that is dissolved in a solution that contains some percentage of ethyl alcohol and is designed to be taken orally), and in syrups where low-calorie intake is required (Whistler, 1973). An exudate gum from the tree Moringa oleifera was also efficient as a suspending agent in zinc oxide suspensions. The properties and performance of M. oleifera gum have been reported to be similar to those of gum tragacanth (Panda et al., 2006). The efficacy of shilajit, a gummy exudate of the plant Styrax officinalis L. (Family: Styracaceae), was evaluated as a suspending agent for the formulation of antacid preparations. Shilajit produced effects on sedimentation volume similar to those produced by sodium carboxymethylcellulose (CMC), but at lower concentrations. It induced better flocculation with a moderate increase in viscosity compared to CMC. It did not interfere with the acid-consuming capacity of the suspensions (Shahjahan and Islam, 1998). The viscosity of gum ghatti (whole gum) has been previously reported (Jefferies et al., I977) to increase with increasing proportion of dispersible gel, a rheological behavior that was also exhibited by the studied Albizia exudate. Thus, both gum ghatti and albizia gum solutions display higher viscosities and are expected to be better emulsifying and suspending agents than gum arabic (Mhinzi, 2002). Emulsification is the formation of stable emulsions by the thorough mixing of two or more immiscible liquids (Fellows, 2002). The breakdown of an emulsion may manifest itself through different physicochemical mechanisms, such as gravitational separation, coalescence, flocculation, Ostwald ripening and phase inversion (Friberg and Larsson, 1997; McClements, 2000). Therefore, the production of high-quality food emulsions that can remain kinetically stable for a certain period of time is desirable. In general, emulsifiers are needed for stabilizing emulsions because they decrease the interfacial tension between the oil and water phases and form a protective coating around the droplets which prevents them from coalescing with each other (McClements, 1999). Gum arabic (Acacia senegal) from Kordofan (Central Sudan) and Damazin (Blue Nile, Western Sudan) were used to emulsify different oils. The most stable emulsion was obtained with cottonseed oil, while groundnut resulted in the lowest stable emulsion. Increasing the stirring time significantly increased the stability of the emulsion, which was also affected by gum grades. Concentration and temperature did not significantly influence emulsion stability (El-Kheir et al., 2008). Another study states that gum arabic used as an emulsifying agent for olive, cottonseed, and cod liver oil and for mineral oil-in-water emulsions retains its viscosity and stabilizing property over a wide range of pHs. Moreover, its emulsions are less viscous than those with other gums (e.g. gum tragacanth, gum karaya and pectin), but still provide equivalent stability (Whistler, 1973). In the case of cod liver oil emulsion, a combination of gum tragacanth and gum arabic proved to be superior to either gum alone in the preparation of stable oil emulsions. The uses of gum ghatti are sometimes similar to those of gum arabic. Indian ghatti is largely derived from Anogeissus latifolia, but gums from entirely different botanical sources are often referred to as ghatti gum by merchants and are exported under this name. This gum is also utilized in the binding of pharmaceutical tablets and for emulsification purposes (Jain and Dixit, 1988). Gum ghatti can be used in many more applications similar to those of gum arabic. Examples are the preparation of stable, powdered, oil-soluble vitamins, in pharmaceutical preparations as an emulsifying agent, and as a stabilizer in table syrup emulsions.

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7.2.3 Laxatives Laxatives are foods, compounds, or drug products that promote bowel movements or loosen stools, most often taken to treat constipation. Before recommending use of laxatives, differential diagnosis should be performed. Gum arabic is used in oral laxatives and in laxative suppositories. Kutira gum can also be used in laxatives: this is another gum of Indian origin that has been exported and used as a substitute for the true tragacanth gums (Astragalus spp.). It also has many points of similarity with karaya gum (Sterculia urens). As stated, the gum can be used as a laxative and in this sense, it is superior to agar-agar. One teaspoonful is equivalent to two teaspoons of agar powder (Howes, 1949). Gum karaya from S. urens, Sterculia villosa (India), and Sterculia setigera (Africa) provides the raw material for emulsifiers, adhesives, fixatives and laxatives (FAO, 1989). Gum karaya, like gum tragacanth, absorbs water to form viscous colloidal sols. The particle size of the powder determines the type of dispersion. Coarse particle size forms discontinuous mucilage—the reason for its effectiveness in laxatives. Karaya gum does not disintegrate or decompose appreciably in the alimentary tract. In a study with 10 dogs, 95% of the orally administered gum was recovered in the feces. It absorbs large quantities of water and therefore acts as a mechanical laxative. It tends to increase fecal nitrogen excretion, did not affect starch digestion in the dogs, and does not inhibit the utilization of vitamin A in rats (Ivy and Isaacs, 1938). However, the fact that ingestion or inhalation of gum karaya has been reported to cause allergic reactions needs to be considered. Sixteen cases of allergic sensitivity to inhalation of the gum and to its oral ingestion as a laxative were reported. Symptoms included hay fever, asthma, dermatitis and gastrointestinal distress (Figley, 1940).

7.2.4 Antiseptic preparations and ophthalmic infections Antiseptic relates to or denotes substances that prevent the growth of disease-causing microorganisms. A mixture of colloidal silver bromide and gum arabic has been utilized in antiseptic preparations. Silver arabate can be used as a substitute for silver nitrate and organic silver compounds for the treatment of ophthalmic infections.

7.2.5 Tablets and pills A tablet is a mixture of active substances and excipients, usually in powder form, pressed or compacted into a solid. Medicinal tablets and capsules are often called pills. About one-third of all prescriptions are compressed tablets. Medicinal tablets are prepared in many shapes and colors to help users distinguish between the different medicines that they take. Some tablets are in the shape of capsules, and are called “caplets”. Sometimes they are stamped with symbols, letters, and numbers, for purposes of identification. Tablet sizes range from a few millimeters to about a centimeter. A wide variety of binders (a material used to bind two or more other materials in a mixture) may be used, including lactose powder, dibasic calcium phosphate, sucrose, corn (maize) starch, microcrystalline cellulose and modified cellulose. Gum arabic can also be used as an adhesive or binder for pharmaceutical tablets, as a part of coatings for pills and as an excipient in the manufacture of pills and plasters. Gum arabic was used as a pill excipient, either alone or in a mixture with equal parts gum tragacanth and acacia. It cannot be used with bismuth salts due to the formation of flaky masses (Howes, 1949).

7.2.6 Hydrophobic drug delivery Gum arabic has a mucoadhesive property with some desirable features of a controlled drug-delivery system, such as localization in specified regions, which improve and enhance drug bioavailability.

Medical, Cosmetic and Biotechnological Uses of Gum Exudates  ◾  315

A novel magnetic nanocarrier, cyclodextrin (CD)-citrate-gum arabic-modified magnetic nanoparticles (GAMNPs), for hydrophobic drug delivery was fabricated taking into consideration the unique properties of both gum arabic and CDs (Takada, 2006). CDs constitute a whole new family of pharmaceutical excipients that have a doughnut-shaped structure with a hydrophilic outer surface and a lipophilic cavity, where poorly water-soluble molecules can shelter their most hydrophobic parts (Bender and Komiyama, 1978; Saenger, 1984). Therefore, grafting CD molecules on GAMNPs may lead to a drug carrier that allows controlled release of a bioactive substance, can form non-covalent inclusion complexes with a wide variety of lipophilic drug molecules enabling the solubilization, stabilization, and transport of hydrophobic drugs, and can be magnetically guided to the local site at the specified time for dosage and elimination (Banerjee and Chen, 2007).

7.2.7 Lycopene Lycopene (C40H56) is a deep red carotenoid pigment found in tomatoes and other red fruits (Fig. 7.2). It is a terpene assembled from eight isoprene units. Lycopene has a melting point of 172-173°C and is insoluble in water. It is the most common carotenoid in the human body and one of the most potent carotenoid antioxidants. Its name is derived from the tomato’s species classification, Solanum lycopersicum. Lycopene is a most powerful carotenoid quencher of singlet oxygen (Di Mascio et al., 1989); singlet oxygen produced during exposure to ultraviolet light is a primary cause of skin aging (Berneburg et al., 1999). To obtain encapsulated lycopene in powdered form, spray-drying or molecular inclusion with gum arabic and β-CD followed by freeze-drying should be performed. The encapsulation efficiency using spray-drying ranged from 94 to 96%, with an average yield of 51%, with microcapsules showing superficial indentations and a lack of cracks and breakages. Lycopeneβ-CD complexes were only formed at a molar ratio of 1:4, and irregular structures of different sizes that eventually formed aggregates, similar to those of β-CD, were observed after freeze-drying. Both drying processes yielded pale-pink, dry, free-flowing powders (Nunes and Mercadante, 2007).

7.2.8 Gelatin- and chitosan-gum arabic coacervates A coacervate is a spherical aggregation of lipid molecules making up a colloidal inclusion, which is held together by hydrophobic forces. The name is derived from the Latin “coacervare”, meaning to assemble together or cluster. Coacervate diameters range from 1 to 100 μm. They possess osmotic properties and form spontaneously from certain dilute organic solutions such as protein (e.g. gelatin) in reaction with gum arabic (Lachman et al., 1970). Encapsulates having shells of cross-linked mixtures of proteins and polysaccharides are widely used in the food and pharmaceutical industry for controlled release of active and flavor compounds. The reader is referred to section 5.2.14 for further information on coacervate uses in foods. To be able to predict the behavior and release characteristics of the microcapsules, a better understanding of the nature and extent of the crosslinking reaction is needed (Fuguet et al., 2007). Several analytical techniques (high-resolution liquid chromatography coupled to high-resolution mass spectrometry) were applied for the characterization of glutardialdehyde (GDA) cross-linked encapsulates made of gelatin and gum arabic. Cross-linking occurred between GDA molecules and lysine and hydroxylysine e-amino groups. Up to eight cross-linked products of different nature were identified. They included pyridinium ions and Schiff bases, and also non-reacted GDA condensation products (Fuguet et al., 2007). Complex coacervation, using gelatin and gum arabic as wall-forming materials, was also used for the manufacture of microcapsules of sex pheromone from the diamondback moth, Plutella

316  ◾  Plant Gum Exudates of the World

B

C

Figure 7.2  (A) Lycopene powder; (B) lycopene structure [courtesy of Jeff Dahl]; (C) lycopene 3D structure [courtesy of Edgar 181].

xylostella (Lepidoptera: Plutellidae). The encapsulated pheromone released from these microcapsules into the air was monitored for over 6 weeks in the field. Results of a field trial showed that the attractiveness of the microcapsules was superior to that of rubber septa loaded with the same amount of pheromone. That study demonstrated that pheromone microcapsules might provide a new method for P. xylostella control (Chen et al., 2007). The formation of electrostatic complexes of gum arabic with chitosan, two oppositely charged polysaccharides, was investigated as a function of biopolymer ratio, total biopolymer concentration, pH and ionic strength. High coacervate yields were obtained in a pH range of 3.5 to 5.0 for a biopolymer ratio of 5. Coacervate yield was drastically diminished at pH values below 3.5 due to a low degree of ionization of gum arabic molecules, and at pH values above 5 due to the low solubility of chitosan. Increasing ionic strength decreased coacervate yield due to shielding of ionized groups (Espinosa-Andrews et al., 2007).

Medical, Cosmetic and Biotechnological Uses of Gum Exudates  ◾  317

7.2.9 Various medical uses 7.2.9.1 Intravenous injections The best grades of gum arabic are used in medicine and in confectioneries (Howes, 1949). In the 1920s, a 7% gum arabic solution was used as part of intravenous saline injections to eliminate the problem of rapid salt escape from the blood vessels. It was believed that the colloid content and osmotic pressure of this injection were equal to those of the blood. In 1933, intravenous injections of gum arabic solutions were recommended for the treatment of nephritic edema. Mixed reports on the success rate (or lack thereof) of such preparations can be found in the literature. When dextran and polyvinylpyrrolidone (PVP) were developed as blood-plasma extenders, they pushed out the use of gum arabic (Whistler, 1973). Symptoms of allergy (e.g. flushing in the face, coldness of the extremities, chills, nausea, vomiting and the like) have been known to occur after injection of gum arabic. Epinephrine was found to eliminate/control these reactions.

7.2.9.2 Activity against leishmania and fungi Gum arabic, a highly branched polysaccharide, is a complex mixture of Ca, Mg and K salts of arabic acid that contains galactose, rhamnose, glucuronic acid, 4-O-methyl glucuronic acid and arabinose residues (Mora and Baraldi, 2002). The molecular structure of gum arabic consists mainly of three components: arabinogalactan (90%) with a low (0.5%) protein content, arabinogalactan (< 10%) with a high (10%) protein content and a third component (< 1%) that includes glycoprotein with ~50% protein content (Woo, 2001). Periodate oxidation of polysaccharides offers a convenient route for the synthesis of polymer-drug conjugates, especially with drugs possessing aliphatic amino functions via imino bonds with the aldehyde groups of the oxidized polysaccharide. In a recent report, the synthesis of a soluble amphotericin-arabinogalactan conjugate of reduced toxicity and enhanced therapeutic efficacy was demonstrated by periodate oxidation of the polysaccharide followed by coupling the amino group containing antibiotic onto the polymer (Ehrenfreund-Kleinman et al., 2002). Leishmaniasis is caused by cutaneous infection with promastigotes of the genus Leishmania upon being bitten by an infected sandfly (van Zandbergen, 2006). Antimonial compounds are the traditional treatment for leishmaniasis. The most common alternative is amphotericin B (AmB) (Matsumori et al., 2005). Paramomycin is an inexpensive alternative with fewer side effects than amphotericin. The polyene antibiotic AmB, C47H73NO17 (Fig. 7.3), is conjugated to the periodateoxidized gum arabic through Schiff linkages in the non-reduced (imine) and reduced (amine) OH

OH

O HO

O

OH

OH

OH

OH

OH

O

O OH

O

O

HO

OH NH2

Figure 7.3  Amphotericin B (courtesy of Klaus Hoffmeier).

318  ◾  Plant Gum Exudates of the World

forms. The drug conjugates are stable, non-hemolytic and non-toxic to the animal’s internal organs and show good antifungal and antileishmanial activity in vitro. Despite the large molecular weight of the polysaccharide, AmB from the conjugates exhibited bioavailability after intravenous injection. Since the highest concentration of AmB was found in the spleen after a single injection, these conjugates may be potential candidates for antileishmaniasis therapy (Nishi et al., 2007).

7.3 FOLK MEDICINE The term folk medicine describes systems of medical knowledge that developed over centuries within various societies before the era of modern medicine. Folk medicines include acupuncture, Ayurvedic medicine, herbal medicine, Unani medicine, spinal manipulation, and traditional Chinese medicine, among much other knowledge and practices all over the globe. In folk medicine, many less known exudates and to some extent, exudates that are not produced commercially, are utilized. Semla gum produced from Bauhinia species native to India, Malaya, China, Bhutan and tropical Africa is a good example (Mantell, 1947). The bark, root and flowers of Bauhinia variegata are used in folk medicine. In many parts of India, the flowers of B. variegata are used in medical formulations (Primdahl, 1993). Another report mentions the use of B. variegata bark and root to heal ulcers, bleeding, piles and dysentery (Misra, 2003). In-vitro testing of the extracts of medicinal plants collected from Islamabad and the Murree region on insulin secretagogue activity was carried out. Dried ethanol extracts of all plants were dissolved in ethanol and DMSO, and tested at various concentrations (between 1 and 40 μg/ml) for insulin release from INS-1 cells in the presence of 5.5 mM glucose (Hussain et al., 2004). Extracts of B. variegata and Bergenia himalaica showed effects at 20 μg/ml. The results suggested that such medicinal plants may be potential natural resources for antidiabetic compounds (Hussain et al., 2004). Chironji gum (Mantell, 1947), commonly called pial or peal gum (Howes, 1949), is tapped as large, clear, vitreous (glassy) tears with a pale or dark color. It is used in folk medicine to treat intercostal pain (Kirtikar and Basu, 1918). Bael fruit, and particularly bael fruit gum, is known for its antiamebic and antihistaminic actions, which are much appreciated in Indian Ayurvedic medicine (Kirticar and Basu, 1948). Bael fruit gum is also used to prepare oil-emulsion coatings (Roy et al., 1975). The fruit pulp of the tree Aegle marmelos (source of the bael fruit) is eaten and much valued in India for its medicinal properties, in particular in cases of diarrhea and dysentery (Parmar and Kaushal, 1982; Morton, 1987a). The genus Albizia comprises ~150 species, 72 of which occur widely in Africa. The generic name was misspelled ‘Albizzia’ for many years (Anderson and Morrison, 1990). Albizia gums are used locally in Africa for cosmetics (see section 7.4) and book binding (Mwamba, 1995). After the first Sahelian drought in 1973-1974, the gum exudates of Albizia zygia and Albizia lebbeck were investigated in a pilot study for their ability to replace acacia as sources of natural food and pharmaceutical emulsifiers (and see 7.2.2) (Ashton et al., 1975). From the bark of certain Albizia species, saponins and fish-stupefying, insecticidal and anthelmintic compounds can be extracted for local native medicinal and other uses (Allen and Allen, 1981). Some well-known and much used Asiatic gums have served different pharmaceutical purposes. The geographic distribution of the tree Toona ciliata M. Roem. covers India, southeast Asia and Australia, and it is cultivated elsewhere as a fast-growing timber tree. Common names for its gum exudates in Australia are cedar gum (Felter and Lloyd, 1898), red cedar gum and moulmein cedar gum (Maiden, 1890). The Indian gum, termed bastard cedar (Maiden, 1890), has been used in that country as a febrifuge (Greenway, 1941). Ketha (or kaith) gum (Smith and Montgomery, 1959) is produced from the tree Limonia acidissima L. (syn. Feronia limonia (L.) Swingle). The powdered

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gum, mixed with honey, is given to overcome dysentery and diarrhea in children. Other parts of the tree, such as the leaves, bark, roots and fruit pulp, are all used for medicinal purposes (Morton, 1987b). Jeol gum (Smith and Montgomery, 1959) also has other common names, such as jhingan gum (Soni, 1995) or modal gum (Parikh et al., 1956a,b). It is exuded by the tree Lannea coromandelica (Houtt.) Merrill and used medicinally in asthma and rheumatism (Parikh et al., 1956a). It has also been used in many parts of India as a nutritive food, especially after the puerperal period in women (Mukherjee and Rohatgi, 1948a). Mango gum is from the tree Mangifera indica L., which grows wild in India and is cultivated across all tropical and subtropical regions. The Negritos of the Philippines apply this tree’s gum-resin mixed with coconut oil directly to scabies and other parasitic diseases of the skin. The gum-resin is also used to cure aphthae and sores caused by herpes and venereal diseases such as syphilis (Quisumbing, 1951). Neem gum (Setia, 1984) comes from the tree Azadirachta indica Adr. Juss. (Fig. 7.4), which is one of the best known trees in India and is also common in Java, Sri Lanka and many other countries (Tewari, 1992). It has been used pharmaceutically in India for many centuries (Smith and Montgomery, 1959). Neem is the source of a wide variety of products, including adhesives, beauty aids, fertilizers, herbs, lumber, pesticides (oil) and numerous pharmaceuticals. Mesquite gum is produced from various species of Prosopis. In the past it has been used as a binder for tablets (see section 7.2.5), as an emulsifier, to encapsulate essential citrus oils, to ease sore throats and irritated eyes and as an antidote to lice. In this last application, the boiled gum is often mixed with mud and plastered on the hair for a day or two. When the “mud pack” is removed, the hair is glossy and free of lice (Balls, 1962). In medicine, it does not perform as well as gum arabic; nonetheless, it may occasionally be the better choice, since its solutions can be combined with basic lead acetate and with ferric salts without precipitating out. Golden apple gum (from Spondias dulcis) (Smith and Montgomery, 1959) and jobo gum (from Spondias mombin in Venezuela) are produced to greater or lesser extents by various species of the genus Spondias. The gum of Spondias purpurea is used to heal open wounds, blood-related ailments,

Figure 7.4  Neem tree (http://en.wikipedia.org/wiki/Image:Neemtree.jpg; courtesy of Manuel Anastácio).

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ulcers in the mouth, thrush, and stomatitis in babies (Basu and Rao, 1981). The gum of S. mombin is employed as an expectorant and to expel tapeworms (Morton, 1987d). The gum of Spondias pinnata has some medicinal applications (Morton, 1987c). Finally the ‘candle nut’ tree, Aleurites moluccanus produces light-colored exudates. All parts of the tree have medicinal uses. Gums of the New World have also been good sources for several pharmacological preparations. Many hundreds of woody species in North, Central and South America yield gums in varying amounts. However, in many cases, secretion is not marked or collection of the gum for local uses or for export is sporadic (Howes, 1949). The few exploited species are leguminous, belonging to the genera Caesalpinia, Piptadenia, and Prosopis. Anadenanthera colubrina var. cebil (formerly Piptadenia cebil ) is an Argentinian species of a genus known as a gum yielder. It occurs in northwest Argentina in much the same areas as Parkinsonia praecox subsp. praecox. The exudate dissolves in water and its viscosity and adhesive properties are comparable to those of gum arabic, to the extent that in times of political unrest in Sudan, this “Brazilian gum arabic” appeared in London markets (Howes, 1949). In Central America and particularly in Mexico, several of the Cactaceae are known for their ability to produce gum, but their commercial importance is limited. In Venezuela, Enterolobium cyclocarpum yields a gum known locally as “goma de caro”. It is dark and only partially soluble (Von Wiesner, 1927), and it is employed as a remedy for bronchitis (Record and Mell, 1924). Miscellaneous and other little-known gums are also of local interest or use in the countries in which they occur. They are produced in small quantities and their future potential is questionable. The commonly cultivated ornamental tree of the tropics, Cassia fistula, is well known for its medicinal uses. Its gum has a dark color and is only slightly soluble in water. In West Africa, natives apply the gum of Cassia sieberiana (derived from a small tree with yellow flower trusses and long pods) mixed with the ground pod to sores (Dalziel, 1937). The tree is common in the savannah and open forests and can also be found in eastern Sudan, Uganda and East Africa. The silk cotton or kapok tree (Ceiba pentandra) can be located in both Old and New World tropics. It yields a dark gum which swells in water and resembles the tragacanth group except for its color. As for its medicinal virtues, the gum is known in India for bowel complaints. Both the gums or gumkinos of the genus Ceratopetalum endemic to New South Wales, C. apetalum and C. gummiferum, are astringent (Maiden, 1901). In the tropics, the horseradish tree Moringa oleifera, which can also be located in northern India, produces white gum that becomes reddish brown or brownish black upon exposure to air. The gum, which swells to a jelly in the presence of water, is used medicinally by the natives of India and Java to treat intestinal complaints (Howes, 1949). Cherry gum (Prunus cerasus) has been collected and used in Europe for technical reasons. Gums from Baluchistan derived from Prunus eburnea have been considered suitable for pharmaceutical and confectionary purposes (Howes, 1949). In East Africa, Schefflera volkensii is common in the evergreen forest, and yields a gum that is used by tribes for colds, coughs and lung ailments (Greenway, 1941).

7.4 COSMETICS AND OTHER PRODUCTS 7.4.1 General The U.S. Food and Drug Administration (FDA) defines cosmetics as: “intended to be applied to the human body for cleansing, beautifying, promoting attractiveness, or altering the appearance without affecting the body’s structure or functions” (Reed, 2007). Cosmetics include many types of products and sometimes manufacturers distinguish between ornamental and skin-care cosmetics.

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7.4.2 Different cosmetic preparations Gum arabic is non-toxic and does not cause dermatological or allergic reactions upon application of cosmetic products that contain it. It is used as an emulsion stabilizer in lotions and protective creams. It serves as an adhesive in the preparation of face masks, a binding agent in formulations of compact cakes and rouges, a foam stabilizer in liquid soap, to prepare hair creams and fixatives, and in protective creams as a stabilizer and film former (Whistler, 1973). In cosmetics, gum tragacanth is used as a suspending agent in various types of toothpastes with glycerol or propylene glycol as humectant. In hair creams and lotions, ∼0.4 to 0.8% gum tragacanth is used due to its ability to promote brilliance, to yield creamy products, to produce films and to promote shelf life (Whistler, 1973). Gum tragacanth can also be included in the formulation of many toiletry preparations such as emollient skin creams and lotions, nail polishes, shaving lotions, dental creams, depilatories and permanent wave fixers. As a binding agent in greaseless creams and hair fixatives, it is similar in its properties to gum arabic (Howes, 1949). Dispersions of gum karaya at high concentrations do not pass through a noticeable gel stage; however, in combination with other gums and proteins, they can be useful in the preparation of cosmetics and pharmaceutical products (Whistler, 1973). Sterculia cinerea A. Rich. is the source of a tragacanth-like gum from the AngloEgyptian Sudan. It is also known as “tartar” gum. If large quantities of this gum were available, its uses would probably be similar to those of gum karaya. In India, the gum of Terminalia crenulata finds its usefulness as incense in the preparation of cosmetics (Setia, 1984). Also the leaves, bark and fruit have medicinal properties (Mantell, 1947).

7.4.3 Perfume Perfume is a mixture of fragrant essential oils and aroma compounds, fixatives, and solvents used to give the human body, objects, and living spaces a pleasant smell. Many techniques are available for microencapsulation (Gutcho, 1976; Sparks, 1981). Microencapsulation of perfumes using a complex coacervation of gelatin and gum arabic to form the capsule wall is common practice (Meyer, 1992). Other hydrocolloids, such as pectin, can also be used. Additional reports also mention a preference for using gum arabic and gelatin for perfume microencapsulation (De Leeuw, 1970; Nakagawa et al., 1987; Michael, 1990). A microencapsulated perfume is protected from evaporation and maintains its original composition, as there is no preferential evaporation of its more volatile components (Meyer, 1992). Perfume can be microencapsulated by dissolving gelatin and pectin in water at 50-55°C, then adding the perfume and stirring. The mixing speed is adjusted to the desired microcapsule size. Then, AcOH is added to form the complex coacervate, a sticky substance made from gelatin and pectin. The mixture is slowly cooled to 10°C. During cooling, the complex coacervate sticks to the perfume droplets, thus forming microcapsules. The microcapsules are hardened with glyoxal under alkaline conditions. After washing and drying, the originally liquid perfume is in the form of free-flowing granules, with 460 g of perfume yielding 444 g of 0.5- to 1.0-mm microcapsules (Meyer, 1992). In the case of gelatin-pectin, the formed thin shell is sufficient to change a fluid perfume into free-flowing granules. The wall is not completely impermeable and some perfume is lost over the years by evaporation. At 60°C, 5% of the encapsulated perfume was lost over the course of a month. This compares favorably with microcapsule walls made from gelatin and gum arabic, where the loss was 55% for 1 month at the same temperature (Meyer, 1992). Encapsulated perfume can be included in aqueous printing ink. Such ink should have printability as well as fragrance-maintaining and fragrant properties. The use of perfume-containing

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microcapsules is known but the application of perfume-containing microcapsules to printing ink is accompanied by unexpected difficulties (Yukio et al., 1975). In other words, conventional inkmaking cannot be applied to the case of using perfume-containing microcapsules in the production of printing ink owing to the necessity of using specific solvents, polymers and binders for making the ink, as well as to the size of the microcapsules and the requirement for effective fragrance-maintenance and fragrant properties (Yukio et al., 1975). To overcome these difficulties, an aqueous printing ink containing perfume-containing microcapsules was prepared by a process involving the encapsulation of single, 15- to 70-micron drops of perfume with the gelatin-gum arabic complex coacervation technique and dispersing the encapsulated perfume in an aqueous solution of a water-soluble polymer (Yukio et al., 1975).

7.4.4 Powdered abrasive cleaners Powdered abrasive cleansers have long been used to scour porcelain sinks and fixtures, hard metallic materials, pots and pans, and similar surfaces which require high levels of mechanical abrasive for cleaning. Microcapsules made by coacervation processes from gelatin and a polyanionic material, and especially such microcapsules having a complex structure, are particularly desirable for use in powdered abrasive cleanser compositions (Michael, 1990). Microcapsules with this complex wall structure can be made by coacervation processes in which at least a major portion of the material to be encapsulated is converted to an emulsion with particle diameters of at least about 50 microns, and another smaller portion of the same material, different material, or mixtures thereof, is converted to an emulsion or suspension with particle diameters of less than about 15 microns before encapsulation; in other words, the coacervation process uses an emulsion with a bimodal distribution. During a typical coacervation process for forming microcapsules, the smaller hydrophobic emulsion particles will be encapsulated first and they, in turn, will coalesce around the larger emulsion core particles to form walls. As stated, all, or a portion of the small wall-inclusion particles can be of a different material than the central core material, preferably a material that can be solubilized by water to disrupt the walls (Michael, 1990).

7.5 BIOTECHNOLOGICAL APPLICATIONS 7.5.1 Recombinant plant gum Gummosis is a common wound response in trees that results in the exudation of a gum sealant from cracks in the bark (Stephen et al., 1990). In general, the exudate is a composite of polysaccharides and glycoproteins that is structurally related to cell-wall components such as galactans and hydroxyproline-rich glycoproteins (Aspinall, 1970). Gum arabic is probably the best characterized of these exudates. Acacia senegal accounts for approximately 80% of the production of gum arabic with Acacia seyal, Acacia laeta, Acacia camplylacantha and Acacia drepanolobium supplying the remaining 20%. Attempts to produce gum arabic in cultured A. senegal cells have been made. Unfortunately, conditions have not been found which lead to the expression of gum arabic in culture (Mollard and Joseleau, 1994). Clearly, new approaches are needed. A new methodology in the field of plant gums has been described which presents a solution to the production of hydroxyproline-rich glycoproteins (HRGPs), repetitive proline-rich proteins (RPRPs) and arabino-galactan proteins (AGPs). The expression of synthetic genes designed from repetitive peptide sequences of such glycoproteins, including the peptide sequences of gum arabic glycoprotein

Medical, Cosmetic and Biotechnological Uses of Gum Exudates  ◾  323

(GAGP), is induced in host cells, including plant host cells (Kielszewski, 2003). Plant HRGPs are modular structural glycoproteins—generally elongated, flexible, rod-like molecules with marked peptide periodicity. Some become cross-linked to form covalent cell-wall networks that control extension growth, increase the tensile strength of the cell wall and impart mechanical resistance to attack by plant pathogens. Other HRGPs, such as the AGPs, do not cross-link and form a protective hydrophilic cushion at the interface between the plasma membrane and cell wall. Yet others, like the GAGP, are protective exudate gum components, acting as plastic sealants at the sites of mechanical injury (Kielszewski, 2003). A biotechnological study demonstrated the feasibility and potential of a synthetic gene approach to the de-novo design of novel glycoprotein-based gums and emulsifiers (Xu et al., 2005). Briefly, a synthetic gene encoding a novel HRGP-based gum, designated gum arabic-8, was expressed in transgenic BY2 Nicotiana tabacum (tobacco) cells. This gene encoded eight repeats of the consensus polypeptide sequence of GAGP. Gum arabic-8 was expressed as a green fluorescent protein (GFP) fusion protein targeted to the culture medium, (GA)(8)GFP. Culture of the transgenic cells in a bioreactor showed that production was associated with cell growth. The extracellular yield of (GA)(8)GFP was 116.8 mg/l after 14 days of culture and accounted for 87% of the total fusion protein expressed. (GA)(8)GFP was purified from the culture medium by a combination of hydrophobic interaction, gel permeation, and reverse-phase chromatography. Functional assays showed that gum arabic-8 exhibits low viscosity in aqueous solution similar to native GAGP. However, the gum arabic module could not emulsify essential oil of orange. Nevertheless, the fusion protein possessed better emulsification properties than the native GAGP (Xu et al., 2005).

7.5.2 Intracellular delivery Carbon nanohorn (CNH) is a recently recognized member of the fullerene family (Iijima et al., 1999). A single CNH has a structure similar to a pudgy single-wall carbon nanotube (SWCNT) (Iijima et al., 1999) with one end closed in a cone-shaped cap (horn). Due to strong van der Waals forces, CNHs form spherical dahlia flower-like assemblies. This distinctive structure may give CNHs potential advantages over normal nanoparticles, nanorods and nanotubes for intracellular delivery (Fan et al., 2007). Isolated CNHs and nanoscale CNH agglomerates can be successfully isolated by a copolymer (gum arabic) through steric stabilization. Gum arabic (Bandyopadhyaya et al., 2002), used as a typical copolymer in this study, is biocompatible and its protein moieties can be conjugated with biological cargos for intracellular delivery. During mild sonication, the hydrophobic polypeptide chains of gum arabic will spontaneously adsorb to the surface of temporarily isolated CNHs, while the hydrophilic arabinogalactan polysaccharide side chains extend into the water, providing a steric barrier (Islam et al., 1997). In-vitro study shows that the modified CNHs are non-toxic and may be used as a promising vehicle for intracellular delivery (Fan et al., 2007).

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324  ◾  Plant Gum Exudates of the World Aspinall, G. O. 1970. Plant gums. In The carbohydrates chemistry and biochemistry. 2nd ed. Vol. 2B. W. Pigman and D. Horton (eds.). pp. 522-36. New York: Academic Press Inc. Balls, E. K. 1962. Early uses of California plants. Berkeley, CA: The University of California Press. Bandyopadhyaya, R., Nativ-Roth, E., Regev, O., and R. Yerushalmi-Rozen. 2002. Stabilization of individual carbon nanotubes in aqueous solutions. Nano Lett. 2:25-8. Banerjee, S. S., and D. H. Chen. 2007. Magnetic nanoparticles grafted with cyclodextrin for hydrophobic drug delivery. Chem. Materials 19:6345-9. Basu, S., and C. V. N. Rao. 1981. Structural investigation on degraded Spondias dulcis gum. Carbohydrate Res. 94:215-24. Bender, M., and M. Komiyama. 1978. Cyclodextrin chemistry. Berlin: Springer-Verlag. Berneburg, M., Grether-Beck, S., Kurten, V. et al. 1999. Singlet oxygen mediates the UVA-induced generation of the photoaging-associated mitochondrial common deletion. J. Biol. Chem. 274:15345-9. Chen, Z. L., Fang, Y. L., and Z. N. Zhang. 2007. Synthesis and assessment of attractiveness and mating disruption efficacy of sex pheromone microcapsules for the diamondback moth, Plutella xylostella (L.). Chinese Sci. Bull. 52:1365-71. Dalziel, J. M. 1937. The useful plants of West Tropical Africa. London: Crown Agents for the Colonies. De Leeuw, G. L. 1970. Coacervation, micro-encapsulage et produits microencapsules. Parfumerie, Cosmitique, Savons 13:358. Di Mascio, P., Kaiser, S., and H. Sies. 1989. Lycopene as the most efficient biological carotenoid singlet oxygen quencher. Arch. Biochem. Biophys. 274:532-8. Ehrenfreund-Kleinman, T., Azzam, T., Falk, R., Polacheck, I., Golenser, J., and A. J. Domb. 2002. Synthesis and characterization of novel water soluble amphotericin B-arabinogalactan conjugates. Biomaterials 23:1327. El-Kheir, M. K. S., Yagoub, A. E. G. A., and A. A. A. Baker. 2008. Emulsion-stabilizing effect of gum from Acacia senegal (L.) Willd. The role of quality and grade of gum, oil type, temperature, stirring time and concentration. Pakistan J. Nutr. 7:395-9. Espinosa-Andrews, H., Baez-Gonzalez, J. G., Cruz-Sosa, F., and E. J. Vernon-Carter. 2007. Gum Arabicchitosan complex coacervation. Biomacromolecules 8:1313-8. Fan, X. B., Tan, J., Zhang G. L., and F. B. Zhang. 2007. Isolation of carbon nanohorn assemblies and their potential for intracellular delivery. Nanotechnology 18(19):Art. No. 195103. FAO. 1989. Arid zone forestry: A guide for field technicians. ISBN 92-5-102809-5. www.fao.org/docrep/ t0122e/t0122e0d.htm Felter, H. W., and J. U. Lloyd. 1898. Acacia (U. S. P.)—acacia. In King’s American dispensatory, 18th edn., 3rd revision, reprinted 1983. Portland, OR: Eclectic Medical Publications. Fellows, P. J. 2002. Food processing technology principles and practice. 2nd edition. Cambridge England: CRC, Woodhead Publishing Limited. Figley, K. D. 1940. Karaya gum hypersensitivity. J. Am. Med. Assoc. 114:747-8. Friberg, S. E., and K. Larsson. 1997. Food emulsions, vol. 1, 159. New York : Marcel Dekker. Fuguet, E., van Platerink, C., and H. G. Janssen. 2007. Analytical characterization of glutardialdehyde crosslinking products in gelatine-gum arabic complex coacervates. Anal. Chim. Acta 604:45-53. Greenway, P. J. 1941. Gum, resinous and mucilaginous plants in East Africa. East African Agric. J. 6:241-50. Gutcho, M. H. 1976. Microcapsules and microencapsulation techniques. Park Ridge, N.J.: Noyes Data Corporation. Howes, F. N. 1949. Vegetable gums and resins. Waltham, MA: Chronica Botanica Company. Hussain, Z., Waheed, A., Qureshi, R. A. et al. 2004. The effect of medicinal plants of Islamabad and Murree region of Pakistan on insulin secretion from INS-1 cells. Phytother. Res. 18:73-7. Iijima, S., Yudasaka, M., Yamada, R., Bandow, S., Suenaga, K., and F. Kokai. 1999. Nano-aggregates of single-walled graphitic carbon nano-horns. Chem. Phys. Lett. 309: 165-70. Islam, A. M., Phillips, G. O., Sljivo, A., Snowden, M. J., and P. A. Williams. 1997. A review of recent developments on the regulatory, structural and functional aspects of gum Arabic. Food Hydrocolloids 11:493-505. Ivy, A. C., and B. L. Isaacs. 1938. Karaya gum as a mechanical laxative. An experimental study on animals and man. Am. J. Dig. Dis. 5:315-21.

Medical, Cosmetic and Biotechnological Uses of Gum Exudates  ◾  325 Jain, J. K., and V. K. Dixit. 1988. Studies on some gums and their derivatives as binding agents. Indian J. Pharm. Sci. 50:113-4. Jain, J. K., and V. K. Dixit. 1998. Studies of some gums and their derivatives as suspending and emulsifying agents. Indian J. Natural Prod. 4:3-8. Jain, S. K. 2000. Human aspects of plant diversity. Econ. Bot. 54:459-70. Jefferies, M., Pass, G., and G. O. Phillips. 1977. Viscosity of aqueous solutions of gum ghatti. J. Sci. Food Agric. 28:173-9. Kielszewski, M. J. 2003. Synthetic genes for plant gums and other hydroxyproline-rich glycoproteins. US Patent 6,570,062. Kirtikar, K. R., and B. D. Basu. 1918. Indian medicinal plants. Allahabad, India: The Indian Press. Kirtikar, K. R., and B. D. Basu. 1948. The wealth of India, raw materials, vol. 1, 33-34. New Delhi: C.S.I.R. Misra, M. K. 2003. Baseline information on medicinal plants conservation and sustainable utilisation. www. frlht.org.in/html/reports/sikkim.pdf Lachman, L., Lieberman, H. A., and J. L. Kanig. (1970) The theory and practice of industrial pharmacy, 420. Philadelphia: Lea & Febiger. Maiden, J. H. 1890. On cedar gum (Cedrela australis, F.v.M.). The Proceedings of the Linnean Society of NSW 2:1047-9. Maiden, J. H. 1901. The gums, resins and other vegetable exudation of Australia. J. Proc. Roy. Soc. N.S. Wales 35:161-212. Mantell, C. L. 1947. The water-soluble gums, 61, 69. New York: Reinhold Publ. Corp. Matsumori, N., Sawada, Y., and M. Murata. 2005. Mycosamine orientation of amphotericin B controlling interaction with ergosterol: Sterol-dependent activity of conformation-restricted derivatives with an amino-carbonyl bridge. J. Am. Chem. Soc. 127:10667-75. McClements, D. J. 1999. Food emulsions: principles, practices and techniques, 378. Boca Raton, FL: CRC Press. McClements, D. J. 2000. Comments on viscosity enhancement and depletion flocculation by polysaccharides. Food Hydrocolloids 14:173-7. Meyer, A. 1992. Perfume microencapsulation by complex coacervation. Chimia 46:101-2. Mhinzi, G. S. 2002. Properties of gum exudates from selected Albizia species from Tanzania. Food Chem. 77:301-4. Michael, D. W. 1990. Powdered abrasive cleansers with encapsulated perfume. US Patent 4,961,871. Mollard, A. and J. P. Joseleau. 1994. Acacia senegal cells cultured in suspension secrete a hydroxyprolinedeficient arabinogalactan-protein. Plant Physiology and Biochemistry, 32:703-709. Mora, P. C., and P. G. Baraldi. 2002. Democosmetic applications of polymeric biomaterials. In Polymeric biomaterials, ed. S. Dumitriu, 2nd edn., 459. New York: Marcel Dekker. Morton, J. F. 1987b. Wood apple. In Fruits of warm climates, 190-1. Miami: Julia F. Morton. Morton, J. F. 1987c. Ambarella. In Fruits of warm climates, 240-2. Miami: Julia F. Morton. Morton, J. F. 1987d. Yellow mombin. In Fruits of warm climates, 245-8. Miami: Julia F. Morton. Mukherjee, S. N., and K. K. Rohatgi. 1948. Studies on gum Jeol (Lannea grandis Super). Part V. Dependence of viscous and electrochemical properties of the aqueous solution on its concentration. J. Indian Chem. Soc. 25:339-48. Mwamba, C.K. 1995. Variations in fruits of Uapaca kirkiana and the effects of in situ silvicultural treatments on fruit parameters. Nairobi: ICRAF. Nakagawa,Y., Kamura,T., Arai, H., Takizawa, M., and S. Konishi. 1987. Solid soap containing dispersed microcapsules. United States Patent 4,749,501. Nishi, K. K., Antony, M., Mohanan, P. V., Anilkumar, T. V., Loiseau, P. M., and A. Jayakrishnan. 2007. Amphotericin B-gum arabic conjugates: Synthesis, toxicity, bioavailability, and activities against Leishmania and fungi. Pharm. Res. 24:971-80. Nunes, I. L., and A. Z. Mercadante. 2007. Encapsulation of lycopene using spray-drying and molecular inclusion processes. Brazilian Arch. Biol. Technol. 50:893-900. Morton, J. F. 1987a. Bael fruit. In Fruits of warm climates, ed.by Curtis F. Dowling, Jr. pp. 87-90. Miami: Julia F. Morton. Panda, D., Si, S., Swain, S., Kanungo, S. K., and R. Gupta. 2006. Preparation and evaluation of gels from gum of Moringa oleifera. Indian J. Pharm. Sci. 68:777-80.

326  ◾  Plant Gum Exudates of the World Parikh, V. M., Ingle, T. R., and B. V. Bhide. 1956a. Studies in carbohydrates. Part III. Investigation of modal gum (Lannea grandis). J. Indian Chem. Soc. 33:119-21. Parikh, V. M., Ingle, T. R., and B. V. Bhide. 1956b. Studies in carbohydrates. Part IV. Investigation of modal gum (Lannea grandis). Structure of the aldobionic acid. J. Indian Chem. Soc. 33:125-8. Parmar, C., and M. K. Kaushal. 1982. Aegle marmelos. In Wild fruits, 1-5. New Delhi: Kalyani Publishers. Primdahl, H. 1993. NIAS Report # 19. Central Himalayan folklore: Folk songs in the rituals of the life-cycle. Copenhagen: Nordic Institute of Asian Studies. Quisumbing, E. 1951. Medicinal plants of the Philippines. Manila: Dept. of Agriculture and Natural Resources, Bureau of Printing. Record, S. J., and C. D. Mell. 1924. Timbers of tropical America. New Haven: Yale University Press. Reed, S. I. 2007. Cosmetics and your health. 2004. Washington, D.C: US Department of Health and Human Services. Roy, A., Mukherjee, A. K., and C. V. N. Rao. 1975. Graded-hydrolysis studies on bael (Aegle marmelos) gum. Carbohydrate Res. 41:219-26. Saenger, W. 1984. Inclusion compounds. London: Academic Press. Setia, R. C. 1984. Development, structure and histochemistry of gum cavities in Pterocarpus marsupium Roxb. and Azadirachta indica Juss. Flora Morphologie, Geobotanik, Oekophysiologie 175:329-37. Shahjahan, M., and I. Islam. 1998. Preliminary evaluation of shilajit as a suspending agent in antacid suspensions. Drug Dev. Ind. Pharmacy 24:1109-12. Smith, F., and R. Montgomery. 1959. The chemistry of plant gums and mucilages. New York: Reinhold Publ. Corp. Soni, P. L. 1995. Some commercially important Indian gum exudates. Indian Forester 121:754-9. Sparks, R. E. 1981. Microencapsulation. In Kirk-Otmer: Encyclopedia of chemical technology, ed. M. Grayson, 3rd edn., vol. 15, 470-93. New York-Chichester-Srisbane-Toronto: John Wiley& Sons. Stephen, A. M., Churms, S. C., and D. C. Vogt. 1990. Exudate gums. Meth. Plant Biochem. 2:483-522. Takada, K. 2006. Oral formulation for gastrointestinal drug delivery. US Patent 7,097,851 B1. Tewari, D. N. 1992. Monograph on neem (Azadirachta indica A. Juss.). Dehra Dun, India: International Book Distributors. van Zandbergen, G., Bollinger, A., Wenzel, A. et al. 2006. Leishmania disease development depends on the presence of apoptotic promastigotes in the virulent inoculum. Proc. Natl. Acad. Sci. 103:13837-42. Verbeken, D., Dierckx, S., and K. Dewettinck. 2003. Exudate gums: occurrence, production, and applications. Appl. Microbiol. Biotechnol. 63:10-21. Von Wiesner, J. 1927. Die rohstoffe des pflanzenreichs. Leipzig: Engelmann. Wapnir R. A., Sherry, B., Codipilly, C. N., Goodwin L. O., and I. Vancurova. 2008. Modulation of rat intestinal nuclear factor NF-kappa B by gum Arabic. Dig. Dis. Sci. 53: 80-7. Whistler, R. L. 1973. Industrial gums, 2nd edn. New York: Academic Press, Inc. Whistler, R. L. 1993. Exudates gums. In Industrial gums: polysaccharides and their derivatives, ed. R. L. Whistler, and J. N. Bemiller, 318-37. San Diego: Academic Press. Woo, D. H. 2001. Stabilization of the emulsion prepared with dietary fiber from corn hull. Food Sci. Biotechnol. 10:348. Xu, J. F. , Shpak, E., Gu, T. Y., Moo-Young, M., and M. Kieliszewski. 2005. Production of recombinant plant gum with tobacco cell culture in bioreactor and gum characterization. Biotechnol. Bioeng. 90:578-88. Yukio, M., Shizuo, M., Kenichiro, Y., and K. Asaji. 1975. Aqueous printing ink containing perfume-containing microcapsules. US Patent 3,888,689.

Chapter 8

Analysis and Identification of Gum Exudates 8.1 INTRODUCTION The analysis and identification of commercial gums can be performed by chemical and physical tests. However, the inclusion of hydrocolloids in foodstuffs makes their isolation and identification much more complex. Raw natural gums in a native state can be identified by shape, size, color, brittleness and type of fracture, among other physical properties. Combined with simple chemical tests, these properties are generally sufficient to identify individual hydrocolloids. If the gums are sold as powders, then color is the only overt physical characteristic and identification by further analysis of physical and chemical properties is required (Glicksman, 1969).

8.2 INDUSTRIAL GUMS 8.2.1 Water solubility Solubility is a physical property that refers to the capacity of a given substance, the solute, to dissolve in a solvent. The mode of gum dispersion or dissolution can provide a first clue to its identification. For example, gum arabic dissolves easily in water, while karaya and tragacanth gums swell, yielding stringy dispersions (Ewart and Chapman, 1952). The way in which unknown gums disperse in water after being wetted with alcohol can help in their identification (Table 8.1). A typical procedure consists of wetting up to 0.5 g of the gum in powdered form with 1 to 2 ml of 95% ethanol then adding 50 ml distilled water. The powder is then suspended in the water by stirring or shaking (Ewart and Chapman, 1952). The suspension is then heated: if it dissolves, heating is stopped at once; if not, heating at 85 to 95°C is continued for another 15 min. Compared observations with characteristic differences are reported in Table 8.1. The major exudate gums all behave differently. Gum arabic dissolves in cold water to form a clear and slightly viscous solution. Gum karaya forms a viscous suspension and its insoluble particles settle on standing. Gum tragacanth swells to form a viscous dispersion in cold or hot water, but does not form a true solution, and gum 327

328  ◾  Plant Gum Exudates of the World

Table 8.1  Dispersion in Water of Alcohol-Wetted Exudates* Gum

Manner of dispersal in water

Arabic

Dissolves in cold water to form a clear, only slightly viscous solution.

Ghatti

Dissolves to form an almost clear solution but some insoluble material may remain as a fine suspension.

Karaya

Forms a viscous suspension. Insoluble particles settle on standing.

Tragacanth

Swells to form a viscous dispersion in cold or hot water, but does not form a true solution.

* Adapted from Ewart and Chapman (1952).

ghatti dissolves to form an almost clear solution, but some insoluble material may remain as a fine suspension (Ewart and Chapman, 1952). The insoluble fraction of gum exudates consists of insoluble foreign matter (twigs, pieces of branches, etc.) and the insoluble gel, which dissolves to some extent on boiling. The amount of insoluble gel is taken as a measure of the value of the gum and has generally been found to vary widely among tree exudate gums, whereas the insoluble matter is unimportant because it can be eliminated by careful separation (Mbuna and Mhinzi, 2002). For food and pharmaceutical applications, the moisture content of gum karaya should be less than 200 g/kg and the insoluble matter content less than 30 g/kg (JECFA/FAO, 1988). The insoluble matter content of Sterculia quinqueloba gum has been reported to exceed the acceptable limit for gum karaya due to a higher proportion of bark and sand (Mbuna and Mhinzi, 2002). This can, however, be improved by careful hand-grading. Dichrostachys cinerea gum complies with the moisture content specification for gum arabic, i.e. not more than 150 g/kg (JECFA/FAO, 1999). The loss in moisture of the gum is in good agreement with data obtained for commercial Tanzanian gum arabic (127.4143.9 g/kg). Acacia senegal gum (Mrosso, 1996) has a cold-water-insoluble gel (CWIG) content of 89 g/kg while gum ghatti (Jefferies et al., 1977) and Acacia polyacantha gum contain 340 and 367 g/kg CWIG content, respectively. As expected, the hot-water-insoluble gel (HWIG) content for those studied samples was significantly lower than the CWIG content, except for S. quinqueloba gum. This situation is similar to that observed for Acacia gums and gum ghatti. The values for S. quinqueloba gum are quite high and are similar to those obtained previously for Khaya grandifoliola gum (CWIG, 737 g/kg; HWIG, 51.6 g/kg) (Aslam et al., 1978). This is not surprising, because S. quinqueloba gum is related to gum karaya (Goldstein and Alter, 1973). The CWIG and HWIG contents of D. cinerea and Acacia pseudofistula gums, on the other hand, resemble those of A. senegal gum, which has a CWIG content of 15.7 g/kg and an HWIG content of 9.6 g/kg, but are higher than those reported previously for commercial Tanzanian acacia gums (Mhinzi and Mosha, 1995). The insoluble fraction of commercial gum ghatti varies from 80 to 230 g/kg and the proportion of this fraction governs the gum’s viscosity (Mbuna and Mhinzi, 2002). This behavior is not observed for S. quinqueloba gum, the viscosity of which is appreciably lower than that of gum ghatti at the same concentration. The viscosity of D. cinerea gum, on the other hand, is similar to that of some acacia gums but slightly higher than the average viscosity of commercial Tanzanian gum arabic at the same concentration. The viscosity of A. pseudofistula gum has been

Analysis and Identification of Gum Exudates   ◾  329

reported to be lower than the average viscosity of commercial Tanzanian acacia gums at the same concentration. It is also lower than that of Acacia drepanolobium gum, which has been suggested to be a major source of commercial Tanzanian acacia gums (Mbuna and Mhinzi, 2002). Further data on the solubility of different major and minor exudates can be found in chapters 3 and 4.

8.2.2 Alcohol precipitability An additional preliminary test for gum identification consists of measuring the rate of settling of its precipitates when alcohol is added to an aqueous solution of the gum. Using this test, gum arabic separates as a curdy precipitate while gum karaya yields fine, filamentous, non-adherent particles (Smith and Montgomery, 1959). For the alcohol-precipitability test, it is suggested that 70 ml of 95% ethanol be added dropwise, with constant stirring, to 20 ml of a 0.5 to 1.0% gum solution, until complete precipitation is achieved. Texture, quality and characteristics of the gum precipitate are then determined, in order to identify the gum (Weinberger and Jacobs, 1929). For example, gum arabic creates a fine, opaque white precipitate that is soluble in excess Stoke’s reagent (made by dissolving 30 g FeSO4 and 20 g tartaric acid in water and diluting, then adding concentrated NH4OH just before use until the formed precipitate redissolves), while in a neutral 20% lead acetate solution, no precipitate is formed (Table 8.2). In basic lead acetate, gum arabic yields a white, curdy precipitate that is insoluble in excess reagent. In a 10% solution of potassium hydroxide, gum arabic has a faint yellow tinge, and its precipitate is soluble in excess neutral ferric chloride (5% solution). In a 4% borax solution or with the addition of two volumes of acetic acid, no reaction is detected and with Millon’s reagent (i.e. metallic mercury dissolved in an equal weight of nitric acid and diluted with an equal volume of water), it yields a fine yellow precipitate (Glicksman, 1969). Table 8.2 summarizes the behaviors of the major exudates with various reagents.

8.2.3 Microscopic identification Microscopic identification is based on reactions of ethanol-precipitated gums with reagents such as chloro-zinc-iodide (i.e. iodine-potassium iodide in zinc chloride solution), ruthenium red (added to a few milliliters of 10% lead acetate solution to produce a wine-red color; ruthenium is a rare transition metal of the platinum group of the periodic table found associated with platinum ores and used as a catalyst in some platinum alloys) and methylene blue (MB—a heterocyclic aromatic chemical compound, C16H18ClN3S, with many uses in a range of fields, such as biology and chemistry. At room temperature it is a solid, odorless, dark green powder that yields a blue solution when dissolved in water. The hydrated form has three molecules of water per molecule of MB (Fig. 8.1) and (Table 8.3). The microscopic method is appropriate for both commercial gums and those that have been isolated from food products (Jacobs, 1958). Gum tragacanth belongs to group reaction I (i.e. it reacts with the reagents: iodine-potassium iodide in zinc chloride solution). Its original alcohol precipitate is stringy, and a translucent blue. The group reaction is blue. Confirmatory test is performed by achieving a bright yellow color upon warming the gum with 10% NaOH solution in a steam bath. Exudates do not have a reaction with Group II (i.e. reagent is alcoholic iodine solution). Gum karaya belongs to group reaction III (i.e. it reacts with the reagent ruthenium red). The original alcohol precipitate of gum karaya is a fine flocculent, which turns into a compact mass upon centrifugation. It swells considerably, and its group reaction yields a strongly stained pink granular mass. Confirmatory test is performed by achieving a pink color upon heating with HCl, and aqueous MB also produces a characteristic blue stain. Gum arabic

*

No precipitate

White, curdy precipitate, settles rapidly

Voluminous flocculent translucent precipitate

Ghatti

Karaya

Tragacanth

Voluminous flocculent precipitate, gels

Negative

No precipitate

No precipitate

Voluminous precipitate, gels

Stringy precipitate, settles rapidly

Translucent flocculent precipitate

White, curdy precipitate, insoluble in excess reagent

Basic lead acetate

Bright yellow stringy precipitate

Negative

Negative

Faint yellow tinge

Potassium hydroxide (10% solution)

Gels

Precipitate coagulates on heating

Negative

Precipitate, soluble in excess reagent

Neutral ferric chloride (5% solution) Alcohol precipitate

Coagulation, long and stringy, adherent

Fine filamentous particles, non-adherent

Fine flocculent precipitation, non-adherent

Very fine flocculation, nonadeherent, well-defined precipitation

Adapted from Jacobs and Jaffe (1931), Weinberger and Jacobs (1929), Glicksman (1969).

White, fine opaque precipitate, soluble in excess reagent

Stoke’s reagent

Arabic

Reagent Gum

Neutral lead acetate (20% solution)

Table 8.2  Behavior of Exudates with Various Reagents*

Negative

Negative

Negative

Negative

Borax (4% solution)

Voluminous flocculent precipitate

Fine precipitate

Fine precipitate

Yellow, fine precipitate

Millon’s reagent

Negative

Négative

Negative

Negative

+2 volumes acetic acid

330  ◾  Plant Gum Exudates of the World

Analysis and Identification of Gum Exudates   ◾  331 N H3C

N

S

CH3

Cl–

+ N

CH3

CH3

Figure  8.1  Methylene blue (http://commons.wikimedia.org/wiki/User:Benjah-bmm27; courtesy of Ben Mills).

belongs to group IV (i.e. it reacts with the reagent H2SO4 when warming cautiously in a steam bath). The gum gives a greenish-brown color with the reagent. This gum precipitate is completely soluble in water, distinguishing it from other gums (Glicksman, 1969). Microscopic identification includes preparation of the sample, preparation of the control and examination. The preparation consists of adding water to the sample under continuous stirring to produce a fluid mixture: 5 to 10 ml of this mixture are added to four volumes of 95% ethanol and centrifuged. If fat is present, the precipitate is washed in ether and the gum is re-precipitated. Table 8.3  Microscopic Identification Method*† Exudate Tragacanth

Karaya

Original alcohol precipitate

Group reaction

Stringy, bluish, translucent

Blue

Fine floccule Compact mass on centrifugation

Swells considerably; strongly stained pink granular mass

(Group I: reagent: chloro-zinc-iodide)

Confirmatory test Warm with 10% NaOH solution in steam bath: turns yellow

Certain gums, e.g. carrageenan, may yield a dull yellow color with NaOH; tragacanth yields bright yellow

Heat with HCl: turns pink

Aqueous methylene blue produces characteristic stain

Precipitate completely soluble in H2O

Complete solution of acacia distinguishes it from other gums

(Group III: reagent: ruthenium red) Arabic

_

Greenish-brown (Group IV: reagent: H2SO4, warmed cautiously in a steam bath)

*

†

Remarks

Adapted from Cannon (1939), Jacobs (1958), Association of Official Agricultural Chemists (1960). For Group II the reagent is alcoholic iodine solution. It can be used for microscopic identification of agar and carrageenan. Identification is carried out by drying a smear on a slide, then flushing with alcohol and irrigating with water.

332  ◾  Plant Gum Exudates of the World

Table 8.4  Reactivity of Exudates with Electrolyte Reagents* Gum

Concentration (%)

Desogen Copper Lead Phosphotungstic Ruthenium (Geigy)† sulfate acetate acid red

Hexol nitrate

Tragacanth

0.5

0.04

4.00

2.00

0.88

6.00

0.038

Arabic

1.0

1.00

–

–

–

3.00

0.95

*

†

Adapted from Deuel and Solms (1951). Values within the table are in milliequivalents of reagent per gram of polysaccharide. Desogen (Ciba-Geigy) is a quaternary ammonium salt.

In the case of gum arabic, a few drops of saturated salt solution are added to facilitate precipitation. The control is prepared by wetting 1 g gum with alcohol, followed by constant stirring and heating to boiling. The gum is precipitated from 5 to 10 ml of the control solution as described for the sample. The examination includes pressing the precipitated gum against a slide to form a 4 × 8 mm smear. The resulting smear depends on the gum. For gum arabic, a white opaque film is produced. The gum smear is covered with chloro-zinc-iodide solution (the group I reagent) and viewed with the naked eye or under a microscope. For direct examination, the slide is placed on a white surface. For microscopic examination, the slide is viewed at 90× magnification; if no characteristic color is produced within at most 2 min, a fresh smear is examined with the next reagent group by adding a drop of tincture of iodine, flushing with alcohol then washing in water, followed by examination. Fresh smears are used for each test with each group (Glicksman, 1969). Polarized light microscopy and various reagents are used to detect and identify hydrocolloids in a dry mix. However, these tests can be adapted as confirmatory tests for gums isolated from different foodstuffs and tentatively identified by other methods. Deuel and Solms (1951) attempted to quantify the precipitation reactions of gums. They noted that many gums with chemical similarity have quite different flocculation values. The milliequivalents of reagent required to produce flocculation or coagulation of 1 g of gum differed (Table 8.4). For example, for a concentration of 0.5 % gum tragacanth, 0.04, 4.00, 2.00, 0.88, 6.00 and 0.038 milliequivalents of Desogen (Geigy), copper sulfate, lead acetate, phosphotungstic acid [PTA—a heteropoly acid with the chemical formula H3PW12O40, which is normally present as a hydrate. It has the appearance of small, colorless-grayish or slightly yellow-green crystals, with a melting point 89°C (24 H2O hydrate). It is odorless and soluble in water (200 g/100 ml). It is not especially toxic, but is a mild acidic irritant. The compound is known by a variety of different names; Fig. 8.2], ruthenium red, or hexol nitrate are used for coagulation or flocculation. For 1.0% gum arabic, 1.00, 3.00 and 0.95 milliequivalents of Desogen, ruthenium red or hexol nitrate are required for coagulation or flocculation (Deuel and Solms, 1951).

8.2.4 Identification of gums in specific foods Specific procedures have been developed for the separation and isolation of gums included in different food items. Sometimes a combination of methods is required to achieve a reliable determination. In frozen desserts, gum identification includes different stages—fat removal by dioxane, protein precipitation, and isolation and purification of the gum by alcohol precipitation (McNulty, 1960). Carrageenan is used as a stabilizer in many dairy products. Its efficacy is due to its strong interaction with milk proteins. Carrageenan can be quantitatively determined in milk products by

Analysis and Identification of Gum Exudates   ◾  333

Figure 8.2  Phosphotungstic acid (PTA) (http://en.wikipedia.org/wiki/File:Phosphotungstate3D-polyhedra.png; courtesy of Ben Mills).

gravimetric methods (Hansen and Whitney, 1960) and colorimetric techniques (Graham, 1966). A procedure for the separation of common vegetable gums in dairy products and especially alginate has also been developed (Bundesen and Martinek, 1954), as has a method for the separation of several gum stabilizers from cheese spreads (Johnson, 1956). Different approaches to isolating and identifying gums in milk-containing products, such as chocolate, cream, white cheese, etc., have been developed by Fouassin (1957). The methods include protein separation from the gum followed by the gum’s isolation and indentification via color reactions with anthrone reagents. Strange (1957) established a method for isolating and detecting arabic, tragacanth, guar and ghatti gums in catsup and related tomato products. Further information can be found elsewhere in this chapter.

8.2.5 Antibodies for the identification of gum arabic and other polysaccharides Nearly a century ago, antibodies specific for a pneumococcal polysaccharide were identified in the serum of rabbits immunized with non-viable pneumococcal cells (Avery and Heidelberger, 1923). Since these antibodies only yielded a precipitin complex with this polysaccharide, they were classified as anti-carbohydrate antibodies (Avery et al., 1932). Since then, it has been shown that many synthetic glycoconjugates of carbohydrates linked to the proteins used to inject animals activate the immune system to produce anti-carbohydrate antibodies in the serum (Hayes and Goldstein, 1974; Bundle and Josephson, 1979). However, the produced antibodies were combined with other serum proteins and were not always appropriate for structural studies, biological function determinations or technical applications. This limitation was avoided when chromatographic methods were adapted for the isolation and purification of antibodies (Cuatrecasas et al., 1968; Pazur et al., 1976). The purity of the preparations was determined by affinity chromatography, ultracentrifugation on density gradients (Pazur et al., 1962), electrophoresis on polyacrylic gels (Davis, 1964) and inhibition by carbohydrate haptens (Pazur and Kelly, 1984). A group of antibodies with specificity

334  ◾  Plant Gum Exudates of the World

for polysaccharide gums was used to develop a method for the identification of polysaccharide gum additives in processed foods. Anti-gum antibodies with specificity for gum arabic (Pazur et al., 1986), mesquite gum (Miskiel and Pazur, 1991), gum xanthan (Pazur et al., 1994) and guar gum (Pazur and Li, 2004) have been prepared and described in the literature. The method for analyzing the food items involves the use of anti-gum antibodies and food extracts in agar-diffusion tests (Ouchterlony, 1949). Detection of polysaccharide gums used as additives in processed foods involves extracting the food in phosphate buffer and testing the extract for a reaction with antigum antibodies by the agar-diffusion method. Reaction of a specific gum with the homologous antibodies establishes the presence of that gum in the food (Pazur and Li, 2004). The method represents a novel application for antibodies. The antibody method is highly specific for the gum, giving it an advantage over other methods of analysis for polysaccharide gums as additives in processed foods (Pazur and Li, 2004). Anti-carbohydrate antibodies can be utilized in fields other than foods, e.g. as a serological method to identify bacteria causing infectious diseases in humans (Lancefield, 1940), analytical method for determining the structure of carbohydrate polymers (Pazur et al., 1994), anti-carbohydrate antibodies specific for the monitoring of hormone therapy in anemia (Pazur et al., 2000), detection of colon tumors (Krupey et al., 1968; Pazur, 1995), vaccines for bacteremia based on polysaccharides in the cell walls of the bacteria (Shinefield et al., 2002) and development of other vaccines that may be used for human diseases (Borman, 2004).

8.3 GROUP ANALYSIS AND IDENTIFICATION SCHEMES 8.3.1 Characteristic reactions of gums In general, there is no single method for the separation and analysis of all gums. Therefore, a clearcut identification needs to make use of several methods, enabling the investigator to categorize gums for subsequent identification by other tests. Characteristic reactions of the very soluble gum arabic, for example, include its non-precipitation in neutral lead acetate solution (and see Table 8.5). Table 8.5  Characteristic Reactions of Commercial Exudates* Exudate

*

Reactions

Arabic

Very soluble; not precipitated by neutral lead acetate solution; 1 drop of 10% ferric chloride gives a precipitate which is soluble in excess ferric chloride.

Ghatti

Very soluble; fresh solutions do not yield a curdy white precipitate with basic lead acetate, distinguishing this gum from gum arabic.

Karaya

Has a very high volatile acid number and gives a pink color when boiled with phosphate, hydrochloric, or trichloroacetic acid.

Tragacanth

Boiling with 10% potassium hydroxide solution yields a yellow stringy precipitate and a yellowtinged solution.

Adapted from Glicksman (1969).

Analysis and Identification of Gum Exudates   ◾  335 A Cl

O

Cl

OH Cl

B

Figure 8.3  Trichloroacetic acid 2D skeleton (A) and 3D (B) (http://en.wikipedia.org/wiki/ File:Phosphotungstate-3D-polyhedra.png; courtesy of Ben Mills).

Gum ghatti is very soluble; its fresh solutions do not yield a curdy white precipitate with basic lead acetate. Gum karaya has a very high volatile acid number and turns pink when boiled with phosphoric, hydrochloric or trichloroacetic acid (Fig. 8.3). If gum tragacanth is boiled in a 10% potassium hydroxide solution, it yields a stringy yellow precipitate in a solution that is tinged with yellow (Glicksman, 1969). A qualitative scheme for gum solution identification was devised by Walder (1949), who suggested adding 0.3 ml of Millon’s reagent solution to 3 ml of an unknown sample. Carrageenan, agar and locust bean gums gelatinize. Quince seed and tragacanth gums give a voluminous flocculent precipitate that does not settle. Arabic and karaya gums give a powdery or fine curdy precipitate (Table 8.6). Gum arabic dissolves in excess of the reagent. Next, add 4% borax to another 3 ml of the solution. Locust bean gum (LBG), carrageenan gum and agar produce a negative reaction. Then 10% potassium hydroxide might be added to another 3 ml of the solution: carrageenan gels, the agar solution clarifies and tragacanth yields a bright yellow precipitate. Finally, upon adding phosphoric acid to another 3 ml of solution, the karaya turns pink (Walder, 1949). Further results of tests on exudates with various reagents are summarized in Table 8.6. Reactions that are useful for characterizing and identifying exudates are also given in Table 8.7. As is the case with precipitates with heavy metals, precipitates with cationic salts quickly disperse upon acidification of the medium. Ammonium sulfate generates a pronounced precipitation reaction with several of the gums but not with alginates, tragacanth, arabic, karaya, or ghatti gums, each of which probably contains uronic acid components (Ewart and Chapman, 1952; Glicksman, 1969). The reactions with Stoke’s acid mercuric nitrate test illustrate the effect

White fine opaque precipitate soluble in excess reagent

†

*

Fine precipitate

Ghatti

Precipitate soluble in excess reagent

Negative

Translucent Negative flocculent precipitate

Stringy Precipitate, settles rapidly

Coagulates; long stringy adherent precipitate

Very fine flocculent nonadeherent precipitate

Alcohol precipitate

Negative

Fine flocculent nonadherent precipitate

Precipitate Fine coagulates filamentous on heating particles, nonadherent

Voluminous Bright Gels precipitate, yellow gels stringy precipitate

White Faint curdy yellow precipitate, tinge insoluble in excess reagent

Basic lead acetate

Ferric chloride (5% solution)

—

Negative

Stringy precipitate on heating

Negative

Schweitzer’s reagent† Negative

Tannic acid (10% solution)

Stringy precipitate on heating

Negative

Sulfuric acid (conc.)

No precipitate

—

—

White curdy Precipitate Precipitate precipitate, settles rapidly

Voluminous Negative flocculent translucent precipitate

White fine opaque precipitate, soluble in excess reagent

Stoke’s reagent

Adapted from Walder (1949). Schweitzer’s reagent: Cupric oxide, ammoniacal. [Preparation: dissolve 5 g of cupric sulfate in 100 ml of boiling water, and add sodium hydroxide until precipitation is complete. Wash the precipitate well, and dissolve it in a minimum quantity of ammonium hydroxide. Bubble a slow stream of air through 300 ml of strong ammonium hydroxide containing 50 g of fine copper turnings. Continue for one hour].

No precipitate

White curdy Negative precipitate settles rapidly

Voluminous flocculent precipitate, gels

No precipitate

Lead acetate (20% solution)

Karaya

Tragacanth Voluminous flocculent translucent precipitate

Arabic

Exudate

Millon’s reagent

Potassium hydroxide (10% solution)

Table 8.6  Result of Tests on Exudates with Various Reagents*

336  ◾  Plant Gum Exudates of the World

Analysis and Identification of Gum Exudates   ◾  337

Table 8.7  Precipitation Reactions of Exudates*

Exudate

1 volume cationic soap† (1% solution)

0.5 volume saturated ammonium sulfate

Diluted Stokes’s acid added dropwise

1 volume 2% papain‡

1 volume 2% gelatin‡

4 volumes 95% ethyl alcohol plus 2-3 drops saturated sodium chloride

Tragacanth Fine opaque precipitate

Negative

Flocculent precipitate, dissolves in excess reagent

Precipitate

Precipitate Voluminous jelly-like precipitate

Karaya

Flocculent precipitate

Negative

Flocculent precipitate, dissolves in excess reagent

Precipitate

Precipitate Flocculent precipitate, discrete particles

Arabic

Very fine precipitate

Negative

Flocculent precipitate, dissolves in excess reagent

Precipitate

Precipitate Fine opaque precipitate, non-settling

Ghatti

Fine precipitate

Negative

Negative

Negative

Precipitate Fine precipitate, non-settling (2-3 volumes)

* † ‡

Adapted from Ewart and Chapman (1952) and Glicksman (1969). Rodalon (alkyl dimethyl benzyl ammonium chloride). Precipitates with papain and gelatin are observed only in weakly acidic medium and most exhibit properties of coacervates rather than true precipitates.

of low pH on precipitation of heavy metal salts of polysaccharide acids. Excess reagent makes the solutions strongly acidic and thus the weakly dissociated acids redisperse. Papain [a cysteine protease (EC 3.4.22.2) hydrolase enzyme present in papaya (Carica papaya) and mountain papaya (Vasconcellea pubescens); Fig. 8.4] and gelatin induce marked precipitation reactions only with those gums that have anionic components. Those precipitates are found only if the pH of the mixture is below the isoelectric point of the protein (Glicksman, 1969).

8.3.2 Cetavlon group identification scheme Cetyltrimethylammonium bromide (cetavlon) precipitation and isolation reactions can also be used for the separation and identification of gums (Proszynski et al., 1965). The separation depends upon classification of the gums into four groups according to their behavior in water

338  ◾  Plant Gum Exudates of the World

Figure 8.4  Papain (http://en.wikipedia.org/wiki/File:Papain_cartoon.png; Author: en:User: Roadnottaken).

and cetavlon. After the initial characterization, the gums are identified by means of their reactions with specific reagents and identification is confirmed by infrared (IR) spectroscopy. The first group includes galactomannans. The second group includes karaya gum: it is partly soluble, gives a very viscous suspension (1% concentration) and precipitates in the presence of cetavlon. The third group includes tragacanth, mesquite and ghatti gums: they are partly soluble (at 1% concentration), not much more viscous than water, and precipitate in the presence of cetavlon. Tragacanth gum can be distinguished from ghatti gum by boiling a fresh test solution with 0.2 volumes of 10% potassium hydroxide. Tragacanth will yield a bright yellow-green solution, while ghatti will turn dull yellow. The fourth group includes gum arabic, carboxymethyl cellulose (CMC), alginate and pectin: these gums are soluble at 1% concentration and precipitate in the presence of cetavlon (Proszynski et al., 1965).

8.4 ADDITIONAL ANALYTICAL METHODS 8.4.1 IR spectroscopy The use of IR spectroscopy for the determination of hydrocolloid constituents dates back to the early 1950s (Newburger et al., 1952, 1953). The first studies investigated gum films cast from water solutions onto glass or polyethylene. Another, more rapid method was to disperse a fine powder of the gum in KCl disks, yielding satisfactory spectra (Prosynski et al., 1965). In a comparison of the Nujol method [Nujol mull is a technique for quantitative infrared analysis of solids. The technique is accurate, generally approachable and reliable. With the increase in popularity of the pressed halide disk as a method of performing quantitative IR analysis in the solid state, the older technique of the Nujol mull is often ignored], the KBr disk technique and the cast-film procedure, Bij et al. (1962) concluded that the quickest qualitative results were obtained with the Nujol procedure. The best quantitative results were obtained with the KBr disk method, although the homogeneity of the disk is questionable. The best but most time-consuming spectra were obtained

Analysis and Identification of Gum Exudates   ◾  339

by the cast-film technique. Most gums have similar functional groups. Therefore, their differences are found in different regions. The 7-15 μm region can be used to fingerprint gums classified into the following groups in accordance with their spectra. Group I: LBG, guar; Group II: karaya; Group III: arabic, ghatti, tragacanth; Group IV: pectin. Practical aspects of spectrophotometric analysis to detect gums in foods have been explored by Gangy (1955, 1961). Although problems are encountered with some gums at certain concentrations, the methods are successful for many of the common gums at normally used levels.

8.4.2  Chromatographic techniques to identify plant gums Plant gums consist of complex, highly branched polysaccharides composed of neutral sugars and hexuronic acid monomers. These natural products were employed long ago as binding agents in different mixtures, as constituent parts of metallo-gallic inks, by the Egyptians in ointments for mummification, and under layers of paints and painted sculptures. Today, plant gums find many applications as thickening agents or emulsion stabilizers in the agroalimentary, cosmetic and pharmaceutical industries. Because of their diversity and chemical complexity, the identification of plant gums requires a series of complex analytical procedures. Paper chromatographic methods have been used for the identification and differentiation of gums in food products (Glicksman, 1969). Detection of hydrolytic end sugars on chromatographs has been used to identify LBG, agar, arabic, pectin, tragacanth and CMC (Becker and Eder, 1956). Detection of thickening agents by anthronesulfuric acid reagent followed by differentiation and identification by paper chromatography has also been proposed (Blumenthal, 1959). Hydrolyzed hydrocolloid sugar residues from meat products have also been isolated and identified using this technique (Grau and Schweiger, 1963). Constituent monosaccharides of any polysaccharide material can be detected and isolated by subjecting the material to complete hydrolysis, followed by chromatographic separation of the resulting sugars. Polysaccharides require hydrolysis under the mildest conditions to avoid any possible degradation of the sugars. Conventionally, complete hydrolysis of a polysaccharide to its constituent monosaccharides involves strong acids such as trifluoroacetic acid (TFA) or sufficiently prolonged hydrolysis. Using a catalytic amount of potassium persulfate (1.48 x 10 -4 M), eight different seed gums were fully hydrolyzed on an alumina support under microwave irradiation. The hydrolysis time varied between 1.33 and 2.33 min, depending upon the seed gum’s structure. Use of a solid support enabled easy separation from the hydrolysates and recycling. However, under microwaving in an aqueous medium, the same amount of persulfate was unable to hydrolyze the seed gums (Singh et al., 2006). A reliable classification can be achieved on the basis of monosaccharide composition after stoichiometric cleavage of glycosidic bonds. Possible specific or total depolymerization reactions have been reported (Biermann, 1988). However, one main difficulty with this involves decomposition of the liberated monomers under the drastic conditions that are necessary to ensure breakdown of the more resistant glycosidic bonds. In this respect, methanolysis may be preferable to the classical acid hydrolysis since it gives higher recoveries of both neutral sugars and uronic acids (Chambers and Clamp, 1971; Chaplin, 1982; Biermann, 1988). Methanolysis and trimethylsilylation can be carried out according to previously published procedures (Ha and Thomas, 1988). Standard carbohydrates or plant gum samples are taken up in methanolic HCl solution which is prepared by adding acetyl chloride to methanol. Methanolysis is conducted at 80°C for 24 h. Thereafter, methanol and HCl are removed using a nitrogen stream, without prior neutralization since the acid has been largely “consumed” at this stage of the methanolysis procedure (Pritchard and Todd, 1977).

340  ◾  Plant Gum Exudates of the World

An excess of the trimethylsilylation agent is added to the dried material. The solution is then heated at 80°C for 2 h. The derivatized samples are then evaporated using rotary evaporation at 50 to 60°C and the residue is immediately dissolved in hexane. Gas chromatography-mass spectrometry (GC-MS) analysis is performed on this solution. Sulfuric acid hydrolysis (according to the Saeman procedure: sugars are released by treating a sample, to which myoinositol has been added as an internal standard, with H2SO4 for 1 h at 30°C. Then, distilled water is added and the mixture is further hydrolyzed for 3 h at 100°C), TFA hydrolysis, and methanolysis combined with TFA hydrolysis were compared for the hydrolysis of water-soluble uronic acid-containing polysaccharides originating from fungi, plants and animals. The released constituent sugar residues were subsequently analyzed by either conventional gasliquid chromatography (GLC) of alditol acetates or high-performance anion-exchange chromatography (HPAEC) with pulsed-amperometric detection (De Ruiter et al., 1992). It was shown that TFA hydrolysis alone is not sufficient for complete hydrolysis. Sulfuric acid hydrolysis of these polysaccharides resulted in low recoveries of 6-deoxysugar residues. The best results were obtained with the combination of methanolysis and TFA hydrolysis. Methanolysis with 2 M HCl prior to TFA hydrolysis resulted in complete liberation of the monosaccharides from pectic material and from most fungal and animal polysaccharides tested. Any incomplete hydrolysis could easily be assessed by HPAEC for the detection of characteristic oligomeric products, which is difficult using alternative methods. Methanolysis followed by TFA hydrolysis of 20 μg water-soluble uranic acidcontaining polysaccharides and subsequent analysis of the liberated sugar residues by HPAEC enabled a rapid and accurate determination of the carbohydrate composition of these polysaccharides in one assay without the need for derivatization (De Ruiter et al., 1992). Many chromatographic techniques have been devised for the classification and quantification of carbohydrates (Churms, 1990). Owing to high sensitivity combined with the ability to achieve efficient separation of complex mixtures, GC and GC-MS have gained general acceptance for the analysis of trimethylsilylated methanolysates of glycoproteins (Chambers and Clamp, 1971; Pritchard and Todd, 1977; Chaplin, 1982) and commercial gums (Ha and Thomas, 1988). In another report, GC electron impact or chemical ionization mass spectrometry (GC-EI-MS and GC-CI-MS, respectively) were found to differentiate between sugar classes and their tautomeric forms (Bleton et al., 1996). These results demonstrate the practical applications of GC-MS for the identification of a wide range of carbohydrate components in plant gums. EI-MS analysis of trimethylsilylated methyl glycosides gave well-resolved peaks in capillary columns, and allowed structural features such as the ring size, nature and position of the sugar molecule substituents to be determined. CI-MS with ammonia as the reagent gas enabled measuring the molecular mass, thus confirming the EI data (Bleton et al., 1996). CI-MS can be very helpful in the identification of unknown compounds or compounds that are not available as standards (e.g., 4-O-methylglucuronic acid). This study was limited to the neutral and acidic monosaccharides contained in plant gums. Three reference gum samples (plum, arabic and tragacanth) were also readily distinguishable by comparison of their chromatographic profiles. This methodical approach can potentially be adapted to the systematic study of a wide variety of natural substances, including gum-resins, resins, plant waxes and other materials commonly found in artistic and archeological contexts (Bleton et al., 1996).

8.4.3 Fourier transform-Raman spectroscopy of gum exudates Fourier transform (FT)-Raman spectroscopy in the near-IR region has a demonstrable advantage over conventional, visible excitation methods, chiefly because problems associated with sample

Analysis and Identification of Gum Exudates   ◾  341

fluorescence are minimized. Its application to the study of biopolymers such as human skin, cotton and silk has been recently described (Edwards and Farwell, 1996). The use of FT-Raman spectroscopy for the characterization of biological material and valuable museum samples has also been demonstrated with recent studies of medieval manuscripts, ancient glass, ivory and archeological remains, including human and animal bones and teeth. A crucial factor in the success of these applications is the ease of sampling for Raman spectrum observation; in fact, no special sample preparation is required and curved or uneven surfaces can be studied just as easily as machined and polished samples (Edwards and Farwell, 1996). The FT-Raman spectra of four technically important gums— locust bean gum, karaya gum (five varieties), tragacanth gum (nine varieties) and ghatti gum (four varieties) were reported (Edwards et al., 1998). Characteristic bands were identified for each gum and assigned to molecular species where possible. Because the gums contain similar chemical components, an integral part of that study was self-deconvolution of the Raman spectra. The spectra provide the first examples of a database for gums using a nondestructive analytical technique (Edwards et al., 1998).

8.4.4 Capillary electrophoresis A variety of techniques have been developed for the identification of plant gums for analytical purposes in food chemistry and/or in artistic or historical works. The usefulness of detection by IR spectroscopy is limited since many of the spectra overlap, but chromatographic techniques have proven very useful for the analysis of historical and artistic works. In early stages of development, paper chromatography was applied, but it had the disadvantages of a long development time, poor resolution, and limited detectability. Although some interesting results have been obtained with the application of thin-layer chromatography on art samples, GC is probably the most widely used technique today, although additional steps are required to obtain the necessary volatile derivatives. Furthermore, techniques such as high-pressure liquid chromatography (HPLC) and MS, as well as combinations of the aforementioned methods, for example GC plus IR spectrometry or GC-MS, have been recently utilized in this field. GC-MS has been applied for the identification of plant gums and animal glues following hydrolysis and group-specific separation of amino acids and sugars (Gröβl et al., 2005). Capillary electrophoresis (CE) is becoming increasingly recognized as a significant analytical separation technique because of its speed, effectiveness, reproducibility, ultra-small sample volumes, and low consumption of solvent. CE has been successfully applied to carbohydrate analysis (Rassi, 1995). However, carbohydrates are usually not easy to separate and detect due to their lack of readily ionizable functional groups and chromophores. Pre-column derivatization is the most widely used means, and most of the methods are based on reductive amination (Larsson et al., 2001). Even though this method gives excellent results, it is generally time-consuming and may result in the cleavage of some important sugar residues. Direct detection with indirect UV (Soga and Serwe, 2000) or refractive index (Ivanov et al., 2000) has been used with CE, but is limited by poor sensitivity and specificity. CE has been used to study the sugar profile of rice (Cao et al., 2004). Operated in a wall-jet configuration, a copper-disk electrode was used as the working electrode, exhibiting a good response for sucrose, maltose, glucose and fructose. A sugar-profile study of rice flour was conducted to determine changes produced during ageing: decreases were observed in the sucrose and maltose contents, and increases in the glucose and fructose contents during storage (Cao et al., 2004). The separation and detection of common mono- and disaccharides by CE with contactless conductivity detection (CCD) has been reported. At high pH values, the sugars are converted to anionic species that can be separated by CE and indirectly detected by CCD.

342  ◾  Plant Gum Exudates of the World

The method was applied to the analysis of glucose, fructose, and sucrose in soft drinks, isotonic beverages, fruit juice, and sugarcane spirits (Carvalho et al., 2003). CE has been used in the analytical determination of hydrocolloids in foods. A micro-method for the quantitative separation and determination of neutral polysaccharides in borate buffer was reported (Fuller and Northcote, 1956), and this same method was used to identify several gums (Cuzzoni and Lissi, 1961). The monosaccharide constituents of plant gums can be separated by CE at pH 12.1 and detected by indirect UV absorbance. The monosaccharides obtained after hydrolysis with 2 M TFA are regularly separated in a background electrolyte consisting of NaOH to adjust the pH, 20 mM 2,6-pyridinedicarboxylic acid as the chromophore for detection and 0.5 mM cetyltrimethylammonium bromide (cetavlon solution) as an additive to reverse the electro-osmotic flow (Gröβl et al., 2005). Based on their electropherograms, plant gums could be identified by their typical compositions as follows: a peak for glucuronic acid, together with a peak for rhamnose was indicative of gum arabic. Peaks of galacturonic acid and fucose indicated gum tragacanth. Locust bean gum showed a major peak for mannose (with a concomitant galactose peak at a ratio of 4:1), whereas a glucuronic acid and mannose peak together with a prominent arabinose peak indicated cherry gum (Gröβl et al., 2005).

8.4.5 Other methods X-ray crystallographic studies have been used effectively with polymers that possess a high degree of linearity but they are of limited usefulness in the identification of irregularly branched gums (Smith and Montgomery, 1959). Another technique that can be applied to the analysis and identification of hydrocolloids is differential thermal analysis (DTA). When a substance is heated, a chemical or physical change can occur that is generally manifested as heat energy. DTA determines the temperature at which these reactions take place when a substance is uniformly heated to high temperatures, including an identification of their endothermic or exothermic nature (Glicksman, 1969). The observed thermal changes may be due to dehydration, transition from amorphous to crystalline form, transition from one crystalline state to another, destruction of the crystalline lattice, or oxidation and decomposition, among other factors (Glicksman, 1969). The nature and intensity of these thermal changes, as well as the range of temperatures in which they take place are characteristic of a particular material, and can assist in its identification (Kulshrestha, 1962; Glicksman, 1969). Several studies using this method have been performed on gum exudates (McNulty, 1960; Kulshrestha, 1962). Published thermograms show variations in peak temperature as well as in characteristic shape. Therefore, DTA offers a “fingerprinting” method for the identification and characterization of different plant gums, as well as of different gums within the same genus, e.g. Acacia (Kulshrestha, 1962).

References Aslam, M., Pass, G., and G. O. Phillips. 1978. Properties of Khaya grandifoliola gum. J. Sci. Food Agric. 29:563-8. Association of Official Agricultural Chemists. 1960. Methods of analysis, 9th ed, 156-157, 212-213, 217-218, 302, 411-413, 541-543. Washington, D.C.: Association of Official Agricultural Chemists. Avery, O. T., and M. Heidelberger. 1923. Immunological relationships of cell constituents of pneumococcus. J. Exp. Med. 38:81-5.

Analysis and Identification of Gum Exudates   ◾  343 Avery, O. T., Goebel, W. F., and F. H. Babers. 1932. Chemoimmunological studies on conjugated carbohydrate-proteins. J. Exp. Med. 55:769-80. Becker, E. and M. Eder. 1956. Paper chromatographic identification of some thickneres in food products. Z. Lebensm. Untersuch. Forsch. 104:187-92. (Chem. Abstr. 51, 1493g). Biermann, C. J. 1988. Hydrolysis and other cleavages of glycosidic linkages in polysaccharides. Adv. Carbohydr. Chem. Biochem. 46:251-71. Bij, J. R., van der Vogel, W. F., and W. Hazenburg. 1962. Infrarotspektroskopie von einigen starke derivation. Starke 14:113-8. Bleton, J., Mejanelle, P., Sansoulet, J., Goursaud, S., and A. Tchapla. 1996. Characterization of neutral sugars methanolysis and trimethylsilylation gums and uronic acids after for recognition of plant gums. J. Chromatography A 720:27-49. Blumenthal, A. 1959. Detection of vegetable thickening agents and polyphosphates especially in mayonnaise. Mitt. Gebiete Lebensm. Hyg. 50:137-44. Borman, S. 2004. ‘Anti’-carbohydrate vaccines. Novel chemical and enzymatic oligosaccharide synthesis techniques could lead to a new generation of carbohydrate-based vaccine agents. Chem. Engineering News 82:31-5. Bundesen, H. N., and M. J. Martinek. 1954. Procedure for the separation, detection and identification of the more common vegetable gums in dairy products, with special reference to alginates. J. Milk Food Technol. 17:79-81. Bundle, D. R., and S. Josephson. 1979. Artificial carbohydrate antigens: synthesis of rhamnose disaccharides common to Shigella flexneri O-antigen determinants. Can. J. Chem. 57:662-8. Cannon, J. H. 1939. Report on gums in drugs. J. Assoc. Offic. Agr. Chemists 22:726. Cao, Y., Wang, Y., Chen, X., and J. Ye. 2004. Study on sugar profile of rice during ageing by capillary electrophoresis with electrochemical detection. Food Chem. 86:131-6. Carvalho, A. Z., da Silva, J. A. F., and C. L. do Lago. 2003. Determination of mono- and disaccharides by capillary electrophoresis with contactless conductivity detection. Electrophoresis 24:2138-43. Chambers, R. E., and J. R. Clamp. 1971. Assessment of methanolysis and other factors used in analysis of carbohydrate-containing materials. Biochem. J. 125:1009. Chaplin, M. F. 1982. A rapid and sensitive method for the analysis of carbohydrate components in glycoproteins using gas-liquid chromatography. Anal. Biochem. 123:336-41. Churms, S. C. 1990. Recent developments of chromatographic analysis of carbohydrates. J. Chromatography 500:555-83. Cuatrecasas, P., Wilchek, M., and C. B. Anfinsen. 1968. Selective enzyme purification by affinity chromatography. Proc. Natl. Acad. Sci., USA, 2:636-42. Cuzzoni, M. T. and T. P. Lissi. 1961. Identification of polysaccharide gums by paper electrophoresis. Farmaco Pavia Ed. Pract. 16: 416-21. Davis, B. J. 1964. Disc electrophoresis-11. Method and application to human serum proteins. Ann. NY Acad. Sci. 121:404-27. De Ruiter, G. A., Schols, H. A., Voragen, A. G. J., and F. M. Rombouts. 1992. Carbohydrate analysis of water-soluble uronic acid-containing polysaccharides with high-performance anion-exchange chromatography using methanolysis combined with TFA hydrolysis is superior to four other methods. Anal. Biochem. 207:176-85. Deuel, H., and J. Solms. 1951. Uber die Electrokoagulation von wasserloslichen poly-sacchariden und anderen hockpolymeren. Kolloid Z. 124:65. Edwards, H. G. M., and D. W. Farwell. 1996. Fourier transform-Raman spectroscopy of amber. Spectrochim. Acta Part A 52:1119-25. Edwards, H. G. M., Falk, M. G., Alvarez-Benedi, S. J., and F. Rull. 1998. FT-Raman spectroscopy of gums of technological significance. Spectrochim. Acta Part A 54:903-20. Ewart, M. H., and R. A. Chapman. 1952. Identification of stabilizing agents. Anal. Chem. 24:1460-4. Fouassin, A. 1957. Alginates, CMC and other thickening materials in milk products and mayonnaise. Rev. Ferment. Ind. Aliment. 12:169-72.

344  ◾  Plant Gum Exudates of the World Fuller, K. W. and D. H. Northcote. 1956. A micro-method for the separation and determination of polysaccharides by zone electrophoresis. Biochem. J. 64: 757-63. Gangy, M. J. 1955. Gums in food. A spectrophotometric method for the detection of certain stabilizers in soft-curd cheeses. J. Assoc. Offic. Agr. Chemists 38:189-93. Gangy, M. J. 1961. Report on gums in food. J. Assoc. Offic. Agr. Chemists 44:512-3. Glicksman, M. 1969. Gum technology in the food industry, 509-50. New York: Academic Press. Goldstein, A. M., and E. N. Alter. 1973. Gum karaya. In Industrial gums, ed. R. L. Whistler, 273-87. New York: Academic Press. Graham, H. D. 1966. Spectrophotometric determination of carrageenan ester sulfate in milk and milk products with barium chloranilate. J. Dairy Sci. 49:1102-8. Grau, R. and A. Schweiger. 1963. Uber den Nachweis von Quellstoffen in Fleisch-waren and mogliche Storinger durch andere Polysaccharide. Z. Lebensm. Untersuch. Forsch. 119: 210-6. Gröβl, M., Harrison, S., Kaml, I., and E. Kenndler. 2005. Characterisation of natural polysaccharides (plant gums) used as binding media for artistic and historic works by capillary zone electrophoresis. J. Chromatography A 1077:80-9. Ha, Y. W., and R. L. Thomas. 1988. Simultaneous determination of neutral sugars and uronic-acids in hydrocolloids. J. Food Sci. 53:574-7. Hansen, P. M. T., and R. M. Whitney. 1960. A quantitative test for carrageenan ester sulfate in milk products. J. Dairy Sci. 43:175-86. Hayes, C. E., and I. J. Goldstein. 1974. Synthesis of a glycoconjugate of galactose and bovine serum albumin. J. Biol. Chem. 249:1904-14. Ivanov, A. R., Nazimov, I. V., Lobazov, A. P., and G. B. Popkovich. 2000. Direct determination of amino acids and carbohydrates by high performance capillary electrophoresis with refractometric detection. J. Chromatography 894:253-7. Jacobs, M. B. 1958. In The chemical analysis of foods and food products, 3rd ed., 476-508. New York: Van Nostrand. Jacobs, M. B., and L. Jaffe. 1931. Method for the identification of the common gums. Ind. Eng. Chem. Anal. Ed. 3:210-2. JECFA/FAO. 1988. In Specifications for identity and purity of certain food additives, vol. 38, 114-6. Rome: FAO. JECFA/FAO. 1999. In Specifications for identity and purity of certain food additives. Food Nutr. Paper No. 52. Rome: FAO. Jefferies, M., Pass, G., and G. O. Phillips. 1977. Viscosity of aqueous solutions of gum ghatti. J. Sci. Food Agric. 28:173-9. Johnson, R. H. 1956. Determination of gums in process cheese spreads. J. Assoc. Offic. Agr. Chemists 39:286-90. Krupey, J., Gold, P., and S. O. Freedman. 1968. Physiochemical studies of the carcinoembryonic antigens of the human digestive system. J. Exp. Med. 128:387-98. Kulshrestha, V. K. 1962. Differential thermal studies on plant gums. J. Polymer Sci. 58:791-808. Lancefield, R. C. 1940. Specific relationship of cell composition to biological activity of hemolytic streptococci. Harvey Lectures 36:251. Larsson, M., Sundberg, R., and S. Folestad. 2001. On-line capillary electrophoresis with mass spectrometry detection for the analysis of carbohydrates after derivatization with 8-aminonaphthalene-1,3,6- trisulfonic acid. J. Chromatography 934:75-85. Mbuna J. J., and G. S. Mhinzi. 2002. Evaluation of gum exudates from three selected plant species from Tanzania for food and pharmaceutical applications. J. Sci. Food Agric. 83:142-6. McNulty, J. A. 1960. Isolation and detection of gums in frozen desserts. J. Assoc. Offic. Agr. Chemists 44:513-6. Mhinzi, G. S., and D. M. S. Mosha. 1995. Some physicochemical properties of Tanzanian commercial Acacia gums (gum arabic). J. Food Sci. Technol. 32:510-2. Miskiel, F. J., and J. H. Pazur. 1991. The preparation and characterization of antibodies with specificity for the carbohydrate units of gum arabic and gum mesquite. Carbohydr. Polymers 16:17-35.

Analysis and Identification of Gum Exudates   ◾  345 Mrosso, H. D. J. 1996. A study of the properties of some Tanzanian Acacia gums. M.Sc. Thesis, University of Dar es Salaam. Newburger, S. H., Jones, J. H., and G. C. Clark. 1952. A technique for obtaining infrared spectra of watersoluble gums. I. Proc. Sci. Sect. Toilet Goods Assoc. 18:38-9. Newburger, S. H., Jones, J. H., and G. C. Clark. 1953. A technique for obtaining infrared spectra of watersoluble gums. Proc. Sci. Sect. Toilet Goods Assoc. 19:25-9. Ouchterlony, O. 1949. Antigen-antibody reactions in gels. Acta Pathol. Microbiol. 26:507-15. Pazur, J. H. 1995. Coupled gel electrophoresis-agar diffusion method for the detection of tumor antigens. J. Chromatography B 663:51-7. Pazur, J. H., and S. A. Kelly. 1984. The identification of antigenic determinants by a coupled inhibition-agar diffusion method. J. Immunol. Meth. 75:107-16. Pazur, J. H., and N. Q. Li. 2004. Application of antibodies for the identification of polysaccharide gum additives in processed foods. Food Additives & Contaminants: Part A 21:1027-34. Pazur, J. H., Jensen, P. J., and A. K. Murray. 2000. Oligosaccharides as immunodeterminants of erythropoietin for two sets of anti-carbohydrate antibodies. J. Prot. Chem. 19:631-5. Pazur, J. H., Kelly-Delcourt, S. A., Miskiel, F. J., Burdett, L., and J. J. Docherty. 1986. The isolation of antigum Arabic antibodies by affinity chromatography. J. Immunol. Meth. 89:19-25. Pazur, J. H., Kleppe, K., and J. S. Anderson. 1962. The application of density-gradient centrifugation for the isolation of enzymes. Biochim. Biophys. Acta 65:369-72. Pazur, J. H., Miller, K. B., Dreher, K. L., and L. S. Forsberg. 1976. Anti-glycosyl antibodies: preparation and characterization of rabbit anti-galactose and anti-lactose antibodies. Biochem. Biophys. Res. Comm. 70:545-50. Pazur, J. H., Reed, A. M., and N. Q. Li. 1994. An immunological method for the determination of the D and L configurations of monosaccharides. Carbohydr. Polymers 24:171-5. Pritchard, D. G., and C. W. Todd. 1977. Gas-chromatography of methyl glycosides as their trimethylsilyl ethers-methanolysis and re-N-acetylation steps. J. Chromatography 133:133-9. Proszynski, A. T., Michell, A. J., and C. M. Stewart. 1965. Australian plant gums. I. Classification and identification of gums from arborescent Angiosperms. Division of Forest Products Technological Paper # 38. Commonwealth. Rassi, Z. E. 1995. Carbohydrate analysis—high-performance liquid chromatography and capillary electrophoresis. Amsterdam: Elsevier. Shinefield, H., Black, S., Fattom, A. et al. 2002. Use of a Staphylococcus aureus conjugate vaccine in patients receiving hemodialysis. New Engl. J. Med. 346:491-6. Singh, V., Tiwari, A., Premlata Kumari, P., and S. Tiwari. 2006. Microwave-promoted hydrolysis of plant seed gums on alumina support. Carbohydr. Res. 341:2270-4. Smith, F., and R. Montgomery. 1959. The chemistry of plant gums and mucilages. New York: Reinhold. Soga, T., and M. Serwe. 2000. Determination of carbohydrates in food samples by capillary electrophoresis with indirect UV detection. Food Chem. 69:339-44. Strange, T. E. 1957. Detection of gums in catsup and related tomato products. J. Assoc. Offic. Agr. Chemists 40:482-6. Walder, W. O. 1949. The polysaccharides. III. Chemical and physical tests for the identification of the polysaccharide gums. Food 18:86-9. Weinberger, W., and M. B., Jacobs. 1929. A comparative precipitation for the qualitative identification of each of the common gums. J. Am. Pharm. Assoc. 18:34-6.

Chapter 9

Miscellaneous Uses of Plant Exudates 9.1 INTRODUCTION Aside from the main applications of plant exudates in foods, adhesives, medicine, cosmetics and biotechnology, other less known, but nevertheless important uses exist. These can be related to paints and painting, inks, lithography, textiles, corrosion inhibition, immersion plating, drilling fluids, oil-well cements, binders, explosives, paper, e-paper and ceramics, among many others. This chapter is dedicated to these miscellaneous uses of plant exudates.

9.2 PAINTS, PIGMENTS AND PAINTING Paint is a semi-finished product in any liquid, liquefiable, or mastic composition which, after application to a substrate in a thin layer, is converted to an opaque solid film. Paint is used to protect, decorate or add functionality to an object or surface by covering it with a pigmented coating. It can be applied to almost any kind of object and is used, for example, in the creation of art, in industrial coating, as a driving aid (road surface markings), or as a barrier to corrosion and water damage. Paint can also be mixed with glaze to create various textures and patterns (http://en.wikipedia.org/wiki/Paint). Incorporating protective colloids into paints is an old tradition, used to control the aggregation and wetting qualities of the pigments in paints as well as to enhance their consistency and setting. Gum arabic has been used to achieve controlled thixotropic properties of paints (thixotropy is the property of some non-Newtonian pseudoplastic fluids to show a time-dependent change in viscosity; the longer the fluid undergoes shear stress, the lower its viscosity). Pigments that can be readily wetted by water, such as titanium dioxide, zinc oxide and the like, require small quantities (<1%) of water to achieve suitable thixotropic properties (Whistler and BeMiller, 1973). The history of painting starts with pre-historic human artifacts and spans all cultures. Archeologists have reportedly found pigments and paint-grinding equipment in Zambia (southern 347

348  ◾  Plant Gum Exudates of the World

Africa) that are thought to date back to between 350,000 and 400,000 years (BBC News, 2000). About 30,000 years ago, cave paintings were created by cave dwellers as decoration. These ancient paints were reportedly based on animal fat (binder) and colored earth or other natural pigments (ochre, for example). The binder provides adhesion, integrity, and toughness to the dry paint film by binding the pigment together. The binder also affects application properties such as flow, leveling and film build, and gloss development. The liquid portion of the paint makes it possible to apply the pigment and binder to a surface. Pigments and binder are what are left on the surface when the paint dries and the liquid portion evaporates. Together, these are called the solid portion of the paint. Paint with higher solids content will provide a thicker dry paint film for a given square-footage per gallon, which results in better coverage and durability compared to paint with lower solids contents. The oldest record of decorative painting can be traced to southern France. Gum arabic and gum tragacanth are beneficial in the field of artistic and historical works (Mills and White, 1994). They have been applied since the 2nd century B.C. as binding media for pigments in Egyptian ointments used for mummification, in mural paintings in Christian catacombs (Schramm, 1988; Mills and White, 1994), in paintings on silk (Schramm, 1988), and in manuscript illumination in the Middle Ages (Doerner, 1989; Mills and White, 1994). To qualitatively and quantitatively evaluate the role and inclusion of exudate gums in ancient wall paintings, samples from Macedonian tombs from the 4th-3rd centuries B.C. were processed by a special analytical procedure (Colombini et al., 2002). This method revealed the presence of a complex paint medium consisting mainly of gum tragacanth and fruit tree gums. Moreover, starch was probably added to plaster, as highlighted by the presence of a huge amount of glucose (Colombini et al., 2002). Lead white (chemical name: basic lead(II)-carbonate; formula: 2Pb(CO3)2 . Pb(OH)2; crystal system: trigonal; refractive index: uniaxial (-), e = 1.94, w = 2.09) is a historically important paint used by artists since antiquity. The darkening of lead white has been well documented in artwork, including paintings. It seems that different binding agents (egg tempera, linseed oil, water, and gum arabic) have an effect on the rate of darkening of lead white, as determined by mid-infrared and visible spectroscopy (Goltz et al., 2003). Plant gums such as gum arabic, gum acacia, gum tragacanth, cherry gum and locust bean gum (LBG, also called carob gum) have also been used historically as binding media in artwork. The monosaccharide constituents of such gums were separated by capillary electrophoresis at pH 12.1 and detected by indirect UV absorbance. The method was applied to identify the plant gums in samples of, for example, watercolors (paints made up of pigments suspended in a water-soluble vehicle), and several types of paint layers, such as gum tempera (tempera colors are paints made up of pigments in a liquid binder consisting of a water and oil emulsion. Depending on the kind of emulsion used, tempera colors are designated gum tempera, egg tempera, casein tempera and wax tempera), and those with egg white or drying oils as additives (Grossl et al., 2005). Gum arabic was used as a binder for paint in ancient Egyptian artifacts. In such artworks, paint containing Egyptian blue pigment is often found to have become brownish-green or even black. Darkened paints from several coffins were investigated using gas chromatography/mass spectrometry (GC/MS) and other methods, to identify the cause of the discoloration (Daniels et al., 2004), and different phenomena were detected: one type of discoloration involved gum arabic throughout the paint layer; other examples showed surface discoloration in the varnish, the paint underneath remaining bright blue. Surface dirt also contributes to darkening. Artificial aging of paints demonstrated that gum arabic binder can discolor sufficiently for the paint to appear black. The poor hiding power and transparency of Egyptian blue contribute to the overall dark appearance (Daniels et al., 2004). In general, pigments are used to color paint, ink, plastic, fabric, cosmetics, food and other materials. Realgar (from the Arabic “rahj al ghar” meaning “powder of the mine”) and orpiment

Miscellaneous Uses of Plant Exudates  ◾  349 A

B

Figure 9.1  (A) Part of realgar’s crystal structure. (B) A unit cell of realgar, showing the As4S4 molecules it contains (http://en.wikipedia.org/wiki/Image:Realgar-3D-balls.png; courtesy of Benjamin-Mills).

are some of the most common yellow pigments. These pigments are natural mineral compounds based on arsenic and sulfur. Realgar is a soft orange-red arsenic ore, AsS, which, in addition to being a pigment, is also used in pyrotechnics and tanning (Fig. 9.1). This mineral crystallizes in a monoclinic system. Realgar can be found in the form of short, vertically striated crystals, but more frequently it is granular and in crusts. Its hardness is 1.5 to 2 (Mohs scale) and its specific gravity is 3.48. The luster is resinous and the color red to orange. Realgar is found in ores of lead, silver, and gold associated with orpiment (i.e. arsenic trisulfide, As2S3) (Fig. 9.2) and stibnite (Sb2S3 —antimony trisulfide). Realgar is found in silver and lead ores in Hungary, Czechoslovakia, and Germany. Good crystals have come from Binnenthal, Switzerland, and Allchar, Macedonia. In the United States it is found in Manhattan, Nevada and in Mercer, Utah, and as deposits from geyser water in Yellowstone National Park. The largest quantities of realgar have been found in Turkish Kurdistan, and in Georgia. Since the late Middle Ages, the pigment has also been synthetically produced. This pigment is most likely the result of sublimation of arsenic, or arsenic oxide and orpiment, with and without the addition of sulfur (Fig. 9.3).

350  ◾  Plant Gum Exudates of the World A

B

C

Figure 9.2  (A) Orpiment’s unit cell (i.e., the crystal structure of a material or the arrangement of atoms in a crystal) (http://en.wikipedia.org/wiki/Image:Orpiment-unit-cell-3D-balls.png); (B) orpiment’s crystal structure consists of sheets (http://en.wikipedia.org/wiki/Image:Orpimentlayer-3D-balls.png); (C) the sheets are stacked into layers (http://en.wikipedia.org/wiki/ Image:Orpiment-layers-stacking-3D-balls.png; courtesy of Benjamin-Mills).

Miscellaneous Uses of Plant Exudates  ◾  351

Figure 9.3  Orpiment crystals (http://nevada-outback-gems.com; courtesy of Chris Ralph).

Orpiment usually forms with realgar and in fact, the two minerals are almost always found together. Orpiment is a common monoclinic arsenic sulfide mineral. It has a Mohs hardness of 1.5 to 2, a specific gravity of 3.46, and it melts at 300 to 325°C. Orpiment takes its name from the Latin auripigmentum (aurum—gold + pigmentum—pigment) due to its deep yellow color. It is also known as “Yellow Orpiment”, “King’s Yellow” and “Chinese Yellow”. Orpiment was used in Egyptian wall paintings dating from the 18th Dynasty in Tell el Amarna. It is mentioned in Greek and Roman literature. The pigment has been described in various medieval manuscripts dating from the 12th to the 15th centuries. It was still in use in the 17th and 18th centuries, despite the fact that there were some sensible alternatives, such as lead-tin yellow, Naples yellow, weld lakes, and the ochres. The problems of corrosion in orpiment or other substances of the AsS system are evident. This system, generally described as the “realgar” group, consists of many chemically similar substances with different crystal lattices, sometimes belonging to different crystal systems. Polymorphism is a recurrent problem in the study of arsenic sulfides by X-ray diffraction. The fading of realgar and its polymorphs in the light has been studied (Daniels and Leach, 2004). A variety of realgar paints were prepared using gum arabic as a binder. Raman spectroscopy and colorimetry were used to follow the fading of realgar paint. Realgar and its products upon alteration are found in a wide range of papyri in the British Museum. One papyrus roll was cut into many sheets, enabling a study of realgar and orpiment paints which had been exposed to various amounts of natural light. Both orpiment and realgar faded to arsenolite; the latter has been seen on papyri as transparent, colorless octahedral crystals. Partly faded areas contained realgar, pararealgar and x-realgar. On one sheet, hematite appeared to have been used as a replacement for realgar (Daniels and Leach, 2004).

9.3 INKS Ink is a complex fluid medium, consisting of solvents, pigments, dyes, resins, lubricants, solubilizers, particulate matter, fluorescers, and other materials. Ink contains various pigments and/or dyes used for coloring a surface to produce an image or text. It is used for drawing or writing. Thicker

352  ◾  Plant Gum Exudates of the World

inks, in paste form, are used extensively in letterpress and lithographic printing. Inks are usually non-Newtonian fluids. Their resistance to flow can be described in terms of viscosity, yield value, thixotropy and dilatancy (Nussinovitch, 1997). About 5,000 years ago, the Chinese began using ink for writing. The ink was a mixture of soot (carbonaceous material) from pine smoke and lamp oil, thickened with gelatin from animal skins and musk. Other cultures developed inks from berries, plants, and minerals available in their areas. Paper was developed and improved in parallel to ink. Early Egyptians, Romans, Greeks, and Hebrews used paper made from the papyrus plant and parchment made from animal skins. The earliest known papyrus writing dates back to 2000 B.C. Ink consists of a colorant and a liquid or paste to carry the color and bind it to the paper. Crushed berries produce a lasting color, as do bark and certain plants. Some minerals can be ground to powder for color. Carbon from soot produces a deep black ink. By 400 A.D., a stable form of ink was developed: a composite of iron salts, nutgalls and gum, the basic formula, which remained in use for centuries. (A gall is an abnormal outgrowth of plant tissue, usually due to insect or mite parasites or fungi (Fig. 9.4). Galls are rich in resins and tannic acid and have been used in the manufacture of permanent inks such as iron-gall ink. A high-quality ink has long been made from the Aleppo gall, found on oaks in the Middle East; it is one of a number of galls resembling nuts and called “gallnuts” or “nutgalls”.) Its color when first applied to paper was a bluish-black, rapidly turning into a darker black and then, over the years, fading to the familiar dull brown color commonly seen on old documents. In the last few years, particular attention has been paid to the analysis of iron-gall inks for their effect on the degradation of paper. These analyses have involved mainly spectroscopic techniques devoted to the determination of iron, while only minor attention has been dedicated to the organic

Figure 9.4  Oak gall (http://adamschneider.net/; courtesy of Adam Schneider).

Miscellaneous Uses of Plant Exudates  ◾  353

components. Nevertheless, thermally assisted hydrolysis-methylation (THM) pyrolysis was proposed as a rapid tool for the characterization of ink’s organic components. The method was applied to several standard and original samples, showing that it is suitable for the characterization of irongall and sepia inks. Moreover, using this method, information on the organic binder can be gained at the same time (Chiavari et al., 2007). Gum arabic is of major importance in industries dealing with various applications of inks and related products. It is unique in its ability to form solutions with more than 50% solids, and it is non-toxic, odorless, colorless and tasteless. Gum arabic is used as a suspending agent for soluble inks, watercolors, quick-drying inks, and typographic and hectographic inks (Nussinovitch, 1997). Gum arabic has good protective colloid properties and as such can be used in many specialpurpose inks. Its effectiveness is designated by its gold number, which is defined as the number of milligrams of gum that, when added to a standard gold dispersion, are sufficient to prevent color change from red to blue when 1 ml of 10% NaCl solution is added (Ellis, 1940). An example of gold numbers for several colloidal materials is 0.1-0.5 for gum arabic, 0.005-0.1 for gelatin, 0.1 for casein, 0.5-2.0 for gum tragacanth, 4-6 for wheat starch and 25 for potato starch (Whistler and BeMiller, 1973). Lamp black, a deep black pigment, is obtained by the imperfect combustion of highly carbonaceous substances. When resins, resinous woods, fatty oils and fats, paraffin and paraffin oil, or coal-tar oils, are burned with an insufficient supply of oxygen, a considerable part of the carbon they contain may be deposited in the form of soot. A fine, light, fluffy powder is derived by collecting the soot from the burning raw material. It is the most familiar of the pure carbon black group of pigments. Lamp black has been in use since prehistoric times, and is probably the oldest pigment known to man. For use as a watercolor, lamp black was mixed with glue, prepared in sticks and sold as India ink (Fig. 9.5). Such ink sticks have been in use almost without change for more than 3,000 years. There are two ways to use the sticks: by applying a small moistened brush to the stick and rubbing it, or by rubbing the end of the stick in a small amount of water to reach the required tone of black (Whistler and BeMiller, 1973). Lamp black was one of the major black

Figure 9.5  India ink drawing (http://www.harrisink.com; courtesy of John R. Harris).

354  ◾  Plant Gum Exudates of the World

pigments in early American house paints. Today, lamp black is used as a black pigment in cement, ceramics, printing ink, crayons, shoe polish, and carbon paper. Early inks were simply dispersions of lamp black in water. Gum arabic was added to such inks as a suspending agent or as a protective colloid (Whistler and BeMiller, 1973). As a suspending agent, gum arabic helps reduce the sedimentation rate of particles in suspension. The suspending agent works by increasing the viscosity of the fluid, thereby slowing down settling in accordance with Stokes’ Law. Gum arabic is used in record (permanent) ink as a protective colloid. Soluble inks have been used in the textile industry for the temporary marking of cloth for cutting or sewing operations. The advantage of this ink is that a hot-water wash after finishing removes it. Such ink is composed of a mixture of dilute acetic acid, albumin, basic dye, gum arabic, molasses and triethanolamine (Poschel, 1933). Gum arabic is included in quick-drying ink. A typical formulation includes sodium nitrate, gum arabic, water-soluble dye, water and preservative (Ellis, 1940). In fabric- and laundry-marking inks, gum arabic is used as a viscosity former and protective colloid. Sometimes metallic pigments serve in such formulations. In inks pigmented with titanium oxide or bronze powder, the pigment is suspended in a solution of gum arabic. Gum arabic is also used in emulsion or typographic inks. In several formulations of hectograph ink, gum arabic is used to obtain the desired viscosity. Decorative (gloss-finish) inks contain gum arabic, as do electrically conductive inks. In the latter, the suspending agent can be lacquer, but water-based inks function well when gum arabic, sodium chloride and citric or tartaric acid are used. In wood-grain inks, gum arabic can be used as a suspending agent (Whistler and BeMiller, 1973). Other than gum arabic, gum tragacanth—a natural vegetable gum, is used in both the textile and paper industries as part of the printer’s ink. The gum is used as an emulsifying agent by increasing aqueous-phase viscosity and lowering the interfacial tension between oil and water, and as a suspending agent via the repelling action of the galacturonic acid salt found in tragacanthic acid and pseudoplastic flow (shear thinning) (Barton, 1994).

9.4 LITHOGRAPHY Lithography is a method of printing on a smooth surface. It was invented by the Bavarian author Alois Senefelder in 1796, and can be used to print text or artwork onto paper or other suitable material (Fig. 9.6). It can also refer to photolithography, a micro-fabrication technique used to make integrated circuits and micro-electromechanical systems. The name “lithography” originates from “lithos” which is the ancient Greek word for stone. In the early days of lithography, a smooth piece of limestone was used. The process included putting an oil-based image on the surface, acid burning the image onto the surface, and then applying gum arabic, which sticks only to the nonoily surface and seals it. The gum arabic is used to protect and etch an image in the lithographic process. During printing, water adheres to the gum arabic surfaces and avoids the oily parts, while the oily ink used for printing does the opposite. Different gums, such as cellulose, starch ethers, arabinogalactan and gum arabic are used in lithographic applications as sensitizers for lithographic plates, elements in the light-sensitive composition, ingredients in the fountain solution used to moisten the plates during painting, and protectors during storage of the plate (Whistler and BeMiller, 1973). The gum arabic used for such applications should be of the best quality. If converted to sodium arabate, it takes on different viscosity characteristics and confers greater resistance to bacterial and mold attack. Purified gum solution can be utilized directly for deep-etch-sensitive coatings, while high-viscosity grades of gum arabic are not recommended due to non-uniformity or the formation of streaks (Whistler and BeMiller, 1973; Meer Corp., 1982).

Miscellaneous Uses of Plant Exudates  ◾  355

Figure 9.6  Lithographic prints by the German biologist Ernst Haeckel (a plate from Ernst Haeckel’s Kunstformen der Natur of 1904).

Lithographic, letterpress and screen-printing inks have higher viscosities and frequently contain thickeners. Letterpress and litho inks can vary in viscosity from under 500 cP for a letterpresstype news ink to over 500 P for special litho ink formulations. In lithography and letterpress, uniform and adequate transfer of ink to the printing plate is ensured by a multitude of rollers in the ink-distribution unit. Rheology of the litho ink is important for roller-to-plate transfer, fidelity in printing, drying speed, holdout, and trapping properties obtained on the substrate (Clarke et al., 1999). Offset lithography is a planographic process where the image and non-image are in the same plane. The image area is oil-receptive and the non-image area is water-receptive: following wetting of the plate with the fountain solution, the ink, when rolled across the plate will only be attracted to the oil-receptive areas (Clarke et al., 1999).

9.5 TEXTILES The word “textile” comes from the Latin word textilis and verb texere, which means “to weave”. Today the word “textile” is defined as any product made from fibers, and when the word “textile” is used with the term “fiber” it refers to any product capable of being woven or otherwise made into fabric. The textile industry is large and of the highest importance in terms of economic value (Nussinovitch, 1997). Another classification of textile defines it as a flexible material comprised of a network of natural or artificial fibers often referred to as thread or yarn. Yarn is produced by

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spinning raw wool fibers, linen, cotton, or other material on a spinning wheel to produce long strands known as yarn. Textiles are formed by weaving, knitting, crocheting, knotting, or pressing fibers together. Sizing is the application of various materials to a fabric to produce stiffness or firmness. Cellulose fabrics are sized with starch or resins. Starch is applied to cellulosics, particularly cotton, to add luster and improve the body of the fabric. Starch adds weight and improves the look of fabrics, particularly inferior ones. Several techniques exist to apply the starch and remove the excess. Gelatin and dextrins may also be used (Nussinovitch, 1997). Gum tragacanth is used in print pastes and sizing agents because of its good release properties. It is used for stiffening silks and crepes. It is also utilized in dressing leather and in preparing leather polishes (Whistler and BeMiller, 1973). Gum arabic is also applied as a sizing agent for cloth. A more limited use of this gum is in silk or rayon, where the gum imparts body to the fabric without interfering with its transparency. Sizing of cotton fabrics gives them a fuller finish but most sizing is lost in washing. Sizing agents consisting of rye starch are common. In some formulations, gum arabic can substitute part of the starch. Acacia gum from Acacia decurrens can be used as a binding agent for vat sizing. Historically, natural dyes were used to color clothing or other textiles (Fig. 9.7). Pigments are bound to textiles by means of polymeric adhesives, initially natural gums and resins. In contrast to a pigment, a dye must have a definite affinity for the fibers themselves. Generally the pigment needs to be in an oil (resin) phase or dispersed in water with standard dispersants. Thickeners such as methylcellulose are recommended in such cases (Nussinovitch, 1997). By the mid-1800s, chemists began producing synthetic substitutes for natural dyes. Today, as the public becomes more aware of ecological and environmental problems related to the use of synthetic dyes, there is renewed interest in natural dyes. Natural dyes cut down significantly on the amount of toxic effluent resulting from the synthetic dye process. Nevertheless, the removal of problematic reactive dyes as well as basic dyes from textile wastewater is under investigation and is attracting a great deal of interest. Such dyes include methylene blue, cibacron reactive black and reactive yellow. The feasibility of using diatomite for this purpose has been considered. An indication that electrostatic interactions play an important role in the adsorption of dyes onto diatomite was noted (Al-Ghouti et al., 2003).

Figure 9.7  Printed textile (indigo discharge and block-printed fabric, designed by William Morris; http://en.wikipedia.org/wiki/Image:Morris_Evenlode_printed_textile.jpg).

Miscellaneous Uses of Plant Exudates  ◾  357

Superabsorbent hydrogel formed by modified gum arabic, polyacrylate and polyacrylamide can also be used for the removal of methylene blue from textile wastewater. A superabsorbent hydrogel exhibited excellent performance in methylene blue absorption. The maximum absorption capacity was 48 mg of dye per gram of superabsorbent hydrogel. The absorption effect was attributed to the formation of ionic complexes between the imine groups of methylene blue and the ionized carboxylic groups of the superabsorbent hydrogel (Paulino et al., 2006). There are a number of major applications for water-based polymers in the textile industry, in which the adhesive properties of the polymers are essential to the final product. Water-based printing inks for textiles can also be conventionally included under this general heading (Nussinovitch, 1997). Gum karaya has been found to be a superior adhesive when partially wetted with water. The gum is modified for the textile industry to have increased solubility, enabling its use for printing operations. Better dissolution is achieved by pressure-cooking the gum karaya suspensions, with the rate of dissolution varying with pressure. Textile gum solutions contain 15 to 18% solids. Gum karaya can also be solubilized by treatment with sodium peroxide, persulfate or persilicate. The hydrocolloid solution is blended with the dye and later used for color printing on cotton fabrics (Knecht and Fothergill, 1924). The question of whether ink jets will ever replace screens for textile printing was discussed in Dawson and Ellis (1994). The many problems involved in developing an ink-jet printer suitable for woven and knitted textiles were outlined, and efforts have focused on adapting existing systems used for paper or carpet substrates. Work devised to produce a modular array of drop-on-demand valves to meet the required criteria was described, together with details of the selection of dyes and chemicals for a practical jet-printing process (Dawson and Ellis, 1994).

9.6 CORROSION INHIBITION Corrosion is the breakdown of essential properties of a material due to reactions with its surroundings. In the most common use of the word, this means the loss of an electron of metal as it reacts with water and oxygen. The use of corrosion inhibitors for metals and alloys which are in contact with an aggressive environment is an accepted practice (Fig. 9.8). Large numbers of

Figure 9.8  Metal corrosion (http://www.paxit.com; courtesy of Paxcam.com).

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organic compounds have been studied to investigate their corrosion-inhibiting potential. These studies revealed that organic compounds, especially those with N, S and O, exhibit significant inhibition efficiency (Raja and Sethuraman, 2008). Unfortunately, most of these compounds are expensive and some are toxic to living things. Plant extracts have become important as an environmentally acceptable, readily available and renewable source for a wide range of inhibitors. Plants are rich sources of ingredients which have very high inhibition efficiency (Raja and Sethuraman, 2008). Therefore, it is not surprising that many environmentally friendly corrosion inhibitors have been studied. For example, the inhibition effect of ethanol extracts of Garcinia kola on the corrosion of mild steel in H2SO4 solutions was evaluated using the hydrogen evolution technique at 30 to 60°C. The mechanism of adsorption inhibition and the type of adsorption isotherm were proposed, based on the trend of inhibition efficiency and kinetics data. The results indicated that the extract inhibits the corrosion of mild steel in acidic medium and that the inhibition efficiency increases with an increase in the concentration of ethanol extracts and decreasing temperature (Okafor et al., 2007). The inhibition efficiency increased upon addition of potassium iodide to the extract, indicating synergism. An activation energy of inhibition of 6.85 kJ/mol calculated for the corrosion process suggested that the ethanol extract of G. kola is physically adsorbed to the metal surface. This environmentally friendly inhibitor could find possible applications in metal-surface anodizing and coatings (Okafor et al., 2007). Another study sought a low-cost and environmentally safe inhibitor that would reduce the corrosion rate of aluminum, and found that Delonix regia extracts do so in hydrochloric acid solutions. The inhibition efficiency increased with increasing concentration of the inhibitor but decreased with increasing exposure time. The authors stated that further investigations, involving electrochemical studies such as the polarization method, should shed further light on the mechanistic aspects of the corrosion inhibition. Such an inhibitor could also find applications in metal-surface anodizing and coatings (Abiola et al., 2007). Gum arabic can be used to inhibit metal corrosion in some applications (Strauss, 1955). Addition of this gum, to up to 2% of the weight of the negative plate of a storage battery, increases the battery’s life by reducing the growth of surface projections. Mixing this gum with zinc oxide (active negative plate material) increases the electrical resistance and as stated, reduces the rate of corrosion (Whistler and BeMiller, 1973). The inhibitory effect of gum arabic on the corrosion of aluminum in alkaline (NaOH) medium was studied (Umoren et al., 2006). Concentrations of gum arabic (inhibitor) were 0.1 to 0.5 g/L and those of NaOH (the corrodent) 0.1 to 2.5 M. Gum arabic inhibited the corrosion of aluminum in NaOH solutions. The inhibition efficiency increased with increasing inhibitor concentration and temperature. The phenomenon of chemical adsorption was proposed to explain this inhibition. That study provided new information on the possible application of gum arabic as an environmentally friendly corrosion inhibitor, even in highly aggressive environments (Umoren et al., 2006).

9.7 IMMERSION PLATING Immersion plating is a process that involves the deposition of a metallic coating on a metal immersed in a liquid solution without any external electric current. It is also known as dip plating. Gum arabic is useful in the immersion plating of copper on aluminum (Whistler and BeMiller, 1973). A method has been reported for fabricating complex 3D silver-coated polymeric microstructures. The approach is based on the creation of a cross-linked polymeric microscaffold via patterned multiphoton-initiated polymerization followed by surface-nucleated electroless silver deposition. The conductivity and reflectivity of the resulting silver-polymer composites and the

Miscellaneous Uses of Plant Exudates  ◾  359

nanoscale morphology of the deposited silver were characterized (Chen et al., 2006). The silvering bath was prepared immediately prior to use by combining filtered aqueous gum arabic, aqueous citrate buffer (citric acid and trisodium citrate, pH 3.5), aqueous silver lactate, and 0.52 M aqueous hydroquinone (Hacker et al., 1988). Submicrometer-thick layers of silver can be deposited in a controlled fashion onto surfaces, including 3D microporous surfaces, without occluding the interior of the structure. The approach is general for silver coating cross-linked polymeric structures based on acrylate, methacrylate, and epoxide resins and provides a new path to complex 3D micrometer-scale devices with electronic, photonic, and electromechanical function (Chen et al., 2006). Another invention deals with a process for electroplating non-conductive surfaces. In this case, either organic or inorganic binders can be used (Sakamoto and Tanimura, 1996).

9.8 DRILLING FLUIDS Drilling fluids are used primarily to keep a borehole open and clean during drilling. The term “fluid” encompasses a broad range of substances, including mud, water and air. Drilling fluids perform up to 20 functions while drilling a well. the major ones being to carry cuttings from the hole and permit their separation at the surface; to cool and clean the bit; to reduce friction between the drill pipe and the wellbore or casing; to maintain the stability of the wellbore; to prevent the inflow of fluids from the wellbore; to form a thin, low-permeable filter cake; to prevent damage to production formation, and to eliminate hazards to the environment and personnel (Chilingarian and Vorabutr, 1983; Darley and Gray, 1988). At any given time in the process of drilling a well, one or more of these functions will take precedence over others. Mud types are classified into three categories according to the base fluid used in their preparation: water (most of the world’s drilling operations), oil (~5 to 10% of the wells drilled use oil muds) and air (a smaller percentage) (Caenn and Chillingar, 1996). In order to improve the performance of drilling fluids, individual additives, including polymers, are developed to affect one or more of the required properties. The use of natural organic, hydrophilic colloids in drilling fluids was proposed in the 1950s (Chillingarian and Beeson, 1950). These included shiraz, ghatti and tragacanth gums. Natural polymers used as treating agents for drilling fluids included starch, which is used as a fluid-loss control agent for all types of mud systems and is particularly useful in saltwater systems. Biopolymers such as xanthan gum, wellan gum, and scleroglucan gum were used as viscosity formers and enhancers. The polysaccharide guar gum and the modified guar gum hydroxypropylguar were used as viscosifiers for completion and fracturing fluids (Chilingar and Croushorn, 1964). Modified natural polymers included carboxymethylcellulose (CMC) (used for fluid-loss control and for the higher molecular weights, by introducing high shear rate viscosity), hydroxyethylcellulose (HEC) (viscosifier for brine waters in clear completion fluids, gravel packs, and fracturing fluids), and carboxymethyl starch (more efficient and with a higher temperature stability than regular starch) (Caenn and Chillingar, 1996). Synthetic polymers include polyacrylates. Their use depends on their molecular weight (i.e. low-MW polymers serve as thinners and deflocculants; medium MW for fluid-loss control, and as flocculants and shale stabilizers; high MW as bentonite extenders and flocculants); other synthetic polymers include polyacrylamides (as flocculants and shale stabilizers) and cationic polymers (as flocculants and to formulate shale-stabilizing mud systems) (Caenn and Chillingar, 1996). Gum arabic is used in the preparation of drilling fluids. Gum ghatti prevents fluid loss in oil-well drilling mud when it is used at low concentrations in neutral mixtures and with high salt concentrations (Whistler and BeMiller, 1973). Gum ghatti has the unique ability to prevent fluid loss at

360  ◾  Plant Gum Exudates of the World

elevated temperatures, which leads to its use in the maintenance of thin wall cakes in oil wells under such temperatures (Whistler and BeMiller, 1973). Low penetration rate, excessive torque and drag, poor hole cleaning and formation damage are major impediments in drilling oil and gas wells. These have a major impact on drilling efficiency and well economics. Bearing this in mind, an attempt was made to design a water-based drilling-fluid system using Indian bentonite clays and tragacanth gum (Mahto and Sharma, 2005). The effect of tragacanth gum on the rheological behavior of three different water suspensions of Indian bentonite was studied and a drilling-fluid system was developed. The filtrates of these drilling fluids were studied for formation damage to the field core. The laboratory investigation revealed that tragacanth gum acts as a good viscosity and fluid-loss control agent. The drilling-fluid filtrate also caused less formation damage (Mahto and Sharma, 2005).

9.9 OIL-WELL CEMENT Oil-well cement is a type of hydraulic cement which has a slow setting rate under the high temperatures reached in oil wells; its uses include tubing support and the bypassing of unwanted zones. The American Petroleum Institute’s Specifications for Materials and Testing for Well Cements (API Specification 10A) includes requirements for eight classes (A through H) and three grades (O—ordinary, MSR— moderately sulfate-resistant, and HSR—highly sulfate-resistant) of oil-well cements. Each class is applicable for use in a specified range of well depths, temperatures, pressures, and sulfate environments. The petroleum industry also uses conventional types of cement with suitable cement modifiers. Recent technologies have provided a new class of cement additives, the so-called rheological modifiers or viscosity-modifying agents (VMAs). This class of additives is usually represented by water-soluble polymers that function by increasing the apparent viscosity of the mix water. The enhanced viscosity facilitates uniform flow of the particles and reduces bleed, or free-water formation, on the fresh paste surface (Skaggs et al., 1997). Examples of VMAs include cellulose ethers [e.g., HEC, hydroxypropylmethyl cellulose (HPMC), sodium CMC, carboxymethylhydroxyethyl cellulose (CMHEC), and the like]; synthetic polymers [e.g., polyacrylates, polyvinyl alcohol (PVA), polyethylene glycol (PEG), and the like]; exopolysaccharides (also known as biopolymers, e.g., welan gum, xanthan, rhamsan, gellan, dextran, pullulan, curdlan, and the like); marine gums (e.g., algin, agar, carrageenan, and the like); plant exudates (e.g., gum arabic, karaya, tragacanth, ghatti, and the like); seed gums (e.g., guar gum, LBG, okra, psyllium, mesquite, and the like), and starchbased gums (e.g., ethers, esters, and related derivatized compounds) (Ohama, 1994). Gum arabic has been utilized in the preparation of oil-well cement (Clark, 1952). Gum ghatti is used in the “acidification” of oil wells. The gum is moistened with a water-insoluble non-aqueous liquid that is inert to both the acid solution and the gum. Then the acid is added with mixing to form a uniform dispersion, which is pumped under pressure to permeate the earth formation. This causes enlarged passageways that increase well productivity. The drilling mud and other clogging deposits are washed out to permit free flow of the oil (Cardwell and Eilers, 1958). Oil wells are drilled and then lined with a steel tubular casing. The process of feeding the casing sections down an oil well (sometimes up to 9 km in length) and then cementing them in place is difficult and positioning problems can occur that lead to extremely expensive repairs (Green et al., 2007). Recently, a device called a centralizer has been developed to avoid such problems. It is located around the external circumference of the steel tubular casing sections and helps the casing sections move down the well without becoming jammed and blocking it. The centralizer also positions the casing away from the wall of the well, allowing cement to pass completely around and all the way down the casing section, reducing the number of repairs (Green et al., 2007).

Miscellaneous Uses of Plant Exudates  ◾  361

9.10 BINDERS AND SPECIAL COATINGS 9.10.1 Glaze binders Paint binders were discussed in section 9.2. However, a binder can have a variety of different uses. It binds ingredients (holds everything together), forms films, and is also known as a non-volatile vehicle. Paint coatings are often named after the resin they contain, for example, epoxy, vinyl, polyurethane, acrylic, etc. Beeswax is reportedly the earliest known pigment binder, whereby the pigment was added to this molten wax. Gum arabic has been used as a glaze binder in ceramics (and see section 9.13) where it has to meet rigid specifications pertaining to bonding power, absence of slip, and stability for long periods at elevated temperatures. Methylcellulose ethers are used in countless products, as film formers and binders. In glazes, they are used to provide thickening, to produce films, to bind, to retain water, to suspend, to harden and to lubricate, as well as to serve as a protective colloid and emulsifier. Since methylcellulose ethers burn away, they do not have any impact on the chemistry of the glaze, only its physical working properties. Many different types of gums are also available as glaze binders. Almost all are intended to make the glaze harden and adhere to the ware. Normally, only small amounts are needed and they are mixed into water before additional ingredients (such as powder) are added. Gum arabic, gum tragacanth, and CMC are popular types, normally used at up to 1%. A gum solution in hot water should be prepared at a higher percentage prior to its addition to the glaze.

9.10.2 Binders for insecticides An insecticide is a pesticide used against insects at all of their developmental stages. Insecticides are used in agriculture, medicine, industry and the household. There are different classes of insecticides: systemic, contact, natural, inorganic, and organic. Their modes of action are varied. Insecticides include heavy metals (lead, mercury, arsenic), as well as nicotine. Various plants, such as tobacco and pyrethrum, have also been used as folk insecticides. Gum arabic has been recommended as a binder for insecticides (Matsudaira, 1953). Gum tragacanth can also be involved in preparing stable emulsions containing 50% insect repellent. Such emulsions are effective as pure repellent compounds against ants, chiggers, certain fleas, mosquitoes and mites.

9.10.3 Non-glare coatings for windshields Specular reflection or glare is defined as the direct reflection of ambient light from a smooth glass surface (Chao, 1984). A non-glare coating reduces glare and reflections that can  occur with untreated plastic or glass. It can be applied to glass, plastic, polycarbonate and even safety lenses. Non-glare coatings for automobile windshields are based on a water-soluble dye dissolved in gum arabic solution. A typical formulation includes 94.5% water, 5% gum arabic, and 0.25% of both a dioctyl ester of sodium sulfosuccinate and brilliant green dye.

9.11 PAPER AND E-PAPER Paper originated in China in 105 A.D. It was produced of flax and hemp, or the bark fibers of certain trees. Paper sheets are composed of small cellulosic fibers held together by secondary (hydrogen) bonds; the sheets are formed by passing a dilute suspension through a screen

362  ◾  Plant Gum Exudates of the World

(Nussinovitch, 1997). The very large tonnages of paper produced annually have encouraged investigations into the possible uses of gums and resins in the various stages of paper production. The first Chinese papermakers used mucilage extracted from roots and stems to strengthen their products. Natural gums such as LBG, guar gum and tamarind gum are presently used for the same purpose, with guar gum being the most common. The gums are added as aqueous solutions and are adsorbed onto cellulose pulp fibers, thus augmenting the hemicellulose formed during refining to yield stronger paper (Nussinovitch, 1997). Beater additives include adhesives, which are widely used to enhance fiber-fiber bonding. Starches are widely used, as are gums such as guar gum, LBG, modified cellulose and polymers such as urea-formaldehyde and melamine-formaldehyde. Some water-soluble gums are added to improve wet web strength. They include LBG, guar gum and anionic polyacrylamides which contribute to strength at solids contents of over 35% (Nussinovitch, 1997). Natural gums and starches are used to a large extent as dry-strength additives. Complementation is achieved with the corresponding anionic and cationic derivatives, sodium CMC and synthetic water-soluble polymers. Gum ghatti is used to emulsify waxes (both petroleum and non-petroleum) for the production of paste emulsions which can be used in the paper industry as barriers and coatings. In addition, salts of ghattic acid have reportedly been used for so-called photo papers which are often specially coated papers with light-sensitive chemicals for use in inkjet or laser printers to make digital prints (Harris-Seybold Co., 1953). A coating of gum arabic on typewriter paper facilitates erasure applications. Many times a double coating is preferred, with short drying periods between applications (Whistler and BeMiller, 1973). Electronic paper, also called e-paper, is a display technology designed to mimic the appearance of ordinary ink on paper. It was first developed in the 1970s by Xerox. The first e-paper consisted of polyethylene spheres (beads) with diameters of ~20 to 100 μm. Each bead was composed of negatively charged black plastic on one side and positively charged white plastic on the other, and as such served as a dipole. The beads were embedded in a transparent silicone sheet, with each bead suspended in a bubble of oil to permit free rotation. The polarity of the voltage applied to each pair of electrodes then determined whether the white or black side would face up, thus giving the pixel a white or black appearance. An electrophoretic display is an information display that forms visible images by rearranging charged pigment particles using an applied electric field. Electrophoretic displays are considered prime examples of the e-paper category, due to their paper-like appearance and low power consumption. Microcapsules for electrophoretic display can be prepared by in-situ polymerization based on urea, melamine and formaldehyde, others by a complex coacervate composed of gelatin and gum arabic (Song et al., 2007). A longer lifetime for the electrophoretic display can be achieved by reducing agglomerization or lateral movement of the nanoparticles. Gelatin-gum arabic microcapsules were found to provide extra-uniform microcapsule coverage on electrodes due to their flexibility relative to melamine-urea microcapsules. Migration of nanoparticles in the two types of microcapsules was also observed when an electric field was applied (Song et al., 2007).

9.12 EXPLOSIVES A dramatic increase in volume and heat enables explosives to perform such tasks as crushing rocks and moving mountains. Explosives consist of either a chemically pure compound (e.g. nitroglycerin, acetone peroxide, TNT, nitrocellulose, RDX, PETN, HMX), or a mixture of an oxidizer and a fuel [e.g. black powder, flash powder, ammonal and ammonium nitrate/fuel oil (ANFO) among

Miscellaneous Uses of Plant Exudates  ◾  363 A

O

O –O

+

N

N+

N

N

O–

N –O

B

–O

O –O

N+

O

+ O N N

O– N N+

N+ N

O

N

O

N+

O–

Figure 9.9  (A) Chemical structure of RDX (http://en.wikipedia.org/wiki/Image:RDX.png; courtesy of Edgar181), and (B) HMX (http://en.wikipedia.org/wiki/Image:HMX.png, courtesy of Edgar181).

many others]. Explosives will often include small percentages of other materials. Examples are the addition of polymers for binding purposes, the incorporation of waxes for safer handling, and the introduction of aluminum to increase total energy and blast effects. Explosive compounds are also often “alloyed”: HMX or RDX (Fig. 9. 9) powders may be mixed (typically by melt-casting) with TNT to form Octol or Cyclotol. Taking a simplified view, the detonation process can be considered a very rapid “redox” reaction between oxidizers (which release oxygen) and fuels that produces large quantities of gases accompanied by the liberation of heat (Sudweeks, 1985). Hydrocolloids have played a big role in the development of the explosives industry (Nussinovitch, 1997). For many years, ammonium nitrate was used as an oxidizer to increase the explosive strength of dynamite, but it was not until after a series of accidents in which ammonium nitrate fires broke out that it was realized that ammonium nitrate itself could be the basis for cheap and effective industrial explosives. Fertilizer-grade ammonium nitrate in the form of porous round particles was found to absorb fuel oil, thereby forming a detonatable combination (Kirk-Othmer, 1980). Due to the low cost and ease of manufacture of ANFO, these mixtures subsequently replaced dynamite in many applications and also expanded the explosives market, making previously uneconomical operations feasible (Nussinovitch, 1997). ANFOs have certain limitations, such as no resistance to water and low-density, limited energy options. To overcome these problems, three approaches have been proposed: predissolving the ammonium in a small amount of water, thickening the solution with hydrocolloids (i.e. guar gum, starch), and if possible, cross-linking the gum thickener to produce a gelled product (Sudweeks, 1985). Powdered gum ghatti is used in ammonium nitrate-semigelatin mixtures as well as explosive powders to improve their resistance to water damage (Whistler and BeMiller, 1973). More modern explosives are either water gels or slurries (Midkiff and Washington, 1974). The slurries are basically composed of one or more solid components suspended in a semisolid continuous gel phase. The presence of hydrocolloids in these mixtures prevents settling of the solid ingredients and this preserves the integrity of the explosive. Typical ingredients for slurry

364  ◾  Plant Gum Exudates of the World

explosives (e.g. Midkiff and Washington, 1974; Kaye, 1980; Sudweeks, 1985) are an inorganic oxidizer, sensitizers, density formers, gelling agents such as the natural polysaccharide guar gum, cross-linking agents, and fuel. A few important factors should be taken into consideration if hydrocolloid products are to be used: the required physical and chemical properties, the cost of the hydrocolloid, its cost stability, and the constancy of supply and consistency of composition (Nussinovitch, 1997). Among the natural gums used in slurry explosives, guar gum is the most popular. A highly important structural feature of this gum with respect to explosives is its non-ionic nature. This enables full hydration in concentrated salt solutions, thereby producing maximum viscosities (Davidson, 1980). Guar gum is very useful in the production of slurry explosives or water gels. Guar gum and guar derivatives are capable of thickening nitrate-salt solutions, the basic component of slurry-explosive formulations. Guar gum, starch and LBG are the hydrocolloids (extracted from natural sources) most commonly encountered in slurry explosives. Other hydrocolloids that have been used include ghatti gum, psyllium seed gum, CMC and tamarind-kernel powder, to name a few. These are hydrocolloids that are either already suitable for use in slurry explosives, or for which conditions may be manipulated to make them suitable. In actual fact, the manufacture of slurry explosives is centered on manipulation, and explosive compositions are generally considered to be trade secrets. Synthetic hydrocolloids and resins in explosives and pyrotechnics are reviewed elsewhere (Nussinovitch, 1997). Less commonly used natural gums (not necessarily exudates) for the production of water-based explosives include agar (as a flash inhibitor in sulfurmining explosives) and alginate (for the production of explosives formulations) (Davidson, 1980). Powdered ghatti gum is used in ammonium nitrate-semigelatin mixtures and powdered explosives to improve their resistance to water damage (Meer Corp., 1980). Tamarind gum powder is used in the explosives industry as a thickener in slurry explosives and as a water barrier in blasting explosives because of its moisture-absorbing capabilities (Ghose and Krishna, 1943; Boyd, 1960). Xanthan and guar gum blends are used to suspend and gel slurried explosives systems containing saturated ammonium-nitrate solutions. Dextran nitrate or nitrate sulfate (dextran derivatives) are used as gelled propellants and explosives.

9.13 CERAMICS The word “ceramic” is most often used to describe dishes, pottery and figurines; but wall tiles, building bricks, high-voltage insulators, and glass products are also ceramics. Ceramics are widely used in many applications, such as nuclear reactors, space vehicles, electronic modules, computers, pumps, valves, metal-processing furnaces and ladles, optical equipment, supports (Walter et al., 1989; Saito et al., 1994), filtration equipment (Eriksson et al., 1993; Lehtovaara and Mojtahedi, 1993; Burrell et al., 1994), lasers and protective coatings (Allen et al., 1993; Dialdo et al., 1995). Critical areas of technology such as communications, construction, transportation, power generation and transmission, sanitation, space exploration and medicine (Eisner, 1995) owe their development in part to ceramics technology (Jones and Berard, 1972). Ceramic products are usually divided into four sectors: structural, including bricks, pipes, and floor and roof tiles; refractory, such as kiln linings, gas-fire radiants, steel- and glass-making crucibles; whiteware, including tableware, wall tiles, decorative art objects (Fig. 9.10) and sanitary ware; technical (also known as engineering, advanced or special, and in Japan, fine), which includes tiles used in the space-shuttle program, gas-burner nozzles, ballistic protection, nuclear fuel uranium oxide pellets, biomedical implants, jet-engine turbine blades, and missile nose cones.

Miscellaneous Uses of Plant Exudates  ◾  365

Figure 9.10  Japanese ceramics (courtesy of Madoka Hirashima).

Gum tragacanth can be used to bind agents in ceramics, since certain grades include low ash content, and the gum helps suspend the various materials in the mass before firing (Whistler and BeMiller, 1973). The inclusion of various resins in archeological materials is well known. An analytical procedure based on alkaline hydrolysis, solvent extraction and trimethyl-silylation followed by GC-MS analysis was used to study the chemical composition of benzoe and storax resins, water-insoluble exudates of Styrax and Liquidambar trees, respectively. All the compounds identified in benzoe resin were detected in an archeological organic residue from an Egyptian ceramic censer (5th to 7th centuries A.D.), thus proving that this resin was used as one of the components of the mixture of organic materials burned as incense. These results provided the first chemical evidence of the presence of benzoe resin in an archeological material from the Mediterranean region (Modugno et al., 2006). Binders (and see section 9.10) play a vital role in formulating piezoelectric ceramic materials. A number of binders such as PVA, methocel, starch, HPMC, HEC, polyvinyl pyrrolidone (PVP), PEG and gum arabic have been studied for solubility, viscosity, pH, thermal behavior and ash content when incorporated in a standard lead zirconium titanate (PZT) formulation. In addition, the resulting PZTs were studied for green density, sintered density, shrinkage characteristics, microstructure, compressive strength and electrical properties. The generated data pinpointed PVA is a potential candidate binder for this purpose (Sangawar et al., 2001).

9.14 MISCELLANEOUS 9.14.1 Varnishes The word “varnish” comes from the Latin vernix, meaning odorous resin. Varnish is a transparent, hard, protective finish or film used in wood finishing and other materials. It is traditionally made up of a combination of drying oil, resin, and thinner or solvent. “Flatting” agents are sometimes added to the composition in order to produce a semigloss effect. After application, the film-forming substances in varnishes harden either directly, or after evaporation of the solvent through certain curing processes. Gum ghatti is used in old and new varnishes. It is also used for emulsifying oils such as kerosene oil.

366  ◾  Plant Gum Exudates of the World

9.14.2 Car polishes Car owners have always had the desire to provide their automobiles with a beautiful, shiny appearance, and to protect the underlying paint from environmental damage such as mud, water spots, and the effects of the sun. Over the years, car owners have come to prefer paste waxes to protect and beautify the exterior painted surfaces of their vehicles because wax finishes are typically more durable than finishes provided by wax-free products. One reason for their durability is that waxes provide harder coatings than greases or oils. Because of their superior hardness, waxes do not thin out when polished to a high-gloss sheen by rubbing with a polishing cloth (Chetan and Louw, 2001). Gum ghatti acts as a stabilizer in car polishes and wallpaper gum sizing. Gum tragacanth is also useful in various types of polishes, such as for cars, furniture and floors (Whistler and BeMiller, 1973).

9.14.3 Cross-linked polystyrene In combination with polyacrylamide, gum ghatti aids in the formation and polymerization of discrete and uniform prills of cross-linked polystyrene (Whistler and BeMiller, 1973). Cross-linked polystyrene is a rigid, transparent insulating material. Its rigidity and ability to resist deformation under load are extremely important where assembled insulators must withstand compression without yielding or loosening over long periods of time. Typical applications of cross-linked polystyrene are UHF, VHF and microwave insulators, as well as communication and electronic equipment. It also has good impact strength, outstanding dielectric properties, and high radiation resistance, as well as being resistant to load deformation.

9.14.4 Photoelectric determinations The protective colloid gum ghatti is used in various photoelectric determinations. Examples are blood sugar determinations (Folin, 1928), and in the stabilization of Nesslerized solutions of ammonia (Looney, 1930). The method of Folin and Malmros (1929) was further improved to determine glucose in very small amounts of blood (Reinecke, 1942). A method for the determination of spinal fluid protein with a photoelectric colorimeter has also been described. The precipitation of protein by sulfosalicylic acid was achieved in the presence of gum ghatti and yielded a stable colloidal suspension which did not change for 30 h. Using such methods permits readings without dilution of protein concentrations from 5.0 to 150.0 mg (Looney and Walsh, 1939). The presence of gum ghatti is required in a turbidimetric method used for the determination of serum globulin and albumin by photoelectric colorimeter. For total protein, the precipitation of a 1% dilution of serum with sulfosalicylic acid in the presence of the gum was employed. The globulin was determined directly in a 10% dilution by precipitation with one-half saturation of ammonium sulfate in the presence of the same protective colloid. The method is applicable to 0.2 ml of serum and can be carried out in 5 to 10 min (Looney and Walsh, 1939). The colorimetric method can also be used to estimate catalase activity. The method yields accurate, reproducible results, and is simplified so that clinical chemistry laboratories can perform this determination without the need for special equipment. In this method, heparinized plasma is reacted with a buffered solution of hydrogen peroxide. After a defined period of time, an aliquot of the reaction mixture is withdrawn and reacted with alkaline ferricyanide (Fig. 9.11). This reaction is based on the principle that, in alkaline solution, peroxide acts as a reducing agent, converting ferricyanide to ferrocyanide. A solution of gum ghatti containing ferric ions is added to the

Miscellaneous Uses of Plant Exudates  ◾  367

Figure. 9.11  3D structure of ferricyanide (http://en.wikipedia.org/wiki/Image:Ferricyanide-3D. png; courtesy of Benjamin-Mills).

ferrocyanide. This ferric-ferrocyanide compound is soluble Prussian blue (in the presence of gum ghatti). The color intensity of the Prussian blue is a measure of non-decomposed hydrogen peroxide substrate, which, in turn, is a measure of catalase activity (Dobkin and Glantz, 1958). Gum ghatti’s role is to stabilize the Prussian blue color in such photoelectric determinations (Whistler and BeMiller, 1973).

9.14.5 Polarographic determinations Polarography is a voltammetric measurement whose response is determined by combined diffusion/ convection mass transport. In analytical chemistry, polarography is an electrochemical method of analyzing solutions of reducible or oxidizable substances. It was invented by a Czech chemist, Jaroslav Heyrovský, in 1922. In general, the technique involves varying the electric potential (or voltage) in a regular manner between two sets of electrodes (indicator and reference) and monitoring the current. Gum ghatti has been used in the polarographic determinations of copper, lead and iron (Whistler and BeMiller, 1973). The polarographic reduction waves for cupric, plumbous, and ferric ions, with sodium pyrophosphate as the base electrolyte, are suitable for the determination of these metals in alloys. As the half-wave potentials for lead and iron are close to one another, one of these metals must be determined by another method if both are present in the sample. If brass samples are to be examined, they should be dissolved in concentrated nitric acid, boiled to expel the oxides of nitrogen, and then diluted in a volumetric flask with sodium pyrophosphate solution. This solution is mixed with a 2% solution of gum ghatti, and examined polarographically. Aluminum-, zinc-, beryllium-, and magnesium-based alloys can be examined in the same way: the aluminum- and zinc-based alloys are dissolved by adding hydrochloric acid followed by concentrated nitric acid (Reynolds and Rogers, 1949).

9.14.6 Abdominal ultrasound imaging and soil analyses Abdominal ultrasound imaging can be carried out by oral or rectal administration of an aqueous imaging composition containing micron-size inorganic particles together with a sufficient amount of a solubilized hydrocolloid to maintain the particles in suspension. The walls of the stomach, duodenum and colon become coated with the particles and are thereby more clearly delineated by the ultrasonic imaging beam. At the same time, ultrasonic waves partially pass through the walls and delineate structures outside them. Wall delineation and wall transparency can thereby be

368  ◾  Plant Gum Exudates of the World

simultaneously achieved (Levene et al., 1992). Natural hydrocolloids such as pectin are especially desirable. In addition to pectin, other examples include: gum ghatti, gum guar, LBG, tragacanth gum, xanthan gum, gum arabic, carrageenan, and agar. In preferred formulations, from 1 to 5 g of the hydrocolloid are employed (Levene et al., 1992). Gum ghatti has also been reported to have the ability to form protective hydration layers around clay particles, in order to maintain dispersions for particle-size analysis (Whistler and BeMiller, 1973).

9.14.7 Vinyl resin emulsions Various methods have been proposed for polymerizing aqueous emulsions of compounds containing terminal ethylene groups. However, such processes have tended to be deficient in that they produce emulsions with a high concentration of small and uniformly sized polymer particles (Wilson, 1950). Other encountered difficulties included lack of emulsion stability and poor filming properties. These problems were overcome by polymerizing normally liquid-polymerizable materials containing terminal ethylene groups as the dispersed phase of an aqueous emulsion protected by a non-polymerizable surface-tension depressant combined with a hydrophilic colloid. The initial amount of monomer did not exceed 25 parts by weight for every 100 parts of water present, and the remainder was added such that this ratio would not be exceeded throughout the polymerization period (Wilson, 1950). By operating in such a manner, fine and uniform emulsions were produced. Gum arabic, tragacanth gum and sodium CMC were successfully used in the preparation of such vinyl resin emulsions (Wilson, 1950; Whistler and BeMiller, 1973).

References Abiola, O. K., Oforka, N. C., Ebenso, E. E., and N. M. Nwinuka. 2007. Eco-friendly corrosion inhibitors: the inhibitive action of Delonix-Regia extract for the corrosion of aluminium in acidic media. AntiCorrosion Methods and Materials 54:219-24. Al-Ghouti, M. A., Khraisheh, M. A. M., Allen, S. J., and M. N. Ahmad. 2003. The removal of dyes from textile wastewater: a study of the physical characteristics and adsorption mechanisms of diatomaceous earth. J. Environ. Manag. 69:229-38. Allen, W. H., Harmon, J. D., and D. E. Linvill. 1993. Evaluation of a ceramic roof coating. Appl. Eng. Agric. 9:309-15. Barton, K. R. 1994. Sulphopolyesters—new resins for water based inks, overprint lacquers and primers. JOCCA-Surface Coatings International 77:180-2. BBC News. 2000. Earliest Evidence of Art Found, 2 May. Boyd, G. 1960. Water-resistant blasting explosives. Australian Patent 229,190; Chem. Abstr. 55:25255. Burrell, K., Gill, C., McKechnie, M. et al. 1994. Advances in separations technology for the brewer: ceramic crossflow microfiltration of rough beer. Tech Q Master Brew. Assoc. Am. 3:42-50. Caenn, R., and G. V. Chillingar. 1996. Drilling fluids: state of the art. J. Petrol. Sci. Eng. 4:221-30. Cardwell, P. H., and L. H. Eilers. 1958. US patents 2,824,833 and 2,824, 834; Chem. Abstr. 52:11400. Chao, P. 1984. Non-glare coating. US Patent 4596745. Chen, Y.-S., Tal, A., Torrance, D. B., and S. M. Kuebler. 2006. Fabrication and characterization of threedimensional silver-coated polymeric microstructures. Adv. Funct. Mater. 16:1739-44. Chetan, P. J., and S. J. V. Louw. 2001. Polish composition and method of use. US Patent 6235824. Chiavari, G., Montalbani, S., Prati, S., Keheyan, Y., and S. Baroni. 2007. Application of analytical pyrolysis for the characterization of old inks. J. Anal. Appl. Pyrolysis 80:400-5. Chilingar, G. V., and A. L. Croushorn. 1964. Gum guar proves useful as mud additive. Canada Petrol. Eng. 5:19-21. Chilingarian, G.V., and P. Vorabutr. 1983. Drilling and drilling fluids, 2nd ed. Amsterdam: Elsevier.

Miscellaneous Uses of Plant Exudates  ◾  369 Clark, C. T. 1952. Set stabilized low consistency calcined gypsum product. US Patent 2,620,279. Chem. Abstr. 47:2454. Clarke, A. E., Bacic, A. L., and A. Gordon. 1999. Industrial, pharmaceutical and cosmetic applications for cultured plant cell gums. European Patent EP0653931. Colombini, M. P., Ceccarini, A., and A. Carmignani. 2002. Ion chromatography characterization of polysaccharides in ancient wall paintings. J. Chromatography 968:79-88. Daniels, V., and B. Leach. 2004. The occurrence and alteration of realgar on Ancient Egyptian papyri. Studies in Conservation 49:73-84. Daniels, V., Stacey, R., and A. Middleton. 2004. The blackening of paint containing Egyptian blue. Studies in Conservation 49:217-30. Darley. H. C. H., and G. R. Gray. 1988. Composition and properties of drilling and completion fluids, 5th ed. Houston, TX: Gulf. Davidson, R. L. 1980. Handbook of water-soluble gums and resins. New York: McGraw-Hill Book Company. Dawson, T. L., and H. Ellis. 1994. Will ink jets ever replace screens for textile printing? J. Soc. Dyes Colourists, 110: 331-7. Dialdo, B., Vanhaelen, M., and O. P. Gosselain. 1995. Plant constituents involved in coating practices among traditional African potters. Birkhauser Verlag Experientia Basel Switzerland 51(1): 95-7. Dobkin, G. B., and M. D. Glantz. 1958. Colorimetric method for the quantitative determination of plasma catalase activity. Clin. Chem. 4:316-22. Doerner, M. 1989. Malmaterial und seine Verwendung im Bilde, Enke, Stuttgart. Eisner, E. R. 1995. Restoring a tooth to form and function after endodonic treatment. Vet. Med. Lenexa, Kan: Veterinary Medicine Publishing Group 90:662-79. Ellis, C. 1940. In Printing inks, 230, 334, 346, 398-9, 417. New York: Reinhold Publishing Corp. Eriksson, T., Isaksson, J., Stahlberg, P. et al. 1993. Durability of ceramic filters in hot gas filtration. Bioresour. Technol. 46:103-12. Folin, O. 1928. New blood sugar method. J. Biol. Chem. 77:421-30. Folin, O., and H. Malmros. 1929. An improved form of Folin’s micro method for blood sugar determinations J. Biol. Chem. 83:115-20. Ghose, T. P., and S. Krishna. 1943. Tamarind seed. A new sizing material for cotton yarn. Indian Text. J. 53:236. Goltz, D., McClelland, J., Schellenberg, A., Attas, M., Cloutis, E., and C. Collins. 2003. Spectroscopic studies on the darkening of lead white. Appl. Spectroscopy 57:1393-8. Green, D. A., Lewis, R., and J. Cripps. 2007. Friction and wear testing for a down-hole oil well centralizer. Wear 263:57-64. Grossl, M., Harrison, S., Kaml, I., and E. Kenndler. 2005. Characterization of natural polysaccharides (plant gums) used as binding media for artistic and historic works by capillary zone electrophoresis. J. Chromatography A 1077: 80-9. Hacker, G. W., Grimelius, L., Danscher, G., Bernatzky, G., Muss, W., Adam, H. and J. Thurner. 1988. Silver acetate autometallography: an alternative enhancement technique for immunogold-silver staining (IGSS) and silver amplification of gold, silver, mercury and zinc in tissues. J. Histotechnol. 11: 213-221. Harris-Seybold Co. 1953. Improvements in manufacture of acids and salts from gums. British Patent 689,623. Jones, J. T., and M. F. Berard. 1972. Ceramics industrial processing and testing. Ames, IA: The Iowa State University Press. Kaye, S. M. 1980. Slurry explosives. In Encyclopedia of explosives and related items, vol. 9, PATR 2700, Seymour M. Kaye, US Army Armament Research and Development Command, S121-47. Dover, NJ. Kirk-Othmer encyclopedia of chemical technology. 1980. 3rd edn, vol. 9. New York: Wiley. Knecht, E., and J. B. Fothergill. 1924. In The principles and practice of textile printing, 2nd ed., 123-4. London: Griffin and Co. Lehtovaara, A., and W. Mojtahedi. 1993. Ceramic filter behavior in gasification. Bioresour. Technol. 46:113-8. Levene, H. B., Barnhart, J. L., Widder, K. J., and E. Villapando. 1992. Abdominal ultrasound imaging. European Patent EP0500023. Looney, J. M. 1930. The determination of blood urea nitrogen by direct nesslerization. J. Biol. Chem. 68:189-95.

370  ◾  Plant Gum Exudates of the World Looney, J. M., and A. I. Walsh. 1939. The determination of spinal fluid protein with the photoelectric colorimeter. J. Biol. Chem. 127:117-21. Mahto, V., and V. P. Sharma. 2005. Tragacanth gum: an effective oil well drilling fluid additive. Energy Sources 27:299-308. Matsudaira, T. 1953. Feed for destroying termites. Japanese Patent 2997. Meer Corp. 1980. The use of gums in wax emulsions. Technical Bulletin No. 1-11. Midkiff, C. R., and W. D. Washington. 1974. Systematic approach to the detection of explosives residues. III. Commercial dynamite. J. Assoc. Offic. Anal. Chem. 57:1092-7. Mills, J. S., and R. White. 1994. The organic chemistry of museum objects. London: Butterworth Heinemann. Modugno, F., Ribechini, E., and M. P. Colombini. 2006. Aromatic resin characterization by gas chromatography-mass spectrometry. Raw and archaeological materials. J. Chromatography A 1134:298-304. Nussinovitch, A. 1997. Hydrocolloid applications: gum technology in the food and other industries, 125-39. London: Blackie Academic & Professional. Ohama, Y. 1994. Polymers in concrete. Boca Raton: CRC Press. Okafor, P. C., Osabor, V. I., and E. E. Ebenso. 2007. Eco-friendly corrosion inhibitors: inhibitive action of ethanol extracts of Garcinia kola for the corrosion of mild steel in H2SO4 solutions. Pigment Resin Technol. 36:299-305. Paulino, A. T., Guilherme, M. R., Reis, A. V., Campese, G. M., Muniz, E. C., and J. Nozaki. 2006. Removal of methylene blue dye from an aqueous media using superabsorbent hydrogel supported on modified polysaccharide. J. Colloid Interface Sci. 301:55-62. Poschel, A. 1933. British Patent 393, 132; Chem. Abstr. 27:5553. Raja, P. B., and M. G. Sethuraman. 2008. Natural products as corrosion inhibitor for metals in corrosive media—a review. Materials Lett. 62:113-6. Reinecke, R. M. 1942. Determination of glucose in minimal quantities of blood. J. Biol. Chem. 143:351-355. Reynolds, C. A., and L. B. Rogers. 1949. Polarographic method for copper, lead, and iron, using a pyrophosphate background solution. Anal. Chem. 21:176-8. Saito, T., Yoshida, Y., Kawashima, K. et al. 1994. Immobilization and characterization of a thermostable β-galactosidase from a thermophilic anaerobe on a porous ceramic support. Appl. Microbiol. Biotechnol. 40:618-21. Sakamoto, Y., and T. Tanimura. 1996. Process for electroplating nonconductive surface. US Patent 5547558. Sangawar, S. R., Agarwal, J. P., and D. B. Sarwade. 2001. A comprehensive study on some binders for piezoelectric ceramics. Indian J. Eng. Mater. Sci. 8:26-35. Schramm, H. B. 1988. Historische, Malmaterialien und ihre Identifikation, Akademische Druck- und Verlagsanstalt, Graz. Skaggs, B., Rakitsky, W., and A. Phyfferoen. 1997. Methods for improved rheological control in cementitious systems. (WO/1997/022564) Song, J. K., Choi, H. J., and I. Chin. 2007. Preparation and properties of electrophoretic microcapsules for electronic paper. J. Microencapsulation 24:11-9. Strauss, H. J. 1955. Growth inhibitor for battery electrodes. US Patent 2,692,904. Sudweeks, W. B. 1985. Physical and chemical properties of industrial slurry explosives. Ind. Eng. Chem. Prod. Res. Dev. 24:432-6. Chillingarian, G. V., and C. M. Beeson. 1950. Iranian gums as treating agents for drilling fluids. AIMS Petroleum Branch Meeting, Los Angeles, CA, October 1950, 18pp, Paper 78G Umoren, S. A., Obot, I. B., Ebenso, E. E., Okafor, P. C., Ogbobe, O., and E. E. Oguzie. 2006. Gum arabic as a potential corrosion inhibitor for aluminium in alkaline medium and its adsorption characteristics. Anti-Corrosion Methods and Materials 53:277-82. Walter, R. P., Kell, D. B., Morris, J. G. et al. 1989. Immobilization of Candida cylindracea lipase on a new range of ceramic support. Biotechnol. Tech. 3:345-8. Whistler, R. L., and J. N. BeMiller. 1973. Industrial gums. New York: Academic Press. Wilson, W. K. 1950. Polyvinyl acetate emulsion. US patent 2,508,343.

Organism Name Index a Acacia, 1, 8, 9, 32, 39, 41, 267, 281 Acacia abyssinica, 43 Acacia abyssinica subsp. abyssinica, 43 Acacia acapulcensis, 116 Acacia adenophora, 45 Acacia albida, 10, 52 Acacia arabica, 78, 89 Acacia bakeri, 43 Acacia benthamii, 43 Acacia binervata, 43, 44 Acacia camplylacantha, 322 Acacia catechu, 43, 44, 78, 127 Acacia cebil, 105 Acacia dealbata, 45, 283 Acacia decurrens, 45, 46, 356 Acacia decurrens var. dealbata, 45 Acacia decurrens var. pauciglandulosa, 45 Acacia dekindtiana, 47 Acacia detinens, 49 Acacia drepanolobium, 46, 322, 329 Acacia elata, 46 Acacia farnesiana, 46 Acacia ferruginea, 47 Acacia fistula, 42 Acacia frigescens, 283 Acacia glomerosa, 113 Acacia harpophylla, 47 Acacia jacquemontii, 47 Acacia karroo, 47 Acacia kirkii, 47 Acacia kirkii subsp. kirkii, 47 Acacia kirkii subsp. mildbraedii, 47 Acacia laeta, 48, 322 Acacia lebbek, 68 Acacia leiophylla, 48 Acacia leucophloea, 48 Acacia maidenii, 49 Acacia mellifera, 49 Acacia mellifera subsp. detinens, 49

Acacia mellifera subsp. mellifera, 49 Acacia minuta, 46 Acacia modesta, 49 Acacia nubica, 49 Acacia obliquinervia, 283 Acacia oerfota, 49 Acacia oswaldii, 50 Acacia pendula, 50 Acacia penninervis, 50 Acacia polyacantha, 328 Acacia pseudofistula, 328 Acacia pycnantha, 4, 51 Acacia retinodes, 51 Acacia salicina, 51 Acacia senegal, 8, 9, 10, 11, 12, 15, 16, 24, 34, 35 39, 40, 41, 43, 98, 107, 115, 116, 125, 129, 174, 278, 313, 322, 328 Acacia seyal, 16, 42, 98, 125, 135, 322 Acacia seyal var. fistula, 42 Acacia seyal var. seyal, 42 Acacia sieberiana, 51 Acacia sieberiana subsp. vermoesenii, 51 Acacia sieberiana var. sieberian, 51 Acacia sieberiana var. vermoesenii, 51 Acacia sieberiana var. woodii, 51 Acacia smallii, 46 Acacia stenocarpa, 42 Acacia stipulata, 71 Acacia stuhlmanii, 51 Acacia verek, 39 Acacia vermoesenii, 51 Acacia verniciflua, 52 Acacia verugera, 51 Acacia wallichiana, 43 Acacia woodii, 51 Acacia xanthophloea, 52 Achradelpha mammosa, 121 Achras mammosa, 121 Achras zapota, 121 Achras zapota var. zapotilla, 121 Achras zapotilla, 121

371

372  ◾  Organism Name Index Actinidia chinensis var. deliciosa, 123 Actinidia chinensis var. hispida, 123 Actinidia deliciosa, 123 Actinidia latifolia var. deliciosa, 123 Adansonia digitata, 163, 164, 165, 167 Adansonia gibbosa, 165, 167 Adansonia perrieri, 167 Adansonia rubrostipa, 167 Adenanthera pavonina, 168, 169, 170 Aegle marmelos, 66, 67, 68, 89, 318 Aeschynomene grandiflora, 98 African blackwood, 209 African greenheart, 137 African locust bean, 136 African mahogany, 170 Afzelia africana, 170, 171 Agboin, 137 Albizia, 68, 69, 70, 71, 72, 74, 111, 172, 173, 313, 318 Albizia amara, 72, 74 Albizia amara subsp. amara, 72 Albizia amara subsp. sericocephala, 72 Albizia chinensis, 69, 71, 72 Albizia lebbeck, 68, 69 70, 318 Albizia marginata, 71 Albizia odoratissima, 68, 69 Albizia procera, 69, 71, 72 Albizia saman, 111 Albizia sericocephala, 72 Albizia stipulate, 69, 71 Albizia zygia, 68, 318 Aleurites javanicus, 73 Aleurites moluccanus, 73, 74, 320 Aleurites pentaphyllus, 73 Aleurites remyi, 73 Aleurites trilobus, 73 Allocebus, 281 Almond, 229 Almond tree, 27 Alternaria alternata, 235 American mangrove, 117 Amritsar-gum, 49 Amygdalus armeniaca, 140 Amygdalus communis, 229 Amygdalus dulcis, 229 Amygdalus persica, 143 Anacardium humile, 104 Anacardium nanum, 104 Anacardium occidentale, 104 Anacardium pumilum, 104 Anadenanthera colubrina, 105, 106, 108 Anadenanthera colubrina var. cebil, 106, 320 Anadenanthera colubrina var. colubrina, 105 Anadenanthera macrocarpa, 105 Anatree, 52 Angelique, 130 Anogeissus acuminata, 173 Anogeissus latifolia, 76, 77, 173, 200, 313

Anogeissus leiocarpa, 173 Anogeissus leiocarpus, 173 Anogeissus pendula, 173 Anogeissus schimperi, 173 Antarctobacter, 279 Antelaea azadirachta, 93 Apricot, 140 Araucaria angustifolia, 124 Araucaria bidwillii, 124 Araucaria cookie, 124 Araucaria cunninghamii, 124 Araucaria heterophylla, 123, 124 Araucaria hunsteinii, 124 Araucaria rulei, 124 Armeniaca vulgaris, 140 Asafetida, 131 Asafoetida, 131 Asparagus racemosus, 220 Aspergillus niger, 235 Assa-foetida, 131 Assyrian plum, 200 Astracantha adscendens, 55 Astracantha gummifera, 52 Astracantha heratensis, 56 Astracantha kurdica, 56 Astracantha microcephala, 57 Astragalus, 15, 314 Astragalus adpressus, 52 Astragalus adscendens, 55 Astragalus brachycalyx, 55 Astragalus gummifer, 15, 52, 53 Astragalus heratensis, 56 Astragalus kurdicus, 56 Astragalus microcephalus, 15, 57 Astragalus verus, 57 Atalaya hemiglauca, 174 Australian cedar, 83 Australian flametree, 64 Australian red cedar, 83 Australian silky oak, 132 Australian teak, 211 Axebreaker, 212 Azadirachta indica, 31, 93, 319 Azadirachta indica var. indica, 93 Azadirachta indica var. siamensis, 93

b Bacillus circulans, 224 Bacillus subtilis, 119, 231, 235 Bael, 66 Bael fruit gum, 67, 68, 318 Baeltree, 66 Balanites aegyptiacus, 125, 126 Balanus albicostatus, 246 Balsamocitrus dawei, 174, 175 Banksia gibbosa, 213

Organism Name Index  ◾  373 Baobab, 64, 163, 165, 166, 167, 168 Barbados cedar, 189 Bassia latifolia, 134 Bassia longifolia, 134 Bastard teak, 126 Basterlebbeck, 69 Bauhinia, 318 Bauhinia alba, 81 Bauhinia carronii, 80, 175 Bauhinia fassoglensis, 175, 176 Bauhinia kirkii, 176 Bauhinia purpurea, 79 Bauhinia retusa, 80 Bauhinia roxburghiana, 80 Bauhinia semla, 80 Bauhinia surinamensis, 80 Bauhinia thonningii, 80, 81, 175 Bauhinia triandra, 79 Bauhinia variegata, 78, 81, 299, 318 Bauhinia variegata var. alboflava, 81 Bauhinia variegata var. candida, 81 Beach almond, 101 Beef-wood, 14 Beetle, 30, 34, 115, 124, 232, 280 Beleric myrobalan, 101 Bel fruit tree, 66 Belleric, 101 Belou marmelos, 66 Bendytree, 118 Bengal kino, 7, 126 Bengal quince, 66 Benin mahogany, 214 Beninwood, 214 Ben oil tree, 225 Benzolive tree, 225 Bergenia himalaica, 318 Berlinia eminii, 176 Be-still tree, 245 Bird cherry, 138 Bisselon, 214 Bitter almond, 125, 229 Blackbead, 111 Black catechu, 43 Black cutch, 43 Black sally, 49 Black siris, 69 Blackthorn, 143 Blackwood, 49, 50 Blueberry ash, 208 Blush alder, 234 Blush carrabeen, 234 Blush carrobean, 234 Boabab, 166, 167 Boarwood, 146 Bohera, 101 Bombax ceiba, 177, 178, 312 Bombax gossypium, 65

Bombax insigne, 180 Bombax malabaricum, 177 Bombax pentandrum, 190 Boraço, 180 Boraso, 180 Borasse, 180 Borassus flabellifer, 180, 181 Bosistoa pentacocca, 181 Bosistoa sapindiformis, 181 Boswellia serrata, 220 Botryodiplodia theobromae, 28, 33 Botryosphaeria dothidea, 28, 117, 123, 143, 230 Bottletree, 62 Bouchardatia neurococca, 224 Boxing-glove cactus, 120 Boxing-glove cholla, 120 Brabejum stellatifolium, 125 Brachychiton, 65 Brachychiton acerifolius, 64 Brachystegia eurycoma, 170 Brachystegia floribunda, 183 Brachystegia globiflora, 176 Brachystegia longifolia, 183 Brachystegia nchangensis, 183 Brachystegia randii, 181 Brachystegia spiciformis, 177, 181, 182, 183 Brinkadora, 120 Broadleaf wattle, 51 Broção, 180 Buchanania lanzan, 82, 299 Buchanania latifolia, 82 Buri palm, 202 Burkea africana, 183, 184 Burma almondwood, 191 Butea frondosa, 126 Butea monosperma, 6, 7, 126, 128 Butea superba, 127 Butterfly-orchid tree, 79 Butterfly tree, 79 Buttontree, 76

c Cabbage-wood tree, 204 Cacao, 110, 118 Cacao bean, 118 Caesalpinia, 320 Caesalpinia coriaria, 106 Caesalpinia eriostachys, 107 Caesalpinia praecox, 107 Cailliea dichrostachys, 207 Cailliea nutans, 207 Callithrix jacchus, 283 Calocarpum mammosum, 121 Camachile, 111 Camel’s foot, 79

374  ◾  Organism Name Index Campsiandra comosa, 118 Candida albicans, 113 Candida parapsilosis, 232 Candleberry, 73 Candlenut, 73 Candlenut tree, 73 Caper tree, 184 Capivi, 212 Capparis nobilis, 184 Capsicum annum, 274 Carabeen, 234 Careya arborea, 185 Carica papaya, 337 Carribin, 234 Cascabela peruviana, 245 Cascabela thevetia, 245 Cashew, 13, 33, 34, 104, 105, 111, 234, 294 Cassia fistula, 186, 187, 320 Cassia grandis, 186, 187 Cassia nicaraguensis, 187 Cassia sieberiana, 187, 231, 320 Cassie, 46 Cassine aethiopica, 135 Cassine glauca, 86 Catechu, 43 Cattle brush, 174 Cedar gum, 318 Cedar wattle, 46 Cedrela australis, 190 Cedrela glaziovii, 189 Cedrela kotschyi, 230 Cedrela mexicana, 189 Cedrela odorata, 188, 189, 190 Cedrela toona, 69, 83, 190 Cedrela velutina, 83 Ceiba caribaea, 190 Ceiba casearia, 190 Ceiba pentandra, 190, 320 Ceiba speciosa, 118 Cerambycid beetle, 30 Cerasus avium, 138 Cerasus avium var. aspleniifolia, 138 Ceratopetalum, 320 Ceratopetalum apetalum, 190, 192, 320 Ceratopetalum gummiferum, 191, 192, 320 Cerbera manghas, 246 Cerbera thevetia, 245 Cercidium praecox, 107 Cercidium praecox subsp. praecox, 107 Cercidium spinosum, 107 Cercidium viride, 107 Cercis siliquastrum, 127 Cercis siliquastrum var. alba, 127 Ceylon rosewood, 69 Ceylon tea, 86 Chain-fruit cholla, 120 Cheirogaleus, 281

Cherana puteh, 191 Chickrassy, 191 Chicle, 3, 121, 122, 257 Chico, 121 Chinaberry, 221 Chinese albizia, 71 Chinese bottletree, 65 Chinese date, 148 Chinese gooseberry, 123 Chinese jujube, 148 Chinese parasol tree, 65 Chirauli nut, 82 Chirauli-nut-tree, 82 Chiraya gum, 201 Chiriri gum, 198 Chittagong tree, 191 Chittagong wood, 191 Chloroleucon leucospermum, 115 Chloroleucon mangense, 115 Chloroleucon mangense var. leucospermum, 115 Chloroleucon mangense var. mangense, 115 Chloroleucon mangense var. vincentis, 115 Chloroxylon swietenia, 84, 85 Chondrostereum purpureum, 28 Chorisia speciosa, 118 Christmas bush, 191 Chukrasia tabularis, 191 Chukrasia velutina, 191 Cigar-box cedar, 189 Cissus populnea, 127, 129 Citrus, 23, 32, 33, 193 Citrus aurantiifolia, 193, 194 Citrus aurantium, 193 Citrus crassa, 193 Citrus decumana, 193 Citrus grandis, 193 Citrus limonelloides, 193 Citrus limonia, 193 Citrus limunum, 193 Citrus maxima, 193 Citrus medica, 193 Citrus sinensis, 193 Cladosporium herbarum, 231 Club cactus, 120 Coachwood, 190 Coatesia paniculata, 212 Cochlospermum gossypium, 65, 215 Cochlospermum religiosum, 65, 217, 231 Cochlospermum, 216 Cocoa, 110 Coconut, 195 Coconut palm, 195 Cocos nucifera, 195, 196, 197 Cola cordifolia, 197 Colletotrichum, 213 Combretum, 198

Organism Name Index  ◾  375 Combretum adenogonium, 198, 200 Combretum collinum, 198, 200 Combretum dalzielii, 200 Combretum erythrophyllum, 198 Combretum fragrans, 198 Combretum glutinosum, 198 Combretum hypopilinum, 200 Combretum lecananthum, 198, 200 Combretum molle, 198 Combretum nigricans, 198, 200 Combretum psidioides, 199 Combretum sokodense, 198 Combretum verticillatum, 200 Combretum zeyheri, 198 Commiphora irrigensis, 129 Commiphora mollis, 129 Common jujube, 148 Conocarpus latifolius, 76 Conocarpus racemosus, 110 Cooba, 51 Copra, 195 Coralwood, 168 Cordia abyssinica, 200 Cordia africana, 200, 201 Cordia gharaf, 200 Cordia myxa, 200 Cordia sinensis, 200 Cordyla africana, 201 Corktree, 118 Corypha elata, 202 Corypha gebanga, 202 Corypha umbraculifera, 202 Corypha utan, 202 Cottontree, 65, 190 Couma utilis, 282 Cow tamarind, 113 Crataeva adansonii, 202 Crateva marmelos, 66 Crow apple, 228 Crow’s ash, 211, 229 Cryptococcus albidus, 232 Cudgerie, 234 Cuminum cyminum, 272, 273 Cussonia arborea, 204 Cussonia barteri, 204 Cussonia djalonensis, 204 Cussonia longissima, 204 Cussonia nigerica, 204 Cussonia spicata, 204 Cutchtree, 43 Cyamopsis tetragonolobus, 16 Cycas circinalis, 204, 205, 207 Cycas lane-poolei, 204 Cycas undulata, 204 Cylindropuntia fulgida, 120 Cytisus pinnatus, 134 Cytospora cincta, 28

d Dahoma, 137 Dead rat tree, 163 Delonix regia, 84, 87, 88, 358 Dendrobium nutans, 212 Derris indica, 134 Desert date, 125 Desert willow, 137 Detarium microcarpum, 165, 170, 171 Devil’s ear, 113 Devils guts, 184 Dhak, 126 Dialium coromandelicum, 219 Dialium guineense, 165 Dianthus, 24 Diaprepes abbreviatus, 175 Dichrostachys cinerea, 172, 207, 328 Dichrostachys cinerea subsp. africana, 207 Dichrostachys cinerea subsp. africana var. africana, 207 Dichrostachys cinerea subsp. africana var. setulosa, 207 Dichrostachys cinerea subsp. argillicola, 207 Dichrostachys cinerea subsp. cinerea, 207 Dichrostachys cinerea subsp. forbesii, 207 Dichrostachys cinerea subsp. lugardae, 207 Dichrostachys cinerea subsp. nyassana, 207 Dichrostachys cinerea subsp. platycarpa, 207 Dichrostachys cinerea var. hirtipes, 207 Dichrostachys cinerea var. lugardiae, 207 Dichrostachys forbesii, 207 Dichrostachys glomerata, 207 Dichrostachys nutans, 207 Dichrostachys nutans var. setulosa, 207 Dichrostachys nyassana, 207 Dichrostachys platycarpa, 207 Dicorynia paraensis, 130 Dindiga tree, 76 Diospyros cordifolia, 295 Diospyros mespiliformis, 130, 165 Diospyros montana, 295 Diospyros sabiensis, 130 Diospyros senegalensis, 130 Distiller’s acacia, 48 Divi-divi, 106 Dolichondrone falcata, 220 Doub palm, 180 Drumstick tree, 225 Dryzone mahogany, 214

e Earpod tree, 113 East Indian kino, 144 East Indian satinwood, 84 East Indian walnut, 68 Echinocarpus australis, 208, 234 Edinam, 130

376  ◾  Organism Name Index Ekki, 133 Elaeocarpus angustifolius, 208 Elaeocarpus grandis, 208 Elaeocarpus obovatus, 208 Elaeocarpus reticulatus, 208 Elaeodendron glaucum, 86 Elaeodendron maculosum, 210 Elephant apple, 89 Elephant’s ear, 113 Elettaria cardamomum, 272 Encephalartos hildebrandtii, 208 Entada africana, 209 Entada sudanica, 209 Entandrophragma angolense, 130 Enterococcus faecalis, 119 Enterolobium cyclocarpum, 113, 187, 320 Erythrophleum africanum, 209, 210 Erythrophleum guineense, 209 Erythrophleum suaveolens, 209 Escherichia coli, 113 Eucalyptus, 1, 24, 25, 30, 81, 144 Euodia pentacocca, 181 European plum, 141 Eutassa heterophylla, 123

f Fagara zanthoxyloides, 131 Faidherbia albida, 10, 52 False lebbeck, 69 False sago, 204 False sasswood, 137 Fern palm, 204 Feronia elephantum, 89 Feronia limonia, 89, 90, 318 Ferula foetida, 131 Fevertree, 52 Ficus sycomorus, 165 Firmiana barteri, 65 Firmiana platanifolia, 65 Firmiana simplex, 65 Flamboyant, 84 Flame bottletree, 64 Flame of the forest, 126 Flame kurrajongs, 64 Flametree, 64, 84 Flat-top thorn, 51 Flindersia australis, 211 Flindersia maculosa, 210, 211 Flood-plain acacia, 47 Floss silktree, 118 Foreigner’s tree, 245 Forest siris, 69 French tamarind, 113

Frywood, 68 Fusarium incarnatum, 115 Fusarium semitectum, 115 Fusicoccum aesculi, 123

g Gage, 141 Galedupa indica, 134 Galedupa pinnata, 134 Gammalu, 144 Garcinia kola, 358 Gardenia erubescens, 165 Garden plum, 141 Garuga pinnata, 211, 212 Gean, 138 Gebang palm, 202 Gedunohor, 130 Geijera muelleri, 212 Geijera paniculata, 212 Genip, 117 Geodorum citrinum, 213 Geodorum nutans, 212 Geodorum purpureum, 213 Ghattitree, 76 Golden apple, 66, 98, 319 Golden shower, 186 Golden wattle, 51 Gossampinus malabaricus, 177 Grapholita molesta, 28 Gray carobean, 208 Green wattle, 45 Grevillea agrifolia, 132 Grevillea candelabroides, 132 Grevillea robusta, 132, 133 Grevillea striata, 14, 132 Grevillea wickhamii, 132 Grewia tiliaefolia, 220 Grey carrobean, 234 Guamacho gum, 136 Guayamochil, 111 Guilandina moringa, 225 Gum arabic, 1–3, 5, 8–13, 16–19, 24, 34, 35, 39, 40–42, 54, 55, 77, 78, 84, 89, 90, 94, 95, 97, 98, 105–108, 115, 116, 122, 123, 127, 137, 138, 140, 142, 175, 200, 207, 209, 216, 217, 219, 224, 228, 230, 258–272, 274–280, 284–286, 294, 297, 311–317, 319–323, 327–329, 332–335, 338, 342, 347–348, 351, 353, 354, 356–362, 365, 368 Gum arabic tree, 39 Gum ghatti, 1, 2, 3, 18, 19, 41, 76, 81, 200, 224, 243, 270, 277, 279, 294, 302, 303, 304, 305, 313, 328, 335, 359, 360, 362, 363, 365, 366, 367, 368

Organism Name Index  ◾  377 Gum kino, 98, 127, 144, 320 Gum num, 202 Gum saracocolla, 228 Gum tragacanth, 1, 2, 3, 5, 13, 17, 18, 19, 41, 52, 54, 55, 59, 66, 78, 80, 108, 120, 215, 216, 229, 230, 262, 264, 267, 269, 270, 277, 278, 279, 294, 296, 297, 302, 303, 304, 313, 314, 321, 327, 329, 332, 335, 342, 348, 353, 354, 356, 361, 365, 366

h Haematostaphis barteri, 231 Hakea gibbosa, 213 Halomonas, 279 Hamilton’s mombin, 82 Harakeke, 136 Hard quandong, 208 Harige hakea, 213 Heptaleurum volkensii, 231 Heritiera trifoliolata, 238 Hibiscus populneoides, 118 Hibiscus populneus, 118 Hibiscus sabdariffa, 11 Hibiscus simplex, 65 Hildegardia barteri, 65 Honeyberry, 117 Hookthorn, 49 Horseradish tree, 225 Huisache, 46 Hymenaea courbaril, 5, 16, 113 Hymenocardia acida, 209

i Illawara flametree, 64 Illipe latifolia, 134 Indian almond, 60 Indian baelfruit, 66 Indian beech, 134 Indian kapok, 177 Indian kino, 144 Indian kino tree, 144 Indian-laburnum, 186 Indian lilac, 93 Indian pea, 98 Indian redwood, 235 Indian tamarind, 236 Indian tragacanth, 57 Indian walnut, 73 Indian wood apple, 89 Inga saman, 111 Inga stipularis, 116 Intsia africana, 170 Ironwood, 95, 133, 238 Isoberlinia globiflora, 176

j Jand, 95 Jandi, 95 Japanese varnishtree,65 Jatropha moluccana, 73 Java olive, 60 Jew plum, 98 Jhingangummi, 219 Judas tree, 127 Jujube, 148 Julbernardia globiflora, 176 Jumping cholla, 120

k Kamol, 131 Kane, 173 Kapok, 190 Kapok tree, 190, 320 Karanja, 134 Karaya, 1–3, 5, 12, 13, 17–19, 39, 42, 57–59, 63, 66, 76,77, 101, 110, 127, 198, 217, 242, 257, 262, 264, 267, 270, 271, 277, 294, 296–299, 302–304, 313, 321, 327–331, 334–339, 341, 357, 360 Karroothorn, 47 Karumtree, 134 Kastnia elegans, 108 Kavrak, 131 Khaya anthotheca, 215 Khaya grandifoliola, 214, 215, 328 Khaya gum, 215, 216 Khaya madagascariensis, 214, 215 Khaya senegalensis, 172, 214, 216 Kher, 39 Kilytree tamarind, 236 Kino gum, see Gum kino Kiwi, 123 Kiwifruit, 123 Koa, 175 Koko, 68 Korari, 136 Kula, 212

l Laddoo, 4 Laddu, 4 Lagerstroemia parviflora, 217, 218, 219 Laguncularia racemosa, 110 Lannea coromandelica, 31, 219, 220, 319 Lannea humilis, 219, 220 Lannea microcarpa, 165 Larix occidentalis, 122 Lasiodiplodia theobromae, 28, 33, 34

378  ◾  Organism Name Index Lasiodiplodia triflorae, 34 Lebbek, 68 Lebbektree, 68 Leopard tree, 210 Leopardwood, 210 Leucaena collinsii, 115 Leucaena leucocephala, 116 Leucaena pallida, 116 Limonia acidissima, 89 Linepithema humile, 280 Liquidambar, 365 Lomaria eriopus, 145 Lontaro, 180 Lophira alata, 133 Lophira procera, 133 Lovetree, 127 Lucky nut, 245 Lucuma mammosa, 121 Lumbangtree, 73 Lysiloma acapulcense, 116, 187 Lysiphyllum carronii, 175

m Macrozamia spiralis, 221 Madagascar mahogany, 214 Madhuca indica, 134 Madhuca longifolia, 134 Madhuca longifolia var. latifolia, 134 Madras thorn, 111 Maiden’s blush, 234 Maize, 10, 314 Makopa, 98 Malabar kino, 144 Malpighia glabra, 266 Mandingo kola, 197 Mangifera glauca, 86 Mangifera indica, 90, 91, 92, 319 Mangifera pinnata, 100 Mango, 34, 90, 266 Mangrove, 117 Manila tamarind, 111 Manilkara achras, 121 Manilkara zapota, 6, 8, 121 Manilkara zapotilla, 121 Manna, 55 Margosa, 93 Marke, 173 Marking nut tree, 233 Marshallus bondari, 34 Maximilianea gossypium, 65 Mazzard cherry, 138 Melia azadirachta, 93 Melia azedarach, 221, 222, 223, 224 Melia azedarach var. japonica, 221

Melia toosendan, 221 Melicocca bijuga, 117 Melicocca oliviformis, 147 Melicoccus bijugatus, 117, 118 Melicope neurococca, 224 Mesquite, 95 Mexican cedar, 189 Microcebus, 281 Miliusa tomentosa, 231 Millettia pinnata, 134 Milo, 118 Mimosa, 45 Mimosa amara, 72 Mimosa catechu, 43 Mimosa chinensis, 71 Mimosa cineraria, 95 Mimosa cinerea, 207 Mimosa colubrina, 106 Mimosa decurrens, 45 Mimosa farnesiana, 46, 47 Mimosa glomerata, 207 Mimosa juliflora, 95 Mimosa lebbeck, 68 Mimosa leucophloea, 48 Mimosa mangensis, 115 Mimosa marginata, 71 Mimosa mellifera, 49 Mimosa nutans, 207 Mimosa odoratissima, 69 Mimosa oerfota, 49 Mimosa procera, 69 Mimosa saman, 111 Mimosa senegal, 39 Mimosa sirissa, 68 Mirza, 281 Mitragyna inermis, 231 Moatree, 134 Monilinia fructigena, 28 Monilinia laxa, 28 Monkey-bread tree, 163 Monkeypod, 113 Monkeysoap, 113 Moringa, 225 Moringa moringa, 225 Moringa oleifera, 225, 227, 228, 313, 320 Moringa pterygosperma, 225 Mountain ebony, 81 Mountain-hickory, 50 Mowra buttertree, 134 Mucara, 57 Mucuna flagellipes, 170, 171 Myall acacia, 50 Myrcia cf. fallax, 282 Myrobalan, 101 Myrobalanus bellirica, 101 Mystroxylon aethiopicum, 135

Organism Name Index  ◾  379 n Nariyal, 195 Naseberry, 121 Neem, 93, 94, 95, 319 Neem gum, 222, 319 Neopanax colensoi, 228 Néverdié, 225 New Zealand flax, 136 New Zealand hemp, 136 Nhom hin, 191 Nhom khao, 191 Nimtree, 93 Norfolk Island pine, 123 Northern bean tree, 175 Nycticebus coucang, 281

o Opopanax, 46 Opopanax chironium, 14 Opuntia ficus-indica, 120, 278 Opuntia fulgida, 120 Opuntia megacantha, 120 Orchid tree, 79 Orchidtree, 81 Otaheite apple, 98 Owenia venosa, 228

p Pachycereus hollianus, 136 Pacific rosewood, 118 Pahudia africana, 170 Palma, 180 Palmira, 180 Palmyra palm, 180 Palmyrapalme, 180 Panax colensoi, 228 Panax elegans, 228 Panax sambucifolius, 137 Paperbarkthorn, 51 Parapiptadenia rigida, 106, 108, 109 Parkia bicolor, 136 Parkia biglobosa, 165 Parkinsonia praecox, 16, 107, 320 Pastinaca opoponax, 14 Patana oak, 185 Peach, 29, 143 Peacock flower, 84 Penaea sarcocolla, 228 Pentaceras australis, 229 Pentaptera tomentosa, 238 Pepper-tree wattle, 46 Pereskia guamacho, 16, 136

Persian lilac, 221 Persian manna, 55 Persica vulgaris, 143 Petaurus norfolcensis, 281, 282 Phaner, 281 Phaseolus coccineus, 280 Phobi nut tree, 233 Phoenix tree, 65 Phoracantha semipunctata, 30 Phormium tenax, 136 Phytophthora citrophthora, 32, 33 Phytophthora drechsleri, 115 Piliostigma thonningii, 175 Piper nigrum, 272 Piptadenia, 320 Piptadenia africana, 137 Piptadenia cebil, 105, 320 Piptadenia colubrina, 106 Piptadenia macrocarpa, 105 Piptadenia rigida, 108 Piptadeniastrum africanum, 137 Pithecellobium caraboboense, 115 Pithecellobium dulce, 111, 112 Pithecellobium leucospermum, 115 Pithecellobium mangense, 16 Pithecellobium minutum, 46 Pithecellobium saman, 111 Pithecellobium vincentis, 115 Pittosporum phillyreoides, 137 Plum, 141 Plum gum, 142, 230 Plum tree, 28, 34, 138, 140, 141 Plutella xylostella, 315–316 Poinciana coriaria, 106 Poinciana regia, 84 Polyclada, 232 Polynesian plum, 98 Polyscias elegans, 228 Polyscias sambucifolia, 137 Pongam, 134 Pongamia glabra, 134 Pongamia mitis, 134 Pongamia pinnata, 134 Poonga oil tree, 134 Popinac, 46 Portia tree, 118 Portulaca oleracea, 278 Pouteria mammos, 121 Prosopis, 12, 95, 97, 319, 320 Prosopis chilensis, 12 Prosopis cineraria, 95, 96 Prosopis flexuosa, 12 Prosopis horrida, 95 Prosopis juliflora, 95 Prosopis juliflora var. horrida, 95 Prosopis juliflora var. juliflora, 95

380  ◾  Organism Name Index Prosopis nigra, 12 Prosopis spicigera, 95 Prosopis vidaliana, 95 Protium aracouchinni, 282 Prune plum, 141 Prunus amygdalus, 229 Prunus armeniaca, 140, 141 Prunus armeniaca var. vulgaris, 140 Prunus avium, 25, 26, 138, 139 Prunus avium var. aspleniifolia, 138 Prunus cerasus, 27, 140, 320 Prunus cerasus var. avium, 138 Prunus communis, 229 Prunus domestica, 28, 141, 142 Prunus dulcis, 27, 229, 230 Prunus dulcis var. amara, 229 Prunus eburnea, 229, 320 Prunus laurocerasus, 140 Prunus macrophylla, 138 Prunus persica, 141, 143 Prunus persica Batsch cv. Benishimizu, 29 Prunus spinosa, 143, 224 Prunus virginiana, 140 Pseudocedrela chevalieri, 230 Pseudocedrela kotschyi, 230, 231 Pseudomonas syringae, 231 Pterocarpus, 5 Pterocarpus erinaceus, 172 Pterocarpus marsupium, 6, 144 Purging cassia, 186 Purple bauhinia, 79 Puya chilensis, 12, 108, 147 Puya coarctata, 108

q Queen sago, 204 Queensland ebony, 175

r Racosperma bakeri, 43 Racosperma binervatum, 43 Racosperma dealbatum, 45 Racosperma decurrens, 45 Racosperma harpophyllum, 47 Racosperma maidenii, 49 Racosperma oswaldii, 50 Racosperma pendulum, 50 Racosperma penninerve, 50 Racosperma vernicifluum, 52 Raintree, 113 Red bauhinia, 175 Red cedar, 83 Red cotton tree, 177 Red mangrove, 117 Red sandalwood tree, 168

Red silk-cotton, 177 Redwood, 137 Repoh,191 Rhamnus zizyphus, 148 Rhetinophloeum viride, 107 Rhizobium, 9, 34 Rhizophora mangle, 117 Rhizopus, 297 Rhodoturula mucilaginosa, 232 Rhus mysurensis, 220–221 Robinia grandiflora, 98 Rochaek, 131 Rock hakea, 213 Rônier, 180 Root beetle, 34 Rose almond, 228 Royal poinciana, 84

s Saccopetalum tomentosum, 231 Saguinus bicolor bicolor, 281, 282 Saguinus oedipus, 283 Salmalia malabarica, 177 Salmonella typhimurium, 235 Saltera sarcocolla, 228 Samanea saman, 16, 111, 114 Sandalwood tree, 168 Sapindus laurifolius, 145 Sapindus trifoliatus, 145 Sapistan, 200 Sapodilla, 121 Sapodilla tree, 8 Sapota aclzras, 147 Sapota zapotilla, 121 Sapote, 121 Sarcostemma brevistigma, 231 Sassyr, 131 Scarlet wistaria tree, 98 Schefflera, 231 Schefflera volkensii, 231, 232, 320 Schinus limonia, 89 Sclerocarya birrea, 165, 232, 233 Sclerocarya birrea subsp. birrea, 232 Sclerocarya birrea subsp. caffra, 232 Sclerocarya caffra, 232 Scrub hickory, 229 Seaside mahoe, 118 Sebesten plum, 200 Securinega virosa, 221 Selu, 200 Semecarpus anacardium, 233 Senegal gum, 39, 328 Senegalia senegal, 39, 328 Senna nicaraguensis, 187 Sesban grandiflorus, 98 Sesbania grandiflora, 98, 99

Organism Name Index  ◾  381 Shittimwood, 42 Siat-ka, 191 Siberian apricot, 140 Sichuan pagoda-tree, 221 Silk cottontree, 65, 190 Silk-cotton tree, 177 Silktree, 71 Silky elm, 238 Silky oak, 132 Silver tree, 238 Silver wattle, 45 Simal, 177 Siristree, 68 Sloanea australis, 208, 234, 235 Sloanea woollsii, 234 Smooth chain-fruit cholla, 120 Soapberry tree, 125 Solanum lycopersicum, 315 Sonoran jumping cholla, 120 Sophora capensis, 246 Sophora oroboides, 246 Sorghum bicolor, 118 Sour cherry, 27 Soymida febrifuga, 235, 236 Soymida roupalifolia, 230 Spanish cedar, 189 Spanish lime, 117 Sphingomonas paucimobilis, 224 Spondias birrea, 232 Spondias cytherea, 98 Spondias dulcis, 98, 319 Spondias mangifera, 100 Spondias mombin, 319, 320 Spondias pinnata, 100, 101, 102, 320 Spondias purpurea, 319 Stangeria eriopus, 145 Stangeria paradoxa, 145 Staphylococcus aureus, 113, 119 Sterculia acerifolia, 64 Sterculia barteri, 65 Sterculia cinerea, 321 Sterculia cordifolia, 197 Sterculia foetida, 60, 61, 299 Sterculia guttata, 61 Sterculia platanifolia, 65 Sterculia quadrifida, 62 Sterculia quinqueloba, 328 Sterculia scaphigera, 62 Sterculia setigera, 63, 64, 66, 209, 215, 216, 217, 314 Sterculia tomentosa, 63 Sterculia tragacantha, 63, 64 Sterculia urens, 57, 58, 59, 60, 63, 66, 314 Sterculia villosa, 63, 64, 314 Stereospermum kunthianum, 209 Stereum purpureum, 28 Strawberry peach, 123 Styrax, 365

Styrax officinalis, 313 Sudanese gum arabic, 39 Sudan teak, 200 Suntang puteh, 191 Surian batu, 191 Sweet acacia, 46 Sweet almond, 229 Sweet cherry, 25, 26, 138 Sweet inga, 111 Sweet-thorn, 47 Swietenia chikrassa, 191 Swietenia chloroxylon, 84 Swietenia febrifuga, 235 Swietenia senegalensis, 214 Sydney wattle, 45 Symphonia globulifera, 146, 147 Syringa berrytree, 221

t Tabayer, 197 Tala palm, 180 Talh, 42 Taliera gebanga, 202 Talisia oliviformis, 147 Tall albizia, 69 Tamarindus indica, 165, 236, 237 Tarrietia argyrodendron, 238 Tawyinma, 191 Terminalia, 238 Terminalia alata, 238, 239, 240, 243 Terminalia altissima, 238 Terminalia arjuna, 234, 238, 239, 240, 243 Terminalia avicennoides, 173 Terminalia bellirica, 78, 101, 103, 238, 239, 239, 240, 243, 244, 295, 299 Terminalia catappa, 238, 239, 240, 243, 299 Terminalia chebula, 238, 240, 241, 243 Terminalia chebula var. tomentella, 78 Terminalia coriacea, 238 Terminalia crenulata, 238, 240, 243, 299, 321 Terminalia elliptica, 78, 238 Terminalia glaucescens, 174 Terminalia macrocarpa, 238 Terminalia macroptera, 238 Terminalia sericea, 238, 240, 243 Terminalia stuhlmannii, 238 Terminalia superba, 238, 240, 243 Terminalia tomentosa, 238 Theobroma cacao, 110, 118 Theobroma cacao subsp. cacao forma leiocarpum, 110 Theobroma cacao subsp. cacao forma pentagonum, 110 Theobroma cacao subsp. sphaerocarpum, 110 Theobroma leiocarpum, 110

382  ◾  Organism Name Index Theobroma pentagonum, 110 Theobroma sativum, 110 Theobroma sphaerocarpum, 110 Thespesia macrophylla, 118 Thespesia populnea, 118, 119 Thespesia populneoides, 118 Thevetia neriifolia, 245 Thevetia peruviana, 245, 246 Thirtythorn, 42 Thouinia hemiglauca, 174 Three-leaf soapberry, 145 Threethorn acacia, 39 Tieghemopanax sambucifolius, 137 Tieghemopanax sambucifolius var. angustifolius, 137 Toddy palm, 180 Toon, 83 Toona australis, 83 Toona ciliata, 69, 83, 190, 318 Toontree, 83 Trachylobium verrucosum, 5 Tragacanth, 52 Tragacanth milk-vetch, 52 Trypanosoma cruzi, 187 Tulip tree, 118 Tumboa bainesii, 148 Tylosema fassoglense, 175, 176

Wattle gum, 1, 4 98 Weeping myall, 50 Welwitschia bainesii, 148 Welwitschia mirabilis, 148 Western larch, 122 West Indian ben, 225 West Indian cedar, 189 Whistling tree, 42 White buttonwood, 110 White mangrove, 110 White silk cottontree, 190 White siristree, 69 Whitethorn, 52 Whitewood, 174 Wild almond, 125 Wild cherry, 26 Wild lemon, 184 Willow acacia, 51 Willow pittosporum, 137 Wine palm, 180 Winterthorn, 52 Wirilda, 51 Wi tree, 98 Women’s tongue tree, 68 Wood apple, 89 Wrightia tinctoria, 221

u

x

Uganda powder-flask fruit, 174 Ulmus, 24 Umbia, 231 Umbrella acacia, 50 Umbrella bush, 50 Umbrellathorn, 51

Xanthorrhoea, 5, 6 Xanthorrhoea preissii, 6 Ximenia aegyptiaca, 125 Ximenia americana, 165

v Vachellia densiflora, 46 Vachellia farnesiana, 46 Valsaria insitiva, 28 Varnishtree, 73 Vasconcellea pubescens, 337 Vegetable hummingbird, 98 Virgilia capensis, 246, 247 Virgilia oroboides, 246, 247 Vitellaria paradoxa, 165 Voryong nhom, 191

w Watsonia borbonica, 147 Watsonia versfeldii, 147

y Yellow carabeen, 234 Yellow oleander, 245 Yellow plum, 98 Yinma, 191

z Zamia spiralis, 221 Zanthoxylum senegalense, 131 Zanthoxylum zanthoxyloides, 131 Zebrawood, 181 Ziziphus jujuba var. spinosa, 148 Ziziphus mauritiana, 165 Zizyphus glabrata, 221 Zizyphus jujuba, 149

General Index a Absolute viscosity, 17 Acacia gums, see Gum arabic and other Acacia gums ACC, see 1-Amino-cyclopropan-l-carboxylic acid Acetic acid, 59, 66, 242 Aching gums, 176 Acid hydrolysis Grevillea robusta gum, 132 gum resistant to, 63 Acidification of oil wells, 360 Adhesives, 269 Adhesives, water-based, 293–310 adhesion mechanisms of hydrogels, 306–307 biological applications, 296–299 bioelectrodes, 298 denture fixatives, 293, 297–298 exudate patches for transdermal drug delivery, 298–299 ostomy devices, 296–297 exudates as wet glues, 302–305 gums as adhesives, 294 hydrocolloid adhesion tests, 299–301 industrial uses of exudate glues, 294–296 general, 294 paper, 294 wood and furniture, 294–296 African gums, see Asiatic, African, and Australian gums Agar 5, 259, 279, 296, 314, 331, 334, 335, 339, 360, 364, 368 gum solution identification, 335 interaction with polysaccharide, 279 AGPs, see Arabinogalactan proteins Agroforestry, 9, 10, 11, 12, 48, 52, 97, 111, 113 Alcohol-wetted exudates, 328 Alditol, 340 Aldobiouronic acids, 76, 219, 230 Alginic acid, 5, 279 Alginate, interaction with polysaccharide, 279

Alkaloids, 145, 172, 183, 210, 231 Allergy symptoms, 285, 317 Amino acid bioavailability of, 285 content, gum solution, 16 deficient, 169 1-Amino-cyclopropan-l-carboxylic acid (ACC), 29, 32 Ammonium nitrate/fuel oil (ANFO), 363 Ammonium sulfate, precipitation reaction using, 335 Amphotericin, 235, 317 Anacardic acid, 105 Analysis and identification of gum exudates, 327–342 capillary electrophoresis, 341–342 chromatographic techniques to identify plant gums, 339–340 Fourier transform-Raman spectroscopy of gum exudates, 340–341 group analysis and identification schemes, 334–338 Cetavlon group identification scheme, 337–338 characteristic reactions of gums, 334–337 industrial gums, 327–334 alcohol precipitability, 329 antibodies for identification of gum arabic and other polysaccharides, 333–334 identification of gums in specific foods, 332–333 microscopic identification, 329–332 water solubility, 327–329 IR spectroscopy, 338–339 ANFO, see ammonium nitrate/fuel oil Animal food, 47, 48, 50 , 52, 84, 280 Animal food, gum exudates in, 280–283 insects, 280–281 mammals and primates, 281–283 Animal glues, 294, 295, 341 Ant, 280, 281 Anthelmintic, 68, 173, 174, 197, 318 Anthocyanin, 29, 264, 265 Antiallergenic, 231 Antibodies, 285, 333–334 Antidote, 97, 130, 319

383

384  ◾  General Index Antifungal activities, 173, 174 Antioxidant, 118, 165, 177, 185, 186, 192, 234, 235, 238, 243, 274, 315 Antimony trisulfide, 349 Antiplasmodial, 173, 235 Antitrypanosomal, 174 Apache, 97 Aphrodisiac, 179, 235 Arabic, see Gum arabic and other Acacia gums Arabic acid, 317 L-Arabinofuranose, 53, 76, 131, 147, 173 α-L-Arabinofuranosyl, 117 Arabinogalactan, 16, 27, 41, 53, 54, 122, 213, 294, 317 323, 354 Arabinogalactan proteins (AGPs), 41, 278 L-Arabinopyranosyl, 209 Arabinose, 41, 54, 66, 98, 105, 107, 110, 111, 117, 120, 132, 136, 140, 183, 219, 230, 232, 240, 241, 317, 342 L-Arabinose, 43, 68, 76, 89, 94, 97, 98, 101, 108, 117, 118, 120, 121, 122, 123, 126, 131, 132, 135, 138, 139, 140, 141, 142, 143, 147, 173, 193, 204, 209, 213, 215, 219, 224, 226, 230 Arachidonic acid, 267 Arsenic trisulfide, 349 Ascorbic acid, 264, 270 Asiatic, African, and Australian gums, 123–149, see also Indian or Asiatic gums and their botanical sources chemical properties, Zanthoxylum zanthoxyloides, 131 chemical structure, Watsonia versfeldii, 147 commercial availability Balanites aegyptiacus, 125 Butea monosperma, 127 Cissus populnea, 127 Ferula foetida, 131 Grevillea robusta, 132 Millettia pinnata, 135 Pereskia guamacho, 136 Phormium tenax, 137 Prunus avium, 140 Prunus domestica, 142 Pterocarpus marsupium, 145 Sapindus trifoliatus, 145 Symphonia globulifera, 147 commercial and functional uses for other parts of tree Actinidia deliciosa, 123 Araucaria heterophylla, 125 Balanites aegyptiacus, 125 Butea monosperma, 127 Cercis siliquastrum, 127 Dicorynia paraensis, 130 Diospyros mespiliformis, 130 Entandrophragma angolense, 131 Grevillea robusta, 132 Madhuca longifolia, 134

Millettia pinnata, 135 Pereskia guamacho, 136 Phormium tenax, 136 Piptadeniastrum africanum, 137 Polyscias sambucifolia, 138 Prunus avium, 140 Pterocarpus marsupium, 145 Sapindus trifoliatus, 145 Symphonia globulifera, 147 Talisia oliviformis, 147 Ziziphus jujuba, 148 common names Actinidia deliciosa, 123 Araucaria heterophylla, 123 Balanites aegyptiacus, 125 Brabejum stellatifolium, 125 Butea monosperma, 126 Cercis siliquastrum, 127 Dicorynia paraensis, 130 Entandrophragma angolense, 130 Ferula foetida, 131 Grevillea robusta, 132 Lophira alata, 133 Madhuca longifolia, 134 Millettia pinnata, 134 Parkia bicolor, 136 Pereskia guamacho, 136 Phormium tenax, 136 Piptadeniastrum africanum, 137 Pittosporum phillyreoides, 137 Prunus armeniaca, 140 Prunus avium, 138 Prunus domestica, 141 Prunus persica, 143 Prunus spinosa, 143 Pterocarpus marsupium, 144 Sapindus trifoliatus, 145 Symphonia globulifera, 146 Ziziphus jujuba, 148 distributional range Actinidia deliciosa, 123 Araucaria heterophylla, 124 Balanites aegyptiacus, 125 Butea monosperma, 126 Cercis siliquastrum, 127 Dicorynia paraensis, 130 Diospyros mespiliformis, 130 Entandrophragma angolense, 130 Ferula foetida, 131 Grevillea robusta, 132 Lophira alata, 134 Madhuca longifolia, 134 Millettia pinnata, 134 Mystroxylon aethiopicum, 135 Parkia bicolor, 136 Pereskia guamacho, 136 Phormium tenax, 136

General Index  ◾  385 Piptadeniastrum africanum, 137 Pittosporum phillyreoides, 137 Polyscias sambucifolia, 137 Prunus armeniaca, 140 Prunus avium, 138 Prunus domestica, 141 Prunus persica, 143 Prunus spinosa, 143 Pterocarpus marsupium, 144 Sapindus trifoliatus, 145 Stangeria eriopus, 146 Symphonia globulifera, 146 Talisia oliviformis, 147 Watsonia versfeldii, 147 Welwitschia mirabilis, 148 Ziziphus jujuba, 148 economic importance Araucaria heterophylla, 123 Dicorynia paraensis, 130 Diospyros mespiliformis, 130 Ferula foetida, 131 Lophira alata, 134 Madhuca longifolia, 134 Parkia bicolor, 136 Phormium tenax, 136 Prunus armeniaca, 140 Prunus avium, 138 Prunus domestica, 141 Prunus persica, 143 Prunus spinosa, 143 Sapindus trifoliatus, 145 Stangeria eriopus, 145 Ziziphus jujuba, 148 exudate Watsonia versfeldii, 147 Zanthoxylum zanthoxyloides, 131 exudate appearance Actinidia deliciosa, 123 Araucaria heterophylla, 124 Balanites aegyptiacus, 125 Butea monosperma, 126 Cissus populnea, 127 Commiphora mollis, 129 Ferula foetida, 131 Grevillea robusta, 132 Madhuca longifolia, 134 Pereskia guamacho, 136 Phormium tenax, 136 Polyscias sambucifolia, 137 Prunus avium, 138 Prunus persica, 143 Pterocarpus marsupium, 144 Sapindus trifoliatus, 145 Stangeria eriopus, 146 Symphonia globulifera, 146 Welwitschia mirabilis, 148 Ziziphus jujuba, 148

exudate availability, Madhuca longifolia, 134 exudate color Dicorynia paraensis, 130 Millettia pinnata, 135 Prunus avium, 138 Prunus domestica, 141 Prunus persica, 143 Pterocarpus marsupium, 144 Symphonia globulifera, 147 exudate properties, Cercis siliquastrum, 127 exudate solubility, Prunus domestica, 141 geographic distribution Araucaria heterophylla, 124 Brabejum stellatifolium, 125 Cissus populnea, 127 Commiphora mollis, 129 Diospyros mespiliformis, 130 Millettia pinnata, 134 Pterocarpus marsupium, 144 Welwitschia mirabilis, 148 Zanthoxylum zanthoxyloides, 131 gum Prunus armeniaca, 140 Pterocarpus marsupium, 144 gum characteristics, Araucaria heterophylla, 125 gum chemical characteristics Actinidia deliciosa, 123 Brabejum stellatifolium, 126 Dicorynia paraensis, 130 Ferula foetida, 131 Grevillea robusta, 132 Millettia pinnata, 135 Mystroxylon aethiopicum, 135 Parkia bicolor, 136 Pereskia guamacho, 136 Phormium tenax, 137 Prunus armeniaca, 141 Prunus avium, 138 Prunus domestica, 141 Prunus persica, 143 Prunus spinosa, 143 Pterocarpus marsupium, 145 gum water solubility Araucaria heterophylla, 124 Butea monosperma, 127 Cissus populnea, 127 Dicorynia paraensis, 130 Ferula foetida, 131 Grevillea robusta, 132 Millettia pinnata, 135 Mystroxylon aethiopicum, 135 Parkia bicolor, 136 Pereskia guamacho, 136 Pittosporum phillyreoides, 137 Polyscias sambucifolia, 138 Prunus avium, 138 Pterocarpus marsupium, 145

386  ◾  General Index Sapindus trifoliatus, 145 Symphonia globulifera, 147 similar gums Cissus populnea, 127 Prunus avium, 140 Prunus domestica, 142 synonyms Actinidia deliciosa, 123 Araucaria heterophylla, 123 Balanites aegyptiacus, 125 Butea monosperma, 126 Cercis siliquastrum, 127 Commiphora mollis, 129 Diospyros mespiliformis, 130 Lophira alata, 133 Madhuca longifolia, 134 Millettia pinnata, 134 Mystroxylon aethiopicum, 135 Piptadeniastrum africanum, 137 Polyscias sambucifolia, 137 Prunus armeniaca, 140 Prunus avium, 138 Prunus persica, 143 Sapindus trifoliatus, 145 Stangeria eriopus, 145 Talisia oliviformis, 147 Welwitschia mirabilis, 148 Zanthoxylum zanthoxyloides, 131 Ziziphus jujuba, 148 tree Araucaria heterophylla, 124 Brabejum stellatifolium, 125 Zanthoxylum zanthoxyloides, 131 uses, Brabejum stellatifolium, 126 Aspartic acid, 174 Astringent, 5, 6, 98, 127, 144, 145, 179, 185, 190, 191, 200, 227, 320 Atherosclerosis, 234 Australian gums, see Asiatic, African, and Australian gums Ayurveda, 234, 312

b Bakery products, , 2, 263, 269 Balsam, 4 Baobab, 64, 163, 165, 166, 167, 168 Bark, 1, 3, 6, 8, 24, 26, 30, 31, 34, 39, 40, 41, 58, 59, 64, 66, 68, 76, 79, 81, 82, 89, 90, 95, 98, 101, 106, 107, 108, 111, 115, 117, 119, 122, 123, 125, 126, 130, 131, 132, 135, 141, 144, 145, 146, 164, 165, 171–173, 175–177, 181, 183, 185, 193, 204, 209, 213, 217, 219, 220, 224, 227, 230, 231, 232, 233, 235, 240, 243, 246, 282, 312, 318, 319, 321, 322, 328, 352, 361 Bassora gum, 52, 78, 140

Bassorin, 53, 54 Beauty aids, 95, 224, 319 Bee plant, 45, 47, 140, 229 Beer, 2, 130, 270, 279 Beetle, 30, 34, 115, 124, 232, 280 Belt, 10, 35, 127 Bengal quince, 66, 67 Beta-glucan, interaction with polysaccharide, 279 Beverage base, 48, 49, 90, 123, 134, 140, 141, 143, 180, 236 Beverages, 2, 18, 41, 42, 100, 105, 165, 264, 270, 278, 279, 342 Bible, 1 Bilharzia, 125 Binders and special coatings, 361 binders for insecticides, 361 glaze binders, 361 non-glare coatings for windshields, 361 Bioelectrodes, 59, 293, 296, 298 Biomass, 10, 11 Biotechnology, see Medical, cosmetic and biotechnological uses of gum exudates Biscuits, 258, 269 Bitter almond, 125, 229 Blennorrhagoeia, 176 Black pepper, 271, 272 Boat, 80, 84, 111, 117, 119, 131, 176, 183, 217 Borers, 30 Bowel, 132, 179, 314, 320 Bread, 2, 263, 269, 274 Breadcrumb, 269 Bronchitis, 111, 113, 132, 320

c Calcium oxalate, 101, 120, 240 Cambium, 24, 25, 30, 31, 32, 76 Camel, 217 Cancer, 118, 119, 149, 234, 235, 243 Canker, 33, 34 Capillary electrophoresis (CE), 341–342, 348 Capsaicin, 274 Carbon nanohorn, 323 Carboxymethylcellulose (CMC), 263, 271, 277, 278, 294, 296, 313, 359, 360, 361, 362, 364, 368 Carboxymethylhydroxyethyl cellulose (CMHEC), 360 Cardiac glycosides, 113, 210, 246 Cardamom, 272 Cardol, 105 Carpusin, 145 Carrageenan, 5, 19, 260, 263, 277, 278, 279, 331, 332, 335, 360, 368 Carving, 84, 89, 165, 192 Cashew, 13, 33, 34, 104, 105, 111, 234, 294 Catechol, 145 Catheter, 6

General Index  ◾  387 Cattle, 69, 95, 97, 127, 171, 217, 220, 224 Cattle feed, 69 Cave paintings, 348 CE, see Capillary electrophoresis Cellulose-acetate membrane, 303, 304, 305 Ceramics, 79, 347, 354, 361, 364–365 Chagualic acid, 108 Cheese, 2, 59, 261, 264, 271, 274, 333 Cheese spread, 2, 59, 271, 333 Chewing gum, 1, 26, 121, 122, 258, 259 Chicle, 3, 121, 122, 257 Chitin, 279 interaction with polysaccharide, 279 Chitinase, 169 Chocolate, 2, 110, 258, 270, 333 Chromatographic techniques, plant gum identification using, 339–340 Citric acid, 354, 359 Citrus essential oil, 97 CLA, see Conjugated linoleic acid Cloth stiffener, 121 CMC, see Carboxymethylcellulose CMHEC, see Carboxymethylhydroxyethyl cellulose Coacervation, 267, 276, 315, 321, 322 Cocoa butter, 110 Colds, 111, 232, 312, 320 Cold-water-insoluble gel, 328 Colloquialisms, 1 Colorless gum, 12, 83, 84, 89, 122, 204, 213, 229, 232, 258, 267, 353 Conductive adhesive, 298 Confectionery, 82, 142, 230, 258–261, 272 Conjugated linoleic acid (CLA), 275 Constipation, 132, 314 Copal, 5, 183 Cornstarch, 6 Corn syrup, 260, 265 Corrosion, 347, 351, 357, 358 Corrosion inhibition, 347, 351, 357–358 Cosmetics, see Medical, cosmetic and biotechnological uses of gum exudates Cotton yarns, 127 Cough 3, 132, 140, 145, 219, 232, 235, 259, 311, 312, 320 Cumin, 272, 273, 274 Cyclodextrin, 274, 315 Cysteine, 169, 174 , 176

d Daphne paper, 72 Deacetylation, 17, 59 Deep-fat frying, 276–277 Dehydration techniques, juice, 265 Demulcent, 101, 179, 242, 311, 312 Denture adhesive, 59, 297 Denture fixatives, 293, 297–298

6-Deoxy-D-fructose, 63 6-Deoxyhexose, 76, 215 Desogen, 332 Detonation process, 363 Dextrin, 77, 269, 356 Dextrorotatory acidic arabinogalactans, 16 Dextrose equivalent, 265 Diarrhea, 6, 67, 89, 145, 172, 176, 210, 286, 312, 318, 319 Dietary fiber, 285 Differential thermal analysis (DTA), 342 Diuretic, 179 Drilling fluids, 79, 347, 359–360 Drum-drying, 267–268 DTA, see Differential thermal analysis

e Egyptian artifacts, 348 EI-MS, see Electron impact-mass spectrometry Electrical resistance, 358 Electron impact-mass spectrometry (EI-MS), 340 Electrostatic model theory, 306 Emetic, 179, 231 Emulsions, 41, 54, 55, 67, 169, 171, 190, 259, 261, 262, 267, 269, 270, 271, 275, 277–279, 312, 313, 318, 321, 322, 339, 348, 354, 361, 362, 368 Encapsulating, 42, 265, 266 Epilepsy, 125 Epithelial cells, 31, 32, 132 Ethylene-mediated response, 24 Ethephon, 23, 25, 27, 29, 31, 58, 76, 138, 140 Ethrel, 32, 33 Ethylene oxide, 41, 55, 297

f Fat-soluble vitamins, 270 Fehling, 131 Fibroblasts, 174 Firewood, 11, 49, 95, 125, 169, 183, 224 Fissures, 13, 96, 106, 126 Flatulence, 132 Flatulent colic, 132 Flavonoids, 113, 172, 210, 231 Flavor, 3, 41–43, 47, 55, 73, 131, 141, 193, 229, 236, 258–261, 263, 264, 266, 267, 269, 270, 271–272, 274, 276, 278, 315 fixatives and emulsifiers, 269–270 Flavoring materials, 43 Flax, 136, 137, 361 Flax fiber industry, 137 Flour, 4, 98, 111, 130, 207, 263, 269, 277, 341 Foam, 42, 111, 265, 270, 279–280, 321 Foaming ability, 42 Fodder, 43, 48, 50, 95, 116, 135, 201, 209, 217, 220

388  ◾  General Index Folk medicine, 40, 42, 47, 48, 49, 52, 55, 62, 75, 81, 82, 84, 101, 110, 111, 113, 117, 122, 123, 131, 134, 137, 138, 140, 145, 148, 177, 179, 180, 190, 193, 204, 222, 229, 233, 235, 318–320 Food additives, 5, 43, 47, 52, 97, 107, 116, 123, 130, 131, 141, 193, 229, 236, 257, 258, 259, 270, 284, 285 Food applications of plant exudates, 257–291 food uses of gum exudates, 258–280 adhesives, 269 bakery products, 269 beverages, 270 coacervation, 276 confectionery, 258–261 deep-fat frying, 276–277 drum-drying, 267–268 emulsions, 277–279 flavor fixatives and emulsifiers, 269–270 foam, 279 frozen products, 262–264 meat products, 270 microencapsulation, 271–275 miscellaneous, 270–271 salad dressings and sauces, 261–262 spray-drying, 264–267 wine, 268–269 gum exudates in animal food, 280–283 insects, 280–281 mammals and primates, 281–283 health-related aspects, 284–286 nutrition, 285–286 safety, 284–285 Fourier transform (FT)-Raman spectroscopy, 340–341 Freeze damage, 193 Freeze-dehydration, 265 Frozen, 3, 55, 332 Frozen products, 262–264 frozen dairy products, ice pops and sherbets, 264 frozen dough, 263 frozen sugar solutions, 263–264 Fruit, 67, 90, 138, 193 pulp, 2, 67, 89, 165, 200, 238, 318, 319 FT-Raman spectroscopy, see Fourier transform Raman spectroscopy Fucose, 53, 54, 342 L-Fucose, 94, 123, 224 Fuels charcoal, 11, 40, 43, 69, 79, 95, 108, 111, 116, 117, 125, 183, 236 fuelwood, 42, 43, 47, 68, 111, 113, 116, 133, 148, 232 Fungi, 23, 28, 33, 138, 174, 230, 280, 317, 340, 352 Fungicide, 29, 34 action, 238 α-L-Furanose, 107 Furniture, 67, 84, 98, 111, 131, 133, 147, 184, 190, 192, 217, 294, 295, 296, 366

g D-Galactan, 117, 209 D-Galactopyranose, 53, 76, 97, 131, 139, 140 β-D-Galactopyranose, 131 D-Galactopyranosyl, 209 β-D-Galactopyranosyl, 217 3-O-β-D-Galactopyranosyl-D-galactose, 76 Galactose, 53, 76, 105, 111, 120, 132, 140, 183, 240, 317 D-Galactose, 59, 68, 76, 89, 97, 101, 117, 120, 131, 138, 173, 193, 213, 226 Galacturonic acid, 53, 68, 76, 107, 110, 120, 136, 183, 241 D-Galacturonic acid, 59, 66, 101, 117, 120, 215 α-D-Galacturonic acid, 217 Gall, 117, 352, 353 Gallic acid, 145 Gas chromatography-mass spectrometry (GC-MS) analysis, 169, 268, 340, 341, 348, 365 Gas-liquid chromatography (GLC), 340 GC-MS analysis, see Gas chromatography-mass spectrometry analysis GDA, see Glutardialdehyde Gellan gum, 5, 360 Ghattic acid, 362 Glaze, 2, 79, 259, 269, 347, 361 Glaze binders, 361 GLC, see Gas-liquid chromatography Glove, 6 Glucomannan, 5, 279 2-O-(D-Glucopyranosideuronic acid)-D-xylose, 108 6-O-β-D-Glucopyranosyluronic acid-D-galactose, 76 2-O-(β-D-Glucopyranosyluronic acid)-D-mannose, 76 Glucose, 105, 110 Glucuronic acid, 41, 89, 105, 110, 120, 140, 173, 183, 240, 317, 342 D-Glucuronic acid, 43, 59, 76, 94, 121, 131, 139, 147, 192, 213, 224 α-D-Glucuronic acid, 107 β-D-Glucuronic acid, 107, 117, 173 Glues, see Adhesives, water-based Glutardialdehyde (GDA), 276, 315 Glycoprotein, 41, 279, 317, 322, 323, 340 Glycosaminoglycan, interaction with polysaccharide, 279 Glycosylphosphatidylinositol (GPI), 278 Golgi, 24, 32 GPI, see Glycosylphosphatidylinositol GRAS, 257, 284 Guar gum, 5, 16, 19, 277, 278, 279, 297, 334, 359, 360, 362, 363, 364 Guinea-worm, 125 Gum accroides, 5, 6

General Index  ◾  389 Gum arabic and other Acacia gums, 39–52 common names Acacia binervata, 43 Acacia catechu, 43 Acacia dealbata, 45 Acacia decurrens, 45 Acacia elata, 46 Acacia farnesiana, 46 Acacia jacquemontii, 47 Acacia karroo, 47 Acacia kirkii, 47 Acacia leucophloea, 48 Acacia mellifera, 49 Acacia modesta, 49 Acacia oswaldii, 50 Acacia pendula, 50 Acacia penninervis, 50 Acacia pycnantha, 51 Acacia retinodes, 51 Acacia salicina, 51 Acacia senegal, 39 Acacia seyal, 42 Acacia sieberiana, 51 Acacia xanthophloea, 52 Faidherbia albida, 52 distributional range Acacia abyssinica, 43 Acacia bakeri, 43 Acacia benthamii, 43 Acacia binervata, 43 Acacia catechu, 44 Acacia dealbata, 45 Acacia decurrens, 45 Acacia drepanolobium, 46 Acacia elata, 46 Acacia farnesiana, 47 Acacia ferruginea, 47 Acacia harpophylla, 47 Acacia jacquemontii, 47 Acacia karroo, 47 Acacia kirkii, 48 Acacia laeta, 48 Acacia leiophylla, 48 Acacia leucophloea, 49 Acacia maidenii, 49 Acacia mellifera, 49 Acacia modesta, 49 Acacia oerfota, 49 Acacia oswaldii, 50 Acacia pendula, 50 Acacia penninervis, 50 Acacia pycnantha, 51 Acacia retinodes, 51 Acacia salicina, 51 Acacia senegal, 40 Acacia seyal, 42 Acacia sieberiana, 51

Acacia stuhlmanii, 51 Acacia verniciflua, 52 Acacia xanthophloea, 52 Faidherbia albida, 52 economic importance Acacia catechu, 43 Acacia dealbata, 45 Acacia decurrens, 45 Acacia elata, 46 Acacia farnesiana, 47 Acacia jacquemontii, 47 Acacia karroo, 47 Acacia leucophloea, 48 Acacia mellifera, 49 Acacia modesta, 49 Acacia oerfota, 49 Acacia pendula, 50 Acacia pycnantha, 51 Acacia senegal, 40 Acacia seyal, 42 Faidherbia albida, 52 exudate, Acacia catechu, 44 exudate production, Acacia senegal, 40 exudate properties, Acacia senegal, 41 gum chemical characteristics Acacia senegal, 41 Acacia seyal, 43 synonyms Acacia bakeri, 43 Acacia binervata, 43 Acacia catechu, 43 Acacia dealbata, 45 Acacia decurrens, 45 Acacia elata, 46 Acacia farnesiana, 46 Acacia ferruginea, 47 Acacia jacquemontii, 47 Acacia karroo, 47 Acacia leucophloea, 48 Acacia maidenii, 49 Acacia mellifera, 49 Acacia oerfota, 49 Acacia oswaldii, 50 Acacia pendula, 50 Acacia penninervis, 50 Acacia senegal, 39 Acacia seyal, 42 Acacia sieberiana, 51 Acacia verniciflua, 52 Faidherbia albida, 52 tree and exudate, Acacia modesta, 49 Gum ghatti, 1, 2, 3, 18, 19, 76, 81, 200, 224, 243, 270, 277, 279, 294, 302, 303, 304, 305, 313, 328, 335, 359, 360, 362, 363, 365, 366, 367, 368 Gum karaya, see Karaya gum Gummosis, 23, 24, , 25, 26, 28, 29, 32–34, 100, 115, 117, 138, 141, 143, 193, 213, 322

390  ◾  General Index Gum-sucker, 1 Gum tragacanth, 1, 2, 3, 5, 13, 17, 18, 19, 41, 52, 54, 55, 59, 66, 78, 80, 108, 120, 215, 216, 229, 230, 262, 264, 267, 269, 270, 277, 278, 279, 294, 296, 297, 302, 303, 304, 313, 314, 321, 327, 329, 332, 335, 342, 348, 353, 354, 356, 361, 365, 366 Gum tragacanth and similar gums, 52–66 commercial availability Astragalus gummifer, 55 Cochlospermum religiosum, 66 Sterculia urens, 59 commercial and functional uses for other parts of tree Cochlospermum religiosum, 66 Sterculia urens, 60 common names Astragalus brachycalyx, 55 Astragalus gummifer, 52 Brachychiton acerifolius, 64 Cochlospermum religiosum, 65 Firmiana simplex, 65 Sterculia foetida, 60 Sterculia quadrifida, 62 Sterculia urens, 57 distributional range Astragalus brachycalyx, 55 Astragalus gummifer, 53 Astragalus heratensis, 56 Astragalus kurdicus, 56 Astragalus microcephalus, 57 Astragalus verus, 57 Brachychiton acerifolius, 64 Cochlospermum religiosum, 66 Firmiana simplex, 65 Sterculia foetida, 61 Sterculia guttata, 61 Sterculia scaphigera, 62 Sterculia setigera, 63 Sterculia tragacantha, 64 Sterculia urens, 57 Sterculia villosa, 64 economic importance Astragalus brachycalyx, 55 Astragalus gummifer, 52 Astragalus heratensis, 56 Astragalus kurdicus, 56 Astragalus microcephalus, 57 Astragalus verus, 57 Brachychiton acerifolius, 64 Firmiana simplex, 65 Sterculia foetida, 60 Sterculia scaphigera, 62 Sterculia tragacantha, 64 Sterculia villosa, 64 exudate, Sterculia tragacantha, 64

exudate appearance Cochlospermum religiosum, 66 Sterculia urens, 58 exudate color Cochlospermum religiosum, 66 Sterculia urens, 58 exudate properties and uses, Sterculia setigera, 63 general, Brachychiton acerifolius, 64 geographic distribution, Sterculia urens, 57 gum, Sterculia scaphigera, 62 gum chemical characteristics Astragalus gummifer, 53 Cochlospermum religiosum, 66 Sterculia urens, 59 gum physical properties, Astragalus gummifer, 54 gum water solubility Astragalus gummifer, 53 Cochlospermum religiosum, 66 similar gums, Cochlospermum religiosum, 66 synonyms Astragalus brachycalyx, 55 Astragalus gummifer, 52 Astragalus heratensis, 56 Astragalus kurdicus, 56 Astragalus microcephalus, 57 Brachychiton acerifolius, 64 Cochlospermum religiosum, 65 Firmiana simplex, 65 Hildegardia barteri, 65 Sterculia setigera, 63 tree, Sterculia villosa, 64 water solubility, Sterculia urens, 58

h Halva, 258, 259, 260 Heartwood, 111, 118, 119, 122, 123, 145, 184, 220 Hemoglobinuria, 176 Herpes, 90, 319 Heteropoly acid, 332 High-performance anion-exchange chromatography (HPAEC), 340 High-pressure liquid chromatography (HPLC), 341 Honey, 67, 89, 95, 133, 232, 261, 263, 319 HPAEC, see High-performance anion-exchange chromatography HPLC, see High-pressure liquid chromatography HPMC, see Hydroxypropylmethyl cellulose Hydrochloric acid, 334, 335, 358, 367 Hydrocolloid(s) adhesion tests, 299–301 natural, 368 Hydrogels, adhesion mechanisms of, 306–307 Hydroxyproline, 54, 135, 136, 174, 230, 232, 322 Hydroxypropylmethyl cellulose (HPMC), 277, 294, 296, 360, 365 Hysteria, 132

General Index  ◾  391 i IAA, see Indole-3-acetic acid Icing, 2, 55, 263, 269 Ice cream, 2, 66, 110, 113, 264, 279 Immersion plating, 358–359 Impotence, 179 India ink, 353 Indian or Asiatic gums and their botanical sources, 66–103, see also Asiatic, African, and Australian gums chemical characteristics Anogeissus latifolia, 76 Azadirachta indica, 94 Limonia acidissima, 89 Mangifera indica, 90 Prosopis juliflora, 97 Sesbania grandiflora, 98 Toona ciliata, 84 commercial availability Anogeissus latifolia, 78 Azadirachta indica, 94 Bauhinia roxburghiana, 80 Bauhinia variegata, 81 Chloroxylon swietenia, 84 Elaeodendron glaucum, 86 Limonia acidissima, 89 Mangifera indica, 90 Prosopis juliflora, 97 Sesbania grandiflora, 98 Spondias pinnata, 101 Terminalia bellirica, 101 Toona ciliata, 84 commercial and functional uses for other parts of tree Anogeissus latifolia, 79 Azadirachta indica, 94 Bauhinia variegata, 81 Buchanania lanzan, 82 Delonix regia, 84 Limonia acidissima, 89 Prosopis juliflora, 98 Sesbania grandiflora, 98 Spondias dulcis, 100 Terminalia bellirica, 101 Toona ciliata, 84 common names Aegle marmelos, 66 Albizia chinensis, 71 Albizia lebbeck, 68 Albizia odoratissima, 69 Albizia procera, 69 Aleurites moluccanus, 73 Anogeissus latifolia, 76 Azadirachta indica, 93 Bauhinia purpurea, 79 Bauhinia variegata, 81 Buchanania lanzan, 82

Buchanania latifolia, 82 Chloroxylon swietenia, 84 Delonix regia, 84 Elaeodendron glaucum, 86 Limonia acidissima, 89 Mangifera indica, 90 Prosopis cineraria, 95 Prosopis juliflora, 95 Sesbania grandiflora, 98 Spondias dulcis, 98 Spondias pinnata, 100 Terminalia bellirica, 101 Toona ciliata, 83 distributional range Aegle marmelos, 67 Albizia amara, 72 Albizia chinensis, 72 Albizia lebbeck, 69 Albizia odoratissima, 69 Albizia procera, 69 Aleurites moluccanus, 75 Anogeissus latifolia, 76 Azadirachta indica, 93 Bauhinia purpurea, 80 Bauhinia roxburghiana, 80 Bauhinia variegata, 81 Buchanania lanzan, 82 Buchanania latifolia, 83 Chloroxylon swietenia, 84 Delonix regia, 84 Elaeodendron glaucum, 86 Limonia acidissima, 89 Mangifera indica, 90 Prosopis cineraria, 95 Prosopis juliflora, 95 Sesbania grandiflora, 98 Spondias dulcis, 100 Spondias pinnata, 100 Terminalia bellirica, 101 Toona ciliata, 83 economic importance Aegle marmelos, 67 Albizia chinensis, 72 Albizia lebbeck, 68 Albizia odoratissima, 69 Albizia procera, 69 Aleurites moluccanus, 73 Bauhinia purpurea, 79 Buchanania lanzan, 82 Buchanania latifolia, 82 Chloroxylon swietenia dc, 84 Mangifera indica, 90 Prosopis cineraria, 95 Terminalia bellirica, 101 exudate appearance Aegle marmelos, 67 Anogeissus latifolia, 76

392  ◾  General Index Azadirachta indica, 93 Chloroxylon swietenia, 84 Delonix regia, 84 Elaeodendron glaucum, 86 Limonia acidissima, 89 Mangifera indica, 90 Prosopis juliflora, 96 Spondias dulcis, 100 Spondias pinnata, 101 Terminalia bellirica, 101 Toona ciliata, 83 exudate color, Anogeissus latifolia, 76 exudate properties Albizia lebbeck, 69 Aleurites moluccanus, 75 Azadirachta indica, 94 Buchanania lanzan, 82 Delonix regia, 84 Elaeodendron glaucum, 86 Mangifera indica, 90 Prosopis cineraria, 95 Sesbania grandiflora, 98 Spondias dulcis, 100 Spondias pinnata, 101 exudate solubility Anogeissus latifolia, 76 Limonia acidissima, 89 exudate uses, Prosopis cineraria, 95 gum chemical characteristics Aegle marmelos, 68 Azadirachta indica, 94 Limonia acidissima, 89 Mangifera indica, 90 Prosopis juliflora, 97 Sesbania grandiflora, 98 Toona ciliata, 84 gum properties Albizia chinensis, 72 Albizia odoratissima, 69 Albizia procera, 71 gum water solubility Aegle marmelos, 67 Chloroxylon swietenia, 84 Elaeodendron glaucum, 86 Prosopis juliflora, 97 Toona ciliata, 84 physical properties, Anogeissus latifolia, 77 similar gums, Limonia acidissima, 89 synonyms Aegle marmelos, 66 Albizia amara, 72 Albizia chinensis, 71 Albizia lebbeck, 68 Albizia odoratissima, 69 Albizia procera, 69 Aleurites moluccanus, 73 Anogeissus latifolia, 76

Azadirachta indica, 93 Bauhinia purpurea, 79 Bauhinia roxburghiana, 80 Bauhinia variegata, 81 Chloroxylon swietenia, 84 Delonix regia, 84 Elaeodendron glaucum, 86 Limonia acidissima, 89 Prosopis cineraria, 95 Prosopis juliflora, 95 Sesbania grandiflora, 98 Spondias dulcis, 98 Spondias pinnata, 100 Terminalia bellirica, 101 Toona ciliata, 83 Indigo, 64, 127, 356 Indole-3-acetic acid (IAA), 29 Industrial gums (analysis), 327–334 alcohol precipitability, 329 antibodies for identification of gum arabic and other polysaccharides, 333–334 identification of gums in specific foods, 332–333 microscopic identification, 329–332 water solubility, 327–329 Ink jets, 357 Inks, 351–354 Insect, 3, 5, 23, 24, 29, 30, 31, 64, 105, 113, 120, 135, 138, 143, 176, 184, 213, 219, 225, 232, 280, 281, 282, 312, 352, 361 Insecticides, binders for, 361 Insect repellent, 105, 361 Intercropping, 11 Interior trim, 111 Irradiation, 41, 339 IR spectroscopy, 338–339

j Jelly, 97, 105, 108, 120, 121, 130, 138, 196, 258, 259, 313, 320, 337 Jujubes, 3, 258

k Kami, 3, 294 Karaya gum, 1, 2, 3, 5, 18, 39, 42, 58, 59, 66, 110, 217, 267, 294, 296, 297, 314, 335, 338, 341 KBr disk technique, 339 Kendu, 295 Ketohexose, 66 Kibble, 13 Kinic acid, 145 Kino, 5–7, 24–25, 30–31, 81, 98, 126, 127, 144, 177, 183, 320

General Index  ◾  393 l Lake pigment, 127 Lamp black, 353, 354 Lap-shear test, 301, 305 Larch, 27, 122 gum, 122 Latex, 3, 6, 7, 8, 30, 31, 121, 122, 257 Laxative agent, 66 Laxatives, 59, 125, 311, 314 LBG, see Locust bean gum Leafflash, 266 Legumes, 116, 170, 171 Leishmaniasis, 317 Leprosy, 130, 176, 233 Letterpress, 352, 355 Lice, 97, 319 Limonene, 122, 265 Linalyl acetate, 266, 267 Linoleic acid, 169, 176, 274, 275 Lipid-oxidation rates, 274 Lithography, 1, 39, 123, 347, 354–355 Litho inks, 355 Locust bean gum (LBG), 5, 19, 263, 277, 278, 280, 335, 341, 342, 348 Low-calorie dressings, 262 Lozenges, 3, 42, 55, 258, 259 Lumbang oil, 75 Lycopene, 315, 316 Lymphoma, 243 Lysine, 165, 176, 276, 315

m Macedonian tombs, 348 Mahogany, 171, 179, 214 Maize, 10, 314 Malnutrition, 111 Maltodextrin, 265, 266, 267, 268, 270, 271, 272, 274, 275 Mango gum, 319 Manna from heaven, 1 α-D-Mannopyranose, 173 Mannose, 105, 110, 132, 141, 173, 240, 241, 269, 342 D-Mannose, 76, 118, 123, 138, 139, 140, 143, 209, 213, 226 Marmoset, 80, 116, 283, 284 Meat products, 263, 270, 272, 339 Mechanical interlocking, 293, 306 Medical, cosmetic and biotechnological uses of gum exudates, 311–326 biotechnological applications, 322–323 intracellular delivery, 323 recombinant plant gum, 322–323

cosmetics and other products, 320–322 cosmetic preparations, 321 general, 320 perfume, 321–322 powdered abrasive cleaners, 322 folk medicine, 318–320 pharmacological applications, 311–318 activity against leishmania and fungi, 317–318 antiseptic preparations and ophthalmic infections, 314 demulcent and emollient qualities, 311–312 gelatin- and chitosan-gum arabic coacervates, 315–316 hydrophobic drug delivery, 314–315 intravenous injections, 317 laxatives, 314 lycopene, 315 suspending and emulsifying agents, 312–313 tablets and pills, 314 MeJA, see Methyl jasmonate Meringue, 59, 258, 271, 279 Mesquite gum, 76, 95, 97, 98, 319, 334 Metallic pigments, 354 Methanolysis, 339, 340, Methanolysis procedure, 339 Methionine, 169, 176 Methylene blue, 329, 331, 356, 357 4-O-Methyl ether, 136 2-O-Methyl-D-galacturonic acid, 120 4-O-(4-O-Methyl-α-D-glucopyranosyl-uronic acid)β-D-galactopyranosyl, 217 4-O-Methylglucuronic acid, 105, 136, 183, 241, 340 4-O-Methyl-D-glucuronic acid, 97, 117, 141, 143, 195, 215 Methyl jasmonate (MeJA), 29 Methyl (4-O-methyl-D-glucoside) uronamide, 97 Microencapsulated perfume, 321 Microencapsulation, 267, 271–275, 276, 321 linoleic acid microencapsulation, 274–275 oleoresins, 271–274 procyanidins, 275 Millon’s reagent, 329, 330, 335, 336 Minor plant exudates, 163–256 agricultural issue, Balsamocitrus dawei, 175 commercial availability Anogeissus leiocarpus, 173 Combretum, 200 Cordia myxa, 200 Cordyla africana, 201 Hakea gibbosa, 213 Khaya senegalensis, 217 Lannea coromandelica, 220 Melia azedarach, 224 Moringa oleifera, 227 Prunus dulcis, 230 Pseudocedrela kotschyi, 230 Saltera sarcocolla, 228

394  ◾  General Index Schefflera volkensii, 232 Sclerocarya birrea, 232 Terminalia, 242 commercial and functional uses for other parts of shrub, Owenia venosa, 228 commercial and functional uses for other parts of tree Adansonia digitata, 165 Afzelia africana, 171 Anogeissus leiocarpus, 173 Brachystegia spiciformis, 183 Ceratopetalum gummiferum, 191 Chukrasia tabularis, 191 Cocos nucifera, 196 Combretum, 200 Cordia myxa, 201 Cordyla africana, 201 Cussonia arborea, 204 Cycas circinalis, 207 Dichrostachys cinerea, 207 Elaeocarpus reticulatus, 208 Encephalartos hildebrandtii, 209 Entada africana, 209 Erythrophleum africanum, 210 Garuga pinnata, 211 Geodorum nutans, 213 Khaya senegalensis, 217 Lannea coromandelica, 220 Melia azedarach, 224 Miliusa tomentosa, 231 Moringa oleifera, 227 Sclerocarya birrea, 232 Semecarpus anacardium, 234 Soymida febrifuga, 235 Tamarindus indica, 238 Terminalia, 243 Thevetia peruviana, 246 commercial uses, Sloanea australis, 235 common names Adansonia digitata, 163 Adenanthera pavonina, 168 Afzelia africana, 170 Anogeissus leiocarpus, 173 Atalaya hemiglauca, 174 Balsamocitrus dawei, 174 Bauhinia carronii, 175 Bauhinia thonningii, 175 Bombax ceiba, 177 Borassus flabellifer, 180 Brachystegia spiciformis, 181 Capparis nobilis, 184 Careya arborea, 185 Cassia fistula, 186 Cedrela odorata, 189 Ceiba pentandra, 190 Ceratopetalum apetalum, 190 Ceratopetalum gummiferum, 191 Chukrasia tabularis, 191

Citrus, 193 Cocos nucifera, 195 Cola cordifolia, 197 Cordia myxa, 200 Corypha utan, 202 Crataeva adansonii, 202 Cussonia arborea, 204 Cycas circinalis, 204 Dichrostachys cinerea, 207 Elaeocarpus obovatus, 208 Elaeocarpus reticulatus, 208 Erythrophleum africanum, 209 Flindersia australis, 211 Flindersia maculosa, 210 Geijera paniculata, 212 Geodorum nutans, 212 Hakea gibbosa, 213 Heritiera trifoliolata, 238 Julbernardia globiflora, 176 Khaya grandifoliola, 214 Khaya madagascariensis, 214 Khaya senegalensis, 214 Lannea coromandelica, 219 Melia azedarach, 221 Miliusa tomentosa, 231 Moringa oleifera, 225 Owenia venosa, 228 Pentaceras australis, 229 Prunus dulcis, 229 Saltera sarcocolla, 228 Sarcostemma brevistigma, 231 Schefflera volkensii, 231 Semecarpus anacardium, 233 Sloanea australis, 234 Sloanea woollsii, 234 Soymida febrifuga, 235 Tamarindus indica, 236 Terminalia, 239 Thevetia peruviana, 245 distributional range Adansonia digitata, 163 Adenanthera pavonina, 168 Afzelia africana, 170 Atalaya hemiglauca, 174 Balsamocitrus dawei, 174 Bauhinia carronii, 175 Bauhinia thonningii, 175 Bombax ceiba, 177 Bombax insigne, 180 Borassus flabellifer, 180 Brachystegia spiciformis, 182 Burkea africana, 183 Careya arborea, 185 Cassia sieberiana, 187 Cedrela odorata, 189 Ceiba pentandra, 190 Ceratopetalum apetalum, 190

General Index  ◾  395 Ceratopetalum gummiferum, 191 Corypha utan, 202 Crataeva adansonii, 203 Cycas lane-poolei, 204 Dichrostachys cinerea, 207 Elaeocarpus obovatus, 208 Elaeocarpus reticulatus, 208 Encephalartos hildebrandtii, 208 Entada africana, 209 Erythrophleum africanum, 209 Flindersia australis, 211 Flindersia maculosa, 210 Garuga pinnata, 211 Geijera paniculata, 212 Geodorum nutans, 212 Hakea gibbosa, 213 Julbernardia globiflora, 177 Khaya grandifoliola, 214 Khaya madagascariensis, 214 Khaya senegalensis, 215 Lagerstroemia parviflora, 217 Lannea coromandelica, 219 Macrozamia spiralis, 221 Melia azedarach, 222 Moringa oleifera, 225 Prunus dulcis, 229 Semecarpus anacardium, 233 Soymida febrifuga, 235 Tylosema fassoglense, 176 Virgilia oroboides, 246 economic importance Atalaya hemiglauca, 174 Borassus flabellifer, 180 Ceiba pentandra, 190 Ceratopetalum apetalum, 190 Citrus, 193 Crataeva adansonii, 202 Elaeocarpus obovatus, 208 Elaeocarpus reticulatus, 208 Flindersia australis, 211 Khaya grandifoliola, 214 Khaya madagascariensis, 214 Khaya senegalensis, 214 Macrozamia spiralis, 221 Melia azedarach, 222 Prunus dulcis, 229 Semecarpus anacardium, 233 Soymida febrifuga, 235 Tamarindus indica, 236 Tylosema fassoglense, 176 exudate Bauhinia carronii, 175 Bauhinia thonningii, 175 Bombax ceiba, 177 Bombax insigne, 180 Careya arborea, 185 Cassia sieberiana, 187

Ceiba pentandra, 190 Citrus, 193 Julbernardia globiflora, 177 Neopanax colensoi, 228 exudate appearance Adansonia digitata, 165 Bouchardatia neurococca, 224 Cocos nucifera, 195 Cordia myxa, 200 Cordyla africana, 201 Corypha utan, 202 Cycas lane-poolei, 204 Elaeocarpus reticulatus, 208 Encephalartos hildebrandtii, 208 Erythrophleum africanum, 209 Pentaceras australis, 229 Virgilia oroboides, 246 exudate color, Encephalartos hildebrandtii, 208 exudate properties Adansonia digitata, 165 Afzelia africana, 170 Anogeissus leiocarpus, 173 Atalaya hemiglauca, 174 Balsamocitrus dawei, 175 Borassus flabellifer, 181 Bosistoa pentacocca, 181 Brachystegia spiciformis, 183 Capparis nobilis, 185 Cassia fistula, 187 Cedrela odorata, 189 Ceratopetalum gummiferum, 191 Chukrasia tabularis, 191 Cocos nucifera, 195 Combretum, 198 Cussonia arborea, 204 Flindersia maculosa, 210 Garuga pinnata, 211 Geijera paniculata, 212 Geodorum nutans, 213 Hakea gibbosa, 213 Khaya senegalensis, 215 Lagerstroemia parviflora, 217 Lannea coromandelica, 219 Macrozamia spiralis, 221 Melia azedarach, 222 Miliusa tomentosa, 231 Moringa oleifera, 225 Prunus dulcis, 229 Pseudocedrela kotschyi, 230 Saltera sarcocolla, 229 Sclerocarya birrea, 232 Semecarpus anacardium, 233 Sloanea australis, 234 Soymida febrifuga, 235 Tamarindus indica, 238 Terminalia, 240 Thevetia peruviana, 245

396  ◾  General Index

functional uses, Careya arborea, 185 functional uses for other parts of tree, Lagerstroemia parviflora, 219 geographic distribution Anogeissus leiocarpus, 173 Bosistoa pentacocca, 181 Bouchardatia neurococca, 224 Capparis nobilis, 184 Cassia fistula, 186 Chukrasia tabularis, 191 Citrus, 193 Cocos nucifera, 195 Cola cordifolia, 197 Combretum, 198 Cordia myxa, 200 Cordyla africana, 201 Cussonia arborea, 204 Cycas circinalis, 204 Heritiera trifoliolata, 238 Miliusa tomentosa, 231 Owenia venosa, 228 Pentaceras australis, 229 Pseudocedrela kotschyi, 230 Saltera sarcocolla, 228 Sarcostemma brevistigma, 231 Schefflera volkensii, 232 Sclerocarya birrea, 232 Sloanea australis, 234 Sloanea woollsii, 234 Terminalia, 240 Thevetia peruviana, 245 gum Anogeissus leiocarpus, 173 Burkea africana, 184 Cedrela odorata, 189 Citrus, 193 Combretum, 198 Cordyla africana, 201 Heritiera trifoliolata, 238 Khaya senegalensis, 215 Lannea coromandelica, 219 Melia azedarach, 222 Miliusa tomentosa, 231 Moringa oleifera, 225 Sarcostemma brevistigma, 231 Sloanea woollsii, 234 gum chemical characteristics Citrus, 193 Combretum, 199 Cussonia arborea, 204 Hakea gibbosa, 213 Khaya senegalensis, 215 Lannea coromandelica, 219 Melia azedarach, 224 Moringa oleifera, 226 Prunus dulcis, 230 Pseudocedrela kotschyi, 230

Saltera sarcocolla, 228 Sclerocarya birrea, 232 gum properties, Cycas circinalis, 207 medicinal properties, Sarcostemma brevistigma, 231 products, Bauhinia thonningii, 175 shrub Bauhinia thonningii, 175 Sarcostemma brevistigma, 231 Thevetia peruviana, 245 similar gums Bouchardatia neurococca, 224 Dichrostachys cinerea, 207 Khaya senegalensis, 217 Melia azedarach, 224 Miliusa tomentosa, 231 Moringa oleifera, 227 Pentaceras australis, 229 Terminalia, 242 solubility, Cordia myxa, 200 synonyms Afzelia africana, 170 Anogeissus leiocarpus, 173 Atalaya hemiglauca, 174 Bauhinia carronii, 175 Bauhinia thonningii, 175 Bombax ceiba, 177 Bosistoa pentacocca, 181 Bouchardatia neurococca, 224 Brachystegia spiciformis, 181 Cedrela odorata, 189 Ceiba pentandra, 190 Chukrasia tabularis, 191 Cola cordifolia, 197 Corypha utan, 202 Cussonia arborea, 204 Cycas circinalis, 204 Dichrostachys cinerea, 207 Elaeocarpus grandis, 208 Entada africana, 209 Flindersia maculosa, 210 Geijera paniculata, 212 Geodorum nutans, 212 Hakea gibbosa, 213 Heritiera trifoliolata, 238 Julbernardia globiflora, 176 Khaya senegalensis, 214 Lannea coromandelica, 219 Macrozamia spiralis, 221 Melia azedarach, 221 Miliusa tomentosa, 231 Moringa oleifera, 225 Neopanax colensoi, 228 Polyscias elegans, 228 Prunus dulcis, 229 Pseudocedrela kotschyi, 230 Saltera sarcocolla, 228 Schefflera volkensii, 231

General Index  ◾  397 Sclerocarya birrea, 232 Sloanea woollsii, 234 Soymida febrifuga, 235 Thevetia peruviana, 245 Tylosema fassoglense, 176 Virgilia oroboides, 246 tree Adansonia digitata, 163 Adenanthera pavonina, 168 Afzelia africana, 171 Bauhinia carronii, 175 Bombax ceiba, 177 Borassus flabellifer, 180 Bosistoa pentacocca, 181 Brachystegia spiciformis, 182 Burkea africana, 183 Cola cordifolia, 197 Crataeva adansonii, 203 Cycas circinalis, 204 Julbernardia globiflora, 177 Lagerstroemia parviflora, 217 Pseudocedrela kotschyi, 230 Schefflera volkensii, 232 Semecarpus anacardium, 233 Sloanea australis, 234 Sloanea woollsii, 234 Soymida febrifuga, 235 Tamarindus indica, 236 Tylosema fassoglense, 176 Virgilia oroboides, 246 uses, Bauhinia thonningii, 175 Miscellaneous uses of plant exudates, 347–370 abdominal ultrasound imaging, 367 binders and special coatings, 361 binders for insecticides, 361 glaze binders, 361 non-glare coatings for windshields, 361 car polishes, 366 ceramics, 364–365 corrosion inhibition, 357–358 cross-linked polystyrene, 366 drilling fluids, 359–360 explosives, 362–364 immersion plating, 358–359 inks, 351–354 lithography, 354–355 oil-well cement, 360 paints, pigments and painting, 347–351 paper and e-paper, 361–362 photo papers, 362 photoelectric determinations, 366–367 polarographic determinations, 367 textiles, 355–357 varnishes, 365 vinyl resin emulsions, 368 Mohs (scale), 15, 349, 351 Monkey, 80, 116, 163, 201

Mono-O-methyl-D-glucuronic acid, 193 Mucic acid, 122 Mucilage, 24, 31, 54, 55, 59, 71, 77, 84, 86, 89, 90, 101, 105, 106, 107, 108, 120, 127, 129, 146, 165, 204, 207, 209, 219, 230, 235, 262, 297, 304, 312, 314, 362 Myrrh, 14, 132, 294

n NAA, see Naphthalene acetic acid α-NAA, see α-Naphthalene acetic acid Naphthalene acetic acid (NAA), 29 Natural dyes, 356 α-Naphthalene acetic acid (α-NAA), 29 Natural fruit acids, 271 Natural gums, 1, 5, 12, 19, 31, 257, 259, 297, 327, 356, 362, 364 Neem gum, 222, 319 New World gums, 104–123 commercial availability Anacardium occidentale, 105 Anadenanthera colubrina, 106 Cylindropuntia fulgida, 121 Inga stipularis, 116 Larix occidentalis, 122 Leucaena collinsii, 116 Manilkara zapota, 121 Parkinsonia praecox, 107 Puya chilensis, 108 Theobroma cacao, 110 commercial and functional uses for other parts of tree Anacardium occidentale, 105 Anadenanthera colubrina, 106 Cylindropuntia fulgida, 121 Laguncularia racemosa, 111 Larix occidentalis, 123 Leucaena collinsii, 116 Manilkara zapota, 122 Melicoccus bijugatus, 118 Parkinsonia praecox, 108 Pithecellobium dulce, 111 Puya chilensis, 108 Rhizophora mangle, 117 Theobroma cacao, 110 Thespesia populnea, 119 common names Anacardium occidentale, 104 Caesalpinia coriaria, 106 Ceiba speciosa, 118 Cylindropuntia fulgida, 120 Enterolobium cyclocarpum, 113 Laguncularia racemosa, 110 Larix occidentalis, 122 Manilkara zapota, 121 Melicoccus bijugatus, 117

398  ◾  General Index Pithecellobium dulce, 111 Rhizophora mangle, 117 Samanea saman, 113 Theobroma cacao, 110 Thespesia populnea, 118 distributional range Anacardium humile, 104 Anacardium occidentale, 104 Anadenanthera colubrina, 105, 106 Caesalpinia coriaria, 106 Ceiba speciosa, 118 Chloroleucon mangense, 115 Cylindropuntia fulgida, 120 Enterolobium cyclocarpum, 113 Inga stipularis, 116 Laguncularia racemosa, 111 Leucaena collinsii, 115 Lysiloma acapulcense, 116 Manilkara zapota, 121 Melicoccus bijugatus, 117 Parkinsonia praecox, 107 Pithecellobium dulce, 111 Rhizophora mangle, 117 Samanea saman, 113 Theobroma cacao, 110 Thespesia populnea, 118 economic importance Caesalpinia coriaria, 106 Ceiba speciosa, 118 Enterolobium cyclocarpum, 113 Larix occidentalis, 122 Pithecellobium dulce, 111 Samanea saman, 113 Theobroma cacao, 110 exudate, Anadenanthera colubrina, 106 exudate appearance Anacardium occidentale, 104 Ceiba speciosa, 118 Cylindropuntia fulgida, 120 Larix occidentalis, 122 Leucaena collinsii, 115 Manilkara zapota, 121 Melicoccus bijugatus, 117 Pithecellobium dulce, 111 Rhizophora mangle, 117 Theobroma cacao, 110 Thespesia populnea, 119 exudate color Anadenanthera colubrina, 106 Leucaena collinsii, 115 exudate properties Anacardium occidentale, 104 Enterolobium cyclocarpum, 113 Parapiptadenia rigida, 108 Parkinsonia praecox, 107 Puya chilensis, 108



functional uses for other parts of tree, Samanea saman, 113 gum Larix occidentalis, 122 Leucaena collinsii, 115 gum chemical characteristics Anacardium occidentale, 105 Anadenanthera colubrina, 106 Ceiba speciosa, 118 Cylindropuntia fulgida, 120 Laguncularia racemosa, 111 Larix occidentalis, 122 Leucaena collinsii, 116 Manilkara zapota, 121 Melicoccus bijugatus, 117 Parkinsonia praecox, 107 Puya chilensis, 108 Rhizophora mangle, 117 Theobroma cacao, 110 gum physical properties, Larix occidentalis, 122 gum properties, Samanea saman, 113 gum water solubility Anadenanthera colubrina, 106 Cylindropuntia fulgida, 120 Laguncularia racemosa, 111 Larix occidentalis, 122 Leucaena collinsii, 116 Lysiloma acapulcense, 116 Manilkara zapota, 121 Melicoccus bijugatus, 117 Pithecellobium dulce, 111 Puya chilensis, 108 Rhizophora mangle, 117 Theobroma cacao, 110 Thespesia populnea, 119 similar gums Anadenanthera colubrina, 106 Cylindropuntia fulgida, 121 Leucaena collinsii, 116 synonyms Anacardium humile, 104 Anadenanthera colubrina, 105, 106 Caesalpinia coriaria, 106 Ceiba speciosa, 118 Chloroleucon mangense, 115 Cylindropuntia fulgida, 120 Laguncularia racemosa, 110 Lysiloma acapulcense, 116 Manilkara zapota, 121 Melicoccus bijugatus, 117 Parapiptadenia rigida, 108 Parkinsonia praecox, 107 Puya chilensis, 108 Samanea saman, 111 Theobroma cacao, 110 Thespesia populnea, 118 Nitric acid, 122, 329, 367

General Index  ◾  399 NMR, see Nuclear magnetic resonance Nuclear magnetic resonance (NMR), 5, 177, 200 Nujol mull, 339 Nut, 73, 74, 82, 104, 105, 118, 130, 229, 233, 234, 243, 245, 269, 352 Nutritional value, 283

o Oil-well cement, 347, 360 Ointments, 59, 82, 296, 339, 348 Oleic acid, 169, 176 Oleoresin, paprika, 4, 5, 14, 123, 271–272, 274 Oligosaccharides, 76, 285 Omega-6 fatty acid, 274 Ornamental 6, 27, 40, 45, 47, 51, 60, 64, 65, 68, 73, 79, 81, 84, 90, 94, 98, 100, 101, 106, 108, 111, 113, 116, 118, 119, 121, 123, 125, 127, 132, 135, 136, 138, 140, 143, 145, 147, 168, 177, 180, 187, 190, 193, 202, 208, 213, 221, 222, 232, 233, 236, 238, 245, 246, 320 Orpiment, 348, 349, 350, 351 Ostomy devices, 296–297 Overrun (ice cream), 113

p Paints, pigments and painting, 347–351 Palmitic acid, 176 Papain, 337, 338 Paper, 339, 341, 347, 352, 354, 357, 361–362 Paper cloth, 73 Paprika, 274 Paprika oleoresin, 274 Papyrus, 294, 351, 352 Paraquat, 31 Pastille, 3, 42, 258, 260 Patch adhesion, 299 Pathogen, 3, 4, 23, 24, 25, 29, 34, 41, 141, 174, 323 Pathological exudation, 23 Pectic acid, 215 Pectin, 19, 145, 259, 269, 271, 278, 285, 294, 313, 321, 338, 339, 368 Peel test, 299, 300, 305 PEG, see Polyethylene glycol Penis, 127 Pentose, 76 Perfume, 5, 321–322 Peripheral cambium, 24 Pesticides, 95, 224, 276, 319 Pharmacological applications, 311–318 activity against leishmania and fungi, 317–318 antiseptic preparations and ophthalmic infections, 314 demulcent and emollient qualities, 311–312 gelatin- and chitosan-gum arabic coacervates, 315–316 hydrophobic drug delivery, 314–315 intravenous injections, 317

laxatives, 314 lycopene, 315 suspending and emulsifying agents, 312–313 tablets and pills, 314 Phenols, 90, 234 Phloem, 25, 30, 32, 105, 281 Phloem, 25, 30, 32, 105, 281 Phospholipid-based emulsions, 169 Phosphoric acid, 335 Phosphotungstic acid (PTA), 332, 333 Photo papers, 362 Photosynthesis, 34 Phosphotungstic acid, 332, 333 Physiological metabolism, 257 Phytosterols, 145 Pinene, 122 Piperine, 271, 272 Polarography, 367 Polyethylene glycol (PEG), 297, 360 Polyphenols, 24, 191, 238, 275, 397 Polysaccharide acid, 76, 132, 137, 337 neutral salt of, 137 precipitation of heavy metal salts, 337 Polysaccharide formation in plants, physiological aspects of, 23–38 borers and gum formation, 30–31 gum ducts, 23, 24, 31–32, 33, 105, 193, 230, 240 gummosis in fruit trees, 32–34 induced inoculation and gum yield, 34–35 stress factors, ethylene and gummosis, 23–29 Polyvinyl alcohol (PVA), 294, 296, 297, 360 Polyvinylpyrrolidone (PVP), 317, 365 Pongam oil, 135 Pottery, 97, 364 Powdered abrasive cleaners, 322 Pressure-cooking, 357 Pressure-sensitive adhesive (PSA), 296, 298, 299, 301, 306 Primate, 281, 283 Printed textile, 356 Probiotic, 267 Probe tack, 299, 301, 302 Procyanidin, 275, Proline, 176, 322 Propylene glycol alginate, 26, 296 Propylene oxide, 41, 55 Proteinaceous, 59, 97, 136, 144, 278 Protein isolates, 280 Protocatechic acid, 145 Prussic acid, 126 PSA, see pressure-sensitive adhesive PTA, see Phosphotungstic acid Pullulan, 263, 264, 294, 296, 360 Pulmonary disorder, 106 PVA, see Polyvinyl alcohol PVP, see Polyvinylpyrrolidone β-L-Pyranose, 107 2,6-Pyridinedicarboxylic acid, 342

400  ◾  General Index q Quantitative tack, 299

r Realgar, 348, 349, 351 Record ink, gum arabic used in, 354 Redox reaction, 363 Resin, 3–6, 14, 23–24, 30–31, 33, 75, 83–84, 90, 106, 121–122, 124–125, 129, 132, 144–146, 183, 201, 226, 229, 257, 293, 295–297, 299, 340, 351–353, 356, 359, 361–362, 364, 365, 368 α-L-Rhamnopyranose, 217 Rhamnose, 41, 53, 66, 98, 105, 110, 111, 117, 120, 135, 136, 138, 140, 174, 183, 200, 230, 241, 317 L-Rhamnose, 43, 59, 63, 66, 68, 89, 117, 118, 120, 131, 132, 139, 140, 143, 171, 209, 215, 216, 219, 226 Role and sources of exudate gums, 1–22 agricultural issues, 9–12 chemical properties, 19 colloquialisms, 1 commercial assessments of gums, 19 definitions, 3–7 gum-sucker, 1 gum yields, 8–9 industrial and other uses, 19 physical properties of gums, 12–19 color, 12–13 hardness and density, 15 polarization, 16 size and shape, 13 solubility, 16–17 taste and smell, 14–15 viscosity and mouthfeel, 17–19 Rope, 119, 135, 137, 176 Rubber, 6, 121, 295, 316

s S-adenosylmethionine (SAM), 29 Safron, 127 Salad, 228, 261 dressings and sauces, 3, 55, 201, 238, 261–262 Salicylic acid, 299 SAM, see S-adenosylmethionine Sap, 13, 30, 34, 120, 121, 144, 147, 181, 197, 281 Saponins, 68, 113, 145, 172, 173, 209, 210, 318 Sapwood, 30, 31 Saturated fatty acids, 169, 274 SCFAs, see Short-chain fatty acids Schiff base, 276, 315 Scorpion, 95 Schweitzer’s reagent, 336 Secretory tissues, 31

Sensitizers, 354, 364 Serine, 230, 232 Sesquiterpenes, 145 Shade tree, 60, 72, 111, 116, 132, 133, 183, 200, 238 Sherbet, 2, 67, 264 Short-chain fatty acids (SCFAs), 267 Single-cell protein, 98 Sizing agent, 121, 122, 356 Skin creams, 321 Skin-irritant, 90 Skin-surface model (SSM), 299, 304 Slow loris, 281, 283 Snake, 95 Soap, 110, 111, 125, 135, 145, 190, 228, 321, 337 Sodium alginate, 5, 19, 42, 297 Sodium caseinate, 42 Sodium hydroxide, 63, 226, 336 Soft candy, 59 Soft drink, 2, 278, 342 Sore throat, 97, 125, 176, 235, 259, 319 Soup, 17, 42, 127, 267 Sources, see Role and sources of exudate gums Spectral analysis, 136 Sphericity, 13 Spray-drying, 13, 41, 264–267, 270, 271, 272, 274, 275, 315 encapsulation via spray-drying, 267 miscellaneous spray-dried products, 266–267 spray-drying of juices, 264–266 Spread, 2, 11, 34, 59, 271, 333 Squirrel glider, 281, 282 SSM, see Skin-surface model Stabilizing agent, 19, 59, 271, 279 Steroids, 113 Sticky point, 265 Stoke’s acid mercuric nitrate test, 335 Stoke’s reagent, 329, 330, 335, 336 Sulfosalicylic acid, 366 Sulfur dioxide, 219 Sulfuric acid, 226, 336, 340 Surface tension, 42, 54, 122, 267, 279, 368 Surfactant, 169, 279 Suspending agent, 312, 313, 321, 353, 354 Syphilis, 90, 125, 130, 227, 319

t Tablet, 59, 78, 97, 129, 213, 217, 259, 285, 313, 314 D-Tagatose, 63 Tamarindineal, 238 Tannic acid, 90, 145, 336, 352 Tannin, 5, 13, 19, 43, 45, 66, 68, 84, 97, 98, 101, 106, 107, 111, 113, 117, 119, 120, 122, 127, 130, 132, 145, 172, 173, 174, 176, 183, 187, 210, 219, 235, 257, 268, 270 Tapping, 3, 8, 9, 35, 40, 58, 76, 96, 115, 121, 132, 181, 219

General Index  ◾  401 Tara gum, 5 Tartaric acid, 238, 329, 354 Tea, 68, 86, 116, 119, 132, 149, 177, 264, 270 Tempera, 348 Tensile strength, 129, 323 Terpenes, 90, 209 Terpenoids, 113 Textiles(s), 1, 3, 19, 39, 59, 66, 82, 95, 97, 121, 145, 147, 224, 238, 294, 347, 354, 355–357 TFA, see Trifluoroacetic acid Thickening, 1, 5, 17, 19, 39, 52, 55, 101, 127, 238, 242, 269, 339, 361, 363, 364 Timber, 43, 60, 68, 84, 119, 125, 126, 130, 138, 171, 177, 184, 211, 228, 230, 232, 238, 318 Tobacco, 110, 127, 145, 294, 323, 361 “To be up a gum tree,” 1 Topping, 3, 269 Tragacanth, see Gum tragacanth and similar gums Traumatic ducts, 31 Trichomes, 31 Turgor pressure, 30 Tragacanthic acid, 54, 354 Tragacanthin, 53, 54 Transdermal drug delivery, exudate patches for, 298–299, 306 Trichloroacetic acid, 334, 335 Triethanolamine, 354 Trifluoroacetic acid (TFA), 339 Trypsin units inhibited (TUI), 176 TUI, see Trypsin units inhibited Tyrosine, 176

u Ulcer, 59, 135, 173, 311, 318, 320 Ultrasound imaging, 367 Unsaturated fatty acids, 169, 274 Uronic acid, , 41, 58, 59, 66, 111, 117, 131, 132, 200, 208, 215, 219, 335, 339, 340

v Varnishes, 5, 79, 89, 348, 365 Vegetable, 5, 11, 14, 111, 118, 134, 165, 171, 176, 185, 227, 261, 263, 264, 265, 269, 270, 295, 297, 333, 354 Veneer, 84, 111, 123, 131, 192, 217, 295 Venereal diseases, 90, 127, 319 Vertebrate poisons, 47, 75, 90, 140, 143, 174, 222, 229, 233, 235 Viagra, 127 Vinyl resin emulsions, 368 Viscosity, 5, 16, 17, 18, 41, 53–55, 59, 77, 79, 95, 97, 100, 106–108, 110, 111, 113, 136, 171, 173, 174, 198, 200, 226, 258, 259, 260, 262, 264, 267, 269, 277, 278, 280, 297, 312, 313, 320, 323, 328, 329, 347, 352, 354, 355, 359, 360, 365

Viscosity-modifying agents (VMAs), 360 Vitamins (s), 118, 165, 167, 264, 266, 270, 271, 313, 314 C, 165, 266, 270, 271 VMAs, see Viscosity-modifying agents

w Warts, 59, 299 Water-based adhesives, see Adhesives, water-based Watercolors, 89, 348, 353 Water ices, 2, 59, 264 Water number, 305 Water-soluble vitamins, 270 Wattle blossom model, 41 Wattle gum, 1, 4, 98 Weed, 45, 46, 47, 51, 69, 79, 183, 222 Wet glues, 302–305 Whey protein concentrate (WPC), 275 Whey protein-maltodextrin conjugate, 271 White spot syndrome virus infection, 135 Wine, 2, 98, 130, 196, 268–269, 270, 275, 329 Wood, 69, 84, 122, 130, 208, 214 Wound dressings, 130 WPC, see Whey protein concentrate

x Xanthan gum, 5, 261, 262, 263, 277, 278, 279, 280, 359, 368 X-ray, 342, 351 Xylan, 107, 137, 285 Xylem, 24, 25, 32 D-Xylopyranose, 120, 139, 173 Xylose, 53, 54, 107, 110, 120, 123, 136, 140, 141, 187, 240, 241 D-Xylose, 63, 66, 76, 89, 108, 118, 121, 126, 137, 138, 139, 140, 147, 213, 226, 230

Y Yarn, 127, 355, 356 Yellow fever, 125 Yield (gum), 8–9, 10, 11, 12, 13, 16, 28, 34, 35, 39, 40, 41, 58, 63, 64, 66, 67, 71, 76, 83, 95, 97, 106, 107, 108, 110, 113, 115, 123, 124, 132, 138, 141, 148, 165, 171, 172, 173, 175, 177, 179, 181, 190, 193, 197, 204, 210, 213, 220, 228, 230, 234, 238, 320 Yield stress, 59

z Zanzibar copal, 5