Sweet Potato: Post Harvest Aspects in Food, Feed and Industry (Food Science and Technology)

FOOD SCIENCE AND TECHNOLOGY SERIES

SWEET POTATO: POST HARVEST ASPECTS IN FOOD, FEED AND INDUSTRY

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FOOD SCIENCE AND TECHNOLOGY SERIES

SWEET POTATO: POST HARVEST ASPECTS IN FOOD, FEED AND INDUSTRY

RAMESH C. RAY AND

K.I. TOMLINS EDITORS

Nova Science Publishers, Inc. New York

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Published by Nova Science Publishers, Inc.  New York

CONTENTS Preface

vii

About the Editors Chapter 1

Chapter 2

Sweet Potato Growth, Development, Production and Utilization: Overview Maniyam Nedunchezhiyan and Ramesh C. Ray Post Harvest Handling, Storage Methods, Pests and Diseases of Sweet Potato Ramesh C. Ray, V. Ravi, Vinayak Hegde, K. Rajasekhara Rao and Keith I. Tomlins

9 1

27

Chapter 3

Physiological Functions and Utilization of Sweet Potato Makoto Yoshimoto

59

Chapter 4

Sweet Potato Starch S. N. Moorthy and S. Shanavas

91

Chapter 5

Sweet Potato Purees and Dehydrated Powders for Functional Food Ingredients Van-Den Truong and Ramesh Y. Avula

Chapter 6

Bio-Processing of Sweet Potato into Food, Feed and Bio-Ethanol Ramesh C. Ray, Samir K. Naskar and Keith I. Tomlins

Chapter 7

Sweet Potato Utilization in Human Health, Industry and Animal Feed Systems Adelia C. Bovell-Benjamin

Chapter 8

Sweet Potato in Animal Nutrition Ibisime Etela

Chapter 9

Sweet Potato and Pigs: Traditional Relationships, Current Practices and Future Prospects Dai Peters

117 163

193 225

245

vi Chapter 10

Index

Contents Sweet Potato Utilization, Storage, Small-Scale Processing and Marketing in Africa Keith Tomlins, Debbie Rees, Claire Coote, Aurélie Bechoff, Julius Okwadi, Jaquelino Massingue, Ramesh Ray and Andrew Westby

271

295

PREFACE Sweet potato (Ipomoea batatas L.), the seventh most important food crop after wheat, rice, maize, potato, barley and cassava, is a staple food in many developing countries of the tropics and sub-tropics, and also serves as animal feed and raw material for several food and feed based industries. This New World crop has high biological efficiency of converting solar energy into edible energy (152 MJ/ha/day) in the form of tuberous (storage) roots and could be the food for the ever growing human population in future. Asia leads in area (60.75%) and production (86.89%) of sweet potato in the world. Sweet potato was originally a herbaceous perennial but was domesticated as an annual and grows best in moderately warm temperature of 21-26oC. It requires light textured soil with the optimum pH of 5.5 -6.5 for good growth of the crop. Current research has focused on development of high starch, high dry matter and coloured (ß-carotene and anthocyanin-rich) sweet potato varieties for industrial applications in addition to traditional usage as food and animal feed. The first chapter in this book by Maniyam Nedunchezhiyan and Ramesh Ray provide an overview on the growth, development, production and utilization of sweet potato. Sweet potato storage roots are subjected to several forms of post harvest losses during harvest, transportation from farmers‘ field to market and storage. These are due to mechanical injury, weight loss, sprouting, diseases and pests. Chapters 2 and 10 in this book deal with these aspects in detail. In Chapter 2, Ramesh Ray and colleagues have discussed the various methods (curing, fungicide treatment, bio-control by antagonistic yeasts, gamma irradiation and storage in controlled atmospheric conditions) that could reduce fungal rot and enhance shelf-life of sweet potato roots in storage. Keith Tomlins and his colleagues, in Chapter 10, have attributed the main challenges for the crop in Africa with respect to post-harvest issues which include the management of storage pests, particularly sweet potato weevils (Cylas spp.), increasing yields and improving the marketing systems along the value chain. Sweet potato contains various kinds of physiologically functional components such as polyphenolics, anthocyanins, fibres and carotenoids in roots and leaves. These physiological functions include the potential for anti-oxidation, anti-diabetics and anti-hypertension. The sweet potato roots or leaves with these functions are commercially used as materials of confectionary, noodles, alcoholic drinks and beverage. In Chapter 3, Makoto Yoshimoto, reviews the recent research work on this topic, mainly concerned with the technological concepts on value addition to ß-carotene and anthocyanin rich sweet potato varieties. Starch is one of the major biochemical components of root and tuber crops. In Chapter 4, Subramony Moorthy and Shanavas have discussed the different characteristics of sweet

Preface

viii

potato starch and its potential applications. Processing technologies have been developed in various parts of the World to convert sweet potatoes into purees and dehydrated forms that can be used as functional ingredients in numerous food products. In Chapter 5, Van Den Truong and Ramesh Avula, review the processing operations involved in these technologies and their effect on quality, storability, nutritional values and rheological properties of sweet potato purees and powders/flours. With high level of carbohydrate, ß-carotene (orangefleshed varieties) and anthocyanin (purple-fleshed varieties), sweet potato purees and dehydrated forms can be used as functional ingredients to impart desired textural properties and phytonutrient content in processed food products. Bio-processing (fermentation) of sweet potato offers novel opportunities to commercialize this crop by developing functional foods and beverages such as sour starch, lacto-pickle, soy sauce, acidophilus milk, etc. through either solid-state or submerged fermentation. Sochu, traditional Japanese distilled liquor with an alcohol content of 20-25% is made from sweet potato. Sweet potato flour and basassae are used as substrates for production of microbial enzymes, organic acids, sodium glutamate, etc. Ramesh Ray and colleagues have discussed these aspects in depth in Chapter 6. In Chapter 7, Adelia Bovell-Benjamin has reviewed the biochemical, bioactive and functional properties of sweet potato relevant to human health, industry and animal feed systems. Sweet potato starch has industrial applications such as sweeteners, citric acid, beverage, noodle production, industrial alcohol and derived products such as glucose and maltose syrups. Two chapters in this book have been exclusively devoted to the utilization of sweet potato as animal feed in traditional livestock system. Ibisime Etela, in Chapter 6, has given an in-depth description on the use of sweet potato roots and leaves as food for cattle, goat, pig and sheep, particularly in Africa, Asia and Latin America. Dai Peters, in Chapter 9, has described four case studies in four different countries (China, Vietnam, Indonesia and Uganda) on the utilization of sweet potato in pig feed systems. She emphasizes that though these four systems share the same characteristics of feeding sweet potato to pigs, the agronomic, ecological, marketing and even socio-cultural contexts vary greatly resulting in distinctly different production and marketing approaches. The subject, post harvest aspects of sweet potato in food, feed and industries, are a topic of current interest. This book attempts to highlight some of the more significant aspects of the subject within a framework of 10 chapters. We are very grateful to the author(s) of each chapter for clearly presenting recent developments and research perspectives. We also appreciate the promptness of the individual authors in providing and processing their manuscripts.

Ramesh C. Ray Keith I. Tomlins

ABOUT THE EDITORS Dr. Ramesh C. Ray, Principal Scientist (Microbiology) and Head, Regional Centre of Central Tuber Crops Research Institute, Bhubaneswar, India is well known for his research work in the field of post harvest technology and bioprocessing of tropical root and tuber crops into value-added products. He has published 95 original research papers and 8 reviews and concept papers in peer reviewed national and international journals, and 30 book chapters. He has developed several foods and industrial processes and is co-inventor of 3 patents. He has edited/co-edited 8 books and is a member of the editorial board of international journals like Annals of Tropical Research and Journal of Environmental Biology. He has been currently selected as American Society of Microbiology International Professor from India. Dr. Keith I. Tomlins is a Reader in Food Safety and Quality at the Natural Resources Institute of the University of Greenwich, UK (www.nri.org). He has experience in international project management, research and consultancy in food safety and quality management of food and drink products worldwide and is a member of the University of Greenwich Research Ethics Committee. He is also an external consultant for a London based marine investigation company. He is the author or co-author of 35 publications in international peer reviewed journals, 24 conference papers and three books. With reference to sweet potato, he is currently (as of 2009) the councilor for publications of the International Society for Tropical Root Crops (www.istrc.org). His expertise in sweet potato research involves the post-harvest aspects in sub-Saharan Africa. He is currently involved in the Harvestplus Reaching End Users project in Uganda and Mozambique which seeks to increase consumption of provitamin A sweet potato.

In: Sweet Potato: Post Harvest Aspects in Food Editors: R. C. Ray and K. I. Tomlins

ISBN 978-1-60876-343-6 © 2010 Nova Science Publishers, Inc.

Chapter 1

SWEET POTATO GROWTH, DEVELOPMENT, PRODUCTION AND UTILIZATION: OVERVIEW Maniyam Nedunchezhiyan and Ramesh C. Ray** Central Tuber Crops Research Institute (Regional Centre), Bhubaneswar - 751019, India

ABSTRACT Sweet potato, a staple food in many of the developing countries of tropics and subtropics also serves as animal feed and raw material for the industries. This New World crop has high biological efficiency of converting solar energy into edible energy. It has spread into Europe, Africa, India, and East Indies through the batatas line and to the Philippines from Central and South America through the kamote line. Asia leads in area (60.75%) and production (86.89%) of sweet potato in the world. Sweet potato, originally the herbaceous perennial is domesticated as an annual and grows best in moderately warm climate and temperature of 21-26° C. It requires light textured soil with the optimum pH of 5.5-6.5. The crop is grown on ridges, mounds and flat beds depending upon the soil and agro-climatic conditions. As sweet potato removes appreciable quantities of plant nutrients, incorporation of 5 tonnes/ha of organic manure and a moderate dose of inorganic fertilizers (50-75 kg N, 25-50 kg P2O5 and 75-100 kg K2O/ha) is recommended. Sweet potato requires one or two weeding followed by earthing up for easing storage root bulking. Dry season planting always produces higher storage root yield than wet season planting but it requires supplemental irrigation. Sweet potato weevil, which is causing losses in certain parts of the world, can be reduced by following integrated pest management techniques. Virus diseases can be avoided by selecting disease free quality planting materials. Development of high starch, dry matter and coloured sweet potato varieties has opened up new vistas in industrial applications apart from traditional usage as food and feed. Sweet potato starch is used in textiles, paper and food manufacturing industries, preparation of liquid glucose and adhesives. ß-carotene and anthocyanins are extracted from coloured sweet potatoes, which are used as food colorants and anti-oxidants. Coloured sweet potato flour is used in various bakery and noodles preparations. Enzymes like sporamin and ß-amyalse are also produced from sweet potato storage roots. Sweet potato leaves are rich in polyphenols (mainly 

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Maniyam Nedunchezhiyan and Ramesh C. Ray

2

chlorogenic acid and iso-chlorogenic acid) which have strong suppressive effects on food poisoning microorganisms. The leaves can be used for food, green drink like tea or medicine.

ABBREVIATIONS CIP CTCRI IPM IW CPE SPFMV USRDA

International Potato Centre; Central Tuber Crops research Institute; Integrated Pest Management; Irrigation water Cumulative Pan Evaporation sweet potato feathery mottle virus; United States Recommended Dietary Allowance

INTRODUCTION Sweet potato [Ipomoea batatas L. (Lam.)] is the seventh most important food crop and next to cassava among the root and tuber crops grown in the world (Ray and Ravi, 2005). It is cultivated through out the tropics, subtropics and warmer temperate regions. Sweet potato is a staple food in many of the developing countries. It is consumed both fresh and in the processed forms. It is also used as animal feed. It has great potential as a raw material for the manufacture of a wide range of industrial products such as starch, liquid glucose, citric acid, mono-sodium glutamate and ethanol (Woolfe, 1992). Sweet potato is expected to play a vital role in combating the food shortages and malnutrition that may increasingly occur as a result of population growth and pressure on land utilization (Naskar et al., 2008b). It can produce high amount of energy per unit area per unit time. On a world scale sweet potato provides significant amounts of energy and protein (Table 1). Its production efficiency of edible energy and protein is outstanding in the developing world. The average energy output/input ratios for rice and sweet potato on Fijian farms were 17:1 and 60:1, respectively (Norman et al., 1984). The protein content of sweet potato on a fresh weight basis is low, but the average protein production/ha from sweet potato in the tropics is same that of cereals, beans and chickpeas (Yamakawa, 1997). Sweet potato is also having additional advantages. It does not normally require high levels of inputs. Weeding by either cultivation practices or herbicides is minimum in sweet potato as the vines grow very rapidly and cover the ground within few weeks after planting. Application of insecticides and fungicides are often not necessary as with the exception of sweet potato weevil, most insect damage is negligible and the fungal diseases are not usually a problem in growing areas (Naskar, 2006). Total crop failure is very rare owing to biotic and abiotic stresses and many farmers plant sweet potato as an insurance crop against food emergency (Yamakawa, 1997). Sweet potato in spite of having many desirable traits, its use as a staple food has declined in many countries. The low status accorded to both roots and vines due to their image as a ‗subsistence‘ crop, a ―poor mans‘ food‖ or something to be eaten only at the times of dire

Sweet Potato Growth, Development, Production and Utilization: Overview

3

need such as famine or war may have been a limiting factor in their exploitation as foods of high nutritional quality (Vinning, 2003). Table 1. Protein yield of various food crops Crop Cassava Sweet potato Yams Bananas Soybean Groundnut Beans Chickpea Rice Maize Sorghum Millet

Average tropical yield (t/ha) 9 7 7 13 .>1 <1 <1 <1 2 >1 1 <1

Protein (%) 1.0 1.6 2.0 1.1 38.0 25.5 22.0 20.0 7.5 9.5 10.5 10.5

Average protein yield (kg/ha) 90 110 140 143 505 217 132 132 151 118 87 58

Adapted from: Norman et al., (1984).

In worldwide, sweet potato research has been neglected in favour of the more prestigious crops like cereals, pulses and plantation crops or other export oriented cash crops. Bulkiness, problems of storage and transportation in tropical conditions, relatively low cash value/unit weight have resulted in a very low level of importance in international trade and the bulk of the crop is still used or sold for domestic purposes (Ray and Ravi, 2005).

ORIGIN AND DISTRIBUTION Sweet potato is a New World crop and originated from either in the Central or South American lowlands (Woolfe, 1992). The dried roots, the oldest remain so far discovered are those from the caves of Chilca canyon of Peru (Engel, 1970), which have radiocarbon dated at 8000-10000 years old. Ugent et al. (1983) reported the archaeological discovery of actual remains of cultivated sweet potato from the Casma valley of Peru, dated at approximately 2000 B.C. Sweet potato spread in historic times was by two lines of transmission: (1) the batatas line, which followed on from the Spanish introduction into Europe continuing after 1500 AD. By the transfer of European grown clones to Africa, India, and the east Indies through Portuguese exploration, and (2) the kamote line whereby Mexican clones were carried to the Philippines by Spanish trading galleons (Woolfe, 1992). The common names of sweet potato such as batatas, tata, mbatata, etc. indicated that sweet potato was introduced into Africa by the Portuguese; the other common names such as bombe, bambai, bambaira and so on associated with the Indian city, Bombay acquired by the British in 1662 may be linked to a later spread of the plant by the British colonial influence (Woolfe, 1992). Also in India and Southeast Asia, sweet potato was introduced in their local

Maniyam Nedunchezhiyan and Ramesh C. Ray

4

names. For example, in Malaysia it is called Spanish tuber, in the Philippines camote, in Guam both camote and batat, and in Ambon, Timor and northern Moluccas batata and their derivative words (Woolfe, 1992). Sweet potato is grown 40° N to 32° S and from sea level to almost 3000 m above mean sea level. In South America, it is grown in the Andes Mountains, in the Amazon jungle, on the great sub-tropical and temperate plains of the Southern zone and under irrigation in the desert on the Pacific coast. In the Caribbean and the Pacific, it is grown on small tropical islands, in Africa at mid elevations and in parts of the tropical low lands and in Asia at a wide range of altitudes and from temperate to tropical zones. Many of the ecosystems where sweet potato grown have poor degraded soils that support very few other crops (Yamakawa, 1997).

AREA AND PRODUCTION Sweet potato was grown in 8.996 million ha in the world during 2006 (FAOSTAT, 2008) (Table 2). Asian countries account nearly 5.466 million ha (60.75%) followed by Africa 3.154 million ha (35.06%). In America, Oceania and Europe, it is cultivated in 0.256 (2.85%), 0.113 (1.26%) and 0.006 million ha (0.08%). The world average sweet potato root yield was 13729 kg/ha. However, the highest productivity of 19634 kg/ha was found in Asia. In Asia, regions of Western and Eastern Asia produced average yield of 42630 and 21219 kg/ha, respectively. The average yield of Southern Asia (8873 kg/ha) and South-Eastern Asia (8038 kg/ha) was below the world average. The productivity in America and Europe was higher (10066 and 11937 kg/ha, respectively) than average productivity of the world (FAOSTAT, 2008). The average yield of Africa and Oceania was very low (FAOSTAT, 2008). In the world the total sweet potato root production was 123.51 million tonnes, in which Africa, America, Asia, Europe and Oceania contribute 12.9 (10.5%), 2.6 (2.1%), 107.3 (86.9%), 0.1 (0.1%) and 0.6 (0.5%) million tonnes, respectively during 2006 (Table 2). The maximum amount of roots (67%) is used as forage for animal production. Only 33 % of the produce is used for food and product development.

GROWTH AND DEVELOPMENT Sweet potato was first described by Linnaeus as Convolvulus batatas in 1753. However, in 1791 Lamarck classified this species within the genus Ipomoea on the basis of the stigma shape and the surface of the pollen grains. Therefore, the name was changed to Ipomoea batatas (L.) Lam. The systematic classification of the sweet potato is as follow: Family Tribe Genus Sub-genus Section Species

Convolvulaceae Ipomoeae Ipomoea Quamoclit Batatas Ipomoea batatas (L.) Lam.

Table 2. Current sweet potato production from selected countries in different regions of the world based on 2006 FAO survey Region / country World Africa Eastern Africa Middle Africa Northern Africa Southern Africa Western Africa Total for Africa America Northern America Central America Latin America Caribbean Total for America Asia Central Asia Eastern Asia Southern Asia South-Eastern Asia Western Asia Total for Asia Europe Eastern Europe Northern Europe Southern Europe Western Europe Total for Europe Oceania Australia and New Zealand Melanesia Micronesia Polynesia Total for Oceania

Area (ha) 8,996,472.00

Tuber production Yield (kg/ha) Quantity (tonnes) 13,728.69 123,509,771.00

Percent of world 100.00

Feed resource (tonnes)* Forage By-product 82,751,546.57 40,758,224.43

1,634,337.00 274,671.00 11,255.00 16,010.00 1,217,974.00 3,154,247.00

4,399.46 4,434.55 28,411.64 3,099.94 3,387.55 4,090.86

7,190,202.00 1,218,042.00 319,773.00 49,630.00 4,125,950.00 12,903,597.00

5.82 0.99 0.26 0.04 3.34 10.45

4,817,435.34 816,088.14 214,247.91 33,252.10 2,764,386.50 8,645,409.99

2,372,766.66 401,953.86 105,525.09 16,377.90 1,361,563.50 4,258,187.01

35,139.00 3,144.00 109,074.00 112,416.00 256,629.00

20,976.72 20,027.67 11,986.57 4,791.77 10,065.87

737,101.00 62,967.00 1,307,423.00 538,671.00 2,583,195.00

0.60 0.05 1.06 0.44 2.09

493,857.67 42,187.89 875,973.41 360,909.57 1,730,740.65

243,243.33 20,779.11 431,449.59 177,761.43 852,454.35

na 4,797,503.00 150,311.00 517,389.00 714.00 5,465,917.00

na 21,218.72 8,873.38 8,037.75 42,630.25 19,634.35

na 101,796,861.00 1,333,767.00 4,158,641.00 30,438.00 107,319,707.00

na 82.42 1.08 3.37 0.02 86.89

na 68,203,896.87 893,623.89 2,786,289.47 20,393.46 71,904,203.69

na 33,592,964.13 440,143.11 1,372,351.53 10,044.54 35,415,503.31

na na 6,479.00 na 6,479.00

na na 11,937.34 na 11,937.34

na na 77,342.00 na 77,342.00

na na 0.06 na 0.06

na na 51,819.14 na 51,819.14

na na 25,522.86 na 25,522.86

1,425.00 110,678.00 515.00 582.00 113,200.00

16,376.84 5,346.67 6,341.75 13,003.44 5,529.42

23,337.00 591,759.00 3,266.00 7,568.00 625,930.00

0.02 0.48 0.003 0.01 0.51

15,635.79 396,478.53 2,188.22 5,070.56 419,373.10

7,701.21 195,280.47 1,077.78 2,497.44 206,556.90

Source: FAOSTAT [2008]. *Estimated as: Forage = 67 percent of ―Quantity‖; By-product = 33 percent of ―Quantity‖.

6

Maniyam Nedunchezhiyan and Ramesh C. Ray

The section Batatas have 13 wild species that are considered to be related to the sweet potato. These are: I. cordatotriloba (I. trichocarpa), I. cynanchifolia, I. grandifolia, I. lacunose, I. leucantha, I. littoralis, I. ramosissima, I. tabascana, I. tenuissima, I. tiliacea, I. trifida, I. triloba and I. umbraticola. In sweet potato identification and delineation of individual genome was difficult due the complex nature of genomes and high polyploidy. Owing to this difficulty the species which had contributed to the evolution of sweet potato could not be easily located (Tandang and Alfonso, 2006). Sweet potato is a hexaploid plant, 2n= 6x = 90. This indicates that the basic chromosome number is x = 15. In section Batatas diploid I. leucantha (BB) and tetraploid I. littoralis (BBBB) have been established to be the probable progenitors of sweet potato (BBBBBB). I. leucantha could be derived from natural crosses between I. cordatotriloba and I. lacunose (Austin, 1977). I. littoralis and I. tiliacea are tetraploids. The other species are diploids with 2n = 2x = 30. I. trifida includes plants that can be 2x, 3x, 4x and 6x and viewed as the probable wild ancestor. The ploidy level of I. tabascana and I. umbraticola is still unknown (Huaman, 1992). The sweet potato is an herbaceous perennial plant. However, it is domesticated as annual plant by vegetative propagation using either vine cuttings or storage roots. The prostate vine system of sweet potato expands very rapidly horizontally on the ground with erect/semierect/spreading/very spreading growth habit. The vegetative propagated sweet potato produces adventitious roots that develop into primary fibrous roots which are branched into lateral roots. The fibrous roots absorb nutrients and water, and anchor the plant as well as store the photosynthetic products. As the plant matures, lateral roots develop into storage roots by accumulating photosynthates. However, due to lignification some roots remain thick pencil roots. Plants grown from true seed form a typical tap root with lateral branches. Later on, the central tap root functions as storage root (Figure 1).

Figure 1.

Post Harvest Handling, Storage Methods, Pests and Diseases of Sweet Potato

7

Sweet potato stem is cylindrical in shape with varied colour and diameter and runs about 1-5 m depends upon cultivar and the availability of water in the soil. Apical shoots and stems vary from glabrous to very pubescent. The internode length can vary from short to very long. The leaves are simple and spirally arranged on the stem in a pattern known as 2/5 phyllotaxis. The leaf lamina can be entire, toothed or lobed. The base of the leaf lamina generally has two lobes that can be almost straight or rounded. The general shape of the leaves varies from round to triangular. The number of lobes generally range from 3 to 7 and can be easily determined by counting the veins that go from the junction of the petiole up to the edge of the leaf lamina. Leaf colour, size, pigmentation, hairiness and petiole length vary according to cultivar and environmental conditions. Sweet potato, under normal conditions does not flower. However, some cultivars produce few to huge numbers of flowers (Huaman, 1992). The inflorescence is generally a cyme and the flower is bisexual. Calyx consists of five sepals in two whorls (2+3). Corolla consists of five petals that are fused forming a funnel. The androecium consists of five stamens with filaments that are covered with glandular hairs and are partly fused to the corolla. The length of the filaments is variable in relation to the position of the stigma. The gynoecium consists of a pistil with a superior ovary, two carpels and two locules that contain one or two ovules. The stigma is receptive early in the morning and the pollination is mainly by bees. The fruit is a capsule, turns brown when mature and can be pubescent or glabrous. Each capsule contains one to four seeds of approximately 3 mm size. The embryo and endosperm are protected by a thick, very hard and impermeable testa. Seed germination is difficult and requires scarification by mechanical abrasion or chemical treatment. Seeds do not have a dormancy period but maintain their viability for many years. The storage roots that develop from adventitious roots show the protective periderm or skin, the cortex, cambium ring and central parenchyma. The amount of latex formed depends on the maturity of the storage root, the cultivar and the soil moisture during the growing period. Storage roots may be formed in cluster or dispersed depending on the cultivar. Storage root vary in shape and size. The skin and flesh too vary in colour from white to orange, red and purple (Huaman, 1992).

SWEET POTATO PRODUCTION SYSTEM Climate and Soil Sweet potato grows best and yields storage roots high in moderately warm climate and temperature of 21-26° C. A well distributed rainfall of 75-150 cm is favourable for its cultivation. It can tolerate drought to some extent but cannot withstand water logging. It requires plenty of sun shine, whereas shade causes reduction in yield. However, sweet potato is grown as intercrop under plantation/orchard crops with the motto of profit maximization and crop intensification (Nedunchezhiyan et al., 2007). In crop intensification and even slight frost and temperature below 10° C checks its growth and development of storage roots. Excess of rainfall and cloudy conditions encourage vine growth and reduce storage root yield. Dry season storage root yields were higher than rainy season yields (Nedunchezhiyan and Byju, 2005). Well drained loam and clay loam soils are good for sweet potato. Though it grows on a variety of soils, sandy loam, with clay sub-soil is ideal. Heavy clay soils restrict

Maniyam Nedunchezhiyan and Ramesh C. Ray

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the storage root development due to compactness and highly sandy soil encourages long cylindrical pencil like roots. Soil pH of 5.5-6.5 is ideal for sweet potato even though it is grown in high acidic conditions. High soil pH invites pox and scurf diseases in sweet potato and at low pH sweet potato suffers aluminum toxicity. Sweet potato is sensitive to alkaline and saline conditions (Dasgupta et al., 2006; Mukherjee et al., 2006).

Variety The variety plays a significant role in yield improvement. Development of location specific varieties is the major objective of the many Research and Development organizations working on sweet potato. The elite clones are developed by following different methods of breeding procedures. The common methods are clonal selection, open pollinated selection, hybridization, mutation and biotechnology (Nayar and Naskar, 1994). Some of the elite varieties those are cultivated in different countries are as follows: Bangladesh: China: India:

Japan: Korea: Malaysia: New Zealand: Papua New Guinea(PNG): Srilanka: Thailand: United States of America: Vietnam:

Lalkothi, Kalmegh, BARI SP-6 and BARI SP-7 Xuzhou 18 Co-1, VL Sakarkand-6, Sree Nandini (75-OP-217), Sree Vardhini (75-OP-219), Co-2, Co-3, Samrat, Sree Bhadra, Sree Arun, Sree Varun, Kalinga, Goutam, Sourin, Kishan, H-41, H-42, H-268 (Varsha), Rajendra Sakarakand – 5, Sree Rethna, Gouri, Sankar, Sree Kanaka, Kamala Sundari, S-1221, WBSP-4, Tripti and BCSP-5, Birsa Sakarakand – 1, Indira Sakarakand – 1 and Bidhan Jagannath. Quick Sweet Hongmi, Hwangmi, Sinjami, Mokpo 34, Shinmi, Wonmi, Poongmi, Borami, Mokpo 32 and Enumi Gendut, Telong, Jalomas, Minamiyutaka, Pisang Kapas, Madu, Bawang, Kangkung Cina, Ikan Selayang, Kangkung Kampung, Bukit Naga, Taiwan and Pasar Borong-1. Owairaka Red, Toka Toka Gold and Beauregard K9, K42, Wanmun murua, Wanmun Large, Koitaki 2 and UIB016 Wariyapola Red, HORDI-C-5, P2-20, 94-3, PH-8 and HORDI-C-15 Maejo, Taiwan, PIS 205, PIS 65-16 and PIS 166-5 Jewel and Hernendez K51, H12 and TV1

Orange Flesh Sweet Potato Orange flesh sweet potato (Figure 2) contains β-carotene which is a precursor of vitamin A. β- carotene content of sweet potato varies with the varieties up to 20 mg/100 g fresh weight (Sakamoto et al., 1987; Yamakawa, 1997). One cup of cooked sweet potato can

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provide 30 mg (50,000 IU) of β-carotene. It could take 23 cups broccoli to provide the same amount (Sakamoto et al., 1987). It has four times United States Recommended Dietary Allowance (USRDA) for β-carotene when eaten with skin.

Figure 2.

Some of the orange flesh sweet potato genotypes available in India are Kamala Sundari, ST14, Gouri, Sree Kanaka, etc. The ST14 line content carotene of 13.83 mg/100 g fresh root (Vimala et al., 2006). In Japan, Benihayato, Kyushu No. 114, in Mozambique, MGCL01, 440215, Resisto and in Thailand, PIS 226-24, PIS 227-6, etc are the high yielding orange flesh varieties.

Purple Flesh Sweet Potato Anthocyanins are a natural, soluble food pigment and contribute to the red, blue, and purple colouring of the flowers and other plant parts. The pigment has applications in pharmaceutical industries due to its bright colour, safe, non-poisonous, rich nutrition and health care function (Rice-Evans and Packer, 1998). It can also be used for cosmetic industry. At present anthocyanin is extracted from bill berry, red grape and straw berry. Red and purple pigmentation in various parts of the sweet potato such as stem, leaf and storage root is also caused by the presence of acylated anthocyanins (Fan et al., 2008). Bassa and Francis (1987) first noted that sweet potato anthocyanins are an effective natural food colorant for preparation of beverages. Sweet potato anthocyanins are comparable to red cabbage in terms of their quality as natural food colorants. The recent detection of the radical scavenging, antimutagenicity and efficacy against liver disease of sweet potato anthocyanins (Terahara et al., 2004) indicated that purple fleshed sweet potatoes (Figure 3) may contribute to maintaining the health of human beings. Ayamurasaki, a high anthocyanin sweet potato variety was developed by the Kyushu National Agricultural Experiment Station (KNAES), Japan in 1995 (Yamakawa et al., 1997). Regional Centre of CTCRI, Bhubaneswar (India) has developed a high anthocyanin line ST13 (CTCRI, 2003). In Indonesia, three high yielding purple fleshed clones (MSU 01017-16,

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Maniyam Nedunchezhiyan and Ramesh C. Ray

MSU 01022-12 and MSU 01002-7) have been identified (Jusuf et al., 2005). The variety PIS from Thailand is rich in anthocyanin (Narin and Reungmaneepaitoon, 2005).

Figure 3.

Planting Time As sweet potato requires moderately warm temperature and light soil; accordingly, it is planted in various countries. Thus it is planted and harvested every month in one part or other in the world. In India sweet potato is grown in all the seasons i.e., kharif (June-August), rabi (October-December) and summer (Janauary-February). However, sweet potato planted during rabi season enjoys warm sunny days and cool nights with moderate rainfall which is conducive for higher storage root yield. In Malaysia, lower yield was observed during wet growing seasons (August to December) and higher root yield was observed in drier growing seasons (January to July) (Zaharah and Tan, 2006). In Solamon Islands, highest root yields were reported when sweet potato was planted between September and February (Bourke, 2005). In Puerto Rico, highest root yields were obtained when planted in November and lowest in crops planted in March or May (Badillo Feliciano, 1976). In Korea, best results were obtained when sweet potato was planted during May-June (Jeong et al., 1986). In Taiwan, high root yields of sweet potato were obtained when the mean daily temperature was maintained around 22° C for the first 60 days after planting (Sajjaponge, 1989). In India, rainfed crops should be planted immediately after onset of monsoon for higher storage root yields (Nedunchezhiyan and Reddy, 2006), whereas dry season crop should be planted in October-November (Nath et al., 2006). In Cameroon, sweet potato is produced in May/June and September/October seasons (Njualem et al., 2005).

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Planting Materials Sweet potato is usually propagated through vine cuttings obtained either from freshly harvested plants or from nursery. However, recurrent use of vines can cause increased weevil infestation, even though there is less change of root yield reduction (Nair, 2006). Vines obtained from nursery are found to be healthy and vigorous. A healthy and vigorous growing vine produces maximum storage root yield. The apical and middle portion of the vine is found to be best compared to bottom portion. Bottom portion usually thick and woody, some times fail to establish, further chance of weevil spread is more due to proximity with the crown portion, where sweet potato weevil multiplies (Nair, 2006). A vine length of 20-40 cm with at least 3-5 nodes is found to be optimum for the storage root production in different parts of India (Nair, 2006). In Cuba, 2530 cm long stem cuttings were found to be ideal. Sweet potato cut vines with intact leaves stored under shade for 2-3 days prior to planting in the main field promoted better root initiation and established the vines quickly (Biswal, 2008). However storing of the vines for a long time caused failure of establishment in the field due to drying. Early established vines are vigorous and produces higher yield. Stored vines were found to superior to fresh vines in respect of leaf area index, crop growth rate, root bulking rate, number of storage root per plant and root and vine yields (Mukhopadhyay et al., 1990). When the vines are to be transported to distant places, leaves can be removed to reduce the bulkiness. This method can be adopted for multiplication of planting materials which involve transportation costs.

Land Preparation and Planting The land is ploughed two to three times to a depth of about 15-20 cm and harrowed to pulverize the soil. Sweet potato is planted on mound, ridge and furrow, raised bed and flat methods in different regions. It is preferable to plant sweet potato on mounds in areas experiencing problems of drainage. Ridges formed across the slope are recommended in sloppy lands for the control of soil erosion. In Vietnam, planting is done on beds formed at a width of 1-1.4 m and 0.4- to 0.5 m height (Ngoan, 2006). Among different methods of land preparation the highest storage root yield was realized when planted on mounds under Indian conditions (Ravindran and Mohankumar, 1985). The higher yield recorded for mounds is probably be due to better soil aeration permitted by mounds and less tendency to soil compaction. In Bangladesh, higher yields were reported with trench planting followed by ridge and flat method of planting in alluvial soils under irrigated conditions (Bhuiyan et al., 2006). Sweet potato cuttings of desirable length (20 cm) are planted in the soil with both ends exposed and the middle portion buried in the soil. Vines are also planted in an inclined position with half of its length buried in the soil. Sweet potato cuttings are also planted horizontally to the soil surface with 5 or 6 nodes. In Orissa (India), farmers plant long size (50-75 cm) vines horizontally (Nedunchezhiyan et al., 2006). However, CTCRI (India) has recommended to plant the cuttings in the soil with both the ends exposed and the middle portion buried (Nair, 2006). Whatever may be the planting method, 1-2 nodes should be below the soil for better establishment. Horizontal planting resulted in higher transplant

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survival and better development of the root system compared to other methods though laborious (Nair, 2000). In Uganda, planting of cuttings showed that there is neither advantage nor disadvantage in planting through the soil (horizontal) and leaving both ends protruding (Kaggwa et al., 2006). Planting of sweet potato vines at depth ranging from 2.5 to 10.0 cm when planted vertically did not have any significant influence on stand establishment and final storage yield (Ravindran and Mohankumar, 1985).

Plant Population High plant population by planting close spacing is generally recommended for sweet potato to achieve maximum storage root yield. A planting distance of 30-60 cm between the rows and 15-20 cm between the plants gives maximum yield (Kaggwa et al., 2006). However, when sweet potato is planted on mounds no specific spacing is followed and vines are planted on mounds by accommodating 3-6 slips/ mounds. In Uganda, a plant population of 25000 to 35000 is suggested (Kaggwa et al., 2006). A significant reduction in yield was observed when the plant population was dropped to 12000/ha (Kaggwa et al., 2006). In Cameroon sweet potato clones 20000 plants/ha was found optimum (Woolfe, 1992). In Bangladesh, maximum root yield was obtained when vines were planted at spacing of 60 x 45 cm with two vines/hill (Bhuiyan et al., 2006) and in alluvial soils 60 x 30 cm spacing was optimum planted on flat bed for high yielding varieties (Golder et al., 2007).

Manures and Fertilizers As sweet potato removes appreciable quantities of plant nutrients, incorporation of considerable amount of organic manure at planting is recommended to maintain soil productivity. Application of manures has significant impact on growth and root yield of sweet potato (Salawu and Mukhtar, 2008). Usually farm yard manure/ cow dung compost or green manure is used as organic manure for sweet potato (Kaggwa et al., 2006). Sweet potatoes grown in fertile soils generally do not receive dressings of organic manure while soils low in organic matter content have to be supplied with organic manures at 5 to 10 tonnes/ha to ensure proper development of storage roots (Nedunchezhiyan and Reddy, 2004). Application of legume green manure is found an alternative to farmyard manure (Reijintjes et al., 1992; Kaggwa et al., 2006). On unit nitrogen basis, farmyard manure, pig manure and poultry manure were equally effective (Nedunzhiyan, 2001). Nitrogen (N) is essential for crop growth. Application of N increased the root yield (George and Mitra, 2001; Satapathy et al., 2005). However, high amount of N application encourages vine growth rather than storage root development. A moderate dose of 50-75 kg N/ha is optimum for root production in sweet potato (Nair et al., 1996; Sebastiani et al., 2006; Biswal, 2008). Higher levels of N sometimes depressed the root yield (Hartemink, 2003). Conjunctive use of fertilizer N and any of the organic manures to supply 50% each of recommended N produced the maximum vine and storage root yield compared to other N management practices (Nedunchezhiyan and Reddy, 2002). Inoculation of Azospirillum (freeliving N2- fixing biofertilizer) was found to increase storage root yield (Desmond and Hill, 1990; Saikia and Borah, 2007), quality (Nedunchezhiyan et al., 2004) and soil fertility status

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in sweet potato field (Nedunchezhiyan and Reddy, 2004). Azospirillum replaces one-third N requirements and reduces cost of cultivation (Nedunchezhiyan and Reddy, 2002; Saikia and Borah, 2007). Nitrogen has been reported to influence the quality characters apart from storage root yield of sweet potato. Continuous use of fertilizer N may in some situation have detrimental effects on root quality. Therefore, use of organic source of N is essential to improve the quality characters. However, in the present day situation per ha yield of starch, vitamin C, βcarotene, etc. is more important than percentage content. Nedunchezhiyan et al. (2003) noticed discernable variation in the quality characters due to different source of N and their combinations. Response of sweet potato to phosphorus (P) is very low. A dose of 25-50 kg P2O5/ha is considered optimum for sweet potato (Mohanty et al., 2005; Akinrinde, 2006; Sebastiani et al., 2006). The relative efficiency of rock phosphate as source of P to sweet potato was equal to single super phosphate in direct effect but superior to it in residual value (Kabeerathumma et al., 1986). Potassium (K) is key element and essential in the synthesis and translocation of carbohydrates from the tops to the roots (Byju and Nedunchezhiyan, 2004). A moderate dose of 75-100 kg K2O is recommended for sweet potato (Mukhopadhyay et al., 1990; Nair et al., 1996; John et al., 2001). However, in China sweet potato responded to very high level of K2O 300 kg/ha (George et al., 2002). The quality characters like starch and protein content was found to increase with increased K levels (Biswal, 2008).

Weeding Sweet potato is a quick growing crop suppresses weeds when grown closely. However, for root yield it is grown with wider spacing. Under such conditions, weeding becomes necessary particularly in the early stages of the growth. Earthing up of the soil also brings about weed control besides improving the physical condition of the soil. About 40-80 % reduction in storage root yield is observed in sweet potato due to weed infestation at different stages of growth (Nedunzhiyan et al., 1998). Celosia argentia – Digitaria sanguinalis – Cleome viscose were the dominating weed community in upland sweet potato ecosystem (Nedunzhiyan, 1996). Due to initial slow growth of sweet potato, the crop - weed competition set at early for water and nutrients (Nedunchezhiyan and Satapathy, 2002). The critical period of crop – weed competition sets between 30-45 days after planting (Nedunzhiyan et al., 1998). For higher yield, weeding and earthing up has to be given between 15-30 and 45-60 days after planting. Herbicides are also used to a limited extent for the control of weeds in sweet potato. Application of Isoproturon 1 kg a.i./ha as pre-emergence 2 days after planting (mixed with dry fine sand and broadcasting) followed by one hand weeding 30 days after planting controlled the weed effectively(Nedunzhiyan, 1996). Alachlor 3.4 or 6.7 kg/ha application gave 88-100% control of weeds in sweet potato plots in North Carolina (Herman et al., 1983). Mulching is not uncommon in upland rainfed conditions in small holder farming system. Mulching provides many benefits to plants by augmenting rhizosphere microflora (Kundu et al., 2006). It also conserves moisture and reduces soil temperature. In Korea in the 1980s, poly ethylene film mulching method was developed for producing good quality sweet potato

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Maniyam Nedunchezhiyan and Ramesh C. Ray

roots (Jeong, 2000). In Japan, black plastic film mulches are used for controlling weeds in high rainfall hilly regions, which also protect the hills from erosion (Yamakawa, 1997). Mulched soil retained higher moisture and enhanced mineral N (29-87%), P (1.4-12.6%) and K (16-36%) availability when applied for dry season sweet potato (Kundu et al., 2006). Sweet potato grows vigorously and produces large quantity of vines when temperature and rainfall are favourable at the cost of storage roots (Nedunchezhiyan and Byju, 2005). Part of the vine preferably the top portion can be removed and used as leaf vegetable or forage or planting material (Satapathy et al., 2006). In sweet potato, root bulking commences about six weeks after planting. Higher root yields are not necessarily associated with greater foliage production (Nedunchezhiyan and Byju, 2005). In rainy season crop removal of 15 cm shoot tip did not affect the root yield at Bhubaneswar, India (Roy Chowdhury and Ravi, 1990).

Irrigation Sweet potato vines are tender and fragile, if sufficient moisture is not available in the soil immediately after planting it dries up. For proper sprouting and establishment of vines sufficient moisture in the soil at the time of planting is ensured. Sweet potato is mostly grown under rainfed conditions. Hence, planting is carried out on rainy day or immediately after rain. Sweet potato is also grown in dry season under protective irrigation. Under such conditions if sufficient moisture is not available after planting, irrigation has to be provided on alternate days initially for the first fortnight and thereafter once in 7-10 days. A total of 1215 irrigations are required for the entire crop period. Irrigation two days prior to harvest can be helpful for easy lifting of roots but this also depends on the soil condition. Moisture stress during crop growth significantly affected the storage root yield (Ravi and Indira, 1996). Sweet potato required on an average of 2 mm of water/ day in the early parts of the growing season and gradually increased to 5-6 mm of water/ day prior to harvest (Gomes and Carr, 2003). Irrigating the sweet potato field at IW (Irrigation water): CPE (Cumulative Pan Evaporation) of 0.6-0.8 in silt clay loam and clay loam soils (Biswal, 2008) and IW: CPE of 1.0 in sandy and sandy loam soils (Nair et al., 1996; Roy Chowdhury et al., 2001) recorded higher root yield. However, when soil moisture was high sweet potato had luxuriant vegetative growth with little or no tuberiz ation (Bourke, 2005; Biswal, 2008).

Pests and Diseases Nematodes and insect pests attack sweet potato storage root and vine. Meloidogyne spp. (root-knot) and Rotylenchulus reniformis are the major known nematode pests of sweet potatoes in the tropics (Mohandas, 2006). They attack the fibres as well as fleshy roots and reduce yield and quality. Also allow other pathogens to penetrate through the wounds. Nematodes can be controlled by applying neem cake 500 kg/ha in the last ploughing before ridge and furrow making. Sree Bhadra variety from India is found to be resistant to root knot nematode (Mohandas, 2006). Sweet potato weevil, Cylas formicarius Fab. is a major pest in most sweet potato growing countries (Ray and Ravi, 2005). Larvae and adult feed on the roots, causing extensive damage both in field and storage in many parts of the world. The weevil can be effectively managed

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by following the integrated pest management (IPM) strategy developed by CIP (International Potato Centre, Peru) as well as by CTCRI, India. The IPM is as follows: (1) dip the vine cuttings in fenthion or fentrothion 0.05% solution for 10 min before planting, (2) re-ridge the crop two months after planting, (3) install synthetic sex pheromone traps @ 1 trap/100 m2 area to collect and kill the male weevils and (4) destroy the crop residues after harvest by burning. IPM practice reduced 50-60% weevil infested storage roots and increased more than 20% storage root yield (Sethi et al., 2003). In sweet potato weevil endemic area early harvest of roots is recommended to avoid the weevil damage (Mohanty et al., 2005). The scarabee, Euscepes postfasciatus (Fairm.) is a serious pest in the drier parts of South America, the Caribbean and the Pacific (Yasuda, 1997). Larvae and adults feed on roots and stems of the sweet potato. The larvae produce narrow tunnels in the roots and like the sweet potato weevil cause the roots to produce bitter toxic terpenoid compounds making them inedible. The sweet potato vine borer, Omphisa anastomosalis has been reported in India, Malaysia and China, where it is considered to be as destructive as the sweet potato weevil (Rajamma and Premkumar, 1994). Wild pigs, rats and other herbivores cause damage and loss in some countries (Ray and Ravi, 2005). In sweet potato, other diseases are observed in field conditions but the severity is less. Fungal diseases are not normally very serious in the tropics in field conditions (Woolfe, 1992). Stem rot, Fusarium oxysporum Schlect. F.sp. batatas is destructive in the United States (Woolfe, 1992). Virus diseases may attack the root or the leaves. They include internal cork disease and mosaic virus. More than 12 virus diseases are identified; among them sweet potato feathery mottle virus (SPFMV) is prominent. Viruses are important in parts of East and West Africa but not in the rest of the world. The virus diseases can be managed through field tolerant varieties, use of virus free planting materials as well as meristem cultured plants (Prasanth et al., 2006).

Harvesting Environment and variety play a significant role in deciding the time of harvest in sweet potato. In grain crops, where single harvesting is followed immediately after maturity; otherwise, grains get shattered or spoiled if retained few more days in the field. Whereas in sweet potato single harvesting and double harvesting (progressive harvesting) are practiced as root yields are not affected by delaying few days after maturity. Staggered harvesting facilitates marketing and realizing reasonable price for the produce. However, in Papua New Guinea, non- marketable storage roots constituted a greater proportion of the total storage roots with progressive harvesting compared to single harvesting although the yield of marketable roots (100 g above) were 2.0-3.4 tonnes/ha higher (Bourke, 2006). Though yield/ha will increase if the crop remains in the ground longer period but the storage root become less palatable and weevil damages and rots become more noticeable with age. The maturity of the storage roots can be determined by cutting the roots. The cut surface of the immature roots gives a dark greenish colour, while in mature roots the cut ends dry clearly. A light irrigation 2-3 days prior to harvesting facilitates easy lifting of the storage roots. After removing the vines the roots are dug out without causing injury (Nair, 2000). Manual harvesting is the most common method in the tropics.

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The yield varies with the location, variety, season of planting, soil conditions and fertility. In general the storage root yield varies from 20-25 tonnes/ha for promising varieties with improved crop management practices (Nair, 2000).

SWEET POTATO UTILIZATION SYSTEM Sweet potato storage roots are utilized primarily as human food after boiling or baking. Roots can also be utilized for animal feed, starch production, as an ingredient in a variety of food and drink products and in protein and enzyme production.

Utilization in Animal Feeds Culled roots and vines are used as animal feed either directly or processed (Nedunzhiyan et al., 2000; Bourke, 2006; Naskar et al., 2008a). Silage, a nutritious feed can be made effectively in small readily transportable quantities using unsalable roots and tops (Otiono et al., 2006). Boiled sweet potato roots can be fed to the level of 40% of total dry matter intake to weaned piglet for better growth rate and nutrient utilization (Gupta et al., 2006).

Utilization for Starch Production Sweet potato storage roots are used as a source of starch. The starch extracted from sweet potato is used in textiles, paper and food manufacturing industries, preparation of liquid glucose and adhesives (Bovell-Benzamin, 2007). In Japan, sweet potato starch is mainly used for liquid glucose production (Yamakawa, 1997; Moorthy and Shanavas, chapter 4 in this book). Sweet potato starch extracted from fresh roots is having unsatisfactory characters due to interference of protein, sugars and fibre (Yamakawa, 1997). However, in frozen root technology above interference can be nullified. Water and water soluble components are subtracted easily from frozen roots during melting, and starch and fibres are separated after that (Yamakawa, 1997). The starch contents of cultivated varieties are about 12-20% on fresh weight basis (Bovell-Benzamin, 2007). However, these cultivars cannot compete with starches of maize and cassava in terms of price. Hence new cultivars should be developed with 29-30% starch along with high amylose content and pasting trait in low temperature (Komaki and Yamakawa, 2005).

Utilization of Coloured Sweet Potato Sweet potato storage root has three kinds of colour pigments, anthocyanin, ß-carotenoids and unidentified flavonoids (Naskar et al., 2007). In the health conscious world, consumers prefer natural food colours to artificial ones. Natural red colour is extracted from insects,

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microorganisms and plants such as red cabbage and red beet. In Japan, in late 1980, anthocyanin pigments in sweet potato storage roots was discovered (Bassa and Francis, 1987). The colour quality and stability of this sweet potato anthocyanin is as high as that of red cabbage. In 1995, Japan released first anthocyanin rich sweet potato variety ‗Ayamurasaki‘. Similarly, orange and yellow coloured sweet potatoes are also documented in different parts of the world. The Regional Centre of CTCRI, Bhubaneswar has released its first orange flesh hybrid sweet potato ‗Gouri‘ in 1998. It contains ß-carotene 4.5-5.5 mg/100 g fresh root (CTCRI, 2003). CTCRI, Thruvananthapuram has released ‗Sree Kanaka‘ a sweet potato variety contains ß-carotene 8.8–10.0 mg/100 g fresh root (CTCRI, 2006). The highly coloured storage root is made into flour with purple and orange colour. Ayamurasaki a purple colour sweet potato is having 35% dry matter which is high enough for making flour (Yamakawa et al., 1997). Similarly, ‗Benihayato‘ an orange coloured sweet potato variety is having more than 30% dry matter (Sakamoto et al., 1987) suitable for flour making (van Hal, 2000). Flour making whole roots with skin (cut into strip and dried) contains more amount of functional component than an inner one alone because skin contains more colouring pigments. Drying roots quickly under 60ºC is important in order to maintain the deep flour colour (van Hal, 2000). Recent research (Bechoff et al., 2009) has shown that losses during drying are generally the least (about 15%) while during storage the losses can be as high as 70%. Baked roots retained about 75% of the original carotenoid content, while flours from sun dried chips registered a loss of 70% (Babu, 2006). Sweet potato flour should be stored better under 15º C and without air especially for orange coloured flour containing carrotenoid. Mixed flour from sweet potato and wheat can be the good materials for many food item such as biscuits, bread, noodles, snacks, cakes and so on (Mais and Brennan, 2008). Substituting 38% of wheat flour (by weight) with boiled and smashed orange flesh sweet potato in bread buns was acceptable to rural consumers and bakers in Central Mozambique because of heavier texture and its attractive golden appearance (Low and Jaarsveld, 2006). The wastes after making flour can also be used for anthocyanin and carotenoid extraction (van Hal, 2000). Sweet potato juice can be made from highly coloured especially orange coloured sweet potatoes. Carrot juice, rich in carotene has acquired more popularity than tomato juice due to its superior taste. Recently, several sweet potato cultivars were developed with higher carotene content than carrot (Yoshimoto, Chapter 3 in this book). However, in order to produce high quality juice from sweet potato, it is necessary to make sweet potato smell and browning (colour degradation) lesser than carrot juice (Tamaki et al., 2007). Hence, new cultivars are developed with high ß-carotene content, low colour degradation, low dry matter content along with high yield. J-Red (Japan) and ST13 (India) varieties are suitable for juice making. The key technology in making sweet potato juice is the decomposition of starch and dextrin by enzymes which makes the filtration easy and improves the texture of juice (Panda and Ray, 2007). Coloured wastes after filtration is left to be reused. Coloured sweet potato can also be fermented to make alcoholic beverage such as beer and wine. Yellow, red and black coloured beverage like beer (sparkling liquor) is being sold in Japan (Yamakawa, 1997). In India, Regional Centre of CTCRI, Bhubaneswar perfected technology for making red wine from anthocyanin rich sweet potato genotype (ST13) (CTCRI, 2003). The key technology to succeed in developing these beverages is enzymatic decomposition of starch to sugars and fermentation by yeast. In Japan, distilled liquor ‗Shochu‘ is made from coloured sweet potato (Yamakawa, 1997).

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Maniyam Nedunchezhiyan and Ramesh C. Ray

Coloured pottage soup and croquette can be made from coloured storage roots in place of potato and pumpkin. Sweet potato soup with a beautiful colour, smooth texture, a bit of sweetness will be preferred than the soups from other crops. Sweetness is undesirable for cooking use. Hence, coloured variety with less sweetness can be developed for soup making (Yamakawa, 1997). Snack foods such as French fries and potato chips will be though as one of the usage of coloured sweet potato. But these products are bit harder than potato when sweet potato roots are fried in the oil. However, to some extent this can be improved by frying under vacuum condition (Yamakawa, 1997).

Utilization for Protein and Enzyme Sweet potato is a low protein (ipomoein/sporamin) crop. It contains 4-7% on a dry weight basis. Sweet potato storage root protein quality is better than maize and beans. However, lysine and s-amino acids are limiting amino acids for infant and children when they consume sweet potato (Yamakawa, 1997). Variation in quantity and quality of crude protein and individual amino acids content is noticed among varieties. So far the usage possibility of sporamin remains unknown except for nutritional aspect. Among enzymes contained in sweet potato ß-amylase is present in high amount. Although the activity of crude ß-amylase from current sweet potato cultivars is about 3000 unit/g and not higher than those from soybean (4000 unit/g) and barley (6000 unit/g), the cost of the sweet potato ß-amylase production is about one-tenth cheaper than the others (Yamakawa, 1997). There is possibility of doubling ß-amylase content (6000 unit/g) in sweet potato storage roots (Yamakawa, 1997). However, it is required to increase heat tolerance of sweet potato ß-amylase whose activity is lost at less than 60º C. As the ß-amylase is water soluble, it can be squeezed from raw roots or frozen roots at first and then condensed by spray drier. The starch can be collected from waste materials afterwards.

Utilization of Tops Usually sweet potato tops are used as livestock food or restored into soil as green manure when sweet potato is harvested. Research evidences suggested that sweet potato tops are rich in nutrition such as protein, vitamins and minerals (Woolfe, 1992). It is necessary to develop new technology to use the top more efficiently and economically as materials for food processing. Sweet potato tops especially leaves have amazing amount of polyphenols composed mainly of chlorogenic acid and iso-chlorogenic acid (Mohapatra et al., 2001). The ethanol extracts of leaves shows the strong suppressive effects to some food poisoning microorganisms. Sweet potato tops can be exclusively produced in separate nursery bed and harvest one month after planting for food processing. The dark green leaves, which are rich in protein and polyphenols can be separated from light green and stems. The former part can be used for food, green drink like tea or medicine (Furuta et al., 1998). The latter part, which is supposed to be composed mainly of fibres can be used for absorbent for poisonous gas, chemicals, metals and against microorganism and so on (Yamakawa, 1997).

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In tropical countries sweet potato are generally processed by simple slicing of storage roots followed by sun drying. The dehydrated roots form an important raw material for starch production. The flour made of chips can be used for various food preparations according to the taste preference of consumers (van Hal, 2000). In the developed countries, sweet potatoes are processed into frozen, canned or flaked products (Bovell-Benjamin, 2007). Sweet potato contained trypsin inhibitor which inhibits the important digestive enzyme trypsin (Sasikaran et al., 2002). The presence of trypsin inhibitor activity in sweet potato could decrease protein digestion and utilization in people whose diets consists of sweet potato as a major component. However, this can be reduced to very low levels or eliminated by normal cooking methods like boiling or baking. Sweet potato is being used as a carbohydrate source in animal feed in several countries. More on the utilization patterns of sweet potatoes are discussed in the subsequent chapters in this book.

ACKNOWLEDGMENTS The authors sincerely thank Dr. Ibisime Etela, Department of Animal Science and Fisheries, University of Port Harcourt, Nigeria for providing the data of Table 2.

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Hartemink, A. E. (2003). Integrated nutrient management research with sweet potato in Papua New Guinea. Outlook on Agric. 32(3): 173-182. Herman, N.D., Monaco, T.J., and Sheets, T.J. (1983). Weed control with alachlor and residues in sweet potato and soil. Weed Sci. 31(4): 567-571. Huaman, Z. (1992). Systematic botany and morphology of the sweet potato plant. Technical Information Bulletin 25. International Potato Centre, Lima, Peru, pp.22. Jeong, B.C. (2000). Current role of sweet potato and its earlier harvesting by improved PE film mulch cultivation in Korea. In: Potential of Root Crops for Food and Industrial Resources, Proc. of 12th Symp. Int. Soc. Trop. Root Crops. September 10-16, 2000. Tsukuba, Japan, pp. 350. Jeong, B.C., Oh, S.K., Park, K.Y., and Rho, S.P. (1986). Effects of fertilizer amount planting density and date on growth and tuber yields in planting sprouted root pieces of sweet potato. Research report of the rural development administration, crops. Korea Republic 28(2): 184-188. John, K.S., Shalini Pillai, P., Nair, G.M. and Chithra, V.G. (2001). Critical concentration as a reflection of potassium requirement of sweet potato in an acid ultisol. J. Root Crops 27(1): 223-228. Jusuf, M., Hilman, Y. and Setiawan, A. (2005). Selection of sweet potato clones with high anthocyanin in Indonesia. In: Concise Papers of the 2nd Int. Symp. Sweet potato and Cassava, held 14-17 June 2005, Kuala Lumpur, Malaysia, pp40-41. Kabeerathumma, S., Mohankumar, B. and Potty, V.P. (1986). Efficacy of rock phosphate as a source of phosphorus to sweet potato. J. Indian Soc. Soil Sci. 34(4): 866-869. Kaggwa, R., Gibson, R., Tenywa, J.S., Osiru, D.S.O. and Potts, M.J. (2006). Incorporation of pigeon pea into sweet potato cropping systems to increase productivity and sustainability in dry land areas. In: 14th Triennial Symp. Int. Soc. Trop. Root Crops, 20-26 November 2006, Central Tuber Crops Research Institute, Thiruvanathapuram, India, p. 186. Komaki, K. and Yamakawa, O. (2005). RandD collaboration with industry – The Japanese sweet potato storey. In: Concise Papers of the 2nd Int. Symp. Sweet potato and Cassava, held 14-17 June 2005, Kuala Lumpur, Malaysia, pp. 3-4. Kundu, D.K., Singh, R. and Roy Chowdhury, S. (2006). Effect of rice straw mulch and irrigation on nutrient availability in soil and tuber yield of sweet potato (Ipomoea batatas L.) in coastal Orissa. In: Root and Tuber Crops: in Nutrition, Food Security and Sustainable Environment. (Eds.) Naskar, S.K., Nedunchezhiyan, M., Rajasekhara Rao, K., Sivakumar, P.S. Ray, R.C., Misra, R.S. and Mukherjee, A.). Regional Centre of Central Tuber Crops Research Institute, Bhubaneswar, pp 117-122. Low, J. and Jaarsveld, P.V. (2006). The potential of golden bread buns biofortified with beta carotene rich sweet potato to add value to rural diets and increase profits of rural bakers in Central Mozambique. In: 14th Triennial Symp. Int. Soc. Trop. Root Crops, 20-26 November 2006, Central Tuber Crops Research Institute, Thiruvananthapuram, India, pp. 26-27. Mais, A. and Brennan, C.S. (2008). Characterisation of flour, starch and fibre obtained from sweet potato (kumara) tubers, and their utilization in biscuit productions. Int. J. Food Sci. Ttechnol. 43: 373- 379. Mohandas, C. (2006). Nematode problems in tuber crops. In: 14th Triennial Symp. Int. Soc. Trop. Root Crops, 20-26 November 2006, Central Tuber Crops Research Institute, Thiruvanathapuram, India, pp. 150-151.

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Mohanty, A.K., Sethi, K., Samal, S., Naskar, S.K. and Nedunchezhiyan, M. (2005). Relationship of optimum stage of harvest with weevil incidence in sweet potato under different agro-climatic conditions of Orissa. Orissa J. Hort. 33 (1): 43-45. Mohapatra, N.P., Pati, S. and Ray, R.C. (2001). Spoilage of sweet potato tubers in tropics. V. Java black rot by Botryodiplodia theobromae Pat: phenol accumulation in culture and in tubers during spoilage. J. Mycopathol. Res. 39: 21- 27. Mukherjee, A., Naskar, S.K., Edison, S. and Dasgupta, M. (2006). Response of orange flesh sweet potato genotypes to salinity stress. In: 14th Triennial Symp. Int. Soc. Trop. Root Crops, 20-26 November 2006, Central Tuber Crops Research Institute, Thiruvanathapuram, India, pp. 151-152. Mukhopathyay, S.K., Sen, H., and Hana, P.K. (1990). Effect of planting materials on growth and yield of sweet potato. J. Root Crops 16(2): 119-122. Nair, G.M. (2000). Cultural and manorial requirements of sweet potato. In: Production Technology of Tuber Crops (Eds.) Mohankumar, C.R., Nair, G.M., George, J. Ravindran, C.S. and Ravi, V., Central Tuber Crops Research Institute, Thiruvananthapuram, Kerala, India, pp. 44-64. Nair, G.M. (2006). Agro-techniques and planting material production in sweet potato. In: Quality Planting Material Production in Tropical Tuber Crops (Ed.) Byju, G., Central Tuber Crops Research Institute, Thiruvanathapuram, India, pp. 55-58. Nair, G.M., Nair, V.M. and Sreedharan, C. (1996). Response of sweet potato to phasic stress irrigation in summer rice fallows. J. Root Crops 22(1): 45-49. Narin, P. and Reungmaneepaitoon, S. (2005). Breeding of sweet potato for health-promoting attributes in Thailand. In: Concise Papers of the Second International Symposium on Sweet potato and Cassava, held 14-17 June 2005, Kuala Lumpur, Malaysia, pp 69-70. Naskar, S.K. (2006). Roots and tuber crops in household food and nutritional security. In: Root and Tuber Crops: in Nutrition, Food Security and Sustainable Environment, (Eds) Naskar, S.K., Nedunchezhiyan, M., Rajasekhara Rao, K., Sivakumar, P.S. Ray, R.C., Misra, R.S. and Mukherjee, A.). Regional Centre of Central Tuber Crops Research Institute, Bhubaneswar, pp. 10-14. Naskar, S.K., Gupta, J.J., Nedunchezhiyan, M. and Bardoli, R.K. (2008a). Evaluation of sweet potato tubers in pig ration. J. Root Crops 34(1): 50-53. Naskar, S.K., Mukherjee, A., Nedunchezhiyan, M. and Rao, K.R. (2008b). Evaluation of sweet potato cultivars for quality traits. In: New RandD Initiatives in Horticulture for Accelerated Growth and Prosperity, 3rd Indian Horticultural Congress, 6-8 November 2008, held at Bhubaneswar, Orissa, India, Abstracts, pp. 340. Naskar, S.K., Mukherjee, A., Ray, R.C. and Moorthy, S.N. (2007). Breeding sweet potato: Value addition for food, feed and industrial use. In: Proc. Root and Tuber Crops Postharvest Management and Value Addition (Eds.) Padmaja, G., Premkumar, T., Edison, S. and Bala Nambisan), Central Tuber Crops Research Institute, Thiruvananthapuram, Kerala, India, pp. 308-314. Nath, R., Kundu, C.K., Majumder, A., Gunri, S., Chattopadhyay, A. and Sen, H. (2006). Productivity of sweet potato as influenced by cultivar, season and staggered harvesting in laterite ecosystem of West Bengal. In: 14th Triennial Symp. Int. Soc. Trop. Root Crops, 20-26 November 2006, Central Tuber Crops Research Institute, Thiruvanathapuram, India, pp. 213.

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Nayar, G.G. and Naskar, S.K. (1994). Varietal improvement in sweet potato. In: Advances in Horticulture Vol. 8. Tuber Crops (EDs. Chadha, K.L. and Nayar, G.G.), Malhotra Publishing House, New Delhi, India, pp. 101-112. Nedunchezhiyan, M and Reddy, D.S. (2002). Nitrogen management in sweet potato (Ipomoea batatas L.) under rainfed conditions. Indian J. Agron. 47(3): 449-454. Nedunchezhiyan, M and Satapathy, B.S. (2002). A note on the effect of weed management practices on nutrient uptake of weeds in sweet potato. Orissa J. Hort. 30(2): 110-112. Nedunchezhiyan, M. and Byju, G. (2005). Effect of planting season on growth and yield of sweet potato (Ipomoea batatas L.) varieties. J. Root Crops 31 (2): 111-114. Nedunchezhiyan, M. and Reddy, D.S. (2004). Growth, yield and soil productivity as influenced by integrated nutrient management in rainfed sweet potato. J. Root Crops 30 (1): 41-45. Nedunchezhiyan, M. and Reddy, D.S. (2006). Effect of time of planting and varieties on growth and yield of sweet potato (Ipomoea batatas L.) under rainfed conditions. In: Root and Tuber Crops: in Nutrition, Food Security and Sustainable Environment, (Eds) Naskar, S.K., Nedunchezhiyan, M., Rajasekhara Rao, K., Sivakumar, P.S. Ray, R.C., Misra, R.S. and Mukherjee, A.). Regional Centre of Central Tuber Crops Research Institute, Bhubaneswar, India, pp 123-127. Nedunchezhiyan, M., Byju, G. and Naskar, S.K. (2007). Sweet potato (Ipomoea batatas L.) as an intercrop in a coconut plantation: Growth, yield and quality. J. Root Crops 33 (1): 26-29. Nedunchezhiyan, M., Reddy, D. S. and Suryaprakasa Rao. J. (2004). Characteristics of dry matter production and partitioning in sweet potato. In: Proc. Natl. Seminar on Physiological Interventions for Improved Crop Productivity and Quality: Opportunities and Constraints, December 12-14, 2003, Sri Venkateswar University, Tirupati, India, pp. 110-115. Nedunchezhiyan, M., Sivakumar, P.S., Naskar, S.K. and Misra, R.S. (2006). Sweet potato: A suitable crop for rice based cropping system. In: Root and Tuber Crops: in Nutrition, Food Security and Sustainable Environment. (Eds) Naskar, S.K., Nedunchezhiyan, M., Rajasekhara Rao, K., Sivakumar, P.S. Ray, R.C., Misra, R.S. and Mukherjee, A.). Regional Centre of Central Tuber Crops Research Institute, Bhubaneswar, pp 135-138. Nedunchezhiyan, M., Srinivasulu Reddy, D. and Haribabu, K. (2003). Nitrogen management practices on quality characters of sweet potato (Ipomoea batatas L. Lam). J. Root Crops 29 (2): 69-72. Nedunzhiyan, M. (1996). Ecological studies on weed flora associated with sweet potato. Orissa J. Hort., 24: 69-73. Nedunzhiyan, M. (2001). Studies on time of planting, genotypes and integrated nitrogen management for rainfed sweet potato (Ipomoea batatas L.). Ph.D. thesis. Acharya N.G. Ranga Agricultural University, Hyderabad, India. Nedunzhiyan, M., Reddy, D. S. and Ravi. A. (2000). Effect of sweet potato vine meal on the digestibility of organic nutrients in pigs. J. Root Crops, 26(2): 23-25. Nedunzhiyan, M., Varma, S.P. and Ray, R.C. (1998). Estimation of critical period of cropweed competition in sweet potato (Ipomoea batatas L.). Adv. Hort. Sci. 12: 101-104. Ngoan, T.N. (2006). Status of root crops production, utilization and marketing in Vietnam. In: 14th Triennial Symp. Int. Soc. Trop. Root Crops, 20-26 November 2006, Central Tuber Crops Research Institute, Thiruvanathapuram, India, p. 9.

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Salawu, I.S. and Mukhtar, A.A. (2008). Reducing the dimension of growth and yield characters of sweet potato (Ipomoea batatas L.) varieties as affected by varying rates of organic and inorganic fertilizer. Asian J. Agric. Res. 2(1): 41-44. Sasikiran, K., Rekha, M.R. and Padmaja, G. (2002). Proteinase and alpha-amylase inhibitors of sweet potato: Changes during growth phase, sprouting and wound induced alterations. Bot. Bull. Acad. Sin. 43(4): 291- 298. Satapathy, M.R., Sen, H., Chattopadhyay, A. and Mohapatra, B.K. (2006). Response of sweet potato cultivars to different cutting management practices. J. Root Crops 32(1): 94-97. Satapathy, M.R., Sen, H., Chattopadhyay, A. and Mohapatra, B.K. (2005). Dry matter accumulation, growth rate and yield of sweet potato cultivators are influenced by nitrogen and cutting management. J. Root Crops 31(1): 129-132. Sebastiani, S.K., Mgonja, A., Urio, F. and Ndondi, T. (2006). Response of sweet potato to application of nitrogen and phosphorus fertilizer, agronomic and economic benefits in the Northern highlands of Tanzania. In: 14th Triennial Symp. Int. Soc. Trop. Root Crops, 2026 November 2006, Central Tuber Crops Research Institute, Thiruvanathapuram, India, p. 205. Sethi, K., Mohanty, A.K., Naskar, S.K. and Nedunchezhiyan, M. (2003). Efficacy of IPM technology over farmers/traditional practices in management of sweet potato weevil (SPW) in tribal areas of Orissa. Orissa J. Hort. 31(2): 65-68. Tamaki, K., Tamaki, T. and Suzuki, Y. (2007) Deodorisation of off-odour during sweet potato juice production by employing physical and chemical deodorants. Food Chem. Doi: 10.1016/j foodchem.2007.03.064. Tandang, L.L. and Alfonso, J.L. (2006). Morphological diversity and cluster analysis in sweet potato varieties in the Northern Philippines highland. In: 14th Triennial Symp. Int. Soc. Trop. Root Crops, 20-26 November 2006, Central Tuber Crops Research Institute, Thiruvanathapuram, India, p. 90. Terahara, N., Konczak, I., Ono, H., Yoshimoto, M. and Yamakawa, O. (2004). Characteristics of acylated anthocyanin in callus induced from storage root of purple-fleshed sweet potato, Ipomoea batatas L. J. Biomed. Biotechnol. 5: 279- 286. Ugent, D., Pozorski, S. and Pozorski, T. (1983). Archeological remains of potato and sweet potato tubers from the Casma valley in Peru [Spanish]. Biol. Lima 5(25): 28-44. van Hal, M. (2000). Quality of sweet potato flour during processing and storage. Food Rev. Int. 16(1): 1-37. Vimala, B., Thushara, R., Nambisan, B. and Sreekumar, J. (2006). Evaluation of orange fleshed sweet potatoes for higher yield and carotene content. In: 14th Triennial Symp. Int. Soc. Trop. Root Crops, 20-26 November 2006, Central Tuber Crops Research Institute, Thiruvananthapuram, India, pp. 55. Vinnings, G. (2003). Select markets for taro, sweet potato and yam. A report for the Rural Industries Research and Development Corporation. RIRDC Publication No. 03/052. RIRDC Project No UCQ-13A. ISBN 0642 586195; ISSN 1440-6845, Kingston, ACT. Woolfe, J.A. (1992). Sweet Potato: An Untapped Food Resource. Cambridge University Press, Cambridge. Yamakawa, O. (1997). Development of new cultivation and utilization system for sweet potato toward the 21st century. In: Proceedings of International Workshop on Sweet potato Production System toward the 21st Century, December 9-10, 1997, Miyakonojo, Miyazaki, Japan, pp. 1-8.

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Yamakawa, O., Yoshinaga, M., Hidaka, M., Kumagai, T. and Komaki, K. (1997). Ayamurasaki: a new sweet potato cultivar. Bull. Kyushu. Natl. Agric. Exp. Stn. 31: 1-22. Yasuda, K. (1997). Integrated control of sweet potato weevils Euscepes postfasciatus and Cylas formicarius (Coleoptera: Curculionidae). In: Proc. Int. Workshop on Sweet Potato Production System Toward the 21st Century, December 9-10, 1997, Miyakonojo, Miyazaki, Japan, pp. 317-322. Zaharah, A. and Tan, S.L. (2006). Performance of selected sweet potato varieties under different growing seasons on bris sandy soil in Malaysia. In: 14th Triennial Symp. Int. Soc. Trop. Root Crops,20-26 November 2006, Central Tuber Crops Research Institute, Thiruvananthapuram, India, pp. 225-226.

In: Sweet Potato: Post Harvest Aspects in Food Editors: R. C. Ray and K. I. Tomlins

ISBN 978-1-60876-343-6 © 2010 Nova Science Publishers, Inc.

Chapter 2

POST HARVEST HANDLING, STORAGE METHODS, PESTS AND DISEASES OF SWEET POTATO Ramesh C. Ray1, V. Ravi2, Vinayak Hegde2, K. Rajasekhara Rao1 and Keith I. Tomlins3

1

Regional Centre, Central Tuber Crops Research Institute, Bhubaneswar 751 019, India 2 Central Tuber Crops Research Institute, Thiruvanathapuram 695 017, India 3 University of Greenwich, Central Avenue, Chatham maritime, Kent ME4 4TB, UK

ABSTRACT Sweet potato storage roots are subjected to several forms of post harvest losses during transportation from farmers‘ field to market and in storage. These are due to mechanical injury, weight loss, sprouting and diseases and pests. The shelf-life of sweet potato roots shows variation with respect to varieties, climatic conditions, harvest procedure, mode of transportation and storage. Pre-harvest foliar application of maleic hydrazide (1000 ppm) combined with evapourative cool chamber storage significantly increased the shelf-life of sweet potatoes. Sweet potato weevil is the single most important storage pest for which no control measures or resistant variety are yet available but can be managed by storing healthy, weevil free roots which can be produced through adequate irrigation and early harvest. Alternately, sweet potatoes can be exposed to 150Gy irradiation or stored at temperatures between 16-18oC to control weevil damage. Several fungi have been found to cause diseases in stored sweet potato. The most important among them are Botryodiplodia theobromae, Ceratocystis fimbriata, Fusarium spp. and Rhizopus oryzae. The other less frequently occurring spoilage fungi include Cochliobolus lunatus (Curvularia lunata), Macrophomina phaseolina, Sclerotium rolfsii, Rhizoctonia solani and Plenodomus destruens. Fungal decay of sweet potato is found associated with decrease in starch, total sugar, organic acid (ascorbic acid) contents with concomitant increase in total sugars, polyphenols, ethylene and in some instances 

Corresponding author: Tel/Fax: 91-674-2470528; E-mail: rc_ray @rediffmail.com

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phytoalexins. Several methods are used to control sweet potato storage diseases. Curing to promote wound healing is found as the most suitable method. Curing naturally occurs in tropical climate where mean day temperature during sweet potato harvesting season (February- April) invariably remains at 32-35oC and relative humidity at 80-95%. Fungicide treatment, bio-control, gamma irradiation and storage in sand and saw dust have moderate impacts in controlling fungal rot and enhancing shelf- life of sweet potato roots. Blanching, antimicrobial agents, anti-browning substances (citric acid, ascorbic acid and sulfite) and modified atmospheric package (MAP) using moderately O2 permeable film (7000 cm3/atm/m2/24 h) in a modified atmosphere of 5% O2, 4% CO2 and 91% N2 under refrigerated conditions or cold chlorination (dipping fresh-cut pieces of sweet potatoes in 200 ppm at 1oC) suppressed the build up of microflora and enhanced the shelf-life of shredded sweet potatoes up to 14 days without significant changes in quality.

ABBREVIATIONS DCNA GM IPM MAP MH PAL RH SPW UV

dichloronitroaniline; genetically modified; integrated pest management; modified atmospheric package; maleic hydrazide; phenylalanine ammonia–lyase; relative humidity; sweet potato weevil; ultra violet

INTRODUCTION Sweet potato roots are important source of secondary staple food for people living in remote villages and hilly regions. It tolerates flood and salinity stress conditions and produces energy (152 MJ/ha/day) in form of edible tuberous (storage) roots. Sweet potato storage roots, like any other vegetable, are subjected to several forms of post harvest losses during transportation from farmers‘ field to market and in storage. These are due to inept post harvest handling, poor storage methods, physical damage during transportation, weight loss, sprouting and pests and diseases. Climate and soil conditions before harvest, infection by fungi and infestation by insect pests in the field may initiate/ enhance post harvest deterioration. Also, careless post harvest handling, which is very common in tropical developing countries, often leads to both quantitative and qualitative losses (Ray and Ravi, 2005). This may be extremely high in some circumstances such as extreme temperatures (<450 C). This chapter discusses the various aspects of post harvest handling, storage methods, pests and diseases of sweet potato and recommends control measures to reduce post harvest losses.

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POST HARVEST HANDLING Sweet potato roots are categorized as ―perishable‖ because the roots, once detached from the plant, cannot be stored for a longer time (compared with durable commodities such as grains) (Woolfe, 1992). The fresh roots, in general, contain high moisture content, usually between 50 and 70% and hence have a relatively low mechanical strength. They also have a very high respiratory rate, and the resultant heat production softens the texture, which leads to damage. In addition, the mechanical injury such as bruising, cuts and abrasions increase the loss of moisture and become entry point for microorganisms. The shelf-life of sweet potatoes varies from few days to few months according to the cultivar and storage conditions. Finally, fresh roots are vulnerable to microbial decay due to fungi and bacteria. Due to these reasons sweet potatoes often incur heavy post-harvest loss of quality (Ray and Ravi, 2005).

STORAGE METHODS Sweet potatoes are often consumed within 2-3 weeks without storing. However, storage often becomes necessary to extend availability of fresh roots throughout the year in some areas/circumstances where production is essentially seasonal. Production is not possible in winter in temperate climates due to frost formation and in the Indian sub-continent during wet monsoon season due to water logging (Ray and Ravi, 2005). Storage of sweet potato is often necessary to avoid gluts in the market. For instance, in Bangladesh and India where sweet potato production is confined mostly to winter season (October –February), there is always a drop in price due to availability of a wide variety of other vegetables depriving farmers a satisfactory return (Jenkins, 1982; Ray and Balagopalan, 1997). Storage provides an opportunity to market sweet potato out of season when prices are higher. Sweet potato can be stored using traditional and modern methods (Ravi et al., 1996). The various methods of sweet potato storage and percentage loss (Table 1) are described in brief.

Methods Used by Maoris’s In this method, roots were placed on the floor, which was previously covered with gravel or dried fern bush. The seed stock was placed at the back and the roots for edible purpose at the front. The cut or bruised roots were placed near the entrance and these were consumed first. The whole store was then sealed and left for sometime. Sweet potato stored by this method entailed heavy losses due to decay and rat damage (Keleny, 1965).

Pits and Clamps Construction of pits and clamps for storage of fresh sweet potato is a more common practice in all sweet potato growing tropical countries. Mean loss of weight of sweet potato roots after eight weeks of storage in bamboo lined pits was the lowest (22.1%) followed by

Ramesh C. Ray, V. Ravi, Vinayak Hegde et al.

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clamp storage (22.4%) where the roots were placed on a layer of grass on the surface of the ground and then covered with grass and soil (Gooding and Campbell, 1964). Table 1. The losses of sweet potato and causes under different storage methods (Ray and Ravi, 2005; modified) Storage methods Bamboo lined pits under thatched roof Clamp under thatched roof

Storage period 8 weeks

3-5 months

% Loss 22.1 82.0 22.4 77.0 30.0

Causes Weight loss Sprouting Weight loss Sprouting Weight loss, rotting

Clamp Pits in open area/corner of the house and covered with paddy straw imulated pit condition in laboratory Pits with alternate layers of wood ash Heap storage Roots piled on a bench like platform made of bamboo Trench 50 cm deep covered with sand and sheltered by a roof Sand Closed cardboard cartoons covered with grass Cool chamber (double layered brick wall filled in with sand)

6 months

< 20.0

Weight loss, rotting

2 months

50.0

Rotting

1-2 months

20-40

2-4 months 2-4 months

20-25 20-25

7 weeks

35 45

Weight loss, rotting, sprouting Rotting/weevil Weight loss/rotting, rodent infestation, weevil Rotting Sprouting, weevil

6-7 weeks -

<30.0 29-35 5-44 -

8 weeks

5-6 weeks

Weight loss Weight loss Sprouting Sprouting

Contrary to the weight loss, mean sprouting of sweet potato roots was 82 and 77 %, respectively, in these two treatments. Thirty per cent loss in weight was observed after three to five month storage in clamps. In Zimbabwe and Malawi, the roots were placed in pits with alternate layer of wood ash and in Papua New Guinea roots were alternated with layers of grass (Bourke, 2005, 2006; Ramakrishna, 2006). In Cameroon, roots placed in dry leaf-lined holes and sprinkled with wood ash were finally covered with dry leaves or grass (Numafor and Lyonga, 1987). In experiments in Uganda, roots stored in pits or clamps during dry season had shelf- life for as long as five months, provided the stores were checked regularly for rotting, rodent or insect damage (CIP, 1997). In Tanzania, pit and clamp storage is practiced (van Oirchot et al., 2007) where it is recommended that stores should not be lined with grass and that ventilation, the store design and cultivar had no impact. On-farm testing in Tanzania (Tomlins et al., 2007) indicated that practical and simple improvements were necessary, without which losses in the proportion of market-quality roots from the store could be as high as 79%. These practical improvements were mainly concerned with the position of stores on the farms. The addition of a new step, dehaulming (removing the plant canopy one

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week before harvest), improved the recovery of market–quality roots by 48%. Variations among the farmers in their attitudes to storing sweet potato suggest that, when transferring methods from the research station to the farm, it is necessary to target those most able to adopt the approach. Transfer of the storage methods to the farmer has also been reported to be critical in Uganda (Hall and Deverau, 2000). These methods of storage practices are however, only satisfactory usually for a period of about two months and unless care is taken to ensure that no cut or bruised roots are stored and adequate ventilation is provided, losses due to rotting is usually between 40 and 50% (van Oirchot et al., 2007). Traditional storage of roots in Malawi entails the placement of roots in pits directly after harvest or after sun curing for about a day. The pits are dug under maize or groundnut silos. The bottom and sides of the pits and subsequent layers of roots are sprinkled with ash. Under these conditions, roots stored beyond three to four months show heavy losses. Elevation of root temperature due to high respiration rate presumably raised temperature inside the pits, which favoured sprouting while rotting was primarily due to the growth of Rhizopus stolonifer (Kwapata, 1983/1984). In India, farmers usually dig pits in an open area or in the corner of the house. Roots are placed in pits and the pits are covered with paddy straw and plastered with mud. Under such conditions, farmers claim storage life of sweet potato up to six months with less than 20% loss (Ray and Balagopalan, 1997). Therefore, pit storage is recommended only as a low cost method of storage because of disadvantages such as heavy loss due to decay, rat damage, inferior quality due to lack of proper curing, and limited keeping quality once removed from the pit.

Heap Heap storage of sweet potato is another common method followed in many tropical countries. In this method, roots are heaped on a plain surface or in the corner of the house and they are covered with thin layer of paddy straw or dried grass. Jenkins (1981, 1982) described a heap storage method being followed by farmers in Bangladesh. Sometimes, roots are piled on a bench-like structure made of bamboo. Only a few farmers construct a special storing structure made of bamboo and plastered with mud. Under such conditions, the length of the storage period varies between two to four months with a post harvest loss of 20 to 25%. Sweet potato roots stored under field conditions at temperatures between 24 to 35 oC and 70 to 90% relative humidity (R.H.) lost about 19.3% of their fresh weight in five weeks. In yet another study, mean weight loss of nearly 20% was observed during 45 days storage due to fungal decay and weevil infestation (Ali et al., 1991). In Vietnam, 75% of the harvest is stored in the house either on the floor or suspended from the ceiling. Here, storage period is reduced if weevils are present (Hoa, 1997). In Nigeria, sweet potato is traditionally stored in the house, heaped on the floor or laid on the shelf. Fires are lit once or twice weekly to fumigate the roots which are often covered with ashes having antifungal properties. Losses of up to 95% were observed in this method (Olorunda, 1979). In the Philippines, sweet potato stored in a trench 50 cm deep, covered with sand and sheltered by a roof resulted in 35% decay and 45% sprouting after 50 days (Mariscal, 1997). The storage of sweet potato roots in Indonesia after six months entailed more than 50% loss (Yakub, 1997).

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Sand / Cardboard Methods Sand storage provided a modified atmospheric condition by limiting the supply of oxygen and maintaining low temperature as well as a barrier for entry of sweet potato weevils. Sweet potato stored in sand suffered less weight loss than those stored under ambient conditions (Ray et al., 1994). Sweet potato roots stored in sand could be stored for up to 45 days without significant loss. Storage in closed cardboard cartoons placed on the soil surface or on rocks covered with grass resulted in mean weight losses of 29.2 to 34.9% and mean sprouting of 5.3 and 44.4%, respectively (Data and Quevedo, 1987). Cured sweet potato could be stored for five months by disinfecting the roots by means of fogging with 1% iprodione. The percentage decay after five months after the treatment was 5-14%, compared with 61% in non-treated roots (Afek et al., 1998, 1999).

Cool Chamber Method Evapourative cool chamber consists of a double walled brick, 4 x 1.5 x 1.5 m size and the gap between the brick wall filled with sand. Here, the sand layer was always kept moist so as to keep the chamber cool (22-27oC). Storing sweet potato inside the cool chamber could significantly increase the shelf-life as compared to ambient conditions inside the concrete room on the floor. In this study, the mean shelf- life of six varieties of sweet potato was 33 days and 39 days under ambient and cool chamber conditions respectively (Shedge et al., 2009). Pre-harvest, foliar spraying of maleic hydrazide (MH, 1000 ppm), at 60, 90 and 105 days (3 sprays) significantly reduced rotting and sprouting of sweet potatoes and increased the shelf life of sweet potato to 37 and 44 days when stored under ambient and cool chamber conditions, respectively.

Cold Storage of Shredded Sweet Potatoes Using Modified Atmospheric Package Recently, there is an increasing demand for freshly cut vegetables at the consumer level. Simple and minimal processing operations including washing, peeling, trimming, cutting and packaging maintains the freshness of commodities (Alzamora et al., 2000). In the presence of air, the shelf- life of perishable produce is limited by two principal factors: (1) metabolic deterioration of the tissue and (2) growth of aerobic spoilage microorganisms. Microbiologically, commodities are considered to be at the end of their shelf- life when the total aerobic counts reach 107 – 109 cfu (colony forming units)/g, the yeast count reach 105 cfu/g or there is visible mould growth (Curlee, 1997). High microbial counts (>108 cfu/g) in combination with physical damage and physiological stress due to poor processing result in undesirable quality changes such as loss of firmness, off-odours and product slimness. Therefore, it is important to control such factors to ensure an extended shelf life for freshly cut products (McConnell et al., 2005).

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Several treatments including blanching, antimicrobial agents (chlorine and Tsunami 200R), anti-browning substances (citric acid, ascorbic acid and sulfite) and modified atmospheric package (MAP) showed that freshly cut sweet potatoes can be stored up to two weeks under refrigerated conditions without significant changes in quality (McConnell et al., 2000; Erturk and Picha 2002; Cobo et al., 2003). Furthermore, the quality of sweet potatoes shredded into 3 x 3 mm pieces could be maintained for 7 days at 4oC in air, but extended up to 14 days using moderately O2 permeable film (7000 cm3/atm/m2/24 h) in a modified atmosphere of 5% O2, 4% CO2 and 91% N2 (MAP). Shredded sweet potatoes stored in MAP showed fewer changes in tissue firmness, dry matter, ascorbic acid, color, ß-carotene, sugars and starch than shredded sweet potatoes stored in air. Higher ethanol was generated in the MAP-stored shredded sweet potatoes after 10 days, but off-odours were not detected in any of the MAP-stored sweet potatoes (McConnell et al., 2005).

Cold Storage Sweet potatoes can be best stored at temperatures between 12 and 15oC at 85 to 95% relative humidity (RH) without loss of quality for up to one year (Woolfe, 1992; Ravi et al., 1996). From the above discussion, it is apparent that there have been quite a number of reports of different storage conditions affecting shelf-life of sweet potato particularly in tropical environment, but what is lacking is a systematic of which factors are important and which is not. These points are discussed in the following section.

CAUSES OF POST HARVEST LOSS Sweet potato roots have high moisture (60-70 %) and reducing sugar (4-15 %) content, and a relatively thin and delicate skin (Woolfe, 1992). They also have a high respiratory rate immediately after harvest and the resultant heat production soften the texture. All these attributes make them a highly ‗perishable‘ commodity. As a consequence, once detached from the plant, sweet potato cannot be stored for a long time. The shelf- life of sweet potato roots varies from a few days to few weeks according to the cultivar, conditions prevailing at the time of harvest, and storage. Because of a very short shelf - life, storage of sweet potato roots is avoided in many parts of the world. In most countries, larger roots are removed from individual plants leaving smaller roots to increase in size and harvested sequentially when needed. In the tropics, storage roots are often left for a short period in the sunlight after harvest and surface dried. Such roots are either consumed at home within 8-10 days or transported to local markets for sale (Ray and Balagopalan, 1997). However, exposure of storage roots to direct sunlight before storage appears to cause more harm leading to excessive loss of moisture causing tissue breakdown. Further, lack of proper curing, packing and improper storage conditions causes skinning, wounding, desiccation and infection by fungi resulting in substantial post harvest losses (Ray and Ravi, 2005). Sweet potato is an important staple crop in Tanzania, grown mainly for home consumption, but marketing is becoming increasingly important (Mtunda et al., 2001). The short shelf- life is a major constraint for marketing. Rees et al. (2001) proposed that the short shelf- life of sweet potato

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was due to breakage, cuts, infestation by weevils, rotting and superficial damages. All these together accounted for 41 to 93% of root damage when sweet potato arrived in the urban Tanzanian markets. The various causes of post harvest losses of sweet potato (Table 1) are discussed below.

Physical Factors Physical factors mostly refer to pre-harvest and harvest conditions. Pre- harvest conditions include principal soil factors such as moisture, temperature etc. The importance of these soil factors varies with agro-ecology. For example, cold has been a constraint only at high altitude (above 2,200m) (Ray and Ravi, 2005). Likewise, excess soil moisture (40%) in the field can cause subsequent post harvest loss (Ray and Ravi, 2005).

1. Mechanical Damage Mechanical damage is the most important harvest factor, much of which is sustained during harvest itself, and during transport and marketing. Harvesting in the tropics is usually manual, employing a variety of tools such as digging sticks, spades, hoes and knives. Mechanical harvesting using tractors or animal-drawn ploughs or specially designed machines are confined to areas of large-scale production. Sweet potato roots are often cut, skinned and bruised by the harvesting implements. Sweet potato roots found to be damaged during harvesting using spade was 26% and 24% in Bangaladesh and India, respectively (Jenkins, 1982; Ray and Balagopalan, 1997). A similar estimate for the percentage of damaged roots have been reported for some parts of China, Indonesia, Papua New Guinea, and Tanzania where hoes are mostly used for harvesting (Ray and Ravi, 2005). An ‗electronic sweet potato‘ fitted with a shock sensor has been used to track sacks of sweet potato in Tanzania and could be applicable to countries where roots are transported by different means such as lorry, motor cycle, cart etc., over rough road surface to markets, increased root damage and loss of quality frequently results (Tomlins et al., 2000). The practice of overfilled heaps or use of polypropylene sacks for transportation and storage have led to physical damage which can be prevented if fewer roots were carefully packed in cardboard boxes, cartoons or crates (Rees et al., 2001; Tomlins et al., 2002). 2. Chilling Injury Cold wet soils of temperate climate before harvest or subsequent exposure to temperature below 13oC cause chilling damage resulting in tissue breakdown and development of offflavour. Chilling also renders the roots more susceptible to attack by microorganisms such as fungi. Sweet potatoes which have not been properly cured are less able to withstand low temperatures than are well-cured roots (Broadus et al., 1980). 3. Cracking Cracking may be caused by nematodes which are microscopic soil inhabitants. Crack initiated early in the growing season are long and deep, while those induced at a latter stage tend to be smaller but are more likely to be infected with microorganisms. Shrinkage and

Post Harvest Handling, Storage Methods, Pests and Diseases of Sweet Potato

35

decay ensue during storage. Control measures include crop rotation, selection of nematode – free planting materials and the use of resistant cultivars (Lawrence et al., 1986).

Physiological Factors 1. Respiration In sweet potato, respiration and transpiration contribute to loss in weight and alteration of internal and external appearance. Transpiration losses are due to evapourative loss of the cellular water caused by vapour pressure difference between the root interior and the outside environment. Most of the works indicated that respiration was highest immediately after harvest than during curing or storage (Picha, 1986; Walter et al., 1989; Afek and Kays, 2004). Wounding of sweet potato roots resulted in an increase in both the respiration rate and subsequent weight loss. Rate of respiration increased in sweet potato roots exposed to a cool temperature of 10oC and a strong relation between respiration and eventual expression of chilling injury was established. Sweet potato roots having 58-78% moisture content showed a low respiratory rate of < 0.5 mg of CO2 per gram dry weight per hour, whereas at moisture levels >75% the rate increased drastically, reaching up to 2.0 mg CO2 per gram dry weight per hour (Afek and Kays, 2004). This indicates that cultivars having low dry matter content may have a shorter storage life. Sweet potato roots also showed an increased respiration in response to ethylene at 20-35oC but showed a much reduced rate at lower temperature. All these studies on respiration and consequently moisture loss were conducted in temperate conditions. However, respiration losses are much greater under tropical conditions. For example, in Bangladesh, the high temperature (< 35o C) and low RH (40%) during summer result in high rate of respiration and rapid evapouration of moisture through the root skin (Jenkins, 1982). Furthermore, loss of moisture leads to a condition known as ‗pithiness‘ in which cavities appear within the tissues. Prolonged moisture losses, as occur in tropical conditions, could result in collapse of tissues which begins at the distal end of the roots and may ultimately cause total desiccation, especially in small sized roots (Picha, 1986). 2. Sprouting Sprouting in sweet potato roots occurs very quickly especially when soil moisture is high and the harvest is delayed. It also occurs during prolonged storage in conditions of high temperature and humidity. In the tropics, sprouts are generally broken off as they appear (Ray and Ravi, 2005; Shedge et al., 2008). Sprouting can be suppressed / inhibited by storing the roots at relatively cool temperature (14o C) (Ray and Ravi, 2005). The other methods for suppressing sprout formation are gamma irradiation and application of growth regulators. Exposure to gamma irradiation (0.03-0.15 kGy) markedly suppressed sprouting. In unirradiated samples, 100% roots sprouted after one-month storage whereas those treated with 0.05 kGy gamma radiation showed 2.5 and 9% sprouting after one and five months, respectively (Lu et al., 1987, 1989). Besides gamma irradiation, growth regulators were found effective as sprout suppressants. Sprouting was reduced in roots, stored for four to eight months with treatment of maleic hydrazide (Jenkins, 1982). Gautam et al. (1991) studied the effect of growth

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Ramesh C. Ray, V. Ravi, Vinayak Hegde et al.

regulators at concentrations between 1000-3000 ppm by dipping sweet potato roots for five minutes. Naphthalene acetic acid at all concentrations either delayed or inhibited sprouting and reduced cumulative weight loss during storage. Ethrel (2 –chloroethyl phosphonic acid) enhanced both sprouting and rooting. Maleic hydrazide delayed sprouting, but more sprouts were produced latter. Cycocel had no significant effect on sprouting. Sprout numbers were significantly reduced by treatment with 3.0 - 9.0% (weight by volume) sodium hypochlorite solution after 102 days of storage, but weight loss was high (Lewthwaite and Triggs, 1995). Sprouting was 99% reduced when roots were stored in diffused light in hut made of bamboo (Icamina, 1985).

Biological Factors Pests 1. Weevils In most parts of the tropics and subtropics, one of the most serious problems in storage is the sweet potato weevil (SPW) (Cylas formicarius Fabricius) and two closely relates species (C. puncticollis Boheman, and C. brunneus) (Sutherland, 1986). Cylas puncticollis is confined to several countries in Africa. However, C. formicarius is more cosmopolitan, being distributed all over the sweet potato growing regions (Smit and Matenogo, 1995; Uritani, 1998). The insect feeds on the vines of the growing crop and migrates down to the roots and infests those roots near the soil surface. Moreover, phenolics of unspecified chemical composition increased significantly for up to 14 days in roots fed upon by adult weevil or larvae (Padmaja and Rajamma, 1982). This coincided with the development of an unpleasant turpentine odour and a bitter taste in the roots. The bitter taste was due to production of phytoalexins such as ipomeamarone and ipomeamaranol (Uritani, 1998). Regardless of the toxicity of this compound, the unpleasant odour makes sweet potato less acceptable for human consumption. Control Measures Integrated pest management (IPM) programme and some pre-harvest cultural practices are mostly followed in various sweet potato growing countries for controlling weevils. These include the use of terminal vine cuttings as planting material, hilling up of soil, sex pheromone traps, irrigation, dipping planting materials in insecticide solution and early harvest (Smit, 1997). Weevil population starts between 2 and 3rd month of the crop and increases rapidly with age of the crop. Although, it attacks all parts of the crop, the main damage is done to the roots by the larvae both in the field and during storage. The pest can breed successfully inside the roots with repeated cycles if there is sufficient food available. The root damage is influenced by season, method of planting, soil type, temperature, rainfall, soil moisture, time of harvest and also cropping pattern (Palaniswami et al., 1990). In India, up to 79% of produce may have weevil infestation (Pillai 1994). In farmer‘s fields in India, root damage was greater in upland (4-50%) than in lowland (0-22%) conditions because of better soil moisture in the latter. The weevil population and root damage was comparatively lower during rainy season or irrigated conditions and higher during summer season or rainfed

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conditions (Palaniswami et al., 1990). When soil moisture is high, the weevil cannot get access to the roots easily through moist soil. Sweet potato planted during rainy season showed lowest weevil incidence (10.9 to 36.5%) whereas those planted during dry season had 47.9 to 87.4% weevil incidence. Dry spell throughout the cropping period results in depletion of soil moisture which favours weevil activity. Similarly, delayed harvest also increases weevil infestation. Therefore, weevil free, better quality sweet potatoes can be produced through adequate irrigation and early harvest (Pillai, 1994). In the case of Cylas puncticollis survival of all the life-stages of sweet potato weevil was greater between 24 and 31oC and lower at 18 or 16oC (Nteletsana et al., 2001). Therefore, weevils can be effectively controlled if the storage temperature was lowered to 16 -18oC because it is not able to accumulate enough thermal units required to complete development. Furthermore, roots immersed in hot water at 52 – 62 oC for 10 min or 42 oC for 30 min could kill all larvae and adult weevils (CIP, 1997; Das, 1998). Ali et al. (1991) reported partial control of weevils using a repellant water trap baited with synthetic pheromone and storage in dry sand mixed with tobacco leaf powder. Sweet potato roots heaped on the floor and covered with a 2-cm thick layer of sand and rice husks were either free from infestation or had negligible infestation after three months of storage (Smit, 1997). Gamma radiation between 150-200 Gy had no effect on surface injury or storage decay when roots were evaluated after one month storage at 13 oC and 90% R.H (Sharp, 1995). During storage, weight loss by irradiated roots was 0.5 to 3.3% more than that of non- treated ones. In some instances, this affected root firmness. An irradiation dose of 150-165 Gy has been recommended for sterilizing female weevils to reduce reproduction and further multiplication and life time (Hallman, 2001; Follett 2006). All stages of the sweet potato weevil may be found in marketed roots. The adult is invariably the stage of insects which requires the highest radiation dose to control (Hallman, 2000). Vapour heat treatment kill SPW pupae in roots (Shimabukuro et al. 1997). Delate and Brecht (1989) and Delate et al. (1990) conducted studies on controlled atmosphere for the control of weevil in stored sweet potatoes. They identified that adults of sweet potato weevil or sweet potato roots infested with immature stages of the pest were exposed to controlled atmospheres containing low oxygen (O2) and increased carbon dioxide (CO2) with a balance nitrogen (N2) for up to 10 days at 25 and 300C. Adults were killed within 4-8 days when exposed to 8% O2 + 40-60% CO2 at 300C. When baked, irradiated sweet potato roots were sweeter than non-irradiated roots but they were not preferred due to the darker appearance (McGuire and Sharp, 1995). The entemopathogenic fungi, Metarrhizium anisopliae and Beauveria bassiana were found to be effective in controlling weevils. However, in the drier regions of Africa, B. bassiana had limited potential for weevil control (Alcazar et al., 1997). In the traditional agricultural systems in the tropics and sub-tropics where inputs are low, the use of weevil resistant varieties is the most economic way of effectively controlling weevils. Several attempts have been made during the past five decades to find resistance to this pest with limited success (Collins et al., 1991; Yasuda, 1997). Significant variations in the amounts of triterpenoid boehmeryl acetate (a known ovipositional stimulant for the pest) were found before and after harvest, with season and between cultivars which are resistant and susceptible to SPW (Son et al., 1991). Mass trapping of male weevils by sex pheromone trap (Figure 1) is one of the most effective IPM practiced in many sweet potato-growing countries. Its female -produced sex pheromone was identified as (Z) –3- dodecenyl (E)-2- butenoate. Control programs involving

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Ramesh C. Ray, V. Ravi, Vinayak Hegde et al.

mass trapping of male weevils have been used with limited success in many Asian countries (Ray and Ravi, 2005). The intensity of trapping used varied from 4 traps/ha to 100 traps/ha. Similar results were obtained using pheromone traps against C. puncticollis and C. brunneus (Pillai et al., 1993; Smit, 1997; Braun and van de Fliert, 1999).

Figure 1. Sex pheromone trap used for capturing male sweet potato weevils at CTCRI farm at Bhubaneswar (Source: Ray and Ravi, 2005).

2. Other Pests Apart from sweet potato weevils, there are nearly 80 species of arthropods infesting sweet potato in storage. The three most important are coffee bean weevils (Araeceras fasciculatus), black fungus beetle (Alphithobius laevigatus) and ground beetle (Gonocephalm sweet potato.) (Talekar, 1987). The first two pests damage the roots completely and cause decay while the ground beetle feeds on the periderm by making irregular galleries. Infestation by A. fasciculatus is generally associated with stored roots, which are soft, or in a state of decay. Treating sweet potato chips with 2-3 % salt prior to drying controls damage by A. fasciculatus in dried chips in storage. Diseases Pre harvest and post harvest infections by pathogenic microorganisms (mostly fungi and to a lesser extent bacteria) are serious causes of post harvest loss of sweet potato roots (Snowdon, 1991). The relative importance of the major pathogens can differ considerably between localities and with environmental conditions (Ray, and Byju, 2003). Different post harvest diseases (Table 2) are described below in brief. 1. Black Rot Black rot, caused by Ceratocystis fimbriata, has been a problem wherever sweet potato is intensively grown. Most references of this rot are from USA, New Zealand and Japan (Clark, 2001), although the disease has virtually been eliminated by use of thiabendazole fungicides on seed roots and by cutting transplants above the soil line. Nevertheless, it is still considered as an important post harvest disease in other tropical, and sub-tropical regions such as Papua

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New Guinea, Haiti and Peru and Vietnam. However, the rot has not been reported from sweet potato growing Asian countries like Bangladesh, China, India, Nepal and Pakistan (Ray and Edison, 2005). The characteristic symptoms of disease are sunken circular lesions, which are initially brown and latter greenish black, and the cooked roots taste bitter. Associated with lesions are minute black bodies (perithecia) with long necks. Infection occurs through wounds or even in healthy roots, and favoured by wet soil, and warm temperatures. Table 2. Microorganisms associated with sweet potato rots in the tropics (Ray and Ravi, 2005; modified) Types of rot

Causative organism

Symptoms

Pre-disposing factors

Avoidance/control measures

Black rot

Ceratocystis filmbriata

Wet soil, humid and warm temperature, contamination in seed roots

Java black rot

Botryodiplodia theobroame

Crop rotation, careful handling of roots, heat treatment for no more than 24 h and curing at 35oC for 2 to 10 days. Cultivation of resistant varieties. Curing and subsequent storage at a temperature between 13-16oC; cultivation of resistant varieties

Fusarium rot

Fusarium spp.

Charcoal rot

Macrophomina phascolina

Sunken circular lesions initially brown and later greenish black. Associated with lesions are minute black bodies (perithecia) with long necks, appeared to naked eye as dark bristles Infected tissues are at first yellowish brown and fairly firm, later darkening to black. After some weeks, affected roots become mummified and skin is pimpled with minute black bodies (pycnidia) Type of decay is variable. End rot is characterized by a dry decay at one or both ends of fleshy roots. Infected tissues shrivel, forming cavities filled with white molds Infected roots show three zones- the advancing edges of the lesion is pale brown and spongy, intermediate zone is reddish brown and firm and the older part is almost black (micro sclerotia)

Wounding during harvesting and handling

Wounding during harvest and handling, infected roots used as seed, infestation by weevils

Minimizing injury during harvesting and handling, curing, cultivation of resistant varieties

Wounding

Minimizing injury during harvesting and handling, and curing

40

Ramesh C. Ray, V. Ravi, Vinayak Hegde et al. Table 2. (Continued)

Types of rot

Causative organism

Symptoms

Pre-disposing factors

Avoidance/contr ol measures

Rhizopus rot

Rhizopus spp.

Wounds during post harvest handling, R.H. (75-85%), high temperature (< 35oC)

Careful handling, curing, cultivation of resistant varieties

Sclerotium rot

Sclerotium rolfsii

Decay beings at one end and under humid conditions, roots shrivel, become soft and watery and the skin ruptures. The mold spreads causing next of decay. Circular lesions, sometimes internal tissues becoming watersoaked yet firm later hand and stringly

Careful handling curing

Spongy rot

Cochliobolus lunatus (Curvularia lunata) Rhizoctonia solani

Infected roots swollen and spongy

Wounds during post harvest handling, warm moist conditions (R.H. 75,-85%; temperature <35oC) Wounding, warm and humid environment

Careful handling, curing

Gliomastix rot

Gliomastix novae-zelandiae

Lesions appear as brown corky tissue

Foot rot

Plenodomus destruen

Lesions appear as brown corky tissue

Bacterial rot

Erwinia crhrysanthemi

Roots become soft and watery similar to Rhizopus rot but differ by the absence of mycelia

Wounding, warm and humid environment Wounding, warm and humid environment Wounding, warm and humid environment Hot, humid weather

Rhizoctonia rot

Pale brown spot on skin, tend to shrivel

Careful handling, curing

Careful handling, curing Careful handling, curing Cultivation of Resistant variety

2. Java Black Rot Java black rot is caused by Botryodiplodia theobromae, the most prominent storage disease in tropical and sub tropical regions such as Bangladesh, India, Philippines, Nigeria, Ghana and the sub-tropical zone of USA (Ray and Punithalingam, 1995; Sowley and Oduro, 2002; Ray and Edison, 2005). The rot usually spreads from the proximal end of the root or from other wound sites. The infected tissues are initially yellowish brown, and latter become black. After 6- 8 weeks of storage, the affected roots show dark patches externally, within which develop numerous pycnidia, and internally the tissues turn yellow, and latter black. Finally, the rotted roots become shriveled, brittle and mummified (Figure 2). Wounding is the most important pre-disposing factor for Botryodiplodia infection. The optimum temperature and R.H. for growth of B. theobromae are 25-350 C and 85-90 %, respectively.

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A

B

C Figure 2. Characteristics of java black rot in sweet potato roots caused by Botryodiplodia theobroame (a) Cut sections of healthy and infected roots (b) Infected roots showing drk coloured pycnidia. (c) Mummified roots (Source: Ray and Ravi, 2005).

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3. Soft Rot Soft rot in sweet potato is caused by Rhizopus stolonifer, R. oryzae and R. nigricans. The rot is widespread in all sweet potato growing countries of temperate as well as in tropical regions (Ray et al., 1997; Sowley and Oduro, 2002; Ray and Edison, 2005). Affected roots usually decay totally due to rapidly developing soft and watery rot. Dry atmospheric conditions do not favour decay, and the root tissue remains firm but shrinks whereas in humid conditions, the roots shrivel, becomes soft and watery, and at places where the skin ruptures there is copious development of coarse white mould bearing globular spore head (sporangia) (Figure 3). The sporangia are at first white but turn black as they mature, and the entire mycelium appears gray. Further colonization of the entire rot can occur within a few days and the mould spread to adjacent roots in a storage pile causing ‗nest of decay‘. Wounds predispose the roots to be attacked and the proximal end is especially susceptible to invasion because the natural presence of dead tissue at the site of wound caused at the time of harvest is advantageous to the fungus. The other pre–disposing factors for Rhizopus infection in sweet potato are R.H. (75-85%), chilling, and high temperature (< 350 C).

A

B Figure 3. Characteristics of Rhizopus rot in sweet potato roots caused by Rhizopus oryzae. (a) Infected roots showing soft-rot (b) Cut section of the infected root (Source: Ray and Ravi, 2005).

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4. Fusarium Rot Fusarium species causes ―Fusarium root rot‖ in sweet potato. The common species found in sweet potato roots are F. solani, F. oxysporum, F. moniliforme and F. pallidoroseum (Sowley and Oduro, 2002; Ray and Edison, 2005). F. oxysporum and F. solani have been recorded on sweet potato in the USA, Brazil, China, India and Israel, while F. pallidoroseum is reported only from India (Ray and Misra, 1995). The type of decay is rather variable. End rot caused by F. oxysporum and F . pallidoroseum is characterized by a dry decay at one or both ends of the fleshy roots, and the lesions are brown with dark margins. Infected roots shrink, sometimes forming cavities filled with white mould (Figure 4). On the other hand, surface rot caused by F. solani appears as pale brown, circular lesions, and the decay remains shallow with white mould. Severe wounding caused by rough handling at harvest, and improper storage resulting in slow wound healing increase the incidence of this disease. Also, wet soil conditions favour the spread of the disease. The disease does not generally spread during storage except when additional wounding occur which provide new infection sites. The pre-disposing factors for Fusarium infection are soil water deficit, mechanical injuries, and insect infestations.

A

B Figure 4. Characteristics of Fusarium rot in sweet potato roots caused by Fusarium oxysporum. (a) Infected roots showing soft-rot (b) Cut section of the infected root (Source: Ray and Ravi, 2005).

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5. Charcoal Rot Macrophomina phaseolina causes ―charcoal rot‖ in sweet potato roots. The disease is wide spread in tropics (Jenkins, 1982), but is less severe as compared to Java black rot or Fusarium rot. Decay of harvested roots usually begins at the point of original attachment to the plant (proximal end) and spreads through the roots. Initially the infected roots show variously shaped, and sized pale brown discoloration of the surface with distinct margin from healthy tissues. Diseased areas remain firm, and dark brown; water loss causes these areas to shrink. Rotting root shows three distinct zones. The advancing edge has a pale brown and spongy tissue; the intermediate zone has reddish brown and firm tissue; the old rotted area has dark Grey to black, and firm tissue. The ‗charcoal‘ appearance results from thousands of minute micro-sclerotia that colonize the interior, but not the surface of the root. Infection occurs through injury. Optimum temperature for growth of the fungus is 31.5oC but it grows even at 42oC. 6. Sclerotium Rot Sclerotium rolfsii causes two diseases of sweet potato: ‗Slerotial blight‘, which develops on sprouts, and mother roots in plant production bed, and ‗sclerotium rot‘ which develops circular spots on stored roots (Clark, 2001). The disease has been recorded from Bangladesh, Cuba, Jamaica, Israel, Mozambique and USA. The symptoms of decay may be variable. The rotting may appear as circular lesions of about one- cm diameter or may be invasive, and the root tissue, which initially remains water soaked but firms latter, becomes hard, and stringy. 7. Spongy Rot Spongy rot is caused by the fungus Cochliobolus lunatus (also Curvularia lunata). It has been reported from India (Ray and Misra, 1995). The infected roots are swollen and spongy, and the inside flesh turns brown to black. 8. Rhizoctonia Rot This rot is caused by the fungus Rhizoctonia solani, and has been reported from India (Ray and Edison, 2005). Infected roots develop pale brown spots, and tend to shrivel. Eventually, the entire root surface may be covered win brownish mould. 9. Gliomastix Rot This rot is caused by the fungus Gliomastix novae – zelandiae. It has been reported in Egypt (Kararah et al., 1981). Lesions appear as irregular brown corky tissues usually slightly depressed. In a humid atmosphere, there is copious growth of black mould with abundant spores (conidia). Optimum temperature and R.H. for the disease development are 270 C and 84-100 % respectively. 10. Foot Rot Foot rot is caused by Plenodomus destruen. It affects the roots in plant production beds, and in the field. It has been reported from USA (Clark, 2001) and Brazil (Rubin et al., 1994).

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11. Pythium Rot It is a major rot of sweet potato in Australia and USA, particularly in cool wet weather, and the causal agent is Pythium ultimum (Ray and Edison, 2005). Infected roots may become dry and crumbly, dark brown to dark gray in color or the decay may spread uniformly through the roots or may appear as a band of dark shrunken tissue which girdles the root. 12. Bacterial Rot Erwinia chrysanthemi causes ‗Erwinia soft rot‘ of sweet potato roots in tropical as well as in temperate regions. Erwinia soft rot is similar to Rhizopus soft rot but primarily distinguished from the latter by the absence of mycelia. Roots infected with Erwinia develop black streaks in the vascular tissue and undergo a soft moist decay (Ray and Edison, 2005). Biochemical Changes Associated with Fungal Rots Microbial spoilage of sweet potato roots is manifested with changes in starch, total sugars, organic acids, enzymes, phenols, ethylene, and phytoalexin contents. 1. Changes in Starch, Total sugars, Protein and Organic Acids One of the first parameter noticed following fungal decay of sweet potato is a decline in starch and ascorbic acid contents (Ray and Pati, 2001). The decline in starch content is either associated with concomitant increase (Acedo et al., 1996) or negligible variation (Ray and Pati, 2001) in total sugar. Like wise, the ascorbic acid contents of four sweet potato varieties was reported to decrease further following infection by B.theobromae or R. oryzae (Thompson, 1979; Ray and Pati, 2001). Oxalic acid concentration was reported to increase significantly in microbial infected tissues (Faboya et al., 1983). The increase in oxalic acid was suggested to aid pathogen penetration by sequestering Ca or Mg in the middle lamella of cell walls, thereby increasing susceptibility of pectates to hydrolysis by cell wall degrading enzymes, i.e. cellulases and pectinases (Swain and Ray, 2007). Oxalic acid may also lower the pH of the tuber tissues to a level suitable for pathogenic enzyme degradative activity. 2. Proline and Carotenoids There is no significant change in proline content between healthy and fungus (Rhizopus or Botryodiplodia) – infected sweet potato roots (Ray and Pati, 2001), although proline accumulation is considered as a measure of stress imposed on plant or plant parts (roots) due to adverse environments such as drought, temperature or microbial infection. On the contrary, roots infected with R. stolonifer contained only 24mg carotenoids /100 g (fwb) as compared with 50mg /100g in uninfected sweet potato roots (Thompson, 1979).

3. Enzyme Activities

In response to wounding of sweet potato by rotting fungi, many enzymes are induced. The enzymes first activated belong to those in the phenyl propanoid pathway i.e. phenylalanine ammonia–lyase( PAL) and trans-cinnamic acid 4-hydroxylase (Uritani, 1998). Peroxidase and polyphenol oxidase activities were reported to subsequently increased (Arinze and Smith, 1982). Likewise, most of the rotting fungi i.e. B. theobroamae and R. oryzae produce cellulolytic and pectolytic enzymes in microbial cultures and infected tissues (Arinze

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and Smith, 1982; Ray, 2003) that facilitated pathogen entry into sweet potato roots (Ray, 2003).

4. Polyphenol Production There are many reports that phenol concentration increases several folds in sweet potato roots following microbial infections (Uritani, 1998, 1999). Total phenolic content was generally higher in and around the lesions of sweet potato infected by B. theobramae, Botrytis cineria, or Rhizopus oryzae (Arinze and Smith, 1982; Mohapatra et al., 2001; Ray, 1997). Further, an increase in phenolic content in the infected tissues was associated with the accumulation of the phytoalexins, ipomeamarone and ipomeamaranol (Arinze and Smith, 1980). The chemistry and biochemical interpretation of phytoalexin vis-à-vis pathogen infection has been reviewed by several workers (Edward and Kessmann, 1992; Uritani et al., 1994; Uritani, 1999). Woolfe (1992) reported that the majority of phenolics in sweet potato are esters formed between quinic acid and caffeic acid. These phenolic esters are O-dihydroxy phenols, chlorogenic acid, isochlorogenic acids and related compounds (Thompson, 1981; Mohapatra et al., 2001). The proposed biosynthetic pathway by which chlorogenic acid and isochlorogenic acid may form in injured sweet potato roots has been outlined (Villegas and Kojima, 1986). Polyphenols can act as antibiotics. Both chlorogenic acid and isochlorogenic acid were found slightly inhibitory to the strains of C. fimbriata (Uritani, 1998) and B. theobromae (Mohapatra et al., 2000). 5. Ethylene Formation Ethylene evolves in plants in response to attack by microorganisms as well as wound stress (Hyodo, 1991). Ethylene production in sweet potato roots greatly increased in response to infection by fungi such as C. fimbriata (Okumura et al., 1999) and B. theobromae (Pati, 2001). Further, the rate of ethylene production increased correspondingly with the extent of fungal penetration by using three strains of C. fimbriata differing in pathogenicity to sweet potato roots (Hirano et al., 1991; Shima et al., 1996, 1997; Yoshioka et al., 2001). It is concluded that ethylene production is induced in sweet potato roots by an injury stimulus brought about by a consequence of fungal invasion, and mechanical wounding does not play any role in this system (Okumura et al., 1999). 6. Phytoalexins Phytoalexins were not present in fresh sweet potato roots, but they were produced by microbial infection (Uritani, 1999) or weevil infestation (Padmaja and Rajamma, 1982). In sweet potato roots, about 30 furanoterpenoid compounds were identified. Ipomeamarone is the main component and recognized as the first example of a phytoalexin. These compounds were investigated primarily to determine if they were responsible for toxicoses in animals fed with ‗mouldy‘ sweet potato roots (Peckham et al., 1972; Pati, 2001). Further, sweet potato genotypes vary considerably in synthesizing phytoalexins following microbial attack (Jenkins, 1982).

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CONTROL MEASURES Rotting fungi have two means of entering the storage roots: through wounds caused during harvest / weevil or insect infestations or through infected vines (used as propagating materials). The following approaches have been made to control post harvest diseases.

Careful Handling Any measure that reduces wounding the roots will help reduce spoilage (Miyazaki and Ino, 1991). Handling of roots particularly during harvesting and transportation that reduces injury is very important (Jenkins, 1982; Aidoo, 1993; Ray and Balagopalan, 1997). The handling and transport system resulted in up to 20% and 86% of roots with severe breaks and skinning injury respectively as reported in survey conducted in Tanzania (Tomlins et al., 2000).

Curing Despite best attention during post harvest handling of sweet potato, some wounding inevitably occurs, even if only as a result of attachment of the roots from the vines. For successful storage and marketing, it is necessary to subject the harvested roots to a preliminary process of curing which has several beneficial effects such as sweetness and palatability (Wang et al., 1998). Most important is that curing facilitates toughen the skin (promoting wound periderm) and healing of wounds thereby reducing the risk of post harvest infection and decay (Ray and Balagopalan, 1997; Sowley and Oduro, 2002). Environmental conditions for proper curing include exposure of sweet potatoes to 29 + 1oC at 90-95% RH for 4-7 days (Kays et al., 1992; Ray et al.; 1994; Ravi et al., 1996). These parameters are more or less ambient in the hot and humid climates of tropical countries (Jenkins, 1981; Ray et al., 1994; Ray and Balagopalan, 1997). Recommended curing and storage practices are difficult to follow in many developing countries because they involve high initial costs for construction of suitable facilities. A simple technique for curing of sweet potato was innovated at Central Tuber Crops Research Institute, India by covering the freshly harvested roots with a polythene sheet raised 6‖ – 8‖ above the tubers spread open in a well ventilated place (Ray and Balagopalan, 1997). The polythene cover is removed during night. The system could generate 85-90% RH at temperature 28-30oC during harvesting season in India (Sep-Nov / Feb – April) which are very ideal for curing. By adapting this simple technology, the shelf life of sweet potatoes increased 60% over uncured roots and fungal infection was drastically reduced (10%). Curing induces suberization of exposed parenchyma cells and development of a wound periderm (Afek et al., 1998). Following curing, storage at 14+ 1oC at 90% RH is generally recommended (Kays et al., 1992). Other low cost curing processes such as storing sweet potatoes in moist saw dust, plastic green house have been developed (Afek and Wiseblum, 1995; Lineberger and Stikeleather, 1998) but additional research in these areas is needed for a meaningful conclusion.

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Pre-harvest curing by removing the plant canopy up to 14 days before harvest has been reported to make the harvested roots less susceptible to damage during harvesting and transport (Tomlins et al., 2002) and improve the marketable shelf-life. Pre-harvest curing also increased the recovery of marketable roots by 48% in roots that had been stored for 16 weeks in either pits or heaps (Tomlins et al., 2007).

Irradiation Exposing sweet potatoes to ultraviolet (UV) radiation effectively decreased the rotting during storage. γ– irradiation 75 Gy was optimum for inhibiting sprouting of sweet potatoes with lower decay and weight loss (Ravi et al., 1996).

Chemical Control Since the roots are directly used as food or feed commodity in many countries (Woolfe, 1992), post harvest application of fungicides is generally avoided to prevent spoilage, as it may imparts residue problem. Application of ά-naphthalene acetic acid (MENA) and maleic hydrazide (MH) effectively controlled the sweet potatoes sprouting during storage Application of benomyl, kocide 101, and captan prevented root rot. Dichloran could control Java black rot and soft rot. Black rot could be controlled by treatment with thiabendazole (TBZ) and benomyl. Captan could control surface rot while ferbam, captan, benomyl or TBZ could control the scurf (Ravi et al., 1996). Some fungicides i.e. dichoronitroaniline (DCNA), benomyl, dichloran, iprodione were found comparatively less effective in controlling various microbial rots of sweet potato (Afek and Wiseblum, 1995; Afek et al., 1998, 1999). In the case of shredded sweet potatoes, cut surfaces provides an entry point for bacteria and the nutrient laden juices from fresh-cut surfaces support microorganisms growth. Chlorination (dipping) of the whole sweet potato roots before slicing did not reduce the microflora build up of shredded sweet potatoes. However, dipping slices in 200ppm chlorine at 1oC reduced the population of all microorganisms (mesophiles, psychrophiles, yeast, and moulds) during further storage for 14 days at 2oC (Ertuk and Picha, 2005).

Bio–Control Biological control, primarily with antagonistic yeasts, has shown promise for control of post harvest diseases of fruits and vegetables (Shi-ping-Tian, 2006). Ray and Das (1998) reported complete growth inhibition in situ by three antagonistic yeast species, i.e. Debaryomyces hansenii, Pichia anomala and Saccharomyces cerevisiae against Botryodiplodia rot of sweet potato. Control of Rhizopus soft rot by UV irradiation (UV -C, 254 nm) and yeast D. hansenii were compared (Stevens et al., 1997). UV -C alone reduced the incidence of all the storage rots (Stevens et al., 1990, 1997, 1999). If D. hansenii was used 2-3 days after UV -C treatment, the result was more significant. It was suggested that UV -C and biological control agent could be used together as an alternative to chemical control of storage rot in sweet potato.

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Resin glucosides extracted from sweet potato periderm were found to inhibit growth of four major rotting fungi, i.e. F. oxysporum, F. solani, R. stolonifer and B. theobromae (Harrison et al., 2001; Stange et al., 2001). But, a relationship between such components and disease resistance was not established.

Resistant Varieties In temperate region, major emphasis is given on ‗storability‘ and post harvest rot resistance in selecting breeding lines (Clark, 1992). Resistant breeding lines were recorded for Botryodiplodia, Fusarium and Rhizopus spp. from several countries, i.e. Bangladesh (Jenkins, 1981), China (Chen et al., 1990), India (Ray and Naskar, 2000) and Peru (Cadenas and Icochea, 1994). However, post harvest rots often occur together as a complex rot involving many micro organisms; it is therefore, necessary to develop genotypes with broad spectrum resistance to major post harvest pathogens. ‗White Regal‘, a multiple-pest and diseaseresistant, cream-fleshed sweet potato was developed jointly by U.S. Dept. of Agriculture, Agricultural research Service and the South Carolina Agriculture and Forestry Research System (Bohac et al., 2001)

Storage Techniques Various cheap but effective storage methods are practiced in tropics for arresting fungal decay and enhancing shelf- life of sweet potato roots. These methods are storage in pits, sand bed, saw dust, earthen pots, heaps in corner of mud house (Jenkins, 1981; Ray and Balagopalan, 1997).

CONCLUSION AND FUTURE PROSPECTS Physical injury and infection through mother plants are found as two most significant pre-disposing factors for rot to spread. The selection of roots that are free from rots, insect damage and physical damage and storage are few selected practices, which can prevent microbial attack and hence deterioration for significant period. Bio-control by antagonistic yeasts can be an alternate approach for arresting microbial rots either singly or in combined treatment with UV- irradiation but these are not widely used and may not be acceptable to consumers. In temperate region, major emphasis is given on storability in selected breeding lines. The same approach has been investigated in East Africa and can be adapted in tropical countries like China, India and Philippines. Furthermore, post-harvest microbial rots often occur together as a complex rot; it is necessary therefore, to develop genotypes with broad spectrum resistance to major post harvest pathogens. Many of the genes which are upregulated or down-regulated during post harvest physiological deterioration of storage root have been investigated in cassava (Huang et al., 2001; Reilly et al., 2007). However, genes involved in controlling dormancy, post-harvest deterioration of storage root and resistance to microbial infection are yet to be understood in sweet potato. Transgenic or genetically

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modified (GM) sweet potatoes offer potential for developing to produce anti-microbial substances in the root skin. New transgenic sweet potatoes with prolonged dormancy can attribute for longer shelf-life. However, GM sweet potatoes are not widely accepted either by consumers or by legislation and policy in many countries. The mechanism of wound healing is little understood and further research is warranted. Availability of simple indigenous methods adopted for storing sweet potatoes by the local people in different parts of the world may need to be explored. Research is needed for the control of post harvest pest and disease of sweet potatoes. One possibility is to explore the potential of wild plants with antimicrobial properties. Such wild plants can be either used for developing sweet potato varieties with antimicrobial properties in roots through breeding or the extracts of their plant parts may be used to control post-harvest pests and diseases of sweet potatoes.

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Bourke, R. M. (2005). Marketed fresh foods: A successful part of Papua new Guiana economy. Dev. Bull. April, pp. 22- 24. Bourke, R. M. (2006). Differences between calendar time and plant time in sweet potato: a potential source of significant experimental error. In: Proc. 14th Triennial Symp. of Int. Soc. Trop. Root Crops., 20-26th November, 2006, Central Tuber Crops Research Institute, Trivandrum, India, pp.253. Braun, A.R. and van de Fliert, E. (1999). Evaluation of the impact of sweet potato weevil (Cylas formicarius) and of the effectiveness of Cylas sex pheromone traps at the farm level in Indonesia. Int. J. Pest Manage. 42: 101-110. Broadus, S.W., Collins, W.W. and Pharr, D.M. (1980). Incidence and severity of hardcore in sweet potatoes as affected by genetic line, curing, and lengths of 10C and 210 C storage. Scient. Hort. 13: 105- 113. Cadenas, C.G. and Icochea, T. (1994). Behaviour of 196 clones of Ipomoea batatas (L) Lam. to Java black rot (Lasiodiplodia theobromae Pat.). Fitopatol. 29: 197-201. CIP (International Potato Centre) (1997). CIP Sweet potato Facts, International Potato Center, Lima, Peru. Chen, L.F., Xu, Y.G. and Fang, Z.D. (1990). Identification of isolates causing root rot of sweet potato and tests on resistance of varieties of sweet potato to root rot. Jiangsu J. Agric. Sci., 6: 27 – 32. Clark, C.A. (1992). Post harvest diseases of sweet potatoes and their control. Post Harvest News and Information, 3: 75 N – 79 N. Clark, C.A. (2001). Research for improved management of sweet potato pests and diseases: cultivar decline and post harvest losses. In: Proc. Int. Symp. Sweet Potato: Food and Health for the Future, CIP, Lima, Peru, 23-29 Nov., 2001. Cobo, H.E., Silva, J.L., and Garner, J. O., Jr (2003). Development of a fresh-cut sweet potato product. In: Inst. Food Technol., Annual Meeting, July 12-16, Abst. No. 45G-6, Chicago, IL. Collins, W.W., Jones, A., Mullen, M.A., Talekar, N.S., Martin, F.W. (1991). Breeding sweet potato for insect resistance: a global over view. In: Sweet potato Pest Management: A Global Perspective, Jansson, R. K. and Raman, K.V., Eds., Westview Press, Boulder, Colorado, USA, pp. 379 - 405. Curlee, J. (1997). Preserving produce. J. Food Qual., 20: 24-30. Das, G.P. (1998). The control of sweet potato weevil in storage. Trop. Sci., 38: 196 - 200. Data, E.S. and Quevedo, M.A. (1987). Village level post harvest practices for root crops, PRCRTC Project Terminal Report. Delate, K M. and Brecht J K (1989) Quality of tropical sweet potatoes exposed to controlledatmosphere treatments for post harvest insect control. J. Am. Soc. Hort. Sci. 114(6): 963968. Delate, K. M., Brecht, J. K. and Coffelt, J. A. (1990) Controlled atmosphere treatments for control of sweet potato weevil (Coleoptera: Curculionidae) in stored tropical sweet potatoes. J. Econ. Entomol. 82(2): 461-465. Ewards, R. and Kessman, H. (1992). Isoflavonoid phytoalexins and their biosysnthetic enzymes. In: Molecular Plant Pathology, A Practical Approach, Vol. II, Gull, S.J., McPherson, M.J and. Bowles, D.J, Eds., Oxford University Press, New York, USA, pp. 45- 62.

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In: Sweet Potato: Post Harvest Aspects in Food Editors: R. C. Ray and K. I. Tomlins

ISBN 978-1-60876-343-6 © 2010 Nova Science Publishers, Inc.

Chapter 3

PHYSIOLOGICAL FUNCTIONS AND UTILIZATION OF SWEET POTATO Makoto Yoshimoto Team of Crop Functionality and Utilization, National Agricultural Research Center for Kyusyu Okinawa Region, Suya 2421, Koshi City, Kumamoto 861-1192, Japan

ABSTRACT Sweet potato contains various kinds of physiologically functional components, polyphenolics, anthocyanins, fiber, and carotenoids in roots and leaves. Polyphenolic contents vary between the varieties and are relatively superior to other commercial vegetables. Polyphenolic components are mainly caffeoylquinic acid derivatives and the pigments of the purple fleshed sweet potato are acylated anthocyanins. The functional components show various kinds of physiological functions, anti-oxidation, anti-diabetes, anti-hypertension, and others in vitro or in vivo. The component content can be increased by the harvest time, the controlled storage, and the use of moderate portion. The sweet potato roots or leaves with these functions are commercially used as not only fresh vegetables but also as a material of confectionery, noodles, alcohol drinks, and beverage. Further the waste of the shochu, a traditional Japanese liquor, is reused as raw material of vinegar-like beverage and breads with high content of polyphenolics. Sweet potato leaves also can be reused as functional feeds for egg-laying hens and beef cattle.

ABBREVIATIONS CA CQA ChA 

caffeic acid; caffeoylquinic acid; chlorogenic acid (3-O-caffeoylquinic acid);

Tel: 81-96-242-7873; Fax: 81-96-249-1002; E-mail:[email protected]

Makoto Yoshimoto

60 4-O-CQA 3,4-diCQA 3,5-diCQA 4,5-diCQA 3,4,5-triCQA FA QA Trp-P-1

4-O-caffeoylquinic acid; 3,4-di-O-caffeoylquinic acid; 3,5-di-O-caffeoylquinic acid; 4,5-di-O-caffeoylquinic acid; 3,4,5-tri-O-caffeoylquinic acid; ferulic acid; quinic acid; 3-amino-1,4-dimethyl-5H-pyrido-(4,3-b) indol

INTRODUCTION Sweet potato represents the sixth most important food crop in the world and will be important in solving the global issues of food, energy, and natural resources and the environment in the 21st century (Kozai et al., 1996). Often called ―almost perfect nourishing food‖ sweet potato contains vitamins, minerals and many other nutrients in favorable ratios (Woolfe, 1992). Further, the sweet potato root has contributed to the development of the regional industries mainly as raw materials for starch and shochu (traditional alcohol drinks in Japan). However, demand for this crop is greatly declining due to diversified eating habits and deregulated import of farm produce, which is seriously affecting the local economy. Therefore, the National Agricultural Research Center for Kyushu Okinawa Region (KONARC), Japan and other research institute are studying ways to enhance value addition of sweet potato by finding new uses. Sweet potato leaves have largely been neglected except for their partial use as livestock feed in Japan and other Asian countries. The consumption of sweet potato leaves as a fresh vegetable is common in some parts of the world (Villareal et al., 1979). Food scientists are becoming increasingly interested in sweet potato leaves because it can contribute to alleviating food shortages and makes good use of natural resources. As sweet potato leaves can be harvested several times in a year, their yield is ultimately higher than many other leafy vegetables (Nwinyi, 1992). Furthermore, as one of the few vegetables that can be grown easily during the monsoon seasons of the tropics, sweet potato leaves are usually the only greens available in some countries after a flood or a typhoon. They are rich in vitamin, iron, calcium, zinc, and protein, and more tolerant of diseases, pests, and high moisture than many other leafy vegetables grown in the tropics (Pace et al., 1985; Woolfe, 1992; Yoshimoto, 2001). People have a great need to maintain and improve their health through the food they eat every day. Of three most important causes of death in Japan and other developed countries, cancer, heart diseases and cerebrovascular diseases, are said to be closely related to hypertension (Matsui, 2002). To prevent and alleviate these diseases, studies are exploring the health-promoting functions of various agricultural products. However, there are only a few studies concerning the sweet potato components that contribute to maintenance and improvement in health. In the recent decade, active research has been conducted regarding its health-promoting functions. These functions are important factors when developing new processing methods of sweet potato. Sweet potato is also an important crop as an industrial material for starch, sugar, and alcohol. Shochu is a traditional Japanese liquor made from rice, sweet potato, and barley. Recently sweet potato shochu becomes very popular alcohol drink

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in Japan (Woolfe, 1992). Therefore, increases in shochu production have resulted in an enormous output of distillery by-products. Some of these by-products have been used as feedstuff (Mahfudz et al., 1996), but most have been discarded into the ocean. Dumping of these by-products into the ocean becomes problematic from the perspective of environmental protection. Optimal treatment of the distillery by-products is important for the success of commercial shochu production. Hence, developing a new use for the shochu-distillery byproducts originating from the sweet potato is necessary from the standpoint both of the economy and of environmental conversion. The chapter describes the possible physiological functions, their related components, and utilizations of sweet potato roots, leaves and residues for food or non-food purposes (Table 1). Table 1. Physiological functions and their related components of sweet potato Function

Related components

Anti-oxidation

Polyphenol, anthocyanin

Antimutagenicity

Polyphenol, anthocyanin

Anti-carcinogenesis

Polyphenol, anthocyanin

Hou (2003); Hou et al., (2003); Kurata et al., (2007); Hagiwara et al., (2002)

Anti-HIV

3,4,5-triCQA

Mahmood et al., (1993); Tamura et al., (2006)

Anti-Alzheimer‘s disease

diCQA

Isoda et al., (2006)

Anti-melanogenesis

Polyphenol

Shimozono et al., (1996)

Reduction of liver injury

Anthocyanin

Suda et al., (1998)

Anti-hypertension

Anthocyanin polyphenol

Yoshimoto et al., (1998): Mishima et al., (2005); Ishiguro et al. (2007a, 2007b)

Antibacterial activity

Fiber, pectin-like polysaccharide

Islam and Jalaluddin (2005); Yoshimoto et al., (2006)

Fiber

Yoshimoto et al., (2005a, 2005b); Takamine et al., (2005)

Fiber

Lund (1984)

Promotion of Bifidobacterium growth Lowering cholesterol level Anti-diabetes

Anthocyanin, polyphenol

Eye protection

Lutein β-carotene

References Cevallos-Casals and Cisneros-Zevallos (2003); Furuta et al., (1998); Hayase and Kato (1984); Islam et al., (2003a); Oki et al., (2002); Yoshimoto et al., (2004) Yoshimoto et al., (1999a); Yoshimoto et al., (1999b); Yoshimoto et al., (2001); Yoshimoto et al., (2002a)

Matsui et al., (2002); Matsui et al., (2004a, 2004b); Terahara et al., (2003); Yoshimoto et al., (2006); Tsubata et al., (2004) Ishiguro and Yoshimoto (2006); Okuno et al., (1998)

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The physiological functions of the related components referred in the present chapter have been demonstrated by in vitro or in vivo study. It should be noted that many of the other physiological functions are proposed but are still undergoing research to explore these potential benefits.

SWEET POTATO ROOT COMPONENTS About 400 years ago, Chinese medical report shows that peoples who do not eat rice, barley, and beans, but eat sweet potato roots have long life (Yamada, 1994). In Japan, sweet potato has been cultivated as an emergency crop in the time of famine and has prevented starvation several times (Duell, 1983). This means that sweet potato is not only an easilycultivated crop, but has also sustained the communities at times of food scarcity. The nutrient composition of sweet potato roots is in details summarized by Woolfe (1992). Accordingly, the root nutrient components particularly not concerned with physiological functions are not described in the present chapter.

Anthocyanins Anthocyanins are the chemical components that give the intense color to many fruits and vegetables such as blueberries, purple sweet potatoes, red cabbage, and red grapes (Harborne and Grayer, 1988; Mazza 1995). Anthocyanins are naturally present as glycosides having an arabinose, glucose or galactose attached to the anthocyanidin nucleus, and thus there are more than one hundred kinds depending on the glycoside structure. The purple-fleshed sweet potato cultivar ―Ayamurasaki‖ for food colorant production is released by KONARC, Miyakonojo, Japan in 1995 (Yamakawa et al., 1997). The main pigments that accumulate in the storage roots of ―Ayamurasaki‖ are anthocyanins with aromatic acyl groups (Odake et al., 1992; Goda et al., 1997; Terahara et al., 1999). These anthocyanins possess high thermo- and photostability as compared with red cabbage, elderberry, and purple corn (Odake et al., 1994; Tsukui et al., 1999). Anthocyanins of the purple-fleshed sweet potato cultivars consist of mono- or di-acylated forms of cyanidin (YGM-1a, -1b, -2, and -3) and peonidin (YGM-4b, -5a, -5b, and -6) (Figure 1) (Oki et. al., 2002). Varieties of purple-fleshed sweet potato are classified as cyanidin- or peondin-rich type by the ratio of peonidin and cyanidin contents in the storage root (Yoshinaga et al., 1999). These differences affect the color hue of the paste, drinks, powder, and extracts of the processed products made from the roots. Incidentally, ―Ayamurasaki‖, which is industrially used as the materials of confectionary, beverage, natural colorants, alcohol drinks, and noodles, is peonidin type (Yoshinaga et al., 1999). Plant tissue culture offers an opportunity to produce large quantities of tissue in a factory setting independent of environmental conditions. A high anthocyanin-accumulating cell line has been generated from the storage root of sweet potato cultivar, ―Ayamurasaki‖ (KonczakIslam et al., 2000; Islam et al., 2002b; 2005). The cell line, due to its outstanding ability to accumulate anthocyanin pigment in the dark, is considered a suitable source of natural food colorant produced by the means of plant cell cultures.

Physiological Functions and Utilization of Sweet Potato

63

OR1 OH O+

HO

O O

O

O HO

OH

O

HO HO

OR3

O

R2 O OH

OH

HO HO

Storage root

OH

Cell line

Anthocyanin

R1

R2

R3

Anthocyanin

R1

R2

R3

YGM*-1a

H

caffeoyl

p-hydroxy benzoic acid

YGM-0a

H

H

H

CH 3

H

H

YGM-1b

H

caffeoyl

caffeoyl

YGM-0b

YGM-2

H

caffeoyl

H

YGM-0d

H

H

caffeoyl

p-coumaric acid

YGM-3

H

caffeoyl

ferulyl

YGM-0f‘

H

H

YGM-4b

CH 3

caffeoyl

caffeoyl

YGM-0g

H

H

ferulyl

YGM-5a

CH 3

caffeoyl

p-hydroxy benzoic acid

YGM-0g‘

CH 3

H

p-coumaric acid

YGM-5b

CH 3

caffeoyl

H

YGM-0i

CH 3

H

ferulyl

YGM-6

CH 3

caffeoyl

ferulyl

YGM-3‘

H

caffeoyl

p-coumaric acid

YGM-7a

H

p-coumaric acid

p-coumaric acid

YGM-7e

CH 3

p-coumaric acid

p-coumaric acid

*YGM is abbreviation of ―Yamagawamurasaki‖ with purple flesh.

Figure 1. Chemical structure of sweet potato anthocyanin.

Through changes in the composition of culture medium as well as environmental factors, the quality of in vitro accumulated anthocyanins can be regulated toward biosynthesis of highly acylated or non-acylated components (Konczak-Islam et al., 2001; Terahara et al., 2004) (Figure 1). The aqueous extract of the cell line exhibits higher antioxidative, antimutagenic, and antiproliferation activities than extract produced from field-grown storage root (Konczak-Islam et al., 2003). Generally, anthocyanin pigments are unstable to light and high temperature (Konczak and Zhang, 2004). Therefore, the stabilization of anthocyanin is significant in the viewpoint of the practical use of the physiological functions. Anthocyanin with aromatic acyl groups are reported to have improved stabilities (Hayashi et al., 1996). Anthocyanins in purple-fleshed sweet potato are stabilized in a complementary manner by the polyphenolics in the root (Oki et al., 2003).

Polyphenols Chlorogenic acid (ChA) and three kinds of dicaffeoylquinic acid (diCQA) derivatives are major polyphenolic components in the raw root of sweet potato varieties, ―Kokei No. 14‖ and ―Kintoki‖, while caffeic acid (CA) and 4-O-caffeoylquinic acid (4-O-CQA) are minor ones (Hayase and Kato, 1984). ChA and diCQA are esters of quinic acid (QA) and bear one- and

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two-caffeoyl groups (Figure 2). Currently, 3,4,5-triCQA which is an ester of QA and threecaffeoyl groups is not detected in the roots but universally in the leaves of sweet potato. HO

OR

OH

O

HO OH ChA

CA

OR

OH HOOC

OH

HOOC

OH

HO

HO OR 3,4-diCQA OR HOOC HO OR 3,4,5-triCQA

OR

OH

OR HOOC

OR

HOOC

OR

HO OH 4,5-diCQA

3,5-diCQA

OR

OH

R = caffeoyl group

O

OH

Figure 2. Chemical structure of sweet potato caffeoylquinic acid derivatives.

ChA and two kinds of diCQAs are major components and 4-O-CQA is a minor component in the raw root of ―Jewel‖ (Walter et al., 1979). ChA and three kinds of diCQAs, 3,4-di-O-caffeoylquinic acid (3,4-diCQA), 3,5-di-O-caffeoylquinic acid (3,5-diCQA), and 4,5-di-O-caffeoylquinic acid (4,5-diCQA) exist, but not CA in the steamed root of ―Beniotome‖ (Shimozono et al., 1996). These reports suggest that there is a compositional difference in CQA derivatives between the varieties of sweet potato roots, and that CA is not a primary component in the raw or steamed root. Polyphenolics including ChA are abundant in the outer tissue (about 80% of total polyphenolic content) of the sweet potato roots (Walter et al., 1979). CA is a minor polyphenolic component in the raw or steamed root (Walter et al., 1979; Shimozono et al., 1996), but a major one in the shochu-distillery by-products treated with koji (Yoshimoto et al., 2004). In order to clarify the origin of CA, polyphenolic composition was compared between the raw and steamed root of the ―Koganesengan‖ variety, a material in shochu production (Yoshimoto et al., 2004). ChA and 3,5-diCQA were dominant polyphenolics, while ChA, 3,4, 3,5-, and 4,5-diCQA, and unknown compounds existed in the steamed root. On boiling a sample of 3, 5-diCQA or 3, 4-diCQA or 4, 5-diCQA, the formation of a mixture of the three isomers, in approximately equivalent amounts, could be detected chromatographically (Scarpati and Guiso, 1964). CA was not detected even in the steamed root, indicating that steaming treatment did not vary ChA or 3, 5-diCQA to CA. CA production in the distillery by-products depends on the hydrolysis of the CQA derivatives by koji enzyme (Yoshimoto et al., 2005a). Storage conditions also influence the polyphenolic content (Picha, 1987). Polyphenolic content and radical-scavenging activities of some sweet potato cultivars increase during storage at low temperature (Ishiguro et al., 2007a). Further noncaffeoylquinic acid component that increases in variety ‗J-Red‘ during storage is identified as caffeoyl sucrose (Figure 3) (Ishiguro et al., 2007a). These results suggest that storage under cultivar-dependent, controlled temperature is one approach for increasing desirable physiologic function associated with the polyphenolic compounds in sweet potato roots.

O

O OH OH

OH Physiological Functions and Utilization of Sweet Potato

65

OH O

HO

OH

O HO

OH

HO O

O OH

O

OH OH

OH

Figure 3. Chemical structure of caffeoylsucrose.

Carotenoids Vitamin A deficiency is a serious nutritional problem in many developing countries. Millions of people suffer from this affliction, which leads to night blindness, xerophtalmia, and prolonged deficiency can impair the immune system (Bates, 1995). Carotenoids represent the most widespread group of naturally occurring pigments in nature. There are a variety of flesh colors, such as white, yellow, orange and purple, in sweet potato roots. β-Carotene (Kimura et al., 2006), luteochrome (β, β-carotene-5,6,5‘,8‘diepoxide) (De Almeida et al., 1986), and acylated anthocyanins (Yoshinaga et al., 1999) are the principal pigments in orange flesh, white flesh, and purple flesh cultivars, respectively. ―Sunny Red‖ and ―J-Red‖ with orange flesh developed in the KONARC contain more than about 14 mg β-carotene/100 g of edible part (Okuno et al., 1998). All 25 sweet potato cultivars with orange-colored flesh show similar carotenoid composition, which consists of mostly β-carotene, and its content of the sweet potato is more than several times of other vegetables as carrot or pumpkin (Takahata et al., 1993). There exists structural isomers, all-trans, 9-cis and 13-cis isomers for β-carotene and the 9-cis isomer has a higher antioxidant potency than that of the all-trans one (Levin and Mokady, 1994). Ratio of 9-cis and 13-cis isomers to total β- carotene content are about 2.6%, indicating that β-carotene isomer of the storage root in these varieties is almost all-trans one (Yoshimoto et al., 2003). Recently, a series of carotenoids with a 5,6-dihydro-5,6-dihydroxyβ-end group, named ipomoeaxanthins are identified from the flesh of deep yellow sweet potato ―Benimasari‖ (Maoka et al., 2007). Physiological functions of these new ipomoeaxanthins are unclear presently and expected to research positively in the future.

Fiber In recent years, new varieties of sweet potato (Ipomoea batatas L.) have been released for the development of new uses from the KONARC, Miyakonojo, Japan. New products, such as juice, powder, and brewed drinks, which are made from flesh-colored sweet potatoes, have been made practicable (Yoshimoto, 2001). However disposition of the shochu waste, the residue from starch industry, and the strained residue from the juice production is a critical

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problem from the viewpoint of environmental protection. Residue from the starch industry of sweet potato has been used as a material of citric acid fermentation. However, utilization of this residue has become increasingly difficult, since the import of foreign-made cheep citric acid. Therefore, development of new use of the residue from starch industry has been demanded for a long time. Sweet potato root has a well-balanced content of soluble and insoluble fiber in a ratio of about 1: 1 (excluding lignin), unlike wheat bran, which is mainly insoluble fiber (Holloway et al., 1985; Englyst et al., 1988). This is to say, sweet potato dietary fiber contains abundantly soluble component, pectin or hemicellulose, suggesting that physiological functions may be higher in the sweet potato fibers than other crop ones.

PHYSIOLOGICAL FUNCTIONS OF SWEET POTATO ROOTS Anthocyanins and Their Related Compounds The sweet potato anthocyanins are ubiquitous bioactive compounds because of its potential antioxidant activities that may exert cardio-protective effects (Knekt et al., 1996; Suda et al., 1998; Yoshimoto et al., 1999a), radical-scavenging (Furuta et. al., 1998), antimutagenic (Yoshimoto et al., 1999b), antidiabetic (Yoshimoto et al., 1998; Matsui et al., 2002), and anticancer (Hou, 2003; Konczak-Islam et al., 2003) activities. Recently, growing demand in the food industry for use of natural food colorants has led to the evaluation of various vegetables as food colorant sources. The sweet potato anthocyanins are superior as a natural food colorant to those from red cabbage, elderberry, and purple corn (Odake et al., 1994, Odake, 1998; Konczak-Islam et al., 2003) due to their positive therapeutic and physiological functions (Kamei et al., 1995; Furata et al., 1998; Yoshimoto et al., 2001; Hou, 2003). Anthocyanin absorption and metabolism are reported in both experimental animals and human using fruits and sweet potato (Miyazawa et al., 1999; Bub et al., 2001; Matsumoto et al., 2001; Cao et al., 2001). Moreover, they also show an ameliorative effect on carbon tetrachloride-induced liver injury (Suda et al., 1997) and decrease postprandial blood glucose levels (Matsui et al., 2002) in rats. Peonidin 3-caffeoylsophoroside-5-glucoside in purplefleshed sweet potato is directly absorbed into rats and present as an intact acylated form in rat plasma (Suda et al., 2002). As its result, the plasma antioxidant capacity was significantly elevated 30 min after the administration of the purple-fleshed sweet potato anthocyanin concentrate. Further, the absorbability of anthocyanins has been evaluated in human administered with a beverage prepared from the extract of the root of purple sweet potato. Two major anthocyanin components, cyanidin 3-caffeoylsophoroside-5-glucoside and peonidin 3-caffeoylsophoroside-5-glucoside, were detected in the plasma and urine (Harada et al., 2004). An acylated anthocyanin, peonidin 3-caffeoylsophoroside-5-glucoside was detected in the urine of healthy volunteers 2 h after ingestion of a purple-fleshed sweet potato beverage (Oki et al., 2006). Some of the subjects with mild under functioning of the liver show the diminished levels of the serum γ-GTP (γ-glutamyl transpeptidase), GOT (glutamicoxalacetic transaminase) and GPT (glutamic-pyruvic transaminase) after 44 days (120 ml/day) of continual ingestion of the high anthocyanin sweet potato juice (Suda et al., 1998).

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However, most of such subjects belong to a group with their high level maintaining history less than five years, but not more than five years. Recent report reveals that oral administration of the beverage containing blackcurrant anthocyanin (4 mg anthocyanin/kg body weight and 1% phytic acid) enhanced absorption of anthocyanin in human as compared to the beverage without phytic acid (Matsumoto et al., 2007). Based on these evidences, the purple-fleshed sweet potato can be recommended as a superior source for the production of foods with health benefits (Suda et al., 2003). Further, phenolic anthocyanins from purplefleshed sweet potato can be considered as excellent novel sources of natural antioxidant for not only the functional food but also dietary supplement markets (Cevallos-Casals and Cisneros-Zevallos, 2003). Recently, new red vinegar has been developed via fermentation with the storage root of purple-fleshed sweet potato (Terahara and Sugita, 2000). The red vinegar has a higher antioxidative activity than white or black vinegars. The red vinegar contains some new components possibly derived from the original purple sweet potato. A major component is caffeoylsophorose with a high antioxidative activity (Terahara et al., 2003) (Figure 4). The administration of caffeoylsophorose following maltose to rat results in the maximal blood glucose level after 30 min being significantly decreased by about 11% compared to the control (Matsui et al., 2004b). Sweet potato has also high contents of polyphenolics (Walter et al., 1979; Yoshimoto et al., 1999b), calcium (Suzuki et al., 1998), cyanidin pigment (Yoshimoto et al., 1999a) in the parts about 5-10 mm from the skin. Analysis of anthocyanin pigments in both portions (outer and inner portions) reveals a large distribution of pigments in the outer portion than in the inner portion (Yoshimoto et al., 1999a). The technique making sweet potato powder unnecessary peeling of the roots for the minimization of the loss of useful components is used on a commercial basis. The powder products can be used all the year round as a material of confectionery, noodles, alcohol drink, and beverage (Yoshimoto, 2001). O

HO

O HO

HO O OH

OH O

O OH OH

OH OH O Figure 4. Chemical structure of caffeoylsophorose. HO

OH

O HO

OH

HO O

O OH

O

OH OH

OH

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Makoto Yoshimoto

Dietary Fiber Substantial epidemiological and physiological studies have shown that dietary fiber has important functions in the diet, with suggestions that it gives protection against cardiovascular disease, colon cancer, and diabetes, the various fiber components having roles in this respect (Woolfe, 1992). Dietary fiber removes a health-harmful factors, such as artificial food color (Takeda and Kiriyama, 1979), aluminum (Takeyama et al., 1996), mutagens (Barnes et al., 1983; Kada et al., 1984) and cholesterol (Lund, 1984) by adsorption of these factors from the body and improves the flora of intestinal bacteria (Mitsuoka, 1995). Dietary fibers have been used as functional foods for protection from a colon cancer and heart disease in Western countries and for a relieve constipation in Japan. Furthermore, dietary fiber has been actively used for a decrease in calorie and improvement of food quality. Therefore, the expansion of the demand of dietary fibers is expected in the future. A predominantly bifidobacterial flora in the intestinal tract is considered to inhibit the growth of harmful bacteria such as pathogenic strains and protect the infants against gastrointestinal diseases (Idota et al., 1994). Consequently, factors that stimulate the growth of bifidobacteria appear to be promising effective substances for the maintenance of intestinal homeostrains. Sweet potato fibers promote effectively the growth of Bifidobacterium adolescentis and B. brevis among five species of Bifidobacterium which exist in the intestinal tract of the human (Yoshimoto et al., 2005b). Boiling-soluble fraction of the ―Ayamurasaki‖ fiber promotes more effectively the growth of B. adolescentis than the fiber itself, suggesting that pectin may be the promoting factor of bifidobacteria. This is also consistent with the relationship between the fiber components and the growth promotion of bifidobacteria. Among the root crops, sweet potato cell wall material has the highest amount of the pectin fraction (Salvador et al., 2000). The number of intestinal bacteria of the sweet potato-dietary fiber-fed rats is higher than those of the control rats, and Bifidobacterium. sp. is found only in the sweet potato-dietary fiber-fed rats (Takamine et al., 2005). These data indicate that the sweet potato starch residue is available as the physiologically functional dietary fiber. The water holding capacity of dietary fiber is thought to be an important determinant of fecal bulking and intestinal transit times with influence gastrointestinal disease (Holloway and Grieg, 1984; Gazzaniga and Lupton, 1987; Wrick et al., 1983). Some types of dietary fiber adsorb mutagenic agents, which would lead to their excretion in the feces and decrease their contact with colonic mucosal cells (Roberton et al., 1991). Water- and oil-holding capacity of the fibers in the varieties with orange-colored flesh is relatively superior to ones from the varieties with yellow- or purple-colored flesh (Yoshimoto et al., 2005b). ―Shiroyutaka‖, ―Koganesengan‖, and ―Kyushu 124‖ fiber adsorb about 90% of the added mutagen (Trp-P-1: 3-amino-1,4-dimethyl-5H-pyrido-(4,3-b)indol), while the commercial sweet potato fiber does only 56%. Commercial sweet potato fiber has been made mainly from the residue of the starch industry of ―Koganesengan‖ roots through a citric acid production. After extraction of citric acid, the residue is treated with 0.25% NaOH and subsequent bleaching with NaOCl. Lower adsorption capacity of the commercial sweet potato fiber seems to be caused by low content of pectin and hemicelluloses (Yoshimoto et al., 2005b). This is also supported by the report that cotton fiber containing cellulose as a main component slightly adsorb Trp-P-1 (Barnes et al., 1983). Takamine et al. (2000) reported that the water- and oil-holding capacities of the dietary fiber made from the residue from starch

Physiological Functions and Utilization of Sweet Potato

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industry of sweet potato roots is superior to some commercial dietary fiber, corn and beet fiber. High capacity of oil holding means to adsorb effectively various kinds of mutagen and cholesterol, because most of these components are lipophilic. Sweet potato fiber is by far the most effective binder of cholesterol at 30%, cassava fraction at 3%, citrus pectin at 8% and the majority of samples at <20% for 28 fiber samples from a variety of commonly consumed tropical fruits and vegetables including sweet potato (Lund, 1984). It has been suggested that pectin with a high methoxyl content is important in reducing serum cholesterol (Mokady, 1973). The methoxyl content of the sweet potato pectin is high at a concentration of 9.7% of a cold water extract; the highest being for onion at 11% and wheat bran having only 0.1% in a study with a series of fruit and vegetables (Holloway, 1983). These reports indicate that the sweet potato pectin is qualitatively and functionally superior to the fruit and vegetable.

SWEET POTATO LEAF COMPONENTS New cultivars of sweet potato whose roots are used for beverage, paste, powder, alcohol drink and natural colorant have been developed in this decade (Yoshimoto, 2001). However, sweet potato leaves have largely been neglected except for their partial use as livestock feed in Japan and other Asian countries (Villareal et al., 1979). Phenolic compounds (natural antioxidants) exist universally in vegetables (Tsushida et al., 1994; Murata et al., 1995; Chuda et al., 1996; Murayama et al., 2002) and in fruits (Coseteng and Lee, 1987; Robards et al., 1999). Dietary antioxidants have attracted special attention because they can protect the human body from oxidative stress, which may cause many diseases including cancer, aging and cardiovascular diseases (Huang and Ferraro, 1991; Peluso et al., 1995; Stevens et al., 1995; Shahrzad and Bitsch, 1996; Shimozono et al., 1996; Hagerman et al., 1998; Kaul and Khanduja 1998; Robards et al., 1999; Prior et al., 1998; Yoshimoto et al., 1999b). Therefore, sweet potato leaves with high nutritive value (Yoshimoto et al., 2002a) and antioxidants, namely phenolics (Islam et al., 2002a; Islam et al., 2003c; Islam, 2005) may become an excellent source material for physiological functional foods.

Nutritional Value Sweet potato leaf is also rich in vitamin B, β-carotene, iron, calcium, zinc and protein, and as a crop is more tolerant of diseases, pests, and high moisture than many other leafy vegetables grown in the tropics (AVRDC, 1985; Woolfe, 1992). Depending on the genotypes and growing conditions, sweet potato leaves are comparable with spinach in nutrient contents (Woolfe, 1992; Yoshimoto et al., 2002a; Ishiguro et al., 2004b). The new cultivar ―Suioh‖ is a bushy plant that is easy to harvest (Ishiguro et al., 2004a). This cultivar is harvested from nursery beds six times a year, from April through October. Total yield of greens is 4.16 kg/kg of seed roots. Sensory evaluation shows that the taste of the cooked leaves and petioles is very good, and that the hot water extract from greens can be used as a substitute for green tea. The average contents of minerals and vitamins are 117 mg calcium, 1.8 mg iron, 3.5 mg total

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carotene, 7.2 mg total vitamin C, 1.6 mg total vitamin E, and 0.56 mg vitamin K/100 g fresh weight of leaves. Levels of iron, calcium and carotene rank among the top, as compared with other major vegetables (Ishiguro et al., 2004a). In sweet potato leaves, average content of β-carotene from five varieties was 6.2 mg/100 g fresh weight, while that from six leafy vegetables was 2.1 mg/100 g fresh weight. Ratio of 9-cis and 13-cis isomers to total β-carotene content in the leaves of five varieties was 21.5%, while that of six commercial vegetables was 14.7%. These results suggest that sweet potato leaves contain higher content of 9-cis and 13-cis isomers than the commercial vegetables (Yoshimoto et al., 2003). The 9-cis isomer has a higher antioxidant potency than that of the all-trans one (Levin and Mokady, 1994), as mentioned previously. Lutein is a member of the xanthophylls family of carotenoids and is found in vegetables and fruits (Mangels et al., 1993). Lutein is believed to mitigate eye disease such as agerelated macular degeneration and cataracts. Green leafy vegetables like spinach and kale have high lutein content (Alves-Rodrigues and Shao, 2004). Purified lutein has been used in dietary supplements and as a food ingredient for eye health in recent years. ―Suioh‖, a sweet potato cultivar is developed specifically for the use of its top at KONARC. Lutein content in ―Suioh‖ leaves grown in the field, ranges from 31.5 mg to 42.6 mg/100 g fresh weight (average content, 36.8 mg/100 g fresh weight) (Ishiguro and Yoshimoto, 2006). The average content in ―Suioh‖ leaves is higher than Ipomoea aquatica leaves (11.9 mg/100 g fresh weight) and exceeds that in other fruits and vegetables listed in a carotenoid database of 120 fruits and vegetables (Ishiguro and Yoshimoto, 2006).

Polyphenols Phenolic acids are bioactive compounds and a diverse group of secondary metabolites universally present in higher plants (Rhodes et al., 1986; Meyer et al., 1998), where they play important roles in the structure of plants and are involved in a number of metabolic pathways (Harborne, 1980). Phenolics also have attracted special attention because they may protect the human body from oxidative stress, which in turn is associated with many diseases including cancer and cardiovascular diseases, as well as aging (Huang and Ferraro, 1991; Peluso et al., 1995; Stevens et al., 1995; Shimozono et al., 1996; Shahrzed and Bitsch, 1996; Kaul and Khanduja, 1998; Prior et al., 1998; Hagerman et al., 1998; Yoshimoto et al., 1999a; Robards et al., 1999). Sweet potato leaves are an excellent source of antioxidative polyphenolics, such as CA, ChA, diCQA, and triCQA (Islam et al, 2002a, 2003a, 2003b, 2003c), superior in this regard to other commercial vegetables, including sweet potato roots and potato tubers (Lugasi et al., 1999; Islam et al., 2002b; Yoshimoto et al., 2001, 2002a, 2003; Ishiguro et al., 2002a, 2004b). Total leaf polyphenol contents of 1389 genotypes, collected from all over the world, were analyzed and characterized in 2000 and 2001 (Islam et al., 2003c). A highly significant (P > 0.001) liner correlation is found between the polyphenol contents of the genotypes from 2000 and the genotypes from 2001 (r = 0.812; n = 700). This result indicates that the yearly variations of total phenolics in leaves of sweet potato genotypes are less. Furthermore, previous data revealed that the highest polyphenol concentration was in leaves (6.19 ± 0.14 g/100 g dry weight), followed by petioles (2.97 ± 0.26 g/ 100 g dry weight), stems (1.88 ± 0.19 g/100 g dry weight), and finally roots (<1.00

Physiological Functions and Utilization of Sweet Potato

71

g/100 g dry weight), indicating that polyphenolic concentrations are organ-dependent (Islam et al., 2002b). The frequency distribution of total leaf polyphenolic content of 1389 genotypes collected from world wide is shown in Figure 5. The highest content found is 17.1 g/100 g dry weight and the lowest is >6.00 g/100 g dry leaf powder of total polyphenolics; the concentration is very high compared to other commercial vegetables (Yoshimoto et al., 2003; Ishiguro et al., 2002, 2004b). CA and five CQA derivatives: ChA, 3,4-diCQA, 3,5-diCQA, 4,5-diCQA, and 3,4,5triCQA are found in sweet potato leaves (Islam et al., 2002a). ChA and diCQA derivatives have been isolated from various plants including sweet potato (Shimozono et al., 1996; Walter et al., 1979), as mentioned above, but there are very few reports on 3,4,5-triCQA. All caffeoylquinic acid derivatives (except CA; P < 0.05) are positively correlated (P > 0.001) with total polyphenol contents of sweet potato leaves. The correlation of total phenolics with ChA (r = 0.84), 3,4-diCQA (r = 0.78), 3,5-diCQA (r = 0.81), 4,5-diCQA (r = 0.85) and 3,4,5triCQA (r = 0.59) are positive and significant. The results indicate that the correlation between total phenolics with different CQA derivatives is an important aspect, which should be kept in mind for better planning for improvement of the desired parameters. ChA, di- and triCQA are esters of quinic acid (QA) and bear one-, two-, and three-caffeoyl groups. Isolation of 3,4,5-triCQA is reported in Securidaka longipedunculata (Polygalaceae) (Mahmood et al., 1993) and Tessaria integrifolia (Asteraceae) (Peluso et al., 1995). Several varieties of sweet potato contain a high content (>0.2%) of 3,4,5-triCQA (Islam et al., 2002b; 2003c), suggesting that the sweet potato leaf is a source of not only mono- and diCQA derivatives but also triCQA.

Figure 5. Frequency distribution of total polyphenol content of 1389 sweet potato genotypes.

Makoto Yoshimoto

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Anthocyanins Fifteen anthocyanin compounds have been identified and characterized in sweet potato leaves (Islam et al., 2002b). The content of cyanidin in leaves was much higher than that of peonidin (Oki et al., 2002), suggesting that the cyanidin type is dominant (Islam et al., 2002b; 2005). The cyanidin type anthocyanins are superior to the peonidin type in antimutagenicity (Yoshimoto et al., 1999a, 1999b) and antioxidative activity (Rice-Evans et al., 1995).

Galacto-Lipid Sixteen novel and ten known galactolipids were isolated and characterized from the sweet potato leaves (Napalitano et al., 2007). Various studies have indicated that glycoglycerolipds exhibit specific biological properties including antiviral (Reshef et al., 1997), antitumor (Shirahashi et al., 1993; Morimoto et al., 1995; Murakami et al., 1995; Shirahashi et al., 1996; Murakami et al., 2003), and anti-inflammatory (Larsen et al., 2003) activities. The physiological and physiological functions of the novel galactolipids derived from sweet potato leaves are not known and are expected to be evaluated by vitro and in vivo studies in the future.

PHYSIOLOGICAL FUNCTIONS OF SWEET POTATO LEAVES Antioxidation Although lipids are essential for human health, certain polyunsaturated fatty acids have many double bonds and cause radical chain reactions with oxygen, and thereby produce various lipid peroxide and oxidized resolvents. Lipid peroxides cause deterioration in cell functions, arterial sclerosis, liver disorders, and retinopathy, and are also involved in carcinogenesis and aging (Halliwell, 1994; Yu, 1994; Nair et al., 2007). The antioxidative or radical-scavenging properties of lipid peroxides are especially interesting because of their potential to provide health protection against reactive oxygen species and free radicals, which have been implicated in more than 100 diseases (Halliwell, 1992). Several authors have reported the antioxidative and radical scavenging activities of sweet potato leaves (Islam et al., 2002b, 2003, 2003c). The polyphenolic content and antioxidative activity in vegetables show a good correlation, with the antioxidative activity of edible chrysanthemum (Chrysanthemum morifolium), which has the highest polyphenolic content among 43 commercial vegetables (Tsusida et al., 1994). The radical-scavenging activity of CQA derivatives in order of effectiveness is 3,4,5-triCQA > 3,4-diCQA = 3,5-diCQA = 4,5-diCQA > CA = ChA. Sweet potato leaves also revealed relatively much higher activity in 1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity than the 43 vegetables mentioned above (Islam et al., 2003b, 2003c). There are significant positive correlations between radical-scavenging activity and the polyphenol concentrations of sweet potato leaves (Islam et al., 2003a). These data indicate that sweet potato leaves are a good supplementary resource of antioxidants.

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Antimutagenicity Cancers can occur through initiation, promotion, and progression in body cells. Initiation is a type of mutation that occurs in cancer and anticancer genes. Therefore, controlling the gene mutation, brought about by the carcinogens, leads to cancer prevention (Berenblum, 1941). The mutagens contained in food may include ingredients of vegetables, mold toxins, and pollutants in food. These mutagens are considered as factors involved in formation and occurrence of human cancers (McCann et al., 1975). Development of screening methods for environmental carcinogens by determining their mutagenicity has enabled various types of mutagens and carcinogens to be detected and identified in daily foods (Ames et al., 1975). It is now known that various types of inhibitors that act against mutagens and carcinogens are present in our daily food, and that they play an important role in reducing the risks of mutagenesis and carcinogenesis (Shinohara et al., 1988). CQA derivatives effectively inhibit the reverse mutations induced by Trp-P-1 on Salmonella typhimurium TA and the antimutagenicity of these derivatives in order of effectiveness is 3,4,5-triCQA > 3,4-diCQA = 3,5-diCQA = 4,5-diCQA > ChA (Yoshimoto et al., 2002b).

Anticarcinogenesis Growth suppression of three kinds of cancer cells, stomach cancer (Kato-III), colon cancer (DLD-1), and promyelocytic leukemia (HL-60) cells, by QA, CA, and CQA derivatives has been researched (Kurata et al., 2007). QA has no effect on the growth of each kind of cancer cells. 3,4,5-TriCQA, however, suppresses the growth of each kind of cancer cells. Promyelocytic leukemia cells (HL-60) are especially sensitive to the CQA derivatives compared with the others. CA and the three kinds of di-CQA derivatives (3,4-diCQA, 3,5diCQA, and 4,5-diCQA) suppress the growth of HL-60 cells. CA exceptionally suppresses the cell multiplication of HL-60. These results show the necessity of the caffeoyl group bound to QA as well as the differential sensitivity of tumor cells to these compounds. Nuclear granulation and DNA fragmentation in HL-60 cells treated with 3,4,5-triCQA suggest that the cellular death is due to apoptosis induction (Kurata et al., 2007).

Antidiabetes International Diabetes Federation reports that the diabetic mellitus population is increasing globally and it is estimated at 246 million persons around the world at 2007. . Insulin-secretion ability in the rat pancreas RIN-5F cells is promoted in order of 3,4,5-triCQA > 3,4-diCQA = 4,5-diCQA = 3,5-diCQA > ferulic acid (FA) > CA > QA = ChA. 3,4,5TriCQA especially shows a remarkable insulin-secretion promoting effect (Tsubata et al., 2004). Ferulic acid (FA) and its amide derivatives stimulate insulin secretion in the rat pancreas RIN-5F cells (Nomura et al., 2003). CQA derivatives except for QA, ChA, and CA reveal higher activity on insulin secretion than FA, indicating that sweet potato leaves containing CQA derivatives may be excellent sources for antidiabetes. However, more research is needed before a direct link is established.

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α -Glucosidase (EC 3.2.1.20), which is a membrane-bound enzyme located at the epitherium of the small intestine. It catalyzes the cleavage of glucose from disaccharides (Hauri et al., 1982). Thus, retardation of the action of this enzyme by any inhibitor may be one of the most effective approaches to control non-insulin-dependent diabetes (Toeller, 1994). Matsui et al. (2004a) reported that the maltase inhibitory effect (IC50) of 3,4-diCQA, 3,5-diCQA, and 4,5-diCQA are at levels of 1,910 μM, 1,890 μM, and 413 μM, respectively. Maltase inhibitory effect (IC50 = 24 μM) of 3,4,5-triCQA is much higher than the other three diCQAs and YGM-6 (one of anthocyanin pigments from sweet potato root with purplecolored flesh), and is about one fifty-sixth of acarbose (IC50: 0.43 μM). In Japan, acarbose as a therapeutic α-glucosidase inhibitor is widely used to delay glucose absorption from the small intestine (Goto et al., 1989; Odaka et al., 1992). Further, Matsui et al. (2004a) indicate that oral administration of 3,4,5-triCQA to diabetic model rats reduces significantly their blood glucose content. Oral administration of 1.0 g and 0.1 g fine powder of the dried sweet potato leaves/kg body weight/day to STZ-induced insulin-deficient diabetic rats for seven days significantly decreased their blood glucose and increased their blood insulin levels. Further, oral administration of sweet potato leaves significantly decreased blood-glucose content in oral starch loading human volunteers (Tsubata et al., 2004). At the later stage of non-insulin-dependent diabetes mellitus (NIDDM), which is the predominant type of human diabetes, symptoms result mainly from decreased secretion of insulin by pancreatic Langerhans cells. Prevention of the NIDDM and inhibition of the serious adverse effects of diabetes such as retinopathy, neuropathy, and cataracts, are important subjects for researchers. Therefore, food materials with antidiabetic effect are desired for diet therapy.

Antihypertension A single oral administration of 3,4-diCQA, 3,5-diCQA, and 3,4,5-triCQA each at a dose of 10 mg/kg in spontaneously hypertensive rats showed antihypertensive effects (Mishima et al., 2005). Spontaneously hypertensive rats, which were orally administered with sweet potato tops exhibited dose-dependent suppression in blood pressure increases in comparison with the control group. These results suggest that sweet potato tops have a hypertensive effect in spontaneously hepertensive rats (SHR), which is at least in part due to the angiotensin I converting enzyme(ACE) inhibitory activity of CQA (Ishiguro et al., 2007b).

Antibacterial Activity Removal of pathogenic fungi in food, extension of storage time by the control of putrefying bacteria, and eradication of parasites are important for the maintenance of human health. Currently, an orientation towards healthy and natural foods is strengthening among consumers, and there may come a situation when it will be difficult to use food preservatives and disinfectants. There is an indication of a worldwide prevalence of infection by Escherichia coli O-157, and surveillance and preventive measures are required for this emerging infectious disease (Itoh and Kai, 1997).

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Lyophilized leaf powder from the ‗Simon-1‘ sweet potato cultivar strongly suppresses the growth of E. coli O-157, and its effect is detectable even after autoclave treatment. Unlike leaves, petioles or stems promote markedly the growth of O-157, suggesting that the antibacterial components exist only in the leaf. The antibacterial extract reveals that the main components are polysaccharides (Islam and Jalaluddin, 2004). In the polysaccharide fraction, the relative quantities of neutral sugars are in the order of xylose > galactose > arabinose > glucose > rhamnose > mannose > fructose. Galacturonic acid accounts for 28.7%, which is the highest among the sugar components detected. These results suggest that the antibacterial component of sweet potato leaves may be pectin-like material (Islam and Jalaluddin, 2005). Furthermore, the water extract from the leaves suppresses effectively the growth of other food-poisoning bacteria such as Staphylococcus aureus and Bacillus cereus as well as pathogenic E. coli (Islam and Jalaluddin, 2005).

Other Physiological Functions Including Anti-HIV HIV infection in humans is one of the most terrible pandemics around the world. Suitable candidates for investigating the potential in counteracting the transmission of HIV infection have been positively screening from various kinds of plants (Mahmood et al., 1993; Lim et al., 1997; Kobayashi et al., 2000; Ma et al., 2000; Tamura et al., 2006). 3,4,5-TriCQA is suggested to depress the transmission of HIV infection by the inhibition of the virus integrase (Tamura et al., 2006) and specific binding to the virus glycoprotein, gp120, which prevents its interaction with CD4 on T-lymphocytes and thus inactivates virus infectivity (Mahmood et al., 1993). A pathogenic hallmark of Alzheimer‘s disease is the formation of senile plaques. βAmyloid peptide (Aβ) is a major component of these plaques. Aβ is shown to have the potential to induce oxidative stress and inflammation in the brain, which are postulated to play important roles in the pathogenesis of Alzheimer‘s disease. Aβ induces the production of hydrogen peroxide and lipid peroxide in neurons. In addition, Aβ has been reported to induce superoxide and proinflammatory cytokines in astrocytes as well as in microglial cells. Antioxidant such as α-tocopherol protect against cytotoxicity in vitro as well as learning and memory deficits induced by Aβ. Furthermore, α-tocopherol and anti-inflammatory agents such as indomethacin reportedly slow the progression of Alzheimer‘s disease (Sano et al., 1997; Rogers et al., 1993). Long-term administration of FA, a phenolic compound, with potent antioxidant and anti-inflammatory activities, induces resistance to Aβ1-42 toxicity in the brain (Yan et al., 2001). Administration of diCQA to Alzheimer-model rats protects against the aging, especially learning and memory deficits induced by Aβ (Isoda et al., 2006).

RELATIONSHIP OF FUNCTIONAL COMPONENT AND STRUCTURE The structural feature responsible for the antioxidative and free radical-scavenging activity of CA is the ortho-dihydroxyl functionality in the catechol (Mahmood et al., 1993). The cathecol structure also plays an important role in the strong antimutagenicity of anthocyanin pigments (Yoshimoto et al., 2001). Therefore, the physiological function of the

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CQA derivatives with plural caffeoyl groups is more effective than with a monocaffeoyl one. The radical scavenging activity and the antimutagenicity of these derivatives in order of efficacy is triCQA > diCQAs > monoCQA, suggesting that the number of caffeoyl groups bound to QA plays a role in the radical scavenging activity of the CQA derivatives. In other words, additional caffeoyl groups bound to QA are necessary for higher function. The 3,4,5triCQA exhibits a greater selective inhibition of HIV replication than other CQA derivatives (Mahmood et al., 1993; Tamura et al., 2006). Thus, although there is no direct association, the CQA derivatives have the potential to protect humans from various kinds of diseases. Especially 3,4,5-triCQA shows remarkable activities for various kinds of physiological functions (Yoshimoto et al., 2002b; Matsui et al., 2004a; Mishima et al., 2005). ChA and diCQA derivatives have been isolated from various plants including sweet potato (Walter et al., 1979; Shimozono et al., 1996), but there are very few reports on 3,4,5-triCQA. Several varieties of sweet potato contain a high content of 3,4,5-triCQA (Islam et al., 2002a; 2003a), suggesting that the sweet potato leaf is a source of not only mono- and diCQA derivatives but also 3,4,5-triCQA. A large scale purification of 3,4,5-triCQA from sweet potato leaves is established in KONARC (unpublished data). As reviewed previously, sweet potato anthocyanins have been reported to possess multifaceted action, including antioxidation, antimutagenicity, anti-inflammatory, and anticarinogenesis. Extensive structure-activity studies have shown that the number of sugar units and hydroxyl groups on aglycons is associated with biological activities of anthocyanins. The activities appear to increase with a decreasing number of sugar units, and with an increasing number of hydroxyl groups on aglycons (Yoshimoto et al., 2001; Hou et al., 2004). Oral intake of anthocyanins from purple sweet potato and red cabbage color suppresses rat colon carcinogenesis induced by 1,2-dimethylhydrazine (DMH) and 2-amino-1 methyl-6-phenylimidazo [4,5-b] pyridine (PhIP) (Hagiwara et al, 2002). Of the six anthocyanins tested, only those with an ortho-dihydroxyphenyl structure on the B-ring suppressed 12-O-tetradecanoylphorbl-13-acette (TPA)-induced cell transformation and activator protein-1 transactivation, suggesting that the ortho-dihydroxypehnyl may contribute to the inhibitory action (Hou et al., 2003). The structural feature responsible for the antioxidative and free radical scavenging activity of CA is the ortho-dihydroxyl functionality in the catechol (Son and Lewis., 2002). These activities might depend on the number of hydroxyl group in the structure (Yoshimoto et al., 2001; Hou, 2003). Cyanidin containing two hydroxyl groups shows stronger activity on antimutagenicity than that of peonidin, which has only one group (Yoshimoto et al., 1999b; 2001). Based on additional studies with enzyme activity, the cyanidins protect against the mutagenesis partly by direct reactions with enzymatically activated carcinogens (heterocyclic amines) rather than by the interaction with metabolic enzyme (Yoshimoto et al., 1999b).

SWEET POTATO USE FOR NON- FOOD Sweet potato root is used to make various processed food and food materials, such as juice, natural food colorant, confectionery, shochu, and starch. This process unavoidably discharged wastes and the cost of disposing of these wastes is a main cause of lowering profitability of food processors. In such a circumstance, it is an important question to find

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ways to use effectively the wastes from food processing. In Japan, studies are actively conducted clarify the characteristics of these wastes and to develop recycling technology. The subjects of these studies include the method of converting wastes from starch production into biodegradable plastics and recycling of waste liquids from shochu making not merely as feed and manure but also as biodegradable farming materials and foods. Treatment of sweet potato waste derived from shochu, starch, and leaves is important in the southern Kyushu area in Japan. Shochu waste is used as a raw material of a vinegar-like beverage (Yoshimoto et al., 2004) and bread (Sho et al., 2008) with high content of polyphenolics. Research of polyphenolic composition in shochu waste demonstrates the enzymatic hydrolysis of CQA derivatives to CA and QA in shochu fermentation process by koji, fungi for traditional fermented products in Japan (Yoshimoto et al., 2005a). CA is a raw material for environmentally degradable, high-performance thermoplastics (Kaneko et al., 2006). Furthermore ethyl caffeate isolated from sweet potato shochu distillery by-products inhibits weed seed germination and radical elongation, suggesting a potential as herbicide (Okuno et al., 2006). Sweet potato leaves also can be used as an animal feed for egg-laying hens (Takenoyama et al., 2007) and beef cattle (Takenoyama et al., 2008). Sweet potato leaves contains high content of polyphenolics (Islam et al., 2002a ) and the leaf extract is used in cosmetics. Starch waste fiber from sweet potato is industrially used for the material of environmentally degradable sheets for agriculture.

CONCLUSIONS Sweet potato root is a resource of anthocyanin pigments with thermo- and photostability. Furthermore, anthocyanin composition in sweet potato affects not only the quality of food colorants (Odake et al., 1994) and paste color (Yoshinaga et al., 1999) but also physiological activities (Islam et al., 2002b; Yoshimoto et al., 1999a, 2001). KONARC (Japan) is currently focusing on development of new varieties of sweet potato with different pigment composition and more thermo- and photostable pigments. Sweet potato leaves have been shown to contain higher levels of oxalic acid than leafy vegetables from temperate climate, highest being reported in spinach (Evensen and Standal 1984). Oxalate concentrations in food crops have long been a concern in human diet, because of the negative health effects associated with high intake of oxalate levels that can cause acute poisoning, resulting in hypocalcaemia. Furthermore, oxalic acid and soluble oxalates can bind calcium, reducing its bioavailability and humans poorly utilize calcium oxalate itself. The average content of oxalic acid of sweet potato variety ―Suioh‖ leaves is 280 mg/ 100 g fresh weight. This content is not high compared with the 930 mg/100 g fresh weight in spinach (Ishiguro et al., 2004b). Oxalic acid contents of other sweet potato varieties tested are also several times less than that of spinach (Yoshimoto et al., 2002a). Sweet potato contains various kinds of physiologically functional components in roots and leaves, which have the potential to maintain human health and mitigate the diseases. However, much of the evidence is based on research using rats and cell cultures and there is no evidence to directly support benefit to humans. Therefore, moderate consumption of these functional components through the intake of the products may be linked with the chemoprevention of the diseases, further epidemiological and efficacy studies on this aspect

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are required. In the worldwide food shortage and increasing food prices, sweet potato is a crop that can contribute to the effective use as not only foods with various kinds of physiological functions, but also the natural resources and the reduction in environmental load.

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Woolfe, J. A. (1992). Sweet potato: an Untapped Food Resource. Cambridge University Press, Cambridge, UK, p. 1-621. Wrick, K.L. (1983). The influence of dietary fiber source on human intestinal transit and stool output. J. Nutr. 113: 1464-1479. Yamada, S. (1994). Satsumaimo-Denrai to Bunka. Shuneido Publication, Kagoshima [In Japanese]. Yamakawa, O., Yoshinaga, M., Hidaka, M., Kumagai, T. and Komaki, K. (1997). Ayamurasaki: a new sweet potato cultivar. Bull. Kyushu Natl. Agric. Exp. Stn. 31: 1-22 [In Japanese]. Yan, J.-J., Cho, J.-Y., Kim, H.-S., Kim, K.-L., Jung, J.-S., Huh, S.-O., Suh, H.-W., Kim, Y.H. with and Song, D.-K. (2001). Protection against amyloid peptide toxicity in vivo long-term administration of ferulic acid. Brit. J. Pharmacol. 133: 89-96. Yoshimoto, M. (2001). New trends of processing and use of sweet potato in Japan. Farming Japan 35: 22-28. Yoshimoto, M., Kurata-A., R., Fujii, M., Hou, D.-X., Ikeda, K., Yoshidome, T. and Osako, M. (2004). Phenolic composition and radical scavenging activity of sweet potato-derived shochu distillery by-products treated with koji. Biosci. Biotechnol. Biochem. 68: 24772483. Yoshimoto, M., Kurata-A., R., Fujii, M., Hou, D.-X., Ikeda, K., Yoshidome, T. and Osako, M. (2005a). Enzymatic production of caffeic acid by koji from plant resources containing caffeoylquinic acid derivatives. Biosci. Biotechnol. Biochem. 69: 1777-1781. Yoshimoto, M., Kurata, R., Okuno, S., Ishiguro, K., Yamakawa, O., Tsubata, M., Mori, S., and Takagaki, K. (2006). Nutritional value and physiological functions of sweet potato leaves. Acta Hort. 703: 107-115. Yoshimoto, M., Okuno, S., Kumagai, T., Yoshinaga, M., and Yamakawa, O. (1999a). Distribution of antimutagenic components in colored sweet potato. Jpn Agric. Res. Quarterly 33: 143-148. Yoshimoto, M., Okuno, S., Yoshinaga, M., Yamakawa, O., Yamaguchi, M. and Yamada, J. (1999b). Antimutagenicity of sweet potato (Ipomoea batatas) roots. Biosci. Biotechnol. Biochem. 63: 537-541. Yoshimoto, M., Okuno, S., Suwa, K., Sugawara, T. and Yamakawa, O. (2002a). Effect of harvest time on nutrient content of sweet potato leaves. Proc. 12th Symp. of the International Society for Tropical Root Crops, pp. 319-323. Yoshimoto, M., Okuno, S., Yamaguchi, M., and Yamakawa, O. (2001). Antimutagenicity of deacylated anthocyanins in purple-fleshed sweet potato. Biosci. Biotechnol. Biochem. 65: 1652-1655. Yoshimoto, M., Yahara, S., Okuno, S., Islam, M.S., Ishiguro, K. and Yamakawa, O. (2002b). Antimutagenicity of mono-, di-, and tricaffeoylquinic acid derivatives isolated from sweet potato (Ipomoea batatas L.) leaf. Biosci. Biotechnol. Biochem. 66: 2336-2441. Yoshimoto, M., Yamakawa, O., and Tanoue, H. (2005b). Potential chemopreventive properties and varietal difference of dietary fiber from sweet potato (Ipomoea batatas L.) roots. Jpn Agric. Res. Quarterly 39: 37-43. Yoshimoto, M., Yamakawa, O. and Tomita, Y. (2003). Sweet potato and carotenoid. Proc. 16th Annual Meeting on Carotenoid Research. 6: 2-4. Yoshimoto, M., Yamakawa, O. and Suda, I. (1998). Physiological function of purple colored flesh sweet potato. Food Processing and Ingredients 33: 15-17 [In Japanese].

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Yoshinaga, M., Yamakawa, O. and Yoshimoto, M. (1999). Genotypic diversity of anthocyanin content and composition in purple-fleshed sweet potato (Ipomoea batatas (L.) LAM). Breed Sci. 49: 43-4. Yu, B.P. (1994). Cellular defenses against damage from reactive oxygen species. Physiol. Rev. 76:139-162.

In: Sweet Potato: Post Harvest Aspects in Food Editors: R. C. Ray and K. I. Tomlins

ISBN 978-1-60876-343-6 © 2010 Nova Science Publishers, Inc.

Chapter 4

SWEET POTATO STARCH S. N. Moorthy and S. Shanavas Central Tuber Crops Research Institute, Sreekariyam, Thiruvanathapyram- 695 017, Kerala, India

ABSTRACT Sweet potato is an important food crop in the tropical countries and the roots are rich in starch. The starch has very desirable physicochemical and functional properties and therefore can have applications in food and industries. This chapter discusses the different characteristics of the starch in comparison with other root and tuber starches and the potential applications. The starch granule size ranges from 4-43 µm, with ‗A‘ type XRD pattern and an amylose content of around 20%. The swelling power and solubility are similar to other root starches. The viscosity and pasting temperature are almost in the same range as cassava. The enzyme digestibility, water binding capacity and rheological properties have also been described. The conditions for the liquefaction and saccharification of sweet potato starch for possible application in the production of ethyl alcohol are given in detail.

ABBREVIATIONS BU DP DSC HPAEC FTIR PV RVA SEM 

Branbender units; Degree of polymerization; Differential Scanning Colorimetry; High Performance Anion Exchange Chromatography; Fourier Transform Infra Red; Peak viscosity; Rapid Visco Analyzer; Scanning Electron Microscopy

Corresponding author: E-Mail: [email protected] Tel: 91-471-2598551; Fax: 91-471-2590063

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INTRODUCTION Starch is one of the major biochemical components in the plant kingdom, especially in the root and tuber crops. The starch content varies from 10-30% and the different starches have different functional properties. The application of the starch in food depends on the starch content and starch properties. Next to cassava, sweet potato has the highest starch content among the root crops and the extraction process is comparatively simple. In developing countries, sweet potatoes are processed into starch, noodles, candy, flour and desserts. In China for example, sweet potato starch production has become an important cottage industry. Moreover, China is the largest grower of sweet potatoes, providing about 80% of the worlds supply. There are more than 2000 varieties of sweet potatoes in China which can be roughly divided into ‗general type‘, ‗high starch type‘ and ‗food consumption type‘ (Liu, 2004). The major content of the dry matter in sweet potato is mainly starch which can be extracted from the roots. The uses of sweet potato starch are primarily determined by its physicochemical properties like starch granule shape and size, amylose content, molecular starch structure and pasting properties, retrogradation tendency, etc. A number of studies on the distinctive properties of sweet potato starch have been undertaken in different laboratories in the last decade. Crystalline structure, gelatinisation, pasting behaviour and retrogradation have been investigated (Takeda, 1986; Noda et al., 1992, 1996; Collado and Corke, 1997; Garcia and Walter, 1998; Katayama et al., 2002; Katayama et al., 2004). The objective of this chapter is to bring together the present knowledge on starch derived from this crop.

STARCH EXTRACTION The properties of sweet potato starch are very similar to cassava starch. However, though the extraction of starch from cassava is widely practiced, starch extraction from sweet potato is not so widely prevalent. The main reasons attributed are that the settling of starch is slow such that the longer residence time can lead to microbial growth and thereby lower the quality; this reduces the price of starch. For getting optimum yield and quality of starch, the correct time of maturity, methodology used for extraction and processing machinery are important. If roots are harvested late, the starch may get converted to sugar and fibre and thus affect yield and quality. Delays in processing sweet potatoes can result in the accumulation of sucrose and reducing sugars (Heinze and Appleman, 1943). Delays between shredding and starch extraction in sweet potato or the roots may lead to the synthesis of toxic compounds such as the alkaloid ipomeamarone, and the derived starch may become inedible and hazardous (Jain et al., 1951). The method of starch isolation (Figure 1) can affect both the physicochemical properties of the starch and the level of non-starch components, which in turn may also affect the physico-chemical properties of the starch indirectly (Lii and Chang, 1978; Takeda et al., 1986). The recovery of starch from sweet potato roots increased by more than 20% by using pectinase and cellulase enzymes. These enzymes act by breaking the pectin-cellulosic matrix of cell membranes resulting in the release of the starch granules. The treatment up to 0.05% concentration of enzyme gives higher yield without affecting its starch properties (Kallabinski and Balagopalan, 1991; Moorthy, 1999). Other methods used to

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improve yield of starch is use of lime (Radley, 1976a) and dilute acetic and lactic acid during extraction.

Figure 1. Course starch production by farming households (Liu, 2004).

BIOCHEMICAL CHARACTERISTICS Though the starch appears to be in the pure form free from other components, thorough investigation of extracted starch have revealed that it is invariably contaminated by various other components (Table 1), i.e., fibre, lipids, proteins and minerals depending on a number of factors such as method of extraction, age of the crop, environmental conditions, etc. Some of these impart desirable qualities to the starch, while others have a detrimental effect on quality. Table 1. Proximate composition of isolated starch Parameters (g/kg) Moisture

Range 139-150

Reference Lii and Chang, 1978

Ash

0.8-1 2.6-5.1 0.7-1.8 0.5-1 4.8-5.4 1.3-2 0.6-6 0.19 980-988

Delpeuch et al., 1978,1979 Lii and Chang, 1978 Delpeuch et al.1978,1979 Lii and Chang, 1978 Delpeuch et al. 1978,1979 Lii and Chang, 1978 Delpeuch et al. 1978,1979 Lii and Chang, 1978 Delpeuch et al., 1978,1979

Fibre Crude protein Crude lipid Phosphorus Starch

The starch content in the extracted starch is nearly more than 95% but this depends on maturity. The moisture content suggested for safe storage of starch is 13% (ISI, 1970; Radley, 1976a), but among tuber and root starches large variation have been found (Kay, 1987; Takeda et al., 1986; Soni et al., 1990; Melo et al., 1994). The root starches contain much

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smaller quantities of native lipids in them, hence the addition of lipids or surfactants was found to enhance the properties of starch quality and it was found that there is no hindrance for the root starches to complex with surfactants or lipids added externally. The phosphorous content in sweet potato is similar to that in cassava starch (Rickard et al., 1991) but both of these are less than that in Irish potato (Hizukuri, 1969). Phosphate is believed to be an important factor in determining the granular strength by forming cross linkages.

GRANULAR CHARACTERISTICS Size and Shape The granule size varies from less than 1µm to more than 100µm. Sweet potato starch granules have been reported as round, oval an polygonal shapes with size ranging between 3 and 28µm(Chen et al., 2003).The size and shape of starch granules from sweet potato are given in Table 2. Madamba et al. (1975) found significant differences among all sweet potato varieties studied (Figure 2). Sweet potato granules are of a similar size to those of cassava and maize but are smaller than those of potato which also have a larger range of granular size (Dreher and Berry, 1983). Starch grains are of variable shape (oval, round, faceted round and polygonal) and are normally non-aggregated. Granule size ranges from 4-43µ, depending on the cultivar. The mean size of the granule ranges between 12.3-21.5µ. The granule size is reported to affect some functional properties like swelling, solubility and digestibility. Bowkamp (1985) reported negative correlation between particle size and susceptibility to amylase and acid degradation for sweet potato cultivars. According to Rasper (1971), particle size including size distribution, is one of the characteristics that most markedly affects the functional properties of starch granules. Smaller granules are reported to have both high solubility and water absorption capacity (Georing and Dehaas, 1972). Earlier studies revealed that sweet potato starch is polygonal or nearly round in shape (Tian et al. 1991; Woolfe, 1992; Shin and Ahn, 1983; Bouwkamp, 1985) and has a centric distinct hilum. Polarisation crosses are comparatively less distinct. Table 2. Size, shape and X-ray diffraction pattern of sweet potato starches Sl.no 1 2 3 4 5

Size (μm) 14-34 3-42 4-40 10-14 4-43

6

9-38

Shape Round polygonal Round polygonal Polygonal oval round non-aggregated Non-aggregated, oval polygonal

X-ray pattern Ca Ca -

Reference Shin and Ahn, 1983 Seog et al., 1987 Delpeuch et al., 1978 Lii and Chang, 1978 Bouwkamp, 1985

-

Madamba et al., 1975

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Figure 2. Frequency curves of the granules sizes of starch of six sweet potato varieties grown in Philippines (Madamba et al., 1975).

Crystalline Structure The Crystalline nature of a starch granule can be defined by the position of the X-ray diffraction peaks (Zoebel, 1988). Table 2 and Figure 3 represent the X-ray pattern of some sweet potato starches. Hizukuri (1969) demonstrated that mixtures of A- and B- type starches produced intermediate pattern (C-type). Sweet potato starch has a variable X-ray pattern between C and A, in contrast to cereal starches such as wheat and corn which have A-type and potato which has B-type pattern (Zoebel, 1988). Sweet potato starch also has ‗A‘ (Takeda et al., 1986; Szylit et al., 1978; Gallant et al., 1982), ‗C‘ (Shin and Ahn, 1983; Zoebel, 1988; Chiang and Chen, 1988) or intermediate pattern (Tian et al., 1991). Takeda et al. (1986) observed ‗A‘ pattern for two varieties while it was ‗CA‘ for another variety with absolute crystallinity of 38%.

Molecular Weight Studies on sweet potato starch has revealed that amylopectin to have peaks at DP (degree of polymerisation) =12 and DP=8. The concentrations of the peaks at DP=6 and DP=7 were 7.1-7.5% and 6.7-7.0%, respectively. Takeda et al. (1986) reported trimodal pattern for the sweet potato amylopectin and Hizukuri (1969) a bimodal distribution. They concluded that sweet potato has a higher proportion of ‗A‘ chains and short ‗B‘ chains compared to potato.

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Figure 3. An X-ray diffraction pattern of sweet potato starch (Chiang et al., 1988).

Chain length has been found to vary in some varieties based on the low viscosity and high reducing values (Woolfe, 1992). Sweet potato amylose appears to have more branches per amylose molecule than that from cassava, potato, wheat or maize, and have a higher molecular weight than maize, wheat and cassava but less than potato. Takeda et al. (1986) suggested this was the reason for the low retrogradation tendency of sweet potato amylose. The degree of polymerization and branching has been reported to have a substantial effect on the physicochemical properties of amylose and amylopectin (Zobel, 1988).

PHYSICOCHEMICAL PROPERTIES Amylose Content Sweet potato can have amylose contents slightly higher than that of cassava but less than that of wheat, maize or potato (Rikard et al., 1991). The amylose content of sweet potato is considered to be one of the most important factors influencing the cooking and textural qualities of storage roots and sweet potato starch based products (Collado et al., 1999). Sweet potato starch amylose content has been reported between 8.5 and 35% (Table.3). Madamba et al. (1975) reported amylose contents of sweet potato starches to be from 29.4 to 32.2 % for the six cultivars. They found that six varieties of sweet potatoes from the Philippines had amylose content that were lower than that of other root crops including cassava. Uehara (1983) found an amylose content of 21.6 % in sweet potato starch. Watanabe et al. (1982) reported that the amylose content of sweet potato starch was 20.9 %. Garcia and Walter (1998) obtained values ranging from 20-25% (by potentiometric titration) for some Peruvian cultivars. Curing had only a minor effect on amylose content (Bertoniere et al., 1966) or a slight increase (Hammet and Barrentin, 1961). In general, sweet potato can have amylose content slightly higher than that of cassava but less than that of wheat, maize or potato

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(Rickard et al., 1991). Delpeuch et al. (1978) concluded that the amylose content in sweet potato was not affected by the manner of cultivation or the year of harvest. Table 3. Physicochemical properties of sweet potato starches Properties

Amylose content (%)

Water binding capacity (%) Swelling volume (ml/g)

Solubility (%)

Digestibility (%) Acid resistance to 16 % sulphuric acid at 50°C

Range 23.2-26.3 29.6-32.4 16.1-24.4 17.5-18.3 13.4-22.5 22 23.6-27.6 8.5-17.3 14.8 17.2-19 25-28 19.4-22.8 27-38 21.5-22 22-25 178.9-185.5 66.3-211.6 46 27.5-33.3 (95°C) 24.5-27.4(85°C) 63-95 (95°C) 32-46 (80°C) 18 13.2-14.4(95°C) 11.4-12.9(85°C) 60-79(95°C) 30-50(80°C) 14.9- 43.3 20.8 43.7% acid -resistant portion, 49.6 % low acid- resistant portion

Reference Hammett and Berrentin, 1961 Madamba et al., 1975 Madamba and San Pedro, 1976 Delpeuch et al., 1979 Shen and Sterling, 1981 Watanabe et al., 1982 Shin and Ahn, 1982 Liu and Liang, 1983 Liu et al., 1985 Takeda et al., 1986a Seog et al .1987 Chiang and Chen, 1988 Martin and Deshpande, 1985 Kitada et al. 1988 Shiotahi et al., 1991 Shin and Ahn, 1983 Seog et al., 1987 Woolfe,1992 Chiang and Chen, 1988 Seog et al., 1987 Seog et al., 1987 Seog et al., 1987 Woolfe, 1992 Chiang and Chen, 1988 Seog et al., 1987 Seog et al., 1987 Seog et al., 1987 Fuwa et al., 1977 Ueda and Jaha, 1983 Nara et al., 1983

Alkali Number The alkali number is a measure of the number of reducing end groups and is related to the molecular weight (Schoch, 1964 a). Seog et al. (1987) reported that the alkali number values of six Korean sweet potato starches ranged between 7.66 and 12.13.

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Swelling and Solubility Swelling power and solubility of starch is an important physicochemical property determining the use of starch in different applications. When starch is heated in the presence of water, the individual granules swell and a portion of the starch dissolves in the surrounding aqueous medium. The degree of swelling and the amount of solubilisation depend on the extent of chemical cross-bonding within the granules (Schoch, 1964b). The pattern of progressive swelling and solubilisation of various starches have been compared over a range of temperatures to provide information about the relative strengths of bonding within granules (Rasper, 1969). Swelling power and solubility indicates the strength of non-covalent bonding between starch molecules and depend on factors that include the amylose-amylopectin ratio, chain length and molecular weight distribution, degree of branching and conformation (Rickard et al., 1991). The swelling and solubility of starch permits comparison of relative bond strength at specific temperatures (Leach et al., 1959). The presence of non-carbohydrate substances in starch such as lipid or phosphate may affect swelling (Leach et al., 1959; Moorthy and Ramanujan, 1986). Swelling power of sweet potato starch varies considerably not only among varieties, but also at different temperatures. Delpeuch and Favier (1980) have reported a two stage swelling but Madamba et al. (1975) found a single stage swelling for the same starch (Figure 4). The lower swelling volume of sweet potato starch has been attributed to a higher degree of intermolecular association compared to cassava or potato starch.

Figure 4. Swelling and solubility patterns of sweet potato starches grown in Philippines (Madamba et al., 1975).

Solubility of starch is influenced by a number of factors that include the source, interassociative forces, swelling power and presence of other components like lipids, surfactants, salts, sugars, etc. The high swelling volume of the sweet potato starch is reflected in its

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solubility, which is similar to cassava starch. It was presumed that the bonding forces might be tenuous but comparatively extensive, immobilising the starch within the granules even at high levels of swelling. Reported solubilities of sweet potato starch ranged from approximately 10-18 % (Madamba et al., 1975). The relatively high swelling of sweet potato is not accompanied by high solubilities. This characteristic was also observed by Leach et al. (1959) in potato. As reviewed by Tian et al. (1991), sweet potato amylose appears to be more branched than that from cassava. Comparative experiments have shown that the swelling and solubility of sweet potato starch (Table 3) are less than those of potato and cassava, but generally more than those of maize (Rasper, 1969; Delpeuch and Favier, 1980). It has therefore been suggested that sweet potato starch has a higher degree of intermolecular association in its starch granules than has potato or cassava starch (Madamba et al., 1975).

Water Binding Capacity The water – binding capacity of starch gels has been commonly determined by the method of Medcalf and Gilles (1965). The values for sweet potato range from 66.3 to 211.6% as shown in Table 3. In general, root and tuberous starches have higher water –binding capacities than those of cereal origin (Banks and Greenwood, 1975), and the majority of workers have demonstrated that sweet potato starch has higher water –binding capacity than potato (93%) (Dreher and Berry, 1983) and cassava starches (72-92%) (Rickard et al., 1991).

DIGESTIBILITY Starch digestibility by enzymes is of importance for evaluating nutritive value and in industrial applications. For raw starches, digestibility of cassava, sweet potato, Colocasia, Xanthosoma and Amorphophallus starches is quite high (65-75%), comparable to corn starch (76%). Sweet potato starch was found to be very susceptible to degradation by -amylase and glycoamylase (Cerning-Beroard and Le Dividich, 1976). Digestibility of raw starch of eight sweet potato varieties by glycoamylases was compared by Noda et al. (1992). Gallant et al. (1982) found that ‗A‘ type starches showed high susceptibility to - amylase. They found that pelletisation increased the raw starch digestibility with bacterial - amylase from 17% to 45%. Scanning electron microscopy (SEM) studies indicated that enzymatic corrosion occurs mainly at the surface of the granules. The susceptibility of sweet potato starch to - amylase after 1-day incubation was found to range from 35.7-65.5 % weight loss among the six cultivars tested.

Degradation by Acid Dilute acids can be used to elucidate the architecture of the starch granule (Banks and Greenwood, 1975). There is an initial attack on the amorphous regions which enhances crystallinity and increases thermal stability (Biliaderis et al., 1981). The solubility on heating

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increases with acid degradation and the viscosity is lowered but granular integrity can be maintained even when 25% of the starch has been hydrolysed (Banks and Greenwood, 1975). The susceptibility of sweet potato starches to acid corrosion showed highly significant differences among cultivars (Rasper, 1969). Nara et al. (1983) investigated the kinetics of acid degradation and found that it could be described by two exponential hydrolysis rates, a fast hydrolysis of the amorphous regions and a slow hydrolysis of the crystalline regions (Table 3). Sweet potato and maize both had a large amount of acid-resistant starch, but the acid-resistant component of sweet potato starch was hydrolysed at a faster rate than that of other starches.

Degradation by Enzymes Enzymatic degradation can be evaluated by quantitative determination of the products from digestion or by measuring the decrease in hot paste viscosity (Rasper, 1969). SEM can also be used to examine the starch granules after attack (Hizukuri, 1969). Characteristics of αamylase action on sweet potato starch granules have been the subject of numerous investigations and reports (Noda et al., 1992). Theses studies have shown that starches vary in their resistance to the action of α-amylase. Starch susceptible to enzyme attack is influenced by several factors such as amylose and amylopectin content, crystalline structure, particle size and the presence of enzyme inhibitors. Among theses granular structure is believed to be most important. Both amylose and amylopectin are attacked by β-amylase in a step wise manner from the non reducing ends, until cleavage reaches, on average, apposition two residues from the branch points. β- amylase can be used to determine external chain lengths and to estimate the number of branch points (Hokama et al., 1980; Lii et al., 1987; Manners, 1989). Lii et al. (1987) reported a β-amylase limit for the amylase of sweet potato of 87.9%, substantially greater than the results of Takeda et al. (1969). In contrast, α-amylase is able to attack the polymers randomly at any α-1, 4-linkage that is sterically accessible. Varietal differences among sweet potato starches in susceptibility to attack by α-amylase have been reported to be highly significant (Madamba et al., 1975).

Retrogradation On cooling, dispersions of gelatinized starch granules in water acquire the consistency of gels. Above a critical concentration the swollen granules become entangled in amylose chains which have diffused out of the starch granules. The resultant composite is in essence an amylose gel with the swollen starch granules as a filter (Gidley, 1989). The above situation may be further complicated where the starch granules are ruptured by shearing or other methods of thermal or mechanical damage (Mestres et al., 1988). Further changes occur on storage, involving recrystallisation (or retrogradation) of the polymer chains. Retrogradation is affected by the amylose and amylopectin concentrations, the presence of other molecules such as sugars, salts and emulsifiers, molecular size, temperature, pH and other non-starch components (Del Rosario and Pontiveros, 1983).

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Takeda et al. (1986a) examined the retrogradation of sweet potato amylose which appeared to retrograde at the same rate as that of cassava but more slowly than that of Irish potato amylose. In contrast, Rasper (1969a) reported that sweet potato amylose retrograded slower rate than that of cassava and also that sweet potato amylopectin retrograded at a greater rate than that of cassava amylopectin. Del Rosario and Pontiveros (1983) found that sweet potato starch retrograded more slowly than wheat, corn and cassava starches and suggested that this was the reason for the observation that bread containing sweet potato flour as a substituent staled at a slower rate than other breads. Retrogradation is usually accompanied by gel hardening and by leakage of water from starch gel during storage. Retrogradation properties of tuber and root starches have been investigated by Differential Scanning Colorimetry (DSC), rheological measurements, FTIR (Fourier Transform Infra Red), Raman spectroscopy and X-ray diffraction. However, most of the information available are on potato and cassava starches (Hoover, 2001).

Sol Stability Sol stability or paste stability reflects the retrogradation tendency of starch pastes. Cassava and sweet potato starches have low retrogradation tendency and therefore exhibits high paste stability.

THERMAL CHARACTERISTICS DSC is an important tool to investigate starch gelatinisation (Biliaderis, 1983, 1990; John and Shastri, 1998; Eliasson, 1994). Most of these DSC studies have been carried out on cereal starches and to some extent on potato and cassava starches (Moorthy et al., 1996; Defloor et al., 1998; Farhat et al., 1999; Stevens and Elton, 1971; Wootton and Bamunuarachchi, 1979; Asaoka et al., 1992), whereas information on the DSC of the other root starches is comparatively limited. As starch grains are heated in aqueous suspension, they take up water. There are thought to be at least three main stages, hydration, swelling and melting of the crystallites (Blanshard, 1979). The gelatinization properties of starch are related to variety of factor including the size, proportion and kind of crystalline organization and ultra-structure of the starch granules (Singh et al., 2005) Gelatinisation temperature is indicative of the temperature at which the starch granules starch gelatinising. The gelatinisation temperature is controlled not only by the water content but also by the presence of salts, sugars and other small molecules. Average gelatinisation temperature for starch from six cultivars of sweet potatoes was found to range from 63.6-70.7 °C by Madamba et al. (1975). A significant positive correlation was found between average gelatinisation temperature and amylose content of the starches. A typical DSC pattern of sweet potato starch is given in Figure 5. Gelatinisation occurred over a range of 12-17°C of temperature change. Barham et al. (1946) found five cultivars had average gelatinisation temperatures from 69-75.5 °C and that the average gelatinisation temperature was reduced after curing the roots. Rasper (1969 b) reported that sweet potato starch began to gelatinise at 77 °C and continued the increase in viscosity until a temperature of 85°C was attained.

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Figure 5. DSC pattern of sweet potato starch (Moorthy, 2002).

Collado et al. (1999) obtained considerable variation in all the DSC parameters of 44 sweet potato varieties. The mean Tonset was 64.6°C and range 61.3-70° C, mean Tpeak 73.9°C (range 70.2-77°C) and mean Tend 84.6°C, range being 80.7-88.5°C and the mean gelatinisation range was 20.1° with a range of 16.1 to 23°C. Garcia and Walter (1998) found the range to be between 58-64°C for Tonset, 63-74°C for Tpeak and 78-83°C for Tend for the two varieties cultivated at different locations. While selection index did not affect the values, location influenced the parameters (Tian et al., 1991). Kitada et al. (1988) found that the gelatinisation temperatures were affected by the region in the sweet potatoes had been grown. Noda et al. (1998) reported that To, Tp, ∆H of 51 sweet potato starches differing in variety or cultivation condition ranged between 55.7-73.1°C, 61.3-77.6 °C and 12.7-16.8 J/g. Noda et al. (1995, 1998) reported that only small variations in chain length distributions (DP6-17) of amylopectin determined by HPAEC (High Performance Anion Exchange Chromatography) were observed in 31 varieties and 51 samples of sweet potato. Noda et al. (1996) did not find effect of fertilisation on the DSC characteristics of two sweet potato varieties. During the growth period, the Tonset was the lowest at the latest stage of development. Table 4 gives the thermal characteristics of some of the common sweet potato starches. They reported that increase in short outer chains of amylopectin reduced the packing efficiency of double helices within the crystalline region, resulting in lower gelatinisation temperature and enthalpy. Valetudie et al (1995) have compared the gelatinisation temperatures of starch from fresh roots and freeze dried roots of sweet potato (Table 5). A major factor controlling swelling is the strength of the internal structure of the granule being the size, amylose content, molecular weight, crystallinity and the internal granular organization (Banks and Greenwood, 1975; Takeda and Hizukuri, 1974; Madamba et al., 1975). Starch gelatinisation may be described either in structural terms as a loss of

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macromolecular organization and order or as a swelling process (which also has major rheological effects). Table 4. Thermal properties of sweet potato starch No 1 2 3 4 5

T onset (°C) 67-75 65.6-68.2 61.3 58-64 67.3

T peak(°C) 73-79 72.8- 74.3 70.2-77 63-74 72.7

T endset (°C) 81.4-84.8 84.6-86.8 80.7-88.5 78-83 79.6

∆H (J/g) 10-12.3 15.1-16.3 15.1-16.3 14.8-18.6 13.6

Reference Chiang and Chen, 1988 Kitada et al, 1988 Collado et al., 1999 Wankhede and Sajjan, 1981 Valetudie et al., 1995

Gelatinisation enthalpy depends on a number of factors like crystallinity, intermolecular bonding, etc. For sweet potato starch, the value for gelatinisation enthalpy lies between 10.018.6 J/ g (Tian et al., 1991; Garcia and Walter 1998; Collado et al., 1999). The effect of variety and environmental conditions was also evident (Garcia and Walter, 1998; Noda et al., 1996). During growth period, the H was lowest at the earliest stage of development in two sweet potato cultivars and the enthalpy ranged between 11.8-13.4 J/ g (Noda et al., 1992).

RHEOLOGICAL PROPERTIES The intrinsic viscosity is related to the ability of polymer molecules to increase the viscosity of the solvent, in the absence of any intermolecular interactions (Young, 1981). Intrinsic viscosity is directly related to molecular size and hence to the degree of polymerisation (Daniels, 1966). The intrinsic viscosity of starches from six cultivars was found to be 120-155ml/g. This indicated that sweet potato starches are not as highly polymerised as potato starch. Rasper (1969) found a maximum viscosity of sweet potato starch of 590 BU (Branbender units), slightly viscous than gelatinised cassava starch but more viscous than corn starch. The use of a lower concentration of starch would result in a general lowering of the paste viscosities and the softening of peak viscosities and breakdown because of reduced friction due to a lesser number of swollen granules (Figure 6) (Collado et al., 1999). Several studies found that sweet potato starch does not show a peak viscosity at 4-6 % (w/v) concentration (Tian et al., 1991). However Lii and Chang (1978) reported a moderate peak and a high set back on cooling with at a starch concentration of 7%. Varietal differences in viscosity have been reported as significant (Madamba et al., 1975; Liu et al., 1985). Sweet potato amylose has a limiting viscosity higher than that of wheat but lower than that of cassava or Irish potato amylose (Takeda et al., 1984, 1986). Similarly, sweet potato amylopectin has a lower limiting viscosity number than Irish potato amylopectin, suggesting smaller or more spherical molecules (Suzuki et al., 1985; Takeda et al., 1986). Since the peak viscosity value indicates how readily the starch granules are disintegrated, cohesive forces within the granules having higher values are stronger than those having lower values. The consistency of the paste after holding at 93°Cfor 15 min, i.e. breakdown viscosity provides an estimate of the resistance of the paste to disintegration in response to heating and stirring. Setback defined as the difference between the breakdown

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viscosity and the viscosity at 50 °C has been directly related to the amount of amylose leached from the granule (Greenwood, 1979).

Figure 6. RVA pasting curve of sweet potato starch at 7% and 11% starch concentration (Collado et al., 1999).

The rheological properties of sweet potato starch have been examined in detail. During heating, the storage modulus (G‘) and loss modulus (G‖) increased while phase angle decreased indicating change from sol to gel. The initial increase in G‘ and G‖ has been attributed to progressive swelling of starch granules leading to close packing. When the starch granules became very soft, deformable and compressible, decrease has been observed. The rheological properties of various root starches have been compared using the Bohlin rheometer and wide variability in the values of G‘ and G‘‘ was observed. During heating the G‘ and G‖ increased and the phase angle from sol to gel was occurring (Figure 7). Both moduli reached a maximum during heating after their values decreased (Garcia and Walter, 1998). Most of the reported values for G‘ and G‘‘ refer to starch pastes that have been held at room temperature for several hours after heating. G; for 6% corn and potato starch solutions at 60°C have been reported to be 132 Pa and 124 Pa, respectively (Evans and Haisman, 1979). However, all the different root starches exhibited uniformity in their elastic behaviour predominating over viscous nature. Sweet potato starch behaves in a similar way to cassava starch in all its viscosity characters. In a study of 44 different sweet potato genotypes using Rapid Visco Analyser (RVA), the correlations among the RVA parameters were reported (Collado et al., 1999). They observed wide variation not only in the PV (peak viscosity) but broadness of peak. The rheological properties of sweet potato starch extracted using an enzymatic process did not vary among the different concentrations of enzyme (Moorthy and Balagopalan, 1999).

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Figure 7. Storage modulus, Loss modulus and Phase angle for Peruvian sweet potato starch (Garcia et al., 1998).

S. N. Moorthy and S. Shanavas

106

Pasting Temperature The consistency of the paste, the properties of the gel and the latter‘s viscosity during the pasting cycle are important for many industrial applications because they influence important quality characteristics (Leelavathi et al., 1987). The Brabender amylograph provides a good method for defining these characteristics. The pasting temperature of sweet potato starch obtained using Brabender Viscograph varied between 66.0 and 86.3°C while microscopic determination gave values between 57-70°C to 70-90°C. Noda et al. (1996) observed the pasting temperatures of starch from two sweet potato cultivars grown at different fertiliser levels to be 70.8 –73.9 °C. Starch pasting properties influence sweet potato eating quality and noodle quality and also are directly responsible for starch industrial uses (Collado et al., 1999). The pasting temperature of sweet potato starch varies between 62-86°C (Tian et al., 1991, Kitahara et al. 1999, Collado and Corke, 1997). In the study conducted by (Katayama et al., 2002) also showed pasting temperatures similar to previous reports.

USE OF ENZYMATIC TECHNIQUES FOR STARCH SEPARATION As the recovery of sweet potato starch is very low and therefore expensive, the enzymatic modification has been employed. With the increased availability of commercial enzymes which break down cellulose and pectin, attempts have been made to use them to improve the extractability of starch. Kallabanski and Balagopalan (1991) studied the effect of cellulolytic and pectinolytic enzymes on the extraction of starch from sweet potato roots, the yield showed a substantial increase.

Properties of Enzymatically Separated Sweet Potato Starch The extract from sweet potato with different concentrations of enzyme (up to 0.2%) contained 90-93% of starch (Table 6) and this indicates that only a small quantity of fibrous material is being extracted. The absence of large amounts of fibre in the enzymatically separated starch from sweet potato indicates that the non-starchy polysaccharides are completely broken down and do not contaminate the starch. The reducing values of the starch from enzyme treatments were small (Table 6) and as expected since the enzymes are pectinolytic and cellulolytic and has not affected the starch granules. The viscosity data of starches from enzymatic and conventional extraction recorded using Brabender Viscograph is given in Table.7. The peak viscosity varied depending on the concentration of starch used. With 5 and 6 % pastes, the peak viscosity increased for the extracts obtained with increasing amounts of the enzymes, up to 0.025 or 0.05 % and with 0.25 (%) enzyme it dropped appreciably. With the 7% paste, there was a fairly steady drop in peak viscosity as the enzyme concentration increased. This is probably due to a weakening on the associate forces rather than to a breakdown of starch granules. The breakdown viscosity was also increased with the higher levels of the enzymes. The pasting temperature did not show any definite pattern, but generally there was a shift to lower temperatures with increasing concentrations of the enzyme.

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Table 5. DSC characteristics of the hydrothermic transition of purified starches and fresh and freeze dried* Sweet potato Starch Fresh tubers Freeze-dried tubers Small starch granules

T onset (°C) 67.3 67.4 67.8 75.6

T peak(°C) 72.7 73.5 73.2 82.6

T endset (°C) 79.6 80.1 81.5 88.3

∆H (J/g) 13.6 6.8 9.3 15.3

*S.N. Moorthy, unpublished results.

Table 6. Properties of enzymatically separated sweet potato starch* Starch conc (%)

5

6

7

Enzyme conc (%) 0.000 0.010 0.025 0.050 0.100 0.0200 0.000 0.010 0.025 0.050 0.100 0.0200 0.000 0.010 0.025 0.050 0.100 0.0200

*S.N. Moorthy, unpublished results.

Peak viscosity (BU) 260 280 300 280 280 220 440 460 500 500 460 400 780 760 740 760 680 600

Breakdown viscosity (BU) 0 0 40 40 100 40 20 40 40 100 120 60 0 60 100 160 200 120

Pasting temperature (°C) 87-95 86-95 85-95 84-95 82-89 82-90 88-95 87-94 86-95 84-92 82-92 82-88 8895 88-95 84-95 84-95 82-90 82-89

Table 7. Viscosity properties of enzymatically separated sweet potato starch (S.N. Moorthy, unpublished results) Enzyme conc (%) 0.000

Starch content (%) 90.33

Reducing value 1.37

Swelling volume (%) 19.50

Solubility (%)

0.010

91.00

1.35

17.50

19.5

0.025

92.05

1.50

20.50

20.2

0.050 0.100

90.92 91.25

1.85 2.25

17.85 17.75

22.3 37.5

0.200

90.85

1.95

18.25

39.5

22.5

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STUDIES ON THE LIQUEFACTION AND SACCHARIFICATION OF SWEET POTATO STARCH Liquefaction and Saccharification Liquefaction studies were repeated for sweet potato (variety: S10) using different concentrations of Termamyl 60 L and one concentration of starch, i.e., 20%. Sweet potato starch was prepared from mature, undamaged roots as in the case of cassava starch. Liquefaction was done at 90C at pH 6.5 and the time course production of reducing sugars was monitored up to 1h at 15 min intervals. The results presented in Table 8 indicate that as in the case of cassava, rapid hydrolysis of 1→ 4 linkages within 15–30 min itself occurred when higher concentration of enzyme was present in the system. After 1 h, around 26-28% starch conversion to dextrins and sugars was observed with 240-480 mg Termamyl. With 30 mg Termamyl, only 11% conversion was observed. As in the case of cassava starch, the low conversion of starch to reducing groups by 30 mg Termamyl did not influence the subsequent saccharification step by 0.05 ml Amyloglucosidase (Table 9). This reconfirmed the finding that a low amount of Termamyl at the liquefaction stage can economise the reaction by reducing the enzyme cost. Saccharification also appears to be almost completed by 48h and hence continuing up to 72h was not necessary, as this will only lead to increase in the operational expenses. Table 8. Enzyme hydrolysis of sweet potato (variety S10) starch using  - amylase – Effect of enzyme concentration on the rate of glucose production* amylase conc. (mg/100 ml slurry)

After 15 minutes Amt. of Percent reducing conversugar sion to formed reducing (g) sugar

After 30 minutes Amt. of Percent reducing conversugar sion to formed reducing (g) sugar

After 45 minutes Amt. of Percent reducing conversugar sion to formed reducing (g) sugar

After 60 minutes Amt. of Percent reducing conversugar sion to formed reducing (g) sugar

30 60 120 480

1.57 2.24 2.52 3.86

1.66 2.61 3.08 4.15

1.98 2.75 3.28 4.69

2.09 3.07 3.67 5.15

8.84 12.57 14.16 21.69

9.34 14.67 17.33 23.36

11.15 15.44 18.42 26.38

11.79 17.25 20.65 28.98

*S.N. Moorthy, unpublished results.

Viscosity Profile of the Liquefaction Reaction The viscosity changes during the liquefaction of sweet potato starch were monitored using the RVA using similar systems as in the case of cassava starch. Tremendous reduction in viscosity was observed when 30 -90 mg Termamyl 60L was added to the 1:10 starch slurry (Table 10). Sweet potato starch required a higher enzyme concentration of 30 mg to reach this stage in RVA. This indicates the possible differences in the initial susceptibility to α-amylase attack of the starches i.e., cassava and sweet potato starch.

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Post-harvest treatments such as the method of starch isolation, as well as genetic factors, may have a profound effect on the properties of sweet potato starch. The environmental conditions during growth of a plant, especially the temperature, constitute one of the important factors affecting the physicochemical characteristics of starch granules, besides genetic and endogenous factors (Hizukuri, 1969). Table 9. Percentage conversion of starch after saccharification by AMG on sweet potato starch slurry (liquefied using two concentrations of Termamyl* Liquefaction

Saccharification

Starch conc. (g)

 - amylase (mg/100ml slurry)

Percent conversion (after 1 h)

AMG conc. (ml/100ml slurry)

Percentage conversion After 24 h

48 h

72 h

20

30

11.79

0.05

85.08

82.73

86.83

20

240

26.43

0.05

80.40

84.69

82.33

*S.N. Moorthy, unpublished results.

Table 10. Viscosity reduction of sweet potato (variety-S10) starch by adding  - amylase as measured using Rapid Visco Analyser* Sl. No.

-amylase conc. (mg)

Peak 1 (cP)

Trough 1 (cP)

Breakdown (cP)

1. 2. 3. 4. 5. 6. 7. 8. 9.

Control 1.2 2.4 3.75 7.5 15 30 60 90

4020.00 1081.00 757.00 496.00 122.00 63.00 17.00 10.00 5.00

2254.00 16.00 10.00 13.00 2.00 -1.00 -1.00 -3.00 -2.00

1766.00 1065.00 747.00 483.00 120.00 64.00 18.00 13.00 7.00

Final Viscosity (cP) 3056.00 23.00 14.00 13.00 5.00 9.00 -1.00 0.00 -2.00

Set back (cP) 802.00 7.00 4.00 0.00 3.00 10.00 0.00 3.00 0.00

Peak time (Sec) 4.07 3.47 3.47 3.40 3.40 3.33 3.33 3.73 3.80

Pasting (C) 77.40 75.80 75.80 75.80 76.75 76.00 Error Error Error

*S.N. Moorthy, unpublished results.

Starch content and dry matter content are the main properties of raw material for starch production. A new sweet potato breeding line, Kanto 116 was developed, featuring low gelatinisation temperature and an altered starch fine structure and having pasting temperature of 20 V (viscosity) lower than those of ordinary cultivars (Katayama et al., 2002). Starch granule from Kanto 116 showed an abnormal morphology characterized by cracking into granules. A number of studies on the distinctive properties of sweet potato starch have been undertaken in the last two decades (Tian et al., 1991; Moorthy, 2002). Kitahara et al. (1996, 1999) reported a new line with low amylose content and two lines having approximately 10°C lower pasting temperatures than ordinary cultivars. Some new sweet potato lines were developed from progenies of a new cultivar, Quick Sweet, having a low pasting temperature (Katayama et al., 2004). The results indicated that this ‗Quick Sweet‘ is a useful breeding material for improving pasting and retrogradation properties in sweet potato starch. The

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potential chemopreventive properties of dietary fiber prepared from sweet potato roots were examined to promote the demand of this residue from the starch industry (Yoshimoto et al., 2005; Yoshimoto, chapter 3 in this Volume). Sweet potato starch has some unique characteristics and is mostly used by the food industry as an ingredient in products such as cakes, breads, biscuits, cookies and noodles (Zang and Oates, 1999). Noodles, bread, boiled rice and pasta have played an important role in the human diet, especially in the Asian countries (Japan, China, Taiwan, Korea, Vietnam and Thailand). Based on the raw materials, various types of noodles are produced throughout the world. In terms of food products, four quality attributes are important being nutritional, phytosanitary, shelf-life and organoleptic. These qualities depend on flour and starch quality. Thus starch properties largely influence noodle quality. Starch with high amylose content and with C-type pasting profile characterized by the absence of a peak viscosity and a constant or increased viscosity during continuous heating and shearing, i.e., good hot paste stability is reported to be suitable for noodle processing (Collado and Corke, 1999).They reported that the textural attributes of sweet potato noodles show high positive correlation with some starch paste properties. It is also reported that the smaller particle size of the granule improves the strength of uncooked noodles without affecting the firmness of cooked noodle (Oh et al., 1985).

CONCLUSION Sweet potato is therefore one of the worlds most important starch producing crops, with 95 % of all roots produced in Asia and Africa. Sweet potato is used as direct food, processed foods, industrial starch and animal feed. The utility of sweet potato is primarily determined by its physicochemical properties, being the amylose/amylopectin ratio, the molecular structure, granule size and inorganic constituents. Pasting properties influence the quality of food processing materials and industrial products. Being a nontraditional source of starch, the characterization of genetic variation and interrelationships of sweet potato starch physical properties that can guide utilisation is therefore essential. An awareness of their potential uses can help in large scale cultivation of these crops and extraction of starch from them. It is also possible to modify the starch properties by simple physical methods such as hydro- thermal or steam-pressure treatments. The latest developments in biotechnology are also being evaluated for their potential to modify the starches. These include fermentation of starch by the use of selective organism or enzymatic modification, which can bring about specific substitutions (Sair, 1967; Raja, 1990; Moorthy, 1999). Current research is seeking to produce a new cultivar and breeding materials with distinctive amylose content and pasting properties. The role of dietary fibre in human nutrition has attracted growing interest in recent years. Most of the research programmes carried out on sweet potato are attempting to reduce the content of crude fibre for improved eating quality. Furthermore, the production of ethanol from biomasses is a growing industry in this continuously developing society. The sweet potato having high starch yield and low gelatinisation temperature may be effective in reducing these production costs. The various improvements in starch properties are useful for providing consumers with starch products and spreading the demand for sweet potato starch.

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Moorthy, S.N. (1999). Effect of steam pressure treatment on the physicochemical properties of Dioscorea starches. J. Agric. Food Chem. 47 : 1695-1699. Moorthy, S.N. and Ramanujam, T. (1986). Variation in properties of starch in cassava varieties in relation to age of the crop. Starch / Stärke 38: 58-61. Moorthy, S.N., Wenham, J.E. and Blanshard, J.M.V. (1996). Effect of solvent extraction on the gelatinisation properties of starch and flour of five cassava varieties. J. Sci. Food Agric. 72: 329-336. Moorthy, S.N.,and Balagopalan, C (1999) .Physicochemical properties of enzymatically separated starch from sweet potato. Trop. Sci. 39: 23-27. Moorthy. S.N. (2002). Physicochemical and functional properties of tropical tuber starches: A Review. Starch/Stärke 54 : 559-592. Nara, S., Sakakwa, M. and Komiya, T. (1983). The acid resistance of starch granules. Starch/Starke 35 (8) 266-270. Noda, T., Takahata, Y., and Nagata, T. (1992). Developmental changes in properties of sweet potato starch. Starch / Stärke 44: 405-409. Noda, T., Takahata, Y. and Nagata, T. (1992). Properties of sweet potato starches from different tissue zones. Starch/ Starke 44: 365-368. Noda, T., Takahata, T., Sato, T. (1995), Distribution of the amylopectin chain length of sweet potato differing in stages of development. tissue zone and variety. J Jpn Soc. Food Sci. Technol. 42: 200-206. Noda, T., Takahata, Y., Sato, T., Ikoma, H., and Mochida, H. (1996). Physicochemical properties of starch from purple and orange fleshed sweet potato roots at two levels of fertilizer. Starch / Stärke 48: 395-399. Noda,T., Takahata, Y. T., Suda, I., Morishita, T., Ishiguro, K., et al. (1998) Relationship between chain length distribution of amylopectin and gelatinization properties within the same botanical origin for sweet potato and buckwheat. Carbohydr. Polym. 37: 153-158. Oh, N.H, Seib, A. P.A., Ward,.A.B. and Deyoe, C.W. (1985). Noodles. IV. Influence of flour protein, extraction rate, particle size and starch damage on the quality characteristics of dry noodles. Cereal Chem. 62: 441-447. Radley, J.A. (1976 b). Examination and analysis of starch and its derivatives. Applied Science Publishers Ltd, London. Radley, J.A. (1976a) .Starch production technology. Applied Science Publishers Ltd, London) pp.189-229. Raja, K.C.M. (1990). Studies on physicochemical and textural qualities of cassava (Manihot esculanta Crantz), PhD Thesis, University of Mysore, India. Rasper, V. (1969). Investigations on starches from major starch crops grown in Ghana. II.Swelling and solubility patterns and amyloelastic susceptibility. J.Sci.Food. Agric. 20: 642-646. Rasper,V. (1971). Investigations on starches from major starch crops grown in Ghana.III. Particle size and size distribution. J. Sci. Food. Agric. 20: 572-580. Rickard, J.E., Asaoka, M. and Blanshard, J.M.V. (1991). The physicochemical properties of cassava starch‘ Trop. Sci. 31: 189-207. Schoch, T.J. (1964 ). Swelling power and solubility of granular starches, In: R.L. Whistler (Ed.), Methods in Carbohydrate Chemistry, Vol IV, Academic Press, New York, pp. 106-109. Seog, H.M., Park, Y.K., Nam, Y.J.. Shin, D.H. and Kim, J. P. (1987). Physicochemical properties of several sweet potato starches, Han’guk Nanghwa Hakhoechi 30 (2): 179-185.

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Shen,M.C. and Sterling, C. (1981). Changes in starch and other carbohydrates in baking Ipomoea batatas. Starch/Starke 33 (8): 261-268. Shin, M. and Ahn, S.Y. (1983). Physicochemical properties of several sweet potato starches, J. Korean Agric. Chem. Soc. 26 : 137-142. Singh, S., Raina, C.S, Bawa, A.S. and.Saxena, D. C. (2005). Effect of heat moisture treatment and acid modification on rheological, textural and differential scanning calorimetry characteristics of sweet potato starch. J. Food Sci. Physical Properties.70: 373-378. Soni, P.L., Sharma, H., Srivatsava, H.C.,and Gharia, M.M. (1990). Physicochemical properties of Canna edulis starch- comparison with maize starch. Starch/Stärke 42:460464. Stevens, D.J. and Elton, G.A.H. (1971). Thermal properties of Starch/Water systems, Starch/Starke 23: 8-11. Susuki, A., Takeda, Y. and Hizukuri, S. (1985). Relationship between the molecular structures and retrogradation of tapioca, potato and kuzu starches. J. Jap. Soc. Starch Sci. 32: 205-212. Szylit, O., Durand, M.,.Borgida, L.P, Atinkpahoun, H., Prieto, F. and Devort-Lavel, J. (1978). Raw and steam-pelleted cassava, sweet potato and yam cayensis as starch sources for ruminant and chicken diets. Anim. Feed Sci. Technol. 3: 73-87. Takeda, C. and Hizukuri, S. (1974). Characterization of the heat dependent pasting behavior of starches Nippon Nogeikagku Kaishi Vol. No. 663-669 Takeda, Y., Tokunaga, N., Takeda, C., and Hizukuri, S. (1986). Physicochemical properties of sweet potato starches. Starch/Stärke 38: 345-350. Tian, S.J., Rickard, J.E., and Blanshard, J.M.V. (1991). Physicochemical properties of sweet potato starch, J. Sci. Food Agric. 57: 459-491. Ueda, S. and Saha, B.C. (1983). Behaviour of Endomycopsis. Enz. Microbial. Technol. 5:196-198 Uehara. S. (1984).Amylose-amylopectin ratio of soluble and insoluble fraction of sweet potato granules treated with urea. J. Agric. Chem.Soc Japan 57(6): 529-533. Valetudie, J.C., Colonna, P., Bouchet, B. and Gallant, D.J. (1995). Gelatinisation of sweet potato, tannia and yam starches. Starch/Stärke 47: 298-306. Wankhede, D.B. and Sajjan, S. (1981). Isolation and physicochemical properties of starch extracted from yam, elephant (Amorphophallus compalunatus). Starch/ Stärke 33: 153157. Watanabe, T., Akiyama,Y., Takahashi, H., Adachi, T., Matsumoto, A. and Matsuda, K. (1982). Structural features and properties of Nageli amylodextrins. Carbohydr. Res. 109: 221-232. Woolfe, J.A. (1992). Sweet Potato: an Untapped Food Resource. Cambridge University Press, Cambridge, pp. 643. Wootton, M. and Bamunuarachchi, A. (1979). Application of differential scanning calorimetry to starch gelatinization. I. Commercial native and modified starches. Starch/Starke 31: 201-204. Yamakawa, O. (1996). A new line of sweet potato with a low amylose content. J. Appl. Glycosci.43: 551-554. Yoshimoto, M., Yamakawa, O. and Tanoue, .H. (2005). Potential chemo preventive properties and varietal difference of dietary fibre from sweet potato (Ipomoea batatas L.) root. JARQ 39 (1):37-43.

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Young, R.J. (1981). Introduction to Polymers. Chapman and Hall, New York. Zoebel, H. F. (1988). Molecules to granules- A comprehensive starch review, Starch/Stärke 40: 44-50. Zang.T. and Oates C.G. (1999). Relationship between α-amylase degradation and physicochemical properties of sweet potato starches. Food Chem. 65. 157-163.

In: Sweet Potato: Post Harvest Aspects in Food Editors: R. C. Ray and K. I. Tomlins

ISBN 978-1-60876-343-6 © 2010 Nova Science Publishers, Inc.

Chapter 5

SWEET POTATO PUREES AND DEHYDRATED POWDERS FOR FUNCTIONAL FOOD INGREDIENTS 1



Van-Den Truong1 and Ramesh Y. Avula2

USDA-ARS Food Science Research Unit, Department of Food, Bioprocessing and Nutrition Sciences, North Carolina State University, Raleigh, NC 27695-7624, USA 2 Department of Food Science and Technology, University of Georgia, Athens, GA 30602, USA

ABSTRACT Processing technologies have been developed in various parts of the world to convert sweet potatoes into purees and dehydrated forms that can be used as functional ingredients in numerous food products. This chapter reviews the processing operations involved in these technologies and their effects on quality, storability, nutritional values and rheological properties of sweet potato purees and powders/flours. For purees, the processing steps include peeling, cutting/grinding, and pre-cooking/finish-cooking with temperature-time program suitable for starch conversion by endogenous amylolytic enzymes to obtain the products with targeted maltose levels and viscosities. The purees can be subsequently preserved by refrigerated and frozen storage, canning, or aseptic packaging. However, poor product quality due to excessive thermal treatments in canning, high cost of investment associated with frozen products and limited package sizes of these preserved forms are the main hurdles for widespread applications of sweet potato purees in the food industry. These problems can be overcome by a new process using a continuous flow microwave system for rapid sterilization and aseptic packaging to produce shelf-stable purees with consistently high quality. Sweet potato purees can be further processed into drum- or spray-dried powders. In many countries, solar drying and 

Paper no. FSR08- … of the Journal Series of the Department of Food, Bioprocessing and Nutrition Sciences, NC State University, Raleigh, NC 27695-7624. Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the U. S. Department of Agriculture or North Carolina Agricultural Research Service, nor does it imply approval to the exclusion of other products that may be suitable.  Corresponding author: Van- den Truong at (919) 513-7781; fax (919) 513-0180; E-mail: [email protected]

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mechanical drying in cabinets and tunnels are common in producing sweet potato dried chips which are pulverized into flours. Extrusion technology and chemical treatments are also applied to produce sweet potato powders for specific functionality. With high levels of carbohydrates, ß-carotene (orange-fleshed varieties) and anthocyanins (purple-fleshed varieties), sweet potato purees and dehydrated forms can be used as functional ingredients to impart desired textural properties and phytonutrient content in processed food products.

ABBREVIATIONS CPV DPPH DS DSC DRI GI HPV NASA ORAC PER SAPP PV RTE

cold paste viscosity; 2, 2-diphenyl-1-picrylhydrazyl; degree of substitution; Differential Scanning Colorimeter; dietary reference intake; glycemic index; hot paste viscosity; National Aeronautics and Space Administration; oxygen radical absorbance capacity; protein efficiency ratio; sodium acid pyrophosphate; peak viscosity; ready- to- eat.

INTRODUCTION Sweet potato ranks the seventh most important food crop in the world and fourth in tropical countries (FAOSTAT, 2004). In comparison to other major staple food crops, sweet potato has the following positive attributes: wide production geography, adaptability to marginal condition, short production cycle, high nutritional value and sensory versatility in terms of flesh colors, taste and texture. Depending on the flesh color, sweet potatoes are rich in ß -carotene, anthocyanins, total phenolics, dietary fiber, ascorbic acid, folic acid and minerals (Woolfe, 1992; Bovell-Benjamin, 2007; ILSI, 2008). Therefore, sweet potato has an exciting potential for contributing to the human diets around the world. However, the world trends in sweet potato production and consumption do not support the position of this highly nutritious vegetable. In the United States, the annual per capita consumption of sweet potato was declined in the last decades from 12 kg to 2 kg while the potato consumption was increased to over 60 kg (USDA, 2002). The situation can be attributable to the inadequacy in sweet potato manufacturing technologies for processed products, and the increased demand of consumers for convenient products. Research efforts have demonstrated that sweet potatoes can be made into liquid and semi-solid food products such as beverages, soups, baby foods, ice cream, baked products, restructured fries, breakfast cereals, and various snack and dessert items (Collins and Walter, 1992; Dansby and Bovell-Benjamin, 2003a; Truong, 1992; Truong et al., 1995; Walter et al., 2001, Woolfe, 1992). Puree and dehydrated forms processed from

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sweet potatoes are the main ingredients that provide the functionality required in these processed products. For the food processing industry, the unavailability of puree and dehydrated forms for diverse functionalities is a limiting factor in the utilization of sweet potatoes in processed foods. Several excellent reviews dealing with processing and quality aspects of sweet potato purees, flakes and powders have been published over the past 20 years (Collins and Walter, 1992; Kays, 1985; van Hal, 2000; Woolfe, 1992). This chapter updates these reviews with recent developments in processing technologies to convert sweet potatoes into purees and powders that can be readily used by the food industry as functional ingredients in processed foods.

SWEET POTATO PUREES AS FUNCTIONAL INGREDIENTS The use of sweet potatoes in the food industry often involves processing of the roots into purees that can be subsequently frozen, canned or packaged in aseptic conditions to produce shelf-stable products for year-round availability of the produce. For pureeing, roots of all sizes and shapes can be processed to make acceptable puree and therefore, the entire harvested crop is utilized including the 30-40% off-grade from the fresh root markets. Purees from the orange-fleshed sweet potatoes have been commercially produced in cans or in frozen form in the U. S (Kays, 1985; Walter and Schwartz, 1993). In Japan, both white- or orangefleshed cultivars are utilized for processing into paste for incorporation into bread and ice cream (Woolfe, 1992). The challenges in puree processing industry are: (1) the difficulty in adjusting the process to account for differences in cultivar types; root handling, curing, and storage; and other parameters in order to produce consistent, and high puree quality, and (2) the preservation technology that could produce shelf-stable product for convenient incorporation in processed foods. A wide range of dry matter (18 – 45%) and starch content (8 – 33.5%, fresh weight basis) exists among sweet potato genotypes (Brabet et al., 1998; Yencho et al., 2008) which have significant impact on processing operations and quality of the purees. Post-harvest handling of sweet potatoes can have significant effect on the purees made from them. Metabolic changes may affect the appearance, texture, flavor and nutrient composition of the purees. Curing by subjecting sweet potatoes to 30C, 85% to 90% relative humidity for 4-7 days as commercially practiced in the U. S. can result in an increase in sugars, and a decrease in starch and alcohol-insoluble solids (Boyette et al., 1997). Several investigators reported that changes in carbohydrate components and enzyme activities (α-amylase, β-amylase, invertases and sucrose synthase) during curing and storage of sweet potatoes are genotype dependent (Huang et al., 1999; Picha, 1986; Takahata et al., 1995; Walter, 1987). In general, amylase activities in sweet potato roots are increased by curing and storage especially during the first few months, then remain fairly constant or decrease to the levels at harvest (Shen and Sterling, 1981; Walter et al., 1976; Zhang et al., 2002). On the other hand, there are genotypes, e.g. Kyukei 123, with relatively constant levels of starch, sucrose and amylase activity throughout storage (Takahata et al., 1995). The activities of α-amylase and β-amylase in raw sweet potatoes affect the processing operations and quality of the purees. When the sweet potatoes are heated to starch gelatinization temperature (60 to 78C), αamylase rapidly degrades the starch to lower molecular weight dextrins which are

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concurrently hydrolyzed into maltose by β-amylase. The degree of starch degradation and maltose formation is dependent on the activities of amylases and heating program in the process of pureeing. Therefore, for a given sweet potato variety, it is expected that cured and stored roots with increasing amylase activities will produce purees which are sweeter and less starchy than those of the just-harvested (green) roots. However, there is a genotype difference in the amounts of maltose produced in the cooked sweet potatoes. Takahata et al. (1994) classified sweet potato varieties into high, moderate and low maltose formation after steaming. The genotypes with high maltose formation in cooked roots tended to have early gelatinization of starch granules (< 70C) and ß -amylase with high heat stability up to 78 82ºC. A new sweet potato breeding line, Kanto 116, was developed in Japan; this genotype has starch with pasting temperature of 51.4 – 52.6ºC, approximately 20ºC lower than those in the common sweet potato cultivars (Katayama et al., 2002).

Processing of Sweet Potato Purees Over the years, techniques have been developed for puree processing in order to produce purees with consistent quality, as mentioned above, despite the variations due to cultivar differences and post-harvest practices. Several methods for sweet potato puree processing were developed since 1960‘s, and the subject was reviewed by Collins and Walter (1992), Kays (1985) and Woolfe (1992). Process operations for pureeing of sweet potatoes (Figure 1) involve washing, peeling, hand-trimming, cutting, steamed blanching or cooking, and grinding into purees which can be subjected to canning or freezing for preservation. Washing: Sweet potatoes are stored without removing the dirt for prolonging storability. In the United States, prior to delivery to the fresh root markets, stored sweet potatoes are passed through the packing line for washing, treating with fungicide and sizing. The roots are generally unloaded from the pallet bins into a tank of water, conveyed to high-pressure spray washers wherein water at 250 psi is directly sprayed at the surface of sweet potatoes as they tumble over rotating brushes. The washed roots are then sorted by size using pitch roller sizers or electronic sensors (Boyette et al., 1997). The size number 1 roots are selected and packed in carton boxes for table stock markets. The misshapen, undersized or jumbo-sized roots, about 30% of the crop, are considered as the rejects and offered to the processing companies. In places where the whole harvest is delivered to the processing factories, sweet potatoes can be washed with revolving drum washer. Truong et al. (1990) described a lowcost washer made of an empty drum with rotating frame holding brushes and having a capacity of 300 kg roots/hr. Peeling and Rewashing: Prior to peeling, the cleaned roots can be preheated in hot water for a short time to provide some benefits including reduction of peeling time and enzymatic discoloration by polyphenolic oxidase (Bouwkamp, 1985). However, several investigators reported that preheating treatment of the unpeeled roots is not necessary (Edmond and Ammerman, 1971). Sweet potato peel can be removed by abrasive rollers, lye solutions, a combination of lye and steam peeling or high pressure steam. In lye peeling, cleaned roots are conveyed into 10-22% lye solution at 104ºC for 3 to 6 min and then transferred to a rotary washer with high-pressure water spray to remove the lye residue, loosened peel and adhere softened tissue. Peeling losses range from 20-40% of the raw material depending on the lye concentration, residence time and root sizes (Scott et al., 1970). Due to the issues on

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equipment corrosion and waste disposal, lye peeling is no longer a common method in the industry. Abrasive peelers with capacity of few hundreds to over a thousand kg roots/hr can be used in peeling sweet potatoes (Kays, 1985; Taylor, 1982; van Hal, 2000). High-pressure steam peeling developed by Harris and Smith (1985, 1986) is being used by many sweet potato processing companies. The technology is referred as a thermal blast process in which the roots are enclosed for a short time (20 to 90 sec) in a chamber pressurized with heated steam, followed by an instantaneous release of pressure. As the pressure suddenly release, the super-heated liquid water beneath the skin surface immediately flashed into vapor, and blasted the peel off the roots. This process can be automated, result in less peeling loss than lye peeling, and produce a product with less enzymatic discoloration (Smith et al., 1980). Studies on the effect of lye peeling on amylase activities, starch hydrolysis, phenolic degradation and carotene loss on the surface of sweet potato roots were conducted by Walter and Schadel (1982), Walter and Giesbrecht (1982). Hagenimana et al. (1992) has shown that α-amylase is strongly localized in the periderm, the vascular cambium and the anomalous cambium of sweet potato roots while β-amylase is abundant and well distributed throughout the root. During lye peeling, heat and alkali gelatinize starch in the root outer layers where thermostable α-amylase results in starch conversion into maltose and dextrins. However, there is limited understanding in these aspects of the steam flash peeling on the surface of sweet potato roots. Trimming and Cutting: Peeled sweet potatoes are next conveyed along a trimming and inspecting line for trimming the surface blemishes and fibrous ends and removing the diseased roots. The materials are then fed to size reduction machine for cutting into slices, strips and cubes or grinding into fine particles using a hammer mill or pulp finisher. Cutting and grinding machines with capacity up to over 1000 kg/hr are being used for this operation. Pureeing Processes: The techniques that have been developed for processing sweet potato into purees are illustrated in Figure 1. The purees can be simply produced by steam cooking of the peeled roots, chunks, slices, strips, cubes or ground particles, and passing the cooked materials through a pulp finisher. However, the aforementioned challenges became an issue in getting the product with consistent quality. Addition of α- and β-amylases can be applied to obtain the desired amount of starch conversion (Hoover, 1966; Szyperski et al., 1986). This method, however, introduces food additives to the process that are usually disliked by consumers. Another approach employs the enzyme activation technique using the endogenous amylolytic enzymes for starch hydrolysis (Hoover and Harmon, 1967), and this process is now commonly used in the food industry. As shown in Figure 1, the peeled sweet potatoes can be either cut into cubes of 2 cm, strips of 2 x 2 x 6 cm and slices of 0.5 - 0.95 cm thick (Walter and Schwartz, 1993; Truong et al., 1994) or mashed using a hammer mill with rotating blades to chop and push the materials through a 1.5 – 2.3 mm mesh screen (Szyperski et al., 1986). Next, the materials are steamed blanched at 65 to 75°C which activates the amylases and gelatinizes the starch for hydrolysis. For the process with slices, strips and cubes, comminuting the blanched materials into puree is carried out at this point using the hammer mill. The blanched puree is pumped into a surge tank and hold at 65 - 75°C for further starch hydrolysis depending on the targeted maltose levels. Raw sweet potato mash as a source of amylases can be optionally added at this stage to increase starch conversion. Alpha- and ß- amylases hydrolyze the starch producing maltose, maltotriose, glucose and dextrins.

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Figure 1. Different processes for sweet potato puree production.

The majority of maltose production is likely completed in the first few minutes of the starch conversion process. Hoover and Harmon (1967) found maltose is the only sugar produced and the majority of maltose was produced in the first 10 minutes of cooking at temperatures of 70 to 80°C. McArdle and Bouwkamp (1986) also reported that rapid heating of raw sweet potato slurries to 80ºC may be optimal for starch conversion. However, further decreases in the molecular size of starch and dextrins occur for up to 60 minutes resulting in the purees with high maltose content and low apparent viscosity (Walter et al., 1976; 1999). In order to control the process to produce a consistent product, the length of conversion time can be adjusted from a few minutes to 1 hour depending on the starch content and amylase activity in the raw materials. After starch conversion, the temperature is raised to 100 - 110°C in a heat exchanger to inactivate the enzymes, and a final grinding step will be carried out with the use of a pulp finisher to obtain the smooth puree. The temperature and time program in the described pre-cook/finish cook process has significant effects on the puree quality. A very fast heating procedure tended to result in puree with low levels of maltose and high viscosity, and a temperature and time program that allows sufficient amylase-hydrolysis on gelatinized starch would produce sweet and more flowable purees (Walter and Schwartz, 1993; Ridley et al., 2005). The developed technologies for puree processing were based mainly on the orangefleshed sweet potato cultivars with high ß-carotene, low dry matter (18-21%) and low starch content [8-10% on fresh weight basis (fwb)] (Walter and Schwartz, 1993; Yencho et al., 2008). This sweet potato type has moist texture after cooking, produces purees that are viscous, but flowable, and can be handled in various processing operations (Truong et al., 1995; Coronel et al., 2005). On the other hand, sweet potatoes with white, yellow and purple

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flesh colors have higher levels of dry matter (25-38%) with potentially different starch properties (Walter et al., 2000), which may present challenges for the commercial production of flowable purees from these materials. Therefore, the processing hurdle in pureeing these sweet potato types could be overcome by either addition of water to decrease the solid levels of the material to 18-21%, amylase hydrolysis of starch components, or a combination of the two treatments. For cost-effective reasons, water addition can be adapted as a simple approach in processing of purple-fleshed sweet potato purees that have flowability similar to the purees from the orange-fleshed sweet potatoes (Steed and Truong, 2008).

Packaging and Preservation of Sweet Potato Purees Canning and Freezing: The finish-cooked puree can be packaged in cans and retorted to produce shelf-stable product. The puree can also be filled in plastic containers for refrigerated or frozen storage (Collins and Walter, 1992; Kays, 1985; Pérez-Díaz et al., 2008; Walter and Wilson, 1992). Ice et al. (1980) and Creamer et al. (1983) reported that pH adjustment of sweet potato puree to 1.5, 4.5 and 11.5 prior to filling in jars followed by pasteurizing at 90ºC could prolong the shelf-life of the product up to 9 months at room temperature. Preservation by canning for low acid food such as sweet potato purees (pH, 5.8 – 6.3) usually involves excessive thermal treatment of the product because heat transfer in the puree is mainly by conduction. Excessive thermal treatment of the product also results in severe degradation of color, flavor, texture, and nutrients. An example is the institutional-size can size 607x 700 which is required to retort for over 165 minutes at 121 °C (Lopez, 1987). The slow- rate of heat transfer from the wall to the center of the can to attain commercial sterilization of the product limits the maximum can size of number 10 for canned sweet potato purees. This size limitation is another obstruction for the wider uses of sweet potato purees as a food ingredient in the food industry. Other issues associated with canning include the difficulty in handling, opening and dispensing of the product, and disposal of emptied cans. Nevertheless, canning does not have the need for special storage, lower capital investment and unit of production is less when comparing to refrigerated and frozen puree. Frozen puree is an established method for preservation which provides the lower degradation on nutritional and sensory quality as compared to can processing. However, preservation by freezing requires considerable investment in frozen distribution and storage as well as space, energy, time-consuming, and poorly controlled defrosting treatment before use. Currently, only limited amount of canned and frozen sweet potato purees are commercially produced by a few companies in the U. S. and Japan. Microwave-assisted Sterilization and Aseptic Packaging: Aseptic processing is considered as a potential alternative to overcome the stated problems associated with canning and low temperature preservation. As opposed to conventional canning, the use of high temperature for a short period of time in aseptic processing can produce a higher quality product with equal or better level of microbiological safety as that in a conventional canning system. Smith et al. (1982) described an improved canning process for sweet potato purees which involved flash sterilization and followed by aseptic filling, that resulted in a shelfstable and high quality product. However, scaling-up of the technology for achieving beyond the cans and process validation were not carried out for commercial development. Since then, further application of aseptic processing and packaging technology of food products in

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flexible containers, has not been successfully carried out for purees from sweet potatoes and other vegetables. Recently, a process for rapid sterilization and aseptic packaging of the orange-fleshed sweet potato purees using a continuous flow microwave system operated at 915 MHz has been successfully developed (Coronel et al.., 2005). This process has the advantage of avoiding long retort processing schedules, maintaining high quality retention, and producing shelf-stable products. The resulting product packed in flexible plastic containers had the color and viscosity comparable to the non-sterilized puree and was shelf-stable for at least 12 months. Purple-fleshed sweet potato purees were also successfully processed into high quality aseptic product using the continuous flow microwave system (Steed et al.., 2008). With this technology, shelf-stable purees with consistently high quality can be packaged into virtually unlimited container sizes (up to 300 gallons) for conveniently utilizing as food ingredients in the food processing industry. This technology can be extended to highly viscous biomaterials and purees from other fruits and vegetables. In this new process, sweet potato puree is loaded into the hopper, and pumped through the system. Microwaves are generated from a 60 kW, 915 MHz microwave generator and delivered to the puree by a waveguide of rectangular cross-section which is split into two sections and led to two specially designed cylindrical applicators. The puree is preheated to 100ºC in the lower applicator, then to sterilizing temperatures of 130 - 135ºC in the upper applicator, stayed in the holding tube for 30 sec, rapidly cooled in a tubular heat exchanger, and then aseptically packaged in aluminumpolyethylene laminated bags (Coronel et al.., 2005; Simunovic et al., 2006). In microwave processing, dielectric properties have a major role in determining the interaction between puree and the electromagnetic energy. Matching the dielectric properties of the material and the required microwave energy for adequate thermal treatment is very important to avoid over- or under- heating in aseptic processing of sweet potato puree (Coronel et al., 2005; Fasina et al., 2003a). The variation in chemical composition of the sweet potato purees is due to cultivars and post-harvest handling of raw materials, as described above, which may affect the microwave heating behavior of the purees. Brinley et al. (2008) developed predictive equations for dielectric constant and dielectric loss factor as a function of processing variables and puree composition such as temperature, moisture, sugar, and starch in the purees. The predictive equations are helpful in scaling up a continuous microwave heating system as well as determining the microwave heating patterns of purees from sweet potatoes with varying flesh colors for commercial operations. A technique for microbial validation of the process using biological indicators containing spores of thermal resistant bacteria (Geobacillus stearothermophilus and Bacillus subtilis) was also developed (Brinley et al., 2007). Other technical aspects associated with the scale-up of this technology such as the application of static mixing devices to improve the uniformity of temperature distribution and process control parameters for extended operating times have been evaluated (Kumar et al., 2008). The first commercial venture on aseptically packaged sweet potato puree using this microwave-assisted sterilization technology has been carried out by a new company in North Carolina, USA. This development opens up a new market opportunity for the sweet potato industry, and potentially increases the utilization of sweet potato purees as functional ingredients in various food products.

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Quality of Sweet Potato Purees Color and Flavor: Discoloration of the peeled and cooked sweet potatoes can affect the puree color. Enzymatic discoloration is characterized by a brown, dark gray or black color. It occurs when polyphenol oxidase catalyzes the oxidative polymerization of phenolic acid during peeling and size reduction of sweet potatoes. This type of discoloration can be minimized or prevented by heat inactivation of the enzymes, lowering the pH with acidulants, or using inhibitors such as sulfite and ascorbic acid (Walter and Wilson, 1992). The nonenzymatic discoloration shows the gray, black or green color upon exposing the cooked sweet potatoes to air. This ―after-cooking darkening‖ is caused by phenolics complexing with metals especially ferrous iron. Sodium acid pyrophosphate (SAPP) which has a strong affinity to metal ions is effective in preventing the non-enzymatic discoloration (Hoover, 1964). SAPP at concentration of about 0.5% has been widely used in the blanching medium or added directly to the material to enhance the color of sweet potato purees. Citric acid added to the puree at 0.2% can preserve the bright orange color of the product (Bouwkamp, 1985). Among the preservation methods, the puree color is greatly degraded by excessive heat treatment during canning caused by the Maillard browning reaction between sugars and amino acids. Frozen storage has minor color changes over 6 months at -17ºC (Collins et al., 1995). For microwave processing and aseptic packaging, high color retention of purees from both orange- and purple-fleshed sweet potatoes has been reported (Coronel et al., 2005; Smith et al., 1982; Steed et al., 2008). The flavor of purees, as in baked sweet potatoes, is dependent on cultivars, curing, storage and cooking methods (Hamann et al., 1980; Wang and Kays, 2001). Starch hydrolysis and maltose formation during cooking is important in the flavor quality of cooked sweet potatoes (Koehler and Kays, 1991; Sun et al., 1994; Walter et al., 1975). Walter and Schwartz (1993) reported that approximately 52 - 82% of starch in Jewel sweet potatoes was hydrolyzed, depending on the heat treatment. Maltose is the predominant sugar in the purees from various cultivars (Table 1) followed by sucrose, glucose, and fructose (Brinley et al., 2008; Ridley et al., 2005). Wider ranges of these sugars and sweetness in cooked sweet potatoes were reported by other investigators (Chattopadhyay et al., 2006; Kays et al., 2005; Truong et al., 1986). Aside from the sugars, the release of bound compounds (e.g. from glycosides) and a group of terpenoids such as linalool, geraniol and -copaene contribute to the aroma of baked and microwaved sweet potatoes, but they were absent in the boiled samples (Wang and Kays, 2001). Thirty volatile compounds have been identified in baked sweet potatoes (Purcell et al., 1980). Several compounds such as 2, 3-pentanedione, 2-furyl methyl ketone, 5-methyl-2-furaldehyde and linalool were correlated with the good sweet potato flavor (Tiu et al., 1985). Rheological Properties: The rheological behavior is an important property of purees processed from fruits and vegetables and it has been studied by numerous researchers. Krokida et al. (2001) compiled data of several fruit and vegetable products and listed values for consistency coefficient and flow behavior index along with the corresponding ranges of temperature and concentration. In the presence of starch, sweet potato purees are naturally viscous and thicker than other processed purees from other commodities such as carrots and tomatoes. Sweet potato purees display shear thinning behavior with a yield stress, as most of fruit and vegetable purees.

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Table 1. Sugar Content (% fresh weight) of the sweet potato purees Cultivar

Glucose

Fructose

Sucrose

Maltose

Beauregard

2.2

1.8

3.3

7.2

Bon 99-447

0.7

0.5

2.2

7.2

Covington

1.5

1.1

3.7

6.1

FTA 94

0.3

0.2

1.1

3.8

Hernandez

2.8

2.3

3.0

7.4

NC 415

1.6

1.2

1.7

9.3

Norton

1.5

1.8

2.3

7.3

O‘Henry

1.9

1.7

1.7

7.6

Okinawa

0.5

0.3

1.3

3.7

Picadito

0.6

0.4

1.14

4.1

Porto Rico

1.3

1.1

3.3

8.8

Pur 01-192

0.3

0.2

1.1

3.6

Suwon 122

0.2

0.1

1.3

3.9

Source: Brinley et al., 2008.

In studying the relationship between rheological characteristics and mouthfeel of sweet potato purees, Rao et al. (1975a) found sweet potatoes to exhibit non-Newtonian, pseudoplastic behavior that fits the Herschel-Bulkley model. Yield stresses of the purees from eight different cultivars with cream, yellow and orange flesh color in their studies ranged from 230 to 663 dyne/cm2 (23 – 66.3 Pa) (Rao and Graham, 1982). Consistency coefficient values ranged from 17.9 to 248.1 dyne-s/cm2 (1.79-24.8 Pa-s) and flow behavior index values varied from 0.333 to 0.564. Apparent viscosity at 97.2 rpm in a coaxial cylinder viscometer ranged from 534 to 2893 centipoise (0.534 – 2.89Pa-s) among the puree samples of the tested cultivars over two months of root storage. Purple-fleshed sweet potato purees with solid content adjusted to 18% as that of the orange-fleshed sweet potato purees also exhibited pseudo-plastic behavior with the flow properties, apparent viscosity and yield stress within these ranges (Steed and Truong, 2008). Both apparent viscosity and yield stress significantly correlated with the mouthfeel attribute of sweet potato purees (Rao et al., , 1975b), and in general they appear to decrease with length of root storage (Rao et al., 1975a). Purees from cured roots were slightly, but not significantly, lower in apparent viscosity than those made from uncured roots (Ice et al., 1980; Hamann et al., 1980). Analysis of viscometric properties

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with the use of Bostwick consistometer and different types of rotational viscometers has been used to assess the quality of sweet potato purees. Apparent viscosity of sweet potato puree decreases with increasing shear rate and temperature (Figure 2). Kyereme et al. (1999) studied the effect of temperature from 15ºC to 90ºC on apparent viscosity of sweet potato puree with a shear rate sweep of 0.001 to 921/s. The flow behavior of sweet potato puree as affected by temperature was well represented by either the Herschel-Bulkley or Modified Casson models. The models can adequately predict the apparent viscosity of sweet potato puree at 50ºC but they did not perform well at higher temperatures. Ahmed and Ramaswamy (2006) observed a deviation in rheological behavior of sweet potato puree infant food at and above 65C that was possibly caused by gelatinization and possible formation of amylase-lipid complex of starch as confirmed by two distinct DSC (Differential Scanning Colorimeter) thermal transition peaks at 54ºC and 95.5ºC. Brinley et al. (2008) reported significant decrease in apparent viscosity of sweet potato puree at 130ºC at which the puree was sterilized in the microwave-assisted aseptic packaging. Sweet potato purees are usually thickened with temperature decreases that may lead to a difficulty in pumping during the processing operations but the phenomenon can be beneficial in providing the desired textural properties in processed food products (Steed et al., 2008). Amylose and amylopectin in the sweet potato puree form a gel network upon cooling. Aside from the steady-shear viscometry described above, the small-amplitude oscillatory tests have been used to characterize the viscoelastic behavior of sweet potato purees.

Figure 2. Apparent viscosity of orange-fleshed sweet potato puree cv. Beauregard at different temperatures (Truong, unpublished data).

Fasina et al. (2003b) and Ahmed and Ramaswamy (2006) reported that purees exhibit gel behavior illustrated by a larger storage modulus (G‘, the elastic component) than loss

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modulus (G‖, the viscous component) through oscillatory rheology. The parallel slopes of G‘ and G‖ with G‘ greater than G‖ throughout the frequency range define the solid-like behavior of a food material (Steffe, 1996). This gel network was further strengthened by the addition of alginate and calcium salts to form a firmer puree (Fasina et al., 2003b; Truong et al., 1995). The puree processing methods affect the viscoelastic properties and textural profiles of restructured products made from sweet potato purees (Walter et al., 1999). Nutritional Values: The nutrient content of sweet potato purees and pastes from varieties with different flesh color is shown in Table 2 (Brinely et al., 2008). It should be noted that the values of the paste samples (> 21% dry matter) would be lower since dilution needs to be carried out for having flowable purees during processing. Sweet potato purees have low protein and fat content, but they are high in calories, minerals such as potassium, phosphorus, magnesium and calcium, and a relatively good source of dietary fiber, 2.0 – 3.2 g/100g fresh weight basis (fwb) (Bovell-Benjamin, 2007; Woolfe, 1992; Yencho et al., 2008). The glycemic index (GI) of steamed, baked or microwaved sweet potatoes were about 63-66, as compared to 65-101 for potatoes cooked by these methods (Soh and Brand-Miller, 1999). Table 2. Nutritional value (% fresh weight) of purees from various sweet potato genotypes Cultivar

Dry matter

Starch

Total Sugar

Protein

Lipid

Ash

Beauregard

19.5

2.3

14.5

0.4

0.1

0.7

Bon 99-447*

24.7

10.6

10.6

1.9

0.1

1.0

Covington

19.3

1.9

12.4

0.4

0.1

0.8

FTA 94*

33.1

10.2

5.4

0.7

0.2

1.1

Hernandez

23.3

3.83

15.4

0.5

0.1

1.0

NC 415*

30.0

12.0

13.8

0.5

0.1

0.9

Norton*

25.9

6.6

12.7

0.4

0.1

0.8

O‘Henry

20.6

2.7

12.9

0.4

0.1

0.8

Okinawa*

32.0

3.2

5.8

0.6

0.1

0.9

Picadito*

31.3

12.5

6.2

0.3

0.1

0.8

Porto Rico*

26.9

2.8

14.5

0.5

0.1

0.8

Pur 01-192*

32.5

13.2

5.3

0.4

0.2

1.0

Suwon 122*

34.4

11.3

5.5

0.6

0.2

1.0

*Dry matter should be adjusted to < 21% for flowable purees Source: Brinley et al., 2008.

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Orange fleshed-sweet potato purees are rich in ß-carotene (Table 3). A wider range of βcarotene content in cooked orange-fleshed sweet potatoes, 6.7 – 16.0 mg/100g fwb, has been reported by different investigators (Huang et al., 1999; Namutebi et al., 2004; BovellBenjamin, 2007). The sweet potato carotenoids exist in an all trans configuration which exhibits the highest provitamin A activity among the carotenoids. van Jaarsveld et al. (2005) and Tanumihardjo (2008) advocate the increased consumption of orange-fleshed sweet potatoes as an effective approach to improve the vitamin A nutrition in the developing countries. Epidemiological studies indicated the beneficial effects of high carotene diets in reducing the risks of cancer, age-related macula degeneration and heart diseases (Kohlmeier and Hasting, 1995; Pandey and Shukla, 2002; van Poppel and Goldbohm, 1995). Carotenoids can be isomerized by heat, acid, air or light during puree processing and storage. When exposed to heat, the molecule may transform to a cis configuration typically at the 9, 13, and 15 carbon positions. The cis form reduces pro-vitamin activity but color remains mostly unaffected. Extremely high temperature processing will cause fragmentation products and release of volatile compounds. Chandler and Schwartz (1988) studied the changes in ßcarotene and its isomerization products as a result of blanching, canning, dehydrating, and cooking. The length and severity of the heat treatment increased ß-carotene loss and isomerization. Blanching, lye peeling, and pureeing actually showed an increase in ß-carotene content but this increase was attributed to enhanced extraction efficiency due to the heat treatment. However, other common sweet potato processing treatments showed significant reductions in ß -carotene content: steam injection – 8.0% loss, canning 19.7% loss, microwaving - 22.7% loss, and baking - 31.4% loss (Chandler and Schwartz, 1988). Lessin et al. (1997) quantified ß-carotene isomers after canning sweet potatoes. The total ß-carotene content increased by 22% from 256.5mg/g (db) in the fresh root to 312.3 mg/g (db) in the canned product which was attributed to increased extraction efficiency. Table 3. Phytonutrients in orange- and purple-fleshed sweet potatoes Varieties

Flesh color

Dry matter (g/100g)

-carotene (fwb) (mg/100g)

Antho cyanins¹

Total phenolic²

Beauregard

Orange

20.5

9.4

na

88.9

Covington

Orange

20.3

9.1

3.8

58.4

Stokes Purple

Dark purple

36.4*

na

80.2

401.6

NC 415

Dark purple

29.0*

na

69

652.5

Okinawa

Light purple

30.0*

na

21.1

458.3

*Dry matter needs to be adjusted to 18-20% for flowable purees; na = not analyzed. ¹mg cyanidin-3-glucoside/100g fw; ²mg chlorogenic acid/100g fw. Sources: Truong et al. (2007); Steed and Truong, 2008; Yencho et al., 2008.

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After canning however, some of the trans- form was transformed to 9-cis (25.3 mg/g), 13-cis (76.6mg/g), and 15-cis (19.4mg/g) forms while 191mg/g (db) remained in the trans configuration. A loss of less than 15% carotene content was observed by microwave sterilization and aseptic packaging of orange-fleshed sweet potato purees (Truong, unpublished data). Thus, the carotene-rich sweet potato purees can be a functional food ingredient which can help reduce the risk of chronic diseases and vitamin A deficiency in many parts of the world. The cooked paste of the purple-fleshed sweet potatoes has attractive reddish-purple color with high levels of anthocyanins and total phenolics (Table 3). The flowable purees with a solid content of 18% made from this material had total phenolic and anthocyanin contents of 314 mg chlorogenic acid equivalent/100g fwb and 58 mg cyaniding-3-glucosdie equivalent/100g fwb, respectively. The 2, 2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity was 47 µmol trolox equivalent/f fwb and oxygen radical absorbance capacity (ORAC) of 26 µmol trolox equivalent/f fwb (Steed and Truong, 2008). Therefore, the purple-fleshed sweet potato purees have polyphenolic content and antioxidant activities in a competitive level with other food commodities known to be a good source of antioxidants such as black bean, red onion, black berries, cultivated blueberries, sweet cherries and strawberries (Wu et al., 2006) 2006). Several clinical studies indicated that consumption of purple-fleshed sweet potatoes may have potential health benefits against oxidative stress associated with liver injury (Suda et al., 2008) and other chronic diseases (Suda et al., 2003).

Utilization of Sweet Potato Purees in Processed Foods Sweet potato purees has been used as an ingredient in numerous food products, including baby food, casseroles, puddings, pies, cakes, ice cream, yogurt, leather, bread, patties and soups (Collins and Walter, 1992; Collins et al., 1990; Collins and Washam-Hutsell, 1986; Hoover et al., 1983; Silva et al., 1988; Woolfe, 1992; Yasufumi and Shigeki, 2000). The most successful commercial application of sweet potato puree is for baby food. Recognizing the similarity in nutrient content of sweet potatoes and fruits, Truong (1987) conceptualized a novel strategy on value-added processing of sweet potatoes into products that have been traditionally produced from fruits. This novel approach was expanded to the development of a process for producing sweet potato puree-based beverages with sensory quality and nutrient content similar to fruit juices. Both orange- and purple-fleshed sweet potatoes were utilized, and the beverages were produced either in a concentrate form for reconstitution to a single strength of 100% sweet potato drinks, or in combination with other fruit juices and flavorings (Truong and Fementira, 1989, 1990). Such development raised interest among research institutions in several sweet potato producing countries including India, Japan, Malaysia, and the United States (Payton et al., 1992; KNAES, 1996; Sankari et al., 2002; Tan et al., 2004). Several patented processes on utilization of sweet potato purees in fruit and vegetable beverages were developed in Japan and the United States (Gladney, 2005; Payton et al., 1992), and currently there are several fruit and vegetable drinks with sweet potato purees as an ingredient being commercialized in these countries. Other commercial utilization of sweet potato puree includes jam and ketchup (Truong, 1994; Fawzia et al., 1999). Restructured products from sweet potato puree with the use of gelling agents such as carboxymethyl cellulose, hydroxymethyl cellulose and alginate-calcium system have also

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been developed. These products, simulated-baked sweet potatoes and restructured French fries have good sensory quality and textural properties (Truong and Walter, 1994; Truong et al., 1995; Utomo et al., 2005). Recently, sweet potato purees have been used in developing carotene-rich curd and fermented beverages with high antioxidant activity (Mohapatra et al., 2007; Saigusa et al., 2005). With the recent commercial development of the microwaveassisted processing and aseptic packaging of sweet potato purees (Coronel et al., 2005; Steed et al., 2008), it is expected that more processed food products from the puree will be developed. In the U. S., sweet potato puree has been used for dehydrating into flakes or powder for various food applications that is described in the following section.

DEHYDRATED POWDER / FLOUR AS FUNCTIONAL INGREDIENT Sweet potato roots can be processed into dehydrated forms such as dried chips and flour for storage and uses in food preparations (Peters and Wheatley, 1997). The flour can add natural sweetness, color, and flavor to processed food products. It can also serve as a source of energy and nutrients and minerals (Table 4), and contributes to the daily nutrient needs for β-carotene, thiamin, iron, vitamin C, and protein. Sweet potato flour provides 14% - 28% of the dietary reference intake (DRI) for magnesium and 20 - 39% for potassium (van Hal, 2000). For individuals diagnosed with celiac disease or with allergies to the gluten in wheat, sweet potato flour can serve as an alternative. Food allergies have become a public health issue in many countries (Maleiki, 2001). About 5% of the population has serious allergies to some foods, including the gluten in wheat and other cereals including rye, barley, triticale, and oats, (Mannie, 1999, Caperuto et al., 2000). In addition, the home production of a simple traditional processed sweet potato foods, as practiced by women and children in tropical countries could increase family income (Alcobar and Parrilla, 1987). Thus, sweet potato flour production for human feeding will aid in promoting year-round consumption, decreasing losses of food, increasing the economic value of the crop besides increasing the efficiency of the food delivery system. Table 4. Composition of sweet potato flour* Parameter Protein Fat Total dietary fiber Ash Phosphorous Total carbohydrates

Native Flour 6.6 1.0 17.5 1.0 0.1 73.0

Spray Dried** 3.18 0.61 5.85 2.7 85.23

Drum Dried 6.5 1.1 17.6 1.3 0.12 73.8

Hot air Dried (Cabinet dried) 6.3 1.1 17.2 1.1 0.11 73.6

*Dry weight basis. **contains added dextrins. Source: Avula et al. 2006; Grabowski et al., 2008.

Sweet potato flour is used as a raw material for processing into other products. A variety of products such as doughnuts, biscuits, muffin, cakes, cookies, extruded products, fried chips, ice cream, porridge, brownies, pies, breakfast foods, and weaning foods have been

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made from sweet potato flour (Greene et al., 2003; Lee, 2005; Toyokawa et al., 1989). In India, dried sweet potatoes grounded into flour are used to supplement flours in bakery products, chapathis, and puddings (Nair et al., 1987). Drying of root slices for sweet potato flour production is also practiced to certain extents in many countries in Asia including Bangladesh, China, Indonesia, Japan, Philippines and Vietnam. In Indonesia, fresh roots are sometimes soaked in 8-10% salt solution, a practice which is reported to inhibit microbial growth during drying (Winaro, 1982). In parts of East and West Africa, where there is a pronounced dry season, roots are peeled, sliced, and sun dried for storage. In Peru, sweet potato flour has been produced for decades, to prepare wheat/sweet potato bread (van Hal, 2000).

Processing of Sweet Potato Flour For sweet potato roots to produce good quality flour, they should be low in total free sugar content, reducing sugar content, ash content, amylase and polyphenol oxidase activities, and have high dry matter with white color (Bovell-Benjamin, 2007; Collado et al., 1997). Roots are still acceptable for processing if the reducing sugars do not exceed 2% on dry weight basis (van Hal, 2000). Generally, controlling the quality of a product is based on the acceptability of the users and food legislation (Bovell-Benjamin, 2007). Dehydration of sweet potato involves washing, peeling, slicing/shredding, blanching, soaking, pressing, and drying (van Hal, 2000; Woolfe, 1992). The losses during peeling and the ease of drying by slicing and shredding have been reported. In traditional practice, the roots, which may or may not be peeled and cooked but more often are directly cut up into pieces and spread out in the sun to dry. They yield dried chips or slices which can be ground in a mortar to flour, and then sieved. Mechanical driers such as cabinet, tunnel, drum, or spray drying as used in large commercial enterprises are highly technical processes using large amounts of energy, which add greatly to the cost of the final product (van Hal, 2000). Solar Drying: Solar drying is the cheapest technique since it uses free and non-polluting energy with a minimum investment in equipment. Drying of sweet potato root slices in direct sunlight or in a solar dryer is frequently carried out. Both white and colored varieties have been found suitable for solar drying. Drying times vary depending on climatic conditions from 4 h to 5 days. Slices were dried until they reached a moisture content of about 6-10% (Winaro, 1982). The use of dehumidified air increased the drying rates by about 6-8%. However, solar drying has a number of disadvantages, such as poor control of energy input and product quality, interruption of drying caused by cloud, rain, and nightfall and frequent contamination of food by microorganisms, dust, and insects (Woolfe, 1992). Mechanical Drying: Drying in a cabinet or tunnel dryer is based on the same principle as solar drying, with the difference being that the air is heated by fuel. In this type of dryer, the drying temperature, drying time and air velocity, and hence total dehydration conditions could be controlled. Slices/dices are also subjected to blanching to inactivate the enzyme responsible for browning reactions and soaked in solution containing sulphur dioxide to inhibit enzymatic and non enzymatic reactions for improving color and retaining quality during storage. Sweet potato slices are exposed to drying temperatures between 50°C - 80°C for 4 - 12 h (Avula et al., 2006; Collado et al.,. 1997; Hathorne et al.,. 2008). Special batch type cabinet dryers for drying sweet potato slices on small and industrial scales were also

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developed (Eusebio et al., 1996; Truong et al., 1990). Air velocity, slice thickness, and airdry bulb temperature were the main variables that affected drying rates of sweet potato slices (Diamante and Munro, 1991). The modified Page equation was found to be the best description for the drying curves of sweet potato slices dehydrated to a moisture content of 10%. Antonio et al. (2008) studied the influence of osmotic dehydration and high temperature short time drying process on dried sweet potato and found that 150°C for 10 min and 160 °C for 22 min were the best drying conditions for drying of sweet potato slices subjected to osmotic treatment and no osmotic treatment, respectively. Drum drying is also used for dehydration of sweet potato puree to produce flakes / powder. Walter et al (1983) and Valdez et al. (2001) dried the cooked and comminuted sweet potatoes in a double drum drier heated with steam at 80 psi. The flakes were milled into <60 mesh particles and stored under nitrogen at -20°C. Drum dried sweet potato flakes were prepared by Manlan et al. (1985), after treating the sweet potato puree with amylase enzyme to reduce viscosity. Avula et al. (2006) prepared drum dried flour by subjecting sweet potato mash to a double drum drier of 60 cm width and 35 cm diameter. The speed of the drum was maintained at 3 rpm with a clearance of 0.3 mm and at a steam pressure of 6 kg/cm2. The sheets of dried sweet potato were collected, crushed and milled in a hammer mill provided with a 500 µm sieve. Fukazawa and Yakushido (1999) reported that drum-dried the sweet potato mash at 80ºC in the first half of the drying cycle and at 55 ºC to 60ºC in the later part of drying produced flour with good orange and purple color. Spray drying of sweet potato puree of 18.2% solids was investigated by Grabowski et al. (2006). The puree was subjected to pre-treatment with α-amylase at 50C - 60C to reduce viscosity and maltodextrin addition to aid in spray drying. Maltodextrin (10-20%) facilitates product recovery by raising the glass transition temperature of the product, thereby reducing stickiness and partially encapsulating the material. The puree was spray dried using a dryer equipped with a 2-fluid nozzle for atomization and a mixed-flow air-product pattern. The predrying treatments and drying temperature impacted the final characteristics and functionality of the spray-dried sweet potato powders. It was demonstrated that good quality sweet potato powder can be produced by spray drying with potential applications in food and nutraceutical products. Modified Flours: The technology in modifying starch has also been applied in developing modified sweet potato flours (Avula et al., 2007a).The most important reaction in the chemical modification of food starches is the introduction of substituent groups (Kim et al., 1996). These chemical modifications are of two types, monofunctional and di - or polyfunctional. Monofunctional reagents react with one or more hydroxyl groups per sugar unit to alter the polarity of the unit, sometimes making it ionic, and markedly influence the rheological properties of the starch. Monofunctional reagents most often used for food starch are acetic anhydride and propylene oxide. The former reacts to produce starch acetate (Moore et al., 1984). The physicochemical properties of acetylated starches depend on their chemical structures, degree of substitution (DS) and acetyl group distributions (Gonzalez and Perez, 2002; Lawal, 2004; Singh et al., 2004). Acetylated sweet potato flour was prepared by treating the native flour with acetic anhydride (Avula et al., 2007a). The native flour (prepared by drying the sweet potato slices at 40 °C and milled into flour and sieved) was mixed with solid NaHCO3 and wetted with distilled water, followed by addition of acetic anhydride. The mixture was allowed to react for 2 h at 40 °C, and later was washed thoroughly with aqueous alcohol (80%) and dried at 40 °C overnight.

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During in vitro alpha amylolysis of different starch granules, the enzyme attack is rather restricted and is usually from outside inwards, i.e. exocorrosion (Hayashida et al., 1989). On the other hand, in vivo the granules are subjected to cumulative actions of salivary amylase, dilute acid (by gastric juices) and pancreatic α- amylase and intestinal microflora and as a result the granules are better digested. The granule degradation was mostly confined to pitting and surface erosion all over. Some researchers have shown ‗onion-type‘ layering of the granules (Tharanathan, 1995). To develop enzyme modified flour, the native flour was subjected to glucoamylase action. The reaction mixture containing native sweet potato flour and the glucoamylase enzyme was incubated at 60 °C for 120 min. It was centrifuged and the sediment was washed with alcohol repeatedly and dried (Avula et al., 2007a).

Storage Stability of Sweet Potato Flour For prolonged storage of sweet potato flour, the packaging material must be impermeable to vapor and gas, resist tearing, protect against contamination from the environment, and be easy to handle (Furuta et al., 1998; van Hal, 2000). Orbase and Autos (1996) showed the advantage of double packaging (polyethylene/muslin cloth) to prevent lumpiness and loss of color of flour stored in polyethylene and polypropylene bags for 5 - 7 months. Auto-oxidation of carotenoids may take place during storage, leading to loss of color and nutritional value. The stability of β-carotene proved to be strongly and adversely affected by storage temperature and light (Woolfe, 1992). The microbial count of flour stored in different packaging materials did not change over time and was below the tolerable limit (TardifDouglin et al., 1993). Out of the four equilibrium sorption models that were evaluated, the Hasley equation gave the best fit to the sorption data. When Hasley equation was used to estimate the thermodynamic functions of sweet potato, it was found that the heat of vaporization and the differential entropy decreased with moisture in an exponential fashion (Millan et al., 2001).

Nutritional Quality of Processed Flour Nutritional Value: Changes in the nutritional value of the sweet potato roots during processing were found to occur due to peeling, soaking, pre-cooking, and drying steps. Flours from peeled and unpeeled roots were found to be different in composition and the flour from the latter was higher in ash and crude fiber. Shrinkage of the slices and decrease of yield were observed during soaking due to plasmolysis. Reduction in solubles, total sugar, starch, amylase, ash content was also observed. Discoloration of sweet potato slices/shreds resulting in low quality brown flour was observed due to the action of oxidase enzymes. Soaking in 2% citric acid solution resulted in final dehydrated product with a red-yellowish tint due to the caramelization of sugars accelerated by the citric acid (Hamed et al., 1973; Widowati and Damardjati, 1992). Martin (1984) found that the flours made from microwave baked sweet potatoes had the amount of starch varied from 40-60%, which was much less than the flours from uncooked sweet potatoes (69-85%). The levels of non-reducing sugars and of protein were unaffected, while the levels of reducing sugars were much higher in flours from microwave-baked sweet

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potatoes. Lowest reduction of total protein, lysine, and methionine during dehydration by solar drying and cabinet drying was observed, with moderate changes at temperatures not exceeding 80°C. Sulphiting treatment given to prevent enzyme darkening of the sweet potato flesh during dehydration can reduce thiamin content of drum dried sweet potato flakes (Hamed et al., 1973; Moy and Chi, 1982). Drum drying process retained more ascorbic acid than sun drying as the latter process exposes ascorbic acid to heat degradation and oxidation. Although the content of most of the amino acids was almost the same for oven and drumdried flours, the lysine content of the drum-dried flour was substantially lower and resulted in its lower protein efficiency ratio (PER) compared to oven-dried flour. The high temperature (120-140°C) applied during drum drying caused a reaction of the ε-amino group of lysine with reducing groups of carbohydrates which caused the lysine to be destroyed irreversibly and as such to become nutritionally unavailable (Walter et al., 1983). Sammy (1970) compared the chemical composition of spray-dried and cabinet-dried sweet potato flours and found that the products were similar except for the higher moisture content of the cabinet dried flour and the higher sugar (both reducing and total sugars) content of the spray dried flour. Lipid oxidation of drum dried sweet potato flakes has been a common problem resulting in reduction of lipid content (Walter and Purcell, 1974). Similarly, spray drying exposes more surface area of sweet potato powders, thus allowing oxidation and degradation to take place (Grabowski et al., 2008).A 50-70% decrease in vitamin C was reported for sweet potato flakes, drum dried at high temperatures (Arthur and McLemore, 1955). Spray drying of sweet potato purees significantly decreased total amount of β-carotene and caused isomerization of the molecule which reduces pro-vitamin A activity as described in the previous section. Isomerization of β-carotene was also found to occur during dehydration in a cabinet drier, drum-dryer, microwaving, or baking, with the quantity of isomer formed related to the severity and length of the heat treatment (Kidmose et al., 2007; Woolfe, 1992). Extruded sweet potato flour from orange-fleshed sweet potatoes showed the lowest losses in total carotenoids as compared to cream-fleshed cultivars (Fonseca et al., 2008). In-vitro Digestibility and Antioxidant Activity: Processed flours which have undergone cooking and drying treatments were more digestible than enzyme modified and acetylated flours (Figure 3). Hot air dried flour was found to be more digestible than drum dried flour, indicating less compactness of the particles in the former. The temperature during hot air drying was more conducive for amylolytic hydrolysis of starch by the endogenous amylases present in sweet potato, which also led to reduction in pasting viscosities (Avula et al., 2006). The higher digestibility of processed flours may be due to comparatively less branching and low molecular weight of the starch constituent fractions (Madhusudhan et al., 1996). The disrupted state of starch granules of drum dried and hot air dried flours would have helped in better penetration of enzyme to facilitate digestion. The degree of amylolysis is dependent on the chemical nature of starch, type of processing, presence of inhibitors, and physical distribution of starch in relation to other dietary components such as cellulose, hemicellulose, and lignin (Rao, 1969; Hale, 1973). The changes in morphological features have also facilitated better digestibility in enzyme modified flour. Starch digestibility is significantly improved by cooking with either dry or moist heat, or fine grinding (Dreher et al. 1981; Leach and Schoch, 1961). Although cooking improved digestibility, a wide variation in digestibility still remained, depending on the cooking conditions.

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Figure 3. Digestibility of sweet potato flours (adapted from Avula et al. 2006, 2007a).

The effect of degree of substitution (DS) on digestibility was inverse and exponential. Acetylated starches sharply reduced the digestibility of gelatinized starch by pancreatic amylase (Wootton and Chaudhry, 1979). Determination and establishment of differences and changes in starch digestibility in variously treated flours is essential in recommending suitable utilization of these flours. Poorly digested flours may also function like dietary fiber and have therapeutic benefits such as, lowering blood glucose in diabetes, or to aid in weight control (Skrabanja et al., 1999). Restricted digestion of starch is critical for infants and senior citizens having reduced digestive capacity and people with physical exhaustion, emotional stress or medical disorders leading to disturbed digestion (Niba, 2003). Antioxidant activity of sweet potato flour varies significantly with the flesh color of the roots. The purple-fleshed genotypes have high levels of polyphenolics and antioxidant activity (Teow et al., 2007). Steam blanching increased the reducing power and scavenging DPPH radical effect of sweet potato flours. Contents of total phenols, flavonoids, and anthocyanins in sweet potato flours were positively correlated with the reducing power and scavenging DPPH radical effects (Huang et al., 2006). Four different polyphenolic compounds, namely 4, 5-di-O-caffeoyldaucic acid, 4-O-caffeoylquinic acid, 3,5-di-Ocaffeoylquinic acid, and 1,3-di-O-caffeoylquinic acid were identified in freeze dried sweet potato flour. Antioxidant activity of daucic acid derivative was found to be very high (Dini et al., 2006). Sweet potato foliage is rich in total phenolic content and antioxidant activity which are about 8- to 18-fold greater than the roots (Truong et al., 2007). Thus, the dry powder of sweet potato leaves can be a good source of antioxidants and its applications to enhance the functional properties of juices, paste, ice cream and other food ingredients have been initiated (Islam, 2006).

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Physical Properties and Functionality of Flour Sweet potato flour being rich in starch, exhibits unique functional properties which will find its suitability in specific product formulations. However, the properties of sweet potato flour may be influenced by the method of preparation, severity of heat treatment, type of modification, the presence of other components such as fiber, protein, etc. The changes in structural characteristics of starches occurring as a result of modification / treatment may also be responsible for bringing specific functionality to the sweet potato flour. Hence, the limited data available for functional properties of sweet potato flour are different from those of starch since extra constituents available in flour (non- starch polysaccharides, protein, fat, etc), restrict access of water into the starch granules (van Hal, 2000). For example, RVA viscoamylograph pasting parameters of flour, were not correlated to the RVA pasting parameters of the purified starch (Jangchud et al., 2003). Particle size and morphology: Pre-treating the sweet potato puree with α-amylase and the addition of maltodextrin prior to spray-drying had significant effects on particle size and bulk density of the powder. Typically, as particle size decreases the bulk density will increase, but this was not apparent in spray-dried sweet potato powder. Bulk density was observed to decrease with amylase treatment (Grabowski et al., 2006). This decrease in bulk density did not match the decreasing particle size, and the phenomenon can be explained by the agglomeration of sticky particles during the drying (Goula et al., 2004). The particle size of the sweet potato powder from rotary atomizer was found to be less than half the size of the particle size of the powder made on dryers with 2-fluid nozzle (Grabowski et al., 2006). When observing particle morphology, some of the granules of enzyme-treated spray dried powder appeared to aggregate as compared to flours without α-amylase addition (Figure 4). These agglomerates take up a larger volume and, thus, would contribute to a smaller bulk density. These aggregated particles may also aid in the slightly increased water solubility of the powders treated with amylase. Morphological features of starch granules of drum dried and hot air-dried flours resembled each other, and the entire granule population seems to be clustered to form an aggregated mass comprising of several small granules, more so during drum drying (Figure 5). Starch granules of native flour were round, spherical of 4-26 µm, while the size of agglomerated granules ranged from 70-220 μm in drum dried, and 40-130 μm in hot air-dried flours (Avula et al., 2006). Chen et al. (2003) reported that the noodle quality was determined by the source and size of the starch granules. Further, the disruption of the granules indicated the complete gelatinization of starch in both drying processes resulting better hydration of the processed flours (Avula et al., 2006). The granular characteristics of starch were partially disappeared in acetylated and enzyme modified flours. Acetylated flour showed indentation as a result of modification, and also the granules appeared as clusters (Figure 5D). The fusion of starch granules in acetylated flour could be attributed to the introduction of hydrophilic groups to the starch molecules, which resulted in increased hydrogen bonding (Singh et al., 2004). Exo-corrosion of enzyme-modified flour (Figure 5E) was noticed, and the penetration of glucoamylase was imminent by the appearance of serrated surfaces and breakage of outer layers in some granules (Avula et al., 2007b). Rheological Properties: The material composition and conditions under which products are spray-dried can have an effect on the physical properties of the resulting powder. Though

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the solids concentration in the puree and reconstituted solutions was the same (18%), the puree viscosity was much greater than the powder viscosity (Figure 6).

a

b

Figure 4. Scanning electron microscope image of spray dried powder. (a). Without amylase treatment, (b) With amylase treatment (adapted from Grabowski et al. 2006).

A

B

D

C

E

Figure 5. Scanning electron micrographs of starch granules in sweet potato flours. A. Native, B. Drum dried, C. Hot Air Dried, D. Acetylated and E. Enzyme modified (adapted from Avula et al., 2006; Avula unpublished data).

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Figure 6. Viscosity of sweet potato puree and reconstituted spray dried powders from 1 to 250 s-1 (adapted from Grabowski et al., 2008).

Starch molecules in the powder are degraded during processing, thus losing the ability to swell and decreasing viscosity (Grabowski et al.., 2008). With more of the spray dried powder solubilized into solution, there was less sweet potato solids to create resistance to flow in the mixture. In order to spray-dry a sticky material like sweet potato puree, maltodextrin is used as carrier to facilitate the drying process by increasing the glass transition temperature of the product. In addition to encapsulation of the sweet potato material by maltodextrin, the interactions of maltodextrin with other polysaccharides present in the powders do not allow the polysaccharides to fully extend in solution, thus decreasing solution viscosity (Grabowski et al., 2006; Vega et al., 2005). Though the sweet potato puree exhibited pseudoplastic behavior which was best fit to Herschel–Bulkley model with distinct yield stress, the flow curve of the reconstituted puree (18% solid ) from the spray dried powder did not have a yield stress and fit the power law model. Powder solutions had much lower consistency coefficient values and higher flow behavior index values than the sweet potato puree. The flow behavior index of less than 1 further demonstrates the pseudo plastic behavior of spray dried sweet potato powder (Grabowski et al.., 2008). When spray dried sweet potato powder was subjected to a temperature ramp under a shear rate of 10/ s, it was found that the viscosity of the suspension decreased As the temperature was increased from 25 to 55 °C, the apparent viscosity increased from 0.042 to 0.070 Pa s as temperature was ramped from 25 to 95 °C, and then increased upon cooling from 95 to 25 °C. Rheologically, the reconstituted sweet potato slurries behaved similarly to pre-gelatinized starch solutions. Thus, spray dried sweet potato powders have a potential to enhance food systems as a thickener with natural colors. Studies on steady and dynamic shear rheological properties of the hot-air dried sweet potato flour dispersions indicated that sweet potato flour slurries at 25 °C showed a shear-

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thinning fluid exhibiting a yield stress. The magnitudes of Casson yield stress, consistency index and apparent viscosity increased with an increase in concentration. Within the temperature range of 25-70 °C, the apparent viscosity obeyed the Arrhenius temperature relationship with high determination coefficient with activation energies ranging 0.015-0.024 KJ/mol. Both power law and exponential type models were used to establish the relationship between concentration and apparent viscosity. Magnitudes of G ' and G '' increased with an increase in flour concentration. G ' values were higher than G '' over the most of the frequency range, and both parameters were frequency dependent (Chun and Yoo, 2006). The porridge made from blends containing fermented sweet potato was about seven times less viscous than the porridge from the traditional sorghum complementary food (Nnam, 2001). Shih et al. (2006) investigated the rheological properties of rice-sweet potato flour mixes as a 100% substitute of wheat flour in gluten-free pan cake. In contrast to the porridge blends reported by Nnam (2001), addition of sweet potato flour (10-40%) enhanced the hydration capacity of the rice batter and resulted in increased batter viscosity, and was comparable with that of the traditional wheat batters. Paste Viscosities: Native sweet potato flour showed unrestricted swelling, exhibiting maximum viscosity at a relatively shorter period of heating. In contrast, the suspensions of the heat processed flour showed reduced viscosity indices (Figure 7). Reheating the slurries of pre-gelatinized materials caused a decrease in paste viscosity leading to ‗thinning‘ of the slurry. The hot air-dried flour paste showed relatively low viscosity compared to drum dried material, though the severity of heat treatment was more in the latter (Avula et al., 2006). The temperature during hot air drying was more conducive for amylolytic hydrolysis by endogenous amylases and hence the breakdown of starch led to lower viscosity. Set back viscosity of drum dried and hot air dried flours has notably decreased, compared to native flour, validating thermal and enzymatic degradation of starch. A low set back value indicates a non-cohesive paste, which has many industrial implications. Reduction in viscosity is particularly important in the preparation of weaning and supplementary foods from starchy raw materials (Muyonga et al., 2001). Acetylated flour showed least paste viscosity showing restricted swelling of starch granules, due to the presence of substituent functional groups. The viscosity values obtained after isothermal holding at 95 °C (hot paste viscosity, HPV) were much lower than peak viscosity (PV) values (Avula et al., 2007b). The tendency toward setback or gel formation was minimized in acetylated flour due to the presence of functional groups that prevent starch chains from association (Moorthy, 2002). The degree of substitution (DS) for a starch derivative is defined as the number of hydroxyl groups substituted per D-glucopyranosyl structural unit of the starch polymer. Since each D-glucose unit possesses three reactive hydroxyl groups, the maximum possible DS value is 3. Therefore, the reactions to form acetylated starches can be controlled with high accuracy by adjusting the molar ratio of the reagent and catalyst in the reaction mixture, in order to obtain the desired DS value (Wang and Wang, 2001). The high pasting profile of the enzyme modified flour shows that the starch molecules were strengthened as a result of modification and resisted breakdown of paste. The formation of enzyme-starch complex would have imparted rigidity to enzyme modified flour resulting in higher pasting viscosities. The peak viscosity of fermented flour was greater than that of unfermented flour (Adeyami and Beckley, 1986). Leman et al. (2005) observed an increase in cold paste viscosity (CPV) of starch treated with maltogenic amylase.

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Figure 7. Viscoamylograms of sweet potato flours. 1. Native, 2. Drum dried, 3. Hot air dried, 4. Acetylated, 5. Enzyme modified (adapted from Avula et al., 2007b; Avula unpublished data).

The thermal and mechanical stability and low retrogradation pattern shown by enzyme modified flours are important characteristics useful for baked and frozen products. High paste viscosities are desirable in flours used as thickeners (Weissenborn et al., 1994), whereas low peak viscosities are desirable for high-calorie food formulations such as weaning and specialty foods. The setback (CPV-HPV) or retrogradation value was lower in acetylated flour compared to enzyme modified flour. A higher set back value is useful in products that require a high viscosity and paste stability at low temperature (Oduro et al., 2000). Use of enzyme modified flour is recommended for manufacture of low-fat-low sugar wafers and other bakery products. Enzyme modified flour showed an improvement in the emulsifying and oil absorption capacity (Taeuful et al., 1992). Pasting properties of the white-fleshed sweet potato cultivar exhibited lower tendency for retrogradation (Osundahunsi et al., 2003). Addition of sweet potato flour and fiber fractions to white wheat flour reduced the pasting properties of the resulting gels by up to seven-folds compared with the wheat flour gel (Mais and Brennan, 2008). The low mean peak viscosity of different genotypes was explained by the endogenous amylase activity in sweet potato

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flour. Indeed sweet potato flours with inhibited amylase activity by using AgNO3 showed much higher peak viscosity (Collado and Corke, 1999). Varieties, amylase concentration and flour particle size are all crucial factors determining the density and viscosity of the pastes (Iwuoha and Nwakanma, 1998). Thermal properties: Thermal properties of modified sweet potato flours, measured by DSC, differed significantly. Endotherm peaks of native flour and its enthalpy appeared between 68 – 78.5°C. The transition temperatures (To, Tp and Tc), and enthalpy (ΔH) of different flours are summarized in Table 5. Higher gelatinization enthalpy of native flour was due to the more stable granular structure and greater crystallinity (Ganga and Corke, 1999). The differences in transition temperatures may be attributed to the differences in granular structure, amylose content and gelatinization temperature between the starches (Moorthy, 2002). A typical DSC (Differential Scanning Colorimeter) endotherm was observed for gelatinization of native flour. However, drum-dried and hot-air dried flours did not show any gelatinization endotherm when heated up to 100°C, which confirmed the changed nature of starch granules as a result of processing. Gelatinization enthalpy depends on a number of factors such as crystallinity and intermolecular bonding. Biladeris (1990) and Leszkowiat et al. (1990) have suggested that higher transition temperatures indicate more stable amorphous regions and lower degree of chain branching. Acetylated flour showed reduced gelatinization temperature and ΔH, compared to native flour (Table 5). Gelatinization temperature of enzyme modified flour has not changed much but the ΔH increased as a result of enzyme treatment. The DSC curve indicates that the behavior of conjugate of starch and enzyme is almost same as that of native flour excepting for a slight difference in peak and conclusion temperatures. The crystallinity of starch granules in enzyme modified flour was comparable with that of native granule even after enzyme modification. The increase in heat energy in enzyme modified flour indicates that the granules are bound by protein (enzyme-starch complex), that resulted in stronger association of the molecules (Avula et al., 2007b). Using a viscograph, Iwe and Onuh (1992) reported a pasting temperature of 79°C when the degree of starch gelatinization of sweet potato flour was 50%. The electrical conductivity of flour/starch suspensions was found to increase upon gelatinization because of the release of ions from starch granules. Hence, the electrical conductivity measurement could be used as an on-line technique to monitor the whole process of starch gelatinization (Chaiwanichsiri et al., 2001). Table 5. DSC Characteristics of sweet potato flours Sweet potato flour Native Acetylated Enzyme Modified

T0 68.0 55.9 73.5

Tp 71.8 63.2 76.9

Tc 78.5 67.3 86.9

ΔH J/g 10.6 1.7 11.4

Source: Avula et al., 2007b.

Cooked sweet potatoes contain more than 22% sugar on a dry weight basis (Truong et al., 1986). Food products containing substances with low molecular weights, such as sugars, have very low glass transition temperatures (Tg), so these components can depress the Tg of the entire system. If the temperature of the spray-dried particle is greater than 20 °C above the glass transition temperature of that product, the particle will exhibit sticky behavior (Bhandari

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and Howes, 1999). The glass transition temperature of sweet potato powder increased with the addition of maltodextrin (Figure 8). Conversely, the glass transition temperature of the powders was reduced as the amount of alpha-amylase allowed to act on the puree was increased (Grabowski et al., 2006). This reduction was expected as the amylase breaks down starch into lower molecular weight dextrins. Additionally, the amylase-treated powders also had higher moisture content, and, thus, the additional water could lower the glass transition temperature (Grabowski et al., 2008). Solubility and Water Absorption: The instant properties of a powder involve its ability to dissolve in water. Since most powdered foods are intended for rehydration, the ideal powder would wet quickly and thoroughly, sink rather than float, and disperse / dissolve without lumps (Hogekamp and Schubert, 2003). The solubility index of spray dried sweet potato powder increased and its water-holding capacity reduced. The water solubility index of the powder increased with increase in the amount of maltodextrin addition. Maltodextrin can form outer layers on the drops and alter the surface stickiness of particles due to the transformation into glassy state (Grabowski et al., 2006). The changes in surface stickiness reduce particle-particle cohesion and particle-wall adhesion during spray drying, resulting in less agglomerate formation and, therefore, lower water-holding capacity of the powders. Drum dried flour showed higher solubility values whereas the acetylated and enzyme modified flours showed the least values, though all the flours showed increasing values with increase in temperature (Figure 9). The increase in solubility was highest at 96°C for drum dried flour followed by hot air dried flour. The pre-gelatinized starch is expected to exhibit high solubility in cold water than unmodified starch (Morrison, 1988).

Figure 8. DSC Thermograms showing showing glass transition temperature with increased levels of maltodextrin (adapted from Grabowski et al. 2006).

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% Solubility

50 40 Native

30

Hot Air Dried Drum Dried Acetylated

20 10 0 0

25

50

75

Temperature (°C)

100

Enzyme Modified

Figure 9. Solubility of sweet potato flours at different temperatures (adapted from Avula et al., 2006, 2007a).

The anamolies, if any, are probably due to starch retrogradation and extent of partial disintegration during milling (Kaur et al., 2002). The solubility of acetylated flour, though slightly increased with temperature, was found to be lower than that of native flour (Figure 9). The substituent groups made the associative bonds stronger in addition to presumably the formation of amylose - lipid complexes. Thus drum dried flour with better solubility even at low temperatures becomes an ideal choice for product formulations (Avula et al., 2006). Drum dried flour exhibited higher swelling power than hot air- dried, acetylated and enzyme modified flours at 30°C - 96°C. The increase in swelling and solubility values of differently treated sweet potato flours, therefore, can be attributed to a greater degree of macromolecular disorganization and also to variations in the degradation of starch during thermal treatments (Tan and Chinnaswamy, 1993). Factors like amylose - amylopectin ratio, chain length and molecular weight distribution, degree / length of branching and conformation determine the degree of swelling and solubility (Rickard et al., 1991). High amylose content and presence of stronger or a higher number of intermolecular bonds can reduce swelling (Delpeuch, 1965). Formation of lipid-starch complex can also offer low swelling volume (Swinkles, 1985) as also the presence of nonstarch carbohydrates and other constituents in the starch (Eliasson and Gudmundsson, 1996; Leach et al., 1959). Enzyme modified flours showed reduced swelling power compared to native flour (Avula et al., 2007a). Thus, highly associated starch granules with an extensive and strongly bonded micellar structures display relatively great resistance towards swelling (Mariam et al., 1996). The presence of protein (enzyme-starch complex), imparts rigidity and contributes to the limited leaching of starch (Colonna et al., 1979). The starchy flour extracted from fermented tubers also exhibited the same trend (Moorthy et al., 1993). Absorption properties of extruded sweet potato flour are considered to be fairly good and quite stable (Iwe and Onuh, 1992).

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The swelling volume of the sweet potato flour from different genotypes in distilled water had a mean of 15.7 ml/g, ranging from 11.8 ml/g to 18.8 ml/g (Collado and Corke, 1999). The difference in morphological structure of granules may also be responsible for the differences in swelling power and solubility (Adebowale et al., 2002). Sediment volume of processed starchy products is an index of starch gelatinization, and thus it provides a clear distinction between various precooked products. Drum dried flour exhibited higher sediment volume than enzyme modified and acetylated flours (Table 6), indicating a high degree of gelatinization in drum dried flour, followed by hot air dried flour (Avula et al., 2007b). The consistency of a cold flour paste in 0.2 N KOH is inversely correlated with viscoamylograph cold paste viscosity. Gel mobility is related to the degree of starch gelatinization, unaffected by starch reassociation, and hence could be a good test for the extent of gelatinization (Unnikrishnan and Bhattacharya, 1988). Drum dried flour showed significantly higher gel consistency followed by hot air dried flour compared to enzyme modified and acetylated flours (Table 6). The values of gel consistency of sweet potato flours were correlated with their swelling and solubility patterns. Excepting acetylated flour, all other treated flours were also correlated with their cold paste viscosities (Avula et al., 2007a; Avula, unpublished data). Table 6. Sediment Volume and Gel Consistency of sweet potato flours Flour Native Drum dried Hot air dried Acetylated Enzyme Modified

Sediment Volume (ml) 10.0 37.4 16.6 9.0 9.0

Gel Consistency (mm) 40.0 274.0 156.0 25.0 20.0

Source: Avula et al. (2006; 2007b).

PRODUCT APPLICATIONS Many studies have reported the feasibility of using sweet potato flour as an alternative to wheat, especially in bakery products (Singh et al., 2008). Commercial bakeries in Peru produced widely accepted bread supplemented with up to 30% sweet potato (Huaman, 1992; Palomar et al., 1981). Substitution levels as high as 65% sweet potato flour has resulted in bread with acceptable loaf volumes, flavor and texture as that of bread made of wheat flour (Greene et al., 2003; Green and Bovell-Benjamin, 2004). Bovell-Benjamin (2007) reviewed the potential utilization of sweet potato in the Ugandan and Kenyan Food systems. Nungo et al. (2000) evaluated the feasibility of several products that included mashenye, mandazi, and chapathi , which were selected as marketable products. In Mali, West Africa, the dehydrated sweet potatoes are usually rehydrated and added to sauce with other condiments and eaten with a stiff cereal porridge or rice (Scheuring et al., 1996). Sweet potato is processed into two local products called Michembe (the roots are withered, cut into slices, and dried) and Matobolwa (dried product made from boiled and sliced roots) in Tanzania. These products can have a shelf-life of 5-8 months. Other products that have been prepared in Tanzania include cakes, chapathis, donuts, kaimati, and buns

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(Gichuki et al., 2005). Other potential sweet potato products include bread, buns, noodles, pancake mixes, chips (Bovell-Benjamin, 2007; Salmah and Zaidah, 2005). The utilization of sweet potato as a main ingredient in making delicious cakes or local desserts is quite popular in Malaysia, and more than 32 sweet potatoes based traditional cakes and desserts are available in the Malaysian market (Zainun and Zahara, 2005). A ready to use flour mix using sweet potato flour to prepare Kuih Kacau Keldek was also developed and found acceptable. An extensive sweet potato recipe list including dishes from China, Ghana, Guyana, India, Japan, and the United States is documented by Hill et al. (1992). In the case of flat bread with less volume (chapathis, poories, buns), high levels of wheat flour substitution have been used successfully (Greene et al. 2003, Hagenimana et al., 1999a; Green and Bovell-Benjamin, 2004). For the salted western type of bread, sweet potato flour has been found to have a negative effect on loaf volume, flavor, color, and texture (Amano. 1996; Greene et al., 2003; Roa et al., 1996). Bread containing 50% sweet potato flour with high-gluten dough enhancers had the highest loaf volumes Hathorn et al. (2008). Golden bread made from fresh roots of medium-intensity orange-fleshed sweet potato varieties is a good source of ß-carotene and is economically viable when the price ratio of wheat flour to raw orange-fleshed sweet potato root is at least 1.5 (Low and van Jaarsveld, 2008). Extruded ready-to-eat breakfast cereal containing 75-100% sweet potato flour are promising products to be included in human diets (Dansby and Bovell-Benjamin, 2003a; 2003b). Fonseca et al. (2008) and Zhang (1998) reported optimal extrusion conditions for βcarotene retention in extruded sweet potato flour and sweet potato / peanut blends. Sweet potato flour from Jalomas and Telong varieties have good potential as raw material for the production of extruded snack food and RTE( ready- to- eat) breakfast food (Lee, 2005). The single screw extruder was used in these studies, and the effect of screw speed, feeder flow rate and moisture content on the extrudate quality were investigated in these studies. The severe heat treatment received by sweet potato extrudates rendered them applicable in soup bases, flour mixes and breakfast foods (Iwe, 2000; Iwe et al., 2001a, b, c; Iwe and Ngoddy, 1998). Gluten-free pan-cakes, mandazis and other processed products showed increase in βcarotene content on incorporation of sweet potato flour (Hagenimana et al., 1999b; Hathorne et al., 2008; Limmongreungrat and Huang, 2007; Oyunga-Obugi et al., 2005; Shih et al., 2006). Conversion of drum dried sweet potato flour to ethanol was studied by Reddy and Basappa (1997). A wine like product containing ethanol up to 8.6% (w/v), with desirable aroma and color was developed by treating drum dried flour with pectinase, and culture filtrate (α-amylase and glucoamylase) of Endomycopsis fibuligera. The inoculated flour was fermented for 3 days. Lactobacillus plantarum MTCC 1407 was used for direct fermentation of sweet potato flour to lactic acid under semi- solid fermentation (Panda and Ray, 2008). Pasta made from alkaline-treated sweet potato flour had the lowest cooking loss with the highest firmness. Cooking losses increased as levels of sweet potato flour decreased (Limmongreungrat and Huang, 2007). The color parameters were highly correlated with the color of dough sheets for whitesalted and yellow-alkaline noodles made from wheat and sweet potato composite flour (Collado et al., 1997; Oyunga-Obugi et al. 2005). Vegetarian products such as pan cakes and tortillas, made with sweet potato were developed for use in nutritious meals for future space explorers. Because of their consumer acceptability, these products were recommended to

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National Aeronautics and Space Administration (NASA)‘s Advanced Life Support Program for inclusion in a vegetarian menu plan designed for Lunar / Mars space missions (Wilson et al., 1998). Sweet potato flour has also been incorporated in cocoa drink, rice-based beverage and instant weaning food (Espinola et al., 1998; Suh et al., 2003; Truong, 1992).

CONCLUSION Sweet potato purees and powders can be used as thickening and gelling agents to impart desired textural properties, and enhance the nutritional values, antioxidant activity as well as natural color (e.g. orange and purple) of numerous food products. Furthermore, these ingredients from sweet potatoes can be used as alternatives to wheat products for individuals diagnosed with celiac disease and incorporated in low glycemic index foods for diabetics. Processing technologies for producing sweet potato purees and powders at small and large scale operations have been developed in different countries. For purees, the new development in aseptic processing using continuous flow microwave heating provides a great opportunity for the sweet potato industry in delivering the nutrient-rich and shelf-stable purees to food processors, institutional food services as well as emergency food relieve organizations around the world. With regard to the dehydrated forms, selection of sweet potato cultivars with high levels of dry matter and phytonutrients should go hand in hand and by adopting technological improvements to reduce processing cost. Aiming at specific functionality, nutrient retention and product storability need to be considered in order to provide competitiveness of these ingredients in the food processing sectors. With growing demand for convenient and healthy foods, sweet potato purees and dehydrated forms have good potential to be used as functional ingredients in processed foods.

REFERENCES Adebowale, K.O., Afolabi, T.A. and Lawal, O.S. (2002). Isolation, chemical modification and physicochemical characterization of Bambarra groundnut (Voandzeia subterranean) starch and flour. Food Chemistry, 78, 305. Adeyami, I.A. and Beckley, O. (1986). Effect of period of fermentation and souring on chemical properties and amylohraph pasting viscosity of Ogi. Journal of Cereal Science, 4, 353-360. Ahmed, J. and Ramaswamy, H. S. (2006). Viscoelastic properties of sweet potato puree infant food. Journal of Food Engineering, 74, 376-382. Alcober, D.I. and Parrilla, L.S. (1987). Gender roles in sweet potato production, processing, and utilization in Eastern visayas, Philippines. Paper presented at an international sweet potato symposium. 20-26 May, VISCA, Baybay, Leyte, The Philippines. Amano, V.L. (1996). Sweet potato: In: Selected Research Papers, July 1994-June 1995, Volume 2: Sweet potato, Rasco Jr., T. E. and Amante, V. R. (eds). SAPPRAD, Manila, The Phillippines. pp. 134.

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In: Sweet Potato: Post Harvest Aspects in Food Editors: R. C. Ray and K. I. Tomlins

ISBN 978-1-60876-343-6 © 2010 Nova Science Publishers, Inc.

Chapter 6

BIO-PROCESSING OF SWEET POTATO INTO FOOD, FEED AND BIO-ETHANOL Ramesh C. Ray1, Samir K. Naskar1 and Keith I. Tomlins2 1

Regional Centre, Central Tuber Crops Research Institute, Bhubaneswar 751 019, India 2 Natural Resources Institute, University of Greenwich, Central Avenue, Chatham maritime, Kent ME4 4TB, UK

ABSTRACT Sweet potatoes are mostly consumed as fresh vegetable or processed into starch and starch based food products such as noodles, vermicelli, macaroni, etc. Bioprocessing (fermentation) of sweet potato offers novel opportunities to commercialize this crop by developing a number of functional foods and beverages such as sour starch, lacto-pickle, lacto-juice, soy sauce, acidophilus milk, sweet potato curd and yoghurt, and alcoholic drinks through either solid state or submerged fermentation. Sochu, traditional Japanese distilled liquor with an alcohol content of nearly 25% is made from rice or barley as well as sweet potato. The sweet potato bagassae (residue after starch extraction) can be enriched with microbial protein (single cell protein) via solid state fermentation that can serve as protein – rich feed for poultry and ruminants. Sweet potato tops, especially leaves are preserved as hay (dehydration) or silage. Sweet potato flour and bagassae are used as substrates for production of microbial enzymes, organic acids, monosodium glutamate, chitosan, etc. In the current global search for alternative fuel for gasoline from renewable (plant) sources, sweet potato is a promising candidate for production of bioethanol.

ABBREVIATIONS CFU DEAE 

colony forming units; Diethylaminoethyl;

Corresponding author: Tel/Fax: 91-674-2470528; E-mail: E-mail: [email protected]

Ramesh C. Ray, Samir K. Naskar and Keith I. Tomlins

164 HPLC LAB MSG NMR MS SCP SSF SSB SmF

high performance liquid chromatography; lactic acid bacteria; monosodium glutamate; nuclear magnetic resonance; mass spectroscopy; single cell protein; solid substrate (state) fermentation; solid state bioprocessing; submerged fermentation

INTRODUCTION Sweet potatoes are mostly consumed as fresh vegetables or they are processed into starch and fermented products that include mono-sodium glutamate (MSG), citric acid, soy sauce, vinegars, ‗sochu‖ (an alcoholic [20-40%, v/v] drink made in Japan and Korea) and bioethanol. Besides sweet potato roots, the vines and wastes are fermented into feed for poultry and ruminants in many Asian countries; for example China, Indonesia and Vietnam. However, the overall demand of sweet potato as a crop has been gradually declining over the last few years, as well as the areas under its production (Ray and Ravi, 2005) with exception of Papua New Guinea (Ramakrishna, 2006) and some African countries (Low and Jaarsveld, 2006). In order to sustain sweet potato in the cropping system and make it a cash rich crop, efforts are to be made to increase its industrial applications. Extraction of starch and production of starch-based commodities such as noodles, vermicelli, etc are one such direction. In recent years, several sweet potato varieties have been released that are rich in poly-phenols and anti-oxidant pigments (β- carotene, lutein and anthocyanins) (Yoshimoto, Chapter 3 in this book). These varieties have the advantage in that they can be processed for the production of functional foods, food additives and beverages (Ray and Sivakumar, 2009). Bioprocessing (fermentation) is a novel way to develop such functional foods, food additives and protein-rich feeds from sweet potato. Also, production of bio-ethanol from sweet potato is another promising opportunity in the current global crisis for gasoline (Ray and Ward, 2006). This chapter reviews the progress made in the development of fermented products from sweet potato by application of bioprocessing technology.

BIOPROCESSING Bio-processing or bioprocess engineering is broadly defined as biologically based (enzymes or microorganisms) techniques or technology to convert biological materials into other forms needed by mankind (Ray et al., 2006). It includes production of food, feed and industrial chemicals, i.e. bio-ethanol, acetone- butanol, enzymes, organic acids, etc, through fermentation and design and operation of fermentation systems, development of food and feed processing systems and many more (Ray et al., 2008).

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Microbial Bio-Processing Microbial bio-processing (fermentation), when compared to chemical processing, has many advantages, including: • • • • •

Uniqueness; bio-processes enable the synthesis of products that cannot be made by any other means; Specificity; bio-processing offers a level of specificity, predictability, and productivity that otherwise would not exist in the manufacture of many products; Cost effectiveness; these capabilities provide for new process designs that are cost effective, energy efficient, and, last but not least, environmentally benign; Scalable; the processes involved in bio-processing are easily scalable and can be economically applied and linked to existing practices. Separation of products; the ability to separate intermediates and end products from unique and complex processed biomass streams is essential to the commercial viability of bio-processing.

Many of the fermented food, feed and industrial enzymes and biochemicals are based on the koji process that belongs to a major bio-processing category known as [solid substrate (state) fermentation (SSF)] (Krishna, 2005). This differs from submerged (SmF) fermentation in the amount of free water that they contain.

Solid State Fermentation (SSF) Solid state fermentation (also called as solid state bio-processing [SSB]) refers to the process where microbial growth and product formation occurs on the surface of solid materials. This process occurs in the absence of ―free‖ water, where the moisture is absorbed to the solid matrix (Zheng and Shetty, 1999; Suryanarayana, 2003). SSF has a number of advantages over SmF. These include a lower cost, improved product characteristics, higher product yield, easier product recovery and reduced energy requirement (Raimbault, 1998; Pandey et al., 2000; Krishna, 2005; Ray et al., 2008). It is of special economic interest for countries that have an abundance of agro-industrial residues that are inexpensive substrates for microbial growth (Krishna, 2005; Ray et al., 2006), besides preventing disposal- linked environmental problems. In recent years, SSF has shown much promise in the development of several bioprocesses and products (Pandey et al., 2000; Ray et al., 2008). Root crops such as sweet potato and cassava, fruit and vegetable wastes have been successfully converted into many value- added products via SSF processes (Zheng and Shetty, 1998 a, b; Krishna, 2005; Ray and Ward, 2006; Ward et al., 2006; Ray et al., 2008). These wastes contain mainly lignocelluloses, besides soluble sugars, starch (in case of root crops), fibres, phenols, and other hydrolysable materials (Tengerdy and Szakacs, 2003) that can be metabolized by a wide range of microorganisms into value-added products such as single- cell protein, microbial enzymes, etc. One of the important criteria in SSF is the selection of suitable microorganism(s). The ability of the microorganisms to grow on solid substrate is the function of their aw (water activity) requirements, their capacity to adhere to and penetrate into the substrate and their

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ability to assimilate mixtures of different polysaccharides from complex heterogeneous substrates (Raimbault, 1998; Pêrez- Guerra et al., 2001). A number of thermophilic bacteria, fungi and yeasts can grow on solid substrates, and find applications in SSF processes. The filamentous fungi are the best adapted microorganisms for SSF owing to their physiological, enzymological and biochemical properties. The growth pattern of fungi in SSF has been studied in detail in many cases and these can be summarized in three phases: • •

•

Germination, germ tube elongation and mycelial branching to loosely cover most of the substrate. Increase in mycelial density with aerial and penetrative hyphal development (Viniegra- González et al., 2003). These features also give them a major advantage over unicellular microorganisms for their colonization of the substrate and the utilization of the available nutrients. In addition, their ability to grow at lower aw and under high osmotic pressure conditions (high nutrient conditions) makes fungi efficient and competitive in the natural microbial ecosystem for the bioconversion of solid substrates (ViniegraGonzález et al., 2003). From a practical application, vegetative growth is preferred over sporulation.

Thermophilic bacteria and yeasts have also been used in traditional cultivation in SSF processes (Doelle et al., 1992; Ray et al., 2008). Bacteria have been used for enzyme and organic acid production, composting, ensiling and some food processing (e.g. koji, sausages, Japanese natto) (Weinberg and Ashbell, 2003). Yeasts have been mainly used for ethanol production and protein enrichment of agricultural wastes (Ward et al., 2006; Ray et al., 2006).

Submerged Fermentation (SmF) In contrast to SSF, SmF is the process of choice for industrial operations because of the very well known engineering aspects such as fermentation modelling, bioreactor design and process control (Ray et al., 2006). However, SSF does have advantages over SmF in microbial cultivation. Sweet potato being rich in starch (10 -15% on fresh weight basis) and many functional attributes (polyphenols and coloured pigments such as β- carotene and anthocyanins) is amenable to microbial bio-processing into varieties of fermented foods, beverages, fermented feeds (silage and single-cell protein) and ethanol with application of either solid state or submerged fermentation (Ray and Ward, 2006).

BIOPROCESSING: FOOD AND BEVERAGES Fermentation has advantages because it improves palatability, textural quality and upgrades nutritive value by enrichment with proteins (Ray and Ward, 2006). Unlike cassava, fewer fermented products are available from sweet potato. All fermented products arise

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through the use of naturally occurring microbial activities, generally believed to be a form of ‗spoilage‘. Spoilage forms that were ‗palatable‘ could be used to inoculate the next batch (Steinkraus, 1989). These primitive processes were eventually replaced with use of starter cultures. Humans have been fermenting foods from root crops for over 1000 years (Ray and Sivakumar, 2009), but it is only in the past 50-60 years that a real scientific understanding of these processes has been gained. Fermented foods and beverages from sweet potato are discussed below.

Sour Starch Starch is the prime component of interest for food and industrial uses of sweet potatoes. Sweet potato starch production in China has faced problems of slow sedimentation and poor separation of starch from some impurities, which produce off-colours in the final product. A traditional fermentation process (SmF) involving the addition of liquid fermentate from peas and beans (called sour liquid containing lactic acid bacteria [LAB]) at the separation stage speeds sedimentation and enhances separation and final product quality (Timmins et al., 1991). Sour liquid is used in enterprises with mechanized equipment. The microbiological composition of sweet potato dough and wet starch was examined. LAB were the principal group of microorganisms enumerated with counts of 1.0 x 106 CFU (colony forming units)/ml in the dough and 7.2 x 103 CFU/ml in the wet starch. A number of isolates were subsequently identified. A mixed population of Leuconostoc dextranicum and Lc. mesenteroides dominated the dough. The wet starch had a more varied population of homo- and hetero-fermentative lactobacilli, which included Lb. brevis, Lb. casei, Lb. acidophilus and Lb. buchneri (Timmins et al., 1991)

Sweet and Sour Flour The possibility of utilizing wheat- sweet potato composite flours in breads and other baked goods has been investigated (van Hal, 2000). Sweet potato flour can act as an important source of β-carotene. The most important quality characteristics of sweet potato flour are moisture content, protein, β-carotene content, microbiological quality, colour, taste and odour. Sweet potato bread has been commercialized on a limited scale in Peru and Japan. A commercial bakery in Peru uses the very simple method of mechanically grating peeled raw sweet potato roots and adding them to the dough, at 30% substitution for the wheat flour (Woolfe, 1992). This appears to be a cheap and practical solution for use in areas where fuel to dry sweet potato into flour is expensive or scarce and where it sun-drying is climatically difficult to achieve (van Hal, 2000). However, before applying this method, it should be ascertained that the baking process destroys trypsin inhibitors (Rekha and Padmaja, 2002), which may be present in the raw sweet potato (Sasikiran et al., 2002).

Gari Gari made from sweet potato has been investigated as a fermented food. In Ghana, Oduro et al. (2000) produced sweet potato gari. The method (a type of SSF) was quite similar to that

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of cassava gari production (Akingbala et al., 1993; Sanni, 1994; Sokari and Karibo, 1996; Osho and Dashiell, 2002). The product had moisture content (3.83%), protein (0.60%), crude fibres (3.5%), ash (1.42%), pH (3.97), titratable acidity (0.50%) and swelling capacity (3.05), which were within the recommended levels.

Lacto Pickles LAB influences the flavour of fermented foods in a variety of ways. In many cases, the most obvious change in lactic acid fermentation is the production of acid and lowering of pH which results in an increase in sourness. Since most of the acid produced in fermentations results from the metabolism of sugars, sweetness is likely decrease as sourness increases (McFeeters, 2004; Montet et al, 2006; Ray and Panda, 2007). Fermentation of vegetables can occur ―spontaneously‖ because of the natural lactic surface microflora, i.e., Lactobacillus spp., Leuconostoc spp., Pediococcus spp., etc; however, the use of a ―starter culture‖ provides consistency and reliability of performance (Molin, 2001), and Lactobacillus. plantarum is the ―starter‖ most frequently used in lactic fermentation of plant materials including sweet potato (Ray and Panda, 2007). β- Carotene (precursor of Vitamin A) and anthocyanin pigments are considered as antioxidants. These pigments have physiological attributes such as anti-cancer and protection against night blindness, aging and liver injury (Yoshimoto et al., 1999). As discussed in Chapter 1, some varieties of sweet potato contain these coloured pigments (Yamakawa, 1997). β- Carotene rich sweet potato roots were pickled by lactic fermentation (SmF) by brining the cut and blanched roots in common salt (NaCl, 2-10%) solution and subsequently inoculated with a probiotic strain of Lactobacillus plantarum MTCC 1407 culture for 28 days. The treatment with 8-10% brine solution was found to be the most acceptable organoleptically. The final product with 8 and 10% brine solutions had a pH of 2.9-3.0, titratable acidity of 2.9- 3.7g/kg, lactic acid of 2.6- 3.2g/kg, starch of 58-68g/kg and β- carotene of 163.0 mg/kg pickles on fresh weight basis (Panda et al., 2007). Like wise, anthocyanin pigment rich- sweet potato (clone ST-13) cubes were pickled by lactic fermentation by inoculating with the same bacterial strain and incubated for 28 days. The lacto- pickle had a pH (2.5-2.8), titratable acidity (1.5 – 1.7 g/ kg), lactic acid (1.0-1.3 g/ kg), starch (56-58 g /kg) and anthocyanin content (390 mg /kg) on pickle fresh weight basis. Principal component analyses reduced the eleven original analytical and proximate variables (pH, titratable acidity, lactic acid, starch, total sugar, anthocyanin, organic mater, ash, fat, protein and calories) of anthocyanin –rich pickle to three independent components (factors), which accounted for 91 % of the total variations (Panda et al., 2009b). Sensory evaluation rated both β- carotene and anthocyanin- rich sweet potato lacto-pickle acceptable based on texture, taste, aroma, flavour and after taste. The flow-chart for lactopickle production is given in Figure 1. Pickled sweet potato petioles have been commercialized in Japan. The petioles are preserved in soy sauce with the addition of little sugar, sesame seeds and chillies and vacuum sealed in plastic bags (Woolfe, 1992).

Bio-Processing of Sweet Potato into Food, Feed and Bio-Ethanol

Figure 1. Flow chart for preparation of sweet potato lacto- pickle (Source: Panda et al., 2009b).

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Sweet Potato Curd and Yogurt Curd and yoghurt, products of lactic acid fermentation of milk, are reported to possess several nutritional and dietary advantages over milk (Berger et al., 1979; Younus et al., 2002). For better enrichment of curd and yoghurt with dietary fibres, starch, minerals and vitamins, vegetables like French bean, lemon, soybean or sweet potato are commonly cofermented with milk (Holzapfel and Schillinger, 1992). While yoghurt is very popular in American and European countries, consumption of curd is very common among Asian people, especially in Indian Sub-continent (Sarkar et al., 1996; Younus et al., 2002). In curd much of the lactose in milk is converted to digestible lactic acid by LAB i.e. Lactobacillus bulgaricus, Streptococcus lactis, St. clemoris, St. thermophilus, etc (Masud et al., 1991; Heller, 2001). The starter culture for yoghurt is Lb. bulgaricus and Streptococcus thermophilus. Partial pre-digestion of protein in curd and yogurt may have beneficial effects for individuals with poor digestive capacity (Collins et al., 1991a, 1991b). A yoghurt like product, having a titratable acidity of 0.85%, was prepared from sweet potato puree, milk, sucrose and freezedried yoghurt inoculum (Collins et al., 1991a). On average, the product contained 19% protein, 3.8% ash, 2.5% dietary fibres, 80% moisture and 8.0-1.9% fat (Collins et al., 1991b). A trained panel gave a mean score of 7.7 (scale 1-10) for flavour, 3.9 (scale 1-5) for body/ texture and 3.8 for appearance and colour (scale 1-5). Similarly, sweet potato curd was prepared by fermenting boiled - carotene-rich sweet potato puree and cow milk with curd (starter) culture (Lactobacillus bulgaricus, Streptococcus lactis, St. diaceticlactis, etc.) (Ray et al., 2005). There were not much variation in pH (3.6-3.9), titratable acidity (10-11.8 g/ kg) and lactic acid (7.9-5.3 g/ kg) contents in curd consisting different concentration of sweet potato puree. However, curd with 12-16% sweet potato puree was most preferred by the consumers. The addition of sweet potato puree (12-16%) made the curd quite firm and imparted flavour, body/texture, minerals, nutrients, anti-diabetic substances, -carotene pigments (antioxidant), dietary fibres and starch (carbohydrate source). The lactic acid bacterial counts in the curd after 18h of fermentation having 8 and 16% sweet potato were 7x 107 and 14x 107 (CFU/ ml), respectively. The consumer evaluation scores ranged from 7-8 (in a hedonic scale of 1-9), from moderate liking to very much liking of the sweet potato curd, taking into consideration the sensory attributes such as colour, texture, flavour, sweetness, appearance, etc (Mohapatra et al., 2007). Similarly, sweet potato curd was prepared using anthocyanin pigments rich sweet potato (Panda et al., 2006). The flow-chart for preparing sweet potato curd is given in Figure 2.

Lacto- Juices Non-alcoholic beverages, from high β-carotene or anthocyanin-rich sweet potato cultivars, possessing a nutritional value comparable with fruit drinks have been formulated (Truong and Fementira, 1990; Baah et al., 2003). The colour of the beverage varied according to the flesh colour of the roots, ranging from yellow to orange or pinkish purple. A rice beverage was prepared by adding sweet potato or a mixture of barley sprouts and sweet potato (1:1). The amylase activity in the mixture with barley sprouts and sweet potato

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decreased more than that of the mixture with only sweet potato. The use of sweet potato resulted in an increase of sweetness, flavour and improved preference in rice beverage (Suh et al., 2003).

Figure 2. Flow-chart for preparation of sweet potato curd (Source: Panda et al., 2006).

For preparation of lacto-juice, fresh juice was fermented with LAB to produce lactojuice. Lacto-juices processed by lactic acid fermentation bring about a change in the beverage assortment for their high nutritive value, vitamins and minerals which are beneficial to human health when consumed (Rakin et al., 2004). Sweet potato roots (boiled and non-boiled) rich in β- carotene pigments were fermented with Lb. plantarum for 48 hour to make lacto-juice. During fermentation both analytical [pH, titratable acidity, lactic acid, starch, total sugar, reducing sugar (g/kg roots), total phenol and β-carotene (mg/kg roots)] and sensory (texture, taste, aroma, flavour and after taste) analyses of sweet potato lacto-juice were evaluated. The fermented juice was subjected to consumers‘ evaluation for acceptability. There were no significant variations in biochemical constituents (pH, 2.2-3.3; lactic acid, 1.19-1.27 g/kg root; titratable acidity, 1.23 - 1.46 g/kg root, etc) of lacto- juices prepared from non-boiled and fully-boiled sweet potato roots except β-carotene concentration [130 ± 7.5 mg/kg (fully-

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boiled roots) and 165± 8.1 mg/kg (non-boiled roots)]. The panellist evaluation scores ranged from 3 - 4.8 (in a hedonic scale of 1-5) from moderate liking to very much liking of sweet potato lacto-juice (Panda and Ray, 2007).The flow-chart for lacto-juice preparation is given in Figure 3. Likewise, lacto-juice was prepared from an anthocyanin-rich sweet potato clone (ST-13). The juice was rich in lactic acid (0.23- 0.37 g/100ml) and anthocyanin pigments (4570mg/100ml juice) (Panda et al., 2009a).

Figure 3. Flow-chart for preparation of sweet potato lacto- juice (Source: Panda et al., 2009a).

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Acidophilus Milk Acidophilus milk is a probiotic drink, which is a product of milk fermentation by the bacteria, Lactobacillus acidophilus. The fermented milk has been reported to have therapeutic value for suppressing toxin-producing organisms in the intestine of humans especially in infants (Perez and Tan, 2006). The acidophilus bacteria contained in milk are able to pass through the stomach and gain predominance in the intestine tract due to the presence of other types of bacteria. L. acidophilus is a lactose-fermenting bacterium that produces lactic acid as a major product of fermentation (Reed, 1982). It is known to have beneficial effects on the maintenance of normal intestinal microflora by producing inhibitors, stimulating the host immune system and reduction of serum cholesterol levels. It also helps in nutritional enhancement by reducing the levels of toxic substances (Ray and Panda, 2007). Acidophilus milk enriched with purees from anthocyanin rich sweet potato varieties (―kinampay‖ and RC 2000) was developed. Addition of sweet potato puree to the acidophilus milk improved the sensory qualities and nutritional values (Perez and Tan, 2006). The flow-chart for production of acidophilus milk enriched with sweet potato puree is given in Figure 4.

Figure 4. Flowchart for production of acidophilus milk using sweet potato purees (Source: Perez and Tan, 2006).

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Soy Sauce Soy sauce, a popular condiment used every day with Asian dishes is traditionally prepared from a mixture of soybeans and wheat, fermented by moulds, especially Aspergillus   oryzae or A.sojae, to give a dark brown salty liquid used as a flavouring agent. The potential replacement of wheat flour with suitable substitutes in soy sauce manufacture, as in the case of bread, could mean a considerable utilization of available resources such as sweet potato flour (Data et al., 1986). The flow -chart for production of soy sauce using sweet potato flour is given in Figure 5. Sweet potato flour (1kg)

Soybean (1kg)

Roast until light brown in colour

Soak overnight

Cook by steaming for 3h or pressure cook for 1.5-2h

Mix Spread on trays Mix with starter of [Aspregillus; (A. oryzae or A. sojae )] spores Incubate for 4-5 days at room “Koji” with heavy growth of Aspregillus spores

Transfer to plastic container. Add 0.925g of slat and 3.55 l if water Incubate at room temperature for 3 months or more (3×) Press and strain to extract sauce liquor Add molasses to increase colour and viscosity

Pasturize at 80°C for 30 min Bottle

Soy sauce

Figure 5. Flow chart for production of soy sauce using sweet potato flour (Source: Data et al., 1986).

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The starter culture was prepared by inoculating pressure-cooked rice with A. oryzae or A. sojae at room temperature for 4-6 days. During the subsequent koji preparation the healthiest growth of mould spores and finally the highest yield of sauce were given by sweet potato flour made from cooked rather than raw roots because cooking gelatinized the sweet potato starch thus rendering it more vulnerable for breakdown by microorganisms. Sensory evaluation revealed no significant difference between the soy sauce made with sweet potato flour and two commercial brand of soy sauce from Philippines in terms of colour, aroma, consistency, flavour and overall acceptability.

Vinegar Vinegar is a condiment made from sugar- or starch-containing materials by an alcoholic fermentation, followed by the microbial oxidation of alcohol to acetic acid. When starchbased material such as sweet potato is used as raw material, the starch requires initial hydrolysis to sugars before alcoholic fermentation by yeasts (Saccharomyces cerevisiae) can take place. The next step, oxidation of the alcohol to acetic acid is carried out by acetic acid bacteria (Acetobacter spp.). The completed vinegar must contain a minimum of 4 g acetic acid/100 ml (Ward, 1989). Recently, new red vinegar has been developed in Japan via fermentation with the storage root of purple fleshed sweet potato cv. Ayamurasaki. The red vinegar had a higher antioxidant activity than white or black vinegars. The red vinegars contained some new components possibly derived from the original purple sweet potato. A major component was isolated using preparative HPLC (High Performance Liquid Chromatography) and the chemical structure was determined to be 6-O-(E) –caffeoyl- (2-O-ß-d- glucopyranosyl) - α-dgkucopyranose (caffeoylsophorose) by MS (mass spectroscopy) and NMR (nuclear magnetic resonance). Because the caffeoylsophorose showed a high antioxidant activity, it plays an important functional role in red vinegar as do anthocyanins and other components (Terahara et al., 2003).

Alcoholic Beverages Shochu Shochu is an alcoholic beverage of Japan, most commonly distilled from barley, sweet potato or rice. Typically it is 25% alcohol by volume, making it weaker than whisky, but stronger than wine and sake (Yamakawa, 2000). The production of koji, a heavy inoculum of Aspergillus kawachii or A. niger on steamed rice provides a source of enzymes which hydrolyze sweet potato starch to sugar. A. niger also produces citric acid (Bindumole et al., 2000) in the first maromi (seed mash), which leaves the pH to 3.2-3.4 and thus inhibits the growth of undesirable microorganisms. Fresh and unpeeled sweet potato is trimmed, washed, steamed and crushed and added (4:1) to the maromi. During fermentation of this main mash, simultaneous starch conversion to sugar by the koji enzymes and fermentation of sugar to alcohol by the yeast S. cerevisiae takes place. The final alcohol concentration of the mash is 13-15%. The mash is then pumped to the still and the alcohol is distilled off. Different

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batches of shochu may be blended to give a uniform product and the alcohol content is adjusted to 20-40% (v/v) before bottling (Woolfe, 1992).

Figure 6. Flow chart for preparation of shochu (Source: Woolfe, 1992).

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Wine and Beer Wine and beer are the other products which can be processed from coloured (anthocyanin or β-carotene) sweet potato cultivars (Yamakawa, 1997) Yellow, red and black coloured beverages (sparkling liquor) are sold in the Kyushu Province in Japan (Yamakawa, 1997, 2000). A process of enzymatically saccharifying the sweet potato pulp (starch) and fermenting the mash into wine using wine yeast Saccharomyces cerevisiae has been developed at the Regional Centre, CTCRI, India. The wine prepared from an anthocyanin sweet potato clone (ST -14) is bright red in colour and is similar to fruit wines. Patents applications have been filed for the biotechnological processes developed for the preparation of red wine from sweet potato (CTCRI, 2003).

BIOPROCESSING: PROTEIN ENRICHED ANIMAL FEED Bearing in mind the increased level of ruminant and poultry farming and the lack of a corresponding increase in feed production, the importance of microbial sources of feed that are rich in protein has been in demand. Methods for the bioconversion of crop and crop residues into microbial feed rich in protein have been developed (Sriroth et al., 2000; Ray et al., 2006).

Silage Ensiling or silage making is an age-old technique of solid or semi-solid state fermentation for the conservation of nutrients in green fodder grasses through fermentation and storing them for round-the-year feeding of animals (Limon, 1991). Production of good quality silage depends upon the rapid fermentation, under anaerobic conditions, of silage raw material carbohydrates to increase acidity and lower the pH to the point at which further microbial activity ceases thus preventing putrefaction and preserving nutrients (McDonald et al., 1991; Nsereko and Rooke, 1999). Sweet potato tops, especially leaves, are very rich in nutrients such as proteins, vitamins and minerals (Woolfe, 1992; Otieno et al., 2006). They also contain polyphenols, in particular, chlorogenic and isochlorogenic acids, which are anti-oxidants (Yamakawa, 2000; Yoshimoto, chapter 3 in this book). One of the constraints in the use of the large quantities of sweet potato foliage for forage is that its availability is concentrated into one or two seasons of the year after harvest, which in general does not coincide with pasture scarcity (Tewe et al., 1998). Preservation as hay (dehydration) or silage may therefore be needed. The latter method is more practical in the humid tropics where quick drying in the field is not possible. Simple small silos can be made with discarded gunny bags, polyethylene sugar bags and related materials, all of which can be afforded by rural farmers in the tropics (CIP, 2000; Giang et al., 2004). The production of silage from sweet potato vines and roots has been studied in China (Zhang, 1995), Japan and the Philippines (Woolfe, 1992; Mariscal et al., 1997)) and more recently in Vietnam and Kenya (CIP, 2000; Aregheore, 2004; Die Peters, chapter 9 in this book). Some of these studies were carried out in relation to the feeding of small ruminants

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such as goats, sheep and pigs, rather than cattle, but their findings may conveniently be discussed in this section. In Japan, the addition of inorganic acids (hydrochloric and sulphuric acid in the ratio of 19:1), mashed sweet potato roots or molasses produced vine silage with high lactic acid and no butyric acid content. Silage of excellent fermentative quality was obtained from sweet potato foliage when no additives such as urea or sweet potato roots were used (CIP, 2000). The addition of sweet potato roots had no noticeable effect on dry matter losses or lactic acid production, but increased acetic and butyric acid concentrations. The vine silage without additives, on the other hand, had acceptable characteristics with an average pH of 3.9, a low concentration of butyric acid and a low (11%) loss of dry matter by putrefaction (Tewe et al., 1998; Tinh et al., 2000).

Single -Cell Protein (SCP) Single cell protein (SCP) is produced from many different microbial types, including algae, yeasts, filamentous fungi and bacteria. The most important organisms participating in the protein enrichment of agricultural wastes are fungi, yeasts and bacteria which convert some of the carbon rich fractions of these wastes into microbial protein. Thus the major substrates for these organisms are typically the different types of carbohydrates available in the wastes (Ward et al., 2008). Large volumes of solid wastes produced from starch processing of sweet potato are suitable substrates for SCP production through SSF. Thus, microbial fermentation results in quick growth of selected microorganisms which are rich in protein and the dried biomass of the end product is referred to, some what incorrectly, as single cell protein (SCP) (Anupama and Ravindra, 2000). Sweet potato wastes (bagassae) are a good candidate for SCP because of its abundant supply in several countries like China, Taiwan, and Japan at reasonable cost. The bagassae contains 2.32% protein and 65.4% total carbohydrates and is itself not a good source of protein for animal feeding (Ray et al., 2006). Fermented sweet potato feed stuffs are reported to be produced and utilized for livestock in China (Jiang et al., 1993) and in Korea (Ahn et al., 1997). Yeasts such as Candida utilis, Pichia burtonii and Saccharomyces spp. are used for SCP production from sweet potato (Yang, 1992; Yang et al., 1993). Sweet potato bagassae was treated with Endomycopsis fibuligera, Candida utilis and Trichoderma koningii via SSF. The protein content of bagassae was found to increase by 26.9% and its cellulose content decreased by 36.16%. The converted sweet potato bagassae was treated as a pig feed and was found to stimulate appetite, and promote growth. Sweet potato distillery wastes are enriched with yeast protein and the feed is utilized for red carp (Cyprinus carpiol) (Mokolensang et al., 2003). Yeast strains did not produce any fungal toxin (Tian, 2006). Therefore, the protein enrichment of sweet potato bagassae with yeast strains by SSF for animal feeds appears to have commercial potential. Microbial cells (Geotrichum sp.) are applied for dehydration of the distilled waste of sweet potato shochu (Yoshi et al., 2001) and the dried product can be used as SCP.

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BIOPROCESSING: FOOD AND FEED ADDITIVES AND BIO-ETHANOL Microbial Enzymes The production of microbial enzymes is an important and rapidly growing industry in many parts of the world. The enzymes produced find a wide range of applications in the food industry, including the hydrolysis of starch in mashes for alcoholic fermentation, clarification of beers and fruit juices, in the manufacture of glucose and fructose syrups, de-hiding of leather. Root crops as a whole, starch, flour or residues in particular could be used as cheap fermentation substrates for the production of microbial enzymes (Pandey et al., 2000; Ray, et al., 2006). Sweet potato bagassae (moisture content, 50-58%; pH, 3.5- 4.33) was used as substrate for protease production by amylolytic fungi in SSF. Several strains of Aspergillus, Rhizopus, Actinomucor and Mucor were tested. Aspergillus and Rhizopus spp. Showed higher proteinase activity than Mucor spp. (Yang and Huang, 1994). In another study, protease was produced using sweet potato supplemented with rice bran and minerals as substrate in SSF. Partially purified protease with DEAE (Diethyl amino ethyl) cellulose- Sephacel column chromatography was thermally stable and was able to retain 80-100% of activity in pH 4.05.5 at 500C for 40 min (Yang and Chiu, 1986).

Organic Acids Lactic and citric acid are important as food additives in the food and non-food industries. They are produced on an industrial scale either by microbial fermentations or by chemical synthesis. In recent years, the fermentation approach has become more prominent because of the increasing market demand for naturally produced lactic acid (Ray et al., 2006). Lactic acid could be produced by Lactobacillus sp. from potato and sweet potato flour (Ray et al., 1991). In a recent study, the production of lactic acid was increased 2.5 fold over the conventional method by applying the response surface methodology (statistical design) and using the amylolytic lactic acid bacterium, Lactobacillus plantarum as the microbial culture and sweet potato flour as the carbohydrate source in SmF (Panda and Ray, 2008). Sweet potato has been used a substrate for citric acid production using Aspergillus niger in SSF (Bindumole et al., 2000). Leangon et al. (1999) studied the biochemical mechanism of citric acid accumulation during SSF of sweet potato using a low citrate-producing mutant of A. niger Yang No. 2. It was found that over production of citric acid in SSF was related to an increased glucose flux through glycolysis. At low glucose fluxes, oxalic acid is accumulated. When the process was operated in a packed-bed reactor in SmF, the bed loading, airflow rate and substrate particle sizes were the important operational parameters. However, yield was extremely low, 0.82 g citrate/ kg sweet potato (Lu et al, 1995, 1997; Zheng et al., 1999). Several countries, notably China, Japan and Vietnam, are now manufacturing citric acid from sweet potato starch or from its by-products (Jiang et al., 1993; Zhang, 1995; Lu et al., 2006).

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The process necessitates the initial breakdown of starch to sugars before these sugars are fermented by moulds, for example, Aspergillus niger, to citric acid. In Sichuan Province, China, the largest sweet potato growing area of the country, citric acid is the fourth most important product from sweet potato after starch, noodles and alcohol (Wiersema et al., 1989; Jiang et al., 1993). In the food industry, citric acid is added as a flavour enhancer or preservative in a wide ranges of products particularly soft drinks. In Japan, a drink consisting of a mixture of citric acid from sweet potato and ascorbic acid crystals, which is added to water to taste, has been commercialized (Woolfe, 1992).

Monosodium Glutamate (MSG) MSG is an important flavour enhancer of a wide range of savoury foods. China is the largest producer and consumer of MSG in the world (Bovell- Benzamin, 2007). The starch has first to be degraded to sugars, which are then converted by microorganisms such as Brevibacterium glutamicum to glutamic acid. This is then converted to MSG salt (Jiang et al., 1993). China uses sweet potato starch as one of the raw materials for production of MSG. In Siachuan Province in China, it is the fifth most important product from sweet potato, almost equal in tonnage to citric acid.

Sugar Syrups The conversion of starch into a range of syrups and other derivatives is becoming increasingly important in some countries where these products can be used to replace more expensive imported sugar extracted from cane or beet. These conversions employ are based on microbial enzymes and can utilize starch sources including sweet potato and cassava, which may be particularly appropriate as they are highly susceptible to saccharification by enzymes (Paolucci et al., 2000). Though starch can be converted into sugars by the use of acids, this method is rapidly giving way to the use of immobilized bacterial enzymes (Zanin and de Morase, 1998), the specific properties of which give rise to a variety of compounds useful in the dessert, bread, fermented milk products, brewing and other industries. Glucose syrup, for example, is produced from starches, including sweet potato starch (Ray and Ward, 2006) by bacterial amylase. However, it has only 70% of the sweetness of sucrose. The partial conversion of glucose into its isomer fructose by bacterial glucose isomerase to give high fructose syrup, or isoglucose, as it is also known, gave rise to a substance with much greater sweetness than sucrose. Isoglucose (which contains at least 42% fructose) has become an important replacement for sucrose in several areas of the food industry where it can be used in lower concentration than sucrose to provide the same sweetness, hence reducing the energy (calorie) content of the food. Another sugar, maltose is produced from starch by the action of β- amylase (Fontana et al., 2001) is useful to the brewing industry.

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Baker's Yeast and other Products To identify improved baker‘s yeast for industrial manufacture of bakery products, yeasts (S. cerevisiae) strains from dried sweet potatoes (hoshi-imo), a traditional preserved food in Japan were isolated and characterized (Nishida et al., 2004). The strain ONY1 had characteristics typical of commercial baker‘s yeast strain (T128). Sweet potato served as the substrate for production of oxytetracycline in SSF (Yang and Yuan, 1990). Attempts have been made to produce microbial hydrogen from sweet potato starch residue (Yokoi et al., 2001).

Alkali Metal Glucoheptonate The alkali metal glucoheptanate is used as water conditioning chelant and the proteincontaining pulp residue as animal food. Alkali metal glucoheptonate has been produced from sweet potato by reducing the size of sweet potatoes to particles to about 1/40cm and slurrying the sweet potato particles. Then, commercial α-amylase is added to the slurry. The slurry was boiled and filtered to separate liquid syrup and a protein-containing pulp residue. The liquid syrup was cooled down and glucoamylase added before boiling again. Subsequently, an alkali metal cyanide was added to the liquid syrup to produce the alkali metal glucoheptanate (www.freepatentsonline.com/5435845.html).

Chitosan Large amounts of waste water containing high concentration of organic matter are produced during distillation of shochu. Fungal treatment of these distillery effluents for production of chitosan was investigated (Yokoi et al., 1998). Absidia atrospora and Gongronella butleri grew well in shochu distillery waste water and sweet potato shochu waste water. Chitosan production was highest from G. butleri strain. Nitar and Stevens (2002) have described an improved method for production of chitosan from mycelia of the fungus G. butleri USDB 0201 by SSF of sweet potato. The chitosan was extracted with NaOH and acetic acid. The resulting extract was clarified using a heat stable commercial α- amylase. The yield (4-6g/100g mycelia) of chitosan increased with increasing duration of fungal growth up to 6th day.

Bio-Ethanol Cane and beet molasses are the first choice for bio-ethanol production all over the world (Ward and Singh, 2002); however, the gap between the demand and supply of molasses has been widened recently world over (Chandel et al., 2007). Hence, demand for alternative sources of energy for bio-ethanol production from diverse raw materials has increased (Ward et al., 2006) including starch from root crops (Ray and Ward, 2006). Ethanol is an ideal fuel supplement or substitute for petrol, and starch from sweet potato can produce 400- 450 litres

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(ethanol)/ton of starch (equivalent to 160-180 litre. ethanol/tonne of raw sweet potato roots) (Ray and Naskar, 2008). Ethanol production potential of sweet potato is nearly 40% higher than other starchy crops such as Jerusalem artichoke (Helianthus tuberosus L.), potato (Solanum tuberosum L.), sugar beet (Beta vulgaris L.), sweet sorghum [Sorghum bicolor (L.) and Fodder beet (Beta vulgaris L.) (Mays et al., 1990). However, the basic processes in the production of ethanol from sweet potato are somewhat cumbersome as compared to molasses, because of the requirement to hydrolyse the starch and include the following processes:     

Milling sweet potato chips or flour through sieve of 0.4 mm. Liquefaction (using dilute inorganic acid or thermostable α-amylase). Saccharification (using amyloglucosidase). Fermentation, and Distillation

The manufacture of ethanol from sweet potato for human consumption as well as fuel, for chemical and pharmaceutical purposes is already established, especially in countries such as China, Japan and Korea. In China, ethanol is the most important product after starch and noodles; in Korea, however, ethanol production has been steadily rising, and in the 2000s represented more than 30% of total production, compared to only about 8% in the case of starch (Scott et al., 2000). Japan uses only 6-8% of its production for ethanol (Yamakawa, 2000) and in India, technology has been standardized for ethanol production from sweet potato flour and roots (Ray and Naskar, 2008) but the process is yet to be commercialized. Sweet potato chips or flour is commonly utilized for ethanol production. The process followed is similar to that for cassava: adding water to the dried chips and boiling, adding enzymes to convert starch to sugar, fermenting the sugar to alcohol and distilling (Wiersema et al., 1989; Reddy and Basappa, 1997; Ray and Naskar, 2008). Various factors, i.e. acid or enzyme concentration, temperature, pH of the mash, fermentation period, cell immobilization, etc were studied on ethanol fermentation from sweet potato in membrane reactors (Azhar and Hamdy, 1981; Yu et al., 1996). One of the process developments made for enzymatic hydrolysis of various starch-containing crops and biomass is the introduction of simultaneous saccharification and fermentation process (Ward et al., 2006). This process employs thermotolerant yeast strains to reduce the number of reactors involved by eliminating the separate (saccharification) reactor. In a recent study, ethanol yield of 258g/kg flour and 95g/kg roots of sweet potato was obtained by applying simultaneous saccharification and fermentation technology employing thermotolerant (≤ 400C) yeast (S. cerevisiae CTCRI 10) strain (Ray and Naskar, 2008).The process partially reduces the production cost as saccharification and fermentation process have been combined. However, the cost (US$) of ethanol production/litre is still higher (0.72) as compared to sugar cane (0.27) and cassava (0.55) (Mohanty et al., 2008). The other approach to make sweet potato ethanol cost effective is to genetically engineer the crop to increase significantly the starch content and consequently conversion to ethanol. Starch is chemically composed of two types of glucan polymers- amylase and amylopectin. The ADP glucose is the precursor for synthesis of both amylase and amylopectin. Therefore, the regulation of ADP glucose pyrophosphorylase (ADPGase) would determine the sink strength (capacity to accumulate photosynthesis products) of the roots in potato, sweet potato

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and other root crops and its over-expression would produce roots with higher starch content. Transgenic potato expressing Escherichia coli glg 16 gene coding the bacterial ADPGase showed remarkably high starch content (60% more than the normal) in tubers (Stark et al., 1992). Researchers of North Carolina State University (USA) are re-engineering sweet potato to make it better suited for producing ethanol. By incorporating genes from bacteria from deep sea thermal vents, the group is studying to create an industrial sweet potato with double the starch content and enriched with liquefying and saccharifying enzymes, i.e. α-amylases and amyloglucosidase. They propose that the special genes incorporated could reduce the costs of the enzymes those are used by biofuel processors to breakdown starch to sugars which are then converted to alcohol by fermentation (http://domesticfuel.com/2007/11/30 /sweet-potato-fuel/).

CONCLUSION AND FUTURE PERSPECTIVES Root crops such as sweet potato for human consumption have limited growth potential as rice and wheat remains the preferred food in most of the world. Value addition of sweet potato by bioprocessing has the potential to lead to newer food, feed and beverage products and contribute to biofuel production. Newer foods include anthocyanin-rich sweet potato wine and vinegar, β- carotene rich lacto-pickle and lacto-juice which have potential functional and nutraceutical properties. The study of fermentation microorganisms could lead to the identification of microbial strains particularly suited for the over-secretion of valuable biological products such as enzymes, amino acids, vitamins, antibiotics and flavour enhancers such as monosodium glutamate. Among the bio-derived products, bio- ethanol from sweet potato has the potential to contribute to the demand for biofuels. However, research is needed to develop improved fermentation processes such as combined liquefaction-saccharificationfermentation by application of process engineering and biotechnology, and genetically engineering the crop with high starch content and self-processing genetic attributes to reduce the cost of ethanol production to compete successfully with sugarcane, sugar beet or other cheaper substrates.

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and Industrial Resources, Twelfth Symposium of International Society of Tropical Root Crops (ISTRC), 10-16 Sept., Tsukuba, Japan, Nakatani, M. and Komaki, K. pp. 8-13. Yang, S.-S. (1992). Utilization of agricultural wastes with solid -state fermentation. In: S.T.Chang, M.H.Wong, P.K. Wong and Y.S.Wong (Eds.), Commercial Press, Hong Kong, pp. 21-30. Yang, S.S. and Chiu, W.F. (1986). Protease production with sweet potato rewsidues by solid state fermentation. www.ncbi.ncm.nih.gov/entrez/guery. Yang, S.S. and Huang, C.I. (1994). Protease production by amylolytic fungi in solid state fermentation. J. Chinese Agric. Chem. Soc. 32: 589- 601. Yang, S.-S. and Yuan, S.S.(1990). Oxytetracycline production by Streptomyces rimosus in solid state fermentation of sweet potato residue. World J. Microbiol. Biotechnol. 6: 236244. Yang, S.-S., Jang, H.-D., Liew, C.-M. and Du Preez, J.C. (1993). Protein enrichment of sweet potato residues by solid -state cultivation with mono-and co-cultures of amylolytic fungi. World J. Microbiol. Biotechnol. 9: 258- 264. Yokoi, H., Aratake, T., Nishio, S., Horose, J., Hayashi, S. and Takasaki, Y. (1998). Chitosan production from sochu distillery waste water by fungi. J. Fermen. Bioeng. 85: 246- 249. Yokoi, H., Sitsu, A., Uchida, A., Hirose, J., Hayashi, S. and Takasaki, Y. (2001). Microbial hydrogen production from sweet potato starch residue. J. Biosci. Bioeng. 9: 58- 63. Yoshi, H., Furuta, T., Ikeda, M., Ito, T., Iefuji, H. and Linko, P. (2001). Characterization of the cellulose-binding ability of Geotrichum sp. MIII cells and its application to dehydration of the distilled waste of sweet potato shochu. Biosci. Biotechnol. Biochem. 65(10): 2187- 2199. Yoshimoto, M. (1997). Sweet potatoes as a multifunctional food. In: Proceedings of the International Workshop on Sweet potato Production System toward the 21st Century, Dec 9-10, 1997, Miyakonojo, Miyazaki, Japan, pp. 273-283. Yoshimoto, M., Okuno, S., Yoshinaga, M., Yamaguchi, M. and Yamada, J. (1999). Antimutagenicity of sweet potato (Ipomoea batatas) roots. Biosci. Biotechnol. Biochem. 63:537-541. Younus, S., Masud, T. and Aziz, T. (2002). Quality evaluation of market yoghurt/ dahi. J Pakistan Nutr 1: 226-230. Yu, B., Zhang, F., Zheng, Y. and Wang, P. (1996). Alcohol fermentation from the mash of dried sweet potato with its dregs using immobilized yeast. Process Biochem 31: 1-6. Zanin, G.M. and de Moraes, F.F. (1998). Thermal stability and energy of deactivation of free and immobilized amyloglucosidase in the saccharification of liquefied cassava starch. Appl. Biochem. Biotechnol. 70-72: 383- 394. Zhang, L.M. (1995). The present situation of sweet potato production and processing in Shandong Province, China. Paper presented at SAPPRAD workshop on sweet potato processing, Jinan, 20-24 November, 1995, Shandong, China, 7p. Zheng- Yoguo, Wang- Zhao and Chen- Xiaolong (1999). Citric acid production from the mash of dried sweet potato with its dregs by Aspergillus niger in an external-loop airlift bioreactor. Process Biochem. 35: 237- 242. Zheng, Z. and Shetty, K. (1998a) Solid-state production of beneficial fungi on apple processing wastes using glucosamine as the indicator of growth. J. Agric. Food Chem. 46: 783- 787.

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Zheng, Z. and Shetty, K. (1998b) Cranberry processing waste for solid state fungal inoculant production. Process Biochem. 33: 323- 329. Zheng, Z. and Shetty, K. (1999) Solid-state fermentation and value- added utilization of fruit and vegetable processing by-products. In: F.J. Francis (Ed.), Encyclopedia of Food Science and Technology, 2nd edn., Wiley Publishers, New York, USA, pp. 2165- 2174.

WEBSITES http://domesticfuel.com/2007/11/30/sweet-potato-fuel/ www.freepatentsonline.com/5435845.html

In: Sweet Potato: Post Harvest Aspects in Food Editors: R. C. Ray and K. I. Tomlins

ISBN 978-1-60876-343-6 © 2010 Nova Science Publishers, Inc.

Chapter 7

SWEET POTATO UTILIZATION IN HUMAN HEALTH, INDUSTRY AND ANIMAL FEED SYSTEMS Adelia C. Bovell-Benjamin Team Lead, Food Processing and Product Development Team Tuskegee University NASA Center for Food and Environmental Systems for Human Exploration of Space (CFESH) Department of Food and Nutritional Sciences Room 300-A Campbell Hall ,Tuskegee University

ABSTRACT Sweet potato (Ipomoea batatas [L.] Lam) is an important root crop in most developing countries, which has not realized its full potential as a mainstream food in human and animal systems. The overall objective of the paper was to review the utilization of sweet potato in human health, industry and animal feed systems. Specifically, the paper summarized the biochemical, bioactive and functional properties of sweet potato; described the potential role of sweet potato in human health; highlighted industrial utilization and emerging applications of sweet potato, with emphasis on sweet potato starch and described the literature regarding the potential usefulness of sweet potato in animal feed systems. A combination of complementary strategies was used to collect information for the review including a systematic review of scientific, government and industry databases. The biochemical, nutritional, bioactive and functional properties of sweet potato make it a potentially good candidate for reducing the global food insecurity, vitamin A deficiency and improving nutritional status worldwide. The sweet potato has antidiabetic properties, that is, the capability to lower blood glucose level and improve glucose tolerance. White-skinned sweet potatoes have antioxidative, radical scavenging and antimutagenic properties and have been associated with reduced liver injury and blood pressure lowering activity. The stems and leaves of sweet potato contain potentially bioactive phytochemicals including chlorogenic acids, which have been shown to improve glucose tolerance in humans and high amounts of polyphenolics, which are protective against diseases linked to oxidation such as cancer and 

Phone: (334)727-8717; Fax: (334)727-8493 ; E-mail: [email protected]

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cardiovascular disease. Sweet potato starch has industrial applications such as sweeteners, citric acid, beverage, noodle production, industrial alcohol, ethanol, fuel and derived products as maltose. In animal feed systems, sweet potato leaves can be used as a protein source for growing pigs, goats, and chickens and for improving ruminant urea utilization. Sweet potato could become a more economically competitive source for use in human health, industry and animal feed systems, and can play a major role as a renewable energy source in the future.

INTRODUCTION Sweet potato (Ipomoea batatas [L.] Lam) is an important root crop in most developing and some developed countries. Over 95% of the global sweet potato crop is produced in developing countries, where it is the most widely grown root crop (Table 1). In the United States (U.S.), the sweet potato is usually called ‗yam‘ although it is distantly related to the true yam (Dioscorea spp.). The sweet potato is a dicotyledonous plant belonging to the family Convolvulaceae, which consists of roughly 50 genera and over a thousand species. I. batatas is the only member of this family with edible roots, which are valuable food sources in human and animal systems (Purseglove, 1991; Woolfe, 1992). All sweet potato cultivars are moreor-less sweet-flavored. The roots of the sweet potato are usually long and conical, with skin color ranging between red, light pink, purple, brown or white, while the flesh could be white, yellow, orange or purple (Figure 1). Some cultivars of I. batatas are grown as ornamental plants. Table 1. Selected sweet potato indicators from different regions of the world Region

Production/ 1,000 tons

Rank vs. 20 other major foods

Utilization 1994-1996 Food Feed

Consumption 1994-1996 kg/capita/y

117,848 2,013 1,675 1,159 1,140

2 5 3 16 4

46 88 85 95 72

49 2 10 0 6

44 9 20 1 7

1,188 967

3 2

85 94

0 0

85 16

655

10

50

40

2

EUROPE Portugal

23

9

21 71

1

U.S.A

604

12

90 3

2

ASIA China Indonesia Vietnam India Japan AFRICA Uganda Rwanda LATIN AMERICA Brazil

FAOSTAT, 2008.

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The sweet potato is native to the tropical parts of the Americas and is one of the oldest root vegetable known to humans. Historically, sweet potato has always been used as a food security or famine item in times of food crises in many countries. Notable examples are: (i) in Japan when typhoons destroyed the rice fields; (ii) in China when famine beleaguered the country in the 1960s; and (iii) in Uganda when virus devastated the cassava crop. However, its uses have diversified considerably in developing countries. Throughout the world, different sweet potato cultivars are grown, with specific cultivars being unique to particular countries and regions. For example, in the U.S., producers tend to grow only one or two major cultivars for regional and national markets, but may grow several cultivars in small amounts for local markets. The two cultivars, which account for most of the current U.S. acreage, are 'Jewel' and ‗Beauregard‘. North Carolina produces the most sweet potatoes in the U.S., roughly 40% of the nation‘s annual production (http://www.answers.com/topic). The state of Mississippi in the U.S., another major sweet potato producer, cultivates roughly 8,200 acres. Sweet potatoes contribute approximately $19 million dollars annually to the state‘s economy (http://www.answers.com/topic). Although sweet potato is among the world‘s most important versatile crop, it has not realized its full potential as a mainstream food in human and animal systems. Some reasons advanced by Vinning (2003) for this under-exploitation of the sweet potato are: (i) it is often grown by small farmers on marginal soils with limited outputs; and (ii) its production is often concentrated in countries with lower per capita incomes. The per capita consumption of sweet potato worldwide is shown in Table 1. The per capita sweet potato consumption in Canada, Europe and Australia is extremely limited and is often restricted to migrant populations (CIP, 1999). Roughly 133,865 million tons of sweet potatoes are produced globally each year (Table 1). Asia is the largest sweet potato producing region followed by Africa, Latin America, Europe and the U.S. China accounts for 90% of all sweet potatoes produced in Asia and an estimated 82% of total world sweet potato production (Table1; FAOSTAT, 2008).

OBJECTIVES AND METHODOLOGY Overall •

To review the utilization of the sweet potato in human health, animal feed systems and industry

Specific • • • •

To summarize the biochemical, bioactive and functional properties of sweet potato; To describe the potential role of sweet potato in human health; To highlight industrial utilization and emerging applications of sweet potato, with emphasis on sweet potato starch; and To highlight the literature regarding the potential usefulness of sweet potato in animal feed systems.

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Methodology A combination of complementary strategies was used to collect information for the review including: a systematic review of scientific, government, and industry sources for information; computerized scientific literature databases (for example, Medline, Social Science Citation Index, Science Direct, etc.); and reviewing government and international organizations publications and databases through the Internet (for example, statistical abstracts, census data and International Potato Center).

USES, BIOCHEMICAL, BIOACTIVE AND FUNCTIONAL PROPERTIES OF SWEET POTATO In the U.S., sweet potatoes are most commonly used in pies and other sweet dishes during the holiday season such as Thanksgiving and Christmas and other festival times. Sweet potato is consumed daily by 66 and 33% of the rural and urban population, respectively, in Papua New Guinea (Sawer, 2001). In parts of West, Central and East Africa, sweet potato is an important source of calories, and is consumed by people of all age groups (Hagenimana et al., 1998). Some examples of the traditional utilization of sweet potatoes around the world include boiling, steaming, baking, canning, drying and milling or frying, incorporating into porridge and eating with stews (Woolfe, 1992). Carver's sweet potato inventions contains 73 dyes, 17 wood fillers, 14 candies, 5 library pastes, 5 breakfast foods, 4 starches, 4 flours and 3 molasses (Carver, 1936) (Table 2). However, sweet potatoes can be utilized in many other ways either as intermediate or bulk ingredients in recipes or as complete value-added products. For example, cooked, mashed sweet potatoes can be used to replace some of the wheat flour in breads, cakes, muffins and cookie recipes. Sweet potato syrup can be processed into starch, noodles, candy, desserts, and flour. In some countries roots are processed to produce starch and fermented to make alcohol. Figure 1 shows some value-added sweet potato products. Furthermore, sweet potato flour can serve as an alternative for individuals diagnosed with celiac disease, or with allergies to the gluten in wheat (van Hall, 2000). Most of the commonly eaten cereals such as wheat contain gluten, a protein to which a high number of individuals are allergic. Celiac disease affects the small intestines due to sensitivity to gluten present in certain cereals including wheat, wheat starch, rye, barley, triticale, and probably oats, and the only effective treatment is strict adherence to a 100% gluten-free diet for life (Caperuto et al., 2000). The uses and potential uses of sweet potato in human nutrition have been discussed extensively elsewhere by Bovell-Benjamin (2007). However, it should be noted that although the roots are usually eaten, young leaves and the tips of vines have also been utilized in human and animal feed systems. The nutritional value of sweet potato is shown in Table 3 and has been discussed extensively elsewhere by Bovell-Benjamin (2007). Overall, most varieties of sweet potato are good sources of vitamins C and E, anthocyanins, dietary fiber, potassium and other minerals. Sweet potatoes are low-fat foods. Orange-, red- and purple-fleshed sweet potatoes are rich sources of β-carotene, the vitamin A precursor and anthocyanins. The leaves, which are eaten

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as a green vegetable in some countries, are rich sources of protein, β-carotene, the B vitamins and ascorbic acid (Figure 2).  

Table 2. List of some value-added products made from sweet potato by George Washington Carver   Food Products

 

Non-Food Products

Flour

Stains

Starch

Dyes

Sugar

Paints

Molasses

Medicine

Mock coconut

Library Paste

Tapioca

Alcohol

Vinegar

Rubber Compound

Egg yolk

Writing Ink

Candy, 14 varieties

Shoe Blacking

Chocolate

Fillers for Wood

Dried Potatoes #1 and #2

Synthetic Cotton

Dry Paste

Synthetic Silk

Potato Nibs

Paper (from vines)

Bisque Powder Breakfast Food Meal After Dinner Mints Yeast Coffee, dry Instant Coffee Granulated Potatoes Lemon Drops

  Sweet potato leaves are also a rich source of dietary lutein with higher levels than cruciferous leafy vegetables (Menelaou et al., 2006). The nutritional value of sweet potato leaves are discussed elsewhere (Islam, 2006). Ideally, fresh sweet potatoes should be stored in a dry, dark, cool, well-ventilated place outside the refrigerator at 13ºC and low humidity. In this environment, they can be stored for three to four weeks. Producers in countries such as Japan and the U.S. store sweet potatoes in refrigerators at 13 to 15ºC with 80% relative humidity (Ramirez, 2008). Under these conditions, they can be stored for four to six months.

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Table 3. Nutritional value of the sweet potato (values per 100 g edible portion) Nutrient Water (g) Energy (kcal, kj) Protein (g) Total lipid (g) Carbohydrate (g) Dietary fiber, total (g) Ash (g) Calcium (mg) Iron (mg) Magnesium (mg) Phosphorous (mg) Potassium (mg) Sodium (mg) Zinc (mg) Copper (mg) Manganese (mg) Selenium (µg) Vitamin C (mg) Thiamin, B1 (mg) Riboflavin B2 (mg) Niacin B3 (mg) Pantothenic acid (mg) Vitamin B6 (mg) Folate (µg) Vitamin B12 (µg) Vitamin A (IU) Vitamin A (µg-RE) Vitamin E (mg-ATE)

Sweet potato (raw) 72.8 105, 439 1.7 0.3 24.3 3.0 1.0 22.0 0.6 10.0 28.0 204 13.0 0.3 0.2 0.4 0.6 22.7 0.1 0.1 0.7 0.6 0.3 14.0 0.0 20,063 2,006 0.3

Baked in skin 72.8 103, 431 1.7 0.1 24.3 3.0 1.1 28.0 0.5 20.0 55.0 348 10.0 0.3 0.2 0.6 0.7 24.6 0.1 0.1 0.6 0.6 0.2 23.0 0.0 21,822 2,182 0.3

Boiled without skin 72.8 105, 439 1.7 0.3 24.3 1.8 1.0 21.0 0.6 10.0 27.0 184 13.0 0.3 0.2 0.3 0.7 17.1 0.1 0.1 0.6 0.5 0.2 11.0 0.0 17,054 1,705 0.3

United States Department of Agriculture, Agriculture Research Service Nutrient Database for Standard Reference, Release 14, 2001.

The biochemical aspects of sweet potato have been extensively discussed elsewhere (Bovell-Benjamin, 2007). Three types of color pigments in the sweet potato roots, namely, anthocyanin, carotenoids and unidentified flavonoids have been shown to have important physiological functions in humans, such as anti-oxidation, anti-cancer and protection against liver injury. Purple-flesh sweet potato compared favorably with blueberries in terms of its antioxidant activity, anthocyanin and phenolic contents (Cevallos-Casals and CisnerosZevallos, 2002). Sweet potatoes with purple-flesh have highly stable pigments, which could be useful as natural colorants in industry (Cevallos-Casals and Cisneros-Zevallos, 2002). Sweet potato peels (SPP) is an emerging new source of fiber, which could be potentially useful for making fiber-enriched breads, while lessening the intrinsic problems associated with the use of fibers. The preparation and characterization of SPP for use as a dietary fiber supplement in space foods was reported elsewhere (Bovell-Benjamin et al., 2007).

Sweet Potato Utilization in Human Health, Industry and Animal Feed Systems

Figure 1. Sweet potato value-added products (Namanda et al., 2005).

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Figure 2. Nutritional Content of Sweet Potato Leaves (FAO, 1990).

The dietary fiber in dehydrated SPP comprises 33.7% of the dry matter (Bovell-Benjamin et al., 2007). SPP fiber is mainly insoluble, but it also contains roughly 11% functional fiber. Bovell-Benjamin et al., (2007) also reported desirable water- and oil-holding capacity of SPP making it a potentially good source of dietary fiber for enhancement of space foods. Bovell-Benjamin et al. (2008) later incorporated SPP in hard red spring wheat (HRSW) bread and investigated its impact on bread quality. Breads were formulated using blanched/dehydrated SPP (BDSPPB) and dehydrated SPP (DSPPB). Proximate composition, dietary fiber, β-carotene, thiamine, loaf volume, color and consumer acceptance of the breads were evaluated. Moisture content was significantly (P<0.05) higher in the BDSPPB than the DSPPB and control (wheat) bread. The BDSPPB contained two times more total dietary fiber than the control. Soluble fiber (SF) in BDSPPB and DSPPB was threefold that of the control bread. From the results, it could be concluded that the addition of SPP as a source of fiber to HRSW bread is a feasible option. The ash, β-carotene and fiber contents of the supplemented breads were significantly higher than that of the control (wheat) bread. The breads supplemented with SPP had SF/IF (insoluble fiber) ratio within the range suggested for a suitable source to be used as food ingredients. The color and aroma of the test breads were equally well-liked by consumers and the loaf volume was acceptable. The dietary fiber composition of the breads revealed that SPP might have a potential usage as a fiber-enriching agent in bread making for consumers. The biochemical, nutritional and functional properties of sweet potato makes it a potentially good candidate for reducing the global food insecurity, vitamin A deficiency and improving nutritional status worldwide especially in developing countries.

SWEET POTATOES IN HUMAN HEALTH Background Research regarding the utilization of sweet potatoes in human health systems has focused mostly on its anti-diabetic and antioxidant properties. Therefore, this section of the paper focuses primarily on the potential usefulness of the sweet potato as an anti-diabetic food in

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human health systems. In humans, insulin is the major hormone which regulates uptake of glucose into most cells from the blood. Usually, insulin is released into the blood by β-cells in the pancreas in response to rising blood glucose levels after meals. However, type 2 diabetes (T2D) or non-insulin dependent diabetes (NIDDM) is characterized by insulin resistance and impaired insulin secretion from the pancreas. In insulin resistance, endogenous glucose production and/or the disposal of glucose into the skeletal muscles are impaired (Stumvoll et al., 2005). The foregoing situations result in increased concentrations of insulin in the blood, which may consequently damage many of the body‘s systems (Miyazaki et al., 2005).

Prevalence of Diabetes In 2007, roughly 246 million people worldwide had diabetes (www.eatlas.idf.org). The global prevalence of diabetes among adults is estimated to be 6.4% by 2030, representing 39 and 60% increases from 2000 and 1995, respectively (Lipscombe, 2007). On the basis of demographic change, the total number of persons with diabetes was projected to rise from 171 million in 2000 to 366 million in 2030 (Wild et al., 2004). It is predicted that the greatest relative increases in the number of individuals with diabetes will occur in sub-Saharan Africa, India and the Middle Eastern Crescent, while the largest absolute increase will occur in India (Wild et al., 2004). In addition, China, the U.S., Indonesia, Pakistan and Brazil are among the top 10 countries with the highest numbers of estimated cases of diabetes for 2030 (Wild et al., 2004). These estimates indicate that diabetes is a growing public health burden in developing countries such as India, Indonesia, sub-Saharan Africa and Brazil.

Consequences of Diabetes Diabetes, a major contributor to cardiovascular disease, is also one of the leading causes of blindness, renal failure, amputations and stroke (Lipscombe, 2007). Other complications of diabetes, which result in increasing disability and reduced life expectancy, include diabetic neuropathy, increased susceptibility to infection, disturbed wound healing, coronary artery and peripheral vascular disease (Miyazaki et al., 2005; www.eatlas.idf.org). According to Wild et al. (2004), Yach et al. (2006) and Lipscombe (2007), the human and economic costs of diabetes are colossal, with the direct healthcare costs of diabetes ranging from 2.5 to 15% of health budgets. This is of particular concern, especially for developing countries, which are unprepared economically and otherwise, to deal with the rising burden of the emerging diabetes epidemic. There is an urgent need for collaborative, global prevention, control and management strategies to address the emerging diabetes epidemic.

Sweet Potato, Diabetes Prevention and Management Strategies, which have been proposed and used for the prevention and management of T2D include : (i) dietary modifications, (ii) increased physical activity and (iii) medications such as oral hypoglycemic agents (Richter et al., 2000; Kumar et al., 2007). New compounds, which increase insulin sensitivity are also being currently used and/or investigated (Ludvik et

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al., 2004). With the consistent increase of diabetes worldwide, attention has been focused on evaluating the effectiveness of natural and nutraceutical products for use in its prevention, control and management (Sotaniemi et al., 1995; Vuksan et al., 2000; Hosoda et al., 2003; Egede et al., 2002). For example, green tea has been studied for its protective role against T2D. Middle-aged Japanese men and women who reported daily consumption of more than 6 and 3 cups of tea and coffee had 33 and 42% , respectively, lower risk for T2D over a 5-year period compared to those who did not consume these beverages (Crespy and Williamson, 2004). Tsuneki et al. (2004) reported improved glucose tolerance when they fed 1.5 g green tea powder in hot water to young healthy volunteers. Contrastingly, in a study of Japanese men (N = 3,224), no relationship was observed between glucose tolerance and green tea (Yamaji et al., 2004). Although uses of various natural products have been documented, there is limited evidence of systematic investigations showing the efficacy of nutraceutical compounds in T2D prevention and management (Yeh et al., 2003). Recent animal and human studies have indicated that the sweet potato plays a role in stabilizing blood glucose and lowering insulin resistance. A Japanese white sweet potato extract called Caiapo has been associated with T2D prevention and management. Caiapo is made from the extract of the skin of the root from a variety of white-skinned sweet potato, which has been eaten raw in Japan for treatment of diabetes, anemia and hypertension. It is really the acidic glycoprotein component which is isolated in Japanese sweet potato cultivars, which is similar to the proteins found in Beauregard sweet potatoes. In a randomized study, 18 males with T2D who consumed 4 g/day of Caiapo as a dietary supplement for six weeks had lower blood glucose levels, and total and low density lipoprotein (LDL) cholesterol levels (Ludvik et al., 2002). To verify the findings of Ludvik et al. (2002), 61 patients with T2D (treated with diet only) participated in a randomized, Placebo -controlled, double blind, follow-up trial (Ludvik et al., 2004). A Placebo is an inactive substance or treatment that looks the same as, and is given the same way as, an active drug or treatment being tested. The effects of the active drug or treatment are compared to the effects of the placebo. The patients consumed 4 g of Caiapo or a Placebo daily for 12 weeks; and blood glucose and HbA1c, which is a measure of long-term glucose control, were observed. Blood glucose, cholesterol and HbA1c levels were significantly lower (P<0.03, P<0.05, P<0.001, respectively) in the Caiapo group than those in the placebo group. Ludvik et al. (2004) concluded that Caiapo promotes T2D management. In another study, McClelland et al. (2007) examined the glycemic index (GI) of sweet potato. Forty individuals, 20 with T2D and 20 without, consumed 50 g carbohydrate from either glucose; dehydrated White Star or Beauregard sweet potato cultivars, after which the change in blood glucose and insulin were measured at 0, 1 and 2h and 0 and 2 h, respectively. The results indicated that the GI of White Star was 44.2 and 28.5 in non-diabetic and diabetic individuals, respectively. For Beauregard, the GI was 32.1 and 30.3 in non-diabetic and diabetic individuals, respectively. It was concluded that consumption of sweet potato lowered blood glucose in individuals with T2D. Another prospective, Placebo-controlled, double blind trial randomized 18 males with T2D to three groups (Ludvik et al., 2003). The men consumed either a placebo, a low dose (2 g) or a high dose (4 g) of Caiapo three times per day for six weeks. Glucose tolerance, glucose disappearance, and insulin secretion were evaluated. The group fed the high dose Caiapo, had a significant (P<0.05) reduction in plasma glucose concentration in the frequently sampled intravenous glucose tolerance test (FSIGT). The males in the low- and high-dose Caiapo groups exhibited 37 and 42% increased insulin sensitivity. Overall, glucose

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tolerance was improved by 72% in the high dose Caiapo group. The authors concluded that Caiapo could potentially play a role in the treatment of T2D. Miyazaki et al. (2005) investigated whether the antidiabetic ingredients of white-skinned sweet potato influences the immune response of human leukocytes. Their (Miyazaki et al., 2005) results indicated that the antidiabetic ingredients of white-skinned sweet potato increased phagocytic activity, phagosome-lysosome fusion in neutrophils and monocytes in a dose-dependent manner in vitro. On the basis of their findings, Miyazaki et al. (2005) concluded that the antidiabetic ingredients from white-skinned sweet potato are useful in the prevention and improvement of diabetic symptoms such as susceptibility to infection and disturbed wound healing. Furthermore, the researchers stated that the white-skinned sweet potato may be a beneficial non-pharmacologic therapy for T2D because it enhances immune activity and has antidiabetic properties as well. The GI is a useful tool in the prevention and management of diabetes by stabilizing blood glucose levels and increasing glucose tolerance. It describes the difference in carbohydrates by ranking them according to their effect on blood glucose levels (Brouns et al., 2005). The sweet potato has been recently identified as a low GI food. Our laboratory investigated the effect of a sweet potato starch syrup on selected metabolic responses of Zucker fatty (fa/fa) rats. Oral glucose tolerance tests (OGTT) were done on rats using a glucose standard; a maple syrup; a corn syrup; and a sweet potato starch syrup and the GI values determined. Rats fed the sweet potato starch syrup had the lowest GI value (66.1±19.1) compared to the corn and maple syrups. In this study, the sweet potato starch syrup was classified as an intermediate-GI food while the corn and maple syrups were assigned high-GI values. After a five-week dietary trial, weight gain, blood glucose concentrations, high density lipoproteins (HDL), LDL, total cholesterol, and triglyceride levels of the rats‘ were compared. Zucker fatty (fa/fa) rats‘ fed the diet supplemented with sweet potato starch syrup had significantly (p<0.05) lower triglyceride levels and higher HDL levels than those fed corn syrup and a glucose standard. Corbitt (2007) also investigated the short term glycemic effects of sweet potato in non-diabetic individuals. Beauregard variety sweet potato showed a low-GI value. Overall, the researcher concluded that if the GI of sweet potato processed by different methods remained low (<55), sweet potato may be useful in the control of blood glucose levels.

SWEET POTATO AND OTHER BIOACTIVE PHYTOCHEMICALS In addition to its antidiabetic properties, sweet potato has potentially bioactive phytochemicals, such as chlorogenic acids (Zheng and Clifford, 2008). In vitro studies have shown that chlorogenic acids inhibit Na+ - dependent D-glucose uptake in rat intestinal brush border membrane vesicles (Welsch et al., 1989). Chlorogenic acids in coffee have also been shown to modify gastrointestinal hormone secretion and glucose tolerance in humans (Johnston et al., 2003). Zheng and Clifford (2008) analyzed the leaves, stem and roots of sweet potato grown in China for chlorogenic acids. The stem and leaves of the sweet potato contained a range of chlorogenic acids, but none were detected in the roots. Antioxidants, which are present in high levels in the sweet potato, have been inversely associated with insulin resistance and high blood sugar levels. The improvement of insulin sensitivity with antioxidants in insulin resistant or diabetic subjects has been demonstrated by

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several clinical trials (Hirai et al., 2000; Hirashima et al., 2000)[5] O. Hirashima, H. Kawano and T. Motoyama et al., Improvement of endothelial function and insulin sensitivity with vitamin C in patients with coronary spastic angina: possible role of reactive oxygen species, J Am Coll Cardiol 35 (2000), pp. 1860–1866. Article | PDF (227 K) | View Record in Scopus | Cited By in Scopus (47). It has been very well established that some orange-fleshed sweet potato varieties contain significant amounts of the antioxidant β-carotene. Ingelsson et al. (2005) have suggested that antioxidants such as β-carotene lower the levels of free radicals that play a role in the mediation of oxidative stress and inflammation. Armlöv et al. (2005) followed a cohort and confirmed that serum levels of β-carotene predicted left ventricular diastolic dysfunction twenty years later. Ingelsson et al. (2005) reported that low serum levels of antioxidants such as β-carotene; predict a higher risk of developing heart failure, independent of established risk factors. Other experimental work in regard to the importance of the sweet potato in human health has been done. Sweet potato leaves is rich in lutein, which is not synthesized in the body. Lutein has the capability to delay the onset of macular degeneration, a major cause of blindness in the world (Bernstein et al., 2004). Sweet potato leaves, which contain high amounts of polyphenolics are protective against diseases linked to oxidation such as cancer, hepatotoxicity, allergies, aging, human immunodeficiency virus and cardiovascular disease (Islam, 2006). Furuta et al. (1998) has demonstrated that antioxidative and radical scavenging activities are observed in all sweet potato varieties with white, yellow, orange and purple flesh. Sweet potato has been associated with reduced liver injury caused by carbon tetrachloride in animal models (Suda et al., 1997). Juice from purple-fleshed sweet potato has been shown to effectively lower blood pressure in humans (Suda et al., 1998). According to Yoshimoto et al. (1999), purple-fleshed sweet potato roots have antimutagenic properties. Mutagens, found in foods, are considered to be risk factors for cancer. Based on its β-carotene content, there is a potential role for sweet potato in cancer prevention and risk reduction.

Sweet Potato and Vitamin A Deficiency More than 230 million of the world‘s children, mostly those in developing countries, have inadequate vitamin A intake, with 13 million of them being affected by night blindness (Schweigert et al., 2003; Stephenson et al., 2000; Underwood and Arthur, 1996). Children in south Asia and Africa are mostly affected by vitamin A deficiency (Mason et al., 2001). The potential role of sweet potato in the prevention of vitamin A deficiency cannot be overlooked. Although sweet potato does not contain vitamin A, it contains precursors or pro-vitamin A (βcarotene and other carotenoids), which the human body converts to vitamin A. In Kenya, orange-fleshed sweet potatoes have been recognized as the least expensive year-round source of pro-vitamin A (Low et al., 1997). Hagenimana et al. (1999) reported that consumption of orange-fleshed sweet potato increased the dietary vitamin A intake in Kenyan children and women. Low et al. (1997) indicated that consumption of orange-fleshed sweet potato could contribute substantially to reducing vitamin A deficiency in Sub-Saharan Africa. The consumption of diets containing primarily orange-fleshed sweet potatoes as a source of βcarotene significantly increased serum retinol (vitamin A status) levels of Indonesian children with marginal vitamin A deficiency (Jalal et al., 1998). van Jaarsveld et al. (2005) also

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concluded that increased consumption of orange-fleshed sweet potato could be a feasible food-based strategy for controlling vitamin A deficiency in children in developing countries. Edible, low-cost vaccines from plants may provide cheap protection for some of the poorest people in the world (Kumar et al., 2007). Hepatitis B is one of the major infectious diseases affecting several million people in developing countries. Suda et al. (2008) examined the effect of purple sweet potato (PSP) beverage rich in acylated anthocyanins on serum hepatic biomarkers in healthy Japanese men. A randomized, double-blind, placebocontrolled, parallel study involving 48 healthy men (30-60 years) with borderline hepatitis who had serum gamma-glutamyl transferase (GGT), aspertate aminotransferase (AST) and alanine aminotransferase (ALT) levels over normal ranges, and negative for hepatitis virus was conducted. The subjects were randomly assigned to either a PSP or a placebo group for an 8-week intervention. Those in the PSP and placebo groups consumed two bottles of the PSP beverage with acylated anthocyanins containing 200.3 and 1.7 mg anthocyanins/125 ml per bottle daily. The PSP beverage group showed lower hepatic marker levels than the placebo group during the ingestion period, particularly the GGT level. The intake of the PSP beverage significantly decreased the serum levels of hepatic biomarkers, particularly the GGT level, in healthy men with borderline hepatitis. In sum, several studies have shown that the sweet potato has antidiabetic properties, that is, the capability to lower blood glucose level and improve glucose tolerance. White-skinned sweet potatoes are useful in preventing and improving diabetic symptoms and could be a beneficial non-pharmacologic therapy for T2D. The stems and leaves of the sweet potato contain potentially bioactive phytochemicals such as chlorogenic acids, which have been shown to improve glucose tolerance in humans. Also, several sweet potato varieties have been shown to have antioxidative, radical scavenging and antimutagenic properties; they have also been associated with reduced liver injury and blood pressure lowering activity.

INDUSTRIAL UTILIZATION OF SWEET POTATO Background Over the years, although the full potential of the sweet potato in human and animal food systems has not been realized, new uses for the crop, such as a source of starch and valueadded processing have been emerging. This section reviews the utilization of the sweet potato in the starch-based industry using Japan and China as examples (Carver, 1936; Komaki and Yamakawa, 2006). The importance of starch in food processing and non-food industry could be attributed to its heterogeneity and versatility (Fuglie et al., 2006). For example, in the food industry, starch is used to impart functional properties such as thickeners in soups and sauces, dough conditioners in bread manufacturing, stabilizers in ice creams, in noodles and other wheat-based foods, in binding and filling (Fuglie et al., 2006). It is converted to sugars and sweeteners and is utilized in beverages and alcohol. The sweetener industry utilizes the largest amount of the starch produced in the world (Fuglie et al., 2006). In the U.S. and Canada, starch is used primarily to produce high-fructose syrup (HFS) for soft drinks (Fuglie et al., 2006). Some examples of non-food industries which make use of starch include: textile, paper, adhesive, plywood and pharmaceutical (Fuglie et al., 2006). To illustrate the

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importance of sweet potato starch in non-food industries, Bendigo (1944) reported success using it in the textile industry. Bendigo (1944) cited several advantages of using sweet potato starch in the textile industry when compared with other starches including: (i) smaller proportions of starch used; (ii) its especially clear color; and (iii) excellent penetration. Traditionally, most starches are derived from maize, cassava, potato and wheat. Roughly 70% of the world starch production is derived from maize (Fuglie et al., 2006). In the U.S., Canada and Mexico, maize accounts for 98% of the starch produced and is also the least expensive source in these countries (Fuglie et al., 2006). The major contributors to starch production in Europe are maize, wheat and potato (LMC International, 2002). In developing countries, root crops are relatively more important as sources of starch than cereal crops, which are usually too expensive. Overall, in Asia maize accounts for approximately 45% of all starch production (Fuglie et al., 2006). In Southeast and South Asia, 90% of the starch is produced from the cassava (Fuglie, 2004). In China, Japan and Korea, there is a high demand for starch from root and tuber crops because of the special traits associated with these (Fuglie et al., 2006). According to Fuglie et al. (2006), root and tuber crops supplied more than 50% of Asia‘s starch needs with 23.5% coming from the sweet potato. The starch potential and quality of the sweet potato has been extensively discussed elsewhere (Bovell-Benjamin, 2007; Moorthy and Shanavas, Chapter 4 in this book). To briefly summarize, starch is the basic reserve polysaccharide of plants consisting of two polymers of glucose; linear amylase and branched amylopectin. Starch is the major carbohydrate (ranging from 73.7 to 90%) in the roots of the sweet potato (Miller, 2003; Zaidul et al., 2008; Garcia and Walter, 1998; Lu and Sheng, 1990). Brabet et al. (1998) and Miller (2003) reported average total starch contents of 61.5 and 81% on dry weight basis for sweet potato starch. This attribute makes starch processing from sweet potato a highly feasible option, which could increase economic and employment activities for farmers and rural households in developing countries where most sweet potato is produced.

SWEET POTATO, STARCH AND INDUSTRY Sweet potato is one of the most important starch-producing crops in the world (Katayama et al., 2006). Starch, the most commonly processed product of sweet potato roots is produced at household, small- and large-scale industry (Piyachomkwan et al., 2004). In Japan, sweet potatoes have been utilized in starch production for several years. The annual yield of sweet potatoes for starch production in the southern part of Japan is roughly 2.1 x 105 tons (Yokoi et al., 2001). It is estimated that in Japan, 20 to 58% of the sweet potato produced is used for starch processing (Kitahara et al., 2007; Fuglie et al., 2006). Most of the sweet potato starch used in Japan‘s food industry is in the production of syrup or glucose, in alcohol production, in starchy noodles, and in traditional confectioneries such as gelatinized cakes (Kitahara et al., 2007). Additionally, sweet potato starch pulp has been used as a raw material for the citric acid manufacturing industry in Japan, however, its use has sharply declined, and it is treated as waste material. Research is continuing to find alternative uses for sweet potato starch pulp. For example, Hayao and Jun (2002) investigated the functionality of sweet potato starch pulp and evaluated the value as food materials. Their results indicated that the sweet potato starch

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pulp contains a functional ingredient with antioxidant capability. It was further indicated that the antioxidant capability is enhanced if dried starch pulp is heat-treated for at least one hour. In China, the biggest processed products from sweet potato are starch, which are mostly processed into starch noodle, one of its traditional foods. Sweet potato starch processing has developed into a profitable industry in China (Fuglie et al., 2006). In 1997, 74% of sweet potato production in China was being used by starch industries or for animal feed (Huang et al., 2003). Over the past 10 years, there has been a sharp growth in the noodle industry in China and the sweet potato starch is used mainly in the production of these (Fuglie et al., 2006). The sweet potato starch also has other industrial applications in China such as: in the production of sweeteners, citric acid, beverage, industrial alcohol, ethanol fuel and derived products as maltose (Lu et al., 2006). Over 10% of the annual production of 100 million tons of sweet potatoes in China is processed into starch, mostly in small-scale enterprises using manual or simple mechanized equipment (Wheatley et al., 1997). Overall, developing countries continue to have a strong incentive to make starch from the sweet potato as a means to decrease the need for imported materials and, thus, conserve monetary resources for use within the country itself.

Emerging Applications of Sweet Potato Starch Increasing demands from consumers regarding environmental issues, their preference for natural rather than synthetic products, and the search for alternatives have created more interest in starch-derived products. Research continues to focus on starch-derived products for use as surfactants and builders, sequestering agents and bleaching boosters (Leygue, 1993). For example, the detergent industry in the United Kingdom is potentially a large market for industrial starch (Entwistle et al., 1998). Additionally, there is increased interest to utilize starch for alcohol production because the global energy crisis has created the need for renewable energy sources (Hosein and Mellowes, 1989; Debnath et al., 1990). Starch is renewable and globally available (Yu et al., 1996). Also, as pointed out more than two decades ago, sweet potato also has potential as a biomass crop because of its high starch production per unit area (Dangler et al., 1984). After investigating the potential of five sweet potato cultivars for biomass production, especially starch, Dangler et al. (1984) reported that ethanol potential from the GaTG-3 sweet potato cultivar compared favorably with that of irrigated North Florida corn. Yu et al. (1996) reported alcohol fermentation from the saccharified mash of dried sweet potato with its dregs. Hosein and Mellowes (1989) hydrolyzed sweet potato for ethanol production. The digestibility of sweet potato starch and the degree of its effect upon the digestion of dietary protein were compared with those of corn and potato starches (Yoshida and Morimoto, 1955). Adult white rats were fed diets containing one of these starches as the sole source of carbohydrate. The coefficients of digestibility of corn, sweet potato and potato starch were found to be 99, 97 and 57%, respectively. When the diets were steamed, all starches were utilized nearly perfectly and no significant differences were observed. Raw sweet potato starch caused diarrhea and markedly decreased the apparent digestibility of dietary protein. However, this effect was decreased when sweet potato starch was purified, and disappeared when it was steamed. Studies are being conducted in Japan to utilize the waste from sweet potato starch production into biodegradable plastics; and to recycle waste

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from distilled liquor as livestock feed, manure, biodegradable farming materials and human food (Pawlak et al., 2002; Yamakawa and Yoshimoto, 2002). Sweet potato starch microparticles have been investigated for its usefulness in drug delivery applications. The in vitro drug release behavior of sweet potato starch microparticles intended for controlled drug delivery applications has been studied (Liu et al., 2007). Diclofenac sodium was used as the model drug candidate. Sweet potato starch microparticles were prepared using a spray-drying technique by varying the polymer concentration and drug loading. The encapsulation efficiencies of sweet potato starch microparticles formulations was between 95 to 98%, suggesting good encapsulating ability of the sweet potato starch polymer by spray drying.

POTENTIAL FOR SWEET POTATO IN ANIMAL FEED SYSTEMS Background Sweet potato is among one of the five most important food crops in developing countries (Phuc et al., 2001). The use of the sweet potato as a feed supplement for animals is an old concept, which has been documented as early as the 1920‘s by the Queensland Department of Agriculture and Stock in Australia. It should be noted that in some parts of the world while sweet potato is an important staple food for humans, others produce it primarily for use as animal feed. For example, in countries such as China, sweet potato is now an important component of animal feed. Over the last three or more decades, with the economic developments and policy reforms in China, the role of sweet potato has shifted. By the 1970s, China was utilizing 50% of the sweet potato produced in the animal feed system, rather than for direct human consumption (Huang et. al., 2003; Woolfe, 1992). However, by the end of the 1990s, human consumption decreased to less than 15%, as most of the crop was being utilized for animal feed and industrial purposes (Huang et al., 2003; Zhang and Li Xiu- Qing, 2004). Despite the changing human consumption patterns of sweet potato in China, it is still an important staple food in some poor, rural areas of China (Wu et al., 2008). Most of the sweet potatoes grown in Australia in the 1920s were utilized as feed supplements for cattle and pigs. In the U.S. and Japan, 10 and 25% of sweet potato roots are used as cattle feed, respectively (Ramirez, 2008). In general, wherever the sweet potato is grown, some part of the plant is used in animal production. In most developed and developing countries where the sweet potato is grown, the foliage has been largely considered as waste material rather than a useful, formal component for incorporation into animal feed systems (Ruiz et al., 1980). However, with the increasing prevalence of poor quality grasses, climate changes, lack of suitable home-grown feed resources, rising energy costs, the high cost of commercial feeds with imported ingredients to resource-poor farmers in developing countries and other constraints to enhanced animal production (An et al., 2004), the need for alternate animal feed resources has become critical. Another factor, which has increased the demand for feed intended for animals and aquaculture fish, is the higher request for animal products by the emerging middle-class in countries such as India and China (Eide, 2008). Moreover, the use of grains such as maize for

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liquid bio-fuel as an alternative to gasoline and diesel derived from petroleum has brought into sharp focus the value of utilizing alternatives in human and animal feed systems. Liquid bio-fuel is mainly produced as ethanol or bio-diesel. The feedstock for ethanol is primarily sugarcane and maize; to a lesser extent wheat, sugar beet and cassava (Eide, 2008). The main producers and consumers of bio-fuels and bio-diesels are Brazil, U.S. and the European Union (EU). However, the U.S. and the EU cannot meet their target of production for internal consumption and will become increasingly dependent on import from developing countries (Eide, 2008). It is hypothesized that as the use of traditional feedstock continues to become more competitive for bio-fuel production, the need for novel, alternative animal feedstock will increase and become more commercially viable. Ideally, the sweet potato is a highly efficient, multi-purpose crop (leaves, vines and roots could be utilized by both human and animals), which can become much more useful as one of the solutions to the aforementioned problems. The following section is intended to highlight the literature regarding the potential usefulness of the sweet potato in animal feed systems. It gives an overview of sweet potato use in animal production and describes a series of studies, which utilized the sweet potato in animal feed systems.

Overview of Sweet Potato Use in Animal Feed Systems In Asia, roots for pigs and vines for cattle are the most commonly cited forms of sweet potato utilization as animal feed in Asia (Table 4). In general, limited quantities of composite feeds are produced industrially. In China, parts of Indonesia (Irian Jaya), Papua New Guinea and Vietnam fresh roots are fed to pigs (Table 4). In Korea, these fresh roots include culls left from sales to the market (Chin, 1989), while in Papua New Guinea, pigs will forage for roots or culls left in the field (Kanua and Rangat, 1989). There is limited information about the use of sweet potato for animal feed in Africa, suggesting that the roots are used primarily for human consumption. In the African countries, the vines and foliage are not widely utilized; this is because they are mostly used in human diets and in the field to improve soil fertility. The vines and foliage are fed mostly to cattle in Argentina, Brazil, Ecuador, the Dominican Republic and Peru. Vines and foliage are fed to pigs and rabbits in Peru and to goats in Ecuador.

Sweet Potato Foliage Pig Feed Although some studies have been undertaken in developing countries to determine and improve the usefulness of sweet potato leaves (SPL) and vines in animal feed systems and it is generally believed that a large potential exists for their utilization, documented information and widespread usage remain scarce. Much more research is needed regarding alternative raw materials and by-products for use in animal feed systems to reduce the substantial feed expenses faced by resource-poor farmers, especially those in developing countries. The need for more research in this area is even more urgent because the projected growth in demand for sweet potato is expected to occur in the market for animal feed (Fuglie and Oates, 2003).

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Table 4. Sweet potato use as animal feed Region ASIA Bangladesh China

India

Part Plant

Form

Animal(s) Fed

Vines Roots Vines

Green Sliced, dried, ground, cooked Green, from ensilage

Cattle Mainly pigs but also cattle, poultry Mainly pigs but also cattle, poultry Pigs

Waste from processing starch, noodles Roots Vines

Waste water Sun-dried chips Green or after ensilage Fresh Fresh Fresh, stored Green Cooked, dried chips, composite feed Unknown Sliced, dried Fresh, sliced and dried Unknown

Pigs Cattle

Vines Vines Vines Damaged roots, vines Surplus roots, vines

Green fodder Green fodder Green fodder Fresh Fresh

Cattle Cattle, pigs Small animals Livestock Livestock, pigs, fish

Roots, vines Roots, vines

Fresh Fresh

Roots Vines Roots Vines Culls, roots Roots Vines

Fresh Green fodder Fresh Green, ground Fresh Fresh Fresh

Peru

Roots Vines

Fresh Fresh

Venezuela

Roots, vines

Fresh

Cattle Dairy and beef cattle, fish Pigs, goats, beef cattle Beef, cattle, goats Pigs Cattle Pigs Pigs Pigs, other farm animals, cattle Cattle, pigs, rabbits Dairy cattle and ruminants Livestock

Indonesia (Java) (Irian Jaya) Papua New Guinea Philippines Taiwan Vietnam

Roots, culs, vines Roots Roots Leaves, vines Roots Vines Roots Roots Vines

AFRICA Egypt Kenya Mozambique Rwanda Uganda LATIN AMERICA Argentina Brazil Ecuador Dominican Republic Haiti Jamaica

Cattle Pigs Pigs Pigs Pigs mainly, poultry Pigs Pigs Pigs Pigs

Sweet potato could substitute for maize in animal feedstock mainly for pig, cattle and small ruminants. For the purposes of this chapter, sweet potato vine includes the leaf and stem and the foliage refers to the vine. The crude protein content of sweet potato foliage is between 68 and 131g/ kg dry matter (Larbi et al., 2007). The roots provide energy derived from starch, while the leaves are rich sources of protein (260 to 330 g/ kg) and fiber (Woolfe, 1992).

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Lysine is the first limiting amino acid in SPL, however, when growing pigs‘ diets were supplemented with SPL and synthetic lysine, their daily live-weight gains of 536 g were similar to those fed a control diet with fish meal as the protein source (An, 2004). An (2004) evaluated the potential of using SPL as a protein source in the diets for growing pigs. The crude protein content of the SPL was 25.5 to 29.8% in dry matter. The researcher further stated that the dry matter, organic matter and crude protein of ensiled SPL was highly digestible in growing pigs, but that of crude fiber was low. An (2004) concluded that SPL can be used fresh, dried or as silage, and can replace fish meal and groundnut cake as a protein source for growing pigs under small farm conditions in central Vietnam. Malavanh and Preston (2006) investigated the intake and digestibility in growing pigs fed different levels of SPL and water spinach as supplements to a mixture of rice bran and cassava root meal. Male pigs were fed ad libitum ratios of SPL and water spinach of 100:0, 75:25 and 50:50 (dry matter basis). The cassava root meal and rice bran (50:50 mixture) was 2% (dry matter basis) of live weight. Increasing the level of water spinach did not affect total dry matter intake, the coefficients of apparent digestibility of dry matter, organic matter, nitrogen and crude fiber or the retention of nitrogen. It was concluded that water spinach and SPL appear to have the same nutritive value when used to supplement a basal diet of cassava root meal and rice bran for growing pigs. Sweet potato vines (SPV) are used extensively in countries such as China, Peru and Indonesia for pig and dairy cattle feed (Achata et al., 1988). Ty et al. (2007) studied the effect of fresh SPV and mulberry leaves (given separately or mixed together) on intake, digestibility and nitrogen retention of growing pigs with a basal diet of broken rice. The intakes of the foliages accounted for 21 to 28% of the total dry matter and approximately 55% of the crude protein. Foliage dry matter intakes were higher when the SPV were all or part of the foliage supplement. The apparent digestibility coefficients of the dry matter and crude protein were higher for the mulberry diet than those, which contained SPV. The researchers concluded that the protein in the fresh foliage of mulberry leaves is well utilized by growing pigs fed a basal diet of broken rice. There were no advantages from giving a mixture of SPV and mulberry leaves compared with either foliage given alone. In the Red River Delta area near Hanoi, two on-farm trials were conducted to determine whether fermented SPV could reduce women's labor and feed processing costs, and improve pig growth efficiency (Peters et al., 2001). First, twelve different mixtures of SPV, corn and cassava meals, rice bran, sun-dried chicken manure and salt were fermented and analyzed for nutritional value. There were no significant differences in nutritional value over time. However, vines fermented with chicken manure had significantly (p<0.001) higher crude protein, dry matter and ash contents than the other fermented treatments. The subsequent three-month on-farm feeding trial compared fresh SPV, vines fermented with cassava meal, and vines fermented with sun-dried chicken manure and cassava meal in terms of pig growth and economic efficiency. Pigs fed the preparation containing chicken manure had significantly higher (P< 0.05) growth rates than those fed fresh vines; neither of these feeds was significantly different from the vines fermented with cassava meal in terms of feed efficiency (P=0.013). The chicken manure preparation was also considerably cheaper (cost per kg of weight gain) than the other two preparations. Zuohua et al. (2001) examined the nutritional value of sweet potato roots ensiled with various special additives and the feeding efficiency of the silage as pig feed. Machine-grated sweet potato roots were ensiled with varying proportions of special additives A, B, C, 10%

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grain stillage, and 20% wheat bran. Crude protein, true protein, crude fiber, crude fat, crude ash, calcium and phosphorus were measured at 0, 2, 4, 6, 9, 12 and 25 weeks of ensiling. Pigfeeding test was done on weaner and finishing pigs. Four feeds with varying proportions of sweet potato silage to total feed were compared: 0, 20, 40 and 60% sweet potato silage. The results indicated that the nutritional value of sweet potato silage did not differ significantly over time except for fat content and pH value. The sweet potato ensiled for more than 9 weeks had better amino acid and nutrient contents than fresh sweet potato. The sweet potato silage mixed with 0.32, 0.5, 0.5, 10 and 20g of special additives A, B, C, with 10% grain stillage and 20% wheat bran, passed for grade B. Daily weight gain was 581g for 0%, 613g for 20%, 579g for 40% and 618g for 60% for a period of 115 days of weaner- finishing pigs. The most important finding was that growth rates could be increased with sweet potato silage, and it can be stored for up to six months without spoilage. Storage of fresh sweet potato roots causes decay that could be harmful to the environment. Another pig-feeding trial examined how much sweet potato silage should be incorporated in the diet to maximize growth and economic efficiency. The greatest efficiency for weaner pigs (20-60 kg live weight per pig) and finishing pigs (60-90 kg live weight per pig) were both observed at the combination of 20% of sweet potato silage and 80% basal diet.

Poultry Feed Nguyen and Ogle (2005) randomly allocated four-week old female Luong Phuong chickens (N = 204) to four treatments and three replicates. The control diet was a mixture of broken rice, rice bran, soybean meal and fishmeal with 16.9 % crude protein in dry matter. The other three diets, which contained duckweed, water spinach and SPV, were given ad libitum in separate feeders in addition to the control diet. The chickens were weighed weekly between 4 and 16 weeks of age and feed consumption recorded daily up to 21 weeks. Total feed dry matter, crude protein intakes and average daily weight gain were similar among treatments. Intakes of duckweed (3.3 g/day) and SPV (2.8 g/day) were significantly (P<0.01) higher than for water spinach (1.8 g/day). Crude protein intake from duckweed as a proportion of total crude protein intake (9.6%) was significantly (P>0.01) higher than from SPV (6.7%) and water spinach (5.2%). There were no differences in carcass yield, but liver and gizzard weights on the diet with duckweed (48.3 and 50.3 g, respectively) were higher than on the control diet (40.0 and 43.3 g, respectively). The control group had highest abdominal fat (81.0 g), more than twice as high than on the experimental diets (P>0.001). The dry matter, crude protein, energy contents, egg weight and egg yolk weight of the meat were similar among treatments. The egg yolk and skin in chickens fed duckweed had the deepest yellow color, followed by those fed the water spinach, SPV and the control diet. Cattle Feed Etela et al. (2008a, b) have reported that sweet potato could be utilized for livestock feed, especially by resource-poor farmers. Bunaji and N‖Dama cows in early lactation were fed foliage from three sweet potato cultivars, dried brewers‘ grains and cottonseed meal supplemented with Guinea grass. The nutrient intake, milk yield and composition were measured (Etela et al., 2008a). Sweet potato foliage had lower milk yield than the dried brewers‘ grains and/or cottonseed meal. The metabolizable energy intakes were higher from the sweet potato foliage than the other diets. The researchers concluded that fresh sweet potato foliage could serve as a sustainable cost-effective supplement to improve the

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nutritional quality of Guinea grass. Etela et al. (2008b) used pre-weaned crossbred calves to further investigate the effects of sweet potato foliage from three cultivars, dried brewers‘ grains and cottonseed meal on their performance. It was concluded that the calves fed sweet potato foliage supplement from one cultivar had better daily live weight gains versus the others, although this was not statistically significant. The performance of calves supplemented with sweet potato foliage was comparable to those fed dried brewers‘ grains and cottonseed meal. In a broader study to evaluate the forage quality and animal production potential of some selected Kenyan sweet potato lines for inclusion in crop/livestock production systems, Karachi (2008) studied the effect of supplementing SPV and cottonseed cake on the growth of weaned, penned Boran calves. The basal diets were supplemented with either dried SPV or cottonseed cake. The weaners supplemented with SPV consumed 30% more total dry matter than those fed grass alone. The weaners supplemented with the SPV had similar growth to those fed the cottonseed cake, therefore compounding feeds with SPV would be a feasible alternative to the more expensive cottonseed cake. Zebu bulls were fed chopped whole sweet potato and sugar cane forage to determine digestibility and voluntary intake (Ffoulkes et al., 1997). The proportions were: (i) on a dry weight basis, whole cane to sweet potato (100:0, 67:33, 33:67, 0:100); and (ii) fresh basis, whole cane to sweet potato (100:0, 45:55, 15:85, 0:100). For the treatment with 33% sweet potato forage, the dry matter consumption index was significantly higher, and digestible dry matter was increased by 34%. Voluntary intake was lower on the sugar cane control diets than in those supplemented with sweet potato. Dry matter digestibility was similar among treatments. Ffoulkes et al. (1997) argued that although the improvement was not as dramatic as expected, the increase in voluntary intake could be attributed to the protein and the physical nature in the sweet potato forage serving as a by-pass nutrient and improving rumen function.

Goat Feed The effect of sweet potato forage and its mixtures with batiki grass on the voluntary intake, growth and digestibility in eight goats was investigated by Aregheore (2004). Four treatments of varying amounts of fresh sweet potato foliage to batiki grass (0:100, 50:50, 75:25, 100:0) were offered. The goats were fed on each dietary treatment for 21 days. Based on the results, it was concluded that sweet potato forage in combination with batiki grass could provide a cheap source of nitrogen in the diets of growing goats.

Sweet Potato Roots Pig Feed Onwueme and Sinha (1991) reported that sweet potato roots could be fed to livestock fresh, as chips or as silage. A three-month pig-feeding trial compared three feeds: cooked fresh sweet potato roots (T1), uncooked roots silage with rice bran (T2), and uncooked roots silage with sun-dried chicken manure (T3). Daily weight gain was 552, 605 and 640 g for T1, T2 and T3, respectively. These differences were not statistically significant perhaps because of the small sample size (42 pigs) and large standard deviations that resulted from large

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variations amongst the practices of the participating farm households, the types of pigs used, and their variable taste for silage feed. The most important finding was that reasonable growth rates could be achieved with uncooked feed. Cooking is labor intensive and fuel demanding (cooking pig feed on rice husks normally takes 2 to 3 hours per day). However, cooking in the ensiled roots decreased trypsin inhibitor, which appeared to allow farmers subsequently to triple the number of pigs raised per cycle of 3 - 4 months. In an earlier study conducted by Fashina-Bombata and Fanimo (1994), the effects of dietary replacement of maize with sundried sweet potato meal on performance, carcass characteristics and serum metabolites of 16 weaner-grower pigs were examined. The pigs were fed 33, 67 and 100% sweet potato meal as a direct replacement for maize in a soybeanbased diet. The average daily feed intake and daily weight gain were significantly decreased as the level of sweet potato meal increased in the diets. The 33% sweet potato meal compared favorably with the control diet. It was concluded that the 33% sweet potato meal and not the other two diets contributed to improved performance in the pigs. Manfredini et al. (1993) evaluated the use of sweet potato chips in heavy pig production. The performance, carcass characteristics and meat quality (aged ham) were measured. Three groups of castrated male pigs (N = 75) were fed diets of maize meal and sweet potato chips (0, 20 and 40%). The suncured sweet potato chips were imported from China. In terms of growth performance and feed efficiency, all groups were similar. Pigs fed the 20 and 40% sweet potato had significantly lower dressing percentage than those fed the maize meal. Carcass length, fat thickness or lean meat contents and meat quality were similar for all pigs. Sensory evaluation did not reveal any differences between the groups fed sweet potato and the control diets. Sweet potato chip appeared to slow down the growth and rearing performances but did not impact upon carcass composition. The researchers concluded that feeding sweet potato up to 40% to heavy pigs as an alternative to maize meal positively impacted carcass traits and meat quality.

Ruminant and Chicken Feed In an older study, Szylit et al. (1978) examined the use of raw and steam-pelleted sweet potato as a starch source for ruminant and chicken diets both in vitro and in vivo. Sun-dried sweet potato chunks were ground or steam-pelleted. The chicken‘s diets contained 16 and 4% crude protein and crude fiber, respectively. The diets were isoenergetic and synthetic lysine and methionine were added. The diets were fed ad libitum to the chickens. The findings indicated that in the in vitro study, the sweet potato starches were well broken down and were good sources of energy for rumen microbial growth. In vivo, they were completely digested by growing chickens. In terms of the steam-pelleting, it increased starch availability and enhanced urea utilization by rumen microflora. It also improved nitrogen retention and feed efficiency of chicken diets. Sweet potato could be appropriate for chicken feeding and for improving ruminant urea utilization.

Sweet Potato Peels Rabbit Feed Akinmutimi and Osuagwu (2008) examined the performance of weaner rabbits fed graded levels of sweet potato peel meal in place of a maize-based diet. Five to seven-week-

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old Weaner rabbits (N = 24) of equal live weight were randomly allocated to four dietary treatments. The control diet (diet 1) was maize-based while the experimental diets contained varying amounts of maize meal and sweet potato peels (11.1, 22.2 and 33.3% in diets 2, 3 and 4, respectively). Each diet was offered ad libitum for 56 days. Diet 2 had the highest weight gain of 10.4 versus 8.8, 9.5 and 8.3 for diets 1, 3 and 4, respectively, and the least feed conversion ratio. Diet 2 also had the highest values for the prime meat parts (thigh, drumstick, shoulder, breast cut and back cut) and hematological and serum chemistry values fell within the normal range for rabbits. When compared to the control diet, diet 2 also had the highest value for gross margin. The authors recommended diet 2 on the basis of growth performance, carcass characteristics, organ weights, hematological and biochemical values. In another experiment, Akinmutimi and Anakebe (2008) investigated the performance of 20 weaner rabbits fed graded levels of yam and sweet potato peel meal in place of a maizebased diet. The rabbits were randomly allocated to five dietary treatment groups. The control diet (diet I) was maize-based. The test ingredients replaced maize at 20, 30, 40 and 50 % in diets 2, 3, 4 and 5, respectively. The yam and sweet potato peel meals were combined in ratio 3:2. Each diet was offered ad libitum for 56 days. There was no significant difference (P>0.05) for all the growth parameters considered except for feed intake. The values for feed intake increased significantly (P<0.05) as the quantity of the test ingredients increased. The feed conversion ratio value was highest for diet 4. Carcass characteristics values showed significant difference for percentage dressed weight and drumstick. The percentage dressed weight for all the treatment groups fell within the normal range of dressing percentage for rabbits. The drumstick value was highest for diet 4. The organ weights showed no significant difference among treatment groups except for the heart, values of which did not follow any specific pattern that could be attributed to the effect of the test ingredients. Biochemical values showed no significant difference except for the value of total protein; this and other biochemical parameters (total protein, urea, creatinine and alkaline phosphatase) fall within the normal range of biochemical indices for rabbits. Gross margin value was highest in diet 4. The researchers recommended diet 4 based on the growth performance, carcass characteristics, organ weights, biochemical indices and economics of the diet.

CONCLUSION AND RECOMMENDATIONS The biochemical, nutritional, bioactive and functional properties of the sweet potato make it a potentially good candidate for reducing the global food insecurity, vitamin A deficiency and improving nutritional status worldwide especially in developing countries. Increased consumption of orange-fleshed sweet potato could be a feasible food-based strategy for controlling vitamin A deficiency in children in developing countries. Several studies have shown that the sweet potato has the capability to lower blood glucose level and improve glucose tolerance. White-skinned sweet potatoes are useful in preventing and improving diabetic symptoms and could be a beneficial non-pharmacologic therapy for T2D. Also, several sweet potato varieties have been shown to have antioxidative, radical scavenging and antimutagenic properties; they have also been associated with reduced liver injury and blood pressure lowering activity. Juice from purple-fleshed sweet potato has been shown to effectively lower blood pressure in humans.

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The stems and leaves of the sweet potato contain potentially bioactive phytochemicals such as chlorogenic acids, which have been shown to improve glucose tolerance in humans. They also contain high amounts of polyphenolics, which are protective against diseases linked to oxidation such as cancer, hepatotoxicity, allergies, aging, human immunodeficiency virus and cardiovascular disease. Sweet potato is an important starch-producing crop, which has developed into a profitable industry in China for starch industries or for animal feed. Over the past decade, there has been a sharp growth in the noodle industry in China and the sweet potato starch is used mainly in the production of these. The sweet potato starch also has other industrial applications in China such as: in the production of sweeteners, citric acid, beverage, industrial alcohol, ethanol fuel and derived products as maltose. Emerging applications for sweet potato starch-derived products include: renewable energy source, alcohol production, drug delivery application, as a biomass crop, surfactants and builders, sequestering agents and bleaching boosters. Sweet potato is utilized as a source of animal feed in many parts of the world and much research is being conducted to confirm its usefulness as such. In animal feed systems, SPL can be used fresh, dried or as silage as a protein source for growing pigs. SPL and water spinach appear to have the same nutritive values for growing pigs. Sweet potato forage in combination with batiki grass could provide an inexpensive source of nitrogen in the diets of growing goats. Sweet potato up to 40% could serve as an alternative to maize meal for heavy pigs. Sweet potato could be appropriate for chicken feed and for improving ruminant urea utilization. Expanded use of sweet potato as animal feed appears to be a promising prospect for both agro-biological and socio-economic reasons. Efforts are being made towards industrial utilization and development of new sweet potato value-added products and animal feed systems. Increasing amounts of sweet potato are being processed into industrial starch, alcohol, noodles and other products, especially in China. Hopefully, as the rising demand for meat and milk continue and the search for natural, functional foods, non-pharmacological medicines and inexpensive animal feeds continue to increase, the sweet potato will become a useful component in human health, industry and animal feed systems.

Recommendations Although sweet potato has been a staple in animal feed systems, their use in the production of nutritionally balanced, manufactured, feed concentrates has not progressed as expected. Therefore, there is need for the development of feeding systems that exploit potentially useful non-grain food resources such as sweet potato, for the formulation of such feed concentrates. Strategies to promote affordable commercialization of these feed concentrates need to be put into place. There is need to expand starch production from the sweet potato in view of its potential as a biomass crop and its renewable energy capability. Plant breeders should consider researching new varieties to improve starch properties and nutritional content in the sweet potato. Protein deficiency in sweet potato roots is one of the key constraints to its utilization in animal feed systems, therefore greater research efforts are needed to improve its efficiency. Overall, there is need for international, large scale, multidisciplinary research to examine and improve every aspect, which could enhance sweet potato utilization in human health, industry and animal feed systems.

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Workshop held in Chengdu, Sichuan, PR China, November 7-8, 2001. Bogor, Indonesia: International Potato Center (CIP). Purseglove, J.W. (1991). Tropical crops. Dicotyledons. Longman Scientific and Technical. John Wiley and Sons, Inc. NY. USA. Ramirez, G.P. (2008). Cultivation, harvesting and storage of sweet potato products. http://www.fao.org (accessed 9/05.08). Richter, L.J., Thanavala Y., Arntzen C.J. and Mason HS. (2000). Production of hepatitis B surface antigen in transgenic plants for oral immunization. Nat. Biotechnol. 18:11411142. Ruiz, M.E., Pezo, D. and Martinez, L. (1980). The use of sweet potato (Ipomoea batatas L.] Lam.) in animal feeding. 1 Agronomic aspects. Trop. Anim. Prod. 5: 144-151. Sawer, W. (2001). The rocky road from roots to rice: a review of the changing food and nutrition situation in Papua New Guinea. PNG Med. J. 44:151-163. Schweigert, F. J., Klingner, J., Hurtienne, A.and Zunft, H. J. (2003). Vitamin A, carotenoid and vitamin E plasma concentrations in children from Laos in relation to sex and growth failure. Nutr J 2:17(doi:10.1186/1475-2891-2-17) (available from http://www.nutritionj. com/content/2/1/17). Sotaniemi, E.A., Haapakoski, E. and Rautio, A. (1995). Ginseng therapy in non-insulindependent diabetic patients. Diabetes Care 18:1373-1375. Stephenson, L. S., Latham, M. C. and Ottesen, E. A. (2000). Global malnutrition. Parasitology 121 (Suppl.):S5-22. Stumvoll, M., Goldstein, B.J. and Van Haeften, T W. (2005). Type 2 diabetes: principles of pathogenesis and therapy. Lancet 365:1333–1346. Suda, I., Ishikawa, F., Hatakeyama, M., Miyawaki, M., Kudo, T., Hirano, K. and Ito, A. (2008). Intake of purple sweet potato beverage affects on serum hepatic biomarker levels of healthy adult men with borderline hepatitis. Eur. J. Clin. Nutr. 62:60-67. Suda, I., Yamakawa, O., Matsugano, K., Sugita, K., Takuma, Y., Irisa, K.and Tokumaru, F. (1998). Changes of serum λ-GTP, GOT and GPT levels in hepatic function-weakling subject by ingestion of high anthocyanin sweetpotato juice. Nippon Shokuhin Kagaku Kogaku Kaishi 45:611-617 (in Japanese). Suda, I., Furuta, S., Nishiba, Y., Matsugano, K. and Sugita, K. (1997). Reduction of liver injury induced by carbon tetrachloride in rats administered purple-colored sweet potato juice. Nippon Shokuhin Kagaku Kogaku Kaishi 44:315-318 (in Japanese). Szylit, O., Durand, M., Borgida, L.P., Atinkpahoun, H., Pireto, F. and Delort-Laval, J. (1978). Raw and steam-pelleted cassava, sweet potato and yam Cayenensis as starch sources for ruminant and chicken diets. Animal Feed Sci. Technol. 3:73-87. Tsuneki, H., Ishizuka, M., Terasawa, M., Wu, J-B, Sasaoka, T. and Kimura, I. (2004). Effect of green tea on blood glucose levels and serum proteomic patterns in diabetic (db/db) mice and on glucose metabolism in healthy humans. BMC Pharmacol. 4: 18. Ty, C., Borin, K.and Phiny, C. (2007). A note on the effect of fresh mulberry leaves, fresh sweet potato vine or a mixture of both foliages on intake, digestibility and N retention of growing pigs given a basal diet of broken rice. Livestock Res. Rural Develop. 19: Underwood, B.A. and Arthur, P. (1996). The contribution of vitamin A to public health. Faseb J 10:1040-1048. van Hall, M. (2000). Quality of sweet potato flour during processing and storage. Food Rev. Int. 16(1): 1-37.

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van Jaarsveld, P.J., Faber, M., Tanumihardjo, S.A., Nestel, P., Lombard, C.J. and Benadé, K. (2005). β-Carotene-rich orange-fleshed sweet potato improves the vitamin A status of primary school children assessed with the modified-relative-dose-response test. Am. J. Clin. Nutr. 81:1080-1087. Vinnings, G. (2003). Select markets for taro, sweet potato and yam. A report for the Rural Industries Research and Development Corporation. RIRDC Publication No. 03/052. RIRDC Project No UCQ-13A. ISBN 0642 586195; ISSN 1440-6845, Kingston, ACT. Vuksan, V., Stavro, M.P. Sievenpiper, J.L., Beljan-Zdrakovic, U., Leiter, L.A., Josse, R.G. and Xu, Z. (2000). Similar postprandial glycemic reductions with escalation of dose and administration time of American ginseng in type 2 diabetes. Diabetes Care 23:12211226. Welsch, C.A., Lachance, P.A. and Wasserman, B.P. (1989). Dietary phenolic compounds: Inhibition of Na+ -dependent D-glucose uptake in rat intestinal brush border membrane vesicles. J. Nutr. 119:1698-1704. Wheatley, C.C., Lin, L., Sun, G. and Song, B. (1997). Improving small-scale sweet potato starch enterprises in Sichuan Province, China. Trop. Sci. 37:228-237. Wild, S., Roglic, G., Green, A., Sicree, R. and King, H. (2004). Global prevalence of diabetes. Estimates for the year 2000 and projections for 2030. Diabetes Care 27:10471053. Woolfe, J. A. (1992). Sweet potato: An Untapped Food Resource. Cambridge University Press, New York, NY.. Wu, X., Sun, C., Yang, L., Zeng, G., Liu, Z. and Li, Y. (2008). β-carotene content in sweet potato varieties from China and the effect of preparation on β-carotene retention in the Yanshu No. 5. Innov. Food Sci. Emerg. Technol. 9:581-586. Yach, D., Stuckler, D. and Brownell, KD. (2006). Epidemiologic and economic consequences of the global economics of obesity and diabetes. Nat. Med. 12:62-66. Yamaji, T., Mizoue, T., Tabata, S., Ogawa, S., Yamaguchi, K., Shimizu, E., Mineshita, M. and Kono, S. (2004). Coffee consumption and glucose tolerance status in middle-aged Japanese men. Diabetologia 47:2145-51. Yamakawa, O. and Yoshimoto, M. (2002). Sweet potato as food material with physiological functions. Acta Hort (ISHS) 583:179-185. Yeh, G.Y., Eisenberg, D.M., Kaptchuk, T.J. and Phillips, R.S. (2003). Systematic review of herbs and dietary supplements for glycemic control in diabetes. Diabetes Care 26:12771294. Yokio, H., Akio, S., Uchida, H., Hirose, J., Hayashi, S. and Takasaki, Y. (2001). Microbial hydrogen production from sweet potato starch residue. J. Biosci. Bioeng. 91:58-63. Yoshida, M. and Morimoto, H. (1955). Utilization of sweet potato starch by rats and its effect on the digestion of dietary protein. J. Nutr. 57:565-577. Yoshimoto, M., Okuno, S., Yoshinaga, M., Yamaguchi, M. and Yamada, J. (1999). Antimutagenicity of sweet potato (Ipomoea batatas) roots. Biosci. Biotechnol. Biochem. 63:537-541. Yu, B., Zhang, F., Zheng, Y. and Wang, P. (1996). Alcohol fermentation from the mash of dried sweet potato with its dregs using immobilized yeast. Process Biochem. 31:1-6. Zhang, Dapeng and Li Xiu-Qing. (2004). Sweet potato as animal feed: The perspective of crop improvement for nutrition quality. In: Fuglie, KO., Hermann, M. (eds.), Sweet potato Post-harvest Research and Development in China. Proceedings of an International

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Workshop, Chengdu, Sichuan, PR China, Nov. 7-8, 2001. Bogor, Indonesia: International Potato Center (CIP). Zheng, W.and Clifford, M.N. (2008). Profiling the chlorogenic acids of sweet potato (Ipomoea batatas) from China. Food Chem. 106:147-152. Zaidul, I.S.M., Absar, N., Kim, S.-J., Suzuki, T., Karim, A.A., Yamauchi, H.and Noda, T. (2008). DSC study of mixtures of wheat flour and potato, sweetpotato, cassava and yam starches. J. Food Eng. 86:68-73. Zuohua, L., Zonghui, L., Jian, H., Feiyun, Y., Zhengze, Z. and Wen, L. (2001). Sweet potato roots silage for efficient feeding of weaner and finishing pigs in China. In: Sweet potato Post-Harvest Research and Development in China. Fuglie, KO, Hermann M. (eds). Proceedings of an International Workshop held in Chengdu, Sichuan, PR China, Nov. 78, 2001. Bogor, Indonesia: International Potato Center (CIP).

In: Sweet Potato: Post Harvest Aspects in Food Editors: R. C. Ray and K. I. Tomlins

ISBN 978-1-60876-343-6 © 2010 Nova Science Publishers, Inc.

Chapter 8

SWEET POTATO IN ANIMAL NUTRITION Ibisime Etela Department of Animal Science and Fisheries, University of Port Harcourt, East-West Road, Choba, PMB 5323, Port Harcourt, Nigeria

ABSTRACT Sweet potato (Ipomoea batatas (L.) Lam.) is a perennial food crop for humans who consume the tuberous roots and tender leaves as green vegetables as dictated by the socio-cultural setting. Besides being a good food source of energy for humans, it is also suitable as animal feed in parts of Africa, Asia, and Latin America, where it has been able to adapt to the environmental conditions. Current world land area, root yield, and quantity produced are 8,996,472 ha, 13,728.69 kg/ha, and 123,509,771 tonnes compared to a meagre 3,154,247 ha, 4,090.86 kg/ha, and 12,903,597 tonnes for Africa, and the 5,465,917 ha, 19,634.35 kg/ha, and 107,319,707 tonnes for Asia, respectively. As feed, the root and vine could be consumed fresh, dried, or in the ensiled form by livestock depending on prevailing weather conditions and resources available to the farmer(s). Feeding strategies range from its being used as sole diet, partial substitute for other feed ingredients or as supplement to low quality dry-season grass or roughage. Although the utilization of the crop in chicken, cattle, goat, pig, and sheep seems, relatively documented, its use in feeding animals such as rabbits, other species of poultry, and micro-livestock such as grasscutter, snail, and so on still call for research attention. For example, the forage contains crude protein (CP) of 112 to 221 g/kg dry matter (DM), neutral detergent fibre (NDF) of 336 to 506 g/kg DM, and metabolizable energy (ME) of 7.5 to 16.4 MJ/kg DM making it capable of contributing to adequate, sustainable and cost-effective animal nutrition.

ABBREVIATIONS BG CRM 

batiki grass; cassava root meal;

Tel: +234 703 437 8380; Fax:- NIL -; E-mail:[email protected]

Ibisime Etela

226 CP DBG DM ILRI MAP ME NDF NRCRI SPF SSA WAD WAP VITAA TIA

crude protein; dried brewers‘ grains; dry matter; International Livestock Research Institute; months after planting; metabolizable energy; neutral detergent fibre; National Root Crops Research Institute; sweet potato forage; Sub-Saharan Africa; West African Dwarf; weeks after planting; Vitamin A for Africa; trypsin inhibitor activity

INTRODUCTION Sweet potato (Ipomoea batatas) is believed to have been first domesticated about 5,000 years ago in the tropical parts of the Americas, they are now cultivated throughout tropical and warm temperate regions and grows best at an average temperature of 24 °C (75 °F). The crop is primarily, grown for human consumption of the starchy tuberous root, which is a staple food source of calories and is consumed by all age groups in most tropical countries. This is, especially, so in parts of West, Central and East Africa where the crop is widely cultivated (Low et al., 1997; Tewe et al., 2003). The crop is propagated either by stem (tips of vines) or root cuttings with the date of maturity varying between 2 and 9 (with an average of 4) months after planting (MAP) depending on the variety or cultivar. In most parts of the tropics, the crop can be maintained in the ground and harvested in piecemeal for home consumption or sold in the market. On the other hand, in the temperate regions it is often cultivated on larger farms and usually harvested before frosts set in. In many parts of SubSaharan Africa (SSA), the vines or forage of the crop has been, successfully, used as supplement for low quality grazing or cut-and-carry (zero-grazing) fodder such as dry-season grasses. Prominent amongst such dry-season grasses are Guinea grass or Green panic (Panicum maximum) and Napier grass (Pennisetum purpureum) that are, commonly, used by smallholder crop-livestock farmers for cows and calves. Elsewhere in Asia such as China and Vietnam, the root as well as the forage is utilized as feed for monogastrics in sweet potato-pig production systems, and in various forms for formulated chicken diets in Africa and other parts of the world. Besides the use of fresh sweet potato roots and vines for feeding farm animals, studies have also been conducted on the best options or strategies for preserving the feed resource under farming systems that do not support harvesting the forage at regular intervals for feeding animals as is obtainable under certain scenarios. According to Onwueme and Sinha (1991), sweet potato roots could be chopped and fed to livestock in the fresh form or as dried chips, while the shoots or tops (also referred to as vines) are fed fresh or as silage too. Among the common methods adopted by resource-poor farmers for the processing and preservation of animal feed resources are chopping of the roots

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and drying them as chips or of the forage then drying them as hay. The other method could be preservation as silage since the crop possesses qualities that favour this method more such as high water contents in the roots (30 to 60 %) and in the forage (80 to 87 %) that could make the process of ensiling less costly in terms of less energy cost. In a study to determine the optimum dietary levels for economic efficiency of sweet potato root and vine in both silage and dried forms for F1 crossbred fattening pigs it was observed that, there were no differences in terms of animal performance due to processing method while, the labor cost for processing was higher for the dried sweet potato meal than for the sweet potato silage (An et al., 2004; Giang et al., 2004a). This chapter shall deal with the utilization of sweet potato in animal nutrition because it is a crop which produces substantial quantities of crop residues that have potential good uses yet so untapped. Sweet potato processing by-products have been identified to be of high feed value that is similar in energy to corn or barley due to its high root starch content (Scott and Wheatley, 1997; Fuglie et al., 2006). Nevertheless, to date, only little has been reported on the use of the crop residues with regard to feed quality of the vines left in the field after root harvesting and the peelings left after post-harvest processing. Such information on sweet potato root and vine yield and quality is needed to develop strategies for optimizing its use to reduce energy and protein deficiencies in smallholder crop-livestock systems (Larbi et al., 2007). Furthermore, dual-purpose sweet potato cultivars (capable of producing high root and vine yields) have high potential to reduce food insecurity and improve nutrition in croplivestock systems in the developing world. Thus, if we assume that about 67 kg of fodder and 33 kg of waste are produced per 100 kg of tuberous root produced, it would be easier to appreciate the enormous feed resource from the crop that can contribute to mitigating feed scarcity under smallholder mixed sweet potato and livestock/poultry farming systems.

CROP YIELDS AND FORAGE QUALITY OF DUAL-PURPOSE SWEET POTATO VARIETIES The use of sweet potato as a feed resource has since been established with its successful utilization for feeding farm animals under certain livestock production systems around the world. For example, either the tuberous roots or the foliage or both have been commonly used for feeding non-ruminants and ruminants alike (Scott, 1992). Although the crop is primarily grown for human consumption (that is, the roots and young leaves used as vegetable), available literature suggests that the foliage as well as the tuberous roots (mostly stale and unmarketable roots) are also suitable as dry season supplements and feed resources for ruminant livestock (Hagenimana, 1999). Current sweet potato production statistics from selected countries of the world highlight the potentials of the crop to ensure the attainment of sustainable animal agriculture especially at the smallholder level (FAOSTAT, 2008). The current production statistics of sweet potato suggests that although it is considered to be a crop of greater importance in low-income or developing countries (such as in parts of Africa, Asia and Latin America), its significance in the food systems of developing countries cannot be ignored either. Asia alone accounts for 86.9 % of sweet potato production from approximately 60.76 % of the world‘s total land area cultivated to the crop (FAOSTAT, 2008). It is noteworthy to

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point out that although Africa accounts for about one-third or 35.06 % of the total world area used for sweet potato cultivation, the output from the continent represents only a meager, 10.45 % of the total world production. In addition, Africa gave the lowest average yield of 4,090.86 kg/ha (4.09 t/ha) root yield with a range of 3,099.94 kg/ha (3.10 t/ha) for Southern Africa to 28,411.64 kg/ha (28.41 t/ha) for Northern Africa. Thus, calling for more research to improve the yields per hectare of land committed to the crop through the breeding of varieties that will yield higher root yields. Such varieties should as well be able to produce high forage yields and sweet potato by-products that would eventually be utilized for feeding livestock without undue competition with humans for use as food (marketable roots). Ongoing global breeding programmes such as the Vitamin A for Africa (VITAA) initiative would be able to bridge these identified gaps if adequate attention is paid to the afore-mentioned shortfalls, especially, in their breeding programmes for β-carotene-rich sweet potato varieties. For example, the production statistics from Eastern and Western Africa suggest that such approach as being proposed above would have great nutritional, social, economic, and environmental impacts in the sub-regions. Highlights of some results from agronomic studies published in the literature indicate the potentials of the crop for both human food and animal feed security (Ramirez, 1992). Initial work on 18 newly developed sweet potato genotypes at the National Root Crops Research Institute (NRCRI) in Nigeria and the International Livestock Research Institute (ILRI-West Africa) also in Nigeria identified three genotypes (TIS-87/0087; TIS-8164; TIS2532.OP.1.13) as the most outstanding dual-purpose genotypes with respect to their recorded fodder and root yields and the corresponding degradation characteristics of their foliage (Larbi et al., 2007). Reported values ranged from 3.52 to 8.14 t/ha dry matter (DM) for fodder yields, 2.49 to 8.40 t/ha DM for root yields, 6.8 to 13.1 % for crude protein, 31.2 to 37.3 % for neutral detergent fibre, and 70.8 to 83.4 % for potential DM rumen degradation at 20 weeks after planting (WAP). However, Gomes and Carr (2001) indicated from their experiment that as the frequency of vine harvesting (defined as the number of harvesting) increased, the total fresh weight of vines increased with a corresponding reduction in storage roots yield and a remarkable stability in total biomass (vine plus storage root) yields. Such reductions in root yields resulting from frequent vines harvest appear to negate the proposal to feed fresh sweet potato vines to farm animals thus, necessitating studies on how to identify the appropriate vine harvesting frequency that will result to optimum vine and root harvests. Thus, An et al. (2003) studying the effect of harvesting interval and defoliation on yield and chemical composition in fifteen sweet potato varieties observed that harvesting frequency of the vines affected root production more than leaf and stem production with root yield decreasing with decreasing harvesting interval and increasing harvesting proportion of vines. The authors then concluded that leaf, stem and root DM yields varied greatly between varieties and planting season suggesting that different varieties should be recommended for different seasons. In another study to determine the effect of cutting management on yield and quality of sweet potato forage grown for dry-season feeding of sheep in Nigeria, it was observed that pruning at six weeks interval optimized the yield and quality of sweet potato forage fed to West African Dwarf (WAD) sheep compared to pruning at 4 or 8 weeks intervals and uncut plots (Olorunnisomo, 2007a). From the above studies, it is evident that to achieve optimum crop yields the farmer needs to identify the right sweet potato variety and adopt an appropriate forage harvesting frequency for feeding his animals to achieve acceptable productivity without unduly sacrificing tuber yields for forage harvesting. Several

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studies on sweet potato forage from different regions of the world on different animal species have reported different figures for chemical composition of the forage. All the values confirm its suitability for utilization by animals in most sweet potato-livestock/poultry production systems, especially, under smallholder or resource-poor crop and livestock farming systems. The mean figures for different results of chemical composition of sweet potato forage and roots by scientists from different economies and continents of the world are presented in Tables 1. Table 1. Chemical composition of sweet potato root from different workers Nutrient content

1

Proximate composition: Dry matter (g /kg) Ash (g /kg DM) Crude protein (g/ kg DM) Neutral detergent fibre (g/ kg DM) Acid detergent fibre (g /kg DM) Acid detergent lignin (g /kg DM) Crude fibre (g /kg DM) Ether extract Nonstructural carbohydrates (g /kg DM) Energy content: Gross energy (MJ/ kg) Metabolism energy (MJ/ kg) Amino acid profile (g/ 16g N): Arginine Cystine Glycine Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Threonine Tyrosine Valine Anti-nutritional factors: Trypsin inhibitory activity (mg trypsin/g) Phytate-phosphate (g /kg) Phytate-phosphorus (% of total P) Total oxalate (g /kg)

Ravindran and Sivekanesan (1996). Olorunnisomo (2007b). 3 Giang et al. (2004a, b). n.a. = (data) not available. 2

Date of harvest (days after planting) n.a.1 n.a.2 n.a.3 891 29 62 n.a. n.a. n.a. 26 19 864

938 40.6 49.5 92.4 40.0 3.8 32.6 11.5 867

191 16 40 139 n.a. n.a. 48 n.a. n.a.

16.99 n.a.

17.10 n.a.

n.a. 15.6

3.4 1.7 4.7 3.1 4.2 5.8 3.7 1.9 6.6 5.9 3.8 5.5

n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a.

n.a. n.a. n.a. n.a. n.a. n.a. 1.5 0.5 n.a. n.a. n.a. n.a.

19 0.64 36 0.67

n.a. n.a. n.a. n.a.

n.a. n.a. n.a. n.a.

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Figure 1 depicts some form of variation in crude protein and neutral detergent fibre contents of sweet potato forage, and the yields in forage and tuberous roots with varying dates at harvest as obtained from different studies.

Figure 1. Variations in crude protein and neutral detergent fibre contents of sweet potato forage (Figure 1a), and the yields in forage and tuberous roots (Figure 1b) with varying dates at harvest obtained from different studies.

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The figure indicates that the crop is a suitable feed resource for farm animals and the forage quality such as crude protein in the leaves or energy content in the tuberous roots differ depending on the variety as well as the agronomic practice adopted. Another advantage of the crop is the relatively high yield and fast rate of re-growth after pruning (between 3 and 12 weeks) compared to most multipurpose trees and shrubs or otherwise referred to as browse plants. Thus, differences in chemical composition as would be observed from various studies on the crop are mostly attributable to differences in varieties used, date of harvest or stage of growth, analytical procedures adopted, and models used for estimating such parameters as metabolisable energy since each model is based on varying assumptions.These differences also account, partly, for differences in animal performances as reported by several workers in the literature. The variations notwithstanding, sweet potato forage has been described as medium quality non-forage feed resource due to its medium protein (15-35 % CP) and is commonly fed to pigs, chickens, and ruminants for egg, milk and meat (Devendra and Sevilla, 2002; Dung et al., 2002). The following section highlights research so far conducted on specific animal species that signify the importance of sweetpotato crop as a feed resource for livestock and poultry, especially, under resource-poor mixed farming systems.

SWEET POTATO FOR FEEDING NON-RUMINANTS OR MONOGASTRICS Sweet potato root possesses the potential to offset any food/feed imbalance that could occur in future as more and more grains such as maize or corn are diverted for feeding the teaming human population and in the face of persistent poverty mostly in the developing world. Although the use of the root for feeding pigs (swine) is well developed in most parts of Asia, other parts of the developing world such as SSA are yet to fully integrate the crop into their crop and livestock production systems. To a greater extent, it appears that most farmers are unaware that the roots could be utilised as an ingredient for broiler chicken and rabbit feeds. An alleged major constraint to its use in this class of animals is said to be the trypsin inhibitor activity (TIA) with a range of between 2.2 and 5.2 mg trypsin inhibited per g sample, depending on the variety and processing method such as temperature (Panigrahi et al., 1996). A recent study on six sweet potato genotypes recorded mean TIA of 12.4 ± 1.23 U/mg (range: 3.9 to 21.8 U/mg) suggesting the need to select and utilize sweet potato genotypes with lower TIA for feeding farm animals (Zhang et al., 2002). The use of sweet potato in the diets of monogastrics in the past have, mostly, concentrated on its usage as an alternative energy source to the conventional use of maize or corn in mixed feeds. Its use this way will often require some form of processing such as drying that also has the advantage of minimizing any trace of TIA.

Sweet Potato for Broilers In Nigeria, sun-dried sweet potato roots have been successfully incorporated into the diets of chicks. In one of such studies when it replaced up to 344.3 g of maize per kg, it was observed that body weight, feed intake, feed conversion, nitrogen retention, mortality and

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relative weights of body parts at 10 weeks of age were not significantly affected compared to the conventional control diet (Job et al., 1979). Furthermore, their study revealed that crude protein contents of liver, gizzard, heart, lungs and breast were not significantly affected by the diets whereas, fat contents decreased following the replacement of 344.3 g of maize per kg with sun-dried sweet potato roots. From the above study, it was shown that sweet potato root was a satisfactory source of energy for chicks. Although the study did not consider the direct or indirect impacts of the reduced fat contents so recorded in the organs, it is very likely that the reported lower fat contents of the body organs might have some significance for human nutrition. Yet, a critical review of the literature suggests strongly that, researches on the utilization of sweet potato foliage, meal or root are very scanty in spite of it being considered a good source of protein that is mainly found in the leaves and other bioactive/nutritionally active pigments such as β-carotene for poultry. Also, the roots contain compounds that are considered to possess some detrimental anti-nutritional factors. However, studies have shown that the concentration of anti-nutritional factors is not so high that could cause any serious side-effect or hinder animal performance. For example, in one of the existing studies it was shown that the TIA and the contents of oxalate and phytate-phosphorus of sweet potato root were too low to be of any significant nutritional concern to broilers (Ravindran and Sivakanesan, 1996). Their study also indicated that sweet potato root meal can replace up to 400 g/kg or 40 % of maize (corn) in broiler diets without adverse effects on performance (Table 2). Table 2. Effects of feeding increasing quantities of sweet potato root meal from 1 to 21 day old broilers Animal performance Number of birds Weight gain/bird (g) Feed intake/bird (g) Feed conversion ratio Mortality Apparent nutrient digestibility coefficient: Dry matter Nitrogen retention Energy metabolism Relative organ weight (g/100 g bodyweight): Heart Liver Spleen Pancreas

Sweet potato root meal inclusion rate (g/kg) 0 200 400 600 40 40 40 40 527 525 519 486 949 977 971 880 1.80 1.86 1.87 1.81 2 2 1 1

S.E.M. n.a. 13.4 26.0 0.04 n.a.

0.73 0.58 0.79

0.74 0.56 0.76

0.73 0.59 0.78

0.71 0.56 0.76

0.03 0.02 0.03

0.68 3.16 0.16 0.36

0.69 3.19 0.18 0.38

0.65 3.16 0.16 0.39

0.71 3.26 0.18 0.38

0.03 0.11 0.01 0.03

Source: Ravindran and Sivakanesan (1996). SEM= Standard Error Means. n.a. = (data) not available.

However, Teguia et al. (1997) did not record positive results from their experiment when sweet potato leaf meal replaced 200 or 300 g of maize per kg in the control finishing broiler diets because, it resulted to depressed body weight gain and increased feed conversion ratio. But in another study to compare the nutritional value of sweet potato vine meal with that of

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Lucerne meal replaced at different levels in starter diets for broiler chickens it was observed that, growth rate and feed conversion ratio were not different from diets containing the Lucerne meal (Farrell et al., 2000). Maphosa et al. (2003) carried out a study on the use of raw sweet potato root meal as an ingredient in broiler diets and concluded that, it should not be added to broiler starter diets but could be used up to 50 % inclusion levels in finisher diets without affecting the performance of the birds. It is obvious from the foregoing that the severity of any negative impact on birds fed diets with sweet potato as a partial or entire source of energy would depend not only on the variety of sweet potato in consideration but also on the age of the birds and their innate ability to metabolize any ingested anti-nutritional factor from the sweet potato feed ingredient. Also, the fact that no serious mention has been made about the presence or effects of anti-nutritional factors in either sun-dried or oven-dried sweet potato root or vine seem to suggest that drying was a simple and effective method of curing sweet potato for use as feed resource for not only poultry but for non-ruminants as well. Ayuk (2004 a, b) demonstrated from two separate studies in Nigeria that sweet potato meal could replace maize at different inclusion rates where the 50 % inclusion rate recorded the highest dressing percentage of 88.40 % with giblet in finishing broilers while, in broiler starter rations replacing maize with sweet potato meal did not significantly decrease palatability and feed consumption.

Sweet Potato for Pigs In a study in Venezuela, González et al. (2002) observed that sweet potato root meal can provide 54 and 58 % of the diet during the growing and the finishing phases of pigs, respectively, making it possible to replace 75 % of the cereal components as illustrated on Table 3. González et al. (2003) evaluated voluntary feed intake of fresh foliage from sweet potato, animal performance, and carcass traits when growing-finishing pigs were fed graded levels of protein in Venezuela with the conclusion that it was possible to record high levels of performance in pigs fed ad libitum sweet potato foliage, provided they also received feed supplements containing 23.7 and 20.6 % protein during the growing and the finishing periods, respectively. Duyet et al. (2003) investigated the effects of varying dietary levels of fresh sweet potato leaves on the reproductive performance of sows (female adult pigs) in Vietnam and concluded that sweet potato leaves could be included up to 50 % in the diets of growing and pregnant gilts (a mature pig that has not given birth before) and up to 20 % during lactation. In the study, they also observed that daily intakes of the fresh sweet potato leaves ranged from 2.0 to 5.0 kg in the growing phase, 5.5 to 6.0 kg in gestation and 6.0 to 7.0 kg in lactation of the sows at the 50 % inclusion level. Chittavong and Preston (2006) investigated the intake and digestibility of fresh sweet potato leaves and fresh water spinach (Ipomoea aquatica) fed to growing pigs at different levels as supplements to a mixture of rice bran and cassava root meal (Table 4). The authors concluded from their study that, water spinach foliage appeared to be slightly inferior to the leaves of sweet potato as protein supplements for growing pigs fed a low-protein basal diet (50:50 mixture of cassava root meal and rice bran). Their conclusion that further studies be conducted to confirm their assertion is a pointer that there were many opportunities for the sweet potato crop although, at the moment the literature shows that there is paucity of information on the use of sweet potato forage as feed resource for animals especially for micro-livestocks.

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Table 3. Variation in dry matter intake (kg/day), daily weight gain (g/day), and feed conversion ratio by pigs fed diets with varying proportions of cereal substitution by sweet potato root meal Animal performance 0 Growing pig (35-60 kg): Dry matter intake (kg/day) Daily weight gain (g/day) Feed conversion ratio Finishing pig (60-90 kg): Dry matter intake (kg/day) Daily weight gain (g/day) Feed conversion ratio Growing-finishing pig (35-90 kg): Dry matter intake (kg/day) Daily weight gain (g/day) Feed conversion ratio

Cereal substitution by sweet potato root meal (%) 25 50 75 100 SEM

1.56 545 2.86

1.51 529 3.14

1.75 588 2.97

1.60 502 3.19

1.49 403 3.69

0.11 35 0.14

2.01 719 2.80

2.13 664 3.20

2.12 645 3.28

2.14 633 3.38

1.96 542 3.62

0.10 43 0.19

1.78 632 2.82

1.89 596 3.17

1.95 617 3.16

1.86 567 3.28

1.73 473 3.65

0.09 27 0.2

Source: González et al. (2002). SEM= Standard Error Mean.

Table 4. Mean values of feed and nutrient intake, apparent digestibility, and nitrogen retention by pigs fed a basal diet of rice bran (RB) and cassava root meal (CVRM) mixture supplemented with different levels of sweet potato leaves (SPL) and water spinach (WS) Animal performance

Average liveweight per pig (kg) Dry matter intake (g DM/day): Sweetpotato leaves Water spinach Mixture of RB and CVRM Total dry matter Nutrient intake (g/day): Organic matter Crude protein Crude fibre Apparent digestibility (g/kg): Dry matter Organic matter Crude protein Crude fibre Nitrogen (N) balance (g/day): Nitrogen retention As percent of N intake As percent of N digested

RB and CVRM + 100% SPL + 0% WS 13.3

RB and CVRM + 75% SPL + 25% WS 13.3

RB and CVRM + 50% SPL + 50% WS 13.3

270 0 270 540

197 65 262 524

136 136 273 545

n.a. n.a. n.a. 22.8

462 74 65

439 68 62

460 71 66

20.7 4.74 1.87

757 775 530 698

718 731 488 726

747 762 508 693

20.1 20.5 35.3 32.2

5.62 47.7 67.3

4.52 43.5 56.6

4.31 38.3 52.4

0.63 4.25 4.13

Source: Chittavong and Preston (2006). n.a = (data) not available. SEM= Standard Error Means.

S.E.M. -

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In another study conducted in Cambodia to determine the effect of fresh sweet potato vine and fresh mulberry leaves, given separately or mixed together on voluntary intake, digestibility and nitrogen retention of growing pigs with a basal diet of broken rice it was observed that, the pigs showed preference for sweet potato vine (Chhay et al., 2007). For example, it was observed that intakes of foliage dry matter were higher when the sweet potato vines formed 100 % of the foliage supplement (247 g DM/day) compared to mulberry leaf meal alone (191 g DM/day) or both sweet potato and mulberry were mixed as supplements (154 g DM/day). An et al. (2004) investigated ileal and total tract digestibility in growing pigs fed cassava root meal (CRM) based diets with inclusion of fresh, dried and ensiled sweet potato leaves (excluding stems) and reported that, ileal digestibility of neutral detergent fibre and total tract digestibility of crude fibre were lower for diet CRM and casein than for diets with sweet potato leaves inclusion either as fresh, dried or ensiled that appeared similar in organic matter, crude protein, neutral detergent fibre and acid detergent fibre digestibility (Table 5). Table 5. Amino acid composition (g/16g N), ileal and total tract digestibilities of fresh, dried and ensiled sweet potato leaves harvested at 60 days after planting and later at 20 days intervals and sun-cured sweet potato vine meal Sweet potato leaves1

Quality indicator

1

Essential amino acids: Arginine Histidine Isoleucine Leucine Lysine Methionine Cystine Phenylalanine Threonine Tyrosine Valine Non-essential amino acids: Alanine Aspartic acid Glutamic acid Glycine Proline Serine Ileal digestibility: Crude protein Neutral detergent fibre Total tract digestibility: Crude protein Crude fibre Neutral detergent fibre Acid detergent fibre

An et al. (2004). Farrell et al. (2000). n.a = (data) not available. 2

Sweet potato vines

Fresh

Dried

Ensiled

Sun-cured2

5.22 2.24 3.73 8.58 4.48 1.49 3.36 7.09 5.22 4.10 5.60

5.20 1.99 4.18 8.83 4.14 1.56 3.20 6.88 5.23 3.95 5.74

4.98 1.85 3.57 9.03 3.92 1.23 2.33 7.14 5.15 3.74 5.42

7.45 2.6 5.7 10.8 6.2 2.6 2.1 6.9 5.6 n.a. 7.2

5.22 10.45 11.57 4.10 3.73 4.10

5.39 11.02 9.87 3.52 3.40 4.06

5.02 11.23 10.00 2.73 3.39 4.71

7.8 18.7 15.7 7.2 5.5 5.6

0.74 0.23

0.74 0.24

0.74 0.25

n.a. n.a.

0.76 0.61 0.57 0.36

0.75 0.61 0.55 0.32

0.77 0.62 0.56 0.36

n.a. n.a. n.a. n.a.

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The authors, thus, concluded that sweet potato leaves have the potential to improve dietary protein and amino acids supply in low fibre diets for pigs and could be utilized either in the fresh, dried or ensiled state depending on the prevailing climatic conditions since their general nutritional properties were almost similar. A similar study to evaluate ensiled sweet potato leaves as protein supplement showed that sweet potato leaves can replace fishmeal and groundnut cake in traditional Vietnamese diets for growing pigs (An et al., 2005). In another study, sweet potato root and vine were ensiled together at different proportions without any additive to ensure its preservation for several months and to determine its suitability as fattening pig feed since sweet potato vine was said to be expensive to purchase during the off-season (Giang et al., 2004b). Giang et al. (2004b) then concluded from their study that, all the five mixtures of sweet potato root and sweet potato vine (namely: 70:30 %, 60:40 %, 50:50 %, 40:60 %, and 30:70 %, respectively), on dry matter basis, were successfully ensiled resulting in good quality products that could be stored for, at least, three months. They also noted that the actual ratios of sweet potato root and vine in the silage, under practical conditions, would depend on the ratios produced at harvest that does not place restrictions on its usability by the resource-poor farmer who will be at liberty to work within a flexible framework by using available resources. The indication from the above scenarios is that, there are no serious restrictions as to the feeding method or state for sweet potato vines, leaves or tubers on animal performance resulting from the state in which the crop was fed rather, it is to be determined based on the convenience of the farmer. Sweet potato as pig feed has been discussed in more details by Die Peters in chapter 9 of this book.

SWEET POTATO FOR FEEDING RUMINANTS Sweet Potato for Goats In recent times, some studies have demonstrated that sweet potato foliage could support growth in goats when fed as supplement to low quality grass as a potential source of cheap nitrogen in the diets of growing goats. Aregheore (2004) fed eight growing female crosses of Anglo-Nubian x Fiji local goats between 8 and 9 months old in Samoa of South Pacific with four freshly chopped and thoroughly mixed batiki grass (BG): sweet potato forage (SPF) diets defined as: T1 (100BG:0SPF); T2 (50BG:50SPF); T3 (25BG:75SPF), and T4 (0BG:100SPF) per cent proportions by weight and recorded the following performance parameters as depicted in Table 6. Lam and Ledin (2004) set up an experiment to evaluate the possibility of replacing Sesbania grandiflora foliage (a browse plant) with fresh sweet potato vines in the diets of growing goats and observed that replacement of Sesbania foliage with 50 % fresh sweet potato vines, on a dry matter basis, resulted in acceptable live weight gains of 60.6 g/day, compared to the 64.0 g/day when Sesbania foliage versus 44.0 g/day when sweet potato vines were sole-fed. In their study, however, it was noted that the advantage of sweet potato over Sesbania was the relatively low yield and slow rate of re-growth after pruning of the latter. In a recent study to determine chemical composition, rumen DM degradation and animal performance of selected tropical wastes in Uganda it was observed that, season had

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significant effect on chemical composition with sweet potato vines harvested during the wet season recording significantly higher crude protein, neutral detergent fibre, and acid detergent fibre contents (Katongole et al., 2008). Table 6. Performance by growing goats fed two combinations of batiki grass and sweet potato forage Animal performance

T1 (100:0)

T2 (50:50)

T3 (25:75)

T4 (0:100)

S.E.M.

Dry matter intake (g DM d-1): Batiki grass Sweetpotato forage Total

851 n.a. 851

425 634 1,059

271 753 1,024

n.a. 858 858

0.25 0.92 0.94

Apparent nutrient digestibility coefficient (g d-1): Dry matter Organic matter Crude protein Neutral detergent fibre Daily liveweight gain

47.3 48.6 38.2 42.8 36

76.6 68.2 76.6 51.1 71

72.4 64.9 73.1 55.8 82

69.7 62.2 62.9 60.6 61

11.25 7.45 15.01 6.57 0.17

Source: Aregheore (2004). SEM= Standard Error Means. n.a = (data) not available.

It was also shown from their study that sweet potato vine wastes were sufficient to provide the crude protein and metabolisable energy required by growing goats under tropical conditions and thus serving as potential cheap feeds, especially, after wilting for better dry matter intake, compared to fresh vines. However, the study could not determine the age at harvest of the vines because they were simply gathered from three markets in the urban area thus it is assumed that the vines were obtained after harvesting roots for sale in the local market which usually takes four to five months, depending on the variety.

Sweet Potato for Sheep In a related study with sheep it was shown that mixing sweet potato forage and root in equal proportions (on dry matter basis) improved nutrient utilization, reduced cost per live weight gain, and maximized economic returns from sweet potato cultivation for sheep (Olorunnisomo, 2007b). Kariuki et al. (1998) working in Kenya fed sole diets of fresh sweet potato vines to Merino sheep and recorded an apparent dry matter digestibility of 501 g/ kg DM. There are also reports of higher dry matter digestibility in animals fed sweet potato foliage from other studies. In addition, efforts are being made at both national and international levels to evaluate forage quality from new varieties of the crop that have been bred for higher tuberous root yields to make them more suitable in sweet potato-livestock farming systems (Etela et al., 1998; Larbi et al., 2007).

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Sweet Potato for Cattle Backer et al. (1980) working with crossbred Brahman bulls in Costa Rica concluded that feeding 12 % of sweet potato roots had no commercial value when fed with the rest diet made of the forage and that it could result to a profit of 38 %. Such a profit margin, no doubt, would be an economic advantage for the small livestock producer. In an earlier study, the success of frequently harvesting sweet potato forage served as unconventional protein source for feeding Zebu and crossbred bulls for fattening over 127 days giving daily live weight gains of 0.68 kg/day (680 g/day), fresh forage intake of 10.58 kg/day, and dry matter intake of 1.45 kg/day (Ffoulkes and Preston, 1977). In a related study it was indicated that sweet potato foliage could be used as nutritious dietary supplement to improve the diets of cattle (Ffoulkes et al., 1978). Other studies have shown that the foliage could also be used as starter feed and partial milk replacer for calves (Orodho et al., 1996). Kariuki et al. (1998) working in Kenya fed sole diets of fresh sweet potato vines to dairy heifers and concluded that sweet potato vines contained nutrient levels that would sustain acceptable growth in heifers and thus possessing the potential to improve cattle production as indicated in Table 7 (Kariuki et al., 1998). Table 7. Performance by pigs, goats, heifers and cows either sole-fed sweet potato vines or as supplement to a basal diet, and rumen degradability characteristics Animal performance Nutrient intake: Dry matter intake (kg/d) Dry matter intake (g/kg0.75/d) Dry matter intake (g/kg0.734/d) Organic matter intake (kg/d) Crude protein intake (kg/d) Neutral detergent fibre intake (kg/d) Metabolisable energy intake (MJ/day) Calcium intake (kg/d) Phosphorus intake (kg/d)

Date of harvest (days after planting) and [source]* 841 n.a.2 1123 n.a.4 4.2 89 n.a. 3.6 0.57 2.1 n.a. 0.021 0.012

n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a.

7.4-8.1 n.a. 131-152 n.a. n.a. n.a. n.a. n.a. n.a.

0.556 71.2 n.a. n.a. 0.060 n.a 4.9 n.a n.a

Nutrient digestibility: Dry matter digestibility Organic matter digestibility Crude protein digestibility Ether extract digestibility Neutral detergent fibre digestibility Acid detergent fibre digestibility Hemicellulose digestibility Cellulose digestibility N-retention (g/day) Average daily gain (g/d)

n.a. n.a. n.a. n.a. n.a n.a n.a. n.a. n.a. 500

n.a. 0.82 0.70 0.77 0.71 0.69 0.92 0.87 n.a. n.a.

n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a.

0.68 0.71 0.66 n.a n.a n.a n.a n.a 0.35 n.a.

Daily milk yield (mL/d): Initial Final Changes in yield

n..a n.a. n.a.

n.a. n.a. n.a.

1,150-1,528 1,209-1,561 -69 to 59

n.a n.a n.a

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239

Date of harvest (days after planting) and [source]* 841 n.a.2 1123 n.a.4

Milk composition (g/100 g): Total solids Ash Protein Fat Lactose

n.a. n.a. n.a. n.a. n.a

n.a. n.a. n.a. n.a. n.a.

12.93-13.28 0.76-0.79 3.73-3.91 3.94-4.08 4.19-4.81

n.a n.a n.a n.a n.a

Rumen degradability characteristics (g/kg DM): Soluble fraction Slowly degradable fraction Degradation rate Potential degradability Effective degradability

276 494 0.05 770 587

n.a. n.a. n.a. n.a. n.a.

133-146 693-752 0.0358-0.0379 837-885 515-548

374 483 0.039 857 694

Kariuki et al. (1998). Dung et al. (2002). 3 Etela et al. (2008a). 4 Katongole et al. (2008). n.a = (data) not available. 2

Figure 2. Trends in daily milk yields by White Fulani cows fed sole sweet potato foliage from three varieties and Guinea grass (Etela et al., 2008a).

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In a recent study by Etela et al. (2008a, b) on White Fulani (Bunaji) cows in early lactation and sole-fed fresh forage from three sweet potato cultivars in Nigeria, it was demonstrated that the cows on sweet potato forage performed relatively better than those on dry-season Guinea grass or Green panic (Panicum maximum) alone in terms of voluntary dry matter intake, changes in milk yields, and rumen degradability characteristics (Table 7). The recorded trend in daily milk yields over the 21-day study revealed that it declined steadily for the dry-season Guinea grass fodder sole-fed cows, while there were generally slight improvements for the cows on sweet potato forage alone (Figure 2). In a similar study, it was demonstrated that Panicum fodder showed improvements in rumen dry matter degradation characteristics following sweetpotato forage supplementation (Etela et al., 2008c). The study also showed that the calves responded differently to the forage supplements from the three different sweet potato varieties in terms of daily live weight gains. Other recent studies observed that the use of sweet potato forage as supplement to dry season Guinea grass in preference for either dried brewers‘ grains (DBG) and/or cottonseed meal (CSM) could serve as sustainable cost-effective measures that incur less environmental costs, and relatively higher efficiency of metabolisable energy utilization for milk production but with slight reductions in milk yields that might be recorded (Etela et al, 2008d).

CONCLUSION This chapter reveals that sweet potato is a crop with high potentials with evidence of its suitability as animal feed for sustainable animal nutrition, especially, under smallholder sweet potato-animal production farming systems. However, the literature shows that this potential of the crop is only minimally being exploited thus making it difficult to derive the inherent full benefits. In Asia where the crop appears to be well-integrated into the pig-sweet potato farming systems, its use under farming systems dominated by other animal species of farm animals such as poultry and ruminant appears not so developed. In Africa, the literature shows that a few works have been done on the utilization of sweet potato in ruminants (cattle; goats; sheep), poultry (mostly in chicken), with very limited studies on pigs. One notable aspect is the unavailability or near absence of relevant literature on its use in rabbit and other micro-livestock and where available they might not be accessible for international readership. Overall, the scope for sweet potato utilization in animal nutrition is limitless both in macro- and micro-livestock species. The paucity of information on sweet potato-animal based farming systems is, partly, due to fewer of such practices well-documented and partly due to the outright neglect of the crop in this regard. Such a practice is experienced in many sweet potato-based research institutes where the crop is being bred for various improved agronomic traits without much interest on the foliage as animal feed in terms of biomass yields (foliage plus tuberous roots) and other quality traits relevant to animal nutrition.

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Etela, I., Larbi, A., Adekunle, I.O., Ikhatua, U.J. and Bamikole, M.A. (2008b). Supplementing Guinea grass with fresh sweet potato foliage for milk production by Bunaji and N‘Dama cows in early lactation. Livestock Science., in press. Etela, I., Larbi, A., Bamikole, M.A., Ikhatua, U.J. and Oji, U.I. (2008c). Rumen degradation characteristics of sweet potato foliage and performance by local and crossbred calves fed milk and foliage from three cultivars. Livestock Science, 115: 20-27. Etela, I. Oji, U.I., Kalio, G.A. and Tona, G.A. (2008 d). Studies on sweet potato forage and dried brewers‘ grains as supplements to green panic for Bunaji cows. Tropical Grasslands, in press. Etela, I., Oji, U.I., and Larbi, A. (1998). In-situ rumen degradation characteristics of wholeplant tops and components of sweet potato (Ipomoea batatas, Lam) cultivars at different maturity stages. In: O.O. Oduguwa, A.O. Fanimo, and O.A. Osinowo (Eds.), Animal Agriculture in West Africa: The Sustainability Question. Proceedings of the Silver Jubilee Anniversary of the Nigerian Society for Animal Production (NSAP)/Inaugural West African Society for Animal Production (WASAP) Conference, March 21-26, 1998, Abeokuta, Ogun State, Nigeria. 650 p. FAOSTAT. (2008). ProdSTAT: Crops, Food and Agriculture Organisation Statistics Division. http://faostat.fao.org/site/567/DesktopDefault.aspx, Retrieved April 12, 2008. FAO (Food and Agriculture Organisation of the United Nations), Rome, Italy. Farrell, D.J., Jibril, H., Perez-Maldonado, R.A. and Mannion, P.F. (2000). A note on a comparison of the feeding value of sweet potato vines and lucerne meal for broiler chickens. Animal Feed Science and Technology, 85: 145-150. Ffoulkes, D., Deb Hovell, F.D. and Preston, T.R. (1978). Sweet potato forage as cattle feed: voluntary intake and digestibility of mixtures sweet potato forage and sugarcane. Tropical Animal Production, 3: 140-144. Ffoulkes, D. and Preston, T.R. (1977). Cassava and sweet potato forage as combined sources of protein and roughage in molasses based diets: effect of supplementation with soybean meal. Tropical Animal Production, 3: 186-192. Fuglie, K.O., Oates, C.G., and Xie, J. (2006). Root Crops, Starch and Agro-Industrialization in Asia. International Potato Centre (CIP), Lima, Peru, 20 p. Giang, H.H., Le Viet, Ly and Ogle, B. (2004a). Digestibility of dried and ensiled sweet potato roots and vines and their effect on the performance and economic efficiency of F1 crossbred fattening pigs. Livestock Research for Rural Development. Volume 16, Art. #50. Retrieved April 7, 2008, from http://www.cipav.org.co/lrrd/lrrd16/7/gian16050.htm. Giang, H.H., Le Viet, Ly and Ogle, B. (2004b). Evaluation of ensiling methods to preserve sweet potato roots and vines as pig feed. Livestock Research for Rural Development. Volume 16, Art. #45. Retrieved April 7, 2008, from http://www.cipav.org.co/lrrd/lrrd16/7 /gian16045.htm. Gomes, F. and Carr, M.K.V. (2001). Effects of water availability and vine harvesting frequency on the productivity of sweet potato in southern Mozambique. I. Storage root and vine yields. Experimental Agriculture, 37: 523-537. González, C., Díaz, I., León, M., Vecchionacce, H., Blanco, A. and Ly, J. (2002). Growth performance and carcass traits in pigs fed sweet potato (Ipomoea batatas [Lam.] L) root meal; Livestock Research for Rural Development (14) 6. Retrieved April 7, 2008, from http://www.cipav.org.co/lrrd/lrrd14/6/gonz146.htm.

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González, C., Díaz, I., Vecchionacce, H. and Ly, J. (2003). Performance traits of pigs fed sweet potato (Ipomoea batatas L.) foliage ad libitum and graded levels of protein. Livestock Research for Rural Development 15 (9). Retrieved April 7, 2008, from http://www.cipav.org.co/lrrd/lrrd15/9/gonz159.htm. Hagenimana, V. (1999). Micro-scale enterprise approach to sweetpotato and potato improvement systems. In: Joseph, K, editor. Enhancing Postharvest Technology Generation Tropical Animal Health and Production and Dissemination in Africa. Mexico City: Sasakawa Africa Association, 1999; 79 pp. Job, T.A., Oluyemi, J.A. and Entonu, S. (1979). Replacing maize with sweet potato in diets for chicks. British Poultry Science, 20: 515-518. Kariuki, J.N., Gachuiri, C.K., Gitau, G.K., Tamminga, S., van Bruchem, J., Muia, J.M.K. and Irungu, K.R.G. (1998). Effect of feeding napier grass, Lucerne and sweet potato vines as sole diets to dairy heifers on nutrient intake, weight gain and rumen degradation. Livestock Production Science, 55: 13–20. Katongole, C.B., Bareeba, F.B., Sabiiti, E.N. and Ledin, I. (2008). Nutritional characterization of some tropical urban market crop wastes. Animal Feed Science and Technology, 142, 275-291. Lam, V. and Ledin, I. (2004). Effect of feeding different proportions of sweet potato vines (Ipomoea batatas L. (Lam.)) and Sesbania grandiflora foliage in the diet on feed intake and growth of goats. Livestock Research for Rural Development. Volume 16, Art. #77. Retrieved April 7, 2008, from http://www.cipav.org.co/lrrd/lrrd16/10/lam16077.htm. Larbi, A., Etela, I., Nwokocha, H.N., Oji, U.I., Anyanwu, N.J., Gbaraneh, L.D., Anioke, S.C., Balogun, R.O. and Muhammad, I.R. (2007). Fodder and tuber yields, and fodder quality of sweet potato cultivars at different maturity stages in the West African humid forest and savanna zones. Animal Feed Science and Technology, 135: 126-128. Low, J., Kinyae, P., Gichuki, S., Oyunga, M.A., Hagenimana, V., and Kabira, J. (1997). Combating Vitamin A Deficiency through the Use of Sweetpotato. Results from Phase I of an action research project in South Nyanza, Kenya. International Potato Center, Lima, Peru. Maphosa, T., Gunduza, K.T., Kusina, J. and Mutungamiri, A. (2003). Evaluation of sweet potato tuber (Ipomea batatas l.) as a feed ingredient in broiler chicken diets; Livestock Research for Rural Development (15) 1. Retrieved April 2, 2008, from http://www.cipav.org.co/lrrd/lrrd15/1/maph151.htm. Olorunnisomo, O.A. (2007a). Yield and quality of sweet potato forage pruned at different intervals for West African dwarf sheep. Livestock Research for Rural Development. Volume 19, Article #36. Retrieved May 18, 2008, from http://www.cipav.org.co/lrrd/lrrd19/3/olor19036.htm. Olorunnisomo, O.A. (2007b). A cost-benefit analysis of sweet potato production for sheep feeding in the southwest of Nigeria. Livestock Research for Rural Development. Volume 19, Article #80. Retrieved April 6, 2008, from http://www.cipav.org.co/lrrd/ lrrd19/6/olor19080.htm. Onwueme, I.C., and Sinha, T.D. (1991). Field Crop Production in Tropical Africa: Principles and Practices. The Netherlands, CTA (Technical Centre for Agricultural and Rural Cooperation), 480 pp. Orodho, A.B., Alela, B.O., and Wanambacha, J.W. (1996). Use of sweet potato [Ipomoea batatas (I.) Lam.] vines as starter feed and partial milk replacer for calves. In: J.

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Ndikumana, and P. de Leeuw. (1996) Sustainable Feed Production and Utilization of Smallholder Livestock Enterprises in Sub-Saharan Africa. Proceedings of the Second African Feed Resources Network (AFRNET), Harare, Zimbabwe, 6–10 December 1993. AFRNET (African Feed Resources Network), Nairobi, Kenya, 201 pp (147-150). Panigrahi, S., Oguntona, E.B. and Roberts, B.R. (1996). Effects of oven-drying tubers of two high-protein sweet potato varieties at different temperatures on their feeding value in broilers. British Poultry Science, 37: 173-188. Ramirez, G.P. (1992). Cultivation, harvesting and storage of sweet potato products. In: Roots, Tubers, Plantains and Bananas in Animal Feeding, Animal Production and Health Paper, FAO, Rome 95: 203-215. Ravindran, V. and Sivakanesan, R. (1996). Replacement of maize with sweet potato (Ipomoea batatas L.) tuber meal in broiler diets. British Poultry Science, 37: 95-103. Scott, G.J. (1992). Sweet potatoes as animal feed in developing countries: present patterns and future prospects. In: Roots, Tubers, Plantains and Bananas in Animal Feeding, Animal Production and Health Paper, FAO, Rome 95: 183-199. Scott, G.J., and Wheatley, C. (1997). Recent Advances in CIP’s Strategy for Collaborative Postharvest Research on Sweetpotato. International Potato Centre Program Report, 19951996, p. 264-269. Teguia, A., Njwe, R.M. and Foyette, C.N. (1997). Effects of replacement of maize with dried leaves of sweet potato (Hypomoea batatas) and perennial peanuts (Arachis glabarata Benth) on the growth performance of finishing broilers. Animal Feed Science and Technology, 66: 283-287. Tewe, O.O., Ojeniyi, F.E., and Abu, O.A. (2003). Sweet potato Production, Utilization, and Marketing in Nigeria, Social Sciences Department, International Potato center (CIP), Lima, Peru. Zhang, Z., Wheatley, C.C. and Corke, H. (2002). Biochemical changes during storage of sweet potato roots differing in dry matter content. Postharvest Biology and Technology, 24: 317-325.

In: Sweet Potato: Post Harvest Aspects in Food Editors: R. C. Ray and K. I. Tomlins

ISBN 978-1-60876-343-6 © 2010 Nova Science Publishers, Inc.

Chapter 9

SWEET POTATO AND PIGS: TRADITIONAL RELATIONSHIPS, CURRENT PRACTICES AND FUTURE PROSPECTS Dai Peters 1724 Maywood Dr., W. Lafayette, IN 406, USA

ABSTRACT Chinese farmers use the greatest volume of sweet potato as pig feed, Vietnamese farmers allocate the greatest proportion of sweet potato production for pig feed, Papuan farmers depend the most on sweet potato as pig feed, and Soroti farmers are the best representatives of this system in Africa. These four cases constitute the most significant examples of feeding sweet potato as pig feed, though such a practice is widespread throughout the world. Though these four systems share the same characteristics of feeding sweet potato to pigs, the agronomic, ecological, marketing, and even sociocultural contexts vary greatly resulting in distinctly different production and marketing systems. A comprehensive assessment of the production and marketing system of each case was thus essential before technological research could be designed or launched to improve the system. Where substantial volume of sweet potato is available and widespread backyard supplemental feed manufacturing is mushrooming, as in China, the logical method for improving the system is to devise technology to make sweet potatobased pellet feed, or to balance the sweet potato-based diet with specific commercial supplements. Where sweet potato is harvested in various seasons a year and other supplemental farm crops are available, the logical methods for improvement are to select clones that are suitable for the different seasons and examine ways of combining different crops in different seasons through processing. In the unique situation of Papua, Indonesia (and Papua New Guinea) where pigs and sweet potato are completely integrated into the lives of humans, it is essential to approach the subject in a holistic manner, taking into consideration the socio-cultural contexts and implications. This review of the assessment and enhancement of these four cases serves as examples of approaches to improving traditional livestock systems. 

E- mail: [email protected]

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ABBREVIATIONS ACIAR ACMD CIP DWG DMY NPN SAAS TIA

Australian Council for International Agricultural Research; African Cassava Mosaic Disease; International Potato Centre; daily weight gain; dry matter yield; non-protein nitrogen; Siachun Academy of Animal Sciences; trypsin inhibitor activity;

INTRODUCTION Even though pig production in the developed countries is based on balanced commercial feed, most small pig producers in the developing world are constrained by the cost of feed imports or shortage of such feed. Sweet potato, along with other crop feedstuff, has been fed as an alternative feed to large-scale and feed-based livestock production as a source of energy while the leaves are a source of protein, and both can be used in fresh and dried form or fermented into silage (Woolfe, 1992). Accounting for 85% of sweet potato production in the world, China‘s sweet potato consumption has declined over the years as living standards have increased. Huang et al. (2003) estimate that 40% of total sweet potato output in China went to animal feed in the mid 1990s, with regional utilization varying from 60% in Sichuan Province to 30% in Shandong Province. Sweet potato is also substantially linked to pig production in north and central Vietnam. In fact, since sweet potato can not compete with cassava as a raw material for starch processing, about 70-80% of roots are fed to pigs, either directly by the producers or indirectly by the root buyers. In addition to China and Vietnam, sweet potato-pig systems used to play an important role in the rural economy of many parts of Asia, including the Philippines, Korea, and Taiwan, and continue to be important in some areas of Indonesia (Bali and Papua) and Papua New Guinea. These systems are also practiced, to a lesser extent, in Latin America and Africa (Scott, 1991). Uganda is the largest sweet potato producer in Africa and sweet potato plays an important role in providing food security to many areas of Uganda where it is cultivated (Bashaasha et al., 1995). This role has become more prominent in areas where cassava, the second most important crop next to banana, has been destroyed by serious epidemics of African Cassava Mosaic Disease (ACMD) which have caused severe food shortages and hardship in Uganda during post-ACMD years (Otim-Nape et al., 1995). Sweet potato-pig systems are particularly well developed on the island of New Guinea where sweet potato roots and vines account for most of the pig feed. Pigs supplement this by foraging, apparently obtaining additional protein from consumption of soil fauna, particularly earthworms (Peters, 2001). Although sweet potato - pig farmers complain about the low profitability of raising pigs, the practice serves three important functions: (1) it generates one of the few sources of cash income for many rural households,

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(2) it provides manure for maintaining and improving soil fertility, and (3) it allows pigs to convert low-value sweet potato into highly desired meat and/or highly marketable commodities. Moreover, pigs of the Papuan farmers enjoy a protected and almost revered status because of their socio-economic importance (Peters, 2001). Pigs are equated with wealth and social importance, and constitute the most important living creature besides people. This chapter reviews the characteristics of systems which use sweet potato as pig feed, and the approaches to improving these systems, in four areas: (1) (2) (3) (4)

Sichuan, China, Northern and central Vietnam, Papua, Indonesia, and Soroti, Uganda.

Most of the review is based on the author‘s research on assessment and interventions between 1996 and 2003 in all four sites. The sweet potato-pig production assessment in Sichuan Province was conducted in 1996 and 1999. The same production assessment in Vietnam was conducted in various provinces between 1997 and 2000, including a large survey in seven provinces in 1998 with a sample size of 160 households. The Vietnam pig marketing survey was conducted in 1999 in 13 provinces, comprising 1,140 samples and nine different survey instruments for nine categories of respondents. The study of human-sweet potato-pig systems in Papua was carried out during three seasons in 2001 and 2002. The review of the role of sweet potato as pig feed in Soroti in Uganda was part of an assessment on the overall sweet potato post-harvest strategies for this area that was conducted in 1997. The intervention research, including sweet potato selection trials, sweet potato root and vine processing technologies, pig feeding trials, and husbandry management trials, followed the site assessments in an attempt to improve these systems in Vietnam and Papua. In China only a few trials were conducted. All trials were conducted on farms in collaboration with local farmers.

ASSESSMENT OF CURRENT SWEET POTATO-PIG FEED SYSTEMS Sichuan, China, northern and central Vietnam, Papua, Indonesia, and Soroti, Uganda were selected for study and this review because of their unique characteristics of sweet potato-pig production. Sichuan, with a population of 84 million, is the most densely populated province of China, and had a pig population of 65 million in 2000. One of the reasons for the immense pig production is attributed to the 3.76 million tons of sweet potato production of low cash value, 60-70% of which is thus fed to pigs (Zou, 2002). The magnitude of the sweet potato and pig production and their interaction makes Sichuan an important example of sweet potato-pig systems. Farmers in northern and central Vietnam plant two or three seasons of sweet potato in a year, usually as a stop-gap between rice crops. These are usually short-season crops, as short as 75 days, but up to 120 days during the winter, with an average of 90 days. The winter

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season constitutes the major crop which produces the majority of the roots for the year. The other seasons are often too short to produce significant roots so the vines are the main harvest. The high market value and demand for sweet potato vines, sold mainly as pig feed, is very unique to northern and central Vietnam. Papua does not have a large human or pig population but pigs and sweet potato, nonetheless, account for the majority of the household economy and activities. Although the sweet potato and pig production in Papua do not occupy a significant position on the world scale, the inseparable human-sweet potato-pig relationship in Papua represents a unique agrosocio-cultural system that warrants documentation and improvement. Papuan farmers are now going through the transition from subsistence pig-raising for self-consumption, social exchange and ceremonial uses to commercial production. Sweet potato originated in South America and was later carried to Asia where it became a major food and feed crop among poor farmers. Fewer examples of such systems can be found in Africa where pigs and sweet potato do not occupy the same prominent roles as in the Asian rural livelihoods. The Soroti area of Uganda, however, is a case from Africa demonstrating that such practices are not confined to Asia and that this system also has the potential to contribute to, and improve, rural livelihoods in Africa. The use of sweet potato as pig feed in these four sites shares some common characteristics as well as diverse qualities due to the different agricultural-economic-cultural contexts. The shared and the distinctive characteristics of these four systems summarize the overall framework of the sweet potato-pig feeding system among poor farmers around the world. Specific characteristics of these four systems are described below.

SHARED CHARACTERISTICS OF THE SYSTEMS The distinctive sweet potato-pig feed systems practiced around the world share the following characteristics (Table 1).

1. Sweetpotato Roots and Vines as a Major Feed Component Generally roots are fed as an energy source and vines as a protein source. The quantities fed, though, vary greatly depending on the following considerations: •

• • •

farmers‘ preferences—Papuan farmers tend to feed large quantities of roots throughout a pig‘s lifespan while Chinese farmers prefer to feed large quantities only to fattening pigs, sweet potato availability—due to high production, Chinese farmers have more sweet potato available for pig feed than in Vietnam or Uganda where production is lower, alternative feeds—in mountainous zones of Vietnam where cassava roots are available as feed; sweet potato vines are fed as a supplement to cassava roots, and post- harvest processing option—in Uganda and Papua vines are not dried and stored, thus only fed during the harvest season; unlike their Chinese and Vietnamese counterparts who either dry or store vines for prolonged feeding periods.

Table 1. The shared and distinctive characteristics of sweet potato (SP)-pig systems in Sichuan, China, northern and central Vietnam, Papua, Indonesia, and Soroti, Uganda Characteristics of SP-pig systems SP roots and vines as a major feed component

Supplemented with other farm crops, or forages Limited commercial supplements Low Crude Protein (CP) diet Unbalanced feeding rations

Poor management of the environment Lack of effective disease control

Sichuan, China

Northern and central Vietnam

Papua, Indonesia

Soroti, Uganda

Feed large quantity of roots for finishing pigs before the pigs are sold Vines are mostly dried and fed throughout the year Supplemented with maize, rice and wheat bran, and commercial feed Commercial feed is common but most farmers not certain of its utility Only 5% lower than the standard pig diet due to high maize and bran in diet Unbalanced feeding rations, but better than Vietnam and Papua, and always cooked twice a day

Roots often supplemented with cassava roots Vines are usually not processed and large quantity fed to pigs after harvest Supplemented with cassava, rice, rice bran, and a little commercial feed On the long coast, small, unmarketable fish and shrimp heads are often fed to pigs Moderate shortage of CP as diet is supplemented by cassava and bran

Feed large quantity of roots throughout pigs‘ life span Vines are harvested each day and fed to pigs fresh daily

Feed sufficient quantity while roots are available, but often uncooked Vines are fed only during harvest. Brew residues, fish bones, grass, mango, papaya, and rooting for worms No supplements have been observed or recorded

Due to lack of storage solutions, often feed large quantity of roots and vines at harvest time

No feeding regime, feed sporadically, sometimes raw and other times cooked, and only SP

Pig pens are often dirty with poor hygiene and temperature fluctuation Little report of loss to disease and illness

Pig pens are often dirty and poorly managed

Pigs roam free in day time and penned in at night

Disease is a problem particularly in the uplands, resulting in reluctance to invest in pigs

Heavy parasite load seriously impedes growth and no disease control measures

Supplemented by foraging grasses and rooting for worms No supplements have been observed or recorded Severe shortage of CP due to few protein sources

Severe shortage of CP, as even vines are not fed regularly No feeding regime, feed sporadically, often feed raw, even when cooked, usually not cooked long enough to boil Tethered to open latrines and exposed to human feces and worms Worms and diseases seldom treated, and no disease control measures

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2. Supplemented by Other Farm Crops or Foraging Maize is an important supplement, along with rice and wheat bran, in China due to high production and low price; whereas the combination of cassava and rice bran mixture is most commonly fed as supplement in Vietnam. In Uganda and Papua, pigs root for worms and forage grasses while tethered or roaming free.

3. Limited Commercial Supplements Feeding sweet potato as pig feed is commonly practiced by poor farmers who have little or no access to commercial supplements. Such supplements have become more available in China, but the quality varies so greatly that with little enforced regulation, farmers are highly suspicious of their efficacy. Along the long eastern seaboard of Vietnam, farmers sometimes have access to unmarketable fish and shrimp scraps as protein supplement.

4. Low Crude Protein Diet Protein supplements are rarely observed. In China, commercial protein supplements have become widespread, but the farmers in remote counties of Sichuan were generally uncertain of their utility or usage, or could not afford to invest in these commercial products. On the coast of Vietnam, it is not uncommon for farmers to add some unmarketable small fish or shrimp to the basic farm-crop diet, but this is done sporadically and seasonally. In Papua and Uganda, the pigs supplement their sweet potato-centered diet with the worms that they root while roaming around the forest, or simply tethered in the field. Otherwise, protein supplements are generally absent from these systems. One good source of protein is the sweet potato leaves, which contain 18-22% crude protein.

5. Unbalanced Feeding Rations In addition to the absence of protein supplements, unbalanced nutrition is further aggravated by the following additional factors: • •

sporadic daily feeding schedules—many farmers, especially in Uganda and Papua, do not follow a daily feeding schedule and feed sporadically, and nutritionally-unbalanced feeding practices—balanced daily feed formulation is absent and farmers generally feed whatever is available, and commonly feed excessive amounts of sweet potato roots or vines at the time of harvest due to lack of means or technology for storage or processing.

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6. Poor Management of the Environment Whether the pigs are confined in pens as in China and Vietnam, tethered as in Uganda, or confined only at night as in Papua, pig health and growth is often adversely affected by conditions of poor sanitation and hygiene.

7. Lack of Effective Disease Control There are varying degrees of disease control in these traditional systems, but in general illness poses a serious threat to investments in pig husbandry. The fear of pig mortality often results in farmers who are unwilling to invest in pig-raising. The farmers feel more exposed to risk if the pigs require cash investment when they suspect that pigs may die from diseases such as pig cholera in Vietnam, excessive parasite burden in Papua, and alleged African swine fever in Uganda.

Distinctive Characteristics of Each System Despite the premise of many shared characteristics, each sweet potato-pig feed system has its unique features derived from the distinctive socio-cultural-ecological context within which it exists. Sichuan, China Yilong County of Sichuan Province alone produces 400,000 tons of fresh sweet potato a year and each household in Yilong, on average, harvests 1.5 tons of sweet potato a year. Due to lack of processing technologies in 1997, 75% of the sweet potato roots were fed to pigs. Since sweet potato is harvested with the onset of winter, the roots are stored for about six months either in pits underground or in hillside caves with very little reported loss. This allows the farmers to allocate them as feed in rational portions. Eighty-three percent of the sweet potato vines are fed to pigs, which are chopped and dried, then stored for times when farmers are too busy to prepare fresh vegetables and grass for the pigs. Silage is not common in Yilong and only a few households engaged in this practice. On average there is only sufficient vine production for approximately four and a half months of pig feeding per year. Pigs are always fed twice daily and Sichuan farmers like to increase the percentage of sweet potato roots as pigs become larger. During the growing period, sweet potato provides 28% of the total feed, green forage 65%, and maize 2% of the total feed. Finishing pigs are fed 49% sweet potato, 42% green forage, and 5% maize (Zou, 2002). Rice and wheat bran produced on-farm are commonly fed to supplement the diet. According to farmers, the increased sweetpotato consumption during finishing gives the meat a sweet flavour. Two systems of pig feeding were observed (Table 2); the most common is the traditionalfeeding system which uses no commercial feed, additives, or protein supplements. All feed sources in this system are mixed and cooked before feeding to pigs. The second type is the mixed-feeding system which combines some commercial protein supplement for piglets with other on-farm available feed sources. This system is not as commonly observed, as it requires cash inputs. On average, the traditional system takes 12 months to raise pigs to approximately

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95 kg, while it takes 10.6 months for the mixed system to raise pigs to 88 kg. The traditional households raise pigs mainly for home consumption while the mixed-feeding households are more commercially oriented and raise pigs for cash income. Table 2. Various characteristics of two pig-raising systems in Sichuan, China: Traditional and mixed-feeding Number (no.) Type of household (hh) Traditional Mixed-feed

# hh 17 10

# Pigs/ hh 3.1 4.8

# Months to finish 12 10.6

Final destination of pigs: for sale in market or consumed at home (per hh) Final Wt Pig sales % Sold (kg) (yuan) pigs/ hh 95 847 59 88 2,040 100

In both systems pigs are raised in pens with gaps between wooden slats to allow manure to fall into a pit below. This manure is mixed with human faeces and urine that are also deposited directly into the same pit. This mixture is used as liquid fertilizer, without composting with any other organic material, for soil fertility maintenance. The cleanliness and management of the environment is uneven, but there is surprisingly little reported loss to diseases and illnesses.

Northern and Central Vietnam Vietnam produces 1.6 – 1.7 million tons of sweet potato roots a year nationwide (General Statistics Office, 2003), as compared to 0.4 million tons from a single county (Yilong, described above) in China. In northern and central Vietnam, 70-80% of sweet potato roots are fed to pigs while only small percentages are consumed at home or sold in the market (Table 3). The situation is quite different in the south where sweet potato is a cash crop rather than a staple crop. Thus, the sweet potato-pig feed system is only practiced in the northern and central provinces of Vietnam, and while farmers using this system traditionally raise two to five pigs per cycle with an average daily weight gain (DWG) of 288 g, the farmers of Dong Nai Province in the south raise 25 pigs per cycle with a nearly doubled DWG (Table 4). The difference between the growth efficiency is largely attributed to the feed. In northern and central Vietnam, sweet potato roots and vines, along with cassava, maize, and rice bran constitute the major part of the diet, which is supplemented by various green forages. The season affects the variation in the amount of sweet potato fed to pigs. Sweet potato is cultivated up to three seasons a year (mainly two) in northern and central Vietnam; its availability is thus scattered in short spurts after each harvest because traditionally there is no means of storing either roots or vines in this sub-tropical climate. Thus, farmers feel obliged to feed large amounts to pigs within a short period after harvest to avoid loss. Most pigs are kept in pens with concrete floors covered with straw during the winter. These pens often have a dunging area for the pigs and manure is collected behind the pens in a pit, composted with other organic material and applied to crops as green manure. A small proportion of pigs are raised on dirt floors, usually covered in soggy straw. Diseases are

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commonly observed and reported in Vietnam, particularly in the upland areas. Diseases are serious enough to deter much cash investment for fear of financial loss due to mortality. Table 3. Sweet potato (SP) production and utilization in seven provinces in northern, central and southern Vietnam (n=160 households (hh) per site)

Location

Ton/hh

Southern Dong Nai Vinh Long Northern & Central Quang Nam Thanh Hoa Ha Bac Hoa Binh* Vinh Phu

Production % hh not planting SP

Fed to pigs

Sweet potato Utilization (%) Sold in Home Processing market consumption starch

0 11.8

100 0

0 0

0 100

0 0

0 0

0.83 1.21 1.15 0 0.80

0 0 0 100 0

87.8 87.3 70.0 0 67.1

0 0 25.0 0 23.3

12.2 12.7 5.1 0 9.7

0 0 0 0 0

*Hoa Binh is an upland province that produces cassava as pig feed.

Table 4. General characteristics of household pig production in seven provinces in northern, central and southern Vietnam (n=160 households per site) Location

Households without pigs (%)

No. pigs per cycle

Initial weight Final weight Months per (kg) (kg) cycle

DWG (g)

2.5

24.9

15.0

83.8

4.4

522

6.54

22

100

7.0

374

Southern VN Dong Nai Vinh Long

72.5

a

Northern-Central VN Quang Nam

0

2.06

5.83

54.8

8

204

Thanh Hoa

0

1.99

12.8

69.9

6.0

319

Ha Bac

0

2.6

14.0

80.6

5.8

383

Hoa Binh

0

4.86

9.5

62.0

7.4

236

Vinh Phu

0

2.52

10.3

52.5

4.7

298

Average

0

2.81

10.5

64.0

6.4

288

a

Vinh Long is a major sweetpotato (SP) producing province and 100% of SP is sold in the fresh market; hence no SP is available for pig feed and therefore there are few pigs. DWG: Daily Weight Gain.

Papua, Indonesia Pigs are regarded as gold among the Dani people in the Baliem Valley in Papua. Women choose husbands based on how many pigs the men own, and a man with large numbers of pigs traditionally has multiple wives. In turn, each wife‘s status in the family is determined by

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her ability to multiply the pigs, and by association, her ability to cultivate sweet potato with which to feed the pigs. Having a few large pigs is more desirable than many little ones because the small pigs may die or be stolen, and they may not grow. Large pigs, on the other hand, generally do not die, cannot be stolen, and have already grown. Having a number of large pigs ensures the person‘s position in the community; it is like wearing lots of gold around one‘s neck, wrists, and fingers. While pigs are gold, sweet potato is the currency used to obtain the gold. Usually each family can have up to 15 or more sweet potato plots in varying stages of cultivation: some have just been planted, some a couple of months, some almost ready to harvest, some being harvested, and some sitting fallow. Each plot contains a mixture of short- and long-season varieties; thus, each plot may also be in varying stages of harvest, ranging from six to nine months on average, but some fields can take up to a year and a half to complete the harvest. The sweet potato-pig system has a high labor cost, especially for women who spend nearly half of the daily working hours tending to sweetpotato and pigs (Table 5). This is both because of the number and distance of the fields from home and the extensive work required for preparing and maintaining the fields. Table 5. The allocation of time for men, women, boys, and girls in Papua, based on three seasons of data recorded by farmers on the time spent on each activity daily (hr/day)

Time spent on resting Time spent on working of which, time spent on SP work of which, time spent on raising pigs

Men 15 8 3.1 0.5

Women 14 10 4.3 1.1

Boys 15 8 0.8 0.1

Girls 14 9 1.1 0.2

Average 14 9 2.3 0.5

Rest includes: sleeping, eating, bathing, relaxing, religious activities, and social interactions. Work includes: studying, cooking, Sweet potato (SP) field work, rice field work, gathering firewood, caring for pigs and other livestock, caring for children, and other miscellaneous work (e.g., construction, fishing, fetching water).

Table 6. Sweet potato root and vine consumption by humans and pigs in each housing compound, Baliem Valley, Papua, Indonesia (kg/compound/day)

a

Roots for humansa Vines for humansa Roots for pigsb Vines for pigsb

December 2001 8.9 5.1 10.4 6.9

June 2002 8.5 5.6 9.9 5.3

December 2002 8.0 3.4 9.9 4.2

The average number of people recorded sharing these roots and vines includes 1.7 adult men, 1.6 adult women, 2.0 boys, and 2.1 girls, or an average of 5.2 people/compound. b On average, 2.5 sows, 2.0 male pigs (mainly castrated), and 6.3 piglets per compound were fed these amounts of sweetpotato.

Humans and pigs both consume an unusually large quantity of sweet potato roots and vines as the staple of the diet (Table 6). Though the common belief is that sweet potato roots for food and feed are distinguished by variety; in practice it is the quality of the roots that

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distinguishes the use. The nice big roots, regardless of variety, are reserved for humans while the inferior and undesirable-looking roots, again regardless of variety, are relegated to pigs. Generally, the women harvest nice roots from the new gardens for human consumption while looking for feed among the second generation roots from the old garden, or even the gardens that have gone into fallow. The women rotate among the new gardens each day to harvest roots for human food, while digging in the old gardens for feed. Due to the competition between food and feed, the farmers can only afford to feed sweet potato roots and vines to pigs once a day. The pigs are thus set out each morning to roam in the fields or forests in order to root for worms and forage for grasses to supplement the insufficient feed. For the pigs, foraging results in excessive exercise, exposure to disease, and beatings by neighbors when they get into the sweetpotato gardens. Moreover, roots are cooked for pigs only once or twice a week when the farmers do baker batu, using hot stones to cook a large amount of roots sufficient for both humans and pigs. The rest of the week pigs are fed raw sweet potato roots, which contain trypsin inhibitor, and have a low protein and mineral content. Consequently pigs take three to five years to reach 70-80 kg from birth, if indeed they do not get stolen or die from diseases first. Premature deaths are common since parasites are rampant in the absence of the lack of separation between human feces and pigs. Although Dani farmers know almost every aspect of sweet potato cultivation, they lack basic knowledge of pig husbandry and disease control. When the highly-valued pigs are struck by illness, Dani farmers routinely pray, conduct rituals, or apply traditional healing methods on the pigs, but seldom consult veterinarians.

Soroti, Uganda Soroti is one of the major sweet potato-producing areas of Uganda, which is the largest producer in Africa, where the average household planted half a hectare per year in 1997 (Table 7). The sweet potato planting areas in Soroti fluctuated with the availability of planting material, rain conditions, and labor availability. Though also marketed as a cash crop, fresh market prices from the previous year did not affect the decision on planting areas because sweet potato was primarily a food and feed crop, especially after the demise of cassava when it was destroyed by epidemics of ACMD, which has caused severe food shortages and hardships in Uganda. When moderate rains are available throughout the sweet potato season, the yields can reach 4.0 – 7.5 tons per hectare. Every three to four years, there would be one year of insufficient rains that caused the yield to drop to 1.5 - 2.5 tons per ha. Neither chemical nor organic fertilizer is applied to the field, and the productivity is maintained solely by the traditional fallow system. Until the alleged African Swine Fever devastated the pig population in this area in 199596, the percentage of households that raised pigs was much higher. By 1997, some 60-80 % of households had pigs, varying according to farmers‘ ability to restock the piglets. Pigs and sweet potato were perceived as ways to gain quick turnaround of cash while cattle and cassava were for the long haul. It was the favored livestock among young people who desired the quick cash. Nevertheless, on average each household could only afford to raise one or two pigs per cycle, and most households raised only one pig per cycle (Table 8). Though considered a profitable venture, many farmers hesitated to raise more because of insufficient sweet potato as feed during the dry season, difficulty in confining the pigs, fear of African Swine Fever, and lack of cash to buy piglets.

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Table 7. Characteristics of sweet potato production in three villages in Soroti, Uganda Village Dokolo Aukot Awoja

Planting area (ha/hh) 1996 1997 0.44 0.55 0.68 0.49 0.84 0.57

Yield (ton/ha) Enough rain Lack of rain 4.2 1.6 5.1 1.8 7.4 2.6

1997 Production (ton/hh) Enough rain Lack of rain 2.8 1.08 2.8 1.08 4.7 1.49

Table 8. Characteristics of pig raising in three villages in Soroti, Uganda Village

hh raising pigs (%)

# pigs/hh

1 pig/hh (%)

Dokolo Aukot Awoja

40 70 80

1.69 2.13 1.67

69 42 67

Growing period (# mo) 7.6 7.9 7.8

Beg..wt. (kg/pig)

End wt. (kg/pig)

Monthly wt gain (kg/mo)

3.1 3.4 4

29.7 19.9 23.9

3.45 2.11 2.7

hh: household; mo: months.

Pig growth was grossly under achieved and the pigs generally reached only 25-30 kg after seven to eight months of rearing. Feed, management, and disease all contributed to this slow growth rate. The pigs were fed twice a day mainly on sweet potato roots and vines, along with other locally available low-value feeds—brew residues, fish bones, grass, mango, and papaya. The roots were often fed uncooked while the vines were fed only during the harvest season as the farmers, unaware of the value of the vine as feed, discarded the vines in the fields as fertilizer upon harvest. The feed is both grossly deficient in crude protein and unbalanced as the feeding regime was at best sporadic. Tethered only loosely to a tree or a stump in the shade, the pigs supplemented their diet by grazing around the tethered area and rooting for worms most of the day. Often pigs were tethered next to open latrines and the exposure to human feces put pigs at risk for infection. Worms and other diseases went untreated most of the time. The negative effects of exposure to disease was verified by the small number of households that treated their pigs for worms, whose pigs, despite being fed the lowest amount of sweetpotato, achieved the highest growth rate.

Improvement of the Sweet Potato-Pig Systems As there are substantial differences among the four areas in their sweet potato-pig systems, the general approach to improvement includes situation analysis, participatory technology development, and scaling up, with an additional monitoring and evaluation component for impact assessment. The situation analysis required a systemic understanding of the human-sweet potato-pig system in Papua, but it required separate assessments of sweet potato production and pig production in China; an additional pig market chain assessment in Vietnam was necessary due to the importance and complexity of pig marketing. Based on the situation analysis, the participatory technology development designed for each of the sub-systems included improvements in sweet potato genetic selection, root and vine processing, and animal husbandry including feed, health, management, and fertility.

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Different technologies are relevant for the various sub-systems and their socio-culturalagronomic contexts. The following section reviews the participatory technology development efforts undertaken by the International Potato Centre (CIP), partly funded by the Australian Council for International Agricultural Research (ACIAR), to improve each of the sub-systems in northern and central Vietnam, and in Papua, Indonesia.

Sweetpotato Selection for Pig Feed Vietnamese farmers grow a range of sweet potato varieties, many of which come from China, and others of unknown origin, most of which have a low starch yield because the more popular varieties were selected for taste for humans and not for pig feed. Sweetpotato breeding and selection trials in Vietnam in earlier years produced two advanced clones (KB1 and K51) which have been widely adopted by farmers (Peters et al., 2005). Later trials on another six clones, from four seasons in 2001 and 2002 identified a promising clone that yields high total dry matter and starch content suitable for pig feed (Table 9). These selections emphasized the total dry matter yield (DMY) from both roots and vines and the total starch yield from the roots. Pigs do show a preference for the roots or vines of certain clones, but do not reject any of them. A conservative estimate of the number of local sweet potato cultivars in Papua puts the figure at well over 1,000, with the number in a single area or community ranging between 28 and 81 (Schneider et al., 1993). Papuan farmers generally maintain all the clones that have been informally introduced or crossed, in the absence of any systematic breeding or selection locally. Therefore the author‘s project undertook to conduct all sweet potato breeding activities on farms in various villages in the Baliem Valley. Trials were conducted in villages at different elevations since sweet potato cultivars are highly site-specific. The villages were Holima, Sinatma and Napua at elevations of 1700, 1850 and 2000m, respectively. Table 9. The total dry matter yield (DMY) of roots and vines and starch yield of roots of the various sweet potato clones included in varietal selection trials during three seasons in Vietnam from 2001 to 2003 (tons/ha) Variety

*

98-8-24 98-5-15 KL5 KL6 98-8-48 98-8-118 Control CV (%)

Winter 2001 DMY Starch yield 6.0 2.35 5.36 2.07 5.53 2.26 5.40 2.16 6.36 2.68 5.83 2.05 4.76 2.21

Spring 2002 DMY Starch yield 10.05 4.13 9.81 3.92 9.17 3.37 8.99 3.11 7.41 2.30 7.94 2.52 9.36 3.53

Winter 2002 DMY Starch yield 5.3 2.27 5.12 2.22 5.24 2.20 4.73 1.75 4.68 1.79 4.6 1.55 4.41 1.85

Spring 2003** DMY Starch yield 6.45 4.41 5.60 3.32 5.42 3.18 5.26 3.25 4.49 3.10 3.58 2.46 5.96 4.05

Average DMY* Starch yield* 6.95 a 3.29 a 6.47 ab 2.88 ab 6.34 ab 2.75 abc 6.10 ab 2.57 bc 5.74 b 2.47 bc 5.49 b 2.15 c 6.12 ab 2.91 ab 10.6 14.5

Letters to the right of the means indicate significant difference (P<0.05) across columns. **As peanut oil becomes more in demand, spring fields are now increasingly allocated to peanut production in the spring, hence reducing sweetpotato production.

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Table 10. Fresh yields and dry matter yields (DMY) from three on-farm selection trials in the Baliem Valley, Papua, Indonesia from December 2002-May 2003 (tons/ha) Variety / Clone BB 97256-9* BB 97258-2 BB 97083-4 BB 97089-12* MSU 99021-5 MSU 99051-1* Cangkuang* Siate* a Helaleke Lama b Mean Significance CV ( % ) LSD 0.05

Holima

Root Yield Sinatma Napua

Mean

Holima

DMY Sinatma Napua

Mean

30.48 20.84 23.46 27.15 16.04 22.48 27.77 26.39 15.91 23.39 ** 19.10 7.75

17.24 8.40 5.15 10.62 5.11 9.55 10.89 7.91 7.73 9.18 * 22.30 6.70

18.34* 13.48 13.18 15.67* 9.36 14.01* 17.06* 14.78* 10.84 14.08 -

10.63 6.62 6.49 10.05 4.08 7.90 10.30 9.34 5.28 7.85 ** 19.10 2.60

6.56 2.55 2.11 3.30 1.24 3.45 3.41 2.79 3.07 3.17 * 25.10 2.43

6.54* 3.95 4.07 5.47* 2.39 4.82* 5.80* 5.19* 3.75 4.66 -

7.29 11.20 10.93 9.24 6.93 10.00 12.53 10.04 8.89 9.67 NS 21.10 -

2.42 2.67 3.62 3.05 1.84 3.12 3.68 3.44 2.91 2.97 NS 21.50 3.00

NS, P>0.05; *, P<0.05; ** P<0.01. a Siate was from Napua and previously not planted in valley sites such as Holima; it was planted here not as a check clone, but as an introduced clone for Sinatma and Holima. b Local variety as control.

Due to the large number of sweet potato clones in Papua, it was anticipated that it would be difficult to improve on the local material. The results, however, showed that some clones had the potential for improvement over the best of the local varieties (Helalekue Lama) after four seasons of on-farm trials (Table 10). The farmers‘ interest in these introduced clones, even the ones that did not perform better than the local check variety, was far greater than had been anticipated. From each on-farm trial harvest, on average at least half of the trial clones were well received by the trial participants and their neighbours and friends.

Root and Vine Processing Starch in sweet potato roots provides an energy source for livestock, but the roots contain insignificant levels of protein. The crude protein content of sweet potato ranges from 1.3 to 10% on dry weight basis (Li, 1974; Purcell et al., 1976; Walter et al., 1984). In general it is about one-third the crude protein content of corn meal. Not only is the crude protein content low in sweet potato, but up to 40% of the total nitrogen has been found to be non-protein nitrogen (NPN) (Purcell at al., 1976). Consequently, low level of available protein poses a major constraint to pig growth in a sweet potato-based diet. As discussed earlier, farmers overcome this constraint by supplementing this diet with rice bran, fish meal, soy beans or residue, sweet potato and cassava leaves, and, to a lesser extent, commercial supplements. In addition to low protein content, trypsin inhibitor and low starch digestibility are additional constraints to sweetpotato-based diets. Unsatisfactory feeding efficiency has been observed when uncooked roots are used as pig feed because trypsin inhibitors cause poor protein digestibility (Chien and Lee, 1980; Yeh and Bouwkamp, 1985). Different levels of

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trypsin inhibitor activity (TIA) in sweet potato cultivars have been reported (Bradbury et al., 1985; Dickey et al., 1984; Lin and Chen, 1980). Bradbury et al. (1984) estimated about 0.032% of trypsin inhibitors present in the total protein of sweet potato. Zhang et al. (1998) estimated sweet potato roots to be about 28% of the TIA level in the soybean seeds and found a positive correlation between TIA and protein content in roots. Therefore, the sweet potatobased diet, if not processed or cooked, may be partially responsible for poor feeding efficiency (Lee and Lee, 1979; Yeh and Bouwkamp, 1985). Poor starch digestibility is another major factor that has been suggested to be responsible for low feed efficiency (Yeh and Bouwkamp, 1985; Tsou and Hong, 1989). Sweet potato starch needs to be broken down by some form of processing for complete uptake. To overcome these constraints, farmers in China and Vietnam diligently cooked sweet potato-based feed daily to eliminate trypsin inhibitor and increase starch digestibility. In turn, the farmers pay the price of high labor and fuel inputs. Where labor or fuel is in short supply, thus limiting the cooking option, as in Uganda and Papua, farmers suffer the consequences of low growth rate and minimum economic return on the investment. The need to cook in order to fully utilize the nutrients in sweetpotato-based feed becomes a socio-cultural limitation to pig growth in sweetpotato-based diets. Storage is another constraint facing sweet potato farmers in the sub-tropical and tropical zones. While Chinese farmers can store roots up to six months because sweet potato in China is grown in temperate climates and harvested at the beginning of the winter; tropical farmers cannot store the roots without some major loss due to weevils, rats, and/or rotting (Ray and Ravi, 2005). To minimize losses, farmers often feed large quantities of roots to pigs during the first two months after harvest, which leads to waste since an excessive quantity of starch does not lead to proportional growth. On the other hand, soon after that farmers may no longer have any starch sources until the next harvest. Low storability of the roots in the tropics and sub-tropics leads to unbalanced feeding and waste of nutrients. In an attempt to overcome these constraints without requiring extra inputs, sweet potato root and vine processing technology development in Vietnam had four objectives: (1) to increase nutritional value, (2) to eliminate the need for cooking, (3) to increase storability and shelf-life, and (4) to save labor. The production of vine silage enables the women to process the vines during the offseason when labor is more abundant, and store the silage for use when feed is limited. Moreover, there is also the economic advantage of ensiling/storing vines, by processing and storing the sweetpotato vines during the harvest season when vines are cheap and feeding them to pigs during the off-season when vines are expensive. Ensiling may also increase nutritional value and feed efficiency if it involves a fermentation process which can convert nitrogen into protein. A silage trial was conducted in Vietnam to compare the nutritional value of twelve different ensiled mixtures of sweetpotato vines, corn and cassava meal, rice bran, sun-dried chicken manure and salt. The nutritional analysis showed that vines ensiled with chicken manure had significantly higher crude protein, dry matter and ash contents, and lower unit costs for each nutrient than the other silage products (Table 11). None of the preparations were found to contain aflatoxin or Salmonella. Escherichia coli, although present in the original samples, disappeared after 14–21 days of fermentation (Peters et al., 2001a). A simple and inexpensive vine-chopping machine was introduced which transformed hours of

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work into minutes and this has been adopted by farmers in several provinces as a labor-saving device. Table 11. Nutrient composition of 90-day sweet potato vine silage in Vietnam (% of dry matter basis)

1

Treatments1

pH

1 2 3 4 5 6 7 8 9 10 11 12 P with chicken manure without chicken manure

Crude protein (CP) bc14.86 e18.59 b14.32 e18.62 a13.19 d17.63 a12.76 d17.53 c15.45 e19.11 a12.60 d17.78 0.000

Ash

a3.65 b3.98 a3.71 b3.99 a3.73 bc4.05 a3.75 bc4.03 a3.66 c4.12 a3.74 b4.03 0.000

Dry matter (DM) a25.04 c31.31 b28.57 c31.85 a25.72 c30.09 b28.47 c31.92 a25.85 c31.63 b29.26 c31.45 0.000

b11.85 d16.46 a10.7 de17.35 bc12.25 de17.1 a10.16 de17.33 c13.54 e18.34 ab11.45 de17.16 0.000

Ether extract (EE) b3.43 bc3.53 de5.01 c4.14 a2.44 ab2.99 ab2.96 b3.23 e5.62 de5.41 de5.21 d4.91 0.000

Crude fiber (CF) bc17.04 abc15.66 bc16.69 abc15.19 bc16.64 ab14.47 a13.97 a13.98 c17.32 abc16.06 abc15.95 abc15.11 0.000

4.03

31.38

18.21

17.29

4.04

15.08

3.70

27.15

13.86

11.66

4.11

16.27

The even numbered treatments contain 10% sun-dried chicken manure while the odd numbered ones do not. The other ingredients include 3-6% of various combinations of corn meal, cassava meal, and rice bran. 2 Letters to the left and to the right of the means are significantly different (P<0.05) across rows or columns respectively.

The use of sweet potato roots as feed faces the constraints of low protein content, poor starch digestibility, high trypsin inhibitor, and limited storage time. To overcome these constraints, farmers in China and Vietnam diligently cook sweet potato-based feed daily to eliminate trypsin inhibitor and increase starch digestibility. In turn, the farmers pay the price of high labor and fuel inputs. Where labor or fuel is in short supply, limiting the cooking option, farmers suffer the consequences of low pig growth rate and minimum economic return on their investment. Such is the case in Papua and Soroti where roots are fed raw three out of every four times and the pig growth is exceedingly slow (discussed below). The need to cook in order to fully utilize the nutrients in sweetpotatobased feed becomes a socio-cultural limitation to pig growth in sweet potato-based diets. In an attempt to overcome these constraints without requiring extra inputs, sweet potato root silage was tested to address the constraints of storability, protein content, starch digestibility, and trypsin inhibitor. The first root silage trial tested twelve different ways of ensiling sweet potato roots. Six treatments with sliced sweet potato roots and six with grated roots were ensiled with cassava leaf meal, rice bran, sun-dried chicken manure and salt. The laboratory analysis showed that silage with chicken manure and cassava leaf meal had

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significantly higher crude protein content than rice bran silage (p< 0.001) (Table 12). However, only treatments with chicken manure had higher dry matter and ash content than the other silage products. No difference was found between chopped or grated roots. Results on aflatoxin, Salmonella and E. coli were the same as in the vine trial (Peters et al., 2002). Table 12. Nutrient composition of the 90-day sweet potato root silage (% of dry basis) in Vietnam Treatments1 Fresh roots 1 (20% rice bran)

pH

2 (20% CLM*)

a3.31

3 (20% CM**) 4 (10% RB, 10% CM) 5 (10 CLM, 10 CM)

1

a3.28 e4.09 c3.69

DM 18.64 a27.63

ab28.85 c30.48 bc29.30

CP 4.35 a9.18

CF 4.74 bc 12.17

EE 1.02 c 9.00

c16.62

bc

a

4.69

c16.59

a

a

3.82

b13.35

ab

b

ab

a

b

0.000 4.74 5.54

11.31

8.85 9.70

d3.81

c30.75

c17.10

6 (10 RB, 10 CLM)

b3.48

b13.17

P With CM With CLM

0.000 3.91 3.38

ab28.51 0.000 30.00 29.09

bc

9.53

0.000 15.14 14.93

0.000 9.36 11.11

10.92

6.03

4.36 6.30

Ash 4.02 b9.13

ab8.42 d16.50 c13.15 c12.39 ab8.63 0.000 14.79 8.47

CLM: cassava leaf meal, CM: chicken manure, RB: rice bran. Six treatments used grated roots and six treatments used sliced roots. 2 Letters to the left of the means are significantly different (P<0.05) across rows.

Based on the results of sweet potato varietal selections, root and vine processing, and balanced crop-feeding methods, a manual covering these issues and pig health was produced in Vietnamese for farmers and extensionists. This manual was later published in English but covered only the issues that had been researched (i.e., the section on pig health was not included) (Peters et al., 2001b). In 2006 an updated manual, which included the use of both sweet potato and other local feedstuffs, became available as a training and technical guide for extensionists and researchers (Tinh et al., 2006). Due to the large volume of sweet potato root and vine production in China, particularly in Sichuan Province, it is logical to consider manufacturing dry pellet feed with sweet potato as the major ingredient instead of maize. This is particularly relevant in Sichuan where there has been an enormous increase in small-scale rural backyard feed manufacturing in recent years. If the technology can be developed, such feed could have large implications for animal feed production and marketing in China. A premix developed by the Sichuan Academy of Animal Sciences (SAAS) contains a mixture of amino acids, minerals and vitamins, and a protein concentrate to supplement a sweetpotato-vines/roots based diet that is deficient in these elements. SAAS experimentations indicated 20% improvement in feed efficiency by using premix while achieving 30% improvement by supplying protein concentrate while lowering the feed/kg weight gain cost by 15-20% (Zou, 2002).

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Pig Husbandry On-farm feeding trials followed the processing trials in Vietnam to test the effects of these silage feeds on pig growth. Sweet potato vine silage feed trials compared vines ensiled with cassava meal and vines ensiled with sun-dried chicken manure and cassava meal in terms of pig growth and economic efficiency. The results showed that pigs fed the preparation containing chicken manure achieved statistically higher growth rates than those fed fresh vines (Table 13). The chicken manure preparation was also significantly cheaper (cost per kg of weight gain) than the other two preparations (Peters et al., 2001b). Another root silage trial compared the effects of cooked fresh sweet potato roots (T1), uncooked root silage with rice bran (T2), and uncooked root silage with sun-dried chicken manure (T3) on growth and economic efficiency. The results showed the daily weight gain of T3 pigs to be 640g, 605 g for T2 pigs, but only 552 g for the T1 control pigs (Table 14). These differences are not statistically significant because of small numbers of pigs (n=42) and a large standard deviation, resulting from high variation among the seven households and the types of pigs. The most important result was that the modest increase of growth was achieved without cooking, which is both labor intensive and fuel demanding. With such constraints lifted, farmers subsequently tripled their pig production (Peters et al., 2002). A number of silage trials followed to help farmers manage the seasonal variation of feed sources. Trials were conducted to combine cassava roots with sweet potato vines, sweet potato roots with peanut stems, and sweet potato roots with sweet potato vines. These trials compared the use of fresh, dried, and ensiled roots, vines and stems on pig growth so that farmers could have a host of choices of feeding methods and combinations. One trial result showed that feeding sweet potato roots ensiled with 15% fresh sweet potato vines yielded the same pig growth with less cash input: this silage uses up the farm crop while yielding better economic efficiency (Peters et al., 2005). Table 13. Performance traits of pigs fed ensiled sweet potato vines under on-farm conditions in Vietnam

Weight

*

Initial weight (kg) Final weight (kg) Total weight gain (kg) Daily weight gain (g) Relative weight gain (%) Feed cost (vnd**/kg weight gain)

100% 93.5% sweet potato fresh sweet potato vine, 6% cassava vine meal, 0.5% salt Mean 20.35 60.40a 40.05a 431a 100.00 10784

SD 3.24 7.79 7.86

Mean 20.75 66.10ab 45.35ab 488ab 113.20 8875

SD 4.06 10 8.18

83.5% sweet potato vine, 6% cassava meal, 10% chicken manure, 0.5% salt Mean SD 21.85 3.92 73.40b 10.47 51.55b 7.99 554b 128.70 7383

P 0.657 0.018 0.013

Letters to the right of the means indicate significant different (P<0.05) across columns (Tukey test by Minitab 12.21). ** vnd = Vietnamese dong.

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Table 14. Performance traits of pigs fed fresh sweet potato (SP) roots and two types of grated sweetpotato root silage under on-farm conditions in Vietnam

Weight

*

Initial weight (kg) Final weight (kg) Total weight gain (kg) Daily weight gain (g/d) Rate of weight gain (%) Cost wt. gain (vnd/kg)

100% fresh SP roots cooked (T1) Mean SD 21.75 4.78 70.96 13.31 49.21 9.92 552 186 226 6724

79.5 SP roots, 20% rice bran, uncooked (T2) Mean SD 22.96 2.86 76.82 12.19 53.86 10.04 605 158 234 7354

79.5 SP roots, 20% manure, uncooked (T3) Mean SD 21.89 2.86 78.93 10.58 57.04 8.73 640 145 261 6767

P 0.628 0.208 0.108 0.283

Results not significantly different due to large SD. SD is large because: 1) high degree of variability across households, 2) variation in pigs, and 3) some pigs like silage feed, some do not.

As farmers in northern Vietnam increase peanut production to meet the demand for export peanut oil processing, the use of peanut stems as feed has the potential of contributing considerably to rural incomes. Responding to farmers‘ need to turn the voluminous, currently unusable peanut stems into a viable pig feed, trials were designed to seek ways of ensiling these stems alone or with sweet potato roots. The results showed that sweet potato roots ensiled with 15%, 30% or 45% peanut leaves, had higher pH (i.e., not as acidic) and crude protein levels than roots ensiled with an equal amount of sweet potato vines. This generates additional income because peanut stems have no cash value while the price of sweet potato vines for pig feed can be quite high during the off-season. A pig-feeding trial showed that pigs grew faster with the treatment of sweet potato roots ensiled with 15% peanut stems than those ensiled with 30% peanut stems or 15% sweet potato vines. As farmers increase pig production as the result of the uncooked diet with silage, many now raise enough pigs per cycle to utilize the manure for biogas production while applying the residue as fertilizer. Biogas utilization can help transform the kitchen from slow and smoke-filled firewood cooking to clean and rapid gas cooking. Farmers may be able to afford such construction with the extra income generated from improved pig production. While pig husbandry interventions in Vietnam mainly focused on feed, the emphases in Papua have been more diverse. While the Dani farmers have extensive knowledge regarding sweet potato cultivation, their knowledge of pig management is limited, despite the fact that they have adopted the cultivation of sweet potato for less than 500 years while they have raised pigs much longer. The widespread pig diseases in the Baliem Valley made it clear that if health was not addressed, the improvement of nutrition would be in vain. A disease survey in the Baliem Valley, based on the clinical post-mortems of 37 pigs from several villages showed that parasites was the most important single disease problem in the Baliem Valley (Cargill, 2003). Both parasites with a direct life-cycle, as well as parasites with an indirect life-cycle, were recorded. Modifying husbandry techniques to reduce parasite burdens and limit their impact on production was suggested as a sustainable venue to control these different classes of parasites. To convert traditional husbandry techniques in Papua to confining pigs in pens 24 hours a day, as in other places in the world, would require changes in the Dani‘s whole way of life.

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Instead of proposing this drastic measure, various modified models that take an integrated approach to enhancing this system were planned and tested. The extended families of Dani live in a compound called a sili, which consists of a few stick and mud structures with straw roofs. These structures include a man‘s round hut, one or more women‘s round huts which house the multiple wives and children, a long rectangular kitchen which consists of several fire pits, one for each woman, and a row of rectangular pig pens across from the kitchen. In another model the women‘s hut is attached to the kitchen, which in turn is attached to the pig pens. There is little separation of the humans and pigs, and pigs often eat human feces and walk freely around the kitchen and over the food. The modified design proposed to set aside a laleken, which is a holding field behind the pig pen that is large enough for pigs to roam, graze, and root for worms. High protein grasses can be planted in the laleken in a closed-in area so that pigs cannot get out to access human feces. This modified system is designed to address various problems with the following specific points built into the design:  

Separate human feces from pigs in order to break the chain of diseases. Plant live fences around the laleken consisting of tree species whose leaves can be used as pig feed while the fast-growing tree can be cut for firewood. This avoids the high expense of wood fences and allows the farmers to build a laleken large enough for pigs to find sufficient feed during the day. Three genera of trees (Glyricidium, Calliandra, and Erythrina) were recommended by the World Agro-forestry Center (ICRAF) for this purpose. Mulberry (Morus sp.) leaves have been tested as pig feed at the Livestock Research Center of Indonesia (Balitnak) with success, and thus were also included.  Plant fodder trees in a few places in the laleken in order to provide shade.  Plant high protein grasses identified in the local area, such as wurikaka, a local grass eaten by pigs and often by humans, with 18.3% of crude protein. Two other grasses, Calopogonium sp. (17.1%) and Sida rhombifolia (15.5%) also have higher protein and lower fiber content than introduced forage grasses such as Paspalum atratum. and Stylosanthes guianensis (Table 15).  Retain pigs in the laleken to eat forage grasses and root for worms during the day and return them to pens at night to prevent them from being stolen.  Provide a water container and a pool in the laleken where pigs are kept—the former for drinking water and the latter for pigs to wallow in when the temperature gets high.  Separate the laleken into various paddocks—while one is being grazed; fallowed grasses are growing in the other ones.  Cultivate sweet potato fields behind the laleken with clones of high dry matter yield in roots and/or high protein yield in vines to provide easy access of feed. Jerusalem artichoke (Helianthus tuberosus), which is also known as a pig feed, was introduced to test its adaptability in the Baliem Valley, but proved not adaptable to the local environment.

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Table 15. Nutritional contents of local grasses and introduced alternative forage feed sources in the Baliem Valley, Papua, Indonesia

*

Locally found grasses Wurikaka Calopogonium Sida rhombifolia Dokop Yelaga Girimi Lukaka Suwiriwi Jagat Introduced forage crops Stylosanthes guianensis Paspalum Setaria Sweetpotato vine*

% Crude protein (on dry basis) 18.32 17.13 15.48 13.80 13.78 11.81 11.19 10.55 6.53 12.18 8.90 6.39 16-20

% Water 7.70 8.43 8.89 10.15 7.77 8.07 9.46 9.98 7.64 9.17 8.35 8.34

% Crude fiber (on dry basis) 30.96 31.86 32.05 28.00 28.03 -26.98 27.77 37.69 34.64 34.36 27.02 14-22

CP content of sweetpotato vines varies with the varieties.

Other related trials were also designed and tested to complement the overall design of the modified management system. All the trials were implemented on farm by the local farmers, under the supervision of project personnel. These included: 





Nutrition and feeding trials. These trials were designed to test the effects of feeding cooked sweet potato roots or silage, instead of mainly uncooked roots (the roots are cooked only 28% of the time), on pig growth. Unlike in Vietnam where a wide range of supplemental crop feeds is available, the available feed here is limited to sweet potato roots and vines, rice bran that is used for silage, and banana trunks. So far the results have shown the positive effects on growth of feeding cooked roots, and the effects of silage were also tested. Water-intake trials. Local pigs are rarely given water except the water that comes with the occasionally cooked roots. It was hypothesized that the lack of water has adverse effects on pig growth, though it is highly possible that pigs find enough water while roaming in the forest. It was also speculated that local pigs may have evolved to need less water than exotic pigs. The water-intake trials tested the effects of a constant water supply versus water that only comes with cooked roots on local and exotic pigs. The bewildering result from the trial is the observation that a higher water intake seems to contribute significantly to growth for local pigs while it made little difference for the exotic pigs. Further trials with greater control are needed before definitive conclusions can be drawn. Disease control with laleken trials. It was hypothesized that pigs kept in the laleken are less susceptible to parasites and therefore grow faster. The trial consisted of three treatments: (A) small laleken with a dunging area, (B) medium-size laleken without a dunging area, and (C) large laleken without a dunging area to control disease but

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

large enough provide additional feed. The laboratory results of the post-mortem of one pig from each group showed worms in kidney, stomach, and intestines in groups B and C, but no worms were found in Group A. This result, combined with the growth data, suggests that: (1) a small laleken or a dunging area is helpful in controlling parasites, and (2) a larger laleken provides additional feed that compensates for the disadvantage of parasites. Therefore, one can hypothesize that the combination of having enough space to root for additional feed and having a dunging area will help reduce parasite burden while improving growth. A subsequent trial, which is currently underway, was designed specifically to test this hypothesis. Fertility trial. The post-mortems, the systematic observations of sow/piglets, the long nursing period (up to 6 months), and the post-weaning practice (lack of boar stimulation) all indicated significantly below-average fertility. A fertility trial tested the length of time for freshly-weaned sows to come into heat with boar stimulation. The data showed the sows were more likely to mate, came into heat in fewer days, have a higher conceiving rate, and bore a greater number of piglets when placed close to a boar (Table 16).

The pig husbandry situation of Soroti resembles that of the Baliem Valley and a number of the research trials on the improvements in the Baliem Vally are relevant to Soroti. Nevertheless, the applications of these research results must be adapted according to the local specificities. In the case of Soroti, where pig diet consisted of few protein sources, Okoth and Epechu (1997) identified maize bran, sunflower cake (sunflower oil residue), and small fish as locally available feed supplements at affordable prices. Epechu (personal communication) later further encountered the availability of cow‘s blood from one local slaughterhouse, which slaughters ten cattle each day, as a free feed. He collected 40 liters of blood a day and processed it by boiling and drying. This dried blood was then mixed with maize bran and other feed, and he then noticed its positive effect on pig growth. Other smaller slaughterhouses in the district also have free blood available for feed. The appropriate alternative protein sources to supplement the basic sweetpotato diet must be identified by evaluating local opportunities. Supply of commercial feed supplements was unreliable in Soroti, but cow‘s blood, the value of which was not recognized locally, was available as a valuable supplement. Table 16. Mating results of sows that are placed closed to a boar to provide mating stimulation, versus the sows that are placed far from the boar and lack stimulation, in the Baliem Valley, Papua, Indonesia

Number of days takes to mate Number of sows mated Number of sows gave birth Total number of piglets in the liters

Sows close to a boar (n=10) 4.7 10 7 32

Sows far from a boar (n=9) 12.5 7 3 9

*Two sows in the group that was placed far from the boar died; one died after mating before giving birth and one did not mate.

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FUTURE PROSPECTS OF SWEET POTATO-PIG FEED SYSTEMS For poor farmers with little access to commercial feed, the sweet potato-pig feed systems have served an important role in their livelihoods by converting low-value crops into a highvalue commodity. It has been a transitional system that sustains farmers while they gradually move away from their poor resource base to more efficient commercial production. This trend has been observed in the now prosperous Asian countries such as Korea and Taiwan where the poor farmers used to engage in such feeding systems when farmers relied on sweet potato as pig feed. During that time, researchers from Taiwan conducted trials on many aspects of the use of sweet potato roots and vines as pig feed in order to assist farmers to improve their pig production. These trials included the use of dried sweet potato chips as a more efficient feed (i.e., lower cost and higher daily weight gain) than fresh roots (Koh et al., 1976). They examined the effects of slicing and solar drying on starch digestibility and the elimination of long cooking that was usually required of most sweet potato in order to break down the starch to enable subsequent absorption of the nutrients by the pigs. Subsequent research explored supplementing sweet potato chips with protein as an adequate energy source for growing finishing pigs (Wu, 1980). Additional studies have investigated the effect of sweet potato chips as pig feed (Wu and Chen, 1985; Wu et al., 1985; Wang et al., 1984) and explored various methods of processing sweet potato chips in order to improve their nutritional value (Yeh et al., 1976-77; Wu, 1980). These research efforts were invaluable to the poor farmers at the time; along with economic development in Korea and Taiwan farmers gradually moved into commercial production, as did the research focus. This trend is expected to occur in China and Vietnam as these two countries make rapid economic advancements. In addition to large feed factories, there is significant backyard commercial feed manufacturing, though highly unregulated, and thus of unreliable quality, all over rural China. The large feed factories have also mushroomed up and down the long coast of Vietnam. Moreover, both the international and national research agenda on pig production and improvement focuses on the access to, and efficient use of, commercial feed in these countries. The general consensus is that the use of feed crops is not the most efficient production system, considering the time and labor involved in processing the crops. Though the poor farmers in these countries are still engaged in the sweet potato-pig feeding practice, the resource-rich farmers with larger numbers of pigs generally rely on commercial feed. Though this trend is also applicable to other less developed areas such as Soroti in Uganda and Papua in Indonesia, this traditional practice is likely to persist longer due to the slower pace of economic development and, in the case of Papua, the cultural significance of sweet potato and pigs to humans. Thus, focusing adapting existing research results to the specific socio-cultural-economic-agronomic conditions of such areas might yield greater benefits for pig production improvement of poor farmers.

CONCLUSIONS Sweet potato, supplemented by other locally available crop-based feedstuff, has made it possible for poor farmers to raise pigs throughout Asia and parts of Africa for hundreds of years. Pigs in turn have provided the poor farmers the badly needed, and often the only source

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of, cash, as well as manure that has sustained the soil fertility and crop productivity in the absence of chemical fertilizer. In this sweet potato-pig feeding system, the pigs efficiently transform the low nutrient and cash value of sweet potato into a high value and high protein commodity. This system has, nevertheless, been beleaguered by low crude protein intake, unbalanced feed ration, lack of protein supplement, and erratic feeding. The combination of small amounts of investment in protein to balance the feed, improved sweet potato varieties, processed sweet potato vines and roots, and coordinated feeding rations proved to be effective in improving the growth and feed efficiency of the pigs. These improved measures have been research, introduced to, and adopted by Vietnamese farmers, many of who have increased pig production scales and thus their income. These benefits clearly demonstrate the importance of such research and development efforts for the resource-poor farmers. Nevertheless, the experience in Taiwan and Korea, the countries where sweet potato-pig feeding system used to practiced, indicates that, farmers adopt the practice of commercial feeding as they garner resources and increase their production scale. Preparing and processing farm feed for large herds of pigs becomes a formidable task and the benefits would be offset by the limited economy of scale of sweet potato-based feeding system; thus farmers are expected to gradually adopt the commercial feeding practices. Thus, research and development to improve such system should focus on areas where farmers will likely remain limited in resources in the near future, such as in Africa and Papua. As farmers in Vietnam and China gradually adopt commercial feeding practices, further research and development in the areas of sweet potato-pig feeding system will have more far-reaching benefits in Africa and Papua where sweet potato is cultivated for both human and pig consumption.

REFERENCES Bashaasha, B., Mwanga, R.O.M., Ocitti p‘Obwoya, C. and Ewell, P.T.(1995). Sweet potato in the Farming and Food System of Uganda: A Farm Survey Report. International Potato Center, Sub-Saharan Region, Nairobi, Kenya. Bradbury, J.H., Baines, J., Hammer, B., Anders, M. and Miller, J.S. (1984). Analysis of sweet potato (Ipomoea batatas) from the highlands of Papua New Guinea: relevance to the incidence of Enteritis necroticans. J. Agric. Food Chem. 32: 469-473. Bradbury, J.H., Hammer, B., Nguyen, T., Anders, M. and Miller, J.S. (1985). Protein quantity and quality and trypsin inhibitor content of sweet potato cultivars from the highlands of Papua New Guinea. J. Agric. Food Chem. 33: 281-285. Cargill, C. (2003). Disease survey report. ACIAR Baliem Valley Pig Parasite Project. Commissioned agency—CIP. International Potato Center (CIP-ESEAP), Bogor, Indonesia. Chien, S.L. and Lee, P.K. (1980). The effect of physical treatment on the available lysine and trypsin inhibitor of sweet potatoes. Taiwan Livestock Res. 13: 75-84. Dickey, L.F., Collins, W.W. and Young, C.T. (1984). Root protein quantity and quality in a seedling population of sweet potatoes. HortScience 19: 689-692. General Statistics Office. (2003). General Statistics Yearbook 2003. Statistical Publishing House, Hanoi, Vietnam.

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Huang, J., Song, J., Qiao, F. and Fuglie, K. O. (2003). Sweet potato in China: Economic Aspects and Utilization in Pig Production. International Potato Center (CIP-ESEAP), Bogor, Indonesia. Koh, F. K., Yeh, T. P. and Yen, H. D. (1976). Effect of fresh sweet potato, sweet potato chips, and sweet potato vines on raising finishing pigs. (in Chinese). J. Chinese Soc. Anim. Sci. 5 (3-4): 55-67. Lee, P.K. and Lee, M.S. (1979). Study on hog feed formula of using high protein sweet potato chips and dehydrated sweet potato vines as the main ingredient. (in Chinese). J. Taiwan Livestock Res. 12: 49-55. Li, L. (1974). Variation in protein content and its relation to other characters in sweet potatoes. J. Agric. Assoc. China. 88:17-22. Lin, Y.H. and Chen, H.L.. (1980). Level and heat stability of trypsin inhibitor activity among sweet potato (Ipomoea batatas L.) lines (Chinese with English summery). Bot. Bul. Acad. Sinica 21:1-13. Okoth, J. R. and Epechu W. (1997). ―A study of the possibility of commercial pig rearing based on a sweetptoato feed system.‖ A report submitted to CIP-Kampala, Kampala, Uganda. Otim-Nape, G. W., Thresh, J. M. and Fargette, D. (1995). Bemisia and cassava mosaic virus disease in Africa. Taxonomy, Biology, Damage, Control and Management. 28:319-350. Peters, D., Tinh, N. T., Thach, P.N., Hoanh, M.T., Yen, N.T. and Fuglie, K.O. (2005) Rural Income Generation through Improving Crop-based Pig Production Systems in Vietnam: Diagnostics, Interventions, Dissemination, Agriculture and Human Values. Peters, D., Tinh, N.T. and Thach, P.N. (2002) Sweetpotato Root Silage for Efficient and Labor-saving Pig Raising in Vietnam. AGGRIPA. Food and Agriculture Organization, Rome. www.fao.org/docrep/article/agrippa/554_en.htm Peters, D., Tinh, N. T. and Thuy, T. T. (2001a) Fermented Sweet potato Vines for More Efficient Pig Raising in Vietnam. AGGRIPA. Food and Agriculture Organization, Rome. www.fao.org/docrep/article/agrippa/x9500e10.htm Peters, D., Tinh, N.T., Minh, T. T., Ton, P. H., Yen, N. T. and Hoanh, M. T. (2001b) Pig Feed Improvement through Enhanced Use of Sweet Potato Roots and Vines in Northern and Central Vietnam. International Potato Center (CIP), Lima, Peru. Peters, W. (2001). Local Human-Sweet potato-Pig Systems Characterization and Research in Irian Jaya, Indonesia: with limited reference to Papua New Guinea. A Secondary Literature Review. International Potato Center (CIP-ESEAP), Bogor, Indonesia. Purcell, A.E., Walter, W.M. and Giesbrecht, F.G. (1976) Distribution of protein within sweet potato roots (Ipomoea batatas L.). J. Agric. Food Chem. 24:64-66. Ray RC and Ravi S (2005). Post harvest spoilage of sweet potato and its control measures. Crit. Rev. Food Sci. Nutr., 35: 623- 644. Schneider J., Widyastuti, C. A., and Diazuli, M. (1993) Sweet potato in the Baliem Valley area, Irian Jaya: A report on collection and study of sweetpotato germplasm, April-May 1993. International Potato Centre (CIP-ESEAP), Bogor, Indonesia. Scott, G. J. (1991) Sweet potato as animal feed in developing countries: Present patterns and future perspectives. Paper presented at the FAO Experts Consultation on ―The Use of Roots, Tubers, Plantains and Bananas in Animal Feeding‖ held at the Centro International de Agricultura Tropical (CIAT), Cali, Colombia, January 21-25, 1991.

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Tinh, N. T., Yen, N. T., Hoanh, M. T., Thach, P. N., Peters, D., Campilan, D., and Fuglie, K.O. (2006). Improving Pig Feed Systems Through Use of Sweet potato and Other Local Feed Resources in Vietnam. International Potato Center (CIP), Hanoi, Vietnam. Tsou, S.C.S. and Hong T.L. (1989). Digestibility of sweet potato starch, In: Improvement of sweetpotato (Ipomoea batatas) in Asia. Rep. Workshop on sweetpotato improvement in Asia, ICAR, India, October 24-28, 1988. International Potato Center, Lima, Peru, pp. 127136. Wang, M. K., Yeh, T. P., and Lee, P. K. (1984). A study on use of high protein sweet potato chips and dehydrated sweet potato vines as the main ingredients of hog feed formula. (in Chinese). Annual Research Report of Animal Industry Research Institute, Taiwan Sugar Corporation, Taiwan. Walter, W.M., Collins, W.W. and Purcell, A.E. (1984). Sweet potato protein: a review. J. Agric Food Chem. 32:695-697. Woolfe, J. A. (1992). Sweet Potato: An Untapped Food Resource. Cambridge University Press, New York. Wu, J. F. (1980). Energy value of sweet potato chips for young swine. J. Anim. Sci. 51 (6): 1261- 1265. Wu, J. F. and Chen, S. Y. (1985). Effects on nutritional value fed varying levels of sun-cured and popping high protein sweet potato chips for growing pigs (in Chinese). J. Chinese Soc. Anim. Sci. 14 (34): 41-46. Wu, J. F., Huang, M. D. and Chen, S. Y. (1985). Effect of dietary sweet potato chips, cassava chips and cassava pamace on nutritional value for growing pigs. (in Chinese). J. Agric. Assoc.China. New Series No. 131. Yeh, T. P., Wung, S. C., Koh, F. K., Lee, S. Y. and Wu, J. F. (1976-77). Improvements in the nutritive values of sweet potato chips by different methods of processing. (in Chinese). Annual Research Report of Animal Industry Research Institute, Taiwan Sugar Corporation, Taiwan. Yeh, T.P and Bouwkamp, J.C. (1985) Roots and vines as animal feed. In: Bouwkamp, J.C. (ed.), Sweet Potato Products: a natural resource for the tropics. CRC Press Inc., Boca Raton, FL, USA, pp 235-253. Zhang, D. P., Collins, W. W. and Andrade, M. (1998). Genotype and fertilisation effects on trypsin inhibitor activity in sweetpotato. HortScience 33:225-228. Zou, C.Y. (2002) Sweetpotato Utilization in Sichuan Pig Production System. Powerpoint Presentation, Sichuan Academy of Animal Sciences, Chengdu, Republic of China.

In: Sweet Potato: Post Harvest Aspects in Food Editors: R. C. Ray and K. I. Tomlins

ISBN 978-1-60876-343-6 © 2010 Nova Science Publishers, Inc.

Chapter 10

SWEET POTATO UTILIZATION, STORAGE, SMALL-SCALE PROCESSING AND MARKETING IN AFRICA Keith Tomlins1, Debbie Rees1, Claire Coote1, Aurélie Bechoff1, Julius Okwadi1, Jaquelino Massingue1, Ramesh Ray2 and Andrew Westby1 1

Natural Resources Institute, University of Greenwich, Central Avenue, Chatham Maritime, Kent, ME4 4TB, UK 2 Regional Centre, Central Tuber Crops Research Institute, Bhubaneswar 751 019, India

ABSTRACT Sweet potato production in Africa accounts for 11% of global production. It is becoming increasingly recognised as an important crop is Africa, particularly with higher global prices of wheat and other food crops and also its importance in food security. However, the post-harvest aspects, particularly processing and marketing are still very much under developed. The new biofortified orange-fleshed varieties, that contain provitamin A, have great potential to contribute to improved health, particularly in the rural communities. The main challenges for the crop in Africa with respect to post-harvest issues include firstly the reduction in storage pests, particularly weevils because damage can reduce the market value and shelf-life, secondly increasing yields and thirdly improving the marketing systems along the value chain. Improving the consumer perception of sweet potato is important because it is still widely considered to be a ‗poor persons‘ crop. This is particularly vital now that biofortified orange fleshed sweet potato containing pro-vitamin A is increasingly more widely available and can contribute to improved health. This chapter refers to work undertaken to reduce storage pests, reducing losses during transport and marketing and consumer studies to explore marketing issues.

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ABBREVIATIONS LC-MS OFSP SSA QTLs WFSP

liquid chromatography- mass spectrometry; Orange fleshed sweet potato; Sub-Saharan Africa; Quantitative trait loci; White fleshed sweet potato

INTRODUCTION Sub-Saharan Africa produces more than 13.5 million tonnes of sweet potato annually (approximately 11% of global production). Since the early 1960s, production in Africa has increased more than fourfold (to 410% of 1960 production) (FAOSTAT 2009). Most production in Africa is predominantly in East Africa (7.6 million tonnes), but it is also widely grown in West Africa (4.3 million tonnes) although less is known about the crop in this region. Sweet potato is a staple in Africa‘s densely populated, intensively cultivated midelevation farming areas. Africa‘s main producers are Nigeria (3.5 million tonnes/annum), Uganda (2.6 million tonnes/annum), Tanzania (960,000 tonnes/annum), Rwanda (940,000 tonnes/annum), Kenya (800,000 tonnes/annum) and Angola (700,000 tonnes/annum). The largest producers on a per capita basis (2003) are Rwanda, Burundi and Uganda (84 to 116 kg per capita per year) (FAOSTAT, 2009). However, the countries that export the most sweet potato from Africa are Egypt, Ghana and South Africa. Sweet potato is regarded as a food security crop, mainly because of its reliable yields under marginal conditions with minimal inputs or intermittent care. It is easily propagated and grows with minimal or no inputs on degraded soils under a range of rainfall patterns. As a robust short season crop, it has frequently proven its usefulness as an adversity recovery crop. This is an advantage for lowincome households whose members depend on diverse livelihood strategies. One of its most important characteristics is its flexible growing season, which allows piecemeal harvesting over a 3–10-month period. However infestation by sweet potato weevil during dry seasons restricts this practice. It is also often widely marketed on a small-scale in rural areas. It is eaten primarily in fresh form, either boiled or roasted. The demand for fresh roots is growing in urban areas, where it is used mainly as a low-cost substitute for bread with breakfast or tea. While most sweet potato consumed is white or yellow fleshed, orange fleshed sweet potato (OFSP) that is biofortified with pro-vitamin A, is increasingly becoming more widespread in production and consumption, particularly in Eastern and Southern Africa. OFSP is important because more than 3 million children under the age of five suffer from vitamin A-related blindness in sub-Saharan Africa (SSA). This deficiency is also one of the leading causes of early childhood death, and a major risk factor for pregnant women in Africa. One of the easiest and most cost-effective ways to introduce more vitamin A into the diet is to eat OFSP. This type of sweet potato is rich in β-carotenes that the body converts easily into vitamin A. OFSP varieties are as easy to grow as traditional white fleshed varieties currently grown and marketed and the market price is similar. Adding 100 g of the sweet 

Corresponding author: Email: [email protected]

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potato to the daily diet can prevent vitamin A deficiency in children, dramatically reduce maternal mortality and lower the risk of mother-to-child transmission of HIV/AIDS (van Jaarsveld et al., 2005). Studies have shown (Low et al., 2001, Kapinga et al., 2005) that addressing Vitamin A deficiency alone should reduce the overall mortality among children under six by nearly 23%. Ex –ante impact assessment study indicated that introducing the new high-β carotene varieties that meet local preferences would benefit an estimated 50 million children under the age of six who are currently at risk in addition to significant benefits for childbearing women (Low et al., 2001, 2007). In Africa, the production, marketing and consumption of sweet potato is still largely at the small-scale level with processing only involving household or small- scale enterprises. In some locations, sweet potato may be dried or boiled and dried to provide access to the crop in the dry season. In ground storage of fresh sweet potato is not possible because of problems with weevil infestation. Post-harvest issues regarding sweet potato in Africa concern storage, transportation and shelf-life, consumer acceptance, processing, marketing and reducing the impact of storage pests.

STORAGE OF FRESH SWEET POTATO IN AFRICA Sweet potato in the fresh form has a limited shelf-life and this can limit availability and marketing opportunities for the farmers and those in the value chain. Storage of fresh sweet potato to extend the season has been practised in a number of tropical countries but with varying degrees of success. In developed countries, storage for one year is feasible (Woolfe, 1992) because the product has a higher market price so that control of temperature and humidity is economically viable. However, in developing countries, with limited resources, limited access to information and with a crop of marginal value, storage is not commonly practised. Traditional storage technologies have been reported in tropical countries such as Bangladesh (Jenkins, 1982) and India (Prasad et al., 1981, Ray and Ravi, 2005). In Africa it has been reported in Kenya (Karuri and Ojijo, 1994, Karuri and Hagenimana, 1995), Uganda (Hall and Devereau, 2000) Malawi (Woolfe, 1992) and Tanzania (Rees et al., 2003a, b; Tomlins et al., 2007b). The success of these low cost storage technologies, however, has been variable (Ray and Ravi 2005). A wide range of factors affecting storage have been investigated and these include the type of store (pit or heap), variety and ventilation which were monitored by measuring O2 and CO2 levels, relative humidity, temperature, root condition and weight loss (van Oirschot et al., 2007). The findings indicated that the main factors that improved storability of fresh sweet potato under tropical conditions were the use of good-quality roots free of damage and disease, not lining the stores with grass, and avoiding temperature build-up in the stores (Ray and Ravi, 2005). Factors that had minimal influence on storage were the type of store (pit or heap), sweet potato variety and ventilation. The study concluded that fresh roots could be stored for up to 12 weeks and that, by this time, stored roots may taste sweeter than freshly harvested ones. In Africa, a factor that can reduce the wider acceptance of methods for storing sweet potato by subsistence farmers is how methods developed on a research station could be transferred to the farmer situation (Hall and Devereau, 2000). This is because subsistence

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farmers often have access to minimal resources and therefore the risks in adopting the methods can be high. How farmers adopt technology has been explored in Tanzania (Tomlins et al., 2007b) and in Uganda (Hall and Devereau, 2000). A combination of on-station and onfarm trials was used to test the feasibility of the method and social compatibility of low-cost storage technologies. The researchers reported that, although the on-station trials provided broad guidelines for store development, specific requirements needed to be devised in conjunction with farmers. In Tanzania, based on the results of on-farm testing that involved 20 subsistence farmers, while both the pit and heap storage methods were suitable (Figure 1), practical and simple improvements were necessary, without which losses in the proportion of market-quality roots from the store could be as high as 79%. These practical improvements were mainly concerned with the position of stores on the farms that ensured that the stores were shaded from direct sunlight and such that they could not be flooded with rainwater. The addition of a novel new step, dehaulming by removing the plant canopy at least 7 days before harvest also improved the recovery of market–quality roots by 48%. However, although the storage methods were developed in order to improve farmer income, most farmers said they would use the stored roots as a subsistence staple for household food security. Furthermore, when transferring methods from the research station to the farm, it is necessary to target those most able to adopt the approach. Additionally, the farmers considered that local market traders may not be keen to sell stored roots. This suggests that for a successful storage strategy to be developed, other actors in the value chain, such as market traders and consumers, need to be included in the process of transferring methods from the research station to the farm. This illustrates that research to improve livelihoods often requires both technological and socio-economic interventions.

Figure 1. Examples of the construction of heap and pit stores in the Lake Zone of Tanzania (Tomlins et al., 2003).

EFFECT OF TRANSPORT OF SWEET POTATO ON THE SHELF-LIFE AND MARKETING In much of Africa, in particular East Africa, sweet potato is now increasing being marketed in urban centres. Marketing systems, however, are usually poorly developed resulting in significant losses in quality (Ndunguru et al., 1998; Thomson et al., 1997). Sweet

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potato roots attract a significant discount (10 to 30%) when shrivelled, cut or broken. Monitoring the damage during handling is key to understanding the causes of the losses and developing means of overcoming them. Fresh sweet potatoes are transported in sacks that can weigh up to 200kg, they are often piled high on lorries and trucks and people are allowed to sit and walk on the sacks (Figure 2).

Figure 2. Examples of poor handling of sweet potato in Tanzania.

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In contrast, for export, partitioned fibreboard cartons filled with between 13.6 and 18.2 kg roots are recommended (Medlicott, 1990). Until recently, little was known about the handling, transport and quality of sweet potatoes in East Africa or where the critical stages in the handling and transport that reduce returns for sweet potato growers occurred. Part of the problem was that the sacks were often transported over 300km and hence are difficult to follow. A novel solution was to use an ‗electronic sweet potato‘ (Figure 3), fitted with impact loggers, which was located at the centre of each sack (Tomlins et al., 2000). In a study in Tanzania (Tomlins et al., 2000), commercial consignments of sweet potato sacks (100 kg), cv. Polista and SPN/0, were surveyed, over two seasons, from harvest to markets at Mwanza and Dar es Salaam. Poor handling and transport resulted in up to 20% of roots with severe breaks and between 35% and 86% with severe skinning injury. Reductions in market value were up to 13%. The novel ‗electronic sweet potato‘ (Tomlins et al., 2000) (Figure 3) was used to follow sacks from the field to the market. The ‗electronic sweet potato‘ had sensors which measured the size of any impacts or vibration that the sacks were subjected to. Analysis of the results from the ‗electronic sweet potato‘ indicated that the most severe impacts (greater than 20g) occurred during unloading and loading from road vehicles and ships. An example output showing the impacts on a sack transported 300km over a 21 hour time period is illustrated in Figure 4. While it had been assumed that the most severe impacts would have the strongest correlation with root injury, a large number of minor impacts between 0.2 and 2 g had the most significant correlation with skinning injury and broken roots (Figure 5). The responses were generally not affected by variety or season. The excessive weight (up to 200kg) and size of the sacks makes them difficult to manhandle and transport effectively and along with vibrational damage during transport and dropping during loading and unloading activities results in the most severe losses in value. Changes in management and packaging, if economically practical, are suggested. Changes in packaging (use of fibreboard boxes) also reduced skinning injury and broken roots by 72% and 60% respectively (Tomlins et al., 2002).

Figure 3. Electronic sweet potato design showing the shock, temperature and humidity dataloggers fitted inside a plastic pipe (6.5 cm diameter and 16 cm in length) (Tomlins et al., 2000).

Sweet Potato Utilization, Storage, Small-Scale Processing and Marketing… 100

sack loaded onto truck at farm

handling of sack at market

Impact (g)

3

75

journey to Dar es Salaam by truck 2

50 sack arrives at market overnight storage at market

1

Drop height (mm)

4

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25

0

0 0

1

2

3

4

5

6

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8

9 10 11 12 13 14 15 16 17 18 19 20 21

Transportation time (hr)

Figure 4. Example graphical output from a shock datalogger for a sack of sweet potatoes that was transported 300km by truck from a farm at Gairo to Tandale market, Dar es Salaam, Tanzania (Tomlins et al., 2000).

160 140 120 100

Cultivar 80

SPN/0 (main season)

60 Polista (main season)

40

Polista 20

(low season)

0 -200

Total Population 200

600

1000

1400

Number of impacts (0.2 to 2 g) Figure 5. Effect of number of impacts between 0.2 and 2 g on skinning injury for sweet potatoes transported in 100kg sacks in Tanzania (Tomlins et al., 2000).

This research led to practical recommendations that the weight of the sacks should be reduced to 100kg or less and where possible fibreboard boxes should be used for transporting

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sweet potatoes. The use of fibreboard boxes was adopted by commercial farmers who used them for transporting sweet potato to supermarkets in Dar es Salaam where the roots are sold for a higher value than in local markets. Since this research was completed, Tandale Market in Dar es Salaam has begun to limit the weight of sacks to 100kg (Ndunguru, personal communication, 2008). Although one of the reasons for this was to improve the quality of the roots, another was to improve the health of the porters carrying the heavy sacks. Furthermore, commercial sweet potato farmers have begun to use the fibre-board boxes to transport them to the higher value supermarket sector.

EXTENDING THE SHELF-LIFE OF SWEET POTATO In East Africa, retailers sell roots as quickly as possible because they do not have access to storage facilities (Kapinga et al., 1997c). To find ways of extending the shelf-life, research in Tanzania (Tomlins et al., 2002) investigated the types of root damage that were most associated with reduced shelf-life and increased weight loss. Skinning injury and broken roots reduced the shelf life the most, as measured by weight loss, when roots were stored under tropical conditions. Skinning injury was also associated with the increased occurrence of rots. Curing of roots prior to transportation can reduce root damage and increase the shelf-life, but this is rarely practised in East Africa probably for reasons of cost and security. Curing involves storing the roots at moderate temperatures (25 – 30 ºC) and high humidity for several days, and is recommended so that a surface layer of protective lignified/suberised wound periderm tissue is formed, especially at wound sites (Wills et al., 1998). A potential alternative to post-harvest curing that overcomes the cost and security issues is pre-harvest curing which is achieved by pruning the plant canopy (dehaulming) before harvest. This approach is low cost and secure and is achieved by removing the plant stem and canopy up to 14 days before harvest. This practice has been reported to reduce injury to roots by 62% in studies in the USA (Bonte and Wright, 1993). van Oirschot (2000) investigated pre-harvest pruning and reported no reduction in damage or weight loss during storage. On the other hand, in another study in Tanzania (Tomlins et al., 2002), pre-harvest curing by pruning the plant canopy 14 days before harvest significantly reduced the level of skinning injury in roots during harvesting and post-harvest handling in sacks along with the reduced occurrence of rotten roots. The shelf-life of the fresh roots was also extended. Rees et al. (2003a) reported a wide range in shelf-life among sweet potato varieties. They found that the main forms of deterioration in sweet potato during marketing were water loss and rotting, and that water loss appears to promote rotting and, therefore, if this can be reduced it should have an impact on the extent of rotting seen in the markets (Rees et al., 2001). In addition to damage to roots resulting from handling and transport, there is a wide range in shelf-life among varieties, which seems to be primarily due to differences in susceptibility to water loss. The susceptibility to water loss in varieties is relatively consistent between seasons (Rees et al., 2003a). The consistency between environments is less clear, but there are some varieties that consistently do better than others. Under sub-optimal humidities (65% ± 10) the wound healing process in sweet potato follows a similar pattern to wound healing under curing conditions. However, the thickness of the desiccated cell layer, and hence the depth of the lignified layer, is affected by both variety and humidity (Figure 6).

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The bar represents around 200 mm. Sections: 15 mm thick, stained with Phloroglucinol/HCl, which stains the lignin red. The sections were taken from (a) Zapallo, (b) Kemb 10 and (c) KSP 20. Figure 6. Lignification starts at the wound boundary. The onset of the lignin layer in wounds of sweet potato kept at 71% RH at 6 days after wounding (van Oirschot et al., 2003).

Figure 7. The relationship between lignification score and percentage root weight loss after 10 weeks of storage for a range of varieties. Each point corresponds to a variety (van Oirschot et al., 2003).

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Some varieties from East Africa consistently failed to produce a lignified layer while in others the layer is often not continuous (van Oirschot et al., 2003, 2007). The continuity of the lignified layer is more important for effectiveness of wound healing than the actual thickness. Wound healing efficiency as measured by lignification was found to be a major factor in the shelf-life of sweet potato varieties (Figure 7). Lignification of wounds correlates with reduced rate of weight loss and fungal infection. A method for assessing efficiency of wound healing termed the lignification score, based on assessing the continuity of lignified layers has been developed. This quick and simple method estimates the probability that wound healing occurs, and does not require a microscope. This could be a suitable method by which breeding programmes could assess their germplasm and has implications for the handling and marketing of sweet potato roots.

CONSUMER ACCEPTANCE OF FRESH SWEET POTATO VARIETIES IN AFRICA Consumer acceptance can play an important role in breeding initiatives and in the introduction of the new orange fleshed varieties that are high in provitamin A. Breeding initiatives for sweet potato in Africa are at a relatively early stage compared to other staple crops (van Oirschot 2000, 2001; Bainbridge et al., 1996; Walker and Crissman, 1996). Varieties grown in many regions are low yielding, and hence the potential for improvements through breeding are high. While the main objectives of breeding programmes have traditionally been an increase in yield and improvement of other production characteristics, the importance of post-harvest characteristics, in particular consumer acceptability, for the acceptance of new varieties is being increasingly recognised (Kapinga et al., 2000). While China is by far the largest producer of sweet potato, the African countries, Nigeria and Uganda are the next two largest producers (FAOSTAT, 2009). However, the majority of sweet potato varieties presently grown are low yielding compared to other regions. However, there is an enormous diversity of sweet potato germplasm in East Africa, and hence great potential for rapid improvements in varietal characteristics through breeding within the region. The success of any newly introduced variety will depend not only on production characteristics, but also on its acceptability to consumers in terms of both sensory and utilisation characteristics. Consumer preferences appear to differ greatly between regions; for example, in North America and in South Africa low dry matter varieties are grown while in East Africa higher dry matter varieties are preferred. In the Lake Zone of Tanzania, a fairly consistent picture has emerged with both consumers and traders preferring a high dry matter content (also expressed as starchy or floury) and good taste (Kapinga et al., 1995; 1997a, b, c,d). This was followed by cooking quality (referring to the time needed for cooking) and the colour of the flesh and skin. Other criteria mentioned were low fibre content, good storability after purchase and root size. The criteria used by traders fit closely to those of the consumers, except that appearance is relatively more important, ranking equally with good taste (Kapinga et al., 2000). Many of the sensory criteria mentioned above are very complex and subjective, and therefore practically difficult to measure instrumentally. Direct consumer testing of new

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varieties is very expensive and time consuming, usually involving the interviewing of at least 100 consumers (Meilgaard et al., 2007). Sensory taste panels can be used to produce sensory profiles of varieties. A Tanzanian study that will be presented here was carried out using the variety Tanzania as a test case, to investigate whether such panels could be used as a means of screening new sweet potato varieties for consumer preference for markets in Tanzania (Tomlins et al., 2004). The procedure would depend upon the identification of a sensory profile that accurately represented the preferences of consumers. Key questions were: how consistent are consumer preferences between locations in Tanzania, how do regional differences influence the sensory characteristics of a variety, and how do preferences differ from year to year. Research findings based on studies over a two-year period involved interviewing 600 consumers at three locations (urban and rural) in the Lake Zone of Tanzania and the preference of 14 locally available sweet potato varieties was evaluated in the cooked form (Tomlins et al., 2004). A simple consumer questionnaire based on consumers‘ first choice preference was used followed by socio-economic questions. A trained sensory panel profiled the cooked sweet potato samples enabling comparisons with preference, location and season. Analysis of the sensory data and consumer responses showed that some varieties were consistently preferred over the two-year period while others were not. The location where the varieties were grown also influenced preference. A model based on the sensory attributes to predict consumer acceptance showed that the sensory attributes starch and stickiness were the most important. Target levels, based on the mean intensity scores of these attributes are suggested as a means of screening new varieties (Figure 8). However, more research is necessary to understand why some varieties are not consistently preferred from one year to another because this can influence breeding trials. For example, other factors affect preferences are also important and could be incorporated in future models that would assist plant breeders. These could include yield, disease resistance, storability, cookability, and susceptibility to damage during transport. Consumer acceptance research on sweet potato has been extended to explore the acceptance of orange fleshed sweet potato varieties (OFSP) that are high in β-carotene, used by the human body to produce vitamin A. The success of biofortification in making an impact depends on the extent to which biofortified crops are consumed by target populations. Consumer acceptance is likely to be a greater challenge for visible traits such as β-carotene than for invisible ones such iron or zinc. Of particular interest are potential obstacles or opportunities for the consumption of β-carotene rich sweet potato. Replacing the pale-fleshed varieties now grown by farmers with new high ß-carotene varieties could benefit an estimated 50 million children under age six who are currently at risk. For example, the majority of children in Burundi, Rwanda and Uganda would benefit, as would about half of the children in Tanzania and to a lesser degree those in Ethiopia, Kenya and South Africa (Walker and Crissman 1996). A field study reported that in western Kenya, OFSP and sweet potato-based food products were acceptable to both producers and consumers in terms of appearance, taste, and texture (Hagenimana et al., 1996). Another field study (Ssbuliba et al., 2001) in the Mpigi and Luwero Districts of central Uganda indicated a large difference in yield between OFSP and traditional white-fleshed varieties (WFSP) and in acceptability tests, children were reported to find OFSP acceptable although farmers preferred pale-fleshed ones. However, the results of this field research were based on acceptability judged by community groups.

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Where C1 = cluster 1, C2 = cluster 2 and C3 = cluster 3, dotted lines illustrate boundaries for cluster 3 (most preferred varieties). Figure 8. Scatter plot of starch and stickiness to illustrate limits for starch and stickiness when selecting sweet potato varieties that are preferred by consumers in Tanzania (Tomlins et al., 2004).

A disadvantage of this approach is that dominant individuals can potentially bias the group, therefore evaluating individual opinions is recommended in consumer studies. This can be overcome by interviewing large number of consumers and obtaining individual opinions through the use of hedonic scales (Meilgaard et al., 2007). Acceptability studies involving 94 school children and 59 mothers with pre-school aged children in the Lake Zone of Tanzania indicated that they found the orange-fleshed varieties as being more acceptable than white-fleshed ones (Figure 9) (Tomlins et al., 2007a). However, the mothers, however generally gave slightly higher acceptance scores than the school children. However, this response was not the same for all consumers since cluster analysis indicated a multi-modal distribution with the majority of adult and children consumers giving high acceptance scores to both OFSP and white flesh varieties. Internal preference mapping suggested that fibrous texture influenced acceptability for the school children whereas it did not for the mothers. Recent work in Uganda (Tomlins unpublished study and Choudhury unpublished study) has explored how acceptance of the orange fleshed sweet potato varied with location, whether consumers were willing to pay more for the orange fleshed varieties than the white or yellows (with or without receiving information about the nutritional benefits) and whether acceptance of the orange fleshed varieties might be initially higher than anticipated because it was the first time the consumers had been exposed to it.

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Consumer acceptability

8 7 6 Sinia 5

Polista

4

Karote Resisto

3 2 1 School children

Mothers

Where: error bars represent the standard deviation; although the scale used by consumers was from 1 to 7, the scale in this graph has been extended to 8 so that the error bars can be shown. Figure 9. Mean acceptability scores for school children (n = 94) and mothers (n = 59) when assessing cooked sweet potato varieties (Tomlins et al., 2007a).

This unpublished work has found that acceptance of the OFSP among adults in rural and urban areas is generally greater than for white and yellow fleshed one but it did vary with location. When consumers were asked about how much they were willing to pay for the OFSP, this was increased if they had received information about the benefits of consuming it. Sensory testing indicated that scores for the orange colour of the cooked roots was not linearly related to the total carotenoid content (and therefore pro-vitamin A). This could be important in marketing because consumers might confuse low carotenoid varieties with high and hence more nutritious ones.

PROCESSING OF SWEET POTATO IN AFRICA Sweet potato storage roots are bulky and perishable. The main forms of deterioration have already been discussed. The bulkiness and perishable nature of the roots can be major constraints on the marketing and availability of the crop. One way in which these constraints cam be addressed is through processing (Owori and Agona 2003). Products where sweet potato has been incorporated as an ingredient include fried products, fufu, gari, porridge, bakery products, ketchups and juices (Owori et al., 2007). Sweet potato processing for human consumption in many African countries has not yet been commercialized. Studies in some countries have, however, investigated the feasibility of sweet potato as a partial substitute for imported wheat flour in snack products. Substitution of wheat flour, either with fresh, grated roots or sweet potato flour, is gaining a foothold in the snack product market in Kenya and Uganda. Promotion of commercial processing of primary products would increase the utilization of sweet potato flour as an ingredient in snack product

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processing (Owori and Agona, 2003). In Mozambique, commercial bakers are substituting OFSP for wheat as an ingredient in bread (Tomlins unpublished study). Rather than adding sweet potato flour, bakers are adding freshly mashed sweet potato. The sweet potato bread or ‗golden bread‘ is being promoted as a source of provitamin A and as a means of increasing incomes for bakers, especially when the cost of wheat flour is high. While many new sweet potato products have been developed in Africa, the priority is still predominantly in the improvement of the quality of the flour after drying and storage (van Hal, 2000). Recent initiatives have focused on the retention of retention of carotenoids in OFSP processed products because of the potential benefits to health and nutrition (Bechoff et al., 2009a). This has been investigated as part of the HarvestPlus Reaching End Users project. It was known that in Africa, losses in carotenoids during drying and storage were large but little was known about where most of these losses were occurring in the process or how to reduce them, particularly when the methods of processing and storage were dependant on minimal capital investment. The research found that the total carotenoid retention during drying was not dependent on the type of dryer (solar or sun). Sweet potato variety, however, had a significant effect on carotenoid retention in drying where carotenoid loss was generally correlated with high initial moisture content and high carotenoid content in fresh sweet potato roots. A variety of different drying techniques can be used. Of different drying techniques, hot air cross flow drying retained significantly more provitamin A than sun drying but solar and sun drying were not significantly different in terms of provitamin A retention. The vitamin A activity in the flours made from OFSP was found to be greater than 1,500 RE (βcarotene:retinol; 13:1) per 100 g including in sun-dried samples. It was concluded that flour from orange-fleshed sweet potato has potential as a significant source of provitamin A. However, while some provitamin A is lost during drying, much greater losses can occur during storage (about 70%) and this was not affected by the packaging (storage at ambient temperature). For low cost storage of sweet potato chips at ambient temperature, the losses of carotenoids during storage are therefore considered to be more of a constraint to the utilisation of dried sweet potato than losses occurring during drying (Bechoff et al., 2009b).

SWEET POTATO TRADE AND MARKETING IN SUB-SAHARAN AFRICA In Africa, sweet potato‘s bulky, perishable and low-value nature tends to limit the distance it is traded, the number of intermediaries involved in the value chain and hence the marketing opportunities. Access to market information by farmers is often limited. Sweet potato prices are rarely available at the national level. Farmers have to rely on traders and neighbours and, where they exist, brokers, to give them an indication of the price. Traders and farmers are increasingly using mobile phones to obtain regular price updates. The positive role played by traders in the value chain is sometimes down played by organizations purporting to assist farmers. Trade in fresh sweet potato is usually undertaken by a large number of small-scale traders selling not more than a few sacks per week and involves little capital to establish a business (Okwadi 2008). In much of sub-Saharan Africa, sweet potato is transported by bicycle by itinerant traders or urban market retailers who travel up to 30 km in search of produce. A typical marketing system for sweet potato in Uganda is illustrated in Figure 10.

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Source: Coote et al. (2007). Figure 10. Typical marketing pathways for sweet potatoes (thickness of line denotes most prevalent routes).

Sacks are also transported by lorries and sometimes boats or canoes. The supply chain is often short; retail traders often deal directly with farmers or they may buy from an itinerant trader who has assembled small quantities of sweet potato from a number of small-scale farmers. Retail traders often work in loosely-formed informal groups, with one or two travelling to the production areas, once or twice a week to obtain supplies, while one trader remains in the market and sells their own and others‘ produce. In some areas it may be feasible for traders to travel to production areas, or rural assembly markets where it is possible to buy sweet potato in bulk, by minibus and then transport the sacks by truck or minibus. Gender roles play an important part in how sweet potato is marketed. In Uganda sweet potato retailing is mostly done by women, who explain ‗it‘s dirty work – men don‘t like it‘ while men tend to be the ones who travel to rural areas and assembly markets to source the produce. Women may sell their own produce at rural periodic markets or in urban markets. They may pay men to go and procure sweet potato from them. In Malawi, female traders from Blantyre travel to the border with Mozambique to assemble several sacks of sweet potatoes, where they pay male traders to go and purchase from farmers (Agar and Coote, 2008). In Quelimane, Mozambique, groups of women travel to the district capital of Maganja da Costa to collect consignments of sweet potato. They camp out in the town and wait for farmers to bring in varying quantities. When they have assembled a sufficient number of sacks they load them onto buses or trucks to take to the markets in the provincial capital (Massingue, 2008). In the past 10 to 15 years there have been a number of initiatives and projects to introduce OFSP varieties to farmers in Africa but few have been sustainable. For example, in some markets in Uganda, traders were very opposed to the product. The common wisdom was that consumers in Kampala did not like it and therefore there was no point in growing or selling it. The HarvestPlus Reaching End Users project has sought to introduce OFSP into Central and Eastern Uganda and into Zambezia Province in Mozambique between 2006 and 2009 and an issue was how to identify a strategy to develop markets for OFSP. Working with the existing sweet potato market chains was the most effective approach. This involved the novel approach of identifying traders and to offer them training on the benefits of OFSP. The

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training material covered the health benefits of eating OFSP; the advantages of selling OFSP because it could be sold for a higher price and showing traders the areas where OFSP was being grown and introducing them to larger-scale growers. This was backed up with frequent radio spot messages telling people about the benefits to be gained from eating OFSP and telling them of the markets where it could be obtained. There has been a rapid growth in commercialisation of OFSP which it is hoped will continue after the end of project implementation. In Africa, there is minimal international trade in fresh sweet potatoes; global exports per annum of sweet potato in 2006 totalled US$90.1 million or which Africa represented just 1.9% (FAOSTAT, 2009). The main sweet potato exporting countries in Africa are Egypt (US$1 million), Ghana (US$0.34 million) and South Africa (US$0.29 million). Elsewhere in Africa, exports are erratic. In Uganda some sweet potato exports are recorded but these are often added to air-freighted higher-value vegetable orders to add weight to the volume. Sweet potatoes do, however, play a big though usually unrecorded role in informal, crossborder trade between African countries, including from Uganda to Kenya and the Sudan and from Mozambique to Malawi. In Uganda, sweet potatoes are taken into Kenya at the Busia and Malabar border crossings as well via informal rural routes (Coote et al, 2007). In Malawi (Mulange District), sweet potato comes from the Zambezia Province in Mozambique to meet the food demands of workers on the tea estates as well as being transported to the industrial city of Blantyre to supply urban markets (Agar and Coote, 2008). Few processed sweet potato products are currently marketed in sub-Saharan Africa (Coote and Okwadi, 2008). Key supply issues include unreliability of supply and poor quality of chips due to poor drying. Farmers complain about the low price of sweet potato chips compared to price of fresh tubers. A major issue is the conversion ratio from fresh to dry sweet potato. Relatively low yields further conspire to make the process financially difficult. In addition, although the financial feasibility is crucial, there are additional factors that need to be taken into consideration including technical parameters and organizational issues as well as those relating to the ease of finding markets for, and selling of, fresh roots. With respect to OFSP, there are technical issues concerning how to preserve the carotenoids. Peters and Wheatley (1997) strike a note of caution while acknowledging that although sweet potato roots can be processed into a number of products, ‗in any given location the range is much more restricted‘.

STORAGE PESTS AND POST-HARVEST LOSSES Damage to sweet potato storage roots by insect pests, even when it occurs before harvest, can be considered a post-harvest problem because it reduces both the nutritional and economic value of the storage roots and can reduce shelf-life during marketing. The most important insect pest of sweet potato storage roots worldwide is the sweet potato weevil (Cylas spp., Coleoptera: Apionidae). In certain areas of East Africa, the so-called rough weevil (Blosyrus spp.), which damages the surface of the root, is also starting to gain economic significance. Root damage by sweet potato weevils constitute a major constraint to sweet potato production and utilization worldwide and yield losses as high as 60–97% has been reported (Smit, 1997). However, even low levels of infestation can reduce root quality

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and marketable yield because the plants produce unpalatable terpenoids in response to weevil feeding (Akazawa et al., 1960; Uritani et al., 1975). Up to 15-20% of roots sent to the market may be spoiled by infestation (Kapinga et al., 1997c) and sell at a discount in markets (Ndunguru et al., 1998). Sweet potato weevils are a problem under dry conditions, because the insects, which cannot dig, can reach roots more easily through cracks that appear in the soil as it dries out. It is for this reason that during the dry season, unlike cassava, sweet potato roots cannot be easily stored in ground for any long period of time. Given the perishability of the root once it has been harvested, this can limit the potential of the crop as a secure food supply. Several attempts have been made to breed for resistance to Cylas spp. The most likely resistance mechanisms include deep rooting (as weevils can only burrow short distances); by selecting varieties that are early maturing to avoid the onset of the dry season and the subsequent increase in Cylas spp. populations; or selecting varieties whose chemical composition makes them unattractive to weevils (non-preference). However, the rate of success in breeding for non-preference has been slow, leading some breeders to conclude that an adequate source of resistance may not exist within the sweet potato germplasms (Stathers et al., 1997). Nevertheless, there are numerous reports of variation among varieties in susceptibility to weevil attack. Among the East African germplasm for example, one variety known as SPN/0 in Tanzania and Tanzania in Uganda, appears to be highly susceptible compared to other less popular varieties (Stathers et al., 2003a, b). A study in Tanzania assessed the extent to which sweet potato varieties presently available in East Africa differ in their susceptibility to field infestation by Cylas spp. and the factors that determine the susceptibility of sweet potato varieties to this pest. Deep rooting was identified as an important characteristic, presumably because roots are less likely to be exposed by soil cracking. The information was used to establish strategies for selection of suitable varieties for East Africa with reduced susceptibility (Stathers et al., 2003c). With respect to methods for assessing variety susceptibility, one conclusion from this study was that the best strategies for assessing varieties may differ by location and how the roots are utilised. In countries where sweet potatoes are grown almost exclusively for marketing, roots infested by Cylas spp. have virtually no economic value. In contrast, in many developing countries the clean portion of partially infested roots can act as a food source, either fresh if consumed immediately, or sliced and sun-dried. A more recent approach to avoiding weevil damage is to explore how sweet potato roots naturally protect themselves against attack (Stevenson et al., 2009). For example, farmers in Uganda consistently report that a sweet potato variety, New Kawogo, suffers lower sweet potato weevil damage (Cylas puncticollis) by harvest time compared to the popular and commercially important susceptible variety, Tanzania (mentioned above). Laboratory bioassays were developed to determine how the performance of weevils differed on susceptible and resistant roots. Liquid chromatography-mass spectrometry (LC-MS) analysis of the root surface and root latex subsequently identified quantitative and qualitative differences in the chemical profiles with higher levels of octadecyl and hexadecyl esters of hydroxycinnamic acids reported in the resistant variety. These compounds were then incorporated into artificial diets for bioassays on C. puncticollis. It was noted that high levels of mortality and developmental inhibition was recorded for the larvae that were fed on the treated diets, and that the effect was dose-dependent. This demonstrates that in contrast to earlier reports on other resistant African sweet potato varieties, resistance in the New Kawogo

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variety is more than simply escape but is active, quantifiable, and hence potentially manageable for breeding purposes. Furthermore, the effect on adults feeding on the resistant roots is demonstrated to be deterrent or toxic. The inheritance of the root latex esters is being studied in new crosses, and mapped in new populations using quantitative trait loci (QTLs) that are currently being developed. It is hoped that a full understanding of their inheritance will lead to the development of new varieties in which resistance can be optimized and hence reduce post harvest losses and increase the shelf-life. Although attempts to breed for resistance to Cylas spp. infestation in Africa have so far shown little success, on-going research is developing a portfolio of approaches to control the pest and hence improve yields and post-harvest quality.

CONCLUSIONS AND FUTURE PERSPECTIVES Sweet potato is becoming increasingly recognised as an important crop is Africa. It has the potential for inclusion as a disaster relief crop in times of hardship such as when global prices of wheat and other food crops are high. It is also becoming important in the improved nutrition and health of children and pregnant mothers through the introduction of provitamin A rich biofortified orange fleshed sweet potato. In Africa, the post-harvest aspects, particularly processing and marketing are still very much under developed and this is exacerbated by low yields. The new biofortified orange fleshed varieties have much potential to contribute to improved health. The main challenges for the crop in Africa with respect to post-harvest issues include: • • •

•

• •

Reduction in post-harvest losses causes by storage pests, particularly weevils because damage can reduce the market value and shelf-life; Improving the shelf-life of sweet potato so as to reduce post-harvest losses Changing the perception of sweet potato which is still widely considered to be a ‗poor persons‘ crop. This is particularly vital now that biofortified orange fleshed sweet potato containing pro-vitamin A is increasingly more widely available and can contribute to improved health; Increasing the role and importance of processing to produce products that have added value. In addition, ensuring that processed products made from OFSP contain sufficient provitamin A is essential if processed OFSP contributes to improved health and nutrition. Developing markets for sweet potato and its processed products as a means of increasing the incomes of small-holder farmers Development of export markets so that international markets can be accessed to provide foreign exchange and local income

REFERENCES Agar, J. and Coote, C. (2008). Malawi sweet potato market study. NRI HarvestPlus REU Project Report.

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Akazawa, T., Uritani, I. and Kubota, H. (1960). Isolation of ipomoeamarone and two coumarin derivatives from sweet potato roots injured by the weevil, Cylas formicarius elegantulus. Archives of Biochemistry and Biophysics, 88: 150–156. Bainbridge, Z., Tomlins, K., Wellings, K. and Westby, A. (1996). Methods for Assessing the Quality Characteristics of Non-grain Starch Staples - Part 4. Advanced Methods. Natural Resources Institute: Chatham, University of Greenwich, UK. ISBN: 0-85954-400-1: 4379. Bechoff, A., Westby, A., Owori, C., Menya, G. and Tomlins, K. (2009a). Effect of drying and storage on the degradation of carotenoids in orange-fleshed sweet potato varieties, Journal of the Science of Food and Agriculture, submitted for publication. Bechoff, A., Dufour, D., Dhuique-Mayer, C, Marouzé C., Reynes, M. and Westby, A. (2009b). Effect of hot air, solar and sun drying treatments on provitamin A retention in orange-fleshed sweet potato. Journal of Food Engineering, 92: 164-171. Bonte, D.R. and Wright, M.E. (1993). Image analysis quantifies reduction in sweet potato skinning injury by pre-harvest canopy removal. HortScience 28: 1201. Coote, C.. and Okwadi, J.. (2008). Financial Viability of Orange-Fleshed Sweet Potato Processing in Uganda. NRI HarvestPlus REU Project Report. Coote, C., Nsubuga, H. and Okwadi, J. (2007). Sweetpotato Rapid Market Access Study, Uganda: Key Marketing Issues and Recommendations for Implementation. Chatham, UK: Natural Resources Institute, University of Greenwich. FAOSTAT (2009). FAO FAOSTAT (http://faostat.fao.org; accessed March 2009). Hall, A. J. and Devereau, A. D. (2000).. Low-cost storage of fresh sweet potatoes in Uganda: lessons from participatory and on-station approaches to technology choice and adaptive testing. Outlook on Agriculture, 29: 275-282. Hagenimana V., Anyango Oyunga M., Low J., Njoroge S.M., Gichuki S.T. and Kabira J. (1999). The effects of women farmers' adoption of orange-fleshed sweet potatoes: Raising vitamin A intake in Kenya. Research Report Series 3, International Centre for Research on Women, International Potato Center (CIP), Nairobi, pp. 24. Jenkins P.D. (1982). Losses in sweet potatoes (Ipomea batatas) stored under traditional conditions in Bangladesh. Tropical Science 24:17-28. Kapinga R, Ewell P, Jeremiah S and Kileo R. (1995). Farmers perspectives on sweet potato and implications for research in Tanzania. A case study, Tanzanian Ministry of Agriculture and the International Potato Center. Kapinga R.E., Jeremiah S.C., Rwiza E.J. and Rees D. (1997a). Preference and selection criteria of sweet potato varieties at farm level in Tanzania: Secondary information compiled, Natural Resources Institute, Technical Report, University of Greenwich, Chatham, UK. Kapinga R.E., Jeremiah S.C., Rwiza E.J. and Rees D. (1997b). Preferences and selection criteria of sweet potato in urban areas of the Lake Zone of Tanzania. Natural Resources Institute, University of Greenwich, Chatham, UK. Kapinga, R., Mtunda, K., Chillosa, D. and Rees, D. (1997c). An assessment of damage of traded fresh sweet potato roots in Mwanza, Dar es Salaam and Morogoro Markets. Roots and Tuber Crops Research Programme, Progress Report for 1996. Ministry of Agriculture and Co-operatives, Research and Training Department, Tanzania. (unpublished)

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INDEX

A abiotic, 2 absorption, 66, 74, 83, 86, 94, 141, 267 acarbose, 74 accuracy, 140 ACE, 74 acetate, 37, 83, 133 acetic acid, 36, 48, 175, 181 acetone, 164 acetylation, 151 acidic, 8, 19, 202, 263 acidification, 156 acidity, 168, 170, 171, 177 ACS, 80 action research, 220, 243 activation, 121, 140, 152 acute, 77 adaptability, 118, 264 adaptation, 85 additives, 121, 164, 178, 179, 186, 187, 211, 251 adhesion, 143 adhesives, 1, 16 adjustment, 123 administration, 21, 66, 67, 74, 75, 83, 88, 223 ADP, 182, 188 adsorption, 68, 87, 154 adsorption isotherms, 154 adult, 14, 36, 37, 158, 222, 233, 254, 282 adults, 15, 37, 201, 283, 288 Advanced Life Support, 147 aerobic, 32 age, 15, 36, 70, 84, 93, 114, 129, 177, 196, 212, 226, 232, 233, 237, 272, 281 agent, 45, 48, 174, 200 agents, 28, 33, 68, 75, 130, 147, 201, 207, 216 age-related macular degeneration, 70

aggregation, 112 aging, 69, 70, 72, 75, 168, 204, 216 agricultural, 37, 60, 166, 178, 185, 187, 189, 190, 221, 248 agricultural crop, 185 agricultural residue, 187 agriculture, 24, 77, 227 aid, 45, 131, 133, 136, 137 air, 11, 12, 16, 17, 19, 32, 33, 125, 129, 131, 132, 133, 135, 137, 139, 140, 141, 142, 143, 144, 145, 149, 160, 284, 286, 289 air-dried, 137, 140 alanine, 205 alanine aminotransferase, 205 alcohol, viii, 59, 60, 62, 67, 69, 113, 119, 133, 134, 163, 175, 180, 182, 183, 194, 196, 205, 206, 207, 216, 218 alcohol production, 113, 206, 207, 216 algae, 178 alkali, 97, 121, 181 alkaline, 8, 146, 215 alkaline phosphatase, 215 allergens, 154 alluvial, 11, 12 alpha, 25, 85, 134, 143, 188 alpha-tocopherol, 85 ALT, 205 alternative, 12, 48, 52, 123, 131, 145, 163, 181, 196, 206, 209, 213, 214, 216, 218, 231, 246, 248, 265, 266, 278 alternative energy, 231 alternative medicine, 218 alternatives, 147, 207, 209 aluminum, 8, 68, 124 Amazon, 4 amide, 73, 84, 86 amines, 76 amino, 18, 60, 68, 76, 78, 79, 125, 135, 149, 179, 183, 211, 212, 235, 236, 261

296

Index

amino acid, 18, 125, 135, 149, 183, 211, 212, 235, 236, 261 amino acids, 18, 125, 135, 183, 235, 236, 261 ammonia, 28, 45 ammonium, 81 amorphous, 99, 100, 142 amplitude, 127 amylase, 18, 25, 94, 99, 100, 108, 109, 111, 116, 119, 121, 122, 123, 127, 132, 133, 134, 136, 137, 138, 140, 141, 143, 146, 149, 151, 154, 158, 170, 180, 181, 182, 188, 206, 220 amyloid, 75, 88, 160 amylopectin, 95, 96, 98, 100, 101, 102, 103, 110, 112, 113, 114, 115, 127, 144, 182, 206 anaerobic, 177 Andes, 4 anemia, 202 angina, 204, 219 Angola, 272 animal agriculture, 227 animal husbandry, 256 animal models, 204, 218 animals, 46, 66, 177, 208, 209, 210, 225, 226, 227, 228, 231, 233, 237, 240 anion, 91, 102 anomalous, 121 antagonistic, vii, 48, 49 antagonists, 54 anthocyanin, vii, viii, 9, 16, 17, 21, 25, 61, 62, 63, 66, 67, 72, 74, 75, 77, 80, 81, 83, 84, 85, 86, 87, 89, 130, 168, 170, 172, 173, 177, 183, 186, 198, 222 antibacterial, 75 antibiotics, 46, 183 anti-cancer, 66, 73, 168, 198 antidiabetic, 66, 74, 193, 203, 205, 221 antigen, 220, 222 anti-inflammatory agents, 75 antioxidant, 65, 66, 70, 75, 78, 82, 85, 87, 130, 131, 136, 147, 150, 152, 157, 161, 170, 175, 198, 200, 204, 207 antioxidative, 79, 219 antioxidative activity, 67, 72, 86, 87 anti-tumor, 72, 83, 86 antiviral, 72 apoptosis, 73, 80 APP, 125 appetite, 178 application, 12, 13, 20, 25, 27, 35, 48, 52, 53, 55, 91, 92, 123, 124, 130, 158, 164, 166, 183, 188, 190, 216 aquaculture, 208 aqueous suspension, 101

Argentina, 209, 210 Arkansas, 80, 81 ARS, 117 artery, 201 arthropods, 38 ascorbic, 27, 33, 45, 55, 56, 118, 125, 135, 180, 197 ascorbic acid, 27, 33, 45, 55, 56, 118, 125, 135, 180, 197 aseptic, 117, 119, 123, 124, 125, 127, 130, 131, 147, 153, 157 ash, 30, 53, 132, 134, 157, 168, 170, 175, 200, 211, 212, 259, 261 Asia, vii, viii, 1, 3, 4, 5, 50, 110, 132, 188, 195, 204, 206, 209, 218, 219, 225, 226, 227, 231, 240, 241, 242, 246, 248, 267, 270 Asian, 4, 25, 38, 39, 60, 69, 78, 80, 110, 150, 155, 158, 161, 164, 170, 174, 221, 248, 267 Asian countries, 4, 38, 39, 60, 69, 110, 164, 267 Aspergillus niger, 179, 180, 184, 185, 190 assessment, 153, 245, 247, 256, 289 assimilation, 186 assumptions, 231 astrocytes, 75 Athens, 117, 161 atmosphere, 28, 33, 37, 44, 51 attachment, 44, 47 attacks, 36 attitudes, 31 Australia, 5, 45, 158, 195, 208 availability, 7, 14, 20, 21, 29, 106, 119, 177, 214, 242, 248, 252, 255, 266, 273, 283 awareness, 110 Aβ, 75

B B vitamins, 197 babies, 184 Bacillus, 56, 75, 124 Bacillus subtilis, 56, 124 bacteria, 29, 38, 48, 68, 74, 75, 124, 149, 161, 164, 166, 167, 173, 175, 178, 183, 184, 185 bacterial, 99, 168, 180, 183 bacterium, 173, 179 baking, 16, 19, 112, 115, 129, 135, 157, 167, 196 Bali, 80, 246 Bangladesh, 8, 11, 12, 20, 29, 31, 35, 39, 40, 44, 49, 50, 52, 132, 210, 273, 289 barley, vii, 18, 60, 62, 131, 163, 170, 175, 196, 227 barrier, 32 beef, 59, 77, 87, 210 beer, 17, 177 beet molasses, 181

Index behavior, 52, 115, 124, 125, 126, 127, 139, 142, 153, 156, 208 Belgium, 52 beneficial effect, 47, 129, 170, 173 benefits, 13, 25, 62, 67, 120, 130, 136, 240, 267, 268, 273, 282, 283, 284, 285 benign, 165 beta-carotene, 219 beverages, viii, 9, 17, 118, 130, 159, 163, 164, 166, 167, 170, 177, 187, 189, 202, 205 bias, 282 binding, 75, 78, 82, 91, 97, 99, 190, 205 bioactive compounds, 66, 70 bioassays, 287 bioavailability, 77, 78 bioconversion, 166, 177 biodegradable, 77, 207 bioethanol, 184 biofuel, 183 biofuels, 183, 218 biogas, 263 biological control, 48 biomarker, 158, 222 biomarkers, 205 biomass, 19, 24, 165, 178, 182, 188, 207, 216, 218, 221, 228, 240 biomaterials, 124, 157 bioreactor, 166, 190 biosynthesis, 54, 57, 63 biotechnological, 177 biotechnology, 8, 110, 183, 187 biotic, 2 birds, 232, 233 birth, 184, 233, 255, 266 birth weight, 184 bleaching, 68, 207, 216 blends, 140, 146, 152, 161 blindness, 65, 168, 201, 204, 272 blood, 66, 67, 74, 82, 83, 87, 136, 193, 201, 202, 203, 204, 205, 215, 217, 222, 266 blood glucose, 66, 67, 74, 87, 136, 193, 201, 202, 203, 205, 215, 222 blood pressure, 74, 193, 204, 205, 215, 217 boats, 285 body weight, 67, 74, 231, 232 boiling, 16, 19, 64, 181, 182, 196, 266 bonding, 98, 99, 103, 137, 142 bonds, 144 border crossing, 286 borderline, 158, 205, 222 boys, 254 brain, 75 branching, 96, 98, 113, 135, 142, 144, 166

297

Brazil, 43, 44, 194, 201, 209, 210 Brazilian, 78, 82, 83 Breads, 200 breakdown, 33, 34, 103, 106, 140, 175, 180, 183 breakfast, 118, 131, 146, 149, 154, 158, 196, 272 breeding, 8, 49, 80, 81, 84, 109, 110, 120, 150, 220, 228, 257, 280, 281, 287, 288 brevis, 68, 167 broad spectrum, 49 broccoli, 9 broilers, 232, 233, 241, 244 buffalo, 150 burning, 15 Burundi, 272, 281 buses, 285 butyric, 178 by-products, 61, 64, 77, 88, 179, 191, 209, 227, 228

C cabbage, 9, 17, 62, 66, 76, 79 cabinets, 118 caffeic acid, 46, 59, 63, 83, 88 caffeine, 219 caffeoylquinic acids, 83, 85 calcium, 60, 67, 69, 77, 86, 128, 130, 159, 212 calcium oxalate, 77 calorie, 68, 141, 180 cambium, 7, 121 Cambodia, 235 Cameroon, 10, 12, 24, 30, 53, 112 Canada, 195, 205, 206, 221 cancer, 60, 68, 69, 70, 73, 79, 80, 82, 84, 129, 156, 160, 193, 204, 216 cancer cells, 73, 82 Candida, 178 candidates, 75 capacity, 66, 68, 69, 79, 82, 85, 91, 94, 97, 99, 118, 120, 121, 130, 136, 140, 141, 143, 165, 168, 170, 182, 200 capsule, 7 carbohydrate, viii, 19, 98, 111, 112, 119, 160, 170, 179, 202, 206, 207 carbohydrates, 13, 111, 115, 118, 131, 135, 144, 148, 156, 157, 158, 160, 177, 178, 203, 229 carbon, 37, 66, 129, 178, 204, 222 carbon dioxide, 37 carbon tetrachloride, 66, 204, 222 carboxymethyl cellulose, 130 carcinogenesis, 61, 72, 73, 76, 78, 79 carcinogenic, 78 carcinogens, 73, 76, 78, 83 cardboard, 30, 32, 34

298

Index

cardiovascular disease, 68, 69, 70, 153, 194, 201, 204, 216 carotenoids, vii, 16, 45, 59, 65, 70, 81, 129, 134, 135, 150, 153, 154, 198, 204, 217, 284, 286, 289 carrier, 139 case study, 289 casein, 235 cash crops, 3 cassettes, 220 catalyst, 140 cataracts, 70, 74 catechins, 218 catechol, 75, 76 cattle, viii, 54, 59, 77, 87, 178, 208, 209, 210, 211, 218, 225, 238, 240, 242, 255, 266 cavities, 35, 39, 43 Celiac disease, 196 cell, 45, 62, 63, 68, 72, 73, 76, 77, 80, 81, 85, 92, 163, 164, 165, 166, 178, 182, 183, 189, 278 cell culture, 62, 77 cell growth, 81 cell line, 62, 63, 81 cell membranes, 92 cellulose, 68, 106, 130, 135, 159, 178, 179, 190, 238 cellulose derivatives, 159 cellulosic, 92 Central America, 5 Central Asia, 5 cereal starches, 95, 101 cereals, 2, 3, 118, 131, 196 cerebrovascular, 60 cerebrovascular disease, 60 cerebrovascular diseases, 60 chain branching, 142 charcoal, 44 chemical properties, 92, 116, 147, 154, 155, 157, 161 chemical structures, 133 chemicals, 18, 56, 83, 164 chemoprevention, 77 chemotaxis, 82 cherries, 130 chicken, 115, 211, 213, 214, 216, 222, 225, 226, 231, 240, 243, 259, 260, 261, 262 chickens, 194, 212, 214, 221, 231, 233, 242 chicks, 231, 241, 243 childbearing, 273 childhood, 272 children, 18, 131, 150, 160, 204, 215, 219, 222, 223, 254, 264, 272, 281, 282, 283, 288, 292 chitosan, 163, 181, 186, 190 chlorination, 28 chlorine, 33, 48

chlorogenic acid, 2, 18, 46, 59, 129, 130, 193, 203, 205, 216, 219, 224 cholera, 251 cholesterol, 61, 68, 69, 83, 173, 202, 203, 220 chopping, 226, 259 chromatography, 85, 179, 287 chromosome, 6 chronic diseases, 130 chrysanthemum, 72 cis, 65, 70, 82, 129, 130, 154 citrus, 69 classes, 263 classification, 4 clay, 7, 14 cleavage, 74, 100 climate change, 208 climatic factors, 24 clinical trial, 204 clinical trials, 204 clone, 168, 172, 177, 257, 258 cluster analysis, 25, 282 clusters, 137 Co, 8, 53, 146, 149, 150, 187, 188, 214, 220, 221, 243, 268, 289 CO2, 28, 33, 35, 37, 273 cocoa, 147 coconut, 23 coding, 183 coffee, 38, 85, 202, 203 cohesion, 143 cohort, 82, 204 Coleoptera, 26, 51, 53, 55, 286 collaboration, 21, 247 Colombia, 185, 269 colon, 68, 73, 76 colon cancer, 68, 73 colon carcinogenesis, 76 colonization, 42, 166 Colorado, 51, 54 colors, 65, 118, 123, 124, 139, 158 commercialization, 216 commodity, 33, 48, 267, 268 communication, 266, 278 communities, 62 community, 13, 220, 254, 257, 281 compaction, 11 compatibility, 274 competition, 13, 23, 228, 255 competitiveness, 147 compilation, 153 complement, 265 complexity, 256 complications, 201

Index components, vii, 16, 49, 52, 57, 59, 60, 61, 62, 63, 64, 66, 67, 68, 69, 75, 77, 79, 82, 87, 88, 92, 93, 98, 100, 119, 123, 135, 137, 142, 159, 168, 175, 233, 242, 292 composition, 36, 53, 62, 63, 64, 65, 77, 80, 81, 85, 87, 88, 89, 93, 111, 113, 119, 124, 134, 135, 137, 148, 151, 152, 154, 159, 160, 167, 185, 186, 200, 212, 214, 228, 229, 231, 235, 236, 239, 241, 260, 261, 287 compost, 12 composting, 166, 252 compounds, 15, 46, 53, 56, 64, 66, 69, 70, 72, 73, 80, 84, 85, 87, 92, 125, 129, 136, 158, 180, 201, 223, 232, 287 concentrates, 159, 216 concentration, 21, 45, 46, 69, 70, 92, 100, 103, 104, 106, 108, 120, 125, 138, 140, 142, 153, 170, 171, 175, 178, 180, 181, 182, 202, 208, 232 concrete, 32, 252 conditioning, 181 conduction, 123 conductivity, 142, 148 configuration, 129, 130 Connecticut, 187 consensus, 267 conservation, 150, 177 constipation, 68 constraints, 177, 208, 216, 258, 259, 260, 262, 283 construction, 47, 254, 263, 274 consumers, 16, 17, 19, 49, 74, 110, 118, 121, 170, 171, 200, 207, 209, 217, 274, 280, 281, 282, 283, 285 consumption, 9, 33, 36, 60, 77, 92, 118, 129, 130, 131, 161, 170, 182, 183, 195, 202, 204, 208, 209, 212, 213, 215, 218, 223, 226, 227, 233, 241, 246, 248, 251, 252, 253, 254, 255, 268, 272, 273, 281, 283 consumption patterns, 208 contamination, 39, 132, 134 continuity, 280 control group, 74, 212 conversion, 61, 108, 109, 117, 121, 122, 156, 175, 180, 182, 186, 215, 231, 232, 234, 286 cooking, 18, 19, 96, 113, 117, 120, 121, 122, 125, 129, 134, 135, 146, 149, 150, 152, 157, 160, 175, 214, 254, 259, 260, 262, 263, 267, 280 cooling, 100, 103, 127, 139 corn, 62, 66, 69, 78, 95, 99, 101, 103, 104, 157, 160, 203, 207, 211, 227, 231, 232, 258, 259, 260 corolla, 7 correlation, 70, 71, 72, 94, 276 correlations, 104 corrosion, 99, 100, 121, 137

299

cortex, 7, 56 cosmetics, 77 Costa Rica, 238 cost-benefit analysis, 243 cost-effective, 123, 212, 225, 240, 272 costs, 11, 47, 110, 150, 183, 201, 208, 211, 240, 259 cotton, 68, 112 covalent, 98 covalent bond, 98 covalent bonding, 98 covering, 47, 261 cow milk, 170 cows, 212, 218, 226, 238, 239, 240, 241, 242 cracking, 109, 287 Cranberry, 191 CRC, 52, 111, 148, 153, 270, 290 creatinine, 215 critical period, 13, 23 CRM, 225, 235 crop production, 221 crop residues, 15, 177, 227 cross-border, 286 crystalline, 100, 101, 102 crystallinity, 95, 99, 102, 103, 142 crystallites, 101 crystallization, 113 crystals, 180 CTA, 221, 243 Cuba, 11, 44, 50 cultivation, 2, 7, 13, 21, 25, 39, 40, 97, 102, 110, 166, 189, 190, 228, 237, 254, 255, 263 cultural practices, 36, 56 culture, 22, 53, 54, 62, 63, 81, 146, 155, 168, 170, 175, 179 curing, vii, 31, 33, 35, 39, 40, 47, 48, 50, 51, 53, 54, 56, 57, 101, 112, 119, 125, 151, 156, 160, 233, 278, 292 curing process, 47, 112 currency, 254 cyanide, 181, 183 cyanobacterium, 86 cycles, 36 cytokines, 75 cytotoxicity, 75

D dairy, 160, 211, 238, 243 database, 70 death, 60, 73, 272 deaths, 255 decay, 27, 29, 31, 32, 35, 37, 38, 39, 40, 42, 43, 44, 45, 47, 48, 49, 212

300

Index

decomposition, 17 defenses, 89 deficiency, 65, 130, 193, 200, 204, 215, 216, 219, 220, 272 deficit, 24, 43 deficits, 75 degradation, 17, 94, 99, 100, 116, 120, 121, 123, 134, 135, 140, 144, 218, 228, 236, 240, 242, 243, 289 degrading, 45 dehydration, 132, 133, 135, 148, 163, 177, 178, 190 delivery, 120, 131, 208 demographic change, 201 density, 21, 137, 142, 166, 202 Department of Agriculture, 117, 159, 198, 208 depressed, 12, 44, 232 derivatives, 59, 63, 64, 71, 72, 73, 76, 77, 78, 80, 82, 88, 114, 159, 180, 289 desert, 4 desiccation, 33, 35 destruction, 160 detection, 9, 85 detoxification, 56 developed countries, 19, 60, 194, 246, 273 developing countries, vii, 1, 2, 28, 47, 65, 92, 129, 193, 194, 195, 200, 201, 204, 205, 206, 207, 208, 209, 215, 227, 244, 269, 273, 287 deviation, 127 diabetes, 59, 61, 68, 74, 87, 136, 201, 202, 203, 218, 219, 220, 221, 222, 223 diabetes mellitus, 74 diabetic neuropathy, 201 diabetic patients, 220, 222 diarrhea, 207 dielectric constant, 124 diesel, 209 diet, 68, 74, 77, 83, 110, 196, 202, 203, 211, 212, 214, 215, 217, 220, 222, 225, 232, 233, 234, 235, 238, 241, 243, 245, 249, 250, 251, 252, 254, 256, 258, 259, 261, 263, 266, 272 dietary, 66, 67, 68, 70, 78, 79, 85, 86, 87, 88, 110, 115, 118, 128, 131, 135, 136, 152, 155, 170, 196, 197, 198, 200, 201, 202, 203, 204, 207, 213, 214, 215, 217, 218, 223, 227, 233, 236, 238, 241, 270 dietary fat, 217 dietary fiber, 66, 68, 78, 79, 85, 86, 87, 88, 110, 118, 128, 131, 136, 152, 196, 198, 200, 217 diets, 19, 21, 79, 115, 118, 129, 146, 185, 204, 207, 209, 211, 212, 213, 214, 215, 216, 217, 221, 222, 226, 231, 232, 233, 234, 235, 236, 237, 238, 241, 242, 243, 244, 258, 259, 260, 287 differential scanning calorimetry, 56, 112, 115, 148 diffusion, 78

digestibility, 23, 91, 94, 99, 135, 136, 156, 161, 184, 207, 211, 213, 217, 218, 221, 222, 232, 233, 234, 235, 237, 238, 241, 242, 258, 259, 260, 267 digestion, 19, 100, 135, 136, 155, 170, 207, 217, 223 dimerization, 82 diploid, 6 disability, 201 disaster, 288, 290 disaster relief, 288 diseases, vii, 1, 2, 8, 15, 27, 28, 38, 44, 48, 50, 51, 55, 60, 68, 69, 70, 72, 129, 188, 193, 204, 216, 249, 251, 252, 255, 256, 263 disinfection, 50 disposition, 65 distillation, 181 distilled water, 133, 145 distribution, 67, 71, 94, 95, 98, 114, 123, 124, 135, 144, 152, 186, 282 diversity, 25, 89, 150, 280 DNA, 73, 83, 84 DNA damage, 84 DNA polymerase, 83 Dominican Republic, 209, 210 double bonds, 72 doughnuts, 131 drainage, 11 dressings, 12 drinking, 264 drinking water, 264 drought, 7, 45 drug delivery, 208, 216 drug release, 208, 220 drug treatment, 219 dry matter, vii, 1, 16, 17, 19, 23, 33, 35, 92, 109, 119, 122, 128, 132, 147, 161, 178, 200, 210, 211, 212, 213, 225, 226, 228, 234, 235, 236, 237, 238, 240, 244, 246, 257, 258, 259, 260, 261, 264, 280 drying, 11, 17, 19, 38, 113, 117, 132, 133, 134, 135, 137, 139, 140, 143, 148, 149, 150, 151, 154, 160, 167, 177, 196, 208, 221, 227, 231, 233, 244, 266, 267, 284, 286, 289 drying time, 132 DSC, 91, 101, 102, 107, 111, 112, 118, 127, 142, 143, 224 dung, 12 duration, 181, 188 dust, 28, 47, 49, 132 dyes, 196

E earth, 53 earthworms, 246

Index Eastern Europe, 5 eating, 60, 106, 110, 196, 254, 286 ecological, viii, 245, 251 ecology, 34 economic development, 208, 267 economic efficiency, 211, 212, 227, 242, 262 Economic Research Service, 159 economics, 24, 215, 219, 223 ecosystem, 13, 22, 166 ecosystems, 4 Ecuador, 209, 210 effluents, 181 egg, 59, 77, 87, 212, 221, 231 Egypt, 44, 52, 210, 272, 286 elderly, 78 electrical conductivity, 142, 148 electromagnetic, 124 electron, 99, 138 electron microscopy, 99 elephant, 115 elongation, 77, 166 embryo, 7 emotional, 136 employment, 206 emulsions, 160 encapsulation, 139, 208 endosperm, 7 endothelial dysfunction, 219 energy, vii, 1, 2, 28, 60, 82, 123, 124, 131, 132, 142, 152, 158, 165, 180, 181, 190, 207, 208, 210, 212, 214, 225, 226, 227, 229, 231, 232, 233, 237, 238, 240, 246, 248, 258, 267 England, 56 enterprise, 243 entropy, 134 environment, 33, 35, 40, 60, 111, 112, 134, 197, 212, 249, 252, 264 environmental conditions, 7, 38, 62, 81, 93, 103, 109, 225 environmental factors, 63 environmental impact, 184, 228 environmental issues, 207 environmental protection, 61, 66 enzymatic, 17, 77, 99, 104, 106, 110, 120, 121, 125, 132, 140, 182, 186, 187 enzyme inhibitors, 100 enzymes, viii, 17, 18, 45, 51, 54, 92, 99, 106, 117, 121, 122, 125, 134, 152, 160, 163, 164, 165, 175, 179, 180, 182, 183 epidemic, 201 epidemics, 246, 255 equilibrium, 134 equilibrium sorption, 134

301

erosion, 14, 134 Escherichia coli (E. coli), 74, 75, 81, 183, 259, 261 ESI, 84 estates, 286 ester, 64, 86 esters, 46, 63, 71, 287 estimating, 231 ethanol, 2, 18, 33, 110, 146, 156, 163, 164, 166, 179, 181, 182, 183, 185, 187, 189, 194, 207, 209, 216, 219 ether, 229, 238, 260 Ethiopia, 281 ethyl alcohol, 91 ethylene, 13, 27, 35, 45, 46, 52 Europe, 1, 3, 4, 5, 195, 206 European Commission, 220 European Union, 209 evolution, 6 ewe, 177 exclusion, 117 excretion, 68 exercise, 255 expert, iv expertise, 9 exploitation, 3, 195 exports, 286 extraction, 17, 68, 92, 93, 106, 110, 112, 114, 129, 163, 186 extraction process, 92 extrusion, 113, 146, 150, 152

F F. solani, 43, 49 failure, 2, 11, 222 family, 70, 131, 194, 253, 254 family income, 131 famine, 3, 62, 195 FAO, 5, 20, 185, 200, 218, 221, 242, 244, 269, 289 farming, 13, 54, 77, 93, 177, 208, 226, 227, 229, 231, 237, 240, 272 farms, 2, 30, 226, 247, 257, 274 fat, 128, 137, 141, 168, 170, 196, 212, 214, 219, 232 fauna, 246 feces, 68, 249, 255, 256, 264 feedstock, 209, 210 fermentation, viii, 17, 24, 66, 67, 77, 86, 87, 110, 146, 147, 155, 156, 163, 164, 165, 166, 167, 168, 170, 171, 173, 175, 177, 178, 179, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191, 207, 223, 259 fermentation technology, 182 fern, 29 fertiliser, 106

302

Index

fertility, 12, 16, 19, 209, 247, 252, 256, 266, 268 fertilization, 19, 82 fertilizer, 12, 13, 21, 25, 114, 252, 255, 256, 263, 268 fertilizers, 1 ferulic acid, 60, 73, 84, 88 fever, 251 fiber, 59, 66, 68, 69, 77, 78, 79, 82, 85, 86, 87, 88, 110, 118, 128, 131, 134, 136, 137, 141, 152, 196, 198, 200, 210, 211, 212, 214, 217, 260, 264, 265 fiber content, 200, 264 fibers, 66, 68, 78, 81, 86, 198 Fiji, 236 fillers, 196 film, 13, 21, 28, 33 filtration, 17 financial loss, 253 Finland, 82 fire, 264 firewood, 254, 263, 264 firms, 44 fish, 208, 210, 211, 249, 250, 256, 258, 266 fish meal, 211, 258 fishing, 254 flavonoids, 16, 85, 136, 198 flavor, 57, 119, 123, 125, 131, 145, 146, 151, 153 flight, 84 float, 143 flood, 28, 60 flora, 23, 68, 83 flow, 117, 124, 125, 126, 127, 133, 139, 146, 147, 148, 149, 153, 157, 168, 170, 172, 173, 174, 284 flow rate, 146 fluid, 133, 137, 140, 153 focusing, 77, 267 folate, 198 folic acid, 118 food additives, 121, 164, 179, 187 food commodities, 130 food industry, 66, 110, 117, 119, 121, 123, 179, 180, 205, 206 food poisoning, 2, 18 food processing industry, 119, 124 food products, viii, 110, 117, 118, 123, 124, 127, 130, 131, 147, 151, 156, 159, 163, 281 food safety, 9 foreign exchange, 288 Fourier, 91, 101 fragmentation, 73, 129 free radical, 72, 75, 76, 204 freeze-dried, 170 freezing, 120, 123, 148 frequency distribution, 71

fresh water, 86, 233 friction, 103 frost, 7, 29 fructose, 75, 125, 179, 180, 205 fruit flies, 52 fruit juice, 130, 156, 179 fruit juices, 130, 179 fruits, 48, 50, 55, 56, 62, 66, 69, 70, 79, 82, 85, 124, 125, 130, 154, 187, 188, 290 frying, 18, 196 FSP, 272, 286 FTA, 126, 128 FTIR, 91, 101 fuel, 132, 163, 167, 181, 182, 183, 191, 194, 207, 209, 214, 216, 259, 260, 262 functional aspects, 150 fungal, vii, 2, 28, 31, 45, 46, 47, 49, 56, 178, 181, 186, 189, 191, 280 fungal infection, 47, 280 fungi, 27, 28, 29, 33, 34, 37, 38, 45, 46, 47, 49, 52, 54, 74, 77, 166, 178, 179, 190 fungicide, vii, 120 fungicides, 2, 38, 48 fungus, 38, 42, 44, 45, 54, 181 Fusarium, 15, 27, 39, 43, 44, 49, 56 Fusarium oxysporum, 15, 43, 56 fusion, 137, 203

G galactolipids, 72, 84 gallbladder, 156 gamma, 37, 53 gamma radiation, 35 gas, 18, 134, 263 gasoline, 163, 164, 209 gastric, 134 gastrointestinal, 68, 203, 219 gel, 100, 101, 104, 106, 127, 140, 141, 145, 159 gel formation, 140 gelatinization temperature, 119, 142, 153 gelation, 112 gels, 99, 100, 141 gene, 73, 183 generation, 156, 291 genes, 49, 52, 55, 73, 183 genetic diversity, 150 genetic factors, 109 genome, 6 genomes, 6 genotype, 17, 80, 119, 120, 152, 157 genotypes, 9, 20, 22, 23, 46, 49, 69, 70, 71, 80, 104, 119, 128, 136, 141, 145, 158, 228, 231

Index geography, 118 Georgia, 117, 161 Germany, 79 germination, 7, 77 gestation, 233 GGT, 205 Gibbs, 217 ginseng, 223 girls, 254 gizzard, 212, 232 glass, 133, 139, 142, 143, 148 glass transition, 133, 139, 142, 143, 148 glass transition temperature, 133, 139, 142, 143 glassy state, 143 glucoamylase, 134, 137, 146, 151, 181 glucose, viii, 1, 2, 16, 57, 62, 66, 67, 74, 75, 82, 87, 108, 121, 125, 136, 140, 179, 180, 182, 188, 193, 201, 202, 203, 205, 206, 215, 216, 219, 220, 222, 223 glucose metabolism, 220, 222 glucose tolerance, 193, 202, 203, 205, 215, 216, 219, 223 glucose tolerance test, 202, 203 glucoside, 66, 78, 129 glutamate, viii, 2, 163, 164, 183 glutamic acid, 180 glycemic index, 118, 128, 147, 157, 202, 218 glycolipids, 83, 85 glycolysis, 179 glycoprotein, 75, 202 glycoside, 62 glycosides, 62, 125 gold, 253, 254 government, 193, 196 grain, 15, 212, 216, 289 grains, 4, 15, 29, 94, 101, 151, 208, 212, 226, 231, 240, 242 granule shape, 92 granules, 94, 95, 98, 99, 100, 103, 104, 109, 115, 116, 134, 137, 142, 145 grape juice, 78 grapes, 62, 83 graph, 283 grass, 30, 31, 32, 184, 212, 213, 216, 217, 218, 225, 226, 236, 237, 239, 240, 241, 242, 243, 249, 251, 256, 264, 273 grasses, 177, 208, 226, 249, 250, 255, 264, 265 grazing, 226, 256 green tea, 69, 202, 218, 222 groups, 62, 63, 64, 71, 76, 97, 108, 133, 135, 137, 140, 144, 196, 202, 205, 214, 215, 226, 266, 281, 285 growth inhibition, 48

303

growth rate, 11, 16, 25, 211, 212, 214, 233, 256, 259, 260, 262 Guam, 4 guidelines, 274 Guinea, 8, 15, 20, 21, 30, 34, 39, 53, 54, 164, 196, 209, 210, 212, 218, 219, 222, 226, 239, 240, 242, 245, 246, 268, 269 Guyana, 146

H Haiti, 39, 210 handling, 28, 39, 40, 43, 47, 50, 56, 119, 123, 124, 275, 276, 278, 280, 290, 292 hardships, 255 harm, 33 harvesting, 15, 20, 21, 22, 28, 34, 39, 47, 48, 85, 222, 226, 227, 228, 237, 238, 241, 242, 244, 272, 278 Hawaii, 79, 152 HDL, 203 healing, 47, 57, 255, 278, 280 health, viii, 9, 16, 22, 60, 67, 68, 70, 72, 74, 77, 80, 130, 152, 171, 193, 195, 200, 201, 204, 216, 218, 219, 251, 256, 261, 263, 271, 278, 284, 286, 288 health care, 9 health effects, 77, 218 healthcare, 201 heart, 60, 68, 129, 204, 215, 219, 232 heart disease, 60, 68, 129 heart failure, 204, 219 heat, 18, 29, 33, 37, 39, 55, 56, 113, 115, 120, 121, 122, 123, 124, 125, 129, 134, 135, 137, 140, 142, 146, 154, 160, 181, 207, 266, 269 heat transfer, 123 heating, 87, 99, 103, 104, 110, 120, 122, 124, 140, 147, 156, 158 hedonic, 170, 172, 282 height, 11 hematological, 215 hemicellulose, 66, 135 hepatitis, 158, 205, 222 hepatitis B, 205, 220, 222 hepatotoxicity, 204, 216 herbicide, 77 herbicides, 2, 13 herbivores, 15 herbs, 81, 223 heterogeneity, 205 heterogeneous, 166 high density lipoprotein, 203 high pressure, 120, 157

304

Index

high temperature, 35, 40, 42, 63, 123, 129, 133, 135, 148 higher quality, 123 highlands, 25, 268 high-performance liquid chromatography, 85 hip, 82 hips, 18, 182, 221, 269, 270, 284 histological, 52 HIV, 61, 75, 76, 81, 82, 85, 273 HIV infection, 75, 82 HIV/AIDS, 273 HIV-1, 81, 82, 85 hog, 269, 270 holistic, 245 hormone, 201, 203, 219 horticulture, 22, 23, 24, 54, 55, 153, 156, 186, 187, 188, 189 host, 173, 262 hot water, 37, 69, 120, 202 household, 22, 206, 248, 251, 252, 253, 255, 256, 273, 274 households, 93, 206, 214, 246, 247, 251, 252, 253, 255, 256, 262, 263, 272 housing, 254 HPLC, 81, 86, 164, 175 HPV, 118, 140, 141 hue, 62 human immunodeficiency virus, 82, 87, 204, 216 humans, 75, 76, 77, 79, 83, 84, 173, 193, 195, 198, 201, 203, 204, 205, 208, 215, 216, 219, 222, 225, 228, 245, 254, 255, 257, 264, 267 humidity, 28, 31, 33, 35, 119, 197, 273, 276, 278 husbandry, 247, 251, 255, 256, 263, 266 hybrid, 17 hybridization, 8 hydration, 101, 137, 140 hydro, 110, 137 hydrogen, 75, 137, 181, 190, 223 hydrogen peroxide, 75 hydrolysis, 45, 64, 77, 100, 108, 111, 121, 122, 123, 125, 135, 140, 157, 160, 175, 179, 182, 184, 186, 219 hydrolyzed, 120, 125, 151, 207 hydrophilic, 137 hydrophilic groups, 137 hydrophobic, 85 hydroxyl, 76, 133, 140 hydroxyl groups, 76, 133, 140 hygiene, 249, 251 hyperglycemia, 84 hypertension, vii, 59, 60, 61, 82, 202 hypertensive, 74, 83 hypotension, 83

hypothesis, 266

I ice, 72, 118, 119, 130, 131, 136, 205, 212, 249, 255 id, 106 identification, 6, 78, 83, 84, 86, 183, 281 immersion, 53 immobilization, 182 immune response, 203, 221 immune system, 65, 173 immunization, 222 impact assessment, 256, 273 implementation, 50, 286 imports, 246 impurities, 167 in situ, 48, 80 in transition, 142 in vitro, 52, 59, 62, 63, 75, 81, 82, 84, 111, 134, 157, 203, 208, 214, 220, 241 in vivo, 59, 62, 72, 79, 88, 111, 134, 214, 218 inactivation, 125, 148 inactive, 202 incentive, 207 incidence, 22, 37, 43, 48, 54, 268 inclusion, 147, 213, 217, 232, 233, 235, 241, 288 income, 131, 156, 227, 246, 252, 263, 268, 272, 274, 288, 291 incomes, 195, 263, 284, 288 incubation, 99 Indian, 3, 11, 21, 22, 23, 29, 55, 112, 156, 170, 187 indication, 74, 236, 284 indicators, 124, 148, 194 indices, 140, 215 indigenous, 50, 185 Indigenous, 188, 219 indomethacin, 75, 85 Indonesia, viii, 9, 21, 31, 34, 51, 57, 80, 132, 156, 164, 194, 201, 209, 210, 211, 219, 222, 224, 245, 246, 247, 249, 253, 254, 257, 258, 264, 265, 266, 267, 268, 269, 291 induction, 55, 73 industrial, vii, viii, 9, 1, 2, 22, 60, 99, 106, 110, 132, 140, 164, 165, 166, 167, 179, 181, 183, 188, 193, 195, 207, 208, 216, 220, 286 industrial application, vii, viii, 1, 99, 106, 164, 194, 207, 216 industrial chemicals, 164 industrialization, 218 industry, iv, viii, 9, 21, 65, 66, 68, 92, 110, 117, 119, 121, 123, 124, 147, 179, 180, 193, 195, 196, 198, 205, 206, 207, 216 infants, 68, 136, 173

Index infection, 28, 33, 40, 42, 43, 45, 46, 47, 49, 52, 55, 74, 75, 81, 82, 201, 203, 256, 280 infections, 38, 46 infectious, 74, 205 infectious disease, 74, 205 infectious diseases, 205 infestations, 43, 47 inflammation, 75, 204 inflammatory, 72, 75, 76, 84 inflammatory disease, 84 informal groups, 285 infrared, 220 infrared spectroscopy, 185, 220 ingestion, 66, 78, 86, 205, 222 inheritance, 288 inhibition, 48, 53, 74, 75, 76, 287 inhibitor, 19, 74, 82, 84, 188, 214, 226, 231, 246, 255, 258, 259, 260, 268, 269, 270 inhibitors, 25, 73, 87, 100, 125, 135, 167, 173, 186, 188, 258 inhibitory, 46, 74, 76, 82, 83, 85, 229 inhibitory effect, 74, 85 initiation, 11, 73 injection, 129, 157 injury, vii, 15, 27, 29, 35, 37, 39, 44, 46, 47, 49, 57, 61, 66, 85, 86, 130, 168, 193, 198, 204, 205, 215, 222, 276, 277, 278, 289, 292 Innovation, 186 inoculation, 20 inoculum, 155, 170, 175 inorganic, 1, 25, 110, 178, 182 insecticide, 36 insecticides, 2 insects, 16, 37, 132, 287 insecurity, 193, 200, 215, 227 institutions, 130 instruments, 247 insulin, 73, 74, 84, 201, 202, 203, 219, 222 insulin resistance, 201, 202, 203 insulin sensitivity, 201, 202, 203, 219 insurance, 2 integrity, 100 intensity, 38, 54, 146, 281 interaction, 75, 76, 124, 247 interactions, 83, 103, 139, 254 interference, 16, 220 intermediaries, 284 intermolecular, 98, 99, 103, 142, 144 intermolecular interactions, 103 international markets, 288 international trade, 3, 286 internode, 7 interpretation, 46

305

interrelationships, 110 interstitial, 54 interstitial pneumonia, 54 interval, 228, 241 intervention, 205, 247 intestinal tract, 68 intestine, 74, 173 intravenous, 202 intrinsic, 103, 198 intrinsic viscosity, 103 invasive, 44 inventions, 196 investment, 117, 123, 132, 251, 253, 259, 260, 268, 284 iodine, 221 ionic, 133 ionization, 84 ions, 125, 142 iron, 60, 69, 125, 131, 221, 281 irradiation, vii, 27, 35, 37, 48, 49, 52, 53, 55 irrigation, 1, 4, 14, 15, 19, 21, 22, 24, 27, 36 Islam, 61, 62, 63, 66, 69, 70, 71, 72, 75, 76, 77, 80, 81, 88, 136, 152, 197, 204, 219 island, 246 isolation, 92, 109 isomerization, 129, 135 isomers, 64, 65, 70, 129 isothermal, 140 isotherms, 154 Israel, 43, 44, 50, 57 Italy, 150, 242

J Jamaica, 44, 210 Japanese, viii, 21, 59, 60, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 159, 161, 163, 166, 202, 205, 220, 222, 223 Java, 22, 39, 40, 44, 48, 51, 53, 55, 156, 210, 291 Jerusalem, 57, 182, 264 juices, 170 Jun, 206, 219 Jung, 88

K Kenya, 56, 150, 151, 153, 155, 177, 204, 210, 219, 220, 237, 238, 243, 244, 268, 272, 273, 281, 283, 286, 289, 290 Keynes, 189 kidney, 266 kinetic studies, 78

Index

306 kinetics, 100 KOH, 145 koji, 64, 77, 88, 165, 166, 175 Korea, 8, 10, 13, 21, 110, 164, 178, 182, 183, 206, 209, 218, 246, 267, 268 Korean, 97, 115

L LAB, 164, 167, 168, 170, 171 labor, 211, 214, 227, 254, 255, 259, 260, 262, 267 lactating, 241 lactation, 212, 218, 233, 240, 242 lactic acid, 93, 146, 156, 161, 164, 167, 168, 170, 171, 173, 178, 179, 185, 186, 187 lactic acid bacteria, 161, 164, 167, 170, 185 Lactobacillus, 146, 156, 168, 170, 173, 179, 186 lactose, 170, 173 Lafayette, 245 lamina, 7 laminated, 124 land, 2, 11, 21, 24, 225, 227 Langerhans cells, 74 language, 189 Laos, 222 large-scale, 34, 206, 246 larvae, 15, 36, 37, 287 larval, 292 lateral roots, 6 latex, 7, 287 Latin America, viii, 5, 195, 225, 227, 246 law, 139, 140, 219 layering, 134 LDL, 83, 202, 203 leaching, 144 leakage, 101 learning, 75 leather, 130, 149, 179 left ventricular, 204, 217 legislation, 50, 132 legume, 12, 111, 113 Lepidoptera, 52, 56 lesions, 39, 40, 43, 44, 46 lettuce, 87 Leuconostoc, 167, 168, 184 leukemia cells, 73, 80 leukocytes, 203 liberty, 236 life expectancy, 201 life span, 249 life-cycle, 263 lifespan, 248 lignin, 66, 135, 229, 279

lignocellulose, 188 limitation, 123, 259, 260 linear, 206 linkage, 100 lipid, 72, 75, 84, 93, 98, 128, 135, 144, 160, 198 lipid peroxides, 72 lipids, 72, 93, 94, 98, 112 lipophilic, 69 lipoprotein, 202 liquefaction, 91, 108, 183, 187 liquid chromatography, 84, 85, 87, 164, 272 liquid water, 121 liquids, 77 liquor, viii, 17, 59, 60, 163, 177, 208 liver, 9, 61, 66, 72, 86, 130, 168, 193, 198, 204, 205, 212, 215, 222, 232 liver disease, 9 livestock, viii, 18, 60, 69, 178, 184, 208, 210, 212, 213, 220, 222, 225, 226, 227, 228, 229, 231, 237, 238, 240, 241, 242, 243, 244, 245, 246, 254, 255, 258, 264, 268, 269 living standards, 246 location, 8, 16, 102, 281, 282, 283, 286, 287 logging, 7, 29 long period, 287 losses, vii, 1, 17, 27, 28, 29, 30, 32, 33, 35, 51, 120, 131, 132, 135, 146, 149, 178, 259, 271, 274, 276, 284, 288 Louisiana State University, 149 Low cost, 53 low molecular weight, 135, 142 low temperatures, 34, 80, 144 low-income, 227, 272 LSD, 258 lungs, 232 lutein, 70, 78, 80, 164, 197, 204 lymphocytes, 75 lysine, 18, 135, 211, 214, 268 lysosome, 203

M M.O., 54, 152, 188 M1, 56 machinery, 92 machines, 34, 121 macromolecules, 112 macular degeneration, 70, 204 magnesium, 128, 131 magnetic, 164, 175 mainstream, 193, 195 maintenance, 60, 68, 74, 150, 173, 252

Index maize, vii, 16, 18, 31, 81, 94, 96, 99, 100, 113, 115, 206, 208, 209, 210, 214, 215, 216, 217, 218, 231, 232, 233, 243, 244, 249, 251, 252, 261, 266 Malaysia, 4, 8, 10, 15, 20, 21, 22, 24, 26, 130, 146, 154, 156, 159, 161, 220 males, 202 malnutrition, 2, 222 maltodextrin, 133, 137, 139, 143 maltose, viii, 67, 117, 120, 121, 122, 125, 156, 158, 180, 194, 207, 216 management, vii, 9, 1, 12, 15, 16, 20, 21, 23, 25, 28, 36, 51, 201, 202, 203, 228, 247, 249, 252, 256, 263, 265, 276 management practices, 12, 16, 23, 25 manganese, 198 mango, 249, 256 manufacturing, 1, 16, 86, 118, 179, 205, 206, 245, 261, 267 manure, 1, 12, 18, 77, 208, 211, 213, 247, 252, 259, 260, 261, 262, 263, 268 mapping, 282 maritime, 27, 163 market, vii, 27, 28, 29, 30, 55, 83, 124, 146, 179, 190, 207, 209, 226, 237, 243, 248, 252, 253, 255, 256, 271, 272, 273, 274, 276, 277, 283, 284, 285, 287, 288, 290, 291 market prices, 255 market value, 55, 248, 271, 276, 288, 291 marketing, vii, viii, 15, 23, 33, 34, 47, 53, 188, 219, 245, 247, 256, 261, 271, 273, 278, 280, 283, 284, 285, 286, 287, 288, 291 markets, 25, 33, 34, 55, 67, 119, 120, 195, 223, 237, 276, 278, 281, 285, 286, 287, 288, 291 mass spectrometry, 84, 272, 287 maternal, 273 matrix, 92, 165 meals, 146, 201, 211, 215 measurement, 142, 217 measures, 24, 27, 28, 35, 39, 40, 54, 55, 74, 187, 240, 249, 268, 269, 291 meat, 212, 214, 215, 216, 221, 231, 247, 251 mechanical energy, 152 mediation, 204 medications, 201 medicine, 2, 18, 218 Medline, 196 melanesia, 5 melanogenesis, 61, 85 melanoma, 85 melting, 16, 101 memory, 75 memory deficits, 75 men, 158, 202, 205, 222, 223, 253, 254, 285

307

meristem, 15 messages, 286 metabolic, 32, 70, 76, 203, 219 metabolic pathways, 70 metabolism, 57, 66, 168, 220, 222, 232 metabolite, 188 metabolites, 70, 214, 218 metal ions, 125 metals, 18, 125 methanol, 81 methyl bromide, 52 Mexico City, 243 mice, 222 microbial, viii, 29, 32, 45, 46, 48, 49, 53, 54, 55, 92, 115, 124, 132, 134, 148, 156, 163, 165, 166, 167, 175, 177, 178, 179, 180, 181, 183, 186, 187, 188, 189, 190, 214, 223 microflora, 13, 28, 48, 56, 86, 134, 168, 173, 214 microglial, 75 microglial cells, 75 Micronesia, 5 microorganism, 18, 165 microorganisms, 2, 17, 18, 29, 32, 34, 38, 46, 48, 132, 164, 165, 166, 167, 175, 178, 180, 183, 185 microparticles, 208, 220 microscope, 86, 138, 280 microscopy, 99 microstructure, 50 microwave, 117, 124, 125, 127, 130, 131, 134, 147, 148, 149, 153, 157, 158 microwave heating, 124, 147 microwaving, 129, 135 Middle East, 201 middle lamella, 45 middle-aged, 223 migrant, 195 migrant population, 195 migrant populations, 195 migration, 85 milk, viii, 149, 163, 170, 173, 180, 184, 186, 212, 216, 218, 231, 238, 239, 240, 242, 243 milk fermentation, 173 minerals, 18, 60, 69, 93, 118, 128, 131, 170, 171, 177, 179, 196, 261 Minnesota, 155 missions, 147, 161 Mississippi, 195 mixing, 124, 237 mobile phone, 284 mobility, 145 modeling, 154 models, 127, 134, 140, 204, 218, 231, 264, 281 modulus, 104, 105, 127

Index

308

moisture, 7, 13, 14, 29, 33, 34, 35, 36, 56, 60, 69, 93, 113, 115, 124, 132, 133, 134, 135, 143, 146, 154, 165, 167, 168, 170, 179, 284 moisture content, 29, 35, 93, 132, 133, 135, 143, 146, 167, 168, 179, 284 molar ratio, 140 molasses, 178, 181, 186, 196, 242 mold, 40, 73 molecular mechanisms, 80 molecular structure, 110, 112, 115 molecular weight, 79, 96, 97, 98, 102, 119, 135, 142, 144 molecular weight distribution, 98, 144 molecules, 98, 100, 101, 103, 137, 139, 140, 142, 154 monocyte, 85 monocytes, 203 monosodium glutamate, 163, 164, 183 monsoon, 10, 29, 60 morning, 7, 255 morphological, 135, 145, 157 morphology, 21, 109, 137 mortality, 82, 231, 251, 253, 273, 287 mosaic, 15, 269 mothers, 282, 283, 288, 292 mould spores, 175 mouse, 83, 85 mouth, 156 Mozambique, 9, 17, 20, 21, 44, 154, 185, 210, 242, 284, 285, 286, 290 multidisciplinary, 216 multiplication, 11, 37, 73 mutagen, 68, 69, 78, 85, 86 mutagenesis, 73, 76 mutagenic, 68 mutant, 179 mutation, 8, 73 mutations, 73 mycelium, 42

N Na+, 203, 223 N-acety, 80 NaCl, 168 naphthalene, 48 nation, 195 National Aeronautics and Space Administration, (NASA) 118, 147, 193 native starches, 158 natural, 6, 9, 16, 42, 60, 62, 66, 67, 69, 74, 76, 78, 79, 82, 86, 131, 139, 147, 152, 166, 168, 198, 202, 207, 216, 270

natural food, 9, 16, 62, 66, 74, 76, 79 natural resources, 60, 78, 82 near-infrared spectroscopy, 185, 220 neck, 254 neem, 14 neglect, 240 nematode, 14, 35 nematodes, 34 Nepal, 39 Netherlands, 56, 243, 291 network, 127, 128 neural network, 154 neural networks, 154 neurons, 75 neuropathy, 74 neutrophils, 82, 203 New Zealand, 5, 8, 38 Niacin, 198 Nigeria, 19, 31, 40, 188, 225, 228, 231, 233, 240, 242, 243, 244, 272, 280 NIRS, 220 nitrogen, 12, 20, 23, 25, 37, 82, 133, 186, 211, 213, 214, 216, 231, 234, 235, 236, 246, 258, 259 NMR, 164, 175 nodes, 11 non-enzymatic, 125 non-insulin dependent diabetes, 201 non-Newtonian, 126 non-pharmacological, 216 normal, 7, 19, 161, 173, 183, 205, 215 normal conditions, 7 nuclear, 164, 175 nuclear magnetic resonance, 164, 175 nucleus, 62 nursing, 266 nutraceutical, 133, 183, 202 nutrient, 16, 20, 21, 23, 48, 62, 69, 80, 88, 119, 128, 130, 131, 147, 159, 166, 189, 212, 213, 232, 234, 237, 238, 243, 259, 268 nutrients, 1, 6, 12, 13, 23, 56, 60, 123, 131, 166, 170, 177, 259, 260, 267 nutrition, 9, 18, 20, 80, 110, 129, 148, 152, 158, 184, 196, 217, 219, 222, 223, 225, 227, 232, 240, 250, 263, 284, 288, 291 nuts, 78

O oat, viii, 225 obesity, 223 observations, 266 obstruction, 123 Oceania, 4, 5

Index oil, 18, 36, 68, 69, 141, 200, 257, 263, 266 oligosaccharides, 159 onion, 69, 130, 134 on-line, 142 oral, 67, 74, 83, 201, 222 oral hypoglycemic agents, 201 organ, 71, 215, 232 organic, viii, 1, 12, 13, 23, 25, 27, 45, 163, 164, 166, 168, 181, 211, 235, 252, 255 organic matter, 12, 181, 211, 235 organism, 39, 40, 110 organization, 87, 101, 102 organizations, 8, 147, 196, 284 organoleptic, 110 orientation, 74 osmotic, 133, 148, 166 osmotic dehydration, 133, 148 osmotic pressure, 166 ovary, 7 oxalate, 77, 229, 232 oxalic, 45, 52, 77, 179, 185 oxalic acid, 45, 52, 77, 179, 185 oxidants, 1, 177 oxidation, vii, 59, 61, 83, 134, 135, 175, 193, 198, 204, 216 oxidative, 69, 70, 75, 85, 125, 130, 204 oxidative stress, 69, 70, 75, 130, 204 oxide, 133 oxygen, 32, 37, 72, 79, 118, 130

P Pacific, 4, 15, 79 packaging, 32, 52, 117, 123, 124, 125, 127, 130, 131, 134, 157, 276, 284 Pakistan, 39, 190, 201, 217 pancreas, 73, 201 pancreatic, 74, 134, 136 Papua New Guinea, 8, 15, 20, 21, 30, 34, 39, 53, 54, 164, 196, 209, 210, 219, 222, 245, 246, 268, 269 parameter, 45 parasite, 249, 251, 263, 266 Parasite, 268 parasites, 74, 255, 263, 265 parenchyma, 7, 47 particle morphology, 137 particles, 121, 133, 135, 137, 143, 181 pasta, 110 pasture, 177 patents, 9 pathogenesis, 75, 222 pathogenic, 38, 45, 68, 74, 75 pathogens, 14, 38, 49, 50, 56

309

pathways, 70, 285 patients, 202, 204, 219, 220, 222 PDI, 152 peanuts, 244 pectin, 61, 66, 68, 69, 75, 83, 92, 106 Pediococcus, 168 peer, 9 peer review, 9 peonidin, 62, 66, 72, 76 peptidase, 186 peptide, 75, 88 PER, 118, 135 per capita, 118, 195, 272 per capita income, 195 perception, 271, 288 performance, 77, 81, 85, 164, 168, 213, 214, 215, 218, 221, 227, 232, 233, 234, 236, 237, 238, 239, 241, 242, 244, 287 periodic, 285 peripheral blood, 82 peripheral vascular disease, 201 peroxidation, 84 peroxide, 72, 75 personal, 79, 266, 278 personal communication, 266, 278 Peru, 3, 15, 20, 21, 25, 39, 49, 50, 51, 132, 145, 148, 150, 167, 188, 189, 209, 210, 211, 217, 218, 220, 242, 243, 244, 269, 270, 293 pest control, 56 pest management, 1, 15, 28, 36 pests, vii, 14, 27, 28, 38, 50, 51, 56, 60, 69, 271, 273, 286, 288, 291 petroleum, 209 pH, vii, 1, 8, 45, 100, 108, 123, 125, 152, 168, 170, 171, 175, 177, 178, 179, 182, 212, 260, 261, 263 phagocytic, 203 pharmaceutical, 9, 182, 205 pharmacokinetic, 78 phenol, 22, 46, 171 phenolic, 46, 50, 53, 56, 67, 75, 78, 81, 84, 85, 121, 125, 129, 130, 136, 158, 160, 198, 223 phenolic acid, 85, 125 phenolic acids, 85 phenolic compounds, 53, 56, 84, 223 phenylalanine, 28, 45 Phenylalanine, 229, 235 pheromone, 15, 36, 37, 38, 51, 54 Philippines, 1, 3, 4, 25, 31, 40, 49, 50, 53, 56, 95, 96, 98, 132, 147, 150, 155, 159, 161, 175, 177, 185, 210, 219, 246 phosphate, 13, 21, 94, 98, 229 phosphorus, 13, 21, 25, 94, 128, 212, 229, 232 photosynthesis, 182

310

Index

photosynthetic, 6 physical activity, 201 physical properties, 86, 110, 111, 137, 157 physicochemical, 91, 92, 96, 98, 109, 110, 111, 112, 113, 114, 115, 133, 147, 151, 153, 155, 156, 160 physicochemical properties, 92, 96, 110, 111, 112, 113, 114, 115, 116, 133, 151, 153, 154, 155, 156, 160 physiological, vii, 32, 49, 55, 57, 59, 61, 62, 63, 66, 68, 69, 72, 75, 77, 78, 80, 88, 166, 168, 198, 223, 292 physiology, 50, 292 phytochemicals, 193, 203, 205, 216 pigments, 16, 17, 59, 62, 63, 65, 67, 74, 75, 77, 84, 87, 164, 166, 168, 170, 171, 198, 232 pistil, 7 Pisum sativum, 157 pitch, 120 placebo, 202, 205 planning, 71 plants, 6, 11, 12, 13, 15, 17, 33, 46, 49, 70, 71, 75, 76, 111, 112, 194, 205, 206, 222, 231, 287 plaques, 75 plasma, 66, 202, 222 plasmolysis, 134 plastic, 14, 47, 123, 124, 126, 139, 168, 276 plastics, 77, 207 play, 2, 15, 46, 70, 73, 75, 194, 203, 204, 246, 280, 285, 286 ploidy, 6 ploughing, 14 PNG, 8, 222 point of origin, 44 poisoning, 2, 18, 77 poisonous, 9, 18 polarity, 133 policy reform, 208 pollen, 4 pollination, 7 pollutants, 73 polyethylene, 134, 177 polymer, 100, 103, 140, 208 polymer chains, 100 polymer molecule, 103 polymerization, 91, 96, 125 polymers, 100, 182, 206 Polynesia, 5 polyphenolic compounds, 64, 136 polyphenols, 1, 18, 27, 46, 63, 70, 81,166, 177 polyploidy, 6 polypropylene, 34, 134 polysaccharide, 61, 75, 87, 158, 206

polysaccharides, 75, 78, 85, 106, 111, 112, 137, 139, 166 polythene, 47 polyunsaturated fat, 72 polyunsaturated fatty acid, 72 polyunsaturated fatty acids, 72 poor, 2, 4, 28, 32, 117, 132, 167, 170, 208, 209, 212, 226, 229, 231, 236, 248, 249, 250, 251, 258, 260, 267, 271, 275, 286, 288 population, vii, 2, 12, 36, 48, 73, 131, 137, 167, 196, 231, 247, 248, 255, 268 population growth, 2 portfolio, 288 Portugal, 194 positive correlation, 72, 101, 110, 259 potassium, 20, 21, 86, 128, 131, 196 poultry, 12, 163, 164, 177, 210, 225, 227, 229, 231, 232, 233, 240 poverty, 231 powder, 37, 62, 65, 67, 69, 71, 74, 75, 87, 131, 133, 136, 137, 138, 139, 143, 150, 151, 202 powders, viii, 117, 119, 133, 135, 137, 139, 143, 147, 151 power, 91, 98, 114, 136, 139, 140, 144, 150 predictability, 165 preference, 19, 171, 207, 235, 240, 257, 281, 282, 287, 292 pregnant, 233, 272, 288 pregnant women, 272 preservative, 180 preservatives, 74, 156 pressure, 2, 35, 74, 87, 110, 114, 120, 121, 133, 157, 166, 175, 193, 204, 205, 215, 217 prevention, 73, 79, 80, 81, 153, 160, 201, 202, 203, 204 preventive, 74, 115 prices, 29, 78, 255, 266, 271, 284, 288 primary products, 283 primary school, 160, 223, 292 probability, 280 probiotic, 168, 173 probiotics, 186 process control, 124, 166 processing variables, 124 producers, 195, 209, 217, 246, 272, 280, 281 product market, 283 production costs, 110, 150 production technology, 114 productivity, 4, 12, 20, 21, 23, 165, 228, 242, 255, 268 profit, 7, 238 profit margin, 238 profitability, 76, 246

Index profits, 21, 185 progenitors, 6 program, 117, 120, 122 proinflammatory, 75 promote, 28, 68, 75, 110, 178, 216, 278 promyelocytic, 73, 80 propagation, 6 property, 98, 125, 152 propylene, 133 prostate, 6 protection, 61, 66, 68, 72, 168, 198, 205 protective role, 202 proteinase, 179 proteins, 93, 166, 177, 202 protocol, 221 proximal, 40, 42, 44 pruning, 228, 231, 236, 278 pseudo, 126, 139 PSP, 205 public, 131, 201, 222 public health, 131, 201, 222 pulses, 3, 156 pumping, 127 pupae, 37 purification, 76 pyrophosphate, 118, 125, 159 pyruvic, 66

Q QA, 60, 63, 71, 73, 76, 77 qualitative differences, 287 quantitative trait loci, 272 quarantine, 52 quercetin, 83 questionnaire, 281 quinic, 46, 60, 63, 71, 78, 85

R R and D, 111 R. oryzae, 42, 45 radiation, 35, 37, 48, 52, 53, 56 radical, 9, 20, 64, 66, 72, 76, 77, 79, 80, 81, 84, 86, 88, 118, 130, 136, 156, 193, 204, 205, 215, 219 radio, 286 rain, 14, 132, 255, 256 rainfall, 7, 10, 14, 36, 272 rainwater, 274 Raman, 51, 101, 217 Raman spectroscopy, 101 RandD, 21, 22

311

range, viii, 2, 4, 7, 91, 94, 98, 99, 101, 102, 118, 119, 120, 128, 129, 140, 146, 165, 179, 180, 200, 203, 204, 215, 225, 228, 231, 257, 265, 272, 273, 278, 279, 286 rat, 29, 31, 66, 67, 73, 76, 79, 203, 223 rats, 15, 66, 68, 74, 75, 77, 79, 83, 84, 86, 203, 207, 221, 222, 223, 259 raw material, vii, 1, 2, 19, 59, 60, 77, 84, 109, 110, 120, 122, 124, 131, 140, 146, 175, 177, 180, 181, 206, 209, 246 raw materials, 60, 110, 122, 124, 140, 180, 181, 209 reactive oxygen species, 72, 89, 204, 219 readership, 240 reagent, 140 reagents, 133 reality, 54 recovery, 31, 48, 92, 106, 133, 165, 272, 274 recycling, 77 red wine, 17, 78, 177 reducing sugars, 92, 108, 132, 134 reduction, 7, 11, 12, 13, 78, 108, 109, 120, 121, 125, 135, 143, 173, 202, 204, 228, 271, 278, 289 reflection, 21 regional, 60, 195, 246, 281 regular, 226, 284 regulation, 182, 250 regulators, 35, 52 rehydration, 143 relationship, 24, 49, 68, 80, 86, 126, 140, 202, 248, 279, 290, 292 relevance, 81, 268 reliability, 168 renal, 201 renal failure, 201 renewable energy, 189, 194, 207, 216 replication, 76 reproduction, 37 research and development, 8, 25, 78, 155, 158, 159, 218, 219, 221, 223, 224, 268 researchers, 74, 125, 134, 203, 211, 212, 214, 215, 261, 267, 274 reservation, 123 residues, 15, 21, 61, 100, 165, 177, 179, 187, 190, 227, 249, 256 resistance, 37, 49, 51, 55, 56, 75, 97, 100, 103, 114, 139, 144, 201, 202, 203, 217, 219, 281, 287, 288 resistence, 291 resources, 60, 78, 80, 82, 88, 174, 207, 208, 216, 221, 225, 226, 227, 236, 241, 268, 273, 274 respiration, 31, 35, 54, 85 respiratory, 29, 33, 35 respiratory rate, 29, 33, 35 response surface methodology (RSM), 20

Index

312

retail, 285 retardation, 74 retention, 19, 124, 125, 146, 147, 161, 211, 214, 222, 223, 231, 232, 234, 235, 238, 241, 284, 289 retinol, 204, 219, 284, 290 retinopathy, 72, 74 returns, 237, 276 reverse transcriptase, 81, 82, 85 rheological properties, viii, 91, 104, 117, 133, 139, 149, 153, 154, 155 rheology, 128, 152 Rhizoctonia solani, 27, 40, 44 rhizosphere, 13 Rho, 21 rice field, 195, 254 rice husk, 37, 214 rigidity, 140, 144 risk, 47, 130, 202, 204, 219, 251, 256, 272, 281 risk factors, 204, 219 risks, 73, 129, 274 RNA, 220 rocky, 222 rodent, 30 room temperature, 104, 123, 175 RTS, 156 ruminant, 115, 177, 194, 214, 216, 222, 227, 240 rural, 17, 21, 177, 185, 196, 206, 208, 246, 248, 261, 263, 267, 271, 272, 281, 283, 285, 286, 290 rural areas, 208, 272, 285 rural communities, 271 rural development, 21 Rwanda, 194, 210, 272, 281 rye, 131, 196

S Saccharomyces cerevisiae, 48, 175, 177 SAE, 151, 217 safety, 123 sales, 209, 252 saline, 8 salinity, 20, 22, 28 Salmonella, 73, 78, 83, 259, 261 salt, 38, 132, 168, 180, 211, 259, 260, 262 salts, 98, 100, 101, 128 Samoa, 236 sample, 64, 213, 231, 247 sand, 13, 19, 28, 30, 31, 32, 37, 49 sanitation, 251 sawdust, 290 scalable, 165 scaling, 123, 124, 256

Scanning Electron Microscopy (SEM), 91, 99, 100, 232, 234, 237 scarcity, 62, 177, 227 school, 160, 223, 282, 283, 292 scientific understanding, 167 scientists, 60, 229 sclerosis, 72 scores, 170, 172, 281, 282, 283 SCP, 164, 178 sea level, 4 search, 163, 207, 216, 284 second generation, 255 secretion, 73, 74, 84, 183, 201, 202, 203, 219 security, 22, 195, 228, 246, 271, 272, 274, 278 sediment, 134, 145 sedimentation, 167 seed, 6, 29, 38, 39, 69, 77, 175 seeds, 7, 168 selecting, 1, 49, 84, 282, 287 semi-arid, 220 senile, 75 senile plaques, 75 senior citizens, 136 sensitivity, 73, 196, 201, 202, 204, 219 sensors, 120, 276 sensory data, 281 separation, 167, 255, 264 series, 65, 69, 209 serum, 66, 69, 83, 86, 158, 173, 204, 205, 214, 215, 218, 220, 222 services, 147 sesame, 168 severity, 15, 51, 55, 129, 135, 137, 140, 233 sex, 15, 36, 37, 51, 54, 222 shade, 7, 11, 256, 264 shape, 4, 7, 92, 94 shares, 248 sharing, 254 shear, 125, 127, 139, 149 sheep, viii, 178, 225, 228, 237, 240, 243 Sheep, 237 shock, 34, 276, 277 shoot, 14, 84 short period, 33, 123, 252 short supply, 259, 260 shortage, 78, 246, 249 shoulder, 215 shrimp, 249, 250 shrubs, 231 similarity, 130 sites, 40, 43, 247, 248, 258, 278 skeletal muscle, 201

Index skin, 7, 9, 17, 33, 35, 39, 40, 42, 47, 50, 67, 83, 121, 194, 198, 202, 212, 280 small intestine, 74, 196 SME, 152 smoke, 263 smokers, 219 social exchange, 248 sodium, viii, 2, 36, 53, 118, 164, 208 soft drinks, 180, 205 soil, vii, 1, 7, 10, 11, 12, 13, 14, 16, 18, 21, 23, 26, 28, 30, 32, 34, 35, 36, 38, 39, 43, 57, 209, 246, 247, 252, 268, 287 soil erosion, 11 soils, 4, 7, 11, 12, 14, 34, 195, 272 solar, vii, 1, 19, 117, 132, 135, 267, 284, 289 solar energy, vii, 1 solid matrix, 165 solid state, 163, 164, 165, 166, 177, 185, 186, 188, 189, 190, 191 solid waste, 178 solid-state, viii solubility, 91, 94, 98, 99, 111, 114, 137, 143, 144, 145, 153 solvent, 103, 114 sorghum, 3, 155, 182 sorption, 134 South Africa, 272, 280, 281, 286, 290 South America, 1, 3, 4, 15, 248 South Asia, 50, 206 South Carolina, 49 South Pacific, 236 Southeast Asia, 3 soy, viii, 20, 152, 154, 163, 164, 168, 174, 175, 258 soy bean, 258 soybean, 18, 87, 152, 170, 186, 212, 214, 242, 259 soybean seed, 259 soybeans, 174 spastic, 204, 219 species, 4, 6, 36, 38, 43, 48, 68, 72, 85, 89, 112, 194, 204, 219, 225, 229, 231, 240, 264 specificity, 165 spectrophotometric, 84 spectrophotometric method, 84 spectroscopy, 164, 175, 220 spectrum, 49 speed, 133, 146 SPF, 226, 236 spices, 81 spinach, 69, 70, 77, 83, 211, 212, 216, 221, 233, 234, 241 spongy tissue, 44 sporadic, 250, 256 spore, 42

313

sprouting, vii, 14, 25, 27, 28, 30, 31, 32, 35, 36, 48, 52, 188 SSB, 164, 165 stability, 17, 99, 101, 110, 120, 134, 141, 148, 158, 190, 228, 269 stabilization, 63 stabilizers, 205 stages, 13, 37, 55, 101, 114, 220, 242, 243, 254, 276 stamens, 7 standard deviation, 213, 262, 283 standards, 112 Staphylococcus, 75 Staphylococcus aureus, 75 starch granules, 92, 94, 99, 100, 101, 103, 104, 106, 107, 109, 114, 120, 134, 135, 137, 138, 140, 142, 144 starch polysaccharides, 78, 137 starvation, 62 statistics, 227, 228 sterilization, 117, 123, 124, 130 stigma, 4, 7 stimulant, 37 stimulus, 46 stock, 29, 120 stock markets, 120 stomach, 73, 173, 266 strain, 168, 181, 182 strains, 46, 68, 178, 179, 181, 182, 183 strategies, 193, 196, 201, 225, 226, 227, 247, 272, 287 strawberries, 130 streams, 165 strength, 29, 94, 98, 102, 110, 130, 182 Streptomyces, 190 stress, 14, 20, 22, 24, 28, 32, 45, 46, 69, 70, 75, 85, 125, 126, 130, 136, 139, 140, 186, 204 stroke, 201 structural characteristics, 137 subjective, 280 sub-Saharan Africa, 9, 201, 272, 284, 286, 290 Sub-Saharan Africa, 204, 221, 226, 244, 272, 284 subsistence, 2, 52, 248, 273 substances, 28, 33, 50, 68, 80, 98, 142, 170, 173 substitutes, 174 substitution, 118, 133, 136, 140, 146, 155, 167, 184, 234 substrates, viii, 163, 165, 166, 178, 179, 183, 189 sucrose, 64, 79, 92, 119, 125, 160, 170, 180 Sudan, 286 sugar, 27, 33, 45, 55, 60, 75, 76, 85, 92, 108, 122, 124, 125, 132, 133, 134, 135, 141, 142, 152, 168, 171, 175, 177, 180, 182, 183, 203, 209, 213, 217, 218

Index

314

sugar beet, 182, 183, 209 sugar cane, 182, 213, 218 sugarcane, 183, 209, 242 sugars, 16, 17, 27, 33, 45, 75, 92, 98, 100, 101, 108, 119, 125, 132, 134, 142, 158, 159, 165, 168, 175, 180, 183, 205 sulfate, 159 sulphur, 132 summer, 10, 22, 35, 36 sunflower, 266 sunlight, 33, 132, 274 super-heated, 121 superoxide, 75, 81, 85 supervision, 265 supplemental, 1, 87, 245, 265 supplements, 70, 208, 211, 221, 223, 227, 233, 235, 240, 241, 242, 245, 249, 250, 251, 258, 266 supply, 12, 32, 92, 178, 181, 221, 236, 265, 285, 286, 287 supply chain, 285 suppression, 53, 73, 74, 82 surface area, 135 surface layer, 278 surfactants, 94, 98, 207, 216 surveillance, 74 survival, 12, 37, 53 susceptibility, 45, 52, 94, 99, 100, 108, 112, 114, 155, 201, 203, 278, 281, 287, 291 suspensions, 112, 140, 142, 148 sustainability, 21 swelling, 91, 94, 98, 99, 101, 102, 104, 111, 140, 144, 145, 168 swelling process, 103 symptoms, 39, 44, 53, 74, 203, 205, 215 synthesis, 13, 57, 92, 165, 179, 182

T Taiwan, 8, 10, 110, 113, 152, 155, 158, 161, 178, 210, 246, 267, 268, 269, 270 tandem mass spectrometry, 84 tannins, 79 Tanzania, 25, 30, 33, 34, 47, 55, 56, 57, 145, 184, 272, 273, 274, 275, 276, 277, 278, 280, 281, 282, 287, 289, 290, 291, 292, 293 target population, 281 target populations, 281 taste, 17, 19, 36, 39, 69, 118, 167, 168, 171, 180, 214, 257, 273, 280, 281 tea, 2, 18, 202, 219, 272, 286 technology, 9, 16, 17, 18, 25, 47, 52, 77, 82, 113, 118, 119, 121, 123, 124, 133, 155, 159, 164, 182, 185, 186, 189, 245, 250, 256, 259, 261, 274, 289

technology transfer, 159 terpenes, 82 textile, 112, 205 textile industry, 206 textiles, 1, 16 Thailand, 8, 9, 10, 22, 83, 110, 159, 189 therapeutic benefits, 136 therapy, 74, 203, 205, 215, 222 thermal properties, 157, 185, 220 thermal stability, 99 thermal treatment, 117, 123, 124, 144, 157 thermodynamic, 134 thermodynamic function, 134 Thermophilic, 166 thermoplastics, 77, 81 thiamin, 131, 135 Thomson, 274, 290, 292 threat, 251 TIA, 226, 231, 232, 246, 259 ticks, 159 time consuming, 281 tissue, 32, 33, 34, 40, 42, 44, 45, 50, 57, 62, 64, 81, 114, 120, 151, 160, 278 titration, 96 T-lymphocytes, 75 tobacco, 37, 220 tolerance, 18, 186, 193, 202, 203, 205, 215, 216, 219, 223 tomato, 17, 125, 151 torque, 152 total cholesterol, 203 total product, 182 toxic, 15, 92, 173, 288 toxic substances, 173 toxicity, 8, 36, 75, 86, 88 toxin, 173, 178 toxins, 73 TPA, 76 trade, 3, 286 trading, 3 traditional practices, 25 training, 261, 285 traits, 2, 22, 206, 214, 233, 240, 242, 243, 262, 263, 281 transcriptase, 81, 82, 85 transfer, 3, 123, 159 transformation, 76, 80, 143 transgenic, 49, 50, 183, 220, 222 transgenic plants, 222 transition, 107, 127, 142, 248 transition temperature, 133, 139, 142, 143 translocation, 13 transmission, 3, 75, 273

Index transpiration, 35, 54 transplant, 11 transport, 34, 47, 48, 56, 271, 276, 278, 281, 285, 292 transportation, vii, 3, 11, 27, 28, 34, 47, 273, 278 traps, 15, 36, 38, 51 travel, 284, 285 trees, 231, 264 trend, 144, 240, 267 trial, 85, 202, 203, 211, 212, 213, 258, 259, 260, 262, 263, 265, 266 tribal, 25 triglyceride, 203 Trp, 60, 68, 73 trucks, 275, 285 trypsin, 19, 167, 214, 226, 229, 231, 246, 255, 258, 259, 260, 268, 269, 270 tsunami, 33 tuber starches, 91, 113, 114, 155 tubers, 21, 22, 25, 47, 52, 53, 54, 55, 70, 82, 107, 144, 150, 153, 154, 183, 186, 188, 236, 241, 244, 286 tubular, 124 tumor, 73, 81, 83, 86 tumor cells, 73 tumorigenesis, 81 type 2 diabetes, 201, 219, 220, 223 typhoon, 60 Tyrosine, 229, 235

U ubiquitous, 66 Uganda, viii, 9, 12, 30, 52, 53, 155, 194, 195, 210, 221, 236, 246, 247, 248, 249, 250, 251, 255, 256, 259, 267, 268, 269, 272, 273, 274, 280, 281, 282, 283, 284, 285, 286, 287, 289, 290, 291 ultraviolet, 48, 56 uniform, 176 unit cost, 259 United Kingdom (UK), 9, 27, 88, 148, 161, 163, 184, 185, 218, 220, 271, 289, 290, 291, 292, 293 United Nations, 150, 218, 242 United States, 2, 8, 9, 15, 118, 120, 130, 146, 159, 161, 194, 198 urban areas, 272, 283, 289 urban centres, 274 urban population, 196 urea, 115, 178, 194, 214, 215, 216 urine, 66, 84, 252 USDA, 118, 159 UV, 28, 48, 49, 56 UV irradiation, 48

315

V vacuum, 18, 168 Valdez, 133, 159 validation, 123, 124 values, viii, 86, 96, 97, 99, 102, 103, 104, 106, 117, 125, 126, 128, 139, 140, 143, 144, 145, 147, 173, 184, 198, 203, 215, 216, 228, 229, 234, 270 vapor, 121, 134 variability, 104, 263 variable, 7, 39, 43, 44, 94, 95, 214, 273 variables, 111, 133, 168 variation, 13, 27, 45, 93, 102, 104, 110, 111, 124, 135, 149, 170, 230, 252, 262, 263, 287 vascular disease, 201 vascular system, 79 vegetables, 29, 32, 48, 55, 56, 59, 60, 62, 65, 66, 69, 70, 71, 72, 73, 77, 78, 79, 82, 85, 87, 124, 125, 154, 164, 168, 170, 186, 187, 188, 197, 225, 251 vehicles, 276 velocity, 132 Venezuela, 210, 233 ventilation, 30, 273 venue, 263 versatility, 118, 205 veterinarians, 255 vibration, 276 Vietnam, viii, 8, 11, 23, 31, 39, 52, 110, 132, 164, 177, 179, 194, 209, 210, 211, 221, 226, 233, 246, 247, 248, 249, 250, 251, 252, 253, 256, 257, 259, 260, 261, 262, 263, 265, 267, 268, 269, 270 Vietnamese, 189, 236, 245, 248, 257, 261, 262, 268 vinegar, 59, 67, 77, 82, 87, 175, 183, 188 virus, 2, 15, 24, 75, 82, 87, 195, 204, 205, 216, 269 viscoelastic properties, 128 viscose, 13 viscosity, 91, 96, 100, 101, 103, 104, 106, 107, 108, 109, 110, 118, 122, 124, 126, 127, 133, 138, 139, 140, 141, 145, 147, 148, 149, 152, 156 visible, 32, 281 vision, 188 vitamin A, 8, 129, 130, 135, 151, 155, 157, 158, 159, 160, 193, 196, 200, 204, 215, 219, 220, 221, 222, 223, 271, 272, 281, 283, 284, 288, 289, 292 vitamin C, 13, 70, 131, 135, 204, 219 vitamin C, 198 vitamin E, 70, 222 vitamin K, 70 vitamins, 18, 60, 69, 170, 171, 177, 183, 196, 261

Index

316

W war, 3 warrants, 248 waste disposal, 121 waste water, 181, 190 wastes, 17, 76, 164, 165, 166, 178, 188, 190, 236, 237 water absorption, 94 water-holding capacity, 143 water-soluble, 82 waveguide, 124 wealth, 247 weight control, 136 weight gain, 203, 211, 212, 213, 214, 215, 234, 236, 237, 238, 240, 243, 246, 252, 261, 262, 263, 267 weight loss, vii, 27, 28, 30, 31, 32, 35, 36, 37, 48, 55, 57, 99, 273, 278, 279, 280 Weinberg, 166, 189 West Africa, 15, 112, 132, 145, 220, 226, 228, 242, 243, 272 Western countries, 68 Western Europe, 5 wheat, vii, 17, 66, 69, 79, 95, 96, 101, 103, 131, 132, 140, 141, 145, 146, 147, 149, 157, 167, 174, 183, 184, 196, 200, 205, 206, 209, 212, 224, 249, 250, 251, 271, 283, 288 whey, 184 wine, 17, 78, 146, 175, 177, 183, 231 winter, 29, 247, 251, 252, 259 wisdom, 285

wives, 253, 264 women, 78, 131, 151, 202, 204, 211, 219, 254, 255, 259, 264, 272, 285, 289 wood, 30, 196, 264 workers, 46, 99, 229, 231, 286 working hours, 254 World Intellectual Property Organization, 157 worms, 249, 250, 255, 256, 264, 266 wound healing, 28, 43, 50, 201, 203, 278, 280, 292 wrists, 254

X X-ray diffraction (XRD), 91, 94, 95, 96, 101

Y yeast, 17, 32, 48, 54, 56, 166, 175, 177, 178, 181, 182, 186, 187, 190, 223 yield loss, 286 yogurt, 130, 149, 161, 170, 184 yolk, 212, 221 yuan, 252

Z Zimbabwe, 30, 244, 290 zinc, 60, 69, 198, 281 Zn, 85