Trans Fatty Acids by Albert J. Dijkstra and Richard J. Hamilton


145661441090459.jpg Author Albert J. Dijkstra and Richard J. Hamilton
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Year 2007
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BLUK122-Dijkstra September 28, 2007 19:12 Trans Fatty Acids i BLUK122-Dijkstra September 28, 2007 19:12 Trans Fatty Acids Edited by Albert J. Dijkstra Richard J. Hamilton Wolf Hamm iii BLUK122-Dijkstra September 28, 2007 19:12  C 2008 by Blackwell Publishing Ltd Blackwell Publishing editorial offices: Blackwell Publishing Ltd, 9600 Garsington Road, Oxford OX4 2DQ, UK Tel: +44 (0)1865 776868 Blackwell Publishing Professional, 2121 State Avenue, Ames, Iowa 50014-8300, USA Tel: +1 515 292 0140 Blackwell Publishing Asia Pty Ltd, 550 Swanston Street, Carlton, Victoria 3053, Australia Tel: +61 (0)3 8359 1011 The right of the Author to be identified as the Author of this Work has been asserted in accordance with the Copyright, Designs and Patents Act 1988. All rights reserved. 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First published 2008 by Blackwell Publishing Ltd ISBN: 978-1-4051-5691-2 Library of Congress Cataloging-in-Publication Data Trans fatty acids / edited by Albert J. Dijkstra, Richard J. Hamilton, Wolf Hamm. p. ; cm. Includes bibliographical references and index. ISBN: 978-1-4051-5691-2 (hardback : alk. paper) 1. Trans fatty acids. I. Dijkstra, Albert J. II. Hamilton, R. J. (Richard John) III. Hamm, Wolf. [DNLM: 1. Trans Fatty Acids. QU 90 T774 2007] QP752.T63.T82 2007 612.3 97 – dc22 2007032665 A catalogue record for this title is available from the British Library Set in 10/12 pt Times by Aptara Inc., New Delhi, India Printed and bound in Singapore by COS Printers Pte Ltd The publisher’s policy is to use permanent paper from mills that operate a sustainable forestry policy, and which has been manufactured from pulp processed using acid-free and elementary chlorine-free practices. Furthermore, the publisher ensures that the text paper and cover board used have met acceptable environmental accreditation standards. For further information on Blackwell Publishing, visit our website: www.blackwellpublishing.com iv BLUK122-Dijkstra September 28, 2007 19:12 Contents Contributors Preface 1 Fatty acids: structure, occurrence, nomenclature, biosynthesis and properties Richard J. Hamilton 1.1 1.2 1.3 1.4 1.5 1.6 2 ix xi Introduction Fatty acid nomenclature 1.2.1 Saturated acids 1.2.2 Monounsaturated acids 1.2.3 Diunsaturated acids 1.2.4 Triunsaturated acids Occurrence Fatty acid biosynthesis 1.4.1 Saturated fatty acids 1.4.2 Monoenoic fatty acids 1.4.3 Polyunsaturated fatty acids Properties of trans fatty acids 1.5.1 Melting points 1.5.2 Ultraviolet spectra 1.5.3 Infrared spectra 1.5.4 Nuclear magnetic resonance spectroscopy Labelling and legislation 1 1 2 2 4 7 7 7 12 12 12 14 15 17 18 20 22 23 Trans fatty acids intake: epidemiology and health implications Geok Lin Khor and Norhaizan Mohd Esa 25 2.1 Introduction 2.2 Food sources of trans fatty acids 2.3 Trans fatty acids intake 2.4 Trans fatty acids in human milk 2.5 Trans fatty acids intake and health implications 2.5.1 Coronary heart disease 2.5.2 Diabetes 2.5.3 Cancer 2.6 Concluding remarks 25 26 30 39 40 40 43 44 45 BLUK122-Dijkstra September 28, 2007 19:12 vi 3 Contents Conjugated linoleic acid effects on body composition and clinical biomarkers of disease in animals and man: metabolic and cell mechanisms Klaus W.J. Wahle, Marie Goua, Simona D’Urso and Steven D. Heys 3.1 General introduction: conjugated linoleic acids and health 3.2 Structure, dietary origins and consumption of CLAs in man 3.2.1 Structure 3.2.2 Origins of CLAs in the human diet 3.2.3 Dietary consumption of CLAs in man 3.3 CLAs in cancer prevention and treatment 3.3.1 Epidemiology of dietary fats and cancer risk 3.3.2 CLAs and breast cancer 3.3.3 CLAs and prostate cancer 3.3.4 CLAs in gastrointestinal cancer 3.3.5 CLAs and other cancers (hepatic, pancreatic and dermal) 3.4 Cellular mechanisms of CLAs’ anti-cancer effects 3.4.1 Inhibition of angiogenesis 3.4.2 Attenuation of cancer metastasis 3.4.3 Reduction of cancer cachexia 3.5 Effect of CLAs on body composition and energy metabolism in animals and men 3.5.1 Body composition in animals 3.5.2 Body composition in man 3.5.3 Possible mechanisms underlying reported changes in body composition 3.5.4 Efficacy of different CLA isomers in regulating body composition 3.6 Other reported health benefits of CLAs 3.6.1 Effects on insulin resistance and diabetes 3.6.2 Modulation of immune functions 3.6.3 Effects of CLAs on biomarkers of cardiovascular disease 3.7 Reported adverse health effects of CLAs in vivo and in vitro 3.8 Conclusions 4 54 54 55 55 56 59 59 60 60 62 64 66 67 72 73 74 75 75 76 78 78 79 80 81 87 90 91 Analysis of trans mono- and polyunsaturated fatty acids Jean-Louis S´eb´edio and W.M. Nimal Ratnayake 102 4.1 4.2 4.3 4.4 102 102 106 106 106 111 113 Introduction Isomeric fatty acids in the human diet Gas chromatography and Fourier transform infrared spectroscopy Direct GC analysis 4.4.1 Analysis of monounsaturated isomers 4.4.2 Isomers of linoleic and -linolenic acids 4.4.3 Resolution of eicosenoic and -linolenic acid isomers 4.4.4 Effect of the type of carrier gas and flow rate on cis and trans isomer resolution and fatty acid quantification 4.4.5 Conjugated fatty acids 4.5 Silver nitrate thin-layer and high-performance liquid chromatography separation of cis and trans isomers 114 116 123 BLUK122-Dijkstra September 28, 2007 19:12 Contents 4.6 4.7 5 Controlling physical and chemical properties of fat blends through their triglyceride compositions Albert J. Dijkstra 5.1 5.2 5.3 5.4 5.5 6 4.5.1 Monounsaturated fatty acid isomers 4.5.2 Conjugated fatty acids Utilisation of pre-fractionation steps prior to chromatographic analysis: the case of dairy fats Conclusion Introduction Defining triglyceride compositions Melting points and sfc The effect of oil processing on triglyceride groups 5.4.1 Hydrogenation 5.4.2 Fractionation 5.4.3 Interesterification 5.4.4 Other oil treatments Using triglyceride groups in product development vii 123 125 127 128 132 132 133 135 136 136 138 139 141 143 Trans isomer control in hydrogenation of edible oils Annemarie Beers, Rob Ariaansz and Douglas Okonek 147 6.1 147 147 147 147 148 148 149 149 149 149 150 150 151 151 153 157 158 160 160 162 162 163 169 169 175 6.2 6.3 6.4 6.5 6.6 Introduction 6.1.1 Hydrogenation process 6.1.2 History of hydrogenation 6.1.3 Reasons for hydrogenation Isomerisation 6.2.1 Geometric and positional isomerisation 6.2.2 Controlling isomerisation Reaction mechanism 6.3.1 ‘Half-hydrogenated’ intermediate 6.3.2 Saturation, positional and geometric isomerisation Industrial hydrogenation 6.4.1 Batch process 6.4.2 Reactor types and features 6.4.3 Reaction parameters 6.4.4 Influence of feedstock on trans 6.4.5 Influence of reaction conditions on trans 6.4.6 Influence of catalyst on trans 6.4.7 Influence of reactor design on trans 6.4.8 Trans isomer control New developments in low trans hydrogenation 6.5.1 Alternative reaction conditions 6.5.2 Alternative hydrogenation processes 6.5.3 Hydrogenation additives 6.5.4 Alternate catalysts Summary BLUK122-Dijkstra September 28, 2007 19:12 viii 7 Contents Fractionation and interesterification Wim De Greyt and Albert J. Dijkstra 181 7.1 7.2 181 182 182 183 185 185 187 191 191 192 196 198 7.3 8 9 Introduction Fractionation 7.2.1 Historical 7.2.2 Fat crystallisation theory 7.2.3 Fat crystallisation practice 7.2.4 Separation processes 7.2.5 Fractionation products Interesterificaton 7.3.1 Historical 7.3.2 Interesterification mechanism 7.3.3 Interesterification practice 7.3.4 Interesterification products Food applications of trans fatty acids John Podmore 203 8.1 Introduction 8.2 Margarine 8.2.1 Table margarine 8.2.2 Cake margarine 8.2.3 Pastry margarine 8.3 Biscuit fats 8.3.1 Dough fats – short dough biscuits 8.3.2 Dough fat – laminated biscuits 8.3.3 Cream filling fat 8.4 Fats for chocolate confectionery 8.5 Fats for sugar confectionery 8.6 Vanaspati 8.7 Synthetic creams 8.7.1 Whipped toppings 8.7.2 Coffee whiteners 8.8 Concluding remarks 203 205 205 208 209 210 210 211 211 211 214 215 216 216 216 217 Food products without trans fatty acids Pernille Gerstenberg Kirkeby 219 9.1 Introduction 9.2 Fat phase 9.3 Margarine and related products 9.4 Manufacturing process 9.5 Optimal processing conditions 9.6 Final remarks 219 219 222 225 230 233 Index The colour plate section follows page 228 235 BLUK122-Dijkstra September 28, 2007 19:12 Contributors Rob Ariaansz BASF Nederland B.V. De Meern, The Netherlands Dr Annemarie Beers BASF Nederland B.V. De Meern, The Netherlands Dr Wim De Greyt De Smet Technologies & Services Zaventem, Belgium Dr Albert J. Dijkstra Consultant to the Oils and Fats Industry St Eutrope-de-Born, France Simona D’Urso Department of Zootechnological Sciences and Nutrition Frederico II University of Napoli Naples, Italy Dr Norhaizan Mohd Esa Department of Nutrition and Dietetics Faculty of Medicine and Health Sciences Universiti Putra Malaysia Serdang, Malaysia Pernille Gerstenberg Kirkeby Gerstenberg Schroeder A/S Brondby, Denmark Dr Marie Goua The Robert Gordon University School of Life Sciences Aberdeen, UK Professor Richard J. Hamilton Consultant in Oils and Fats Chemistry Merseyside, UK Wolf Hamm Harpenden, UK Professor Steven D. Heys Department of Surgical and Nutritional Oncology Medical School, Aberdeen University Aberdeen, UK Professor Geok Lin Khor Department of Nutrition and Dietetics Faculty of Medicine and Health Sciences Universiti Putra Malaysia Serdang, Malaysia Douglas Okonek BASF Catalysts LLC Iselin, NJ, USA John Podmore Consultant to the Oils and Fats Industry Liverpool, UK Dr W.M. Nimal Ratnayake Nutrition Research Division Food Directorate Health Products and Food Branch Health Canada Ottawa, Ontario, Canada Professor Jean-Louis S´eb´edio INRA, Unit´e de Nutrition Humaine Mass Spectrometry Platform Saint Gen`es Champanelle, France Professor Klaus W.J. Wahle The Robert Gordon University School of Life Sciences Aberdeen, UK BLUK122-Dijkstra September 28, 2007 19:12 Preface Over the last several decades, a great deal of work has been carried out on trans fatty acids within a number of interrelated fields, such as nutrition, health, food science and industrial processing. In chapters written by leading experts, this volume offers a clear perspective of the current position of trans fatty acids in commerce and academic research. The book is designed as an aid to researchers and professionals in nutrition and health and those providing analytical services to the food industry. Readers seeking ways to formulate oil blends without trans fatty acids and those wishing to alter the composition of oils and fats by means of interesterification, fractionation and hydrogenation will find a large amount of research described and many applications outlined. They will also find methods of adjusting the formulation of their products and their processing. The book is written in a readerfriendly style, which will permit newcomers to the area to grasp the ways in which the field is progressing. Each chapter contains many of the latest references and significant areas of research. Chapter 1 introduces trans fatty acids and puts them in their proper context in relation to the many other saturated and unsaturated acids found in nature. It shows how trans acids are produced both in industry and by natural biohydrogenation in animals and plants. It outlines some of the properties of trans fatty acids and contrasts them with those of their cis isomers. Chapters 2 and 3 deal with the health implications and the epidemiology of trans fatty acids. Intakes of trans acids in the USA, Central America, Nigeria, Iran, India, China, Hong Kong, New Zealand, Australia, Hungary, the Czech Republic, Poland, Bulgaria and Spain are considered. A number of studies, e.g. the Zutphen Elderly, the Scottish Heart and Health, the Seven Countries, the Nurses Health and the EURAMIC case control, have been referenced. The results are considered without bias and the authors are not afraid to point out where further research is needed to confirm the original conclusions. In the consideration of conjugated linoleic acid (Chapter 3), the authors discuss the synthetic products that can be used for human and animal supplementation. With the realization that not all trans fatty acids have the same biological effect came the realization that it is important to know more than just the total trans fatty acid content in a food. Chapter 4 explains how direct GC, GC-MS, AgNO3 -TLC and HPLC are used to determine the trans fatty acid composition of various food products. Some recommendations for the best analysis of cis/trans monounsaturated fatty acids are given, whilst the need for pre-fractionation in some instances is highlighted. Chapter 5 introduces the concept of triglyceride groups and demonstrates that, for most components used in constituting fat blends, the triglyceride group composition can be calculated. It illustrates how hydrogenation, fractionation and interesterification cause the triglyceride group composition to change and it also highlights how product development can be facilitated by specifying fat blends on the basis of their triglyceride group composition. Chapter 6 provides a wide survey of the industrial hydrogenation process in the field of edible oil processing, its mechanism and how process parameters affect the trans fatty acid BLUK122-Dijkstra September 28, 2007 19:12 xii Preface content of the hydrogenation product. In addition, the chapter provides insight into the latest developments comprising the use of catalysts other than the usual nickel, the use of additives and unconventional process conditions and their effect on trans fatty acid formation. Chapter 7 deals with major modification processes that do not alter the trans fatty acid content of the oil or fat being processed: fractionation and interesterification. After outlining the basics, examples are provided that illustrate what kind of products suitable for low-trans or trans-free oil blends can be arrived at by these modification processes. The last two chapters are food product oriented and cover both compositional and processing aspects. Chapter 8 reviews products such as various margarines, dough fats and shortenings that still contain trans fatty acids. In Chapter 9, their low-trans or trans-free equivalents are introduced and their processing requirements highlighted. Solutions are provided for dealing with slow crystallisation of low-trans fat blends, which cover both the use of adjuvants and the adaptation of the cooling equipment and its process conditions. We express our thanks to the authors for their excellent contributions that provide fresh insight into this interesting and exciting field of study. We are indebted to our friends and colleagues for their helpful comments and criticisms. Finally, we are grateful for all the help we have received from Blackwell Publishing. Albert J. Dijkstra Richard J. Hamilton Wolf Hamm BLUK122-Dijkstra September 25, 2007 19:41 1 Fatty acids: structure, occurrence, nomenclature, biosynthesis and properties Richard J. Hamilton 1.1 INTRODUCTION Trans fatty acids have been present in the Western diet for as long as milk and butter have been staple commodities. However, in the last century with the discovery of catalytic hydrogenation by Sabatier and Senderens (Hastert, 1996; Hoffmann, 1989), food technologists came to recognise the improved physical characteristics which trans fatty acids could bestow on food products. The protection of the foodstuffs from the off flavours, which developed when highly unsaturated oils were incorporated into foods, was an added advantage which hydrogenation gave. However, in the last 50 years, studies have been conducted into the effects of increased quantities of trans fatty acids on human health and nutrition. The result has been the requirement for food processors to be able to claim that they have low or no trans fatty acids in their products (Korver and Katan, 2006). To appreciate the reason for this changed consideration, we first need to look at the constituents of oils and fats. As far as the world production is concerned, the major vegetable oils and fats are soya, palm, rape (canola), sunflower, cotton, groundnut, coconut, palm kernel and corn. The major animal fats, by comparison, are butter, tallow, lard and fish. During the year 2005, the production split between the animal and vegetable groups of oils and fats was 78.5% vegetable oils and 21.5% animal fats. In Chapters 8 and 9 on applications, we will see how the two sources of oils and fats are utilised. Oils and fats are made up of: r r r r lipids, viz. triacylglycerols (also called triglycerides), diacylglycerols (diglycerides), waxes, phosphoglycerols, sphingolipids, free fatty acids and hydrocarbons; certain vitamins; pigments and antioxidants. These lipids cover a wide range of different chemical structures but there are two common features. Most lipids are water insoluble and they can all be biosynthetically related to fatty acids. The triacylglycerols account for 90–95% by weight of oils and fats and in many senses are the most important part of these items of commerce. A generalised formula for a triacylglycerol is shown in Fig. 1.1. BLUK122-Dijkstra September 25, 2007 19:41 2 Trans Fatty Acids O H2C O R2 C O CH H2C Fig. 1.1 O C R1 O O C R3 General formula for a triacylglycerol. If the fatty acids in this triacylglycerol, R1 COOH, R2 COOH and R3 COOH, are all identical, i.e. R1 = R2 = R3 , the triacylglycerol would be referred to as a monoacid triacylglycerol or a single-acid triacylglycerol. More usually, each triacylglycerol will have two or three different fatty acids. Gunstone (1967) claimed that over 300 fatty acids were known in nature. By the time of a more recent book in 1996, he estimated that there were over 1000 fatty acids (Gunstone, 1996). Thus the diversity of these oils and fats (Gunstone, 2004) is considerable as will be manifested in Chapter 4 on analysis. One simplifying feature is that the major fatty acids, in nature, have an even number of carbon atoms. In addition, there are usually only five to seven major fatty acids in most commercially important oils and fats. 1.2 FATTY ACID NOMENCLATURE Fatty acid nomenclature is complicated by the fact that many acids were well known before any system of naming them had been determined. Thus the names of oleic, stearic and palmitic acids were well established before any rules were developed. 1.2.1 Saturated acids Fatty acids are named according to the number of carbon atoms in the chain. In turn, the name of the fatty acids refers back to the name of the saturated hydrocarbon with the same number of carbon atoms. So stearic acid has 18 carbon atoms and is related to the alkane with 18 carbon atoms, i.e. octadecane. To obtain the name of the acid, the ‘e’ is removed from octadecane giving ‘octadecan’ and the ending ‘oic’ is added to indicate the carboxylic acid. Thus, octadecan(e) → octadecan(oic) acid → octadecanoic acid, which is the full and correct name for stearic acid. Whilst it is convenient to use the trivial names, such as oleic and linoleic acid, many of the acids encountered later in our discussions have no simple trivial names. Even the use of formulae, as given in Tables 1.1 and 1.2, is not very quick and easy. An alternative shorthand method has been devised. This system reduces the acid to the minimum statement that is needed to define it. Chain length 4 6 8 10 12 14 16 18 20 22 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00 Docosanoic Eicosanoic Octadecanoic Hexadecanoic Tetradecanoic Dodecanoic Decanoic Behenic Arachidic Stearic Palmitic Myristic Lauric Capric Caprylic Caproic Butyric Common name C H2 C H2 C H2 C H2 C H2 C H2 C H2 C H2 H2 C H2 C H2 C H2 C H2 C H2 C H2 C H2 C CH3 (CH2)20 COOH CH3 (CH2)18 COOH H3C H3C H3C H3C H3C H3C H3C H3C Structure C H2 C H2 C H2 C H2 C H2 C H2 C H2 H2 C H2 C H2 C H2 C H2 C H2 C H2 C COOH C H2 C H2 C H2 C H2 C H2 C H2 H2 C H2 C H2 C H2 C H2 C H2 C COOH C H2 C H2 C H2 C H2 C H2 H2 C H2 C H2 C H2 C H2 C COOH C H2 C H2 C H2 C H2 H2 C H2 C H2 C H2 C COOH C H2 C H2 C H2 H2 C H2 C H2 C COOH C H2 C H2 H2 C H2 C COOH C H2 H2 C COOH COOH September 25, 2007 Octanoic Hexanoic Butanoic Proper name Structures of saturated fatty acids. Shorthand notation Table 1.1 BLUK122-Dijkstra 19:41 Structure, occurrence, nomenclature, biosynthesis and properties 3 BLUK122-Dijkstra September 25, 2007 19:41 4 Trans Fatty Acids In the case of stearic acid, first the total number of carbon atoms in the chain is stated, i.e. 18, and then the number of double bonds is given which, in the case of stearic acid, is 0. The shorthand system then inserts a colon between the number of carbon atoms and the number of double bonds and so, for stearic acid, the shorthand is 18:0. Stearic acid is shown in Table 1.1, where the long straight chain is given by the zigzag representation. Some of the main straight-chain saturated fatty acids are also given in Table 1.1. 1.2.2 Monounsaturated acids Oleic acid is an unsaturated fatty acid that can be represented by the formula shown in Fig. 1.2. Thus oleic acid has 18 carbon atoms, and it has one double bond at position 9 from the carboxyl end. Since oleic acid has 18 carbon atoms and one ethylenic double bond, the name is based on octadecene. In this instance the ‘e’ is removed and the ending for the carboxylic acid group octadecen(e) → octadecen(oic) acid. Thus is added 9-octadecenoic acid. In the case of oleic acid, the double bond is in the cis configuration (also called the Z configuration from the German zusammen, meaning together). Thus to specify oleic acid precisely, the full name would be 9c-octadecenoic acid or 9Z -octadecenoic acid. An isomer of oleic acid is elaidic acid, which has a trans double bond at the 9-position. The shorthand for this acid would therefore be 9t-octadecenoic acid. If the EZ system is to be used, the letter referring to the trans configuration is E, which stands for the German word entgegen, meaning opposite. These two acids are shown in Fig. 1.2. From a chemist’s point of view, the most important part of a fatty acid is the carboxylic acid group. The position of the double bond is therefore quoted with reference to the carboxylic acid group, i.e. 9 in the case of oleic acid. Using the shorthand method oleic acid is 18:1. Since the double bond is at the ninth carbon atom and the configuration of the double bond is cis, the name becomes 9c-18:1. It is also possible to denote the position of the double bond by using the symbol . Oleic acid is described as a 9 acid, whilst petroselinic acid is a 6 acid. Some of the main monounsaturated fatty acids are given in Table 1.2. O C H Oleic acid 9c-octadecenoic acid H or OH 9Z-octadecenoic acid O C Elaidic acid Fig. 1.2 H H 9t-octadecenoic acid or 9E-octadecenoic acid Structures of oleic and elaidic acids. OH 14 14 16 18 18 18 18 22 14:1 5c 14:1 9c 16:1 9c 18:1 6c 18:1 9c 18:1 9t 18:1 11c 22:1 13c Erucic Oleic Petroselenic Palmitoleic 13c-Docosenoic Erucic 11c-Octadecenoic Vaccenic acid 9t-Octadecenoic 9c-Octadecenoic 6c-Octadecenoic 9c-Hexadecenoic Myristoleic H3C HC CH CH3 (CH2)7 CH=CH (CH2)11 COOH CH3 (CH2)5 CH=CH (CH2)9 COOH CH3 (CH2)7 CH=CH (CH2)7 COOH CH3 (CH2)7 CH=CH (CH2)7 COOH CH3 (CH2)10 CH=CH (CH2)4 COOH CH3 (CH2)5 CH=CH (CH2)7 COOH CH3 (CH2)3 CH=CH (CH2)7 COOH CH3 (CH2)7 CH=CH (CH2)3 COOH Structure C OH O September 25, 2007 9c-Tetradecenoic 5c-Tetradecenoic Common name Structures of monoenoic acids. Shorthand Chain Proper notation length name Table 1.2 BLUK122-Dijkstra 19:41 Structure, occurrence, nomenclature, biosynthesis and properties 5 COOH  -Linolenic acid -Linolenic acid Rumenic acid 6c,9c,12c-18:3 9c,12c,15c-18:3 9c,11t-18:2 COOH COOH COOH Structure Linoleic acid Name September 25, 2007 9c,12c-18:2 Shorthand notation Structures of polyunsaturated acids. 6 Table 1.3 BLUK122-Dijkstra 19:41 Trans Fatty Acids BLUK122-Dijkstra September 25, 2007 19:41 Structure, occurrence, nomenclature, biosynthesis and properties 1.2.3 7 Diunsaturated acids Linoleic acid is a diunsaturated acid with two double bonds and 18 carbon atoms and is named from the diunsaturated hydrocarbon octadecadiene (Table 1.3). Octadecadien(e) → octadecadien(oic) acid → 9, 12-octadecadienoic acid Again, the stereochemistry of the double bonds is known to be cis and so the correct name for linoleic acid is 9c,12c-octadecadienoic acid, with its shorthand name 9c,12c-18:2. There is another system of numbering the position of the double bond, which came into operation because of the way in which the fatty acid is built up during biosynthesis. In Section 1.4, it will be seen that the starting point for biosynthesis is a two-carbon unit that becomes the methyl end of the final fatty acid. Each time that another two-carbon unit is added to the chain, the name of the new fatty acid would alter and the position of any double bond would also alter with respect to the chemist’s fixed point, i.e. numbering from the carboxyl group. It was recognised that it might be advisable to use a system of nomenclature, which started at the methyl end of the acid chain. This is called the n-x system or the  system. Thus linoleic acid is 9c,12c-18:2, where the carboxyl group is the starting point for the numbering. The alternative name for linoleic acid starts the numbering at the methyl end. In this case the double bond is now of six carbon atoms from the methyl group, and the position of the double bond is represented as n-6 or 6. The  tells us that we start counting from the methyl end. Linoleic acid would be described as 6,9-18:2 in this alternative system. The  notation for monounsaturated acids is given in Table 1.2. Rumenic acid is a conjugated diene fatty acid, 9c,11t-18:2, which is dealt with in Chapter 3. 1.2.4 Triunsaturated acids The structures of two of the major triunsaturated acids  -linolenic acid and -linolenic acid are given in Table 1.3. Their full names are 6c,9c,12c-octadecatrienoic acid and 9c,12c,15coctadecatrienoic acid respectively. The name derived as above from octadeca with the trienoic added shows that there are three ethylenic double bonds. Octadeca(ne) → octadecatrienoic acid → 9c,12c,15c-octadecatrienoic acid 1.3 OCCURRENCE Of the saturated fatty acids, palmitic acid is the most widely occurring in both animal fats and vegetable oils, whilst stearic acid is found in lesser quantities in vegetable oils. Stearic acid is present in large quantities only in animal tallows and in vegetable fats, such as cacao butter and Borneo tallow. Butyric acid is found in butterfat (also referred to as anhydrous milk fat) produced from cow’s milk. Caprylic, capric and myristic acids are present in coconut and palm kernel oil. Oleic acid is the most widely distributed monounsaturated fatty acid. In some oils it is found in high proportions, ranging from 50 to 80%, e.g. olive, cashew and pistachio. BLUK122-Dijkstra September 25, 2007 19:41 8 Trans Fatty Acids 40 35 Percentage 30 25 C16 20 C18 15 10 5 0 5 6 7 8 9 10 11 12 13 14 15 16 Position of double bond Fig. 1.3 Trans isomeric monoene C16 and C18 fatty acids in butter. Whereas most of the unsaturated fatty acids in nature have a cis double bond, there are some acids that have the trans configuration. We can concern ourselves mainly with trans fatty acids from now on. There are three main sources of trans fatty acids in the human diet; viz., they can be derived from animals or from the plant kingdom, or produced in the processing of oils and fats. In animals, trans fatty acids are derived from dietary lipids. It is believed that biohydrogenation by bacteria in the rumen of the dietary lipids results in a mixture of trans fatty acids. Such fatty acids are found in all ruminant milk fats. Rumenic acid (9c,11t-18:2) is the major conjugated fatty acid in ruminant fats. Rossell (2001) reported the trans content of subcutaneous adipose tissue in beef, sheep and pig to be 1.3–6.6%, 11.0–14.6% and 1.1–1.4% by weight respectively. In the case of farm animals, where the feed may contain trans fatty acids, the animal will metabolise some of the trans fatty acids and place some trans fatty acids in the adipose tissue. Hay and Morrison (1970) showed that amongst the trans isomers in butterfat, the monenoic C16 and monoenoic C18 are the major components (Fig. 1.3). The major isomer for C16 is palmitelaidic acid 9 (32%) and for C18 trans vaccenic acid 11 (36.1%). Trans fatty acids in most vegetable oils are present, if at all, in very minor proportions and in some oils, at the trace level. In the vegetable kingdom, trans fatty acids do occur naturally and sometimes in significant quantities; i.e. there is 6–12% of eleostearic acid 9c,11t,13t-18:3 in cherry oils, which have now been accepted as safe for food oils (Comes et al., 1992). Petroselaidic acid, 6t-18:1, is found along with petroselinic acid in Heracleum nipponicum, Conium maculatum, Phelopterus litoralis, Ligusticum acutifolium, Bupleurum falcatum, Osmorhiza aristata, Conioselinum univittatum, Hedera japonica, Panax schinseng and Aralia elata (Placek, 1963). In the plant kingdom, conjugated triene fatty acids often have one or more trans double bonds, e.g. jacaric acid 8c,10t,12c-18:3, calendic acid 8t,10t,12c-18:3, catalpic acid 9t,11t,13c-18:3, punicic acid 9c,11t,13c-18:3 and -eleostearic acid 9t,11t,13t-18:3. There are also conjugated tetraenoic acids - and -parinaric acids 9c,11t,13t,15c-18:4 and 9t,11t,13t,15t-18:4 respectively. In addition the biosynthetic pathways given in Section 1.3 BLUK122-Dijkstra September 25, 2007 19:41 Structure, occurrence, nomenclature, biosynthesis and properties 9 involve trans double bonds even when cis double bonds are being generated. So it can be seen that trans fatty acids occur naturally in both animals and plants. In 1983, Sommerfeld stated that ‘hardened oils do NOT contain trans fatty acids isomers other than those produced by the microflora of ruminants. Therefore claims that trans fatty acids isomers are “synthetic” “non-physiologic” or “unnatural” are unjustified if these words are used to imply “not produced by the living organism” ’. The presence in nature of conjugated linoleic acid double bonds contains trans which is further confirmation of Sommerfeld’s statement. Conjugated linoleic acid is covered in full in Chapter 3. The third source of trans fatty acids in foods is where they are produced in processing. Why was hydrogenation introduced into the oils and fats industry? Initially, it was to remedy a shortage of solid fats. At its simplest, hydrogenation is the addition of two hydrogen atoms across the ethylenic double bond of the fatty acid. It was recognised that the more unsaturated the fatty acid, the more likely it was for the fatty acid to be oxidised, which leads to oxidative rancidity. By removing two double bonds from linolenic acid, a monoenoic acid would be formed, which would resist oxidation better. Triene → diene → monoene → saturated acid (1.1) If the hydrogenation could proceed by the route suggested by Equation 1.1, the triene linolenic acid would yield the saturated acid, i.e. stearic acid. However, under industrial conditions, hydrogenation with a nickel catalyst is partial, giving rise to a mixture of products. From the above, it is still not obvious why there should be any trans fatty acid formed. Dijkstra (2002) suggested an amendment to the Horiuti–Polanyi mechanism in which the monoene M forms a semihydrogenated intermediate MH (Eq. 1.2). M + H → MH, where M represents monoene (1.2) Dijkstra explains that the hydrogen concentration is too low for these intermediates to go on to form stearic acid. In turn this allows dissociation to occur as in Eq. 1.3. MH → M + H (1.3) When an individual acid, e.g. oleic acid, is considered in these reactions, the changes can be represented as shown in Fig. 1.4. When a fatty acid with a single cis double bond is partially hydrogenated, adsorption to (Step 1) and desorption from (Steps 3–5) the catalyst surface occurs, which produces a mixture of fatty acids. Some of the acids have a trans double bond. It is believed that the adsorption mechanism (Step 1) involves the formation of carbon nickel bonds between the metal catalyst and the carbon atoms of the 9 double bond C9 and C10 to give a structure (a). One hydrogen atom is then transferred (Step 2), probably from a Ni–H atom on the surface of the catalyst near the adsorbed fatty acid, to the carbon atom C9 to give structure (b). If the addition goes further, another hydrogen atom is added, the C Ni bond is broken and the hydrogen adds to C10 , with the formation of stearic acid as a desorption (Step 3).

Author Albert J. Dijkstra and Richard J. Hamilton Isbn 978-1405156912 File size 2.9 MB Year 2007 Pages 497 Language English File format PDF Category Chemistry Book Description: FacebookTwitterGoogle+TumblrDiggMySpaceShare Trans fatty acids (TFAs) have been used for many years to impart desirable physical characteristics to fats and fat blends used in food manufacturing. However, clinical trials and epidemiological studies conducted over the last thirty years have shown that TFAs can increase “bad” cholesterol levels in the blood while reducing “good” cholesterol. Accordingly, they are also linked with increased risks of coronary heart disease, thrombosis and strokes. For this reason, the food industry has been obliged to find alternatives to TFAs, thus enabling it to meet the presumed consumer demand for “low” or “no” trans fats products. The issue is becoming more and more pressing. For example, US labelling regulations now require that food manufacturers state the trans fat content of their products on the packaging. This book provides an overview of trans fatty acids in oils and fats used in food manufacture. Topics covered include: the chemistry and occurrence of TFAs; analytical methods for determining the fatty acid composition including TFAs of foods; processing techniques for reducing, minimising or even avoiding the formation of TFAs; TFA alternatives in food; health and nutrition concerns and legislative aspects. It is directed at chemists and technologists working in edible oils and fats processing and product development; food scientists and technologists; analytical chemists and nutritionists working in the food industry.     Download (2.9 MB) Nuts: Properties, Consumption and Nutrition Betaine: Chemistry, Analysis, Function And Effects Membrane Lipidomics For Personalized Health Lipidomics: Comprehensive Mass Spectrometry of Lipids The Chemistry Of Food Load more posts

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