Chemical and Functional Properties of Food Components

Chemical and Functional Properties of Food Components Second Edition

Chemical and Functional Properties of Food Components Series SERIES EDITOR

Zdzislaw E. Sikorski Chemical and Functional Properties of Food Proteins Edited by Zdzislaw E. Sikorski

Chemical and Functional Properties of Food Components, Second Edition Edited by Zdzislaw E. Sikorski

Chemical and Functional Properties of Food Lipids Edited by Zdzislaw E. Sikorski and Anna Kolakowska

Chemical and Functional Properties of Food Components Second Edition EDITED BY

Zdzislaw E. Sikorski, Ph.D. Professor of Food Science Department of Food Chemistry and Technology Gdan´sk University of Technology, Poland

CRC PR E S S Boca Raton London New York Washington, D.C.

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Library of Congress Cataloging-in-Publication Data Chemical and functional properties of food components / editor, Zdzislaw E. Sikorski.-2nd ed. p. ; cm. -- (Chemical and functional properties of food components series) Includes bibliographical references and index. ISBN 1-58716-149-4 (alk. paper) 1. Food--Analysis. 2. Food--Composition. I. Sikorski, Zdzislaw E. II. Series. TX545 .C44 2002 664′.07--dc21

2002276808

This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. A wide variety of references are listed. Reasonable efforts have been made to publish reliable data and information, but the author and the publisher cannot assume responsibility for the validity of all materials or for the consequences of their use. Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming, and recording, or by any information storage or retrieval system, without prior permission in writing from the publisher. All rights reserved. Authorization to photocopy items for internal or personal use, or the personal or internal use of specific clients, may be granted by CRC Press LLC, provided that $.50 per page photocopied is paid directly to Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923 USA. The fee code for users of the Transactional Reporting Service is ISBN 1-58716-1494/02/$0.00+$1.50. The fee is subject to change without notice. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. The consent of CRC Press LLC does not extend to copying for general distribution, for promotion, for creating new works, or for resale. Specific permission must be obtained in writing from CRC Press LLC for such copying. Direct all inquiries to CRC Press LLC, 2000 N.W. Corporate Blvd., Boca Raton, Florida 33431. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation, without intent to infringe.

Visit the CRC Press Web site at www.crcpress.com © 2002 by CRC Press LLC No claim to original U.S. Government works International Standard Book Number 1-58716-149-4 Library of Congress Card Number 2002276808 Printed in the United States of America 1 2 3 4 5 6 7 8 9 0 Printed on acid-free paper

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Dedication I am honored to dedicate this volume to Professor Owen R. Fennema.

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Preface Water, saccharides, lipids, proteins, and minerals — the main components — form the structure of and are responsible for the sensory and nutritional properties of foods. Other constituents, present in lower quantities, especially colorants, flavor compounds, vitamins, probiotics, and additives, also contribute to different aspects of food quality. The catabolysis that takes place in raw materials postharvest, as well as chemical and biochemical changes and interactions of components during storage and processing, affect all aspects of food quality. These processes can be effectively controlled by the food processor who knows food chemistry. The contents of this book go beyond that of a standard food chemistry text. This volume contains a concise, yet well-documented presentation of the current state of knowledge on the content, structure, chemical and biochemical reactivity, functional properties, and biological role of the components most important to food quality. The first two chapters describe in general terms the contents and role of different constituents in food quality and structure. The main components are presented in Chapters 3–7, while Chapter 8 deals with their impact on the rheological properties of foods. Chapters 9 and 10 discuss the effects of different constituents on the color and flavor of foods, while Chapters 11–14 are concerned primarily with the biological value and safety aspects of the constituents. Most chapters have the character of monographs prepared by specialists in the respective areas. They are based on the personal research and teaching experience of the contributors, as well as on critical evaluation of the present state of knowledge as reflected in the current world literature. The large lists of references in the chapters include both English papers and papers published in other languages. This volume is addressed to food scientists in industry and academia, food science graduate students, nutritionists, and all persons interested in the role and attributes of various food components. I am honored to dedicate this volume to Professor Owen R. Fennema, University of Wisconsin – Madison, whom I met in person during three IUFoST congresses. Fennema’s books, especially the excellent Food Chemistry, have been an invaluable source of information and inspiration to me, my students, and probably most food professionals in the world. Zdzislaw E. Sikorski

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Acknowledgment As the editor, I have had the privilege to work with colleagues from universities and research institutions in Australia, The Netherlands, Poland, Taiwan, and the United States, who have contributed to this volume, sharing their knowledge and experience. Their acceptance of my conception of the book and of the editorial suggestions is highly appreciated. Special thanks are due to those contributors who prepared their chapters ahead of the deadline. It was possible to publish the book without delay only because of the understanding of Dr. Eleanor Riemer and Sara Kreisman of CRC Press, who agreed to accept several chapters even after the deadline. I also want to thank several of my coworkers in the department of food chemistry and technology of the Gdan´sk University of Technology, Poland, who willingly helped me in different ways, especially in handling the computer. Last but not least my gratitude goes to my wife, Krystyna, who generously tolerated a husband heavily involved for the past 40 years in writing and editing food science books. Zdzislaw E. Sikorski Gdan´sk University of Technology

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Editor Zdzislaw E. Sikorski received his B.S., M.S., Ph.D., and D.Sc. degrees from the Gdan´sk University of Technology (GUT) and his doctor honoris causa from the Agricultural University in Szczecin, Poland. He served as head of the department of food chemistry and technology and dean of the faculty of chemistry at GUT and was visiting researcher and professor at the Ohio State University, Columbus, Ohio; CSIRO, Hobart, Australia; DSIR, in Auckland, New Zealand; and National Taiwan Ocean University, Keelung. He is currently professor at GUT and, since 1996, chairman of the Committee of Food Technology and Chemistry of the Polish Academy of Sciences. He has published 200 journal articles, 11 books (in Polish, English, Russian, and Spanish), and 8 book chapters in marine food science and food chemistry. He holds seven patents.

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Contributors Agnieszka Bartoszek, Ph.D. Department of Pharmaceutical Technology and Biochemistry Gdan´sk University of Technology Gdan´sk , Poland Maria Bielecka, Ph.D. Professor Division of Food Science Institute of Animal Reproduction and Food Research of the Polish Academy of Sciences Olsztyn, Poland Yan-Hwa Chu, Ph.D. Food Industry Research and Development Institute Taiwan, Republic of China Barbara E. Cybulska, Ph.D. Department of Pharmaceutical Technology and Biochemistry Gdan´sk University of Technology Gdan´sk , Poland Peter E. Doe, Ph.D. Professor Department of Engineering University of Tasmania, Hobart Tasmania, Australia Lucy Sun Hwang, Ph.D. Professor Graduate Institute of Food Science and Technology National Taiwan University Taiwan, Republic of China

Jen-Min Kuo, Ph.D. Professor Department of Food Health Chai-Nan University of Pharmacy and Science Taiwan, Republic of China Tadeusz S. Matuszek, Ph.D. Department of Mechanical Engineering Gdan´sk University of Technology Gdan´sk , Poland Julie Miller Jones, Ph.D. Department of Home Economics College of St. Catherine St. Paul, Minnesota Michal Nabrzyski, Ph.D. Professor Emeritus Department of Bromatology Medical Academy of Gdan´sk Gdan´sk , Poland Krystyna Palka, Ph.D. Department of Animal Food Products Agricultural Academy Kraków, Poland Bonnie Sun Pan, Ph.D. Professor Department of Marine Food Science National Taiwan Ocean University Taiwan, Republic of China

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Adriaan Ruiter, Ph.D. Professor Emeritus Department of the Science of Food of Animal Origin Utrecht University The Netherlands

Alphons G.J. Voragen, Ph.D. Professor Department of Agrotechnology and Food Sciences Wageningen University The Netherlands

Zdzislaw E. Sikorski, Ph.D. Professor Department of Food Chemistry and Technology Gdan´sk University of Technology Gdan´sk , Poland

Jadwiga Wilska-Jeszka, Ph.D. Professor Emeritus Institute of Technical Biochemistry Technical University of £ód´z ´ Poland Lódz,

Piotr Tomasik, Ph.D. Professor Department of Chemistry Academy of Agriculture Kraków, Poland

Chung-May Wu, Ph.D. Professor Department of Food Science and Nutrition Hungkuang Institute of Technology Taiwan, Republic of China

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Table of Contents Chapter 1 Food Components and Their Role in Food Quality ..................................................1 Zdzislaw E. Sikorski Chapter 2 Chemical Composition and Structure of Foods......................................................11 Krystyna Palka Chapter 3 Water and Food Quality ..........................................................................................25 Barbara Cybulska and Peter Edward Doe Chapter 4 Mineral Components ...............................................................................................51 Michal Nabrzyski Chapter 5 Saccharides ..............................................................................................................81 Piotr Tomasik Chapter 6 Food Lipids............................................................................................................115 Yan-Hwa Chu and Lucy Sun Hwang Chapter 7 Proteins ..................................................................................................................133 Zdzislaw E. Sikorski Chapter 8 Rheological Properties of Food Systems ..............................................................179 Tadeusz Matuszek Chapter 9 Food Colorants.......................................................................................................205 Jadwiga Wilska-Jeszka

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Chapter 10 Flavor Compounds.................................................................................................231 Chung-May Wu, Jen-Min Kuo, and Bonnie Sun Pan Chapter 11 Probiotics in Food..................................................................................................259 Maria Bielecka Chapter 12 Major Food Additives............................................................................................273 Adriaan Ruiter and Alphons G.J. Voragen Chapter 13 Food Safety............................................................................................................291 Julie Miller Jones Chapter 14 Mutagenic, Carcinogenic, and Chemopreventive Compounds in Foods.............................................................................................307 Agnieszka Bartoszek Index ......................................................................................................................337

1

Food Components and Their Role in Food Quality Zdzislaw E. Sikorski

CONTENTS 1.1

Main Food Components...................................................................................1 1.1.1 Introduction ..........................................................................................1 1.1.2 Contents and Role in Food Raw Materials .........................................2 1.1.3 Factors Affecting Food Composition...................................................4 1.2 Quality of Foods ..............................................................................................5 1.3 Functional Properties of Food Components....................................................5 1.4 Role of Chemistry and Processing Factors .....................................................6 1.4.1 Introduction ..........................................................................................6 1.4.2 Effect on Safety and Nutritional Value................................................7 1.4.3 Effect on Sensory Quality....................................................................7 References..................................................................................................................8

1.1 MAIN FOOD COMPONENTS 1.1.1 INTRODUCTION Foods are derived from plant material, carcasses of animals, and single-cell organisms. They are composed mainly of water, saccharides, proteins, lipids, and minerals (Table 1.1). These main components serve as nutrients by supplying the human body with the necessary building materials and source of energy, as well as elements and compounds indispensable for the metabolism. Some plant polysaccharides are only partly utilized for energy. However, as dietary fiber, they affect various processes in the gastrointestinal tract in different ways (Kritchevsky and Bonfield, 1995). Foods also contain a host of other constituents present in smaller quantities, especially nonprotein nitrogenous compounds, vitamins, colorants, flavor compounds, and functional additives. Many of the minor components originally present in foods are nutritionally essential, e.g., vitamins (some can be utilized by the body) and amino acids. Numerous groups, including tocopherols, ubiquinone, carotenoids, ascorbic acid, thiols, amines, and several other nonprotein 1-5871-6149-4/02/$0.00+$1.50 © 2002 by CRC Press LLC

1

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Chemical and Functional Properties of Food Components

TABLE 1.1 Main Components in Typical Foods Water

Saccharides

Proteins

Lipids

Minerals

Vitamins

Juices Fruits Milk Vegetables Jellies Lean fish Lean meat

Saccharose Honey Cereals Chocolate Potato Cassava Fruits

Soybean Beans Meat Fish Wheat Cheese Eggs

Oils Lard Butter Chocolate Nuts Egg yolk Pork

Vegetables Fruits Meat Fish products Dairy products Cereals Nuts

Vegetables Fruits Fish liver Meat Cereals Milk Yeast

nitrogenous compounds, serve as endogenous muscle antioxidants, playing an essential role in postmortem changes in meat (Decker et al., 2000). Other minor components are useless or even harmful if present in excessive amounts. Most food raw materials are infected with different microorganisms — putrefactive and often pathogenic — and some contain parasites. A variety of compounds are added intentionally during processing to serve as preservatives, antioxidants, colorants, flavorings, sweeteners, and emulsifying agents and to fulfill different other technological purposes. The chemical nature and role of functional food additives are presented in detail in Chapter 12.

1.1.2 CONTENTS

AND

ROLE

IN

FOOD RAW MATERIALS

Polysaccharides, proteins, and lipids are involved in different structures of the plant and animal tissues used for food. The structures built from these materials are responsible for the form and tensile strength of the tissues and create the necessary conditions for the metabolic processes to occur. Compartmentation resulting from these structures plays a crucial biological role in the organisms. Some other saccharides, proteins, and lipids are stored for reserve purposes. Other constituents are either bound to different cell structures or distributed in soluble form in the tissue fluids. The content of water in various foods ranges from a few percent in dried commodities, e.g., milk powder, through about 15% in grains, 16–18% in butter, 20% in honey, 35% in bread, 65% in manioc, and 75% in meat — to about 90% in many fruits and vegetables. Most of the water is immobilized in the plant and animal tissues by the structural elements and various solutes, contributes to buttressing the conformation of the polymers, and interacts in metabolic processes. Saccharides are present in food raw materials in quantities ranging from about 1% in meats and fish, to about 4.5% in milk, 18% in potatoes, and 15–20% in sugar beets, to about 70% in cereal grains. Polysaccharides participate in the formation of structures in plants. They are also stored in plants as starch and in muscles as glycogen. Other saccharides are dissolved in tissue fluids or perform different biological functions: in free nucleotides, as components of nucleic acids, or bound to proteins and lipids.

Food Components and Their Role in Food Quality

3

The protein content in foods is given mainly as crude protein, i.e., as N × 6.25. The 6.25 nitrogen-to-protein (N:P) conversion factor has been recommended for most plant and animal food products under the assumption that the N content in their proteins is 16% and they do not contain nonprotein N. The N content in the proteins in various foods, however, is different, since it depends on the amino acid composition. Furthermore, the total N consists of protein N and of N contained in numerous nonprotein compounds, e.g., free peptides and amino acids, nucleic acids and their degradation products, amines, betains, urea, vitamins, and alkaloids. In some foods the nonprotein N may constitute up to 30% of total N. In many of these compounds the C:N ratio is similar to the average in amino acids. However, the N content in urea (47%) is exceptionally high. Most of the nonprotein nitrogen compounds can be utilized by the organism as a source of nitrogen. The average conversion factor for estimation of true protein, based on the ratios of total amino acid residues to amino acid N, determined for 23 various food products is 5.68 and for different classes of foods, 5.14–6.61 (Table 1.2). The N:P factor of 4.39, based on analysis of 20 different vegetables, has been proposed by Fujihara et al. (2001) for estimating the true protein content in vegetables. A common N:P factor of 5.70 for blended foods or diets has been recommended by Sosulski and Imafidon (1990). Proteins make up about 1% of the weight of fruits, 2% of potatoes, 3.2% of bovine milk, 12% of eggs, 12–22% of wheat grain, about 20% of meat, and 25–40% of different beans. They serve as the building material of muscles and other animal tissues and, in plants and animals, play crucial metabolic roles as enzymes and enzyme inhibitors, participate in the transport and binding of oxygen and metal ions, and perform immunological functions. During their development cereal grain and legume seeds deposit large quantities of storage proteins in granules known also as protein bodies. In soybeans these proteins constitute 60–70% of the total protein content, and the granules in 80% are made of proteins. Lipids constitute below 1% of the weight of fruits, vegetables, and lean fish; 3.5% of milk; 6% of beef; 32% of egg yolk; and 85% of butter. The lipids contained in the food raw materials in low quantities serve mainly as components of proteinphospholipid membranes and perform metabolic functions. In fatty commodities the majority of the lipids are stored as depot fat in the form of triacylglycerols. The lipids of numerous food fishes, such as orange roughy, mullets, codfish, and sharks,

TABLE 1.2 N:P Conversion Factors in Foods Product

Factor

Product

Factor

Dairy products Egg Meat and fish Cereals and legumes

6.02–6.15 5.73 5.72–5.82 5.40–5.93

Potato Leafy vegetables Fruits Microbial biomass

5.18 5.14–5.30 5.18 5.78–6.61

Source: From Sosulski, F.W. and Imafidon, G.I., J. Agric. Food Chem., 38, 1351, 1990.

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Chemical and Functional Properties of Food Components

as well as some crustaceans and mollusks, also comprise wax esters. Some shark oils are very rich in hydrocarbons, particularly in squalene (Sikorski et al., 1990). Furthermore, the lipid fraction of food raw materials harbors different sterols, vitamins, and pigments that are crucial for metabolism.

1.1.3 FACTORS AFFECTING FOOD COMPOSITION The content of different components in food raw materials depends on the species and variety of the animal and plant crop, the conditions of cultivation and harvesting of the plants, the feeding and age of the farm animals or the season in which fish and marine invertebrates are caught, and postharvest changes taking place in the crop during storage. The food industry, by establishing quality requirements for raw materials, can encourage producers to control within limits the contents of the main components in their crops, e.g., saccharose in sugar beets, starch in potatoes, fat in various meat cuts, pigments in fruits and vegetables and in the flesh of fish from aquaculture, or protein in wheat and barley, as well as the fatty acid composition of lipids in oilseeds and meats. The contents of desirable minor components such as natural antioxidants can also be effectively controlled to retard the oxidation of pigments and lipids in beef meat (Matsumoto, 2000). Contamination of the raw material with organic and inorganic pollutants can be controlled by observing recommended agricultural procedures in using fertilizers, herbicides, and insecticides and by restricting certain fishing areas seasonally to avoid marine toxins. The size of predatory fish like swordfish, tuna, or sharks that are fished commercially can be limited to reduce the risk of too high a content of mercury and arsenic in the flesh. The composition of processed foods depends on the applied recipe and on changes taking place due to processing and storage. These changes are mainly brought about by endogenous and microbial enzymes, active forms of oxygen, heating, chemical treatment, and processing at low or high pH (Haard, 2001). Examples of such changes are: • Leaching of soluble components, e.g., vitamins and minerals during washing, blanching, and cooking • Drip formation after thawing or due to cooking • Loss of moisture and volatiles due to evaporation and sublimation • Absorption of desirable or harmful compounds during salting, pickling, or smoking • Formation of desirable or harmful compounds due to enzyme activity, e.g., development of a typical flavor in cheese or decarboxylation of amino acids in fish marinades • Generation of desirable or objectionable products due to interactions of reactive groups induced by heating or chemical treatment, e.g., flavors or carcinogenic compounds in roasted meats or trans fatty acids in hydrogenated fats • Formation of different products of oxidation of food components, mainly of lipids, pigments, and vitamins • Loss of nutrients and deterioration of dried fish due to the attack by flies, mites, and beetles

Food Components and Their Role in Food Quality

5

1.2 QUALITY OF FOODS The quality of a food product, i.e., the characteristic properties that determine the degree of excellence, is a sum of the attributes contributing to the satisfaction of the consumer with the product. The composition and the chemical nature of the food components affect all aspects of food quality. The total quality reflects at least the following attributes: • Compatibility with the local or international food laws, regulations, and standards, concerning mainly proportions of main components, presence of compounds regarded as identity indicators, contents of contaminants and additives, hygienic requirements, and packaging • Nutritional aspects, i.e., the contents of nutritionally desirable constituents, mainly proteins, essential amino acids, essential fatty acids, vitamins, fiber, and mineral components • Safety aspects affected by the compounds that may constitute health hazards for the consumers and affect the digestibility and nutritional use of the food, e.g., heavy metals, toxins of different origin, pathogenic microorganisms, parasites, and enzyme inhibitors • Sensory attributes — color, size, form, flavor, and taste — and rheological properties, obviously affected by the chemical composition of the product, as well as the effects resulting from processing and culinary preparation • Shelf life at specific storage conditions • Convenience aspects, which are reflected by the size and ease of opening and reclosing the container, suitability of the product for immediate use or for different types of thermal treatment, ease of portioning or spreading, and transport and storage requirements • Ecological aspects regarding suitability for recycling of the packaging material and pollution hazards For many foods one of the most important quality criterion is freshness. This is especially so in numerous species of vegetables, fruits, and seafood. Fish of valuable species at the state of prime freshness, suitable to be eaten raw, may have a market price that is ten times higher than that of the same fish after several days of storage in ice but still very fit for human consumption. The characteristic freshness attributes of different foods are usually evaluated by sensory examination and by determination of specific indices, e.g., nucleotide degradation products in fish.

1.3 FUNCTIONAL PROPERTIES OF FOOD COMPONENTS The term functional properties has evolved to have a broad range of meanings. That corresponding to the term technological properties implies that the given component present in optimum concentration, subjected to processing at optimum parameters, contributes to the desirable sensory characteristics of the product, usually by interacting with other food constituents. Hydrophobic interactions,

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Chemical and Functional Properties of Food Components

hydrogen bonds, ionic forces, and covalent bonding are involved. Thus the functional properties of food components are affected by the number of accessible reactive groups and by the exposure of hydrophobic areas in the given medium. Therefore the functional properties displayed in a system of given water activity and pH and in the given range of temperature can be to a large extent predicted from the structure of the respective saccharides, proteins, and lipids. They can also be improved by appropriate, intentional enzymatic or chemical modifications of the molecules, mainly those that affect the size, charge density, or hydrophilic and hydrophobic character of the compounds, or by changes in the environment, regarding both the solvent and other solutes. The functional properties of food components make it possible to manufacture products of desirable quality. Thus pectins contribute to the characteristic texture of ripe apples and make perfect jellies. Various other polysaccharides are good thickening and gelling agents at different ranges of acidity and concentration of various ions. Alginates in the presence of Ca2+ form protective, unfrozen gels on the surface of frozen products. Some starches are resistant to retrogradation, thereby retarding staling of bread. Fructose retards moisture loss from biscuits. Mono- and diacylglycerols, phospholipids, and proteins are used for emulsifying lipids and stabilizing food emulsions and foams. Antifreeze proteins decrease ice formation in various products, and gluten plays a major role in producing the characteristic texture of wheat bread. Technologically required functional effects can also be achieved by intentionally employing various food additives — food colors, sweeteners, and a host of other compounds — that are not regarded as foodstuffs per se, but are used to modify the rheological properties or acidity, increase the color stability or shelf life, or act as humectants or flavor enhancers (Rutkowski et al., 1997). During the recent two decades the term functional has also been given to a large group of products and components, also called designer foods, pharmafoods, nutraceuticals, or foods for specific health use, that are regarded as health enhancing. These foods, mainly drinks, meals, confectionery, ice cream, and salad dressings, contain various ingredients (e.g., oligosaccharides, sugar alcohols, or choline) that are claimed to have special physiological functions like neutralizing harmful compounds in the body and promoting recovery and general good health (Goldberg, 1994). Foods containing probiotics, mainly dairy products, have been treated in detail in Chapter 11.

1.4 ROLE OF CHEMISTRY AND PROCESSING FACTORS 1.4.1 INTRODUCTION The chemical nature of food components is of crucial importance for all aspects of food quality. It decides on the nutritional value of the product, its sensory attractiveness, the development of desirable or deteriorative changes due to interactions with other constituents and to processing, and the susceptibility and resistance to spoilage during storage. Food components that contain reactive groups, many of them essential for the quality of the products, are generally labile and

Food Components and Their Role in Food Quality

7

easily undergo different enzymatic and chemical changes, especially when treated at elevated temperatures or in conditions promoting the generation of active species of oxygen.

1.4.2 EFFECT

ON

SAFETY

AND

NUTRITIONAL VALUE

Food is regarded as safe if it does not contain harmful organisms or compounds in concentrations above the accepted limits (see Chapter 13). The nutritional value of foods depends primarily on the contents of nutrients and nutritionally objectionable components in the products. Processing may increase the safety and biological value of food by inducing chemical changes, increasing the digestibility of the components, or by inactivating undesirable compounds, e.g., toxins or enzymes catalyzing the generation of toxic agents from harmless precursors. Freezing and short-term frozen storage of fish inactivate the parasite Anisakis, which could escape detection during visual inspection of herring fillets used as raw material for cold marinades produced at mild conditions. Thermal treatment brings about inactivation of myrosinase, the enzyme involved in hydrolysis of glucosinolanes. This arrests the reactions that lead to the formation of goitrogenic products in oilseeds of Cruciferae. Heat pasteurization and sterilization reduce the number of vegetative forms and spores, respectively, to the acceptable level of pathogenic microorganisms. Several other examples of such improvements of the biological quality of foods are given in the following chapters of this book. However, there are also nutritionally undesirable side effects of processing: destruction of essential food components as a result of heating, chemical treatment, and oxidation. Generally known is the partial thermal decomposition of vitamins, especially thiamine, loss of available lysine and sulfur-containing amino acids, or generation of harmful compounds (e.g., carcinogenic heterocyclic aromatic amines, lysinoalanine, and lanthionine or position isomers of fatty acids) not originally present in foods. Thanks to the unprecedented development of analytical chemistry, applying efficient procedures of enrichment and separation, combined with the use of highly selective and sensitive detectors, has made it possible to determine various products of chemical reactions in foods, even in very low concentrations. In recent years new evidence of side effects has been accumulated in respect to chemical processing of oils and fats. Commercial hydrogenation of oils not only brings about the intended saturation of selected double bonds in the fatty acids, and thereby the required change in the rheological properties of the oil, but also results in the generation of a large number of trans-trans and cis-trans isomers that are absent in unprocessed oils.

1.4.3 EFFECT

ON

SENSORY QUALITY

Many of the desirable sensory attributes of foods stem from the properties of the raw material: the color, flavor, taste, and texture of fresh fruits and vegetables or the taste of nuts and milk. These properties are in many cases carried through to the final products.

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Chemical and Functional Properties of Food Components

In other commodities the characteristic quality attributes are generated in processing. The texture of bread develops due to interactions of proteins, lipids, and saccharides with each other and with various gases (Eliasson, 1998; Wrigley et al., 1998; Preston, 1998). The bouquet of wine is due to fermentation of saccharides and a number of other biochemical and chemical reactions. The delicious color, flavor, texture, and taste of smoked salmon are generated as a result of enzymatic changes in the tissues and the effect of salt and smoke (Doe et al., 1998). Optimum foam performance of beer depends on the interactions of peptides, lipids, the surfaceactive components of hop, and gases (Hughes, 1999). The flavor, texture, and taste of cheese result from fermentation and ripening, while the appealing color and flavor of different fried products are due to reactions of saccharides and amino acids (Sikorski, 2001). The sensory attributes of foods are related to the contents of many chemically labile components. These components, however, just as most nutritionally essential compounds, are prone to deteriorative changes in severe heat treatment conditions, oxidizing conditions, or application of considerably high doses of chemical agents (e.g., acetic acid or salt), which are often required to ensure safety and sufficiently long shelf life of the products. Thus loss in sensory quality takes place in oversterilized meat products, due to degradation of sulfur containing amino acids and the development of an off-flavor; in toughening of the texture of overpasteurized ham or shellfish, due to excessive shrinkage of the tissues and drip; and in deterioration of the texture and arresting of ripening in herring, due to preservation at too high a concentration of salt. Optimum parameters of storage and processing ensure the retention of the desirable properties of the raw material and lead to development of intended attributes of the product. In the selection of these parameters the chemistry of food components and of the effect of processing must be studied. The eager food technology student can find all the necessary information in at least two excellent textbooks on food chemistry, published by Belitz et al. (2001) and Fennema (1996); in numerous books on food lipids, proteins, and saccharides; and in current international journals.

REFERENCES Belitz, H.D., Grosch, W., and Schieberle, P., Lehrbuch der Lebensmittelchem, 4th ed., Springer-Verlag, Berlin, 2001. Decker, E.A., Livisay, S.A., Zhou S., Mechanism of endogenous skeletal muscle antioxidants: chemical and physical aspects, in Antioxidants in Muscle Foods: Nutritional Strategies to Improve Quality, Decker, E., Faustman, C., and Lopez-Bote, C.J., Eds., Wiley Interscience, New York, 2000, p. 25. Doe, P. et al., Basic principles, in Fish Drying and Smoking: Production and Quality, Doe, P.E., Ed., Technomic Publishing Co., Inc., Lancaster, PA, 1998, p. 13. Eliasson, A.C., Lipid-carbohydrate interactions, in Interactions: The Keys to Cereal Quality, Hamer, R.J. and Hoseney, R.C., Eds., American Association of Cereal Chemists, Inc., St. Paul, MN, 1998, p. 47. Fennema, O.R., Ed., Food Chemistry, 3rd ed., Marcel Dekker, New York, 1996.

Food Components and Their Role in Food Quality

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Fujihara, S., Kasuga, A., and Aoyagi, Y., Nitrogen-to-protein conversion factors for common vegetables in Japan, J. Food Sci., 66, 412, 2001. Goldberg, I., Functional Foods: Designer Foods, Pharmafoods, Nutraceuticals, Chapman & Hall, New York, 1994. Haard, N.F., Enzymic modification in food systems, in Chemical and Functional Properties of Food Proteins, Sikorski, Z.E., Ed., Technomic Publishing Co., Lancaster, PA, 2001, p. 155. Hughes, P., Keeping a head: optimizing beer foam performance, in Bubbles in Food, Campbell, G.M. et al., Eds., Eagan Press, St. Paul, MN, 1999, p. 129. Kritchevsky, D. and Bonfield, Ch., Eds., Dietary Fiber in Health & Disease, Eagan Press, St. Paul, MN, 1995. Matsumoto, M., Dietary delivery versus exogenous addition of antioxidants, in Antioxidants in Muscle Foods: Nutritional Strategies to Improve Quality, Decker, E., Faustman, C., and Lopez-Bote, C.J., Eds., Wiley Interscience, New York, 2000, p. 315. Preston, K.R., Protein-carbohydrate interactions, in Interactions: The Keys to Cereal Quality, Hamer, R.J. and Hoseney, R.C., Eds., American Association of Cereal Chemists, Inc., St. Paul, MN, 1998, p. 81. Rutkowski, A., Gwiazda, S., and Dabrowski, ˛ K., Food Additives and Functional Component, Agro & Food Technology, Katowice, 1997 (in Polish). Sikorski, Z.E., Chemical reactions in proteins in food systems, in Chemical and Functional Properties of Food Proteins, Sikorski, Z.E., Ed., Technomic Publishing Co., Inc., Lancaster, PA, 2001, p. 191. Sikorski, Z.E., Kolakowska , A., and Pan, B.S., The nutritive composition of the major groups of marine food organisms, in Seafood: Resources, Nutritional Composition, and Preservation, Sikorski, Z.E., Ed., CRC Press, Boca Raton, FL, 1990, p. 29. Sosulski, F.W. and Imafidon, G.I., Amino acid composition and nitrogen-to-protein conversion factors for animal and plant foods, J. Agric. Food Chem., 38, 1351, 1990. Wrigley, C.W. et al., Protein-protein interactions: essential to dough rheology, in Interactions: The Keys to Cereal Quality, Hamer, R.J. and Hoseney, R.C., Eds., American Association of Cereal Chemists, Inc., St. Paul, MN, 1998, p. 17.

2

Chemical Composition and Structure of Foods Krystyna Palka

CONTENTS 2.1 2.2

Introduction ....................................................................................................11 Protein Food Products....................................................................................12 2.2.1 Meat....................................................................................................12 2.2.2 Milk and Milk Products.....................................................................14 2.2.3 Eggs....................................................................................................15 2.3 Saccharide Food Products..............................................................................16 2.3.1 Cereal and Cereal Products................................................................16 2.3.2 Potatoes ..............................................................................................18 2.3.3 Honey .................................................................................................20 2.3.4 Nuts ....................................................................................................20 2.3.5 Seeds of Pulses...................................................................................20 2.4 Edible Fats......................................................................................................21 2.5 Fruits and Vegetables .....................................................................................21 References................................................................................................................23

2.1 INTRODUCTION Foods are edible fragments of plant or animal tissues in a natural or processed state that, after being eaten and digested in the human organism, may be a source of different nutrients. Taking as a base the dominant nutritional component, food products may be divided into four groups: • • • •

Protein food products Saccharide food products Edible fats Fruits and vegetables

The particular groups of chemical constituents participate in building the structure of food products as components of specialized tissues. For this reason this chapter presents, in addition to chemical composition, the morphology of the selected products from each group. 1-5871-6149-4/02/$0.00+$1.50 © 2002 by CRC Press LLC

11

12

Chemical and Functional Properties of Food Components

2.2 PROTEIN FOOD PRODUCTS 2.2.1 MEAT Meat is the edible part of animal, chicken, or fish carcasses. Its chemical composition is as follows: 60–85% water, 8–23% protein, 2–15% lipids, 0.5–1.5% saccharides, and about 1% inorganic substances (Table 2.1). These quantities change significantly depending on the kind, age, sex, level of fattening, and part of the animal carcass. The largest fluctuations are observed in the contents of water and lipids. Water is a solvent of organic and inorganic substances and an environment of biochemical reactions. It also participates in the maintenance of meat protein conformation. Meat proteins include sarcoplasmic, myofibrillar, and connective tissue proteins. Among the sarcoplasmic proteins are heme pigments and enzymes, which influence the color, smell, and structure of meat. Myofibrillar proteins and collagen are able to retain and hold water in meat structure and to emulsify fat. Therefore they influence the rheological properties of meat products. Mineral elements are in enzymatic complexes and other structures that play an important biochemical role. They can affect the technological properties of meat, e.g., water-holding capacity, as well as the sensory characteristics. Meat is also a good source of B group vitamins. The main structural unit of striated muscle tissue is a multinucleus cell called muscle fiber. Its length varies from several millimeters to hundredths of a millimeter, and the diameter is within the range 10–100 µm (Figure 2.1a). The thickness of muscle fibers affects the meat tenderness. The muscle fiber contains typical somatic cell compounds, sarcoplasmic reticulum, and myofibrils. The sarcoplasmic reticulum has the capacity of reversible binding of calcium ions. Myofibrils are the main structural element of muscle fiber, making up 80% of its volume. They have a diameter of 1–2 µm and are situated parallel to the long axis of the fiber (Figure 2.1b). The spaces between myofibrils are filled up with a semiliquid sarcoplasm, which forms the environment of enzymatic reactions and takes part in conducting nervous impulses into the muscle. Each myofibril consists of two different protein structures: myofilaments. These are myosin thick (15 nm × 1.5 µm) and thin (7 nm × 1 µm) filaments made from actin, tropomyosin, and troponin. Inside the muscle fiber there is also a cytoskeleton — the protein structures assuring the integrity of muscle cells. Cytoskeletal proteins such as titin and nebulin are located in myofibrils and anchored in the Z line. Desmin is made up of costamers, which connect the myofibrils; vinculin connects myofibrils and sarcolemma. Postmortem changes in cytoskeletal proteins probably play a role in the improvement of meat functional properties, especially its tenderness and water-holding capacity. The muscle fiber is covered by a thin membrane called sarcolemma and a layer of connective tissue called endomysium. Bundles of muscle fibers are surrounded by perimysium, and whole muscle is surrounded by epimysium. At the ends of the muscle epimysium forms tendons, which connect the muscle to the bone (Figure 2.2). Both the quantity and kind of connective tissue affect the technological and nutritional properties of meat.

Chemical Composition and Structure of Foods

13

TABLE 2.1 Chemical Composition of Foods Rich in Proteins

Product

Water (%)

Crude Protein Nx6.25 (%)

Lipids (%)

Saccharides (%)

Mineral Components (%)

Beef, lean Pork, lean Veal Lamb Chicken: Light meat Dark meat Herring Oyster Cow milk Sheep milk Sour cream (25%) Yogurt, low fat Quarg Ripened cheese Milk powder Whole egg, without shell White Yolk Whole egg powder

71.5 72.0 75.0 71.5

21.0 20.0 20.0 19.5

6.5 7.0 3.5 7.0

1.0 1.0 1.0 1.5

1.0 1.0 1.0 1.0

75.0 76.0 60.0 85.0 88.0 82.0 68.0 85.0 64.0–75.0 35.0–50.0 3.0

23.0 20.0 18.0 7.5 3.0 6.0 3.0 5.0 9.0–14.0 20.0–35.0 26.0

2.0 4.5 15.5 1.5 3.5 6.5 25.0 1.0 12.0–18.0 20.0–30.0 26.0

1.0 1.0 0.5–1.5 0.5–1.5 4.5 4.5 4.0 7.5 2.5 2.0 38.0.

1.0 1.0 0.5 0.7 1.5 5.0 6.0

73.5 88.0 48.5 3.5

13.0 11.0 16.0 47.5

12.0 traces 32.0 43.0

1.0 0.5 1.0 to 0.5

1.0 0.5 1.0 4.0

Source: Adapted from Hedrick, H.B. et al., Principles in Meat Science, Kendall-Hunt Publishing Co., Dubuque, 1994; Kirk, R.S. and Sawyer, R., Pearson’s Composition and Analysis of Foods, Longman Science, London, 1991; Renner, E., Cheese: Chemistry, Physics and Microbiology, Vol. 1, Fox, P.F., Ed., Chapman & Hall, London, 1993, 557; Sikorski, Z.E., Seafood Raw Materials, WNT, Warsaw, 1992; Tamime, A.Y. and Robinson, R.K., Yoghurt: Science and Technology, CRC Press, Boca Raton, FL, 1999.

FIGURE 2.1 Scanning electron microscope (SEM) micrographs of bovine semitendinosus muscle: transverse section (a) and longitudinal section (b). F, muscle fiber; MF, myofibril. (From Palka, K., unpublished.)

14

Chemical and Functional Properties of Food Components

FIGURE 2.2 Schematic structure of skeletal muscle: tendon (1), epimysium (2), perimysium (3), endomysium (4), sarcolemma (5), myofibril (6), muscle fiber (7), and bundle of muscle fibers (8).

2.2.2 MILK

AND

MILK PRODUCTS

Milk is a liquid secretion of the mammary glands of female mammals, consisting of 80–90% water and 10–20% dry mass. It is an oil-in-water (O/W) emulsion composed of fat and fat-soluble vitamins; the aqueous phase contains proteins, mineral salts, lactose, and water-soluble vitamins. The chemical composition of milk (Table 2.1) depends on species and breed, lactation period, and nutritional and health conditions of the animal. The proteins of milk are made up of caseins and whey proteins. Milk proteins, caseins, and several enzymes, mainly hydrolases and oxidoreductases, are very important in the manufacturing of cheeses and yogurts (Figure 2.3). After drying they are used in the food industry as milk powder, caseinates, and casein hydrolyzates. Nonprotein nitrogenous compounds constitute about 0.2% of milk.. The milk fat is made up of about 98% triacylglycerols and 1% phospholipids. It also contains smaller amounts of di- and monoacylglycerols, sterols, higher fatty acids,

FIGURE 2.3 SEM micrograph of protein matrix in yogurt. (From Domagala, J., unpublished. With permission.)

Chemical Composition and Structure of Foods

15

carotenoids, and vitamins. In cow milk fat over 500 fatty acid residues have been identified. The polyenoic fraction constitutes about 3% of the total fatty acids and is composed mainly of linoleic and oc-linolenic acids. The milk fat is easily digestible because of a relatively low melting temperature and great dispersion (droplets of 5–10 µm in diameter). Because of the latter, it is susceptible to hydrolysis and oxidation. The main saccharide of milk is lactose. During heat treatment of milk, lactose is involved in Maillard reactions. Lactose is used for the production of baby formulas, low-caloric foods, bread, drugs, and microbiological media. The milk minerals are composed mainly of calcium and phosphorus in the form of calcium phosphate. Phosphorus is also present in milk in the form of phosphoproteins. These components have important nutritional and technological significance. The total content of Ca and P in milk is about 0.12 and 0.10%, respectively. About 6–9% of milk volume is made up of gases, mainly CO2, N2, and O2. Oxygen present in milk may cause oxidation of unsaturated fatty acids. For this reason air is removed from milk during processing. Milk contains vitamins essential for the growth and development of young organisms, especially vitamins from the B group and vitamin A. The quantity of vitamin A depends on the season.

2.2.3 EGGS The hen egg consists of a shell, egg white, and yolk (Figure 2.4). The 0.2- to 0.4mm-thick shell constitutes 10–12% of the egg mass and consists of about 3.5% organic and 95% mineral components. The shell has a many-layer structure. Two of the layers are made of keratin and collagen fibers. The next two layers are calcinated and on the surface are covered by a thin membrane (cuticula) that contains two thirds of the shell pigments. The shell protects the egg against microbiological contamination and makes the exchange of gases possible.

FIGURE 2.4 Schematic structure of hen egg: shell (1), membranes (2), air chamber (3), rare white (4), dense white (5), yolk (6), and chalazae (7).

16

Chemical and Functional Properties of Food Components

The egg white — about 60% of the egg mass — composed mainly of water and a mixture of proteins, has a many-layer structure too. Starting from the shell there are four fractions of white: external thin, external thick, internal thin, and internal thick, which make up 23, 57, 17, and 2.5%, respectively, of the egg white mass. Mucin structures called chalazae keep the yolk in central position in the egg. During long storage the chalazae lose their elasticity, and the egg white loses part of its water, due to evaporation. The egg yolk — about 30% of the egg mass — has a spherical shape, a diameter of about 3–3.5 cm, and a color ranging from dark to light orange, depending on the quantity of lipids and carotenoid pigments in the fodder. It is surrounded by a thin and elastic vittelin membrane build of keratin and mucin fibers. The egg yolk, being an O/W emulsion, stabilized by lecithin, has a very high viscosity. The viscosity of the yolk decreases during storage, as a result of water permeation from the white through the vittelin membrane. Egg yolks are utilized as a stabilizer in manufacturing mayonnaise. The chemical composition of the egg (Table 2.1) is rather stable. As the only source of food for the embryo, it contains all substances essential for life. There is about 6.6 g of very well-balanced proteins in one egg. About two thirds of yolk mass are lipids, mainly unsaturated. Cholesterol makes up about 2.5% of the dry mass of the yolk. The egg is also a source of vitamins A, B, D, E, and K and the best dietary source of choline. The minerals S, K, Na, P, Ca, Mg, and Fe are in free form or bound to proteins and lipids. The eggs and egg products, thanks to their texture-improving properties, emulsifying effect, and foaming ability, are multifunctional components used in food technology in liquid or dried form.

2.3 SACCHARIDE FOOD PRODUCTS 2.3.1 CEREAL

AND

CEREAL PRODUCTS

Cereals are fruits of cultivated grasses that may be used as raw materials for production of food and feed. The major cereals are: wheat, rye, barley, oats, millet, rice, sorghum, and maize. The share of cereal products in the human diet is estimated at 50–60%. The shape of grains varies from elongated (rye) to spherical (millet), but the anatomical structure of cereal grains is rather similar. The essential anatomical elements of cereal grains are: seed coat (bran), endosperm, and germ. Commercially the most important cereal is wheat. A wheat grain is about 1 cm long and has a diameter of 0.5 cm. It is egg-shaped with a deep crease running along one side and a number of small hairs, called the beard, at one end (Figure 2.5). The grain is surrounded by a five-layer coat called bran that makes up 15% of the mass of the whole grain. It is rich in B vitamins and contains about 50% of the total mass of minerals of the grain. The bran consists of cellulose and is indigestible for humans. It is separated during flour production and used as animal fodder. The germ, about 3% of the mass of the grain, is situated at the base of the grain. It contains the embryo, which is rich in lipids, proteins, B vitamins, vitamin E, and

Chemical Composition and Structure of Foods

17

FIGURE 2.5 Schematic structure of wheat grain: longitudinal section (a) and transverse section (b); beard (1), bran (2), endosperm (3), crease (4), scutellum (5), and germ (6).

minerals, mainly iron. A membranous tissue called scutellum separates the germ from the endosperm. It is a rich source of thiamine — about 60% of all its content in the grain. The starchy endosperm makes up 80–90% of the wheat grain and is a reserve of food for the germ. The starch granules are embedded in a protein matrix, while the periphery of the endosperm is composed of a single aleurone layer. The aleurone layer is rich in proteins and contains high amounts of minerals, vitamins, and enzymes. However, it is usually removed during milling. Considering the size, most of the starch granules in the endosperm cells of wheat may be located in two ranges — large, 15–40 µm in diameter; and small, 1–10 µm in diameter — whereas those in the subaleurone endosperm cells are 6–15 µm in diameter. The chemical composition of cereal (Table 2.2) is dependent on species, cultivate, and time and conditions of growth, harvest, and storage. The starch constitutes about 80% of the grain dry mass. In bread making the most important properties of starch are its water-holding capacity, gelatinization, and susceptibility to hydrolysis. The protein content of cereal grains is in the range of 7–18%. From the technological point of view, proteins, mainly gluten proteins, as well as enzymes — amylases, proteases, and lipases — are important during dough making. Cereal grains also contain 2–4% of lipids, mainly triacylglycerols of unsaturated fatty acids and phospholipids.

18

Chemical and Functional Properties of Food Components

TABLE 2.2 Chemical Composition of Cereals and Cereal Products

Product

Water (%)

Crude Protein Nx6.25 (%)

Saccharides (%)

Lipids (%)

Mineral Components (%)

Grains Wheat Rye Maize Rice paddy Millet

15.0 15.0 15.0 15.0 15.0

11.0 9.0 10.0 7.5 10.5

68.5 70.5 67.0 75.5 65.0

2.0 1.5 4.5 0.5 4.0

1.5 1.5 1.5 1.0 3.0

Wheat flour (97%) Wheat flour (50%) Rye flour (97%) Rye flour (60%)

13.5 13.5 13.5 13.5

10.0 8.5 7.5 5.5

70.5 75.0 73.0 78.5

3.0 1.5 2.0 1.5

1.5 0.5 1.5 0.5

Wheat bread Rye bread Rusks

37.5 46.0 7.0

8.0 6.5 8.5

57.5 45.0 75.0

1.5 1.0 5.5

2.0 2.0 1.5

Flour

Bread

Source: Adapted from Fox, B.A. and Cameron, A.G., Food Science: A Chemical Approach, Hodder and Stoughton, London, 1986; Kent, N.L., Technology of Cereals with Special Reference to Wheat, Pergamon Press, Oxford, 1975.

The mineral elements, mainly P and K, and to a smaller extent, also Mg and Ca, make about 2% of the grain mass. Vitamins of the B group and vitamin E are also present in the grains. The milling technique can be modified to increase or decrease the yield of flour from a given amount of grain. The percentage of flour produced is termed the extraction rate of flour. Whole flour, containing the bran, germ, scutellum, and endosperm of the grain, has an extraction rate of 100%. An extraction rate of 70% means that the flour is almost entirely composed of crushed endosperm. As the percentage of flour increases, the amount of dietary fiber in flour increases too. It is an important nutritional aspect connected with cereal products.

2.3.2 POTATOES The potato is a swollen underground stem or tuber that contains a store of food for the plants. In the tuber a bud end and a stem end can be distinguished. The hollows, called eyes, are spirally arranged around the tuber surface. The tuber section is divided into the pith, parenchyma, vascular system, cortex, and periderm (Figure 2.6). Each potato tuber is a single living organism, and its water is indispensable in all the vital processes. Water transports any substances moving in the interior of the

Chemical Composition and Structure of Foods

19

FIGURE 2.6 Schematic structure of potato, longitudinal section: eye (1), periderm (skin) (2), parenchyma (3), vascular ring (4), and pith (5).

tuber. It also protects the tubers against overheating (by transpiration). The water constitutes about 75% of the potato (Table 2.3). The major constituent of the potato is starch (about 20%). With regard to starch content there are potato cultivates of a low (to 14%), medium (15–19%), and high (above 20%) starch content. Potato is also a valuable source of ascorbic acid — up to 55 mg/100 g. Its ash consists of about 60% K and 15% P2O5. The chemical composition of potato tubers changes during storage, due to evaporation and catabolic processes. In many parts of the world potatoes are the main saccharide source in human food and animal fodder and are also widely used as raw material for starch manufacture and in the fermentation industry.

TABLE 2.3 Chemical Composition of Potato and Honey Potato Water Dry matter: Starch Saccharides Proteins Cellulose Lipids Mineral components

% 76.0 24.0 17.5 1.5 2.0 1.0 0.5 1.0

Honey Water Saccharides: Fructose Glucose Maltose Trisaccharides Saccharose Proteins, vitamins, and mineral components

% 17.0 82.5 38.5 31.0 7.0 4.0 1.5 0.5

Source: Adapted from Lisi´n ska, G. and Leszczy´nski, W., Potato Science and Technology, Elsevier Applied Science, London, 1989; Ramsay, I., Honey as a food ingredient, Food Ingredient Process. Int., 10, 16, 1992.

20

Chemical and Functional Properties of Food Components

FIGURE 2.7 SEM micrographs of starch granules in different starchy raw materials: potato (a), wheat (b), and maize (c). (From Juszczak, L., unpublished. With permission.)

The shape and size of starch granules are specific for different starchy raw materials (Figure 2.7).

2.3.3 HONEY Honey is produced by honeybees from the flower nectar of plants. Fresh honey is a clear, very aromatic, dark-amber-colored liquid. It is very sticky and hygroscopic, with a density of about 1.40 g/cm3. Honey is an oversaturated solution of glucose and fructose, easy crystallizing. After crystallization its color is brighter. It is a very stable product. At a temperature of 8–10°C and a humidity of 65–75% it may be stored for many years. Honey is a high-caloric food easy assimilated by the human organism. Honey is used in the manufacturing of alcoholic beverages, i.e., in wine production. In medicine it is prescribed for heart, liver, stomach, skin, and eye illnesses. In the food industry honey is used as a very effective sweetener (25% sweeter than sucrose); a very well binding, concentrating, and covering additive; and a taste intensifier. The chemical composition of honey (Table 2.3) is dominated by glucose and fructose. Honey also contains many other valuable components, like enzymes, organic acids, mineral elements, nonprotein nitrogenous compounds, vitamins, aroma substances, and pigments.

2.3.4 NUTS Nuts are composed of a wooden-like shell and a seed, covered by a yellow or brown skin. Each part makes up about 50% of the nut mass. Inside of the seed is a germ. The seeds of nuts consist of about 60% lipids rich in unsaturated fatty acids, 16–20% easily digested proteins, 7% saccharides, vitamins B1 (10 mg/100 g) and C (30–50 mg/100 g), and P, Mg, K, and Na. With regard to their high quantity of easily assimilated nutrients, nuts may be used in diets of convalescents and children.

2.3.5 SEEDS

OF

PULSES

To this group belong peas, beans, lentils, soybeans, and peanuts. All of them have fruits in the form of pods. Their shape and size depend on the cultivar. Inside the pod are seeds used as raw material in the food industry.

Chemical Composition and Structure of Foods

21

The dry mass of pulse seeds consists of saccharides (14–63%), proteins (28–44%), and lipids (1–50%). The other constituents are mineral elements (mainly K and P) and vitamins from the B group. Soybean is the most valuable pod plant, due to its high quantity and good quality of protein. Soy products in the form of meat extenders and analogs are used all over the world. Soybean is also a raw material in the oil industry.

2.4 EDIBLE FATS Food products like butter, lard, margarine, and plant oils are regarded as “visible” fats. They make up about 45% of the total fat consumed by man, while the “invisible” fats, which are natural components of foods like meat, fish, eggs, and bakery products, make up about 55%. Visible fats are composed mainly of triacylglycerols. They also contain fatsoluble vitamins A, D, and E and additives added during processing, like antioxidants, colorants, or preservatives. The consistency of fats depends on the content of unsaturated fatty acid residues. The oils of plant and fish origin are rich in long-chain polyenic fatty acids. Butter consists of 16–18% water, 80–82.5% lipids, 0.5% proteins, and 0.5% saccharides.

2.5 FRUITS AND VEGETABLES Fruits and vegetables are rich sources of vitamins and minerals, as well as terpenes, flavonoids, tannins, chinons, and phytoncides. They make food more attractive because of smell and color. The fruits and vegetables are living organisms, and their chemical composition is very changeable. The predominant constituent of fruits and vegetables is water, which may represent up to about 96% of the total weight of the crop. The water in fruits and vegetables may be in free or bound form. A relatively high amount of free water improves the taste of fruits and vegetables consumed in their raw state, as well as the accessibility of soluble components. Most of the solid matter of fruits and vegetables is made of saccharides and smaller amounts of protein and fat. The total saccharide content in the fresh weight of fruits and vegetables ranges from about 2% in some pumpkin fruits to above 30% in starchy vegetables. Generally vegetables contain less than 9% saccharides. The polysaccharides — cellulose and hemicellulose — are largely confined to the cell walls. The di- and monosaccharides — sucrose, glucose, and fructose — are accumulated mainly in the cell sap. The proportions of the different saccharide constituents can fluctuate due to metabolic activity of the plant, especially during fruit ripening. The majority of proteins occurring in fruits and vegetables play enzymatic roles that are very important in the physiology and postmortem behavior of the crop. The protein content in vegetables is lower than 3%, except in sweet maize (above 4%). In fruits it ranges from below 1% to above 1.5%. They are found mainly in the cytoplasmic layers.

22

Chemical and Functional Properties of Food Components

The lipids of fruits and vegetables are, like the proteins, largely confined to the cytoplasmic layers, in which they are especially associated with the surface membranes. Their content in fruits and vegetables is always lower than 1%. Lipid and lipid-like fractions are particularly prominent in the protective tissues at the surfaces of plant parts — epidermal and corky layers. Plant tissues also contain organic acids formed during metabolic processes. For this reason fruits and vegetables are normally acidic in reaction. The quantity of organic acids is different, from very low, about 2 miliequivalents of acid/100 g in sweet maize and pod seeds, to very high, up to 40 miliequivalents/100 g in spinach. For the majority of fruits and vegetables the dominant acids are citric acid and malic acid, each of which can, in particular examples, constitute over 2% of the fresh weight of the material. Lemons contain over 3% of citric acid. Tartaric acid accumulates in grape and oxalic acid in spinach. The fruits in general show a decrease in overall acidity during the ripening process. The total amount of mineral components in fruits and vegetables is in the range of 0.1% (in sweet potatoes) up to about 4.4% (in kohlrabi). The most abundant mineral constituent in fruits and vegetables is potassium (Table 2.4). Generally vegetables are a better source of minerals than fruits. The mineral elements influence not only the growth and crop of fruits and vegetables, but also their texture (Ca), color (Fe), and metabolic processes (microelements). The diversity of form shown by fruit and vegetable structures is extremely wide. Among the vegetables there are representatives of all the recognizable morphological divisions of the plant body — whole shoots, roots, stems, leaves, and fruits. Fruits may also be classified into a number of structural types. The individual seed-bearing structures of the flower called carpels constitute the gynoecium. The seed-containing cavity of a carpel is called the ovary, and its wall develops into the pericarp of the fruit. The edible fleshy part of a fruit most commonly develops from the ovary wall, but it may be also derived from the enlarged tip of stem from which floral organs arise, and sometimes leaf-like structures protecting the flowers may also become fleshy, e.g., in pineapple.

TABLE 2.4 Mineral Components of Fruits and Vegetables (mg/100 g of Raw Mass) Component

mg

Rich Source

K Na Ca Mg P Cl S Fe

350 65 150 50 120 90 80 2

Parsley (above 1000 mg) Celery Spinach (up to 600 mg) Sweet maize Seeds and young growing parts Celery Plants with higher quantity of proteins Parsley (up to 8 mg)

Source: Adapted from Duckworth, R.B., Fruit and Vegetables, Pergamon Press, London, 1966.

Chemical Composition and Structure of Foods

23

The most metabolic activity of plants is carried out in the tissue called parenchyma, which generally makes up the bulk of the volume of all soft edible plant structures. The epidermis, which sometimes is replaced by a layer of corky tissue, is structurally modified to protect the surface of the organ. The highly specialized tissues collenchyma and sclerenchyma provide mechanical support for the plant. Water, minerals, and products of metabolism are transported from one part to another of the plant through the vascular tissues, xylem and phloem, which are the most characteristic anatomical features of plants on the cross section. The structure of fruits is dominated by soft parenchymatous tissue, while conducting and supporting structures are rather poorly developed. An exception is the pineapple, in which conducting tissues are very prominently represented. The subtle structure and proportions of individual tissues influence the texture, properties, and suitability for processing of fruits and vegetables.

REFERENCES Duckworth, R.B., Fruit and Vegetables, Pergamon Press, London, 1966. Fox, B.A. and Cameron, A.G., Food Science: A Chemical Approach, Hodder and Stoughton, London, 1986. Hedrick, H.B. et al., Principles of Meat Science, Kendall-Hunt Publishing Co., Dubuque, IA, 1994. Kent, N.L., Technology of Cereals with Special Reference to Wheat, Pergamon Press, Oxford, 1975. Kirk, R.S. and Sawyer, R., Pearson’s Composition and Analysis of Foods, Longman Science, London, 1991. Lisi´nska, G. and Leszczy´nski, W., Potato Science and Technology, Elsevier Applied Science, London, 1989. Ramsay, I., Honey as a food ingredient, Food Ingredient Process. Int., 10, 16, 1992. Renner, E., Nutritional aspects of cheese, in Cheese: Chemistry, Physics and Microbiology, Vol. 1, Fox, P.F., Ed., Chapman & Hall, London, 1993, p. 557. Sikorski, Z.E., Seafood Raw Materials, WNT, Warsaw, 1992 (in Polish). Tamime, A.Y. and Robinson, R.K., Yoghurt: Science and Technology, CRC Press, Boca Raton, FL, 1999.

3

Water and Food Quality Barbara Cybulska and Peter Edward Doe

CONTENTS 3.1 3.2

Introduction ....................................................................................................25 Structure and Properties of Water..................................................................26 3.2.1 Water Molecule ..................................................................................26 3.2.2 Hydrogen Bonds ................................................................................27 3.2.3 Properties of Bulk Water ...................................................................28 3.2.4 Thermal Properties of Water..............................................................32 3.2.5 Water as a Solvent .............................................................................33 3.2.6 Water in Biological Materials............................................................36 3.2.6.1 Properties ............................................................................36 3.2.6.2 Water Transport...................................................................39 3.3 Water in Food.................................................................................................40 3.3.1 Introduction ........................................................................................40 3.3.2 Sorption Isotherms and Water Activity .............................................41 3.3.2.1 Principle ..............................................................................41 3.3.2.2 Measurement of Water Activity..........................................43 3.3.3 Water Activity and Shelf Life of Foods ............................................44 3.4 Water Supply, Quality, and Disposal.............................................................45 3.4.1 Water Supply......................................................................................45 3.4.2 Water Quality .....................................................................................45 3.4.2.1 Standards and Treatment ....................................................45 3.4.2.2 Water Pollution ...................................................................47 3.4.3 Wastewater Treatment and Disposal..................................................48 References................................................................................................................49

3.1 INTRODUCTION Water is the most popular and most important chemical compound on our planet. It is a major chemical constituent of Earth’s surface, and it is the only substance that is abundant in solid, liquid, and gaseous form. Because it is ubiquitous, it seems to be a mild and inert substance. In fact, it is a very reactive compound characterized by unique physical and chemical properties that make it very different from other popular liquids. The peculiar water properties determine the nature of the physical and biological world.

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25

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Chemical and Functional Properties of Food Components

Water is the major component of all living organisms. It constitutes 60% or more of the weight of most living things, and it pervades all portions of every cell. It existed on our planet long before the appearance of any form of life. The evolution of life was doubtlessly shaped by physical and chemical properties of the aqueous environment. All aspects of living cells’ structure and function seem to be adapted to water-unique properties. Water is the universal solvent and dispersing agent, as well as a very reactive chemical compound. Biologically active structures of biomacromolecules are spontaneously formed only in aqueous media. Intracellular water is not only a medium in which structural arrangement and all metabolic processes occur, but an active partner of molecular interactions, participating directly in many biochemical reactions as a substrate or a product. Its high heat capacity allows water to act as a heat buffer in all organisms. Regulation of water contents is important in the maintenance of homeostasis in all living systems. Only 0.003% of all sweet water reserve participates in its continuous circulation between the atmosphere and the hydrosphere. The remaining part is confined in the Antarctic ice. The geography of water availability has determined, to a large degree, the vegetation, food supply, and habitation in the various areas of the world. For example, Bangladesh has one of the world’s highest population densities — made possible through the regular flooding of the Ganges River and the rich slits it deposits in its wake. In Bangladesh, the staple food — rice — grows abundantly and is readily distributed. In other societies the food must be transported long distances or kept over winter. Stability, wholesomeness, and shelf life are significant features of such foods. These features are, to a large degree, influenced by the water content of the food. Dried foods were originally developed to overcome the constraints of time and distance before consumption. Canned and frozen foods were developed next. The physical properties, quantity, and quality of water within food have a strong impact on food effectiveness, quality attributes, shelf life, textural properties, and processing.

3.2 STRUCTURE AND PROPERTIES OF WATER 3.2.1 WATER MOLECULE Water is a familiar material, but it has been described as the most anomalous of chemical compounds. Although its chemical composition, HOH or H2O, is universally known, the simplicity of its formula belies the complexity of its behavior. Its physical and chemical properties are very different from compounds of similar complexity, such as HF and H2S. To understand the reasons for water’s unusual properties, it is necessary to examine its molecular structure in some detail. Although a water molecule is electrically neutral as a whole, it has a dipolar character. The high polarity of water is caused by the direction of the H–O–H bond angle, which is 104.5°, and by an asymmetrical distribution of electrons within the molecule. In a single water molecule, each hydrogen atom shares an electron pair with the oxygen atom in a stable covalent bond. However, the sharing of electrons between H and O is unequal, because the more electronegative oxygen atom tends

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FIGURE 3.1 Water molecule as an electric dipole.

to draw electrons away from the hydrogen nuclei. The electrons are more often in the vicinity of the oxygen atom than of the hydrogen atom. The result of this unequal electron sharing is the existence of two electric dipoles in the molecule, one along each of the H–O bonds. The oxygen atom bears a partial negative charge δ–, and each hydrogen a partial positive charge δ+. Since the molecule is not linear, H–O–H has a dipole moment (Figure 3.1). Because of this, water molecules can interact through electrostatic attraction between the oxygen atom of one water molecule and the hydrogen of another.

3.2.2 HYDROGEN BONDS Such interactions, which arise because the electrons on one molecule can be partially shared with the hydrogen on another, are known as hydrogen bonds. The H2O molecule, which contains two hydrogen atoms and one oxygen atom in a nonlinear arrangement, is ideally suited to engage in hydrogen bonding. It can act both as a donor and as an acceptor of hydrogens. The nearly tetrahedral arrangement of the orbital about the oxygen atom allows each water molecule to form hydrogen bonds with four of its neighbors (Figure 3.2). An individual, isolated hydrogen bond is very labile. It is longer and weaker than a covalent O–H bond (Figure 3.3). The hydrogen bond’s energy, i.e., the energy required to break the bond, is about 20 kJ/mol. These bonds are intermediate between those of weak van der Waals interactions (about 1.2 kJ/mol) and those of covalent bonds (460 kJ/mol). Hydrogen bonds are highly directional; they are stronger when the hydrogen and the two atoms that share it are in a straight line (Figure 3.4). Hydrogen bonds are not unique to water. They are formed between water and different chemical structures, as well as between other molecules or even within a molecule. They are formed wherever an electronegative atom (oxygen or nitrogen) comes in close proximity to a hydrogen covalently bonded to another electronegative atom. Some representative hydrogen bonds of biological importance are shown in Figure 3.5.

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Chemical and Functional Properties of Food Components

FIGURE 3.2 Tetrahedral hydrogen bonding of five water molecules.

Hydrogen bond 0.177 nm

Covalent bond 0.0965

FIGURE 3.3 Two water molecules connected by hydrogen bonds.

Intra- and intermolecular hydrogen bonding occurs extensively in biological macromolecules. A large number of the hydrogen bonds and its directionality confers very precise three-dimensional structures upon proteins and nucleic acids.

3.2.3 PROPERTIES

OF

BULK WATER

The key to understanding water structure in solid and liquid form lies in the concept and nature of the hydrogen bonds. In the crystal of ordinary hexagonal ice (Figure 3.6), each molecule forms four hydrogen bonds with its nearest neighbors.

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FIGURE 3.4 Directionality of the hydrogen bonds.

FIGURE 3.5 Some hydrogen bonds of biological importance.

Each HOH acts as a hydrogen donor to two of the four water molecules and as a hydrogen acceptor for the remaining two. These four hydrogen bonds are spatially arranged according to the tetrahedral symmetry. The crystal lattice of ice occupies more space than the same number of H2O molecules in liquid water. The density of solid water is thus less than that of liquid water, whereas simple logic would have the more tightly bound solid structure more

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Chemical and Functional Properties of Food Components

FIGURE 3.6 Structure of ice.

dense than its liquid. One explanation for ice being lighter than water at 0°C proposes a reforming of intermolecular bonds as ice melts so that, on average, a water molecule is bound to more than four of its neighbors, thus increasing its density. But as the temperature of liquid water increases, the intermolecular distances also increase, giving a lower density. These two opposite effects explain the fact that liquid water has a maximum density at a temperature of 4°C. At any given instant in liquid water at room temperature, each water molecule forms hydrogen bonds with an average of 3.4 other water molecules (Lehninger et al., 1993). The average translational and rotational kinetic energies of a water molecule are approximately 7 kJ/mol, the same order as that required to break hydrogen bonds; therefore, hydrogen bonds are in a continuous state of flux, breaking and reforming with high frequency on a picosecond time scale. A similar dynamic process occur in aqueous media with substances that are capable of forming hydrogen bonds. At 100°C liquid water still contains a significant number of hydrogen bonds, and even in water vapor there is strong attraction between water molecules. The very large number of hydrogen bonds between molecules confers great internal cohesion on liquid water. This feature provides a logical explanation for many of its unusual properties. For example, its large values for heat capacity, melting point, boiling point, surface tension, and heat of various phase transitions are all related to the extra energy needed to brake intermolecular hydrogen bonds. That liquid water has structure is an old and well-accepted idea; however, there is no consensus among physical chemists as to the molecular architecture of the hydrogen bond’s network in the liquid state. The available measurements on liquid water do not lead to a clear picture of liquid water structure. It seems that the majority

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of hydrogen bonds survive the melting process, but obviously rearrangement of molecules occurs. The replacement of crystal rigidity by fluidity gives molecules more freedom to diffuse about and to change their orientation. Any molecular theory for liquid water must take into account changes in the topology and geometry of the hydrogen bond network induced by the melting process. Many models have been proposed, but none has adequately explained all properties of liquid water. “Iceberg” models postulated that liquid water contains disconnected fragments of ice suspended in a sea of unbounded water molecules. The most popular, the so-called “flickering clusters” model, suggests that liquid water is highly organized on a local basis: the hydrogen bonds break and reform spontaneously, creating and destroying transient structural domains (Figure 3.7). However, because the half-life of any hydrogen bond is less than a nanosecond, the existence of these clusters has statistical validity only; even this has been questioned by some authors who consider water to be a continuous polymer. Experimental evidence obtained by x-ray and neutron diffractions strongly support the persistence of a tetrahedral hydrogen bond order in the liquid water, but with substantial disorder present. Stillinger (1980) created a qualitatively water-like structure by computer simulation. The view that emerges from these results is the following: liquid water consists of a macroscopically connected, random network of hydrogen bonds. This network has a local preference for tetrahedral geometry, but it contains a large proportion of strained and broken bonds that are continually undergoing topological reformation. The properties of water arise from the competition between relatively bulky ways

FIGURE 3.7 “Flickering clusters” of H2O molecules in bulk water.

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Chemical and Functional Properties of Food Components

of connecting molecules into local patterns characterized by strong bonds and nearly tetrahedral angles and more compact arrangements characterized by more strain and bond breakage. According to the model proposed by Wiggins (1990), two types of water structure can be distinguished: high-density water and low-density water. In dense water the bent, relatively weak hydrogen bonds predominate over straight, stronger ones. Low-density water has many ice-like straight hydrogen bonds. Although hydrogen bonding is still continuous through the liquid, the weakness of the bonds allows the structure to be disrupted by thermal energy extremely rapidly. High-density water is extremely reactive and more liquid, whereas low-density water is inert and more viscous. A continuous spectrum of water structures between these two extremes could be imagined. The strength of water–water hydrogen bonding, which is the source of water density and reactivity, has great functional significance; this explains solvent water’s properties and its role in many biological events. A common feature of all theories is that a definite structure of liquid water is due to the hydrogen bonding between molecules and that the structure is in the dynamic state as the hydrogen bonds break and reform with high frequency.

3.2.4 THERMAL PROPERTIES

OF

WATER

The unusually high melting point of ice, as well as the heat of water vaporization and specific heat, is related to the ability of water molecules to form hydrogen bonds and to the strength of these bonds. A large amount of energy, in the form of heat, is required to disrupt the hydrogenbonded lattice of ice. In the common form of ice, each water molecule participates in four hydrogen bonds. When ice melts, most of the hydrogen bonds are retained by liquid water, but the pattern of hydrogen bonding is irregular, due to the frequent fluctuation. The average energy required to break each hydrogen bond in ice has been estimated to be 23 kJ/mol, while that to break each hydrogen bond in water is less than 20 kJ/mol (Ruan and Chen, 1998). The heat of water vaporization is much higher than that of many other liquids. As is the case with melting ice, a large amount of thermal energy is required for breaking hydrogen bonds in liquid water, to permit water molecules to dissociate from one another and to enter the gas phase. Perspiration is an effective mechanism of decreasing body temperature because the evaporation of water absorbs so much heat. A relatively large amount of heat is required to raise the temperature of 1 g of water by 1°C because multiple hydrogen bonds must be broken in order to increase the kinetic energy of the water molecules. Due to the high quantity of water in the cells of all organisms, temperature fluctuation within cells is minimized. This feature is of critical biological importance, since most biochemical reactions and macromolecular structures are sensitive to temperature. The unusual thermal properties of water make it a suitable environment for living organisms, as well as an excellent medium for the chemical processes of life.

Water and Food Quality

3.2.5 WATER

AS A

33

SOLVENT

Many molecular parameters, such as ionization, molecular and electronic structure, size, and stereochemistry, will influence the basic interaction between a solute and a solvent. The addition of any substance to water results in altered properties for this substance and for water itself. Solutes cause a change in water properties because the hydrate envelopes that are formed around dissolved molecules are more organized and therefore more stable than the flickering clusters of free water. The properties of solutions that depend on solute and its concentration are different from those of pure water. The differences can be seen in such phenomena as the freezing point depression, boiling point elevation, and increased osmotic pressure of solutions. The polar nature of the water molecule and the ability to form hydrogen bonds determine its properties as a solvent. Water is a good solvent for charged or polar compounds and a relatively poor solvent for hydrocarbons. Hydrophilic compounds interact strongly with water by an ion–dipole or dipole–dipole mechanism, causing changes in water structure and mobility and in the structure and reactivity of the solutes. The interaction of water with various solutes is referred to as hydration. The extent and tenacity of hydration depends on a number of factors, including the nature of the solute, salt composition of the medium, pH, and temperature. Water dissolves dissociable solutes readily, because the polar water molecules orient themselves around ions and partially neutralize ionic charges. As a result, the positive and negative ions can exist as separate entities in a dilute aqueous solution without forming ion pairs. Sodium chloride is an example where the electrostatic attraction of Na+ and Cl– is overcome by the attraction of Na+ with the negative charge on the oxygens and Cl– with the positive charge on the hydrogen ions (Figure 3.8). The number of weak charge–charge interactions between water and the Na+ and Cl– ions is sufficient to separate the two charged ions from the crystal lattice. To acquire their stabilizing hydration shell, ions must compete with water molecules, which need to make as many hydrogen bonds with one another as possible. The normal structure of pure water is disrupted in solution of dissociable solutes. The ability of a given ion to alter the net structure of water is dependent on the strength of its electric field. Among ions of a given charge type (e.g., Na+ and K+ or Mg+2 and Ca+2), the smaller ions are more strongly hydrated than the larger ions, in which the charge is dispersed over a greater surface area. Most

FIGURE 3.8 Hydration shell around Na+ and Cl–.

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Chemical and Functional Properties of Food Components

cations, except the largest ones, have a primary hydration sphere containing four to six molecules of water. Other water molecules, more distant from the ion, are held in a looser secondary sphere. The electrochemical transfer experiments indicate a total of 16 molecules of water around Na+ and about 10 around K+. The bound water is less mobile and more dense than HOH molecules in the bulk water. At some distance, the bonding arrangements melt into a dynamic configuration of pure water. Water is especially effective in screening the electrostatic interaction between dissolved ions, because, according to Coulomb’s law, the force (F) between two charges q+ and q– separated by a distance r is given as: F = q+ · q–/εr2

(3.1)

where ε is the dielectric constant of the medium. For a vacuum, ε = 1 Debye unit, whereas for bulk water, ε = 80; this implies that the energies associated with electrostatic interactions in aqueous media are approximately 100 times smaller than the energies of covalent association, but increase considerably in the interior of a protein molecule. In thermodynamic terms, the free energy change, ∆G, must have a negative value for a process to occur spontaneously. ∆G = ∆H – T∆S

(3.2)

where ∆G represents the driving force, ∆H (the enthalpy change) is the energy from making and breaking bonds, and ∆S (the entropy change) is the increase in randomness. Solubilization of a salt occurs with a favorable change in free energy. As salt such as NaCl dissolves, the Na+ and Cl– ions leaving the crystal lattice acquire greater freedom of motion. The entropy (∆S) of the system increases; where ∆H has a small positive value and T∆S is large and positive, ∆G is negative. Water in the multilayer environment of ions is believed to exist in a structurally disrupted state because of conflicting structural influences of the innermost vicinal water and the outermost bulk-phase water. In concentrated salt solutions, the bulkphase water would be eliminated, and the water structure common in the vicinity of ions would predominate. Small or multivalent ions, such as Li+, Na+, H3O+, Ca+2, Mg+2, F–, SO4–2, and PO4–3, which have strong electric fields, are classified as water structure formers because solutions containing these ions are less fluid than pure water. Ions that are large and monovalent, most of the negatively charged ions and large positive ions, such as K+, Rb+, Cs+, NH4+, Cl–, Br–, I–, NO–3, ClO4, and CNS–, disrupt the normal structure of water; they are structure breakers. Solutions containing these ions are more fluid than pure water (Fennema, 1985). Through their varying abilities to hydrate and to alter water structure and its dielectric constant, ions influence all kinds of water solute interactions. The conformation of macromolecules and the stability of colloids are greatly affected by the kinds and concentrations of ions present in the medium.

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Water is a good solvent for most biomolecules, which are generally charged or polar compounds. Solubilization of compounds with functional groups such as ionized carboxylic acids (COO –), protonated amines (NH3+), phosphate esters, or anhydrides is also a result of hydration and charge screening. Uncharged but polar compounds possessing hydrogen bonding capabilities are also readily dissolved in water, due to the formation of hydrogen bonds with water molecules. Every group that is capable of forming a hydrogen bond to another organic group is also able to form hydrogen bonds of similar strength with water. Hydrogen bonding of water occurs with neutral compounds containing hydroxyl, amino, carbonyl, amide, or imine groups. Saccharides dissolve readily in water, due to the formation of many hydrogen bonds between the hydroxyl groups or carbonyl oxygen of the saccharide and water molecules. Water–solute hydrogen bonds are weaker than ion–water interactions. Hydrogen bonding between water and polar solutes also causes some ordering of water molecules, but the effect is less significant than with ionic or nonpolar solutes. The introduction into water of hydrophobic substances such as hydrocarbons, rare gases, and the apolar groups of fatty acids, amino acids, or proteins is thermodynamically unfavorable because of the decrease in entropy. The decrease in entropy arises from the increase in water–water hydrogen bonding adjacent to apolar entities. Water molecules in the immediate vicinity of a nonpolar solute are constrained in their possible orientations, resulting in a shell of highly ordered water molecules around each nonpolar solute molecule (Figure 3.9a). The number of water molecules in the highly ordered shell is proportional to the surface area of hydrophobic solute. In the case of dissolved hydrocarbons, the enthalpy of formation of the new hydrogen bonds often almost exactly balances the enthalpy of creation in water, a cavity of Hydrophylic "head group"

(a)

(b)

FIGURE 3.9 Cage-like water structure around the hydrophobic alkyl chain (a) and hydrophobic interactions (b).

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Chemical and Functional Properties of Food Components

the right size to accommodate the hydrophobic molecule. However, the restriction of water mobility results in a very large decrease in entropy. According to ∆G = ∆H – T∆S

(3.3)

if ∆H is almost zero and ∆S is negative, ∆G is positive. To minimize contact with water, hydrophobic groups tend to aggregate; this process is known as hydrophobic interaction (Figure 3.9b). The existence of hydrophobic substances barely soluble in water but readily soluble in many nonpolar solvents, and their tendency to segregate in aqueous media, has been known for a long time. However, the origin of this hydrophobic effect is still somewhat controversial. The plausible explanation is that hydrophobic molecules disturb the hydrogen bonded state of water, without having any compensatory ordering effects. Apolar molecules are water structure formers: water molecules cannot use all four possible hydrogen bonds when in contact with hydrophobic, water-hating molecules. This restriction results in a loss of entropy, a gain in density, and increased organization of bulk water. Amphipathic molecules, i.e., compounds containing both polar or charged groups and apolar regions, disperse in water if the attraction of the polar group for water can overcome possible hydrophobic interactions of the apolar portions of the molecules. Many biomolecules are amphipathics: proteins, phospholipids, sterols, certain vitamins, and pigments have polar and nonpolar regions. When amphipathic compounds are in contact with water, the two regions of the solute molecule experience conflicting tendencies: the polar or charged hydrophilic regions interact favorably with water and tend to dissolve, but the nonpolar hydrophobic regions tend to avoid contact with water. The nonpolar regions of the molecules cluster together to present the smallest hydrophobic area to the aqueous medium, and the polar regions are arranged to maximize their interactions with the aqueous solvent. In aqueous media, many amphipathic compounds are able to form stable structures, containing hundreds to thousands of molecules, called micelles. The forces that held the nonpolar regions of the molecules together are due to hydrophobic interactions. The hydrophobic effect is a driving force in the formation of clathrate hydrates and the self-assembly of lipid bilayers. Hydrophobic interactions between lipids and proteins are the most important determinants of biological membrane structure. The three-dimensional folding pattern of proteins is also determined by hydrophobic interactions between nonpolar side chains of amino acid residues.

3.2.6 WATER

IN

BIOLOGICAL MATERIALS

3.2.6.1 Properties Water behaves differently in different environments. Properties of water in heterogenous systems such as living cells or food remain a field of debate. Water molecules may interact with macromolecular components and supramolecular structures of biological systems through hydrogen bonds and electrostatic interactions. Solvation of biomolecules such as lipids, proteins, nucleic acids, or saccharides resulting from these interactions determines their molecular structure and function.

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Various physical techniques, i.e., nuclear magnetic resonance (NMR), x-ray diffraction, and chemical probes (exchange of H by D), indicate that there is a layer of water bound to protein molecules, phospholipid bilayers, and nucleic acids, as well as at the surface of the cell membranes and other organelles. Water associated at the interfaces and with macromolecular components may have quite different properties from those in the bulk phase. Water can be expected to form locally ordered structures at the surface of water-soluble, as well as waterinsoluble, macromolecules and at the boundaries of the cellular organelles. Biomacromolecules generally have many ionized and polar groups on their surfaces and tend to align near polar water molecules. This ordering effect exerted by the macromolecular surface extends quite far into the surrounding medium. According to the association–induction theory proposed by Ling (1962), fixed charges on macromolecules and their associated counterions constrain water molecules to form a matrix of polarized multilayers having restricted motion, compared with pure water. The monolayer of water molecules absorbed on the polar sorption site of the molecule is almost immobilized and thus behaves, in many respects, like part of the solid or like water in ice. It has different properties than additional water layers defined as multilayers have. The association–induction theory has been shared by many researchers for many years. Unfortunately, elucidation of the nature of individual layers of water molecules has been less successful, due to the complexity of the system and lack of appropriate techniques. Measurements of the diffusion coefficients of globular protein molecules in solution yield values for molecular size that are greater than the corresponding radii determined by x-ray crystallography. The apparent hydrodynamic radius can be calculated from the Stokes–Einstein relation: D = kBT/6πηaH

(3.4)

where D is the diffusion coefficient, kB is the Boltzman constant, T is the temperature, η is the solution viscosity, and aH is the molecule radius (Nossal and Lecar, 1991). Similarly, studies utilizing NMR techniques show that there is a species of associated water that has a different character than water in the bulk phase. By these and other methods it was found that, for a wide range of protein molecules, approximately 0.25–0.45 g of H2O is associated with each gram of protein. The hydration forces can stabilize macromolecular association or prevent macromolecular interactions with a strength that depends on the surface characteristic of the molecules and the ionic composition of the medium. The interaction between a solute and a solid phase is also influenced by water. Hydration shells or icebergs associated with one or the other phase are destroyed or created in this interaction and often contribute to conformational changes in macromolecular structures — and ultimately to changes in biological and functional properties important in food processing. Biophysical processes involving membrane transport are also influenced by hydration. The size of the hydration shell surrounding small ions and the presence of water in the cavities of ionic channels or in the defects between membrane lipids strongly affect the rates at which the ions cross a cell membrane.

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Chemical and Functional Properties of Food Components

The idea that intracellular water exhibits properties different from those of bulk water has been around for a long time. The uniqueness of the cytoplamic water was deduced from: • The observation that cells may be cooled far below the freezing point of a salt solution iso-osmotic with that of the cytoplasm. • Properties of the cytoplasm, which in the same conditions should bind water like a gel. • Osmotic experiments in which it has often been observed that part of cell water is not available as a solvent. This water has been described as osmotically inactive water, bound water, or compartmentalized water. According to a recent view, three different kinds of intracellular water can be distinguished: a percentage of the total cell water appears in the form of usual liquid water. A relevant part is made up of water molecules that are bound to different sites of macromolecules in the form of hydration water, while a sizeable amount, although not fixed to any definite molecular site, is strongly affected by macromolecular fields. This kind of water has been termed vicinal water. Most of the vicinal water surrounds the elements of the cell cytoskeleton. Vicinal water has been extensively investigated, and it has been found that some of its properties are different from those of normal water. It does not have a unique freezing temperature, but an interval ranging from –70 to –50°C; it is a very bad solvent for electrolytes, but nonelectrolytes have the same solubility properties in it as in usual water; its viscosity is enhanced, and its NMR response is anomalous (Giudice et al., 1986). The distribution of various types of water inside the living cells is a question that cannot be answered yet, especially because in many cells marked changes have been noted in the state of intracellular water as a result of biological activity. The possibility that water in living cells may differ structurally from bulk water has incited a search for parameters of cell water that deviate numerically from those of bulk water. The diffusion coefficient for water in the cytoplasm of various cells has been determined with a satisfactory precision. It has been found that the movement of water molecules inside living cells is not much different and is reduced by a factor of between 2 and 6, compared with the self-diffusion coefficient for pure water. According to Mild and Løvtrup (1985), the most likely explanation of the observed values is that part of the cytoplasmic water, the vicinal water close to the various surface structures in the cytoplasm, is structurally changed to the extent that its rate of motion is significantly reduced, compared with the bulk phase. In heterogenous biological materials and foods, water exists in different states. It is thought that water molecules in different states function differently. Water associated with proteins and other macromolecules has traditionally been referred to as bound water. However, to designate such water as bound can be misleading because, for the most part, the water molecules are probably only transiently associated, and at least a portion of the associated water has to be constantly rearranged, due to the thermal perturbations of weak hydrogen bonds.

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Water molecules are constantly in motion, even in ice. In fact, the translational and rotational mobility of water directly determines its availability. Water mobility can be measured by a number of physical methods, including NMR, dielectric relaxation, ESR, and thermal analysis (Chinachoti, 1993). The mobility of water molecules in biological systems may play an important role in a biochemical reaction’s equilibrium and kinetics, formation and preservation of chemical gradients and osmotic pressure, and macromolecular conformation. In food systems, the mobility of water may influence the engineering processes — such as freezing, drying, and concentrating chemical and microbial activities, and textural attributes (Ruan and Chen, 1998). 3.2.6.2 Water Transport Water transport is associated with various physiological processes in whole living organisms and single cells. When cells are exposed to hyper- or hypo-osmotic solutions, they immediately lose or gain water, respectively. Even in an isotonic medium a continuous exchange of water occurs between living cells and their surroundings. Most cells are so small and their membrane so leaky that the exchange of water molecules measured with isotopic water reaches equilibrium in a few milliseconds. The degree of water permeability differs considerably between tissues and cell types. Mammalian red blood cells and renal proximal tubules are extremely permeable to water molecules. Transmembrane water movements are involved in diverse physiological secretion processes. How water passes through cells has begun to come clear only in the last five years. Water permeates living membranes through both the lipid bilayer and specific water transport proteins. In both cases water flow is passive and directed by osmosis. Water transport in living cells is therefore under the control of ATP and ion pumps. The most general water transport mechanism is diffusion through lipid bilayers, with a permeability coefficient of 2–5 × 10-4 cm/sec. The diffusion through lipid bilayers depends on lipid structure and the presence of sterol (Subczy´nski et al., 1994). It is suggested that the lateral diffusion of the lipid molecules and the water diffusion through the membrane is a single process (Haines, 1994). A small amount of water is transported through certain membrane transport proteins, such as a glucose transporter or the anion channel of erythrocytes. The major volume of water passes through water transport proteins. The first isolated water transporting protein was the channel-forming integral protein from red blood cells. The identification of this protein has led to the recognition of a family of related water-selective channels, the aquaporins, that are found in animals, plants, and microbial organisms. Water flow through the protein channel is controlled by the number of protein copies in the membrane. In red blood cells, there are 200,000 copies/cell; in apical brush border cells of renal tubules, it constitutes 4% of the total protein (Engel et al., 1994).

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Chemical and Functional Properties of Food Components

3.3 WATER IN FOOD 3.3.1 INTRODUCTION Water, with a density of 1000 kg m-3, is denser than the oil components of foods; oils and fats typically have densities in the range 850–950 kg m-3. Glycerols and sugar solutions are denser than water. Unlike the solid phase of most other liquids, ice is less dense than liquid water; ice has lower thermal conductivity than water. These properties have an effect on the freezing of foods that are predominantly water based; the formation of an ice layer on the surface of liquids and the outside of solids has the effect of slowing down the freezing rate. Because a molecule of water vapor is lighter (molecular weight = 18) than that of dry air (molecular weight = about 29), moist air is lighter than dry air at the same temperature. This is somewhat unexpected, because the popular conception is that humid air (which contains more water) is heavier than dry air. At room temperature, water has the highest specific heat of any inorganic or organic compound, with the sole exception of ammonia. It is interesting to speculate why the most commonly occurring substance on this planet should have one of the highest specific heats. One of the consequences of this peculiarity in the food industry is that heating and cooling operations for essentially water-based foods are more energy demanding. To heat a kilogram of water from 20 to 50°C requires about 125 kJ of energy, whereas heating the same mass of vegetable oil requires only 44 kJ. A sponge holds most of its water as liquid held in the intestacies of the sponge structure. Most of the water can be wrung out of the sponge, leaving a matrix of air and damp fibers. Within the sponge fibers the residual water is more tenuously held — absorbed within the fiber of the sponge. If the sponge is left to dry in the sun, this adsorbed water will evaporate, leaving only a small proportion of water bound chemically to the salts and to the cellulose of the sponge fibers. Like water in sponge, water is held in food by various physical and chemical mechanisms (Table 3.1). It is a convenient oversimplification to distinguish between “free” and “bound” water. The definition of bound water in such a classification poses problems. Fennema (1985) reports seven different definitions of bound water. Some of these definitions are based on the freezability of the “bound” component, and others rely on its availability as a solvent. He prefers a definition in which bound water is “that which exists in the vicinity of solutes and other nonaqueous constituents, exhibits reduced molecular activity and other significantly altered properties as compared with ‘bulk water’ in the same system, and does not freeze at –40°C.” The moisture content can be measured simply by weighing a sample and then oven drying it, usually at 105°C overnight; the difference in mass is the moisture content in the original sample. However, much confusion is caused by reporting the moisture content simply as a percentage without specifying the basis of the calculation. It should be made clear whether the moisture content is calculated on a wet basis (moisture content divided by original mass) or on a dry basis (moisture content

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TABLE 3.1 Classification of Water States in Foods Class of Water Constitutional Vicinal

Multilayer

Free

Entrapped

Description An integral part of nonaqueous constituent Bound water that strongly acts with specific hydrophilic sites of nonaqueous constituents to form a monolayer coverage; water–ion and water–dipole bonds Bound water that forms several additional layers around hydrophilic groups; water–water and water–solute hydrogen bonds Flow is unimpeded; properties close to those of dilute salt solutions; water–water bonds predominate Free water held within matrix or gel that impedes flow

Porportion of Typical 90% (Wet Basis) Moisture Content Food <0.03% 0.1–0.9%

1–5%

5% to about 96%

5% to about 96%

divided by the “bone dry” or “oven dry” mass). Even the term bone dry mass can cause confusion among non-English speakers; it was once misinterpreted as the “mass of the dry bones.” For example, in foods containing significant quantities of fat or salt, the moisture content may be calculated as the mass of water in a sample divided by the dry solids that are not salt or fat; in this case, the moisture content should be reported as calculated on a salt-free, fat-free, dry basis.

3.3.2 SORPTION ISOTHERMS

AND

WATER ACTIVITY

3.3.2.1 Principle Since 1929 it has been recognized that the chemical and microbial stability, and thus the shelf life, of foods is not directly related to its moisture content, but to a property called water activity (Tomkins, 1929). Essentially, water activity is a measure of the degree to which water is bound within the food, and thus unavailable for further chemical or microbial activity. Water activity is defined as the ratio of the partial pressure of water vapor in or around food to that of pure water at the same temperature. Relative humidity of moist air is defined in the same way, except that by convention, relative humidity is reported as a percentage, whereas water activity is expressed as a fraction. Thus if a sample of meat sausage is sealed within an airtight container, the humidity of the air in the headspace will rise and eventually equilibrate to a relative humidity of say 83%, which means that the water activity (aw) of the meat sausage is 0.83. The relationship between water activity and moisture content for most foods at a particular temperature is a sigmoidal-shaped curve called the sorption isotherm (Figure 3.10). The term equilibrium moisture content curve is also used. Sorption

42

Chemical and Functional Properties of Food Components

Moisture content (dry basis)

4.0

3.0

2.0

Desorption

Adsorption 1.0

0.2

0.4 0.6 Water activity

0.8

1.0

FIGURE 3.10 A typical sorption isotherm for food.

isotherms at different temperatures can be calculated using the Clausius–Clapeyron equation from classical thermodynamics: d ( ln a w ) ∆H ------------------- = -------d(1 ⁄ T ) R

(3.5)

where aw is the water activity, T is the absolute temperature, ∆H is the heat of sorption, and R is the gas constant. A complication arises from one of the methods of measuring sorption isotherms for food. Food that has previously been dried and then is rehydrated will have a different sorption isotherm (adsorption isotherm) from that which is in the process of drying (desorption isotherm). This difference is due to a change in water-binding capacity in foods that have been previously dried. Many mathematical descriptors for sorption isotherms have been proposed. One of the more famous is that of Brunauer et al. (1938), the B.E.T. isotherm, which is based on the concept of a measurable amount of monomolecular layer (vicinal) water for a particular food. Wolf et al. (1985) compiled 2201 references on sorption isotherm data for foods. An example of the type, detail, and accuracy of sorption isotherm data available in the literature is presented in Table 3.2. Iglesias et al. (1975) proposed the following three-parameter equation to fit sorption isotherm data for a range of foods: aw = exp(–a' θr) where a' and r are the parameters listed in Table 3.2, and θ = X/Xm.

Water and Food Quality

43

TABLE 3.2 Sorption Isotherm Data for Cod and Corn Product Coda Cornb

a b

Temperature (°C)

Xm

30 4.5 15.5 30 38 50 60

7.68 8.30 7.68 7.30 6.35 6.89 5.11

r 1.2398 2.2345 2.4862 2.5663 2.3711 2.1203 2.2185

a' 1.3490 1.9748 2.0949 1.7950 1.8618 1.5936 1.7430

Adsorption, after Jason (1958). Desorption, after Chen and Clayton (1971).

Source: From Iglesias, H.A. et al., J. Food Technol., 10, 289, 1975.

X is the equilibrium moisture content and Xm, in units of g/100 g dry basis, is the B.E.T. monomolecular moisture content for the food listed in Table 3.2. However, there are nearly as many equations to sorption isotherms as there are researchers in this field. 3.3.2.2 Measurement of Water Activity Many methods of measuring water activity have been developed by researchers. These include direct vapor pressure measurement, equilibration with a stable hygroscopic substance that has a known sorption behavior, and various types of hygrometers (Doe, 1998). Water activity is most conveniently measured by the measurement of relative humidity in the headspace over a food sample in a sealed container. Commercially available instruments for water activity determination use various methods for measuring the relative humidity: hair hygrometer (Lluft), electrical hygrometer (Nova Sina), and dew point temperature (Aqualab). The hygrometer-based instruments are prone to drift and must be calibrated regularly against saturated solutions of various inorganic salts. Hygrometer-based instruments are also prone to hysteresis at high humidities. The Aqualab CX2 water activity meter (Decagon Devices Inc., Pullman, WA) detects water condensation on a chilled mirror (dew point temperature). The instrument is sensitive to water activity units of <0.001. Readings take 5 min or less and are accurate to ±0.003 water activity units. Care must be taken with any measurement of water activity to ensure that the sample is representative of the food under test. Dried fish, for example, will have moisture and salt contents, and thus water activity, varying widely from thin, exposed flesh to the relatively moist interior. If the worst-case scenario for the growth of potentially toxic or spoilage organisms is of interest, the sample of flesh for water activity determination should be excised from the thickest, most moist region of the fish.

44

Chemical and Functional Properties of Food Components

3.3.3 WATER ACTIVITY

AND

SHELF LIFE

OF

FOODS

Many of the chemical and biological processes that cause deterioration of foods — and ultimately spoilage — are water dependent. Microbial growth is directly linked to water activity. No microbes can multiply at a water activity below 0.6. Dehydration is arguably the oldest form of food preservation; the sun drying of meat and fish has been traced to the beginning of recorded history. Drying relies on removing water, thus making it unavailable for microbial growth. Salting or curing has the same effect. A saturated solution of common salt has a water activity of close to 0.75. Thus, by adding sufficient salt to foods, the water activity can be lowered to a level where most pathogenic bacteria are inactivated, but the moisture content remains high. Intermediate moisture content foods (IMFs) such as pet food and continental sausages rely on fats and water-binding humectants such as glycerol to lower water activity. Fat, which is essentially hydrophobic, does not bind water, but acts as a filler for IMFs to increase the volume of the product. The effect of several humectants is for each to sequester an amount of water independently of the other humectants that may be present in the food. Each thus lowers the water activity of the system according to the equation of Ross (1975): awn = aw0 · a w1 · a w2 · a w3 · etc. where awn is the water activity of the complex food system, and a w0 etc. are the water activities associated with each component of the system. For example, the water activity of a food with a moisture content of 77% (wet basis) and a salt content of 3% (wet basis) can be calculated as follows: 100 g of the food comprises 77 g of water, 20 g of bone dry matter, and 3 g of salt. The contribution to the water activity due to the salt can be calculated (according to Raoult’s law of dilute solutions), using the molecular weights of water (18) and salt (58.5), as: a w1 = (77 × 18)/(77 × 18 + 3 × 58.5) = 0.89 The water activity for the salt-free solid matter of the food is found from its sorption isotherm at that moisture content, e.g., a w0 = 0.90. Thus the water activity of the salted food is: a wn = a w0 · a w1 = 0.9 × 0.89 = 0.8 None of the dangerous pathogenic bacteria associated with food, such as Clostridium or Vibrio spp., which cause botulism and cholera, can multiply at water activity values below about 0.9. Thus drying or providing sufficient water-binding humectants is an effective method of preventing the growth of food-poisoning bacteria. Only osmophilic yeasts and some molds can grow at water activities in the range 0.6–0.65. Thus, by reducing the water activity below this value, foods are microbially stable — unless the packaging is such that the food becomes locally

Water and Food Quality

45

wet again, in which case local spoilage can occur, e.g., when condensation occurs within a hermetically sealed package subjected to rapid cooling. There are various chemical reactions that proceed and may be accelerated at low values of water activity. Maillard reactions leading to lysine loss and brown color develop peaks at aw values around 0.5–0.8. Nonenzymatic lipid oxidation increases rapidly below aw = 0.4. Enzymic hydrolysis decreases with water activity to aw = 0.3, after which, it is negligible.

3.4 WATER SUPPLY, QUALITY, AND DISPOSAL 3.4.1 WATER SUPPLY Just as water is an integral part of any food, the supply, quality, and disposal of water is of prime consideration in the establishment and operation of all food processing. Potable (drinkable) water may be required for addition to the product, and will certainly be required for cleanup. Nonpotable water may be required for heat exchangers and cooling towers. Boiler feed water must be conditioned within close limits of pH and hardness. Brennan et al. (1990) in their book Food Engineering Operations list four types of water used in the food and beverage industries: • • • •

General-purpose water Process water Cooling water Boiler feed water

The siting and consequent viability of a food processing plant may well depend on a guaranteed, regular supply of suitable quality water and an environmentally acceptable method of disposal. Developed countries now have strict regulations for the emisson of wastewater. Developing countries are becoming increasingly aware of the problems of wastewater disposal. At a recent symposium in Indonesia a fish-drying processor was asked what his main technical problems were. He nominated water pollution, not for reasons of meeting environmental control regulations, but because the fish farmers further down the river were complaining about his wastewater.

3.4.2 WATER QUALITY 3.4.2.1 Standards and Treatment There are a number of international standards for potable (drinkable) water quality in existence. The World Health Organization (WHO) has a standard for potable water quality as part of the Codex Alimentarius. The standard detailed in Table 3.3 is from the U.S. Departmental Protection Agency. There is also a large Environment Circular (EC) directive relating to the quality of water intended for human consumption (80/778/EEC) that is contained in the joint circular from the Department of the Environment, Circular 20/82, 2 Marsham Street, London SW1P 3EB, and the Welsh Office, Circular 33/82, Cathays Park, Cardiff CF1 3NQ, issued on 19 August 1982.

46

Chemical and Functional Properties of Food Components

TABLE 3.3 Primary Maximum Contaminant Levels in Potable Water Contaminant

Level (mg/l unless Specified)

Arsenic Cadmium Lead Nitrate (as N) Silver Endrin Methoxychlor 2.4 D Total trihalomethanes Carbon tetrachloride Vinyl chloride para-Dichlorobenzene 1,1,1-Trichloroethane Barium Chromium Mercury Selenium Fluoride Lindane Toxaphene 2,4,5-TP silvex Trichloroethylene 1,2-Dichloroethane Benzene 1,1-Dichloroethylene Radium 226 and 228, combined Gross β particle Gross α particle Turbidity Coliform bacteria

0.05 0.010 0.05 10 0.05 0.0002 0.1 0.1 0.10 0.005 0.002 0.075 0.2 1 0.05 0.002 0.01 4.0 0.004 0.005 0.01 0.005 0.005 0.005 0.007 5 pC/l 4 millirem/year 15 pC/l 1–5 tu 1/100 ml, monthly average

Source: From the U.S. Departmental Protection Agency.

In most cases water will require some treatment to assure that it meets food hygiene requirements and does not constitute a public health hazard. Surface water from rain runoff into rivers or impoundments is likely to contain atmospheric solutes, minerals from the ground, organic matter from vegetation, microbial contamination from birds and wild and domestic animals, and human waste. Water from underground aquifers will have much of the surface contamination filtered out, but it is likely to be high in dissolved mineral content. Treatment for bringing water quality within the required standard may involve screening, sedimentation, coagulation and flocculation, filtration, and other physical or chemical treatments to remove microorganisms, organic matter, or dissolved minerals.

Water and Food Quality

47

Metal screens are used to remove particles larger than about 1 mm in size. Settling ponds remove smaller particles. Insoluble, suspended matter is usually removed by sand filters. Coagulating and flocculating agents act to bind smaller particles into clumps that then settle or can be screened or filtered. Microorganisms can be inactivated by heat, chemical disinfection, ultraviolet radiation, or ultrasonic treatment. Most town water supplies are chlorinated or have ozone added for chemical disinfection. Treatment to remove dissolved mineral matter is more complex. Dissolved bicarbonates of calcium, magnesium, sodium, and potassium cause alkalinity; soluble calcium and magnesium salts cause hardness. Alkalinity and hardness may need to be adjusted for some food processing operations. For example, the formation of a “head” on beer is critically dependent on water hardness. Excessively hard water may cause discoloration and toughening of certain foods. On the other hand, hardness may be required to prevent excessive foaming in clean-up operations. Iron and manganese salts may be present in water supplies forming organic slimes that tend to clog pipes. Aeration, filtering, and settling are effective for the removal of iron bicarbonates. Insoluble oxides of manganese are formed through chlorination. Excessive amounts of dissolved gases, carbon dioxide, oxygen, nitrogen, and hydrogen sulfide cause problems in boiler feed water, corrosion, and bacterial formation. Treatment for this is by boiling and venting off the noncondensable gases or by chemical dosing. Small amounts of hydrocarbons such as kerosene and diesel cause tainting in foods. Separating fuels from processing areas, personal hygiene, cleaning of stations around food processing operations, and good housekeeping can prevent this problem. 3.4.2.2 Water Pollution Polluted water is described as polluted if it poses a risk to the health of humans, fish, or other animals. Microbiologically polluted water contains bacteria and other microorganisms that may be hazardous or toxic. Human and animal wastes from sewage and farmyard runoff are the principal sources of microbiological pollution. Polluted water can be an indirect hazard, as fish and shellfish may become contaminated and eaten. Water can be polluted by organic and inorganic chemicals. Domestic and industrial pesticides are a major source of chemical pollution, as are detergents. Many of these substances are slow to degrade and may be concentrated in the food chain with disastrous consequences for fish and bird life. Biodegradable substances tend to deplete oxygen, resulting in a reduction of aerobic bacteria and fish. Food waste is high in biochemical oxygen demand (BOD). BOD is defined as the quantity of oxygen (in units of mg liter–1) required for a microorganism to oxidize the waste at a particular temperature (20°C) in 5 days. Food wastes contain large quantities of organic matter that break down naturally by oxidation; however, this oxygen demand is at the expense of other natural biochemical processes in waterways, which become oxygen depleted and lifeless if the BOD

48

Chemical and Functional Properties of Food Components

is too high. Food wastes can range in BOD from 500–4000 mg liter–1, which is higher than for domestic sewage (200–400 mg liter–1). An excess of nutrients, such as phosphorus and nitrogen in polluted water, will lead to an excessive growth of plant matter in waterways and algal blooms. Besides clogging waterways and adding toxins, this extra plant material contributes to the BOD of the water. Suspended matter, even if chemically and biologically inert, can contribute to pollution. These particles will eventually settle out and cause silting and an anaerobic environment at the bottom of waterway. Water pollution is most effectively prevented by removing the pollutants before they get into the waterways. This can be effected through good housekeeping practices, such as not discharging fatty material and detergents into the domestic sewage system, proper design of landfill areas, pretreatment of industrial wastes, and separation of storm water from sewage, so as to not overload treatment plants.

3.4.3 WASTEWATER TREATMENT

AND

DISPOSAL

The ultimate aim of any food processing operation is to have an environmentally neutral impact. Reuse, recycle, and sustainability are today’s catchwords. For a food operation to be truly environmentally sustainable, it should recycle all water not incorporated in the product or vented to the atmosphere. The reality is that it is currently considered uneconomic to recycle wastewater from food processing operations. Current practice is to treat wastewater to limit its effect on receiving waters. Treatment of wastewater mirrors the water treatment methods described above, i.e., a combination of physical, chemical, and biological treatments. A physical process treats suspended, rather than dissolved, pollutants. The pollutants may simply be allowed to settle or float to the top naturally, or the process may be aided mechanically, which will cause smaller particles to stick together, forming larger particles that will settle or rise faster — a process known as flocculation. Chemical flocculants may also be added to produce larger particles. A final treatment stage of filtration through a medium such as sand can result in very clear water. Ultrafiltration, nanofiltration, and reverse osmosis are processes that force water through membranes and can remove colloidal material and even some dissolved matter. Absorption (adsorption, technically) on activated charcoal is a physical process that can remove dissolved chemicals. Air or steam stripping can be used to remove gas or low-boiling liquid pollutants from water; vapors removed in this way are also often passed through beds of activated charcoal to prevent air pollution. These last processes are used mostly in industrial treatment plants, though activated charcoal is common in municipal plants for odor control. Wastewater from food processing operations usually contains significant solid matter that can be removed by physical processes. Fats and oils can be skimmed from the surface of settling tanks; heavier suspended matter can be removed as sludge, which can then be dewatered, dried, and used as animal feed, fertilizer, or fuel. An alternative method for the removal of oils and fats is aeration, a process in which air bubbles blown from the bottom of a settling tank carry fine solids and grease to the surface.

Water and Food Quality

49

Chemical treatments of wastewater are much the same as those described above for process water treatment. BOD can be effectively reduced by biological treatment. Both aerobic and anaerobic fermentation of the organic material is used. Depending on the scale of the operation, bioreactors range in size from 7.5 m diameter and 2–3 m in depth to 1- to 2-m-deep lagoons covering several hectares. However, for longterm sustainable operation there must be provision for sludge removal. Where area for treatment is not a limitation and there is sufficient isolation, so smell is not a deterrent, wastewater is sprayed directly on the ground, where it breaks down under the action of sunlight and in-ground bacteria. A typical municipal treatment plant would comprise a preliminary treatment plant in which large or hard solids are removed or crushed. The effluent then passes through a primary settling basin in which organic suspended matter will either settle out or float to the surface to be skimmed off. The next part of the process is usually referred to as secondary treatment, wherein the remaining dissolved or colloidal organic matter is removed by aerobic biodegradation. This promotes the formation of less offensive, oxidized products. The treatment unit should be sufficiently large to remove enough of the pollutants to prevent significant oxygen demand in the receiving water after discharge. Sewage and wastewater can also be treated anaerobically. Closed reactors facilitate odor control, although anaerobic lagoons are also used. Such lagoons are deeper than those for aerobic types, with grease allowed to accumulate on the surface to control odor emission. Methane produced as an end product of the biochemical pathway can be used for heating the reactors in cold weather. A problem with the anaerobic digestion process is its sensitivity to pH and temperature variation and the susceptibility of the active microorganisms to chemical disinfectants.

REFERENCES Brennan, J.G. et al., Food Engineering Operations, 3rd ed., Elsevier Applied Science, London, 1990, p. 523. Brunauer, S., Emmet, P.H., and Teller, E., Adsorption of gases in multilayers, J. Am. Chem. Soc., 60, 309, 1938. Calabrese, E.J., Gilbert, C.E., and Pastides, H., Eds., Safe Drinking Water Act: Amendments, Regulations, and Standards, Lewis Publishers, Chelsea, MI, 1989. Chen, C.S. and Clayton, J.T., The effect of temperature on sorption isotherms of biological materials, Trans. A.S.A.E., 14, 927, 1971. Chinachoti, P., Water mobility and its relation to functionality of sucrose-containing food systems, Food Technol., 47, 134, 1993. Doe, P.E., Ed., Fish Drying and Smoking Production and Quality, Technomic Publishing Co. Inc., Lancaster, PA, 1998, p. 22. Engel, A., Waltz, Th., and Agre, P., The aquaporin family of membrane water channels, Curr. Opin. Struct. Biol., 4, 545, 1994. Fennema, O.R., Food Chemistry, 2nd ed., Marcel Dekker Inc., New York, 1985. Giudice, E. et al., Water in biological systems, in Modern Bioelectrochemistry, Gutmann, F. and Keyzer, H., Eds., Plenum Press, New York, 1986, p. 282. Haines, Th.H., Water transport across biological membranes, FEBS Lett., 346, 115, 1994.

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Iglesias, H.A., Chirife, J., and Lombardi, J.L., An equation for correlating equilibrium moisture content in foods, J. Food Technol., 10, 289, 1975. Jason, A.C., A study of evaporation and diffusion processes in the drying of fish muscle, in Fundamental Aspects of the Dehydration of Foodstuffs, Soc. Chem. Ind., London, 1958, p. 103. Lehninger, A.L., Nelson, D.L., and Cox, M.M. Principles of Biochemistry, 2nd ed., Worth Publishers, Inc., New York, 1993, p. 181. Ling, G.N., A Physical Theory of the Living State, Ginn (Blaisdel), Boston, MA, 1962. Mild, K., and Lovtrup, S., Movement and structure of water in animal cells. Ideas and experiments, Biochim. Biophys. Acta, 822, 155, 1985. Nossal, R. and Lecar, H., Eds. Molecular and Cell Biophysics, Addison-Wesley Publishing Co., Reading, MA, 1991, p. 9. Ross, K.D., Estimation of water activity in intermediate moisture foods, Food Technol., 29, 26, 1975. Ruan, R.R. and Chen, P.L., Water in Foods and Biological Materials, Technomic Publishing Co. Inc., Lancaster, PA, 1998. Stillinger, F.H., Water revisited, Science, 209, 451, 1980. Subczy´nski, W.K. et al., Hydrophobic barriers of lipid bilayer membranes formed by reduction of water penetration by alkyl chain unsaturation and cholesterol, Biochemistry, 33, 7670, 1994. Tomkins, R.G., Studies of the growth of moulds. 1., Proc. R. Soc. B, 105, 375, 1929. Wiggins, Ph.M., Role of water in some biological processes, Microbiol. Rev., 54, 432, 1990. Wolf, W., Spiess, W.E.L., and Jung, G., Sorption Isotherms and Water Activity of Food Materials, Science and Technology Publishers, Hornchurch, Essex, England, 1985.

4

Mineral Components Michal Nabrzyski

CONTENTS 4.1 4.2

Contents and Role of Minerals in Foods ......................................................51 Interaction with Dietary Components............................................................54 4.2.1 Effect on Absorption ..........................................................................54 4.2.2 Building Body Tissue and Regulating Body Processes ....................57 4.3 Role in Food Processes..................................................................................57 4.3.1 Effect on Oxidation............................................................................57 4.3.2 Effect on Rheological Properties .......................................................67 4.3.3 Other Effects ......................................................................................68 4.4 Effect of Storage and Processing on the Mineral Components in Foods ....68 4.5 Chemical Nature of Toxicity of Some Mineral Food Components..............70 4.5.1 Introduction ........................................................................................70 4.5.2 Arsenic ...............................................................................................70 4.5.3 Mercury ..............................................................................................71 4.5.4 Cadmium ............................................................................................72 4.5.5 Lead ....................................................................................................74 4.5.6 Interactions of Elements ....................................................................77 References................................................................................................................77

4.1 CONTENTS AND ROLE OF MINERALS IN FOODS Minerals represent from 0.2–0.3% of the total intake of all nutrients in the diet. They are so potent and so important that without them the organism would not be able to utilize the remaining 99.7% of the food. The main mass of these minerals constitutes the macroelements; the trace elements constitute only a hundredth of a percent of the total mass of daily eaten nutrients. Foods that are good sources of minerals are given in Table 4.1. Dietary minerals are necessary for maintenance of normal cellular metabolism and tissue function. These nutrients participate in a multitude of biochemical and physiological processes important for health. Because of their broad biochemical activity, many of these compounds are intentionally used as functional agents in a variety of foods. On the other hand, some cations may induce a diversity of undesirable effects that influence the nutritional quality of foods.

1-5871-6149-4/02/$0.00+$1.50 © 2002 by CRC Press LLC

51

52

Chemical and Functional Properties of Food Components

TABLE 4.1 Contents of Selected Minerals in Some Foods Mineral Calcium

Potassium

Magnesium

Zinc

Iron

Food Swiss cheese, low sodium Sardines in tomato sauce Cod in tomato sauce Yogurt, natural Milk Orange Carrot Tuna in own sauce Potato Wheat seeds Porcine liver Beef Oat, flaked Carrot Pork Orange Milk Wheat meal (550) Cheese (45% fat) Sardine in tomato sauce Tuna in own sauce Yogurt, natural Milk Oyster Peas, yellow dried Oats, flaked Liver chicken a. pig Egg (yolk) Beef Whole milk powder Hard cheese Wheat meal Fish Bee honey Porcine liver Egg (yolk) Oat, flaked Wheat seeds Pork Beef Wheat meal (550) Egg (white)

Amount (mg/100 g) 960 437* 335* 189* 120* 42 41 25* 10 502 350 342 335 290 260 177 157 126 107 27* 24* 12* 9* up to 100 4.2 3.1 3.6; 4.5 3.6 3.8 3.1 2.4 0.6 0.4–1.2 0.08–1 22 7.2 4.6 3.3 2.3 2.6 1.1 0.2

Reference Feltman, 1990

Wojnowski, 1994 Wojnowski, 1994 Wojnowski, Wojnowski, Wojnowski, Wojnowski, Wojnowski, Wojnowski, Wojnowski, Wojnowski, Wojnowski, Wojnowski, Wojnowski,

1994 1994 1994 1994 1994 1994 1994 1994 1994 1994 1994

Lopez et al., 1983 Marzec et al., 1992 Marzec et al., 1992 Marzec et al., 1992 Marzec et al., 1992 Marzec et al., 1992 Marzec et al., 1992 Marzec et al., 1992 Marzec et al., 1992 Marzec et al., 1992 Gajek et al., 1987 Wojnowski, 1994 Wojnowski, 1994 Wojnowski, 1994 Wojnowski, 1994 Wojnowski, 1994 Wojnowski, 1994 Wojnowski, 1994 Wojnowski, 1994

Mineral Components

53

TABLE 4.1 (CONTINUED) Contents of Selected Minerals in Some Foods Mineral Copper

Food Oysters Liver, calf Liver, beef Wheat germ

Chromium

Fluoride

Iodide

Selenium

Amount (mg/100 g) 6; 17 7 3 0.9; 2

Sunflower seeds Tuna Salmon Ham

2 0.5 0.2 0.03; 0.08

Spices Cacao Paprika, pepper, curry Hawthorn Cheese, drowned Whole-meal bread Beef Kidney, liver Black teas

>0.1–0.5 0.2 ~0.05 0.025 >0.01 ~0.02 <0.004 <0.0015 3–34

Fish, canned Shellfish Marine fish, oyster, shrimp, lobster Milk powder

0.09–0.8 0.03–0.15 0.02–0.1 0.06

Tortilla chips Potato chips Pork kidney, braised Tuna, canned Salmon, canned Milk

1.0 0.97 0.21 0.12 0.08 0.002

Reference Lopez et al., 1983; Williams, 1982 Williams, 1982 Williams, 1982 Marzec et al., 1992; Williams, 1982 Williams, 1982 Williams, 1982 Williams, 1982 Marzec et al., 1992; Williams, 1982 Wilpinger et al., 1995 Wilpinger et al., 1995 Wilpinger et al., 1995 Wilpinger et al., 1995 Wilpinger et al., 1995 Wilpinger et al., 1995 Wilpinger et al., 1995 Wilpinger et al., 1995 Nabrzyski and Gajewska, 1995 WHO, 1984 WHO, 1984 Causeret, 1962 Paslawska and Nabrzyski, 1975 Feltman, 1990 Feltman, 1990 Feltman, 1990 Feltman, 1990 Feltman, 1990 Feltman, 1990

Note: * = author’s unpublished data. Source: From Causeret, J., in Fish as Food, Academic Press, New York, 1962, 205; Feltman, J., in Prevention’s Giant Book of Health Facts, Rodale Press, Emmaus, PA, 1990; Gajek, O.M. et al., Roczniki PZH, 38, 14, 1987; Lopez, A. et al., J. Food Sci., 48, 1680 and 1961, 1983; Marzec, Z. et al., in Tables of Trace Elements in Food Products, National Food and Nutrition Institute, Warsaw, 1992; Nabrzyski, M. and Gajewska, R., Z. Lebensm. Unters. Forsch., 201, 307, 1995; Paslawska, S. and Nabrzyski, M., Bromat. Chem. Toxicol., 8, 73, 1975; WHO, in Fluorine and Fluorides, WHO, Geneva, 1984; Williams, D.M., in Clinical Biochemical and Nutritional Aspects of Trace Elements, Alan R. Liss, Inc., New York, 1982; Wilpinger, M. et al., Z. Lebensm. Unters. Forsch., 201, 521, 1995; Wojnowski, W., in Chemiczne i funkcjonalne wlasciwosci skladników z˙ywnosci , Sikorski, Z.E., Ed., Wydawnictwa Naukowo-Techniczne, Warszawa, 1994.

54

Chemical and Functional Properties of Food Components

Minerals play an important role in plant life. They function as catalysts of biochemical reactions, are responsible for changes in the state of cellular colloids, directly affect the cell metabolism, and are involved in changes in protoplasm turgor and permeability. They often become the centers of electrical and radioactive phenomena in living organisms. Minerals are usually grouped in two categories: the macroelements required in our diets in amounts greater than 100 mg, and the microelements required in milligram quantities or less per day. The macroelements include calcium, magnesium, phosphorus, sodium, potassium, sulfur, and chlorine. The microelements are comprised of iron, zinc, copper, manganese, iodine, cobalt, nickel, molybdenum, chromium, fluorine, selenium, vanadium, boron, silicon, and a few others of which their biological functions have not yet been fully recognized. Actually, mineral deficiency states are more likely to occur than vitamin insufficiency states. At increased risk of mineral deficiencies are people who eat low-calorie diets, the elderly, pregnant women, people using certain drugs such as diuretics, vegetarians, and those living in areas where soils are deficient in certain minerals. There is increasing evidence that those humans whose nutritional status is suboptimal in certain trace elements, such as selenium, may be at greater risk for certain forms of cancer and heart disease. Suboptimal intake can be due to soil depletion, the effects of acid rain, and the overrefining, overprocessing of foods and other factors. Minerals occur in foods in many chemical forms. They are absorbed from the intestines as simple cations, as part of an anionic group, or in covalent or noncovalent associations with organic molecules. The chemical form of minerals in foods strongly influences their intestinal handling and biological availability. Thus, the iron in the form of hemoglobin in meats is more bioavailable than inorganic iron. This may also be true for selenium in selenomethionine and for the organic chelates of dietary chromium and zinc. Factors that affect mineral solubility or their reduction to a suitable form for cellular uptake, or those that influence the transfer through the mucosa or transport into circulation, govern the rate and efficiency of uptake of the minerals. For example, iron and zinc are much more bioavailable from human breast milk than from cow’s milk or comparable infant formula. The intrinsic molecular associations of these minerals with low-molecular-weight binding compounds in human mammary secretions is thought to convey this enhanced absorbability (Rosenberg and Solmons, 1984). Some minerals can produce chronic toxicity when absorbed and retained in excess of the body’s demands. Homeostatic mechanisms, often hormonally mediated, regulate the absorption of certain minerals and thereby protect against excessive accumulation. Recently developed speciation analysis makes it possible to determine the forms of minerals that are present in food and the environment, and may cause specific physiological or pharmacological effects in organisms.

4.2 INTERACTION WITH DIETARY COMPONENTS 4.2.1 EFFECT

ON

ABSORPTION

Various nutritional and nonnutritional components of the diet, other nutrients in vitamin–mineral supplements, or assorted medications can interact with minerals in

Mineral Components

55

the gastrointestinal tract and influence their absorption. For example, amino acids may perform as intraluminar binders for some trace minerals. Large, complex, and poorly digestible proteins, on the other hand, may bind minerals tightly and diminish their absorption. Triacylglycerols and long-chain fatty acids derived from triacylglycerols may form soaps with calcium and magnesium and decrease the bioavailability of these two nutrients. Lactose has been implicated in the enhanced absorption of calcium from milk. Pectins, cellulose, hemicellulose, and polymers produced by the Maillard reaction during cooking, processing, or storage may bind minerals in the lumen and thus reduce their biological availability. Interaction between and among minerals, or with anionic species, are important determinants of mineral absorption. Absorption of iron is hindered by fiber and phosphates and promoted by ascorbic acid, copper, and meat protein. Ascorbic acid also enhances absorption of selenium, but reduces the absorption of copper. A high protein intake appears to increase the excretion of calcium, whereas vitamin D ingestion promotes the retention of calcium. Intestinal parasites, dietary fiber phytates, and excessive sweating interfere with zinc absorption. Phytates, oxalates, and tannates can interfere with the absorption of a number of minerals. Certain medications such as tetracycline can also inhibit absorption of minerals, while others such as didoquin or dilatin may actually promote uptake of certain minerals. Apparently, chemically similar minerals share certain “channels” for absorption, and the simultaneous ingestion of two or more such minerals will result in competition for absorption. When unphysiological imbalances among competitive nutrients exist as the result of leaching from water pipes, storage in unlacquered tin cans, or improper formulation of vitamin–mineral supplements, nutritionally important consequences of this mineral–mineral interaction can result. Finally, to participate in a nutritionally relevant process for the organism as a whole, a mineral must be transported away from the intestine. The concentration of circulating binding proteins and the degree of saturation of their metallic binding sites may influence the rate and magnitude of transport of recently absorbed minerals (Rosenberg and Solomons, 1984). Minerals require a suitable mucosal surface across which to enter the body. Resection or diversion of a large portion of small bowel obviously affects mineral absorption. Extensive mucosal damage due to mesenteric infarction or inflamatory bowel disease or major diversion by jejunoileal bypass procedures reduces the available surface area. Minerals whose absorption occurs primarily in the proximal intestine, e.g., copper or iron, are affected differently than those absorbed more distally, e.g., zinc. In addition, the integrity of the epithelium, the uptake of fluids and electrolytes, the intracellular protein synthesis, the energy-dependent pumps, and the hormone receptors must be intact. Intrinsic diseases of the small intestinal mucosa may impair mineral absorption. Such conditions as celiac sprue, dermatitis herpetiformis, infiltrative lymphomas, and occasionally inflammatory bowel disease produce diffuse mucosal damage. Protein energy malnutrition causes similar damage, and tropical enteropathy affects part of the population of developing countries living under adverse nutritional and hygienic conditions.

56

Chemical and Functional Properties of Food Components

TABLE 4.2 Mean Daily Intake, RDA or SAI, and Absorption Percentage of Minerals from the Gastrointestinal Tract Milligram per Adult Mineral

RDAa or SAIb

Daily intake

Calcium Chloride Magnesium Phosphorus Potassium Sodium

960–1220 1700–5100 145–358 1670–2130 3300 3000–7000

Macroelements 800–1200 a 750b 280–350b 800–1200 a 2000b 500b

Chromium

<0.15

Microelements 0.05–0.20b

Cobalt Copper Fluorine Iodine Iron Manganese Molybdenum Nickel Selenium Vanadium Zinc

Boron Silicon c d

0.003–0.012 2.4 <1.4 <1.0 15 5.6; 8 >0.15 0.16–0.20 0.06–0.22 0.012–0.030 12; 18

0.002a,d 1.5–3.0b 1.5–4b 0.15a 10–15a 2–3b 0.075–0.250b 0.05; 0.3 0.055–0.070 0.01–0.025 12–15a

Microelements Recently Considered Essential 1–3 1–2 21–46; 200 21–46

Percentage of Absorption

10–50 Highc 20–60 Highc Highc Highc

<1 or 10–25 in form of GTF* 30–50 25–60 Highc 100 10–40 40 70–90 <10 ~70 <1 30–70

Highc 3; 40

more than 40% 0.002 mg of cobalt containing vitamin B12.

As can be seen from above, the absorption of most metals from the gastrointestinal tract is variable (Table 4.2) and depends on many external and internal factors. Thus the quantity of metal ingested rarely reflects that which is bioavailable. In fact, under most circumstances, only a small fraction of ingested metals is absorbed, while the great majority passes out of the gut in the feces. The Recommended Dietary Allowance (RDA) represents standards of nutrition set by the Food and Nutrition Board of the U.S. National Academy of Sciences (Feltman, 1990). It contains the levels of essential nutrients that are adequate to meet the nutritional needs of the normal, healthy population. Individuals may differ in their precise nutritional requirements. To take these differences into account, the

Mineral Components

57

RDA provides a “margin of safety,” i.e., it sets the allowances high enough to cover the needs of most healthy people. For additional nutrients that are necessary to keep the body healthy for which the RDA has not yet been established, a “safe and adequate daily intake” (SAI) is estimated. The functions of minerals in the body involve building tissue and regulating numerous body processes. Their role in the human body is summarized in Table 4.3.

4.2.2 BUILDING BODY TISSUE

AND

REGULATING BODY PROCESSES

Certain minerals, including calcium, phosphorus, magnesium, and fluorine, are components of bone and teeth. Deficiencies during the growing years cause growth to be stunted and bone tissue to be of poor quality. A continual adequate intake of minerals is essential for the maintenance of skeletal tissue in adulthood. Potassium, sulfur, phosphorus, iron, and many other minerals are also structural components of soft tissue (Solomons, 1984; Eschleman, 1984). Minerals are an integral part of many hormones, enzymes, and other compounds that regulate biochemical functions in the organism. For example, iodine is required to produce the hormone thyroxine, chromium is involved in the production of insulin, and hemoglobin is an iron-containing compound. Thus the production of these substances in the organism depends on adequate intake of the involved minerals. Minerals can also act as catalysts. Calcium is a catalyst in blood clotting. Some minerals are catalysts in the absorption of nutrients from the gastrointestinal tract in the metabolism of proteins, fat, and carbohydrates, and in the utilization of nutrients by the cell. Minerals dissolved in the body fluids are responsible for nerve impulses and the contraction of muscles, as well as for water- and acid-base balance. They play an important role in maintaining the respiration, heart rate, and blood pressure in normal limits. Deficiency of minerals in the diet may lead to severe, chronic clinical signs of diseases, frequently reversible after their supplementation in the diet, or following the total parenteral nutrition. Their influence on biochemical reactions in living systems also makes it possible to use them intentionally in many food processes.

4.3 ROLE IN FOOD PROCESSES 4.3.1 EFFECT

ON

OXIDATION

Because minerals are an integral part of many enzymes, they play an important role in food processing, e.g., in alcoholic and lactic fermentation, meat aging, and dairy food production. Many compounds used as food additives or for rheological modification of some foods contain metallic cations in their structure. A number of these compounds function as antimicrobials, sequestrants, antioxidants, flavor enhancers, and buffering agents, and sometimes even as dietary supplements (Table 4.4). Some heavy metal ions actively catalyze lipid oxidation. Their presence even in trace amounts has long been recognized as potentially detrimental to the shelf life of fats, oils, and fatty foods. They can activate molecular oxygen by producing superoxide, which then, through dismutation and other steps of biochemical changes, turns

58

Chemical and Functional Properties of Food Components

TABLE 4.3 Biological Role of Some Minerals Mineral

Calcium

Magnesium

Phosphorus

Potassium

Sodium

Chromium

Function

Deficiency

Macroelements Bone and tooth formation; Stunted growth; rickets; blood clotting, cell osteomalacia; permeability; nerve osteoporosis; tetany stimulation; muscle contraction; enzyme activation Component of bones and Seen in alcoholism or renal teeth; activation of many disease; tremors leading enzymes; nerve to conclusive seizures stimulation; muscle Stunted growth; rickets contraction Bone and tooth formation; energy metabolism component of ATP and ADP; protein synthesis component of DNA and RNA; fat transport; acidbased balance; enzyme formation Osmotic pressure; water Nausea; vomiting; balance; acid-based muscular weakness; rapid balance; nerve heart beat; heart failure stimulation; muscle contraction, synthesis of protein; glycogen formation Osmotic pressure; water Rare: nausea, vomiting, balance; acid-based giddiness, exhaustion, balance; nerve cramps stimulation; muscle contraction; cell permeability

Sources

Milk, hard cheese, salmon and small fish eaten with bones, some dark green vegetables, legumes

Green leafy vegetables, nuts, whole grains, meat, milk, seafood

Milk, meat, poultry, fish, eggs, cheese, nuts, legumes, whole grains

Meats, fish, poultry, whole grains, fruits, vegetables, legumes

Table salt, salted foods, MSG and other sodium, additives, milk, meat, fish, poultry, eggs, bread

Microelements Trivalent chromium Impaired growth; glucose Whole-grain cereals, increases glucose intolerance; elevated condiments, meat tolerance and plays role blood cholesterol products, cheese, in lipid metabolism; brewer,s yeast useful in prevention and treatment of diabetes; hexavalent chromium is toxic

Mineral Components

59

TABLE 4.3 (CONTINUED) Biological Role of Some Minerals Mineral

Function

Deficiency

Organ meats (liver, Rarely observed, but if exists, pernicious anemia kidney), fish, dairy products, eggs with hematological and neurologic manifestations may be observed due to vitamin B12 deficiency Anemia, neutropenia, Liver, kidney, oysters, leucopenia, skeletal nuts, fruits, dried legumes demineralization .

Cobalt

Cofactor of vitamin B12; plays role in immunity

Copper

Necessary for iron utilization and hemoglobin formation; constituent of cytochrome oxidase; involved in bone and elastic tissue development Hemoglobin and Anemia; decrease in myoglobin formation; oxygen transport and essential component of cellular immunity; many enzymes muscle weakness Cofactor of large number In animals: of enzymes; in aging chondrodystrophy, process has a role as an abnormal bone antioxidant (Mndevelopment, superoxide dismutase); reproductive difficulties; important for normal in humans: shortage of brain function, evidence reproduction, and bone structure Cofactor of enzymes Reduces conversion of xantine and aldehyde hypoxantine and xantine oxidase; copper to uric acid, resulting in antagonist development of xantine renal calculi; deficiency state may be potentiated by high copper intake Constituent of many Delayed wound healing; enzyme systems; carbon impaired taste sensitivity; dioxide transport; retarded growth and vitamin A utilization sexual development; dwarfism Resistance to dental decay Tooth decay in young children

Iron

Manganese

Molybdenum

Zinc

Fluoride

Sources

Liver, lean meats, legumes, dried fruits, green leafy vegetables, whole grain, fortified cereals Tea, whole grain, nuts moderate levels: fruits, green vegetables; organ meat and shellfish contain very absorbable manganese

Grain, legumes

Oysters, fish, meat, liver, milk, whole grains, nuts, legumes

Drinking water rich in fluoride; seafood; teas

60

Chemical and Functional Properties of Food Components

TABLE 4.3 (CONTINUED) Biological Role of Some Minerals Mineral

Function

Deficiency

Sources

Iodine

Synthesis of thyroid Goiter; cretinism, if Iodized salt, seafood, food hormones that regulate deficiency is severe grown near the sea basal metabolic rate Selenium Protects against number of Cataract; muscular Broccoli, mushrooms, cancers dystrophy; growth radishes, cabbage, celery, depression; liver onion, fish, organ meats cirrhosis; infertility; cancer; aging due to deficiency of selenoglutathione peroxidase; insufficiency of cellular immunity Boron Prevents osteoporosis in Probably impairs growth Foods of plant origin and (recently considered postmenopausal women; and development vegetables essential; still has beneficial in treatment of to be proven) arthritis; builds muscle Source: Eschleman, M.M., in Introductory Nutriton and Diet Therapy, Lippincott J.B. Co., London, 1984; Hendler S.S., in The Doctor’s Vitamin and Mineral Encylopedia, Simon and Schuster, New York, 1990.

into hydroxyl free radicals. Three cations are involved in the activity of superoxide dismutase (SOD). This enzyme has been patented as an antioxidant agent for foods. Three types of metalloenzymes of SOD exist in living organisms: Cu Zn-SOD, Fe-SOD, and Mn-SOD. All three types of SOD catalyze dismutation of superoxide anions to produce hydrogen peroxide in vivo. There is evidence of increased lipid oxidation in apple fruit during senescence. SOD activity may also be involved in reactions induced by oxygen, free radicals, and ionizing radiation and could help to protect cells from damage by peroxidation products (Du and Bramlage, 1994). Besides SOD, catalase, ceruloplasmin, albumin, appotransferrin, and chelating agents (e.g., ethylenediaminetetraacetic acid (EDTA), bathocupreine, cysteine, and purine) are capable of inhibiting the oxidation of ascorbic acid induced by trace metals. Copper-induced lipid oxidation in ascorbic acid-pretreated cooked ground fish may be inhibited in the presence of natural polyphenolic compounds, the flavonoids, which are effective antioxidants, and prevent the production of free radicals (Ramanathan and Das, 1993). In the presence of ADP-chelated iron and traces of copper, oxygen radicals are generated in the sarcoplasmic reticulum of muscle food. Muscle contains notable amounts of iron, a known prooxidant, and trace amounts of copper, also a catalyzing peroxidative reaction (Hultin, 1994; Wu and Brewer, 1994). Iron occurs associated with heme compounds and as nonheme iron complexed to proteins of low molecular weight. Reactive nonheme iron can be obtained by release of iron from hem pigments or from the iron storage protein, ferritin. Iron is

Mineral Components

61

TABLE 4.4 Selected Mineral Compounds Used as Food Additives Chemical Name of Compound and (INS)

Synonyms or Other Chemical Name

Calcium alginate (404)

Calcium alginate

Calcium (302) Calcium (213) Calcium (509) Calcium

Calcium ascorbate dihydrate Monocalcium benzoate Calcium chloride

ascorbate benzoate chloride citrate (333)

Calcium dihydrogen phosphate (341i)

Calcium disodium ethylenediaminetetra acetace (385) Calcium glutamate (623) Calcium hydroxide (526) Calcium hydrogen carbonate (170ii) Calcium lactate (327)

Tricalcium citrate; tricalcium salt of beta hydroxytricarballyl ic acid Calcium dihydrogen tetraoxophosphate; monobasic calcium phosphate; monocalcium phosphate Calcium disodium EDTA Monocalcium DI-Lglutamate Slaked lime Calcium hydrogen carbonate

Calcium sorbate (203)

Calcium dilactate hydrate Calcium sorbate

Magnesium chloride (511) Magnesium carbonate (504i)

Magnesium chloride hexahydrate Magnesium carbonate

Functional Class and Comments

ADI, TADI, PMTDI, (mg/kg of body weight)

Thickening agent; stabilizer Antioxidant

ADI “not specified”

Antimicrobial agent; preservative Firming agent

ADI 0–5.0

Acidity regulator; firming agent; sequestrant

ADI “not specified”

Buffer, firming, raising, leavening and texturing agent; used in fermentation processes

MTDI 70.0

Antioxidant; preservative; sequestrant Flavor enhancer; salt substitute Neutralizing agent; buffer; firming agent Surface colorant; anticaking agent; stabilizer Buffer; dough conditioner Antimicrobial, fungistatic, preservative agent

ADI 0–2.5

Firming, color retention agent Anticaking and antibleaching agent

ADI “not specified”

ADI “not specified”

ADI “not specified” ADI “not limited” ADI “not specified”

ADI 0–25.0 (as sum of calcium, potassium, and sodium salt) ADI “not specified” ADI 0–50.0 continued

62

Chemical and Functional Properties of Food Components

TABLE 4.4 (CONTINUED) Selected Mineral Compounds Used as Food Additives Chemical Name of Compound and (INS)

Synonyms or Other Chemical Name

Functional Class and Comments

Magnesium gluconate (580) Magnesium glutamate DI-L- (625)

Magnesium gluconate dihydrate Magnesium glutamate

Buffer; firming agent in yeast food Flavor enhancer; salt substitute

Magnesium hydrogen phosphate (343ii)

Magnesium hydrogen ortophosphate trihydrate; dimagnesium phosphate Magnesium hydroxide Magnesium carbonate hydroxide hydrated Magnesium DI-D,Llactate

Dietary supplement

Magnesium hydroxide (528) Magnesium hydroxide carbonate (504ii)

ADI, TADI, PMTDI, (mg/kg of body weight) ADI “not specified” ADI “not specified” (group ADI for α glutamic acid and its monosodium, potassium, calcium, magnesium, and ammonium salts) MTDI 70 (expressed as phosphorus from all sources)

Alkali; color adjunct

ADI “not limited”

Alkali; anticaking, color retention and drying agent Buffering agent; dough conditioner; dietary supplement Anticaking and neutralizing agent Firming agent

ADI “not specified”

Potassium acetate

Antimicrobial agent; preservative; buffer

Potassium alginate (402)

Potassium alginate

Thickening agent; stabilizer

Potassium aluminosilicate (555) Potassium ascorbate (303) Potassium benzoate (212)

Potassium aluminosilicate Potassium ascorbate

Anticaking agent

ADI “not specified” (also includes the free acid) ADI “not specified” (group ADI for alginic acid and its ammonium, calcium, and sodium salts) No ADI allocated

Antioxidant

ADI “not specified”

Potassium benzoate

Antimicrobial agent; preservative

ADI 0–5,0 (expressed as benzoic acid)

Magnesium lactate D,L- (also magnesium lactate L) (329) Magnesium oxide (530) Magnesium sulfate (518) Potassium acetate (261)

Magnesium oxide Magnesium sulfate

ADI “not limited”

ADI “not limited” ADI “not specified”

Mineral Components

63

TABLE 4.4 (CONTINUED) Selected Mineral Compounds Used as Food Additives Chemical Name of Compound and (INS)

Synonyms or Other Chemical Name

Functional Class and Comments

ADI, TADI, PMTDI, (mg/kg of body weight)

Potassium bromate (924a) Potassium carbonate (501i) Potassium chloride (508)

Potassium bromate

Oxidizing agent

ADI withdrawn

Potassium carbonate

Alkali; flavor

ADI “not specified”

Potassium chloride, sylvine, sylvite

Seasoning and gelling agent; salt substitute

ADI “not specified”

Potassium or sodium copper chlorophyllin (141ii) Potassium dihydrogen phosphate (340i)

Potassium or sodium chlorophyllin

Color of porphyrin

ADI 0–15

Buffer; sequestrant; neutralizing agent

MTDI 70.0

Potassium hydrogen carbonate (501ii) Potassium hydrogen sulfite (228)

Monopotassium dihydrogen ortophosphate; monobasic potassium phosphate Potassium bicarbonate Potassium hydrogen sulfite

Alkali; leavening agent; buffer Preservative; antioxidant

ADI “not specified”

Potassium glutamate (622) Sodium alginate (401)

L-Monopotassium L-glutamate Sodium alginate

Sodium aluminium phosphate acidic (541i)

Salp. Sodium trialuminium tetradecahydrogen; octaphosphate tetrahydrate (A);

Flavor enhancer; salt substitute Thickening agent; stabilizer Raising agent

ADI 0–0.7 (group ADI for sulfur dioxide and sulfites; expressed as sulfur dioxide, covering sodium, and potassium metabisulfite, potassium and sodium hydrogen sulfite, and sodium thiosulfate) ADI “not specified” ADI “not specified” ADI 0–0.6

continued

64

Chemical and Functional Properties of Food Components

TABLE 4.4 (CONTINUED) Selected Mineral Compounds Used as Food Additives Chemical Name of Compound and (INS)

Sodium aluminium phosphate basic (541ii)

Sodium ascorbate (301) Sodium benzoate (211) Sodium dihydrogen phosphate (339i)

Disodium ethylenediaminetetra acetate (386) Sodium glutamate (621)

Sodium iron III–ethylenediamine tetraacetatetrihydrate

Synonyms or Other Chemical Name trisodium dialuminium pentade cahydrogen octaphosphate (B) Kasal. Autogenous mixture of an alkaline sodium aluminum phosphate Sodium L-ascorbate Sodium salt of benzenecarboxylic acid Monosodium dihydrogen monophosphate (ortophosphate) Disodium EDTA Disodium edeteate Monosodium Lglutamate (MSG); glutamic acid monosodium salt monohydrate Ferric sodium edeteate; sodium iron EDTA; sodium feredetate

Sodium or potassium metabisulfite (223, 224)

Disodium or potassium pentaoxodisulfate

Sodium nitrite (250)

Sodium nitrite

Sodium nitrate (251)

Sodium nitrate; cubic or soda niter; chile salpeter

Functional Class and Comments

ADI, TADI, PMTDI, (mg/kg of body weight)

Emulsifier

ADI 0–0.6

Antioxidant

ADI “not specified”

Antimicrobial, preservative

ADI 0–5.0

Buffer; neutralizing agent; sequestrant in cheese, milk, fish, and meat products Antioxidant; sequestrant, preservative, synergist Flavor enhancer

MTDI 70.0

Nutrient supplement (provisionally considered to be safe in food fortification programs) Antimicrobial; preservative; bleaching agent; antibrowning agent

ADI acceptable

Antimicrobial; color fixative Antimicrobial; color fixative

ADI 0–2.5 (as calcium disodium EDTA) ADI “not specified”

ADI 0–0.7 (group ADI for sulfur dioxide and sulfites expressed as SO2, covering sodium and potassium salt) ADI 0–0.1 ADI 0–5.0

Mineral Components

65

TABLE 4.4 (CONTINUED) Selected Mineral Compounds Used as Food Additives Chemical Name of Compound and (INS) Sodium phosphate (339iii)

Sodium or potassium sorbate (201, 202)

Synonyms or Other Chemical Name Trisodium phosphate; trisodium monophosphate; ortophosphate; sodium phosphate; Sodium or potassium sorbate

Functional Class and Comments

ADI, TADI, PMTDI, (mg/kg of body weight)

Sequestrant; emulsion stabilizer; buffer

MTDI 70.0

Antimicrobial; fungistatic agent

ADI 0–25.0

Notes: INS = international numbering system; prepared by the Codex Committee for Food Additives for the purpose of providing an agreed upon international numerical system for identifying food additives in an ingredient list as an alternative to the declaration of the specific name (Codex Alimentarius, 2nd ed., Vol. 1, Sec. 5.1, 1992). ADI = acceptable daily intake; estimate of the amount of a substance in food or drinking water, expressed on a body weight basis, for a standard human weight of 60 kg, that can be ingested daily over a lifetime without appreciable risk for health. ADI “not specified” and ADI “not limited” are terms applicable to a food substance of very low toxicity that, on the basis of the available data — chemical, biochemical, toxicological, and other, as well as total dietary intake of the substance, arising from its use at levels to achieve the desired effect and from its acceptable background in food — does not, in the opinion of JECFA, represent a hazard to health. For this reason and those stated in individual evaluations, the establishment of ADI in numerical form is not deemed necessary. An additive meeting this criterion must be used within the bound of good manufacturing practice, i.e., it should be technologically efficacious and should be used at the lowest level necessary to achieve this effect; it should not conceal inferior food quality or adulteration, and it should not create a nutritional imbalance. TADI = temporary ADI; term established by JECFA for a substance for which toxicological data are sufficient to conclude that use of the substance is safe over a relatively short period of time during which the substance can be evaluated for further safety data, but are insufficient to conclude that use of the substance is safe over a lifetime. A higher-than-normal safety factor is used when establishing a TADI, and an expiration date is established by which time appropriate data to resolve the safety issue should be submitted to JECFA. MTDI = maximum tolerable daily intake, or provisional maximum tolerable daily intake (PMTDI); a term used for description of the end point of contaminants with no cumulative properties. Its value represents permissible human exposure as a result of the natural occurrence of the substance in food or drinking water. In the case of trace elements that are both essential nutrients and unavoidable constituents of food, a range is expressed, the lower value representing the level of essentiality and the upper value the PMTDI. Source: FAO/WHO Ed., Summary of Evaluations Performed by the Joint FAO/WHO Expert Committee on Food Additives 1956–1993, ILS Inst., Geneva, 1994; WHO, 44th Meeting of the Joint FAO/WHO Expert Committee on Food Additives, Geneva, 1996.

66

Chemical and Functional Properties of Food Components

part of the active site of lipoxygenase, which may participate in lipid oxidaton. Reducing components of the tissue-like superoxide anion, ascorbate, and thiols can convert the inactive ferric iron to active ferrous iron. There are also enzymic systems that use reducing equivalents from NADPH to reduce ferric iron. A number of cellular components are capable of reducing ferric to ferrous iron, but under most conditions the two major reductants are superoxide and ascorbate (Hultin, 1994). In some cases reduction of ferric iron can be accomplished by enzymically utilizing electrons from NADH and, to a lesser extent, NADPH through an enzymic system associated with both the sarcoplasmic reticulum and mitochondria. Ferrous iron can activate molecular oxygen by producing superoxide. Superoxide may then undergo dismutation spontaneously or by the action of SOD and produce the hydrogen peroxide that can interact with another atom of ferrous iron to produce the hydroxyl radical. The hydroxyl radical can initiate lipid oxidation. It is generally accepted that ferrous iron is the reactive form of iron in oxidation reaction. Since it is likely that most iron ordinarily exists in the cell as ferric iron, the ability to reduce ferric to ferrous iron is critical. Development of rancidity and warmed-over flavor, a specific defect that occurs in cooked and reheated meat products following short-term refrigated storage, has been directly linked to autooxidation of highly unsaturated, membrane-bound phospholipids and to the catalytic properties of nonheme iron (Oelinngrath and Slinde, 1988; Pearson et al., 1977; Hultin, 1994). Dietary iron may influence muscle iron stores and thus theoretically may also affect the lipid oxidation in muscle food, e.g., pork. There appears to be a threshold for dietary iron level (between 130 and 210 ppm) above which muscle and liver nonheme iron and total iron, and muscle thiobarbituric acid reactive substances begin to increase because of porcine muscle lipid oxidation (Miller et al., 1994a, 1994b). The secondary oxidation products, mainly aldehydes, are the major contributors to warmed-over flavor and meat flavor deterioraton, because of their high reactivity and low flavor thresholds. Ketones and alcohols have a high flavor threshold, thus causing off-flavors less often. Exogenous antioxidants can preserve the quality of meat products. Radical scavengers appear to be the most effective inhibitors of meat flavor deterioration. However, different substrates and systems respond in different ways. Active ferrous iron may be eliminated physically by chelation with EDTA or phosphates, or chemically by oxidation to its inactive ferric form. Ferroxidases are enzymes that oxidize ferrous to ferric iron in the presence of oxygen according to the formula: 4Fe2+ + O2 + 4H+ → 4Fe3+ + 2H2O Ceruloplasmin, a copper protein of blood serum, is a ferroxidase. Oxidation of ferrous to ferric iron tends to be favored in extracellular fluids, while chelation is more likely intracellular (Hultin, 1994). Sodium chloride has long been used for food preservation. Salt alters both the aroma and the taste of food. Addition of sodium chloride to blended cod muscle accelerates the development of rancidity (Castell et al., 1965; Castell and Spears,

Mineral Components

67

1968). This salt-induced rancidity is inhibited by chelating agents such as EDTA, sodium oxalate, and sodium citrate and by nordihydroguaiaretic acid and propyl gallate. Although sodium chloride and other metal salts act as prooxidants, they have a strong inhibiting effect on Cu2+-induced rancidity in the fish muscle. The most effective concentration of NaCl for this antioxidant effect is between 1 and 8% (Castell et al., 1965; Castell and Spears, 1968). Castell and Spears (1968) also showed that the other heavy metal ions were effective in producing rancidity when added to various fish muscles. The relative effectiveness was of the following decreasing order: Fe2+ > V2+ > Cu2+ > Fe3+ > Cd2+ > Co2+ > Zn2+, while Ni,2+ Ce2+, Cr3+, and Mn2+ had no effect in the used concentrations. Of those tested, Fe2+,V2+, and Cu2+ were by far the most active catalysts. There were, however, important exceptions. The comparative effectiveness of the metal ions was not the same for muscles taken from all the species tested. EDTA is reported to be effective as the metal ions sequester and is approved for use in the food industry as a stabilizer and antioxidant. It acts also as an inhibitor of Staphylococcus aureus by forming stable chelates in the media with multivalent cations that are essential for cell growth. The effect is largely bacteriostatic and easily reversed by releasing the complexed cations with other cations for which EDTA has higher affinity (Kraniak and Shelef, 1988). The addition of phosphate — pyro-, tripoly-, and hexametaphosphate — also protects cooked meat from auto-oxidation. Ortophosphate gives no protection. The mechanism by which phosphates prevent autooxidation appears to be related to their ability to sequester metal ions, particularly ferrous iron, which is the major prooxidant (Pearson et al., 1977). The addition of NaCl increases retention of moisture in meat and meat products.

4.3.2 EFFECT

ON

RHEOLOGICAL PROPERTIES

The interaction between metal ions and polysaccharides often affects the rheological and functional properties in food systems (Ha et al., 1989). In aqueous media, neutral polysaccharides have little affinity for alkali metal and alkali earth metal ions. On the other hand, anionic polysaccharides have a strong affinity for metal counterions. This association is related to the linear charge density of the polyanions. The linear charge density is expressed as the distance between the perpendicular projections of an adjacent charged group on the main axis of the molecule. The higher the linear charge density, the stronger the interaction of counterions with anionic groups of the molecule. Such anionic hydrocolloids (0.1% solutions) as alginate, karaya, arabic, and ghati have higher calcium-binding affinity (Ha et al., 1989). An important functional property of alginates is their capacity to form gels with calcium ions. This makes alginates extensively suited to prepare products such as fruit and meat analogs. They are also widely used in biotechnology as an immobilization agent of cells and enzymes. The method involves diffusion of calcium ions through alginate and a cross-linking reaction with the alginate carboxylic group to form the gel (Ha et al., 1989; WHO, 1993a, 1993b). Carrageenans are reported to stabilize casein and several plant proteins against precipitation with calcium and are used to prepare texturized milk products (Samant et al., 1993).

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4.3.3 OTHER EFFECTS Sodium reduction in the diet is recommended as a means of preventing hypertension and subsequent cardiovascular disease, stroke, and renal failure. Reducing or substituting NaCl requires an understanding of the effects caused by the new factors introduced. Several methods have been proposed for reducing the sodium content in processed meat without an adverse effect on the quality (flavor, gelation), or shelf life of the products. This includes a slight sodium chloride reduction, replacing some of the NaCl with other chloride salt (KCl or MgCl2) or nonchloride salt, or altering processing methods (Barbut and Mittal, 1985). Calcium ion is a known activator of many biochemical processes. The calciumactivated neutral protease (CANP) plays an important role in postmortem tenderizing of meat. The function of the metal ion in such an enzyme is believed to be either neutralization of the charges on the surface, by preventing electrostatic repulsion of subunits, or effecting of a conformational change required for association of the subunits. Thus the metal ions must be present in a specific state to perform this function. The metallic cation in solution exists as aqua complex ions in equilibrium with their respective hydroxy complex: M(H2O)m+ ⇔ MOH(m – 1)+ + H+ aqua hydroxy-complex complex ion (weak base) The acid ionization constant (pKa) of the aqua complex ion determines whether or not the ion would form complexes with a protein. This depends greatly on the pH of the medium. Since the ionization constant of low charge is 12.6, the ion would form a stable complex only with negatively charged protein in alkaline media. It cannot bind to cationic proteins because it does not share electrons to form a covalent bond. This consideration explains why the activity of Ca2+-activated protease is optimum in the alkaline pH range. Thus a decrease in its activity at acidic pH values may partly be due to a change in the electronic state of Ca2+ (Asghar and Bhatti, 1987; Barbut and Mittal, 1985). Generally, sodium and potassium react only to a limited extent with proteins, whereas calcium and magnesium are somewhat more reactive. Transition metals, e.g., ions of Cu, Fe, Hg, and Ag, react readily with proteins, many forming stable complexes with thiol groups. Calcium cations and ferrous, cupric, and magnesium cations may be integral parts of certain protein molecules or molecular associations. Their removal by dialysis or sequestration appreciably lowers the stability of the protein structure toward heat and proteases.

4.4 EFFECT OF STORAGE AND PROCESSING ON THE MINERAL COMPONENTS IN FOODS The effect of normal storage on mineral components is rather low and may be connected mainly with changes of humidity or contamination; however, high changes of mineral

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69

components may occur during canning, cooking, drying, freezing, peeling, and all the other steps involved in preserving, as well as in food processing, for direct consumption. The highest losses of minerals are encountered in the milling and polishing process of cereals and groats. All milled cereals undergo a significant reduction of nutrients. The extent of the loss is governed by the efficiency with which the endosperm of the seed is separated from the outer seed coat (bran) and the germ. The loss of certain minerals and vitamins is deemed so relevant to health that in many countries a supplementation procedure has been introduced for obtained food products to enrich them with the lost nutrients, e.g., iron to the bread. In some countries regulations have been issued for standards of identity for enriched bread. If bread is labeled “enriched,” it must meet these standards. In white flours, the losses of magnesium and manganese may reach up to 90%. These minerals remain mainly in the bran — the outer part of the cereals. For this reason, it seems reasonable to recommend consumption of bread baked from whole meals instead from white meals. Recommended, sometimes steady, consumption of bran alone, for dietary purpose, should be done with great care because it may also contain many different contaminants, such as toxic metals and organic pesticides. During preparation for cooking or canning, vegetables should be thoroughly washed before cutting to remove dirt and traces of insecticide spray. Root vegetables should be scrubbed. The dark outer leaves of greens are rich in iron, calcium, and vitamins, so they should be trimmed sparingly. Peeling vegetables and fruit should be avoided, whenever possible, because minerals and vitamins are frequently concentrated just beneath the skin. Potatoes should be baked or cooked in their skins, even for hashed browns or potato salad. However, True et al. (1979) showed that cooking potatoes by boiling whole or peeled tubers, as well as microwave cooking and oven baking, may have a negligible effect on the losses of Al, B, Ca, Na, K, Mg, P, Fe, Zn, Cu, Mn, Mo, J, and Se. Microwaved potatoes retain nutrients well, and contrary to popular belief, peeling potatoes does not strip away their vitamin C and minerals. Whenever practical, any remaining cooking liquid should be served with the vegetable or used in a sauce or gravy soup. To retain minerals in canned vegetables, one should pour the liquid from the can into a saucepan and heat at low temperature to reduce liquid; add vegetables to remaining liquid and heat before serving. Low temperatures reduce shrinkage and loss of many other nutrients. Cooking and blanching leads to the most important nutrient losses. In the liquid of cooked vegetables about 30–65% of potassium, 15–70% of magnesium and copper, and 20 to over 40% of zinc is leached. Thus it is reasonable to use this liquid for soup preparation (Rutkowska, 1975; Trzebska-Jeske et al., 1973). The losses depend on both the kind of vegetables cooked and the course of the applied process. Steam blanching generally results in smaller losses of nutrients, since leaching is minimized in this process. Frozen meat and vegetables thawed at ambient temperatures lose many nutrients, including minerals in the thaw drip. To avoid these nutrients losses, the drip should be added to the pot where the meal is prepared for consumption. Frozen fruits should be eaten without delay, fresh, just after thawing, together with the secreted juice. Foods blanched, cooked, or reheated in a microwave oven generally retain about the same or even higher amounts of nutrients as those cooked by conventional methods.

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Chemical and Functional Properties of Food Components

4.5 CHEMICAL NATURE OF TOXICITY OF SOME MINERAL FOOD COMPONENTS 4.5.1 INTRODUCTION A diet consisting of a variety of foods provides the best protection against potentially harmful chemicals in food. This is because the body tolerates very small quantities of many toxic substances, but has only a limited ability to cope with large quantities of any single one. Almost any chemical can have a harmful effect if taken in a large quantity. This is especially true for trace minerals, and to some degree, also for macroelements, as well as vitamins. For this reason, it is important to understand the difference between toxicity and hazard. Many foods contain toxic chemicals, but these chemicals do not present a hazard if consumed in allowable amounts. Toxic compounds of such metals as arsenic, mercury, cadmium, and lead contaminate the environment and may enter the food supply. A number of minerals can produce chronic toxicity when absorbed and retained in excess of the body’s demands. The proportion of elements accumulated by the organism is different than the proportion in the environment, and this results in their concentration within the organism. Some of the elements are necessary to the organism for metabolic processes; others, however, that are accumulated in high proportions — sometimes specifically in some organs — according to present knowledge do not have any metabolic significance for the organism (e.g., arsenic, cadmium, mercury, and lead) and are recognized as toxic. Their toxicity is a function of the chemical form and the dose that enters the body. It is also a function of accumulation in the body tissues. For this reason, it is very important to have information about the chemical form of the discussed metals. Currently this may be done by applying speciation analysis, which makes it possible to differentiate the chemical form of the examined element and assess the safety level of the metal residue in foods or drinking water.

4.5.2 ARSENIC Pentavalent and trivalent arsenicals react with biological ligands in different ways. The trivalent form reacts with the thiol protein groups, resulting in enzyme inactivation, structural damage, and a number of functional alterations. The pentavalent arsenicals, however, do not react with -SH groups. Arsenate can competitively inhibit phosphate insertion into the nucleotide chains of DNA of cultured human lymphocytes, causing false formation of DNA because of instability of the arsenate esters. Dark repair mechanisms are also inhibited, leading to peristence of these errors in the DNA molecules. Binding differences of the trivalent and pentavalent forms lead to differences in accumulation of this element. Trivalent inorganic arsenic is accumulated in a higher level than its pentavalent form. The organic arsenic compounds are considered less toxic or nontoxic in comparison to inorganic arsenic, of which trivalent arsenicals are the most toxic forms. Dietary arsenic represents the major source of arsenic exposure for most of the general population. Consumers eating large quantities of fish usually ingest significant amounts of arsenic, primarily as organic compounds, especially those with structures similar to arsenobetaine and arsenocholine, as well as various other arsenic

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71

derivates. Fish of many species contain arsenic between 1 and 10 mg/kg. Arsenic levels at or above 100 mg/kg have been found in bottom feeders and shellfish. Both lipid and water-soluble organoarsenic compounds have been found, but the watersoluble forms, mainly the quaternary arsonium derivates, constitute the larger portion of the total arsenic in marine animals (Vaessen and van Ooik, 1989; WHO, 1989). Studies in mice have demonstrated that after administration of arsenobetaine and arsenocholine over 90% of the dose was absorbed; about 98% of the administered dose of arsenobetaine was excreted unchanged in the urine, and 66 and 9% of the single oral dose of arsenocholine was excreted in the urine and feces, respectively, within 3 days. The majority of arsenocholine was oxidized to arsenobetaine in the animal organism and, in this form, was excreted in the urine. The retention of arsenocholine in the animal body, following administration, was greater than the retention of arsenobetaine. The fate of organic arsenicals in man still has not been fully clarified. Little available information on the organoarsenicals present in fish and other seafood may indicate that these compounds appear to be readily excreted in the urine in an unchanged chemical form, with most of the excretion occuring within 2 days of ingestion. Volunteers who consumed flounder excreted 75% of the ingested arsenic in urine within 8 days of eating the fish. The excreted arsenic was in the same chemical form as it was in the fish. Less than 0.35% was excreted in the feces. There are no data on tissue distribution of arsenic in humans after ingestion of arsenic present in fish and other seafood. Also, there have been no reports of ill effects among ethnic populations consuming large quantities of fish that result in organoarsenic intakes of about 0.05 mg/kg of body weight per day (WHO, 1989). Inorganic tri- and pentavalent arsenicals are metabolized in man, dog, and cows to less toxic methylated forms, such as monomethylarsenic and dimethylarsenic acids (Peoples, 1983).

4.5.3 MERCURY Organic mercury compounds, especially methylmercury, are recognized as more dangerous for man than the inorganic ones. Most foods, except fish, contain very low amounts of total mercury (<0.01 mg/kg), which is almost entirely in the form of inorganic compounds. Over 90% of mercury in fish and shellfish is in the form of methylmercury. This is so because fish feed on aquatic organisms that contain this compound, ultimately originating from microorganisms that biomethylate inorganic mercury. Marlin is the only pelagic fish known to have more than 80% of the total muscle mercury present as inorganic mercury (Cappon and Smith, 1982). The amount of methylmercury is especially high in large, old fish of predatory species like the shark and swordfish. In fish of freshwater species, the mercury content depends on the concentration of mercury in water and sediment and on the pH of water. The concentration of methylmercury in most fish is generally less than 0.4 mg/kg, although predators such as the swordfish, shark, and pike may contain up to several milligrams of methylmercury per kg in their muscles. The intake of methylmercury depends on fish consumption and the concentration of methylmercury in the fish consumed.

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Many people eat about 20–30 g of fish per day, but certain groups eat 400–500 g per day. Thus the daily dietary intake of methylmercury can range from about 0.2 to 4 µg/kg of body mass. Studies of the kinetics of methylmercury after ingestion showed that its distribution in the tissues is more homogenous than that of other mercury compounds, with the exception of elemental mercury. The most important features of the distribution pattern of methylmercury are a high blood concentration, a high erythrocyte/plasma concentration ratio (about 20), and a high deposition in the brain. Another important characteristic is slow demethylation, which is a critical detoxification step. Methylmercury and other mercury compounds have a strong affinity for sulfur and selenium. Although selenium has been suggested to provide protection against the toxic effect of methylmercury, no such effect has been demonstrated. A variety of effects have been observed in animals treated with toxic doses, but some of these, such as renal damage and anorexia, have not been observed in humans exposed to high doses. The primary tissues of concern in humans are the nervous system and particularly the developing brain, and these have been the main reason for the wide range of epidemiologial studies. Methylmercury passes about ten times more readily through the placenta than other mercury compounds. The dermal absorption of methylmercury is similar to that of inorganic mercury salts. The LD50 values after oral administration are 25 mg/kg of body weight in old rats (450 g of body mass) and 40 mg/kg in young rats (200 g). The clearance halftime of methylmercury is about 74 days for the human body and 52 days for the blood compartment (WHO, 2000).

4.5.4 CADMIUM Cadmium shares chemical properties with zinc and mercury, but in contrast to mercury, it is incapable of environmental methylation, due to the instability of the monoalkyl derivate. Similarities and differences also exist in the metabolism of Zn, Cd, and Hg. Metallothioneins and other Cd-binding proteins hold or transport Cd, Zn, and Hg within the body. Metallothioneins are metal-binding proteins of relatively low molecular mass with a high content of cysteine residues that have a particular affinity for cadmium, as well as for zinc and copper, and can affect its toxicity. Its synthesis in organisms is induced by the above-mentioned metals and is involved in the storage of these metals in organs. Zinc metallothionein can detoxify free radicals. Cadmium-induced metallothionein is able to bind cadmium intracellularly and in this way protects the organism against the toxicity of this metal. Cadmium is transported in the plasma as a complex with metallothionein and may be toxic to the kidney when excreted in the glomerular filtrate. Most cadmium in urine is bound to metallothionein. This protein occurs in the organism as at least four genetic variants. The two major forms, I and II, are ubiquitous in most organs, particularly in the liver and kidney, and also in the brain. Metallothionein isolated from adult or fetal human livers contained mainly zinc and cooper, whereas that from human kidneys contained zinc, copper, and cadmium.

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The metals are bound to the peptide by mercaptide bounds and are arranged in two distinct clusters: a four-metal cluster called the α domain and a threemetal cluster called cluster β, at the C terminal of the protein. The α cluster is an obligate zinc cluster, whereas the zinc in cluster β may be replaced by copper or by cadmium. Interaction with metallothionein is the basis for metabolic interactions between these metals. Metallothionein III is found in the human brain and differs from I and II by having six glutamic acid residues near the terminal part of the protein. Metallothionein III is thought to be a growth inhibitory factor, and its expression is not controlled by metals; however, it does bind zinc. Another proposed role for metallothionein III is participation in the utilization of zinc as a neuromodulator, since metallothionein III is present in the neurons that store zinc in their terminal vesicles. Metallothionein IV occurs during differentiation of stratified squamous epithelium, but it is known to have a role in the absorption or toxicity of cadmium. Metallothionein in the gastrointestinal mucosa plays a role in the gastrointestinal transport of cadmium. Its presence in cells of the placenta impairs the transport of cadmium from maternal to fetal blood and across blood–brain barriers, but only when the concentration of cadmium is low. Newborns are virtually cadmium free, whereas zinc and copper are readily supplied to the fetus. Rapid renal concentration occurs mainly during the early years of life. Cadmium bound to metallothionein in food does not appear to be absorbed or distributed in the same way as inorganic cadmium compounds. Low dietary concentration of calcium promotes absorption of cadmium from the intestinal tract of experimental animals. A low iron status in laboratory animals and humans has also been shown to result in greater absorption of cadmium. In particular, women with low body iron stores, as reflected by low serum ferritin concentrations, had an average gastrointestinal absorption rate that was twice as high (about 10%) as that of a control group of women (about 5%). High iron status results in decreasing total and fractional cadmium accumulation from diets, whereas low iron status in organisms promotes accumulation of cadmium. Studies in rats with reduced iron status showed that the inclusion of wheat bran — containing phytate hindering the absorption of iron, calcium, and other minerals — into their diets increased the uptake of cadmium. The LD50 value for rats and mice treated orally ranges from about 100–3000 mg/kg of body mass after a single dose of cadmium chloride. The high affinity of Cd for –SH groups and the ability of imparting moderate covalency in bounds result in increased lipid solubility, bioaccumulation, and toxicity. In humans, after normal levels of exposure, about 50% of the body burden is found in the kidneys, about 15% in the liver, and about 20% in the muscles. Like in animals, the proportion of cadmium in the kidney decreases as the liver concentration increases. The lowest concentrations of cadmium are found in the brain, bone, and fat. Accumulation in the kidney continues to 50–60 years of age in humans and falls thereafter, possibly due to age-related changes in the kidney integrity function. In contrast, cadmium levels in the muscle continue to increase over the course of life. The average cadmium concentration in the renal cortex of nonoc-

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cupationally exposed persons, age 50, varies between 11 and 100 mg/kg in different regions. The diet is the major route of human exposure to cadmium. Contamination of foods with cadmium results from its presence in soil and water. Concentrations of cadmium in foods range widely, and the highest average concentrations are found in mollusks, kidneys, livers, cereals, cocoa, and leafy vegetables. A daily intake of about 60 µg would be required to reach a concentration of 50 mg/kg in the renal cortex of persons 50 years of age, assuming an absorption ratio of 5%. About 10% of the absorbed daily dose is rapidly excreted (WHO, 1989, 2001).

4.5.5 LEAD The Joint FAO/WHO Expert Committee on Food Additives (JECFA) and other WHO committees have recognized that infants and children are the groups at highest risk to lead exposure from food and drinking water. Lead as an anthropogenic contaminant finds its way into air, water, and surface soil. Lead-containing manufactured products also contribute to the lead body burden. The domestic environment, in which infants and children spend the greater part of their time, is of particular importance as a source of lead intake. In addition to exposure from general environmental sources, some infants and young children, as a result of normal, typical behavior, can receive high doses of lead through mouthing or swallowing of nonfood items. Pica, the habitual ingestion of nonfood substances, which occurs among many young children, has frequently been implicated in the etiolgy of lead toxicity. In the United States, on average, 2-year-old children may receive about 45% of their daily lead intake from dust, 40% from food, 15% from water and beverages, and 1% from inhaled air (WHO, 1986). Lead absorption is heavily influenced by food intake; much higher rates occur after fasting than when lead is ingested with a meal. This effect may be due mainly to competition from other ions, particularly iron and calcium, for intestinal transport pathways. Absorption is also affected by age; the typical absorption rates in adults and infants are 5–10% and about 50%, respectively. Children absorb lead from the diet with greater efficiency than adults (WHO, 2000). After absorption and distribution in blood, where most lead is found in erythrocytes, it is initially distributed to soft tissues throughout the body. Subsequently, lead is deposited in the bone, where it eventual accumulates. The half-life of lead in blood and other soft tissues is 28–36 days. Lead that is deposited in physiologically inactive cortical bones may persist for decades without substantially influencing the concentrations of lead in blood and other tissues. On the other hand, lead that is accumulated early in life may be released later when bone resorption is increased, e.g., as result of calcium deficiency or osteoporosis. Lead that is deposited in physiologically active trabecular bones is in equilibrium with blood. The accumulation of high concentrations of lead in blood when exposure is reduced may be due to the ability of bones to store and release lead. Dietary lead that is not absorbed in the gastrointestinal tract is excreted in the feces. Lead that is not distributed to other tissues is excreted through the kidney and, to a lesser extent, by biliary clearance (WHO, 2000).

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The biochemical basis of lead toxicity is its ability to bind to biologically important molecules, thereby interfering with their function by a number of mechanisms. At the subcellular level, the mitochondrion appears to be the main target organelle for toxic effects of lead in many tissues. Lead has been shown to selectively accumulate in the mitochondria. There is evidence that it causes structural injury to these organelles and impairs basic cellular energetics and other mitochodrial functions. It is a cumulative poison, producing a continuum of effects, primarily on the hematopoietic system, the nervous system, and the kidneys. At very low blood levels, lead may impair normal metabolic pathways in children. At least three enzymes of the heme biosynthetic pathway are affected. Lead at about 10 µg/100 cm 3 in blood interferes with δ-aminolevulinic acid dehydratase (WHO, 1986). Alteration in the activity of the enzymes of the heme synthetic pathway leads to accumulation of the intermediates of the pathway. There is some evidence that accumulation of δ-aminolevulinic acid exerts toxic effects on neural tissues through interference with the activity of the neurotransmitter γ-aminobutyric acid. The reduction in heme production per se has also been reported to adversely affect nervous tissue by reducing the activity of tryptophan pyrollase, a heme-requiring enzyme. This results in an increased metabolism of tryptophan via a second pathway, which produces high blood and brain levels of the neurotransmitter serotonin.

TABLE 4.5 Provisional Tolerable Weekly Intake (PTWI) of Toxic Elements Element

PTWI (µg/kg of body weight)

Arsenic Cadmium Lead

15.0 7.0 25.0

Mercury

3.3 as methylmercury; 5.0 as total mercury

Comments For inorganic arsenic — When blood lead levels in children exceed 25 µg/100 cm3 (in whole blood), investigations should be carried out to determine the major sources of exposure, and all possible steps should be taken to ensure that lead levels in food are as low as possible With the exception of pregnant and nursing women who are at greater risk to adverse effects from methylmercury

Note: PTWI = provisional tolerable weekly intake; this term refers to contaminants such as heavy metals with cumulative properties. Its value represents permissible human weekly exposure to those contaminants unavoidably associated with the consumption of otherwise wholesome and nutritious foods. Source: WHO, 30th Meeting of the Joint FAO/WHO Expert Committee on Food Additives, Cambridge, 1986; WHO, 33rd Meeting of the Joint FAO/WHO Expert Committee on Food Additives, Cambridge, 1989; WHO, 53th Meeting of the Joint FAO/WHO Expert Committee on Food Additives, Geneva, 2000; WHO, 55th Meeting of the Joint FAO/WHO Expert Committee on Food Additives, Geneva, 2001.

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TABLE 4.6 Metal Toxicity in Man

Metal

Toxic Effects

Daily Intake (mg per adult person)

Source of Exposure

Inorganic compounds cause abnormal skin hyperpigmentation, hyperkeratosis, skin and lung cancer; organoarsenic compounds present in fish are less toxic or nontoxic

0.0–0.29

Contaminated water, food containing residue of arsenic pesticides, and veterinary drug; fish and shellfish are the richest sources of organic compounds arsenobetaine and arsenocholine

Cadmium

Accumulates mainly in liver and renal cortex; nephrotoxicity, decalcification, osteoporosis, osteomalacia, and Itai Itai disease; embryo toxic in early gestation; impairs immune system, calcium and iron absorption; hypertension and cardiovascular disease; kidney is the critical organ At blood levels greater than 40 µg/100 cm3, exerts a significant affect on hemopoietic system, resulting in anemia; affects central nervous system

<0.01–0.1

Oysters, cephalopods, crops grow on land fertilized with high doses of phosphate and sewage sludge contaminated; cadmium leaching from enamel and pottery glazes; contaminated water

<0.1–0.2

Methylmercury compounds easily pass the blood–brain and placetal barriers; causes severe neurological damage, greater in young children; in animals, also renal damage and anorexiaa

<0.02–0.1

Food contaminated from leaching of glazes of ceramic food ware, as well as from motor vehicle exhausts, atmospheric deposits, canned foods, and water supply from plumbing system Fish and shellfish; meat from animals fed with mercury-dressed grains

Lead

Mercury

>90%, organoarsenic compounds High, inorganic trivalent compounds 3–10%; cadmium bound to metallothionein is well absorbed

5–10% in adult person 40–50% in children

>90% as methylmercury compounds 15% as inorganic mercuric compounds

a

Information from WHO, 53th Meeting of the Joint FAO/WHO Expert Committee on Food Additives, Geneva, 2000.

Source: Nabrzyski, M. and Gajewska, R., Roczniki PZH, 35, 1, 1984; Nabrzyski, M. et al., Roczniki PZH, 36, 113, 1985; WHO, Arsenic, WHO, Geneva 1981; WHO, 30th Meeting of the Joint FAO/WHO Expert Committee on Food Additives, Cambridge, 1986; WHO, 33rd Meeting of the Joint FAO/WHO Expert Committee on Food Additives, Cambridge, 1989; WHO, 53th Meeting of the Joint FAO/WHO Expert Committee on Food Additives, Geneva, 2000; WHO, 55th Meeting of the Joint FAO/WHO Expert Committee on Food Additives, Geneva, 2001.

Chemical and Functional Properties of Food Components

Arsenic

Absorption

Mineral Components

77

Lead interferes with vitamin D metabolism, since it inhibits hydroxylation of 25-hydroxy-vitamin D to produce the active form of vitamin D. The effect has been reported in children, with blood levels as low as 10–15 µg/100 cm3 (WHO, 1986). Measurements of the inhibitory effects of lead on heme synthesis are widely used in screening tests to determine whether medical treatment for lead toxicity is needed for children in high-risk populations who have not yet developed overt symptoms of lead poisoning.

4.5.6 INTERACTIONS

OF

ELEMENTS

Data concerning the toxicity of the four discussed toxic minerals are presented in Tables 4.5 and 4.6. The uptake of elements is not entirely independent of one another. Elements of similar chemical properties tend to be taken up together. Sometimes one element has an inhibiting effect on another, or there can be a synergistic effect, e.g., enhancement of absorption of calcium in the presence of adequate amounts of phosphorus, or cadmium and lead hindering calcium and iron absorption, or zinc and copper antagonism and their influence on the ratio of Zn/Cu on copper deficiency.

REFERENCES Asghar, A. and Bhatti, A.R., Endogenous proteolytic enzymes in skeletal muscle: their significance in muscle physiology and during postmortem aging events in carcasses, Adv. Food Res., 31, 343, 1987. Barbut, S. and Mittal, G.S., Rheological and gelation properties of meat batters prepared with three chloride salts, J. Food Sci., 53, 1296, 1985. Cappon, C.J. and Smith, J.C., Chemical form and distribution of mercury and selenium in edible seafood, J. Anal. Toxicol., 6, 10, 1982. Castell, C.H., MacLeam, J., and Moore, B., Rancidity in lean fish muscle. IV. Effect of sodium chloride and other salts, J. Fish. Res. Bd. Can., 22, 929, 1965. Castell, C.H. and Spears, D.M., Heavy metal ions and the development of rancidity in blended fish muscle, J. Fish. Res. Bd. Can., 25, 639, 1968. Causeret, J., Fish as a source of mineral nutrition, in Fish as Food, Vol. 2., Borgstrom, G., Ed., Academic Press, New York, 1962, p. 205. Du, Z. and Bramlage, W.J., Superoxide dismutase activities in Senescin Apple Fruit (Malus domestica borkh), J. Food Sci., 59, 581, 1994. Eschleman, M., Ed., Introductory Nutrition and Diet Therapy, Lippincott J.B. Co., London, 1984. Feltman, J., Ed., Prevention’s Giant Book of Health Facts, Rodale Press, Emmaus, PA, 1990. FAO/WHO, Ed., Summary of Evaluations Performed by the Joint FAO/WHO Expert Committee on Food Additives 1956–1993, International Life Science Inst. Press, Geneva, 1994. Gajek, O.M., Nabrzyski, R., and Gajewska, R., Metallic impurities in imported canned fruit and vegetables and bee honey, Roczniki PZH, 38, 14, 1987 (in Polish). Ha, Y.W. et al., Calcium binding of two microalgal polysaccharides and selected industrial hydrocolloids, J. Food Sci., 54, 1336, 1989. Hendler, S.S., Ed., The Doctor’s Vitamin and Mineral Encylopedia, Simon and Schuster, New York, 1990.

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Hultin, H.O., Oxidation of lipids in seafoods, in Seafoods: Chemistry, Processing Technology and Quality, Shahidi, F. and Botta, J.R., Eds., Chapman & Hall, London, 1994, p. 49. Kraniak, J.M. and Shelef, L.A., Effect of ethylenediaminetetraacetic acid (EDTA) and metal ions on growth of Staphylococcus aureus 196 E in culture media, J. Food Sci., 53, 910, 1988. Lopez, A., Ward, D.R., and Williams, H.L., Essential elements in oysters (Crassostrea virginica) as affected by processing method, J. Food Sci., 48, 1680, 1983. Marzec, Z. et al., Eds. Tables of Trace Elements in Food Products. National Food and Nutrition Institute, Warsaw, 1992 (in Polish). Miller, D.K. et al., Dietary iron in swine affects nonheme iron and TBAR’s in pork skeletal muscles, J. Food Sci., 59, 747, 1994a. Miller, D.K. et al., Lipid oxidation and warmed-over aroma in cooked ground pork from swine fed increasing levels of iron, J. Food Sci., 59, 751, 1994b. Nabrzyski, M. and Gajewska, R., Determination of mercury, cadmium and lead in food, Roczniki PZH, 35, 1, 1984 (in Polish). Nabrzyski, M. and Gajewska, R., Aluminium and fluoride in hospital daily diets and teas, Z. Lebensm. Unters. Forsch., 201, 307, 1995. Nabrzyski, M., Gajewska, R., and Lebiedzi´nska, A., Arsenic in daily food rations of adults and children, Roczniki PZH, 36, 113, 1985 (in Polish). Oelingrath, I.M. and Slinde, E., Sensory evaluation of rancidity and off-flavor in frozen stored meat loaves fortified with blood, J. Food Sci., 53, 967, 1988. Paslowska , S. and Nabrzyski, M., Assay of iodine in powdered milk, Bromat. Chem. Toxicol., 8, 73, 1975 (in Polish). Pearson, A.M., Love, J.D., and Shorland, F.B., “Warmed over” flavor in meat, poultry, and fish, Adv. Food Chem., 23, 2, 1977. Peoples, S.A., The metabolism of arsenic in man and animals, in Arsenic Industrial, Biomedical, Environmental Perspectives (Proceedings of the Arsenic Symposium), Lederer, W.H. and Fensterheim, R.J., Eds., Van Nostrand Reinhold Co., New York, 1983, p. 125. Ramanathan, L. and Das, N.P., Effect of natural copper chelating compounds on the prooxidant activity of ascorbic acid in steam-cooked ground fish, Int. J. Food Sci. Technol., 28, 279, 1993. Rosenberg, J.H. and Solomons, N.W., Physiological and pathophysiological mechanism in mineral absorption, in Absorption and Malabsorption of Minerals, Vol. 12., Solomons, N.W. and Rosenberg, J.H., Eds., Alan R. Liss, Inc., New York, 1984, p. 1. Rutkowska, U., The effect of the grinding process on contents of copper, zinc, and manganese in rye and wheat flour, Roczniki PZH, 26, 339, 1975 (in Polish). Samant, S.K. et al., Protein-polysaccharide interactions: a new approach in food formulation, Int. J. Food Sci. Technol., 28, 547, 1993. Solomons, N.W., Ed., Absorption and Malabsorption of Mineral Nutrients, Alan R. Liss, Inc., New York, 1984, p. 269. True, R.H. et al., Changes in the nutrient composition of potatoes during home preparation, III, Min. Am. Potato J., 56, 339, 1979. Trzebska-Jeske, I. et al., The effect of mechanical processing on nutritional value of groats produced in Poland, Roczniki PZH, 24, 717, 1973 (in Polish). Vaessen, H.A.M.G. and van Ooik, A., Speciation of arsenic in Dutch total diets: methodology and results, Z. Lebensm. Unters. Forsch., 189, 232, 1989. WHO, Environmental health criteria, 18, in Arsenic, WHO, Geneva, 1981. WHO, Environmental health criteria, 36, in Fluorine and Fluorides, WHO, Geneva, 1984.

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79

WHO, Food Additives Series, 21, Toxicological Evaluation of Certain Food Additives and Contaminants, 30th Meeting of the Joint FAO/WHO Expert Committee on Food Additives, Cambridge, U.K., 1986. WHO, Food Additives Series, 24, Toxicological Evaluation of Certain Food Additives and Contaminants, 33rd Meeting of the Joint FAO/WHO Expert Committee on Food Additives, Cambridge, U.K., 1989. WHO, Food Additives Series, 30, Toxicological Evaluation of Certain Food Additives and Naturally Occuring Toxicants, paper presented at 39th Meeting of the Joint FAO/WHO Expert Committee on Food Additives, Geneva, 1993a. WHO, Food Additives Series, 32, Toxicological Evaluation of Certain Food Additives and Contaminants, paper presented at 41st Meeting of the Joint FAO/WHO Expert Committee on Food Additives, Geneva, 1993b. WHO, Summary of Evaluations Performed by the Joint FAO/WHO Expert Committee on Food Additives (1956–1993 First through 41st Meeting), WHO, Geneva, 1994. WHO, Food Additives Series, 35, Toxicological Evaluation of Certain Food Additives and Contaminants, paper presented at 44th Meeting of the Joint FAO/WHO Expert Committee on Food Additives, Geneva, 1996. WHO, Food Additives Series, 44, Safety Evaluation of Certain Food Additives and Contaminants, paper presented at 53rd Meeting of the Joint FAO/WHO Expert Committee on Food Additives, Geneva, 2000. Williams, D.M., Clinical significance of copper deficiency and toxicity in the world population, in Clinical Biochemical and Nutritional Aspects of Trace Elements, Vol. 6., Prasad, A.S., Ed., Alan R. Liss, Inc., New York, 1982, p. 277. Wilpinger, M., Schönsleben, I., and Pfanhauser, W., Chrom in öesterreichischen Lebensmitteln, Z. Lebensm. Unters. Forsch., 201, 521, 1995 (in German). Wojnowski, W., Skladniki mineralne, in Chemiczne i funkcjonalne wlasciwosci skladników zywnosci, Sikorski, Z.E., Ed., Wydawnictwa Naukowo-Techniczne, Warszawa, 1994, p. 76 (in Polish). Wu, S.Y. and Brewer, M.S., Soy protein isolate antioxidant effect on lipid peroxidation of ground beef and microsomal lipids, J. Food Sci., 59, 702, 1994.

5

Saccharides Piotr Tomasik

CONTENTS 5.1 5.2 5.3 5.4

Natural Food Saccharides, Occurrence, Role, and Applications ..................81 Carbohydrate Structure ..................................................................................82 Carbohydrate Chirality...................................................................................88 Carbohydrate Reactivity.................................................................................89 5.4.1 Chemical and Physical Transformations of Mono-, Di-, and Oligosaccharides Essential in Food Chemistry ..........................89 5.4.1.1 Reactions of Aldehyde and Ketone Functions...................89 5.4.1.2 Reactions of the Hydroxyl Groups ....................................92 5.4.1.3 Reactions of Glycosidic Bond............................................97 5.4.1.4 Specific Reactions of Saccharides......................................97 5.4.2 Chemical and Physical Transformations of Polysaccharides............99 5.4.2.1 Depolymerization of Carbohydrates.................................102 5.4.2.2 Chemical Modification of Polysaccharides without Attempted Depolymerization............................................103 5.4.2.3 Cross-Linked Polysaccharides..........................................105 5.4.3 Enzymatic Transformations of Carbohydrates ................................105 5.4.4 Cereal and Tuber Starches ...............................................................107 5.5 Functional Properties of Carbohydrates ......................................................107 5.5.1 Taste..................................................................................................107 5.5.2 Colorants ..........................................................................................109 5.5.3 Flavor and Aroma ............................................................................110 5.5.4 Texture..............................................................................................110 5.5.5 Encapsulation ...................................................................................111 5.5.6 Polysaccharide Containing Biodegradable Materials......................112 References..............................................................................................................113

5.1 NATURAL FOOD SACCHARIDES, OCCURRENCE, ROLE, AND APPLICATIONS Nature commonly utilizes saccharides as a source of energy, structure-forming material, water-maintaining hydrocolloids, and even sex attractants. All organism cells contain saccharide components in their membranes. Frequently, saccharides exist in naturally derivatized forms, e.g., aminated, as in chitin and chitosan;

1-5871-6149-4/02/$0.00+$1.50 © 2002 by CRC Press LLC

81

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Chemical and Functional Properties of Food Components

esterified; alkylated, as in glycosides; oxidized; reduced; or linked to proteins, lipids, and other structures, such as hemoglobin and hesperidin. Lower monosaccharides, i.e., aldo- and keto-bioses, -trioses, and -tetroses, do not exist naturally in a free state. Glyceroaldehyde and hydroxyacetone in phosphorylated forms are the products of alcoholic fermentation and glycolytic sequence. Erythrose and erythrulose also appear in phosphorylated forms in the pentose cycle of glucose, while ketopentose–ribulose can be found as its phosphate ester (Table 5.1).

5.2 CARBOHYDRATE STRUCTURE Carbohydrates are either polyhydroxyaldehydes (aldoses, oses) or polyhydroxyketones (ketoses, uloses); there is an electron gap at their carbonyl carbon atom. Typically, aldehydes and ketones accept nucleophiles such as water to form hydrates or alcohols to form hemiketals (5.1 and 5.3) and hemiacetals (5.4 and 5.6), respectively. In pentoses, pentuloses, hexoses, hexuloses, and higher carbohydrates, one of the hydroxyl groups can play the role of internal nucleophile. Thus, open-chain structure (5.2 and 5.5) cyclizes into internal hemiacetals and ketals, all with either five- (5.1 and 5.3) or six- (5.4 and 5.6) membered cycles.

Structures 5.1 — 5.6

Since all their carbon atoms are sp3-hybridized, the bond angles in the cycle should be about 109ο to provide strainless conformations. It implies nonplanar conformations of the cycles (Siemion, 1985). In some cases, the pyranose ring formation can be either obstructed or blocked, and a five-membered furanose ring dominates for the given sugar. The molecular

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structure of di- and higher saccharides is additionally controlled by a potential energy benefit resulting from the formation of intramolecular hydrogen bonds, as in cellobiose (5.7a), lactose (5.7b), maltose (5.8 and 5.9), and sucrose (5.10).

Structure 5.7

Structures 5.8 — 5.10

Both maltose structures correspond to two energy minima, available thanks to intramolecular hydrogen bonds. Two hydrogen bonds might stabilize the sucrose molecule, provided the fructosyl moiety takes the furanosyl structure. Indeed, such possibility is employed in nature. In polysaccharides, the structural factors are even more important. A number of different saccharide units in the chain, branching of the chain, and the presence of either more-polar groups (COOH, PO3H2, and SO3H) or less-polar groups (OCH3

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TABLE 5.1 Essential Natural Saccharides in Food and Their Occurrence and Applications Saccharide

Occurrence

Applications

Monosaccharides and Their Natural Derivatives Pentoses D-Apiose L-Arabinose D-Xylose

Hexoses L-Fucose D-Galactose

D-Glucose

D-Manose L-Rhamnose

Parsley and celery Plant gums, hemicelluloses, saponins, protopectin Accompanies L-arabinose

Mother milk, algae, plant mucus, and gums Oligo- and polysaccharides, plant mucus and gums, saponins, glycosides Plants and animals, honey, inverted sugar, saponins

Alcoholic fermentation; furan-2aldehyde production Reduction of xylitol; sucrose substitute; alcoholic fermentation; production of furan-2-aldehyde

Diagnostics in liver tests

Alcoholic fermentation; sweetener; energy pharmacopeial material; nutrient; food preservative

Algae, plant mucus, oranges Plant mucus and gums, pectins, saponins, glycosides

Hexuloses D-Fructose

Fruits, honey, inverted sugar

D-Glucosylamine

Chitin, chitosan

L-Sorbose

Rowan berries

Lactose

Disaccharides (oses) Mammalian milk

Maltose Sucrose

Starch, sugar beet, honey Sugar beet, sugar cane

Agar

Red algae

Alginates

Brown algae

Non-cavity-causing sweetener; sweetener for diabetics; food humidifier and preservative Pharmaceutical aid; antiarthritic drugs; ion exchanger Synthesis of ascorbic acid

Improves the taste of dairy products; fermenting component of milk Alcoholic fermentation; common sweetener; caramel production; food preservation

Polysaccharides Microbiological nutrient; gelforming agent; emulsifier; bread staling retardant; meat texturizer; meat substitute Thickener; gel-forming agent; food and beer foam stabilizer

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85

TABLE 5.1 (CONTINUED) Essential Natural Saccharides in Food and Their Occurrence and Applications Saccharide Carrageenans ι, κ, γ, µ, ν

Occurrence Red seaweed

Cellulose

Plants

Dextran

Frozen sugar beet

Furcellaran

Red seaweed

Gatti gum Guaran gum

Anageissus latifolia tree Leguminous plants

Gum Arabic

Senegal acacia

Gum karaya Gum locust bean Gum tragacanth Glycogen Hemicelluloses: Arabinogalactan Galactan Mannans, xylans Heparin Hialuronic acid Inulin Pectins

Sterculiacea tree (India) Locust bean Astragalus species (Middle East) Liver, muscle

Protopectin

Larch Plants Liver, tongues Connective tissues Endive, Jerusalem artichoke Plants, mainly apples, citrus, sugar beet Plants and nonmatured fruits

Starch Amylose, amylopectin

Tubers, grains, some fruits

Tamarind flour

Tamarind tree (India)

Xanthan gum

Semiartificial gum

Applications Gel-forming agent; stabilizer; protein fiber texturizer; milk fat anticoagulant; milk clarifying agent Saccharification to glucose; dietary fiber; chromatographic sorbent Chromatographic sorbent (Sephadex); blood substitute Gel-forming agent; filler; marmalade stabilizer; protein precipitation Emulsifier; stabilizer Food; cosmetics; pharmaceutical thickener and stabilizer Emulsifier; antistaling stabilizer; flavor fixative Foam stabilizer; thickener Thickener; adhesive Thickener; stabilizer Glucose reservoir Emulsifier; stabilizer Alcoholic fermentation; reduction to alcohol Blood anticlotting agent Water absorbent Prebiotic Gel-forming agent; beer stabilizer Decomposes to pectins on plant maturation and cooking Food filler; thickener; gel-forming agent, bakery products; saccharification to syrups Thickener; marmalade; jelly; ice cream; mayonnaise stabilizer Hydrocolloid stabilizer

and NHCOCH3) than the OH group are crucial for the overall structure of polysaccharide. Amylose and cellulose are the most regularly built; they form polymer chains of α-D- and β-D-glucose units, respectively. In very random cases, amylose is branched with short chains (Ball et al., 1998). The amylose chain is originally long and randomly coiled (Figure 5.1), but it turns into a more ordered, helical

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x x FIGURE 5.1 Randomly coiled amylose chain and its helical complex, formed as a result of its interaction with a nonpolar fragment.

structure. Helical complexes are formed if hydrocarbons, alcohols, lipids, fatty acids, and bar-like anions, such as I5–, OCN–, are present in the amylose environment (Tomasik and Schilling, 1998a, 1998b). Such compounds and anions, potential guests of the complex, either have hydrophobic fragments or are fully hydrophobic. The possibility of the reduction of the energy of the system by interactions of hydrophobic sides of amylose and the potential guest is the driving force of the formation of a helical complex. Thus, its cavity is hydrophobic and all hydroxyl groups of the D-glucose units are situated on the external surface of the helix, as well as on the edges of its cavity (the V-type amylose). The number of glucose units in one helix turn depends on the guest molecule present in the helical complex. With KOH as a guest, one turn involves six glucose units. Inclusion of KBr reduces the turn to four glucose units, whereas inclusion of tert-butanol and α-naphthol requires the turns of seven and eight glucose units, respectively (Tomasik and Schilling, 1998a). An additional stabilization of the amylose helix comes from the doublehelix formation (Imberty et al., 1991). Depending on the helix–helix interactions and, in consequence, their mutual arrangement, A- and B-type amylose is formed (Figure 5.2). Recently distinguished C-type amylose appears to be a combination of both A and B patterns.The conformation of β-D-glucose units bound in cellulose in the 1→4' manner offers a particularly strong hydrogen bond cross-linked macrostructure of this polysaccharide. Glycans with 1,2-, 1,3-, and particularly 1,6-linked units have a more irregular, loosely jointed structure. The heterogenicity of the polysaccharide structural units and their volumes introduce further regularities or irregularities in the macrostructure. A decrease in the group polarity, e.g., by methylation, and number results in a more irregular polysaccharide structure. An opposite effect can be achieved in the presence of more polar groups, or even less polar, but suitably oriented groups. For instance, chitin, a polysaccharide with acetylamino groups, has a very regular, compact structure that provides insolubility of chitin in water. This polysaccharide is a common insect carapace-forming

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FIGURE 5.2 The crystallographic A- and B-types of amylose depend on the structure of double amylose helices.

FIGURE 5.3 Scheme of amylopectin molecule.

material. Because of this property, chitin has found several technical applications (Goosen, 1997). Amylopectin (Figure 5.3) presents a special case. It is a highly branched homopolymer of α-D-glucose units. The 1→6-linked terminal branches, which occur at about every 8th glucose unit, contain 15–30 glucose units. These branches can also participate in the formation of helical complexes. Some guest molecules may situate in areas around branching sites in the amylopectin molecule. In spite of an irregular, bulky structure, amylopectin also forms a double helix (Imberty et al., 1991). Because of functional properties, the structure of the polysaccharide matrix, the tertiary structure, is also essential. In solution, polysaccharides such as amylose form separate fibrils that, upon coiling, turn either into micelles at a low-temperature gradient or into gels at a high-temperature gradient. Both amylose and amylopectin participate in the starch granule organization (Gallant et al., 1997). Their seminative mixture has specific functional properties. It strongly depends on the amylose-toamylopectin ratio; size of granules (Table 5.2); content of residual components of

88

Chemical and Functional Properties of Food Components

TABLE 5.2 Selected Properties of Various Botanical Origin Starches Starch Origin Barley Maize Oat Potato Rice Rye Triticale Waxy maize Wheat a

Amylose Content (%)

Granule Size µm) (µ

Gelation Temperature (°C)

Protein Content (%)a

Lipid Content (%)a

19–22 21–24 23–30 18–23 8–37 24–30 23–24 1–2

5–40 10–30 5–15 1–100 2–10 8–60 2–40 10–30

51–59 67–100 87–90 59–68 68–78 55–70 55–62 62–72

up to 1.22 0.32 up to 0.39 0.15 up to 2.82 0.32 0.27 up to 0.31

up to 0.20 0.60 up to 0.62 0.06 up to 1.00 0.22 0.39 up to 0.20

24–29

2–36

59–64

0.24

0.36

Average values on dry basis.

native starch, e.g., lipids, proteins, and mineral salts; and random esterification with phosphoric acid, the latter exclusively in the case of potato amylopectin. The amylose-to-amylopectin ratio decides on aqueous solubility of starch and texture of its gels, resulting from a penetration of water into starch granules (swelling) and from pushing the granule interior into a solution where the gel network is formed. The size of granules is essential for smoothness of products prepared from starch (puddings, gels). In practice, not all starch granules swell and participate in the gel formation. Larger granules are more susceptible to gelation and chemical modification (Lii et al., 2001b). The nutritional value of starches usually increases with content of residual components; however, in several cases, when starch is subjected to chemical modifications or is used for specific nonnutritional purposes, such “contaminants” are nonbeneficial. Cellulose that is completely insoluble in water forms microfibrils that are composed of crystallites and amorphous regions. Such regions may be also distinguished inside of starch granules. Roughly, they form concentric crystalline and amorphous layers surrounding the hilum, the origin of the granule growth (Gallant et al., 1997). Amorphous regions contain amylopectin (Szymo´nska et al., 2000). The structure of granules is developed on plant vegetation by enzymatic debranching of so-calledplant glycogen (Erlander, 1998). These enzymes reside inside of starch granules and can be activated on starch processing.

5.3 CARBOHYDRATE CHIRALITY Chirality is a property resulting from a lack of symmetry of molecules. All carbohydrates, including polysaccharides, have centers of asymmetry and therefore are chiral. Chirality is expressed as a concentration-independent specific rotation, [α]°:

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89

[α]° = (α · 100)/lc

(5.1)

where α is an angle of twist determined polarimetrically, l is the length of the polarimetric tube, and c is the concentration of saccharide in g/100 cm3. Chirality of freshly prepared aqueous solutions of saccharides is either variable or constant in time, which points to mutarotation or lack of mutarotation, respectively (see below).

5.4 CARBOHYDRATE REACTIVITY 5.4.1 CHEMICAL AND PHYSICAL TRANSFORMATIONS OF MONO-, DI-, AND OLIGOSACCHARIDES ESSENTIAL IN FOOD CHEMISTRY 5.4.1.1 Reactions of Aldehyde and Ketone Functions Mutarotation — Only reducing sugars, e.g., those with a hydroxyl group at the anomeric carbon atom, mutarotate. They reversibly, either spontaneously, or on acid or base catalysis, transform through the pyranose and furanose ring opening followed by ring-closure (5.11.a and 5.14 into 5.12 and 5.11b). An open-chain structure is not typical for saccharides. Aqueous D-glucose at 25°C has approximately 0.003% of the open-chain compound.

Structures 5.11 — 5.13

90

Chemical and Functional Properties of Food Components

Mutarotation has limited, rather diagnostic, significance in food chemistry and technology. Practical use of this reaction is demonstrated in milk powder manufacture. Evaporation of milk at a rate lower than mutarotation of lactose yields a product with less α-lactose isomer, which crystallizes in prism- or pyramid-like form. Fast milk evaporation gives an amorphous mixture of α- and β-lactose (5.7b). Reduction to Alcohols — The industrial scale reduction involves either NaBH4 or electrochemical and catalytic (Raney nickel) hydrogenation. Resulting open-chain polyols, the sugar alcohols (5.12 and 5.13), have a new chiral center. In consequence, each ketose (5.14) yields two alcohols, whereas aldoses (5.11a and 5.11b) yield only one alcohol. Addition to the Carbonyl Group — The internal, cyclic hemiacetal formation is one of the illustrations of such addition. The H2N–X nucleophiles, with X being NH2 (hydrazine), NHAr (arylhydrazines), OH (hydroxylamine), NHCONH2 (semicarbazide), NHCSNH2 (thiosemicarbazide), or alkyl (primary amine), produce hydrazones, arylhydrazones, oximes, semicarbazones, thiosemicarbazones, and alkyl imines (Schiff bases), respectively, following the following path: 5.4 + 5.15 → 5.16 → … → 5.21.

Structures 5.15 — 5.21

Hydrazones and arylhydrazones (5.20) react with the second molecule of the corresponding reagent into osazones (5.21). The reactions with mono-, di-, and lower

Saccharides

91

oligosaccharides have some analytical value. Reactions with H2N–X nucleophiles in which X = CH(R)COOH, the amino acids, nucleotides, and proteins, as well as NH3+ (ammonia) produce aldosylamino acids and aldosylamines, respectively (4.15 with X = CH(R)COOH or H). Aldoses undergo the Amadori rearrangement and subsequently turn into caramels, the natural brown food colorants, and/or heteroaromatic compounds — derivatives of pyrrole, imidazole, and pyrazine. Ketoses react similarly into ketosylamino acids or ketosylamines, which, in the first step, undergo the Heyns rearrangement (5.17–5.23). These rearrangements are the first steps of either thermal or enzymatic (the Maillard reaction) reactions resulting in the browning of food and the aroma of roasted, baked, or fried foodstuffs.

Structures 5.22 — 5.23

Oxidation — The oxidation of aldoses (5.24) with bromine or chlorine in alkaline solution (hypobromites and hypochlorites, respectively) leads to aldonic acids that readily self-esterify (lactonize) into δ- (5.25) and γ- (5.26) lactones residing with free acid (5.27) in equilibrium. β-Conformers oxidize more readily than α-conformers.

Structures 5.24 — 5.27

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Chemical and Functional Properties of Food Components

Glucono-δ-lactone (4.25) has found its application in baking powders, raw fermented sausages, and dairy products where the slow release of acid is required. The oxidations with Cu2+ (the Fehling, Benedict, and Barfoed tests) and Bi3+ (the Nylander test) ions are the only analytical tests for reducing sugars, e.g., those with the hydroxyl group at the anomeric carbon atom. 5.4.1.2 Reactions of the Hydroxyl Groups Esterification — Saccharides are commonly esterified with acyl chlorides, as well as organic and inorganic acid anhydrides. These reactions can be run either exhaustively with involvement of all hydroxyl groups of saccharide molecules or selectively. In the latter case, a protection (blocking) of certain hydroxyl groups is required. For instance, all hydroxyl groups of D-glucose, except that at C3, can be protected in reaction with acetone in acidic medium. Resulting 1,2,5,6-di-Oisopropylidene-α-D-glucofuranose (5.28), after acylation at a nonprotected hydroxyl group to give monoacylated diketal (5.29), is then decomposed with carboxylic acid into 3-monoacylated saccharide (5.30). Such reactions can be applied to polysaccharides, although polysaccharides readily esterify carboxylic acids simply on heating of their blends (Tomasik and Schilling, 2002).

Structures 5.28 — 5.30

The acylation of mono- and oligosaccharides and their derivatives, mainly sorbitol and sucrose, with higher fatty acids yields surface-active agents and fat replacers. Hydrolysis of acyl groups can be achieved by either interesterification (water or alcohols) or ammonolysis.

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93

Etherification — There are several methods of sugar etherification. They are: • The hydrochloride catalyzed Fischer glycosidation with alcohols • The exhaustive Haworth methylation with dimethyl sulfate in alkaline medium, with retention of configuration at the anomeric carbon atom • The Irvine-Purdie exhaustive methylation, which involves methyl iodide in the presence of Ag2O • The Koenigs-Knorr glycosidation, which is the substitution of an α-halo atom of α-halopentacetyl sugars with methanol in the presence of Ag2CO3 Such reactions with small alkyl groups are important for saccharide structural analysis. Halogenation — The hydroxyl group at C1 is readily substituted with a halide atom (X) when a pentacetylated saccharide is treated with HX in acetic acid. Such saccharides are suitable for synthesis of desoxysaccharides. Exhaustive replacement of all hydroxyl groups can be achieved with reagents suitable for such reaction with simple alcohols, i.e., COCl2, SOCl2, POCl3, PCl3, and PCl5. Chlorination of some sugars results in products of increased sweetness (Table 5.3). Dehydration — It is an intramolecular elimination of one water molecule producing 1,6- (5.31), 3,6- (5.32), or 1,2- (5.34) anhydrosugars, as well as being in equilibrium with saccharide enol (5.33) and ketone (5.35). Anhydrosugars can be utilized for the synthesis of some derivatives, such as amino sugars and others. Dehydration is the first step of sugar caramelization. Further heating of dehydrated saccharides results in the formation of three subsequent compounds called caramelan, caramelen, and caramelin (Tomasik et al., 1989): 6C12H22O11 – 12 H2O = 6C12H12O9 (caramelan) 6C12H22O11 – 18 H2O = 2C36H18O24 (caramelen) 6C12H22O11 – 27 H2O = 3C24H26O13 (caramelin) Reduction — A multistep reaction leads to desoxysaccharides. It involves 1halopentaacetylated saccharide, which is dehalogenated with zinc into acetylated glucal (5.35). Hydrolyzed glucal accepts sulfuric acid, the SO3H residue of which is readily hydrolyzed into deoxysugar (5.41). Oxidation — Apart from CO2 and H2O, there are three series of products that result from the oxidation of saccharide. They are 2,3-dialdehydes (5.43 and 5.49) formed on the oxidative cleavage of saccharides (5.42 and 5.48) with periodates, the sole oxidants providing such course of oxidation. Such dialdehydes are considered toxic. Further oxidation of dialdehydes leads to glyceric acid (5.45), glyoxalic acid (5.47), hydroxypyruvic acid (5.46), and erythronic acid (5.51), as shown below for the oxidative cleavage of sucrose (5.42) and maltose (5.48). The oxidation of monosaccharides, e.g., D-galactose (5.52), with strong oxidants proceeds at both C1 and C6 atoms, leaving dicarboxylic, aldaric acids (5.53). Aldaric

94

Chemical and Functional Properties of Food Components

TABLE 5.3 RS of Various Substances in 10% Aqueous Solutions (RS of Sucrose = 1.0) Substance Sucrose β-D-Fructopyranose Inverted sugar D-Glucopyranose αβD-Mannopyranose αβD-Galactopyranose Maltose D-Lactose, αβD-Galactosucrose Raffinose Stachyose 1'-Chloro-1'-desoxysucrose 4-Chloro-4-desoxysucrose 6-Chloro-6-desoxysucrose 1',4,6'-Trichloro-1',4,6tridesoxygalactosucrose Mannitol Sorbitol Xylitol Honey Molasses Saccharin Cyclamates Aspartame Neohesperidin dihydrochalcone

RS 1.00 1.80 1.30 0.70 0.80 0.30 Βitter 0.32 0.32 0.20 0.30 Tasteless 0.01 0.10 0.20 0.05 Bitter 20.00 0.40 0.60 0.85–1.2 0.97 0.74 200–700 30–140 200 2000

acids can lactonize into lactones (5.54). Lactones produce uronic acids (5.55) when reduced with sodium amalgam. The oxidation at C1 can be prevented by protection of the 1–OH group. The glycosidic bond in oligosaccharides offers sufficient protection. Application of weak oxidants offers direct route to uronic acids. Complex Formation — The hydroxyl groups offer two types of interactions with molecules having either a clearly dipole character or charge, i.e., ions. The hydrogen atoms of these groups are capable of interactions with electron-excessive sites of dipoles and anions, whereas lone electron pairs of the oxygen atom are electron donors for cations and the positive side of dipolar molecules. The complex formation is a general ability of saccharides. Fruitful results were noted in the cases of Ca2+ salts, preferable chloride, and hydrogen carbonate. The cation forms fairly stable compounds. This property was widely utilized in

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95

Structures 5.31 — 5.35

Structures 5.36 — 5.41

96

Chemical and Functional Properties of Food Components

Structures 5.42 — 5.51

sugar manufacture for the separation of sucrose from its syrups. Saccharide alcohols also coordinate metal ions. Depending on cations, their optical rotation is affected to a different extent, but always in the order of Na+ < Mg2+ < Zn2+, Ba2+ < Sr2+ < Ca2+. Complexes of saccharides with a wide variety of cations

Saccharides

97

Structures 5.52 — 5.55

were prepared and characterized (Angyal, 1989). Saccharides also complex to other, nonmetallic compounds, e.g., organic food components such as polysaccharides and proteins. They are sorption complexes with involvement of hydrogen bonds. The energies of the complex formation are low and do not exceed 4 kJ/mole (Tomasik et al., 1995). Nevertheless, they are essential in food texturization and thermal stability (Ciesielski and Tomasik, 1998; Ciesielski et al., 1998). The complexation itself can seriously affect the sugar metabolism and biotechnological processes, as well as transport of metal ions in the organism. 5.4.1.3 Reactions of Glycosidic Bond As a typical acetal bond, a glycosidic bond readily hydrolyzes in an acid-catalyzed reaction. In this manner, di- and oligosaccharides can be split into monosaccharides. It is a common method for manufacturing of invert sugar, a mixture of α-D-glucose and β-D-fructose, from sucrose. 5.4.1.4 Specific Reactions of Saccharides In strongly acidic media, saccharides produce furan derivatives in a sequence of reactions that are rearrangements and dehydrations followed by cyclization. Similar products are available thermally. Pentoses and hexoses give furan-2-aldehyde and 5-hydroxymethylfuran-2-aldehyde, respectively. Both of these products are responsible for the specific aroma of caramel and burnt sugar. In weakly acidic and neutral media the reactions proceed at a lower rate. Reductones (4.55–4.57), compounds with the carbonyl group vicinal to an endiol moiety, which are formed, are stable at pH < 6 and act as natural antioxidants. They transform into deoxysugars, uloses (5.58). The latter undergo cyclization into 5-hydroxymethylfuran-2-aldehyde (5.62). Corresponding osuloses (5.63) in similar sequences of transformations yield diacetylformosine (5.69).

98

Chemical and Functional Properties of Food Components

Structures 5.56 — 5.62

In acid-based reactions 2-acetyl-3-hydroxyfuran (isomaltol) (5.76), 3-hydroxy2-methylpyran-4-one (5.77), and maltol (5.79) are formed. They are responsible for the baked bread aroma.

Saccharides

99

Structures 5.63 — 5.69

Endiols (4.80) can isomerize into other saccharides in the Lobry de Bruyn–van Ekenstein rearrangement. Thus, D-glucose (5.4) can isomerize into mannose (5.81) and fructose, (5.1) accompanied by a small amount of D-psicose (5.83). Alkaline medium provides isomerization to disaccharides, which turn from aldoses into ketoses, as shown for lactose (5.7b) isomerized to lactulose (5.84). Since the enolization is not restricted to the 2 and 3 positions, a number of products are formed that undergo subsequent aldol condensations and the Cannizzaro oxidation. They are all 2-hydroxy-3-methyl, 3,4-dimethyl-2-hydroxy, 3,5-dimethyl2-hydroxy, and 3-ethyl-2-hydroxy-2-cyclopenten-1-ones; sugar acids; acetic acid; hydroxyacetone; three isomeric hydroxy-2-butanones; γ-butyrolactone; and such furan derivatives as furyl alcohol, 5-methyl-2-furyl alcohol, and 2,5-dimethyl-4hydroxy-3(2H)-furanone. They are food flavoring agents.

5.4.2 CHEMICAL AND PHYSICAL TRANSFORMATIONS OF POLYSACCHARIDES Although several polysaccharides found their large-scale applications, only few of them, e.g., starch, cellulose, and hemicelluloses, are modified on an industrial scale.

100

Chemical and Functional Properties of Food Components

Structures 5.70 — 5.79

Saccharides

101

Structures 5.80— 5.84

Products of their modifications are widely utilized in food technology and everyday food preparations. Food processing such as cooking, baking, frying, and pickling usually deal with food carbohydrate transformations. The functional group reactivity in polysaccharides is, to a great extent, obstructed by their macrostructure. These potential reaction sites that do not reside on the surface may be unavailable for many reagents, as they are either hidden inside the macrostructure or involved in the formation of intra- and intermolecular hydrogen bonds crucial for the macrostructure properties. Many reactions of polysaccharides are governed by heterogenicity of the reaction system. Only randomly reacting polysaccharides are solvent soluble. Among polysaccharides utilized either on or after transformation, hemicelluloses are exclusive. They are water soluble or they swell. Problems of solubility and compactness are encountered particularly in cellulose and starch, which are fibrillar and granular, respectively. The reactivity in terms of the rate and degree of transformation can be controlled by either application of suitable reagents or loosening of the compact structure with involvement of a physical action. The solvent effect (water in case of starch and higher alcohols (Ruck, 1996) in case of cellulose) is the most commonly used tool. But high pressure; sonication with ultrasounds; ultraviolet, microwave, and ionizing radiation; thermolysis; freezing; and glow plasma might

102

Chemical and Functional Properties of Food Components

also be suitable for loosening a compact polysaccharide structure (Szymo´nska et al., 2000; Tomasik and Zaranyika, 1995). Pasting and gelatinization of starch by heating it in water or immersing it in aqueous alkali delivers pregelatinized starch. Because such processing destroyed several intra- and intermolecular bonds, pregelatinized starch is well water soluble and chemically more active. When granular starch is passed under pressure through narrow nozzles, so-called α-starch with improved solubility in water is formed. However, such physical modifications of macrostructure usually result in a depolymerization of the polysaccharide. Starch granules are composed of amylose and amylopectin, forming crystalline and amorphous regions of granule. Polysaccharides in an amorphous region are more susceptible to enzymatic digestion than those in crystalline regions (so-called resistant starch). Resistant starch is used as prebiotic — a nutrient for probiotic bacteria colonizing human intestine. Controlled swelling of starch granules in water can remove a significant part of the amorphous interior of starch granule, producing empty domains within granules. Potentially, such granules can be utilized as natural microcapsules for colorants and aromas. Functional properties of starch depend on the amylose-to-amylopectin ratio. For some purposes, amylose-rich starch is more beneficial, and for the others, application of an amylopectin-rich (waxy) starch has a priority. Genetically engineered starches enriched in such components are available on the market. 5.4.2.1 Depolymerization of Carbohydrates If not utilized in the pulp industry, hemicelluloses are hydrolyzed in the acidcatalyzed process, mainly to monosaccharides and to furan-2-aldehyde (pentosanes) and 5-hydroxymethylfuran-2-aldehyde (5.62) (hexosanes). Monosaccharide-containing syrups, after purification, are either fermented or utilized as wood molasses for feeding ruminants. In another approach, xylose, the least soluble component of syrup, is allowed to crystallize. Separated xylose is then hydrogenated over an Ni/Al catalyst at 120°C under 6 × 106 Pa into xylitol. Hemicelluloses, together with proteins, are capable of the Maillard reaction and may contribute to the overall secondary aroma of processed foodstuffs (Tomasik and Zawadzki, 1998). The acid-catalyzed hydrolysis of cellulose, the saccharification, results in splitting the terminal D-glucose unit of the fibrilles. Thus, under thorough control of the reaction conditions, D-glucose is the sole product. Glucose syrup either is a source of pharmaceutical grade D-glucose or is fermented to ethanol. The β-glycosidic bond of cellulose can be split thermally. Perhaps the most ancient polysaccharide processing — the dry wood distillation — delivers charcoal, water, tar, methanol, acetone, acetic acid, and gases. Liquid and gaseous fractions result from the thermolysis of thermally split D-glucose. Thermolysis of cellulose with α-amino and α-hydroxy acids produces several aromas potentially interesting for food and cosmetic industries. Starch and pectins also generate aromas on heating with these acids (Baczkowicz ˛ et al., 1991; Sikora et al., 1998). Depolymerization of starch yields dextrins — one of the most useful products of the food industry. The most frequent dextrinization involves proton catalysis or heat. Hydrochloric

Saccharides

103

acid is a superior catalyzing proton donor, but organic acids are also capable of starch dextrinization. Such processes extended in time can lead in the saccharification of starch to oligosaccharides and, finally, to D-glucose, maltose, and glucose syrups, which are used directly as sweeteners or are fermented. Thermal (up to 260°C) dextrinization of starch produces canary yellow dextrins called British gums. They differ in properties and applications from dextrins from acid hydrolysis. Dextrins are commonly used as food thickeners, plasticizers, and adhesives. The physical methods mentioned above can also be used in the manufacture of dextrins in readily controlled processes. Depolymerization of polysaccharides to formaldehyde seems to be particularly promising to the chemical industy as the versatile, renewable source of and key process for utilization of polysaccharides in the 21st century (Okkerse and van Bekkum, 1996). Reduction of formaldehyde delivers methanol, one of the most important chemical reagents. 5.4.2.2 Chemical Modification of Polysaccharides without Attempted Depolymerization Polysaccharides offer practically the same kind of reactivity as monosaccharides, except reactions on the anomeric carbon atom, because in a majority of polysaccharides the hydroxyl group at this atom takes part in the polysaccharide chain formation via the glycosidic bonds. In long chains of polysaccharide, only terminal saccharide units contain free hydroxyl groups at the anomeric carbon atom. It should be mentioned that even such minute modification in this position can be reflected by changes in rheological properties of polysaccharide solutions, pastes, and gels. There are some polysaccharides naturally containing some functional groups. Thus, chitin contains acetamido groups. Alginates, many plant gums (Arabic, gatti, karaya, tragacanth, and xanthan, the latter semisynthetic), pectins, some galactans, and xylans contain carboxylic groups. Heparin, furcellaran, and carrageenans carry sulfate function. These groups can be utilized in chemical modifications of these polysaccharides. Limitations in possibility of chemical modifications of starch result from steric hindrance of reaction sites, solubility, viscosity of reaction medium, and susceptibility to side reactions; among them, depolymerization almost always accompanies intended modification. As a rule, polysaccharides are soluble, although frequently only sparingly, in water and dimethyl sulfoxide. Polysaccharides solubilize on xanthation, i.e., on reaction with CS2 in alkaline medium, to form syrups of xanthates. On acidification polysaccharides could be recovered. Such procedure was utilized for several decades for production of artificial silk from cellulose. Polysaccharides undergo hydrolysis; reduction to alcohols; oxidation to aldehydes, ketones, and carboxylic acids; esterification with inorganic (sulfuric, phosphoric, nitric, boric, and sillylic acids) and organic acids; etherification; acetylation with aldehydes; halogenation with the same reagents as mono- and disaccharides; ammination (usually via halogenated polysaccharides); carbamoylation with acylamides or isocyanides; and metallation. Only some of the large number of potential modifications achieved approval by food laws of particular countries. Thus far only starch, cellulose, and pectin are chemically modified for nutritional purposes and

104

Chemical and Functional Properties of Food Components

can be implemented into foodstuffs. If biodegradable materials are also considered, modification of other polysaccharides can be taken into account. Practical modification of pectins is limited to changes in degree of their methylation. In this manner the strength of their jellies can be controlled. Modifications of cellulose for use in the food industry are limited to its esterification and etherification. Mainly, cellulose acetate is produced. It is used for special membranes for treating water and fruit juices. Among ethers, methyl- and methylhydroxypropyl celluloses pay particular attention. They are available in methylation with common methylating agents and propylene oxide. Carboxymethyl cellulose (CMC) is the product of the reaction of cellulose with chloroacetic acid. Products of degree of substitution from 0.3–0.9 are available. All 2-, 3-, and 6-hydroxyl groups do react. Modified and derivatized celluloses have found their application in the food industry as nondigestible components of low-calorie meals. CMC is a texturizing agent and edible adhesive. Chemical modification of starch for nutritional purposes involves oxidation, but only with a limited number of oxidants; esterification, with a limited number of esterifying reagents; etherification; and complex formation. Metal derivatives might have some significance as carriers of bioelements and therapeutic agents, first of all, insulin substitutes (Tomasik et al., 2001). Oxidation of starch to aldaric and uronic acid-type carboxylic starches for practical purposes should leave no more than one carboxylic group per each 25th glucose unit. The oxidation should be carried out with a possible high depolymerization degree and the formation of the smallest possible number of the terminal anomeric carbon atoms. Gels from oxidized starches have low viscosity and good transparency. Such oxidation is provided by sodium hypochlorite. This oxidant only randomly oxidizes the 6-hydroxymethyl groups of starch. The latter groups are readily oxidized with nitrogen oxides. Metal ioncatalyzed air oxidation of starch results in simultaneous formation of carboxyl and carbonyl starches. The most useful esters of starch are phosphates, commonly used gelating agents, acetates, and adipates — the film forming materials. Only these preparations are utilized in foods, which have a low degree (0.2–0.0001) of esterification. The most important and widely used starch esters are those prepared by using monochloroacetic acid (carboxymethyl starch), ethylene oxide (hydroxymethyl starch), and propylene oxide (hydroxypropyl starch). Side chains introduced into starch by esterification or etherification can undergo dissociation. For instance, all starch sulfates, starch phosphates, and carboxymethyl starches dissociate in aqueous solution, leaving a negative charge on starch. They are called anionic starches. If starch was etherified with a reagent introducing tetralkylammonium salt function, the dissociation developed a positive charge on the starch and such starch belonged to cationic starches. Polysaccharides are important complexing agents for inorganic and organic gases, liquids, and solids. Usually surface sorption is involved, but in the case of starch, inclusion complexes inside of the amylose helix and eventually short helices of amylopectin, as well as inside of the amylopectin branches, and capillary complexes involving capillaries between starch granules are also formed. All of them exist in a natural, native form; they can also be formed in several common operations of food processing, e.g., dough formation, beating of foam, and scrambling yolk with sugar.

Saccharides

105

Formation of inclusion complexes of starch becomes a more common method of protecting some volatile, as well air-sensitive, food components (microencapsulation). Such complexes are essential for food texturization and overall stabilization. Cationic starches are used as detergents and cellulose pulp components, whereas anionic starches readily form complexes with proteins (Schmitt et al., 1998). The latter are attempted in utilization as biodegradable plastics and meat substitutes. 5.4.2.3 Cross-Linked Polysaccharides Polysaccharide cross-linking frequently occurs when it is acetalated, esterified, or etherified with bi- and polyfunctional reagents, e.g., POCl3, polyphosphates, dianhydrides of tetraioic acids, dialdehydes, dicarboxydiamides, vinyl monomers, and so on. Usually such compounds have enhanced water-binding capacity, lower aqueous solubility, and shear force stability. Retrogradation is a very common reaction of gels of starch polysaccharides. It leads to enhanced molecular-weight systems. Amylose gels retrograde even within hours, whereas retrogradation of amylopectin gels takes days and even weeks. Retrogradation of gels is manifested by dendrite formation in the gel and in bread by bread staling. The phenomenon is due to orientation of chains of amylose in respect to one another to aggregate with involvement of intermolecular hydrogen bonds. The retrogradation affinity depends on starch variety and decreases in the order: potato > corn > wheat > waxy corn starch. Evidently, the retrogradation rate and nature of the formed amylose crystals depend on the starch source, amylose:amylopectin ratio, and storage temperature. Low temperature, around the freezing point, and polar gel additives favor retrogradation. Retrograded starch is utilized as a component of low-calorie food.

5.4.3 ENZYMATIC TRANSFORMATIONS

OF

CARBOHYDRATES

With few exceptions, enzymatic processes in carbohydrates cause degradation. Enzymes are used in the form of pure or semipure preparations or together with their producers, i.e., microorganisms. Currently, semisynthetic enzymes are also in use. Alcoholic fermentation is the most common method of utilization of monosaccharides, sucrose, and some polysaccharides, e.g., starch. Lactic acid fermentation is another important enzymatic process. Lactic acid bacteria metabolize mono- and disaccharides into lactic acid. This acid has a chiral center; thus either D(–), L(+), or racemic products can be formed. In the human organism, only the L(+) enantiomer is metabolized, whereas the D(–) enantiomer is concentrated in blood and excreted with urine. Among lactic acid bacteria, only Streptococcus shows specificity in the formation of particular enantiomers, and only the L(+) enantiomer is produced. Enzymatic reduction of glucose-6-phosphate (5.85) into inositol-1-phosphate with cyclase and reduced NAD coenzyme, followed by hydrolysis with phosphatase, presents another nondegrading enzymatic process proceeding on hexoses. Inositol (5.86) plays a role in the growth factor of microbes. Its hexaphosphate, phytin, resides in the aleurone layer of wheat grains.

106

Chemical and Functional Properties of Food Components

There are also known bacteria that polymerize mono- and oligosaccharides. Leuconostoc mesenteroides polymerizes sucrose into dextran — an almost linear polymer of 400 or more α-D-glucose units. Dextran is also generated in frozen sugar beets. This causes difficulties in sugar manufacturing if the beets have to be stored at low temperature. Dextran serves as a blood substitute and chromatographic gel (Sephadex). Other polysaccharides synthesized by bacteria are levan, a polymer of β-D-fructose; pullulan, a polymer of α-D-glucose; and xanthan gum, a polymer of β-D-glucose and α- and β-D-mannoses. The enzymatic oxidation of sucrose with glucose oxidase to D-glucose-δlactone consumes oxygen dissolved in beer and juices. In this manner the rate of undesirable processes caused by oxidation, e.g., color and taste changes, is decreased. All essential enzymatic polysaccharide transformations deal with degradation (Figure 5.4). In the case of cellulose, this degradation leads to glucose. Endoglucanase and cellobiohydrolase attack the amorphous regions of the compact structure of cellulose, producing D-glucose and cellobiose, respectively. Starch, amylose, and amylopectin are not necessarily so deeply degraded. There are several amylolytic enzymes capable of starch degradation. They provide high specificity of their action (Figure 5.4). Synthesis of cyclodextrins (cycloglucans, Schardinger dextrins) presents a special case. Slightly hydrolyzed starch is transformed into cyclic products composed of six, seven, and eight α-D-glucose units, α-, β-, and γ-cyclodextrins. The yield of cyclodextrins declines with the number of glucose units in cycles.

Amylo - 1.6 - α - gluconase (Dextrinase) γ−

β−

α−

Glucoamylase

Cyclodextrin

Bacillus macerans β - Amylase Glucose

α - Glucosidase Glucse

α - Amylase

Maltose Glucse isomerase

Pullulanase and Glcogenase

Fructose Dextrin

Dextrin

FIGURE 5.4 Enzymatic transformations of starch.

Saccharides

107

Although higher-membered cyclodextrins are also formed in the reaction mixtures, their minute yield seriously limits their potential applications. Cyclodextrins are sometimes cross-linked into cyclodextrin resins with interesting inclusion properties.

5.4.4 CEREAL

AND

TUBER STARCHES

All botanical varieties of starches can be primarily classified into tuber and cereal starches. Differences in size and shape of granules, the amylose/amylopectin ratio, and protein (7–13%), lipid (1.5–6%), other carbohydrate (5–23%), and mineral (1–3%) content, not necessarily on whether a given starch belongs to one of the above two classes. Potato starch, the tuber starch, has the largest granules (up to 150 µm), and as the sole starch, it has amylopectin esterified with phosphoric acid (Seidemann, 1966). However, starch granules of wild yam (Diascorea dumetrorum), which has one of the finest granules ever seen, also originate from tuber starches (Nkala et al., 1994). Generally, cereal starches are richer in lipids (e.g., cornstarch), and tuber starches are richer in proteins, although the oat, a cereal starch, is one of the richest in lipids and proteins (see Table 5.2). Polysaccharides and lipids, as well as proteins, in granules usually reside therein in native complexes. These complexes are stronger in cereal starches. Thus, potato starch can readily be isolated relatively free of proteins, whereas the complete defatting of cornstarch could not be afforded. The main difference between tuber and cereal starches comes from their crystallographic pattern: A for tuber and B for cereal starches. These two patterns result from different mutual orientations of amylose helices inside the granule, e.g., single (A-type) and double (B-type) (Figure 5.3). These differences determine several essential properties of both classes of starches. They are swelling, gelation, and course of pasting, and affinity to various physical, physicochemical, and chemical modifications. There are also differences in the taste, digestibility, and nutritive value of particular starches. The most common sources of starch in various regions of the world are potato, maize, cassava (manioc, tapioca, yucca), and rice. Popularity of a given starch and starchy plants do not go together. For instance, in many regions of the world wheat and rye are very commonly used. Wheat starch is only randomly isolated, and rye starch is only exceptionally available. Rye grains contain mucus, which seriously obstructs isolation of starch from this source.

5.5 FUNCTIONAL PROPERTIES OF CARBOHYDRATES 5.5.1 TASTE Saccharides are usually associated with sweet taste, although among them are also bitter and nonsweet saccharides (Table 5.3). Except for sucrose, the sweetness decreases with the number of monosaccharide units going toward oligo- and polysaccharides, because only one monosaccharide unit interacts with mucoprotein of the tongue receptor.

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Chemical and Functional Properties of Food Components

Because a number of powerful synthetic and natural nonsaccharide sweeteners are available on the market, apart from reduction to saccharide alcohols, other derivatizations of saccharides, even if they increase their sweetness (Table 5.3), have no practical significance. The following carbohydrate sweeteners are in common use (their relative sweetness (RS) in respect to 10% aqueous solution of sucrose is given in Table 5.3): • D-glucose: because of fast resorption, it is a source of immediately available energy. It is used in injections and infusion fluids for children and patients in their recovery period. Its digestion requires insulin. It causes tooth cavities. • D-fructose: the most readily water-soluble sugar. It does not crystallize from stored juices. Because of its hygroscopicity, it retains moisture in sugar-preserved food and intensifies its flavor and aroma. Metabolism of D-fructose delivers less energy than sucrose. This saccharide neither causes nor accelerates tooth cavities. It accelerates ethanol metabolism. In the organism, D-fructose metabolizes into glycogen, animal starch being the energy reservoir stored in the liver. • Lactose: sparingly water-soluble (20% at room temperature) sugar present in mammalian milk (4.8–5.1%). It is utilized as a carrier of other sweeteners. It improves flavor, produces a good image of food processed in microwave ovens, and improves the taste of dairy products. • Sucrose: the most common sweetener for its pleasant taste. It is widely used as a preservative of marmalades, syrups, and confitures. Osmotic phenomena are involved. Due to competition of microorganisms and preserved foodstuffs for water molecules, the microorganism tissues undergo plasmolysis. Aqueous solutions containing 30% sucrose do not ferment, and 60% of the solutions are resistant to all bacteria but Zygosaccharomyces. • Maltose: slightly hygroscopic disaccharide of mild and pure sweet impression. Its solutions have low viscosity. Its color is stable regardless of temperature. • Starch syrups: they result from starch saccharification. The saccharification can be carried to various stages. The first sweet product, maltotetraose syrup (RS = 0.25), is viscous. As the saccharification proceeds, the viscosity of syrups decline and their RS increases. Syrups are water soluble, do not retrograde, and are readily digested. Glucose syrup, the final product of saccharification, may be converted by isomerization into fructose syrups (Table 5.4) or hydrogenated to D-sorbitol. Apart from the sweetness and low energetic value (17.5 kJ/g), texturizing and filling properties of syrups are utilized in practice. • Malt extract from barley malt obtained by aqueous extraction: contains 4–5% sucrose; spare amounts of D-glucose, D-fructose, and maltose; proteins; and mineral salts. • Maple syrup and maple sugar from juice of Acer saccharium maple trees: contains 98% saccharides, 80–98% of which is sucrose. • Sugar alcohols (D-sorbitol, D-xylitol, and D-mannitol): perfectly water soluble, soluble in alcohol, and more stable at low and high pH values than

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109

TABLE 5.4 Saccharide Content (%) in Various Starch Syrups Syrups Glucose Conversion Saccharide

Low

High

Very High

Maltose

Fructose

Glucose Fructose Maltose Higher saccharides

15 — 11 48

43 — 20 13

92 — 4 2

10 — 40 28

7–52 42–90 4 3–6

saccharides. Their sweet taste lasts for a prolonged time and is accompanied by a cool impression. They metabolize without insulin. The energetic values of xylitol, sorbitol, and mannitol are 17, 17, and 8.5 kJ/g, respectively. Therefore, they can be used as sweeteners for diabetics and consumers with obesity. Because of hygroscopicity, they are used as food humectants. • Compounded sweeteners, blends of various sweeteners: the composition of such blends depends on the purpose they are designed for. Usually they are blends of various saccharides, but sorbitol, sugar syrups, and even malic acid are also compounded. • Honey: this natural product has a composition dependent on the harvest time, geographical region, and origin and kind of flowers from which the nectar was collected. Even the variety of insects is a factor. Fructose, glucose, and maltose constitute approximately 90% of the total sugar content. There is also a rich variety of free amino acids and other organic acids, minerals, pigments, waxes, enzymes, and pollen. The latter may act allergizing. Honey may contain toxic components from poisonous plants, although there are several poisonous plants that give nonpoisonous honey. In some countries aqueous solutions of honey are fermented into honey-flavored wine (mead).

5.5.2 COLORANTS Sugars are utilized for generation of caramel, a brown colorant for food (Tomasik et al., 1989). For this purpose sugar is burnt (caramelized). Various additives (caustic soda, caustic sulfite, ammonia, and their combinations) catalyze this process. In laboratory tests some proteogenic amino acids and their sodium and magnesium salts proved to be suitable catalysts (Sikora et al., 1994). Catalysts accelerate the process and decrease caramelization temperature, usually between 130 and 200°C, providing that there is good tinctorial strength. Products prepared by noncatalyzed burning of sugars at 200–240°C have poor tinctorial strength and serve as flavoring agents. There is a concern about harm coming from the free radical character of caramels. However, they were proven (Barabasz et al., 1990) to be nonmutagenic. Thermal processing of saccharides and polysaccharides containing foodstuffs

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Chemical and Functional Properties of Food Components

results in development of brown color; it originates from caramelization and dextrinization, respectively. Brown-colored dextrins, even if they contain free radicals, are nonmutagenic because such free radicals are unusually stable (Ciesielski and Tomasik, 1996). Depending on the catalyst used, caramels differ from one another in their isoelectric point. If colored matter does not fit the isoelectric point, micels of the caramel irreversibly discharge and the caramel separates. Four types and several classes of caramels with widely different properties are manufactured. This variety provides a selection of a proper colorant to all types of foodstuffs.

5.5.3 FLAVOR

AND

AROMA

Burning of sugar in noncatalyzed processes results in formation of particularly high amounts of furan-2-aldehyde and its derivatives. They constitute the flavor and aroma typical for caramels. Many foodstuffs (meat, fish, dough, potato, cocoa, coffee, and tobacco) on thermal treatment (baking, frying, roasting, and smoking) develop specific aromas. They are volatile derivatives of pyrazine, imidazole, pyrrole, and pyridine formed on thermal reactions of saccharides and proteins, nucleotides, and amino acids. Saccharides and polysaccharides — starch and cellulose (Baczkowicz ˛ et al., 1991), pectins (Sikora et al., 1998), and hemicelluloses (Tomasik and Zawadzki, 1998) — heated with amino acids develop scents specific for polysaccharide, amino acid, and reaction conditions. Thus, supplementation of saccharides and polysaccharides with amino acids and proteins, as well as supplementation of protein-containing products with saccharide, can be useful in generation, modification, and enrichment of flavor and aroma of foodstuffs and tobacco.

5.5.4 TEXTURE More concentrated aqueous solutions of carbohydrates form viscous liquids. This property is most commonly utilized in practice for texturizing foodstuffs. In such solutions sugar–sugar interactions (complexation) are responsible for this effect. It was found that although interactions in various monosaccharide–monosaccharide, disaccharide–disaccharide, and monosaccharide–disaccharide combinations brought . ´ no particularly promising texturizing result (Mazurkiewicz and Nowotny- Rózanska , 1998), certain blends of either mono- or disaccharide with polysaccharides showed remarkable increase in viscosity and adhesiveness (Mazurkiewicz et al., 1993). On such, edible glues and adhesives could be prepared. Such interactions are commonly utilized in texturization of puddings, jellies, foams, and so on. Some oligosaccharides and the majority of polysaccharides form hydrocolloids, which build up their own macrostructure. They give an impression of jelly formation, thickening, smoothness, stabilization against temperature and mechanical shocks, aging, and resistance to sterilization and pasteurization. Plant gums, pectins, and alginates are particularly willingly utilized for this purpose. Recently, considerable attention was paid to textural properties of polysaccharide–polysaccharide interactions where both interacting polysaccharides were starches of various origins (Obanni and Bemiller, 1997;

Saccharides

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Lii et al., 2001a). One should note that the texturizing effect of a given saccharide or polysaccharide and its various blends is developed as a function of time necessary for the formation of a gel network (a physical cross-linking). The pH and temperature may also be essential factors. If protons (pH < 7) or hydroxyl anions (pH > 7) and temperature do not evoke any structural changes in interacting species, the texturizing effect is reversible in pH and temperature. If retrogradation does not take place, texturization is also reversible in time. Saccharides, oligosaccharides, and polysaccharides form also complexes with mineral salts, proteins, and lipids. Such complexes also contribute to foodstuff texture. Apart from combinations of natural saccharides, oligosaccharides, and polysaccharides with involvement of lipids and proteins, chemically modified polysaccharides are also utilized for texturization. Cross-linked starches are important texturizing agents. The degree of cross-linking is an important factor. It should not be higher than 0.2. Among cross-linked starches, those esterified with phosphoric acid are particularly favored. All starches can be cross-linked by esterification with phosphoric acid (in practice, either with salts of meta- or orthophosphates, as well as POCl3 and PCl5), but at the same degree of substitution, phosphorylated potato starch gives superior results, while cornstarch phosphate is the poorest. Starch sulfate ester is used as a thickener and emulsion stabilizer. It is a typical anionic starch used as a component of anionic starch–protein complexes constituting meat substitutes (Tolstoguzov, 1991, 1995). Other anionic starches, as well as pectins, alginic acid, carrageenans, furcellaran, heparin, xanthan gum, and carboxymethyl cellulose, are anionic polysaccharides; their application in food texturization is now under study (Clark and Ross-Murphy, 1987; Schmitt et al., 1998; Zaleska et al., 2001a, 2001b). Anionic polysaccharides are particularly good texturizing agents in the presence of mineral salt cations (Na+, K+, Mg2+, and Ca2+). Among many available modified polysaccharides, application of only few of them is legal in view of the food law of particular countries. Some restrictions are put on the method of their manufacture and the purity of such products. The replacement of saccharide sweeteners (first of all sucrose) in food with various natural and synthetic sweeteners of very high RS (currently, mainly saccharine, aspartame, and cyclamates) is a task. It is also a demand of consumers looking for low-calorie food. Also, diabetics are looking for food free of insulin-requiring saccharides and polysaccharides. Following such demands, problems are encountered in providing the anticipated texture of sweet products manufactured without saccharides (Mazurkiewicz et al., 2001).

5.5.5 ENCAPSULATION Various foodstuffs loose their original, beneficial flavor, aroma, taste, and color on processing. It is a common result of evaporation of volatile components or decomposition of certain food components under the influence of oxygen or light. In this manner the quality of foodstuffs decreases. In order to avoid such effects, volatile and unstable products are either protected in processed sources or, after processing, are supplemented by fragrances, colorants, and other components.

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Such goals are met by encapsulation and supplementation of microcapsule closed additives. Saccharides are suitable for making such microcapsules. Compression of additives (guest molecules) with a saccharide forming the matrix of the microcapsule (the host molecule) is a common practice. It is beneficial if there are some other-than-mechanical interactions between the guest and host that decrease the rate of evaporation or reaction of the guest from the microcapsule. Granular starch can encapsulate guests in capillaries between granules; gelatinized starch, amylose, and amylopectin can trap certain molecules inside helices generated in contact with guest molecules. Coacervation or coprecipitation of host and guest and suspension of the guest molecule in polysaccharide gels, followed by drying, is another common procedure. Microcapsules can be made on the formation of polysaccharide–protein complexes in the presence of a potential host. Preswelled granular starches are potential natural microcapsules (Lii et al., 2001b). α-, β-, and γ-cyclodextrins are the most effective compounds for microencapsulation of food components (Szejtli, 1984). Cyclodextrins take a form of toruses with cavities of 0.57, 0.78, and 0.95 nm in diameter, respectively. Their height is 0.78nm. Upper and bottom edges of the toruses have secondary and primary hydroxyl groups, respectively. All hydroxyl groups reside on the external surface of toruses, making cyclodextrins hydrophilic. Simultaneously, their cavity interior is hydrophobic. Cyclodextrins are water-soluble hosts for hydrophobic guests. The formation of inclusion complexes is controlled by the dimensional compatibility of the guest and host cavity. Commercially available dextrins are, in fact, inclusion complexes of cyclodextrins with two water molecules closing the entrance to the cavity. The formation of cyclodextrin inclusion complexes is reversible and, therefore, is governed by concentration of guests competing for a place inside the cavity.

5.5.6 POLYSACCHARIDE CONTAINING BIODEGRADABLE MATERIALS There is a growing concern about fully biodegradable plastic — packing and wrapping foils, containers, equipment of fast-food restaurants, and superabsorbents. Currently, several products made of polyethylene modified into biodegradable material are in use throughout the world. Biodegradability of such materials was afforded by admixture of 6–15 w-% of natural components, such as starch, cellulose, wood, or proteins, into polyethylene. Polyurethane foams used as thermal insulators and packing materials contain up to 20% starch. The level of starch in copolymers of ethylene with either vinyl chloride, styrene, or acrylic acid may reach 50%. Of course, the effect of biodegradation of such material has more aesthetic significance than ecological. Although degradation of the finely pulverized synthetic portion of such materials is accelerated, it still takes several decades for depolymerization to come to its end. Apparently, the simplest biodegradable plastics could be prepared of starch solely by compression of up to 106 kPa, provided starch was moisturized up to its natural water-binding capacity (~20 w-%) ( Kudla and Tomasik, 1992). Following the idea of full biodegradability of materials, attention has been paid to the compositions of plain carbohydrates with either unmodified or modified

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proteins and of modified carbohydrates with unmodified and modified proteins. Such compositions are processed to generate carbohydrate–protein complexes. The thermodynamic and electrical compatibilities of components should be reached in order to afford the best functional properties of materials. Because of the chemical nature of proteins (cationic character), carbohydrates should be anionic, i.e., on dissociation the negative charge should be left on polysaccharide moiety. The COOH, PO3H2, and SO3H groups provide such properties. Whenever modification of a carbohydrate is required to make it anionic, the degree of derivatization should not exceed 0.1. It should neither increase the hydrophilicity of the product nor, if possible, decrease its molecular weight.

REFERENCES Angyal, S.Y., Complexes of metal cations with carbohydrates in solution, Adv. Carbohydr. Chem. Biochem., 47, 1, 1989. Ball, S.G., van de Wal, M.H.B.J., and Visser, R.G.F., Progress in understanding the biosynthesis of amylose, Trend Plant Sci., 3, 462, 1998. Baczkowicz, ˛ M. et al., Reactions of some polysaccharides with biogenic amino acids, Starch/Staerke, 43, 294, 1991. Barabasz, W. et al., On mutagenicity of caramels, Starch/Staerke, 42, 69, 1990. Ciesielski, W. and Tomasik, P., Starch radicals. Part I, Carbohydr. Polym., 31, 205, 1996. Ciesielski, W. and Tomasik, P., Starch radicals. III, Z. Lebensm. Unters. Forsch., A207, 292, 1998. Ciesielski, W., Tomasik, P., and Baczkowicz, ˛ M., Starch radicals. IV, Z. Lebensm. Unters. Forsch., A207, 299, 1998. Clark, A.H. and Ross-Murphy, S.B., Structural and mechanical properties of biopolymer gels, Adv. Polym. Sci., 53, 57, 1987. ´´ , Suppl. 4, 112, 1998. Erlander, S., Biosynthesis of starch, Z˙˙ywn . Technol. Jakosc Gallant, D.J., Bouchet, B., and Baldwin, P.M., Microscopy of starch: evidence of a new level of granule organization, Carbohydr. Polym., 32, 177, 1997. Goosen, M.F.A., Application of Chitin and Chitosan, CHIPS, Weimar, TX, 1997. Imberty, A. et al., Recent advances in knowledge of starch structure, Starch/Staerke, 43, 375, 1991. Kudla , E. and Tomasik, P., Effect of high pressure on starch matrix, Starch/Staerke, 44, 167, 1992. Lii, C.-y. et al., Polysaccharide: polysaccharide interactions in pastes, Pol. J. Food Nutr. Sci., submitted, 2001a. Lii, C.-y. et al., Granular starches as dietary fiber and natural microcapsules, Int J. Food Sci. Technol., accepted, 2001b. . ´ Mazurkiewicz, J. and Nowotny- Rózanaksa , M., Viscosity of aqueous solutions of saccharides, Pol. J. Food Nutr. Sci., 7/2, 171, 1998. Mazurkiewicz, J., R¸ebilas, K., and Tomasik, P., Aspartame as texturizing agent for foodstuffs, Z. Lebensm. Unters. Forsch., A212, 369, 2001. Mazurkiewicz, J., Zaleska, H., and Zaplotny, J., Studies in carbohydrate based glues and thickeners for foodstuffs. Part I. Glucose–sucrose–apple pectin ternary systems, Starch/Staerke, 45, 175, 1993. Nkala, B. et al., Starch from wild yam from Zimbabwe, Starch/Staerke, 46, 85, 1994.

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Obanni, M. and Bemiller, J.N., Preparation of some starch blends, Cereal Chem., 74, 431, 1997. Okkerse, C. and van Bekkum, H., Starch 96: The Book, Van Doren, H. and Van Swaaij, N., Eds., Carbohydrate Research Foundation, Noordwijkerhout, 1996, chap. 1. Ruck, H., The new organosolv pupls: will they otrival starch as an industrial raw material?, ´´ ., Suppl. 2, 138, 1996. Z˙˙ywn . Technol. Jakosc Schmitt, C. et al., Structure and technofunctional properties of protein-polysaccharide complexes. A review, Crit. Rev. Food Sci. Nutr., 38, 689, 1998. Seidemann, J., Die Staerkeatlas, Paul Parey, Berlin, 1966. Siemion, I.Z., Biostereochemistry, PWN, Warsaw, 1985, chap. 1 (in Polish). Sikora, M., Tomasik, P., and Araki, K., Thermolysis of pectins with amino acids, Pol. J. Food Nutr. Sci., 7/3, 391, 1998. Szejtli, J., Cyclodextrin Inclusion Complexes, Academiai Kiado, Budapest, 1984. Szymo´nska, J., Krok, F., and Tomasik, P., Deep freezing of potato starch, Int. J. Biol. Macromol., 27, 307, 2000. Tolstoguzov, V.B., Functional properties of food protein and role of protein: polysaccharide interaction, Food Hydrocoll., 4, 429, 1991. Tolstoguzov, V.B., Some physico-chemical aspects of protein processing foods. Multicomponent gels, Food Hydrocoll., 9, 317, 1995. Tomasik, P. et al., Potato starch derivatives with some chemically bound bioelements, Acta Pol. Pharm. Drug Res., 58, 447, 2001. Tomasik, P., Palasi´nski, M., and Wiejak, S., The thermal decomposition of carbohydrates. Part I. The decomposition of mono-, di-, and oligo-saccharides, Adv. Carbohydr. Chem. Biochem., 47, 203, 1989. Tomasik, P. and Schilling, C.H., Complexes of starch with inorganic guests, Adv. Carbohydr. Chem. Biochem., 53, 263, 1998a. Tomasik, P. and Schilling, C.H., Complexes of starch with organic guests, Adv. Carbohydr. Chem. Biochem., 53, 346, 1998b. Tomasik, P. and Schilling, C.H., Chemical modification of starch, Adv. Carbohydr. Chem. Biochem., in press, 2002. Tomasik, P., Wang, Y.J., and Jane, J., Starch: sugar complexes, Starch/Staerke, 47, 185, 1995. Tomasik, P. and Zaranyika, M.F., Nonconventional methods of modification of starch, Adv. Carbohydr. Chem. Biochem., 51, 243, 1995. Tomasik, P. and Zawadzki, W., Reaction of plant material with biogenic amino acids, Pol. J. Food Nutr. Sci., 7/1, 29, 1998. Zaleska, H., Ring, S., and Tomasik, P., Complexes of potato starch with casein, Int. J. Food Chem. Technol., 36, 509, 2001a. Zaleska, H., Ring, S., and Tomasik, P., Electrosynthesis of potato starch: whey protein isolate complexes, Carbohydr. Polym., 45, 89, 2001b.

6

Food Lipids Yan-Hwa Chu and Lucy Sun Hwang

CONTENTS 6.1 6.2 6.3

Introduction ..................................................................................................115 Chemical Constituents of Oils and Fats ......................................................116 Processing of Oils and Fats .........................................................................118 6.3.1 Introduction ......................................................................................118 6.3.2 Receiving..........................................................................................118 6.3.3 Preparation .......................................................................................118 6.3.4 Extraction .........................................................................................118 6.3.5 Refining ............................................................................................119 6.3.5.1 Degumming.......................................................................119 6.3.5.2 Chemical Refining ............................................................119 6.3.5.3 Physical Refining ..............................................................120 6.3.5.4 Bleaching ..........................................................................120 6.3.5.5 Deodorizing.......................................................................120 6.3.5.6 Dewaxing ..........................................................................120 6.3.6 Modification .....................................................................................121 6.3.6.1 Hydrogenation...................................................................121 6.3.6.2 Interesterification ..............................................................121 6.3.6.3 Fractionation .....................................................................121 6.4 Changes of Lipids Due to Storage ..............................................................121 6.5 Interactions of Lipids with Other Components in the Food System..........122 6.6 Functional Fatty Substances ........................................................................123 6.6.1 Structured Lipids..............................................................................123 6.6.2 Polyenoic Fatty Acids ......................................................................126 6.6.3 Vegetable Lecithin............................................................................128 6.6.4 Tocopherol and Phytosterol .............................................................129 6.6.5 Sesame Lignans................................................................................130 References..............................................................................................................131

6.1 INTRODUCTION Lipids include oils, fats, and fat-like substances that have a greasy feel and are insoluble in water but soluble in certain organic solvents such as ether, alcohol, and hexane. They are the major component of the human diet, serving as a source of

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115

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energy, providing essential nutrients (linoleic acid, linolenic acid, and vitamins A, D, E, and K), and facilitating the absorption of fat-soluble vitamins. In most developed countries, lipids may contribute up to 40% of the energy in the diet of the population; this is much higher than the 30% or less recommended by most health organizations. High intake of total dietary fat is associated with increased risk of coronary heart disease, obesity, and some types of cancers. However, oils and fats play a vital functional and sensory role in food products. Consumers are allured by the flavor, texture, and aroma of fat-rich foods. Fats interact with other components to develop and fabricate texture, mouth feel, and the overall sensation of lubricity of foods. The role of lipids in food quality should not be disregarded by the tendency to overemphasize dietary fat as “negative” nutrients. This chapter will review the properties of oils and fats, oil processing, functional lipids, and utilization of some by-products from oil processing.

6.2 CHEMICAL CONSTITUENTS OF OILS AND FATS Oils and fats are water-insoluble, hydrophobic substances of vegetable or animal origins that consist mainly of triacylglycerols (TAGs). The esterification of one molecule of glycerol with three molecules of fatty acids (FAs) yields three molecules of water and one molecule of TAG. The FAs contribute both the chemical and physical properties of the TAGs. Most FAs in nature are straight-chain acids that contain an even number of carbon atoms. All acids with 12-, 14-, 16-, and 18-carbon atoms are major FAs. Saturated FAs contain no double bonds, whereas unsaturated ones contain at least one double bond. Polyenoic FAs (PEFAs) contain at least two double bonds and mostly exist as nonconjugated PEFA types, in which double bonds between the carbons are separated by one carbon atom. The geometry of double bonds, as well as the number of double bonds, determines the reactivity of unsaturated FAs. A trans linkage produces less irregularity in the straight-chain structure; thus the trans FAs are usually higher melting and less reactive. Most naturally occurring FAs are cis forms. cis acids may be converted to trans isomers in the course of processing, involving heat and hydrogenation. The average degree of unsaturation of oils and fats is determined by the iodine value; the average molecular weight is measured by the saponification number. The FA compositions of oils and fats are determined by gas liquid chromatography analysis of methyl esters of FAs after methanolysis of fats and oils. The most widely distributed naturally occurring saturated FAs are lauric (C14:0), palmitic (C16:0), and stearic (C18:0) acids. The richest common sources of lauric acid are coconut oil, palm kernel oil, and babassu butter, which contain at least 40% of this acid. Palmitic acid is a major component of palm oil (45–50%) and lard and tallow (25–30%) (Tables 6.1 and 6.2). Stearic acid can be manufactured by hydrogenation of FAs. A variety of unsaturated FAs occur naturally in large quantities. These acids contain an even number of carbon atoms; 18-carbon atoms containing one, two, and three double bonds occur most frequently. The most abundant monoenic acid in vegetable oils and animal fats is oleic acid (C18:1). Rich sources of C18:1 are olive oil (70%), peanut oil (40%), sesame oil (40%), rice bran oil (45%), Camellia oleifera tea seed oil (80%), beef tallow (40%), and lard (45%).

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TABLE 6.1 Fatty acid composition of some vegetable oils (%) Oil Babassu Canola Coconut Corn Cottonseed Olive Palm Palm kernel Peanut Safflower Sesame Soybean Sunflower

C10:0 6

C12:0 44

C14:0 16

7

48

17

50

0.8 1 1 16

3.6

C16:0 8 3.9 8 12 25 14 46 8 12 6 10 11 7

C18:0 3 2 3 2 2 2.6 5 2 3 2 5.2 4 4

C18:1 15 64 6 27 18 72 39 14 47 13 41.2 23 19

C18:2 2 19 2 57 53 10 9 2 31 77 43.3 54 68

C18:3

C 20:5

C 22:6

5

9

9

0.1 1 0.4

0.4 0.2 7 0.5

TABLE 6.2 Fatty acid composition of animal fats (%) Oil Beef tallow Butter Chicken Lard Mackerel

C4:0C12:0

12

C14:0 3

C16:0 26

C 18:0 22

C 18:1 42

C 18:2 2

C 18:3 0.2

11 1 1.3 6

26 22 25 16

10 10 16 3

28 41 46 15

2 20 9 2

1 2 0.3 1

The most important and widely distributed PEFAs are linoleic (cis,cis-9,12octadecadienoic) and linolenic (cis,cis,cis-9,12,15-octadecatrienoic) acids. Linoleic acid, one of the nutritionally essential FAs, is the most abundant PEFA and is widely distributed in common vegetable oils such as soybean oil (50%), sunflower oil (65%), corn oil (50%), and sesame oil (40%). Linolenic acid distributed in nature is a major acid of the highly unsaturated vegetable oils. Rich sources are linseed (45–50%) and perilla (65%) oils. Highly unsaturated FAs with three to six double bonds always occur in marine animal fats. The most known and important acids are eicosapentaenoic acid (EPA, C20:5) and docosahexaenoic acid (DHA, C22:6). Fish species, location site, type of fat within the fish, and environmental effects cause a wide variation of FAs in marine animal fats. All oils and fats contain small amounts of nonglyceride components. Some of these components are removed from crude oils during refining to produce final products with satisfactory sensory properties. These minor components include phosphatides, unsaponifiable matters, chlorophyll, and alteration products.

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6.3 PROCESSING OF OILS AND FATS 6.3.1 INTRODUCTION Crude oil contains relatively small and variable amounts of nonglyceride impurities. The quality and yield of finished oil are affected by some of the undesirable impurities that are not properly removed during processing. The oil-insoluble impurities consist of seed fragments, excess moisture, meal fines, and a waxy substance. These oil-insoluble impurities are normally and readily removed by filtration. However, the oil-soluble impurities such as free FAs, phosphatides, gummy or mucilaginous substances, color bodies, proteins, hydrocarbons, ketones, and aldehydes are more difficult to remove. A series of unit operations are required to remove objectionable impurities with the least detrimental effect on finished oil quality and minimum oil loss.

6.3.2 RECEIVING Receiving, sampling, drying, storage, and cleaning are the typical operations of oilbearing materials prior to oil processing. The moisture content of the raw material is one of the prime factors for extended storage and final product quality. High moisture of oil-bearing materials results in reduced oil and protein content and darker color and increased refining loss of the extracted oil. For proper storage and subsequent processing, the contaminants must be removed and the grains or seeds must be dried to around 12–13% water content prior to storage. During storage, it is a routine practice to monitor the temperature of grains or seeds. If heating is occurring, the grains or seeds must be processed immediately. Otherwise, rotation of the grains or seeds is required to avoid severe heating and damage.

6.3.3 PREPARATION Proper preparation of grains or seeds is required for extraction of the oil, either by solvent or mechanical methods. The unit operations typically involve scaling, cleaning, cracking, conditioning, and flaking. The grains or seeds are scaled and cleaned to remove contaminants. For soybeans, cracking separates the hulls from the meats and the hulls are then removed by aspiration. After dehulling, the meats are conditioned to soften the cracks that are pliable for the subsequent flaking. During flaking, the meats are generally passed to the flaking rolls to squeeze the meats into flakes of approximately 0.30 mm in thickness. For oil-bearing materials with high oil content, such as sunflower, canola, peanut, or sesame, the purpose of conditioning or cooking is to break down the oil cell walls to the point where the oil is available to be expelled. In addition, protein coagulation in the meal, adjustment of the moisture content of the meal, and reduction in oil viscosity for proper pressing are also included.

6.3.4 EXTRACTION Mechanical extraction is used to press the oil-bearing materials with high oil content. Oil from a mechanical pressing operation contains meal fines in high concentrations,

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which are removed by filtration. The filtered oil can be used either for direct consumption or for subsequent refining. Sesame and peanut oils, as the typical pressed oils with unique flavors, are widely consumed in Oriental countries. Olive oil, an important product in the Mediterranean area, is also obtained by mechanical extraction from the fruit of the Olea europaea L. tree. For oleaginous materials having a low oil content (18–20%), such as soybean and rice bran, solvent extraction is often applied for oil recovery. Hexane is widely accepted as the most effective solvent used today. Most of the extractors currently used are designed as countercurrent flow devices. The solid material flows in an opposite direction of solvent-oil miscella with an increasing oil concentration. The miscella containing around 25–30% oil after extraction is subjected to solvent distillation to recover the oil. The extracted solid material, commonly known as white flakes, is also conveyed to the desolventizing process. A combination of mechanical and solvent extraction is often applied to oilseeds with high oil content, e.g., sunflower, safflower, corn germ, and canola. The most efficient method of extracting the oil is mechanically expelling about 60% of the oil and then using solvent extraction of the remaining oil.

6.3.5 REFINING 6.3.5.1 Degumming Degumming is an optional process and is used to remove phosphatides and foreign materials that are present in crude oil. Phosphatides are an excellent emulsifier that interfere with the oil–water separation in the acidulation process and cause neutral oil loss. Water degumming is effective for water-hydratable phosphatides. The phosphatides contained in soybean oil from good-quality beans are 90% hydratable and can be removed by water hydration. Severely damaged beans contain increased amounts of nonhydratable phosphatides (NHPs), mainly calcium and magnesium salts of phosphatidic acids. For the removal of NHPs, several acid treatments are used to produce a lower phosphorus degummed oil. Pretreatment of oil with phosphoric acid, citric acid, or other agent with proper time, temperature, and agitation conditions, followed by water hydration, is effective in removing NHPs from the oil. 6.3.5.2 Chemical Refining The purpose of chemical or physical refining is to remove nonglyceride impurities that consist of free FAs and mucilaginous substances, phosphatides, chlorophyll, and color bodies. Alkali refining is associated with the proper choice of alkalies, amounts of alkalies, and refining practice to produce refined oil without excessive saponification of neutral oil. The concentration and amount of caustic alkali solution to be used for refining the crude oil varies with the content of FAs in the oil. If excess caustic alkali solution is used, prolonged heating will result in saponification of the oil and neutral oil losses.

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6.3.5.3 Physical Refining Traditional alkali refining is replaced by physical refining, in which the use of chemicals is reduced. The most widely used method is steam refining. The crude oil quality is very important in order to obtain high-quality refined oil. The oil before physical refining should be efficiently degummed to remove phospholipids, as well as heavy metals, and bleached to remove pigments. The phospholipid content of the oil must be sufficiently low ⎯ less than 5 mg/kg phosphorus before steam stripping and less than 20 mg/kg phosphorus before bleaching. By applying superheated steam under low pressure and at a temperature higher than 220°C, both FAs and undesirable volatiles are removed. The quality of physically refined oil is close to that of alkalirefined oils, but losses of neutral oil are lower and the environment is less polluted (Cmolik and Pokorny, 2000). 6.3.5.4 Bleaching The bleaching process is used to remove color bodies and other minor impurities. The bleaching adsorbent, usually a clay product, removes residual soap from alkali refining, aldehydes and ketones from decomposed peroxides, and color bodies. The color of bleached oil is widely measured by the Lovibond tintometer color scale. 6.3.5.5 Deodorizing The deodorizing process is used to improve the taste, odor, color, and stability of the oils by the removal of FAs; various flavor and odor compounds classified as aldehydes, ketones, alcohols, and hydrocarbons; and oxidation products and pigments. Deodorization is primarily a high-temperature, high-vacuum, steam distillation process. High-temperature treatment bleaches the oil by destruction of the carotenoids. Some minor compounds, including tocopherols and phytosterols, are partially removed by deodorization. Typical conditions for deodorization of vegetable oil in semicontinuous deodorizers are: a temperature of 245–260°C, a holding time of 15–40 min, an absolute pressure of 3–6 mm of Hg, 3–8% stripping and sparge steam based on oil throughput, and oil cooled to 60°C in the deodorizer. 6.3.5.6 Dewaxing In some vegetable oils such as sunflower, safflower, corn, rice bran, and canola oil, waxy materials may appear as sediments during storage at lower temperatures. To avoid a hazy appearance of oils, dewaxing is usually done by chilling the oils in a continuous heat exchanger to about 0–5°C for 4–16 h to complete the growth of the wax crystals. After stabilization, the temperature is normally increased to about 15°C, and the proper amount of a filter aid is metered into the chilled oil to facilitate filtration. The wax content of the filtered oil should be reduced to a level of about 10 µg/g in order to obtain an oil with a good cold storage stability.

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6.3.6 MODIFICATION 6.3.6.1 Hydrogenation Hydrogenation is the reaction of oils and fats with hydrogen gas in the presence of a catalyst. A nickel catalyst is normally used in the edible oil industry. Hydrogenation is designed to saturate the double bonds in the TAGs. Isomerization of the cis orientation to the trans position of double bonds also occurs during hydrogenation. Both the FA composition and physical properties of the oils and fats are modified. The modified oils and fats can be used for specific applications such as the manufacture of margarines, bakery and confectionary fats, and shortenings. 6.3.6.2 Interesterification Interesterification is a process to prepare functional plastic fats by exchanging FA within and between TAGs. Chemical and enzymatic methods are the two types of interesterification presently in use. The most commonly used catalyst for chemical interesterification is sodium methoxide. In order to maintain the catalyst activity, the water content of the oils and fats should be less than 0.01% (w/w), and the levels of free FAs and peroxides should be as low as possible, preferably less than 0.05% (w/w). Lipase-catalyzed interesterifications are classified into random (no regiospecificity) and specific (1,3-regiospecific) categories. Random lipases include those from Candida rugosa, Geotrichum candidum, and Staphylococcus aureus. Specific lipases include pancreatic lipase and the enzymes from Mucor miehei, Aspergillus niger, Pseudomonas fluorescens, and Rhizopus arrhizus. 6.3.6.3 Fractionation This process involves partial crystallization under controlled conditions and separation of the remaining liquid from the solidified part. Dry, solvent, and detergent fractionations are normally used in this system. The first system is the simplest separation; it involves cooling the oil to a desired end temperature and then filtering the liquid oil on a vacuum filter or in a membrane press filter. The latter two systems, involving solvent or detergent separation of the crystallized phase from the liquid phase, are not widely used, due to their high production costs, capital investments, and contamination.

6.4 CHANGES OF LIPIDS DUE TO STORAGE The oxidative stability of lipids depends on several factors, including the degree of unsaturation, nature of unsaturation (position of double bonds), antioxidant content (tocopherols and synthetic antioxidants), prooxidant content (trace metals and enzymes), and storage conditions (exposure to heat, light, oxygen, and moisture). Hydrolysis and oxidation are the two basic reactions that cause the deterioration of fat or oil. Lipids undergo auto-oxidative degradation during storage. The higher the storage temperature of the lipids, the faster the oxidation. Light, particularly ultraviolet light, also has a great effect on oxidation rates. Light-induced oxidation

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Chemical and Functional Properties of Food Components

of oleic acid occurs about 30,000 times faster than autoxidation. For the fat or oil itself, the greater the degree of unsaturation of the FA residues, the higher the rate of oxidation. Lipid oxidation leads to the formation of hydroperoxides, which are very unstable and decompose to form secondary reaction products such as aldehydes, ketones, alcohols, acids, and hydrocarbons, which are described as having objectionable off-odors and off-flavors. During the initial or induction phase, oxidation proceeds at a relatively low rate. Peroxides are formed during this period. After a certain critical amount of oxidation has occurred, the reaction enters a second phase. The sample begins to smell and taste rancid in the beginning or early second phase. As fat or oil oxidation continues, the peroxides decompose to generate volatile and nonvolatile secondary products. Lipid hydroperoxides can be measured by peroxide value (PV) and 2thiobarbituric acid (TBA) tests. The resistance of a fat or an oil to oxidative rancidity can be measured by the Schaal oven test, Swift test, and oil stability index (OSI) analysis. Most of the vegetable oils contain natural antioxidants, the most important of which are tocopherols. Maximizing the natural tocopherol content of the oils during refining is of great importance for extending the shelf life of finished products. However, the addition of antioxidants is the most commonly used method of retarding lipid oxidation in fat or oil. Some of the more popular synthetic antioxidants used are phenolic compounds such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), mono-tert-butyl-hydroquinone (TBHQ), and propyl gallate (PG). The presence of metals in the fat or oil greatly accelerates the oxidation process. Inactivation of the catalytic effect of these metals, e.g., copper, manganese, and iron, can be achieved by the use of a sequestering agent. Citric acid is one of the most common chelating agents used in the fat and oil industry. Lipid oxidation reactions can also be retarded by other means besides using antioxidants or sequestering agents. One method is to reduce the concentration of oxygen in the fat or oil, e.g., by packing the products under vacuum or nitrogen. Oxygen is about three times more soluble in lipids than in water. There is likely to be sufficient oxygen present in the oil phase to cause lipid oxidation if oxygen is not excluded from the aqueous phase.

6.5 INTERACTIONS OF LIPIDS WITH OTHER COMPONENTS IN THE FOOD SYSTEM Lipids are indispensable to production, structure, and palatability of food, besides being an essential nutrient. Lipids solubilize taste and aroma constituents of food and act as precursors of important food aroma and flavor compounds. Lipids have been important bakery ingredients for shortening the texture of the finished baked products. Shortening, a baker’s term, is used to tenderize baked products by acting as a shortening agent, which interferes with gluten development during mixing, and by lubricating gluten proteins, allowing expansion during proofing and baking of yeast bread. Lipids contribute to the incorporation and retention of air in the form

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123

of small bubbles distributed throughout a batter; these small bubbles are important to the grain and volume of baked products. An emulsion is formed when oil and water are shaken together. The water phase is dispersed in droplets in the oil phase, such as margarine, giving a water-in-oil (W/O) emulsion. Oil dispersed in an aqueous phase is called an oil-in-water (O/W) emulsion. The length of time for separation of these two phases depends on the size of the droplets — large droplets rise faster than small ones. The use of surfactant decreases the free energy at the oil–water interface, lowering interfacial tension and slowing the rate of coalescence. Polar lipids, with large-charged or uncharged polar groups, giving these lipids amphiphilic nature, act as emulsifiers and surface-active agents (surfactants) in foods and as a necessary component in food structures. Surfactants modify the gelatinization behavior of starch by raising the swelling temperature. In starch solution, a helix is formed with a hollow cylinder with a hydrophilic outer surface and a hydrophobic inner surface. Straight-chain alkyl molecules can fit into the inner space. In this way, the FA part of emulsifiers such as glycerol monostearate (GMS) can form a complex with gelatinized starch, retarding starch crystallization in bread crumbs and slowing the staling process. Unsaturated FAs have a bend due to the double bond in the hydrocarbon chain, limiting their ability to form complexes with helical sections of amylose and amylopectin. Mutual interaction of lipids and proteins contributes significantly to the physical properties of many food systems of technological interest, such as emulsions and foams. The hydrophobic regions may interact with the lipophilic parts of surfactants. In dough formation, the addition of anionic surfactants acting as dough strengtheners promotes gluten protein aggregation, even at a lowered pH level, by binding the lipophilic tail of the surfactant to the hydrophobic regions on the protein molecule surface. Lipids contribute to foam structure of whipped cream and constitute an essential phase in food emulsions, such as milk, mayonnaise, and gravy. Lipids also provide a pleasant creamy or oily mouth feel to many food products and contribute to the juiciness of meat. They prevent crystallization and provide smoothness to crystalline candies and frozen desserts. During deep frying, lipids act as heat-transfer agents and react with the protein and carbohydrate components of food, developing unique flavors and odors, as well as a brown color, all of which are desirable to the consumer.

6.6 FUNCTIONAL FATTY SUBSTANCES 6.6.1 STRUCTURED LIPIDS Structured lipids (SLs) are defined as TAGs restructured or modified to change their FA composition or their positional distribution in TAG molecules by chemical or enzymatic reaction, such as direct esterification, acidolysis, alcoholysis, or interesterification, depending on the types of substrates available (Lee and Akoh, 1998).

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Chemical and Functional Properties of Food Components

Direct esterification: R1–COOH + R–OH → R1–COOR + H2O Acidolysis: R1–COOR + R1–COOH → R2–COOR + R1–CO–OH Alcoholysis: R–COOR1 + R2–OH → R–COOR2 + R1–OH Interesterification: R1–COOR2 + R3–COOR4 → R1–COOR4 + R3–COOR2 SLs, especially mono-long and di-medium chain-length MLM types, can provide medium-chain FAs (MCFAs) as a quick energy source and long-chain FAs (LCFAs) as essential FAs to hospital patients (Figure 6.1). Medium-chain TAGs (MCTs) primarily contain FAs with chain lengths of 6–12 carbons. Their smaller molecular size and relatively high solubility in water contribute to different digestive and absorptive properties, compared to those of long-chain TAGs (LCTs). MCTs are mainly metabolized via the portal vein, providing quick energy (Bach and Babayan, 1982). However, MCTs alone cannot provide essential FAs. Through enzymatic transesterification, it is possible to incorporate a desired acyl group onto a specific position of the TAG, whereas chemical transesterification does not provide for this regiospecificity, due to the random nature of the reaction. Thus, lipase-catalyzed transesterification can provide regio- or stereospecific SLs for nutritional, medical,

M

L

M

L

M

L

MCT

LCT Sn-1,3-specific lipase

M

L

L

M

L

M

L

M

L

M

M

L

L

L

M

L

M

M

FIGURE 6.1 Structured lipids produced from an MCT and an LCT catalyzed by sn-1,3specific lipase. M = medium chain FA; L = long chain FA.

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125

and food applications. For example, TAG contains an n-3 or n-6 PEFA, such as EPA, DHA, γ-linolenic acid (GLA), or arachidonic acid, at the sn-2 position of the glycerol backbone, and two MCFAs at the sn-1 and sn-3 positions. This MLM type of SL can provide the essential FAs and retain the assimilation advantages of the MCT. Irimescu et al. (2000) developed an enzymatic procedure to produce 1,3-dicapryloyl2-eicosapentaenoylglycerol (MLM type). The maximal molar content of the MLM in the glycerides of the reaction mixture was up to 91%; the total yield was 88% and no purification of the intermediates was necessary. FAs liberated from food during absorption are metabolized more easily if they are short or medium chain, i.e., C10 or below. The sn-2 monoacylglycerols can be absorbed directly. Therefore, essential or desired FAs are most efficiently utilized from the sn-2 position in acylglycerols. In accordance with this, TAGs with shortchain FAs (SCFAs) or MCFAs at the sn-1 and sn-3 positions and PEFAs at the sn2 position are rapidly hydrolyzed with pancreatic lipase (sn-1,3-specific lipase) and absorbed efficiently into mucosal cells. SCFAs or MCFAs are used as a source of rapid energy for infants and patients with fat malabsorption-related diseases. LCFAs, especially DHA and arachidonic acid, are important in both the growth and development of an infant, while n-3 PEFAs have been associated with reduced risk of cardiovascular disease in adults (Christensen et al., 1995; Jensen et al., 1995). SLs also can be used as low-calorie fats consisting of SCFAs and LCFAs. Because SCFAs provide fewer calories per unit of weight and LCFAs are poorly absorbed and thus impart less energy, these fats have a lower energy density than natural fats (Willis et al., 1998). The best-known representatives of this low-calorie fat group are Caprenin and Salatrim. Caprenin, containing one molecule of behenic acid (C22:0) and two molecules of caprylic acid (C8:0) or capric acid (C10:0), is a commercially available low-calorie SL. It has been produced by reaction of monobehenin with free FAs (Kluesener et al., 1992). Its energy value using young rats as the test model is 4.3 kcal/g, approximately half the energy in traditional fats and oils (Ranhotra et al., 1994). Caprenin has similar properties to cocoa butter and can be used in chocolate candy bars to replace cocoa butter. Caprenin can also be used in soft candy and in confectionery coating for nuts, fruits, and cookies. According to a 91-day feeding study in rats, Caprenin has no observable adverse effect, because the amount of Caprenin is greater than 15% (w/w) in the diet or greater than 83% of total dietary fat (Webb et al., 1993). Salatrim (an acronym for short- and long-chain acid triacylglycerol molecules) consists of a mixture of LCFAs and SCFAs esterified to glycerol. Salatrim, developed by Nabisco Inc., is a family of fats composed of TAGs that delivers fewer calories than other fats. Nabisco discovered that TAGs containing mixtures of LCFAs and SCFAs functioned like normal fats but provided fewer calories when consumed. The energy value of Salatrim is between 4.7 and 5.1 kcal/g (Willis et al., 1998). By using Salatrim, Hershey Foods Corporation creates a 50% reduced-fat semisweet chocolate baking chip named Benefat. Benefat contains fewer calories than normal cocoa butter and is only partially absorbed by the body (Tarka, 1996). The SCFAs in Salatrim are acetic acid, propionic acid, butyric acid, or mixtures including any combination of these three. The LCFAs in Salatrim are provided by completely hydrogenated vegetable oils, such as canola or soy. The completely hydrogenated fats contain

126

Chemical and Functional Properties of Food Components

predominantly stearic acid; this is unique among LCFAs because stearic acid is nonhypercholesterolemic. In addition, when fed as a component in Salatrim, stearic acid is poorly absorbed. Five 90-day feeding trials of rats were conducted with various Salatrim compositions. The results indicated that Salatrim fed to rats at levels as high as 7.9 g/kg/day did not cause any adverse effects (Smith and Finley, 1995).

6.6.2 POLYENOIC FATTY ACIDS Dietary PEFAs have important physiological effects on the regulation of biological processes involving eicosanoid production, signal transduction, and maintenance of membrane fluidity. Two families of PEFAs, designated as n-6 and n-3, normally are present in the tissues and body fluids. The n-6 PEFA linoleic acid (18:2, n-6) is primarily found in plants. Arachidonic acid converted by desaturation and elongation of linoleic acid is the main substrate for synthesis of prostaglandins, thromboxane, leukotrienes, and platelet-activating factor, which are eicosanoid mediators of inflammation; thrombosis and bronchoconstriction; inflammation and chemotaxis, and bronchial hypersensitivity (Okuyama et al., 1997). High amounts of these molecules cause an immunosuppressive effect. The n-3 PEFAs having anti-inflammatory and immunomodulatory effects act as inhibitors of arachidonic acid metabolism. The metabolic pathway of n-3 PEFAs is different from that of n-6 PEFAs. These two families have different physiological functions and act in concert with one another to regulate biological processes. The n-3 FA α-linolenic acid is converted to EPA and DHA (Figure 6.2) which are the precursors of the 3-series of prostaglandins and the 5-series of leukotrienes. Vegetable oils and fish are the predominant sources of n-3 PEFAs in the diet. Fish are the major source of EPA (20:5) and DHA (22:6), whereas vegetable oils are the major source of α-linolenic acid (ALA; 18:3). ,Soybean and canola oils are

α -Linolenic

∆ 6-Desaturase

C20:4

C18:4 Elongase

DHA(C22:6)

C22:5

EPA(C20:5) Elongase

Prostaglandins (3-series) Thromboxanes (5-series) Leukotrienes

FIGURE 6.2 Metabolism of n-3 linolenic acid.

∆ 5-Desaturase

∆ 4-Desaturase

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127

the primary sources of ALA. The contents of ALA in soybean and canola oils are around 7.8 and 9.2%, respectively. Flaxseed and perilla oils are rich sources of n-3 PEFA, the contents of which are more than 50%. Mackerel, menhaden, herring, cod liver, and salmon are rich in EPA and DHA. However, the content of n-3 FA can vary appreciably among fish of different types. Many reports state that EPA and especially DHA are important for human development, particularly of the brain and eye (Connor et al., 1992; Uauy et al., 1992). Supplementation of infant formula with EPA and DHA clearly improves visual acuity; supplementation with both arachidonic acid and DHA produces right balance. Linoleic acid, known as n-6 essential FA, is the major constituent of vegetable oils obtained from corn, safflower, soybean, and sunflower. Linoleic acid can be stored, oxidized to supply energy, or metabolized to a GLA, cis-6,9,12-octadecatrienoic acid. GLA then can be metabolized to dihomogammalinolenic acid (DGLA) and arachidonic acid (Figure 6.3). These metabolites are critical for the development of many tissues, especially the brain, which by weight contains about 20% of n-6 essential FA. The conversion of linoleic acid to GLA catalyzed by ∆6 desaturase in humans is well established as a rate-limiting metabolic step (Kies, 1989), with small amounts of linoleic acid being converted to GLA and its metabolites. This bioconversion is depressed under stressful conditions, probably resulting from the ∆6 desaturase defect. In such cases an essential fatty acid deficient status may be avoided by direct intake of GLA. Infants are proportionally somewhat more limited in their ∆6 desaturase supply than adults. Therefore, infants may have difficulty in forming adequate amounts of all these acids if linoleic acid is the only dietary source of n-6 essential FA. This is the reason why GLA, DGLA, and arachidonic acid are present in human milk. Besides, the below-normal plasma or adipose tissue concentrations of GLA, DGLA, or arachidonic acid may also be found in: people with diabetes,

Linoleic acid ∆ 6-Desaturase

γ - Linolenic acid Elongase

Prostaglandins (1-series)

Dihomo - γ - Linolenic acid ∆ 5-Desaturase

Arachidonic acid Cyclooxygenase

Prostaglandins (2-series) Thromboxanes FIGURE 6.3 Metabolism of n-6 linoleic acid.

Lipoxygenase

Leukotrienes  (4-series)

128

Chemical and Functional Properties of Food Components

alcoholic people, women with premenstrual syndrome, aged people, middle-aged individuals who will develop a stroke, and middle-aged individuals who will later develop heart disease (Carter, 1988). GLA and its metabolites are effective in the suppression of inflammation and in the treatment of diabetic neuropathy, atopic eczema, age-related diseases, alcoholism, cardiovascular disease, and gastrointestinal, gynecological, neurological, and immunological disorders. Evening primrose oil is rich in GLA (7–15%). Two seed oils other than evening primrose oil have been found to contain substantial amounts of GLA. These are borage oil, containing 21–25% GLA, and black currant oil, containing about 15–20% GLA. Microorganisms of the genus Spirulina are another source of GLA. Dried Spirulina species contain around 10% lipid, and of that, 20–25% is GLA. Fungi such as those of the Rhizopus and Mortierella species can also produce GLA.

6.6.3 VEGETABLE LECITHIN Vegetable lecithin, an edible by-product of oil processing, is primarily a mixture of phospholipids such as phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, and phosphatidic acid (Figure 6.4) and contains minor quantities of glycolipids and oligosaccharides. The degumming of oil with water yields lecithin sludge and degummed oil. Continuous agitated thin-film evaporation reduces the moisture of the lecithin sludge to less than 1%, resulting in a highly viscous semiliquid product. The major vegetable lecithin is soybean lecithin. Lecithin purification is of commercial importance, as the sludge is contaminated with carbohydrates, proteins, or other impurities. Removal of fines by filtration is easy in the state of the miscella or crude oil. It is difficult to filter impurities in the state of highly viscous finished lecithin. Standardized fluid lecithins typically contain

 CH2 –O–R (β form) R'O–CH

O

 CH2 –O–P–O–R" (α form) OH R" = CH2-CH2-N+(CH3)3 (Phosphatidylcholine)  R" = CH2-CH2-NH3+ (Phosphatidylethanolamine) R" = C6H6-(OH)6 (Phosphatidylinositol) R" = H (Phosphatidic acid) R'  = Fatty acid R   = Fatty acid or -HPO4-R" FIGURE 6.4 Some phospholipids in plants.

Food Lipids

129

62–64% acetone insolubles (AIs) and have an acid value below 30. Treating the lecithin sludge with acetone can enhance the AI content of lecithin up to 95–98%. Because of its surface-active properties, lecithin has been widely used in the processing of foods, including baked foods, beverages, and confections. Lecithin can be modified from the basic viscous W/O emulsifier type to various forms with different physical and functional properties. In W/O emulsions such as margarine or ice frosting, basic lipophilic lecithin is suitably used in conjunction with monoacylglycerols. The apparent hydrophilicity of lecithin can be increased by modification of lecithin through acetylation, hydroxylation, solvent fractionation, and deoiling. Hydrophilic lecithin having the property of water dispersibility can be used in O/W emulsions. Lecithin, especially phosphatidylcholine, is an important constituent of all human cells. Diet supplementation with lecithin improved serum lipoprotein patterns. It decreased the levels of total cholesterol, low-density lipoprotein (LDL) cholesterol, and TAGs, and increased the levels of high-density lipoproteins (Canty, 2000).

6.6.4 TOCOPHEROL

AND

PHYTOSTEROL

The richest sources of vitamin E in the diet are vegetable oils. α-Tocopherol is the major contributor to the total vitamin E activity in some oils, but others contain substantial amounts of γ-tocopherol (Figure 6.5). Typically, wheat germ, sunflower, cottonseed, and safflower oils contain about 1700, 500, 400, and 350 mg of αtocopherol equivalent kg–1, respectively. Tocopherols are concentrated in deodorizer distillate (DOD) during the deodorization step. As a result, DOD is a good source of natural tocopherols that are used to make natural vitamin E. DOD is composed of FAs, mixed mono-, di-, or triacylglycerols, sterols, tocopherols, sterol esters, hydrocarbons, and oxidation by-products. DOD is frequently collected and sold. A R1 CH3 CH3

CH3

CH3

CH3

O

R2

CH3

R3

Compound α−Tocopherol β−Tocopherol γ−Tocopherol δ−Τocopherol

R1 CH3 CH3 H H

FIGURE 6.5 Structure of the tocopherols.

R2 CH3 H CH3 H

R3 CH3 CH3 CH3 CH3

130

Chemical and Functional Properties of Food Components

Cholesterol

HO

β-Sitosterol

HO

Stigmasterol

HO

Campesterol

HO

FIGURE 6.6 Structures of animal and plant sterols.

series of chemical and physical treatments such as saponification, esterification, and molecular distillation can be used to concentrate tocopherols and sterols. Plant sterols, also called phytosterols, have been reported to include over 250 different sterols and related compounds in various terrestrial and marine materials (Akihisa et al., 1991). Sitosterol, stigmasterol, and campesterol are the commonly consumed plant sterols. The predominant sterol class in vegetable oils is 4-desmethyl sterols. Sitosterol usually contributes more than 50% of desmethyl sterols. The other most significant desmethyl sterols include campesterol, stigmasterol, ∆5-avenasterol, ∆7-avenasterol, and ∆7-stigmastenol. Brassicasterol is a typical sterol for rapeseed and other Cruciferae. Stanol occurs in significant amounts in corn bran and fiber oil (Piironen, et al., 2000). These plant sterols have similar chemical structures to cholesterol (Figure 6.6) and the capacity to lower plasma cholesterol and LDL cholesterol. The higher the dietary intake of plant sterols from the diet, the lower the serum cholesterol level.

6.6.5 SESAME LIGNANS Sesame (Sesamum indicum L.) is usually processed into oil with a characteristic roast flavor, which is used as a condiment in Oriental countries. Sesame seed and

Food Lipids

131

FIGURE 6.7 Structures of antioxidants in sesame seed and oil.

its oils are reported to have bioactive compounds such as sesamin, sesamolin, sesaminol, and sesamol (Kamal-Eldin et al., 1994; Umeda-Sawada et al., 1998) (Figure 6.7). All these compounds in the oil showing strong antioxidant activity give excellent oil stability during storage. However, after oil pressing, some sesame lignans might still remain in the defatted sesame. Lignan glucosides are the major compounds in the defatted sesame flour. They are known to have multiple biological functions such as antioxidant activity (Yamashita et al., 1998; Hirose et al., 1992), anticarcinogenicity (Hirose et al., 1992), antihypertensive effect (Kita et al., 1995) in rats, and alleviation of liver damage caused by alcohol or carbon tetrachloride (Akimoto et al., 1993) in mice. In addition, Sugano et al. (1990) reported on the hypocholesterolic activity of sesamin. They showed that sesamin reduced both blood and liver cholesterol levels of rats fed with purified diets containing sesamin and cholesterol. This phenomenon may be due to the inhibition of intestinal absorption of cholesterol by sesamin. Also, it was found that sesamin reduced the activity of hepatic 3-hydroxy-3-methylglutaryl CoA reductase, the key enzyme in cholesterol synthesis.

REFERENCES Akihisa, T., Kokke, W., and Tamura, T., Naturally occurring sterols and related compounds from plants, in Physiology and Biochemistry of Sterols, Patterson, G.W. and Nes, W.D., Eds., American Oil Chemists’ Society, Champaign, IL, 1991, p. 172. Akimoto, K. et al., Protective effects of sesamin against liver damage caused by alcohol or carbon tetrachloride, Ann. Nutr. Metab., 37, 218, 1993. Bach, A.C. and Babayan, B.K., Medium-chain triglycerides: an update, Am. J. Clin. Nutr., 36, 950, 1982. Canty, D., Lecithin, choline, and heart disease, INFORM, 11, 537, 2000.

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Chemical and Functional Properties of Food Components

Carter, J.P., Gamma-linolenic acid as a nutrient, Food Technol., 42, 72, 1988. Christensen, M.S., Mullertz, A., and Hoy, C.E., Absorption of triglycerides with defined or random structure by rats with biliary and pancreatic diversion, Lipids, 30, 521, 1995. Cmolik, J. and Pokorny, J., Physical refining of edible oils, Dur. J. Lipid Sci. Technol., 102, 472, 2000. Connor, W.E., Neuringer, M., and Reisbeck, S., Essential FA: the importance of n-3 FA in the retina and brain, Nutr. Rev., 50, 21, 1992. Hirose, N. et al., Suppressive effect of sesamin against 7,12-dimethylbenz[a]anthracene induced rat mammary carcinogenesis, Anticancer Res., 12, 1259, 1992. Irimescu, R. et al., Enzymatic synthesis of 1,3-dicapryloyl-2-eicosapentaenoylglycerol, J. Am. Oil Chem. Soc., 77, 501, 2000. Jensen, M.M., Christensen, M.S., and Hoy, C.E., Intestinal absorption of octanoic, decanoic and linoleic acids: effects of triacylglycerol structure, Ann. Nutr. Metab., 38, 104, 1995. Kamal-Eldin, A., Appelqvist, L.A., and Yousif, G., Variations in the composition of sterols, tocopherols and lignans in seed oils from four sesamum species, J. Am. Oil Chem. Soc., 71, 149, 1994. Kies, C., Evening primrose oil: a source of gamma linolenic acid, Cereal Food World, 34, 1016, 1989. Kita, S. et al., Anthihypertensive effect of sesamin. II. Protection against two-kidney, oneclip renal hypertension and cardiovascular hypertrophy, Biol. Pharmacol. Bull., 18, 1283, 1995. Kluesener, B.W., Stipp, G.K., and Yang, D.K., Selective Esterification of Long Chain Fatty Acid Monoglycerides with Medium Chain FA, U.S. Patent 5,142,071, 1992. Lee, K.T. and Akoh, C.C., Structured lipids: synthesis and applications, Food Rev. Int., 14, 17, 1998. Okuyama, H., Kobayashi, T., and Watanabe, S., Dietary FA: the n-6/n-3 balance and chronic elderly diseases: excess linoleic acid and relative n-3 deficiency syndrome seen in Japan, Prog. Lipid Res., 35, 409, 1997. Piironen, V. et al., Plant sterols: biosynthesis, biological function and their importance to human nutrition, J. Sci. Food Agric., 80, 939, 2000. Ranhotra, G.S., Gelroth, J.A., and Glaser, B.K., Usable energy value of a synthetic fat (caprenin) in muffins fed to rats, Cereal Chem., 71, 159, 1994. Smith, R.E. and Finley, J.W., Chemistry, testing and application of Salatrim low calorie fat, Manufacturing Confectioner, 75, 85, 1995. Sugano, M. et al., Influence of sesame lignans on various lipid parameters in rats, Agric. Biol. Chem., 54, 2669, 1990. Tarka, S.J., Hershey creates a new reduced fat baking chip, Candy Industry, 161, 36, 1996. Uauy, R.D. et al., Visual and brain function measurements in studies of ω-3 fatty acid requirements in infants, J. Pediatr., 120, 168, 1992. Umeda-Sawada, U., Ogawa, M., and Igarashi, O., The metabolism and n-6/n-3 ratio of essential FA in rats: effect of dietary arachidonic acid and mixture of sesame lignans (sesamin and episesamin), Lipids, 33, 567, 1998. Webb, D.R. et al., A 91-day feeding study in rats with caprenin, Food Chem. Toxicol., 31, 935, 1993. Willis, W.M., Lencki, R.W., and Marangoni, A.G., Lipid modification strategies in the production of nutritionally functional fats and oils, Crit. Rev. Food Sci. Nutr., 38, 639, 1998. Yamashita, K. et al., Sesame seed lignans and γ-tocopherol act synergistically to produce vitamin E activity in rats, J. Nutr., 122, 2440, 1998.

7

Proteins Zdzislaw E. Sikorski

CONTENTS 7.1

7.2

7.3

7.4

7.5

Chemical Structure.......................................................................................134 7.1.1 Introduction ......................................................................................134 7.1.2 Amino Acid Composition ................................................................134 7.1.3 Hydrophobicity.................................................................................137 7.1.3.1 Average Hydrophobicity...................................................137 7.1.3.2 Surface Hydrophobicity....................................................137 Conformation ...............................................................................................138 7.2.1 Native State ......................................................................................138 7.2.2 Denaturation .....................................................................................141 Functional Properties ...................................................................................141 7.3.1 Introduction ......................................................................................141 7.3.2 Solubility ..........................................................................................142 7.3.2.1 Effect of the Protein Structure and Solvent .....................142 7.3.2.2 Effect of Ions ....................................................................143 7.3.2.3 Importance in Food Processing ........................................144 7.3.3 Water-Holding Capacity...................................................................144 7.3.4 Gelling and Film Formation ............................................................145 7.3.4.1 Gel Structure.....................................................................145 7.3.4.2 Interactions of Components..............................................146 7.3.4.3 Binding Forces and Process Factors ................................146 7.3.4.4 Importance in Food Processing ........................................147 7.3.5 Emulsifying Properties.....................................................................148 7.3.5.1 Principle ............................................................................148 7.3.5.2 Factors Affecting Emulsification ......................................149 7.3.5.3 Determination of Emulsifying Properties ........................150 7.3.6 Foaming Properties ..........................................................................150 Proteins as Functional Components in Foods .............................................151 7.4.1 Muscle Proteins................................................................................151 7.4.2 Legume Proteins ..............................................................................153 7.4.3 Milk Proteins....................................................................................153 7.4.4 Egg Proteins .....................................................................................154 7.4.5 Mycoprotein .....................................................................................154 Effects of Heating ........................................................................................155 7.5.1 Introduction ......................................................................................155

1-5871-6149-4/02/$0.00+$1.50 © 2002 by CRC Press LLC

133

134

Chemical and Functional Properties of Food Components

7.5.2 Rheological Changes........................................................................156 7.5.3 Changes in Color .............................................................................157 7.5.4 Development of Volatile Compounds ..............................................158 7.5.5 Reactions at Alkaline pH .................................................................159 7.6 Oxidation ......................................................................................................160 7.7 Enzyme-Catalyzed Reactions ......................................................................162 7.7.1 Introduction ......................................................................................162 7.7.2 Changes in Milk Proteins ................................................................162 7.7.3 Role of Enzymes in Muscle Foods .................................................162 7.7.4 Transglutaminase-Catalyzed Reactions ...........................................166 7.7.5 Other Enzyme Applications in Foods..............................................167 7.8 Chemical Modifications ...............................................................................168 7.8.1 Introduction ......................................................................................168 7.8.2 Alkylation.........................................................................................169 7.8.3 Acylation ..........................................................................................170 7.8.4 N-Nitrosation ....................................................................................171 7.8.5 Reactions with Phosphates............................................................... 172 References..............................................................................................................173

7.1 CHEMICAL STRUCTURE 7.1.1 INTRODUCTION Proteins are linear condensation products of various α-L-amino acids (a.a.) that differ in molecular weight, charge, and nonpolar character (Table 7.1), bound by trans-peptide linkages. They differ in number and distribution of various a.a. residues in the molecule. The chemical properties, size of the side chain, and sequence of the a.a. affect the conformation of the molecule, i.e., the secondary structure containing helical regions, β-pleated sheets, and β-turns; the tertiary structure or the spatial arrangement of the chain; and the quaternary structure — the assembly of several polypeptide chains. The conformation affects the biological activity, nutritional value, and functional role of proteins as food components.

7.1.2 AMINO ACID COMPOSITION In most proteins the proportion of each of the different a.a. residues, calculated as a percent of the total number of residues, ranges from 0 to about 30%. In extreme cases it may even reach 50%. Cereal proteins are generally very poor in Lys. Several major grains are deficient in Thr, Leu, Met, Val, and Trp. In most collagens there are no Cys and Trp residues, while the content of Gly, Pro, and Ala is 328, 118, and 104 residues/1000 residues, respectively. Paramyosin, abundant in the muscles of marine invertebrates, is rich in Glu (20–24%), Asp (12%), Arg (12%), and Lys (9%). The antifreeze fish serum glycoproteins contain several a.a. sequences of Thr-X2-Y-X7, where X is predominantly Ala and Y a polar residue. The antifreeze proteins of type I usually contain more than 60 mol% of Ala. Thr and Y, and in various antifreeze

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TABLE 7.1 Selected Properties of Proteinogenic Amino Acids

Amino Acid

Abbreviation

pKa1

pKa2

pKR

Isoelectric Point pI

Side Chain Hydrophobicity (Ethanol → Water) kJ/mol

Glycine Alanine Valine Leucine Isoleucine Proline Phenylalanine Tyrosine Tryptophan Serine Threonine Cysteine Methionine Asparagine Glutamine Aspartic acid Glutamic acid Lysine Arginine Histidine

Gly Ala Val Leu Ile Pro Phe Tyr Trp Ser Thr Cys Met Asn Gln Asp Glu Lys Arg His

2.34 2.34 2.32 2.36 3.26 1.99 1.83 2.20 2.38 2.21 2.15 1.71 2.28 2.02 2.17 1.88 2.19 2.20 2.18 1.80

9.60 9.69 9.62 9.60 9.68 10.60 9.13 9.11 9.39 9.15 9.12 8.35 9.21 8.80 9.13 3.65 4.25 8.90 9.09 5.99

— — — — — — — 10.07 — 13.60 13.60 10.28 — — — 3.65 4.24 10.56 12.48 6.00

6.0 6.0 6.0 6.0 6.0 6.3 5.5 5.7 5.9 5.7 5.6 5.0 5.7 5.4 5.7 2.8 3.2 9.6 10.8 7.5

0 3.1 7.0 10.1 12.4 10.8 11.1 12.0 12.5 0.2 1.8 4.2 5.4 –0.04 –0.4 2.2 2.3 6.2 3.1 2.1

Note: pKa1 = –log [H+] [a.a.+/–]/[a.a.+], pKa2 = –log [H+] [a.a.–]/[a.a.+], pKR = negative logarithm of dissociation constant of a.a. group in aqueous solution.

proteins, other polar residues, form hydrogen bonds with ice crystals, inhibiting thereby the crystal growth. The β-caseins contain 14% of Pro residues. The molecule has a polar N-terminal region (1–43) with a charge of –12 and an apolar fragment, containing most of the Pro residues. Such sequence favors the temperature-, concentration-, and pH-dependent associations into threadlike polymers, stabilized mainly by hydrophobic adherences. Lysozyme, a basic protein of egg whites and other organisms, containing four -S-S- cross-links in a single polypeptide, retains its enzymatic activity in acidic solution even after heating to 100°C. The Bowman–Birk trypsin inhibitor consists of 71 a.a. residues in one polypeptide chain with loops due to seven -S-S- bonds. The bovine serum albumin has 1 SH group and 17 intramolecular -S-S- bridges per molecule. Grain prolamines are very rich in Glu (up to 55%) and Pro (up to 30%). Among the 225 residues of phosvitin of egg yolk, there are 122 Ser, most of them phosphorylated (SerP). The typical sequences of phosvitin are: … Asp-(SerP)6-Arg-Asp … and … His-Arg-(SerP)6-Arg-His-Lys … . Most food proteins, however, do not differ very much in a.a. composition. Generally the contents of acidic residues are the highest, and those of His, Trp, and

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Chemical and Functional Properties of Food Components

Pro - α1 Polyrybosome

Pro - α1 Pro - α2 Hydroxylases

Procollagen

Glycosyltransferases Endopeptidases

Tropocollagen

Collagen fibers

FIGURE 7.1 Posttranslational modifications in collagen. (From Sikorski, Z.E., Proteins, in Chemical and Functional Properties of Food Components, Sikorski, Z.E., Ed., Technomic Publishing Co. Inc., PA, 1997. With permission.)

sulfur containing a.a. are the lowest. However, the number of residues capable of accepting a positive charge is often higher, especially in plant proteins, since about 50% of side chain carboxyl groups are amidated. Many a.a. residues undergo posttranslational enzymatic amidation, hydroxylation, oxidation, esterification, glycosylation, methylation, or cross-linking. Some segments of the polypeptide chains may be removed (Figure 7.1). Modified residues in a given protein can be used for analytical purposes, e.g., hydroxyproline (ProOH), which is characteristic for collagens. Posttranslational modifications may result in covalent attachment of various groups to the proteins. They may change the ionic character of the molecule, e.g., the phosphoric acid residues or saccharides. The residues involved in phosphorylation and binding of saccharide moieties are Ser, Thr, LysOH, ProOH, His, Arg, and Lys. Among the proteins containing many phosphorylated a.a. residues is αS-casein.

Proteins

137

In the central region of αS1-casein SerP occurs in sequences: … SerP-Ala-Glu … , … SerP-Val-Glu … , … SerP-Glu-SerP … , and … SerP-Ile-SerP-SerP-SerP-Glu … . Such distribution favors oligomer formation, due to hydrophobic interactions of the apolar fragments of the molecules, with the charged sequences exposed to the solvent. High contents of saccharides are characteristic for the allergenic glycoproteins of soybeans (up to about 40%), several egg white proteins (up to 30%), albumins of cereal grains (up to 15%), whey immunoglobulins (up to 12%), and collagens of marine invertebrates (up to 10%). In κ-casein there is a hydrophobic N-terminal part (1–105) and a hydrophilic macropeptide (106–169), or a glycomacropeptide, with a saccharide moiety (0.5%) of N-acetylneuraminic acid, D-galactose, N-acetylgalactosamine, and D-mannose residues.

7.1.3 HYDROPHOBICITY 7.1.3.1 Average Hydrophobicity The nonpolar character of an a.a. can be expressed by hydrophobicity, i.e., change of the free energy (Fta) accompanying the transfer of the a.a. from a less polar solvent to water. Exposure of an a.a. with a large hydrocarbon side chain to the aqueous phase results in a corresponding decrease in entropy due to structuring of water around the chain. The hydrophobicity of the side chain of an a.a. is: Ftr = Fta – FtGly, where FtGly is the hydrophobicity of Gly. The average hydrophobicity (Ftav) of a protein can be estimated as Ftav = ΣFta/n, where n is the number of a.a. residues in the protein molecule. It is not possible to predict the conformation and behavior of a protein in solution on the basis of Ftav. However, proteins of high Ftav yield bitter hydrolysates. 7.1.3.2 Surface Hydrophobicity Most hydrophobic a.a. residues of a globular protein are burried in the interior of the native molecule. However, some of them form hydrophobic clefts or occur on the surface as individual residues or patches of residues. Phe, Tyr, and Try residues in food proteins can be monitored by measuring the intrinsic fluorescence. They absorb ultraviolet radiation and emit fluorescence in the order: Phe Tyr Trp

260 nm 275 nm 283 nm

283 nm 303 nm 343 nm

The intensity of fluorescence and the wavelength of maximum intensity depend on the polarity of the environment. Thus a Try residue located in a nonpolar region emits fluorescence at 330–332 nm, and in complete exposure to water at 350–353 nm. Furthermore, electron withdrawing groups, like carboxyl, azo, and nitro groups, as well as different salt ions, have a quenching effect on fluorescence. However, measurements of intrinsic fluorescence and of fluorescence quenching have not found wide application in hydrophobicity determinations, because they are restricted to the effect of aromatic a.a. residues.

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Chemical and Functional Properties of Food Components

The simplest and most commonly used are hydrophobic probes, based on the phenomenon that the quantum yield of the fluorescence of compounds containing some conjugated double bond systems is about 100 times higher in a nonpolar environment than in water. Thus hydrophobic groups can be monitored by aromatic or aliphatic probes and fluorescence measurements. Most often used are 1-anilinonaphthalene-8-sulfonate (ANS) (Formula 7.1) and cis-parinaric acid (CPA) (Formula 7.2). The binding of triacylglycerols or sodium dodecylsulfate may also be determined.

H N

-

SO 3

ˆ Formula 7.1

CH3 CH2 (CH = CH)4 (CH2 )7 COOH Formula 7.2

7.2 CONFORMATION 7.2.1 NATIVE STATE In a natural environment the proteins spontaneously fold from an extended form L to the native conformation N, which is affected by the primary structure L ↔ N. This is accompanied by a decrease in free energy: –RTlnK = ∆G = ∆H – T∆S, where R is the gas constant, T is the temperature, H is enthalpy, S is entropy, and K is the equilibrium constant (K = [N]/[L]). The conformation of proteins in solutions is affected by hydrogen bonds between water and hydrophilic residues resulting in enthalpy changes, as well as hydrophobic effects caused by nonpolar groups in the aqueous environment, bringing about entropy changes. This is reflected in the total free energy change ∆Gt: ∆Gt = ∆Hp + ∆Hw – T∆Sp – T∆Sw, where the subscripts p and w refer to protein and water, respectively. The native conformation is stabilized by various forces. The dipole–dipole interactions, depolarization, and dispersion forces are significant only at a very close distance (r) of the atoms because the energy decreases with r–6. The hydrogen bonds, abundant in proteins, differ in energy from about 2 to about 12 kJ/mol, depending on the properties and direction of the groups involved. The strength of the H-bonds does not depend significantly on temperature, but increases with

Proteins

139

pressure. The energy of the ionic bonds is affected by the dielectric constant and may reach into the hydrophobic core of a protein about 21 kJ/mol between the ionized residues of Asp and Lys. The energy of hydrophobic interactions increases with temperature and decreases with increasing pressure. Covalent bonds other than those in the polypeptide chain, although of highest energy, are generally very limited in number. However, some proteins rich in such bonds may have high thermal stability, e.g., mature collagens containing different cross-links generated in reactions of the oxidized ε-NH2 group of Lys and LysOH:

Prot

NH2

lysyl oxidase

Prot

C

H O H

O Prot

C

H O

+

H O

O

C C

CH2 Prot

Prot

CH

CH

H2O Prot

H C

Prot

CH

C

Prot

OH N NH

CH2 Prot Prot N

O

CH Prot

CH

CH

Prot

Prot NH2

H C

Prot

N

CH

CH

Prot

N CH2

N

Prot

CH2

Prot

N

Reaction 7.1

Other examples would be in the Maillard reaction of the saccharide moieties of the molecules and as proteins containing many -S-S- bridges, e.g., several proteinase inhibitors. A very significant effect on the properties of proteins is exerted by their quaternary structures and micellar associations. Soybean glycinin composed of six basic and six acidic subunits has a structure of two superimposed rings. In each ring the three acidic and three basic subunits are arranged alternatively. Thus ionic interactions are possible both within each ring and between the rings. Because the conformation of the oligomer is buttressed by noncovalent forces, the addition of urea and changes in pH and ionic strength lead to dissociation of the protein into subunits.

140

Chemical and Functional Properties of Food Components

In unheated milk the caseins are present as a colloidal dispersion of particles containing about 6–7% calcium phosphate, known as micelles, and as smaller particles without calcium phosphate. These forms are in an equilibrium that is affected by temperature, pH, and the concentration of Ca2+. In fresh milk about 80–90% of the mass of caseins is in the micellar form. The micelles are very porous and hydrated, have a diameter ranging from a few to about 600 nm, and have a weight average molecular mass of 600 MDa. Numerous investigations have resulted in various models of the structure of casein micelles. According to one group of models the micelles are formed from several hundreds subunits, called submicelles, that differ in composition and size. In these models either the subunits are linked by calcium phosphate or the calcium phosphate is located as discrete packages within the submicelles. According to the calcium phosphate nanocluster model there are no subunits, but the polypeptide chains form a matrix in which calcium phosphate nanocluster-like particles are embedded (Figure 7.2). The outer parts of the micelles are occupied by hydrophilic polypeptide chains, including the macropeptide of κ-casein and Ca2+-sensitive peptides, and form a hairy layer (Holt and Rogi´n ski, 2001).

FIGURE 7.2 Calcium phosphate nanocluster model of a casein micelle. Substructure arises from the calcium phosphate nanocluster-like particles in the micelles (dark spheres). There is a smooth transition from the core to the diffuse outer hairy layer that confers steric stability on the micelle. (Courtesy of Holt and Rogi´nski, 2001.)

Proteins

141

a)

b)

c)

ss

M2+

ss

ss ss

FIGURE 7.3 a: Protein denaturation of native molecule. b: Molecule changes conformation with ruptured disulfide bridges and ionic bonds. c: Denatured molecule with randomly extended polypeptide chains. (From Sikorski, Z.E., Proteins, in Chemical and Functional Properties of Food Components, Sikorski, Z.E., Ed., Technomic Publishing Co. Inc., PA, 1997. With permission.)

7.2.2 DENATURATION The native conformation of proteins is generally stabilized by rather small energy. The net thermodynamic stability of the native structure of many proteins is as low as about 40–80 kJ/mo–1. The unfolding enthalpy of metmyoglobin and lysozyme is about 285 and 368 kJ/mo1, respectively. Therefore ionizing radiation, shift in pH, change in temperature or concentration of various ions, or addition of detergents or solvents may cause dissociation of the oligomers into subunits, unfolding of the tertiary structure, and uncoiling of the secondary structure (Figure 7.3). These changes are known as denaturation. Exposure of the a.a. residues originally buried in the interior of the molecule changes the pI, surface hydrophobicity, and the biochemical properties of proteins. Denaturation may be reversible, depending on the degree of deconformation and environmental factors. This may affect the value of determinations of enzyme activity used as a measure of severity of heat processing in food operations. For monitoring milk pasteurization the determination of γ-glutamyltransferase can be used, since the enzyme undergoes complete inactivation after 16 sec at 77°C and no reactivation has been evidenced (Zehetner et al., 1995). Generally food processing causes irreversible denaturation followed by reactions of the thermally denatured proteins with other components that may lead to loss in food quality. However, in foods denaturation may have beneficial or detrimental effects. The main effects comprise changes in pI, hydration, solubility, viscosity of solutions, biological activity, and reactivity of a.a. residues.

7.3 FUNCTIONAL PROPERTIES 7.3.1 INTRODUCTION The functional properties important for the processor are attributes that, at proper concentration of the respective components or additives and at appropriate conditions, provide for the desirable characteristics of the product. These properties of proteins are displayed in interactions with the surrounding solvent, ions, other

142

Chemical and Functional Properties of Food Components

TABLE 7.2 Functional Properties of Proteins Displayed in Interactions with Different Food Constituents Interactions with Water Wet ability Swelling Rehydration Water holding Solubility

Water and Proteins Viscosity inducing Gelling Fiber forming Dough forming Membrane forming

Lipids or Gases Emulsifying ability Emulsion stabilization Foaming ability Foam stabilization

proteins, saccharides, and lipids, and in surface phenomena. The most important one in food processing can be roughly grouped accordingly (Table 7.2). They affect the appearance, color, juiciness, mouth feel, and texture of a large variety of foods, as well as cutting, mincing, mixing, formation of dough, fibers, foils, bubbles, shaping, and transporting of food materials. The functionalities of proteins can be modified by using enzymatic and chemical processes that change the structure of proteins. They depend also on the pH, ionic strength, and temperature in the food system. Through a better understanding of the tertiary structure of many food proteins, it should be possible to modify functionality using genetic engineering. To evaluate the functionality of some proteins in different systems, the quantitative structure–activity relationship approach may be applied (Nakai and Li-Chan, 1988).

7.3.2 SOLUBILITY 7.3.2.1 Effect of the Protein Structure and Solvent The solubility or extractability of proteins is often defined in food chemistry as the percent of the total quantity of protein contained in the food material that can be extracted by water or a suitable solvent in specified conditions. It depends on the properties of the protein and solvent, pH, concentration and charge of other ions, and temperature. Generally proteins rich in ionizable residues, of low surface hydrophobicity, are soluble in water or dilute salt solutions. Here belong the proteins of the egg white. Those abundant in hydrophobic groups readily dissolve in organic solvents. The classification of cereal proteins into albumins, globulins, prolamines, and glutelins soluble in water, dilute salt solutions, 60–80% aliphatic alcohols, and 0.2% NaOH, respectively, may also be used for characterization of other proteins. Stabilization by cross-linking is of crucial importance; e.g., the solubility of collagen from different connective tissues depends on the type and age of the tissue. Young tropocollagen can be solubilized in neutral or slightly alkaline NaCl solution; tropocollagen containing intramolecular covalent bonds is soluble in citric acid solution at pH 3, while mature collagen with covalent intermolecular cross-links is not soluble in cold, dilute acids and buffers. It can, however, be partially solubilized in a highly

Proteins

143

comminuted state or after several hours of treatment in alkaline media. Differences in solubility are essential for various procedures of isolation of individual proteins and groups of proteins from foods (Kristinsson, 2001). Denaturation may decrease solubility; e.g., fish protein concentrate produced by extraction of minced fish with boiling azeotropic isopropanol is scarcely soluble in water. In organic solvents, due to their low dielectric constant, the energy of interactions between charged a.a. residues is higher than in water. This may favor unfolding of the molecules and exposition of the hydrophobic residues, which can not be counterbalanced by entropy forces. Thermal denaturation followed by aggregation due to interactions of the exposed reactive groups leads generally to loss in solubility. On the other hand, if heating brings about deconformation of the quaternary and tertiary structures, it may increase the solubility, as in collagen. Adding antioxidants to the defatted soy flour prior to alkaline extraction enhances the solubility of the protein isolate in proportion to the decrease in oxidation of thiol groups (Boatright and Hettiarachchy, 1995). 7.3.2.2 Effect of Ions In water solutions the solubility of proteins has a minimum pI (Figure 7.4). Because at such pH there is no electrostatic repulsion between the molecules, the hydration layer alone can not prevent aggregation. Although the attraction of water dipoles by ionized groups of opposite charges in a.a. residues largely offsets the electrostatic binding between the ions, the net balance of the attraction and change

ˆ

FIGURE 7.4 Effect of pH on the solubility of proteins.

144

Chemical and Functional Properties of Food Components

in solvent entropy favors salt bridge formation. At pH values below or above the pI of the protein, the solubility increases due to repelling of the positive or negative ions, as well as to increased interaction of the charged polypeptide chains with water dipoles. The pI of a protein may shift slightly with changing concentration of salts in the solution. The effect of ions on the solubility of a protein depends on their ionic strength µ:µ= 0.5 ΣmiZi2, where mi is the molarity of the solution in respect to the given ion and Zi is the charge of the ion. The effect of ions on the solubility of a protein also depends on their effect on the surface tension of the solvent, the dipole moment, and the reduction of the molecular surface area of the protein upon aggregation. Various ions, depending on their size and charge, favor or decrease the solubility of proteins. In the low range of concentration, i.e., µ = 0.5 – 1.0, the solubility increases with the concentration of neutral salts. This is known as salting in. The ions have a screening effect on the charged protein molecules. Being surrounded by water dipoles, they add to the hydration layer, which favors solubilization of the macromolecules. At higher concentrations the effect depends mainly on the ability of the salts to affect the water structures. 7.3.2.3 Importance in Food Processing The solubility versus pH curve can be used for selecting parameters for extraction of proteins from different sources. Adding a required amount of salt to the meats during cutting and mixing in a silent cutter is a prerequisite for extracting myofibrillar proteins from the tissue structures and forming a sausage batter of adequate quality. CaCl2 is used to precipitate the whey proteins, while CaSO4 coagulates soy proteins in tofu manufacturing. The solubility also contributes to gelling and emulsification. It may also be required for efficient use of various protein isolates as functional food additives in products differing in pH and salt content. The loss in solubility due to abuse treatment is often indicative of protein denaturation and subsequent cross-linking. Therefore solubility data, if used to characterize commercial protein products, should be determined in standardized procedures. In the methodology of solubility assays the following factors must be considered: size and disintegration of the sample, pH and ionic strength of the solvent, proportion of sample size to that of the solvent, number of extractions, foaming during blending and stirring, temperature and time of extraction, and separation of nonproteinaceous material ( Kolakowski, 2001).

7.3.3 WATER-HOLDING CAPACITY The ability of many foods to retain water is affected by the involvement of proteins in different structures. In meat and fish tissues the state of water depends on various interactions of water structures with proteins and other solutes. Furthermore, because of the fibrous nature of the muscle and compartmentation, water is also held in meat by physical entrapment. Alterations in the spatial arrangement of the proteins and in the integrity of the tissue structures caused by biochemical and processing factors are responsible for shrinking or swelling of the material and thus for retaining or

Proteins

145

exudation of water. Classical investigations on the effect of pH, divalent cations, postmortem changes, freezing and thawing, heating, salting, polyphosphates, and citrates on the water-holding capacity (WHC) of meat were made by Hamm (1960). WHC has a large impact on the texture and juiciness of meat and fish products. Decrease in WHC brings about excessive cooking loss and thawing drip. Changes in WHC may be also used for evaluating the effect of processing on the structure of proteins and on the quality of muscle foods. To be used as a quality index, WHC should be determined in standardized procedures. WHCs are based on measurements of loss of water from the original sample, due to centrifugation, pressing, or capillary force, or on measuring the quantity of liquid separated under the action of a force from a sample with added water or aqueous solution (Regenstein and Regenstein, 1984).

7.3.4 GELLING

AND

FILM FORMATION

7.3.4.1 Gel Structure A gel consists of a three-dimensional lattice of large molecules or aggregates capable of immobilizing solvent, solutes, and filling material. Food gels may be formed by proteins and polysaccharides that may participate in gel formation in the form of solutions, dispersions, micelles, or even in disrupted tissue structures, as in meat and fish products. Generally gelation is a two-step phenomenon (Damodaran, 1989). The first step usually involves dissociation of the quaternary structure of the protein, followed by unfolding. In several proteins heating to about 40°C is sufficient, and some fish protein sols turn slowly into gels, even at 4°C. Preheating at 25–40°C, called “ashi” or setting, is applied prior to cooking in manufacturing gelled, elastic fish meat products. During setting the endogenous transglutaminase leads to formation of cross-links between myosin heavy chains. In ovalbumin solutions gelling starts at 61–70°C. In the second step, at higher temperatures, the unfolded molecules rearrange and interact, initially usually with their hydrophobic fragments, forming a lattice. Ovalbumin gels increase in firmness when heated to about 85°C. Subsequent cooling generally stabilizes the gel structure. If the rate of the structuring stage is lower than that of denaturation, the unfolded molecules can rearrange and form an ordered lattice of a heat-reversible, translucent gel. Too rapid interactions in the denatured state lead to an irreversible coagulum, due to random associations to insoluble, large aggregates. In the gel network there are zones, where the polymers interact, and large segments, where the macromolecules are randomly extended. The lattice is responsible for the elasticity and the textural strength of the product. In multicomponent gels all constituents may form separate or coupled networks, or else one component, not involved in network formation, may indirectly affect the gelling by steric exclusion of the active molecules. Such exclusion increases the concentration of the active component in the volume of the solution where the gel is formed. In gels made from the mince of squid meat at 1.5% NaCl, the added carrageenan and egg whites form separate networks that support the structure made of squid proteins, while added

146

Chemical and Functional Properties of Food Components

starch fills the lattice and retains water (Gomez-Guillen et al., 1996). Proteins and polysaccharides that have opposite net charges, when in mixed solutions, may form different soluble and insoluble complexes held by ionic bonds. Lipid-filled milk protein gels containing small fat globules with a narrow particle size distribution have a smooth texture and a high shear modulus. A three-dimensional network of partially unfolded molecules is also in proteinaceous films. These films are usually made by preparing a protein solution at pH values far from the pI, controlling denaturation of the molecules due to heating or shear, adding plasticizers, degassing, casting or extruding through a nozzle, and drying to evaporate the solvent. 7.3.4.2 Interactions of Components The structure of gels depends on the components and the process parameters. Proteins containing over 30% hydrophobic residues form coagulum-type gels, e.g., hemoglobin and egg white albumin. The gelling-type proteins contain less hydrophobic residues and are represented by some soybean proteins, ovomucoid, and gelatin. The interaction of different macromolecules may decrease the gel strength, may have no influence on the rheological properties of the gel, or else may have a synergistic effect. Casein micelles in a whey protein matrix may enhance or decrease the gelling, depending on pH. Heat coagulation of sarcoplasmic proteins impairs the gelation of actomyosin in gels made from the meat of pelagic fish. The proteinase-catalyzed softening known as modori in minced heated fish products may be decreased by adding protease inhibitors from potato, bovine plasma, porcine plasma, or egg white. Inhibitors from various legume seeds are also effective against fish muscle proteinases (Benjakul et al., 2001a, 2001b; Matsumoto and Noguchi, 1992). The impact of other factors may be controlled by applying optimum processing parameters. 7.3.4.3 Binding Forces and Process Factors The hydrophobic interactions prevail at higher temperatures and probably initiate the lattice formation, while hydrogen bonds increase the stability of the cooled system. The electrostatic interactions depend on pH, charge of the molecules, ionic strength, and divalent ions. Intermolecular -S-S- bridges, as well as covalent bonds formed due to the activity of transglutaminases, may also add to the gel formation. In gelled fish products -S-S- bonding occurs during cooking at about 80°C (Hossain et al., 2001). Gels stabilized mainly at low temperatures by hydrogen bonding are heat reversible, i.e., they melt due to heating and can be set again by cooling, while gels stabilized by hydrophobic interactions and covalent bonds are heat stable. Depending on the properties and concentration of the protein, ionic strength, and pH, even a coagulum-type gel like that of ovalbumin can be melted by repeated heating and set again when cooled (Shimizu et al., 1991). Heat-induced gels may melt under increased pressure at room temperature, while cold-set gels of gelatin are resistant to such conditions (Doi et al., 1991). Optimum ionic strength and concentration of Ca2+ is required for producing well-hydrated heat-set gels from whey proteins.

Proteins

147

There is generally a pH range at which the gel strength in the given system is highest. It depends on the nature of the polymers participating in cross-linking and increases with protein concentration. At the pI of the proteins, due to the lack of electrostatic repulsion, the rate of aggregation is usually high, leading to less-ordered, less-expanded, and less-hydrated gels. In heat-induced gels made of water-washed chicken breast minced muscle at a pH of 6.4 and a low NaCl concentration, the myofibrils, insoluble at such conditions, form local networks of aggregates, with large voids between them. Increasing the pH to 7.0 results in a gel with an evenly distributed network of myofibrils and an additional network of fine strands, smaller intramyofibrillar spaces, increased stress and strain values, and higher WHC (Feng and Hultin, 2001). The ovalbumin gel has optimum rheological properties at pH 9, while at pH < 6 it is brittle and has low elasticity. Transparent ovalbumin gel can be made by heating at a pH other than the pI at a certain salt concentration. In a two-step procedure transparent gels can be made from ovalbumin, bovine serum albumin, and lysozyme over a broad range of salt concentration by heating the protein solutions first without salt and after cooling by repeated heating in the presence of added salt (Tani et al., 1993). The pH range for gelation of whey proteins is 2.5–9.5, although near the pI, which is about 5, the gels are opaque, coarse, and may turn into curd-like coagulum. In the neutral to alkaline pH the gels made of fat-free whey protein isolates or purified β-lactoglobulin are translucent, smooth, and elastic. In acid conditions, if high shear force is applied for a short time at denaturation temperature, aggregation of the whey proteins to microparticles occurs. This leads to well-hydrated gels of a smooth, nonelastic texture, similar to that of a fat emulsion. In a slightly alkaline environment at a temperature of above 60°C, insoluble aggregates are formed due to denaturation of β-lactoglobulin, the major component of whey proteins. The rheological properties of whey protein gels, at different pH values, depend also on the concentration of Ca2+. The -S-S- bridges are responsible for the thermal stability of gels. Such bonds add to the elasticity of heat-set whey protein gels at neutral to alkaline pH values, but not in acidic conditions when the thiol has low reactivity (Jost, 1993). Ascorbic acid improves the formation of heat-set gels of ovalbumin and fish proteins by undergoing rapid oxidation to dehydroascorbic acid, which affects polymerization by intermolecular -S-S- bridges. In making edible films from wheat gluten, the exposed SH groups of the protein, heat-denatured in an alkaline solution, form -SS- cross-links due to air oxidation during drying (Roy et al., 1999). 7.3.4.4 Importance in Food Processing Gelling is important for the quality of comminuted-type, cooked sausages and gelled fish products. The gel strength of such commodities is mainly affected by the properties of myosin and processing conditions. Comminuting of the meat with salt results in unfolding of the myosin microfibrils and increases the surface hydrophobicity. This leads to hydrophobic associations in the lattice structure. Heating to 50–80°C favors deconformation of the myosin heads (Figure 7.5) and their interactions. Although myosin has the highest gel-forming ability of all muscle proteins,

148

Chemical and Functional Properties of Food Components

‘

FIGURE 7.5 Schematic representation of the myosin molecule. (From Sikorski, Z.E., Proteins, in Chemical and Functional Properties of Food Components, Sikorski, Z.E., Ed., Technomic Publishing Co. Inc., PA, 1997. With permission.)

the whole myofibrillar protein fraction, the sarcoplasm, and the connective tissue proteins are also capable of gelation. The overall gel strength depends on the concentration and interactions of different proteins. Edible films may be used for their barrier properties to prevent the migration of water, oil, oxygen, and volatile aroma compounds between food and the environment. The coatings prevent oxidative browning of sliced fruits and vegetables due to their antioxidant properties. The oxygen radicals’ scavenging capacity of films made of commercial concentrated whey protein powder has been found to be higher than that of coatings based on calcium caseinate. The addition of carboxymethyl cellulose to the formulation increases the antioxidant capacity of the products (Le Tien et al., 2001). Films can also find application as enzyme supports and carriers of food ingredients. For edible sachets used for delivering premeasured quantities of ingredients in food processing, the heat seal ability of the material is important. Antimicrobial agents added to edible coatings used for food protection may affect the mechanical strength and barrier properties of the material (Ko et al., 2001). Different films have unique functional properties best suited to fulfill the needs of specific food applications. The films can be made either of proteins or of composite materials with saccharides or lipids. For these purposes, collagen, gelatin, casein, total milk proteins, whey proteins, wheat gluten, corn zein, water-soluble fish proteins, and soy proteins are used. The barrier properties, appearance, tensile strength, thermal stability, and heat seal ability of the products depend on the characteristics and proportions of the gelling components, interactions and contents of plasticizers, and conditions of fabrication. Films made of whey protein are transparent, bland, and flexible; have very high oxygen, oil, and aroma barrier properties in an environment of low humidity; and are poor protection against water vapor migration. Some of their characteristics depend on the degree of thermal denaturation of the protein before casting. Increasing the degree of denaturation by heating leads to higher tensile strength and insolubility and to lower oxygen permeability of the films (Perez-Gago and Krochta, 2001). Water vapor permeability may be decreased by adding lipids, either by laminating a lipid layer over a protein film or by uniformly dispersing the lipid in the proteinaceous component. The result depends on the properties and amount of added lipid.

7.3.5 EMULSIFYING PROPERTIES 7.3.5.1 Principle Proteins help to form and stabilize emulsions, i.e., dispersions of small liquid droplets in the continuous phase of an immiscible liquid. The decrease in the diameter of

Proteins

149

the droplets due to agitation exponentially increases the interfacial area. The work (W) required for the increase in surface area (∆A) can be decreased by lowering the surface tension (z): W = z ∆A, due to attachment of proteins to the droplets. The protein film around the lipid globules, with its electrostatic charge and steric hindrance, prevents flocculation, i.e., formation of clusters of globules, and thus more rapid creaming due to the action of gravitational force: V = 2 r2 g ∆P/9 µ, where V is the velocity of the droplet, g is the gravitational force, ∆P the difference in density of both phases, µ the viscosity of the continuous phase, and r the radius of the droplet or cluster of droplets. Stable films around the fat globules also prevent the coalescence of the dispersed phase, i.e., joining of the fat globules to form a continuous phase. Furthermore, soluble proteins increase the viscosity of the dispersing phase, thus reducing the rate of creaming and coalescence. The efficiency of proteins as emulsifiers depends on their surface hydrophobicity and charge, steric effects, elasticity and rigidity, and viscosity in solution. Globular proteins that have stable structures and are very hydrophilic are good emulsifiers only when unfolded. However, the emulsifying properties do not increase linearly with the hydrophobicity of the protein, as they depend on the hydrophile/lipophile balance (HLB), which is defined as: HLB = 20 Wh/Wt, where Wh is the weight of the hydrophilic groups and Wt is the total weight of the molecule. The emulsifiers with HLB < 9 are regarded as hydrophobic; HLB = 11–20, hydrophilic; and HLB = 9–11, intermediate. There is an effect of protein solubility, as the molecules must be able to migrate to the surface of the fat globules. However, in comminuted sausage batters, in the presence of salt the insoluble proteins may also participate in the formation of fat dispersions. After a few minutes of homogenization, about 90% of the initially insoluble meat proteins of the stroma can be found in the emulsion layer (Nakai and Li-Chan, 1988). The quantity of protein required for stabilization of an emulsion increases with the volume of the dispersed phase and with the decrease in diameter of the droplets. The concentration of proteins forming a monomolecular layer at the interface is of the order of 0.1 mg/m2, and the effective concentrations are in the range of 0.5–20 mg/m2. For a high rate of film formation, the required concentration of protein in the emulsion may be as high as 0.5–5%. 7.3.5.2 Factors Affecting Emulsification The pH of the environment affects the emulsifying properties by changing the solubility and surface hydrophobicity of proteins, as well as the charge of the protective layer around the lipid globules. Ions alter the electrostatic interactions, conformation, and solubility of the proteins. However, in many foods, mainly comminuted meat batters, the concentration of NaCl is considerably high for sensory reasons. Thus small changes in the salt content within the accepted range may have no significant effect on the properties of proteins. Heating to about 40–60°C, causing partial unfolding of the protein structure without loss in solubility, may induce gelation of the protective layer, as well as decrease the viscosity of the continuous phase. Therefore moderate heating may improve the emulsifying properties of proteins.

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Chemical and Functional Properties of Food Components

7.3.5.3 Determination of Emulsifying Properties Several procedures are used to determine the efficiency of proteins in emulsifying lipids and the stability that the proteins impart to the emulsions. The emulsifying capacity is represented by the volume of oil (cm3) that is emulsified in a model system by 1 g of protein when oil is added continuously to a stirred aliquot of solution or dispersion of the tested protein. It is determined by measuring the quantity of oil at the point of phase inversion. The latter can be detected by a change in color, viscosity, or electrical resistance of the emulsion, or the power taken by the stirrer engine. The emulsifying capacity decreases with an increasing concentration of protein in the aqueous volume. It is affected by the parameters of emulsification, depending on the equipment, as well as by the properties of the oil. The emulsion stability is measured as the final volume of the emulsion after the initial volume has been centrifuged or standing for several hours at specified conditions. It may also be determined as the quantity of oil or cream separated from the emulsion, or the time required for the emulsion to release a specified quantity of oil.

7.3.6 FOAMING PROPERTIES Food foams are dispersions of gas bubbles in a continuous liquid or semisolid phase. Foaming is responsible for the desirable rheological properties of many foods, e.g., the texture of bread, cakes, whipped cream, ice cream, and beer froth. Thus foam stability may be an important food quality criterion. However, foams are often a nuisance for the food processor, e.g., in the production of potato starch or sugar and in the generation of yeast. Residues of antifoaming aids in molasses may drastically reduce the yield in citric acid fermentation. The gas bubbles in food foams are separated by sheets of the continuous phase, composed of two films of proteins adsorbed on the interface between a pair of gas bubbles, with a thin layer of liquid in between. The volume of the gas bubbles may make up 99% of the total foam volume. The contents of protein in foamed products are 0.1–10% and of the order of 1 mg/m2 interface. The system is stabilized by lowering the gas–liquid interfacial tension and formation of rupture-resistant, elastic protein film surrounding the bubbles, as well as by the viscosity of the liquid phase. The foams, if not fixed by heat setting of the protein network, may be destabilized by drainage of the liquid from the intersheet space, due to gravity, pressure, or evaporation, by diffusion of the gas from the smaller to the larger bubbles, or by coalescence of the bubbles resulting from rupture of the protein films. Factors facilitating the migration of the protein to the interface and formation of the film are important for foaming. The foaming capacity or foaming power, i.e., the ability to promote foaming of a system, measured by the increase in volume, is affected mainly by the surface hydrophobicity of the protein. The stability and strength of the foam, measured by the rate of drainage and the resistance to compression, respectively, depend on the flexibility and the rheological properties of the film. Other components of the system, mainly salts, sugars, and lipids, affect the foam formation and stability by changing either the properties of the proteins or the

Proteins

151

viscosity of the continuous phase. The standard whey protein concentrates that contain 4–7% of residual milk lipids have significantly inferior foaming properties compared with lipid-free isolates. Excellent foaming ability is characteristic for egg white proteins, especially ovalbumin, ovotransferrin, and ovomucoid. Chilling of egg whites below room temperature or the presence of sugar or lipids decreases foaming, a pH value of <6 increases the foaming capacity, and heating of the dried proteins at 80°C for a few days before use increases foam stability. The foaming of whey protein isolates can be improved by addition of Ca2+ or Mg2+. The ions are effective only immediately after the salts are added. According to Zhu and Damodaran (1994) the ions might cause unfolding and polymerization of the proteins at the interface via ionic linkages. On the other hand, prolonged incubation of the isolate solution with the salts slightly reduces the film-forming ability, possibly by promoting aggregation and micellization of the protein.

7.4 PROTEINS AS FUNCTIONAL COMPONENTS IN FOODS 7.4.1 MUSCLE PROTEINS The meat of slaughter animals, fish, mollusks, and crustaceans is predominantly used to prepare different dishes, a variety of canned, smoked, marinated, salted, and dried products, and a large number of sausage assortments. In these products the functional properties of the muscle proteins are responsible for the desirable sensory attributes. However, an increasing proportion of the raw material, mainly less suitable for producing high-quality products of the meat, poultry, and fish industry, is used for manufacturing protein concentrates, preparations, and hydrolysates. These products can be incorporated into various food products for nutritional reasons and as functional ingredients. Much research has been devoted to working out optimum parameters of producing different protein concentrates from fish and krill (Lanier, 1994). While the products have high nutritional value and many are tasteless and odorless, some, manufactured in denaturing conditions, lack the desired functional properties. A good example is the fish protein concentrate obtained by hot azeotropic isopropanol extraction. On the other hand, a concentrate of myofibrillar proteins known as surimi, produced mainly from fish and to a lesser extent from poultry and meat, is highly functional. Surimi is originally a Japanese product obtained by washing minced fish flesh several times with fresh water. This treatment removes most of the sarcoplasmic proteins, including enzymes and pigments, nonprotein nitrogenous compounds, various odorous substances, other soluble components, and fat. The remaining myofibrillar proteins have higher gel-forming ability than the original protein mixture. Nowadays fish surimi is produced mainly on board vessels (Toyoda et al., 1992). The typical commercial surimi is made from Alaska pollock. In order to prevent deterioration of its functional properties during frozen storage, different cryoprotectants, predominantly saccharides, are added prior to freezing (Figure 7.6). Surimi is used mainly for manufacturing traditional Japanese gelled products, obtained by

152

Chemical and Functional Properties of Food Components

White Fish

Water

Water

Washing

Wastewater, Scales

Heading Gutting

Heads, Viscera

Washing

Wastewater, Scales

Meat Separating and Mincing

Skin, Fins, and Bones

Leaching

Water 3x

Draining

Water-Soluble Components

Refining

Scraps of Skin, Scales

Dewatering

Cryoprotectants

Surplus Water

Mixing

Surimi

FIGURE 7.6 Flow sheet of the process used for manufacturing surimi.

mixing it with salt, grinding, forming, and steaming or broil cooking (kamaboko), or frying (tempura). Another growing outlet is the production of a variety of fabricated products, including molded (shrimp-type) and fiberized (crab-leg-type) shellfish analogs (Wu, 1992). The most important topics in this area in the last two decades have been the suitability of fish of different lean and fatty species, including freshwater fish, as raw material for surimi (Holmes et al., 1992; Luo et al., 2001); mechanisms of protein changes in frozen stored material and selection of optimum cryoprotectants (Matsumoto and Noguchi, 1992); the effect of different ingredients on the texture and water binding of various gelled products (Yoon and Lee, 1990); and other factors affecting gelation of surimi (Niwa, 1992; Jiang et al., 1998).

Proteins

153

7.4.2 LEGUME PROTEINS Soybean proteins are used as a variety of traditional products, e.g., soy milk or fermented items, defatted flour, grits, concentrates, or isolates. The traditional products are prepared according to procedures known in the Orient, involving water extraction, cooking, coagulation of the proteinaceous curd, roasting, and fermentation, often in combinations with other components. Different forms of concentrated or isolated protein products are prepared by milling, toasting, extraction of fat and saccharides, and isolation of protein fractions. The antinutritional factors present in soybeans are usually inactivated or removed in processing. The “beany” or “painty” off-flavor in soy milk due to volatiles generated in lipoxygenase-catalyzed reactions is prevented by thermal denaturation of the enzyme before or during grinding with water (Kwok and Niranjan, 1995). The protein isolates may be “tailor-made” to have the desirable functional properties. Grits, flours, and isolates for food applications are produced also from other legumes, mainly peanuts, beans, broad beans, and peas (Lampart-Szczapa, 2001).

7.4.3 MILK PROTEINS Because of very high biological value and absence of antinutritional factors, except for some allergenic activity, milk proteins have found various application in formulated foods and as meat extenders. Initially only the caseins were used, but recently the recovery of whey proteins and their fractions was made economically feasible. Least soluble is acid casein. Its solubility and foaming properties can be improved by glycosylation of the ε-NH2 groups. Sodium and calcium caseinates prepared by acid precipitation and neutralization are soluble and very heat stable, and have a high WHC and emulsifying, foaming, and gelling ability. Rennet casein, richer in calcium, has low solubility in the presence of Ca2+. Precipitates produced by heat denaturation of the whey proteins and coprecipitation with casein by addition of acid or calcium salts are more soluble and have higher nutritional value than the acid and rennet casein. Different whey protein concentrates and isolates are manufactured by complexing with phosphates or polysaccharides, by gel filtration, ultrafiltration, or heat denaturation. At a pH of about 4.2 and at 55–65°C α-lactalbumin undergoes isoelectric precipitation due to dissociation of the Ca2+ and hydrophobic interactions (Bramaud et al., 1995). Other minor whey proteins also precipitate, while the soluble β-lactoglobulin is separated, concentrated by ultrafiltration, neutralized, and spray dried. The product has superior WHC and gelling properties in meat products. β-lactoglobulin, however, denatures and forms insoluble aggregates at temperatures above 60°C at pH 8. This is a limitation for the use of whey protein isolates in pasteurized products. The thermal stability of β-lactoglobulin can be improved by controlled hydrolysis. Doucet et al. (2001) have shown that hydrolysis of a whey protein isolate by Alcalase, when less than 16% and 4% of β-lactoglobulin and α-lactalbumin, respectively, remained unhydrolyzed, induced gel formation. Gelation was preceded by formation of aggregates. The structure of the gel was stable over a temperature range of 30–65°C. Other undenatured forms of

154

Chemical and Functional Properties of Food Components

whey proteins are also used as foam stabilizers and gelling agents; some are soluble under acidic conditions. The purified α-lactalbumin fraction is more suitable for infant food formulations than whey protein concentrate, since human milk does not contain β-lactoglobulin. The functional properties of milk proteins in foods have recently been expertly treated by Holt and Rogi´nski (2001). These authors described the antihypersensitive, opioid, immunomodulatory, and calcium-binding milk peptides, the antiviral properties of various milk components, and the antimicrobial activity of lactoperoxidase, lactoferrin, lactoferricins, casein peptides, and peptides from α-lactalbumin.

7.4.4 EGG PROTEINS Egg albumen is used in various food formulations because of its foaming properties and heat gelling ability, while egg yolk serves as an emulsifying agent. The functional properties of egg proteins have recently been treated by Ternes (2001). The strength of egg white gels can be increased by preheating the dry protein at 80°C before use (Kato et al., 1990a). In gels formed by preheated egg whites the molecular weight of aggregates is much smaller than it is in gels made of nonpreheated proteins. Preheating of dry egg whites confers a lower enthalpy and temperature of denaturation on the protein. This results in increased flexibility of the molecules, leading to more cohesive interfacial films, i.e., improved surface functional properties. The more cohesive films composed of overlapping polypeptides are better capable of expanding under stress than the films formed from nonpreheated proteins (Kato et al., 1990b). Egg white and egg yolk gels can also be prepared without heating by applying high pressure (Hayashi et al., 1989). The albumen and yolk from fresh eggs form stiff gels after 30 min of exposure to a pressure above 6000 and 4000 kg/cm,2 respectively. The pressure-induced gels are more adhesive, elastic, and digestible than the boiled egg. Lysozyme, which makes up 3.5% of the total egg white proteins and can be easily separated by ion-exchange techniques (Le´snierowski and Kijowski, 2001), is recognized as a safe, antimicrobial agent to be used for food preservation. It is stable up to about 100°C, has maximum activity at a pH range of 5.3–6.4, and inhibits several pathogenic bacteria, including Listeria monocytogenes, Clostridium botulinum, Yersinia enterocolitica, and Campylobacter jejuni (Kijowski and Le´snierowski, 1999).

7.4.5 MYCOPROTEIN One of the results of research of the second half of the 20th century on single-cell protein for human food and for animal feed was the development of the process of mycoprotein manufacturing. The product has been approved in several European countries for general food use. It has the form of insoluble hyphae, typically 400–700 µm × 3–5 µm with low frequency of branching. Mixing with proteinaceous binders, flavorings, and colors, followed by forming and heating, leads to meat product analogs. The mycoprotein can also be used in extruded commodities and as fat replacers in yogurt and ice cream (Rodger, 2001).

Proteins

155

7.5 EFFECTS OF HEATING 7.5.1 INTRODUCTION Heating controls the rate of different enzymatic and chemical reactions. As applied in food processing, it affects the conformation of proteins, enzyme activity, solubility, and hydration, and leads to thermal and hydrolytic rupturing of peptide bonds, thermal degradation and derivatization of a.a. residues, crosslinking, oxidation, and formation of sensory-active compounds. Most of these reactions are reflected in foods as desirable or detrimental changes in color, flavor, juiciness, rheological properties, enzyme activity, and toxicity. These processes are affected by the temperature and time of heating, pH, oxidizing compounds, antioxidants, radicals, and other reactive constituents, especially reducing saccharides. Some of the undesirable reactions can be minimized. Stabilizers, e.g., polyphosphates and citrate, which bind Ca2+, increase the heat stability of whey proteins at neutral pH. Lactose present in whey in sufficiently high concentrations may protect the proteins from denaturation during spray drying (Jost, 1993). The heat-induced unfolding of a protein usually proceeds in several steps, since separate domains of the molecule denature at different temperatures, depending on the forces stabilizing their structure. The molecular transition temperature, i.e., the point at which major changes in conformation occur, can be determined by different techniques, mainly by differential scanning calorimetry. The susceptibility of proteins to thermal denaturation depends on their structure, predominantly on the number of cross-links, as well as on the simultaneous action of other denaturing agents. Salt bridges, side chain–side chain hydrogen bonds, and a large proportion of residues in α-helical conformation increase the thermal stability of many proteins (Kumar et al., 2000). In some proteins the first changes appear at 35–40°C. The peak maximum temperature of transition of myosin in the myofibrils ranges from 43°C in cod muscle to 60°C in the bovine M. semimembranosus (Howell et al., 1991). Sodium choride decreases the thermal stability of meat proteins by up to about 30%. In the experiments of Fernandez-Martin et al. (2000), pressurization of sausage formulations at 300 MPa at 10°C for 20 min significantly destabilized the proteins. However, the thermal stability of proteins in formulations heated under hydrostatic pressurization was higher than that in control samples. The stabilizing effect was related to the temperature of heating. Heating of soluble collagen brings about uncoiling of the superhelix and unfolding and separation of the polypeptide chains from each other, if they are not bound by stable bonds. This results in a decrease in viscosity of the solution. The denaturation temperature Td can be measured in the range of rapid change in viscosity. Insoluble collagen fibers shrink, due to heat denaturation, by up to 75% of their original length. The shrinkage temperature Ts is usually about 20°C higher than Td. It increases with cross-linking and in fish collagen with the contents of PrOH. The denatured collagen turns into gelatin after prolonged boiling in water, due to partial hydrolysis. This phenomenon affects the rheological properties of cooked meats containing much connective tissue.

156

Chemical and Functional Properties of Food Components

Thermal changes comprise loss in solubility due to aggregation of the proteins, e.g., β-lactoglobulin and immunoglobulins, or increase in solubility as a resulting of the breaking down superstructures, as in collagen. Heating of many proteins to 105–140°C at a low water content, in conditions resembling those during extrusion cooking, leads to increased solubility. This regards proteins that have an open random coil structure and low number of -S-S- bonds and are not able to form many covalent nondisulfide cross-links (Mohammed et al., 2000). Further effects of heating include formation of gels, e.g., in most types of sausages, kamaboko, meat gels, and several types of cheeses; development of gas-retaining structures, as in dough and bread; hydrolytic changes; alteration of the rate of proteolysis; modification of the nutritive value; and inactivation of some allergens.

7.5.2 RHEOLOGICAL CHANGES Proteins are primarily responsible for the texture of meat, poultry, fish, meat and fish gels, cheese, bread, cakes, and many other foods.The texture of muscle foods is affected mainly by: • The contents and cross-linking of collagen, and the morphological structure of the tissues, e.g., meat, fish, and squid • The biochemical state of the muscle, i.e., interactions of the proteins of the myofibril (e.g., in rigor mortis, cold shortening, and thaw rigor), as well as the proteolytic changes during aging of the meat • Mechanical disintegration of the muscle structure Treatment abuse of food during storage, processing, and preparation may lead to toughening and partial loss of the gel-forming ability of frozen stored fish, shrinking and toughening of pasteurized ham, toughening and formation of the grainy structure in casein curd, and separation of fat layers in sausages. The thermal changes in meat commence at about 40°C — some of the meat proteins in solution coagulate at that temperature. Further heating results in shrinkage of collagen, at 50–60°C, followed by gelatinization in a moist environment. At about 65°C hardening of the myofibrils occurs. The final texture of the product depends on hardening of the myofibrillar structure and gelatinization of collagen in the given meat at the particular state of postmortem changes, heated according to a particular time–temperature regime. The rheological changes in meat and fish are emphasized by drip loss, 20–40% of the original weight, and by shrinkage. In making bread, the wheat flour, when mixed with water, forms a viscoelastic dough that retains gas and sets, due to heating during baking. The agent responsible for these dough properties is gluten, which develops in mixing of the flour with water. Dry gluten contains 80–90% proteins, 5–10% saccharides, 5–10% lipids, and minerals. The gluten proteins are composed of 40–50% gliadin, 35–40% glutenin, and 3–7% soluble proteins. During mixing with water the flour particles, containing starch granules embedded in the protein matrix, are progressively hydrated and form the viscoelastic dough. SH/SS interchange reactions result in formation of intermolecular -S-S- bridges. Generally the resistance to extension of the dough increases

Proteins

157

to a peak value. Overmixing usually results in a decrease in resistance and is caused by excessive breaking of the -S-S- bonds, not accompanied by formation of new intermolecular bridges. This ends in depolymerization of the protein and thus increased solubility and decreased viscosity of the dough. The required mixing time can be controlled, within limits, by changing the pH, adding oxidants, or mixing in an inert atmosphere. The gas-retaining ability depends on the viscosity of the hydrated protein–carbohydrate–lipid system. Rice and corn flours do not decrease the gas diffusion rate as effectively, because the doughs prepared from them are not as viscoelastic as the gluten-containing doughs. The relatively high gas retention of rye flour doughs is due to the viscosity of soluble pentosans. A similar effect can be achieved in gluten-free doughs by adding surfactants, particularly natural flour lipids, monoacylglycerols, or xanthan gum (Hoseney and Rogers, 1990). During baking the expansion of the dough stops due to polymerization or cross-linking, as a result of SH/SS interchange reactions. The setting prevents further expansion of the dough and the collapse of the loaf of bread. Very severe heating of foods, at much higher temperatures and times than those required for sterilization, may lead to formation of isopeptide cross-links between the free NH2 group of Lys and the carboxylic group of Asp or Glu: O HN

CH

O

C

HN

(CH2)2

CH

C

(CH2)2

COOH

C

heating

+

O

NH NH2

(CH2)4

(CH2)4 HN

CH

HN

C

CH

C O

O ε - N (γ - glutamyl) lysylamide crosslink

Reaction 7.2

These reactions tighten the structure of the products and may decrease the biological availability of Lys, as well as the digestibility of the proteins.

7.5.3 CHANGES

IN

COLOR

Pig, sheep, beef, and whale contain about 0.2–2.4, 4.5–5.5, 1–20, and 50 mg of myoglobin in 1 g of muscle, respectively. The total content of all chromoproteins in the red muscles of fish ranges from a few to 20 mg/g and is about 20 times higher than that in the white muscles. Changes in the chromoproteins due to oxidation or reduction, denaturation, curing, and reactions with sulfur-containing compounds lead to desirable or undesirable alterations in color.

158

Chemical and Functional Properties of Food Components

Beef heated to 58–60°C internal temperature is rare; to 66–68°C, medium rare; to 73–75°C, medium; and to 80–82°C, well done. The recommended end point temperature in pork is 77°C and in poultry 77–82°C. The reactions of myoglobin in cured, heated meat resulting in formation of the heat-stable nitrosylhemochromogen and a nitrite–protein complex proceed according to Killday et al. (1988) as follows:

-

OH

OH

NO

NO

Fe3+

Fe2+

Fe2+

N

N

N autoreduction

NH

+

NO

NH

NH

Globin metmyoglobin

heating

reduction

NO 2

NO Fe2+ + NO 2 Globin

Globin (or Globin radical)

Globin nitrosyl myoglobin radical

nitrosyl myoglobin

nitrosylhemochromogen

Reaction 7.3

In proteinaceous foods rich in saccharides or secondary lipid oxidation products, the Maillard reaction prevails. The generation of pyrraline from Lys can be used as an indicator of thermal changes in proteins:

HOH2C

CHO N (CH2)4 HC

NH2

COOH Pyrraline

Formula 7.3

7.5.4 DEVELOPMENT

OF

VOLATILE COMPOUNDS

Severe heating of proteinaceous foods leads not only to generation of flavor compounds due to the Maillard reaction, but also to thermal degradation of Met and Cys residues in proteins, as well as of different low-molecular-weight compounds. These reactions are discussed in Chapter 10 of this volume.

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159

7.5.5 REACTIONS

AT

ALKALINE PH

Alkaline treatment is used for peeling of fruits and vegetables, for producing protein isolates, for removing nucleic acids from single-cell protein preparations, and for inactivating mycotoxins and proteinase inhibitors. In protein solutions and in foods, severe changes in reactive a.a. residues take place at high pH values, even at temperatures as low as 50°C. They lead to cross-linking and formation of nontypical a.a. residues. Cross-linking is based on β-elimination, mainly in Cys, Ser, SerP, or Thr, followed by a nucleophilic addition of the ε-NH2 of Lys, δ-NH2 of ornithine, and SH of Cys residues, or of NH3 to the double bond of dehydroalanine or 3-methyldehydroalanine: O HN

CH

O

O OH-

C

HN

C

CHR

CHR

Y

Y

HN

+ H2O

C

C

+ Y

C

-

CHR dehydroalanine residue

where: R=H, CH3; Y=OH, OPO3H2, SH, SR+, SSR

O HN

C

O

C

HN

CH

CH2 +

NH

NH2

(CH2)4

(CH2)4 HN

C

CH2

CH

HN

CH

C

C O

O ε - N (γ - glutamyl) lysylamide crosslink

Reaction 7.4

Reactions of Cys at alkaline pH also liberate free sulfur and a sulfide ion: O HN

CH

HN

CH2 -

S

OH

S

S

CH2 CH

C

HN

CH

S

C

C

CH2 S

+ H2O

-

S

CH2 C O

HN

CH

O

CH

O

OH

HN

C

C

+ H2O + S 2 -

O

Reaction 7.5

-

+ S

CH2 C O

CH2

-

C

S

CH2 C

-

CH2 HN

HN

C

CH2

S

HN

O

O

C

HN

CH

C O

160

Chemical and Functional Properties of Food Components

At a given temperature the overall rate of reaction depends on the rate of βelimination and on the conformation of the protein. This is because the accessibility of the dehydroalanine residue for the nucleophilic attack depends on the spatial arrangement of the reacting groups. The reaction can be inhibited by acylating the nucleophilic groups in proteins or by adding thiol compounds, which compete with a.a. residues for the dehydroalanine double bond: NH

NH R

S + H2C

+

+ H

C C

O

R

S

CH2 C

H

C

O

Reaction 7.6

Alkaline conditions favoring cross-linking in proteins lead to racemization of a.a.: L-a.a. ↔ D-a.a., i.e., after the first step in the reaction sequence the carboanions recombine with protons to the L and D forms. The rate of racemization is affected mainly by the properties of the residues — the lowest is in aliphatic a.a. — and the structure of the protein. Generally the process rate is about 10 times higher in proteins than in free a.a. Severe heating at an alkaline pH may decrease the digestibility and biological value of proteins that result from cross-linking and racemization. The rate of absorption of some D-a.a. in an organism is lower than that of the corresponding L forms. Not all D-a.a. can be metabolized. Furthermore, some of the modified residues, mainly lysinoalanine, induce pathological kidney changes in experimental animals.

7.6 OXIDATION In most proteinaceous foods the oxidation of a.a. residues in proteins is initiated by radicals and different reactive forms of oxygen — singlet oxygen 1O2, superoxide anion radical O2– , and hydroxyl radical •OH — that are generated in the watery environment by light, ionizing radiation, catalytic action of cations, and the activity of enzymes. Lipid peroxides and other oxidation products are also involved. Polyphenols, present in many foods, are prone to oxidation to quinones by oxygen at neutral and alkaline pH values. They can also act as strong oxidizing agents in different products. H2O2, if abused as an bactericidal agent, e.g., in the treatment of storage tanks, packaging materials, or proteinaceous meals, may also cause oxidation of proteins. The effect of oxidative changes in proteins depends on the activity of the oxidizing agent, the presence of sensitizers, e.g., riboflavin, chlorophyll, and erythrosine, the temperature, and the reactivity of the a.a. residues. Several tissues contain various prooxidants, including transition metals and heme pigments, lipoxygenases, and peroxidases, as well as endogenous antioxidants, like glutathione, superoxide dismutase, and catalase. Abstraction of a hydrogen atom on the α-carbon or in the a.a. side chain of a protein leads to the formation of protein radicals. These may polymerize with other

Proteins

161

protein or lipid radicals. Different scission products may also be formed. H2S and free sulfur may be generated due to oxidation of the –SH group. The sulfur-containing a.a. are converted to many oxidized compounds, including cysteine sulfenic, sulfinic and sulfonic acids, mono- and disulfoxides, and mono- and disulfones. The a.a. most prone to oxidation in different model systems and in foods are Met, Cys, Trp, Tyr, and His. Oxidation of Try leads to kynurenine (Friedman and Cuq, 1988), and of His to Asp:

R

N

HN

N

CH2

CH2

CH

CH

H2N

CH2 CH

H2N

COOH

H2N

COOH

COOH

O2

C O

H2N

CH2

N

CHO CH2

CH H2N

O O

C O

HN

CH2

CH

COOH

kynurenine

H2N

CH COOH

H2N

COOH

N-formylkynurenine

Reaction 7.7

N NH CH2 H2N

+

CH2

hν, O2

H2N

C

O

+ other products

NH2

CH

CH

NH2

COOH

sensitizer

COOH

COOH Reaction 7.8

In food systems the oxidation of proteins is often preceded by lipid oxidation, mainly by the primary lipid peroxide products or the radicals produced due to their breakdown (O’Grady et al., 2001).

162

Chemical and Functional Properties of Food Components

The products of oxidation affect the flavor of foods, either directly or by reacting with precursors. Their biological value depends generally on the degree of change due to scission, polymerization, and oxidation. Furthermore, essential a.a. in oxidized foods may become limiting in the diet. Formation of protein–protein and protein–lipid cross-links decreases the digestibility of proteins.

7.7 ENZYME-CATALYZED REACTIONS 7.7.1 INTRODUCTION Reactions in proteins and other nitrogenous compounds catalyzed by endogenous enzymes are responsible for desirable and undesirable sensory attributes of foods — color, flavor, and texture — as well as for the development of compounds that are nutritionally beneficial or have detrimental effects on human health. The use of added enzymes or enzyme sources is also an essential part of many traditional methods of food processing. Since the conditions of enzymatic reactions are much milder than those applied in chemical treatments, different added enzymes are being used to an increasing extent to modify the functional properties of food proteins. Some proteins affect the sensory and functional properties of foods by exhibiting enzymatic activity in their natural environment or when added intentionally during processing in the form of enzyme-rich materials, pure enzyme preparations, or starter cultures of microorganisms. The examples of effects involving protein changes include loss of prime freshness in fish after the catch, rigor mortis and tenderization in meat, ripening of salted fish and cheese, softening of fish gels, fermentation in soybean processing, and proteolytic changes in wheat flour. Enzymatic modification of proteins in food systems has recently been treated exhaustively by Haard (2001).

7.7.2 CHANGES

IN

MILK PROTEINS

In milk the phosphatases may dephosphorylate the caseins. Thiol oxidase may participate in oxidation of SH groups to disulfides. Endogenous and bacterial proteinases catalyze extensive modifications in milk proteins. Plasmin, the alkaline serine proteinase associated with casein micelles and milk fat membrane, attacks βcasein and αs1-casein. Several endogenous plasmin activators and inhibitors control the degradation of milk proteins. The enzyme activity is the highest at pH 7.5 and is only slightly reduced during high-temperature, short-time pasteurization of milk. Heat-stable extracellular proteinases produced by psychrotropic bacteria present in chilled milk hydrolyze different caseins and whey proteins. They can cause a bitter note in UHT milk, age gelation of sterilized milk, and flavor defects in fermented products. Proteinases of somatic cells present in milk, especially from cows in late lactation, may also decrease the yield of cheese and lead to development of bitterness in pasteurized milk (Holt and Rogi´nski, 2001).

7.7.3 ROLE

OF

ENZYMES

IN

MUSCLE FOODS

The sensory quality of meat and seafood is significantly affected by endogenous proteases. The lysosomes contain, among other enzymes, at least 12 cathepsins,

Proteins

163

which can exert a concerted action on proteins and peptides. The optimum pH for the activity of cathepsins is generally in a low acidic range. However, many enzymes retain high activity at pH values one or two units away from the optimum. Cathepsins are released from the lysosomes in stored beef into the sarcoplasm. Most of the meat cathepsins hydrolyze at least some proteins of the myofibrils. Proteolysis by cathepsins has been regarded as one of the factors coresponsible for tenderization of meat. However, not all of these enzymes have a significant effect on intact meat proteins in the usual temperature conditions of postslaughter handling and chilling of the animal carcasses. Furthermore, although they are able to hydrolyze myosin and actin, only insignificant degradation of these main proteins of the myofibrils takes place during tenderization of meat. They can, however, participate in the concerted action of various proteinases in aging meat and fish. The muscles also contain nonlysosomal proteinases capable of hydrolyzing several myofibrillar proteins responsible for the structural integrity of the muscle fibers, especially the cytoskeletal proteins. Calpains, the calcium-activated neutral metalloproteinases, require the cysteinyl thiol group for activation. The highest activity of calpains against isolated myofibrils is in the pH range of 7.0–7.5, while at pH 6 and 4.5 the activity is about 80% and 40% of the maximum value, respectively. One form of the enzyme, called microcalpain, requires at least 0.1–0.5 mM Ca2+ for activation, the optimum concentration being 1 mM; the second form, µcalpain, is activated at micromolar concentrations of Ca2+. Due to the loss of the Ca2+-retaining ability of the reticulum in the muscle postmortem, the concentration of Ca2+ in the sarcoplasm may increase up to about 0.1 mM. There is a cause-andeffect relationship between the activity of µ-calpain and the decrease of muscle strength (Purslow et al., 2001). The enzyme rapidly degrades the cytoskeletal protein desmin, causing depolymerization of the intermediate filaments that bind neighboring Z-discs in the myofibril. The major fragments resulting from the breakdown are further cleaved by cathepsins. The known variations in the rate of tenderization of various muscles are due to the differences in the activity of calpains and calpastatin — a family of endogenous inhibitor proteins that are strictly calpain specific and are located in the same cellular area as the enzyme. The meat tenderization process also involves degradation of other cytoskeletal proteins — titin, nebulin, and desmin (Jiang, 2000; Kijowski, 2001). The changes in proteins catalyzed by endogenous enzymes affect the sensory quality of various salted, cold-smoked, and marinated fish products. In lightly salted salmon, sturgeon, herring, anchovy, Baltic sprats, and fish of many other species, the hydrolytic processes lead to development of tender texture. The flavor becomes predominantly fishy and salty, with meaty, cheesy, and slightly rancid notes (Sikorski et al., 1995). The enzymes involved in ripening of salted, uneviscerated fish, like herring, are mainly those of the pyloric appendages. The suitability of fish for salt ripening is affected by the activity of the endogenous proteases, which fluctuates seasonally and depends on the feeding intensity of the fish. Excessive proteolysis, in products stored too long at too high a temperature, leads to unacceptable softening of the flesh. On the surface of overripe salted fish white “bloom” of crystallized peptides and a.a., mainly Tyr, may appear. In raw herring marinades the ripening occurs due to muscle cathepsins.

164

Chemical and Functional Properties of Food Components

High activity of muscle proteases during the spawning migration may bring about changes that increase the emulsifying ability of salmon meat during the spawning period (Kawai et al., 1990). Different endogenous proteinases are involved in the disintegration of the structure of fish gels known as modori that often occurs due to slow cooking in the temperature range of 50–70°C. In such gels hydrolysis of myofibrillar proteins, particularly myosin, was evidenced. Early reports indicated the heat-stable alkaline proteinases, found in the muscles of several fish species, to be involved. The activity of these enzymes is usually not detectable below 50°C. Further investigations revealed that cathepins B, L, and L-like contribute to the disintegration of the gel structure by hydrolyzing the myosin heavy chain, light chains, actin, and troponins, and that these undesirable effects can be inhibited by using cysteine proteinase inhibitors. A very thorough discussion of the role of different proteinases in the modori softening has been presented by Jiang (2000). A high degree of proteolysis is involved in manufacturing edible fish sauces, silage for animal feed, and hydrolyzates for use as functional ingredients in foods and as bacterial peptones (Sikorski et al., 1995; Lopetcharat et al., 2001). Fish sauces belong to a group of traditional, fermented products typical for Southeast Asia. They are manufactured by salting different small fish, mainly Stolephorus spp., Ristelliger spp., Sardinella spp, Engraulis spp., Clupea spp., Scomber colias, and Decapterus spp., according to a variety of recipes. The proportions of fish to salt range from 1–6 and the fermentation time, usually at ambient temperature, from about 2–18 months. Endogenous and bacterial enzymes are involved in developing the typical flavor of the sauces. The undiluted filtrate of the autolysate is regarded as the first grade fish sauce; the brine extract of the nonhydrolyzed residue is of lower sensory quality and nutritional value. Various proteolytic enzymes from animal, plant, and microbial sources added in the process can increase the rate of proteolysis and even improve the quality of the products (Venugopal et al., 2000). Fish silage is typically made from by-catch fish and filleting offal by mincing, acidifying with formic acid or a mixture of formic and sulfuric acid, and proteolysis catalyzed by endogenous enzymes. After about 2 days at 30–40°C most of the tissues are solubilized. The silage containing 70–80% water can be used as such after removal of the solids and the fatty layer, or else the liquid can be concentrated to the required degree. The product, manufactured commercially in large scale, is used as a feed component for pigs, poultry, and fish. Fish hydrolysates are produced mainly from lean fish of underutilized species or from the filleting of by-products in a process catalyzed by added proteinases of plant, animal, or microbial origin (Figure 7.7). The product can be used as a source of a.a. in growth media for microorganisms, as a replacement for milk in animal feeding, or as a functional ingredient in foods (Liceaga-Gesualdo and Li-Chan, 1999; Mukhin et al., 2001). Partial autoproteolysis has been successfully utilized for producing in industrial conditions food – grade, thermally coagulated, frozen protein gel from Antarctic krill. The protein recovery is about 80% of the protein content in the whole krill ( Kolakowski and Sikorski, 2000).

Proteins

165

Fish Meat Water, 1:2 Endopeptidases

Mincing

NaOH or HCl

Hydrolysis Optimum Temperature

Enzyme Inactivation 100oC

Insolubles

Filtration

Evaporation

Vapors

Drying

Vapors

Fish Peptone

FIGURE 7.7 Flow sheet of the process used for manufacturing fish hydrolyzates.

Other possible applications of proteolytic enzymes in seafood processing include descaling fish, peeling and deveining shrimp, tenderizing squid, isolating pigments from shellfish waste, and reducing the viscosity of fish meal stick waters. Squid muscles contain very active proteinases ( Koladziekska , 1999). High proteolytic activity causes extensive degradation of the myofibrillar proteins in the course of extraction of these proteins for analytical purposes. There are significant differences in the autoproteolytic activity in the muscles of squid of different species. Trimethylamine oxide demethylase, present in the muscles of many gadoid fishes, affects the functional properties of fish proteins indirectly by catalyzing the formation of formaldehyde:

CH3 H3C

N

demethylase

O

CH3

CH3

CH3 Reaction 7.9

O

NH + HC H

166

Chemical and Functional Properties of Food Components

which may participate in cross-linking. These reactions are most important in frozen stored gadoid fish (Sikorski and Kostuch, 1982; Sikorski and Kolakowska , 1994; Sotelo and Rehbein, 2000).

7.7.4 TRANSGLUTAMINASE-CATALYZED REACTIONS Transglutaminase (TGase), or protein-glutamine γ-glutamyltransferase, catalyses the transfer of the acyl group of glutamine residues in proteins or peptides on primary amines or a water molecule:

O Prot

(CH2)2

C

NH2 + H2N

O

TGase

R

Prot

(CH2)2

Prot

(CH2)2

Prot

(CH2)2

C

NH

R + NH3

acyl transfer

O Prot

(CH2)2

C

NH2 + H2N

O

TGase (CH2)4

Prot

C

NH

(CH2)4

Prot + NH3

crosslinking

O Prot

(CH2)2

C

NH2 + H2O

O

TGase

C

OH + NH3

deamidation

Reaction 7.10

It participates in several physiological processes in plant and animal organisms. It is also produced as an extracellular enzyme by Streptoverticillium sp., Physarium sp., and other microorganisms. The red sea bream TGase cloned in Escherichia coli is an intracellular enzyme. Generally the activity of TGase of plant and microbial origin is independent on Ca2+, while the enzyme present in animal tissues is Ca2+ dependent. However, the Ca2+ requirement depends not only on the source of the enzyme, but also on the type of substrate. In the active site of TGase is a thiol group in the sequence -Tyr-Gly-Gln-Cys-Trp-. TGases occur in the form of a monomer, dimer, or tetramer, soluble in the cytosol or bound in mitochondria and lysosomes. Although they have a maximum activity at 50°C, they can be effectively used for modification of food proteins in the temperature range of 5–20°C. The optimum pH range for the activity of TGase of different origins is 6–9.5. The role of TGase in food processing is due to the protein cross-linking effect, incorporation of amines, and deamidation of glutamine residues. The effect of the enzyme activity expressed as cross-linking depends also on the concentration of NaCl, as well as on the properties of the protein substrate (Ashie and Lanier, 2000; Kolakowski and Sikorski, 2001). The deamidation activity of TGases of various origin is affected by the enzymes’ substrate specificity (Ohtsuka et al., 2000).

Proteins

167

Endogenous TGase activity is responsible for the formation of ε(γglutamyl)lysine cross-links in dried fish (Kumazawa et al., 1993), in frozenstored surimi (Haard et al., 1994), and in the polymerization of the myosin heavy chain during setting of surimi in manufacture of kamaboko (Kumazawa et al., 1995). Commercially produced microbial TGase has found numerous applications in food processing. It can be used for increasing the gel strength of kamaboko made of surimi produced from fish of low gel-forming ability, for improving the rheological properties of dairy products, and in manufacturing various meat commodities. Reactions catalyzed by added TGase can lead to “tailor-made” protein preparations, e.g., edible films of defined barrier properties from whey proteins, and to covalent binding of saccharides to plant proteins rich in Glu residues (Colas et al., 1993). Ca2+-independent TGase derived from Streptoverticillium can induce gelation of glycinin and legumin at 37°C, and the gels are more rigid and elastic than thermally gelled products (Chanyongvorakul et al., 1995). This enzyme added at optimum concentration to fish skin gelatin increases the melting point, strength, and viscosity of the gels. The activity of TGase during storage of the product, which might change the rheological properties of the gel, can be arrested by heating to 90°C just after incubation of the gelatin solution with the enzyme (Gómez-Guillen et al., 2001). Crosslinking of proteins catalyzed by TGase does not impair the nutritional value of the products.

7.7.5 OTHER ENZYME APPLICATIONS

IN

FOODS

Wheat lipoxygenase and soybean lipoxygenase, catalyzing oxidation of fatty acids, generate oxidized reaction products that improve the dough-forming properties and baking performance of flour. A similar role is performed by polyphenol oxidase and peroxidase. Enrichment of proteins in specific a.a. can be achieved in the plastein reaction, i.e., protease-catalyzed transpeptidation in concentrated solutions of a.a. ethyl esters and protein hydrolyzates (Figure 7.8). Incubation of a protein hydrolyzate, concentrated to 30–40%, with ethyl esters of Lys, Met, or Trp, e.g., with an appropriate endopeptidase at pH 4–7 at about 37°C, leads after a few days to accumulation of peptides of 2–3 kDa enriched in the respective a.a. residues. Plasteins free of Phe residues can also be obtained for phenylketonuric patients. The rate of incorporation of a.a. into the plastein increases with the hydrophobicity of the a.a. Thus selective removal of hydrophobic a.a. from the hydrolyzate and decrease of its bitter taste are possible. Cyclic adenosine monophosphate-dependent protein kinase is useful for phosphorylation of a.a. residues in mild conditions. The modification makes the soybean proteins soluble in media rich in calcium and improves their emulsifying properties (Seguro and Motoki, 1990). In a papain-catalyzed reaction, at room temperature, proteins can be acylated and enriched in SH groups using N-acetyl-homocysteinethiolactone (Sung et al., 1983):

168

Chemical and Functional Properties of Food Components

Protein

Endopeptidases

Hydrolysis

Exopeptidases, Organic Solvent

Modification of Peptides

Endopeptidases, Amino Acid Asters

Plastein Reaction

Undesirable Amino Acids, Impurities

Amino Acids, Small Peptides

Extraction

Ethanol

Plasteins

FIGURE 7.8 Utilization of the plastein reaction. O H3C

CO

NH

CH

C

CH2 C H2

S + H2N

Prot

papain pH 10

H3C

CO

NH

CH

CO

NH

Prot

(CH2)2 SH

Reaction 7.11

7.8 CHEMICAL MODIFICATIONS 7.8.1 INTRODUCTION Chemical additives and reactions are used to change the color and several properties of different foods and isolated proteins. Typical examples include the use of sodium nitrite in the curing of meat, chemical modifications of dough proteins for improving the texture of many baked goods, and applications of polyphosphates in the meat industry. The intended modification in the properties of proteins can be achieved by changing the charge, hydrophobicity, and steric parameters of the molecules, due to cross-linking or alterations of the a.a. residues. Ascorbic acid and its oxidation product dehydroascorbic acid have been known as flour improvers in the baking of bread. Dehydroascorbic acid and its breakdown products — threose, glyoxal, diacetyl, and methyl glyoxal — are involved in Maillard-type reactions leading to protein cross-linking (Fayle et al., 2000). Many experiments on chemical modification of a.a. residues serve the purpose of studying the structure–function relationship in respect to proteins in different food systems under the conditions prevailing during processing and storage.

Proteins

169

7.8.2 ALKYLATION The carbonyl compounds formed due to autoxidation of lipids and in catabolic processes postmortem in muscles, or introduced with wood smoke, can bring about undesirable effects by interacting with a.a. residues. On the other hand, some carbonyl compounds are used intentionally to modify the proteins. Formaldehyde can harden the collagen dope in the manufacturing of sausage casings, protect fodder meals against deamination by the rumen microflora, and bind immobilized enzymes on supports. In reducing conditions, alkylation of amino, indole, thiol, and thioether groups, and binding of saccharides to a.a. residues are possible: 2Prot

NH2 + 4HCHO + NaCNBH3

pH 9 0o C

2Prot

N(CH3)2 + NaHCNBO 3 + H2O

Reaction 7.12

For alkylation of amino, phenol, imidazole, thiol, and thioether groups in a.a. residues of proteins, reactions with haloacetates and haloamides can also be used: Prot

SH + ICH2COOH

Prot

S CH2COOH + HI

Reaction 7.13

Prot —NH2 + ICH2CONH2

Prot

NH CH2 CONH2 + HI

Reaction 7.14

The digestibility of such derivatives is generally somewhat lower than that of the unmodified proteins. Malonaldehyde, a typical lipid oxidation product, can form cross-links in proteins by reacting with two amino groups: O H

O C CH2 C

H

+ 2 Prot

NH2

Prot

N CH CH2 CH N Prot + H2O

Reaction 7.15

There is also a possibility that aliphatic monoaldehydes generated in lipid autoxidation can participate in cross-linking of proteins. Formaldehyde can react in food systems with amino, amide, hydroxyl, and thiol groups in a.a. residues of proteins, even at room temperature. Some of these reactions result in cross-linking of the proteins. In cheese the biogenic formaldehyde reacts with the N-terminal His of γ2-casein to form spinacine:

170

Chemical and Functional Properties of Food Components

N N NH NH HCHO HN

CH2 CH H2N

COOH

COOH spinacine Reaction 7.16

Other carbonyl compounds produced in cheese by lactic acid bacteria form other derivatives in reactions with His (Pellegrino and Resmini, 1996).

7.8.3 ACYLATION Acylation of nucleophilic groups is intended to increase the hydrophobicity of the protein, introduce additional ionizable groups, or contribute to cross-linking: O O O

+ H2N

Prot

OOC

(CH2)2 C

NH

Prot

O Reaction 7.17

The acylating agents may react with amino, imidazole, hydroxyl, phenol, and thiol groups in a.a. residues. The rate of reaction depends on the properties of the nucleophiles, the pH, the steric factors resulting from the protein conformation, and the presence of inhibitors. The amino and tyrosyl groups can be acylated easily, while His and Cys derivatives hydrolyze readily. Acylation of hydroxyl groups in a.a. residues of proteins proceeds in the presence of an excess of acetic anhydride only after the amino groups have been acylated. For the formation of isopeptide linkages N-carboxyanhydrides of a.a. are suitable. The degree of acylation depends on the nature of the protein, the acylating agent, and the process conditions, and may reach up to 95% of lysyl residues. Some food proteins are rich in phosphoric acid residues. The acid may either form ester bonds with Ser residues, as in caseins and egg proteins, or stabilize the native conformation of protein micelles by electrostatic interactions with negatively charged groups and calcium ions, as in caseins. In soy proteins Ser and Thr residues can be esterified and Lys amidated with cyclic sodium trimetaphosphate at pH 11.5 and 35°C (Sung et al., 1983):

Proteins

171

O Prot

Ser

O O-

OH

P +

Prot

Lys

O

Prot

Ser

O

P

O

O

P

O O

O + P2O 7 4 + H+

P O

O

O

NH2

pH 11 - 12 - H2O

-

pH 11 - 12

Prot

pH<5

Lys

H

O O-

N

P

O O

P

O

P

O

O

-

+ H+

O -

O

Reaction 7.18

The Nεtriphospholysine residues protect the NH2 group during heating in an alkaline environment and hydrolyze at pH < 5. For chemical phosphorylation other reagents are also effective, e.g., phosphorus oxychloride and phosphorus pentoxide. The reactivity of these compounds may, however, lead to undesirable cross-linking of the proteins:

Prot

NH2 + POCl3

Prot HOOC

Prot

Prot

NH

NH

+

POCl2 + H + Cl

CO

-

Prot + Cl2PO 2- + H+

Reaction 7.19

Acylation of a.a. residues generally improves WHC, as well as emulsification and the foaming capacity of the proteins. The pI shifts toward lower values, and the solubility increases over that of the unmodified protein, above the pI, and decreases in the acidic range. This is important, e.g., for wheat gluten, which has low solubility in the neutral pH range. The positive change in the functional properties is not in all cases achieved at the highest degree of modification, since it depends on the change in surface hydrophobicity that is affected by the nature of the protein and the acylating agent. The biological availability of acylated proteins depends on the kind of the acyl group and the extent of acylation. Isopeptides are generally well utilized, while the availability of other derivatives usually decreases with the increasing size of the acylating moiety and the degree of acylation.

7.8.4 N-NITROSATION The nitrous acid generated in foods at low pH values, from endogenous or added nitrites, decomposes easily to yield the nitrosating agents nitrous anhydrate and nitrosonium ion:

172

Chemical and Functional Properties of Food Components

2HO

O

N O

N O

N

O + H2O

+

H

O

N O

N

N

O

O + HO

N O

H Reaction 7.20

Reactions of these compounds with the secondary and tertiary amines contained in many foods lead to the known carcinogens N-nitrosoamines: -

O

N

O

NH + O

N

O

N

NO 2

O

or

R R

R

H N

R

O

or

N

O

+ HNO 2

+ -H

+

O

H

N

N

R R

N

N

O

Reaction 7.21

R R N+ N O R

R R N R

-

N O

O

N O

R R

N

N O + R O

N O

Reaction 7.22

The rate of N-nitrosation increases with the pKa of the amine and depends on the pH — it is highest at a pH range of 2–4. The reaction can be inhibited by compounds capable of binding the nitrosating agents — in meat curing, sodium ascorbate is very effective. Foods low in amines and nitrites generally contain about 1–10 ppb, while cured and heavy smoked meat and fish contain up to several hundred ppb of N-nitroso compounds.

7.8.5 REACTIONS

WITH

PHOSPHATES

In acid environments proteins may form protein–phosphate complexes of low solubility. The metaphosphates, which are less hydrated than the ortophosphates, form complexes that are less soluble than those with ortophosphates. This has been utilized for the modification of functional properties of protein concentrates and preparations, for separation of proteins in different food processing operations, and in treatment of protein-containing food plant effluents.

Proteins

173

Polyphosphates improve the sensory quality of many food products. They prevent the separation of butter fat and aqueous phases in evaporated milk, and the formation of gel in concentrated milk sterilized by high-temperature short-time (HTST). They also stabilize the fat emulsion in processed cheese by disrupting the casein micelles and thus enhance the hydrophobic interactions between lipids and casein. Polyphosphates are also used in meat processing for increasing the WHC and improving the texture of many cooked products. The mechanisms involved in different applications depend on the properties of the phosphates and the commodities, as well as the parameters of processing. In meat products the increase in WHC, texture improvement, and the decrease in drip may be caused by increasing the pH, complexing of Ca2+ and Mg2+, binding of phosphates to proteins, rupturing the cross-links between myosin and actin, and dissolving some proteins. Phosphates facilitate the manufacture of meat products of low sodium content. To produce an emulsion-type sausage of acceptable quality, at least 2.5% salt is required. The contents of salt can be decreased to 1.5–2.0% without loss in product quality by adding phosphates in amounts of 0.35–0.5%. Generally, proprietary blands of several polyphosphates are used, to give the best quality and to prevent precipitation of orto- and pyrophosphates in brines rich in Ca2+. Polyphosphates are added as cryoprotectants to frozen fish minces. They are also applied in form of dips to fish fillets prior to freezing to prevent thaw drip losses and to improve the texture of canned fish. Mainly, about 10% solutions of Me5P3O10 and Me4P2O7 are used for 1–2 min. Different proprietary mixtures are also applied, e.g., Na4P2O7 + Na2H2P2O7 or Na3PO4 + Na4P2O7 + Na2H2P2O7.

REFERENCES Ashie, I.N.A. and Lanier, T.C.,Transglutaminases in seafood processing, in Seafood Enzymes: Utilization and Influence on Postharvest Seafood Quality, Haard, N.F. and Simpson, B.K., Eds., Marcel Dekker, New York, 2000, chap. 6. Benjakul, S., Visessanguan, W., and An, H., Properties of cysteine proteinase inhibitors from black gram and rice bean, J. Food Biochem., 25, 211, 2001a. Benjakul, S., Visessanguan, W., and Srivilai, C., Porcine plasma protein as proteinase inhibitor in bigeye snapper (Priacanthus tayenus) muscle and surimi, J. Sci. Food Agric., 81, 1039, 2001b. Boatright, W.L. and Hettiarachchy, N.S., Soy protein isolate solubility and surface hydrophobicity as affected by antioxidants, J. Food Sci., 60, 798, 1995. Bramaud, C., Mimar, P., and Daufin, G., Thermal isoelectric precipitation of α-actalbumin from a whey protein concentrate: influence of whey-calcium complexation, Biotechnol. Bioeng., 47, 121, 1995. Chanyongvorakul, Y. et al., Physical properties of soy bean and broad bean 11S globulin gels formed by transglutaminase reaction, J. Food Sci., 60, 883, 1995. Colas, B., Caer, D., and Fournier, E., Transglutaminase catalyzed glycosylation in vegetable protein: effect on solubility of pea legumin and wheat gliadins, J. Agric. Food Chem., 41, 1811, 1993.

174

Chemical and Functional Properties of Food Components

Damodaran, S., Interrelationship of molecular and functional properties of food proteins, in Food Proteins, Kinsella, J.E. and Soucie, W.G., Eds., American Oil Chemists’ Society, Champaign, IL, 1989, chap. 3. Doi, E. et al., Melting of heat-induced ovalbumin gel by pressure, Food Hydrocoll., 5, 409, 1991. Doucet, D., Gauthier, S.E., and Foegeding, E.A., Rheological characterization of a gel formed during extensive enzymatic hydrolysis, J. Food Sci., 66, 711, 2001. Fayle, S.E. et al., Crosslinkage of proteins by dehydroascorbic acid and its degradation products, Food Chem., 70, 193, 2000. Feng, Y. and Hultin, H.O., Effect of pH on the rheological and structural properties of gels of water-washed chicken-breast muscle at physiological ionic strength, J. Agric. Food Chem., 49, 3927, 2001. Fernández-Martin, F., Fernández José Carballo, P., and Jiménez-Colmenero, F., DSC study on the influence of meat source, salt and fat levels, and processing parameters on batters pressurization, Eur. Food Res. Technol., 211, 387, 2000. Friedman, M. and Cuq, J.L., Chemistry, analysis, nutritional value, and toxicology of tryptophan in food: a review, J. Agric. Food Chem., 36, 1079, 1988. Gómez-Guillen, M.C. et al., Effect of microbial transglutaminase on the functional properties of megrim (Lepidorhombus boscii) skin gelatin, J. Sci. Food Agric., 81, 665, 2001. Gómez-Guillen, S. et al., Effect of heating temperature and sodium chloride concentration on ultrastructure and texture of gels made from giant squid (Dosidicus gigas) with addition of starch, κ-carragenan and egg white, Z. Lebens. Unters. Forsch., 202, 221, 1996. Haard, N.F., Enzymic modification of proteins in food systems, in Chemical and Functional Properties of Food Proteins, Sikorski, Z.E., Ed., Technomic Publishing Co., Inc., Lancaster, PA, 2001, chap. 7. Haard, N.F., Simpson, B.K., and Pan, B.S., Sarcoplasmic proteins and other nitrogenous compounds, in Seafood Proteins, Sikorski, Z.E., Pan, B.S., and Shahidi, F., Eds., Chapman & Hall, New York, 1994, chap. 3. Hamm, R., Biochemistry of meat hydration, in Advances in Food Research, Vol. 10, Chichester, C.O., Mrak, E.M., and Stewart, G.F., Eds., Academic Press, Inc., New York, 1960, chap. 8. Hayashi, R. et al., Application of high pressure to food processing: pressurization of egg white and yolk, and properties of gels formed, Agric. Biol. Chem., 53, 2935, 1989. Holmes, K.L., Noguchi, S.F., and MacDonald, G.A., The Alaska pollock resource and other species used for surimi, in Surimi Technology, Lanier, T.C. and Lee, C.M., Eds., Marcel Dekker, New York, 1992, chap. 3. Holt, C. and Rogi´nski, H., Milk proteins: biological and food aspects of structure and function, in Chemical and Functional Properties of Food Proteins, Sikorski, Z.E., Ed., Technomic Publishing Co., Inc., Lancaster, PA, 2001, chap. 11. Hoseney, R.C. and Rogers, D.E., The formation and properties of wheat flour doughs, CRC Crit. Rev. Food Sci. Nutr., 29, 73, 1990. Hossain, M.I. et al., Contribution of the polymerization of protein by disulfide bonding to increased gel strength of walley pollack surimi gel with preheating time, Fisheries Sci., 67, 710, 2001. Howell, B.K., Matthews, A.D., and Donnelly, A.P., Thermal stability of fish myofibrils: a differential scanning calorimetric study, Int. J. Food Sci. Technol., 26, 283, 1991. Jiang, S.T., Enzymes and their effects on seafood texture, in Seafood Enzymes: Utilization and Influence on Postharvest Seafood Quality, Haard, N.F. and Simpson, B.K., Eds., Marcel Dekker, New York, 2000, chap. 15.

Proteins

175

Jiang, S.T., Ho, M.L., and Chen, H.C., Purified NADPH-sulfite reductase from Saccharomyces cerevisiae effects on quality of ozonated mackerel surimi, J. Food Sci., 63, 777, 1998. Jost, R., Functional characteristics of dairy proteins, Trends Food Sci. Technol., 4, 283, 1993. Kato, A. et al., Excellent gelation of egg white preheated in the dry state is due to a decreasing degree of aggregation, J. Agric. Food Chem., 38, 1868, 1990a. Kato, A. et al., Enthalpy of denaturation and surface functional properties of heated egg white proteins in the dry state, J. Food Sci., 55, 1280, 1990b. Kawai, Y., Hirayama, H., and Hatano, M., Emulsifying ability and physicochemical properties of muscle proteins of fall chum salmon Oncorhynchus keta during spawning migration, Nippon Suisan Gakkaishi, 56, 625, 1990. Kijowski, J., Muscle proteins, in Chemical and Functional Properties of Food Proteins, Sikorski, Z.E., Ed., Technomic Publishing Co., Inc., Lancaster, PA, 2001, chap. 10. Kijowski, J. and Le´snierowski, G., Separation, polymer formation and antibacterial activity of lysozyme, Pol. J. Food Nutr. Sci., 8/49, 3, 1999. Killday, K.B. et al., Structural characterization of nitrosylhemochromogen of cooked cured meat: implications in the meat-curing reaction, J. Agric. Food Chem., 36, 909, 1988. Ko, S. et al., Physical and chemical properties of edible films containing nisin and their action against Listeria monocytogenes, J. Food Sci., 66, 1006, 2001. Kolakowski , E., Protein determination and analysis in food systems, in Chemical and Functional Properties of Food Proteins, Sikorski, Z.E., Ed., Technomic Publishing Co., Inc., Lancaster, PA, 2001, chap. 4. Kolakowski , E. and Sikorski, Z.E., Endogenous enzymes in Antarctic krill: control of activity during storage and utilization, in Seafood Enzymes: Utilization and Influence on Postharvest Seafood Quality, Haard, N.F. and Simpson, B.K., Eds., Marcel Dekker, New York, 2000, chap. 18. Kolakowski , E. and Sikorski, Z.E., Transglutaminase and its applications in food industry, Z˙˙ywnosc ´ ´ , 3, 5, 2001 (in Polish). Kolodziejska , I., Enzymatic and functional properties of squid proteins. Characteristics and possibilities of utilization, Zeszyty Naukowe Politechniki Gda´nskiej, Chemia, 44, 1, 1999 (in Polish). Kristinsson, H.G., Evaluation of different methods to isolate cod (Gadus morhua) muscle myosin, J. Food Biochem., 25, 249, 2001. Kumar, S., Tsai, C.-J., and Nussinov, R., Factors enhancing protein thermostability, Protein Eng., 13, 179, 2000. Kumazawa, Y. et al., Suppression of surimi gel setting by transglutaminase inhibitors, J. Food Sci., 60, 715, 1995. Kumazawa, Y. et al., Formation of ε(gamma-glutamyl)lysine cross-link in cured horse mackerel meat induced by drying, J. Food Sci., 58, 1086, 1993. Kwok, K.C. and Niranjan, K., Review: effect of thermal processing on soymilk, Int. J. Food Sci. Technol., 30, 263, 1995. Lampart-Szczapa, E., Legume and oilseed proteins in Chemical and Functional Properties of Food Proteins, Sikorski, Z.E., Ed., Technomic Publishing Co., Inc., Lancaster, PA, 2001, chap. 14. Lanier, T.C., Functional food protein ingredients from fish, in Seafood Proteins, Sikorski, Z.E., Pan, B.S., and Shahidi, F., Eds., Chapman & Hall, New York, 1994, chap. 10. Le Tien, C. et al., Milk protein coatings prevent oxidative browning of apples and potatoes, J. Food Sci., 66, 512, 2001. Le´snierowski, G. and Kijowski, J., Isolation of lysozyme from hen egg white by ion-exchange techniques and its spray drying dehydration, Pol. J. Food Nutr. Sci., 10/51, 43, 2001.

176

Chemical and Functional Properties of Food Components

Liceaga-Gesualdo, A.M. and Li-Chan, E.C.Y., Functional properties of fish protein hydrolyzate from herring (Clupea harengus), J. Food Sci., 64, 1000, 1999. Lopetcharat, K et al., Fish sauce products and manufacturing: a review, Food Rev. Int., 17, 65, 2001. Luo, Y.K. et al., Comparsion of gel properties of surimi from Alaska pollock and three freshwater fish species: effects of thermal processing and protein concentration, J. Food Sci., 66, 548, 2001. Matsumoto, J. J. and Noguchi, S.F., Cryostabilization of protein in surimi, in Surimi Technology, Lanier, T.C. and Lee, C.M., Eds., Marcel Dekker, New York, 1992, chap. 15. Mohammed, Z.H., Hill, S.E., and Mitchell, J. R., Covalent crosslinking in heated protein systems, J. Food Sci., 65, 221, 2000. Mukhin, V.A. et al., A protein hydrolysate enzymatically produced from the industrial waste of processing Icelandic scallop Chlamys islandica, Appl. Biochem. Microbiol., 37, 292, 2001. Nakai, S. and Li-Chan, S., Hydrophobic Interactions in Food Systems, CRC Press, Boca Raton, FL, 1988. Niwa, E., Chemistry of surimi gelation, in Surimi Technology, Lanier, T.C. and Lee, C.M., Eds., Marcel Dekker, New York, 1992, chap. 16. O’Grady, M.N., Monahan, F.J., and Brunton, N.P., Oxymyoglobin oxidation and lipid oxidation in bovine muscle: mechanistic studies, J. Food Sci., 66, 386, 2001. Ohtsuka, T. et al., Comparison of deamidation activity of transglutaminases, J. Food Sci., 66, 25, 2001. Pellegrino, L. and Resmini, P., Evaluation of the stable reaction products of histidine with formaldehyde or with other carbonyl compounds in dairy products, Z. Lebensm. Unters. Forsch., 202, 66, 1996. Perez-Gago, M.B. and Krochta, J.M., Denaturation time and temperature effects on solubility, tensile properties, and oxygen permeability of whey protein films, J. Food Sci., 66, 705, 2001. Purslow, P.P. et al., Patterns of variation in enzyme activity and cytoskeletal proteolysis in muscle, in Congress Proceedings, Vol. 1, 47th International Congress of Meat Science and Technology, Kraków, Meat and Fat Research Institute, Warszawa, 2001, p. 38. Regenstein, J. M. and Regenstein, C.E., Food Protein Chemistry, Academic Press, Inc., Orlando, FL, 1984. Rodger, G., Production and properties of mycoprotein as a meat alternative, Food Technology, 55, 36, 2001. Roy, S. et al., Physical and molecular properties of wheat gluten films cast from heated filmforming solutions, J. Food Sci., 64, 57, 1999. Seguro, K. and Motoki, M., Functional properties of enzymatically phosphorylated soybean proteins, Agric. Biol. Chem., 54, 1271, 1990. Shimizu, A. et al., Melting of the ovalbumin gels by heating: reversibility between gel and sol, Nippon Shokuhin Kogyo Gakkaishi, 38, 1050, 1991. Sikorski, Z.E., Proteins, in Chemical and Functional Properties of Food Components, Sikorski, Z.E., Ed., Technomic Publishing Co. Inc., Lancaster, PA, 1997. Sikorski, Z.E., Gildberg, A., and Ruiter, A., Fish products, in Fish and Fishery Products: Composition, Nutritive Properties and Stability, Ruiter, A., Ed., CAB International, Wallingford, 1995, chap. 11. Sikorski, Z.E. and Kolakowska , A., Changes in proteins in frozen stored fish, in Seafood Proteins, Sikorski, Z.E., Pan, B.S., and Shahidi, F., Eds., Chapman & Hall, New York, 1994, chap. 8.

Proteins

177

Sikorski, Z.E. and Kostuch, S., Trimethylamine N-oxide demethylase: its occurrence, properties, and role in technological changes in frozen fish, Food Chem., 9, 213, 1982. Sotelo, C.G. and Rehbein, H., TMAO-degrading enzymes, in Seafood Enzymes: Utilization and Influence on Postharvest Seafood Quality, Haard, N.F. and Simpson, B.K., Eds., Marcel Dekker, New York, 2000, chap. 7. Sung, H.Y. et al., Improvement of the functionalities of soy protein isolate through chemical phosphorylation, J. Food Sci., 48, 716, 1983. Tani, F. et al., Heat-induced transparent gel from hen egg lysozyme by a two-step heating method, Biosci. Biotech. Biochem., 57, 209, 1993. Ternes, W., Egg proteins, in Chemical & Functional Properties of Food Proteins, Sikorski, Z.E., Ed., Technomic Publishing Co., Inc., Lancaster, PA, 2001, chap. 12. Toyoda, K. et al., The surimi manufacturing process, in Surimi Technology, Lanier, T.C. and Lee, C.M., Eds., Marcel Dekker, New York, 1992, chap. 4. Venugopal, V. et al., Enzymes in fish processing, biosensors, and quality control: a review, Food Biotechnol., 14, 21, 2000. Wu, M.C., Manufacture of surimi based products, in Surimi Technology, Lanier, T.C. and Lee, C.M., Eds., Marcel Dekker, New York, 1992, chap. 10. Yoon, K.S. and Lee, C.M., Effect of powdered cellulose on the texture and freeze-thaw stability of surimi-based shellfish analog products, J. Food Sci., 55, 87, 1990. Zehetner, G. et al., Inactivation kinetics of gamma-glutamyltransferase during the heating of milk, Z. Lebensm. Unters. Forsch., 201, 336, 1995. Zhu, H. and Damodaran, S., Effects of calcium and magnesium ions on aggregation of whey protein isolate and its effect on foaming properties, J. Agric. Food Chem., 42, 856, 1994.

8

Rheological Properties of Food Systems Tadeusz Matuszek

CONTENTS 8.1 8.2 8.3

Introduction ..................................................................................................179 Flow Properties of Liquid and Semisolid Food Systems............................181 Effect of Composition and Processing Parameters on the Rheological Behavior of Food Systems...........................................191 8.3.1 Energy, Stress, and Deformation .....................................................191 8.3.2 Structure Development.....................................................................193 8.3.3 Glass Transition and State Diagrams ..............................................195 8.3.4 Dynamics Map of the Food System ................................................196 8.4 Importance of the Rheological Properties of Foods for Process Design and Control...................................................................199 8.4.1 Simplified Rheological Principles ...................................................199 8.4.2 Case Behavior of Fluid Food System..............................................201 References..............................................................................................................203

8.1 INTRODUCTION Most food systems are built of a network of many small particles and macromolecules and held together by a wide range of intermolecular and colloidal forces. Their structure, texture, stability, and functionality are strongly influenced by the strength of these interactions. Moreover, the texture of a final food system depends strongly on the history of structural changes during processing. At the current state of art, we do not understand the mechanisms whereby subtle changes in food system interactions control the structure and mechanical properties of foods. General strategy in food systems is to determine quantitatively the relationships between interactions, structure, and rheology related to the food functionality. From the structure point of view, it means the complete specifications of the relative distributions of particle in space. In the case of rheology, it means the frequency-dependent relationship between stress and strain at a small deformation rate, as well as dependent behavior at large deformations. The food functionality in general can be expressed through the hurdle technological effect, which was achieved at the final stage of food processing. Each particular food product can be assessed by a certain set of 1-5871-6149-4/02/$0.00+$1.50 © 2002 by CRC Press LLC

179

180

Chemical and Functional Properties of Food Components

hurdles that differs in quality and intensity, depending on the technology used (Gorris, 1995). The hurdles might influence the stability and the sensory, nutritive, technological, and economic properties of a product. The hurdles affecting the shelf life of foods also influence other food properties, including texture. The effects of several physical, chemical, and mechanical treatments should be carefully considered in developing new processes and products. It is not enough to describe the composition of a food product and to determine the conditions and types of unit operation necessary to achieve the required quality. How the major food components, such as water, salt, hydrocolloids, starches, lipids, proteins, flavors, and additives, interact with each other and affect the product quality with respect to microstructure, texture, and appearance should be examined. From a food engineering point of view, food functionality is the specific response of foods to applied forces encountered during preparation, processing, storage, and consumption (Kokini et al., 1993). The understanding of food at the molecular level involves the application of both theoretical and experimental techniques of chemistry, physics, mathematics, fluid mechanics, biochemistry, and biophysics to understand how the molecular properties and interactions affect the final quality of the product. If the texture is to be controlled, then the effect of individual components of the formulation should be known. The forces affecting foods during engineering operations may include the various forms of energy applied, e.g., transport fluxes related to the mass and heat flow; electromagnetic energy, including light, microwave, and infrared radiation; and chemical reactions, which are responsible for transferring food from one thermodynamic state to another through changes in enthalpy, entropy, and resulting free energies. The energy deposited and the resulting forces usually expose their effects at any level in the hierarchy of food structure, i.e., from the molecular level to the formation of phases, networks, aggregates, cells, and finally, the food products themselves. Many food systems are formed in conditions far away from thermodynamic equilibrium because all food components can potentially interact chemically with one another to varying degrees. Most food materials and their complex systems are biologically active and physically unstable with continuous changes of their structure. Those physical, chemical, and mechanical instabilities in many food systems are a direct result of the nonequilibrium nature of these systems. During food processing, the raw material has its chemical and physical properties extensively altered. This results in a final product whose appearance is very different from the original, primary native microstructure. Most processing operations are strongly related to the structural aspects of water as a main solvent and plasticizer and to the contribution of water to hydrodynamic properties of food systems. The thermodynamic aspects describing water relation in equilibrium, with its surroundings at a certain relative humidity, pressure, and temperature, should also be considered. Many systems involve complex mixtures of molecules in low-water environments, and interfacial phenomena with all forces of intermolecular interactions play a very important role in food functionality. Overall, the objective of food systems is to develop a predictive methodology for substantially improving the ability of producers to create new food products of specified properties and controlled consistency

Rheological Properties of Food Systems

181

Quantitative analysis of deformation

Quantitative determination of state with influence on the transportation phenomena within the structure system

Characterization of a flow with the range of structural and phase transition effect

Measurement of the stress/shear rate

Mathematical model selection

Structural model selection

Property calculation and its transition in food processing

FIGURE 8.1 Outline of general methodology of the functional food properties seen as deformation and property changes. (From Matuszek, T.S., paper presented at 9th World Congress of Food Science and Technology, Budapest, 1995.)

in food processing. Therefore, the kinetic and thermodynamic aspects of possible physical and chemical interactions have to be investigated to obtain a complete understanding of all dynamic processes leading to food functionality (Figure 8.1).

8.2 FLOW PROPERTIES OF LIQUID AND SEMISOLID FOOD SYSTEMS The flow properties are critical for attaining accuracy and quality in designing food processing machines and food industry plants. They are also vital in modeling processing operations. Various energy and heat treatments of food include thermal conductivity, thermal diffusivity, density, consistency and concentration changes, specific enthalpy, specific heat, texture, and mechanical and rheological properties. Foods are mostly nonhomogeneous and structure formation means that various states of aggregation occur during processing. The engineering phase of processing usually involves changes in the structure of raw materials. The food technologist and engineer would like to be able to predict the properties of any formulation of

182

Chemical and Functional Properties of Food Components

components over a wide range of processing and storage conditions. In order to make this happen, it is necessary to understand more about factors that affect: • All levels of food structure organization • The kinetics of competitive adsorption of the food components at fluid interfaces • The developing time-dependent properties of food formulations • Fouling problems and their effects on processing performance for different types of membranes that are created within the microstructure of the systems All these factors are related to the theory of flow for predicting the rates of molecular transport and their relationships to molecular and consequently food microstructure properties. This molecular flow information leads to a better understanding of surface rheological factors and of the organization and motions, together with intermolecular interaction, of molecules at interfaces. Intermolecular forces are responsible for many of the bulk properties of foods. A realistic processing description of the relationships among pressure, volume, temperature, energy, and other properties of the material must include the effects of attractive and repulsive forces between molecules. Repulsive forces prevent the molecules from approaching one another too closely and account for the low compressibility of liquids. Intermolecular forces between near and distant neighbors dictate the ordered molecular arrangements in crystalline solids. These forces also account for the solid elasticity of and for a very complex, condensed phase. Furthermore, the properties of structure influenced by velocity of propagation of disturbances in it, such as local density, temperature changes, and kinetic and temperature instabilities, are neither constant nor uniform. The time and energy variations for all occurrences in the various regions of food structure correspond to their conversion to flow properties like viscosity, surface tension, and diffusion of liquids through membranes and other barriers. In food products that are complex physiological systems containing various types of solutions, as well as fibrous, cellular, and crystalline components, the relationship shown in Figure 8.2 exists. It follows that the study of food texture involves several areas: • The structure, in terms of both micro- and macrostructure • The evaluation of the rheological properties considered as physical properties • The evaluation of rheological and textural properties by the human sense organs • The interrelationship of the physical and sensory measurements of food structure In this respect, the texture comprises all physical characteristics of foods related to the response to applied force and measured objectively in terms of force, distance, and time. Texture depends on the various constituents and structural elements of foods in which the microstructure components are formed and then clearly recognized in terms of flow and deformation during different processing treatments.

Rheological Properties of Food Systems

183

Molecular and chemical composition (energy of primary structure)

Primary structure geometry and resistance Energy applied

Food engineering operation levels (molecular ultrastructure, microstructure, and macrostructure)

Waste utilization processes

Food microstructure in and after exit from processing plant

Rheological properties of food structure

Final texture arrangements

Functional food factors

Nutritional Food related     value      law responsibilities

FIGURE 8.2 Evolution of food structure arrangements from raw materials and the processing method used to transform them into products.

Fluid flow may be steady or unsteady, uniform or nonuniform, and it can also be laminar or turbulent, as well as one-, two-, or three-dimensional, and rotational or irrotational. One-dimensional flow of incompressible fluid in food systems occurs when the direction and magnitude of the velocity at all points are identical. In this case, flow analysis is based on the single dimension taken along the central streamline of the flow, and velocities and accelerations normal to the streamline are negligible. In such cases, average values of velocity, pressure, and elevation are considered to represent the flow as a whole. Two-dimensional flow occurs when the fluid particles of food systems move in planes or parallel planes and the streamline patterns are identical in each plane. For an ideal fluid there is no shear stress and no torque; additionally, no rotational motion of fluid particles about their own mass centers exists. In general, food can be classified as Newtonian and non-Newtonian. Its viscosity depends strongly on the shear rate (Figure 8.3). Shear stress versus shear rate curves may have the shape represented by curves 1–7 (Figure 8.4). Some of the most difficult material properties of fluid and semisolid foods to determine experimentally are viscometric functions and steady shear rheological properties. The flow properties of a liquid and semisolid food system should be measured in the following instances:

184

Chemical and Functional Properties of Food Components

Non-Newtonian food systems

Viscoelastic

Rheostable

With flow limit

Nonrheostable

Antithixotropic flow

Without flow limit

Nonlinear viscoplastic

Bingham’s viscoplastic

Thixotropic flow

With flow limit

Without flow limit

Pseudoplastic flow with relaxation

Dilatant flow with condensation effects

FIGURE 8.3 Different types of non-Newtonian liquids and semisolid foods.

• When new food products have to be manufactured with clearly specified rheological characteristics • When rheological properties must be carried through various steps of engineering operations without any changes • When rheological properties indicate directly or indirectly the quality of the final product • When rheological properties chosen to describe the texture of the product appear to be the most successful on the market • When continuous process evaluation of the rheological properties plays an essential role in development of new products and designing better equipment There are three main rheological properties of materials: viscous flow, plastic flow, and elastic deformation. The stress deformation behavior of elastic materials is represented by a straight line through the origin. However, in this case, the

Rheological Properties of Food Systems

185

w

(1)

f lo

τ

st

ic

types of Bingham’s liquids

) ed liz

ea

ea

lin

(id

n-

flo

w

no pl

as

tic

(3)

w flo tic s a pl

Bi

ng

ha

m ’s

Shear stress

rp

la

(2)

-lin on

ear

n

ic

st opla

eld + yi

ss stre

d

pseu

low cf sti

(4) thixotropy liquids

(5)

pla

do

seu

p

flo

w

τ0

dilatation and rheopexy liquids flow

ni ew

to

(6)

N

Yield stress

an

liq

ui

d

*

(7)

Shear rate

D

FIGURE 8.4 Relationship between shear stress and shear rate for different foods’ flow characteristics.

deformation is reversible upon removal of the force. Many foods show time-dependent rheological behavior and a combination of these, such as viscoelasticity and viscoplasticity. To characterize Newtonian and non-Newtonian food properties, several approaches can be used, and the whole stress–strain curve can be obtained. One of the most important textural and rheological properties of foods is viscosity (or consistency). The evaluation of viscosity can be demonstrated by reference to the evaluation of creaminess, spreadability, and pourability characteristics. All of these depend largely on shear rate and are affected by viscosity and different flow conditions. If it is related to steady flow, then at any point the velocity of successive fluid particles is the same at successive periods of time for the whole food system. Thus, the velocity is constant with respect to time, but it may vary at different points with

186

Chemical and Functional Properties of Food Components

z

1 A

F

V

δz

δx θ

2

F A x interplates fluid

y

FIGURE 8.5 Sample shear flow: definition of shear stress, strain, and shear rate.

respect to distance. Flow is unsteady when conditions at any point in a fluid food system change with time. Most practical food engineering problems involve steady flow conditions and are based on the Newton suggestion. The thin layer of liquid between two small planes of area A (Figure 8.5) is considered to be part of a laminar flow. For a greater velocity, the middle layer pulls forward with an equal force F, while the layer below, which has lesser velocity, pulls the middle layer back with an equal force F. These two equal and opposite parallel forces form a shear couple and produce a shear stress of magnitude F/A. Newton suggested that the shear stress is directly proportional to the velocity gradient: F/A ~ dV/dz

(8.1)

∴ F/A = ηdV/dz (8.2) or τ=η⋅D

(8.3)

where η is the constant of proportionality and is called the dynamic viscosity and dV/dz = D is called the velocity gradient, or shear rate. The two planes are separated by a distance ∂z, and the shear strain ∂θ = ∂x/∂z. Because this has taken place in time ∂t, the rate of change of shear strain is ∂θ/∂t ≅ dV/dz = velocity gradient, where dV is the velocity of the upper layer relative to the lower. Newtonian liquids show a stress–strain relationship represented by a straight line (Figure 8.6a). In Figure 8.6b there are viscosities of two Newtonian fluids at different shear rates. These two materials, represented by 1 and 2, may have the same apparent viscosity when there is no direct proportionality between shear stress and the rate of shear. The flow behavior for non-Newtonian stress–strain relationship

Rheological Properties of Food Systems

τ

a)

187

η

b) 1 2

D

   D

FIGURE 8.6 a: Newtonian liquid. b: Viscosities of two Newtonian fluids at different shear rates.

is represented by different curves (Figure 8.7). The term non-Newtonian is applied to all materials that do not obey the direct proportionality between shear stress and rate of shear. For a non-Newtonian fluid, the viscosity has no meaning unless the shear rate is specified and the apparent viscosity is not constant. Apparent viscosity (ηapp) can be used for easy comparison between Newtonian and non-Newtonian fluids at particular shear rates. It is usually defined as the ratio of the shear stress over the rate of shear. During food engineering operations, many fluids deviate from laminar flow when subjected to high shear rates. The resulting turbulent flow gives rise to an apparent increase in viscosity as the shear rate increases in laminar flow, i.e., shear stress = viscosity × shear rate. In turbulent flow, it would appear that total shear stress = (laminar stress + turbulent stress) × shear rate. The most important part of turbulent stress is related to the eddies’ diffusivity of momentum. This can be recognized as the atomic-scale mechanism of energy conversion and its redistribution to the dynamics of mass transport processes, responsible for the spatial and temporal evolution of the food system. In general, there are three main types of non-Newtonian liquids and semisolids: • Time-independent, for which the rate of shear depends only on the shear stress • Time-dependent, for which the relationship between the rate of shear and shear stress depends on the time of shear • Viscoelastic, which has characteristics of both elastic solids and viscous liquids In time-independent liquid food products, the flow curve is linear but intersects the shear stress axis at a positive value of shear stress. This value is known as a yield stress. The significance of the yield stress is that it is the stress that must be exceeded before the material will flow. This type of flow can be characterized by the following rheological equation (for the Bingham–Schwedoff model):

188

Chemical and Functional Properties of Food Components

a)

τ

η

τ

D b)

τ

η

τ

D c)

τ

2 1

η

3

τ0

τ

D τ

d)

τ

e)

1 2 3 D

D

FIGURE 8.7 Non-Newtonian flow behavior. a: Structural viscosity (for high molecular solution). b: Dilatant flow (suspension with high concentration). c: Viscoplastic with flow limits: 1, ideal plastic; 2 or 3, nonlinear plastic flow. d: 1, thixotropy flow; 2, antithixotropy flow; 3, viscoelastic flow; e:rheopexy flow.

τ = ηpl ⋅ D + τ0

(8.4)

where τ0 is the yield stress and ηpl is the Bingham plastic viscosity. To the same family of curves belong pseudoplastic materials. These fluids show a decrease in apparent viscosity with an increase in the rate of shear and are typical of the majority of non-Newtonian liquid food products. The way most often used to describe the properties of these materials is an empirical Ostwald-de Waele power law equation: τ = k ⋅ Ds

(8.5)

Rheological Properties of Food Systems

189

where k is the consistency index and s is the flow behavior index, which for pseudoplastic materials is less than 1 and greater than zero (0 < s < 1). This equation can be used to describe the rheological properties of any timedependent fluid if applied over a limited range of shear rate. Many examples are known in most of the existing procedures for solving engineering problems in the food industry. They include the case study of processing concentrated fruit juices with suspended pulp particles, dairy cream, more-or-less-concentrated tomato puree, apple puree, butter, minced meat, and infant foods. Among the food products that exhibit pseudoplastic behavior are all that contain soluble high-molecularweight substances and insoluble matter. Products that contain crystals and other particles like fat globules dispersed in a liquid phase, e.g., molten chocolate and ice cream mix, have a yield stress. The apparent viscosity for a pseudoplastic material is ηapp = k ⋅ Ds – 1. There are many pseudoplastic food products that display more complex rheological behavior and with a yield stress that can be characterized in two ways, either by an extension of the power law rheological equation of Herschel–Bulkley: τ = k ⋅ Ds + τ0

(8.6)

or by an equation developed by Casson: τ1/2 = k0 + ki ⋅ D1/2

(8.7)

where k0 is the Casson yield stress and ki is the Casson plastic viscosity. Among this type of non-Newtonian materials are dilatant fluids. They show an increase in apparent viscosity with an increase in rate of shear and are not commonly found among liquid food products. They can be represented by power law Equation 8.5, but in this case the flow behavior index, s, would be greater than 1 and less than infinity (1 < s < ∞). Such “shear thickening” is observed in materials with suspensions of solids at a high solid content, when approaching the point of tightest packing. For example, corn-flour pastes can be dilatant. There are other foods that possess the shear rate. Those food systems, when placed under steady flow at a constant rate, show a changing shear stress over time until an equilibrium value is achieved. Time-dependent behavior can be interpreted from viscoelasticity, thixotropy, or a combination of the two, and the power law equation is not adequate for proper evaluation of such a system (Shoemaker and Figoni, 1984). Time-dependent materials can be subdivided into two classes: thixotropic and rheopectic. Time-dependent liquid foods for which the apparent viscosity decreases with time of shearing are known as thixotropic materials, whereas rheopectic fluids are those for which the apparent viscosity increases with time of shearing. In a thixotropic flow, the response to shear is instantaneous, and the time-dependent behavior can be observed as the shearing process continually alters the structure of the system. These structural changes include disentanglement of polymer molecules in solution and deflocculation of globules in emulsion. The rate of structure breakdown during shearing at a given rate depends on the number of linkages available for breaking and therefore decreases with time. In the case with rheopectic fluids, the structure builds up in shearing; this phenomenon can be regarded as the reverse

190

Chemical and Functional Properties of Food Components

shear

recovery

Shear stress

Time

FIGURE 8.8 Flow behavior of a symmetrically thixotropic system. (Adapted from Harris, J., Rheology and Non-Newtonian Flow, Longman Group, Ltd., London, 1977.)

of thixotropy. In fact, rheopectic behavior is often referred to as antithixotropy. Thixotropy is generally defined as the continuous decrease of apparent viscosity with time under shear and subsequent recovery of viscosity when the flow is discontinued. The simplest example of such a system undergoing structural changes, known as symmetrically thixotropic fluid, is shown in Figure 8.8. Once shearing is stopped (the external force is no longer acting), the rate of the system structural recovery is the same as the rate of structural breakdown under steady shear. In foods, the time needed for recovery may vary significantly from one thixotropic product to another. The time dependency can be observed in food systems such as concentrated emulsions, sols, and gels. Semisolid foods belong, in general, to a group than can be characterized by viscoelastic parameters. Viscoelasticity is due to the delayed motion and retarded response of a system to a shear resulting from a joint viscous and elastic nature. Jellies and deserts fall into this category. Jams are also included; however, some additional measure of elasticity of the product is required. Measurements of stress or viscosity decay at a constant or steady shear rate have also been used to characterize structural breakdown. The classical approach to characterizing structural breakdown is the measurement of the hysteresis loop (Figure 8.7d and e). The area enclosed by the loop is the first indication of the degree of structural breakdown and depends on the previous shear history and both the rate of change in shear and the maximum value of the shear rate. The relationship between rheological properties and the food hysteresis loop area is very complicated and has a complex shear history. Many food systems show viscoelastic behavior with timedependent flow properties similar to that shown in Figure 8.9. Among others, viscoelastic rheological behavior of such a food system can be characterized by a creep compliance test, where a constant stress is applied and the strain is followed as a function of time (t). Creep compliance is generally expressed in terms of a ratio: strain (τ) over stress. In this case, stress relaxation is also normally expressed in terms of a ratio: stress (τ) over strain. For an ideal elastic solid, the stress or strain

Rheological Properties of Food Systems

steady shear Shear stress (strain or compliance)

191

relaxation

elastic solid B viscoelastic liquid viscoelastic solid

C

D

A Time

FIGURE 8.9 Flow behavior of a viscoelastic system. Regions AB and CD represent viscoelastic behavior; region BC represents structural breakdown during steady shear.

will be independent of time, and the stress divided by the strain will be the elastic modulus of the material. In real food polymers, a distinction can be made between a viscoelastic solid, which contains some cross-links that are permanent, and a viscoelastic liquid, where, under the influence of stress, the relative movement of whole molecules will be observed. As shown in Figure 8.9, in the case of a viscoelastic solid, after application of the stress, the strain will eventually reach a constant value, and upon removal of the stress, the strain will finally return to the remaining value of food primary energy, which was not entirely dissipated. For a viscoelastic liquid, a permanent deformation will remain after removal of the stress. In the stress relaxation area, the deformation value will decay to zero for a viscoelastic liquid, whereas for a solid, it will reach a constant, nonzero value. It can also be seen as either a decreased value to the zero or a constant, nonzero value, as pointed out by the dashed line. Both values characterize the rheology parameters of foods under certain conditions. One of the reasons for this is that the factors of time-dependent foods are not necessarily related to their elastic modulus. This can be explained by the series of small deformations without rupture, which are dependent in different ways and are based on the primary molecular microstructure of foods. The time required for the stress to relax to a definite fraction of its initial value is the relaxation time.

8.3 EFFECT OF COMPOSITION AND PROCESSING PARAMETERS ON THE RHEOLOGICAL BEHAVIOR OF FOOD SYSTEMS 8.3.1 ENERGY, STRESS,

AND

DEFORMATION

Stress and strain or deformation can be useful in microscopic or molecular descriptions of how the observed phenomena come about. They have directional properties that distinguish an elongation from a shear, for example. When the stress and strain may depend on time, it can be either the unchanging equilibrium state or a steady

192

Chemical and Functional Properties of Food Components

flow in which strain increases at a constant rate. The magnitude is also important; i.e., if doubling the strain leads to a doubling of the stress, then the behavior — because of the geometry and time patterns being identical — is called linear. In food industrial practice, nonlinear phenomena are mostly the rule, and the way rheological behavior actually appears depends on the time scale of the process in which it is observed. The ratio of a material’s relaxation time to the time over which behavior is observed is called the Deborah number. As the Deborah number becomes smaller, the behavior changes from a solid to a fluid. In case of suspensions and dispersions of solid particles in a fluid, the effects of concentration, size, shape, and arrangement of the dispersed particles must also be considered. In general, for the effect of composition and processing parameters of the food system, the external mechanical work needed to make a material deform or generate a flow pattern is used in three ways: • It is stored reversibly so that the material can give back the energy as mechanical work. • It is transformed to chemical energy in bonds or weak links between particles. • It is dissipated into heat and lost. Among all the deformations and flow patterns investigated in food science, one in is of particular importance: steady flow. In this case, the geometry is shearing, the dependence on time is a steady increase in the shear, and the magnitude is arbitrary. The most common behavior in the food system is shear thinning or the pseudoplasticity curve, also known as a viscoelastic characteristic of materials such as polymers. In these, elasticity arises from the tendency of the polymer segments to take on random equilibrium arrangements, due to their thermal motion. A viscous contribution results from friction as one segment slides past another. The same friction also tends to drag the molecule out of its equilibrium shape. However, at low shear rates, the viscous stress is too small to do this, so the shape of the molecule and also the food system’s viscosity do not change. At larger shear rates, the viscous stress can deform the molecule into a shape in which the flow pattern occurs with more lowering of the viscosity. At a higher shear rate, the molecules cannot be deformed anymore. The shear rate can then be increased indefinitely without a further drop in viscosity. The equilibrium, considered as a configuration of the molecule, is restored when shearing stops, so that the deformation is a means of storing mechanical work in a recoverable manner. Energy can also be stored in other ways on a microscopic scale, e.g., by electrical charges being forced near each other in colloidal systems and by emulsion drops being distorted from the spherical shape. In this case, the surface tension gives them stabilizing surfactant layers on dispersed particles being pressed into each other. The mechanical work put into a food system with respect to the chemical transformation is typically associated with changes in the bonding between food components. In accordance with such changes, energy can be used to break links initially holding particles in chains or aggregates, leading eventually to all the

Rheological Properties of Food Systems

193

particles being unbounded. Because the aggregation of particles causes a greater disturbance to the flow, such a system would be shear thinning. Due to the passage of time, it would also be thixotropic when steady flow was started. In other foods, the effect of composition and processing parameters can be achieved by different ways of storing work, e.g., shear thickening. In this case, the particles stick together when they collide, and the link formation promoted by shearing is less likely. It would lead to rheopexy when an increase in velocity takes place, with time at the onset of flow. These phenomena occur only in highly concentrated dispersions of particles; i.e., randomly arranged particles interface with each other greatly in flow conditions. If the interaction between particles allows layering within a certain time needed to accomplish this process, rearrangement of the food dispersed system will be more perfect in slower flows at low shear rates. The viscosity should then increase with shear rate. This final effect of composition and rheological behavior of such a food system is strongly related to the size of particles. If the particles are unequal in size, very small ones can fit into gaps between larger ones, allowing flow at a higher concentration than that for equal-size particles. At the same concentration, the dispersion with a wide range of particle sizes has a lower viscosity than one with uniform particles. In some cases, the effect of food system composition regarding process parameters can be interpreted by catastrophic changes in component organization, i.e., antithixotropy, hysteresis, and relaxation period of time. Such an abrupt change can be observed, for instance, in shear thickening when a critical shear rate has been exceeded. In general, the rheological properties of the food system have to be described in terms of particle sizes, shapes, surfaces, volumes, lengths, and their frequencies. Such structural characteristics of food systems are in reality the visual representations of highly ordered biological molecules. By combining such structural and functional data in equations that can then be integrated into mathematical and rheological models, opportunities are being created for analyzing complex food system responses and dissecting them into data of processing parameters and simpler, more interpretable food texture, quality, and functionality.

8.3.2 STRUCTURE DEVELOPMENT A specific food product can be made by using a variety of recipes and processes that differ in their demand on the functional ingredients. A detailed understanding of any effect of food system composition involves the following issues: • Thermodynamic consideration: is the reaction feasible to be carried out in the practice of food engineering? Is a particular process likely to take place, and can it be ascertained by theoretical consideration of energy associated with the reaction? To what extent can it be calculated because of the enthalpy change, free energy, and entropy change, and can the equilibrium be kept constant? • Food system reaction kinetics: it is important to know, because of the final effect of food system composition, how fast the reaction is. It may be perfectly feasible from a thermodynamics point of view, yet of no practical value because it takes place far too slowly.

194

Chemical and Functional Properties of Food Components

• Reaction mechanisms: it is necessary to be familiar with what actually happens in all changes during a food engineering operation and to keep it under control because of the rheological parameters and their influence on food system composition. The fullest understanding of a reaction involves a study of the possible mechanisms by which one set of bonds is broken, while another one is formed during the same process conditions. • Separation of the product: a reaction mechanism intended to make one particular product will be useful only if it is relatively easy to separate that product from the mixture remaining at the end of the reaction. There are several possible results of physical separation: interruption of liquid bridging, lubrication, competition for absorbed water, cancellation of electrostatic charges and molecular forces, and modification of crystalline lattice. All these results can influence flowability and reaction mechanisms in different food systems. They can also be used for the evaluation of flowability by the following methods: direct flow rate, angle of repose, shear and tensile strength, unconfined yield stress, angle of internal friction, and cohesion measurements, as well as plots of the whole flow function. All of them are worthy in order to gain knowledge relevant to the processing parameters of non-Newtonian liquid and semisolid food systems, particularly in the following areas: • Methodology adequate for characterization of non-Newtonian materials with regard to changes taking place during shearing and heating • Relationships between the flow properties and residual time in continuous processes • Better use of flow characteristics for the design of process equipment • The effect of residual time for food quality with regard to microbiology, nutrition, and sensory and functional properties Understanding the thermodynamics, reaction kinetics and mechanisms, and separation process requires accurate analysis of confirmation and physical interaction in the absence of water or in the low-mixture environments. There are some processes, e.g., grinding, where the primary cell structure is changed significantly and can liberate the internal cell components. These liberated components can be purified, and their functional properties can be exploited to create foods whose textures are completely different from those of original raw materials, e.g., bread, biscuits, or sausages. Furthermore, by following this method, it is possible to use the natural texturizing properties of certain components. Such agents as emulsifiers, hydrocolloids, and proteins have opened up — through emulsifying, whipping, softening, preventing of crystallization, thickening, gelling, and stabilizing facilities — new development possibilities in a wide range of food products: namely, beverages, cream soup, sauce, salad dressing, bread, biscuits, pastry, sausage and meat spreads, jam, gel, cream and whipped desserts, ice cream, and confectionery. These new agents, combined with improved processing parameters and preservation

Rheological Properties of Food Systems

195

technologies, have led to the development of new foods with varied textures, such as those of liquids, semisolids, solids, pastes, gels, and foams. Either single or several texturizing agents can often lead to the desired effect for food preparation; the proper ingredients must be correctly selected and dosed, as well as incorporated at a precise processing stage in various processing systems.

8.3.3 GLASS TRANSITION

AND

STATE DIAGRAMS

A complete textural evaluation with respect to the processing parameters and rheological behavior of the food system may be logistically impossible. More importantly, not all these data may be required, because some factors influencing the structural composition effect are probably multicorrelated parameters and more or less sensitive than others. The complex force deformation and property frequency change–response profiles of a variety of food materials are particularly amenable to fractal (Peleg, 1997 and Peleg and Hollenback, 1984) and to the glass phase transition. Food system composition effects can be characterized in terms of their fractal or noninteger dimension, as well as through the weight fraction of solids, when they are transformed into the viscous liquid state. The application of fractals in image analysis (Kalab et al., 1995) and glass transition processes related to rheological changes in food systems with various aspects of food science, including texture evaluation, has only recently been addressed (Roos, 1995; Kokini et al., 1995). The common view of glass transition structure is that both the short-range and longrange orders are absent, and the structure formation process is best described as a continuous random. It has been reported (Roos, 1995) that glass transition is a second-order phase transition. In some cases, the local ordering in food system composition prevails over an intermediate range of several atomic or molecular units. In the phase transition process, for gas-to-particle conversion, the following are included: homogenous, heteromolecular nucleation (formation of a new, stable liquid or solid ultrafine particle involving one gaseous species only); homogeneous, heteromolecular nucleation (formation of a new particle involving two or more gaseous species, typically one of these being water); and heterogeneous, heteromolecular condensation (growth of preexisting particles due to deposition of molecules from the gas phase). Glass phase transition processes result in exciting changes in free volume, molecular mobility, and physical properties of amorphous materials and can be detected from changes in mechanical, thermal, and dielectric properties of a food system. Knowledge of the relationships between glass transition temperature Tg and physiochemical changes is very important in predicting the effects of composition on food rheological behavior in various processes, including, among others, agglomeration, baking, extrusion, dehydration, freezing, and storage conditions. Tg of food system components can influence food properties, cause deteriorative changes, and be useful for visualizing processing parameters through the use of state diagrams. These drawings can also be used to show the relationships among components of a food system, temperature, and stability of food materials, as well as to predict changes under various process conditions (Figures 8.10 and 8.11). The case of cereal proteins in the prediction of material process phases is shown in Figure 8.12.

196

Chemical and Functional Properties of Food Components

Temperature

extrusion

water and solids

dehydration - drying - evaporation

freezing

solids and water Tm curve

T’m

ice, solids, and water

T’g Tg curve

-1350C 0

Weight fraction of solids

C’g

1.0

FIGURE 8.10 State diagram of water-plasticizable materials. Food solids can be transformed into the glassy state in processes that remove water, e.g., extrusion, dehydration, and freezing. The glass transition temperature Tg decreases with increasing water content. Maximally freeze-concentrated solids have a glass transition at T'g, and the corresponding concentration of solids in the maximally freeze-concentrated phase C'g. Equilibrium melting of ice occurs at T'm. (From Roos, Y.H., Food Technol., 49, 97, 1995.)

8.3.4 DYNAMICS MAP

OF THE

FOOD SYSTEM

The glass transition processes in foods may result from a rapid removal of water from solids. Based on that, e.g., the Tg values of anhydrous polysaccharides are high, and the food materials may decompose at temperatures below Tg (Kokini et al., 1994; Roos and Karel, 1991b). The glass temperature transition affects viscosity, stickiness, crispness, collapse, crystallization, and ice formation, and can strongly influence deteriorative reaction rates. This provides a new theoretical and experimental framework for the study of food systems: to unify structural and functional aspects of foods, described in terms of water dynamics and glass dynamics. The term water dynamics indicates the mobility of the plasticizing diluent and a theoretical approach to understanding how to control the water movement in glassforming food systems. The term glass dynamics deals with the time and temperature dependence of relationships among composition, structure, and thermomechanical properties, as well as the functional behavior of food systems. The functional aspects, in terms of water dynamics and glass dynamics, and the appropriate kinetic description of the nonequilibrium thermomechanical behavior of food systems have been illustrated as a dynamics map, shown in Figure 8.13.

Rheological Properties of Food Systems

197

solution

rubber

Temperature

solubility

crystallization collapse stickiness

eutectic point Tm 108[Pa s] equilibrium ice formation and melting ice and rubber

T’m glass maximum ice formation T’g ice and glass

106 [Pa s]

nonequilibrium ice formation 1011[Pa s] delayed ice formation glass

Concentration

C’g

FIGURE 8.11 State diagram for food materials, showing the Tg curve and isoviscous states above Tg. Maximally freeze-concentrated solids with a solute concentration of C'g have Tg at T'g. Ice melting within maximally freeze-concentrated materials occurs at T'm. The equilibrium melting curve shows the equilibrium melting point Tm as a function of concentration. (From Roos, Y.H. and Karel, M., Food Technol., 45, 66, 1991b.)

The dynamics map represents both the equilibrium and nonequilibrium aspects. The equilibrium regions are described through two dimensions of temperature and composition. The major area of the dynamics map, shown in Figure 8.13, represents a nonequilibrium region of the most far-reaching technological consequences to aqueous food systems. The nonequilibrium regions require for their description the third dimension of time, expressed as t/τ, where τ is a relaxation time. Nonequilibrium physical states determine the time-dependent thermomechanical, rheological, and textural properties of food systems. Based on the Williams–Landel–Ferry (WLF) mechanism, the glass transition, as in the food’s reference state, can be concluded and identified from the dynamics map. The dynamics map can be used to estimate the mobility transformation in water-compatible food polymer systems in terms of the critical variables of time, temperature, moisture content, and pressure (Peleg, 1993). The glass transition as a reference state can be used to explain all transformation in time, temperature, and structure composition effects between different relaxation states for technologically practical food systems in their nonequilibrium nature. Among others, specific examples include reduced activity and shelf stability of freeze-dried

198

Chemical and Functional Properties of Food Components

free-flow region loosely held network

Temperature

flashing-off moisture heating

expansion

Tg + 1000C wetting and mixing

cooling

rubber

glass dry material Moisture [%]

FIGURE 8.12 Transformations in cereal proteins during the wetting, heating, and cooling or drying stages of extrusion cooking, as seen on a hypothetical phase diagram. (From Kokini, J.L. et al., Trends Food Sci. Technol., 5, 281, 1994.)       mobility transformation map      reactive

equilibrium vapour phase crystalline solid

aw

biological steady state   1

defined here only

     equilibrium      dilute solution      room temperature nonequilibrium

RVP       nonequilibrium

       0

     reference state nonequilibrium

e su r

concentration

pr

es

tim

e

stable

FIGURE 8.13 A four-dimensional dynamics map with axes of temperature, concentration, time, and pressure, which can be used to describe mobility transformation in nonequilibrium glassy and rubbery systems. AW, water activity; RVP, relative vapour pressure. (From Slade, L. and Levin, H., Crit. Rev. Food Sci. Nutr., 30, 115, 1991.)

Rheological Properties of Food Systems

199

proteins and living cells, graininess and iciness of ice cream, lumping of dry powder, and the bloom on chocolate, as well as recipe requirements for gelatin desserts, cooking of cereals and grains, expansion of bread during baking, collapse of cake during baking, cookie baking effects of flour and sugar, and staling of baked products. Glass dynamics has proven to be a very useful concept for elucidating the physiochemical mechanisms of structural/mechanical changes in various melting and (re)crystallization processes, including the gelatinization and retrogradation of starches. Glass dynamics can also be used to describe the viscoelastic behavior of amorphous polymeric network-forming proteins such as gluten and elastin (Slade and Levin, 1991). These unified concepts, based on water dynamics and glass dynamics, have been used to explain and predict the functional and rheological properties of food systems during processing and their effects on time-dependent structural and mechanical factors related to quality and storage stability of food microstructures.

8.4 IMPORTANCE OF THE RHEOLOGICAL PROPERTIES OF FOODS FOR PROCESS DESIGN AND CONTROL 8.4.1 SIMPLIFIED RHEOLOGICAL PRINCIPLES The rheology of food systems is important in many food applications. Rheology as the science concerned with the deformation and flow of matter involves, in most rheological tests, a force to a material measuring its flow or change in shape. Most of the textural properties that can be recognized when people consume foods are largely rheological in nature, e.g., smoothness, hardness, tenderness, creaminess, brittleness. The stability and appearance of foods often depend on the rheological characteristics of their components. Rheological properties of the food system materials can be divided into those that deform and those that flow. They can be further subdivided into ideal (strain rate independent) and nonideal (strain rate dependent) material. Ideal solid food materials deform in elastic; its properties are described by Hookean manner. Ideal liquid flows viscously; its properties are described by Newtonian manner. In both cases the behaviors are independent of the strain rate. Most food systems are nonideal (strain dependent), and their rheological properties are complicated and vary with the direction of stress application. There are three commonly applied types of stress: compressive, directed toward the material; tensile, directed away from the material; and shearing, directed tangentially to the material (Figure 8.14). Strain is the response of a material to stress. Therefore, there are three types of strain: compressive, tensile, and shear. The ratio of stress to strain is called the modulus (E). It can be compression, tensile, or shear modulus. When an elastic material is compressed, the stress–strain relationship is a straight line at the origin, and the slope is given by the tangent of angle β, called Young’s modulus of elasticity. Rheologically, food system materials may deform in three ways: elastic, plastic, or viscous. Deformation or strain in an ideal elastic body occurs instantly at the moment stress is applied and is directly proportional to stress; it disappears instantly and completely when stress is removed (point P depicted in Figure 8.14, limit of the stress proportionality).

200

Chemical and Functional Properties of Food Components

   Q

σt

  R Z

S    

Tensile    P Fo tgβ=E

-ε

ε

   E

    Compression Fo

        S

P         

Shear

       Z     Q              σc FIGURE 8.14 Fundamental types of stress (σt-tensile or σc-compression) acting on the body.

Deformation in an ideal plastic material does not begin until a certain value of stress upper yield point is reached (strain from point S to point Q). Deformation is permanent, and no recovery occurs when the stress is removed. The strain at point S is still elastic, but without proportionality between stress and deformation. Point R in the tensile test represents the maximum or ultimate stress of the material, and point Z represents the stress and deformation at rupture of the food system materials. In an ideal viscous body, deformation occurs instantly at the moment when stress is applied. In comparison with an elastic body, the strain is proportional to the rate of strain and is not recovered when stress is removed. The stress σt (tensile test) or σc (compression test) is usually referred to the original cross-sectional area (Fo). The test pieces are subjected to a gradually increasing tensile or compression load in testing equipment such as an Instron model. During this increasing load, the corresponding elongation ∆L (or shortening) over the gauge length Lo is continuously measured. The elongation ∆L (or shortening) consists of an “elastic” and a “permanent” part of deformation. The latter can be measured by removing the stress. Using the principles of strength of materials, the strain is ε = ∆L/Lo. In the rheological structure of most food systems there is a viscous element present, and the deformation curves are often highly influenced by the rate of the imposed strain. This is due to the fact that the material relaxes (or flows) while tested under compression and the resultant deformation of this flow is dependent on the nature of the viscous element (Szczesniak, 1963; Peleg and Bagley, 1983). In the viscoelastic food systems, where during processing it is caused to oscillate sinusoidally, the strain curve may or may not be a sine wave. In cases when a periodic oscillatory strain is applied on a food system like fluid material, oscillating stress can be observed. The ideal elastic solid produces a shear stress wave in phase with

Rheological Properties of Food Systems

201

the strain wave. In the perfect viscous liquid, the stress is 90° out of phase with the applied strain. For viscoelastic materials there are both viscous and elastic properties, described by complex modulus G, known as the transversal or compression modulus. It consists of two parts that describe two viscoelastic properties of food system materials. The first part is called the storage or rigidity modulus, G' = τo cosϕ/γo, and represents the elastic character of the material. The second part is called the loss modulus G′′ = τo sinϕ/γo, and represents the viscous character of the material. The angle ϕ is an intermediate phase angle with a value between 0 and 90°, and τo and γo are the amplitudes of the stress and strain waves, respectively. In addition, the effect of time and temperature on the behavior of the materials manifests a great influence on the rheological properties of the food systems.

8.4.2 CASE BEHAVIOR

OF

FLUID FOOD SYSTEM

Accurate and reliable rheological data are necessary for the design and control of fluidmoving machines, the sizing of pumps and other transport processes, the estimation of velocity, the shear and residence time distribution in continuous mixing, and the evaluation of heating rates. Temperature differences occur in heat processing of foods. The nonuniform distribution of heat is due to the fact that the heat field intensity is not homogenous over the entire object of application. It depends on the coefficient of retention, heat absorption, and the heat resistance at the walls of the equipment. For many foods, the temperature effects are related to the changes in apparent viscosity: ln ηappa = a + b/T

(8.8)

where ηapp is the apparent viscosity, T is the temperature in Kelvin degrees, and a and b are constants. The complex nature of rheological behavior in molten chocolate is demonstrated below. Chocolate is a suspension of solid particles in a fluid medium. The main solid particles in chocolate are cocoa and sugar, and the fluid is cocoa butter. There are other minor ingredients such as the surface active agents, water, milk solids, and butter fat. Cocoa butter is Newtonian and time dependent. Large quantities of solid particles, as well as surface and moisture active agents, can change the flow behavior pattern of molten chocolate to a non-Newtonian flow. A typical flow curve for molten chocolate has a yield stress, and the apparent viscosity falls rapidly with an increasing rate of shear (Figure 8.15). Many factors influence the flow behavior of chocolate. The most important ones are fat content, type and quantity of surface active agent, moisture content, temperature, degree of shearing, and particle size and distribution. The latter, in accordance with quality parameters and consumer acceptance, should not contain cocoa particles larger than 15 µm in diameter. Molten chocolate is, in many cases, time dependent, which can be expressed by: τ = k ⋅ t–m

(8.9)

where τ is the shear stress, t the time, k the constant, and m the index of time dependency.

202

Chemical and Functional Properties of Food Components

τ η

τ = f (D)

(1)

τ = f (D) (2)

η = f (D) (3) D

FIGURE 8.15 Relationship among shear stress, viscosity, and shear rate as flow behavior of molten chocolate; for 1 the temperature is 35°C, and for 2 it is 45°C (arbitrary scale).

Chocolate can be characterized by a yield stress and plastic viscosity, i.e., as the Bingham plot. Another curve was established by Casson and reported by Holdsworth (1971) in which chocolate is characterized by the yield value and plastic viscosity. The Bingham plot is mainly used for process design and its control in the production of plain chocolate. In the case of Casson plots, some molten chocolates, particularly those containing active surface agents, did not give straight-line relationships. To overcome this difficulty, another expression was developed (Elson, 1977): τ = ηp ⋅ D + B ⋅ sinh–1 D + τ0

(8.10)

where τ is the shear stress, D is the rate of shear, ηp is the plastic viscosity, τ0 is the yield stress, and B is the interaction effect. The flow behavior of molten chocolate can also be affected by changes in processing conditions. These may lead to different values, because of the effect of non-Newtonian flow at the walls of the processing equipment. The wall shear rate is often characterized by the Nusselt number equation, which contains the so-called δ factor. The δ factor is the ratio of the wall shear rate for a non-Newtonian fluid to that of a Newtonian fluid at the same flow rate. For power law fluids, this factor can be calculated: δ = (3n + 1)/4n

(8.11)

where n is the flow behavior index. The temperature-dependent properties of molten chocolate would have a major effect on heat transfer. Some assumptions are made that during many heating operations the temperature-dependent effects are more relevant than the degree of pseudoplasticity of the fluid. Solutions are often obtained

Rheological Properties of Food Systems

203

in cases where heat is generated due to viscous dissipation of energy and by phase transition changes. The prediction of temperature and velocity profiles are also very important in a wide range of different heat transfer situations. Attempts to calculate and predict the heat transfer rates in processing design, e.g., in agitated vessels, are complicated by difficulties in accounting for the geometry of the system and by the complex rheological behavior of most liquids and semisolid foods. Heat transfer to both Newtonian and non-Newtonian food systems and the prediction of the rate of heat transfer in both jacketed vessels and vessels containing heating coils, for agitation produced by paddles, turbines, propellers, and anchors, can be considered by using general types of correlation: Nu = f (Re, Pr, Vi, dimensionless geometrical factor)

(8.12)

where Nu is the Nusselt number, Re is the Reynolds number, Pr is the Prandtl number, Vi is η/ηw (the viscosity ratio), and ηw is the viscosity at the wall of equipment. For most non-Newtonian food systems, it is obvious that because the shear rate throughout the material in the vessel varies, so does the apparent viscosity. This leads to a problem in specifying the viscosity, which is to be used in the Re, Pr, and Vi numbers, when this type of equation (8.12) is applied in process design and control. The prediction of heat transfer coefficients in the equipment handling nonNewtonian food products, based on knowledge of the flow curve and its dependency, changes for which it will be encountered, is a prerequisite to any process design and control consideration.

REFERENCES Elson, C.R., Increased Design of Efficiency through Improved Product Characterisation, paper presented at Symposium of Chemical Engineering, West South Branch, U.K., 1977, p. 96. Gorris, L.M., Food Preservation by Combined Processes, paper presented at 1st Main Meeting “Copernicus Programme,” Porto, Portugal, 1995, p. 10. Harris, J., Rheology and Non-Newtonian Flow, Longman Group, Ltd., London, 1977. Holdsworth, S.D., Applicability of rheological models to the interpretation of flow and processing behaviour of fluid food products, J. Texture Stud., 2, 393, 1971. Kalab, M., Alan-Wojtas, P., and Miller, S.S., Microscopy and other imaging techniques in food structure analysis, Trends Food Sci. Technol., 6, 177, 1995. Kokini, J.L. et al., The development of state diagrams for cereal proteins, Trends Food Sci. Technol., 5, 281, 1994. Kokini, J.L., Cocero, A.M., and Madeka, M., State diagrams help predict rheology of cereal proteins, Food Technol., 49, 74, 1995. Kokini, J.L., Eads, T., and Ludescher, R.D., Research needs on the molecular basis for food functionality, Food Technol., 47, 36S, 1993. Matuszek, T.S., Raw Materials and Food Processing with Regard to the Predictive Microstructure, paper presented at 9th World Congress of Food Science and Technology, Budapest, 1995, p. 136. Peleg, M., On the use of the WLF model in polymers and foods, Crit. Rev. Food Sci. Nutr., 32, 59, 1993.

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Chemical and Functional Properties of Food Components

Peleg, M., Contact and fractures as components of the rheological memory of solid foods, J. Texture Stud., 3, 194, 1997. Peleg, M. and Bagley, E.B., Physical Properties of Foods, AVI Publishing Co., Westport, CT, 1993. Peleg, M. and Hollenbach, A.M., Flow conditioners and anti-caking agents, Food Technol., 38, 93, 1984. Roos, Y.H., Glass transition-related physiochemical changes in foods, Food Technol., 49, 97, 1995. Roos, Y.H. and Karel, M., Plasticizing effect of water on thermal behaviour and crystallisation of amorphous food models, J. Food Sci., 56, 38, 1991a. Roos, Y.H. and Karel, M., Applying the state diagrams in food processing and product development, Food Technol., 45, 66, 1991b. Shoemaker, C.F. and Figoni, P.I., Time-dependent rheological behaviour of foods, Food Technol., 38, 112, 1984. Slade, L. and Levin, H., Beyond water activity: recent advances based on an alternative approach to the assessment of food quality and safety, Crit. Rev. Food Sci. Nutr., 30, 115, 1991. Szczesniak, A.S., Objective measurement of food texture, J. Food Sci., 28, 410, 1963.

9

Food Colorants Jadwiga Wilska-Jeszka

CONTENTS 9.1 9.2

Introduction ..................................................................................................205 Carotenoids...................................................................................................206 9.2.1 Structure ...........................................................................................206 9.2.2 Occurrence .......................................................................................209 9.2.3 Carotenoids Used as Food Colorants ..............................................210 9.2.4 Physical and Chemical Properties ...................................................212 9.2.5 Biological Activity ...........................................................................213 9.3 Chlorophyll...................................................................................................215 9.4 Heme Pigments ............................................................................................217 9.5 Anthocyanins................................................................................................219 9.5.1 Occurrence and Structure.................................................................219 9.5.2 Chemical Properties .........................................................................220 9.5.3 Biological Activity ...........................................................................222 9.5.4 Stability of Anthocyanins’ Color in Food .......................................223 9.6 Betalains .......................................................................................................224 9.6.1 Occurrence and Structure.................................................................224 9.6.2 Chemical Properties .........................................................................225 9.7 Quininoid Pigments......................................................................................226 9.8 Some Other Natural Pigments .....................................................................226 9.8.1 Riboflavin and Riboflavin 5′phosphate............................................226 9.8.2 Turmeric, Curcumin .........................................................................227 9.8.3 Caramel ............................................................................................227 9.9 Synthetic Organic Colors.............................................................................228 References..............................................................................................................228

9.1 INTRODUCTION Color is an important quality aspect of both unprocessed and manufactured foods. Natural colorants are unstable; thus the color of food products may provide an indication of biochemical and chemical changes during processing and storage. However, color cannot be studied without considering the human sensory system. Perception of color is related to three factors: spectral composition of light source, physical object characteristics, and eye sensitivity. Fortunately the characteristic of

1-5871-6149-4/02/$0.00+$1.50 © 2002 by CRC Press LLC

205

206

Chemical and Functional Properties of Food Components

the human eye for viewing color is fairly uniform, and it is not difficult to replace the eye by some instrumental sensor or photocell. The color of food is the result of the presence of natural pigments or added dyes. Natural pigments are generally considered the pigments occurring in unprocessed food, as well as those that can be formed upon heating, processing, or storage. These pigments can be divided into five groups: • • • •

Carotenoids: isoprenoid derivatives Chlorophylls and hemes: porphyrin pigments Anthocyanins: 2-phenylbenzopyrylium derivatives Miscellaneous, naturally occurring colorants such as betalains, cochineal, riboflavin, and curcumin • Melanoidins and caramels: formed during food heating and storage All these natural pigments are unstable and participate in different reactions, so the food color is strongly dependent on conditions. The use of synthetic organic colors has been recognized for many years as the most reliable and economical method of restoring some of the food’s original shade to the processed product. An even more important application of synthetic dyes is using them to improve and standardize the appearance of those products that have little or no natural color present, such as dessert powders, table jellies, ice, and sugar confectioneries. The synthetic organic colors are superior to the natural pigments in tinctorial power, range and brilliance of shade, stability, ease of application, and cost-effectiveness. However, from a health safety viewpoint, they are not accepted by the consumers, so over the past years increasing interest in natural food colorants has been observed.

9.2 CAROTENOIDS 9.2.1 STRUCTURE Carotenoids are the naturally occurring tetraterpene pigments widely distributed throughout the living world. The name carotenoids has been derived from the major pigment of the carrot (Daucus carote L). β-carotene, a symmetrical molecule of 40 carbon atoms, consists of 8 isoprene units having 11 conjugated double bonds and 2 β-ionone rings (Formula 9.1). The term carotenoids designates a group of structurally related colorants that are mainly found in plants. At present, more than 600 carotenoids have been identified. Their basic structure is a symmetrical tetraterpene skeleton, formed by headto-tail condensation of two 20-carbon units. (Formula 9.1). Based on their composition, carotenoids are subdivided into two groups: carotenes, which contain only carbon and hydrogen atoms, e.g., α-, β-, and γ-carotenes and lycopene (Formulae 9.2–9.4); and xanthophylls — oxocarotenoids — which contain at least one oxygen function, such as hydroxy, keto, or epoxy groups (Formulae 9.5–9.9). Carotenoids can also contain additional isoprene chains, homocarotenoids, or if less than 40 carbon atoms, apocarotenoids (Formulae 9.10 and 9.11). In some carotenoids allenic or acetylenic groups are found.

Food Colorants

207

β β

β - Carotene (1) ε β α - Carotene (2) Ψ β γ - Carotene (3) 7

14'

15

12'

10'

8'

6'

1 3 Ψ 5

8

10

12

14

15'

4' Ψ 2'

7'

Lyckopene (4) Formulae 9.1–9.4 Carotenes

The color of carotenoid pigments is the result of the presence of a system of conjugated double bonds. A minimum of seven conjugated double bonds is required for the yellow color to appear. The increase of double bonds results in a shift of the major adsorption bands to the longer wavelengths, and the hue of carotenoids becomes more red. Because of the highly conjugated double-bond system, carotenoids show ultraviolet and visible absorption spectrum characteristics. For most carotenoids, three peaks, or two peaks and a shoulder, are absorbed in the range of 400–500 nm. Absorption maxima and molecular extinction values are significantly affected by the solvent used. Thus, for all-trans-β-carotene, the respective wavelength maximum and E1% 1cm are 435 nm and 2592 in petroleum ether, but 465 nm and 2396 in chloroform (Barua et al., 2000). In unprocessed plants, usually all-trans (all E) double-bond configurations occur, but cis isomers of each carotenoid are also possible. Processing and storage can cause

208

Chemical and Functional Properties of Food Components

OH β HO

Lutein (5) OH O O

HO Violaxanthin (6)

HO β - Crytoxanthin (7)

OH O

OH

Capsanthin (8) O

O

Canthaxanthin (9)

Formulae 9.5–9.9 Xanthophylls

Food Colorants

209

CHO β β - Apo - 8' - carotenal (10) CH3O O Bixin

C HO O

(11) Formulae 9.10 and 9.11 Apocarotenoids

isomerization of carotenoids in foods and affect the color. The compounds with all-trans configurations have the deepest color. Increasing the number of cis bonds results in gradual lightening of the color. The cis isomers not only absorb less strongly than the all-trans isomer, but they also show a so-called cis peak at 330–340 nm. Many carotenoids have chiral centers that are due to the presence of asymmetric carbon atoms. However, natural carotenoids exist only in one of the possible enantiomeric forms, because the biosynthesis is enantiomere selective.

9.2.2 OCCURRENCE Carotenoids appear to be synthesized de novo by photosynthetic higher plants, mosses, algae, and nonphotosynthetic bacteria and fungi. All photosynthetic tissues contain carotenoids: higher plants in the chloroplasts, although the color is masked by the chlorophylls, and some bacteria in photosynthetic membranes. The chloroplasts, present in green unripe fruits, in most cases gradually change into chromoplasts on ripening, and carotenoid synthesis, often of novel pigments, is enormously stimulated. Typical examples are the tomato and red pepper. Oxygen but not light is required for carotenoid synthesis. In all photosynthetic organisms carotenoids have two major functions: as accessory pigments for light harvesting and in the prevention of photooxidative damage. In plants they are essential components of the light-harvesting antennae, where they can absorb photons and transfer the energy to chlorophyll. The major carotenoids that carry out this function in plants are lutein, violaxanthin, neoxanthin, and β-carotene. The other function of carotenoids is to protect against photooxidation processes that are caused by the excited triplet state of chlorophyll. Carotenoid molecules, with nine or more conjugated carbon–carbon double bonds, can absorb triplet state energy from chlorophyll and thus prevent the formation of harmful singlet oxygen. The main carotenoids of green leaves are lutein, violaxanthin, cryptoxanthin, and β-carotene; the others are produced in smaller quantities. Common carotenoids

210

Chemical and Functional Properties of Food Components

in fruits are β-carotene, lycopene, and different xanthophylls. The latter group are usually present in esterified form. Some of the carotenoids, such as β-carotene, lycopene, and zeaxanthin, are very widely distributed and so become important as food components. However, the content of carotenoids usually does not exceed 0.1% dry weight (Table 9.1) In the plant products carotenoids may occur as simple or very complex mixtures; some of the most complex are found in citrus fruits. The simplest carotenoids usually exist in animal products, because the animal organism is limited in its ability to absorb and deposit them. The compounds, which have been isolated only from animal tissues, mainly xanthophylls, are the result of metabolic changes, generally oxidative, in the ingested carotenoids. Crude vegetable oils contain carotenoids, but bleaching and hydrogenation leads to almost complete degradation of these pigments. Particularly rich in carotenoids (0.05–0.2%) is crude palm oil, containing mainly α- and β-carotenes. Egg yolk contains only xanthophylls, mainly lutein, zeaxanthin, and cryptoxanthin (0.3–8.0 mg/kg).

9.2.3 CAROTENOIDS USED

AS

FOOD COLORANTS

The most commonly used natural carotenoid extracts for foodstuffs are annatto, paprika, and saffron. Many other sources, including alfalfa, carrot, tomato, citrus peel, and palm oil, are also utilized. Annatto (E 160(b)) is an orange-yellow oil-soluble natural pigment extracted from the pericarp of the seed of a Bixa orellana L. tree. The major coloring component of this extract is the diapocarotenoid bixin (Formula 9.11). Several other pigments, mainly degradation products of bixin, are also present, including transbixin, norbixin, and trans-norbixin. Bixin is a methyl ester of a dibasic fatty acid that, on treatment with alkalis, is hydrolyzed to water-soluble norbixin. Two types of annatto are therefore available: an oil-soluble extract containing bixin and a watersoluble extract containing norbixin. Paprika oleoresin (E 160(c)) is an orange-red oil-soluble extract from sweet red peppers Capsicum annum. The major coloring compounds are xanthophylls: capsanthin (Formula 9.8), capsorubin as their dilaurate esters, and β-carotene. The presence of characteristic flavoring and spicy pungency components limits application of this extract in foodstuffs. Saffron, an extract of flowers of Crocus sativus, contains the water-soluble pigment crocin; the digentiobioside of apocarotenic acid, crocetin; zeaxanthin, a βcarotene; and characteristic flavoring compounds. The yellow color of this pigment is attractive in beverages, cakes, and other bakery products. However, use of this colorant is restricted by its high price. Carrot extracts (E 160(a)), carrot oil, palm oil, and related plant extract are also available on the market. Their main components are β- and α-carotenes (Formulae 9.1 and 9.2, respectively). Processes for the commercial extraction of carotene from carrots were developed. Purified crystalline products contain 20% α-carotene and 80% β-carotene and may be used for coloring fat-based products as dispersion of microcrystals in oil. Individual carotenoid compounds — β-carotene, β-apo-8'carotenal (Formula 9.10), apocarotenoic ethyl ester, and canthaxanthin (Formula 9.9) — are synthesized

Vegetable or Fruit

β-Carotene

α-Carotene

Lycopene

Lutein

Violaxanthin

β-Cryptoxanthin

Total

Kale Spinach Lettuce White cabbage Red paprika Green paprika Tomato Broccoli Carrot Blackberry Strawberry Nectarine Apricot Grapefruit Orange

8.68 3.68 1.68 0.034 3.78 0.11 0.89 0.32 9.54 0.13 0.006 0.40 0.90 0.59 0.013

0.15 0.09 0.04 — 0.51 0.01 0.15 — 4.89 0.02 0.0002 0.14 0.02 — 0.006

— — — — 0.13 — 11.44 — — — — — — 2.77 —

18.6 9.54 2.92 0.08 0.25 0.41 0.21 0.8 0.36 0.65 0.04 0.98 0.041 0.02 0.02

5.81 3.04 2.36 0.07 — 0.12 — 0.18 — 0.06 0.003 0.51 0.02 0.005 0.22

0.12 — 0.03 0.002 — 0.002 — 0.011 — 0.008 0.0005 0.08 0.06 0.012 0.05

34.76 17.31 8.48 0.25 30.37a 0.70 12.7 1.56 15.90 0.90 0.05 2.40 1.13 3.50 0.40

a

Food Colorants

TABLE 9.1 Quantities of Different Carotenoids in Some Vegetables and Fruits (mg/100 g of Edible Portion)

Includes 13.94 mg/100 g of capsanthin/capsorubin and 5.0 mg/100 g of capsolutein.

Source: Adapted from Muller, H., Z. Lebensm. Unters. Forsch. A, 204, 88, 1997.

for use as food colorants for edible fats and oils. Their properties are given in Table 9.2. The carotenoids pigments, in combination with surface active agents, are also available as microemulsions for coloring foods with a high water content. 211

212

Chemical and Functional Properties of Food Components

TABLE 9.2 Properties of Carotenoids Used as Food Colorants Solubility (g/100 ml) at 20°C Carotenoid

Color

β-Carotene Apocarotenoid ester Apocarotenal Canthaxanthin

Yellow Yellow to orange Orange to red Red

Oils 0.05–0.08 0.7 0.7–1.5 0.005

Ethanol 0.01 0.1 0.1 0.01

λmax 455–456 448–450 460–462 468–472

Vitamin A Activity (IU/mg) 1.67 1.2 1.2 0

Source: Adapted from Klaui, H. and Bauernfeind, J.C., Carotenoids as Colorants and Vitamin A Precursors, CRC Press, Inc., Boca Raton, FL, 1981.

9.2.4 PHYSICAL

AND

CHEMICAL PROPERTIES

Carotenoids are extremely lipophilic compounds that are almost insoluble in water. In aqueous surroundings they tend to form aggregates or adhere to surfaces. They are soluble in nonpolar organic solvents such as hexane, halogenated hydrocarbons, or tetrahydrofurane. In oils their solubility is rather low, particularly in a pure crystalline state. In the organism they are located in cellular membranes or in lipophilic compartments. In some plants hydroxylated carotenoids are esterified with various fatty acids, which make them even more lipophilic. With their extended system of conjugated double bonds, the carotenoids contain a reactive electron-rich system that is susceptible to reactions with electrophilic compounds. This structure is responsible for high sensitivity of carotenoids to oxygen and light. The central chain of conjugated double bonds can be oxidatively cleaved at various points, giving rise to the family of apocarotenoids. Most carotenoids (but not vitamin A) serve as singlet oxygen quenchers. Singlet oxygen 1O2 interacts with carotenoid to give triplet states of both molecules. The energy of excited carotenoid is dissipated through vibrational interaction with the solvent to recover the ground state. Carotenoids are the most efficient naturally occurring quenchers of singlet oxygen. They may also participate in the propagation step of the oxidation process as chain-breaking antioxidants that scavenge reactive peroxyl radicals. However, carotenoids serve this function best at low oxygen tensions. At higher oxygen levels, a carotenoid intermediate radical might add oxygen to form carotenoid peroxyl radicals, which could act as prooxidants, initiating the process of lipid peroxidation. On the other side, radicals and peroxides, occurring in food as a result of lipid oxidation, accelerate oxidative degradation of carotenoid pigments, which leads to formation of epoxides located at the β-ionone ring, β-apo-carotenones, and β-apocarotenals of different chain lengths. Lipoxygenase involved in the decay of vegetable matter may also cause the destruction of carotenoids. Antioxidants, including ascorbic acid and its derivatives, tocopherols, and polyphenolics, are used to suppress this oxidative degradation. Due to oxidative degradation of carotenoids, aroma compounds are also formed, including β-ionone with an odor threshold value of 14 ng/g in water. The formation

Food Colorants

213

of β-ionone in dehydrated carrots causes the undesired off-flavor “odor of violets.” Unsaturated ketones derived from carotenoid degradation are readily further oxidized. The stability of carotenoids in frozen and heat-sterilized foods is quite high, but it is poor in dehydrated products, unless the products are packaged in inert gas. Dehydrated carrots fade rapidly.

9.2.5 BIOLOGICAL ACTIVITY Carotenoids are known to have different biological functions. According to Berg et al. (2000) the most important functions of some groups of carotenoids are: • • • • • •

Provitamin A activity: β-carotene, α-carotene, and β-cryptoxanthin Antioxidant activity: all carotenoids Cell communication: β-carotene, canthaxanthin, and cryptoxanthin Immune function enhancers: β-carotene Ultraviolet skin protection: β-carotene and lycopene Macula protection: lutein and zeaxanthin

The best documented and established function of some carotenoids is their provitamin A activity, especially of β-carotene. One mole of β-carotene can theoretically be converted, by cleavage of C 15 = C 15' double bond, to yield two moles of retinal (Reaction 9.1). However, the physiological efficiency of this process appears to be only 50%. The observed average efficiency of intestinal β-carotene absorption is only two thirds of the total content. Thus, a factor of 1/6 is used to calculate the retinol equivalent (RE) from β-carotene, but only 1/12 from the other provitamin A carotenoids in food (Combs, 1992). In fruits and vegetables β-carotene content is used as a measure of the provitamin A content. The other very important biological function of carotenoids is linked with their antioxidant activity. An antioxidant has been defined as a substance that, at low concentration relative to an oxidizable substrate, can suppress, delay, or prevent oxidation of the substrate. Carotenoids act as antioxidants against lipid peroxidation by quenching singlet oxygen and trapping free peroxyl radicals. The structure of carotenoid, in particular the length of the polyene chain, significantly influences its antioxidant properties. Different methods have been used for determination of antioxidant activity. Rice-Evans et al. (1997) have used a method based on the ability to quench the colored ABTS radicals to compare antioxidant activity of some carotenoids. The results were calculated as the Trolox equivalent of antioxidant capacity (TEAC). The activity of Trolox, the water soluble α-tocopherol analog, was given a value of 1. A higher value in this assay indicated a higher activity of the carotenoid (Table 9.3). Lipid peroxidation is a problem not only in the edible oil, but also in the human body. Excess production of oxygen radical species and particularly hydroxyl radicals can affect lipid cell membranes to produce lipid peroxides and reactive oxygen species (ROS), which are linked to a variety of diseases, such as cancer and cardiovascular disease, and acceleration of the aging process.

214

Chemical and Functional Properties of Food Components

β

15 15'

β

β - carotene β - carotene - 15, 15' - oxygenase

CHO β Retinal alcohol       retinal aldehyde dehydrogenase        reductace

CH2OH β

Retinol Reaction 9.1 Formation of vitamin A from b-carotene

TABLE 9.3 Antioxidant Activities of Some Carotenoids Carotenoid Lycopene β-Cryptoxanthin β-Carotene Lutein Zeaxanthin α-Carotene

TEAC (mM) 2.9 2.0 1.9 1.5 1.4 1.3

Source: Adapted from Rice-Evans, C. et al., Free Rad. Res., 26, 381, 1997.

Food Colorants

215

It was observed that people with low carotenoid intake or low blood levels have an increased risk of degenerative diseases. In a number of these diseases free radical damage plays a role in the pathophysiology of the disease. Earlier studies were focused mainly on β-carotene and the lycopene protective effect against prostate and lung cancer, but there is as yet no definitive proof for a causal relationship or for a beneficial antioxidant effect of carotenoids. The cancer-preventing effect of β-carotene has been investigated in several intervention trials. However, only in one of these studies, the Linxian study, was a protective effect found for a combined β-carotene, vitamin E, and selenium supplementation. In the other studies, no protective effect was found, and in some cases, a higher risk of lung cancer has been observed after high doses of β-carotene. Therefore, the conclusion from these studies is that high-dose supplements of β-carotene are contradicted for heavy smokers, but could give a beneficial effect to individuals with a poor baseline carotenoid status. Probably a diet rich in high-carotenoid-containing fruits and vegetables is more efficacious than individual carotenoid compounds, because it represents a lower, regular intake of several constituents with several mechanisms of action as opposed to a high intake of one constituent with limited functions (Berg et al., 2000).

9.3 CHLOROPHYLL Chlorophyll is the most widely distributed natural plant pigment and acts as a catalyst in biochemical photosynthesis. In higher plants and algae, except the blue-greens, chlorophyll is found in chloroplasts, while in blue-green algae and photosynthetic bacteria, it is located on the intracellular lamellae. In living plant tissues chlorophyll is present in colloidal suspension in chloroplast cells, in the form associated with protein and saccharides. The chlorophyll pigments are the same in all plants. Apparent differences in color are due to the presence of other associated pigments, in particular xanthophylls and carotenes, which always accompany the chlorophylls and act as a sunscreen for the light-sensitive chlorophyll. Typical leaf material contains chlorophylls (about 2.5 mg/g), xanthophylls (0.3 mg/g), and carotenes (0.15 mg/g ) (Humphrey, 1980). In many fruits chlorophyll is present in an unripe state and gradually disappears during ripening, as the yellow and red carotenoids take over. The chlorophylls are tetrapyrrole pigments in which the porphyrin ring is in the dihydro form, and the central metal atom is magnesium (Formula 9.12). There are two chlorophylls: blue-green and yellow-green, occurring in a ratio of about 3:1. The yellow-green chlorophyll differs from the blue-green chlorophyll in that the methyl group on carbon 3 is replaced with an aldehyde group. Chlorophyll is a diester: one group is esterified with methanol and the other with phytyl alcohol. The important chemical characteristics of chlorophylls are: • The easy loss of magnesium in dilute acids or replacement of Mg2+ by other divalent metals • The hydrolysis of the phytyl ester in dilute alkalis or transesterification by lower alcohols • The hydrolysis of the methyl ester and cleavage of the isocyclic ring in stronger alkalis

216

Chemical and Functional Properties of Food Components CH3

CH

CH2

1       2

H3C

N

8 H

7

N

O O

3

N Mg N

R

4

CH2CH3

CCH2CH2 H 6         5

C

O

OCH3

CH3 O

Chlorophyll a R= —CH3 Chlorophyll b R= —CHO

Formula 9.12 Chlorophyll

Removal of magnesium gives olive-green phaeophytin a and b. Replacing magnesium by iron or tin ions yields grayish brown compounds, while copper or zinc ions retain the green color. Upon removal of the phytyl group by hydrolysis in dilute alkali or by the action of chlorophyllase, green chlorophyllins or cholorphylids are formed. Removal of magnesium and the phytyl group results in phephorbide formation (Figure 9.1). Chlorophylls and pheophytins are lipophylic, due to the presence of the phytol group, while chlorophyllins and pheophorbids without phytol are hydrophylic. The copper complexes of both pheophytin and pheophorbid have the metal firmly bound; it is not liberated even by the action of concentrated hydrochloric acid, and it is not removed to any appreciable extent upon metabolism; thus it is acceptable for the coloration of foodstuffs. Both coppered and uncoppered chlorophyll and their derivatives are available as food colorants. The oil-soluble chlorophylls (uncoppered and coppered pheophytin) are not widely used for food coloring, because commercial purification has not proven to

Food Colorants

217

CHLOROPHYLID (green)

chlorophilase

phytol

CHLOROPHYLL (green)

phytol

acid Mg2+

alkali Mg

methanol

2+

acid

PHEOPHYTIN        (olive-green)

phytol

CHLOROPHYLLIN (green)  

phytol Mg2+

alkali acid PHEPHORBIDE           (olive-brown)

FIGURE 9.1 Transformation of chlorophyll pigments.

be as satisfactory as that for the water-soluble derivatives. Their stability is good toward light and heat but poor to acid and alkaline conditions. Applications are found in canned products and confectioneries on the levels of 0.5–1 g/kg. The water-soluble chlorophyllins (uncoppered and coppered sodium or potassium pheophorbide) have good stability toward light and heat and moderate stability to both acid and alkalis. Food color usage is in canned products, confectioneries, soups, and dairy products.

9.4 HEME PIGMENTS The color of meat is the result of the presence of two pigments: myoglobin and hemoglobin. In both pigments the heme group is composed of the porphyrin ring system and the central iron atom bound with globin. In myoglobin, the protein portion has a molecular weight of 17,000, and in hemoglobin about 67,000. The central iron atom has six coordination bonds, each representing an electron pair accepted by the iron from five nitrogen atoms; four from the porphyrin ring and one from a histidyl residue of the globin. The sixth bond is available for binding with any atom that has an electron pair to donate, e.g., O2 or NO. The oxidation state of the iron atom and physical state of globin play an important role in meat color formation.

218

Chemical and Functional Properties of Food Components

In fresh meat, in the presence of oxygen, the reversible reaction of myoglobin (Mb) with oxygen occurs and results in the formation of bright-red-colored oxymyoglobin (MbO2). In both pigments the iron is in ferrous form, and upon oxidation to ferric state, the brownish metmyoglobin (MMb) is formed.

MbO2 red

Mb purplish red

MMb brownish

Reaction 9.2 Basic transformation of myoglobin

The oxymyoglobin and myoglobin exist in a state of equilibrium with oxygen. The ratio of these pigments depends on oxygen pressure. In meat there is a slow oxidation of the heme pigments to metmyoglobin. Metmyoglobin cannot bind oxygen. Heating of meat results in the denaturation of the globin linked to iron, as well as in the oxidation of iron to the ferric state and formation of different brown heme pigments named hemichrome. In the curing of meats, the heme pigments react with nitrite of the curing mixture, and the red-colored nitrite–heme complex nitrosomyoglobin is formed, but it is not particulary stable. More stable is the pigment with a denatured globin portion, named nitrosylhemochromogen, found in meat heated at temperatures above. The reactions of heme pigments in meat have been summarized in Figure 9.2 and presented in Figure 7.3. In the presence of thiol compounds as reducing agents in the reversible reaction, myoglobin may form a green sulfmyoglobin. Other reducing agents, e.g., ascorbate, lead to formation of cholemyoglobin. This reaction is irreversible. A potential source of red and brown heme pigments is animal blood and its dehydrated protein extracts, which mainly consist of hemoglobin and may be used as red and brown colorings to meat products. However, in most countries their usage as a food coloring agent is not permitted.

heating

NO dMMb                        MMb                         MMbNO brownish                    brownish                    bright red

heating                         oxidation        reduction                          reduction

NO

heating

-O2  MbO2                              Mb                               MbNO                         dMbNO  red                             purplish red                     bright red                    bright red +O 2

FIGURE 9.2 Transformation of myoglobin in meat; dMMb and dMbNO, denatured forms of pigments.

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9.5 ANTHOCYANINS 9.5.1 OCCURRENCE

AND

STRUCTURE

Anthocyanins are among the most important groups of plant pigments. They are present in almost all higher plants and are the dominant pigments in many fruits and flowers, giving red, violet, or blue color. They play a definite role in attracting animals in pollination and seed dispersal. They may also have a role in the mechanism of plant resistance to insect attack.

R3' 2'

HO

+

7 6

4' 5'

O

8

OH

3'

6' 2

R5'

3 4

5

OH OH Formula 9.13 Flavylium cation

Anthocyanins are part of the very large and widespread group of plant constituents known as flavonoids, which possess the same C6–C3–C6 basic skeleton. They are glycosides of polyhydroxy and polymetoxy derivatives of 2-phenylbenzopyrylium or flavylium cation (Formula 9.13). Differences between individual anthocyanins are: the number of hydroxyl groups in the molecule; the degree of methylation of these hydroxyl groups; the nature, number, and position of glycosylation; and the nature and number of aromatic or aliphatic acids attached to the glucosyl residue. From about 20 known naturally occurring anthocyanidins, only 6 occur most frequently in plants: pelargonidin, cyanidin, peonidin, delphinidin, petunidin, and malvidin (Table 9.4). Substitution of the hydroxyl and methoxyl groups affect the color

TABLE 9.4 Naturally Occurring Anthocyanidins Anthocyanidin

R3'

R5'

λmax(nm)

Color

Pelargonidin (Pg) Cyanidin (Cy) Peonidin (Pn) Delphinidin (Dp) Petunidin (Pt) Malvidin (Mv)

H OH OCH3 OH OCH3 OCH3

H H H OH OH OCH3

520 535 532 546 543 542

Orange Orange-red Orange-red Bluish-red Bluish-red Bluish-red

220

Chemical and Functional Properties of Food Components

of the anthocyanins. An increase in the number of hydroxyl groups tends to deepen the color to a more bluish shade. An increase in the number of methoxyl groups increases redness. Because of the possibility of different -ose and acid substitutions at different positions, the number of anthocyanins is 15–20 times greater than the number of anthocyanidins (Mazza and Miniati, 1993). The -ose molecules most commonly bonded to anthocyanidins are glucose, galactose, rhamnose, arabinose, and di- and trisaccharides, formed by combinations of these four monosaccharides. The most common class of anthocyanins are 3-monosides, 3-biosides, 3,5-diglycosides, and 3,7-diglycosides; however, glycosylation of 3', 4', and 5' hydroxyl groups is also possible. The composition and content of anthocyanins in fruits are very diversified (Table 9.5).

TABLE 9.5 Anthocyanins in Some Fruits: Composition and Content Fruits Blackberry Bilberry Black current Chokeberry Cranberry Strawberry Red grapes

Main Anthocyanins Cy 3-Glu, Cy 3-Rut Dp 3-Gal, Mv 3-Glu, Pt 3-Glu Cy 3-Rut, Cy 3-Glu, Dp 3-Rut, Dp 3-Glu Cy 3-Gal, Cy 3-Arab, Cy 3-Glu, Cy 3-Xyl Cy 3-Gal, Cy 3-Arab, Pn 3-Gal, Pn 3-Arab Pg 3-Glc, Cy 3-Glc Mv 3-Glu, Dp 3-Glu, Pt 3-Glu, Pn 3-Glu, 3-acetylglucoside, 3-p-coumarylglucoside

Total Anthocyanins (mg/100 g) 83–326 250–490 250 520–800 78 7–30 30–750

Source: Adapted from Macheix, J.J. et al., Fruit Phenolics, CRC Press, Boca Raton, FL, 1990; and Wang, H. et al., J. Agric. Food Chem., 45, 304, 1997.

9.5.2 CHEMICAL PROPERTIES In aqueous media, most of the natural anthocyanins behave like pH indicators, being red at low pH, bluish at intermediate pH, and colorless at high pH. According to Brouillard (1982), in acidic and neutral media four anthocyanin structures exist in equilibrium: the red flavylium cation (AH+), blue or red quinonoidal base (A), colorless carbinol pseudobase (B), and colorless chalcone (C) (Reaction 9.3). The pH of the medium plays a particularly important role in the equilibrium between these different anthocyanin forms, and consequently in color modification. In strongly acid solution, at a pH below 2, the red cation AH+ is the dominant form. As the pH is increased, a rapid proton loss occurs to yield the red or blue quinoidal base A, usually existing in two forms (Figure 9.3). On standing, a further reaction occurs, i.e., hydration of flavylium cation AH+, to give colorless carbinol pseudobase B. Relative amounts of forms AH+, A, B, and C at equilibrium vary with both pH and the structure of anthocyanins. For the common anthocyanin 3-glycosides

Food Colorants

221

OH

OH O

HO

A

B

+

O

HO

OH

OH

OH O

HO

+

- H /H2 O

C

O Gl

O Gl

O Gl

OH

OH

AH+: Flavylium cation

OH

CE: E - Chalcone

B: Carbinol pseudobase -H+

+H+

+

+H

- H+

O

OH

OH

HO

OH O

HO

O

O

O

Gl

O

OH

O Gl

Gl

O

OH

OH

CZ: Z - Chalcone

A: Quinonoidal bases

Reaction 9.3 Structural anthocyanin transformations in aqueous media

or 3,5-diglycosides, the principal product formed on raising the pH above 3 is the colorless carbinol pseudobase B (Figure 9.3). At this pH, however, small amounts of the blue quinoidal base and the colorless chalcones are also present and increase with increasing pH. Between pH values of 4 and 6 very little color remains, since the amounts of the colored forms (AH+ and A) are very small (Reaction 9.3). By varying the substitution pattern of the flavylium ring, anthocyanidin, which exists primilarly in quinoidal or chalcone form, can be prepared (Jacobucci and Sweeny, 1983), but such anthocyanin compounds are not found in plants. The color of anthocyanins containing media depends on different factors. The most important are structure and concentration of anthocyanin pigments, pH, and presence of copigments and metallic ions, all of which influence the color shade. Also important are the temperature and presence of oxygen, phenoloxidase, ascorbic acid, and sulfur dioxide, all of which influence the anthocyanins’ degradation rate and color stability. 100

% of total

AH

+

B

50 A C

0

1

2

4

3

5

pH FIGURE 9.3 Distribution of anthocyanin structures as functions of pH.

6

222

Chemical and Functional Properties of Food Components

The structure of the anthocyanin molecule has a marked effect on the color intensity and stability. The increase of the number of hydroxyl groups in B-ring shifts the absorption maximum to longer wavelengths, and the color changes from orange to bluish red. Methoxyl groups replacing hydroxyl groups reverse this trend. The hydroxyl group at C-3 is particularly significant because it shifts the color from yellow-orange to red. The same hydroxyl, however, destabilizes the molecule; the 3-deoxyanthocyanidins are much more stable than the other anthocyanidins. Similarly, the presence of a hydroxyl group at C-5 and a substitution at C-4 both stabilize the colored forms. Glycosylation also affects the stability of these pigments; the half-life of anthocyanidins is significantly lower than that of their corresponding 3glucosides. Anthocyanins containing two or more aromatic acyl groups, such as cinerarin or zebrinin, are stable in neutral or weakly acidic media. This is possibly a result of hydrogen bonding between phenolic hydroxyl groups in anthocyanidins and aromatic acids. Brouillard (1981) observed that diacylated anthocyanins are stabilized by sandwich-type stacking caused by the hydrophobic interaction between the anthocyanidin ring and the two aromatic acyl groups. The increase in anthocyanins’ concentration results in an increase in absorbance at λmax, greater than expected according to the Beer–Lambert law. It is probably connected with anthocyanins’ self-association. Intermolecular copigmentation of anthocyanins with other flavonoids, some phenolic acids, alkaloids, and other compounds, including anthocyanins themselves, increases the color intensity (hyperchromic effect) and causes a shift in the wavelength (batochromic shifts), giving purple to blue colors. The intensity of the copigmentation effect depends on several factors, including type and concentration of both anthocyanins and copigments, pH, and temperature of the solvent (Brouillard et al., 1991). The pH value for the maximum copigmentation effect is about 3.5 and may vary slightly, depending on the pigment–copigment system. Color intensification by copigmentation increases with increasing ratios of copigment to anthocyanins. Increasing temperature strongly reduces the color-intensifying effect. The copigmentation phenomenon is widespread in nature and also occurs in fruit and vegetable products such as juices and wines. In the presence of metals anthocyanins can form purplish blue or slate-gray pigments called lakes. This reaction may induce color changes, if fruit products, during processing or storage, are in contact with metals such as tin, aluminum, or iron.

9.5.3 BIOLOGICAL ACTIVITY Anthocyanins are natural colorants belonging to the large family of phenolic compounds: flavonoids. For many years they have been known to display different pharmacological and biological activities, such as vasoprotective, anti-inflamatory, and radioprotective agents. Additionally, they prevent cholestrol-induced arteriosclerosis and heart disease. However, the most important properties of anthocyanins seem to be their activities as potent free radical scavengers and powerful chainbreaking antioxidants. Similar to other flavonoids, they can react with reactive oxygen radicals, such as hydroxyl radical, superoxide anion radicals, and lipid

Food Colorants

223

peroxyl radical, and inhibit lipid peroxidation at the early stage. This is very important because in vivo lipid peroxidation has been implicated as the primary cause of coronary heart disease, atherosclerosis, cancer, and aging. The antioxidant effectivity of anthocyanin pigments is structure dependent and for the main aglicons, it is about two times higher than those of vitamins C and E. Recently, increasing attention has been focused on anthocyanins as natural antioxidants, because of their ubiquitous presence in plant products, particularly in fruits, juices, and red wine. The daily intake of anthocyanins in humans is as high as 200 mg/day. Despite relatively high potential intake in humans, the physiological impact of the anthocyanins is not well recognized, because of the lack of pure compounds and their low stability. Anthocyanin-enriched materials, of different purities, from the skin of grapes and other by-products of wine and juice manufacture are produced in different countries. One of the better known, commercially available anthocyanin concentrates is the extract of Vaccinium myrtillus, bilberry (VMA), which contains glycosides of delphinidin and cyanidin and is used to treat various microcirculation diseases resulting from capillary fragility (Wang et al., 1997). Red wine — much more than white wine and grape juice — is also recognized as a rich source of natural antioxidants. It has been demonstrated that red wine has superoxide radical scavenging potential and is able to effectively inhibit oxidation of low density lipoproteins (LDLs) in vitro and in vivo. However, in all these products not only anthocyanins but also other phenolic antioxidants, such as flavonols and flavanols, are present and may influence the biological and antioxidant activity. Therefore, the consumption of fruits rich in anthocyanins and red wine appears to be a good means to impede the lipid oxidation process responsible for different diseases and aging.

9.5.4 STABILITY

OF

ANTHOCYANINS’ COLOR

IN

FOOD

Anthocyanins appear to have low stability in all products manufactured from fruits. This limits the use of these pigments as food colorants. Two main groups of factors are responsible for the stability of anthocyanins’ color in fruits during processing: the initial composition of the fruit, with regard to anthocyanins and other constituents, including enzymatic systems; and the processing factors, such as temperature, light, and presence of oxygen. Several enzymes and in particular phenolases, peroxidases, and β-glucosidases can decrease the quality of the initial product during the extraction of fruit juices or the preparation of processed products, leading to browning and loss of color by enzymatic degradation of anthocyanins. Anthocyanins themselves are not good substrates for o-diphenol oxidase, but are instead oxidized by chlorogenic acid ↔ chlorogenoquinone redox shuttle phenomena. Thus enzymatic oxidation of chlorogenic acid may by combined with nonenzymatic oxidation and polymerization of anthocyanins. The same phenomenon has been observed in the presence of catechins. Ascorbic acid may have a protective effect with regard to anthocyanins, since it reduces the o-quinones formed before their polymerization. However, ascorbic acid, as well as products of its degradation, increases anthocyanins’ degradation rate. Sulfur dioxide, widely used in fruit processing, at concentrations as low as 30 mg/kg, inhibits the enzymatic degradation of anthocyanins. At high concentrations

224

Chemical and Functional Properties of Food Components

of the order of 500–2000 mg/kg, it forms a colorless SO2–anthocyanin complex. This is a reversible reaction: after removal of sulfur dioxide, the color turns red again. Regardless of the favorable action of high temperatures on the blockage of enzymatic activities, anthocyanins are readily destroyed by heat during processing and storage. A high-temperature, short-time process was recommended for best pigment retention. For instance, in red fruit juices heated 12 min at 100°C, anthocyanin losses appear to be negligible. The reaction listed above can proceed with different rates and can bring about different changes in color, depending on the composition of food products. Most frequently the red color slowly turns brown. However, in correctly processed and stored fruits, color changes are so slow that they only slightly affect consumer appreciation of fruit products. Anthocyanin concentrate may be used as a food colorant at a pH <4.

9.6 BETALAINS 9.6.1 OCCURRENCE

AND

STRUCTURE

Betalains occur in centrospermae, mainly in red beets, but also in some cactus fruits and mushrooms. They consist of red-violet betacyanins (λmax ~ 540 nm) and yellow betaxanthins (λmax ~ 480 nm). About 50 betalains have been identified. The major betacyanin is betanin (Formula 9.14), glucoside of betanidin, which accounts for GlO

GlO

H +

N

HO

COO

+

-

N

HO

N

COOH

HOOC

-

N

COOH

H

H

Betanin

COO

H

HOOC H

H

Isobetanin Formula 9.14 Betanin and isobetanin

75–95% of the total pigments of beets. The other red pigments are isobetanin (C-15 epimer of betanin), prebetanin, and isoprebetanin. The latter two are sulfate monoesters of betanin and isobetanin, respectively. Unlike anthocyanins, betanins cannot be hydrolyzed to aglycone by acid hydrolysis without degradation. The major yellow pigments are vulgaxanthin I and II (Formula 9.15). High betalain content in beetroot, on average 1% of the total solids, makes this vegetable a valuable source of the food colorant.

Food Colorants

225

R O COO

-

+NH

HOOC N

H

COOH

H R = —NH2 vulgaxanthin I R = —OH vulgaxanthin II Formula 9.15 Vulgaxanthins

9.6.2 CHEMICAL PROPERTIES The color stability of betanin solution is strongly influenced by pH and heating. Betanin is stable at pH values of 4–6, but thermostability is greatest between pH values of 4 and 5. As a result of betanin degradation cyclo-DOPA and betalamic acid are formed (Reaction 9.4). This reaction is reversible (Czapski, 1985). Light and air have a degrading effect on betanin. These effects are cumulative, but some protection may be offered by antioxidants such as ascorbic acid. Small amounts of metallic ions increase the rate of betanin degradation. Therefore a chelating agent can stabilize the color. Many protein systems present in food products also have some protective effect.

GlO

H +

N

HO

COO

O H

-

+ H2O - H2O

GlO

H

+ HO

N

COOH

H

HOOC H

HOOC H

N

COOH

H N

COOH

H

Betanin

Cyclodopa glucoside Reaction 9.4 Degradation of betanin

Betalamic acid

226

Chemical and Functional Properties of Food Components

Beetroot red (E 162), available as liquid beetroot concentrate and as beetroot concentrate powders, is suitable for products of relatively short shelf life, which do not undergo as severe heat treatment as meat and soya protein products, ice cream, and gelatin desserts.

9.7 QUININOID PIGMENTS These pigments are widely distributed. They are the major yellow, red, and brown coloring materials of roots, wood, and bark. They also occur at high levels in certain insects. The largest group is that of anthraquinone pigments. The most important qininoid pigments commercially available for use in foodstuffs are cochineal and cochineal carmine. Cochineal (E 120) is the red coloring matter extracted from the dried bodies of female insects of the species Dactylopius coccus Costa or Coccus cacti L. These insects are cultivated on the cactus plants in Peru, Equador, Guatamala, and Mexico. The major pigment of cochineal is polyhydroxyanthraquinone C-glycoside, carminic acid (Formula 9.16), which may be present at up to 20% dry weight of the mature insects. Cochineal extract or carminic acid are rarely used as coloring materials for food, but are usually offered in the form of their lake. Aluminum complexes (lakes) can be prepared with ratios of cochineal and aluminum varying from 8:1 to 2:1, having corresponding shades from pale yellow to violet. CH3

O

OH Gl

HOOC

OH

HO O

OH

Formula 9.16 Carminic acid

Cochineal carmine is insoluble in cold water, dilute acids, and alcohol and slightly soluble in alkali, giving a purplish red solution. The shade becomes more blue at higher pH values. Cochineal carmine is stable toward light and heat, but the stability to sulfur dioxide is poor. In powdered form this pigment can be used for coloring various instant foodstuffs, in alkaline solutions, and in ammonia for coloring different foods, including baked products, yogurts, soups, deserts, confectioneries, and syrups.

9.8 SOME OTHER NATURAL PIGMENTS 9.8.1 RIBOFLAVIN

AND RIBOFLAVIN

5′′PHOSPHATE

Riboflavin, vitamin B2 (Formula 9.17), is a yellow pigment present in many products of plant and animal origin. Milk and yeast are the best sources of riboflavin.

Food Colorants

227

CH2OH (HCOH)3 CH2 H3C

N

H3C

N

N

O

NH O

Formula 9.17 Riboflavin

It is an orange-yellow crystalline powder, intensively bitter tasting, that is very slightly soluble in water and ethanol, affording a bright green-yellow fluorescent solution. Riboflavin is stable under acidic conditions, but unstable in alkaline solution and when exposed to light. Reduction produces a colorless leuko form, but color is regenerated again in contact with air. Riboflavin-5'-phosphate sodium salt is much more soluble in water than the unesterified riboflavin and is not so intensely bitter. It is one of the physiologically active forms of vitamin B2. It is more unstable to light than riboflavin. Both forms can be used as coloring and an enriching food additive to cereal, dressing, and cheese.

9.8.2 TURMERIC, CURCUMIN Turmeric or curcumin is the fluorescent-yellow-colored extract from the rhizome of various species of curcuma plant, Curcuma longa L. The main pigment of curcuma is curcumin (Formula 9.18). O

O OCH3

H3CO

HO

OH Formula 9.18 Curcumin

Turmeric oleoresin is insoluble in water but soluble in alkalis, alcohols, and glacial acetic acid. This pigment has a strong characteristic odor and sharp taste, and is utilized for both its taste and color properties as an additive to canned products, soups, mustards, and other products.

9.8.3 CARAMEL Caramel is the amorphous dark brown coloring material formed by heating saccharides in the presence of selected accelerators. It consists of a mixture of volatile and nonvolatile low-molecular-weight compounds and high molecular compounds. The composition and coloring power of caramel depend on the type of raw material and

228

Chemical and Functional Properties of Food Components

process used. Both Maillard-type and caramelizing reactions are involved, and the commercial products are extremely complex in composition. More-detailed information on caramel is given in Chapter 5.

9.9 SYNTHETIC ORGANIC COLORS The synthetic food colorants, according to their chemical structure, belong to mono-, di-, and trisazo, triarylmethane, xanthene, quinoline, and indigoid. They can also be divided into water-soluble, oil-soluble, insoluble (pigment), and surface marking colors. Water solubility is conferred on many dyes by introducing to the molecule at least one salt-forming group. The most common is the sulfonic group, but carboxylic acid residues can also be used. These dyes are usually isolated as sodium salts. They have colored anions and are known as anionic dyes. The other dyes containing basic groups, such as –NH2, –NH–CH3, or –N(CH3)2, form water-soluble salts with acids. These are cationic dyes and their colored ions are positively charged. If both acidic and basic groups are present, an internal salt is formed. Oil-soluble or solvent-soluble colors lack salt-forming groups. Pigments are the colors having no affinity for most substrates. They are thus generally insoluble in water, fats, and solvent, so they color by dispersion in the food medium. Precipitation of water-soluble colors with aluminum, calcium, or magnesium salts (generally with aluminum) forms water-insoluble lakes. Lakes may be prepared from all classes of water-soluble food colors, and they are one of the most important groups of food color pigments. The stability of synthetic food colors toward the condition prevailing in food processing depends on product composition, temperature, and time of exposition. Generally, they are resistant to boiling and baking, but light has a destructive effect on all of the colors. The use of synthetic colors is the most reliable and economical method of coloring those products that have little or no natural color present, such as dessert powders, table jellies, and sugar confectioneries. The synthetic organic dyes are superior to the natural colorants in consistency of strength, range and brilliance of shade, stability, ease of application, and costeffectiveness. However, the manner in which synthetic colorants are employed, from a safety viewpoint, has much to be desired. Therefore, regulations were introduced to control the use of these added food colorants.

REFERENCES Barua, A.B. et al., Vitamin A and carotenoids, in Modern Chromatographic Analysis of Vitamins, De Leenheer, A.P., Lambert, W.E., and Van Bocxlaer, J.F., Eds., Marcel Dekker, Inc., New York, 2000, p. 7. Berg, H. et al., The potential for the improvement of carotenoid levels in foods and the likely systematic effect, J. Sci. Food Agric., 80, 880, 2000. Brouillard, R., Origin of exceptional color stability of the Zebrina anthocyanin, Phytochemistry, 20, 143, 1981.

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Brouillard, R., Chemical structure of anthocyanins, in Anthocyanins as Food Colours, Markakis, P., Ed., Academic Press, New York, 1982, p. 1. Brouillard, R. et al., pH and solvent effects on the copigmentation reaction of Malvin by polyphenols, purine and pyrimidine derivatives, J. Chem. Soc. Perkin Trans., 2, 1235, 1991. Combs, G.F., Jr., The Vitamins: Fundamental Aspects in Nutrition and Health, Academic Press Inc., San Diego, 1992, p. 121. Czapski, J., The effect of heating conditions on losses and regeneration of betacyanins, Z. Lebensm. Unters. Forsch., 180, 21, 1985. Humphrey, A.M., Chlorophyll, Food Chem., 5, 57, 1980. Jacobucci, G.A. and Sweeny, J.G., The chemistry of anthocyanins, anthocyanidins and related flavylium salts, Tetrahedron, 39, 3005, 1983. Klaui, H. and Bauernfeind, J.C., Carotenoids as food colours, in Carotenoids as Colourants and Vitamin A Precursors, Academic Press, New York, 1981, p. 47. Macheix, J.J., Fleuriet, A., and Billot, J., Fruits Phenolics, CRC Press, Boca Raton, FL, 1990, p. 239. Mazza, G. and Miniati, E., Anthocyanins in Fruits Vegetables and Grains, CRC Press, Boca Raton, FL, 1993, p. 1. Muller, H., Determination of the carotenoid content in selected vegetables and fruits by HPLC and photodiode array detection, Z. Lebensm. Unters. Forsch. A, 204, 88, 1997. Rice-Evans, C. et al., Why do we expect carotenoids to be antioxidants in vivo, Free Rad. Res., 26, 381, 1997. Wang, H., Coa, G., and Prior, R.L., Oxygen radical absorbing capacity of anthocyanins, J. Agric. Food Chem., 45, 304, 1997.

10

Flavor Compounds Chung-May Wu, Jen-Min Kuo, and Bonnie Sun Pan

CONTENTS 10.1 Sources of Flavors in Foods ........................................................................232 10.1.1 Flavors Formed Naturally in Plants.................................................232 10.1.1.1 Spices and Herbs ..............................................................232 10.1.1.2 Fruits .................................................................................232 10.1.1.3 Vegetables .........................................................................233 10.1.2 Flavors Produced by Microbes or Enzymes....................................233 10.1.3 Flavors Produced by Heating or Cooking .......................................233 10.1.4 Flavors from Flavorants Added .......................................................233 10.2 Molecular Structure and Odor of Flavor Compounds ................................234 10.2.1 Volatility and Intensity of Aroma Compounds................................234 10.2.2 Flavor Compounds and Their Odors ...............................................234 10.3 Changes in Flavor During Food Storage and Processing ...........................235 10.3.1 Changes Due to Nature of Flavor Compounds ...............................235 10.3.2 Changes Due to Continuing Aroma Biogenesis..............................236 10.3.3 Changes Due to Tissue Disruption or Enzyme Reactions ..............236 10.3.3.1 Introduction.......................................................................236 10.3.3.2 Allium ...............................................................................236 10.3.3.3 Brassicas ...........................................................................237 10.3.3.4 Mushrooms .......................................................................237 10.3.3.5 Formation of Green-Grassy Notes in Disrupted Tissues.237 10.3.3.6 Glycosides as Flavor Precursors.......................................238 10.3.4 Changes Due to Processing .............................................................238 10.3.4.1 Maillard Reaction .............................................................238 10.3.4.2 Lipid Oxidation.................................................................239 10.3.4.3 Interaction of Lipids in the Maillard Reaction ................240 10.3.4.4 Extrusion ...........................................................................241 10.3.4.5 Concentration and Other Processes..................................241 10.3.5 Changes Due to Storage of Food Products .....................................241 10.4 Use of Flavors in Food Industry..................................................................242 10.4.1 Functional Properties of Flavor Compounds...................................242 10.4.2 Collection or Production of Flavoring Materials ............................243 10.4.2.1 Natural Flavor Materials...................................................243 10.4.2.2 Organic Chemicals Used in Flavorings............................244 10.4.3 Flavor Manufacturing.......................................................................245 1-5871-6149-4/02/$0.00+$1.50 © 2002 by CRC Press LLC

231

232

Chemical and Functional Properties of Food Components

10.4.3.1 Flavor Compounding ........................................................245 10.4.3.2 Process Flavor...................................................................246 10.5 Biotechnological Production of Flavors ......................................................246 10.5.1 Microbial Production of Flavor Compounds...................................246 10.5.2 Enzymatic Generation of Flavor Compounds .................................248 10.5.3 Recombinant DNA Technology for Flavor Formations ..................249 10.6 Applications of Flavors................................................................................250 References..............................................................................................................251

10.1 SOURCES OF FLAVORS IN FOODS 10.1.1 FLAVORS FORMED NATURALLY

IN

PLANTS

10.1.1.1 Spices and Herbs Since antiquity, spices, herbs, and condiments have been considered virtually indispensable in the culinary arts. They have been used to flavor foods and beverages the world over. Spices can be grouped according to the parts of the plant used: leaves (bay and laurel); fruits (allspice, anise, capsicum, caraway, coriander, cumin, dill, fennel, paprika, and pepper); arils (mace); stigmas (saffron); flowers (safflower); seeds (cardamom, celery seed, fenugreek, mustard, poppy, and sesame); barks (cassia and cinnamon); buds (clove and scallion); roots (horseradish and lovage); and rhizomes (ginger and turmeric). Most of the spices and herbs contain volatile oils, called essential oils, which are responsible for the characteristic aroma of spices. Some spices (capsicum, ginger, mustard, pepper, and horseradish) are pungent, while paprika, saffron, safflower, and turmeric are valued for their colors. Many spices have some antioxidant activities (Chen et al., 1999). Rosemary and sage are particularly pronounced in antioxidant effects. Cloves, cinnamon, mustard seed, and garlic contain antimicrobial activities (Firouzi et al., 1998). Some spices have physiological and medicinal effects. Spiced foods contain substances that affect the salivary glands (Pruthi, 1980). 10.1.1.2 Fruits Citrus fruits contain peel oil, the essence from which oil is obtained during concentration of the juice process. Citrus oils are characterized by a high percentage of terpene hydrocarbons (limonene, C H ), which contribute little to aroma. The unique characteristics of limonene are its relative insolubility in dilute alcohol and its susceptibility to oxidation, causing off-flavor production. If the monoterpenes are removed, the resulting oil is called terpene-free or terpeneless oil. Aldehydes, esters, and alcohols are the main contributors to the aromas of citrus oil. These compounds are relatively polar and soluble in water; therefore, they are satisfactory for applications in food and beverage. Fruits other than citrus contain much less volatile aromatic compounds and cannot form essential oil in distillates. However, their juices, juice concentrates, 10

16

Flavor Compounds

233

extracts of dehydrated fruits, and distillates (essence) can be used as flavorants directly added to foods. 10.1.1.3 Vegetables Vegetables contain some flavor compounds, the concentrations of which are mostly too low to obtain essential oils. In the tissues of some vegetables, volatile compounds are enzymatically produced when they are disrupted. Vegetables have the function of flavoring only after their cells are disrupted or after being oil-fried. Vegetable flavors are classified in the category of savory flavor, while fruit flavors are classified as sweet flavors. In addition to the three natural flavor categories described above, tea, coffee beans, cocoa beans, flowers (i.e., rose and jasmine), peppermint, and balsam are natural products with flavoring properties (Arctander, 1960; Furia and Bellanca, 1975).

10.1.2 FLAVORS PRODUCED

BY

MICROBES

OR

ENZYMES

Fermentation has been known and commercially exploited for centuries. Products like spirit, liquor, wine, beer, and other alcoholic beverages; vinegar; cheese and yogurt; miso, soy sauce, and fermented bean curd; ham and sausage; fish sauce; cured vanilla beans, tea, and cocoa; pickles and sauerkraut; dough, bread, and other bakery products have special flavor notes that can also be used as seasonings. Biotechnology for the production of flavoring materials has been developed in the past decade. The technology relating to the production of flavors include cell and tissue culture; microbial fermentation; and bioconversion of substrates using whole microbial cells, plant cells, or enzymes (Harlander, 1994; Kringer and Berger, 1998). For example, in a model system, using lipoxygenase (LOX) extracted from mullet gill in place of roe LOX to react with roe lipid, resulted in a very slight decrease in unsaturated fatty acids and a pronounced increase in green and fresh fish-like flavor notes (Pan and Lin, 1999). Fish oil modified with algal LOX yields an aroma more desirable than that of the untreated fish oil (Hu and Pan, 2000).

10.1.3 FLAVORS PRODUCED

BY

HEATING

OR

COOKING

The flavors of foods such as wheat, peanuts, and sesame, after being cooked, are quite different from those of the raw materials. Flavor formation from flavor precursors in the processed foods is primarily via the Maillard reaction, caramelization, thermal degradation, and lipid–Maillard interactions.

10.1.4 FLAVORS

FROM

FLAVORANTS ADDED

Flavorings play essential roles in the production of a wide range of food products versatile in aroma to allow consumer choices and to meet consumer needs. In this regard, flavor

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Chemical and Functional Properties of Food Components

manufacturers require expertise in flavor formulations, research, and technical services, while flavor users need fundamental knowledge of flavor applications.

10.2 MOLECULAR STRUCTURE AND ODOR OF FLAVOR COMPOUNDS 10.2.1 VOLATILITY

AND INTENSITY OF

AROMA COMPOUNDS

The flavor of food is largely perceived as a result of the release of odorous compounds, usually present in trace amounts in foods, into the air in the mouth and then to the olfactory epithelium in the nose. The volatility is caused by the evaporation or rapid sublimation of an odoriferous substance. It is proportional to the vapor pressure of the substance and inversely proportional to its molecular weight. Therefore, an aroma compound must be volatile. Other characteristics relate to aroma compounds; among them flavor intensity is the most important. Threshold is used most extensively for quantification of flavor intensity. Psychophysically, a threshold can be defined as the minimum concentration of a stimulus that can be detected (absolute threshold), discriminated (just noticeable difference), or recognized (recognition threshold). In general, the detection thresholds are lower than the recognition thresholds, if the difficulty in measuring both is compared (Pangborn, 1981). The relationship between the molecular structure of an aroma compound and its threshold is still unclear. Volatility of a compound may not relate to its threshold. For example, the threshold of ethanol (boiling point is 78°C) is much higher than octanol (boiling point is 195°C) or other homologous alcohol. Ethanol has high volatility but low odor intensity. It is often used as a solvent in compounded flavors. In general, sulfur- or nitrogen-containing compounds and heterocyclic compounds have very low threshold values. An odor unit is defined as the ratio of concentration to threshold. This unit quantifies the contribution of a specific component or a fraction to the total odor of a mixture; however, it says nothing about the odor quality of the final mixture, and it does not imply anything about the relationship between the stimulus concentration and the intensity of sensation above the threshold (Teranishi et al., 1981).

10.2.2 FLAVOR COMPOUNDS

AND

THEIR ODORS

The relationship between the molecular structure of a chemical compound and its odor has been the subject of much research and conjecture. It is still not possible to predict the aromatic profile from the structure of a given chemical, and it is not possible to assume changes in flavor profile based on molecular structure modification. Even stereoisomers may differ in odor both qualitatively and quantitatively. Nevertheless, the relationship between structure and odor can be summarized as follows. Small molecules — such as ethanol, propanol, and butanol among alcohols; acetaldehyde and propionaldehyde among aldehydes; and acetic acid, propionic acid, and butyric acid among acids — are highly volatile and exhibit pungent ethereal, diffusive, harsh, or chemical odor characteristics. Only in extreme dilution of these

Flavor Compounds

235

compounds will a desirable odor become perceptible. Bigger molecules of alcohols, aldehydes, and acids are mild and desirable at 5–10°C. Molecules containing alcohols, aldehydes, and acids reduce their volatility and odor intensities with increases in molecular size at temperatures higher than 10°C. Compounds containing functional groups such as -OH, -CHO, -CO, and -COOH play important roles in exporting the odors of a compound. Acid is sour, aldehyde yields a fresh note, and ester is fruity. However, an elongated alkyl group enhances the fatty or oily note. Ketones having two alkyl groups attached to a carbonyl group give more fatty aroma than the corresponding aldehydes. Ester has a fruity note. When the initial alkyl group in alcohol or acid or both is relatively large in molecular size or with its own characteristic note, the resulting ester maintains this note in addition to the fruity note. Examples include citronellyl acetate, having a fresh rosy–fruity odor, which inherits the rosy note from citronellol; and bornyl acetate, having a sweet herbaceous–piney odor with a balsamic undertone, which maintains the odor of borneol. The boiling point of ethyl acetate is 77°C, and its molecular weight is 88. Those of its reactant ethyl alcohol are 78°C and 46, while those of the acetic acid are 118°C and 60, respectively. Ester has a higher molecular weight but a lower boiling point in comparison to the precursor alcohol and acid. Many esters such as ethyl acetate have fresh notes. Aldehyde has a relatively low boiling point. For example, acetaldehyde has a molecular weight of 44, while its boiling point is 21°C. Therefore, aldehydes are often used for their fresh note. For example, decanal contributes to the fresh note in orange aroma. Lactones are cyclic compounds with relatively high boiling points and an ester functional group. They have the characteristic ester notes: fruity, oily, and sweet. γ-Undecalactone, with a peach-like aroma, has a boiling point of 297°C. Heterocyclic compounds generally have very low thresholds. Thiazoles, thiolanes, thiophenes, furans, pyrazines, and pyridines are normally present in larger numbers and higher concentrations in cooked, fermented, and processed seafoods or meat products than in fresh ones (Pan and Kuo, 1994). Essential oil, oleoresin, or other natural flavoring raw materials have many valuable trace components that play important roles in aroma. These components are not commercially available now because of their complexity and low threshold. It is not feasible to undergo a complicated manufacturing process for the very little amount needed. The only source available is the natural product.

10.3 CHANGES IN FLAVOR DURING FOOD STORAGE AND PROCESSING 10.3.1 CHANGES DUE

TO

NATURE

OF

FLAVOR COMPOUNDS

A volatile compound evaporates continuously, even at room temperature. Higher temperature accelerates the evaporation. Some food ingredients such as lipids and proteins may trap flavor compounds to some extent and reduce their volatility. Different flavor compounds have different volatility. An aged food may not only lose its total flavor, but also change its proportions of the flavor components, resulting in a changed odor.

236

Chemical and Functional Properties of Food Components

Many flavor compounds contain double bonds or aldehyde groups, which are susceptible to oxidation, cleavage, polymerization, or interaction among components (Sinki et al., 1997). Alcohols can be oxidized to the corresponding aldehyde and then acid. Alcohol and acid can react to form ester. Ester can be hydrolyzed to alcohol and acid at neutral or alkaline pH. Aldehyde and alcohol can be dehydrated by catalysis to form hemiacetal, and the reverse reaction can occur in acidic conditions or in water.

10.3.2 CHANGES DUE

TO

CONTINUING AROMA BIOGENESIS

The amount of secondary metabolites such as aroma compounds produced by a plant during its life cycle is a balance between formation and elimination. The two opposing functions are directly controlled by two main groups of factors. The intrinsic factors are comprised of all internal, or hereditary, properties (e.g., genotype and ontogeny), while extrinsic factors are comprised of all external, or environmental properties (e.g., pressure, wind, light, temperature, soil, water, and nutrients). Therefore, a plant material such as citrus fruits (Nagy and Shaw, 1990) or the essential oils (Lawrence, 1986) may have quite a different flavor quality due to the culture conditions and maturity. The typical flavor of climatic fruit such as bananas, peaches, pears, and cherries does not have the flavor during early fruit formation; it develops fully during a rather short period of ripening. During that time, minute quantities of lipids, carbohydrates, proteins, and amino acids are enzymatically converted to volatile flavors (Reineccius, 1994a). During postharvest handling, the plant continues the biogenesis of aroma.

10.3.3 CHANGES DUE REACTIONS

TO

TISSUE DISRUPTION

OR

ENZYME

10.3.3.1 Introduction Some food flavors are not present in the intact plant tissues, but are formed by enzymatic processes when the plants are cut or crushed. Under these circumstances, the cells are ruptured, and the flavor precursors are released and exposed to enzymes. Unique examples of this kind of flavor formation are described below. 10.3.3.2 Allium Garlic, onion, shallot, green onion, and chive belong to the allium genus. Members of this genus contain volatile sulfur compounds, including thiols, sulfides, disulfides, trisulfides, and thiosulfinates (Block and Calvey, 1994; Yamaguchi and Wu, 1975; Yu and Wu, 1989). The enzymatic flavor formation reaction of the allium genus can be generalized as follows: 2 RSOCH2CHNH2COOH → RSSOR + 2 NH3 + CH3COCOOH where R is methyl, propyl, 1-propenyl, or allyl. The 1-propenyl compound has been identified as the lacrimator in onions. Allicin, the active odor principle of fresh garlic,

Flavor Compounds

237

is diallyl thiosulfinate. In common with all thiosulfinates, allicin readily forms diallyl disulfide and diallyl trisulfide at room temperature. The addition of soybean oil in the process of garlic disruption can slow down the conversion of allicin (Kim et al., 1995). 10.3.3.3 Brassicas The brassicas of importance as foods include turnips, rutabagas, mustards, and the cole crops — cabbage, broccoli, cauliflower, and brussels sprouts. The production of isothiocyanates in brassicas is via an enzymatic reaction on specific glycosides. Some of the isothiocyanates, especially allylthiocyanate, are highly pungent and are mainly responsible for the odors of brown mustard, horseradish, cabbage, and other crucifers. Any process that destroys or inactivates enzymes in these plants will cause decreases in aroma production, resulting in a less distinctive flavor. This is usually the case when brassica foodstuffs are commercially preserved. 10.3.3.4 Mushrooms 1-Octen-3-ol occurs in many mushroom species. It contributes significantly to the flavor of edible mushrooms, such as Agaricus campestris (Tressl et al., 1982) and Agaricus bisporus (Wurzenberger and Grosch, 1982; Chen and Wu, 1984). 1-Octen-3-ol is formed enzymatically from linoleic acid, which was shown to be the major fatty acid in A. bisporus. Enzymes involved in the pathway of formation of 1-octen-3-ol include LOX, hydroperoxide lyase, and allene oxide synthases (Grechkin, 1998). Shiitake (Lentinus edodes) is one kind of edible mushroom highly prized in China and Japan. Due to the difficulties of postharvest storage, the mushroom has been traditionally preserved in dried form. The differences between the fresh shiitake and the dried shiitake lie in the contents of eight-carbon compounds (i.e., 3-octanone, 1-octen-3-ol, 3-octanol, n-octanol, and cis-2-octen-l-ol) and sulfurous compounds (i.e., dimethyl disulfide and dimethyl trisulfide). Fresh shiitake contains more eightcarbon compounds than dried shiitake, while dried shiitake contains more sulfurous compounds than fresh shiitake (Chang et al., 1991). The formation of volatile shiitake is affected greatly by the pH during blending. 1-Octen-3-ol and 2-octen-l-ol are predominantly formed around pH values of 5.0–5.5, while the formation of predominantly sulfurous compounds such as dimethyl disulfide and dimethyl trisulfide is around pH 7.0. Two enzymatic systems are probably responsible for the formation of eight-carbon and sulfurous compounds. An enzymatic reaction is likely to occur in dried shiitake, yielding more volatile sulfur compounds than fresh shiitake (Chen et al., 1984). 10.3.3.5 Formation of Green-Grassy Notes in Disrupted Tissues Six-carbon compounds such as hexanal, 3Z-, and 2E-hexenal at high concentrations were detected in ruptured tissue of apples, grapes, and tomatoes (Schreier and Lorenz, 1981). These compounds, when they occur, are only in trace amounts in intact plant cells. Aliphatic C-6 components, which contribute to the green note of fruits, are formed from unsaturated C-18 fatty acids by enzymatic activity after cellular disruption. LOX is involved in the reaction (Galliard and Matthew, 1977).

238

Chemical and Functional Properties of Food Components

(Z)-3-Hexen-l-ol, (E)-2-hexenal, hexanol, (E)-2-hexen-l-ol, and hexanal are formed in bell peppers (Capsicum annuun var. grossum, Sendt) after tissue disruption (Buttery and Ling, 1992). 10.3.3.6 Glycosides as Flavor Precursors There are two forms of monoterpene derivatives in grapes: free and glycosidic conjugates. The free form consists of compounds with interesting flavor properties such as geraniol, nerol, linalool, linalool oxides, α−terpineol, cirronellol, hotrienol, and flavorless polyhydroxylated compounds (polyols), which under mild acidic hydrolysis conditions can yield odorous volatiles. The flavorless glycoside forms, consisting of β-D-glucopyranosides and diglycosides; and 6-O-α−L-arabinofuranosyl-β-D-glucopyranosides, 6-O-α−L-rhamnopyranosyl-βD-glucopyranosides (rutinosides), and 6-O-β-D-apiofuranosyl-β-D-glucopyranosides of predominantly geraniol, nerol, and linalool, together with monoterpenes, are present at a higher oxidation state than the free forms. As most of these compounds have interesting sensory properties, their glycosides make up a potential aroma reserve that is more abundant than in their free counterparts. The glycosidically bound volatiles can be released by either acid or enzyme hydrolysis (Wu and Liou, 1986). β-Glucosidase, the most abundant glycosidase, is present with α−arabinosidase and α−rhamnosidase in grapes and berries of various cultivars. Enzyme treatment of juice or wine increases the concentrations of volatile monoterpene flavorants. Prolonged aging of wine or its exposure to elevated temperatures increases the concentration of free volatile monoterpenes through hydrolysis of glycosidic precursors in wine (Gunata et al., 1992; Straus et al., 1986). Other plants such as papaya (Schreier and Winterhalter, 1986), nectarine (Takeoka et al., 1992), and tea leaves (Lee et al., 1984; Kobyashi et al., 1992) also contain glycosides as precursors of flavors.

10.3.4 CHANGES DUE

TO

PROCESSING

10.3.4.1 Maillard Reaction The Maillard reaction plays an important role in flavor development, especially in meat and savory flavor (Buckholz, 1988). Products of the Maillard reaction are aldehydes, acids, sulfur compounds (e.g., hydrogen sulfide and methanethiol), nitrogen compounds (e.g., ammonia and amines), and heterocyclic compounds such as furans, pyrazines, pyrroles, pyridines, imidazoles, oxazoles, thiazoles, thiophenes, di- and trithiolanes, di- and trithianes, and furanthiols (Martins et al., 2001). Higher temperature results in production of more heterocyclic compounds, among which many have a roasty, toasty, or caramel-like aroma. Sugar, ascorbic acid, amino acids, thiamine (de Ross, 1992; Ames and Hincelin, 1992; Guntert et al., 1992, 1994; Yoo and Ho, 1997), and peptides (Ho et al., 1992; Izzo et al., 1992; de Kok and Rosing, 1994) are potential reactants of the Maillard reaction. They are present in most foods, so the Maillard reaction occurs commonly when these foods are cooked. The conditions of cooking determine the aroma of the cooked foods. For example, the major volatiles identified from water-boiled duck meat are the common

Flavor Compounds

239

degradation products of fatty acids, while roasted duck meat contains not only the volatiles found in raw duck meat, but also pyrazines, pyridines, and thiazoles (Wu and Liou, 1992), which are Maillard reaction products. The wax gourd (Benincasa hispida, Cogn), also known as winter melon or gourd melon, a vegetable, is used to produce beverages, candy, and jams that are popular in Taiwan. The flesh of the gourd melon is white in color. The major volatile compounds of fresh gourds are (E)-2-hexenal, n-hexanal, and n-hexyl formate, while the 2,5-dimethylpyrazine, 2,6-dimethylpyrazine, 2,3,5-trimethylpyrazine, 2-methyl pyrazine, and 2-ethyl-5-methyl pyrazine are the major volatile compounds of the wax gourd beverage, which is brown in color. The beverage is prepared by cooking sliced wax gourd and sugar at alkaline pH for about 3–4 h, or even longer, followed by diluting with water and serving as a nonalcoholic beverage. The pyrazine compounds not present in the fresh wax gourd are likely formed from the sugar added and the endogenous amino acids during processing of the beverage (Wu et al., 1987). This example shows changes in the flavor of foods during processing in which the Maillard reaction plays an important role. Hundreds of patents have been granted worldwide for processes and reaction products based on Maillard technology applied to manufacturing meat and savory flavors (Buckholz, 1988; Mottram and Salter, 1988; Ouweland et al., 1988). The Maillard reaction may produce mutagenic components, pigments, and antioxidants, all of which are discussed in other sections of this book. 10.3.4.2 Lipid Oxidation The oxidation products of lipids include volatile aldehydes and acids. Therefore, lipids are one of the major sources of flavors in foods. For example, much of the desirable flavors of vegetables such as tomatoes, cucumbers, mushrooms, and peas (Ho and Chen, 1994); fresh fish (Hsieh and Kinsella, 1989), fish oil (Hu and Pan, 2000); and cooked shrimp (Kuo and Pan, 1991; Kuo et al., 1994), as well as many deep-fat fried foods such as French-fried potatoes (Salinas et al., 1994) and fried chicken (Shi and Ho, 1994), are contributed by lipid oxidation. LOX-catalyzed lipid oxidation produces secondary derivatives, e.g., tetradecatrienone, which is a key compound of shrimp (Kuo and Pan, 1991). The major difference between the flavors of chicken broth and beef broth is the abundance of 2,4-decadienal and γ-dodecalactone in chicken broth (Shi and Ho, 1994). Both compounds are well-known lipid oxidation products. A total of 193 compounds has been reported in the flavor of chicken. Forty-one of them are lipid-derived aldehydes. The core flavor of mashed potatoes consists of naturally occurring and thermally generated compounds. These compounds arise mainly from the oxidation of fatty acids, especially highly unsaturated fatty acids, and from the degradation and interaction of sugar and amino acids. The extent to which these reactions affect the flavor of the final product depends on the age of the raw materials, storage conditions, and processing techniques. For example, both lipid oxidation and nonenzymatic browning reactions increase with the age of the raw potato (Salinas et al., 1994). Garlic develops its aroma from enzymatic reactions, as described before. When garlic slices are deep fried, microwave heated, or oven baked, the aroma changes (Yu et al., 1993) and contributes a different kind of garlic flavor to foods. A novel

240

Chemical and Functional Properties of Food Components

S-compound was identified from the interaction of garlic and heated edible oil (Hsu et al., 1993). Also, alliin and deoxyalliin, two important flavor precursors of garlic, can react with 2,4-decadienal, which is one of the major oxidation products of fatty acids to form aroma (Yu et al., 1994). Deep-fat frying is a universal cooking method. Stir frying is common in some cuisines, especially in Chinese cooking. Changes of volatile compounds in oils after deep-fat frying or stir frying and subsequent storage were studied (Wu and Chen, 1992). Soybean oil was heated by deep frying at 200°C for 1 h, with the addition of water, and then stored at 55°C for 26 weeks. All samples contained aldehydes as major volatiles. During heating and storage, total volatiles increased 260- to 1100-fold. However, aldehyde content decreased from 62–87% to 47–67%, while volatile acid content increased from 1–6% to 12–33%. Hexanoic acid increased to 26–350 ppm in the oils after storage. Hexanoic acid has a heavy, acrid-acid, fatty, rancid odor, often described as “sweat-like,” that is responsible for the rancid note. Water addition to deep-fried oils tends to retard the formation of volatile compounds during deep frying. Freshly stir-fried Chinese food has a much better flavor quality than after it is aged. The main change in volatile constituents of stir-fried bell peppers during aging is the production of volatile carbonyl compounds from autoxidative breakdown of unsaturated fatty acids (Wu et al., 1986). Generally, the undesirable flavor qualities of food are associated more closely with lipids than with proteins and carbohydrates. Lipids are responsible for the rancidity of lipid-containing foods. The term warmed-over flavor (WOF) is used to describe the rapid development of oxidized odor in cooked meat upon subsequent holding. The rancid or stale odor becomes readily apparent within 48 h, in contrast to the more slowly developed rancidity that becomes evident only after frozen storage for a period of months. Although WOF was first recognized as occurring in cooked meat, hence its name, it also develops in raw ground meat exposed to air. Overheating of meat protects it against WOF by producing Maillard reaction products possessing antioxidant activity (Pearson and Gray, 1983). Recently, phospholipids, e.g., lecithin, were classified as nutraceutical foods (Colbert, 1998). The off-flavor associated with lecithin produced in fermented dairy products includes 2,4-nonadienal, 2,4-decadienal, and hydrogen peroxide (Suriyaphan et al., 2001). Flavor chemistry of lipid foods has been reviewed and compiled elsewhere in the last decade (Ho and Chen, 1994; Min and Smouse, 1989; Shahidi and Cadwallader, 1997; Shahidi, 1998). 10.3.4.3 Interaction of Lipids in the Maillard Reaction The Maillard reaction and the oxidation of lipids are two of the most important reactions for the formation of aromas in cooked foods. Interactions between lipid oxidation and the Maillard reaction have received less attention, despite the fact that lipids, sugars, and amino acids exist in close proximity in most foods. Lipids, upon exposure to heat and oxygen, are known to decompose into secondary products, including alcohols, aldehydes, ketones, carboxylic acids, and hydrocarbons. Aldehydes and ketones produce heterocyclic flavor compounds reacting with amines and

Flavor Compounds

241

amino acids, via Maillard-type reactions in cooked foods (Shibamoto and Yeo, 1992). Lipid degradation products such as 2,4-decadienal and hexanal can interact with Maillard reaction intermediates to form long-chain alkylpyrazines, as well as other heterocyclic compounds (Farmer and Whitefield, 1993). 10.3.4.4 Extrusion Extrusion cooking is a process whereby foodstuffs of low-moisture content (10–30%) are submitted to the action of heat, pressure, and mechanical shearing for a short time (20 sec to 2 min). Extrusion can have a significant effect on flavor and aroma profiles of food products manufactured through this process, e.g., extrusion of wheat flour products (Hwang et al., 1994). Depending on raw material composition, flavor development during processing may be an important consideration for product quality. Certain mechanisms such as nonenzymatic browning and lipid oxidation are considered to have significant implications in the flavor characteristics of food products. Oxidation and volatility of flavor compounds are important factors to be considered during heating and extrusion cooking at different temperatures and moisture contents. Lipid oxidation products are the major compounds of aroma generation in the extrudates prepared from wheat flour at a high moisture content and low die temperature. By lowering moisture content, lipid degradation compounds decreased, and the Maillard reaction products dominated the flavor profile. The lipid oxidation products significantly increased during storage of samples extruded at low moisture content and high die temperature (Villota and Hawkes, 1988). Retention of aroma compounds during extrusion cooking of different formulations, e.g., starch, starch-caseinate, and biscuit mix, was studied (Sadafian and Crouzet, 1987). Several aroma compounds — limonene, p-cymene, linalool, geraniol, terpenyl acetate, and β-ionone — were added in different ways: water emulsion, oil solution, capsules, or inclusion complexes in β-cyclodextrin. During the extrusion process, the major loss of free volatiles reaches more than 90%. It is controlled by water stripping during the expansion phase of the extrudate. Flavor retention is increased through encapsulation of volatile compounds in natural or artificial walls or as inclusion complexes in β-ionone. 10.3.4.5 Concentration and Other Processes Some foods have special treatment in processing that may affect the composition of volatile components. As an example, in hybrid passion fruit, the presence of about 1–2% starch makes heat processing, i.e., pasteurization and concentration, impossible or impractical, unless the starch is removed before processing. However, the step of removing starch and concentration causes loss of volatile compounds of fruit juice (Kuo et al., 1985).

10.3.5 CHANGES DUE

TO

STORAGE

OF

FOOD PRODUCTS

Food preservation is designed to prevent undesirable changes in food and food products. However, flavor changes in food products during storage occur continuously for processed foods, although the deterioration of flavor quality is not significant in most cases.

242

Chemical and Functional Properties of Food Components

Nonenzymatic reactions that occur during processing and storage of food products are detrimental if foods contain reducing compounds or if these compounds are produced during storage as a result of oxidation, acid hydrolysis, enzymatic reactions, or physicochemical changes. Water mediates the nonenzymatic browning reaction by controlling the liquid phase viscosity; by dissolution, concentration, and dilution of reactants; and by effects on the reaction pathways, due to activation energy limitations in dehydrated foods (Saltmarch et al., 1981). Citrus juice can have the problem of off-flavor formation during processing and storage. Changes in volatile components in aseptically packaged orange juice during storage at room temperatures were monitored. Quantities of several desirable flavor components decreased during storage, while amounts of two undesirable components, α-terpineol and furfural, increased progressively with prolonged storage (Moshonas and Shaw, 1987). The ultrahigh temperature (UHT) processing of milk owes its commercial success to the observation that the rate of destruction of microorganisms increases more rapidly with temperature than the rates of the accompanying color and flavor changes. At very high processing temperatures, high sterility may be achieved with minimal adverse nutritional and chemical effects. However, UHT milk darkens in color during storage. This effect is noticeable after a few months at 20°C. It becomes more pronounced at higher temperatures and longer storage times. The milk also deteriorates in taste. The ε-amino group of lysine in milk proteins may react extensively with lactose through the Maillard reaction before milk develops a marked off-flavor, discoloration, or instability (Moller, 1981). Spray-dried whey may also undergo the problem of browning via the Maillard reaction.

10.4 USE OF FLAVORS IN FOOD INDUSTRY 10.4.1 FUNCTIONAL PROPERTIES

OF

FLAVOR COMPOUNDS

Taste, aroma, texture, and visual appearance play very important parts in the appeal of all prepared foods. Food flavorings are compounded from natural and synthetic aromatic substances. The compounded flavors may or may not be found in nature. Reasons for using flavors in foods include (Giese, 1994a, 1994b): • Flavors can be used to create a totally new taste. This does not happen very often, but some new flavors have been enormously successful, such as those used by Coca-Cola® or Pepsi-Cola®. • Flavoring ingredients may be used to enhance, extend, round cut, or increase the potency of flavors already present. • Processing operations such as heating may cause a loss of flavor, while some flavors already present may need supplementation or strengthening. • Flavor ingredients can simulate other more expensive flavors or replace unavailable flavors. • Flavors may be used to mask less desirable flavors. This function does not imply that flavors are being used to hide spoilage, but rather to cover harsh or undesired tastes naturally present in some processed foods.

Flavor Compounds

243

Recent research has shown that flavor compounds provide not only sensory quality to food, but also other functional properties, including antioxidative activity, antimicrobial activity, and health-promoting functions. The antioxidative activity was found in the essential oils of cloves, nutmeg (Dorman et al., 2000), Terminalia catappa L. leaves (Wang et al., 2000); aroma compounds of soybeans and mung beans (Lee and Shibamoto, 2000); and extracts of several members of the allium genus (Yin and Cheng, 1998). Such aroma compounds may be used to prevent lipid oxidation in food preparation or food processing with health-related properties that are based on their antioxidative activity. Antimicrobial activity was found in the essential oils of various herbs, spices (Firouzi et al., 1998), onions, garlic (Block, 1985), mustard, and horseradish (Delaquis and Mazza, 1995). Ninety-three different commercial essentials oils were screened for activity against 20 Listeria monocytogene strains in vitro; the results correlated with the actual chemical composition of each oil. Strong antimicrobial activity was often correlated with essential oils containing a high percentage of monoterpenes, eugenol, cinnamaldehyde, thymol (Lis-Balchin and Deans, 1997), and isothiocyanates (Delaquis and Mazza, 1995). Flavors with antimicrobial activity can be useful adjuncts in food preservation systems. Moreover, antimutagenic, anticarcinogenic, and antiplatelet activity were found in sulfur-containing compounds of several allium members (Chen et al., 1999).

10.4.2 COLLECTION

OR

PRODUCTION

OF

FLAVORING MATERIALS

10.4.2.1 Natural Flavor Materials The main activities of flavor industries are collection or production of flavoring materials, manufacturing flavor, studies on flavor application, and technical services. The sources, names, characteristics, and major flavor components of natural flavoring materials such as spices, herbs, etc. have been summarized in several books (Arctander, 1960; Furia and Bellanka, 1975; Reineccius, 1994b). A large portion of the constituents in natural flavor materials is not flavor compounds. These nonflavor compounds have to be removed to produce concentrated flavorants. There are two major methods to reach this purpose as follows. Distillation — The essential oils are the distilled fraction of aromatic plants. Most often, they are steam distilled. These oils, which are primarily responsible for the characteristic aroma of the plant material, are generally complex mixtures of organic compounds. For example, during the concentration of citrus juices, a layer of essential oil is formed in the condensate. This oil is called essence oil. Terpenes can be removed from both essential oil and essence oil to obtain folded oil. Some fruit or vegetable distillates containing flavor compounds are called essence. Although no essential oil layer is obtained from vegetable distillate, it is used as a flavoring raw material. Citrus peels, rich in essential oils, are expressed to get coldpressed oils. Solvent Extraction — Essential oils do not contain hydrophilic flavoring components, antioxidants, or pigments. The nonvolatile flavoring constituents of aroma plants are recoverable by extraction. The selection of solvent is limited depending on its toxicity, regardless of whether or not it remains in the final product. Two kinds

244

Chemical and Functional Properties of Food Components

of solvents are used: a polar solvent such as ethanol (e.g., vanillin is soluble in ethanol and therefore this alcohol is used to prepare vanilla bean extract) and a nonpolar solvent such as petroleum ether. Most aroma compounds are oil soluble. Therefore, petroleum ether is used as the solvent to extract plant aroma. The extract, after removal of the solvent, is called concrete. Concrete may contain wax and fatty acids in large proportions and is further purified by ethyl alcohol extraction. The product is called absolute. The nonvolatile flavoring constituents of herbs and spices are recoverable by extraction. In practice, a solvent is chosen that dissolves both the essential oil and the nonvolatiles present. The resulting solvent-free product is known as oleoresin. A disadvantage of the oleoresins is that they are very viscous, making them difficult to handle or mix in processing operations. Several products have been developed into extractives, which are convenient to use and avoid handling problems. Extractives can be dispersed in salt, dextrose, or other carriers to create dry-soluble spices. They may also be dispersed in fats to make fat-based soluble spices. Emulsification of extracts with starches and gums, followed by spray drying, produces encapsulated spices. Solubilization of extracts with glycerol, isopropyl alcohol, and propylene glycol produces liquid-soluble spices (Giese, 1994b). 10.4.2.2 Organic Chemicals Used in Flavorings Organic chemicals used in flavorings include: • Hydrocarbons, such as limonene, pinene, ocimene, α-phellandrene, and β-caryophyllene • Alcohols, such as hexanol, cis-3-hexen-l-ol, geraniol, citronellol, eugenol, and 1-menthol • Aldehydes, such as acetaldehyde, hexanal, 2,4-decadienal, citral, and vanillin • Ketones, such as diacetyl, ionone, and nootkatone • Acids, such as acetic acid, butyric acid, and pyroligenious acid • Esters, such as ethyl acetate, linalyl acetate, ethyl phenyl acetate, and methyl dihydrojasmonate • Lactones, such as γ-nonalactone, δ-decalactone, and γ-undecalactone • Hemiacetals, such as acetaldehyde, diethylacetal and citral dimethyl acetal • Ethers, such as diphenyl oxide and rose oxide • Nitrogen-containing compounds, such as trimethylamine • Sulfur-containing compounds, such as dimethylsulfide, thiolactic acid, and allyl disulfide • Heterocyclic compounds, such as furans, pyrazines, pyridines, and thiazoles The names, chemical structures, physical and sensory properties, and uses have been summarized in several books (Arctander, 1969; Furia and Bellanca, 1975; Reineccius, 1994b). Many organic chemicals being used in flavorings are produced by synthetic methods and are commercially available. More and more natural compounds are used in flavorings, due to the increasing demand for natural flavorings. They are produced or prepared by isolation of the compound from natural sources or by biotechnological methods.

Flavor Compounds

245

Thousands of flavoring raw materials may form a flavor. A large number of the flavoring raw materials are supplied by different manufacturers and stocked. Therefore, a strict quality control system for the flavoring raw materials, as well as the products, is very important.

10.4.3 FLAVOR MANUFACTURING 10.4.3.1 Flavor Compounding From thousands of flavor raw materials, 20–50 items are commonly selected and mixed with different ratios to blend a flavor. This is called flavor compounding, which is a kind of formulation. The raw material may be organic chemicals, essential oils, extracts, oleoresins, or processed flavors. Knowledge of their nature, physical and organoleptic properties, and applications is needed by flavorists. Flavor compounding requires at least 3–5 years of training. How a flavor is formulated and modified is shown using strawberry flavor (Table 10.1). The characteristic notes of strawberry are fruity, sweet, green, and a little bit oily and sour. Ethyl butyrate and methyl cinnamate have a fruity note; cis-3-hexen-l-ol and ethyl hexanoate are green; benzaldehyde and 2,5-methyl-4-hydroxy-3 (2H) furanone are sweet; butyric acid is sour; and γ-undecalactone is oily–fruity. Formula 1 was originally designed for use in cake mix. Therefore, compounds of low boiling points, e.g., ethyl acetate, were not used. The solvent was propylene glycol, which has a boiling point of 187.3°C, so the flavor compound was heat stable. However, the application of this flavor in cake resulted in a sensory characteristic like pineapple, not strawberry. Pineapple is oily, fruity, and sweet. Since butter, sugar, and milk were among the ingredients in the cake mix, oily or fatty and sweet notes were derived from those ingredients. Therefore, formula 1 was modified by reducing the amount of γ−undecalactone, benzaldehyde, and 2,5-dimethyl-4-hydroxy-3 (2H) furanone and increasing the amount of ethyl butyrate, ethyl hexanoate, cis-hexen-l-ol, butyric acid, and methyl cinnamate. The

TABLE 10.1 Formulas of Strawberry Flavors Ingredient Ethyl butyrate Ethyl hexanoate cis-3-Hexen-1-ol Benzaldehyde Butyric acid 2,5-Dimethyl-4-hydroxy-3 (2H) furanone Methyl cinnamate γ-Undecalactone Propylene glycol Total

Formula 1

Formula 2

1.5 1.0 1.0 0.3 0.4 2.0 1.3 0.9 91.6 100.0

3.0 2.0 2.0 0.2 0.8 1.0 2.0 0.5 88.5 100.0

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Chemical and Functional Properties of Food Components

application test showed that formula 2 gave the cake a strawberry flavor, although this modified flavor did not smell like strawberry before application. 10.4.3.2 Process Flavor Process flavors include processed (reaction) flavors, fat flavors, hydrolysates, autolysates, and enzyme modified flavors. Production of dairy flavor by enzyme modification of butterfat is an example (Lee et al., 1986; Manley, 1994), while meat flavor produced by enzymatic reactions has a much longer history. Raw meat has little flavor. Characteristic meat flavor varies with the species of animal and temperature and type of cooking. Both water-soluble and lipid-soluble fractions of meat contribute to meat flavor. The water-soluble components include precursors that upon heating are converted to volatile compounds described as “meaty.” Many desirable meat flavor volatiles are synthesized by heating water-soluble precursors such as amino acids and carbohydrates. The Maillard reaction, including formation of Strecker degradation compounds and interactions between aldehydes, hydrogen sulfide, and ammonia, is important in the formation of the volatile compounds of meat flavor. Theoretically, other kinds of flavors formed during cooking could also be obtained from heat processing. The contingency is the availability of the precursors, which may be too expensive to be isolated from natural raw materials or synthesized. The most practical way to characterize process flavorings is by their starting materials and processing conditions, since the resulting composition of volatiles is extremely complex — comparable to the composition of cooked foods. Process flavorings are produced every day by housewives in kitchens, by food industries during food processing, and by the flavor industry. The International Organization of the Flavor Industry (IOFI) has guidelines for the production and labeling of process flavorings (IOFI, 1990). Some key points are: the reactants are strictly appointed; flavorings, flavoring substances, flavor enhancers, and process flavor adjuncts shall be added only after processing is completed; the processing conditions should not exceed 15 min at 180°C or proportionately longer at lower temperatures; and the pH should not exceed 8.0. Process flavors are very successful in some cases, but unsuccessful in many others. Natural flavor materials such as meat extract or aromatic chemicals may be added to process flavors to enrich some notes or to increase the overall intensity.

10.5 BIOTECHNOLOGICAL PRODUCTION OF FLAVORS 10.5.1 MICROBIAL PRODUCTION

OF

FLAVOR COMPOUNDS

Food products labeled as containing “all natural flavors” have a much higher market price than similar products containing artificial flavors. This preference has led to a strong upsurge in the requirement for natural flavor. The increasing demand for these flavor compounds now exceeds their supply from traditional sources. This has motivated research efforts toward finding alternative, natural ways of obtaining natural flavor compounds. In the United States, the Code of Federal Regulations states that products produced or modified by living cells or their components, including enzymes, can be designated as “natural.” Thus, the use of biotechnological methods using

Flavor Compounds

247

microorganisms, enzymes, and recombinant DNA seems to be a promising economical and enviroment-friendly process for generating natural flavor compounds. Traditional fermentation using microbial activity is commonly used for the production of nonvolatile flavor compounds such as acidulants, amino acids, and nucleotides. The formation of volatile flavor compounds via microbial fermentation on an industrial scale is still in its infancy. Although more than 100 aroma compounds may be generated microbially, only a few of them are produced on an industrial scale. The reason is probably due to the transformation efficiency, cost of the processes used, and our ignorance to their biosynthetic pathways. Nevertheless, the exploitation of microbial production of food flavors has proved to be successful in some cases. For example, the production of γ-decalactone by microbial biosynthetic pathways lead to a price decrease from $20,000/kg to $1,200/kg U.S. Generally, the production of lactone could be performed from a precursor of hydroxy fatty acids, followed by β-oxidation from yeast bioconversion (Benedetti et al., 2001). Most of the hydroxy fatty acids are found in very small amounts in natural sources, and the only inexpensive natural precursor is ricinoleic acid, the major fatty acid of castor oil. Due to the few natural sources of these fatty acid precursors, the most common processes have been developed from fatty acids by microbial biotransformation (Hou, 1995). Another way to obtain hydroxy fatty acid is from the action of LOX. However, there has been only limited research on using LOX to produce lactone (Gill and Valivety, 1997). Vanillin, perhaps the most important aroma compound, occurs in the bean of Vanilla planifolia. At present in the world flavor market, only 0.2% of this compound is extracted from beans; the remainder is produced synthetically. Thus, the production of vanillin via microbial transformation has been the most extensively investigated. Figure 10.1 shows some of the possible routes for the production of natural vanillin by microorganisms. The transformation of the natural stilbene isorhapontin to vanillin is catalyzed by a microbial stilbene dioxygenase. This process has led to many patents (Hadegorn and Kaphammer, 1994). Alternative precursors are eugenol (Washisu et al., 1993) and isoeugenol (Shimoni et al., 2000). However, the bioconversion gave relatively low yields. Direct use of ferulic acid (Figure 10.1 to produce vanillin is perhaps the most promising approach, because this precursor is a constituent of various grasses and crops, and is a product of the microbial oxidation of lignin). An example is the use of sugar beet pulp or maize bran as the source of ferulic acid to produce vanillin using two fungi (Bonnin et al., 2001). However, its recovery as a pure precursor is difficult, and the existence of numerous side reactions may explain the low bioconversion yields.

Isorhapontin Coniferaldehyde Vanillin

Eugenol Ferulic acid

FIGURE 10.1 Proposed pathways for the biosynthesis of vanillin.

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Chemical and Functional Properties of Food Components

Benzaldehyde is the second most important material after vanillin. It is used as an ingredient in cherry and other natural fruit flavors in the flavor industry. Natural benzaldehyde is generally extracted from fruit kernels such as apricots. Nowadays, the fermentation of natural substrates such as phenylalanine offers an alternative route for the biosynthesis of natural benzaldehyde (Moller et al., 1998). However, production via the fermentation process will become commercially acceptable only if sufficient yields can be obtained, which has been difficult until now. Other applications of microorganisms used in the production of flavor compounds are listed in Table 10.2.

TABLE 10.2 Aroma Compounds Produced by Microorganisms Aroma Compounds Acetic acid Diacetyl Geosmin 2-Acetyl-pyrroline Lactone Linalool Benzaldehyde Vanillin 1-Octen-3-ol Jasmonate

Microorganisms Bacteria Bacteria Bacteria Bacteria Yeast Yeast Fungi Fungi Fungi Fungi

10.5.2 ENZYMATIC GENERATION

OF

Reference Sharpell and Stemann, 1979 Cheetham, 1996 Pollak and Berger, 1996 Romanczyk et al., 1995 Benedetti et al., 2001 Welsh, 1994 Fabre et al., 1996 Bonnin et al., 2001 Assaf et al., 1995 Miersch et al., 1993

FLAVOR COMPOUNDS

More than 3000 enzymes have been described in the literature, but only 20 are available for use in commercial processes (Armstrong and Brown, 1994). Lipases, esterases, LOXs, glycosidases, proteases, and nucleases are the major enzymes for flavor generation. Among them, lipases seem to be the most important enzyme in commercial utilization. The lipase-catalyzed reactions include hydrolysis, esterification, and transesterification. The reactions can be performed not only in aqueous systems, but also in organic solvents (Jaegar et al., 1994). Based on these outstanding features, lipases are being increasingly used to synthesize “natural” flavoring materials such as esters (Langrand et al., 1990). (S)-2-Methylbutanoic acid methyl ester, which is known as a major apple and strawberry flavor ingredient, was synthesized using lipase in organic media. The reaction efficiencies among 20 microbial lipases were compared (Kwon et al., 2000). Isoamyl acetate, one of the most employed flavor compounds in the industry, could be produced by using immobilized lipase (Krishna et al., 2001). Lowmolecular-weight esters (LMWEs) are flavoring agents for fruit-based products. Screening 27 commercial lipases showed that enzymes from Candida cylindracea, Pseudomonas fluorescens, and Mucor miehei (immobilized) promoted synthesis of LMWEs in nonaqueous systems (Welsh et al., 1990). The LMWE has also been produced using plant seedling lipase (Liaquat and Apenten, 2000).

Flavor Compounds

249

A green note is present in a wide variety of fresh leaves, vegetables, and fruits. The characteristic aroma compounds responsible for the green note include trans2-hexenol, cis-2-hexenol, trans-3-hexenol, cis-3-hexenol (leaf alcohol), hexanol, hexanal, and cis-2-hexenal (Whitehead et al., 1995). These compounds are biosynthetically produced using LOX pathway enzymes as reported (Hatanaka, 1993; Fabre and Goma, 1999). The commercial processes for generating green odor compounds have been established using LOX pathway enzymes as shown in Figure 10.2. Four major enzymes — lipolytic enzyme, LOX, hydroperoxide lyase (HPLS), and alcohol dehydrogenase (using baker yeast as a source) — are involved in the formation of green odor compounds (Hatanaka, 1993). Lipids — commercial soybean oil or vegetable oil — are hydrolyzed to fatty acid by lipolytic enzymes. Fatty acid 13-hydroperoxides are formed from the action of a specific LOX and then cleaved by HPLS into C6-green odor compounds. Among the various sources containing LOX activity, soybeans (Gardner, 1989), peas (Chen and Whitaker, 1986), tomatoes (Riley et al., 1996), potatoes (Galliard and Phillips, 1971), cucumbers (Hornostaj and Robinson, 1999), and microorganisms (Bisakowski et al., 1997) are worth mentioning. HPLS is not available in commercial sources. It is used as a vegetable homogenate. Mungbean seedlings (Rehbock et al., 1998) and guava (Tijet et al., 2000) show higher HPLS activity than several other sources in producing green odor. Continous generation of green odor volatiles using a bioreactor immobilized with LOX and HPLS is being investigated (Cass et al., 2000).

10.5.3 RECOMBINANT DNA TECHNOLOGY FOR FLAVOR FORMATIONS The application of recombinant DNA technology in the flavor industry is less advanced than it is in the pharmaceutical and food industries. However, this technology seems to have the most potential in future research. Nowadays, the recomlipid lipolytic enzyme

linoleic acid

linolenic acid

lipoxygenase

13-hydroperoxide

13-hydroperoxide

hydroperoxide lyase

cis-3-hexanal

hexanal alcohol dehydrogenase

hexenol

isomerase

trans-2-hexanal

alcohol dehydrogenase

cis-3-hexenol

alcohol dehydrogenase

trans-2-hexenol

FIGURE 10.2 Formation of green odor compounds via lipoxygenase pathway enzymes.

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Chemical and Functional Properties of Food Components

binant DNA technology is being increasingly used in several areas, including the production of aroma chemicals, improvement of flavor profiles through genetic engineering, removal of off-flavors, and enzymatic formation of flavor aldehyde (Muheim, 1998). Fermentative or enzymatic processes are used to produce many flavor compounds. However, most of the above-mentioned techniques have been only reasonably applied so far, due to the fact that production of aroma chemicals in generally very small amounts is making their recovery an expensive endeavor. Recombinant DNA technology is helping to achieve efficient production of flavor compounds. A good example is the production of green note compounds via LOX pathway enzymes. Many plant LOXs from soybean seeds (Steczko et al., 1991), pea seeds (Hughes et al., 1998), and potato tubers (Royo et al., 1996), and hydroperoxide lyases from guava (Tijet et al., 2000), alfalfa (Noordermeer et al., 2000), and peppers (Matsui et al., 1996) have been cloned and expressed in Escherichia coli or yeast. The green note compounds produced from such recombinant yeast cells bearing enzyme genes are identical to those from the native enzymes. In addition, higher amounts of flavor compounds (such as leaf alcohol) have been produced in the presence of such recombinant enzymes than in the presence of native enzymes.

10.6 APPLICATIONS OF FLAVORS In food processing, choosing the right type of flavor, dosage, and method of adding the flavor is important in flavor applications. A flavor can be admired only after suitable application. Due to different application conditions, flavors are made to have different characteristics, e.g., solubility in water or oil, or heat stability or unstability, to meet the requirements. There is no general rule for flavor application. Flavor users should have some basic knowledge of flavor, food chemistry, and processing and then they can handle flavor applications work very well. For example, citral is the key compound of lemon flavor. If the flavor has undergone thermal treatment severe enough to let it be oxidized, then the hemiacetal form can be added to replace citral and cause changes in flavor. Limonene is a major constituent in citrus oils. It has to be removed to prevent off-flavor production in food processing and storage. The extent of evaporation loss of each flavor ingredient is different in food processing. Some food components such as starch, lipids, and proteins can trap flavor compounds and reduce their volatilities. Some foods have their own flavors or flavor production. Therefore, modification of flavor formulas is needed to meet the identity of different processed foods. Studies on flavor application for each food product are required to find the right strength, form, and step. Technical supports to flavor users are standard services provided by flavor makers. Flavors can be used to develop new food products. At the 1995 IFT Food Expo, flavor manufacturers created unique berry flavors that do not exist naturally and are more exciting than ever. Mayberry, pepperberry, juneberry, mountainberry, bugleberry, and bellberry were all fabricated by creative flavor manufacturers (Sloan, 1995). Creating new flavors for innovative flavor applications is a challenge to the flavor industry, thus leading to the development of more and new quality food products for quality living.

Flavor Compounds

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REFERENCES Ames, J.M. and Hincelin, O., Novel sulfur compounds from heated thiamine and xylose/thiamine model systems, in Progress in Flavor Precursor Studies, Schreier, P. and Winterhalter, P., Eds., Allured Publishing Corp., Carol Stream, IL, 1992, p. 379. Arctander, S., Perfume and Flavor Materials of Natural Origin, 1960, available from Maria G. Arctander, 6665 Valley View Blvd., Las Vegas, NV 89118. Arctander, S., Perfume and Flavor Chemicals, published by author, 1969, available from Maria G. Arctander, 6665 Valley View Blvd., Las Vegas, NV 89118. Armstrong, D.W. and Brown, L.A., Aliphatic, aromatic and lactone compounds, in Bioprocess Production of Flavor, Fragrance and Color Ingredients, Gabelman, A., Ed., Wiley, New York, 1994. Assaf, S., Hadar, Y., and Dosoretz, C.G., Biosynthesis of 13-hydroperoxylinoleate, 10-oxo8-decenoic acid and 1-octen-3-ol from linoleic acid by a mycelial-pellet homogenate of Pleurotus pulmonarius, J. Agric. Food Chem., 43, 2173, 1995. Benedetti, F. et al., Synthesis of all stereoisomers of cognac lactones via reduction and enzymatic resolution strategies, Tetrahedron: Asymmetry, 12, 505, 2001. Bisakowski, B., Perraud, X., and Kermasha, S., Characterization of hydroperoxides and carbonyl compounds obtained by lipoxygenase extracts of selected microorganisms, Biosci. Biotech. Biochem., 61, 1262, 1997. Block, E., The chemistry of garlic and onions, Sci. Am., 252, 114, 1985. Block, E. and Calvey, E.E., Facts and artifacts in allium chemistry, in Sulfur Compounds in Foods, Mussinan, C.J. and Keelan, M.E., Eds., American Chemical Society, Washington, D.C., 1994, p. 63. Bonnin, E. et al., Aspergillus niger I-1472 and Pycnoporus cinnabarinus MUCEL 39533, selected for the biotransformation of ferulic acid to vanillin, are also able to produce cell wall polysaccharide-degrading enzymes and feruloyl esterases, Enzyme Microb. Technol, 28, 70, 2001. Buckholz, L.L., Maillard technology as applied to meat and savory flavors, in Thermal Generation of Aromas, Parliment, T.H., McGorrin, R.J.M., and Ho, C.-T., Eds., American Chemical Society, Los Angeles, 1988, p. 406. Buttery, R.G. and Ling, L., Enzymatic production of volatiles in tomatoes, in Progress in Flavor Precursor Studies, Schreier, P. and Winterhalter, P., Eds., Allured Publishing Corp., Carol Stream, IL, 1992, p. 137. Cass, B.J. et al., Production of tomato flavor volatiles from a crude enzyme preparation using a hollow-fiber reactor, Biotechnol. Bioeng., 67, 372, 2000. Chang, C.H., Chung, C.C., and Wu, C.M., Volatile components of various shiitake products (Lentinus edodes Sing), Food Sci. (Taiwan), 18, 199, 1991. Cheetham, P.S.J., Combining the technical push and the business pull for natural flavors, in Biotechnology of Aroma Compounds, Berger, R.G., Ed., Springer, Berlin, 1996, p. 3. Chen, A.O. and Whitaker, J.R., Purification and characterization of a lipoxygenase from immature English peas, J. Agric. Food Chem., 34, 203, 1986. Chen, C.C. et al., Effects of pH value on the formation of volatiles of shiitake (Lentinus edodes), an edible mushroom, J. Agric. Food Chem., 32, 999, 1984. Chen, C.C. and Wu, C.M., Studies on the enzymic reduction of 1-octane-3-one in mushroom (Aragicus bisporus), J. Agric. Food Agric., 32, 1342, 1984. Chen, Y. et al., Process-induced health-promoting substance in foods, Food Rev. Int., 15, 473, 1999. Colbert, L.B., Lecithins tailored to your emulsification needs, Cereal Foods World, 43, 686, 1998.

252

Chemical and Functional Properties of Food Components

de Kok, P.M.T. and Rosing, E.A.E., Reactivity of peptides in the Maillard reaction, in Thermally Generated Flavors: Maillard, Microwave and Extrusion Process, Parliment, T.H., Ed., American Chemical Society, Washington, D.C., 1994, p. 158. de Roos, K.B., Meat flavor generation from cysteine and sugars, in Flavor Precursors, Teranishi, R. et al., Eds., American Chemical Society, Washington, D.C., 1992, p. 203. Delaquis, P.J. and Mazza, G., Antimicrobial properties of isothiocyanates in food preservation, Food Technol., 11, 73, 1995. Dorman, H.J.D. et al., In vitro evaluation of antioxidant activity of essential oils and their components, Flavour Fragr. J., 15, 12, 2000. Fabre, C. and Goma, G., A review of the production of green notes, Perfumer Flavorist, 24, 1, 1999. Fabre, C.E., Blanc, P.J., and Goma, G., Production of benzaldehyde by several strains of Ischnoderma benzoinum, Sci. Aliment., 16, 61, 1996. Farmer, L.J. and Whitefield, F.B., Aroma compounds formed from the interaction of lipid in the Maillard reaction, in Progress in Flavor Precursor Studies, Schreier, P. and Winterhalter, P., Eds., Allured Publishing Corp., Carol Stream, IL, 1993, p. 387. Firouzi, R., Azadbakht, M., and Nabinedjad, A., Anti-listerial activity of essential oils of some plants, J. Appl. Anim. Res., 14, 75, 1998. Furia, T.E. and Bellanca, N., Fenaroli’s Handbook of Flavor Ingredients, 2nd ed., CRC Press, Cleveland, OH, 1975. Galliard, T. and Matthew, J.A., Lipoxygenase-mediated cleavage of fatty acids to carbonyl fragments in tomato fruits, Phytochemistry, 16, 339, 1977. Galliard, T. and Phillips, D.R., Lipoxygenase from potato tubers, Biochem. J., 124, 431, 1971. Gardner, H.W., Soybean lipoxygenase-1 enzymatically forms both (9S)- and (13S)-hydroperoxides from linoleic acid by a pH-dependent mechanism, Biochim. Biophys. Acta, 1001, 274, 1989. Giese, J., Modern alchemy: use of flavors in food, Food Technol., 116, 106, 1994a. Giese, J., Spices and seasoning blends: a taste for all seasons, Food Technol., 98, 88, 1994b. Gill, I. and Valivety, R., Polyunsaturated fatty acids, part 2: biotransformations and biotechnological application, Tibtech, 15, 470, 1997. Grechkin, A., Recent developments in biochemistry of the plant lipoxygenase pathway, Prog. Lipid Res., 37, 317, 1998. Gunata, Z. et al., Role of enzymes in the use of the flavor potential from grape glycosides in wine-making, in Progress in Flavor Precursor Studies, Schreier, P. and Winterhalter, P., Eds., Allured Publishing Corp., Carol Stream, IL, 1992, p. 219. Guntert, M. et al., New aspects of the thermal generation of flavor compounds from thiamine, in Progress in Flavor Precursor Studies, Schreier, P. and Winterhalter, P., Eds., Allured Publishing Corp., Carol Stream, IL, 1992, p. 361. Guntert, M. et al., Thermal degradation of thiamine (Vitamin B1), in Sulfur Compounds in Foods, Mussinan, C.J. and Keelan, M.E., Eds., American Chemical Society, Washington, D.C., 1994, p. 199. Hadegorn, S. and Kaphammer, B., Microbial biocatalysis in the generation of flavor and fragrance chemicals, Annu. Rev. Microbiol., 48, 773, 1994. Harlander, S., Biotechnology for the production of flavoring materials, in Source Book of Flavors, Reineccius, G., Ed., Chapman & Hall, New York, 1994, p. 155. Hatanaka, A., The biogeneration of green odour by green leaves, Phytochemistry, 34, 1201, 1993. Ho, C.T. and Chen, Q., Lipids in food flavors, an overview, in Lipids in Food Flavors, Ho, C.T. and Hartman, T.G., Eds., American Chemical Society, Washington, D.C., 1994, p. 2.

Flavor Compounds

253

Ho, C.T. et al., Peptides as flavor precursors in Maillard reactions, in Flavor Precursors, Teranishi, R., Takeoka, G.R., and Guntert, M., Eds., American Chemical Society, Washington, D.C., 1992, p. 193. Hornostaj, A.R. and Robinson, D.S., Purification of hydroperoxide lyase from cucumbers, Food Chem., 66, 173, 1999. Hou, C.T., Microbial oxidation of unsaturated fatty acids, Adv. Appl. Microbiol., 41, 1, 1995. Hsieh, R.J. and Kinsella, J.E., Lipoxygenase generation of specific volatile flavor carbonyl compounds in fish tissues, J. Agric. Food Chem., 37, 280, 1989. Hsu, J.P., Jeng, J.G., and Chen, C.C., Identification of a novel S-compound from the interaction of garlic and heated edible oil, in Progress in Flavor Precursor Studies, Schreier, P. and Winterhalter, P., Eds., Allured Publishing Corp., Carol Stream, IL, 1993, p. 391. Hu, S.P. and Pan, B.S., Aroma modification of fish oil using macro algae lipoxygenase, J. Am. Oil Chem. Soc., 77, 343, 2000. Hughes, R.K. et al., Characterization of authentic recombinant pea seed lipoxygenase with distinct properties and reaction mechanisms, Biochem. J., 333, 33, 1998. Hwang, H.I. et al., Aroma generation in extruded and heated wheat flour, in Lipids in Food Flavors, Ho, C.T. and Hartman, T.G., Eds., American Chemical Society, Washington, D.C., 1994, p. 144. International Organization of the Flavor Industry, IOFI guidelines for the production and labeling of process flavorings, in Code of Practice for the Flavor Industry, 2nd ed., International Organization of the Flavor Industry, Geneva, 1990, p. F1. Izzo, H.V., Yu, T.-H., and Ho, C.-T., Flavor generation from the Maillard reaction of peptides and proteins, in Progress in Flavor Precursor Studies, Schreier, P. and Winterhalter, P., Eds., Allured Publishing Corp., Carol Stream, IL, 1992, p. 315. Jaegar, K.E. et al., Bacterial lipases, FEMS Microbiol. Rev., 15, 29, 1994. Kim, S.M. et al., Effect of soybean oil on garlic volatile compounds isolated by distillation, J. Agric. Food Chem., 43, 449, 1995. Kobyashi, A. et al., Glycosides in fresh tea leaves: precursors of black tea flavor, in Progress in Flavor Precursor Studies, Schreier, P. and Winterhalter, P., Eds., Allured Publishing Corp., Carol Stream, IL, 1992, p. 257. Kringer, U. and Berger, R.G., Biotechnological production of flavours and fragrances, in Appl. Microbiol. Technol., 49, 1, 1998. Krishna, S.H. et al., Enzymatic synthesis of isoamyl acetate using immobilized lipase from Rhizomucor miehei, J. Biotechnol., 87, 193, 2001. Kuo, J.M. and Pan, B.S., Effect of lipoxygenase on formation of cooked shrimp flavor compound: 5, 8, 11-tetradecatriene-2-one, Agric. Biol. Chem., 55, 847, 1991. Kuo, J.M. et al., 1994. Identification of 12-lipoxygenase in the hemolymph of tiger shrimp (Penaeus japonicus Bate), J. Agri. Food Chem., 42, 1620, 1994. Kuo, M.C. et al., Changes in volatile components of passion fruit juice as affected by centrifugation and pasteurization, J. Food Sci., 50, 1208, 1985. Kwon, D.Y., Hong, Y.J., and Yoon, S.H., Enantiomeric synthesis of (S)-2-methylbutanoic acid methyl ester, apple flavor, using lipases in organic solvent, J. Agric. Food Chem., 48, 524, 2000. Langrand, G.R. et al., 1990. Short chain flavor esters synthesis by microbial lipases, Biotechnol. Lett., 12, 581, 1990. Lawrence, B.M., Essential oil production: a discussion of influencing factors, in Biogeneration of Aromas, Parliment, T.H. and Croteau, R., Eds., American Chemical Society, Washington, D.C., 1986, p. 363. Lee, K.G. and Shibamoto, T., Antioxidant properties of aroma compounds isolated from soybeans and mung beans, J. Agric. Food Chem., 48, 4290, 2000.

254

Chemical and Functional Properties of Food Components

Lee, K.M. et al., Production of a romano cheese flavor by enzymic modification of butterfat, in Biogeneration of Aromas, Parliment, T.H. and Croteau, R., Eds., American Chemical Society, Washington, D.C., 1986, p. 370. Lee, M.H. et al., Flavor components and qualities of Oolong tea, J. Food Sci. (Taiwan), 11, 126, 1984. Liaquat, M. and Apenten, R.K.O., Synthesis of low molecular weight flavor esters using plant seedling lipases in organic media, J. Food Sci., 65, 295, 2000. Lis-Balchin, M. and Deans, S.G., Bioactivity of selected plant essential oils against Listeria monocytogenes, J. Appl. Microbiol., 82, 759, 1997. Manley, C., Process flavors, in Source Book of Flavors, Reineccius, G., Ed., Chapman & Hall, New York, 1994, p. 139. Martins, S.I.F.S., Jongen, W.M.F., and van Boekel, M.A.J.S., A review of Malliard reaction in food and implications to kinetic modelling, Trends Food Sci. Technol., 11, 364, 2001. Matsui, K. et al., Bell pepper fruit fatty acid hydroperoxide lyase is a cytochrome P450 (CYP74B), FEBS Lett., 394, 21, 1996. Miersch, O. et al., Jasmonates from different fungal species, Nat. Pro. Lett., 2, 293, 1993. Min, D.B. and Smouse, T.H., Flavor Chemistry of Lipid Foods, American Chemical Society, Champaign, IL, 1989. Moller, A.B., Chemical changes in ultra heat treated milk during storage, in Maillard Reactions in Food, Ericksson, C., Ed., Pergamon Press, Oxford, 1981, p. 357. Moller, J.K.S., Hinrichsen, L.L., and Anderson, H.J., Formation of amino acid (L-leucine, Lphenylalanine) derived volatile flavor compounds by Moraxella phenylpyruvica and Staphylococcus xylosus in cured meat model system, Int. J. Food Microbiol., 42, 101, 1998. Moshonas, M.G. and Shaw, P.E., Flavor evaluation of fresh and aseptically packaged orange juice, in Frontiers of Flavor, Charalambous, G., Ed., Elsevier Science Publishing, Amsterdam, 1987, p. 133. Mottram, D.S. and Salter, L.J., Flavor formation in meat-related Maillard systems containing phospholipids, in Thermal Generation of Aromas, Parliment, H., McGorrin, J.M., and Ho, C.T., Eds., American Chemical Society, Los Angeles, 1988, p. 442. Muheim, A., The impact of recombinant DNA technology on the flavor and fragrance industry, Perfumer Flavorist, 23, 21, 1998. Nagy, S. and Shaw, P.E., Factors affecting the flavor of citrus fruit, in Food Flavours: Part C. The Flavor of Fruits. Morton, I.D. and Macleod, A.J., Eds., Elsevier Science Publishing, Amsterdam, 1990, p. 93. Noordermeer, M.A. et al., Characterization of three cloned and expressed 13-hydroperoxide lyase isoenzymes from alfalfa with unusual N-terminal sequences and different enzyme kinetics, Eur. J. Biochem., 267, 2473, 2000. Ouweland, G.A.M., Demole, E.P., and Enggist, P., Process meat flavor development and the Maillard reaction, in Thermal Generation of Aromas, Parliment, H., McGorrin, J.M., and Ho, C.T., Eds., American Chemical Society, Los Angeles, 1988, p. 433. Pan, B.S. and Kuo, J.M., Flavor of shellfish and kamboko flavorants, in Seafoods: Chemistry, Processing Technology and Quality, Shahidi, R. and Botta, J.R., Eds., Blackie Academic and Professional, Glasgow, 1994, p. 85. Pan, B.S. and Lin, C.M., Aroma formation in dried mullet roe as affected by lipoxygenase, in Flavor and Chemistry of Ethnic Foods, Shahidi, F. and Ho, C.T., Eds., Plenum Publishing Co., 1999, p. 251. Pangborn, R.M., A critical review of threshold, intensity and descriptive analysis in flavor research, in Flavor ’81, Schreier, P., Ed., Walter de Gruyter, Berlin, 1981, p. 1.

Flavor Compounds

255

Pearson, A.M. and Gray, J.I., Mechanism responsible for warmed-over flavor in cooked meat, in The Maillard Reaction in Foods and Nutrition, Waller, G.R. and Feather, M.S., Eds., American Chemical Society, Washington, D.C., 1983, p. 287. Pollak, F.C. and Berger, R.G., Geosmin and related volatiles in bioreactor-cultured Streptomyces citreus CBS 109.60, Appl. Environ. Microbiol., 62, 1295, 1996. Pruthi, J.S., Spices and Condiments: Chemistry, Microbiology, Technology, Academic Press, London, 1980, p. 44. Rehbock, B., Ganber, D., and Berger, R.G., Efficient generation of 2E-hexenal by a hydroperoxide lyase from mung bean seedlings, Food Chem., 63, 161, 1998. Reineccius, G., Source Book of Flavors, Reineccius, G., Ed., Chapman & Hall, New York, 1994a, p. 63. Reineccius, G., Natural flavoring materials, in Source Book of Flavors, Reineccius, G., Ed., Chapman & Hall, New York, 1994b, p. 176. Riley, J.C.M., Willemot, C., and Thompson, J.E., Lipoxygenase and hydroperoxide lyase activities in ripening tomato fruit, Postharvest Biol. Tech., 7, 97, 1996. Romanczyk, L.J. et al., Formation of 2-acetyl pyrroline by several Bacillus cereus strains isolated from cocoa fermentation boxes, J. Agric. Food Chem., 43, 469, 1995. Royo, J. et al., Characterization of three potato lipoxygenases with distinct enzymatic activities and different organ-specific and wound-regulated expression patterns, J. Biol. Chem., 271, 21012, 1996. Sadafian, A. and Crouzet, J., Aroma compounds retention during extrusion cooking, in Frontiers of Flavor, Charalambous, G., Ed., Elsevier Science Publishing, Amsterdam, 1987, p. 623. Salinas, J.P. et al., Lipid derived aroma compounds in cooked potatoes and reconstituted dehydrated potato granules, in Lipids in Food Flavors, Ho, C.T. and Hartman, T.G., Eds., American Chemical Society, Washington, D.C., 1994, p. 108. Saltmarch, M., Vagnini-Ferrari, M., and Labuza, T.P., Theoretical basis and application of kinetics to browning in spray-dried whey food systems, in Maillard Reactions in Food, Eriksson, C., Ed., Pergamon Press, Oxford, 1981, p. 331. Schreier, P. and Lorenz, G., Formation of “green-grassy” notes in disrupted plant tissues: characterization of the tomato enzyme systems, in Flavour ’81, Schreier, P., Ed., Walter de Gruyter, Berlin, 1981, p. 495. Schreier, P. and Winterhalter, P., Precursors of papaya (Carica papaya, L.) fruit volatiles, in Biogeneration of Aromas, Parliment, T.H. and Croteau, R., Eds., American Chemical Society, Washington, D.C., 1986, p. 85. Shahidi, F., Flavor of Meat, Meat Products and Seafoods, 2nd ed., Blackie Academic and Professional, London, 1998. Shahidi, F. and Cadwallader, K.R., Flavor and Lipid Chemistry of Seafoods, ACS Symposium Series 674, American Chemical Society, Washington, D.C., 1997. Sharpell, F. and Stemann, C., Development of fermentation media for the production of butyric acid, in Advance in Biotechnology, Vol. II, Moo-Young, M., Ed., Pergamon, Toronto, 1979, p. 71. Shi, H. and Ho, C.T., The flavor of poultry meat, in Flavor of Meat and Meat Products, Shahidi, R., Ed., Blackie Academic and Professional, London, 1994, p. 52. Shibamoto, T. and Yeo, H., Flavor compounds formed from lipids by heat treatment, in Flavor Precursors Thermal and Enzymatic Conversions, Teranishi, R. et al., Eds., American Chemical Society, Washington, D.C., 1992, p. 175. Shimoni, E., Ravid, U., and Shoham, Y., Isolation of a Bacillus sp. capable of transforming isoeugenol to vanillin, J. Biotechol., 78, 1, 2000.

256

Chemical and Functional Properties of Food Components

Sinki, S., Assaf, R., and Lombarco, J., Flavor changes: a review of the principal causes and reactions, Perfumer Flavorist, 22, 23, 1997. Sloan, A.E., Ingredients add more fun, flavor, freshness and nutrition, Food Technol., 16, 102, 1995. Steczko, J. et al., Effect of ethanol and low temperature culture on expression of soybean lipoxygenase L-1 in Escherichia coli, Prot. Express. Purif., 2, 221, 1991. Straus, C.R. et al., Role of monoterpenes in grape and wine flavor, in Biogeneration of Aromas, Parliment, T.H. and Croteau, R., Eds., American Chemical Society, Washington, D.C., 1986, p. 222. Suriyaphan, O., Cadwallader, K.R., and Drake, M.A., Lecithin associated off-aromas in fermented milk, J. Food Sci., 66, 517, 2001. Takeoka, G.R. et al., Free and bound flavor constituents of whitefleshed nectarines, in Flavor Precursors Thermal and Enzymatic Conversions, Teranishi, R., Takeoka, G.R., and Guntert, M., Eds., American Chemical Society, Washington, D.C., 1992, p. 116. Teranishi, R., Buttery, R.G., and Guadagni, D.G., Some properties of odoriferous molecules, in Flavor ’81, Schreier, P., Ed., Walter de Gruyter, Berlin, 1981, p. 133. Tijet, N. et al., Purification, molecular cloning and expression of the gene encoding fatty acid 13-hydroperoxide lyase from guava fruit (Psidium guajava), Lipid, 35, 709, 2000. Tressl, R., Bahri, D., and Engel, K.-H., Formation of eight-carbon and ten-carbon components in mushrooms (Agaricus campestris), J. Agric. Food Chem., 30, 89, 1982. Vill, I. and Valivety, R., Polyunsaturated fatty acids, part 2: biotransformations and biotechnological applications, Tibtech, 15, 470, 1997. Villota, R. and Hawkes, J.G., Flavoring in extrusion, an overview, in Thermally Generated Flavors: Maillard, Microwave, and Extrusion Processes, Parliment, T.H., Ed., American Chemical Society, Washington, D.C., 1988, p. 280. Wang, H.F. et al., Composition and antioxidative activity of essential oil from Terminalia catappa L. leaves, Taiwanese J. Agric. Chem. Food Sci., 38, 27, 2000. Washisu, Y. et al., Manufacture of Vanillin and Related Compounds with Pseudomonas, Japanese Patent 52279, 1993. Welsh, F.W., Overview of bioprocess flavor and fragrance production, in Bioprocess Production of Flavor, Fragrance, and Color Ingredients, Gabelman, A., Ed., Wiley, New York, 1994, p. 1. Welsh, F.W., Williams, R.E., and Dawson, K.H., Lipase mediated synthesis of low molecular weight flavor esters, J. Food Sci., 55, 1679, 1990. Whitehead, I.M., Muller, B.L., and Dean, C., Industrial use of soybean lipoxygenase for the production of natural green note flavor compounds, Cereal Foods World, 40, 193, 1995. Wu, C.M. and Chen, S.Y., Volatile compounds in oils after deep frying or stir frying and subsequent storage, JAOCS, 69, 858, 1992. Wu, C.M. and Liou, S.E., Effect of tissue disruption on volatile constituents of bell peppers, J. Agric. Food Chem., 34, 770, 1986. Wu, C.M. and Liou, S.E., Volatile components of water-boiled duck meat and Cantonese style roasted duck, J. Agric. Food Chem., 40, 838, 1992. Wu, C.M., Liou, S.E., and Chiang, W., Volatile compounds of the wax gourd (Benincasa hispida, Cogn) and a wax gourd beverage, J. Food Sci., 52, 132, 1987. Wu, C.M., Liou, S.E., and Wang, M.C., Changes in volatile constituents of bell peppers immediately and 30 minutes after stir frying, JAOCS, 63, 1172, 1986. Wurzenberger, M. and Grosch, W., The enzymic oxidative breakdown of linoleic acid in mushrooms (Psalliota bispora), Z. Lebensm. Unters. Forsch., 175, 186, 1982.

Flavor Compounds

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Yamaguchi, M. and Wu, C.M., Composition and nutritive value of vegetables for processing, in Commercial Vegetable Processing, Luh, B.S. and Woodroof, J.G., Eds., AVI Publishing Company, Inc., Westport, CT, 1975, p. 652. Yin, M.C. and Cheng, W.S., Antioxidant activity of several Allium members, J. Agric. Food Chem., 46, 4097, 1998. Yoo, S.S. and Ho, C.T., Pyrazine generation from the Malliard reaction of mixed amino acids in model systems, Perfumer Flavorist, 22, 49, 1997. Yu, T.H. and Wu, C.M., Stability of allicin in garlic juice, J. Food Sci., 54, 977, 1989. Yu, T.H., Wu, C.M., and Ho, C.T., Volatile compounds of deep-oil fried, microwave-heated, and oven-baked garlic slices, J. Agric. Food Chem., 41, 800, 1993. Yu, T.H., Wu, C.M., and Ho, C.T., Meat-like flavor generated from thermal interactions of glucose and alliin or deoxyalliin, J. Agric. Food Chem. 42, 1005, 1994. Yu, T.H., Wu, C.M., and Liou, Y.C., Volatile compounds from garlic, J. Agric. Food Chem., 37, 725, 1989.

11

Probiotics in Food Maria Bielecka

CONTENTS 11.1 Introduction ..................................................................................................259 11.2 Scientific Basis of Probiotic Functionality and Justification of Their Use .................................................................................................260 11.3 Probiotic Strain Selection ............................................................................261 11.4 Probiotic Effects...........................................................................................263 11.4.1 Introduction ......................................................................................263 11.4.2 Intestinal Infections..........................................................................264 11.4.3 Immune Stimulation.........................................................................264 11.4.4 Effect on Nonspecific Immune Responses ......................................264 11.4.5 Effect on Specific Immune Responses ............................................265 11.4.6 Factors that Influence the Efficacy of LAB ....................................266 11.4.7 Future ...............................................................................................266 11.5 Probiotic Foods ............................................................................................266 11.5.1 Food Products Containing Probiotics ..............................................266 11.5.2 Efficacy of Probiotic Products .........................................................267 11.5.3 Safety................................................................................................268 11.5.4 Critical Questions Related to Probiotics .........................................268 11.6 Recommendation for Future Research ........................................................269 References..............................................................................................................269

11.1 INTRODUCTION The increasing consumer awareness that diet and health are linked is stimulating the innovative development of novel products by the food industry. The new products, which should satisfy the consumer needs, are functional foods containing probiotic microorganisms with scientifically supported health claims for improving one’s state of well-being and helping reduce the risk of diseases. Probiotic bacteria are used as the active ingredient in functional foods, most frequently in bioyogurt, and also in dietary adjuncts and health-related products. The health benefits attributed to probiotic bacteria can be categorized as either nutritional benefits or therapeutic benefits. The term probiotic is derived from the Greek language and means “for life.” It was first used by Lilly and Stillwell (1965) to describe “substances secreted by one microorganism which stimulated the growth of another” and thus was contrasted with the term antibiotic. After several modifications, Schrezenmeir and de Vrese (2001) 1-5871-6149-4/02/$0.00+$1.50 © 2002 by CRC Press LLC

259

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proposed the following definition of probiotics: “A preparation of or a product containing viable, defined microorganisms in sufficient numbers, which alter the microflora (by implantation or colonization) in a compartment of the host and by that exert beneficial health effects in this host.” This definition confines the probiotic concept to effects produced by viable microorganisms, but is application independent of the probiotic site of action and route of administration. Therefore, this definition may include such sites as the oral cavity, the intestine, the vagina, and the skin. In the case of probiotic foods, the health effect is usually based on alteration of the gastrointestinal (GI) microflora and therefore based on survival during GI transit. Thus the validity of the condition of the appropriate number in the definition is underlined. Although there are numerous probiotic products for human consumption on the market, there is a lot of skepticism regarding their beneficial effects. This has in part been due to some reports of their positive health benefits that have been published with little scientific backup. Furthermore, many of the microorganisms included in these products are not viable and have not been selected either for specific beneficial properties or for their ability to survive in the GI tract. If health claims regarding probiotic bacteria are to be substantiated, it is imperative to establish which strains have been used and from which source they have been obtained.

11.2 SCIENTIFIC BASIS OF PROBIOTIC FUNCTIONALITY AND JUSTIFICATION OF THEIR USE The total mucosal surface area of the adult human GI tract is up to 300 m2, making it the largest body area interacting with the environment. The huge surface would suggest a great capacity for effective absorptive area, for defensive exclusion of infections, and toxic and allergenic material from the internal milieu. The gutassociated lymphoid tissue (GALT) makes the GI tract the largest lymphoid or immune organ in the human body. It has been estimated that there are approximately 1010 immunoglobulin (Ig) (antibody)-producing cells per meter of small bowel, thus accounting for ~80% of all immunoglobulin-producing cells in the body (Targan and Shanahan, 1994). Sterile at birth, the GI tract rapidly acquires a commensal enteric microflora, resulting in the creation of a complex intestinal ecosystem. This microflora adds an additional competitive component to the defense capability through competitive exclusion. It is also essential for mucosal immune education. The balance of this commensal microflora may be altered by physiological changes in endogenous acid and bile secretion, diet and bowel movements, colonization by pathogens, liver or kidney diseases, pernicious anemia, cancer, radiation, oral use of antibiotics or immunosuppressive agents, surgical operations of the GI, immune disorders, and emotional stress. Many of these parameters are influenced by age, particularly in the late decades of life. It is estimated that the intestines of humans contain ~1014 viable bacteria cells; this number is about 10 times higher than that of all eucariotic cells in the human body (Mitsuoka, 1996). The intestinal microflora of healthy humans is confined to the distal ileum and the colon. It consists of over 400 species belonging to about 40

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genera. Most of them are obligatory anaerobic, and some of them attain high population levels. Approximately 30–40 bacterial species constitute 99% of the cultivable fecal microflora of a healthy human. Some of these are present in populations of at least 1010–11 colony forming units (cfu) per gram of feces (wet weight). These live bacteria make up ~30% of the fecal mass. The fecal microflora is a representative of the microflora of the colon. While the numerically predominant genera of bacteria detected in the feces of different individuals are the same, there is variation in the occurrence and population size of bacterial species. Gibson (1998) distributed the gut bacteria into three groups: beneficial (Lactobacillus and Bifidobacterium), harmful (Pseudomonas aeruginosa, Staphylococcus, and Clostridium), and opportunistic (Enterobacteriaceae, Eubacterium, and Bacteroides). In healthy subjects, well-balanced and beneficial bacteria dominate. Beneficial bacteria play useful roles in the aspects of nutrition and prevention of disease. They produce essential nutrients such as vitamins and organic acids, which are absorbed from the intestines and utilized by the gut epithelium and by vital organs such as the liver. Organic acids also suppress the growth of pathogens in the intestines. Other intestinal bacteria produce substances that are harmful to the host, such as toxins and carcinogenic substances. When harmful bacteria dominate in the intestines, essential nutrients are not produced and the level of harmful substances rises. These substances may not have an immediate detrimental effect on the host, but they are thought to be contributing factors to aging, cancer, liver and kidney diseases, hypertension, arteriosclerosis, and reduced immunity. Little is known regarding which intestinal bacteria are responsible for these effects. The normal balance of intestinal flora may be maintained or restored to normal from an unbalanced state by a well-balanced diet or by oral bacteriotherapy. Oral bacteriotherapy, using intestinal strains of lactic acid bacteria (LAB), such as Lactobacillus and Bifidobacterium, can restore normal intestinal balance and produce beneficial effects.

11.3 PROBIOTIC STRAIN SELECTION Although progress in probiotic research has been achieved, not all of the available probiotic bacteria on the market have adequate scientific documentation. If nutritional and health benefits are to be derived from products containing probiotic bacteria, the mechanisms by which these benefits are derived should be understood and those strains demonstrating the most promise in this regard should be used. Consequently, it is necessary to establish rational criteria for screening and selection of candidate microorganisms and also to evaluate the efficacy of the selected strains or food products in well-controlled human dietetic or clinical trials. As a result of the food industry collaboration with scientists and clinicians, supported by EU-funded programs that aim to promote the generation and dissemination of consensus, the following criteria for the selection and assessment of probiotic microorganisms have been established: • Be of human origin • Demonstrate nonpathogenic behavior

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• Exhibit resistance to technological processes (i.e., viability and activity in delivery vehicles) • Prove resistance to gastric acid and bile • Adhere to gut epithelial tissue • Be able to persist in the GI tract • Possess antimicrobial activity • Modulate immune responses • Have the ability to influence metabolic activities (e.g., β-galactosidase activity, vitamin production, and cholesterol assimilation) In addition, these requirements were further expanded by Berg (1998) and Salminen et al. (1996, 1998a), who stated that: • Each potential probiotic strain should be documented. • Extrapolation of data, even from closely related strains, is not acceptable. • Only well-defined strains, products, and study populations should be used in trials. • Where possible, all human studies should be randomized, double blind, and placebo controlled. • Results should be confirmed by independent research groups. • Preferentially, the study should be published in a peer-reviewed journal. In the development of probiotic foods, the strains of LAB such as Lactobacillus and Bifidobacterium have been most commonly used. This is primarily due to the perception that they are desirable members of the intestinal microflora, colonizing the intestines of newborns as one of the first genera (Goldin and Gorbach, 1992; Berg, 1998). In addition, LAB have traditionally been used in the production of fermented dairy products and have “generally recognized as safe” (GRAS) status. The requirement that the strains of probiotic bacteria used should be of human origin is based on the observation that only human strains can be adhesive and colonize the human GI tract, which is the first step in promoting colonization resistance (Huis in’t Veld et al., 1994). It has been proposed that species specificity does occur and for strains to be beneficial to a particular host they should be isolated from that species. This is not well documented. Subsets of probiotic bacteria currently employed in the dairy food industry are not of human origin and therefore do not meet the criteria, as outlined above, for the selection of probiotic microbes acceptable for human consumption. The bifidobacterial strains isolated from market bioyogurt were identified phenotypically and genetically as Bifidobacterium animalis (Roy et al., 1996; Roy and Sirois, 2000; Bielecka et al., 2000a). The results of our studies showed that these strains survived at low pH and bile, and adhered well to Caco-2 and HT-29 cell lines, as well as to colon epithelium of humans and rats (Bielecka et al., 2000b). Additionally, the strains belonging to B. animalis species, either isolated from bioyogurts or from rats and adults consuming bioyogurts, were unusually homogenous. Recently, a Bifidobacterium strain, isolated from market bioyogurt, was classified as Bifidobacterium lactis — the new species genetically most similar to B. animalis (Meile et al., 1997). The name B. lactis has been given for honoring the source of isolation and justifying its

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use in bioyogurt. Cai et al. (2000), comparing B. animalis JCM 1190T and B. lactis JCM 11602T found their phenotypic and genetic similarity: B. animalis and B. lactis were the most closely related species in the phylogenetic tree and showed a high similarity in 16S rRNA sequences (98.8%). The levels of DNA–DNA hybridization between the type strains of B. lactis and B. animalis ranged from 85.5–92.3%, showing that they represent a single species (a genospecies is characterized by a DNA–DNA similarity of more than 70% and a 16S rRNA similarity of more than 95%). The most often isolated Bifidobacterium species from the human colon of adults are B. catenulatum, B. longum, B. adolescentis, B. bifidum, and B. pseudocatenulatum. Rarely isolated are B. angulatum and B. animalis. Among species of Lactobacillus isolated either from human feces or directly from intestinal homogenized mucosa as potentially adherent probiotic bacteria are L. paracasei, L. salivarius, L. acidophilus, L. crispatus, L. gasseri, L. reuteri, L. rhamnosus, and L. plantarum (Molin et al., 1993). No single dominant species was found among the isolates. A critical criterion of selection is that the probiotic strain must be tolerated by the immune system and should not provoke the formation of antibodies against the probiotic. This latter property, in conjunction with the ability of some LAB to survive and colonize in the gut, has given rise to further applications, which involve their use as live vectors for oral immunization, i.e., introducing antigens targeting the GALT and aiming to induce a mucosal immune response (Marteau and Rambaud, 1993). Strain viability and maintenance of desirable characteristics during product manufacture and storage is also a necessity for probiotic strains. The ability to multiply rapidly on relatively cheap nutrients is a distinct advantage, as ease of culturing is important for technical application of the strains. Strain survival depends on such factors as the final product pH, the presence of other microflora, the storage temperature, and the presence or absence of microbial inhibitors in the product. Exploitation of the latest biotechnological advances in culture production, preservation, and storage should aid in maintaining high numbers of probiotic bacteria in products.

11.4 PROBIOTIC EFFECTS 11.4.1 INTRODUCTION A number of benefits in the ingestion of probiotics have been reported. According to Vaughan et al. (1999), the beneficial effects of probiotic strains — demonstrated and proposed — are the following: • Increased nutritional value (better digestibility and increased absorption of minerals and vitamins) • Alleviation of lactose intolerance • Positive influence on intestinal flora • Prevention of intestinal tract infections • Improvement of immune system • Reduction of inflammatory reactions • Prevention of cancer • Antiallergic activity

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• • • •

Regulation of gut motility Reduction of serum cholesterol Prevention of osteoporosis Improved well-being

11.4.2 INTESTINAL INFECTIONS The primary claim regarding probiotics is their beneficial influence on the intestinal ecosystem, which in turn may provide protection against GI infections and inflammatory bowel diseases. The desirable effects on human health include antagonistic activity against pathogens and antiallergenic action and other effects on the immune system. Whereas some of these claims remain controversial, well-planned clinical trials increasingly support them for carefully selected probiotic strains (Ouwehand et al., 1999). Some probiotic strains have been selected as bacteriolytic against Salmonella, Escherichia coli, and Staphylococcus aureus in associated cultures with the pathogens (Bielecka et al., 1998). The strains increased Bifidobacterium population numbers in the colons of both healthy and Salmonella-infected rats and protected the natural balance of intestinal microflora (Bielecka et al., 2002). Bouhnik et al. (1996) and Matsumoto et al. (2000) observed an increase in Bifidobacterium population numbers in feces of healthy volunteers after 2 weeks of bioyogurt consumption. Bifidobacterium species and L. acidophilus administered in milk were effective in reducing Candida and Clostridium difficile occurrences in feces (Corthier et al., 1985). The mechanism by which protection is offered by these probiotics has not yet been fully established. However, one or more of the following are possible: competition for nutrients, secretion of antimicrobial substances, blocking of adhesion sites, attenuation of virulence, blocking of toxin receptor sites, immune stimulation, and suppression of toxin production.

11.4.3 IMMUNE STIMULATION One of the most interesting aspects of probiotic supplementation is directed toward immune responses. Orally administered probiotic strains of LAB exert a positive impact on nonspecific and specific host immune responses. Nonspecific immune responses constitute the first line of host defense.

11.4.4 EFFECT

ON

NONSPECIFIC IMMUNE RESPONSES

The results of many experimental studies (Perdigon and Alvarez, 1992; PaubertBraquet et al., 1995; De Petrino et al., 1995) have shown that the consumption of certain strains of LAB is able to enhance: • Phagocytic activity of peritoneal and pulmonary macrophages and blood leukocytes • Secretion of lysosomal enzymes, reactive oxygen, nitrogen species, and monokines by phagocytic cells • In vivo clearance of colloidal carbon, an indicator of phagocyte function of the reticuloendothelial system

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Similar results have been reported for human subjects. Ingestion of fermented milk containing L. acidophilus LA1 or B. bifidum Bb12 for 3 weeks resulted in increased phagocytic activity of peripheral blood leukocytes (Schiffrin et al., 1997). This increase in phagocytosis was coincidental with colonization by LAB. The results of several animal studies indicate that the ability to enhance phagocyte cell function is strain dependent. Structural differences in cell wall composition of different LAB strains are suggested to be responsible for differences in efficacy. Furthermore, strains that are able to survive in the GI tract, adhere to the gut mucosa, and persist above a critical level are more efficient at stimulating phagocytic cells (Schiffrin et al., 1997). The results of studies of a large number of Bifidobacterium strains belonging to different species showed a large diversity in survival at low pH and bile, and in the adherence to the colon epithelium between strains belonging to the same species, excluding B. animalis, in which the strains were uncommonly homogenous (Bielecka et al., 2000b). These and other results proved the importance of careful probiotic strain selection. Recent studies of Gill (1998) have shown that the magnitude of response also depends on the dose of LAB. Mice receiving a milk-based diet containing 1011 cfu/day of L. rhamnosus HN001 for 10 days showed significantly greater phagocytic activity than mice receiving 109 or 107 LAB.

11.4.5 EFFECT

ON

SPECIFIC IMMUNE RESPONSES

Specific immune responses can be classified into broad categories: humoral immunity (HI) and cellular-mediated immunity (CMI). HI is affected by antibodies produced by plasma cells (mature B lymphocytes) that bind specifically to antigenic epitopes on the surface of pathogenic organisms and with the aid of complement kill these pathogens. Specific classes of antibodies have specific functions. For example, IgA antibodies predominate at the mucosal surfaces and prevent adherence of pathogens to the gut mucosa. IgG and IgM are involved in systemic neutralization of bacterial toxins and promote phagocytosis by monocytes–macrophages via opsonization. Antibodies are effective at neutralizing or eliminating extracellular pathogens and antigens (Gill, 1998)*. CMI is mediated by T lymphocytes. On exposure to an antigen or pathogen, T lymphocytes of predetermined clones proliferate or produce cytokines. Through these cytokines, T cells influence the activities of other immune cells, e.g., by augmenting the ability of macrophages to kill intracellular pathogens and tumor cells. In addition, subsets of T cells act as helper cells (CD4+) for antibody production, as mediators of delayed type hypersensitivity (DTH), or as cytotoxic cells (CD8+) against virus-infected cells and cancer cells. CMI is particularly effective against intracellular pathogens and tumor cells (Gill, 1998). Several studies in experimental animals and humans have demonstrated the immunostimulatory effects of lactic cultures on several aspects of humoral and cellmediated immunity (Nader de Macias et al., 1992; Perdigon et al., 1990; Kaila et al., 1992). Whether the immunoenhancing effects of LAB are related to their immunogenicity is not known. It is well documented that mucosal antibodies prevent the * Reprinted form Int. Dairy J. Vol. 8, pp. 535-544, 1998, El Sevier Science, Oxford, U.K. With permission.

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adherence of pathogenic microorganisms to gut epithelium. It is likely, therefore, that antilactobacilli antibodies in gut secretions may interfere with the ability of LAB to adhere and proliferate in the gut. If adherence and colonization to gut epithelium are essential for LAB to exert beneficial immunoenhancing effects, it will be desirable to select strains that do not elicit an immune response to themselves.

11.4.6 FACTORS

THAT INFLUENCE THE

EFFICACY

OF

LAB

Several factors have an impact on the ability of LAB to influence immune function (Gill, 1998; De Petrino et al., 1995; Paubert-Braquet, 1995; Portier et al., 1993): • A large variation exists in the ability of LAB to affect the immune system. • The effect of LAB on the immune system is dose dependent, with a higher intake of LAB resulting in a superior response, compared with that of a lower intake. • Live cultures are more efficient at enhancing certain aspects of immune function than killed cultures. • Lactic cultures delivered in fermented products induce a superior response, compared to cultures given in unfermented products. There is no information on the efficacy of LAB in relation to host age, physiological status, and dietary intake. All these factors may have an important bearing on the ability of LAB to influence host responses.

11.4.7 FUTURE There is now strong evidence that certain strains of LAB are endowed with the capacity to stimulate both nonspecific and specific immune functions. This highlights the opportunity for the dairy and health food industries to develop novel, valueadding, immunity-enhancing food products. However, many significant gaps remain in our knowledge. Therefore, future studies should be directed at: • • • •

Demonstrating the relevance of immunomodulation to better health Defining the effective dose for each strain Elucidating the mechanisms by which LAB act on the immune system Identifying new strains that are able to inhabit desired anatomical sites in the gut and modulate desired immune functions

11.5 PROBIOTIC FOODS 11.5.1 FOOD PRODUCTS CONTAINING PROBIOTICS Products containing probiotics come in a variety of formats: • Conventional foods: probiotic-containing yogurts, fluid milk, and cottage cheese; consumed primarily for nutritional purposes, but also for probiotic benefits • Food supplements or fermented milks: food formulations whose primary purpose is to be a delivery vehicle for probiotic bacteria and their fermentation

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end products; consumed for health effects, in monoculture (Yakult, Japan), mixed cultures (Actimel, Danone, LC1, Nestle) and others • Dietary supplements: capsules and other formats designed to be taken by healthy individuals to improve health In the development of probiotic-containing food products, the product concept must take into account the desire of consumers for health-enhancing foods, but not at the expense of taste, convenience, and pleasurable nature of product. The ability to communicate messages on health to the consumer is extremely important, e.g., “promotes GI health,” “supports the body’s natural immune function,” but it must be scientifically accurate and in accordance with actual legislation, which may differ from country to country. In addition to communications on health benefits of probiotic products, another important area of communication is on viable count or active ingredients in probiotic products. Statements as to content and counts of bacteria in commercial products are frequently not accurate, claiming the presence of certain genera, species, or strain of probiotic, and rarely harbor any messages on probiotic potency. In countries where there is no legislation requiring this type of labeling, the consumer is unable to make an informed choice based on a guaranteed probiotic content of a food product. In the long run, the failure of the industry to self-regulate in this regard may be its undoing. Consumers, unable to identify a potent product, may find a specific probiotic product ineffective and turn away from the entire product category.

11.5.2 EFFICACY

OF

PROBIOTIC PRODUCTS

Probiotic consumption can be justified only if a health effect or reduction in risk of disease can be realized by the consumer. Substantiation of health effects is a challenge the probiotic industry is now facing, in large part because of the high cost associated with conducting controlled clinical or epidemiological evaluations. These health effects are believed to be genera, species, and strain specific. In many cases controlled studies have not been done; however, a lack of proof has a great influence on the use of health claims. There is no motivation for companies or consumers to invest in technology supported mainly by testimonial, inference, or supposition. Therefore, the clinical evaluation of commercial products must be conducted and is essential for labeling health claims. The few probiotic strains whose effect in human health is supported by clinical evaluations have a legitimate marketing advantage, even though the strains may be no more effective than other, untested bacteria. Salminen et al. (1996) and Fonden et al. (2000) listed the number of variables that must be controlled for clinical evaluation of probiotics: • Strain or combination of strains • Growth conditions of strain • Format for delivery (dried, supplemented in a food product, grown in a food product) • Consumption level of active ingredient • Test population

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• Validated biomarkers in combination with clinical end point • Clinical protocol, with preference to blinded, placebo-controlled formats

11.5.3 SAFETY Although the safety of traditional lactic starter bacteria has never been in question, the more recent use of intestinal isolates of bacteria (bifidobacteria, intestinal lactobacilli, and enterococci), to be delivered as probiotics in high numbers to consumers with potentially compromised health, has raised the question of safety. These intestinal isolates do not share the centuries-old tradition of being consumed as components of fermented dairy products. However, their presence in commercial products over the past few decades has not given any indication of a safety concern. The safety of lactobacilli and bifidobacteria has most recently been reviewed by Salminen et al. (1998b). The general conclusion is that the pathogenic potential of lactobacilli and bifidobacteria is quite low. This is based on the prevalence of these microbes in fermented foods, as commensal colonizers of the human body, and the concomitant low level of infection attributed to them. A report from the LAB Industrial Platform (Guarner and Schaafsma, 1998) indicated that the overall risk of infection from LAB (excluding enterococci) is very low, but that L. rhamnosus deserved particular surveillance, due to the greater proportion of infections attributed to this species, compared with infections by other lactobacilli. One commercial strain of L. rhamnosus, GG, has been used repeatedly in clinical trials and human studies, including one involving enteral feeding of premature infants (Saxelin, 1997). Regarding the safety of enterococci, the picture is less clear. Foods containing enterococci are consumed on a regular basis. However, safety reports seem to agree that the enterococci pose a greater threat than other LAB. Giraffa et al. (1997) concluded that the enterococci, although a group of phenotypically heterogeneous organisms, display potential pathogenic properties. Adams and Marteau (1995) excluded the enterococci from LAB, which they regard as having low pathogenic potential. Enterococci have been isolated from clinical infections: Enterococcusmediated infections of the biliary tract, the abdomen, burn wounds, surgical wounds, and many others (Jett et al., 1994). Often, enterococci are isolated as pure cultures from these infections, showing their primary pathogenic nature (Aquire and Collins, 1993). In the United States, vancomycin-resistant enterococci comprise a worrisome source of nosocomial infections. This forms a serious threat to humans, as it is known that gene transfer between enterococci and related organisms can occur rather easily. In this respect, transfer of the VanA gene from Enterococcus faecium to Staphylococcus aureus has already been observed in vitro (Noble et al., 1992). These observations and contradictory characteristics of enterococci make the use of these microorganisms more and more questionable as food fermentation agents (Arthur et al., 1996).

11.5.4 CRITICAL QUESTIONS RELATED

TO

PROBIOTICS

Sanders and Huis in’t Veld (1999), in their extensive review, outlined the following critical questions related to probiotics:

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• Identification of physiologically relevant biomarkers that can be used to assess parameters of probiotic effectiveness in humans (strain, dose, strain growth, delivery conditions) • Definition of active principle(s) • Stability parameters for active principle(s) • Resolution of taxonomy of probiotic species and development of userfriendly methods for conducting speciation assessments • Science-driven implementation of findings in commercial products • Epidemiology and properly controlled human intervention studies to confirm probiotic efficacy

11.6 RECOMMENDATION FOR FUTURE RESEARCH If probiotics are to be used to treat and prevent infection, the first studies that must be undertaken are to characterize fully (phenotypical and genotypical traits) the microorganisms that will be used. If they do not demonstrate anti-infective traits in vitro, it seems unlikely that they can be efficacious in humans. Scientific rationale for the selection of the best species or strain for use as probiotics is not possible without more information on the mechanisms by which probiotics exert their beneficial effects in vivo. The benefits of probiotics are often demonstrated under defined experimental laboratory conditions, but these beneficial effects fail to materialize in clinical trials, often because the trials are not properly controlled or consist of too few subjects. Large, double-blind, clinical trials are essential for establishing the practical and scientific logic of the probiotic concept. The full potential of therapeutic manipulation of the enteric flora with probiotics may not be optimally realized until our understanding of the normal flora is complete. The interaction between the host and the commensal flora requires basic investigation. Further information concerning the molecular basis of probiotic strains can have an impact on the development of strains with safe and effective novel probiotic effects. There is enormous potential for metabolic engineering, as has already been demonstrated for several LAB. Indigenous bacteria vectors, such as Lactobacillus, might be considered safer than the Salmonella and virus vectors presently considered for these purposes. The use of prebiotics in association with useful probiotics may be a worthwhile approach, as prebiotics preferentially stimulate some probiotic strains. Combination of probiotic and prebiotic as synbiotic can also enhance probiotic effectiveness.

REFERENCES Adams, M.R. and Marteau, P., On the safety of lactic acid bacteria from food, Int. J. Food Microbiol., 27, 263, 1995. Aquirre, M. and Collins, M.D., Lactic acid bacteria and human clinical infection, J. Appl. Bacteriol., 75, 95, 1993.

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Arthur, M., Reynolds, P., and Courvalin, P., Glycopeptide resistance in enterococci, Trends Microbiol., 4, 401, 1996. Berg, R.D., Probiotics, prebiotics or “conbiotics”? Trends Microbiol., 6, 89, 1998. Bielecka, M., Biedrzycka, E., and Biedrzycka, El., Isolation and identification of bifidobacterial strains, Med. Sci. Monitor Int. Med. J. Exp. Clin. Res., 6 (Suppl. 3), 123, 2000a. Bielecka, M. et al., Interaction of Bifidobacterium and Salmonella, Int. J. Food Microbiol., 45, 151, 1998. Bielecka, M., Biedrzycka, E., and Majkowska, A., Selection of bifidobacterial strains capable for colonisation of gastrointestinal tract, Med. Sci. Monitor Int. Med. J. Exp. Clin. Res., 6 (Suppl. 3), 123, 2000b. Bielecka, M. et al., The influence of bifidobacteria on pathomorphological pattern and microflora of gastrointestinal tract in non-infected and Salmonella-administered rats, Br. J. Nutr. Suppl., in print. Bouhnik, Y. et al., Effects of Bifidobacterium sp. fermented milk ingested with and without inulin on colonic Bifidobacteria and enzymatic activities in healthy humans, Eur. J. Clin. Nutr., 50, 269, 1996. Cai, Y., Matsumoto, M., and Benno, Y., Bifidobacterium lactis Meile et al. 1997 is a subjective synonym of Bifidobacterium animalis (Mitsuoka 1969) Scardovi and Trovatelli 1974, Microbiol. Immunol., 44, 815, 2000. Corthier, G., Dubos, F., and Raibaud, P., Modulation of cytotoxin production by Clostridium difficile in the intestinal tracts of gnotobiotic mice inoculated with various human intestinal bacteria, Appl. Environ. Microbiol., 49, 250, 1985. De Petrino, S.F. et al., Protective ability of certain lactic acid bacteria against an infection with Candida albicans in a mouse immunosuppression model by corticoid, Food Agric. Immunol., 7, 365, 1995. Fonden, R. et al., Effect of fermented dairy products on intestinal microflora, human nutrition and health: current knowledge and future perspectives, Bull. IDF, 352, 1, 2000. Gibson, G.R., Dietary modulation of the human gut microflora using prebiotics, Br. J. Nutr., 80 (Suppl. 2), S209, 1998. Gill, H.S., Stimulation of the immune system by lactic cultures, Int. Dairy J., 8, 535, 1998. Giraffa, G., Carminati, D., and Neviani, E., Enterococci isolated from dairy products: a review of risk and potential technological use, J. Food Prot., 60, 732, 1997. Goldin, B.R. and Gorbach, S.L., Probiotics for humans, in Probiotics: The Scientific Basis, Fuller, R., Ed., Chapman & Hall, London, 1992, p. 355. Guarner, F. and Schaafsma, G.J., Probiotics, Int. J. Food Microbiol., 39, 237, 1998. Huis in’t Veld, J.H.J., Havenaar, R., and Marteau, P., Establishing a scientific basis for probiotic R&D, Trends Biotechnol., 12, 6, 1994. Jett, B.D., Huycke, M.M., and Gilmore, M.S., Virulence of enterococci, Clin. Microbiol. Rev., 7, 462, 1994. Kaila, M. et al., Enhancement of the circulating antibody secreting cell response in human diarrhoea by a human Lactobacillus strain, Pediatr. Res., 32, 141, 1992. Lilly, D.M. and Stillwell, R.H., Probiotics: Growth promoting factors produced by microorganisms, Science, 147, 747, 1965. Marteau, P. and Rambaud, J.C., Potential of using lactic acid bacteria for therapy and immunomodulation in man, FEMS Microbiol. Rev., 12, 207, 1993. Matsumoto, M. et al., Effect of Bifidobacterium lactis LKM 512 yoghurt on fecal microflora in middle to old aged persons, Microb. Ecol. Health Dis., 12, 77, 2000. Meile, L. et al., Bifidobacterium lactis sp. nov., a moderately oxygen tolerant species isolated from fermented milk, Syst. Appl. Microbiol., 20, 57, 1997. Mitsuoka, T., Intestinal flora and human health: Asia Pacific, J. Clin. Nutr., 5, 1, 2, 1996.

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Molin, G. et al., Numerical taxonomy of Lactobacillus spp. associated with healthy and diseased mucosa of the human intestines, J. Appl. Bacteriol., 74, 314, 1993. Nader de Macias, M.E. et al., Inhibition of Shigella sonnei by Lactobacillus casei and Lact. Acidophilus, J. Appl. Bacteriol., 73, 407, 1992. Noble, W.C., Virani, Z., and Cree, R.G.A., Co-transfer of vancomycin and other resistance genes from Enterococcus faecalis NCTC 12201 to Staphylococcus aureus, FEMS Microbiol. Lett., 93, 195, 1992. Ouwehand, A.C. et al., Probiotics: mechanisms and established effects, Int. Dairy J., 9, 43, 1999. Paubert-Braquet, M. et al., Enhancement of host resistance against Salmonella typhimurium in mice fed a diet supplemented with yoghurt or milks fermented with various Lactobacillus casei strains, Int. J. Immunother., 11, 153, 1995. Perdigon, G. and Alvarez, S., Probiotics and the immune state, in Probiotics, Fuller, R., Ed., Chapman & Hall, London, 1992, p. 146. Perdigon, G. et al., Prevention of gastrointestinal infection using immunobiological methods with milk fermented with Lactobacillus casei and Lactobacillus acidophilus, J. Dairy Res., 57, 255, 1990. Portier, A. et al., Fermented milks and increased antibody responses against cholera in mice, Int. J. Immunother., 9, 217, 1993. Roy, D. and Sirois, S., Molecular differentiation of Bifidobacterium species with amplified ribosomal DNA restriction analysis and alignment of short regions of the ldh gene, FEMS Microbiol. Lett., 191, 17, 2000. Roy, D., Ward, P., and Champagne, G., Differentiation of bifidobacteria by use of pulsedfield gel electrophoresis and polymeraze chain reaction, Int. J. Food Microbiol., 29, 11, 1996. Salminen, S. et al., Lactic acid bacteria in health and disease, in Lactic Acid Bacteria: Microbiology and Functional Aspects, 2nd ed., Salminen, S. and von Wright, A., Eds., Marcel Dekker Inc., New York, 1998a, p. 211. Salminen, S., Isolauri, E., and Salminen, E., Clinical uses of probiotics for stabilising the gut mucosal barrier: successful strains and future challenges, Antonie van Leeuwenhoek, 70, 251, 1996. Salminen, S. et al., Demonstration of safety of probiotics: a review, Int. J. Food Microbiol., 44, 93, 1998b. Sanders, M.E. and Huis in’t Veld, J.H.J., Bringing a probiotic-containing functional food to the market: microbiological, product, regulatory and labelling issues, Antonie van Leeuwenhoek, 76, 293, 1999. Saxelin, M., Lactobacillus GG: a human probiotic strain with thorough clinical documentation, Food Rev. Int., 13, 293, 1997. Schiffrin, E.J. et al., Immune modulation of blood leukocytes in humans by lactic acid bacteria: criteria for strain selection, Am. J. Clin. Nutr., 66, 515S, 1997. Schrezenmeir, J. and de Vrese, M., Probiotics, prebiotics, and synbiotics: approaching a definition, Am. J. Clin. Nutr., Suppl. 73, 361S, 2001. Targan, R. and Shanahan, F., Inflammatory Bowel Disease from Bench to Bedside, Williams & Wilkins, Baltimore, 1994. Vaughan, E.E., Mollet, B., and de Vos, W.M., Functionality of probiotics and intestinal lactobacilli: light in the intestinal tract tunnel, Curr. Opin. Biotech., 10, 505, 1999.

12

Major Food Additives Adriaan Ruiter and Alphons G.J. Voragen

CONTENTS 12.1 Introduction ..................................................................................................273 12.2 Classification ................................................................................................274 12.3 Preservatives.................................................................................................275 12.3.1 Introduction ......................................................................................275 12.3.2 Sulfite ...............................................................................................276 12.3.3 Nitrite ...............................................................................................277 12.3.4 Sorbic Acid.......................................................................................277 12.3.5 Benzoic Acid ....................................................................................278 12.4 Antioxidants .................................................................................................278 12.5 Flavorings, Colorants, and Sweeteners........................................................279 12.6 Stabilizers, Emulsifiers, and Thickening Agents.........................................281 12.7 Clarifying Agents and Film Formers...........................................................283 12.8 Acidulants.....................................................................................................283 12.9 Fat Substitutes and Fat Mimetics ................................................................284 12.10 Prebiotics ......................................................................................................285 References..............................................................................................................287

12.1 INTRODUCTION The addition of certain substances to foodstuffs was practiced in ancient times, mostly for improving keeping properties. Salt was added to perishable foodstuffs such as meat and fish from the prehistoric ages on. Smoke curing can also be considered as the fortuitous addition of constituents to food, as wood smoke contains a number of compounds that are absorbed by the food during the smoke-curing process or are deposited onto the surface. These treatments not only prolong the shelf life of the food but also add to the flavor. The preparation of any food product includes the addition of a number of ingredients that are not considered to be additives, but clearly improve some properties of the food, such as keeping quality, and are originally intended as such. For example, preparation of a marinade in sour wine or vinegar is a technique for preserving fish that was already known to the Romans, but acetic acid is not an additive in the strict sense of the word. In some cases, it is not so easy to determine whether or not the substance under consideration is an additive. It is helpful to keep in mind that an additive is intended as an aid, for some purpose or another, not as an ingredient. 1-5871-6149-4/02/$0.00+$1.50 © 2002 by CRC Press LLC

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The Joint Food and Agriculture Organization/World Health Organization (FAO/WHO) Expert Committee on Nutrition (1955) defined food additives as “nonnutritive substances which are intentionally added to foodstuffs, mostly in small quantities, with the aim of improving the appearance, the flavor, the taste, the composition or the shelf-life.” In a more recent wording, these food additives are described as “substances generally not intended as a foodstuff or as a characteristic ingredient of a foodstuff which, irrespective of any nutritional value, are added, for any technological or sensoric reason, to a foodstuff during manufacturing, preparation, packaging, transport or storage, and from which it is expected that either the substance itself or reaction or decomposition products become a permanent component of the foodstuff or the raw material” (van Dokkum, 1985; Kamsteeg and Baas, 1985). In the latter definition, the term improvement is not included, and the remaining presence of the compound, or reaction products from that compound, is included in the definition. This may be the result of a shift in the attitude toward additives. The ranking, by the public, of actual food hazards was almost inverse to that given by Wodicka (1977), in which microbiological and nutritional risks were ranked at the top and food additives at the very bottom. To some extent, this inversion lasts even today (Hall, 1999). The preparation of any food product includes the addition of a number of ingredients that are not considered to be additives, but clearly improve some properties of the food, such as keeping quality, taste, flavor, or texture, and are originally intended as such. The origin of food additives often remains a point of discussion. There is a continuing demand, from the consumer’s side, for “natural” additives. No additive, however, is completely free from impurities. Products of chemical synthesis should be purified, eliminating starting materials and compounds resulting from side reactions. It has to be stated that enzyme-catalyzed synthesis or modification more and more replaces purely chemical synthesis of modification. “Natural” compounds should be purified as well in order to remove accompanying substances that have no significance in the final product. Generally speaking, purification is more difficult and more complicated for “natural” additives, as it is also much more problematic to characterize the raw material, which may contain a great many ill-defined compounds whose toxicities are largely unknown (Ruiter, 1989). Feberwee (1989) points out that official legislation does not discriminate between safe natural and safe artificial food additives. The main difference in safety evaluation between these two categories is the long experience of man with natural additives (Lüthy, 1989).

12.2 CLASSIFICATION Additives are mostly listed and classified into categories: • • • • •

Preservatives to extend the shelf life of foodstuffs Antioxidants to protect lipids in food from attack by oxygen Flavor enhancers to improve the perception of taste and flavors Sweeteners to replace sugars in giving a sweet taste to the product Colorants to improve the appearance of a foodstuff

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• Emulsifying agents to enable and maintain a fine partition of oils or fats in water (or a partition of water in oils or fats) and of gas in liquid (foam) • Thickening and gel-forming agents • Clarifying agents • Film formers • Glazing agents • Acidulants • Fat substitutes and replacers • Substances improving nutritional value • Pro- and prebiotics • Many other substances, such as anticlotting agents, moisteners, antifoaming agents, flour improvers, leavening agents, baking powders, melting salts, stiffening agents, complexing agents, fillers, and enzymes. With respect to reactivity of additives, it is preferable to make another classification, in which three groups can be distinguished: • Substances that, simply by their presence, lead to the desired improvement. Most colorants, sweeteners, and some preservatives belong to this class. Many of these additives do not display a strong reactivity toward other constituents during preparation and storage of the foodstuffs to which they are added. • Substances that are added because of their reactivity toward undesirable components already present or arising during manufacturing or storage and that may be bound by these added substances. The reaction may be directed toward these components themselves or toward their precursors. Antioxidants are an example of this category, as well as some peculiar substances reacting with matrix components to make desirable components such as flavor compounds. • Food additives that participate, for a part, in fortuitous reactions that, in some cases, may be undesirable. This classification, however, also has its limits. First, there is hardly any additive that does not take part in some chemical reaction at all. Furthermore, some food additives may also participate in unintentional reactions. Therefore, in this presentation some additives are discussed individually, with emphasis on their reactivity toward matrix compounds.

12.3 PRESERVATIVES 12.3.1 INTRODUCTION Preservatives are added in order to protect a variety of foodstuffs against microbial spoilage. This protection is possible, in many cases, because of a chemical reaction between the preservative and the microorganisms. It may therefore be expected that these compounds show some reactivity toward food components as well.

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Many preservatives are comparatively reactive compounds, e.g., sulfite, nitrite, and sorbic acid, but some show a moderate reactivity only, e.g., benzoic acid. Sulfite, nitrite, sorbic acid, and benzoic acid are discussed below.

12.3.2 SULFITE Disinfection by the vapors of burning sulfur is an old technique that was frequently used to decontaminate wine casks. Some sulfur dioxide was left in these vessels, preventing the wine from unwanted microbial infections. At present, sulfites are used both as preservatives and as agents that stop browning reactions. In food, the HSO3– species predominates, while in dehydrated food it is expected that S(IV) mainly exists as metabisulfite (HS2O52–), which is in equilibrium with HSO3– and SO32– (Wedzicha et al., 1991). Because of the nucleophilicity of the sulfite ion, many reactions with food components are possible (Wedzicha, 1991), one of these being the reversible addition to carbonyl compounds. It is suggested that the sulfite rather than the bisulfite ion acts as the nucleophilic agent (Wedzicha et al., 1991). This reaction has many implications for foodstuffs. For example, aroma components possessing a carbonyl group become involatile and do not contribute anymore to the overall flavor. Other nucleophilic reactions include the cleavage of S–S bonds in proteins and addition to C=C bonds of α,β-unsaturated carbonyl compounds. Control of nonenzymatic browning is based on this latter reaction (McWeeny et al., 1974). A key intermediate of the Maillard reaction, i.e., 3,4-deoxyhexulos-3ene, is efficiently blocked by a fast reaction with sulfite, leading to formation of 3,4dideoxy-4-sulfohexosulose, which is much less reactive and in which sulfite is irreversibly bound. Ascorbic acid browning is also inhibited by the addition of sulfite (Wedzicha and McWeeny, 1974). The same holds for polyphenol oxidase-catalyzed oxidation of natural phenols in fruit. The mechanism of the inhibition is by reaction of o-quinone intermediates with sulfite, which leads to nonreactive sulfocatechols (Wedzicha, 1995). An undesirable reaction of sulfite in food is the cleavage of thiamin by means of an attack at the pyrimidin moiety (Zoltewicz et al., 1984). This was one of the reasons for a ban, in many countries, on the use of sulfite in meat. Another reason is the preserving effect on the meat color, which makes stale meat look as if it were fresh. Sulfite, however, is unable to reduce metmyoglobin back to myoglobin (Wedzicha and Mountfort, 1991). An important reaction, in a quantitative respect, is the cleavage of disulfide bonds in meat proteins, in particular, in lean meat. The reducing capacities of sulfite should be emphasized as well. In fact, cleavage of S–S bonds by sulfite can be considered a reduction. This property of sulfite makes it useful as an additive to flour for biscuit making (Wedzicha, 1995). The cleavage of disulfide bonds in wheat proteins speeds up and facilitates the production of a satisfactory dough. A quite different type of reaction, which may also occur in food, is the reduction of azo dyes to colorless hydrazo compounds. Like in the reaction with carbon compounds, the reactive species is SO32- and not HSO3– (Wedzicha and Rumbelow, 1981).

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12.3.3 NITRITE lt has been known for a long time that small amounts of saltpeter (KNO3) are able to cause a reddish discoloration of meat, which is characteristic for many meat products. In about 1900 it was established that it was not nitrate, but its reduction product, i.e., nitrite, that was responsible for this color development. Some decades later, nitrite was recognized as a potent inhibitor of microorganisms, including pathogens, in many meat products. In particular, the inhibition of Clostridium botulinum, with accompanying toxin formation, was established. The role of nitrite in the characteristic cured meat flavor was still noticed later on. The inhibitive action of nitrite is pH dependent, which led to the assumption that undissociated nitrous acid is the active substance. However, this is a hypothetical acid from which equimolar parts of H2O, NO, and NO2 are formed. In the 1960s it became clear that nitric oxide (NO) is the active species. Nitric oxide can also be generated through reduction of nitrite, e.g., by ascorbate or isoascorbate (Wirth, 1985). Nitric oxide shows a strong binding to iron and is able to block iron atoms in biologically active compounds important in cell metabolism, in particular in the outgrowth of germinated spores (Woods et al., 1989). In meat products preserved with nitrite, NO binds to heme iron, thus forming nitrosomyoglobin (Giddings, 1977). There is some evidence that inhibition of C. botulinum outgrowth in nitrite-cured meat products is mainly due to iron binding in such a way that this is no longer available for outgrowth of Clostridium spores. This strong binding also explains the antioxidative properties of nitrite in these products (Grever and Ruiter, 2001). Fat is also able to bind some nitric oxide. The amount incorporated in fat is considerably higher in unsaturated than in saturated lipids. Furthermore, nitrite is able to react with intermediates of the Maillard reaction, such as 3-deoxyosulose (Wedzicha and Wei Tian, 1989). The reaction of nitrite with secondary or tertiary amines, though unimportant in quantitative respect, leads to N-nitroso compounds, which, for a considerable part, are potent carcinogens. These compounds may rearrange to form highly electrophilic diazonium ions that react with cellular nucleophiles such as water, proteins, and nucleic acids. Nitrate ingested with food or drinking water is partially reduced to nitrite in the body and contributes more than nitrite in meat products to the possible endogenous formation of N-nitroso compounds. A ban on the use of low amounts of nitrite as an additive is therefore not very rational and deprives the consumer of a very effective guard against a number of pathogenic microorganisms, in particular C. botulinum, but also Clostridium perfringens and Staphylococcus aureus. Finally, nitrite may react in physiological concentrations and under gastric pH conditions with naturally occurring, as well as synthetic, antioxidants (Kalus et al., 1990). There are no indications for the formation of hazardous reaction conditions from a viewpoint of mutagenicity.

12.3.4 SORBIC ACID The preserving properties of sorbic acid were recognized around 1940. During the late 1940s and the 1950s, sorbic acid became available on a commercial scale,

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resulting in its extensive use as a food preservative throughout the world (Sofos and Busta, 1983). As a straight-chain trans-trans dienoic fatty acid (FA) (CH3–CH = CH–CH = CH–COOH), it is susceptible to nucleophilic attack (Khandelwal and Wedzicha, 1990b). The lowest electron density is associated with position 3. Nucleophilic groups, e.g., the thiol group, however, may bind to the carbon atom at the 5 position as the terminal methyl group delocalizes the charge (Khandelwal and Wedzicha, 1990a; Wedzicha, 1995). Sorbic acid inactivates several intracellular enzymes by this mechanism. It passes the cell wall in its undissociated form only, which explains its low activity at higher pH values. The pKa value at 25°C amounts to 4.76. It is mainly active against yeasts, molds, and strictly aerobic bacteria. The toxicity toward mammals is low. Sorbic acid is easily oxidized. This oxidation is accompanied by the development of a glyoxal-like flavor in sorbic acid preparations and a brown color in a wide variety of model foods in which sorbic acid was included. Amino acids accelerate color development (Wedzicha et al., 1996).

12.3.5 BENZOIC ACID This compound is relatively stable during food processing and in food products. It was proposed in 1875 by H. Fleck as a replacer for salicylic acid and can be considered as one of the first safe food preservatives. Like sorbic acid, it is mainly active against yeast and molds, but the growth of micrococci, Escherichia coli, and many other bacteria is retarded as well. As is the case with sorbic acid, benzoic acid penetrates the cell wall in the undissociated form. As a consequence, it is active at lower pH values only (pKa at 25°C = 4.19) and therefore serves as a preservative for sour products such as fruit juices and jams. In shrimp preservation it is applied as a powder that is spread over the shrimps, passes cell walls, and then ionizes in the intracellular fluid to yield protons that acidify the alkaline interior of the cell. The main cause of its activity, however, is biochemical effects (Eklund, 1980) such as inhibition of oxidative phosphorylation and of enzymes from the citric acid cycle (Chipley, 1983). In mayonnaise preserved by benzoic acid, the undissociated acid is mainly present in the lipid phase, which can be considered as a reservoir for the aqueous phase. Benzoic acid is often combined with sorbic acid in order to reduce its peculiar flavor. It has to be stated, however, that this is at least partly caused by impurities in the benzoic acid preparation used.

12.4 ANTIOXIDANTS Antioxidants can be defined as “substances that, when present in low concentrations compared to those of an oxidizable substrate, significantly delay or inhibit oxidation of that substrate” (Halliwell and Gutteridge, 1989). Antioxidants are frequently added to unsaturated fats and oils in order to protect these against oxidative deterioration. For this reason, they are also added to a variety of food products containing unsaturated lipids. Antioxidants frequently applied are esters of gallic acid, butylated hydroxyanisole (BHA), butylated hydroxytoluene

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FIGURE 12.1 Antioxidants. Top: from left to right, alkyl gallates, the two isomers of BHA. Bottom: fom left to right, BHT and TBHQ.

(BHT), and tertiary butylhydroxyquinone (TBHQ). Of these, TBHQ is by far the most potent antioxidant. In both BHA and BHT, the butyl groups are also of a tertiary structure (Figure 12.1). Antioxidants are naturally present in many foodstuffs and are of great importance as inactivators of radical formation. Some antioxidative enzyme systems are produced in the human body and are supposed to play an important role in the cellular defense against oxidative damage (Langseth, 1995). Many of the antioxidants present in food have the function of terminating chain reactions. A variety of compounds such as phenols, aromatic amines, and conjugates can function as chain-breaking antioxidants. They react with the chain-propagating radical species, which results in the formation of radical species incapable of extracting hydrogen atoms from unsaturated lipids. These radicals may rapidly combine with other radicals or, if a polyphenolic structure is present (e.g., gallic acid esters), disproportionate into their original state and a quinoid form. Since there are synergistic effects between antioxidants, commercial preparations usually contain mixtures of these antioxidants. As oxidative rancidity is strongly catalyzed by some heavy metal ions, in particular Cu++, antioxidant mixtures often contain sequestrants (e.g., citric acid and ethylenediaminetetraacetic acid (EDTA)) in order to complex these ions. Reductants such as ascorbic acid, which decrease the local concentration of oxygen, are also able to decrease the formation of peroxy radicals. Fat oxidation by bacteria can be suppressed by the addition of preservatives such as benzoic acid or sorbic acid.

12.5 FLAVORINGS, COLORANTS, AND SWEETENERS Artificial flavorings are frequently added to a variety of foodstuffs. These preparations mostly consist of a large number of different compounds, of which some

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show a considerable reactivity. The way in which flavor components interact with the food matrix and how this influences flavor perception has been reviewed by Bakker (1995). Many interactions are of a pure chemical nature and may result from the presence of aldehydes and their reactivity toward amino and thiol groups of proteins. Another frequently occurring type of interaction is the formation of hydrogen bonds between food compounds and polar flavor components such as alcohols. Starch, starch-derived maltodextrins, and β-cyclodextrin are able to form inclusion complexes with many flavor components. Many other interactions, although of great influence on flavor perception, are of a physical nature and therefore not mentioned in this chapter. Food additives such as dyes and sweeteners are not intended to react with matrix compounds or to undergo other reactions. Some reactions may occur, however, and a few examples are given here. As for food dyes, many of these are azo compounds, which implies the possibility of reduction, e.g., by the action of certain bacteria. The loss of color, in these cases, is an indication of spoilage. Bisulfite is also able to reduce azo dyes (Wedzicha and Rumbelow, 1981). Sweeteners have been applied to foodstuffs for many years. Compounds such as saccharin, sodium cyclamate, aspartame, and several others are well known and hardly need to be discussed here. In later times, sweeteners such as sucralose and thaumatin appeared on the scene. Sucralose is a sucrose derivative obtained by chlorination, by which the D-glucopyranosyl unit is converted to a galactopyranosyl unit chlorinated at position 4, while the fructofuranosyl unit is chlorinated at positions 1 and 6. This results in an intense sweetness (600 times that of sucrose) and a greater stability toward acids (Figure 12.2).

FIGURE 12.2 Sucralose.

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Thaumatin is a protein from katemfe fruit (Thaumatococcus danielli), with the strongest sweetening properties hitherto known (2500 times as sweet as sucrose). The protein is freely soluble in water, consists of 207 amino acids, and shows a molecular weight of 22 kDa and an I.E.P. of 11.5. The electrical charge in the molecule is thought to be a major factor in the interaction with taste receptors (Boy, 1994). It synergizes with aspartame and with flavor enhancers such as 5'-nucleotides and sodium glutamate. Apart from this, it masks the aftertaste of saccharin. It also masks metallic and bitter taste components. Taste interactions between sweeteners are not uncommon. Another example is the synergism between aspartame and acesulfame K. A 70/30 blend, in some cases, shows a taste that cannot be distinguished from sugar. Acesulfam K also shortens the long, sweet aftertaste of sucralose (Meyer, 2001). Apart from taste interactions, some sweeteners also show synergism with flavors. Some sweeteners may undergo chemical reactions, thereby losing their sweet properties. The instability of saccharin at higher temperatures is well known. Apart from this, saccharin is subject to some degradation under acidic conditions, yielding sulfobenzoic acid, which has a disagreeable phenolic flavor. Another example is aspartame, which is the methyl ester of N-L-α-aspartyl-L-phenylalanine. Because of its nature, the stability in aqueous systems is limited. The maximum stability is between pH values of 3 and 5 and decreases at higher temperatures with concomitant loss of sweetening power. The main degradation product is 3,6dioxo-5-(phenylmethyl)-2-piperazinoacetic acid (Furda et al., 1975). Other decomposition products are listed by Stamp and Labuza (1989), who added some novel components to this group. These all have in common the absence of a sweet taste. Apart from this, aspartame shows remarkable reactivity toward a number of aldehydes that may be present in foodstuffs and contribute to flavor (Hussein et al., 1984; Cha and Ho, 1988), and thaumatin reacts with carrageenans if these are present (Ohashi et al., 1990). Many unintended and sometimes unwanted reactions of artificial dyes, sweeteners, and other additives with the food matrix are imaginable and should always be taken into consideration when the consequences of such additions to food are discussed.

12.6 STABILIZERS, EMULSIFIERS, AND THICKENING AGENTS The most important representatives of these compounds are polysaccharides: starch and starch derivatives (α-1,4 D-glucans); cellulose and cellulose derivatives (β-1,4 D-glucans); plant extracts (pectins: α-1,4 D-galacturonans); seaweed extracts (carrageenan, agar, and alginates); seed flour (guar and locust bean galactomannans, tamarind xyloglucans, and konjac glucomannans); exudate gums (arabic, karaya, and tragacanth); and microbial gums (xanthan, gellan, and curdlan). Polymers are made of one or more types of sugar residues and are covalently attached in linear, linearly branched, and branched structures. Their anomeric form (α/β), types of linkages (1,2; 1,3; 1,4; 1,4,6; 1,3,6; etc.), presence of functional groups (carboxyl, phosphate, sulfate, esters, and ethers), and molecular weight distribution determine their conformation in aqueous systems (stiff

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or rod-like, random coil, helices), the intra- and intermolecular interactions between molecules (dimerization, association, ionic interactions, hydrophobic interactions), and the interactions with other molecules (other polysaccharides, proteins, and lipids). These interactions are the basis for viscous behavior, gelling, water binding, film forming, bulking, stabilizing, and emulsifying properties. Some polysaccharides act synergistically in imparting these functions, e.g., locust bean gum and carrageenan, locust bean gum and xanthan, pectin and alginate. Important parameters for applications are pH, heat and shear stability, syneresis properties, shelf life, and compatibility with other food constituents. Derivatives of these polysaccharides with improved functional properties are also used. Emulsifiers are amphophilic compounds that concentrate at oil or water interfaces, causing a significant lowering of interfacial tension and a reduction in the energy needed to form emulsions. They can be anionic, cationic, and nonionic compounds that have one or more of the following characteristics: surface active, viscosity enhancer, solid absorbent, or hydrophilic/lipophilic balance (HLB). They are added to food emulsions to increase emulsion stability and to attain an acceptable shelf life. Polysaccharides are not surface-active agents, but rather macromolecular stabilizers that generally function through enhancement of viscosity and enveloping oil droplets in oil-in-water (O/W) emulsions. The emulsifiers used in food manufacture were categorized by Artz (1990) (cf. Table 12.1). Only lecithin is of natural origin. Its main source is soybean, but it is also present in corn, sunflower, cottonseed, rapeseed, and eggs. Emulsifiers stabilize emulsions in various ways. They reduce interfacial tension and may form an interfacial film that prevents coalescence of droplets. In addition, ionic emulsifiers provide charged groups on the surface of the emulsion droplets and thus increase repulsive forces between droplets. Emulsifiers can also form liquid crystalline microstructures such as micelles at the interface of emulsion droplets. These are formed only at emulsifier concentrations larger than the critical micelle-forming concentration. These microstructures have a stabilizing effect.

TABLE 12.1 Food Emulsifier Categories Category Lecithin (naturally occurring) and lecithin derivatives Glycerol FA esters Hydroxycarboxylic acid and FA esters Lactylate FA esters Polyglycerol FA esters Polyethylene and propylene glycol FA esters Ethoxylated derivatives of monoglycerides Sorbitan FA esters

Typical Application — — Baking goods, margarine — Baked goods O/W emulsions — Antistaling

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Proteins also have a major influence on emulsion stability, although various types of instability may occur: instability caused by coalescence or flocculation, and cream layer formation caused by differences in density between oil droplets and the aqueous phase. In practice, the latter problem is the most difficult to solve. Creaming can be retarded by increasing the viscosity of the aqueous phase and by reducing the diameter of oil droplets or the density difference. The density difference between an oil droplet and serum can be reduced by loading as much protein as possible on the oil droplet surface. An open, random-coil protein, such as sodium caseinate, is expected to give less protein loaded on the oil surface than compact proteins do. It has been shown that open-structure proteins show a lower equilibrium surface load than compact structure proteins (Zwijgers, 1992). The higher the equlibrium surface load, the better the emulsion-stabilizing protein. In line with the foregoing, milk protein hydrolysates are useful foamers and emulgators. The foam- and emulsion-forming properties of milk peptides are even superior to those of intact milk proteins, as long as these show both charged and hydrophobic areas (Caessens et al., 1999). The selection of emulsifiers to prepare food emulsions is mainly based on their HLB number. This index is based on the relative percentage of hydrophilic to lipophilic groups within the emulsifier molecule. Lower HLB numbers indicate a more lipophilic emulsifier, while higher numbers indicate a more hydrophilic emulsifier. Emulsifiers showing HLB numbers between 3 and 6 are best for waterin-oil (W/O) emulsions, and emulsifiers with numbers between 8 and 18 are best for O/W emulsions.

12.7 CLARIFYING AGENTS AND FILM FORMERS Clarifying agents or flocculants are used to eliminate turbidity or suspend particles from liquids, e.g., chill haze in beer, precipitates in fruit juices and wines, and haze in oils. Often, they provide a nucleation site for suspended fines. Examples of clarifying agents are lime in sugar juice clarification, pectic enzymes to break down pectins in fruit juices, and gelatin for clarification of fruit juices. Film formers are used to coat food by providing it with a protective layer and so making it more attractive in appearance or increasing its palatability. Film formers may not impart flavor or mouth feel of their own to the food. Examples are starches to coat proteins to prevent Maillard reactions, mineral oils to seal pores of eggs, and sodium caseinate to encapsulate fat in whiteners.

12.8 ACIDULANTS Food acidulants find their application, for the greater part, in beverages and in fruit and vegetable processing. Apart from pH lowering, acidulants provide buffer capacity, impair sourness and tartness, enhance the effect of preservatives, and for some acidulants such as citric acid, prevent discoloration caused by trace metals (Seifert, 1992).

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FIGURE 12.3 D-Gluconolactone.

Besides acids, other components that produce or release acids are applied as acidulants, in particular when a slow release of acid is of importance. A well-known slow-release acidulant is glucono-δ-lactone (GDL), which is used in bakery products, dairy products, and in particular, meat products (Watine, 1995) (Figure 12.3). The use of GDL in the maturation of dry sausages is well known. During preparation of these sausages, GDL standardizes acidification, strongly reduces risk of contamination, and improves quality. GDL gradually lowers the pH to 5.4, and after filling the sausage casings, the temperature is lowered to 0–4°C for some hours. During this period the growth of starters and undesirable bacteria is inhibited. Then the temperature is increased so that fermentation can take place normally.

12.9 FAT SUBSTITUTES AND FAT MIMETICS Dietary fat contributes to the combined perception of mouth feel, taste, and aroma. Fat also contributes to creaminess, appearance, palatability, texture, and lubrication properties of foods, and it increases the feeling of satiety during meals. Apart from this, it is able to carry lipophilic flavor compounds and can act as a precursor for flavor development. A very important characteristic of fat is its suitability to be used for frying. Due to their high caloric value, there is an increasing tendency to replace fats and oils with components that are not calorific but can impart the same technological and sensory functionalities. Two types of fat replacers can be distinguished: fat substitutes and fat mimetics. Fat substitutes are lipid- or fat-based macromolecules that physically and chemically resemble triacylglycerols (e.g., sucrose polyesters or alkyl glycoside polyesters). Fat mimetics are protein- or carbohydrate-based compounds that imitate organoleptic or physical proteins or triacylglycerols (Voragen, 1998). Fat substitutes physically and chemically resemble fats and oils, as these are esters of polyols. They are stable at cooking and frying temperatures. Many carbohydrate-based fat substitutes are mixtures of sucrose esters formed by chemical transesterification or interesterification of sucrose with one to eight FAs. The class with six to eight FAs are called sucrose FA polyesters. These molecules are too large to be broken down by intestinal lipase enzymes and, for that reason, do not show any caloric value (Voragen, 1998).

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Olestra, in this respect, is a promising compound. The stability of Olestra is comparable to natural fats and even better. Applied as a frying medium, it appears to undergo slower oxidative and hydrolytic degradation (Lindley, 1996). The functionality and potential application of the sucrose FA polyesters is governed by the type of fatty esters used in the manufacture. The melting character depends on the length and the degree of saturation of the FA in a similar way. In theory, this melting character may be adjusted by a right choice of FA (Lindley, 1996). The esters containing one to three FAs are called sucrose FA esters (SFEs). Unlike sucrose FA polyesters, the SFEs are easily hydrolyzed and absorbed by digestive lipases, and are thus caloric. SFEs containing five to seven free hydroxyl groups with one to three FA esters show both hydrophilic and lipophilic properties and therefore give excellent emulsifying and surface-active properties. In addition, they are effective lubricants, anticaking agents, thinning agents, and antimicrobials (Voragen, 1998). Other carbohydrates modified to FA esters are sorbitol, trehalose, raffinose, and stachyose. Saccharide-based fat mimetics differ strongly from fats and oils. Generally they absorb a substantial amount of water and are therefore not suitable for frying. As they can carry only water-soluble flavors, they lack the flavor of fats and oils. Inulin and starch hydrolysates (dextrose equivalent ~ 2) are striking examples of a fat mimetic. The fat substitution is based on its ability to stabilize water into a creamy structure that has a fat-like mouth feel (Blomsma, 1997). Most carbohydrate-based fat replacers are extracted from by-products rich in cell wall polysaccharides. Polydextrose, which can be applied both as a carbohydrate and as a fat replacer, is obtained by vacuum thermal polymerization of glucose, using citric acid as a catalyst and sorbitol as a plasticizer (Voragen, 1998).

12.10 PREBIOTICS In Chapter 11, it is stated that the use of prebiotics in association with useful probiotics may be a worthwhile approach, as prebiotics may stimulate some probiotic strains. The term prebiotics is derived from the Greek and can be translated as “prior to life.” Generally, prebiotics comprise food additives that are barely or not digested in the small intestine and end up in the colon, where they may stimulate beneficial bacteria by serving as fermentation substrates. Promotion and regulation of health is the aim of these bioactive products that present an important trend in the presentday production of foods. Nondigestible carbohydrates are the main representatives of class of food additives. There are three main types of carbohydrates that are indigestible in the human small intestine: nonstarch polysaccharides, resistant starch, and nondigestible oligosaccharides (NDOs). As the average daily ingestion of the latter group is lower than the level considered safe, i.e., not over 15 g/day, supplementation of NDOs could be beneficial (Voragen, 1998). These can be used in a wide range of processed foods, including dairy products, confectioneries, bakery products, ready meals, breakfast cereals, and drinks. Other significant beneficial effects are:

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• Replacement of sugar and fat • Reduction of the number of unwanted bacteria in the colon • Fiber enrichment of foods hitherto poor in fiber, e.g., white bread, dairy products, transparent drinks • Prevention of tooth decay • Regulation of lipid metabolism (van Haastrecht, 1995) Two specific groups of NDOs, which are commercially available, have to be mentioned: fructo-oligosaccharides (FOSs), obtained by transfructosylation of sucrose using a β-D-fructosyltransferase or by hydrolysis of inulin by endo-inulinase; and galacto-oligosaccharides (GOSs), obtained by transgalactosylation of lactose using β-galactosidase. Inulin is a virtually linear fructose polymer in which the fructose molecules are linked by β-(2-1) bonds with an average degree of polymerization ranging from 2–60 (average length of 10). Most oligosaccharides have a moderate reducing power by which they are still liable to Maillard reactions when used in food to be heat processed. FOSs of the GFn type (composed of fructofuranosyl residues and one terminal, nonreducing glucosyl residue, obtained by transfructosylation), e.g., lactosucrose and glycosylsucrose, have no reducing power. FOSs by hydrolysis of inulin can be of the GFn type or of the Fm type, the latter having a reducing fructofuranosyl residue (Figure 12.4).

FIGURE 12.4 Two types of FOSs (sucrose of comparison). (After van Haastrecht, J., Int. Food Ingredients, 1995.)

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At pH < 4 and treatments at elevated temperatures or prolonged storage at ambient conditions, oligosaccharides present in a food can be hydrolyzed, resulting in loss of nutritional and physicochemical properties. For FOSs it is reported that in a 10% solution of pH 3.5, less than 10% is hydrolyzed after heat treatments of 10 sec at 145°C, 5 min at 45°C, or 60 min at 70°C. After 2 days at 30°C, less than 5% is hydrolyzed. The stability can greatly differ for the various classes of oligosaccharides, depending on the sugar residues present, their ring form, and anomeric configuration and linkage types. Generally β-linkages are stronger than α-linkages, hexoses are more strongly linked than pentoses and deoxysugars, and pyranoses are more strongly linked than furanoses. Finally, resistant starch is a class of dietary carbohydrates that are attracting an increased interest from food manufacturers, due to the beneficial effects these might have on human health. These starches escape digestion and absorption in the small intestine of humans and reaches the large bowel, where fermentation takes place. As a result, the pH in the colon is lowered and short-chain FAs are formed. They further increase fecal bulk and may protect against colon cancer, improve glucose tolerance, and lower blood lipid levels. The most important forms of resistant starch in the diet are botanically encapsulated starch present in intact foods, starches with a B-type crystalline structure present in unheated foods, starch retrogradated as a result of full gelatinization and dispersion by processing, and thermally or chemically modified starches (Voragen, 1998).

REFERENCES Artz, W., Emulsifiers, in Food Additives, Bramen, A.L., Davidson, R.M., and Salminen, S., Eds., Marcel Dekker Inc., New York, 1990, p. 347. Bakker, J., Flavor interactions with the food matrix and their effects on perception, in Ingredient Interactions: Effects on Food Quality, Goankar, A.G., Ed., Marcel Dekker Inc., New York, 1995, p. 411. Blomsma, C.A., Ingenious inulin, Int. Food Ingredients, (2), 22, 1997. Boy, C., Thaumatin: a taste-modifying protein, Int. Food Ingredients, 6, 23, 1994. Caessens, P.J.W.R. et al., β-Lactoglobulin hydrolysis. 1. Peptide composition and functional properties of hydrolysates obtained by the action of plasmin, trypsin, and Staphylococcus aureus V9 protease, J. Agric. Food Chem., 47, 2973, 1999. Cha, A.S. and Ho, C.T., Studies of the interaction between aspartame and flavor vanillin by high-performance liquid chromatography, J. Food Sci., 53, 562, 1988. Chipley, J.R., Sodium benzoate and benzoic acid, in Antimicrobials in Foods, Branen, A.L. and Davidson, P.M., Eds., Marcel Dekker Inc., New York, 1983, p. 11. van Dokkum, W., Additieven en contaminanten (Additives and contaminants), Voeding in de praktijk, 6, 1, 1985. Eklund, T., Inhibition of growth and uptake processes in bacteria by some food preservatives, J. Appl. Bacteriol., 48, 423, 1980. Feberwee, A., Legal aspects of food additives of natural origin, paper presented at International Symposium Food Additives of Natural Origin, Plovdiv, Bulgaria, 1989, p. 22. Furda, I. et al., Decomposition products of L-aspartyl-L-phenylalanine methyl ester in various food products and formulations, J. Agric. Food Chem., 23, 340, 1975. Giddings, G.G., The basis of color in muscle foods, J. Food Sci., 42, 288, 1977.

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Chemical and Functional Properties of Food Components

Grever, A.B.G. and Ruiter, A., Prevention of Clostridium botulinum outgrowth in heated and hermetically sealed meat products by nitrite: a review, Eur. Food Res. Technol., 213, 165, 2001. van Haastrecht, J., Oligosaccharides: promising performers in new product development, Int. Food Ingredients, 1, 23, 1995. Hall, R.L., 1999, Food safety: elusive goal and essential quest, IUFoST Founders Lecture, Sydney, October 1999, Food Australia, 51, 601, 1999. Halliwell, B. and Gutteridge, J.M.C., Free Radicals in Biology and Medicine, 2nd ed., Clarendon Press, Oxford, 1989. Hussein, M.M. et al., Determination of reactivity of aspartame with flavor aldehydes by gas chromatography, HPLC and GPC, J. Food Sci., 49, 520, 1984. Joint FAO/WHO Expert Committee on Nutrition, Technical Report Series, 97, 4th report, Geneva, 1955, p. 29. Kalus, W.H., Münzner, R., and Filby, W.G., Isolation and characterization of some products of the BHA-nitrite reaction: examination of their mutagenicity, Food Additives Contaminants, 7, 223, 1990. Kamsteeg, J., E = Eetbaar (E = Edible), Becht, Amsterdam, 2001. Khandelwal, G.D. and Wedzicha, B.L., Derivatives of sorbic acid-thiol adducts, Food Chem., 37,159, 1990a. Khandelwal, G.D. and Wedzicha, B.L., Nucleophilic reactions of sorbic acid, Food Additives Contaminants, 7, 685, 1990b. Langseth, L., Oxidants, Antioxidants, and Disease Prevention, ILSI Europe Concise Monograph Series, ILSI Europe, Brussels, 1995. Lindley, M.G., Olestra: the ultimate in fat substitution?, Int. Food Ingredients, 3, 35, 1996. Lüthy, J., Safety Evaluation of Natural Food Additives, paper presented at International Symposium Food Additives of Natural Origin, Plovdiv, Bulgaria, 1989, p. 35. McWeeny, D.J., Knowles, M.E., and Hearne, J. F., The chemistry of non-enzymic browning in foods and its control by sulphur, J. Sci. Food Agric., 25, 735, 1974. Meyer, S., Taste Interactions of Acesulfame Potassium and Other High Intensity Sweeteners with Fruit Flavours in Different Food Proteins, paper presented at 2nd IUPAC International Symposium on Sweeteners (2nd IUPAC-ISS), Hiroshima, Japan, 2001, p. 55. Möhler, K., Formation of Curing Pigments by Chemical, Biochemical or Enzymatic Reactions, paper presented at International Symposium on Nitrite in Meat Products, Zeist, The Netherlands, 1973, p. 13. Ohashi, S. et al., The decrease of thaumatin’s sweetness intensity upon interaction with carrageenan, Food Hydrocoll., 4, 323, 1990. Ruiter, A., Safety of food: the vision of the chemical food hygienist, in Food Science: Basic Research for Technological Progress: Proceedings of the Symposium in Honour of Professor W. Pilnik, Wageningen, The Netherlands, 25 November, 1988, Roozen, J.P., Rombouts, F.M., and Voragen, A.G.J., Eds., 1989, p. 19. Seifert, D., Functionality of food acidulants, Int. Food Ingredients, 3, 4, 1992. Sofos, J.N. and Busta, F.F., Antimicrobials in Foods, Branen, A.M. and Davidson, R.M., Eds., Marcel Dekker Inc., New York, 1983, p. 141. Stamp, J.A. and Labuza, T.R., Mass spectrometric determination of aspartame decomposition products: evidence for β-isomer formation in solution, Food Additives Contaminants, 6, 397, 1989. Voragen, A.G.J., Technological aspects of functional food-related carbohydrates, Trends Food Sci. Technol., 9, 328, 1998. Watine, Ph., Glucono-delta-lactone: functional properties and applications, Int. Food Ingredients, 3, 39, 1995.

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Wedzicha, B.L., Sulphur dioxide: the most versatile food additive?, Chem. Britain, 1030, 1991. Wedzicha, B.L., Interactions involving sulfites, sorbic acid, and benzoic acid, in Ingredient Interactions: Effects on Food Quality, Goankar, A.G., Ed., Marcel Dekker Inc., New York, 1995, p. 529. Wedzicha, B.L., Bellion, I., and Goddard, S.J., Inhibition of browning by sulfites, in Nutritional and Toxicological Consequences of Food Processing, Friesman, M., Ed., Plenum Press, New York, 1991a, p. 217. Wedzicha, B.L. and McWeeny, D.J., Non-enzymic browning of ascorbic acid and their inbibition: the production of 3-deoxy-4-sulphopentosulose in mixtures of ascorbic acid, glycine and bisulphite ion, J. Sci. Food Agric., 25, 577, 1974. Wedzicha, B.L. and Mountfort, K.A., Reactivity of sulphur dioxide in comminuted meal, Food Chem., 39, 281, 1991. Wedzicha, B.L., Rimmer, Y.L., and Khandelwal, G.D., Catalysis of Maillard browning by sorbic acid, Lebensmittel-Wiss.u.-Technol., 24, 278, 1991b. Wedzicha, B.L. and Rumbelow, S.J., The reaction of an azo food dye with hydrogen sulphite ions, J. Sci. Food Agric., 32, 699, 1981. Wedzicha, B.L. and Wei Tian, Kinetics of the reaction between 3-deoxyhexulose and nitrite ion, Food Chem., 31, 189, 1989. Wirth, F., Pökeln: Farbbildung und Farbhaltung by Brühwurst (Curing: formation and maintaining of color in fermented sausages), Fleischwirtschaft, 65, 423, 1985. Wodicka, V.O., Food safety: rationalizing the ground rules for safety evaluation, Food Technol., 9, 31, 1977. Woods, L.F.J., Wood, J.M., and Gibbs, P.A., Nitrite, in Mechanisms of Action of Food Preservation Procedures, Gould, G.W., Ed., Elsevier, London, 1989, p. 225. Zoltewicz, J.A., Kauffman, G.M., and Uray, G., A mechanism for sulphite ion reacting with vitamin B2 and its analogues, Food Chem., 15, 75, 1984. Zwijgers, A., Outline of milk protein concentrate, Int. Food Ingredients, 3, 18, 1992.

13

Food Safety Julie Miller Jones

CONTENTS 13.1 13.2 13.3 13.4 13.5 13.6 13.7

Introduction ..................................................................................................291 Consumer Attitudes toward the Food Safety Problem................................293 Tests to Determine Food Safety ..................................................................294 Food Safety Concerns ..................................................................................296 Microbial Contamination of Food ...............................................................296 Risk-Benefit as It Applies to Food ..............................................................298 Nutritional Evaluation of Food Processing .................................................300 13.7.1 Effects on Vitamins ..........................................................................300 13.7.2 Effects on Minerals ..........................................................................302 13.8 Newer and Novel Technologies ...................................................................302 13.8.1 Irradiation .........................................................................................302 13.8.2 Biotechnology ..................................................................................303 13.9 Additives.......................................................................................................303 References..............................................................................................................304

13.1 INTRODUCTION Safe food — it is what every individual expects in every mouthful and every government strives to give its populace. Since food is the object of our earliest preferences and the subject of our strongest prejudices, food safety is a gut issue. Yet what seems on the surface to be both basic and imperative is not at all simple, and in fact, is not achievable in the absolute sense. It is extremely hard to accept even the idea that food is relatively — not absolutely — safe. What appears to threaten food, threatens in a very direct and visceral way. An understanding of basic definitions about safety and toxicity is crucial. First, all compounds, no matter how salutary, can be ingested in some manner or in some quantity that will cause toxicity. Toxicity is the capacity of a substance to produce some adverse effect or harm. Even essential components such as water and vitamins can be consumed at toxic levels. Too much pure water can cause renal shutdown; excessive vitamins can cause minor problems such as flushing or nausea or major problems such as liver damage, teratogenicity, and death. The 1538 Paracelsus motto, “Only the dose makes the poison,” operates for food components (Jones, 1992).

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Second, what is safe for one is not safe for another. Individuals who have allergies, inborn or acquired errors of metabolism, or certain diseases can ingest food in a usual and customary manner and yet suffer adverse and even, in rare instances, fatal outcomes. Thus, foods that are safe for most are not safe for all. Third, how the food is used or produced may alter its safety. Combinations of foods and drugs or a certain food with a bizarre or poor diet can render an otherwise safe food as harmful. A food may contain an unexpected contaminant such as a mycotoxin or toxin, acquired during certain growing or feeding conditions. Thus, what is usually safe harbors a masquerading toxin. Since absolute safety is unattainable, relative safety is what is sought. Relative safety is the probability that no harm will come when the food is consumed in a usual and customary manner. Even relative safety when it comes to food is a big order, because it requires constant diligence by each party who comes in contact with the food. Any glitch in the system from the field to the table can introduce a potential hazard. The starting material, i.e., the food itself, must not have high levels of naturally occurring toxicants. Safety must be maintained by growing the food in an environment free of pollutants or contaminants. Plant raw materials must be free of infestations, harmful residues, mold, and mycotoxins. Animal raw materials should not contain any veterinary drug residues or any abnormal constituents transferred from feedstuffs. Metal particles, weed contaminants, or other incidental components from harvesting or processing must be vigilantly prevented. During transportation from the field to plant or market, carriers must handle the food to maintain its quality. Care must be exercised so that proper temperatures and moisture levels are maintained and no infestation occurs during any point of the storage, shipping, and processing. Handling conditions during manufacturing, storage, shipping, and marketing must not allow microbial or chemical contamination. Prevention of natural deterioration and further contamination is often done through packaging, together with other techniques such as modified atmosphere packaging. Packaging and the other applied techniques must not introduce risks of their own, such as micromigration of nonfood polymers into the foodstuff or alternative microbial risks. Once in the consumer’s hands, food must provide the expected nutrients during its shelf life. Furthermore, food must be handled properly to prevent contamination. Unfortunately, the home and food service setting are the most common places for food mishandling. Thus the process that is taken for granted as both simple and imperative is anything but. Even when all steps happen according to proper protocol, the food may still not be safe, as the person ingesting it may react adversely to it, choke on it, or have a food–drug interaction that renders a usually safe food component injurious. While scientists know that “safe” is not risk-free, this notion is not held by consumers. In addition to the tension created by convincing consumers that no food is riskfree, there is tension around food. One reason is because there is a vast separation between the food consumer and the producer. There has been a tremendous decrease in the number of people in industrialized countries who have any connection with farming and food production. The childhood story where the little red hen grows the wheat, harvests and mills the wheat, and bakes the bread is the closest that most

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modern consumers come to the production and processing of food. Some are even far removed from preparation of food. In countries like the U.S. and the U.K., safe storage and preparation techniques are no longer learned at home because very little food is prepared. Plated meals and deli food, which are heated to serving temperature, usually in a microwave, have become the norm for some families.

13.2 CONSUMER ATTITUDES TOWARD THE FOOD SAFETY PROBLEM Consumer concerns about food safety are, in part, a protest to scientific and technological complexity and a lack of trust in government, big business, and its advertising. For some, science has become the problem, not the answer. Even for those who believe in the promise science holds, scientific complexity can be confusing. Two experts espousing different assumptions, extrapolations, and interpretations reach diametrically opposed positions often using the same data. Disagreement of scientists is not the only source of confusion. Media-savvy, self-appointed experts or consumer groups’ spokespeople with easy-to-understand messages, albeit specific agendas, add to the multiplicity of positions consumers hear. The messages from these sources are straightforward and are not tied, as ethical scientists are, to the conflicting evidence produced by the data. It is nearly impossible for anyone, including the consumer, to sort through the cacophony to find the truth. Groups that position themselves as anti big business and technology and pro consumer and environment also have a credibility edge. This is particularly true in areas where fear abounds and technology such as irradiation or biotechnology is unfamiliar. Lack of trust in government food safety agencies has been made worse by the dioxin scare in Europe, where the Belgian government failed to inform the public when they were first aware of the problem. In cases where the U.K. government has had to change its position and its statements, as in the case of mad cow disease, credibility was severely eroded. Exacerbating the problem is the quality of information given to the public. Information about food in the media is often too simplistic, too boring, too incomplete, or too biased. Sixty-second news bytes drastically distill a 10-year study, take an item out of context, or reflect the findings of a single study, which is not in agreement with a whole body of other studies. The news commentator has neither the time nor the knowledge to interpret what this news item means to someone who eats this food once a week. Information from scientists is often filled with jargon and presented in a dry, incomprehensible manner. Often both activist groups and advertisers select scientific literature that supports their point of view, but does not fairly represent the full body of knowledge. Sometimes discredited data, the most egregious examples, or highly controversial data are used to heighten worry. Some groups use statements about vulnerable groups to increase impact and fear. For example, there was a recent report and media campaign on pesticide residues in children. Studies have shown that sources are more believable if they report that a food or component is not safe, rather than affirming that the food is safe (Occhipinti and Siegal, 1994).

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Along with increased complexity, there is in some countries such as the United States decreased scientific literacy coupled with greater fear of chemicals and technology. The realization that human life has always entailed exposure to chemicals and that everything ingested and inhaled is composed of chemicals is not a shared assumption. Even more elusive to most consumers is the fact that naturally occurring chemicals are more abundant and can be more toxic than synthetic ones. Most consumers believe the converse: that natural chemicals are innocuous and synthetic ones are nefarious. Ironically, for food chemicals much more is known about the synthetic chemicals added to food than those that occur naturally. Furthermore, with respect to food there is a romanticization of the “good old days.” Careful analysis shows much shorter life spans, long hours of preparation in the kitchen, poor availability of produce in the late winter months, and other problems that are not seen in the romantic look at the “good old days.”

13.3 TESTS TO DETERMINE FOOD SAFETY Human beings have always been intuitive toxicologists, relying on their senses of sight, taste, and smell to detect harmful or unsafe food, water, and air. When asked, some consumers still feel that they are the prime determiners of food safety and try to rely on themselves. Scientists and savvy consumers have come to recognize that our senses are not adequate to assess the dangers inherent in exposure to a chemical substance, especially one in which the ill effect is either cumulative or delayed. The sciences of toxicology and risk assessment have developed to assess the safety of foods and their constituents; they use the following toxicity tests, which are performed on all compounds used as intentional additives and pesticides: • Acute tests: using at least two species of experimental animals to determine lethal dose 50 (LD50) - the dose which kills half of the animals. • Metabolic tests: done early in the protocol to track the fate of the compound in the body. If metabolites are formed, their fates and toxicity must also be determined. Different species are used to test whether the metabolism is the same and to see which species will be most similar to humans. • Subacute tests: require the feeding of a range of doses below the LD50 to at least two species for 2–3 months. A threshold or no observable effect level (NOEL) is determined from the highest dose that produces no harm in the most sensitive species. • Chronic tests: feeding a compound at doses 100–1000 times that which a human would likely ingest, to determine chronic toxicity. Two to three species fed for a lifetime are used in these tests, which not only assess the health of the animal but determine if there are any reproductive or offspring abnormalities. After the various forms of testing are done and indicate that an additive may be safely used, the NOEL is divided by a safety factor so that the acceptable daily intake (ADI) can be determined. The ADI is expressed as milligrams of the test substance per kilogram of body weight per day. The safety factor is

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arbitrary and may vary according to the test material and circumstances. Often a factor of 100 is chosen. The rationale for 100 is that if the average sensitivity of humans to a particular compound is 10 times greater than that for the most sensitive test animal, and if the most sensitive humans are 10 times more sensitive than the test animals, the use of the factor 100 (10 × 10) would mean that the most sensitive individual could safely ingest the amount equivalent to the ADI (Francis, 1993). Two possible food contaminants require special consideration in choosing a safety factor: carcinogens and prions. For carcinogens, the 100-fold safety factor may be inadequate, and factors as high as 5000 have been proposed. Some scientists adhere to the idea that there is for some carcinogens no threshold or tolerance level. Currently, more believe that there is a threshold level, but answering what is a safe level is difficult for several reasons. Lag times between exposure to a carcinogen and the development of a tumor may be at least 20 years. Dietary, genetic, and environmental factors may all play a role in detoxifying or in amplifying the effect of a carcinogen or tumor promoter. Even the concentration of the substance may be critical; at some concentrations the compound may act as a tumor inhibitor and at others it may act as a tumor promoter. Prions are a special case because no one is clear on how they get into food in the first place, let alone how much is required to cause an effect and why some individuals are susceptible, while others may not be. Setting an ADI for a substance like this is impossible without much more information. For all chemicals, carcinogens or not, a final step must be completed after establishing the ADI; a value must be assigned for the amount that would be allowed in a particular foodstuff. Consumption estimates for foods or commodities that might contain the chemical are needed along with estimates of total intake from all sources. This calculation is used to establish the maximum residue level (MRL) for any particular commodity. Constant monitoring and reevaluation of these estimated intakes make certain that estimates reflect real exposure. Recent data indicate that the intake estimates used to calculate the MRL may need some modification. More specific food product consumption data for high-risk groups are needed. Sampling procedures are often too aggregate to target these groups. More consideration of food consumed away from home is needed, because this market segment now accounts for about half of all U.S. consumer food expenditures. Even with the best scientific methods, extrapolations and judgments are required in order to infer human health risks from animal data. Basic toxicological concepts, assumptions, and interpretations were found according to a recent survey to differ greatly between toxicologists and laypeople, as well as among toxicologists working in industry, academia, and government. Toxicologists were found to be sharply divided in their opinions about the ability to predict a chemical’s effect on human health on the basis of animal studies and other laboratory methods being employed in lieu of animal tests (Ames and Gold, 2000). This difference of opinion creates public policy tensions. Renowned toxicologist Bruce Ames stated that minimizing minuscule hypothetical risks may damage public health by diverting resources and distracting the public from major risks. In addition,

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renowned epidemiologists such as Mike Osterholm state that the avoidance of possible risks from processes like irradiation may continue to allow food-borne disease that could be significantly reduced (Diaz and Noel, 2001).

13.4 FOOD SAFETY CONCERNS Food-borne disease has always topped the list of food safety concerns for most government bodies around the world. Highly publicized outbreaks of Salmonella, Listeria, and Escherichia coli have placed food-borne disease at the top of the consumer’s list of food safety concerns as well. This has not always been the case. Chemicals and pesticides used to be a much greater fear than food-borne disease. Not all are roughly equal as consumer concerns. Joint expert committees of the Food and Agriculture Organization/World Health Organization (FAO/WHO) continuously evaluate new data to ensure that the chemicals allowed in the food supply are safe and that the levels ingested do not exceed the ADI. With science now increasing its ability to detect substances to the attogram level, more must be done to help the consumer move from the position of “zero tolerance.” In recent years concerns associated with food produced with antibiotics or hormones or by biotechnology or treatment with irradiation have increased. Mad cow disease and other prion-related diseases have created great fear and economic havoc. The terrorist events of 2001 have shocked the food industry, government, and consumer into recognizing the possibility that some form of bioterrorism may be transmitted through food and water. How a food safety concern is viewed varies by the group. Scientific groups judge a hazard on known deaths or cases of illness. Consumers have many concerns about potential problems that may occur but have not as yet been documented. This is also reflected in some European regulatory responses invoking the precautionary principle. This entails the failure to approve use of a substance because of a lack of ability to prove its safety, even though there is little or no good data proving it unsafe.

13.5 MICROBIAL CONTAMINATION OF FOOD Pathogenic bacteria are responsible for the majority of food-related outbreaks in the United States. Opportunity for contamination exists at every stage in the food chain. Actual incidence of food-borne disease is unknown, even in countries with fairly sophisticated monitoring systems, because the number of cases are severely underreported. The newly installed PulseNET system by the Centers for Disease Control and Prevention (CDC) in Atlanta is an attempt to have better tracking and obtain better data regarding certain microorganisms. The most recent estimates from the CDC in the United States suggest that there are 76 million illnesses, 325,000 hospitalizations, and 5,000 deaths each year from foodborne disease. Surprisingly, the actual pathogen is identified in less than 20% of the illnesses. In other words, known pathogens account for an estimated 14 million illnesses, 60,000 hospitalizations, and 1,800 deaths. Of the known pathogens, Salmonella, Listeria,

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and Toxoplasma species account for 75% of the cases and are responsible for 1,500 deaths each year. Campylobacter jejuni is the leading reported cause of diarrheal illness (Altekruse et al., 1999). Staphylococcus aureus, Clostridium perfringens, Yersinia enterocolitica, and pathogenic strains of E. coli, as well as the parasites giardia, cyclospora, and cryptosporidium, are also problems and are in the news often for their potential to cause very large or lethal outbreaks. E. coli, Listeria, and botulism are of significant concern because of their high degree of morbidity and mortality (Yang et al., 2000). Unknown agents account for the remaining 62 million illnesses, 265,000 hospitalizations, and 3,200 deaths. Overall, food-borne diseases appear to cause more illnesses but fewer deaths than had been previously estimated in the United States (Mead et al., 1999). The increased incidence of all types of viral, bacterial, and parasitic infections is due not only to better reporting, detection, and surveillance, but also to changes in our consumption patterns. People in many Western nations buy more preprepared, prepackaged foods; demand out-of-season and exotic foods from all around the globe; utilize new technologies, such as modified atmosphere; demand food with less salt and fat; and use food services and delis more often. Coupled with these changes, consumers also desire fewer additives that might slow microbial growth. Greater pollution of areas such as the Gulf Stream, as in the case of Vibrios, also means more food-borne disease. More eating out and deli food means the possibility of greater contamination, because a greater number of people are handling the food and there are more potential steps for errors. All these trends can impact the microorganisms and chemicals found in food. Another factor increasing the incidence of food-borne disease is an increase in vulnerable populations: the very young, the very old, the chronically ill, and the immunocompromised. In most countries the increase in life span, number of transplants, and other conditions requiring immunosuppressing drugs raises the number of people in the at-risk groups. Another factor that affects the incidence of food-borne disease is the lack of knowledge about food preparation and storage. A study by the U.S. CDC traced 77% of the microbial disease outbreaks to food service establishments, 20% to homes, and 3% to food processing plants. From these data it can be seen that while increased food safety programs such as Hazard Analysis Critical Control Point (HACCP) or Longitudinally Integrated Safety Assurance (LISA) are being mandated in many parts of the world, there needs to be a plan to reduce problems in food service and an education program to tell consumers about safe food handling and preparation. Another contributing factor may be consumer preference. While food safety is preferred at a logical level, it must be balanced against other attributes of the product. Flavor preference for a soft cheese made with unpasteurized milk or raw fish may outweigh the small risk of contracting Listeria, E. coli, or a parasite. Price may impact the choice of a specific food, if the safer food is more expensive to produce. Interestingly, food safety is an income-elastic good. As incomes rise, so does the premium a consumer will pay for food that is perceived to be safer, yet at the same time, those with more income and education often engage in riskier food safety behaviors (Yang et al., 2000; Swinbank, 1993).

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Interestingly, traditional market mechanisms do not work directly with respect to food safety issues. First, food safety attributes are not readily determined at the point of purchase. Competing food products are rarely appraised according to alternative levels of microbiological spoilage or probability of contaminated cans. Second, a less safe product is usually not intentionally supplied. The problem often lies in accidental contamination or a change in the process handling, shipping, storage, or product composition such that microbial growth is allowed or contamination occurs. Consumers are often unaware that there are long-term as well as short-term consequences of food-borne disease. Sometimes the acute effects of food-borne disease do not end in two or three days. Several significant food-borne pathogens are capable of triggering chronic disease, and even permanent tissue or organ destruction, probably via immune mechanisms. Arthritis, inflammatory bowel disease, hemolytic uremic syndrome, Guillain-Barre syndrome, and possibly several autoimmune disorders can be triggered by food-borne pathogens or their toxins. Research is needed to more fully understand the mechanisms by which the immune system is inappropriately activated by these common food-borne disease-causing agents (Mead et al., 1999; Bunning et al., 1997). Understandably consumers react viscerally to a dread outcome. If a supplier makes a mistake, the company will be pilloried in all forms of media. One mistake in a million (an undetectable number) that gives rise to the death of two people will not only affect the sales of the particular product, but those of all products of that type and by that manufacturer. Many companies fold in the face of such an adverse event. To prevent such negative consequences, many industry programs are in place worldwide. Mandatory HACCP, good manufacturing practice (GMP), and other such programs require sanitary conditions for food production and help minimize chances for contamination. International Standards Organization (ISO) 9001 and ingredient specification programs ensure that the raw materials incorporated into food products meet required low levels of contamination and reduce both corporation and consumer risk.

13.6 RISK-BENEFIT AS IT APPLIES TO FOOD The risk-benefit concept is clear-cut in many aspects of our lives. For instance, in medicine the treatment of disease has inherent and sometimes lethal risks, but the benefits afforded by the treatment are believed by most to outweigh the risks. In this case the risk is vital and the benefit is vital. In sports, the activity may contribute to health (vital) and well-being (nonvital), but it may pose a risk of injury (vital). However, the risk is voluntary and the athlete may feel in control. With food the risk-benefit may be much less apparent to the consumer. Chemicals may inhibit microorganisms but may pose some risk. Since risk is present in the food, it is involuntary, and the consumer has a sense of outrage because there is no sense of control with respect to its use. Adding to the imbalance in the risk equation are many reports stating the risks of its use and virtually none touting the benefits. For example, with pesticides in food the risks include a possible increase in the number of cancers, a reduction in the immune response, estrogenic effects, and environmental concerns. The benefits stating that pesticides reduce vector-borne disease, decrease the amount of fossil fuel required to mechanically cultivate a field, reduce the number of bug

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parts and droppings in food, and increase crop yield to feed a burgeoning global population are only rarely reported. In the same manner risks of additives are often cited by various groups, while the benefits remain unsung in articles to which the consumer has ready access. For instance, a preservative can have several important benefits: • Formation of a cancer-producing mycotoxin may be arrested by additives inhibiting mold growth. • Food costs can be reduced because staling and oxidation are retarded and less expensive packaging and transportation solutions are required. • Food waste is reduced. • Oxidized fats with their attendant health risks are reduced. • Preservatives make possible foods that meet consumer wants of convenience. Looking at the risks and not the benefits of chemicals or technologies associated with food is like an accountant shearing a ledger in half and considering the liabilities without the assets. However, even if judgments of risk and benefit are considered, they have been found to be inversely related (Alhakami and Slovic, 1994). Activities or technologies that are judged high in risk tend to be judged low in benefit, and vice versa. In situations where there is high risk, there tends to be a confounding of risk and benefit in people’s minds. Risk gurus Paul Slovic and his colleagues at Decision Research in Eugene, OR, found that perceived risk is often not related to the probability of injury. Communicating risk is about trust. Trust can be easily destroyed but is very difficult to establish. Once there is the element of distrust, it fuels more distrust. Risk communicators should be aware that risks that people can choose to avoid (e.g., skiing) give a sense of control and that risks that are familiar (e.g., Salmonella from potato salad or disease from smoking) or have been around a long time (e.g., food-borne disease) are easily tolerated and often minimized. Risks that are poorly tolerated are involuntary risks, such as exposure to small amounts of pesticide residues in food and those risks that have unknown effects (e.g., biotechnologyproduced tomatoes) or long-delayed effects (which are possible with prion exposure). The framing of risks makes a tremendous difference in their acceptance. A study reported in the New England Journal of Medicine showed that 44% of respondents would select a procedure for a lung cancer treatment when told they had a 68% chance of surviving, but only 18% would select the procedure if they were told they had a 32% chance of dying. It is no wonder that the consuming public has an inordinate fear of some food additives and pesticides, because the information is always reported in terms of increased risk rather than possible reduced risk, due to less mold or bacterial growth. Some risks were accepted when consumers were faced with a choice about risks. For instance, consumers in California were asked if they would accept food irradiation. The responses were varied but had strong negative leanings. If the same consumers were asked if they would accept irradiation as a way to use less pesticide or reduce a microbial hazard, then irradiation acceptance was increased (Bruhn, 1999).

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Consumers thus appear quite capable of understanding and using the risk-benefit concept for making decisions about food choices. It is mandatory that all sides of the story get a hearing so that these informed choices can be made considering both the risks and benefits. The final word about risk-benefit is that the definitions of the risks and the benefits are not the same in all cases. The definition of benefit needs to be clear. For some countries, the benefit is reduced postharvest food losses. The value of this benefit can vary with the country involved. Different weights may be assigned if there is danger of severe food shortage versus simply an increase in the cost of the substance. Thus, the science and art of risk assessment are difficult because each step in the process is value laden.

13.7 NUTRITIONAL EVALUATION OF FOOD PROCESSING Food processing both maintains and destroys nutrients. In a few cases nutrients are even more available after processing. This seeming paradox will be explored. For most foods, processing reduces the nutrient content, compared to the freshly harvested item. However, processing makes food and the nutrients within available at a later date, so the loss incurred must be compared with what would happen to the diet if no processing was utilized. For some foods, processing makes the nutrients more available because toxic factors and antinutrients are destroyed. Cassava, soybeans, and corn are all examples of important classes of food that are made either less toxic or more nourishing through processing. Cyanide is removed from cassava with grinding and soaking; enzyme inhibitors and lecithins are destroyed during the heating of the soybean; and niacytin releases niacin when corn is processed with lime (CaO). All nutrients (except water) may undergo either chemical or physical changes during processing that render them inactive or less bioavailable. This occurs for macro- as well as micronutrients. During browning, the amino acid lysine can react with carbohydrates to lower the biological value of protein. Fat oxidation can decrease the level of essential fatty acids in the diet and can lower the overall food quality by introducing free radicals and other oxidized products into the diet. Hydrogenation alters the nutrition properties of oil by increasing the degree of hydrogenation and by introducing trans fats to the diet. Adding plant stanols to reduce cholesterol is another way the nutritive effect of fats can be changed by processing. With each pressing of olive oil, fewer and fewer phenolics, with their anitoxidant properties, are available. Altering particle size of grains is one way that processing can change the physiological effect of nondigestible carbohydrates. Pregelatinizing starch causes greater elevation of blood glucose than the equivalent starch item that has not undergone pregelatinization treatment. Heat treatment and Maillard reactions can increase resistant starch and may therefore increase the amount of material in the food behaving like fiber.

13.7.1 EFFECTS

ON

VITAMINS

Vitamin loss during processing and cooking of various foodstuffs has been of interest to nutritionists, processors, and consumers. Vitamin C, the most labile vitamin, is

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lost during canning, blanching, fresh or frozen storage, drying, and irradiation. Losses can be 100% if the conditions of processing and storage are not controlled. For example, a study of processed mashed potatoes fortified with vitamin C shows the lability of this vitamin. Cumulative losses of vitamin C were: 56% for addition of the vitamin to freshly mashed potatoes, 82% for drum-dried potatoes, 82% for flakes stored 4.3 months at 25°C, and 96% for reconstituted mashed potatoes held 30 min on a steam table. One serving (100 g) would contain 10 ppm — 2% of the adult U.S. Recommended Dietary Allowance (RDA). A more stable isomer used to fortify the mashed potatoes would yield about 201 ppm (about 33% of the RDA of vitamin C per serving) (Wang et al., 1992). Thiamin and folate, while not as labile as ascorbate, are easily lost during processing. Thiamin is extremely water soluble and destroyed by heat, so much can be leached into the cooking or storing liquids during preparation of both meats and vegetables. Losses in the making of soy flour are minimal, but losses in the making of soy flour into tofu stored in water are 85% or greater (Fernando and Murphy, 1990). In addition to losses due to leaching, thiamin content can decrease markedly when subjected to basic pH. The splitting under alkaline conditions of the two rings of thiamin causes loss of all biological activity for humans. Thus, a quick bread with bicarbonate leavenings can lose up to 75% of the thiamine in the finished baked product because of the synergistic effect of both heat and pH. Sulfites used as preservatives will also cleave thiamine. Folic acid is easily lost during storage of fresh vegetables at room temperature and through many heat processes. Oxidative destruction of 50–95% of the folate can occur with protracted cooking or canning. Currently in the United States folate is added to all enriched or fortified cereal and flour products in order to increase this nutrient to prevent neural tube defects and to reduce coronary disease and some cancers. Thus, the processed, fortified product will have more folate. Riboflavin is unstable to light; therefore, riboflavin-containing foods subjected to either ultraviolet or visible light can show significant losses of riboflavin. Riboflavin is much less water soluble than thiamin, but long-term storage in water can cause leaching. For instance, tofu stored in water can lose 80–90% of the riboflavin. Pyridoxine (vitamin B6) losses in food are dependent on the temperature and on the specific form of the vitamin. Thermal processing and low moisture storage of certain foods result in reductive binding of pyridoxal to lysine in proteins, making it unavailable. Thus canning and drying losses can be substantial. Losses in canned infant formulae are of particular concern because the formulae may be an infant’s only food source. During blanching there is not much measurable loss of vitamin B-6 content, but recent studies have shown that the loss of bioavailability or absorbability may be significant. Most meats, a good source of vitamin B-6, lose little during preparation. Fat-soluble vitamins show somewhat greater stability than water-soluble vitamins. They are not as easily destroyed by normal cooking and are not leached into the cooking water. However, vitamin A changes slowly from the all-trans form, the most biologically active form, to the cis form during canning and with long times on a steam table. Carotenoids, currently valued for their antioxidant and possible anticarcinogenic potential, also oxidize to some degree during heat

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treatment. Traditional canning causes greater losses of vitamin A and carotenes than high-temperature short-time (HTST) processing (Chen et al., 1995). Little loss occurs in frozen blanched vegetables, but vitamin A and other carotenoids easily oxidize in drying when no antibrowning additives such as sulfite are used. Vitamin E is not very stable to heating followed by freezing and is lost in milling as the germ is removed from white flour. Some vitamin E isomers are lost during the processing of oil. In many countries the vitamin D content of food is increased through fortification of dairy products. Vitamin K is not greatly affected by heat but is lost to light, so vitamin K-containing oils retain their vitamin content if stored in amber bottles. The whole class of phytochemicals that have beneficial effects on the body are also affected by processing. These compounds can be fat soluble or water soluble. Their effects can be changed by processing, as seen in the differences between green and black teas. Firing while the leaf is still green making green tea retains more antioxidants than allowing the leaf to wither to make black tea. The removal of the skin in the making of white wine can change the number of phytochemicals. The use of sulfite to prevent browning in the drying of golden raisins causes an increase in the antioxidant capacity of the raisin over those with no sulfite present.

13.7.2 EFFECTS

ON

MINERALS

Minerals are lost into the cooking liquid if the liquid is not ingested. Minerals are retained in the bran and germ fragments of the grain and are therefore lost to those who ingest only refined grain products. However, even if the whole grain is ingested the bioavailability of the mineral may be impaired because the mineral is tightly bound to the bran of the germ. Furthermore, some minerals may be made more available during the cooking process, while others become less bioavailable. While effects of various nutrients and certain nonnutrient components of food on mineral utilization have been studied, less is known about the effects of food processing and preparation procedures. Fermentation during the production of beer, wine, yogurt, and African tribal foods affects bioavailability of zinc and iron. Baking changes the chemical form of iron in fortified bread products, and these changes can affect bioavailability. The availability of iron in milk-based infant formula depends on whether iron is added before or after heat processing. Food packaging (e.g., tin cans) can alter food composition and thus potentially affect mineral bioavailability. Maillard browning has been reported to cause slight decreases in zinc availability.

13.8 NEWER AND NOVEL TECHNOLOGIES 13.8.1 IRRADIATION Treating fresh or frozen meats with ionizing radiation is an effective method to reduce or eliminate food-borne human pathogens. The irradiation dose, processing temperature, and packaging conditions strongly influence the results of irradiation treatments on both the microbiological and nutritional quality of meat. Radiation doses up to 3.0 kGy have little effect on the vitamins in chicken and pork but have very substantial effects on food-borne pathogens. Even vitamins such as thiamin,

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which are very sensitive to ionizing radiation, are not significantly affected by the U.S. Food and Drug Administration maximum-approved radiation dose to control Trichinella, but at larger doses they are significantly affected (Fox et al., 1995).

13.8.2 BIOTECHNOLOGY Biotechnology is viewed as a new process. In actuality, it is an extension of an old process. Time-honored processes such as fermentation and plant and animal husbandry employ biotechnology. However, in the last 20 years the technology has taken a giant step forward by using gene-splicing techniques to speed up the process and make it more precise. It allows changes that were never before achievable because genes that could not be incorporated with normal breeding techniques can be with biotechnology. Biotechnology has the potential to both increase and decrease available nutrients in the same way that plant breeding can. Care must be exercised that the nutrient content of a food is not reduced when another attribute is engineered into it. Golden rice is an example where vitamin A is incorporated into food for use in parts of the world where the number-one cause of preventable blindness in children is vitamin A deficiency. Rice is a great vehicle because most of the regions where this deficiency is a problem are rice-eating regions. One food safety concern about genetic engineering is that toxic components naturally found might be increased. Attempts to breed or genetically engineer plants with natural herbicides or pesticides or herbicide-resistant plants could increase the potential toxicity if many foods would carry a natural pesticide. Scientists must not be lured into the common belief that nature is benign and chemicals from the lab are noxious. Another food safety concern regards allergenicity. The transfer of a protein into a food through biotechnology could lead to allergic reactions for persons not expecting that particular protein in a totally different kind of food. In 2000, Starlink corn with cry9C protein was not approved for human food use because the regulatory authorities thought that there were inadequate data assuring that the protein was not allergenic. This subsequently was the cause of a massive voluntary recall. Currently the ability of laboratories and regulatory agencies to determine if a food has been produced by biotechnology is limited. Accuracy on different food products varies, so much more research is needed in this area. Another big concern is that bioengineered crops will adversely affect the environment. Some reports have suggested that BT-corn will adversely affect other species or that some bioengineered products will become dominant strains.

13.9 ADDITIVES Food additives can enhance the safety and nutritional quality of a food or vice versa. By preventing oxidation of fat and easily oxidized vitamins, antioxidants ensure that safety is enhanced and the intended nutritional value of the food is delivered. Antibrowning agents such as sulfite retain phytochemicals and vitamins A and C but lower the amount of thiamine, folate, and pyridoxal. Sorbic acid can prevent

304

Chemical and Functional Properties of Food Components

mold and possible mycotoxins but can form protein adducts in the stomach that affect the availability of the protein. Vitamins C and E react with nitrite to prevent the formation of nitrosamines. This reaction will use the vitamins and thus they will not be available for other functions. Phosphates are antimicrobial because of their sequestering capacity. This capacity can have an antinutritional effect because of mineral-binding ability. Vitamins themselves are added to fortify and enrich products, making food have more nutrients than it might otherwise. Sometimes food is highly fortified to give consumers the idea that if they eat one serving, they do not need to pay attention to other parts of their diet. Consumers need to be educated that there is much more to food that is beneficial than just vitamins and minerals. New products that replace entire foods or macronutrients, such as fat replacers, must be evaluated both for their nutritional contribution and for their dietary impact. These foods may help some people reach needed dietary goals. In other cases, they introduce risks such as overconsumption and abuse, vitamin leaching or competition, and gastrointestinal problems. In some instances additives that were intended for use in microamounts are now being used in macroquantities. They may exceed the ADI and have effects that would make them unsafe at high levels of use. Additives, like all food components, need to be looked at with the risks and benefits in mind. Contrary to popular belief, food additives can be regarded as the safest and most studied constituents of our food supply. This is as it should be. Furthermore, surveillance of food additives is a mandatory consequence of their use; their safety must be continually ensured, considering any change in usage patterns and new data. This constant vigilance can make consumers feel that science and technology is untrustworthy, because they perceive that science changes its mind. In fact, just the reverse should be true. Since additive safety is constantly being challenged to ensure that only the most wholesome food products are on the market, fear should be lessened. Unfortunately, this usually is not the case. Substances should never be added to food without careful analysis and a conservative approach to their use. A clear benefit to the end user must be present before a food additive should be allowed.

REFERENCES Alhakami, A.S. and Slovic, P., A psychological study of the inverse relationship between perceived risk and perceived benefit, Risk Anal., 14, 1085, 1994. Altekruse, S.F. et al., Campylobacter jejusi: an emerging foodborne pathogen, Emerging Infect. Dis., 5, 28, 1999. Ames, B.N. and Gold, L.L., Paracelsus to parascience: the environmental cancer distraction, Mutat. Res., 447, 3, 2000. Bruhn, C.M., Consumer perceptions and concerns about food contaminants, Adv. Exp. Med. Biol., 459, 1, 1999. Bunning, V.K., Lindsay, J.A., and Archer, D.L., Chronic health effects of microbial foodborne disease, World Health Stat. Q., 50, 51, 1997. Chen, B.H., Peng, H.Y., and Chen, H.E., Changes of carotenoids, color, and vitamin A content during processing of carrot juice, J. Agric. Food Chem., 44, 1912, 1995.

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Diaz, A. and Noel, C., “Beating Bacteria in the Food We Eat. Irradiation: It Sounds Bad, But is It?” ABC news commentary, February 28, 2001. Fernando, S.M. and Murphy, P.A., HPLC determination of thiamin and riboflavin in soybeans and tofu, J. Agric. Food Chem., 38, 163, 1990. Fox, J.B.J. et al., Gamma irradiation effects on thiamin and riboflavin in beef, lamb, pork, and turkey, J. Food Sci., 60, 596, 1995. Francis, F.J., How do we test for safety of food?, Sci. Food Agric., 5, 2, 1993. Jones, J.M., Food Safety, Eagan Press, St. Paul, MN, 1992. Mead, P.S. et al., Food related illness and death in the United States, Emerging Infect. Dis., 4, 607, 1999. Occhipinti, S. and Siegal, M., Reasoning about food and contamination, J. Personality Soc. Psychol., 66, 243, 1994. Swinbank, A., The economics of food safety, Food Policy, 18, 83, 1993. Wang, X.Y. et al., Vitamin C stability during preparation and storage of potato flakes and reconstituted mashed potatoes, J. Food Sci., 57, 1136, 1992. Yang, S., Angulo, F.J., and Altekruse, S.F., Evaluation of safe food-handling instructions on raw meat and poultry products, J. Food Prot., 63, 1321, 2000.

14

Mutagenic, Carcinogenic, and Chemopreventive Compounds in Foods Agnieszka Bartoszek

CONTENTS 14.1 Introduction ..................................................................................................308 14.2 Role of Mutagens in Carcinogenesis...........................................................309 14.3 Metabolic Activation and Formation of DNA Adducts by Food Mutagens and Carcinogens ................................................................310 14.4 Tests for Mutagenicity and Carcinogenic Properties of Food Components..................................................................................................315 14.5 Food-borne Mutagens and Carcinogens ......................................................317 14.5.1 Introduction ......................................................................................317 14.5.2 Mycotoxins.......................................................................................318 14.5.3 Nitrosamines.....................................................................................319 14.5.4 Mutagens in Heat-Processed Foods.................................................320 14.5.4.1 Heterocyclic Aromatic Amines.........................................320 14.5.4.2 Polycyclic Aromatic Hydrocarbons..................................322 14.5.4.3 Effect of Commercial Processing and Cooking Techniques ........................................................................323 14.5.5 Mutagens in Tea, Coffee, and Alcoholic Beverages .......................324 14.5.6 Other Risk Factors ...........................................................................325 14.6 Chemopreventive Food Components ...........................................................326 14.6.1 Anticarcinogenic Food Components ...............................................327 14.6.2 Cancer Chemoprevention.................................................................330 14.7 Summary ......................................................................................................331 References..............................................................................................................333

1-5871-6149-4/02/$0.00+$1.50 © 2002 by CRC Press LLC

307

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Chemical and Functional Properties of Food Components

14.1 INTRODUCTION Factors and substances able to induce changes in the genetic code are called mutagens. Those that can cause cancer, excluding genetic susceptibility, are called carcinogens. Such factors are omnipresent in the human environment; they can be of natural origin or formed as a result of numerous chemical processes. To these factors belong a variety of synthetic chemicals, combustion products, water and air pollutants, sunlight and ionizing radiation, cigarette smoke, alcohol, and some food components. Such factors like specific occupational exposures or cigarette smoking are clearly high-risk conditions for cancer. Diet is a major environmental variable; however, its impact on tumor development is vague, since it may both promote and inhibit carcinogenesis. A fundamental observation in cancer epidemiology during the last century was that cancer incidence and mortality rates vary dramatically across the globe (Parkin, 1998). In addition, rates of cancer among populations migrating from low- to highincidence countries change markedly; in most cases they approximate the rates in the new region within one to three generations. For instance, the replacement of foods of plant origin with foods of animal origin, notably meat products and dairy products, increases cancer incidence, especially the risk of breast, colon, prostate, and rectum cancers (Bingham, 1999). These cancers are virtually absent in the populations of some countries of the developing world; the general overall cancer burden there is strikingly lower. Similar conclusions were inevitable in the case of epidemiological studies on prostate cancer incidence and breast cancer incidence in migrants to the United States from Poland (Staszewski and Haenszel, 1965) and Japan (Wynder et al., 1991), respectively. These cancers are relatively infrequent in the countries of origin, but in the investigated populations of immigrants they reached the level observed in the United States, even within one generation. Such lines of evidence indicate that the primary determinants of cancer rates are not genetic factors, but rather environmental and lifestyle factors that could, in principle, be modified to reduce cancer risk. It has been estimated that approximately 35% of cancer deaths in the United States are attributable to dietary habits (Anon., 1993). Not surprisingly, the presence of potential mutagens and carcinogens, as well as anticarcinogenic substances in foods, has become of widespread interest. The majority of mutagens and carcinogens found in foods are formed during food processing, especially thermal processing. However, the processing and heating of foods have invaluable advantages. They increase shelf life of foods, which can then be economically priced, decrease the risk of diseases caused by food-borne pathogens, improve taste and nutritive value of food, and provide easy-to-prepare and time-saving convenience foods. Therefore, it is of utmost importance to establish what processes are responsible for mutagen and carcinogen formation in food and to clarify their involvement in transformation of a normal cell into a cancerous one. This field of research is progressing rapidly, and it may be expected that the gathered knowledge should bring about new technologies that will keep the current benefits of food processing, while minimizing the formation of harmful compounds. It should also enable the elaboration of sound dietary recommendations aimed at diminishing cancer risk.

Mutagenic, Carcinogenic, and Chemopreventive Compounds in Foods

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14.2 ROLE OF MUTAGENS IN CARCINOGENESIS Transformation of a normal cell into a cancerous one manifests itself macroscopically as an uncontrolled cellular growth, resulting in the formation of a tumor consisting of cells that do not differentiate into their specialized tissues, may metastasize and invade other sites of the body, and eventually lead to the death of the organism. Each cancer arises from a single cell. This implies that once the abnormal behavior arises (e.g., loss of control over cell division), such capacity is handed to daughter cells. Cancer is thus a disease that fundamentally involves the structure and function of DNA. Recent developments in the area of molecular carcinogenesis have demonstrated that neoplastic transformation involves the accumulation of multiple genetic alterations in critical cancer-related genes. Therefore, cancer is often referred to as a disease of genes (Sugano, 1999). Cancer-related genes are numerous and include oncogenes; tumor suppressor genes; genes involved in regulation of the cell cycle, development, DNA repair, and drug metabolism; genes involved in immune response and angiogenesis; and other correlates of metastasis. It has been evidenced that certain alleles of these genes contribute to cancer susceptibility and are mutated in tumors. The alleles conferring increased risk for cancer might require an environmental influence to have their effect. The genetic background modifies the risk of disease for exposed individuals (risk might be raised or lowered). In the majority of cases in which diet is involved in the carcinogenic process, susceptibility genes are thought to be most relevant (Dean, 1998; Sinha and Caporaso, 1999). The process of carcinogenesis in humans (originally identified in animals), resulting in genetic alterations in cancer-related genes, proceeds in a multistage manner over a long latent period (Anon., 1997; Sugano, 1999). At the onset of cancer development, two major stages can be distinguished: initiation and promotion. Carcinogens responsible for the changes that can lead to the conversion of a healthy cell into a neoplastic cell are divided into genotoxic and epigenetic (Taylor, 1982). Genotoxic carcinogens, acting at the initiation stage, include mainly substances displaying mutagenic properties. Most mutagenic and carcinogenic food components belong to the group of genotoxins. The name originates from their ability to damage cellular genetic material. The damage usually involves the formation of a covalent bond between DNA and a mutagen after any required host-controlled biochemical activation. The sites, which most frequently undergo such modifications, are nitrogenous bases, guanine in particular (Swenberg et al., 1985). DNA adducts interfere with proper pairing between complementary bases and diminish the fidelity of DNA replication, which in turn may result in incorporation of incorrect nucleotides into the daughter DNA molecule. In this way, as a result of replication, the promutagenic lesion, such as a DNA adduct, unless repaired by cellular repair systems, becomes fixed in a form of mutation, i.e., as a change in the genetic code. For genotoxic food-borne carcinogens, DNA binding is crucially important; without DNA adduct formation, such agents do not induce cancers (Swenberg et al., 1985). Not all DNA adducts are critical lesions; only those altering the important cancer-related genes by causing specific mutations following DNA replication are essential for neoplastic transformation. The cell bearing mutated gene(s) may be

310

Chemical and Functional Properties of Food Components

eliminated by various mechanisms, protecting the organism against development of abnormal cells, or it may persist within tissue. However, it needs to undergo cycles of cell duplication, involving epigenetic control mechanisms, to generate a permanently altered, mutated cell that expresses preneoplastic characteristics, giving rise to a clone of initiated cells. Such a clone of cells susceptible to cancerous growth, if exposed to one or more factors (mostly epigenetic), called promoters, may proliferate to a definable focus of preneoplastic cells. This stage is known as promotion. Epigenetic factors operating as promoters of cancer usually require high and sustained exposures. Their effects, unlike those of genotoxins, are reversible (Weisburger and Williams, 2000). To such factors belong many natural and man-made chemicals, including those present in food. The mechanisms of promotion are less understood than those of genotoxin action, but they are thought to involve stimulation of cell proliferation, blockage of communication pathways between normal and mutated cells, and more. Also, partially reduced oxygen molecules such as hydroxyl radical or superoxide radical, often referred to as oxygen radicals, act at the stage of promotion. They arise as a side effect of normal metabolism, and their formation is believed to underlie the cancer-promoting effect of a high-protein and high-fat diet, since these food constituents are intensively metabolized. Oxygen radicals can bind to various cellular components, including DNA; they have also been shown to influence gene expression (Ames et al., 1993; Burcham, 1999). The initiation and promotion of neoplastic transformation is followed by the final stage of the carcinogenic process, known as progression, which comprises the growth of the tumor and its spread to other body parts. There are several lines of evidence that at least some carcinogens present in food products are able to give rise to the described above sequence of events in higher and lower vertebrates (Anon., 1993).

14.3 METABOLIC ACTIVATION AND FORMATION OF DNA ADDUCTS BY FOOD MUTAGENS AND CARCINOGENS The vast majority of carcinogens, such as those in foods, accounting for a large fraction of the human cancer burden, do not possess mutagenic and carcinogenic properties in themselves. In order for these properties to be revealed, the metabolic activation in an organism is required, leading to the formation of electrophilic metabolites capable of binding to nucleophilic centers in DNA. Therefore, in literature the name promutagen or procarcinogen is often used to describe the compounds that must be converted by cellular enzymes into ultimate genotoxic mutagens and carcinogens. Metabolic activation of carcinogens involves many enzymatic systems, known as phase I enzymes. The most important is the cytochrome P450 complex, consisting of several different isoenzymes, which are particularly active in the liver. Other enzymes include peroxidases, quinone reductases, epoxide hydrolases, sulfotransferases, and others. Their variety reflects the diversity of chemical structures of compounds to which an organism is exposed. These may be harmful substances or needed ones, or even those indispensable for its proper functioning. One could argue that the activation of carcinogens is an undesirable side effect of metabolic pathways,

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which were developed in the course of evolution most probably in order to improve the utilization of nutrients and elimination of unwanted or harmful substances. Competing with enzymatic activation are detoxification processes involving phase II enzymes. These enzymes catalyze the attachment of polar groups to increase water solubility of normal metabolites, as well as foreign compounds, and thereby facilitate elimination. To the enzymes responsible for removal of mutagens and carcinogens belong most of all glutathione-S-transferases and glucuronyltransferases; however, phase I enzymes are sometimes also involved in the initial stages of detoxification. It even happens that activation and detoxification run in parallel and are catalyzed by the same enzymatic system. For instance, epoxidation of benzo[a]pyrene by cytochrome P450 in position 7/8 results in the formation of a carcinogenic metabolite, while in position 4/5 it produces an inactive derivative excreted readily from the organism. Below are given some examples of well-established metabolic activation pathways for a few classes of mutagenic compounds found in food, along with the major products of reaction of their main toxic metabolites with DNA, more precisely, with guanine, which is the preferred site of binding of electrophilic intermediates. Metabolic activation of aflatoxin B1, belonging to the class of mycotoxins, is catalyzed by cytochrome P450. The metabolic conversion of this compound can follow many pathways; however, only the epoxidation in position 8/9 produces the ultimate carcinogen: O

O

O

O

O

O cytochrome P450 O

O

O

OCH3

O

O

OCH3

Formula 14.1

This metabolite binds to the N7 position of guanine, giving an unstable adduct 8,9-dihydro-8-(N7-guanyl)-9-hydroxy-aflatoxin B1, which either undergoes spontaneous depurination or rearrangement to a stable 8,9-dihydro-8-(2,6-diamino-4-oxo3,4-dihydropyrimid-5-yl-formamide)-9-hydroxy-aflatoxin B1, following the opening of the imidazole ring (Wakabayashi et al., 1991). The formation of nitrosamines in the reaction of amines with nitrites under acidic conditions in the stomach can be considered as nonenzymatic activation of amines present in food. Nitrosamines undergo further metabolism, catalyzed enzymatically by cytochrome P450, involving hydroxylation (Anon., 1993). The hydroxylated derivative is unstable and in a series of spontaneous reactions gives rise to methyl carbo-cation, which alkylates guanine in position O6, thus in the site taking part in the formation of hydrogen bonds in DNA with complementary base cytosine.

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Chemical and Functional Properties of Food Components

O

O

O O

O

HO

O

O O

+DNA

O

OCH3

N

HN

O O

O

H2N

OCH3

N

N

sugar

O

O

O

H

O

O

OH N

HN O H2N

O

OCH3

NH

N

sugar

Formula 14.2

H 3C

H 3C N

NH + NO2 + H

O + H 2O

cytochrome      P450

H 3C

H 3C H

H 3C N HO

N

H 2C

-H 2O

N

N

O

N

O + CH2O

H 2C

N

N

OH

H 3C

unstable

H 2C

H H

N

N

H 2C

N

N

H

CH3 + N2

Formula 14.3

Metabolic activation of benzo[a]pyrene consists of three enzymatic reactions. First, the formation of epoxide in position 7/8 is catalyzed by cytochrome P450; epoxidation in position 4/5 results in detoxification of this compound. Then, epoxide hydrolase converts the epoxide into 7,8-dihydrodiol, which is subsequently oxidized to 7,8-diol-9,10-epoxide. The formation of four different diastereoisomers is feasible, among which anti-9,10-epoxide derived from (-)-7,8-dihydrodiol is by far most

Mutagenic, Carcinogenic, and Chemopreventive Compounds in Foods

313

CH3 N

HN

H 2N

N

N

sugar Formula 14.4

Formula 14.5

carcinogenic (Dipple and Bigger, 1990). In DNA, this derivative reacts most frequently with guanine in such a way that position 10 of benzo[a]pyrene and position N7 of guanine become linked together. Aromatic compounds substituted with amino groups, e.g., heterocyclic aromatic amines present in protein food products, are usually activated by cytochrome P450 to hydroxylamines. This type of metabolism is observed in the case of 3-amino-1methyl-5H-pyrido[4,3-b]indole (Trp-P-2). After further spontaneous rearrangements, hydroxylamine derivatives produce electrophilic intermediates, which are able to modify DNA bases (Sugimura and Sato, 1983). One of the possible structures of DNA adducts formed by Trp-P-2 with guanine is given in Formula 14.7.

314

Chemical and Functional Properties of Food Components

CH 3

CH 3

cytochrome P450

N

N

N

N

NH 2

NH-OH

H

H

N

N - SO4 -2 N

NH

O

N

SO 4

NH

H

H

unstable Formula 14.6

CH3 O N

N

N

N

H

H

N

NH

N

NH2

H

Formula 14.7

In this case, the position C8 of guanine has been modified. The group of heterocyclic aromatic amines includes so many different compounds that a large variety of chemical structures of DNA adduction products formed by them can be expected. The normal metabolic processes taking place in the organism generate numerous partially reduced oxygen molecules. They are responsible for many detrimental effects to the cells. Oxygen radicals may cause peroxidation of cell membrane lipids, oxidation of proteins, and modification of DNA components. Reaction with DNA leads to the formation of a variety of promutagenic lesions (Ames et al., 1993; Halliwell, 1999), usually called oxygen DNA adducts. Formula 14.8 gives examples of such adducts resulting from hydroxylation of nucleobases. It is nowadays generally accepted that the enzymatic systems implicated in metabolism of carcinogens may be the reason for different susceptibility of humans to cancer (van Iersel et al., 1999; Manson and Benford, 1999; Wolf, 2001). Therefore, the genes coding enzymes responsible for biotransformation of carcinogens have been included in the list of cancer-related genes. Importantly, many dietary compounds can influence various phase I and II enzymes by induction or inhibition. For example, cytochrome P450 isoenzyme CYP1A2 (phase I) activity may be induced by polycyclic aromatic

Mutagenic, Carcinogenic, and Chemopreventive Compounds in Foods

O

NH2 N

N

N

HN

OH

OH N

N

H 2N

N

N sugar

sugar

HO

315

HO

adenosine

guanosine

O

NH2 OH

CH3

H N

N OH

O

N

O

OH

sugar

N

OH

sugar

thymidine

cytosine Formula 14.8

hydrocarbons in grilled and smoked foods and inhibited by naringenin in grapefruit. Similarly, the phase II enzyme glutathione-S-transferases can be induced by many nonnutrient phytochemicals, dietary lipids, and reactive oxygen species (Sinha and Caporaso, 1999). Current research attempts to relate genetically correlated sensitivity and environmental exposures, including dietary impact, to individual cancer risk.

14.4 TESTS FOR MUTAGENICITY AND CARCINOGENIC PROPERTIES OF FOOD COMPONENTS Food products contain thousands of compounds — some of nutritive value — nonnutritive components, numerous additives, substances formed during processing, and pesticide residues. Their safety is of utmost importance for human health protection, including cancer risk assessment. In order to evaluate the carcinogenicity of individual food constituents and their mixtures, often of unknown chemical structure, as well as the impact of cooking procedures, short-term reliable and inexpensive tests are necessary. Since cancer risk associated with chemical compounds is thought to stem mainly from their ability to induce mutations, mutagenicity

316

Chemical and Functional Properties of Food Components

is used in the assessment of carcinogenic properties of food components. Such ability can be detected with the aid of bacteria whose culturing is easy, quick, and economical. In the case of bacterial mutagenicity tests, it is assumed that the factors capable of damaging bacterial DNA can interact in a similar way with the DNA of higher organisms. The evaluation of carcinogenicity, i.e., the ability of substances to induce cancers, is performed mainly in mice and rats. The method most widely used to evaluate mutagenic activity is the Ames test (Ames et al., 1975). It utilizes mutant strains of Salmonella typhimurium unable to synthesize histidine, thus dependent on an outer source of this amino acid. The back mutation in the appropriate gene makes the bacteria histidine independent. The frequency of back mutations increases in the presence of mutagenic factors. To mimic metabolic activation of mutagens, typical for mammalian cells but often absent in bacteria, microsomal fraction (usually isolated from rat liver) is added concomitantly with the substance studied. Currently, an array of Salmonella strains is available that enable not only the evaluation of the overall mutagenic activity of a given compound, but also the type of mutation it induces. Moreover, the techniques of genetic manipulation offered by modern molecular biology allowed the construction of bacterial strains expressing various animal and human genes coding enzymes implicated in activation of chemical carcinogens. For instance, a strain of Salmonella typhimurium expressing mammalian cytochrome CYP1A2 and NADPH cytochrome P450 reductase, two enzymes believed to be most important for the metabolism of food-borne mutagens and carcinogens, has been constructed (Aryal et al., 1999). However, as pointed out by many researchers, in vitro mutagenicity tests are in some cases overly sensitive and may not reflect exposures and mechanisms of biological relevance to humans. Therefore, it is generally accepted that mutagenic properties of a given compound detected in bacteria need to be assessed in appropriate in vivo assays (MacGregor et al., 2000). For instance, commercially available transgenic Muta Mouse® and the Big Blue™ mouse and rat models, though they use bacterial transgene as the mutational target, assure metabolic conversion of a compound typically tested for higher organisms. After exposition on mutagenic substance in an animal, the bacterial transgene is recovered and the frequency of its mutation assayed in the natural “host,” which is Escherichia coli. To assess carcinogenicity, several doses of potential carcinogens are administered to animals. The highest of them correlates to the maximum tolerated dose (MTD) that does not cause severe weight loss or other life-threatening signs of toxicity. As a result of such studies, the lowest dose is determined at which carcinogenic effects are still observed. The next level below that is assumed not to have a biological effect, the so-called “no effect level.” This value, divided by a safety factor of either 100 or 1000, correcting for difference in sensitivity between animals and humans, is considered the acceptable daily intake (Anon., 1988). Such studies are usually very lengthy, so shorter alternative carcinogenicity assays are being developed. The new animal tumorigenesis models are designed with the aid of genetic engineering and are characterized by rapid development of tumors. In the literature, for example, there are described transgenic mouse models overexpressing oncogene c-myc (Ryu et al., 1999) or c-myc and tumor growth factor TGFα (Thorgeirsson

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317

et al., 1999), immunodeficient (SCID) mice (Salim et al., 1999), and knockout p53deficient mice not expressing the tumor suppressor p53 gene (Park et al., 1999). There is a continuous debate regarding whether carcinogenicity of compounds can indeed be predicted based on mutagenicity tests. The data gathered so far show that for certain groups of chemical carcinogens a very good overlap exists between the bacterial mutagen and animal carcinogen group, providing support for the Ames test as appropriate method for identifying causative agents for human cancers. However, the usage of short-lived species like rodents to estimate carcinogenic effects in a long-lived species such as the human must be taken with caution. In order to achieve a long life span, humans evolved mechanisms rendering them more resistant to cancer. In addition, essential differences were shown between metabolic activation and detoxification, as well as the DNA adduct formation by heterocyclic food-borne amines, i.e., a vital DNA lesion initiating cancerous transformation, in rodents and in humans. Thus rodent models do not accurately represent the human response to this type of compound (Turteltaub et al., 1999). Although neither in vitro mutagenicity tests nor carcinogenicity tests in animals can fully reflect the consumer’s health risk associated with a given chemical, they play an essential role since they enable the identification of those substances in foods that require detailed toxicological evaluation and whose consumption in larger amounts should be avoided.

14.5 FOOD-BORNE MUTAGENS AND CARCINOGENS 14.5.1 INTRODUCTION The idea that nutrition is an important factor in the risk of cancer is not new. Reports from the 19th and 20th centuries, based on observations made during clinical practice, often indicated diet as a risk factor. More recently, albeit already classic, Doll and Peto’s survey of epidemiological evidence pointed to links between meat consumption and increased incidence of specific cancers (Doll and Peto, 1981). Mutagens and carcinogens found in food products can be classified into three categories (Sugimura and Sato, 1983). (Mutagens are understood here as compounds giving positive results in the Ames test. Those able to induce tumors in experimental animals are considered to be carcinogenic.) The first category includes natural compounds such as mycotoxins and substances of plant origin. The second category contains substances formed as a result of food storage, cooking, and processing. The third category of food-borne mutagens and carcinogens is derived from pesticides, fungicides, and additives. Contrary to public belief, compounds belonging to the third group appear to have only marginal significance in the etiology of human cancer, due to the very low concentrations to which people are exposed. In this chapter, mainly mutagens and carcinogens arising as a result of food processing are described, because these substances are believed on one hand to represent the major dietary cancer risk factor, and on the other hand the health hazard that can be readily reduced by changing food storage and preparation technologies. A large group of potential mutagenic and carcinogenic substances of plant origin was omitted, although humans may consume as much as a few grams of them daily (Ames and Gold, 1990).

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Chemical and Functional Properties of Food Components

Potential plant mutagens and carcinogens belong to a variety of classes of chemical compounds, e.g., hydrazine derivatives, flavonoids, alkenylbenzenes, pyrrolizidine alkaloids, phenolics, saponins, and many other known and unknown compounds. Plants produce these toxins to protect themselves against fungi, insects, and animal predators. For example, cabbage contains at least 49 natural pesticides and their metabolites, few of which were tested for carcinogenicity and mutagenicity, some of which turned out positive. However, there is no evidence that plant-based food increases cancer risk. In contrast, epidemiological studies demonstrate that phytochemicals found in edible plants exhibit numerous activities preventing carcinogenesis. Therefore, their role will be discussed in a chapter concerning anticarcinogenic food components.

14.5.2 MYCOTOXINS Mycotoxins are highly toxic compounds produced by molds, mostly in the genera Aspergillus, Penicillium, and Fusarium. They represent the most dangerous contamination, arising mainly during storage of numerous food commodities, e.g., corn or peanuts. Tropical and subtropical climates are particularly favorable locations for mycotoxin production because of often poor food harvesting and storage practices. Among several classes of compounds belonging to the group of mycotoxins, carcinogenic properties have been demonstrated only for three of them. These are aflatoxins and sterigmatocystin, inducing liver cancers, and ochratoxin A, implicated in the development of kidney cancers in experimental animals (Wakabayashi et al., 1991): Aflatoxin B1 is the most carcinogenic mycotoxin and, based on available toxicological and epidemiological data, has been classified as a human hepatocarcinogen (Anon., 1987). O

O

O

O

O

O

O

O

O

OCH 3

O

OCH 3

O

aflatoxin G1

aflatoxin B1

COOH CH 2 CH

NH

O

OH

O

C O

CH 3

ochratoxin A Formula 14.9

Cl

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319

14.5.3 NITROSAMINES A number of nitroso compounds, N-nitrosamines among them, are potent carcinogens. The most common carcinogenic nitrosamines, found mainly in protein food, are N-nitroso-dimethylamine (NDMA), N-nitroso-diethylamine (NDEA), Nnitroso-pyrrolidine (N-Pyr), and N-nitroso-piperidine (N-Pip). These compounds supposedly increase the risk of colon, rectum, stomach, pancreas, and bladder cancers. Nitrosamines are most prevalent in cured meats, but have also been detected in smoked fish, soy protein foods dried by direct flame, and food-contact elastic nettings. Dietary surveys indicated weekly mean intakes of these compounds amounting to about 3 µg per person (Anon., 1988; Cassens, 1995). In addition, the precursors of nitrosamines, especially nitrate, are abundant in some leafy and root vegetables (Table 14.1). Nitrate and nitrite are also formed endogenously in the human body. In mammalian organisms, following enzymatic conversion of L-arginine, nitric oxide is produced, which in turn may be converted to nitrite and nitrate (Hibbs et al., 1987). A portion of nitrate, either ingested or endogenously formed, carried out in the blood, is secreted by salivary glands into the oral cavity. Here nitrate can be reduced by microbial flora and swallowed. Thus it ends up in the gastric environment, similar to the nitrite ingested with food. Under the acidic conditions of the stomach, the nitrosation of amines present in food by nitrite occurs, giving rise to N-nitrosamines. Animal studies suggest, however, that in vivo formation of nitrosamines does not occur to a significant extent, and from a cancer risk perspective, preformed N-nitroso compounds consumed in cured meat or fish seem to be much more significant (Anon., 1997).

TABLE 14.1 Most Important Sources of N-Nitrosamines and Their Precursors (Nitrites and Nitrates) in the Human Environment Substance

Source

N-Nitrosamines

Cured meat (especially bacon) Smoked fish Soy protein foods dried by direct flame Some alcoholic beverages Food-contact elastic nettings Rubber baby bottle nipples Cosmetics Cured meat Baked goods and cereals Vegetables Nitrate reduction in vivo Drinking water Natural constituent of beets, celery, lettuce Nitrate fertilizer residues

Nitrites

Nitrates

320

Chemical and Functional Properties of Food Components

The presence of nitrites has both a positive and negative impact on food safety. On one hand, in many countries, a correlation between stomach and liver cancers, induced probably by nitrosamines, and the amount of nitrites consumed is observed (Fine et al., 1982). On the other hand, nitrites inhibit the growth of Clostridium botulinum, thus reducing the risk of food contamination by botulinum toxins. Moreover, under the acidic conditions of the stomach, where they are involved in the formation of carcinogenic nitrosamines, nitrites are capable of neutralizing carcinogens formed as a result of protein pyrolysis (Pariza, 1982). Since the presence of nitrites is mainly a consequence of vegetable cultivation and food processing, changes in technology may lead to a considerable decrease of the amounts of these compounds in food products, thereby diminishing the risk of cancers induced by nitrosamines. Nonetheless, they are likely to remain a necessary additive of preserved foods, since an alternative to nitrites as curing agents and microbiological preservatives has not been found so far. It has been learned, though, that the formation of carcinogenic nitrosamines during thermal processing, e.g., frying, of cured meats can by largely inhibited by the addition of antioxidants, e.g., ascorbate and α-tocopherol. The addition of such compounds has now become a standard procedure (Cassens, 1995).

14.5.4 MUTAGENS

IN

HEAT-PROCESSED FOODS

In the 1960s, with the advent of experimental models of chemical carcinogenesis and the publication of the mutagenicity test by Ames et al. (1975), the detection of specific chemical carcinogens in the human diet became plausible. Surprising news was that cooking of proteinaceous foods under normal cooking conditions promotes mutagenesis. Mutagens were found in grilled and fried meat and fish, and methanol extracts of their charred parts were found in smoke condensates produced while cooking these foods, as well as in heated, purified proteins and amino acids. Most of the examined mutagens proved carcinogenic in mice and rats, inducing cancers of various organs (Nagao, 1999). The formation of mutagens in canned foods is also associated with sterilization, although temperatures applied in this case are relatively low: 110–120°C. Mutagenic substances produced during canning have not been chemically characterized so far (Krone et al., 1986). In the case of other protein foods, such as milk, cheese, eggs, or legumes, the presence of mutagenic substances was detected only after thermal processing associated with a change of color resulting from burning etc. (RobbanaBarnat et al., 1996). 14.5.4.1 Heterocyclic Aromatic Amines Heterocyclic aromatic amines (HCAs) are formed during thermal processing of many kinds of foods, especially foods containing much protein. They may be associated with increased incidence of human tumors in the colon, breast, stomach, liver, and other organs. However, so far gathered data do not allow final

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conclusions to be drawn (Anon., 1997). Around 20 different food-derived HCAs have been isolated to date. The products of amino acids and protein pyrolysis whose chemical structures are given below are produced in temperatures higher than 300°C. Therefore, they are detected mainly in the surface layers of meat and fish subjected to open-flame broiling. These compounds are strong mutagens, though they usually are not very potent carcinogens (Sugimura and Sato, 1983; Nagao, 1999): Another type of HCA is generated in the dry crusts of foods baked at 150–200°C. These are derivatives of quinoline, quinoxaline, and pyridine formed in the reaction of creatine or creatinine with amino acids and sugars. All the reactants are thus natural constituents of meat. These HCAs, examples of whose chemical structures are given below, belong to the strongest food-borne mutagens known and are carcinogenic in rodents (Wakabayashi et al., 1991); the compound designated IQ was shown to be carcinogenic in nonhuman primates (Adamson et al., 1994). They are found in the crusts of fried or broiled meat and fish, as well as in fried and baked meats and heated meat extracts (Krone et al., 1986): CH3 N N

N

N H

NH2

N H

NH2

N

NH2

R

R

Trp-P-1: R=CH3 Trp-P-2: R=H

Glu-P-1: R=CH   3 Glu-P-2: R=H

Phe-P-1

Trp-P-1:  3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole Trp-P-2:  3-amino-1-methyl-5H-pyrido[4,3-b]indole Glu-P-1:  2-amino-6-methyldipyrido[1,2-a:3',2'-d]imidazole Glu-P-2:  2-aminodipyrido[1,2-a:3',2'-d]imidazole Phe-P-1:  2-amino-5-phenylpyridine Formula 14.10 NH2

N

H 3C

N

NH2

N N

CH3 N

CH3

N

CH3

NH2 N

N

N

IQ

MeIQx

              IQ: 2-amino-3-methylimidazo[4,5-f]quinoline

MeIQx: 2-amino-3,8-dimethylimizado[4,5-f]quinoline     PhIP: 2-amino-1-methyl-6-phenylimizado[4,5-b]pyridine

Formula 14.11

PhIP

N

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Chemical and Functional Properties of Food Components

Compounds PhIP and MeIQx are most prevalent of the HCAs in the human diet. Daily consumption may be as high as several nanograms per person. These amounts ingested by humans may not be sufficient to induce cancers by themselves. At least such a conclusion can be drawn from comparison with animal intakes. However, many environmental factors may be implicated in neoplastic transformation in man. HCAs may be one of these factors (Nagao, 1999). Since HCAs belong to the most abundant food-borne substances possibly affecting cancer risk, much research is devoted to clarifying their impact on tumor induction. It was found that dietary polyenoic fat, e.g., corn oil used for frying meat patties, significantly enhances PhIP mammary carcinogenesis in rats, and it was suggested that PhIP initiates the carcinogenic process, while dietary fat serves as a promoter (Ghoshal et al., 1999). Particularly worrying are results of experiments performed in rats, which demonstrated that PhIP is passed via the liver to the breast and is secreted to milk of lactating animals. The newborn pups received a dose sufficient to induce tumors. Such a route of exposure may also exist in other mammals, including humans. This would mean that humans are exposed to HCAs in foods continuously from early life, even in utero (Felton, 1994; Paulsen et al., 1999). 14.5.4.2 Polycyclic Aromatic Hydrocarbons Polycyclic aromatic hydrocarbons (PAHs) containing a system of condensed aromatic rings are formed as a result of incomplete combustion of organic matter. PAHs are associated with elevated risk of cancers in various tissues, especially skin and lung. It has been established that for carcinogenicity of these compounds, the metabolites arising from epoxidation of the so-called “bay region” (Chapter 15.3) are responsible. In food, PAHs are produced mostly during heating, especially open-flame heating such as grilling of meat. Under such conditions, fat from meat drips onto a hot surface, e.g., hot coal during grilling, and is incinerated. The smoke from the fat pyrolysis containing PAHs is adsorbed on the meat. The levels of these compounds that can potentially be produced are relatively large: the surface of a 2-lb well-done steak was reported to contain an amount of benzo[a]pyrene equivalent to that found in the smoke from 600 cigarettes (Pariza, 1982). In the case of smoked meat and fish, smoke used during processing is also a source of carcinogenic PAHs (Sikorski, 1988). In addition, a number of food products contain measurable amounts of these hydrocarbons resulting from environment pollution, e.g., fish caught in heavily industrialized regions. The concentration of PAHs detected in foods is in the range of several to several hundred nanograms per 1 g of food product (Anon., 1993). In feeding studies in which volunteers consumed heavily charbroiled beef, a dose-dependent formation of PAH–DNA adducts in white blood cells was observed. Their level increased after 1–4 days following ingestion and they were eliminated within about 7 days. It was thus unequivocally demonstrated that food-borne PAHs are capable of incurring damage to human DNA (Schoket, 1999).

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14.5.4.3 Effect of Commercial Processing and Cooking Techniques The content of food-borne mutagens resulting from processing is relatively small but very variable and is estimated to amount to 0.1–500 ng/g of a given food product. The World Cancer Research Fund panel of experts evaluated the evidence and indicated that consumption of grilled or barbecued meat, consumption of fried foods, and a diet high in cured meats possibly increase the risk of certain human cancers. They concluded, however, that “there is no convincing evidence that any method of cooking modifies the risk of cancer” (Anon., 1997). This statement has been argued against by several researchers who demonstrate in their studies that the formation of food carcinogens depends strongly on the cooking technique applied and must be thus reflected by the differences in health hazard. This is of special concern in the case of animal protein foods, because their processing involves methods particularly liable to generation of carcinogenic HCAs and PAHs. Another cookingassociated exposure to PAHs and HCAs is fumes, which are produced abundantly during stir frying. Lung cancer is the most common cause of cancer death among women in Taiwan, though most of them are nonsmokers. There are recent reports confirming the association between the PAH–DNA adduct level in lung tissue and lung cancer incidence in Chinese women, many of whom reported that they stirfried meat daily (Yang et al., 2000). The temperature applied during processing has a decisive influence on the kind of HCAs formed, while the amount depends on cooking time and method, as well as the type of food (Bartoszek, 2001). Their content, however, can be effectively reduced. For instance, mutagens of HCA type were not detected in beef either processed in a microwave oven or stir fried for 3 min on high heat (Miller, 1985). It has also been established that mutagenicity of cooked meat decreases (mostly fried hamburgers were analyzed) after microwave pretreatment, causing the leakage of juices and thereby diminishing the content of sugars and creatinine, i.e., precursors of some HCAs. Addition of onion and some vitamins also effectively reduced mutagenicity of cooked hamburgers (Kato et al., 1998, 2000; Edenharder et al., 1999). Cured meat and fish are the main source of nitrite and the greatest contributors of preformed carcinogenic N-nitrosamines in the human diet. It turns out that another traditional way of preserving protein foods, salting, also modifies cancer risk. Epidemiological studies showed that cancer rates are highest in those parts of the world where diets are traditionally very salty, e.g., in Japan, China, or Chile. Salt is used extensively as a preservative and flavor enhancer throughout the world, but it was demonstrated to increase stomach cancer risk in a dose-dependent manner. This carcinogenicity enhancement is probably due to damage to the mucosal layer facilitating Helicobacter pylori infection (Anon., 1997). In addition, commercial foods may contain traces of chemicals used in packaging and migration from food-contact materials can occur during their processing, storage, and preparation. These chemicals include monomers of polymeric materials used in packaging, such as vinyl chloride and acrylamide classified by the International Agency for Cancer Research (1987) in group 2A (probable human

324

Chemical and Functional Properties of Food Components

carcinogens). To this group also belongs cadmium, which along with lead, arsenic, and other carcinogenic heavy metals, may contaminate foods, especially organ meats, including the liver and kidney, in which these metals tend to concentrate (Rojas et al., 1999). Cooked meals are characteristic of most civilizations, and preparation and enjoyment of cooked food is intrinsic to social and family life. Meat and fish may be cooked using water, fat, more or less fierce heat, direct flame, and other methods. Curing and smoking have been used as a means of preserving meat and fish for thousands of years. Modern food technologies employ basically the same methods, only on a larger scale, to provide easy-to-prepare and time-saving convenience foods devoid of microbial contamination and with an increased shelf life. Relatively recently, it has been realized that all of the above benefits must be weighed against the possibility of formation of a variety of carcinogenic compounds as a result of food processing.

14.5.5 MUTAGENS

IN

TEA, COFFEE,

AND

ALCOHOLIC BEVERAGES

Coffee brewed from roasted beans and those prepared from instant powder, including the caffeine-free type, all display mutagenic activity. Apart from natural mutagens such as caffeic acid and its precursors chlorogenic and neochlorogenic acids, these drinks contain mutagenic products of pyrolysis: methylglyoxal and less active glyoxal and diacetyl (Ames, 1986): H 3C

H

H 3C

C

O

C

O

C

O

C

O

C

O

C

O

H

H

glyoxal

methylglyoxal

H 3C

diacetyl

Formula 14.12

These pyrolysis products were also found in roasted tea and brandy-type alcoholic beverages (Sugimura and Sato, 1983). In addition, as a result of ethanol metabolism, mutagenic acetaldehyde is formed, while in coffee and tea caffeine, an inhibitor of DNA repair synthesis is present and may also contribute to cancer risk. These observations, made during studies carried out with the aid of microorganisms and experimental animals, suggested that tea and coffee might pose a serious health hazard, especially because both of these drinks are consumed in substantial amounts almost all over the world. Epidemiological studies, whose results became available 10 years later, showed how misleading the extrapolation of data between species could be. No convincing evidence that daily consumption of tea or coffee increases cancer risk was found. In contrast, it turned out that regular green tea intake decreases it, owing to the presence of numerous phytochemicals exhibiting anticarcinogenic properties, which will be discussed later in this chapter. Caffeine, previously regarded as a harmful compound, has become an important (because of substantial

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325

FIGURE 14.1 Antioxidative properties of selected alcoholic beverages (based on Bartosz et al., Biochem. Mol. Biol. Int., 46, 519, 1998). The high antioxidative activity of beers may, to a considerable extent, result from the addition of antioxidants, vitamin C in particular.

intake) factor in carcinogenesis prevention, mainly because it helps to combat obesity, constituting a well-documented risk factor of many widespread diseases, including heart ailments and cancer (Anon., 1997; El-Bayoumy et al., 1997). The opposite must be said in the case of alcoholic beverages. Experimental results did not indicate that they might play a role in the potentiation of cancer risk. This notion was somehow supported by the epidemiological studies carried out in France, which lead to the discovery of the so-called “French paradox.” Contrary to the common belief among this country’s population, despite high alcohol intake, the frequency of heart failures and possibly also tumor incidence is lower than that in other states. Currently, it is postulated that antioxidant substances present in colored alcoholic beverages and particularly abundant in red wine (Figure 14.1) offer such protection. The studies carried out in France are the only ones, they failed to demonstrate alcohol as a cancer risk factor. The data gathered in other regions indicate alcohol as an important cause of carcinogenesis. The risk of cancer development increases with the amount of alcohol consumed and becomes particularly high when accompanied by cigarette smoking (Anon., 1997; Doll, 1999).

14.5.6 OTHER RISK FACTORS A number of epidemiological studies indicated that high consumption of fat contributes to the development of breast and large intestine cancers in humans (Ames, 1986). Carcinogenic effects are also ascribed to high-calorie and protein-rich diets. Animal studies suggest that all the mentioned risk factors come to play after initiation of tumorigenesis, while their mode of action relies on the increased production of oxygen radicals. Reactive oxygen species are generated in the organism as a result of normal metabolism. A diet rich in nutrients increases the intensity of metabolic processes and thus also oxygen radical production. These radicals are implicated in the induction of endogenous oxidative damage

326

Chemical and Functional Properties of Food Components

of macromolecules, including the formation of so-called oxygen DNA adducts (e.g., 8hydroxy-2'-deoxyguanosine) and protein carbonyl derivatives (Youngman et al., 1992; Chevion et al., 2000). This type of lesion is believed to play a significant role in the process of aging and in the variety of degenerative age-related disorders, including cancer. The animal studies showed that calorie and protein restriction markedly inhibits both carcinogenesis and accumulation of endogenous oxidative damage (Youngman et al., 1992; Rogers et al., 1993; Burcham, 1999). Convincing support is also lent by reports demonstrating that the diet containing ingredients with antioxidant properties considerably inhibits cancer development (Anon., 1997; Thomas, 2000). Moreover, although fats do not display mutagenic activity per se, some of their constituents, such as cholesterol and unsaturated fatty acids, are easily oxidized during thermal processing, giving rise to reactive molecules that in turn may trigger a chain reaction of lipid peroxidation, leading to the formation of mutagens, promoters, and carcinogens. These include radicals, fatty acid epoxides and peroxides, aldehydes (e.g., malondialdehyde, which binds covalently with DNA), and others (Ames, 1986). Another important mechanism by which fat modulates carcinogenesis — some researchers claim the most important — involves its interference with synthesis of prostaglandins and leukotrienes, as well as the development of insulin resistance, which in turn stimulates proliferation of cells (colonic epithelium cells in particular) (Woutersen et al., 1999; Bruce et al., 2000). Another class of food-borne substances that have been postulated to influence the frequency of cancer development are xenoestrogens. Xenoestrogens penetrate into the organisms with food and they mimic or change the activity of estrogens produced endogeneously. To these compounds, whose ability to promote the development of estrogen-dependent cancers (e.g., breast cancer) has been documented, belong polychlorinated biphenyls (PCBs), formed during drinking water chlorination; pesticide residues, DDT in particular; and some components of plastics used for food packaging. In the case of DDT and certain PCBs, their association with breast cancer incidence was evidenced based on human-derived biological material. These substances are extremely stable and persist in the environment for many years, even in countries where DDT has been banned long ago. It is estimated that the decreased exposition to xenoestrogens would decline the frequency of breast cancer by 20%, i.e., by 36,000 cases in the United States alone (Davis et al., 1993).

14.6 CHEMOPREVENTIVE FOOD COMPONENTS Laboratory studies carried out over the past 20 years demonstrated that food, one of the major components of the human environment, contains numerous mutagens and carcinogens. As described earlier in this chapter, they may be naturally occurring, but most of them are of anthropogenic origin and are found in food mainly as a result of thermal processing of fat and protein-rich food products. These findings were followed by epidemiological investigations, which confirmed the health risk associated with the consumption of foods with high protein and calorie content. They revealed, however, that edible vegetables and fruits, apart from nutritive macroelements, contain numerous microelements and nonnutritive phytochemicals displaying different anticarcinogenic and other health-promoting biological activities, effectively

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327

reducing human cancer risk (for the most extensive review see Anon., 1997). The latter, until recently, have been regarded as unimportant to human health. In the 1990s, the results of numerous investigations carried out in different populations were published and demonstrated unequivocally a rare situation in the case of epidemiological studies: that a high content of vegetables and fruits in the diet was associated with decreased cancer incidence. As a result of research on anticarcinogenic food components, a number of substances displaying such chemopreventive properties have been characterized: lycopene found in tomatoes (Giovannucci, 1999), epigallocatechins in tea (Fujiki et al., 2000), sulforaphane in broccoli (Zhang et al., 1994), and resveratrol in grapes (Jang et al., 1997), to name only a few most extensively investigated. Chemopreventive potential exhibited by plant foods has nowadays become one of the major and most promising fields of cancer research, because it may help to diminish the global cancer burden simply by implementing specific dietary recommendations (Schatzkin, 1997; Wolf, 2001). In addition, phytochemicals isolated from edible plants are tested with the aim to develop dietary supplements, which could protect humans against cancer, as well as become a means of cancer chemotherapy enhancement.

14.6.1 ANTICARCINOGENIC FOOD COMPONENTS A number of natural and synthetic compounds are able to prevent cancer induction or development when administered to animals before or concomitantly with carcinogens. These substances include vitamins, microelements, compounds of plant origin, medicines, and others (Table 14.2). Although the studies on the modes of action of cancer preventive agents are still on the way in many laboratories and bring new discoveries each day, it has been realized even before they were undertaken that any factor capable of counteracting the production of carcinogenic metabolites, inhibiting the initiation or promotion of tumorigenesis, and inhibiting metastasis by malignant cells, may be considered an anticarcinogen. Anticarcinogens are divided into three groups, depending on the stage of carcinogenesis they act at (Ames, 1986; Anon., 1993; Caragay, 1992). The first of these groups includes blocking agents, which protect cells at the stage of initiation of neoplastic transformation. The second group includes suppressing agents, which are important during cancer promotion and uncontrolled growth of initiated cells. Factors making cells more resistant to neoplastic transformation constitute the third group. Blocking agents protect cells against substances that could initiate changes leading to malignancy. There are three major mechanisms (groups) of their activity. First, they prevent the formation of carcinogens from precursors. For instance, vitamin C inhibits, via an unknown mechanism, the formation of carcinogenic nitrosamines from amines and nitrites present in food (Caragay, 1992). It has been also found that lactic acid bacteria from both fermented dairy (Gilliland, 1990) and nondairy (Thyagaraja and Hosono, 1993) foods display antimutagenic activity, owing to the ability to bind mutagens. In this binding, peptidoglycan present in the bacterial cell wall is involved, and this property is not abolished after sterilization. Similar physicochemical sequestering of mutagenic and carcinogenic aromatic substances is displayed by chlorophyllin, the sodium and copper salt of chlorophyll

328

Chemical and Functional Properties of Food Components

TABLE 14.2 Examples of Anticarcinogenic Foodborne Substances: Their Occurrence and Major Chemopreventive Activity Type of Preventive Factor Blocking agents

Suppressing agents

Factors making cells more resistant to neoplastic transformation

Substance

Source

Chemopreventive Activity

Vitamin C Vitamin E Carotenes

Antioxidant Antioxidant Antioxidant

Lycopene Epigallocatechins Chlorophyllin

Citrus fruit Plant oils Carrot (and other orange vegetables) Tomatoes Tea Green vegetables

Peptydoglycan Glutathione

Cell wall of lactic bacteria Garlic

Isothiocyanates

Broccoli

Genistein, daidzein Genistein Retinoids

Soy, sorgo

Isotiocyanates

Cruciferous vegetables

Isoflavones

Soy

Diallyl sulfide

Garlic

Hn–3 fatty acids Vitamin D + Ca + P

Fish oil

Soy Orange-colored vegetables

Restricted calorie diet containing increased levels of vitamin D + Ca + P

Antioxidant Antioxidant Aromatic carcinogen sequestering Carcinogen sequestering Chemical binding of electrophiles Detoxifying enzyme induction Antiestrogenic activity Inhibition of angiogenesis Stimulation of cell differentiation Inhibition of oncogene activation Stimulation of cell maturation Anti-Helicobacter pyroli activity Modulation of signal transduction Inhibition of cell proliferation

(Ardelt et al., 2001). To the second group of blocking agents belong the factors that protect cells against DNA damage. These mechanisms are best recognized. They involve the reduction of synthesis or inhibition of enzymes responsible for metabolic activation of carcinogens (phase I enzymes) and induction of enzymes taking part in detoxification of harmful substances (phase II enzymes). The ability to modulate the activity of cytochrome P450 isoenzymes, often implicated in carcinogen activation, is displayed by numerous compounds, e.g., phenols, found in edible plants. The detoxifying enzymes, especially glutathione-S-transferases, are effectively induced by isothiocyanates present in cruciferous vegetables, e.g., broccoli. The compounds capable of trapping DNA-damaging species belong to the third group of blocking agents. The removal of toxic metabolites is usually

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329

accomplished by nucleophilic substances, first of all glutathione and other sulfurcontaining compounds abundantly found in garlic and onion, which can bind electrophilic DNA-reactive intermediates. Vitamins C and E, trapping oxygen radicals in lipid membranes, as well as β-carotene and other polypropenes, present in all chlorophyll-containing food products and particularly effective in the neutralization of singlet oxygen, protect DNA against oxidative damage. Compounds containing selenium play similar roles. Selenium is an essential component of the active site of glutathione peroxidase, the enzyme responsible for destroying hydrogen peroxide and other peroxides generated during lipid peroxidation. Also, polyphenols, major phytochemicals present in all kinds of foods of plant origin, display antioxidative properties. Suppressing agents, constituting the second group of anticarcinogenic factors, influence the process of transformation of the initiated (precancerous) cell into a truly malignant cell. Numerous nonnutritive phytochemicals display the ability to slow down or inhibit cancerous growth. Also, in this case several protective mechanisms can be distinguished (Wattenberg, 1997). They involve stimulation of cell differentiation (retinol), inhibition of oncogene activation (isothiocyanates), and selective inhibition of proliferation of tumor cells and antiangiogenic activity (genistein present in soy), disabling the growth of new blood cells necessary to supply neoplasm with nutrients and oxygen. Generally, the mechanisms of action of suppressing agents are poorly understood at the moment, as are the processes preventing cancer development at the later stages of carcinogenesis. Factors belonging to the third group render cells more resistant to neoplastic transformation. These mechanisms are least known. They include stimulation of cell maturation, activity believed to be responsible for reducing breast cancer growth by soy isoflavones, and inhibition of cell divisions in target cells. Proliferation increases the probability of conversion of promutagenic DNA damage into mutation, and thus reduction of its rate in a way protects cells against neoplastic transformation. It has been demonstrated that dietary enrichment in calcium, phosphate, and vitamin D slows down the rate of cell divisions (Anon., 1997; Wattenberg, 1997). Garlic components can also be included in this group of anticarcinogenic agents because of their antimicrobial activity against Helicobacter pylori, a risk factor in the case of gastric cancers. Garlic components inhibit the growth of these bacteria and thereby prevent damage to epithelium, making this tissue more resistant to harmful effects of carcinogens (Anon., 1997). Vegetables and fruits are the major sources of dietary anticarcinogens that can protect human organisms against neoplastic diseases by different mechanisms, at various stages of carcinogenesis. Thus the diet rich in plant-derived foods appears to be a realistic, nonpharmacologic, prophylactic approach against cancer. Apart from numerous anticarcinogenic substances, it also provides meals of low-calorie and protein content. All these factors reduce cancer risk in humans. Therefore, the food and pharmaceutical industry share an interest in edible plants as a means of cancer chemoprevention. In the case of the food industry, the prevention will probably rely on dietary recommendations ensuring high intake of protective phytochemicals, as well as enrichments of foods with anticarcinogenic vitamins and minerals. The pharmaceutical industry has begun to develop preparations, based on edible plants, exhibiting desirable activities from a prophylactic cancer perspective.

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Chemical and Functional Properties of Food Components

14.6.2 CANCER CHEMOPREVENTION Cancer chemoprevention can be defined as the prevention of neoplastic diseases by providing people with one or more chemical substances in the form of special preparations or as naturally occurring dietary components. Cancer development is a slow, multistage process that takes about 20 years on average. The number of new cancer cases estimated around the world for only 25 different cancers in 1990 amounted to 8.1 million (Parkin, 1998). If this number is multiplied by 20 years of latent development, it may be expected that more than 160 million people are, at this moment, at one of the stages of neoplastic transformation, which is life threatening. These people are the target population of cancer prevention, thus chemoprevention. Anticarcinogenic compounds found in edible foods display many advantages from the chemoprevention point of view. Any substance consumed as a chemopreventive agent is supposed to be ingested by healthy people for a long time; therefore, it must be devoid of toxicity. Numerous components of fruit and vegetables fulfill this condition. Another desirable property of edible plants is the fact that they represent a well-known element of human life and thereby facilitate the decision of adopting health-promoting activities. For about 10 years, very extensive studies have been carried out on numerous compounds, both natural ones and their artificial derivatives, with potential applicability in cancer chemoprevention. Here are four examples of promising substances isolated from edible plants. OH SO

OH

H 3C

H HO

NCS

sulforaphane

O OH

O H

OH

OH

OH O

OH

epigallocatechin gallate

HO

resveratrol

OH

lycopene

Formula 14.13

OH

Mutagenic, Carcinogenic, and Chemopreventive Compounds in Foods

331

Sulforaphane is one of the isothiocyanates produced by vegetables from the cruciferous family. Broccoli is a particularly abundant source of sulforaphane. It is capable of inducing liver phase II enzymes responsible for detoxification of mutagens and carcinogens (Zhang et al., 1994). Another promising compound, epigallocatechin gallate, was isolated from green tea. This compound, which is a very potent antioxidant, constitutes about 50% of the dry weight of green tea extract (Mitscher et al., 1997; Fujiki et al., 2000). It is present in black tea extracts as well, though in smaller amounts. Antioxidative properties are also displayed by lycopene, one of the major carotenoids present in tomatoes, processed tomatoes in particular (Giovannucci, 1999). Another chemopreventive compound, resveratrol, belongs to phytoalexins and was isolated from grapes. Resveratrol was demonstrated to activate different mechanisms preventing cancer development. Studies in animals showed that it induced phase II enzymes, scavenged oxygen radicals, stimulated cell differentiation, and thus inhibited carcinogenesis at various stages of neoplastic transformation. The health-promoting properties of red wine are also ascribed to resveratrol (Jang et al., 1997). Moreover, it has recently been postulated that dietary supplementation with food antioxidants may provide a safe and effective means of enhancing response to cancer chemotherapy (Conklin, 2000). Much more research is needed to validate this claim; however, the stimulation of oxygen radical formation by antitumor drugs is a known cause of side effects of chemotherapy like cardio- or nephrotoxicity. The approved chemoprotectants used clinically to date are not neutral to the organism either. In contrast, certain antioxidative food components, in doses that are without adverse effects, could improve the quality of life of patients by ameliorating chemotherapyinduced side effects and also enhance activity of antitumor drugs by different mechanisms (e.g., inhibition of topoisomerase II). The discovery of anticarcinogenic properties of many plant-borne compounds present in food is undoubtedly one of the most important developments, encouraging the hope that the cancer death toll can be diminished. The fact that these substances are found in liked and widely appreciated food products should facilitate the utilization of their precious chemopreventive properties.

14.7 SUMMARY Numerous epidemiological surveys demonstrate that consumption of protein foods increases cancer risk in humans. This increase can be at least partially ascribed to mutagens and carcinogens present in such foods. The majority of mutagens and carcinogens found in foods result from preservation and processing, especially cooking at high temperatures. The processing of foods, however, into palatable products available all year-round is essential to sustain life. Preservation methods, such as salting, curing, or smoking, eliminate the risk of various forms of microbial contamination, some of which may be life threatening. Apart from this practical significance, preservation and cooking give food specific taste and flavor and are the pleasures of life and intrinsic parts of cultures. Food can thus be a source of carcinogenic risk; however, when the appropriate dietary recommendations are followed, it may play a protective role. Figure 14.2

332

Chemical and Functional Properties of Food Components

clearly shows that many food-borne cancer risk factors are readily avoidable. The incorporation of elements preventing cancer development into the diet does not seem to be particularly difficult, though the change of food preferences may be a tough decision for many people. It is often argued that the amounts of carcinogenic substances in food are so small that they should be readily detoxified within the organism. Food, however, is not the only source of mutagens and carcinogens in our surroundings. In the polluted environment, there is a plethora of factors that may increase cancer risk. Carcinogenic food components thus represent an additional burden, the one perhaps most effectively delivered into the human body. Therefore, the levels of these substances in food should be as small as possible. This applies to both the food industry and every household. Modern technologies used in future food processing should ensure that while food products retain the desirable properties, the formation of potential carcinogens is minimal. Equally important for reducing cancer risk are changes in cooking and the dietary habits displayed by people. Widespread research on anticarcinogenic phytochemicals may eventually result in the development of protocols enabling the enrichment of commercially available foods in cocktails of chemopreventive substances, similar to current vitamin supplementation. Lung cancer Pancreas cancer Colorectal cancer Breast cancer Prostate cancer

Obesity

High calorie content

Heat processing

Meat

Alcohol

Fiber

Vitamin C

Carotenoids

Fruits

Vegetables

Kidney cancer

Decreased risk convincing

probable

possible

Increased risk

FIGURE 14.2 The influence of some food components and dietary preferences on the risk of development of the most frequent human cancers (based on Anon., Food, Nutrition and the Prevention of Cancer: A Global Perspective, AICR, Washington, D.C., 1997).

Mutagenic, Carcinogenic, and Chemopreventive Compounds in Foods

333

REFERENCES Adamson, R.H. et al., Induction of hepatocellular carcinoma in nonhuman primates by the food mutagen 2-amino-3-methylimidazo-[4,5-f]quinoline, Environ. Health Perspect., 102, 190, 1994. Ames, B.N., Food constituents as a source of mutagens, carcinogens, and anticarcinogens, in Genetic Toxicology of the Diet, Knudsen, I., Ed., Alan R. Liss, Inc., New York, 1986, p. 3. Ames, B.N. and Gold, L.S., Chemical carcinogenesis: too many rodent carcinogens, Proc. Natl. Acad. Sci. U.S.A., 87, 7772, 1990. Ames, B.N., McCann, J., and Yamasaki, E., Methods for detecting carcinogens and mutagens and the salmonella/mammalian microsome mutagenicity test, Mutat. Res., 31, 347, 1975. Ames, B.N., Shigenaga, M.K., and Hagen, T.M., Oxidants, antioxidants, and the degenerative diseases of aging, Proc. Natl. Acad. Sci. U.S.A., 90, 7915, 1993. Anon., International Agency for Research on Cancer, Overall evaluations of carcinogenicity: an updating of IARC Monographs, vol. 1 to 42, in IARC Monographs on the Evaluation of Carcinogenic Risk to Humans, IARC, Lyon, France, 1987, Suppl. 7. Anon., A scientific status summary by the Institute of Food Technologists’ Expert Panel on Food Safety and Nutrition: the risk/benefit concept as applied to food, Food Technol., 42, 119, 1988. Anon., A Scientific status summary by the Institute of Food Technologists’ Expert Panel on Food Safety and Nutrition: potential mechanisms for food-related carcinogens and anticarcinogens, Food Technol., 47, 105, 1993. Anon., World Cancer Research Fund and American Institute for Cancer Research, in Food, Nutrition and the Prevention of Cancer: A Global Perspective, AICR, Washington, D.C., 1997. Ardelt, B. et al., Chlorophyllin protects cells from the cytostatic and cytotoxic effects of quinacrine mustard but not of nitrogen mustard, Int. J. Oncol., 18, 849, 2001. Aryal, P. et al., Development of a new genotoxicity test system with Salmonella typhimurium OY1001/1A2 expressing human CYP1A2 and NADPH-P450 reductase, Mutat. Res., 442, 113, 1999. Bartosz, G. et al., Simple determination of peroxyl radical-trapping capacity, Biochem. Mol. Biol. Int., 46, 519, 1998. Bartoszek, A., Mutagens and carcinogens in protein food products, in Chemical and Functional Properties of Food Proteins, Sikorski, Z.E., Ed., Technomic Publishing Co., Inc., Lancaster, PA, 2001, p. 453. Bingham, S.A., High-meat diets and cancer risk, Proc. Nutr. Soc., 58, 243, 1999. Bruce, W.R., Giacca, A., Medline, A., Possible mechanisms relating diet and risk of colon cancer, Cancer Epidemiol. Biomarkers Prev., 9, 1271, 2000. Burcham, P.C., Internal hazards: baseline DNA damage by endogenous products of normal metabolism, Mutat. Res., 443, 11, 1999. Caragay, A.B., Cancer-preventive foods and ingredients, Food Technol., 46, 65, 1992. Cassens, R.G., Use of sodium nitrite in cured meats today, Food Technol., 49, 72, 1995. Chevion, M., Berenshtein, E., Stadtman, E.R., Human studies related to protein oxidation: protein carbonyl content as a marker of damage, Free Rad. Res., 33, 99, 2000. Conklin, K.A., Dietary antioxidants during cancer chemotherapy: impact on chemotherapeutic effectivness and development of side effects, Nutr. Cancer, 37, 1, 2000. Davis, D.L. et al., Medical hypothesis: xenoestrogens as preventable causes of breast cancer, Environ. Health Perspect., 101, 372, 1993.

334

Chemical and Functional Properties of Food Components

Dean, M., Cancer as a complex developmental disorder: nineteenth Cornelius P. Rhoads memorial award lecture, Cancer Res., 58, 5633, 1998. Dipple, A. and Bigger, C.A.H., Mechanism of action of food-associated polycyclic aromatic hydrocarbon carcinogenesis, Mutat. Res., 259, 263, 1990. Doll, R., The Pierre Denoix Memorial Lecture: nature and nurture in control of cancer, Eur. J. Cancer, 35, 16, 1999. Doll, R. and Peto, R., The causes of cancer: quantitative estimates of avoidable risks of cancer in the United States today, J. Natl. Cancer Inst., 66, 1191, 1981. Edenharder, E. et al., Antimutagenic effects and possible mechanisms of action of vitamins and related compounds against genotoxic heterocyclic amines from cooked food, Mutat. Res., 444, 235, 1999. El-Bayoumy, K. et al., Dietary control of cancer, Proc. Soc. Exp. Biol. Med., 216, 211, 1997. Fine, D.H. et al., Endogenous syntheses of volatile nitrosamines: model calculations and risk assessment, in N-Nitroso Compounds: Occurrence and Biological Effects, Bartsch, H. et al., Eds., IARC, Lyon, France, 1982, Publ. 41. Fujiki, H. et al., Green tea as a cancer preventive, in Dietary Anticarcinogens and Antimutagens: Chemical and Biological Aspects, Johnson, I.T. and Fenwick, G.R., Eds., Royal Society of Chemistry, Cambridge, U.K., 2000, p. 12. Ghoshal, A. and Snyderwine, E., Excretion of food-derived heterocyclic amine carcinogens into breast milk of lactating rats and formation of DNA adducts in the newborn, Carcinogenesis, 14, 2199, 1993. Gilliland, S.E., Health and nutritional benefits from lactic acid bacteria, FEMS Microbiol. Rev., 87, 175, 1990. Giovannucci, E., Tomatoes, tomato-based products, lycopene, and cancer: review of the epidemiological literature, J. Natl. Cancer Inst., 91, 317, 1999. Halliwell, B., Oxygen and nitrogen are pro-carcinogens: damage to DNA by reactive oxygen, chlorine and nitrogen species: measurement, mechanism, and the effects of nutrition, Mutat. Res., 443, 37, 1999. Hibbs, J.B., Jr., Taintor, R.R., and Vavrin, Z., Macrophage cytotoxicity role for L-arginine deiminase and iminonitrogen oxidation to nitrite, Science, 235, 473, 1987. Jang, M. et al., Cancer chemopreventive activity of resveratrol, a natural product derived from grapes, Science, 275, 218, 1997. Kato, T. et al., Mutagenicity of cooked hamburger is controlled by reducing sugar content in ground beef, Mutat. Res., 471, 1, 2000. Kato, T. et al., Mutagenicity of cooked hamburger is reduced by addition of onion to ground beef, Mutat. Res., 420, 109, 1998. Krone, A.C., Yeh, S.M.J., and Iwaoka, W.T., Mutagen formation during commercial processing of foods, Environ. Health Perspect., 67, 75, 1986. MacGregor, J.T., Casciano, D., and Muller, L., Strategies and testing methods for identifying mutagenic risks, Mutat. Res., 455, 3, 2000. Manson, M.M. and Benford, D.J., Factors influencing the carcinogenicity of food chemicals, Toxicology, 134, 93, 1999. Miller, A.J., Processing-induced mutagens in muscle foods, Food Technol., 39, 75, 1985. Nagao, M., A new approach to risk estimation of food-borne carcinogens — heterocyclic amines — based on molecular information, Mutat. Res., 431, 3, 1999. Pariza, M.W., Mutagens in heated foods, Food Technol., 36, 53, 1982. Park, C.B. et al., Heterozygous p53-deficient mice are not susceptible to 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) carcinogenicity, Cancer Lett., 139, 177, 1999. Parkin, D.M., The global burden of cancer, Semin. Cancer Biol., 8, 219, 1998.

Mutagenic, Carcinogenic, and Chemopreventive Compounds in Foods

335

Paulsen, J.E. et al., Neonatal exposure to the food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine via breast milk or directly induces intestinal tumors in multiple intestinal neoplasia mice, Carcinogenesis, 20, 1277, 1999. Robbana-Barnat, S. et al., Heterocyclic amines: occurrence and prevention in cooked food, Environ. Health Perspect., 104, 280, 1996. Rogers, A.E., Zeisel, S.H., and Groopman, J., Diet and carcinogenesis, Carcinogenesis, 14, 2205, 1993. Rojas, E. et al., Are metals dietary carcinogens?, Mutat. Res., 443, 157, 1999. Ryu, D.-Y. et al., In vivo mutagenicity and hepatocarcinogenicity of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) in bitransgenic c-myc/λlacZ mice, Cancer Res., 59, 2587, 1999. Salim, E.I. et al., Low-dose-dependent carcinogenic potential of 2-amino-3-methylimidazo[4,5-f]quinoline in the immunodeficient (SCID) mouse colon, Nutr. Cancer, 34, 220, 1999. Schatzkin, A., Dietary change as a strategy for preventing cancer, Cancer Metastasis Rev., 16, 377, 1997. Schoket, B., DNA damage in humans exposed to environmental and dietary polycyclic aromatic hydrocarbons, Mutat. Res., 424, 143, 1999. Sikorski, Z.E., Smoking of fish and carcinogens, in Fish Smoking and Drying: The Effect of Smoking and Drying on the Nutritional Properties of Fish, Burt, J.R., Ed., Elsevier Applied Science, Barking, England, 1988, p. 78. Sinha, R. and Caporaso, N., Diet, genetic susceptibility and human cancer etiology, Am. Soc. Nutr. Sci., Suppl., 556s, 1999. Staszewski, W. and Haenszel, W., Cancer mortality among the Polish-born in the United States, J. Natl. Cancer Inst., 35, 291, 1965. Sugano, H., The cancer problem: carcinogenesis and prevention from the viewpoint of the natural history of cancer, Anticancer Res., 19, 3787, 1999. Sugimura, T. and Sato, S., Mutagens: carcinogens in foods, Cancer Res., Suppl., 43, 2415s, 1983. Swenberg, J.A. et al., Relationship between DNA adduct formation and carcinogenesis, Environ. Health Perspect., 62, 17, 1985. Taylor, S.L., Mutagenesis vs carcinogenesis, Food Technol., 36, 65, 1982. Thomas, M.J., The role of free radicals and antioxidants, Nutrition, 16, 716, 2000. Thorgeirsson, S.S. et al., Carcinogenicity and mutagenicity of heterocyclic amines in transgenic mouse models, Cancer Lett., 143, 245, 1999. Thyagaraja, N. and Hosono, A., Antimutagenicity of lactic acid bacteria from ‘Idly’ against food related mutagens, J. Food Protect., 56, 1061, 1993. Turteltaub, K.W. et al., Macromolecular adduct formation and metabolism of heterocyclic amines in humans and rodents at low doses, Cancer Lett., 143, 149, 1999. van Iersel, M.L.P.S., Verhagen, H., and van Bladeren, P.J., The role of biotransformation in dietary (anti)carcinogenesis, Mutat. Res., 443, 259, 1999. Wakabayashi, K., Sugimura, T., and Nagao, M., Mutagens in foods, in Genetic Toxicology, Li, A.P. and Heflich, R.H., Eds., The Telford Press, Caldwell, NJ, 1991, p. 303. Wattenberg, L.W., An overview of chemoprevention: current status and future prospects, Proc. Soc. Exp. Biol. Med., 216, 133, 1997. Weisburger, J.H. and Williams, G.M., The distinction between genotoxic and epigenetic carcinogens and implication for cancer risk, Toxicol. Sci., 57, 4, 2000. Wolf, C.R., Chemoprevention: increased potential to bear fruit, Proc. Natl. Acad. Sci. U.S.A., 98, 2941, 2001. Woutersen, R.A. et al., Dietary fat and carcinogenesis, Mutat. Res., 443, 111, 1999.

336

Chemical and Functional Properties of Food Components

Wynder, E.L. et al., Comparative epidemiology of cancer between the United States and Japan: a second look, Cancer, 67, 746, 1991. Yang, S.-C. et al., Identification of benzo[a]pyrene 7,8-diol 9,10-epoxide N2-deoxyguanosine in human lung adenocarcinoma cells exposed to cooking oil fumes from frying fish under domestic conditions, Chem. Res. Toxicol., 13, 1046, 2000. Youngman, L.D., Park, J.-Y.K., and Ames, B.N., Protein oxidation associated with aging is reduced by dietary restriction of protein or calories, Proc. Natl. Acad. Sci. U.S.A., 89, 9112, 1992. Zhang, Y. et al., Anticarcinogenic activities of sulforaphane and structurally related synthetic norbonyl isothiocyanates, Proc. Natl. Acad. Sci. U.S.A., 91, 3147, 1994.

Index A Absolute, 244 Absorption spectrum, visible, 207–209 Acceptable daily intake (ADI), 65, 294–296, 304 Acer saccharium maple tree, 108 Acesulfame K., 281 Acetaldehyde boiling point of, 235 flavoring from, 244 formation of, 324 hemiacetal, 244 molecular weight of, 235 odor of, 234 Acetate bornyl, 235 citronellyl, 235 ethyl, 235 potassium, 62 starch ester, 104 Acetic acid boiling point of, 235 from dry wood distillation, 102 for fish preservation, 273 flavoring agent, 99, 244 from microorganisms, 248 molecular weight of, 235 odor of, 234 in Salatrim, 125 Acetone, 102, 128–129 Acetyl-3-hydroxyfuran, 98 Acetylation, 129 Acetylgalactosamine, 137 Acetylneuraminic acid, 137 Acid casein, 153 Acids acetic, see Acetic acid acetylneuraminic, 137 acid casein, 153 acrylic, 112 as additives, see Additives aldaric, 93–94, 104 aldosylamino, 90 alginic, 111 amino, see Amino acids aminobutyric, 75 aminolevulinic, 75 antioxidants, see Antioxidants antistaling agents, 282 apocarotenic acid, 210 arachidonic acid, 125–127 aroma of, see Aroma ascorbic, see Ascorbic acid aspartic, 134, 135 behenic, 125 benzenecarboxylic, 64

benzoic, 278–279 betalamic, 225 boric acid, 103 butyric, see Butyric acid caffeic acid, 324 capric, 125 caprylic, 125 carboxylic, 35, 103, 240 carminic, 226 chloroacetic, 104 chlorogenic, 223, 324 cis-parinaric acid (CPA), 138 citric, see Citric acid dehydroascorbic, 147, 168 dihomogammalinolenic, 127 dimethylarsenic, 71 docosahexaenoic, 117 EDTA, see Ethylenediaminetetraacetic acid (EDTA) eicosapentaenoic, 117, 125, 126 erythronic, 93, 96 ester formation, 236 fatty, see Fatty acids (FAs) ferulic, 247 folic, 301 formic, 164 galactaric, 97 galacturonic, 97 gallic, 278 gastric, 262 gluconic, 91 glutamic, see Glutamic acid glyceric, 93, 96 glyoxalic, see Glyoxalic acid hexanoic, 240 hialuronic, 85 hydrochloric, 102–103, 216 from hydroperoxides, 122 hydroxy, 102, 247 hydroxycarboxylic, 282 hydroxypyruvic, 93, 96 hydroxytricarballylic, 61 ketosylamino, 91 lactic, see Lactic acid bacteria (LAB) lauric, 116 linoleic, see Linoleic acids linolenic, see Linolenic acid lipid oxidation product, 239 Maillard reactions, 238 malic, 22, 109 monochloroacetic, 104 monomethylarsenic, 71 mucic, 97 neochlorogenic, 324 nitric, 103 nitrous, 277 nordihydroguiaiaretic, 67

nucleic, 3, 37, 159 oc-linolenic, 15 odor of, 234–235 oleic acid, 116, 121–122 oxalic, 22 palmitic, 116 PEFA, 116–117, 125–127 phenolic, 222 phosphatidic, 119, 128 phosphoric, see Phosphoric acid propionic, 125, 234 pyroligenious, 244 ricinoleic, 247 salicylic, 278 SCFA, 125 sillylic, 103 sorbic, 277–279, 303–304 stearic, 116, 125–126 sulfobenzoic, 281 sulfonic, 161 sulfuric, 93, 103, 164 tartaric, 22 tetraioic, 105 thiobarbituric, 66, 122 thiolactic, 244 trans fatty acids, 4, 7, 116 uric, 59 uronic, 94, 104 Acidulants, 247, 275, 283 Acrylamide, 323–324 Acrylic acid, 112 Actin cross-link rupture, 173 hydrolyzing of, 163–164 myofilaments from, 12 Activity, water, 41–45 Actomyosin, 146 Acute tests, 294 Acylation, 170–171 Additives, 61–65, 273, 303–304 as acidulants, 283–284 amount of, quality attribute, 5 antioxidants, see Antioxidants benefits of, 299 benzoic acid, 278–279 carcinogens and mutagens formed from, 317 as clarifying agents, 283 classification of, 274–275 for color, 279–281 compression of, 112 consumer demand, 297 definition of, 274 as emulsifiers, 281–283 as fat substitutes, 284–285 as film formers, 283 for flavoring, 279–281 honey, 20 nitrite, see Nitrite

337

338

Chemical and Functional Properties of Food Components

prebiotics, 285–287 as preservatives, 275–278 protein solubility, 144 riboflavin, see Riboflavin sorbic acid, 277–279, 303–304 as stabilizers, 281–283 sulfite, 276, 301–303 as sweeteners, 279–281 as thickening agents, 281–283 Adducts, oxygen DNA, 314–315, 317 Adenine, 29 Adenosine diphosphate (ADP), 58, 60 Adenosine triphosphate (ATP), 39 Adhesives CMC, 104 dextrins, 103 from saccharides, 85, 110 ADI, 65, 294–296, 304 Adipates, 104 ADP, 58, 60 Adsorption isotherm, 42–43 Aeration, 47–48 Aflatoxins, 311, 318 Agar, 84, 281 Agaricus bisporus, 237 Agaricus campestris, 237 Agents anticlotting, 275 antifoaming, 150, 275 antimicrobials, 148 antistaling, 282 blocking, 327–328 buffering, 57, 61–65 bulking, 281 chelating, see Chelating agents clarifying, 275, 283 complexing, 104, 275 drying, 62 emulsifying, see Emulsifying agents emulsion forming, 283 firming, 61–62 flavor, 99 foaming, 153–154, 283 gelling, 6 glazing, 275 leavening, 61–63, 275 neoplastic transformation resisting, 327–329 nitrosating, 172 preservation, 273 raising, 61–63 stiffening, 275 suppressing, 327–329 surface active, 92, 123, 129 texturing, see Texturing agents thickening, see Thickening agents thinning, 285 vasprotective, 222 AI, 128–129 ALA, 126–127; see also Linolenic acid Alanine, 134–135 Alaska pollock, 151 Albumin bovine serum, 135, 147 in eggs, 146, 154 oxidation of ascorbic acid, 60 saccharides in, 137

solubility of, 142 Alcalase, 153 Alcohol aliphatic, 142 butanol, 86, 234 cancer risk factor, 325, 332 citronellol, 235, 244 dehydration of, 236 dehydrogenase, 214, 249 ethanol, see Ethanol ethyl, 235 eugenol, 243–244, 247 favor threshold of, 66 flavoring from, 233, 244 geraniol, 238, 241, 244 hexanol, 244, 249 honey in, 20 from hydroperoxides, 122 isopropyl, 244 leaf, 249–250 from lipid oxidation, 240 lipid solvent, 115 1-methol, 244 mutagen formation in, 324–325 odor of, 234–235 oxidation of, 236 propanol, 234 reduction, 90 vanillin, 244 Alcoholism, 58, 127–128, 131 Aldaric acid, 93–94, 104 Aldehydes acetaldehyde, see Acetaldehyde alcohols, reduction to, 90 boiling point of, 235 carbonyl group, addition to, 90–91 in chicken, 239 in chlorophyll, 215 citral, 244, 250 citrus peel oil aroma, 232 cleavage, 236 2,4-decadienal, 244 dehydration of, 236 from DNA, 249–250 flavoring from, 240–241, 244 hexanal, 237–239, 244, 249 from hydroperoxides, 122 lipid oxidation product, 239 Maillard reactions, 238, 246 molecular weight of, 235 mutagen formation from, 326 mutarotation, 89–90 nucleophile acceptance, 82 odor of, 234–235 in oil, 120 oxidase, 59, 66 oxidation of, 91–92, 103, 236 polymerization of, 236 propionaldehyde, 234 reactions of to carbohydrates, 89–92 to proteins, 280 retinal, 213–214 in soybean oil, 240 vanillin, 244, 247–248 in yellow-green chlorophyll, 215 Aldol condensation, 99 Aldoses, 82, 91–92, 99 Aldosylamines, 90

Aldosylamino acids, 90 Aleurone layer, 17, 105 Alfalfa, 210, 250 Algae, 84 Alginate an anionic hydrocolloid, 67 in brown algae, 84 calcium, 61 carboxylic groups in, 67, 103 emulsifier, 281 gel formation, 6, 67 pectins and, 282 potassium, 62 sodium, 63 stabilizer, 281 for texture, 110 thickening agent, 281 Alginic acid, 111 Alkali, 62–63, 119 Alkaloids, 3, 222 Alkenylbenzenes, 318 Alkyl glycoside polyesters, 284 Alkyl imines, 90 Alkylation, 169–170 Alkylpyrazines, 241 Allene oxide, 237 Allergenicity, 303 Allergens, 156 Alliin, 240 Allium genus, 236–237, 243 Allspice, 232 Allyl disulfide, 244 Allythiocyanate, 237 Aluminium phosphate, sodium, 63–64 Aluminosilicate, 62 Aluminum anthocyanins reaction to, 222 complexes, lakes, 226, 228 in fruits and vegetables, 69 Amadori rearrangement, 90, 91 Ames test, 316–317 Amidation, posttranslational enzymatic, 136 Amide, 35 Amines antioxidant, 1–2 aromatic, carcinogenic heterocyclic, 7 carbohydrate reactivity, 90 flavor from, 240–241 incorporation of, 166 Maillard reactions, 238, 240–241 nonprotein N in, 3 Amino acids alkaline pH, reaction with, 159–160 alkylation of, 169–170 caramel catalysts, 109 cellulose thermolysis, 102 chemical modification of, 168 composition of, 134–137 conformation, 134, 138–141 denaturation of, 141 destabilization of, 155 in eggs, 154 for emulsions and foams, 148–151 enzyme-catalyzed reactions, 162–167

Index

in film formation, 145–148 flavor from, 240–241, 247 in fried food, 8 functional properties of, 141–142 gelation of, 145–148 in gluten, 156 heating of, 155–160 hydrophobicity, 36, 137–138 as intraluminar binders, 55 in legumes, 153 Maillard reactions, 238, 240–241 in milk, 153–154 in muscles, 151–152 mycoprotein, 154 N-nitrosation of, 171–172 nonprotein N in, 3 oxidation of, 160–162 pH, effect of, 143–144 phosphate reactions, 172–173 in potatoes, 239 pressurization of, 155 process flavor from, 246 in proteins, 134–173 reaction to, by water, 35 solubility of, 142–144, 156 water retention in, 144–145 Aminobutyric acid, 75 Aminolevulinic acid, 75 Ammonia catalyzation agent, 109 Maillard reactions, 238, 246 solvent for, 35 specific heat of, vs. water, 40 Ammonium, 34 Ammonolysis, 92 Amnhydrides, 35 Amorphous layers in starches, 88, 102 Amphipathic molecules, 36 Amylases, 17 Amylopectin, 87–88 in potatoes, 107 retrogradation, 105 in starch, 85, 102, 104 Amyloses to amylopectin ratio, 102 in helical complexes, 86–87, 104, 107 retrogradation, 105 in starch granules, 85, 88, 102 structure of, 86 Anageissus latifolia tree, 85 Anchovy, 163 Anemia, pernicious, 59, 76, 260 Angiogenesis, 328 Angle of internal friction, 194 Angle of repose, 194 Anhydrosugars, 93 Anilinonaphthalene-8-sulfonate (ANS), 138 Anionic dyes, 228 Anionic starch, 104, 111 Anisakis parasite, 7 Anise, 232 Annatto, 210 Anorexia, 76 ANS, 138 Anthocyanin, 206, 219–224 Anthocyanins, 219–224 Anthraquinone, 226

339

Anthropogenic contaminant, 74 Anti-inflammatory agent, 126, 222 Antibiotics in food, 296 Antibleaching agent, 61 Antibodies, 265 Antibrowning agent, 64, 303 Anticaking agent, 61–62, 285 Anticarcinogenicity, 131, 243, 326–329 Anticlotting agents, 275 Antiestrogenic activity, 328 Antifoaming agents, 275 Antifreeze proteins, 6, 134–135 Antihypertensive effect, 131, 154 Antimicrobials agents, in edible coatings, 148 essential oils of herbs and spices, 243 lysozyme, see Lysozyme in milk proteins, 154 mineral compounds as, 57, 61–65 spices and herbs, 232 sucrose FA esters, 285 Antimutagenicity, 243 Antioxidants, 243, 278–279, 303 additives as, 274–275 alcoholic beverages, 325 in allium genus members, 243 amines, see Amines anthocyanins, 222–223 anticarcinogenic action of, 326, 328 ascorbic acid, see Ascorbic acid carotene, see Carotene carotenoids, see Carotenoids catalase, 60, 160 cloves, 243 control of, in food, 4 cryptoxanthin, see Cryptoxanthin EDTA, see Ethylenediaminetetraacetic acid (EDTA) in essential oils, 243 flavonoids, see Flavonoids from flavorings, 243 glutathione, see Glutathione lipid stability, 121 lutein, see Lutein lycopene, see Lycopene meat preservation, 66 mineral compounds as, 57, 61–64 mung bean, 243, 249 nitrite, see Nitrite nitrosamine formation inhibitor, 320 nutmeg, 243 in olive oil, 116–117, 300 polyphenolics, 212, 279, 329 raisins, 302 reductones, 97 rosemary, 232 sage, 232 sesame, see Sesame SOD, 57–60, 66, 160 sodium chloride, see Sodium chloride solubility of, 143 soy, see Soy soybeans, see Soybeans

spices, 232 in tea, 302, 331 TEAC, 213 Terminalia catappa L. leaves, 243 thiols, see Thiols tocopherals, see Tocopherols in tomatoes, 331 ubiquinone, 1–2 warmed-over flavor protection, 240 zeaxanthin, 210, 213–214 Antiplatelet, 243 Antistaling agents, 282 Antithixotrophy, 184, 188–190, 193 Antiviral properties, 154 Apocarotenic acid, 210 Apocarotenoids bixin, 209–210 formula for, 209 properties of, 212 structure of, 206 vitamin A in, 212 Apoise, 84 Apparent viscosity, 201, 203 Apples, 6, 85, 237, 248 Appotransferrin, 60 Apricot, 211, 248 Aquaporins, 39 Arabic gum, 85 anionic hydrocolloid, 67 carboxylic function in, 103 emulsifier, 281 stabilizer, 281 thickening agent, 281 Arabinofuranosyl, 238 Arabinogalactan, 85 Arabinose, 84, 220 Arabinosidase, 238 Arachidonic acid, 125–127 Arginine, 134–136, 319 Arils, 232 Aroma, 110 of allium plants, 236–237 baked food, 91 of brassicas, 237 bread, baked, 98 burnt sugar, 97 of cake mix, before preparation, 245–246 caramel, 97, 238 from carotenoid degradation, 212–213 from cellulose thermolysis, 102 citrus peel oil, 232 compounds acetic acid, 234 acetyl-pyrroline, 248 benzaldehyde, 245, 248 diacetyl, see Diacetyl geosmin, 248 jasmonate, 248 lactone, see Lactones linalool, 238, 241, 248 from microorganisms, 248 octen-3-ol, 248 from DNA, 249–250 extraction of, by solvent, 244 from extrusion cooking, 241 from fish oil, treated, 233

340

Chemical and Functional Properties of Food Components

fried food, 91, 123 green note, 249 from hemicellulose, 102 ionone, 212–213 from lipid oxidation, 240–241 from Maillard reactions, 240–241 microbial, 247 from monoterpene derivatives, 238 of mung beans, 243 odor unit, 234–235 oranges, 235 from oxidation of lipids, 122, 243 roasted food, 91, 238 of soy, 243 from starch, 102 storage of, in starch granules, 102 structure of, 234–235 toasty food, 238 undecalactone, 235 vanillin, 244, 247–248 Aromatic plants, 243 Arsenic, 70–71 in predatory fish, 4 PTWI, 75 toxic effects on humans, 76, 323–324 water contamination level, 46 Arsenobetaine, 70–71 Arsenocholine, 70–71 Arteriosclerosis, 222–223, 261 Arthritis, 60, 298 Arylhydrazine, 90 Arylhydrazones, 90–91 Ascorbate calcium, 61 heme, reaction with, 218 nitrite reduction, 277 nitrosamine formation inhibitor, 320 potassium, 62 sodium, 64 Ascorbic acid anthocyanins, 221, 223 antioxidant properties, 1–2, 212 betalain, effect on, 225 browning, inhibition of, 276 in flour, 168 gel formation, 147 Maillard reactions, 238 mineral absorption, 55 oxidation of, 60 in potatoes, 19 sulfite, reaction to, 276 Ashi, 145 Asparagine, 135 Aspartame, 94, 111, 281 Aspartic acid, 134, 135 Aspergillus, 318 Aspergillus niger, 121 Association-induction theory, 37 Astragalus, 85 ATP, 39 Autolysates, 246 Avenasterol, 130 Azo groups, 137, 276, 280

B B vitamins; see also Riboflavin; Thiamine in eggs, 16 in infant formula, 301 in meat, 12 in milk, 15 in minerals, 59 in nuts, 20 pyridoxine, 301 in seeds of pulses, 21 in wheat grain, 16–17 Babassu butter, 116–117 Baby formula bioavailability of minerals in, 54 DHA and EPA in, 127 fatty acids in, 125 iron in, 302 α-lactalbumin in, 154 lactose in, 15 vitamin B6, 301 Bacon, 319 Bacteria, 248 anticarcinogenic action of, 328 coliform, 46 in dairy products, 327 Enterobacteriaceae, 261 Lactic acid bacteria (LAB), see Lactic acid bacteria (LAB) peptones in, 164 vitamins in, 261 Bacteriotherapy, 261 Bacteroides, 261 Bakery products, 284 Baking, 101, 110 Baking powder, 92 Balsam, 233 Baltic sprats, 163 Banana, 236 Barfoed test, 92 Barium, 46, 96 Barks, spices from, 232 Barley, 16, 88, 108 Bathocupreine, 60 Batochromic shifts, 222 Bay, 232 Beans, 20–21; see also Legumes flavoring from, 233 proteins in, 3, 153 Beard, of wheat grain, 16–17 Beef; see also Meat broth, 239 chromium in, 53 composition of, 13 fatty acids in, 117 HCAs in cooked, 323 iron in, 52 lipids in, 3 myoglobin in, 157 myosin transition temperature, 155 potassium in, 52 temperature during cooking, 158 zinc in, 52 Beer alginates in, 84 antioxidant, 325 fermentation of, 302

flavoring from, 233 foam, 8, 84, 150 oxygen in, reduction of, 106 turbidity in, 283 water hardness, impact on, 47 Beer-Lambert law, 222 Beetles, 4 Beets, 224–226, 319; see also Sugar beets Behenic acid, 125 Bell peppers, 238, 240 Bellberry, 250 Benedict test, 92 Benefat, 125 Benincasa hispida, 239 Benzaldehyde, 245, 248 Benzene, 46 Benzenecarboxylic acid, 64 Benzoate calcium, 61 potassium, 62 sodium, 64 Benzoic acid, 278–279 B.E.T. isotherm, 42–43 Betalains, 3, 206, 224–226 Betalamic acid, 225 Beverages, 233, 283, 285–286 BHA, 122, 278 BHT, 122, 278–279 Bifidobacterium, 261–265, 268 Bilberry, 220, 223 Bile, 262 Bingham-Schwedoff model, 187–188 Bingham's viscoplastic flow, 184–185, 188, 202 Biochemical oxygen demand (BOD), 47–49 Biodegradable materials, 105, 112–113; see also Packaging Biotechnology, 296, 303 Bioyogurt, 262–263 Bismuth, 92 Bisulfite, 280 Bixa orellana L. tree, see Annatto Bixin, 209–210 Black currant, 128, 220 Blackberry, 211, 220 Blanching, 4, 69 Bleaching carotenoid degradation, 210 of oil-bearing materials, 120 Blindness, 303 Blocking agents, 327–328 Blood anticlotting agent, 85 calcium in, clotting catalyst, 57 ceruloplasmin in, 66 lead in, 74 lipid levels in, 287 minerals in, 58 probiotics, impact on, 264 substitutes, 85 Bloom on chocolate, 199 on fish, 163 BOD, 47–49 Boiling point, 33, 235, 245 Boltzman constant, 37

Index

Bones, 58–60, 74 Borage oil, 128 Boric acid, 103 Borneol, 235 Boron biological function of, 60 in fruits and vegetables, 69 microelement, 54 RDA, 56 Botulism, 44, 154, 277, 297, 320 Bound water, 38, 40–41 Bovine semitendinosus muscle, 13 Bowman-Birk trypsin inhibitor, 135 Brain development, 127, 301 Bran, 16–18 cadmium uptake, 73 ferulic acid source, 247 mineral bioavailability, 69, 302 Brandy, 325 Brassicas, 237 Brassicasterol, 130 Bread ascorbic acid in, 168 bicarbonate leavenings, 301 chromium in, 53 composition of, 18 dough making, see Dough enriched, definition of, 69 flavoring from, 233 gas-retaining structures in, 156 iron in, 302 lactose in, 15 lipids in, 122–123 making of, 17 minerals in, 58 staling, see Antistaling agents; Staling texture of, 8, 150 thiamine in, 301 water content of, 2 white, 285–286 Bread crumbs, 123 Brine, 173 British gums, 103 Broccoli anticarcinogenic action of, 328–329 carotenoids in, 211 chemopreventive properties of, 327 flavor of, 237 selenium in, 60 sulforaphane source, 331 Bromate, potassium, 63 Bromine, 34, 91–92 Bronchial hypersensitivity, 126 Bronchoconstriction, 126 Browning of food, 45, 91 Brussels sprouts, 237 Bubbles, in foam, 150 Buds, spices from, 232 Buffering agents, 57, 61–65 Bugleberry, 250 Bulk-phase water bound water vs., 40 organization of, 36 properties of, 28–32, 37–38 structural influence of, 34 Bulking agents, 281

341

Burnt sugar, 97 Butanol, 86, 234 Butter dietary fat in, 3, 21 fat separation in, 173 fatty acids in, 117 water content of, 2 Butterfat, 246 Butylated hydroxyanisole (BHA), 122, 278 Butylated hydroxytoluene (BHT), 122, 278–279 Butyric acid flavoring from, 244 odor of, 234 in Salatrim, 125 in strawberry flavoring, 245 Butyrolactone, 99

C Cabbage, 60, 237, 318 Cacao, 53 Cactus fruits, 224 Cadmium, 70, 72–74 calcium absorption, 77 chloride, 73 iron absorption, 77 PTWI, 75 for rancidity inhibition, 67 toxic effects on humans, 76, 323–324 water contamination level, 46 Caffeic acid, 324 Caffeine, 324–325 Calcium absorption of, 55, 77 alginate, 61 anticarcinogenic action of, 329 ascorbate, 61 benzoate, 61 biological function of, 57–58 blood-clotting catalyst, 57 in carrots, 52 caseinate, 148, 153 in cereals, 18 in cheese, 52 chloride, 61, 94 citrate, 61 in cod, 52 compounds, food additives, 61 dihydrogen phosphate, 61 dilactate hydrate, 61 disodium EDTA, 61 in eggs, 16 excretion of, 55 for food texturization, 111 in fruits and vegetables, 22, 69 gel formation, 67, 146 glutamate, 61 hydrogen carbonate, 61, 94 hydroxide, 61 ions, in water, 33 lactate, 61 lead and, 74 macroelement, 54 in milk, 15, 52

in oranges, 52 phosphate, 140 RDA, 56 react with proteins, 68 rheological properties of whey, 147 in saccharide alcohols, 96 salts of phosphatidic acid, 119 in sardines, 52 soap formation, 55 sorbate, 61 transglutaminase-catalyzed reactions, 166 treatment to remove from water, 47 in tuna, 52 water structure former, 34 in yogurt, 52 Calcium-activated neutral protease (CANP), 68 Calpains, 163 Camellia oleifera tea seeds, 116 Campesterol, 130 Campylobacter jejuni, 154, 297 Cancer, 60, 309–310 from arsenic, 76 bladder, 319 blocking agents, 327 breast, 308, 325–326, 332 causing properties, testing for, 315–317 chemoprevention, 330–331 colon, 287, 308, 319, 326, 332 factor alcoholic beverages, 325 diet, 308, 325 dietary fat, 116, 325 reactive oxygen species, 213, 315, 325 gastric, 329 intestine, 325 kidney, 318, 332 Linxian study, 215 liver, 318, 320 lung, 215, 332 neoplastic transformation resisting agents, 327 pancreas, 319, 332 prevention caffeine, 324–325 β-carotene, 215 carotenoids, 332 fiber, 332 fruits and vegetables, 327, 332 probiotics, 263 selenium supplements, 215 vitamin C, 332 vitamin E, 215 prostate, 215, 308, 332 rectum, 308, 319, 332 risk alcoholic beverages, 325, 332 cigarette smoking, 325 heat processing, 332 high calorie content, 332 meat, 332 obesity, 332 stomach, 319–320, 323 suppressing agents, 327 Candida

342

Chemical and Functional Properties of Food Components

cylindracea, 248 probiotics impact on, 264 rugosa lipase, 121 Candy, 123, 125 Canning, 320 Cannizzaro oxidation, 99 Canola, 117–120, 126–127 CANP, 68 Canthaxanthin, 208, 210, 212–213 Caprenin, 125 Capric acid, 125 Caprylic acid, 125 Capsanthin, 208–210 Capsicum, 232 Capsicum annum, 209–210, 238 Capsorubin, 210 Caramel, 109–110 Amadori rearrangement before, 91 aroma of, 97, 238 colorant for food, 91, 109, 206, 227–228 dehydration of saccharides, 93 flavor, after caramelization, 233 sucrose in, 84 Caraway, 232 Carbohydrates alcohols, 90, 96–97 aldehyde, 89–92 in biodegradable materials, 112–113 carbonyl group, addition to, 90–91 in cereals and cereal products, 107 chirality, 88–89 dehydration of, 93 depolymerization of, 102–103 encapsulation using, 111–112 esterification, 92 etherification, 93 fat substitutes, 285 flavor, undesirable, 240 glycosidic bond, 97 halogenation of, 93 hydroxyl groups, 92–97 ketone, 89–92 modification of, 103–107 mutarotation, 89–90 oxidation of, 91–94 process flavor from, 246 reactivity of, 89–107 reduction of, 93 relative sweetness, 94 resistant starch, see Resistant starch retrogradation in, 105 structure of, 82–88 taste of, 107–109 texture in, 110–111 in tubers, 107 Carbon dioxide in milk, 15 oxidation of saccharides, 93 polysaccharides reaction to, 103 transportation, cellular, 59 treatment to remove from water, 47 Carbon tetrachloride, 46, 131 Carbonate magnesium, 61 potassium, 63 Carbonyl compounds

aldehyde and, 90–91 ketone and, 90–91 protein modification, 169 solvent for, 35 water and, 29 Carboxylic acid, 35, 103, 240 Carboxylic groups, 103, 137, 228 Carboxymethyl cellulose (CMC), 104, 111, 148 Carboxymethyl starch, 104 Carcinogens, 308–318 N-nitrosoamines, 172, 277 safety factor for, 295 Cardamom, 232 Cardiovascular disease; see also Heart disease factor cadmium, 76 reactive oxygen species, 213 prevention of, 68 risk of, 125 Carminic acid, 226 Carotene anticarcinogenic action of, 328–329 antioxidant, 214 chlorophyll and, 215 formula for, 207 in fruits and vegetables, 209–211 intercellular communication agent, 213 lycopene, see Lycopene in palm oil, 210 photooxidation protection, 209 properties of, 212 retinal from, 213–214 structure of, 206 ultraviolet skin protection, 213 vitamin A in, 212–213 zeaxanthin, 210, 213–214 Carotenoids in alfalfa, 210 in annatto, 210 anticarcinogenic action of, 332 antioxidant, 1–2, 213, 331 apocarotenoids, see Apocarotenoids biological activity, 213 carotenes, see Carotene in carrot, 210 in citrus peel, 210 color of, 207–209 destruction of, in deodorizing of oil, 120 as food coloring, 210–212 homocarotenoids, 206 lycopene, see Lycopene in milk, 14–15 neoxanthin, 209 oxidation of, 301–302 oxocarotenoids, see Xanthophylls in palm oil, 210 in paprika, 210 pigments from, 16, 206 properties of, 212–213 in red pepper, 209–210 in saffron, 210 structure of, 206–209 synthesis of, 209–210

in tomato, 210 vitamin A in, 212–213 xanthophylls, see Xanthophylls zeaxanthin, 210, 213–214 Carrageenans casein stablizer, 67 emulsifier, 281 for food texturization, 111 locust bean gum and, 282 in red seaweed, 85 in squid meat gels, 145 stabilizer, 281 sulfate function, 103 thaumatin reactions with, 281 thickening agent, 281 Carrots anticarcinogenic action of, 328 calcium in, 52 carotenoids in, 206, 210, 211 oil from, 210 pigments from, 52, 206 potassium in, 52 Caryophyllene, 244 Caseins acylation of, 170 antimicrobial activity of, 154 enzyme-catalyzed reactions in, 162 for film formation, 148 lipid interaction in cheese, 173 in milk, 14, 140, 153 phosphorylated amino acid residues in, 136–137 processing of, 153 proline in, 135 rheological changes to, 156 stablizer, 67 in whey, 146 Cassava, 107, 300 Cassia, 232 Casson equation, 189, 202 Castor oil, 247 Catabolic processes, 169 Catalase, 60, 160 Cataracts, 60 Catechins, 223 Cathepsins, 162–164 Cationic dyes, 228 Cationic starch, 104 Cations, 54; see also Minerals Cauliflower, 237 Caustic soda, 109 Celery apiose in, 84 nitrates in, 319 selenium in, 60 sodium in, 22 spice from seeds, 232 Celiac sprue, 55 Cellobiohydrolase, 106 Cellobiose, 83, 106 Cellular-mediated immunity (CMI), 265 Cellulose acetate, 104 aroma of, 110 in biodegradable materials, 112 CMC, 104 degradation of, 106

Index

depolymerization of, 102 emulsifier, 281 esterification, 104 etherification, 104 in fruits and vegetables, 21 mineral bioavailability, 55 modification of, 99–104 in plants, 85 in potatoes, 19 solubility, 101–102 stabilizer, 281 thermolysis of, 102 thickening agent, 281 in wheat bran, 16 Cereals, 16–18 barley, 16, 88, 108 cadmium in, 74 folate in, 301 mineral bioavailability after processing, 69 minerals in, 58–59 nitrites in, 319 N:P conversion factor in, 3 oats, see Oats phase diagram, 198 proteins in, 134 saccharides in, 2, 137 solubility of, 142 starch in, 107 Cerium, 67 Ceruloplasmin, 60, 66 Cesium, 34 Chalazae, 15–16 Charcoal, 48, 102 Cheese alkylation of, 169–170 calcium in, 52, 58 chromium in, 53, 58 composition of, 13 enzyme-catalyzed reactions in, 162 fat emulsion in, 173 flavoring from, 233 gelation of, 156 milk protein in, 14 minerals in, 58 mutagen formation in, 320 phosphorus in, 58 potassium in, 52 sensory attributes of, cause of, 8 sequestrant for, 64 yield of, 162 zinc in, 52 Chelating agents, 60 bathocupreine, 60 betalains, 3, 206, 224–226 citric acid, see Citric acid cysteine, see Cysteine EDTA, 60, 66–67 iron, see Iron phosphates, see Phosphate purine, 60 sodium citrate, 67 sodium oxalate, 67 Chemotaxis, 126 Cherry, 236, 248, 325 Chicken; see also Meat broth, 239 composition of, 13

343

fatty acids in, 117 fried, 239 gels from, 147 lipid oxidation in, 239 radiation, effect on vitamins, 302 Chile saltpeter, 64 Chinons, 21 Chips, 53 Chirality, 88–89, 105 Chitin, 81, 86–87, 103 Chitosan, 81 Chive, 236 Chloride calcium, 61 magnesium, 61 potassium, 63 RDA, 56 sodium, see Sodium chloride Chlorination, 47, 280, 326 Chlorine in fruits and vegetables, 22 macroelement, 54 oxidation of aldoses, 91–92 water structure breaker, 34 Chloroacetic acid, 104 Chlorodesoxysucrose, 94 Chloroform, 207 Chlorogenic acid, 223, 324 Chlorogenoquinone, 223 Chlorophyll, 215–217 anticarcinogenic action of, 327–328 photooxidation protection, 209 pigments from, 206 removal of, 119 sensitizer, 160 Chloroplasts, 209 Chocolate, 125, 189, 201–203 Chokeberry, 220 Cholemyoglobin, 218 Cholera, 44 Cholesterol cancer risk factor, 326 chromium impact on, 58 decreasing level of, 129–131, 300 in egg yolk, 16 probiotics impact on, 262, 264 structure of, 130 Choline, 6, 16 Chondrodystrophy, 59 Chromatographic sorbent, 85 Chromium in beef, 53 bioavailability, 54 biological function of, 58 in bread, 53 in cacao, 53 in cheese, 53 in curry, 53 in hawthorn, 53 for insulin production, 57 in kidneys, 53 in liver, 53 microelement, 54 in paprika, 53 in pepper, 53 for rancidity inhibition, 67 RDA, 56 in spices, 53

water contamination level, 46 Chromoplasts, 209 Chromoproteins, 157 Chronic tests, 294 Cinerarin, 222 Cinnamaldehyde, 243 Cinnamon, 232 Cirronellol, 238 Cis fatty acids, 7, 116, 121 Cis-parinaric acid (CPA), 138 Citral, 244, 250 Citrate calcium, 61 sodium, 67 for stabilizing, 155 Citric acid as catalyst, 285 chelating agent, 122 discoloration prevention by, 283 enzymes from, inhibition of, 278 fermentation of, 150 in fruits and vegetables, 22 as sequestrant, 279 as solvent, 142 treatment of oil, before degumming, 119 Citronellol, 235, 244 Citrus fruit anticarcinogenic action of, 328 carotenoids in, 210 oil aroma, 232 essence oil, 243 limonene in, 232, 250 Clarifying agents, 275, 283 Clathrate hydrates, 36 Clausius-Clapeyron equation, 41–42 Cleaning, 118 Clostridium botulinum, 44, 154, 277, 297, 320 difficile, 264 in gut, 261 illness from, 297 perfringens, 277, 297 water activity level, 44 Cloves, 232, 243 Clupea, 164 CMC, 104, 111, 148 CMI, 265 Coacervation, 112 Coalescence, 283 Coatings, 125, 148 Cobalt biological function of, 59 microelement, 54 for rancidity inhibition, 67 RDA, 56 Coca-Cola, 242 Coccus cacti L., 226 Cochineal, 206, 226 Cocoa aroma, 110 cadmium in, 74 flavoring from, 233 rheological properties of, 201 Cocoa butter, 125, 201 Coconuts, 116–117 Code of Federal Regulations, 246 Codfish

344

Chemical and Functional Properties of Food Components

calcium in, 52 DHA and EPA in, 127 lipids in, 3–4 myosin transition temperature, 155 rancidity in, 66 sorption isotherm data for, 43 Codliver oil, 127 Coefficient of retention, 201 Coffee, 110, 233, 324–325 Cohesion, 194 Colas, 242 Cole crops, 237 Coliform bacteria, 46 Collagen in egg shell, 15 for film formation, 148 formaldehyde and, 169 heating of, 155–156 hydroxyproline in, 136 posttranslational modifications in, 136 rheological properties of, 156–157 saccharides in, 137 solubility of, 142–143 thermal stability of, 139 water retention, in meat, 12 Collapse, 196 Collenchyma, 23 Color scale, Lovibond tintometer, 120 Colorants, food, 6, 205–206 additives as, 274–275, 279–281 anthocyanins, 219–224 betalains, 224–226 caramel, see Caramel carotenoids, see Carotenoids chlorophyll, see Chlorophyll chromoproteins, 157 curcumin, 206, 227 fixative, 64 from flavonoids, 219–224 heme, 217–218 microcapsules for, 102 perception of, 205–206 quininoid, 226 retention agent, 62 riboflavin, see Riboflavin sorbic acid, 277–279, 303–304 synthetic organic colors, 228 tetrapyrrole pigments, 215–217 tetraterpene pigments, 206–215 thermal processing, 109–110 turmeric, 227, 232 Compartmentalized water, 38 Complex force deformation, 195 Complex formation, 104 Complex modulus, 201 Complexing agents, 275 Compression modulus, 199, 201 Compressive modulus, 199–200 Compressive strain, 199–200 Compressive stress, 199–200 Concentration, 234 Concrete, 244 Conditioning, 118 Confitures, 108 Conformation, 155 Coniferaldehyde, 247 Constitutional water, 41

Containers, biodegradable, 105, 112–113; see also Packaging Contaminants, 5; see also Pollution Cookies, 125 Cooking aroma of, 240 carbohydrate transformation, 101 carcinogens and mutagens formed after, 317 drip formation during, 4 extrusion, 241 leaching of vitamins and minerals during, 4, 69 Maillard reactions, 238 methods, cancer risk, 323–324 mineral bioavailability, 55 mutagen formation during, 320 WHC impact on, 145 Copigmentation, 222 Copper bioavailability of, 55 biological function of, 59 catalyzation agent, 279 chlorophyll, reaction with, 216 deficiency, zinc effect on, 77 in fruits and vegetables, 69 in ham, 53 lipid oxidation, 60 in lipids, 122 in liver, 53 loss of, during processing, 69 metallothioneins and, 72 microelement, 54 oxidations with, 92 oxygen radicals, generation of, 60 in oysters, 53 for rancidity inhibition, 67 RDA, 56 react with proteins, 68 in salmon, 53 in sunflower seeds, 53 in tuna, 53 in wheat, 53 Copper chlorophyllin potassium, 63 sodium, 63 Coprecipitation, 112 Coriander, 232 Corn bran, 130 for film formation, 148 flour, 157, 189 lecithin from, 282 linoleic acid in oil, 117, 127 oil from, 117–120 processing of, 300 retrogradation in, 105 sorption isotherm data for, 43 Starlink, 303 storage of, mycotoxin activity, 318 Cornstarch, 107 Cosmetics, 85 Costamers, 12 Cottage cheese, 266 Cottonseed, 117, 129, 282 Coulomb's law, 34 Covalent bonds, 27–28, 139, 146 Cow's milk

bioavailability of minerals in, 54; see also Milk composition of, 13 fatty acid residues in, 15 CPA, 138 Cracking, 118 Cranberry, 220 Creaminess, 185 Creaming, 149, 283 Creatine, 321 Creatinine, 321 Creep compliance test, 190–191 Cretinism, 60 Crispness, 196 Crocetin, 210 Crocin, 210 Crocus sativus, 210 Cross-linking from acylation, 170–171 from alkylation, 169 of amino acid residues, 136, 159–160 in gelation, 145 during phosphorylation, 171 polysaccharides, 105 of proteins, 142 rupture of, 173 starches, 111 in transglutaminase-catalyzed reactions, 166 Cruciferae anticarcinogenic action of, 328 brassicasterol in oilseeds, 130 goitrogenic products in oilseeds, 7 odor of, 237 Crude protein, 3, 13, 18 Crustaceans, 3–4, 151–152 Cryoprotectant, 151–152, 173 Cryptosporidium, 297 Cryptoxanthin antioxidant, 214 in egg yolk, 210 formula for, 208 in fruits and vegetables, 211 in green leaves, 209–210 intercellular communication agent, 213 vitamin A in, 213 Crystallites in starches, 88, 102 Crystallization, 196 Cubic niter, 64 Cucumbers, 239, 249 Cumin, 232 Curcumin, 206, 227 Curd flavoring from, 233 from gelation of whey, 147 rheological changes to, 156 from soybeans, 153 Curdlan, 281 Curing, 273 binding of nitrosating agents, 172 color changes from, 157 for food preservation, 44 heme pigments, 218 of meat, nitrosamines, 319 nitrite in, 168, 277, 323 nitrosamine formation during, 320, 323

Index

Curry, 53 Cyanide, 300 Cyanide sulfide, 34 Cyanidin, 219, 223 Cyclamates, 94, 111 Cyclization, 97 Cyclodextrins, 106–107, 112, 241 Cycloglucans, 106 Cyclooxygenase, 127 Cyclospora, 297 Cysteine, 60 alkaline pH, reaction with, 159 in collagen, 134 enzyme inhibitor, 164 hydrolyzing of, 170 oxidation of, 161 properties of, 135 sulfenic, 161 thermal degradation of, 158 in transglutaminase, 166 Cytochrome oxidase, 59 Cytochrome P450 complex, 310–315 Cytokines, 265 Cytoskeletal proteins, 12, 163 Cytosol, 166 Cytotoxic cells, 265

D Dactylopius coccus Costa, 226 Daidzein, 328 Dairy products, 14–15; see also specific types fermentation of, 240, 262, 268 fiber enrichment in, 285–286 flavor of, 246 GDL in, 92, 284 lactic acid bacteria in, 327 lactose in, 108 minerals in, 59 N:P conversion factor in, 3 rheological properties of, 167 vitamin D fortification, 302 Daucus carote, 52, 206 DDT, 326 Deamination, 166, 169 Deborah number, 192 Decadienal, 240, 244 Decalactone, 244, 247 Decalcification, 76 Decanal, 235 Decapterus, 164 Decarboxylation, 4 Deformation complex force, 195 in an ideal body, 199–200 rheological property, 181, 184–185 types of, 199 Degumming oil, 119 Dehydration, 44, 93, 97, 276 Dehydroalanine, 159–160 Dehydroascorbic acid, 147, 168 Delayed type hypersensitivity (DTH), 265 Delphinidin, 219, 223 Demethylation, 72

345

Denaturation of proteins, 141 color changes from, 157 in egg whites, 154 film formation and, 148 gelation and, 145 solubility after, 143 in soy milk, 153 temperature, 155 in whey, 153, 155 Dendrite formation, 105 Density of water, 29–30, 32, 36 Deodorizer distillate (DOD), 129 Deodorizing of oil, 120 Deoiling, 129 Deoxyalliin, 240 Deoxysugars, 97 Depot fat, 3 Dermatitis herpetiformis, 55 Desaturase, 126, 127 Deserts, 190 Designer foods, 6 Desmin, 12, 163 Desorption isotherm, 42–43 Desoxyglucosulose, 98 Desoxysaccharides, 93 Detergents, 48, 105 Detoxification, 72, 311 Dew point temperature, 43 Dewaxing of oil, 120 Dextran, 85, 106 Dextrins, 102, 110, 112 Dextrose, 244 DGLA, 127 DHA, 125–126 Diabetes, 58 fatty acids levels in, 127 food for, 111 sweeteners, 108–109 Diacetyl flavoring from, 244 formosine, 97, 99 from microorganisms, 248 mutagenic pyrolysis product, 324 protein modification, 168 Diacylglycerols, 6, 14–15 Dialdehydes, 93, 105 Diallyl sufide, 328 Diallyl thiosulfinate, 236–237 Dialysis, 68 Diascorea dumetrorum, 107 Diaso, 228 Diazonium, 277 Dicarboxydiamides, 105 Dichlorobenzene, 46 Dichloroethane, 46 Dichloroethylene, 46 Didoquin, 55 Dielectric constant (ε), 34 Dielectric relaxation measurement, 39 Diesel in water supply, 47 Dietary fat, 21 cancer risk factor, 325–326 composition of, 116–117 edible, colorants for, 211 glutathione, see Glutathione HCA activation by, 322 in milk, 14–15 minetics, 284 RDA, 116

substitutes, 284–285 Dietary fiber cellulose, 85 in flour, 18 plant polysaccharides as, 1 zinc absorption, 55 Dietary supplement antioxidants, 331 chemopreventives, 326–327 magnesium hydrogen phosphate, 62 probiotics, 275 probiotics as, 267 vegetable lecithin, 129 Diethylacetal, 244 Differential scanning calorimetry, 155 Diffusion coefficient, 37, 38 Diffusivity of momentum, 187 Diglycosides, 238 Dihomogammalinolenic acid (DGLA), 127 Dihydrogen phosphate calcium, 61 potassium, 63 sodium, 64 Diketal, monoacylated, 92 Dilatant flow, 184, 185, 189 Dilatin, 55 Dill, 232 Dimagnesium phosphate, 62 Dimethyl-2-hydroxy, 99 Dimethyl disulfide, 237 Dimethyl-hydroxyacetone, 99 Dimethyl sulfoxide, 103 Dimethylarsenic acids, 71 Dimethylsulfide, 244 Dioxin, 293 Diphenyl oxide, 244 Dipole moment, 26 Direct flow rate, 194 Disaccharides, 84 in fruits and vegetables, 21 lactose, see Lactose maltose, see Maltose properties of, 89–99 sucrose, see Sucrose Disodium EDTA, 61, 64 Disodium pentaoxodisulfate, 64 Dispersion droplet size, 15 Dissociable solutes, 33 Distillation, 102, 130, 243 Dithianes, 238 Dithiolanes, 238 DNA adducts, 314–315, 317, 325–326 arsenic impact on, 70 of Bifidobacterium, 262–263 cancer and, 309–310 damage protection, 328 for flavor compounds, 246–247 flavoring from, 249–250 hydrogen bond in, 29 modification of, 310–315 PAH damage to, 322 protein synthesis of, 58 repair inhibitor, 324 Docosahexaenoic acid, 117 DOD, 129 Dodecylsulfate, sodium, 138

346

Chemical and Functional Properties of Food Components

Dough aroma, 110 conditioner, mineral compounds as, 61–62 flavoring from, 233 formation of, 17, 156–157 gas-retaining structures in, 156 lipids in, 123 lipoxygenase in, 167 proteins in, 142 saccharides in, 104 sulfite, additive to, 276 Drinks, 285–286 Drip formation from cooking, 4 decrease in, 173 in ham, 8 during rheological changes, 156 in shellfish, 8 after thawing, 4, 69 WHC impact on, 145 Drugs, 15 Drying, 39 Drying agents, 62 DTH, 265 Duck, 238–239 Dwarfism, 59 Dyes, 206, 228 Dynamic viscosity, 186

E Ecology, 5 Eczema, atopic, 128 EDTA, see Ethylenediaminetetraacetic acid (EDTA) Effluent treatment, 48–49, 172 Eggs, 15–16 acylation of, 170 amino acids in, 135 composition of, 13 fat in, 21 iron in, 52 lecithin from, 282 lipids in, 3 lysozyme in, 135, 154 mineral oil on, 283 minerals in, 58–59 mutagen formation in, 320 N:P conversion factor in, 3 phosvitin in, 135 proteins in, 3, 135, 142, 154 serine in, 135 white, see White, egg yolk, see Yolk, egg zinc in, 52 Eicosanoid production, 126 Eicosapentaenoic acid (EPA), 117, 125–126 Elastic deformation, 199 Elastic modulus, 191 Elastin, 199 Electrostatic interactions, 26–27, 143–144 Elongase, 126, 127 Emulsification, 144, 148–151, 171 Emulsifying agents

additives as, 275, 281–283 agar, 84 calcium caseinate, 153 egg yolk, 154 HLB number of, 283 mineral compounds as, 64 polysaccharides, 84–85, 281–282 sodium caseinate, 153 Emulsion forming agents, 283 Emulsion stablizer, 65 Emulsions, 190 Enantiomers, 105 Encapsulation, 111–112, 241, 244 Endiols, 99 Endive, 85 Endoglucanase, 106 Endoinulinase, 286 Endomysium, 12, 14 Endopeptidases, 136, 168 Endosperm, 16–18, 69 Endrin, 46 Engraulis, 164 Enolization, 99 Enterobacteriaceae, 261 Enterococcus faecium, 268 Enteropathy, tropical, 55 Enthalpy, 34 of egg whites, 154 of hydrophobic substances in water, 35–36 of proteins, 138, 141 rheological property, 193 Entrapped water, 41 Entropy, 34 of hydrophobic substances in water, 35–36 of proteins, 137 rheological property, 193 solvent, 143–144 Environmental impact of processing, 48–49, 172 Enzymes activity denaturation, 141 role of minerals in, 58–59 amylases, 17 catalyzed reactions in proteins, 162–167 cathepsins, 162–164 esterases, 248 flavoring from, 236–238, 246–247 glycosidase, 238, 248 hydrolases, 14 lipases, 17, 121, 248 lipoxygenase, see Lipoxygenase (LOX) in meat, 12 myrosinase, 7 nucleases, 248 oxidoreductases, 14 phase II, 311 proteases, 17, 146, 248 tryptophan pyrollase, 75 EPA, 117, 125–126 Epigallocatechin, 327–331 Epimysium, 12, 14 Epithelium, 329 Epoxides, 212, 310, 326 Erythrocytes, 39, 74

Erythronic acid, 93, 96 Erythrose, 82 Erythrosine, 160 Erythrulose, 82 Escherichia coli hydroperoxide lyases in, 250 illness from, 296–297 in mutagenic activity testing, 316 prevention benzoic acid, 278 probiotics, 264 red sea bream TGase cloned in, 166 ESR, 39 Essence, 243 Essential oils antimicrobial activity of, 243 aroma of, 235 of cloves, 243 definition of, 232 distillation of, 243 flavor of, 236 from vegetables, 233 Esterases, 248 Esterification of amino acid residues, 136 of cellulose, 104 of chlorophyll, 215 citrus peel oil aroma, 232 lipase-catalyzed reaction, 248 of starch, 104 of tocopherols and sterols, 130 Esters aspartame, 94, 111, 281 butylated hydroxyanisole (BHA), 122, 278 butylated hydroxytoluene (BHT), 122, 278–279 emulsifier, food, 282 ethyl acetate, 235, 244–245 fatty acids, see Fatty acids (FAs) flavoring from, 244 gallic acid, 278–279 glycerol fatty acid, 282 hydrolyzing of, 236 hydroxycarboxylic fatty acid, 282 lactylate fatty acid, 282 linalyl acetate, 244 methyl dihydrojasmonate, 244 odor of, 235 polyethylene fatty acid, 282 polyglycerol fatty acid, 282 of polyols, 284 propylene glycol fatty acid, 282 raffinose, 94, 285 sorbitan fatty acid, 282 sorbitol, see Sorbitol stachyose, 94, 285 sucrose fatty acid esters (SFE), 284–285 TBHQ, 122, 278–279 trehalose, 285 Estrogens, 326 Ethanol an extraction solvent, 243–244 fermentation of glucose syrup, 102 metabolism of, 108 threshold of, 234 Ether, 115

Index

Etherification, 93, 104 Ethers diphenyl oxide, 244 flavoring from, 244 rose oxide, 244 Ethyl-2-hydroxy-2-cyclopenten-1, 99 Ethyl acetate, 235, 244–245 Ethyl butyrate, 245 Ethyl hexanoate, 245 Ethyl phenyl acetate, 244 Ethylene oxide, 104 Ethylenediaminetetraacetic acid (EDTA), 60 ferrous iron, elimination of, 66 rancidity inhibitor, 66–67 as sequestrant, 279 Eubacterium, 261 Eugenol, 243–244, 247 Evaporation, 4, 16 Evening primrose oil, 128 Extraction alkaline, 143 azeotropic isopropanol, 151 of fat and saccharides from soybeans, 153 of myofibrillar proteins, 144 of oil, 118–119 solvent, 243–244 Extractives, 244 Extrusion, 241 Exudate gums arabic, see Arabic gum emulsifiers, 281 karaya, see Karaya gum stabilizers, 281 thickening agents, 281 tragacanth, see Tragacanth gum Eyesight, 20, 127

F FA, see Fatty acids (FAs) Fats, 116–117; see also Lipids antioxidants in, 278–279 density of, 40 flavor of, 246 as IMF filler, 44 oxidation of, 279 processing of, 118–122 rancid odor, 66–67, 122, 240 removal from water, 48 storage of, 121–122 substitutes, 275, 304 transportation, cellular, 58 Fatty acids (FAs), 116–117 cancer risk factor, 326 in cereals, 17 cis, 116 in edible fats, 21; see also Dietary fat esters, 282 green aroma from, 249 hydrogenation of, 116 lactone production, 247 linoleic acid, see Linoleic acid lipoxygenase catalyzing oxidation of, 167

347

long-chain, 124–126 medium-chain, 124–125 in milk, 14–15 in nuts, 20 oxidation of, 15, 239 polenoic, 126–128 in potatoes, 239 ricinoleic, 247 short-chain, 125 in soap formation, 55 sorbic acid, 277–279, 303–304 structured lipids, 124–126 trans, 116 unsaturated, decrease in, 233 Fehling test, 92 Fennel, 232 Fenugreek, 232 Fermentation process biotechnology in, 303 for flavor compounds, 247 flavoring from, 233 mineral bioavailability in, 302 mineral compounds in, 61 products of, 82 saccharides in, 84–85, 105, 108 of soybean proteins, 153 Ferric sodium edeteate, 64 Ferritin, 60, 73 Ferroxidases, 66 Ferulic acid, 247 Fiber, 332 Fillers, 85, 275 Film formation, 145–149 additives for, 275, 283 edible, from whey proteins, 167 from egg whites, 154 from phosphates, 104 from polysaccharides, 281–282 Filtration, 46–48, 153 Firming agents, 61–62 Fischer glycosidation, hydrochloride catalyzed, 93 Fish; see also specific types Anisakis parasite in, 7 aroma, 110 arsenic in, 70–71 ashi, 145 calcium in, 58 chromoproteins in, 157 cobalt in, 59 cooking of, 324; see also Cooking enzyme-catalyzed reactions in, 162–167 fat in, 21 fatty acids in, 117 feed for, 164 flavoring from, 233 fluoride in, 53 gadoid, 165–166 gelation of, 145, 146 hydrolysates, 164–165 iodide in, 53 lipid oxidation in, 60, 239 lipids in, 3 marinades, decarboxylation of amino acids in, 4 mercury in, 71 minerals in, 52–53, 58–60 modori, 146

N:P conversion factor in, 3 oil from, 116–131, 233, 328 phosphorus in, 58 polyphosphates in processed, 173 potassium in, 58 preservation agents, 273 proteins in, 151–152 rheological changes to, 156 saccharides in, 2 sauces, 164 selenium in, 60 sequestrant for, 64 setting of, 145 silage, 164 smoked, 319 sodium in, 58 solubility of, 143 storage of, 151 surimi, 151 trimethylamine in, 165 water in tissue, 43, 144–145 zinc in, 52, 59 Flaking of oil-bearing materials, 118 Flavonoids anthocyanins, 219–224 antioxidant, 60 carcinogenicity, 318 cyanidin, 219, 223 delphinidin, 219, 223 in fruits and vegetables, 21 malvidin, 219 mutagenicity, 318 pelargonidin, 219 peonidin, 219 petunidin, 219 Flavor, 250 additives for, 6, 279–281 agents, 99 of allium plants, 236–237 of brassicas, 237 from carbohydrates, 107–109 in cheese, 4 Code of Federal Regulations, 246 compounding, 245–246 after cooking, 233 distillation of, 243 from DNA, 249–250 enhancement, by additives, 274 from enzymes, 248–249 in extrusion cooking, 241 fixative, 85 of fresh fish, 233 in fried food, 123 fruit, 232–233 green-grassy notes in fruit, 237–238 after heating, 233 of herbs, 232 intensity, 234 IOFI, 246 Maillard reactions, 238–239 manufacture of, 245–246 in meat, 4, 66 from microbes, 233, 247–248 from minerals, 57, 61–64 of mushrooms, 237 natural products with flavoring properties, 233 "odor of violets", 212–213

348

Chemical and Functional Properties of Food Components

from organic chemicals, 244–245 from oxidation of lipids, 122, 239–241 process, 246 production of, 243–250 properties of, 242–243 roasted food, 130 savory, 233, 238–239 from sorbic acid, 278 of spices, 232 structure of, 234–235 sweet, 233 vegetable, 233 Flaxseed, 127 Flickering clusters water model, 31, 33 Flies, 4 Flocculation, 46–48, 149, 283 Flounder, 71 Flour ascorbic acid in, 168 for biscuit making, 276 composition of, 18 corn, 157, 189 dietary fiber in, 18 emulsifier, 281 extraction rate of, 18 folate in, 301 germ removal, 302 from guar seeds, 281 from konjac seeds, 281 from locust beans, 281 rice, 157 rye, 157 soy, 143, 301 stabilizer, 281 sulfite, additive to, 276 tamarind, 85, 281 thickening agent, 281 vitamin E in, 302 wheat, 156–157 Flow, analysis of, 181–191, 194, 202 Flowers, 233 Fluid flow, 183 Fluoride, 53, 59; see also Fluorine Fluorine biological function of, 57 microelement, 54 RDA, 56 water contamination level, 46 water structure former, 34 Foam additives in, 275 beating of, 104 properties of, 150–151 stabilization, 142, 153–154 texture of, 110 in whipped cream, 123 Foaming, 142, 144, 171 Foaming agents egg albumin, 154 milk peptides, 283 milk proteins, 153, 283 Folate, 301, 303 Folded oil, 243 Folic acid, 301 Food composition of, 2–4 functional properties of, 5–6

groups, 11 processing, see Processing of food quality of, 5–8 safety of, 7, 291–304 storage of, see Storage Food poisoning, 44 Formaldehyde, 103, 165, 169 Formic acid, 164 FOS, 286 Fractals, 195 Fractionation of oil, 121 Free energy change, 34–36, 137–138, 193 Free peptides, 3 Free radicals, 60, 72, 110; see also Radicals, oxygen Free water, 41 Freezing, 101–102, 151 Freezing point depression of, 33 impact on, by water mobility, 39 of vicinal water, 38 of water-based foods, 40 Freshness, 5 Frosting, 129 Fructo-oligosaccharides (FOS), 286 Fructofuranosyl, 280 Fructopyranose, 94 Fructose, 84, 106 in barley malt, 108 from D-glucose, 99 in fruits and vegetables, 21 in honey, 19–20, 109 to retard moisture loss, 6 syrup, 108, 109 Fructosyltransferase, 286 Fruits, 21–23; see also specific types alkaline treatment of, 159 analogs, 67 anthocyanins in, 223 anticarcinogenic action of, 329, 332 from cactus, 224 carotenoids in, see Carotenoids citrus, see Citrus fruit confectionery coating for, 125 copper in, 59 flavor of, 232–233, 236, 248 iron in, 59 katemfe, 281 lipids in, 3 minerals in, 58–59 N:P conversion factor in, leafy, 3 oxidation of, 148 potassium in, 58 processing of, 283 proteins in, 3 spices from, 232 water content in, 2 Frying aroma, 110, 240 carbohydrate transformation, 101 chicken, 239 flavor from, 240 lipid action during, 123 methods, cancer risk, 323–324 mutagen formation during, 320 nitrosamine formation during, 320 potatoes, 239

Fucose, 84 Fungi, 128, 248 Fungicides, 317 Fungistatic agent, 61, 65 Furan derivatives arabinose in, 84 aromas from, 235 from burning sugar, 110 in caramel, 110 flavor of, 245 flavoring agent, 99, 244 from hemicellulose, 102 Maillard reactions, 238 production of, 97 in strawberry flavoring, 245 sucrose in, 84 Furcellaran, 85, 103, 111 Furfural, 242 Fusarium, 318

G Galactan, 85, 103 Galactaric acid monolactone, 97 Galacto-oligosaccharides (GOS), 286 Galactopyranose, 94 Galactopyranosyl, 280 Galactose, 84, 97 bonded to anthocyanidins, 220 in casein, 137 oxidation of, 93–94 Galactosidase, 262 Galactosucrose, 94 Galacturonans, 281 Galacturonic acid, 97 Gallic acid, 278–279 GALT, 260 Garlic anticarcinogenic action of, 328–329 antimicrobial activity of, 232, 243 aroma of, 239–240 soybean oil with, 236–237 Gas, 15 Gastric acid, 262 Gastrointestinal disorders, 127–128, 260–261, 263 Gatti gum, 85, 103 GDL, 92, 284 Gelatin, 146 from denatured collagen, 155 for film formation, 148 in fruit juice, 283 Gelatinization, 17, 88, 107, 199 Gelation of actomyosin, 146 denaturation and, 145 of lipids, 123 of proteins, 144–146 steric exclusion, 145 of whey proteins, 153 Gellan gums, 281 Gelling agent additives as, 275 calcium caseinate, 153 egg albumen, 154 β-lactoglobulin, 153

Index

mineral compounds as, 63 phosphates, 104 polysaccharides, 84–85, 281–282 proteins, 142 sodium caseinate, 153 whey proteins, 153–154 Gels for coacervation, 112 enzyme-catalyzed reactions in, 162–164 from fish, 146 formation of, 87–88, 111 for frozen products, 6 from heating of proteins, 156 milk protein in, 146 modori, 146, 164 from oxidized starches, 104 retrogradation, 105 strength of, increasing, 167 structure of, 145–146 from surimi, 151–152 time-dependency of, 190 translucent, 145 Genistein, 328–329 Geosmin, 248 Geotrichum candidum lipase, 121 Geraniol, 238, 241, 244 Germ corn, 119 mineral bioavailability, 69, 302 nut, 20 removal from white flour, 302 wheat, 16–18, 129 Ghati gum, 67 Giardia, 297 Ginger, 232 GLA, 125–128 Glass dynamics map, 196–198 Glass phase transition, 195–199 Glazing agents, 275 Globulins, 142 Glow plasma, 101–102 Glucans, 281 Gluconate, magnesium, 62 Gluconic acid, 91 Glucono-δ-lactone (GDL), 92, 284 Glucopyranose, 94 Glucopyranosides, 238 Glucopyranosyl, 280 Glucose, 84 in barley malt, 108 bonded to anthocyanidins, 220 from cellulose, 102, 106 in fruits and vegetables, 21 in helical complexes, 86 in honey, 19–20, 109 isomeritization of, 99 polymerization of, 285 production of, 106 pullulan, 106 reaction protection, 92 from starch, 103 structure of, 89 syrup, 108, 109 tolerance, 58 transporter, for water, 39 xanthan gum, see Xanthan gum Glucosephosphate, 105 Glucosidases, 223, 238

349

Glucosinolanes, 7 Glucosylamine, 84 Glucuronyltransferases, 311 Glutamate calcium, 61 magnesium, 62 potassium, 63 sodium, 64 Glutamic acid cadmium and, 73 in paramyosin, 134 properties of, 135 sodium glutamate, 64 Glutamine enzyme-catalyzed reactions in, 166–167 properties of, 135 in transglutaminase, 166 Glutathione anticarcinogenic action of, 311, 328–329 antioxidant, 160 in dietary fat, 315 Glutelins, 142 Gluten in cereals, 17 in dough, 156–157 for film formation, 147–148 glass dynamics of, 199 texture from, 6 Glycans, 86; see also Polysaccharides Glyceric acid, 93, 96 Glyceroaldehyde, 82 Glycerol, 282 Glycerol monostearate (GMS), 123 Glycerold, 282 Glycerols density of, 40 esterification of, 116 extract solubilization, 244 as humectants, 44 Glycine in collagen, 134 properties of, 135 in transglutaminase, 166 Glycinin, 167 Glycogen, 2, 85, 88, 108 Glycolipids, 128 Glycomacropeptide, 137 Glycosidase, 238, 248 Glycosides, 84 Glycosidic bond, 97 Glycosylation of acid casein, 153 of amino acid residues, 136 of anthocyanins, 219, 222 Glycosylsucrose, 286 Glycosyltransferases, 136 Glyoxalic acid, 93, 96, 168, 324 GMS, 123 Goiter, 60 GOS, 286 Gourd melon, 239 Grain, 59; see also Cereals; specific types amino acids in, 134 composition of, 16, 18 glutamic acid in, 135 mineral bioavailability, 58–59, 302

proline in, 135 water content of, 2 Grapefruit, 211, 314–315 Grapes chemopreventive properties of, 327, 331 flavor of, 237 monoterpene in, 238 red, anthocyanins in, 220 Gravy, 123 Green onion, 236 Grilling, 314–315, 320, 322 Grinding, 194, 300 Grits, 153 Gross alpha particle, 46 Gross beta particle, 46 Guar, 281 Guaran gum, 85 Guava, 249–250 Guillan-Barre syndrome, 298 Gums arabic, see Arabic gum British, 103 curdlan, 281 emulsifier, 281 exudate, 281 gatti, 85, 103 gellan, 281 ghati, 67 karaya, see Karaya gum locust bean, 85, 282 microbial, 281 plant, 84 stabilizer, 281 for texture, 110 thickening agent, 281 tragacanth, see Tragacanth gum xanthan, see Xanthan gum Gut-associated lymphoid tissue (GALT), 260 Gynecological disorders, 127–128

H HACCP, 297 Halide, 93 Haloacetates, 169 Haloamides, 169 Halogenation, 93 Ham copper in, 53 flavoring from, 233 overpasteurization of, 8 rheological changes to, 156 Hardness of water, 47 Haworth methylation, 93 Hawthorn, 53 Hazard Analysis Critical Control Point (HACCP), 297, 298 HDL cholesterol, 129 Health foods, 6 Heart disease; see also Cardiovascular disease factor arachidonic acid, 127–128 dietary fat, 116 prevention of

350

Chemical and Functional Properties of Food Components

anthocyanins, 222–223 caffeine for, 324–325 folate, 301 treatment of, honey for, 20 Heat absorption, 201 Heat pasteurization, 7 Heat resistance, 201 Heating, 4, 242 Heavy metals, 5, 120 Helical complexes, 86–87 Helicobacter pylori, 323, 328–329 Hematopoietic system, 75 Heme; see also Nonheme cholemyoglobin, 218 compounds, 60 hemichrome, 218 iron, nitric oxide binding to, 277 lead, impact on, 75, 77 metmyoglobin, 218 myoglobin in, 217–218 nitrite, reaction with, 218 nitrosomyoglobin, 218 nitrosylhemochromogen, 158, 218 oxidation of, 218 oxymyoglobin, 218 pigments from, 12, 160, 206, 217–218 sulfmyoglobin, 218 thiols, reaction to, 158 Hemiacetals, 82, 236, 244 Hemicellulose arabinogalactan, 85 arabinose, 84, 220 aroma of, 110 in fruits and vegetables, 21 galactan, 85, 103 hydrolyzing of, 102 mannans, 85 mineral bioavailability, 55 modification of, 99–102 solubility, 101 xylans, 85, 103 Hemichrome, 218 Hemiketals, 82 Hemoglobin coagulum-type gel, 146 iron in, 54, 57 pigments, 12, 160, 206, 217–218 saccharides in, 82 transporter, for water, 39 Hemolytic uremic syndrome, 298 Hemopoietic system, 76 Heparin, 85, 103, 111 Herbs, 232, 243, 243–245 Herring Anisakis parasite in, 7 composition of, 13 DHA and EPA in, 127 enzyme-catalyzed reactions in, 163 salt concentration in, 8 Herschel-Bulkley equation, 189 Hesperidin, 82 Heteroaromatic compounds, 91 Heterocyclic aromatic amines (HCA), 320–324 Heterocyclic compounds flavoring from, 244 furans, see Furan derivatives

mutagens, 320–324 pyrazine, see Pyrazine pyridine, see Pyridine thiazoles, see Thiazoles threshold value, 234 Heteromolecular condensation, 195 Heteromolecular nucleation, 195 Hexametaphosphate, 67 Hexanal flavoring from, 237–239, 244 green aroma, 249 Hexane cartenoid solvent, 212 lipid solvent, 115, 119 Hexanoic acid, 240 Hexanol, 244, 249 Hexosanes, 102 Hexoses, 82, 84, 97 Hexuloses, 82, 84 Heyns rearrangement, 91 HI, 265 Hialuronic acid, 85 High-density lipoproteins (HDL) cholesterol, 129 Hilum, 88 Histidine alkylating agent, 169–170 hydrolyzing of, 170 oxidation of, 161 in phosphorylation of saccharides, 136 properties of, 135 residues, 135, 217 HLB, 149, 282, 283 Homeostasis, 26 Homeostatic mechanisms, 54 Homocarotenoids, 206 Honey, 20, 109 glucose in, 84 maltose in, 84 relative sweetness, 94 water content of, 2 zinc in, 52 Hops, 8 Hormones in food, 296 Horseradish, 232, 237, 243 Hotrienol, 238 HPLS, 237, 249 Human breast milk bioavailability of minerals in, 54 fatty acids in, 127 fucose in, 84 Humectants effect of, on water activity, 44 food additives as, 6 sugar alcohols, 108–109 Humoral immunity (HI), 265 Husbandry, animal and plant, 303 Hydration, 33 Hydration water, 38 Hydrazine carbohydrate reactivity, 90 carcinogenicity, 318 heating in alkaline, 171 mutagenicity, 318 Hydrazo compounds, 90–91, 276 Hydrocarbons flavoring from, 244 from hydroperoxides, 122

from lipid oxidation, 240 reaction to water, 33, 35 squalene, 4 Hydrochloric acid, 102–103, 216 Hydrocolloids alginate, 67 arabic gum, see Arabic gum calcium-binding, 67 ghati, 67 karaya gum, see Karaya gum saccharides, 81 tragacanth gum, see Tragacanth gum Hydrogen bonds in gels, 146 in proteins, 138–139 in water, 27–39 Hydrogen carbonate calcium, 61 potassium, 63 Hydrogen peroxide destruction of, 329 off-flavor in dairy products, 240 production of, 60, 66 Hydrogen phosphate, magnesium, 62 Hydrogen sulfide Maillard reactions, 238, 246 treatment to remove from water, 47 Hydrogen sulfite, potassium, 63 Hydrogenation carotenoid degradation, 210 of oil-bearing materials, 121, 300 Hydrolases, 14 Hydrolysates bitter, 137 fish, 164–165 milk protein, 283 process flavor, 246 starch, 285 Hydrolysis of chlorophyll esters, 215 cow's milk, 15 of denatured collagen, 155 enzymic, 45 of esters, 236 of beta-lactoglobulin, 153 lipase-catalyzed reaction, 248 lipid deterioration, 121 of myofibrillar proteins, 164 of proteins, with endopeptidases, 168 starch property, 17 Hydrolyzates, 164, 167 Hydroperoxide, 122 Hydroperoxide lyase (HPLS), 237, 249 Hydrophile/lipophile balance (HLB), 149, 282, 283 Hydrophilic interactions, 41 Hydrophobicity, 35–36 from acylation, 170–171 of proteins, 137–144, 147–151 Hydroscopic, 20 Hydroxide, 61, 62 Hydroxy-2-methylpyran-4, 98 Hydroxy-3-methyl, 99 Hydroxy acids, 102, 247 Hydroxyacetone, 82, 99 Hydroxycarboxylic, 282

Index

Hydroxycarboxylic acid, 282 Hydroxylamine, 90, 313 Hydroxylases, 136 Hydroxylation of amino acid residues, 136 of nitrosamines, 311 of vegetable lecithin, 129 Hydroxyls acylation of, 170 on anomeric carbon atom, 103 dehydration of, 93 esterification, 92 etherification, 93 halogenation of, 93 metal ions with, 96 oxidation of, 93–94 radicals, generation of, 66, 213 reactions of, 92–97 reduction of, 93 solvent for, 35 water and, 29 Hydroxymethl starch, 104 Hydroxymethylfuran-2-aldehyde, 97 Hydroxyproline, 136 Hydroxypropyl starch, 104 Hydroxypyruvic acid, 93, 96 Hydroxytricarballylic acid, 61 Hygienic requirements, 5 Hygrometers, 43 Hygroscopicity, 108 Hyperchromic effect, 222 Hyperkeratosis, 76 Hypertension, 68, 76, 261 Hypobromites, 91–92 Hypochlorite, 91–92 Hypoxantine, 59 Hysteresis measurement of loop, for structural breakdown, 190–191 parameter, rheological process, 193 in rheopexy flow, 188 in viscoelastic flow, 188

I Ice chemical properties of, 29–31 color of, 206 density of, 40 formation of, 196 thermal properties of, 32 Ice cream, 150, 154, 189 Iceberg water model, 31 Icing, 129 Imidazoles acylation of, 170 alkylation of, 169 aromas from, 91, 110 Maillard reactions, 238 Imine, 35 Immune function enhancer, 213, 263–266 Immunoglobulins, 137, 156, 260 Immunological disorders, 126–128

351

Immunomodulatory effect, 154, 264–266 Indigoid, 228 Indole group, 169 Infant formula B vitamins in, 301 bioavailability of minerals in, 54 DHA and EPA in, 127 fatty acids in, 125 iron in, 302 lactalbumin in, 154 lactose in, 15 Infertility, 60 Infiltrative lymphomas, 55 Inflammation, 126–128 Inflammatory bowel disease, 55, 263–264, 298 Inhibitors, enzyme amount of, quality attribute, 5 calpains and calpastatin, 163 cysteine proteinase, 164 proteins as, 3 Inositol, 105 INS, 65 Insulin chromium requirement, 57 glucose digestion, 108 resistance, 326 substitutes, 104 Interesterification, 92, 121 Intermediate moisture content foods (IMFs), 44 International numbering system (INS), 65 International Organization of the Flavor Industry (IOFI), 246 Intestinal infections, 264 Intrinsic fluorescence, 137–138 Inulin, 85, 285–256 Invert sugar, 97 Iodide, 53, 86 Iodine biological function of, 57, 60 in dietary fat, degree of unsaturation, 116 microelement, 54 RDA, 56 water structure breaker, 34 IOFI, 246 Ion pumps, 39 Ionic strength, 144 Ionization constant, 68 Ionizing radiation, 101–102 Ionone, 212–213, 241, 244 Iron ADP-chelated, 60 anthocyanins reaction to, 222 in beef, 52 bioavailability of, 54–55, 302 biological function of, 57, 59–66 cadmium and, 73 chlorophyll, reaction with, 216 dietary level, 66 EDTA and, 64 in eggs, 16, 52 in fruits and vegetables, 22, 69 in heme, 217 lead and, 74 in lipids, 122

in liver, 52 microelement, 54 nitric oxide binding to, 277 in oats, 52 in pork, 52 for rancidity inhibition, 67 RDA, 56 react with proteins, 68 treatment to remove from water, 47 in wheat, 16–17, 52 Irradiation of food, 296, 302–303 Irvine-Purdie methylation, 93 ISO 9001 for food safety, 298 Isoamyl acetate, 248 Isoascorbate, 277 Isocyanides, 103 Isoelectric point of proteinogenic amino acids, 135 Isoeugenol, 247 Isoflavones, 328 Isoleucine, 135 Isomaltol, 98, 100 Isomerase, 249 Isomers cis-trans, 7 trans-trans, 7 Isoprenoid derivative, see Carotenoids Isopropyl alcohol, 244 Isothiocyanates, 237, 243, 328–331 Itai Itai disease, 76

J Jams, 190, 278 Jasmine, 233 Jasmonate, 248 Jellies color of, 206 formation of, 110 pectin, 104 viscoelastic food, 190 Jerusalem artichoke, 85 Juices anthocyanins in, 223 benzoic acid in, 278 citrus, flavor of, 242–243 enzyme treatment of, 238 oxygen in, reduction of, 106 precipitates in, 283 Juneberry, 250

K K, see Potassium Kale, 211 Kamaboko, 151–152, 156, 167 Karaya gum, 85 anionic hydrocolloid, 67 carboxylic function in, 103 emulsifier, 281 stabilizer, 281 thickening agent, 281 Katemfe fruit, 281 Keratin, 15–16

352

Chemical and Functional Properties of Food Components

Kerosene, 47 Ketones, 66 alcohols, reduction to, 90 carbonyl group, addition to, 90–91 from carotenoid degradation, 213 diacetyl, see Diacetyl flavor from, 240–241 from hydroperoxides, 122 ionone, 244 from lipid oxidation, 240 mutarotation, 89–90 nootkatone, 244 nucleophile acceptance, 82 odor of, 235 in oil, 120 oxidation of, 91–92, 103 reactions of, 89–92 saccharide dehydration, 93 Ketopentose-ribulose, 82 Ketoses, 82, 99 Ketosylamines, 91 Ketosylamino acid, 91 Kidneys cadmium in, 74 chromium in, 53 lead in, 75 selenium in, 53 Kinase, 167 Kinetics, 193 Koenigs-Knorr glycosidation, 93 Kohlrabi, 22 Konjac, 281 Krill, 151, 164 Kynurenine, 161

L L. acidophilus, 264–265 L. rhamnosus, 268 Labeling, 5, 267 Lactalbumin, 153–154 Lactate, 61–62 Lactic acid bacteria (LAB), 105, 261–269, 327–328 Lactobacillus, 261–265, 268–269 Lactoferricins, 154 Lactoferrin, 154 Lactoglobulin, 147, 153–154, 156 Lactones, 93–94 decalactone, 244 flavoring from, 244 from microorganisms, 248 nonalactone, 244 odor of, 235 production of, 247 undecalactone, 244 Lactonize, 91–92 Lactoperoxidase, 154 Lactose, 108 calcium absorption, 55 formation of, 83 intolerance, 263 isomeritization of, 99, 101 Maillard reactions in, 242 in milk, 15, 84 mutarotation, 90 relative sweetness, 94

transgalactosylation of, 286 Lactosucrose, 286 Lactulose, 99, 101 Lactylate, 282 Lakes, 222, 226, 228 Lamb, 13 Laminar flow, 183, 186 Lanthionine, 7 Larch, 85 Lard, 21, 116–117 Laurel, 232 Lauric acid, 116 Laws, regulations, & standards, 5 LCFA, 124–126 LCT, 124 LDL cholesterol decreasing level of, plant sterols, 130 decreasing level of, vegetable lecithin, 129 wine, oxidation inhibitor, 223 Leaching, 4, 301 Lead, 70, 74–77 calcium absorption, 77 iron absorption, 77 PTWI, 75 toxic effects on humans, 76, 323–324 water contamination level, 46 Leaf alcohol, 249–250 Leavening agents, 61–63, 275 Leaves, spices from, 232 Lecithin in egg yolk, 16 emulsifier, 282 as nutraceutical food, 240 off-flavor in, 240 vegetable, 128–129 Legumes; see also Beans gum from, 85 minerals in, 58–59 mutagen formation in, 320 N:P conversion factor in, 3 peanuts, see Peanuts peas, see Peas protease inhibitor, 146 soybeans, see Soybeans Legumin, 167 Lemons, 22, 250 Lentils, 20–21 Lentinus edodes, 237 Lethal dose, 294 Lettuce, 211, 319 Leucine, 134, 135 Leuconostoc mesenteroides, 106 Leucopenia, 59 Leukotrienes, 126, 127, 326 Levan, 106 Lignin, 247 Lime, 61, 283, 300 Limonene, 232, 241, 244, 250 Linalool, 238, 241, 248 Linalyl acetate, 244 Lindane, 46 Linear charge density, 67 Ling's association-induction theory, 37 Linoleic acid in cow's milk, 15

green aroma formation, 249 from lipids, 115–117 octen-3-ol formation, 237 in polyenoic fatty acid, 126–127 Linolenic acid green aroma formation, 249 from lipids, 115–117 in polenoic fatty acid, 126–127 in structured lipids, 125 from vegetable oil, 126–127 Linseed oil, 117 Linxian study of carotene, 215 Lipases in cereals, 17 flavor from, 248 LMWE in, 248 types of, 121 Lipids, 115–116, 122–123 acidolysis of, 123–124 alcoholysis of, 123–124 alkylation of, 169 autoxidation of, 169 in beef, 3 in beer foam, 8 in butter, 3, 21 in cereals and cereal products, 17–18, 107 in codfish, 3–4 composition of, 116–117 in crustaceans, 3–4 in egg yolks, 3, 16 emulsification of, 148–151 esterification of, 123–124 in film formation, 148 in fish, 3 flavor from, 239 in fruits and vegetables, 3, 22 in gluten, 156 green aroma from, 249 hydrophobic interactions with proteins, 36 interesterification of, 123–124 lateral vs. water diffusion, 39 lecithin, 128–129 Maillard reactions and, 240–241 in meat, 12 metabolism of, 58, 285–286 in milk, 3 in mollusks, 3–4 in mullets, 3–4 in nuts, 20 in orange roughy, 3–4 oxidation in apples, 60 degradation of pigments, 212 flavor from, 239–241 lipoxygenase, 65–66 mineral catalyst, 57 nonenzymatic, 45 protein oxidation, 161 PEFAs, 126–128 permeability, 39 peroxidation, see Peroxidation, lipid peroxides, 160 phytosterols, 120, 129–130 in potatoes, 19, 107 processing of, 118–122

Index

in protein-phospholipid membranes, 3 in protein-rich food, 13 rancid odor from, 66–67, 122, 240 in seeds of pulses, 21 in sesame, 116–119, 130–131 in shark, 3–4 in starches, 88 storage of, 121–122 structured, 123–126 tocopherals, see Tocopherols in tubers, 19, 107 in vegetables, 3 vitamin E, 129 volatility, reduction by, 235–236 warmed-over flavor from, 240 water transport, cellular, 39 in wheat germ, 16–17 Lipoxygenase (LOX) carotenoids, destruction of, 212 fatty acid catalyzation, 167 flavoring from, 233, 248 green aroma, 237, 249–250 hydroxy fatty acid from, 247 lactone production, 247 lipid oxidation, 65–66 metabolism of PEFAs, 127 octen-3-ol formation, 237 prooxidant, 160 soy milk flavor, 153 Liquid phase viscosity, 242 Liquor, 233 LISA, 297 Listeria illness from, 296–297 monocytogenes, 154, 243 Lithium, 34 Liver cadmium in, 74 chromium in, 53 copper in, 53 glycogen from, 85 heparin from, 85 iron in, 52 minerals in, 59–60 potassium in, 52 zinc in, 52 Liver disease, 20, 60 Lobry de Bruyn-van Ekenstein rearrangement, 99 Lobster, 53 Locust bean, 85, 281, 282 Long-chain fatty acids (LCFA), 124–126; see also Fatty acids (FAs) Long-chain triacylglycerols (LCT), 124 Longitudinally Integrated Safety Assurance (LISA), 297 Loss modulus, 201 Lovage, 232 Lovibond tintometer color scale, 120 Low-calorie food CMC in, 104 lactose in, 15 retrograde starch in, 105 structured lipids in, 125 sucrose FA polyesters in, 284 sweeteners for, 111

353

Low-density lipoprotein (LDL) cholesterol decreasing level of, plant sterols, 130 decreasing level of, vegetable lecithin, 129 wine, oxidation inhibitor, 223 Low-molecular-weight esters (LMWE), 248 LOX, see Lipoxygenase (LOX) Lubricants, 285 Lumen, 55 Lung cancer, 215 Lutein antioxidant, 214 in egg yolk, 210 formula for, 208 in fruits and vegetables, 211 in green leaves, 209–210 macula protection, 213 photooxidation protection, 209 Lycopene anticarcinogenic action of, 328 antioxidant, 214, 331 chemopreventive properties of, 327 formula for, 207 in fruits, 210 in grapefruit, 211 in paprika, 211 structure of, 206, 330 in tomato, 211 ultraviolet skin protection, 213 Lymphocytes, 265 Lysine alkaline pH, reaction with, 159 amidation of, 170 browning, reactions during, 300 in cereals, 134 in dried fish, 167 in hydrolyzate, 167 Maillard reactions with, 45, 242 in paramyosin, 134 in phosphorylation of saccharides, 136 pyridoxine binding, 301 processing of, 7 properties of, 135 Lysinoalanine, 7, 160 Lysosomes in muscle food, 162–163 probiotics, impact on, 264 transglutaminase in, 166 Lysozyme in eggs, 135, 154 enthalpy of, 141 transparent gels from, 147

M Mace, 232 Mackerel, 117, 127 Macroelements, 51, 54, 70 Macula protection, 213 Mad cow disease, 293, 296 Magnesium biological function of, 57–58

in bread, 69 carbonate, 61 in cereals, 18 chloride, 61, 68 in chlorophyll, 215–216 compounds, food additives, 61–62 in eggs, 16 for food texturization, 111 in fruits and vegetables, 22 glutamate, 62 hydrogen phosphate, 62 hydroxide, 62 ions, in water, 33 lactate, 62 loss of, during processing, 69 macroelement, 54 in milk, 52 in nuts, 20 oxide, 62 RDA, 56 react with proteins, 68 in saccharide alcohols, 96 salts of phosphatidic acid, 119 in sardines, 52 soap formation, 55 sulfate, 62 treatment to remove from water, 47 in tuna, 52 water structure former, 34 in yogurt, 52 Maillard reactions blocking, by sulfites, 276 in caramel, 228 of carbohydrates, 91 dehydroascorbic acid in, 168 flavor development, 238–239 flavoring, effect on, 233, 246 of hemicelluloses, 102 of lactose in heat-treated milk, 15 lipid oxidation and, 240–241 mineral bioavailability, 55 nitrite interaction, 277 oligosaccharides, 286 in protein-rich foods, 102, 139, 158 resistant starch, increasing, see Resistant starch starch, to prevent, 283 warmed-over flavor protection, 240 water activity level, 45 zinc bioavailability after, 302 Maize composition of, 16, 18 ferulic acid source, 247 organic acid in, 22 properties of, 88 proteins in, 21 starch source, 107 Malic acid, 22, 109 Malonaldehyde, 169 Malondialdehyde, 326 Maltol, 98, 100 Maltose, 108 in barley malt, 108 formation of, 83 in honey, 19, 84, 109 oxidative cleavage of, 93 relative sweetness, 94

354

Chemical and Functional Properties of Food Components

from starch, 84, 103 syrup, 109 Maltotetraose syrup, 108 Malts, 108 Malvidin, 219 Manganese biological function of, 59 in bread, 69 in fruits and vegetables, 69 in lipids, 122 microelement, 54 for rancidity inhibition, 67 RDA, 56 treatment to remove from water, 47 Manioc, 2, 107 Mannans, 85 Mannitol, 89, 94, 108–109 Mannopyranose, 94 Mannose, 84, 89, 99, 106, 137 Maple syrup, 108 Margarine fat in, 21 hydroxycarboxylic acid in, 282 manufacture of, 121 a W/O emulsion, 129 water-in-oil emulsion, 123 Marinades, 7, 273 Marlin, 71 Marmalade, 85, 108 Maximum residue level (MRL), 296 Maximum tolerable daily intake (MTDI), 65 Maximum tolerated dose (MTD), 316 Mayberry, 250 Mayonnaise benzoic acid in, 278 egg yolk in, 16 lipids in, 123 preservation of, 278 MCFA, 124–125 MCT, 124–125 Mead, 109 Meat, 12–13; see also Beef; Chicken; Pork; Poultry aging of, 57 analogs, 67, 154 aroma, 110 B vitamins in, 301 cancer risk factor, 317, 332 chromium in, 58 cobalt in, 59 cooking of, 324; see also Cooking dietary fat from, 21, 115–126 enzyme-catalyzed reactions in, 162–167 extenders, 153 flavor of, 4, 238–239, 246 GDL in, 284 gelation of, 145, 156 HCAs in, 321 iron in, 59 irradiation of, 302–303 magnesium in, 58 manganese in, 59 mineral bioavailability in, 54 minerals in, 58–60 mutagen formation in, 323 N:P conversion factor in, 3 oversterilization of, 8

phosphorus in, 58 plasma, protease inhibitor, 146 postmortem changes in, 1–2, 12 potassium in, 58 process flavor of, 246 proteins in, 3, 151–152 rheological changes to, 156 saccharides in, 2 saltpeter in, 277 selenium in, 60 sequestrant for, 64 sodium in, 58 substitutes, 84, 105, 111 sulfite, reaction to, 276 surimi, 151 warmed-over flavor in, 66, 240 water content of, 2, 144–145 zinc in, 59 Medium-chain fatty acids (MCFA), 124–125; see also Fatty acids (FAs) Medium-chain triacylglycerols (MCT), 124–125 Melanoidin, 206 Menhaden, 127 Mercaptide bounds, 73 Mercury, 70, 71–72 metallothioneins and, 72 in predatory fish, 4 PTWI, 75 react with proteins, 68 toxic effects on humans, 76 water contamination level, 46 Mesenteric infarction, 55 Metabisulfite in dehydrated food, 276 potassium, 64 sodium, 64 Metabolic tests, 294 Metallothioneins, 72–73 Methane, 49 Methanethiol, 238 Methanol, 102, 103 Methionine in grains, 134 in hydrolyzate, 167 oxidation of, 161 properties of, 135 thermal degradation of, 158 Methol, 244 Methoxychlor, 46 Methyl cinnamate, 245 Methyl dihydrojasmonate, 244 Methyl glyoxal, 168 Methylation, 104, 136 Methyldehydroalanine, 159 Methylglyoxal, 324 Methylmercury, 71–72 Metmyoglobin, 141, 218, 276 Micelles acylation of, 170 casein, 140, 173 definition of, 36 from emulsifiers, 282 enzyme-catalyzed reactions in, 162 formation of, 87 in gel structure, 145 in proteins, 139

in whey, 146 Microbial contamination of food, 296 Microbial gums, 281; see also Gums Microcalpain, 163 Microcirculation diseases, 223 Microelements, 54 Microencapsulation, 105, 111–112 Microfibrils, 88 Microwaved food mineral loss in, 69 mutagen formation in, 323 polysaccharides in, 101–102 Milk, 14–15 bioavailability of minerals in, 54 bitterness in, 162 calcium in, 52, 55, 58 carrageenans used in, 67 caseins in, 140 clarifying agent, 85 composition of, 13–14 enzyme-catalyzed reactions in, 162 evaporated, 173 fat anticoagulant, 85 fermented, probiotics in, 265–267 for film formation, 148 gels, protein, 146 lactose in, 15, 55, 84, 108 lipids in, 3, 123 magnesium in, 52, 58 minerals in, 58–59 mutagen formation in, 320 pasteurization, 141 phosphorus in, 58 potassium in, 52 probiotics in, 266–267 protein hydrolysates, 283 proteins in, 3, 146, 153–154 riboflavin in, 226 saccharides in, 2 selenium in, 53 sequestrant for, 64 of sheep, 13 sodium in, 58 soy, 153 substitutes, 164 ultrahigh temperature processing of, 242 zinc in, 59 Millet, 16, 18 Milling mineral bioavailability after, 69 of soybeans, 153 vitamin bioavailability after, 302 of wheat grain, 17, 18 Minerals, 51–54; see also specific types absorption of, 54–57 in cereals and cereal products, 18, 107 deficiency in, 54 in fruits and vegetables, 22 functions of, 57–60 leaching of, from food, 4 in potatoes, 19, 107 processing of, 302 in protein rich food, 13 RDA, 56–57 in tubers, 19, 107

Index

Miscella, 119 Miso, 233 Mites, 4 Mitochondria, 66, 75, 166 Models Bingham-Schwedoff, 187–188 Flickering clusters, 31, 33 Iceberg, 31 Stillinger, 31–32 of water, 31–32 Wiggins, 32 Modori, 146, 164 Moisteners, 275 Moisture content, 40–41 dynamics map, 197 extrusion cooking, 241 of oil-bearing materials, 118 retention of, 108 Molasses, 94, 150 Mold mycotoxins in, 318 prevention benzoic acid, 278 sorbic acid, 278, 303–304 water activity level, 44 Molecular weight of acetic acid, 235 of dietary fat, saponification number, 116 of dry air, 40 ethyl acetate, 235 of katemfe fruit, 281 LMWE, 248 of salt, 44 in volatility of aroma compounds, 234 of water vapor, 40 Mollusks, 3–4, 74, 151–152 Molybdenum biological function of, 59 in fruits and vegetables, 69 microelement, 54 RDA, 56 Mono-tert-butyl-hydroquinone (TBHQ), 122, 278–279 Monoacylglycerols absorption of, 125 for emulsions and foams, 6 in gluten-free dough, addition of, 157 in milk fat, 14–15 vegetable lecithin, use with, 129 Monoaso, 228 Monobasic calcium phosphate, 61 Monobasic potassium phosphate, 63 Monobehenin, 125 Monocalcium benzoate, 61 Monocalcium DI-L-glutamate, 61 Monocalcium phosphate, 61 Monochloroacetic acid, 104 Monoglycerides, 282 Monokines, 264 Monomethylarsenic acids, 71 Monopotassium dihydrogen ortophosphate, 63 Monopotassium glutamate, 63 Monosaccharides, 84 in fermentation process, 105 in fruits and vegetables, 21

355

from hemicellulose, 102 oxidation of, 93–94 polymerization of, 106 properties of, 89–99 Monosodium dihydrogen ortophosphate, 64 Monosodium L-glutamate (MSG), 58, 64 Monoterpenes, 232, 238, 243 Mortierella, 128 Mountainberry, 250 MRL, 296 MSG, 58, 64 MTD, 316 MTDI, 65 Mucic acid, 97 Mucin, 15–16 Mucor miehei, 121, 248 Mullets, 3–4, 233 Multilayer water, 41 Mung beans, 243, 249 Muscles activity, role of minerals in, 58–60 composition of, 60 glycogen from, 85 structure of, 12, 14 Muscular dystrophy, 60 Mushrooms betalains in, 224 flavor of, 237 lipid oxidation in, 239 selenium in, 60 Mustard, 232, 237, 243 Mutagens, 308–318 Mutarotation, 89–90 Mutton, 157 Mycoprotein, 154 Mycotoxins, 159, 299, 311, 317–318 Myofibrillar proteins concentrate of, 151 extraction of, 144 in gels, 147, 151 in muscle fiber, 12–14 Myoglobin, 276 Myosin cross-link rupture, 173 filaments in muscle, 12 in gelation, 145, 147–148 hydrolyzing of, 163 in modori, 164 polymerization of, 167 transition of, from heat, 155 Myrosinase, 7

N NAD, 105 NADH, 66 NADPH, 66 Nanofiltration of water, 48 Naphthol, 86 Naringenin, 314–315 NDO, 285–286 Nebulin, 12, 163 Nectarine, 211, 238 Neochlorogenic acid, 324 Neohesperidin dihydrochalcone, 94

Neoplastic transformation resisting agents, 327–329 Neoxanthin, 209 Nephrotoxicity, 76 Nerol, 238 Nervous system, 75 Neurological disorders, 127–128 Neutralizing agent, 61–62 Neutropenia, 59 Newtonian food systems, 183–184 NHP, 119 Niacin, 300 Niacytin, 300 Nickel catalyzation agent, 121 microelement, 54 for rancidity inhibition, 67 RDA, 56 Nicotinamide adenine dinucleotide (NAD) carbohydrate enzymatic transformation, 105 NADH, 66 NADPH, 66 Nitrate sources of, 319 water contamination level, 46 water structure breaker, 34 Nitric acid, 103 Nitric oxide, 277 Nitrite Clostridium botulinum inhibitor, 320 as food additives, 277 protein pyrolysis neutralization, 320 sodium, 64, 218 sources of, 319 Nitro groups, 137 Nitrogen compounds, flavoring from, 244 excessive amount of, 48 Maillard reactions, 238 in milk, 14–15 sources of, 3 threshold value, 234 treatment to remove from water, 47 Nitrogen-to-protein (N:P) conversion factor, 3 Nitrosamines, 319–320 blocking of by Vitamin C, 304, 327 by Vitamin E, 304 hydroxylation of, 311 Nitrosation, 171–172, 319 Nitrosomyoglobin, 218, 277 Nitrosylhemochromogen, 158, 218 Nitrous acid, 277 NMR, 37, 39 No observable effect level (NOEL), 294 NOEL, 294 Non-Newtonian food systems, 183–184, 187, 194 Nonadienal, 240 Nonalactone, 244 Nondigestible oligosaccharides (NDO), 285–286 Nonheme iron, 60, 66

356

Chemical and Functional Properties of Food Components

Nonhydratable phosphatides (NHPs), 119 Nonhypercholesterolemic, 125–126 Nonlinear viscoplastic flow, 184 Nonrheostable food systems, 184 Nootkatone, 244 Norbixin, 209–210 Nordihydroguiaiaretic acid, 67 Nuclear magnetic resonance (NMR) imagining, 37, 39 Nucleases, 248 Nucleic acids, 3, 37, 159 Nucleotides, 247 Nusselt number equation, 202–203 Nutmeg, 243 Nutraceuticals, 6 Nutrient supplement, 64, 84 Nutrition; see also Dietary supplement additives, definition of, 274 amount of, quality attribute, 5, 7 processing of food, 300 RDA, 56–57 Nuts, 20, 58–59, 125 Nylander test, 92

O Oats, 16 iron in, 52 potassium in, 52 properties of, 88 starch in, 107 zinc in, 52 Obesity, 116, 324–325, 332 Oc-linolenic acids, 15 Ochratoxin A, 318 Ocimene, 244 Octanol, 234 Octaphosphate tetrahydrate, 63 Octen-3-ol, 237 Odor, 234–235; see also Aroma Oil; see also Lipids; Oil-in-water (O/W) emulsion; Water-inoil (W/O) emulsion aldehydes in, 120, 240 antimicrobials in, 243 antioxidants in, 116–117, 243, 278–279, 300 aroma, 232–233 bleaching of, 120 borage, 128 brassicasterol in, 130 Camellia oleifera tea seed, 116 canola, 117–120 carotene in, 210 carotenoids in, 120, 210 from carrots, 120, 210 castor oil, 247 citrus fruit aroma, 232 essence oil, 243 limonene in, 232, 250 cleaning of, 118 coconuts, 116–117 codliver, 127 composition of, 116–117

conditioning of, 118 corn, 117–120, 127 cottonseed, 117 cracking of seeds to extract, 118 degumming of, 119 density of, 40 deodorizing of, 120 dewaxing of, 120 distillation of, 243 essential, see Essential oils esterification of, 232 evening primrose, 128 extraction of, 118–119 fat in, 21 fish, 116–131, 233, 239, 328 flaking, 118 flaxseed, 127 folded, 243 folded oil, 243 fractionation of, 121 garlic and, 239–240 goitrogenic products in, 7 haze in, 283 heavy metals in, 120 hydrogenation of, 7, 121, 300 ketones in, 120 lecithin, 129 linseed, 117 lipid peroxidation in, 213 mineral, on eggshells, 283 moisture content of, 118 from monoterpenes, 232 Oil stability index (OSI) analysis, 122 olive, 116–117, 300 palm, 116–117, 210 peanut, 116–119 perilla, 117, 127 phosphatides in, 119–120 phosphorus in, 120 pigments in, 243 pollution from processing of, 120 processing of, 118–122 removal from water, 48 rice bran, 116, 119–120 safflower, 117–120, 127 saponification of, 119 saturated fats in, 116 scaling of, 118 sesame, 116–119 shark, 4 soybean, 117, 236–237, 240, 249 specific heat of, 40 squalene in, 4 storage of, 121–122 sulfur compound, garlic in, 239–240 sunflower, 117–120, 127 temperature, 118 terpene-free, 232 tocopherols in, 120 treatment of, 119 unsaturated fat in, 116 vegetable, 116–131, 210, 249 Vitamin E in, 129, 302 from wheat, 129 Oil-in-water (O/W) emulsion, 123; see also Water-in-oil (W/O) emulsion

egg yolk, 16 milk, 14 polyethylene fatty acid esters in, 282 polysaccharide activity, 282 propylene glycol fatty acid esters in, 282 vegetable lecithin, 129 Oil stability index (OSI) analysis, 122 Olea europaea L. tree, 119; see also Olive oil Oleic acid, 116, 121–122 Oleoresin, 235, 244 Olestra, 285 Oligosaccharides formation of, 137 galatose in, 84 in health foods, 6 in lecithin, 128 nondigestible, 285–286 polymerization of, 106 properties of, 89–99 from starch, 103 Olive oil, 116–117, 300 Oncogene activation, 328 Onion anticarcinogenic action of, 323, 328–329 antimicrobial activity of, 243 flavor of, 236 lacrimator of, 236 selenium in, 60 Opioid effect, 154 Opsonization, 265 Orange roughy, 3–4 Oranges aroma, 235 calcium in, 52 carotenoids in, 211 mannose in, 84 potassium in, 52 Organoarsenic compounds, 71 Ornithine, 159 Ortophosphate, 65, 67 Osazones, 90 OSI, 122 Osmosis, 39 Osmotic, 33, 38–39, 58 Osteomalacia, 58, 76 Osteoporosis cadmium effect on, 76 lead effect on, 74 prevention of boron for, 60 calcium for, 58 probiotics, 264 Ostwald-de Waele power law, 188–189 Osuloses, 97 Ovalbumin, 145–147, 151; see also White, egg Ovomucoid, 146, 151; see also White, egg Ovotransferrin, 151; see also White, egg Oxalates, 55 Oxalic acid, 22 Oxazoles, 238 Oxidation

Index

of amino acid residues, 136 of carotenoids, 212 of cholesterol, 326 of chromoproteins, 157 cost of food, impact on, 299 of DNA, 329 of fatty acids, 326 flavor from, 239–241 of heme, 218 of lipids alcohol from, 240 in apples, 60 aroma from, 240–241 carboxylic acids from, 240 degradation of pigments, 212 deterioration from, 121 flavoring from, 239–241 food quality, 300 hydrocarbons from, 240 ketones from, 240 Maillard reactions and, 240–241 mineral catalysists, 57 nonenzymatic, 45 prevention of, 243 vs. proteins, 161 lipoxygenase, see Lipoxygenase (LOX) of milk, 15 of minerals, 57–60 protection from, see Antioxidants of protein vs. lipids, 161 for saccharides, 91–94 of sorbic acid, 278 of vegetables, 301 warmed-over flavor from, 240 Oxide, magnesium, 62 Oxidizing agent, 63 Oxidoreductases, 14 Oximes, 90 Oxocarotenoids, see Xanthophylls Oxygen (O) anthocyanins, degradation rate, 221 BOD, 47–49 DNA adducts, 314–315 in milk, 15 radicals, generation of, see Radicals, oxygen treatment to remove from water, 47 Oysters, 13, 52–53, 59, 76

P P-cymene, 241 Packaging biodegradable, 105, 112–113 effects, on irradiation treatments, 302 methods, cancer risk, 323–324 type of, quality attribute, 5 xenoestrogens in, 326 PAH, 322–324 Palm, 116–117, 210 Palmitic acid, 116 Pancreatic lipase, 121, 125 Papain, 167

357

Papaya, 238 Paprika, 53, 210–211, 232 Paramyosin, 134 Parasites; see also specific types amount of, quality attribute, 5 illness from, 297 zinc absorption, 55 Parenchyma, 23 Parsley, 22, 84 Passion fruit, 241 Pathogens, 5, 44; see also specific types PCB, 326 Peaches, 236 Peanuts, 20–21 cooking, flavor after, 233 oil from, 116–119 proteins in, 153 storage of, mycotoxin activity, 318 Pears, 236 Peas, 20–21 lipid oxidation in, 239 LOX activity in, 249–250 proteins in, 153 zinc in, 52 Pectins alginate and, 282 aroma of, 102, 110 carboxylic groups in, 103 emulsifier, 281 for food texturization, 111 methylation of, 104 mineral bioavailability, 55 modification of, 103–104 a polysaccharide, 85 rhamnose in, 84 stabilizer, 281 for texture, 110 texture from, in apples, 6 thickening agent, 281 Peeling, 69 PEFA, 116–117, 125–127 Pelargonidin, 219 Penicillium, 318 Pentosanes, 102 Pentoses, 82, 84 apoise, 84 arabinose, 84, 220 furan derivatives, see Furan derivatives xylose, 84, 102 Pentuloses, 82 Peonidin, 219 Pepper, 53, 232 Pepperberry, 250 Peppermint, 233 Peppers, 250 Pepsi-Cola, 242 Peptides in beer foam, 8 chain, hydrogen bond in, 29 Maillard reactions, 238 Peptones, bacterial, 164 Peptydoglycan, 328 Perchlorate, 34 Perilla oil, 117, 127 Perimysium, 12, 14 Peroxidases, 160, 167, 223, 310 Peroxidation, lipid

anthocyanins impact on, 222–223 carotenoids impact on, 212–213 mutagen formation after, 326 selenium, effect of, 329 SOD impact on, 60 Peroxide value, 122 Peroxides, 326 Peroxyl radicals, 279; see also Peroxidation, lipid Pesticides, 298–299, 317, 326 Pet food, 44 Petroleum ether, 207, 244 Petunidin, 219 PH acid ionization constant, 68 anthocyanins, as indicators, 220–221 of aspartame, 281 balance, minerals for, 57–58 of benzoic acid, 278 of betalains, 225 in colon, 287 for copigmentation, 222 during emulsification, 149–150 for enzymes, 163 after GDL, 284 for gelation, 146–147 for hydrolyzates, 167 lowering, by acidulants, 283 of N-nitrosation, 172 of plant tissue, 22 for process flavor, 246 reactions, alkaline, 159–160 regulators, mineral compounds as, 61–63 of saccharides, 97 of shiitake, 237 of sorbic acid, 278 for texture, 111 for transglutaminase, 166 water-holding capacity of meat, 145 of water, mercury concentration, 71 water treatment for, 47 Phaeophytin, 216–217 Phagocytic activity, 264–265 Pharmafoods, 6 Phellandrene, 244 Phenolases, 223 Phenolic acid, 222 Phenolics, 318 Phenoloxidase, 221 Phenols, 169–170 Phenylalanine benzaldehyde from, 248 fluorescence, intrinsic, 137 plasteins, removal from, 167 properties of, 135 Phenylbenzopyrylium, 206, 219–224 Phenylketonuric, 167 Phephorbide, 216–217 Phloem, 23 Phosphatases, 162 Phosphate anticarcinogenic action of, 329 antimicrobial activity of, 304 auto-oxidation protection, 67 bioavailability of iron, 55

358

Chemical and Functional Properties of Food Components

calcium, 140 effluent treatment with, 172 film formation from, 104 gelling agent, 104 reactions with proteins, 172–173 sodium, 65 solvent for, 35 in starch, 104 starch ester, 104 wastewater treatment and disposal with, 172 water structure former, 34 Phosphatides in oil, 119–120 Phosphatidic acid, 128 Phosphatidylcholine, 128–129 Phosphatidylethanolamine, 128 Phosphatidylinositol, 128 Phospholipids as amphipathic molecules, 36 in cereals, 17 for emulsions and foams, 6 in milk fat, 14–15 as nutraceutical food, 240 rancidity and warmed-over flavor, 66 in vegetable lecithin, 128–129 water layer in, 37 Phosphoric acid, 103, 170 for food texturization, 111 posttranslational modifications in, 136 potato esterification, 88, 107 treatment of oil, before degumming, 119 Phosphorus biological function of, 57, 58 calcium absorption, 77 in cereals, 18 in eggs, 16 excessive amount of, 48 in fruits and vegetables, 22, 69 level in oil, 120 macroelement, 54 in milk, 15 in nuts, 20 oxychloride, 171 pentoxide, 171 RDA, 56 in seeds of pulses, 21 Phosphorylation of amino acid residues, 167 inhibition of by benzoic acid, 278 reagents, 171 of saccharides, 136 Phosvitin, 135 Photooxidation, 209 Physarium, 166 Phytates, 55 Phytin, 105 Phytoalexins, 331 Phytoncides, 21 Phytosterols, 120, 129–130 Pica, 74 Pickles, 233 Pickling, 4, 101 Pigments annatto, 210 anthocyanin, 206, 219–224 anthraquinone, 226

beetroot red, 226 betalains, 3, 206, 224–226 caramel, see Caramel carotenoid, see Carotenoids chlorophyll, see Chlorophyll cochineal, 206, 226 crocin, 210 curcumin, 206, 227 in essential oils, 243 heme, 12, 160, 206, 217–218 hemoglobin, 12, 160, 206, 217–218 lakes, 222, 226, 228 melanoidin, 206 oxidation of, 4 phenylbenzopyrylium, 206, 219–224 polyhydroxyanthraquinone Cglycoside, 226 porphyrin, see Porphyrin pigments quininoid, 226 riboflavin, see Riboflavin synthetic organic colors, 228 tetrapyrrole, 215–217 tetraterpene, 206–215 types of, 206 Pigs, 164 Pike, 71 Pineapple, 22–23, 245 Pinene, 244 Pinoresinol, 131 Plant gums, 84 Plant sterols, see Phytosterols Plasma, 146 Plasmin, 162 Plasmolysis, 108 Plasteins, 167–168 Plastic deformation, 199 Plasticizers, 103, 148, 180 Plastics, biodegradable, 105, 112–113 Platelet-activating factor, 126 PMTDI, 65 Polar compounds, 33 Pollution amount of, quality attribute, 5 cancer risk factor, 332 from oil processing, 120 safety of food, impact on, 297 of water, 47–49 Polychlorinated biphenyls (PCB), 326 Polycyclic aromatic hydrocarbons (PAH), 322–324 Polydextrose, 285 Polyenoic fatty acids (PEFAs), 116–117, 125–127 Polyethylene, 112, 282 Polyglycerol, 282 Polyhydroxyaldehydes, 82 Polyhydroxyanthraquinone Cglycoside, 226 Polyhydroxyketones, 82 Polymerization, 147, 162 Polyols, 238 Polyphenol oxidase, 167 Polyphenolic compounds anticarcinogenic action of, 328–329 antioxidants, 212, 279, 329 gallic acid esters, 278–279

oxidation inhibitor, 60 oxidation of, 160, 276 Polyphosphates, 145, 155, 173 Polypropenes, 329 Polyrybosome, 136 Polysaccharides, 84–85 acetylation, 103, 105 agar, 84 alginate, see Alginate amylopectin, see Amylopectin amyloses, see Amyloses arabic gum, see Arabic gum arabinogalactan, 85 aroma of, 110 carbamoylation, 103 carrageenans, see Carrageenans cellulose, see Cellulose chirality, 88–89 complexing agents, 104 depolymerization of, 102 dextran, 85, 106 emulsifier, 281–282 esterification, 92, 103, 105 etherification, 103, 105 fat substitutes, 285 film formation in, 145 furcellaran, 85, 103, 111 galactan, 85, 103 galatose in, 84 gatti gum, 85, 103 as gelling agents, 6, 145, 281–282 glycogen, see Glycogen guaran gum, 85 halogenation of, 103 hemicellulose, see Hemicellulose heparin, 85, 103, 111 hialuronic acid, 85 hydrolysis of, 103 inulin, 85, 285–256 karaya gum, see Karaya gum locust bean gum, 85, 282 mannans, 85 metallation, 103 minerals and, 67 modification of, 99–107 nonstarch, 285 oxidation of, 103 pectins, see Pectins protopectin, 85 reduction of, 103 solubility, 101 stabilizer, 281–282 starch, see Starch structure of, 83–86 in tamarind flour, 85 texture in, 110–111 as thickening agents, 6, 281–282 tragacanth gum, see Tragacanth gum xanthan gum, see Xanthan gum xylans, 85, 103 Polyurethane foams, 112 Poppy, 232 Pork; see also Meat composition of, 13 iron in, 52, 66 myoglobin in, 157 radiation, effect on vitamins, 302 temperature during cooking, 158

Index

Trichinella in, 302–303 Porphyrin pigments chlorophyll, see Chlorophyll heme, 12, 160, 206, 217–218 from potassium copper chlorophyllin, 63 from sodium copper chlorophyllin, 63 Potassium acetate, 62 alginate, 62 aluminosilicate, 62 ascorbate, 62 in beef, 52 benzoate, 62 bicarbonate, 63 biological function of, 57–58 bromate, 63 carbonate, 63 in carrots, 52 in cereals, 18 in cheese, 52 chloride, 63, 68 chlorophyllin, 63 compounds, food additives, 62–63 dihydrogen phosphate, 63 in eggs, 16 for food texturization, 111 in fruits and vegetables, 22, 69 glutamate, 63 hydrogen sulfite, 63 ions, in water, 33–34 in liver, 52 loss of, during processing, 69 macroelement, 54 metabisulfite, 64 in milk, 52 in nuts, 20 in oats, 52 in oranges, 52 in potatoes, 19 RDA, 56 react with proteins, 68 in seeds of pulses, 21 sorbate, 65 treatment to remove from water, 47 water structure breaker, 34 in wheat, 52 Potatoes, 18–19; see also Sweet potatoes aroma, 110 fried, 239 lipid oxidation in, 239 LOX activity in, 249–250 mashed, 239 minerals in, 69 N:P conversion factor in, 3 properties of, 88 protease inhibitor, 146 proteins in, 3 retrogradation in, 105 saccharides in, 2 starch in, 107 vitamin fortification, 301 Poultry; see also Chicken; Duck; Meat feed for, 164 Maillard reactions, 238–239 minerals in, 58

359

surimi, 151 Pourability, 185 Powdered milk composition of, 13 mutarotation, 90 proteins in, 14 water content of, 2 Powered milk iodide in, 53 zinc in, 52 Prebiotics, 285–287; see also Probiotics additives as, 275 inulin, 85, 285–256 resistant starch, see Resistant starch Premenstrual syndrome, 127–128 Preservatives acidulants, 247, 275, 283 additives as, 274–278 benefits of, 299 benzoic acid, 278–279 glucose in, 84 mineral compounds as, 61–64 sorbic acid, 277–279, 303–304 for sour products, 278 sucrose, see Sucrose sulfites, 276, 301–303 Pressure dynamics map, 197 Pressurization, 101–102 Prions, 295 Probiotics; see also Prebiotics additives as, 275 basis of use, 260–261 definition of, 259–260 effects, 263–266 efficacy of, 267–268 research on, 268–269 safety of, 268 strain selection, 261–263 Processing of food, 4, 7–8 cancer risk factor, 332 carcinogens and mutagens formed after, 317 denaturation during, 141 flavor changes during, 241–242 flow analysis, 181–191 gelation, 145–148 methodology of, 179–181 methods, cancer risk, 323–324 mineral bioavailability, 55, 68–69 protein solubility, 144 rheological properties after, 156–157 WHC impact on, 145 Procollagen, 136 Prolamines, 142 Proline, 134, 135 Prooxidants, 212 Propanol, 234 Property frequency change-response profile, 195 Propionaldehyde, 234 Propionic acid, 125, 234 Propyl gallate, 67, 122 Propylene glycol boiling point of, 245 fatty acid esters, 282 as solvent, 244

Propylene oxide, 104 Prostaglandins, 126, 127, 326 Prostate cancer, 215 Proteases in cereals, 17 flavor from, 248 inhibitors of, 146 Protein bodies, 3 Protein-phospholipid membranes, 3 Proteinase inhibitors, 159 Proteins, 134 acylation of, 170–171 alkylation of, 169–170 amino acid composition, 134–137 as amphipathic molecules, 36 in beans, 3 in biodegradable materials, 112 in butter, 21 cancer risk factor, 331–332 in cereals and cereal products, 107 chemical modification of, 168 conformation, 134, 138–141 denaturation of, 141 destabilization of, 155 in eggs, 3, 154 emulsifier, 283 emulsion stability, 282 for emulsions, 6, 148–151 enzyme-catalyzed reactions, 162–167 ferritin, 60 film formation, 145–148 flavor, undesirable, 240 foams, 6, 148–151 in food, 3 in fruits, 3 in fruits and vegetables, 21 function of, in body, 3 functional properties of, 141–142 gelation of, 145–148 in gluten, 156 heating of, 155–160 hydrophobicity in, 36, 137–138 legume, 153 in meat, 3, 12 in milk, 3, 153–154 mineral bioavailability, 55, 68 in muscles, 151–152 mycoprotein, 154 myofibrillar, see Myofibrillar proteins N-nitrosation of, 171–172 in nuts, 20 oxidation of, 160–162 pH, effect of, 143–144 phosphate reactions, 172–173 in potatoes, 3, 19, 107 precipitation, 85 pressurization of, 155 pyrolysis, 320 react to minerals, 68 in seeds of pulses, 21 solubility of, 142–144, 156 in soybeans, 3 stabilizer, 283 in starches, 88 thaumatin, 280–281 thickening agent, 283 in tubers, 19, 107

360

Chemical and Functional Properties of Food Components

volatility, reduction by, 235–236 in water, 37 water retention in, 144–145 water transport, cellular, 39 in wheat, 3, 16–17 Proteolysis, 156, 163–164 Protonated amines, 35 Protopectin, 84–85 Provisional maximum tolerable daily intake (PMTDI), 65 Provisional tolerable weekly intake (PTWI), 75 Pseudomonas aeruginosa, 261 Pseudomonas fluorescens, 121, 248 Pseudoplastic flow, 184, 188–189 Psicose, 99, 101 PTWI, 75 Puddings, 110 Pullulan, 106 PulseNET system, 296 Pumpkins, 21 Purine, 60 Pyrazine, 91 aromas from, 110, 235 flavoring from, 244 Maillard reactions, 238–239 in roasted duck, 238–239 Pyridine aromas from, 110, 235 flavoring from, 244 a HCA, 321 Maillard reactions, 238 in roasted duck, 238–239 Pyridoxal, 303 Pyridoxine, 301 Pyrimidin, 276 Pyroligenious acid, 244 Pyrometaphosphate, 67 Pyrrole, 91, 110, 238 Pyrrolizidine alkaloids, 318

Q Quarg, 13 Quaternary structures dissociation of, 145 in marine animals, 71 in proteins, 139 solubility of, 143 Quininoid, 226 Quinoline, 228, 321 Quinones, 160, 310 Quinoxaline, 321

R Racemization of amino acids, 160 Radiation dosage, effect on vitamins, 302–303 irradiation, 296, 302–303 radioprotective agent, 222 ultraviolet, see Ultraviolet radiation Radicals, oxygen, 160–162

in apples during senescence, 60 lipid peroxidation, caused by, 314, 326 promotion of mutagenic cells, 310 scavenging of, 66, 148, 331 trapping of, 329 Radioprotective agent, 222 Radishes, 60 Radium 226 and 228, 46 Raffinose, 94, 285 Raising agents, 61–63 Raisins, 302 Rancidity, 66–67, 122, 240 Raney nickel catalytic hydrogenation, 90 Raoult's law of dilute solutions, 44 Rapeseed, 130, 282 RDA, 56–57, 301 Reactive oxygen species (ROS) cancer risk factor, 213, 315, 325 glutathione, see Glutathione probiotics, impact on, 264 Recommended Dietary Allowance (RDA), 56–57, 301 Recycling, 5 Red pepper, 209–210 Red sea bream, 166 Red seaweed, 85 Reductants, 279 Reduction, 93, 157 Reductones, 97 Relative humidity of moist air, 41, 43 Relative sweetness (RS), 94, 108 Relative vapor pressure (RVP), 198 Renal disease, 58, 68 Renal proximal tubules, 39 Rennet casein, 153 Reproduction, 59 Resistant starch, 102, 285, 287, 300 Resveratrol, 327, 330–331 Reticuloendothelial system, 264 Retinal, 213–214 Retinoids, 328 Retinol, 329 Retrogradation, 105 Reverse osmosis, 48 Rhamnopyranosyl, 238 Rhamnose, 84, 220 Rhamnosidase, 238 Rheological properties, 179–181, 199–203 angle of internal friction, 194 angle of repose, 194 calcium, impact on, 147 cohesion, 194 creep compliance test, 190–191 of dairy products, 167 Deborah number, 192 deformation, 191–192, 199–200 of dilatant fluids, 185, 189 direct flow rate, 194 dynamics map, 196–198 flow analysis, 181–191, 194 flow behavior index, 202 foaming, 150 of gel, 146–147 glass phase transition, 195–199 heat, 201–203 of hydrogenated oil, 7

image analysis, 195 kinetics, 193 of materials, 184 mathematical characterization of, 195 of meat, 12, 155 modification of, 6, 67 in non-Newtonian food systems, 184–189 of polysaccharides, 103 of proteins, 156–157 of pseudoplastic materials, 188–189 quality attribute, 5 reaction mechanisms, 194 rheopectic, 189–190 shear strength, 194 shear thickening, 189, 193 shear thinning, 192–193 shearing, 183–191, 202 steady flow, 192 stress-strain relationship, 185–189, 191–192 structure, 190–191, 193–195 tensile strength, 194 thermodynamics, 193 thixotropic, 185, 189–190, 193 time, 185–189 viscoelastic, 190–192 viscosity, 183–191 yield stress, 185, 187–188, 194, 201–202 Rheopetic fluids, 189–190 Rheopexy flow, 188, 193 Rheostable food systems, 184 Rhizomes, 232 Rhizopus arrhizus, 121, 128 Riboflavin pigments from, 206, 226–227 processing of, 301 sensitizer, 160 Rice, 16, 18 bran, 116, 119–120 flour, in dough, 157 golden, 303 properties of, 88 starch source, 107 for vitamin A deficiency, 303 Ricinoleic acid, 247 Rickets, 58 Rigidity modulus, 201 Ristelliger, 164 RNA, 58 Roasting, 110 Roe, 233 Roots, 232; see also Tubers ROS, see Reactive oxygen species (ROS) Rose, 233 Rose oxide, 244 Rosemary, 232 Rotational mobility of water, 39 RS, 94, 108 Rubidium, 34 Rutabagas, 237 Rutinosides, 238 RVP, 198 Rye, 16, 18 flour, in dough, 157

Index

properties of, 88 starch source, 107

S Saccharides, 81–82 alcohols, 90, 96–97 aldehydes, see Aldehydes aroma of, 110 binding of, to amino acid residues, 169 in biodegradable materials, 112–113 bonded to anthocyanidins, 220 in butter, 21 caramel, see Caramel carbohydrates, see Carbohydrates carbonyl group, addition to, 90–91 in cereals and cereal products, 2, 18 chirality, 88–89 as cryoprotectant, 151 dehydration of, 93 depolymerization of, 102–103 encapsulation using, 111–112 enol, 93 esterification of, 92 etherification of, 93 fat mimetic, 285 in fish, 2 in fried food, 8 fructose, see Fructose in fruits and vegetables, 21 glucose, see Glucose in gluten, 156 glycosidic bond, 97 halogenation of, 93 in honey, 19 ketones, see Ketones in meat, 2, 12 in milk, 2, 15 modification of, 103–107 mutarotation, 89–90 in nuts, 20 oxidation of, 91–94 phosphorylation of, 136 polysaccharides, see Polysaccharides in potatoes, 2, 19 in protein rich food, 13 reactivity of, 89–107 reduction of, 93 relative sweetness, 94 retrogradation in, 105 in seeds of pulses, 21 solvent for, 35 structure of, 82–88 sucrose, see Sucrose in sugar beets, 2 taste of, 107–109 texture in, 110–111 Saccharin, 94, 281 Saccharine, 111 Saccharose, 19 Safe and adequate daily intake (SAI) level, 56–57 Safety, food, 291–304

361

Safflower linoleic acid in oil, 127 oil from, 117 processing of, for oil, 118–120 spice from, 232 tocopherol in, 129 Saffron, 210, 232 Sage, 232 SAI, 56–57 Salatrim, 125–126 Salicylic acid, 278 Salmon calcium in, 58 copper in, 53 DHA and EPA in, 127 enzyme-catalyzed reactions in, 163–164 selenium in, 53 sensory attributes of, cause of, 8 Salmonella vs. Lactobacillus, for vector choice, 269 for mutagenic activity testing, 316 outbreaks of, 296 prevention, probiotics, 264 risk of, 299 typhimurium, 316 Salt extractive dispersal, 244 in meat processing, 144, 273 sodium chloride, see Sodium chloride substitutes, 61–63, 68 Salting absorption of compounds during, 4 for food preservation, 44 in, definition of, 144 methods, cancer risk, 323 Saltpeter, 64, 277 Saponins, 84 carcinogenicity, 318 galatose in, 84 glucose in, 84 mutagenicity, 318 rhamnose in, 84 saponification, 116, 119, 130 Sarcolemma, 12, 14 Sarcoplasm, 148 Sarcoplasmic proteins, 146, 151 Sarcoplasmic reticulum calcium ion binding, 12 ferric iron reduction, 66 oxygen radicals in, 60 postmortem changes in, 163 Sardinella, 164 Sardines, 52 Saturated fats and oils, 116 Sauerkraut, 233 Sausages fat dispersion in, 149 flavoring from, 233 formaldehyde in manufacture of, 169 GDL in, 92, 284 gelling in, 147, 156 as IMFs, 44 low salt, 173 processing of, 144 rheological changes to, 156

Scaling, 118 Scallion, 232 SCFA, 125 Schaal oven test, 122 Schardinger dextrins, 106 Schiff bases, 90 Scission of proteins, 162 Sclerenchyma, 23 Scomber colias, 164 Screening, of water, 46–48 Scutellum, 17–18 Seafood; see also specific types arsenic in, 70–71 enzyme-catalyzed reactions in, 162–167 fluoride in, 59 iodine in, 60 magnesium in, 58 minerals in, 52–53, 58–60 Seasonings, 233 Seaweed, 281 Seeds of Pulses, 20–21, 22 Seizures, 58 Selenium anticarcinogenic action of, 329 bioavailability of, 54, 55 biological function of, 60 in chips, 53 in fruits and vegetables, 69 in kidneys, 53 mercury and, 72 microelement, 54 in milk, 53 RDA, 56 in salmon, 53 supplementation, 215 in tuna, 53 water contamination level, 46 Selenoglutathione peroxidase, 60 Selenomethionine, 54 Semicarbazide, 90 Senegal acacia, 85 Sensitizers, 160 Sequestrants antinutritional effects, 304 carcinogen, 328 for cheese, 64 citric acid, see Citric acid EDTA, see Ethylenediaminetetraacetic acid (EDTA) for fish, 64 in lipids, 122 for meat, 64 for milk, 64 mineral compounds as, 57, 61–65 Serine alkaline pH, reaction with, 159 bonding with phosphoric acid, 170 in phosphorylation of saccharides, 136 properties of, 135 Serotonin, 75 Sesame, 130–131 cooking, flavor after, 233 linoleic acid in, 117 oil from, 116–119 spice from, 232 Setting, 145, 157, 167

362

Chemical and Functional Properties of Food Components

Settling ponds, 47, 48 Sewage, 48–49 Shallot, 236 Shark lipids in, 3–4 mercury in, 71 size of, 4 squalene in oil, 4 Shear modulus, 146, 199 Shear rate, 183–192, 202 Shear strain, 186, 199–200 Shear strength, 194 Shear stress, 183–192, 199–200 Shear thickening, 189, 193 Shear thinning, 192–193 Shelf life, 5–6, 57 Shellfish analogs, 151–152 arsenic in, 70–71 fluoride in, 53 manganese in, 59 mercury in, 71 overpasteurization of, 8 Shiitake, 237 Short-chain fatty acids (SCFA), 125 Shortening, 122 Shrimp iodide in, 53 lipid oxidation in, 239 peeling and deveining of, 165 preservation of, 278 tetradecatrienone in, 239 Silage, 164 Silicon, 54, 56 Silk, 103 Sillylic acid, 103 Silver, 46, 68 Singlet oxygen quencher, 212–213, 329 Sitosterol, 130 Skin disease honey to treat, 20 hyperpigmentation, 76 macula protection, 213 ultraviolet radiation protection, 213 Smoke curing, 273; see also Curing absorption of compounds during, 4 aroma, 110 cytochrome P450 activity, 314–315 of fish, nitrosamines, 319 mutagen formation during, 320 PAHs in, 322 SOD, 57–60, 66, 160 Soda niter, 64 Sodium alginate, 63 aluminum phosphate, 63 ascorbate, 64, 172 benzoate, 64 biological function of, 58 caseinate, 153, 283 chlorophyllin, 63 citrate, 67 dihydrogen phosphate, 64 dodecylsulfate, 138 in eggs, 16 feredetate, 64

for food texturization, 111 in fruits and vegetables, 22, 69 glutamate, 64, 281 hypochlorite, 104 ions, in water, 33–34 iron EDTA, 64 kasal, 64 macroelement, 54 metabisulfite, 64 methoxide, 121 nitrate, 64, 168 nitrite, 64 in nuts, 20 oxalate, 67 phosphate, 65 RDA, 56 react with proteins, 68 reduction of, in food, 68 in saccharide alcohols, 96 sorbate, 65 treatment to remove from water, 47 trialuminum tetradecahydrogen, 63 trimetaphosphate, 170 water structure former, 34 Sodium chloride cross-linking in proteins, 166 free energy change in water, 34 in meat batters, 149–150 moisture retention, 67 preservation agent, 66 for rancidity inhibition, 67 reduction of, in food, 68 as solvent, 142 thermal stability of meat, 155 in water, 33 Solutions, 190 Solvent fractionation, 129 Solvents ethanol, see Ethanol petroleum ether, 207, 244 water, 33–36 Sonication, 101–102 Sorbate, calcium, 61 Sorbate, potassium, 65 Sorbate, sodium, 65 Sorbic acid, 277–278, 279, 303–304 Sorbitan fatty acid esters, 282 Sorbitol acylation of, 92 FA ester, 285 formula for, 89 hydrogenation of glucose syrup, 108 as plasticizer, 285 relative sweetness, 94 Sorbose, 84 Sorghum, 16 Sorgo, 328 Sorption isotherm, 41–45 Sour cream, 13 Sour taste, 283 Soy anticarcinogenic action of, 328–329 denaturation of proteins in milk, 153 dried, 319 flavoring from, 233

Soybeans, 20–21 acylation of, 170 in allium processing, 237 antioxidant, 243 degumming of, 119 emulsifying properties of, 167 fermentation of, 162 flour, solubility of, 143 frying oil from, 240 gels from, 146 glycoproteins in, 137 green aroma from oil, 249 lecithin from, 128, 282, 300 linoleic acid in, 117, 127 LOX activity in, 167, 249–250 oil from, 117 PEFAs in, 126–127 processing of, 117–119, 144, 300 proteins in, 3, 146, 153 saccharides in, 137 solubility of, in calcium, 167 structure of, 139 Speciation analysis, 54, 70 Specific heat of ammonia, 40 of vegetable oil, 40 of water, 32, 40 Specific rotation, 88–89 Spectrum, visible absorption, 207–209 Spices, 53, 232, 243–245 Spinach, 22, 211 Spinacine, 169–170 Spirulina, 128 Spoilage of food, 44, 280 Sprats, Baltic, 163 Spreadability, 185 Squalene, 4 Squid, 145, 156, 165 Stabilizers additives as, 281–283 carrageenans, see Carrageenans caseins, see Caseins citrate, 61, 67, 155 EDTA, see Ethylenediaminetetraacetic acid (EDTA) ester, starch sulfate, 111 mineral compounds as, 61–65 polyphosphates, 145, 155, 173 polysaccharides, 281–282 proteins, 283 sodium phosphate, 65 starch, 281 Stachyose, 94, 285 Staked lime, 61 Staling of bread, 6 cost of food, impact on, 299 retardant agar, 84 GMS, 123 sorbitan fatty acid esters, 282 retrogradation of gels, 105 Staphylococcus aureus gene transfer by, 268 in gut, 261 illness from, 297 inhibitor of, 67

Index

lipase, 121 prevention, nitrite, 277 prevention, probiotics, 264 Starch alpha-starch, 102 anionic, 104, 111 antifoaming agents in, 150 aroma of, 102, 110 in biodegradable materials, 112–113 carboxymethyl, 104 cationic, 104 from cereals, 107 complex formation, 104 degradation of, 106 depolymerization of, 102–103 dextrinization, 102–103 emulsifier, 281 esterification, 104 etherification, 104 in extrusion cooking, 241 in fermentation process, 105 film former, 283 gelatinization of, 17, 88, 107, 199, 300 granules, 20, 87–88, 107 hydrolysates, see Hydrolysates hydroxymethl, 104 hydroxypropyl, 104 maltose in, 84 modification of, 99–104 oxidation of, 104 phosphates, see Phosphate polysaccharides, see Polysaccharides in potatoes, 19, 107 pregelantinized, 102 removal of, before processing, 241 resistant, 102, 285, 287, 300 retrogradation, 105, 199 solubility, 101–102 as a stabilizer, 281 sulfates, 104 surfactants, modification by, 123 thickening agent, 281 from tubers, 19, 107 waxy, 102 in wheat endosperm, 17 Steady flow, 192 Stearic acid, 116, 125–126 Sterculiacea tree, 85 Steric exclusion, 145 Sterigmatocystin, 318 Sterilization, 7, 320 Sterols as amphipathic molecules, 36 DOD in, 129 in milk fat, 14–15 plant, 130 structure of, 130 for water transport, cellular, 39 Stickiness, 196 Stiffening agents, 275 Stigmas, spices from, 232 Stigmasterol, 130 Stilbene isorhapontin, 247 Stillinger water model, 31–32 Stokes-Einstein relation formula, 37 Stolephorus, 164

363

Stomach illness, 20 Storage, 4, 7–8 carcinogens and mutagens formed after, 317 of eggs, 16 of fish, 151 flavor changes during, 235–238, 241–242 flow analysis, 181–191 of lipids, 121–122 methods, cancer risk, 323–324 mineral bioavailability, 55, 68–69 modulus, 201 of potatoes, 19 requirements, adherence to, quality attribute, 5 retrogradation rate, 105 rheological properties after, 156–157 Strain, 199–200 Strain rate, 199 Strawberry anthocyanins in, 220 carotenoids in, 211 esters in, 248 formulas for, 245–246 Strecker degradation compounds, 246 Streptococcus, 105 Streptoverticillium, 166–167 Stress, 199–200 Stress-strain relationship, 186–188, 190–191 Stroke, 68, 127–128 Strontium, 96 Structural viscosity flow, 188 Structure, 181–191, 190–191 Structured lipids, 123–126 Sturgeon, 163 Styrene, 112 Subacute tests, 294 Sublimation, 4 Sucralose, 280, 281 Sucrose, 108 acylation of, 92 in barley malt, 108 enzymatic oxidation of, 106 in fermentation process, 105 formation of, 83 in fruits and vegetables, 21 honey vs., 20 invert sugar, 97 in maple syrup, 108 oxidative cleavage of, 93 polymerization of, 106 relative sweetness, 94 substitutes, 84 in sugar beets, 84 in sugar cane, 84 TAG substitutes, 284 transfructosylation, 286 Sugar alcohol, 6, 108–109 burnt, 97 confectioneries, coloring for, 206 invert, 97 Maillard reactions, 238 in potatoes, 239 substitutes, additives as, 274 Sugar beets

dextran in, 85, 106 ferulic acid source, 247 maltose in, 84 saccharides in, 2 sucrose in, 84 Sugar cane, 84 Sulfate, 34, 62, 103 Sulfides, 236 Sulfite, 276, 301–303 Sulfmyoglobin, 218 Sulfobenzoic acid, 281 Sulfocatechols, 276 Sulfonic acid, 161 Sulforaphane, 327, 330–331 Sulfotransferases, 310 Sulfur amino acids residues containing, 135 biological function of, 57 compound flavoring from, 244 garlic in oil, 239–240 dioxide, see Sulfur dioxide in eggs, 16 in fruits and vegetables, 22 macroelement, 54 Maillard reactions, 238 mercury and, 72 threshold value, 234 Sulfur dioxide anthocyanins, degradation rate, 221, 223–224 cochineal carmine stability, 226 in wine, 276 Sulfuric acid, 93, 103, 164 Sunflower copper in, 53 lecithin from, 282 linoleic acid in, 117 linoleic acid in oil, 127 oil from, 117 processing of, for oil, 118–120 tocopherol in, 129 Superoxide dismutase (SOD), 57–60 endogenous antioxidant, 160 hydrogen peroxide production, 66 Suppressing agents, 327–329 Surface active agents, 92, 123, 129 Surface tension, 192 Surimi, 151–152, 167 Sweet potatoes, 22 Sweeteners additives as, 274–275, 279–281 glucose in, 84 honey, 20 sucrose, 84 Sweetness from carbohydrates, 107–109 increasing, 93 relative, 94, 108 Swift test, 122 Swordfish, 4, 71 Synergist, 64 Syrups from carbohydrates, 108 from depolymerization of carbohydrates, 102, 103 fructose, 108 glucose, 108

364

Chemical and Functional Properties of Food Components

maltotetraose, 108 maple, 108 saccharide content in, 109 from starch, 85, 108 sucrose in, 108 of xanthates, 103

T T cells, 265 TADI, 65 TAG, see Triacylglycerols (TAGs) Tallow, 116–117 Tamarind, 85, 281 Tannins, 21, 55 Tapioca, 107 Tar, 102 Tartaric acid, 22 Tartness, 283 TBA, 66, 122 TBHQ, 122, 278–279 Tea anticarcinogenic action of, 328 antioxidant, 331 chemopreventive properties of, 327 flavor of, 238 flavoring from, 233 fluoride in, 53 green vs. black, 302 minerals in, 59 mutagen formation in, 324–325 processing of, 302 TEAC, 213 Teeth, 58–60, 108, 285–286 Temperature apparent viscosity and, 201 of carmelization, 109 denaturation, 155 for deodorizing of oil, 120 effects formula for, 201 on irradiation treatments, 302 flow property, 181–191 fluctuation within cells, 32 glass phase transition, 195–199 heat field intensity, 201 hydrophobicity, 139 Maillard reactions, 238 melting, of cow's milk, 15 of oil-bearing materials, 118 oxidation and, 121 protein heating, 155–160 retrogradation rate, 105 shrinkage, 155 in solubility assays, 144 swelling, of starch, 123 for texture, 111 for transglutaminase, 166 ultrahigh, 242 of whey proteins, 153 Temporary acceptable daily intake (TADI), 65 Tempura, 151–152 Tensile modulus, 199–200 Tensile strain, 199–200 Tensile strength, 194

Tensile stress, 199–200 Terminalia catappa L. leaves, 243 Terpenes, 21, 232, 243 Terpenyl acetate, 241 Terpineol, 238, 242 Tertiary butylhydroxyquinone (TBHQ), 122, 278–279 Tertiary structures, 143 Testing of food, 294–296 Tests, 294–296 acute, 294 Ames, 316–317 Barfoed, 92 Benedict, 92 for cancer, 315–317 chronic, 294 creep compliance test, 190–191 Fehling, 92 metabolic, 294 for mutagens, 315–317 Nylander, 92 Schaal oven, 122 subacute, 294 Swift, 122 Tetany, 58 Tetracycline, 55 Tetradecatrienone, 239 Tetrahydrofurane, 212 Tetraioic acids, 105 Tetralkylammonium salt function, 104 Tetrapyrrole pigments, 215–217 Tetraterpene pigments, 206–215 Texture in carbohydrates, 110–111 complex formation for, 97 development of, 6, 8 dynamics map, 196–198 flow property, 181–191 of gels, 145–147, 156–157 impact on, by water mobility, 39 of protein-rich food, 156–157 rheological properties of, 199 Texturing agents agar, 84 carrageenans, 111 CMC, 104 mineral compounds as, 61 starch, 105 TGase, 145–146, 166–167 Thaumatin, 280–281 Thaumatococcus danielli, 281 Thermal conductivity, 40 Thermal stability complex formation for, 97 of gels, 147 of beta-lactoglobulin, 153 of proteins, 139, 141, 155–160 Thermodynamics, 193 Thermolysis, 101–102 Thiamine antibrowning agent impact on, 303 Maillard reactions, 238 in nuts, 20 processing of, 301 radiation, effect on, 302–303 sulfite, reaction to, 276 thermal decomposition of, 7 in wheat scutellum, 17

Thiazoles aromas from, 235 flavoring from, 244 Maillard reactions, 238 in roasted duck, 238–239 Thickening agents additives as, 275, 281–283 dextrins, 103 mineral compounds as, 61–63 polysaccharides, 84–85, 281–282 proteins, 283 starch sulfate ester, 111 Thinning agents, 285 Thiobarbituric acid (TBA), 66, 122 Thioether group, 169 Thiolactic acid, 244 Thiolanes, 235 Thiols acylation of, 170 alkaline pH, reaction with, 160 alkylation of, 169 in allium, 236 antioxidant, 1–2 arsenical, react with, 70 disulfide creation in milk, 162 gels, impact on, 147 heme, reaction with, 158 oxidation of, 143 in transglutaminase, 166 transition metals and, 68 Thiophenes, 235, 238 Thiosemicarbazide, 90 Thixotropic flow definition of, 189–190 non-Newtonian behavior, 188 in nonrheostable systems, 184 shear stress vs. shear rate, 185 after shear thinning, 193 Threonine alkaline pH, reaction with, 159 in antifreeze fish serum glycoproteins, 134–135 esterification of, 170 in phosphorylation of saccharides, 136 properties of, 135 Threose, 168 Threshold of flavor, 234 Thrombosis, 126 Thromboxanes, 126 Thymine, 29 Thymol, 243 Thyroid, 60 Thyroxine, 57 Time, 187–191, 197 Tin, 216, 222, 302 Tissue disruption, 237–238 Titin, 12, 163 Toasting, 153 Tobacco, 110 Tocopherols, 129–130 analog, 213 antioxidant, 1–2, 122, 212 destruction of, in deodorizing of oil, 120 lipid storage, 121 nitrosamine formation inhibitor, 320 TEAC, 213

Index

Tofu, 144, 301 Tomato anticarcinogenic action of, 328 antioxidant, 331 carotenoids in, 209, 210, 211 chemopreventive properties of, 327 flavor of, 237 lipid oxidation in, 239 LOX activity in, 249 Tongues, 85 Torque, 183 Toxaphene, 46 Toxins, 5, 70–77, 291, 294–296 Toxoplasma, 296–297 Tragacanth gum, 85 anionic hydrocolloid, 67 carboxylic function in, 103 emulsifier, 281 stabilizer, 281 thickening agent, 281 Trans fatty acids, 4, 7, 116 Transesterification, 248 Transgalactosylation, 286 Transglutaminase (TGase), 145–146, 166–167 Translational mobility of water, 39 Transpeptidation, 167 Transportation, 5, 181–191 Transversal modulus, 201 Trehalose, 285 Tremors, 58 Triacylglycerols (TAGs) binding of, 138 in cereals, 17 decreasing level of, vegetable lecithin, 129 hydrogenation, 121 interesterification, 121 in lipids, 3, 21, 116–117 in milk, 14–15 minetics, 284 in Salatrim, 125 soap formation, 55 structured lipids, 123–126 substitutes, 284–285 Triarylmethane, 228 Triaso, 228 Tricalcium salt of beta, 61 Trichinella, 302–303 Trichloroethane, 46 Trichloroethylene, 46 Trihalomethanes, 46 Trimethylamine, 165, 244 Tripolymetaphosphate, 67 Trisaccharides, 19 Trisodium dialuminum pentadecahydrogen octaphosphate, 64 Trithianes, 238 Trithiolanes, 238 Triticale, 88 Trolox equivalent of antioxidant capacity (TEAC), 213 Tropocollagen, 136, 142 Tropomyosin, 12 Troponin, 12, 164 Tryptophan in collagen, 134

365

fluorescence, intrinsic, 137 in grains, 134 in hydrolyzate, 167 oxidation of, 161 properties of, 135 pyrollase, 75 residues, 135 in transglutaminase, 166 Tubers potatoes, see Potatoes starch in, 107 sweet potatoes, 22 yam, 107 Tuna calcium in, 52 copper in, 53 magnesium in, 52 selenium in, 53 size of, 4 Turbidity, 46, 283 Turbulent flow, 187 Turgor, 54 Turmeric, 227, 232 Turnips, 237 Tyrosine bloom in fish, 163 fluorescence, intrinsic, 137 in grains, 134 oxidation of, 161 properties of, 135 in transglutaminase, 166 Tyrosyls, 170

U Ubiquinone, 1–2 Ultrafiltration of water, 48 Ultrasound, 47, 101–102 Ultraviolet radiation, 47, 101–102 absorption of, by amino acids, 137 absorption of, by carotenoid pigments, 207–209 lipid deterioration, 121 riboflavin destruction, 301 skin protection, 213 Undecalactone, 235, 244–245 Unsaturated fats and oils, 116 Urea, 3, 139 Uric acid, 59 Uronic acid, 94, 104

V V-type amylose, 86 Vaccinium myrtillus, 220, 223 Valine, 134, 135 Van der Waals interactions, 27 Vanadium, 54, 56, 67 Vanilla beans (Vanilla planifolia), 233, 243–244 Vanillin, 244, 247–248 Vaporization of water, 32 Vasprotective agents, 222 Veal, 13; see also Beef; Meat

Vegetables, 21–23; see also specific types alkaline treatment of, 159 anticarcinogenic action of, 328–329, 332 boron in, 60 cadmium in, 74 calcium in, 58 flavor of, 233 green aroma from oil, 249 iron in, 59 lecithin, 128–129 lipid oxidation in, 239 lipids in, 3 magnesium in, 58 minerals in, 58–60 nitrites in, 319 N:P conversion factor in, leafy, 3 oil from, 116–131, 210 oxidation of, 148 potassium in, 58 processing and storage of, 69, 283 storage of, 301 vitamin E, 129 water content in, 2 Vibrio, 44, 297 Vicinal water B.E.T. isotherm, 42 definition of, 38, 41 structural influence of, 34 Vinculin, 12 Vinegar, 233, 273 Vinyl chloride, 46, 112, 323–324 Vinyl monomers, 105 Violaxanthin, 208–211 Viscoelastic flow, 187–188 Viscoelastic food systems creep compliance test, 190–191 flow behavior in, 189–191 glass dynamics of, 199 in non-Newtonian flows, 184 oscillating stress measurements of, 200–201 Viscometric functions, 183–184 Viscoplastic flow, 184 Viscosity Bingham plastic, 188 of dilatant fluids, 189 of egg yolk, 16 glass phase transition, 196 liquid phase, 242 in non-Newtonian flows, 186–191 of pseudoplastic flow, 188–189 rheological property, 182–186 of rheopetic fluids, 189 of thixotropic materials, 189 Viscous deformation, 199–200 Vitamin A antibrowning agent impact on, 303 in cartenoids, 212 changes in during food processing, 301–302 in eggs, 16 fat-soluble, 21 formation of from β-carotene, 214 in golden rice, 303 from lipids, 115–116 in milk, 15 oxidation of, 302

366

Chemical and Functional Properties of Food Components

utilization of, 59 Vitamin B group, see B vitamins Vitamin C antibrowning agent impact on, 303–304 anticarcinogenic action of, 327–329, 332 antioxidant effectivity, 223 blocking agent, 328 fortification with, 301 in nuts, 20 in potatoes, 69 Vitamin D anticarcinogenic action of, 329 calcium retention, 55 in dairy products, 302 in eggs, 16 fat-soluble, 21 lead interference with metabolism of, 76 from lipids, 115–116 Vitamin E antibrowning agent impact on, 303–304 anticarcinogenic action of, 328–329 antioxidant effectivity, 223 cancer prevention, 215 changes in during food processing, 302 in eggs, 16 fat-soluble, 21 from lipids, 115–116 in vegetable oils, 129 in wheat germ, 16–17 Vitamin K in eggs, 16 from lipids, 115–116 storage of, 302 Vitamins anticarcinogenic action of, 327 from bacteria, 261 deficiency in, 54 effect on, by food processing and storage, 300–301 in eggs, 16 in fruits and vegetables, 69 leaching of, from food, 4 in milk, 14–15 nonprotein N in, 3 production of, 262 radiation, effect on, 302–303 sources of, meat, 12 thermal decomposition of, 7 thiamine, 7 Vittelin membrane, 16 Vodka, 325 Volatility of aroma compounds, 234 Vulgaxanthin, 224–225

W Warmed-over flavor, 66, 240 Washing, 4 Wastewater treatment and disposal, 48–49, 172 Water, 25–26

activity, 41–45 alkalinity, 47 bound water, 38, 40–41 bulk-phase water, see Bulk-phase water in butter, 21 carbohydrate structure, 82 in cereals and cereal products, 18 classes of, 41 constitutional water, 41 contamination levels for potable, 46 cytoplamic, 37–38 density of, 40 drinkable, 45 from dry wood distillation, 102 dynamics map, 196–198 electrostatic attraction in, 26–27 entrapped water, 41 in food, 2 free water, 41 in fruits and vegetables, 21 in honey, 19 hydration water, 38 hydrodynamic radius formula, 37 during interestification, 121 intracellular, 37–38 liquid phase viscosity, 242 MCT solubility in, 124 in meat, 12 in milk and milk products, 14 mobility of, 39 models, 31–33 molecular structure of, 26–32, 34 Multilayer water, 41 nonpotable, 45 oxidation of proteins in, 160 oxidation of saccharides, 93 plasticizable material, state diagram, 196 pollution, 47–49 polysaccharide solubility in, 103 potable, 45 in potatoes, 19 in protein rich food, 13, 142 quality, 45–47 retention, starch property, 17 in silage, 164 as solvent, 33–36 supply, 45 in surimi production, 152 thermal properties of, 32 transportation, cellular, 39 treatment, 46–48 types of, 45 wastewater treatment and disposal, 48–49 Water-holding capacity (WHC) acylation, impact on, 171 of beta-lactoglobulin, 153 calcium caseinate, 153 of meat, 145, 173 pH, effect on, 147 sodium caseinate, 153 Water-in-oil (W/O) emulsion, 123 frosting, 129 icing, 129 margarine, see Margarine vegetable lecithin, 129

Wax esters, 3–4 Wax gourd, 239 Waxy corn/maize dewaxing of oil, 120 properties of, 88 retrogradation in, 105 Whale, 157 WHC, see Water-holding capacity (WHC) Wheat acylation of, 171 composition of, 16–18 cooking, flavor after, 233 copper in, 53 extrusion cooking of, 241 for film formation, 147–148 flour, gluten in dough, 6, 156–157 iron in, 52 lipoxygenase, 167 oil from, 129 potassium in, 52 properties of, 88 proteins in, 3 proteolytic changes in, 162 retrogradation in, 105 starch source, 107 zinc in, 52 Whey coatings from, 148 enzyme-catalyzed reactions in, 162 for film formation, 148 foaming properties, 150–151 gels from, 146–147 heat stability of, 155 Maillard reactions in, 242 in milk, 14, 153–154 processing of, 144 saccharides in, 137 Whipped cream, 123, 150 White cabbage, 211 White, egg composition of, 13, 15–16 foaming properties, 151, 154 gels from, 145–147, 154 lysozyme in, 135 protease inhibitor, 146 proteins in, 145–147, 151 saccharides in, 137 solubility of, 142 in squid meat gels, 145 Whiteners, 283 Wiggins water model, 32 Williams-Landel-Ferry (WLF) mechanism, 197 Wine anthocyanins in, 223 as an antioxidant, 325 antioxidants in, 223 bouquet of, 8 casks, decontamination of, 276 enzyme treatment of, 238 fermentation of, 302 flavoring from, 233 grape processing for, 302 honey in, 20, 109 in marinades, 273 precipitates in, 283 resveratrol in, 331

Index

sulfur dioxide in, 276 Winter melon, 239 WLF, 197 WLF mechanism, 197 Wood, 112 Wood molasses, 102 Wounds, healing of, 59 Wrappings, biodegradable, 105, 112–113; see also Packaging

X X-ray crystallography, 37 X-ray diffraction, 37 Xanthan gum, 85, 103, 106 emulsifier, 281 for food texturization, 111 in gluten-free dough, addition of, 157 locust bean gum and, 282 stabilizer, 281 thickening agent, 281 Xanthates, syrups of, 103 Xanthation, 103 Xanthene, 228 Xanthophylls in animal tissues, 210 canthaxanthin, see Canthaxanthin capsanthin, see Capsanthin chlorophyll and, 215 cryptoxanthin, see Cryptoxanthin in egg yolk, 210 formula for, 208 lutein, see Lutein in paprika, 210 in red pepper, 209, 210 structure of, 206 violaxanthin, see Violaxanthin

367

Xantine, 59 Xenoestrogens, 326 Xylans, 85, 103 Xylem, 23 Xylitol, 84, 94, 102, 108–109 Xylose, 84, 102

lipids in, 3, 16 phosvitin in, 135 serine in, 135 xanthophylls in, 210 Young's modulus of elasticity, 199 Yucca, 107

Y

Z

Yam, 107 Yeast alcohol dehydrogenase source, 249 aroma compounds from, 248 bakers, 249 generation of, 150 hydroperoxide lyases in, 250 lactone production, 247 minerals in, 58 prevention benzoic acid, 278 sorbic acid, 278 riboflavin in, 226 water activity level, 44 Yersinia enterocolitica, 154, 297 Yield stress, 185, 187–188, 194, 201–202 Yogurt calcium in, 52 composition of, 13 fermentation of, 302 flavoring from, 233 magnesium in, 52 milk protein in, 14 mycoproteins in, 154 probiotics in, 266 Yolk, egg composition of, 13, 15–16 emulsifying agent, 154

Z-disks, 163 Z line, 12 Zeaxanthin, 210, 213–214 Zebrinin, 222 Zinc in beef, 52 bioavailability, 54–55, 302 biological function of, 59 in cheese, 52 chlorophyll, reaction with, 216 copper antagonism, 77 dehalogenation using, 93 in eggs, 52 in fish, 52 in fruits and vegetables, 69 in honey, 52 in liver, 52 loss of, during processing, 69 metallothioneins and, 72–73 microelement, 54 in oats, 52 in oysters, 52 in peas, 52 in powered milk, 52 for rancidity inhibition, 67 RDA, 56 in saccharide alcohols, 96 in wheat, 52 Zygosaccharomyces, 108