Food lipids chemistry, nutrition, and biochemistry

Food Lipids Chemistry, Nutrition, and Biotechnology Second Edition, Revised and Expanded edited by Casimir C.. Handbook of Indigenous Fermented Foods: Second Edition, Revised and Expande

Food Lipids

Chemistry, Nutrition, and Biotechnology

Second Edition, Revised and Expanded

edited by Casimir C AkohThe Univeristy of GeorgiaAthens, GeorgiaDavid B MinThe Ohio State UniversityColumbus, Ohio

ISBN: 0-8247-0749-4

This book is printed on acid-free paper

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PRINTED IN THE UNITED STATES OF AMERICA

FOOD SCIENCE AND TECHNOLOGY

A Series of Monographs, Textbooks, and Reference Books

EDITORIAL BOARD

Senior Editors

Additives P Michael Davidson University of Tennessee–Knoxville

Dairy science James L Steele University of Wisconsin–Madison

Flavor chemistry and sensory analysis John H Thorngate III University

of California–Davis

Food engineering Daryl B Lund University of Wisconsin–Madison

Food proteins/food chemistry Rickey Y Yada University of Guelph

Health and disease Seppo Salminen University of Turku, Finland

Nutrition and nutraceuticals Mark Dreher Mead Johnson Nutritionals

Phase transition/food microstructure Richard W Hartel University of

Wisconsin–Madison

Processing and preservation Gustavo V Barbosa-C á novas Washington

State University–Pullman

Safety and toxicology Sanford Miller University of Texas–Austin

1 Flavor Research: Principles and Techniques, R Teranishi, I

Horn-stein, P Issenberg, and E L Wick

2 Principles of Enzymology for the Food Sciences, John R Whitaker

3 Low-Temperature Preservation of Foods and Living Matter, Owen R.

Fennema, William D Powrie, and Elmer H Marth

4 Principles of Food Science

Part I: Food Chemistry, edited by Owen R Fennema

Part II: Physical Methods of Food Preservation, Marcus Karel, Owen

R Fennema, and Daryl B Lund

5 Food Emulsions, edited by Stig E Friberg

6 Nutritional and Safety Aspects of Food Processing, edited by Steven

R Tannenbaum

7 Flavor Research: Recent Advances, edited by R Teranishi, Robert A.

Flath, and Hiroshi Sugisawa

8 Computer-Aided Techniques in Food Technology, edited by Israel

Saguy

9 Handbook of Tropical Foods, edited by Harvey T Chan

10 Antimicrobials in Foods, edited by Alfred Larry Branen and P Michael

Davidson

11 Food Constituents and Food Residues: Their Chromatographic

Determination, edited by James F Lawrence

12 Aspartame: Physiology and Biochemistry, edited by Lewis D Stegink

and L J Filer, Jr.

13 Handbook of Vitamins: Nutritional, Biochemical, and Clinical Aspects,

edited by Lawrence J Machlin

14 Starch Conversion Technology, edited by G M A van Beynum and J.

18 Citrus Fruits and Their Products: Analysis and Technology, S V Ting

and Russell L Rouseff

19 Engineering Properties of Foods, edited by M A Rao and S S H.

Rizvi

20 Umami: A Basic Taste, edited by Yojiro Kawamura and Morley R.

Kare

21 Food Biotechnology, edited by Dietrich Knorr

22 Food Texture: Instrumental and Sensory Measurement, edited by

Howard R Moskowitz

23 Seafoods and Fish Oils in Human Health and Disease, John E.

Kinsella

24 Postharvest Physiology of Vegetables, edited by J Weichmann

25 Handbook of Dietary Fiber: An Applied Approach, Mark L Dreher

26 Food Toxicology, Parts A and B, Jose M Concon

27 Modern Carbohydrate Chemistry, Roger W Binkley

28 Trace Minerals in Foods, edited by Kenneth T Smith

29 Protein Quality and the Effects of Processing, edited by R Dixon

Phillips and John W Finley

30 Adulteration of Fruit Juice Beverages, edited by Steven Nagy, John A.

Attaway, and Martha E Rhodes

31 Foodborne Bacterial Pathogens, edited by Michael P Doyle

32 Legumes: Chemistry, Technology, and Human Nutrition, edited by

Ruth H Matthews

33 Industrialization of Indigenous Fermented Foods, edited by Keith H.

Steinkraus

34 International Food Regulation Handbook: Policy · Science · Law,

edited by Roger D Middlekauff and Philippe Shubik

35 Food Additives, edited by A Larry Branen, P Michael Davidson, and

Seppo Salminen

36 Safety of Irradiated Foods, J F Diehl

37 Omega-3 Fatty Acids in Health and Disease, edited by Robert S Lees

and Marcus Karel

38 Food Emulsions: Second Edition, Revised and Expanded, edited by

K å re Larsson and Stig E Friberg

39 Seafood: Effects of Technology on Nutrition, George M Pigott and

Barbee W Tucker

40 Handbook of Vitamins: Second Edition, Revised and Expanded,

edited by Lawrence J Machlin

41 Handbook of Cereal Science and Technology, Klaus J Lorenz and

Karel Kulp

42 Food Processing Operations and Scale-Up, Kenneth J Valentas,

Leon Levine, and J Peter Clark

43 Fish Quality Control by Computer Vision, edited by L F Pau and R.

Olafsson

44 Volatile Compounds in Foods and Beverages, edited by Henk Maarse

45 Instrumental Methods for Quality Assurance in Foods, edited by

Daniel Y C Fung and Richard F Matthews

46 Listeria, Listeriosis, and Food Safety, Elliot T Ryser and Elmer H.

Marth

47 Acesulfame-K, edited by D G Mayer and F H Kemper

48 Alternative Sweeteners: Second Edition, Revised and Expanded,

ed-ited by Lyn O'Brien Nabors and Robert C Gelardi

49 Food Extrusion Science and Technology, edited by Jozef L Kokini,

Chi-Tang Ho, and Mukund V Karwe

50 Surimi Technology, edited by Tyre C Lanier and Chong M Lee

51 Handbook of Food Engineering, edited by Dennis R Heldman and

Daryl B Lund

52 Food Analysis by HPLC, edited by Leo M L Nollet

53 Fatty Acids in Foods and Their Health Implications, edited by Ching

Kuang Chow

54 Clostridium botulinum: Ecology and Control in Foods, edited by

Andreas H W Hauschild and Karen L Dodds

55 Cereals in Breadmaking: A Molecular Colloidal Approach,

Ann-Charlotte Eliasson and K å re Larsson

56 Low-Calorie Foods Handbook, edited by Aaron M Altschul

57 Antimicrobials in Foods: Second Edition, Revised and Expanded,

edited by P Michael Davidson and Alfred Larry Branen

58 Lactic Acid Bacteria, edited by Seppo Salminen and Atte von Wright

59 Rice Science and Technology, edited by Wayne E Marshall and

62 Carbohydrate Polyesters as Fat Substitutes, edited by Casimir C.

Akoh and Barry G Swanson

63 Engineering Properties of Foods: Second Edition, Revised and

Expanded, edited by M A Rao and S S H Rizvi

64 Handbook of Brewing, edited by William A Hardwick

65 Analyzing Food for Nutrition Labeling and Hazardous Contaminants,

edited by Ike J Jeon and William G Ikins

66 Ingredient Interactions: Effects on Food Quality, edited by Anilkumar

69 Nutrition Labeling Handbook, edited by Ralph Shapiro

70 Handbook of Fruit Science and Technology: Production, Composition,

Storage, and Processing, edited by D K Salunkhe and S S Kadam

71 Food Antioxidants: Technological, Toxicological, and Health

Perspec-tives, edited by D L Madhavi, S S Deshpande, and D K Salunkhe

72 Freezing Effects on Food Quality, edited by Lester E Jeremiah

73 Handbook of Indigenous Fermented Foods: Second Edition, Revised

and Expanded, edited by Keith H Steinkraus

74 Carbohydrates in Food, edited by Ann-Charlotte Eliasson

75 Baked Goods Freshness: Technology, Evaluation, and Inhibition of

Staling, edited by Ronald E Hebeda and Henry F Zobel

76 Food Chemistry: Third Edition, edited by Owen R Fennema

77 Handbook of Food Analysis: Volumes 1 and 2, edited by Leo M L.

Nollet

78 Computerized Control Systems in the Food Industry, edited by Gauri

S Mittal

79 Techniques for Analyzing Food Aroma, edited by Ray Marsili

80 Food Proteins and Their Applications, edited by Srinivasan

Damo-daran and Alain Paraf

81 Food Emulsions: Third Edition, Revised and Expanded, edited by Stig

E Friberg and K å re Larsson

82 Nonthermal Preservation of Foods, Gustavo V Barbosa-C á novas, Usha R Pothakamury, Enrique Palou, and Barry G Swanson

83 Milk and Dairy Product Technology, Edgar Spreer

84 Applied Dairy Microbiology, edited by Elmer H Marth and James L.

Steele

85 Lactic Acid Bacteria: Microbiology and Functional Aspects: Second

Edition, Revised and Expanded, edited by Seppo Salminen and Atte

von Wright

86 Handbook of Vegetable Science and Technology: Production,

Composition, Storage, and Processing, edited by D K Salunkhe and

S S Kadam

87 Polysaccharide Association Structures in Food, edited by Reginald H.

Walter

88 Food Lipids: Chemistry, Nutrition, and Biotechnology, edited by

Casimir C Akoh and David B Min

89 Spice Science and Technology, Kenji Hirasa and Mitsuo Takemasa

90 Dairy Technology: Principles of Milk Properties and Processes, P.

Walstra, T J Geurts, A Noomen, A Jellema, and M A J S van Boekel

91 Coloring of Food, Drugs, and Cosmetics, Gisbert Otterst ä tter

92 Listeria, Listeriosis, and Food Safety: Second Edition, Revised and Expanded, edited by Elliot T Ryser and Elmer H Marth

93 Complex Carbohydrates in Foods, edited by Susan Sungsoo Cho,

Leon Prosky, and Mark Dreher

94 Handbook of Food Preservation, edited by M Shafiur Rahman

95 International Food Safety Handbook: Science, International

Regula-tion, and Control, edited by Kees van der Heijden, Maged Younes,

Lawrence Fishbein, and Sanford Miller

96 Fatty Acids in Foods and Their Health Implications: Second Edition,

Revised and Expanded, edited by Ching Kuang Chow

97 Seafood Enzymes: Utilization and Influence on Postharvest Seafood

Quality, edited by Norman F Haard and Benjamin K Simpson

98 Safe Handling of Foods, edited by Jeffrey M Farber and Ewen C D.

Todd

99 Handbook of Cereal Science and Technology: Second Edition,

Re-vised and Expanded, edited by Karel Kulp and Joseph G Ponte, Jr.

100 Food Analysis by HPLC: Second Edition, Revised and Expanded,

edited by Leo M L Nollet

101 Surimi and Surimi Seafood, edited by Jae W Park

102 Drug Residues in Foods: Pharmacology, Food Safety, and Analysis,

Nickos A Botsoglou and Dimitrios J Fletouris

103 Seafood and Freshwater Toxins: Pharmacology, Physiology, and

Detection, edited by Luis M Botana

104 Handbook of Nutrition and Diet, Babasaheb B Desai

105 Nondestructive Food Evaluation: Techniques to Analyze Properties

and Quality, edited by Sundaram Gunasekaran

106 Green Tea: Health Benefits and Applications, Yukihiko Hara

107 Food Processing Operations Modeling: Design and Analysis, edited

by Joseph Irudayaraj

108 Wine Microbiology: Science and Technology, Claudio Delfini and

Joseph V Formica

109 Handbook of Microwave Technology for Food Applications, edited by

Ashim K Datta and Ramaswamy C Anantheswaran

110 Applied Dairy Microbiology: Second Edition, Revised and Expanded,

edited by Elmer H Marth and James L Steele

111 Transport Properties of Foods, George D Saravacos and Zacharias

B Maroulis

112 Alternative Sweeteners: Third Edition, Revised and Expanded, edited

by Lyn O ’ Brien Nabors

113 Handbook of Dietary Fiber, edited by Susan Sungsoo Cho and Mark

116 Food Additives: Second Edition, Revised and Expanded, edited by A.

Larry Branen, P Michael Davidson, Seppo Salminen, and John H Thorngate, III

117 Food Lipids: Chemistry, Nutrition, and Biotechnology: Second Edition,

Revised and Expanded, edited by Casimir C Akoh and David B Min

118 Food Protein Analysis: Quantitative Effects on Processing, R K.

Owusu-Apenten

119 Handbook of Food Toxicology, S S Deshpande

120 Food Plant Sanitation, edited by Y H Hui, Bernard L Bruinsma, J.

Richard Gorham, Wai-Kit Nip, Phillip S Tong, and Phil Ventresca

121 Physical Chemistry of Foods, Pieter Walstra

122 Handbook of Food Enzymology, edited by John R Whitaker, Alphons

G J Voragen, and Dominic W S Wong

123 Postharvest Physiology and Pathology of Vegetables: Second Edition,

Revised and Expanded, edited by Jerry A Bartz and Jeffrey K Brecht

124 Characterization of Cereals and Flours: Properties, Analysis, and

Ap-plications, edited by G ö n ü l Kaletun ç and Kenneth J Breslauer

125 International Handbook of Foodborne Pathogens, edited by Marianne

D Miliotis and Jeffrey W Bier

Additional Volumes in Preparation

Handbook of Dough Fermentations, edited by Karel Kulp and Klaus

Lorenz

Extraction Optimization in Food Engineering, edited by Constantina

Tzia and George Liadakis

Physical Principles of Food Preservation: Second Edition, Revised

and Expanded, Marcus Karel and Daryl B Lund

Handbook of Vegetable Preservation and Processing, edited by Y H.

Hui, Sue Ghazala, Dee M Graham, K D Murrell, and Wai-Kit Nip

Food Process Design, Zacharias B Maroulis and George D.

Saravacos

Preface to the Second Edition

Readers’ responses to the first edition, published in 1998, were overwhelming, and

we are grateful The response reassured us that there was indeed great need for atextbook suitable for teaching food lipids, nutritional aspects of lipids, and lipidchemistry courses to food science and nutrition majors The aim of the first editionremains unchanged: to provide a modern, easy-to-read textbook for students andinstructors The book is also suitable for upper-level undergraduate, graduate, andpostgraduate instruction Scientists who have left the university and are engaged inresearch and development in the industry, government, or academics will find thisbook a useful reference Again, we made every effort to select contributors who areinternationally recognized experts We thank them for their exceptional attention todetails and timely submissions

The text has been updated with new information The indexing has been proved We changed the order of chapters and added two new chapters, ‘‘ConjugatedLinoleic Acid’’ and ‘‘Food Applications of Lipids.’’ While it is not possible to coverevery aspect of lipids, we feel we have added and covered most topics that are ofinterest to our readers The book still is divided into five main parts: Chemistry andProperties; Processing; Oxidation; Nutrition; and Biotechnology and Biochemistry.Obviously, we made some mistakes in the first edition Thanks go to our stu-dents for pointing out most of the obvious and glaring errors Based on readers’ andreviewers’ comments, we have improved the new edition — we hope without creatingnew errors, which are sometimes unavoidable for a book this size and complexity

im-We apologize for any errors and urge you to contact us if you find mistakes or havesuggestions to improve the readability and comprehension of this text

Special thanks to our readers and students, and to the editorial staff of MarcelDekker, Inc., for their helpful suggestions toward improving the quality of thisedition.

Casimir C Akoh David B Min

Preface to the First Edition

There is a general consensus on the need for a comprehensive, modern textbook offood lipids that will provide a guide to students and instructors, as well as cover thetopics expected of students taking a food lipids or lipid chemistry course as foodscience and nutrition majors The text is suitable for undergraduate and graduateinstruction In addition, food industry professionals seeking background or advancedknowledge in lipids will find this book helpful It is envisaged that this book willalso serve as a reference source for individuals engaged in food research, productdevelopment, food processing, nutrition and dietetics, quality assurance, oil process-ing, fat substitutes, genetic engineering of oil crops, and lipid biotechnology It isexpected that students and others using this book will have backgrounds in chemistryand biochemistry

Every effort was made to involve internationally recognized experts as tributors to this text Considerable efforts were made by the authors to start frombasics and build up and to provide copious equations, tables, illustrations, and figures

con-to enhance teaching, comprehension, and con-to drive the lecture materials home anisms of reactions are given to help in the understanding of the underlying principles

Mech-of lipid chemistry and hopefully will lead to solutions Mech-of adverse reactions Mech-of lipids

in the future We believe that the end product of this work provides state-of-the-artand authoritative information that covers almost all aspects of food lipids and willserve as a unique text for instruction throughout the world The text is reader-friendlyand easy to understand Adequate references are provided to encourage persons whoneed to inquire further or need detailed information on any aspect covered in thisbook

The text is divided into five main parts, namely: Chemistry and Properties;Processing; Oxidation; Nutrition; and Biotechnology and Biochemistry.

Part I is devoted to introductory chapters on the nomenclature and classification

of lipids, chemistry of phospholipids, waxes and sterols, emulsion and emulsifiers,

frying, and on the analysis of lipids including trans fatty acids It is important to

understand the structure and chemistry of lipids and some basic concepts beforemoving on to more complex and applied topics

Part II deals with the technology of edible oils and fats processing includingrefining, recovery, crystallization, polymorphism, chemical interesterification, andhydrogenation

Part III describes the key oxidation reactions in both edible oils and plant andanimal or muscle tissues Lipid oxidation is a major cause of quality deterioration

of processed and unprocessed foods Methods to measure lipid oxidation in fats andoils are given The mechanism of antioxidant actions in arresting or improving theoxidative stability of foods is discussed This section has tremendous implicationsfor food technologists and nutritionists as the consumer continues to demand andexpect nothing but high-quality foods and food products

Part IV deals with the role of fats and oils in overall nutrition The importance

of antioxidants in nutrition and food preservation is presented Excess fat intake isassociated with many disease conditions This section describes various omega fattyacids and their sources, the role of dietary fats in atherosclerosis, eicosanoids pro-duction, immune system, coronary heart disease and obesity The various types oflipid-based synthetic fat substitutes are discussed

Part V introduces the new biotechnology as applied to lipids and production

of value-added lipid products The microbial lipases used in enzyme biotechnologyare discussed The potential for replacing chemical catalysis with enzyme catalysisare described further in the chapters dealing with enzymatic interesterification andstructured lipids Lipid biotechnology and biosynthesis chapters set the stage for abetter understanding of the chapter on genetic engineering of plants that producevegetable oil and for further research in lipid biotechnology, a dynamic area ofincreasing industrial interest

We feel that we covered most of the topics expected for a food lipids course

in this text It is hoped that this edition will stimulate discussions and generate helpfulcomments to improve upon future editions Unavoidably, in a book of this size andcomplexity, there are some areas of overlap Efforts are made to cross reference thechapters as such

Finally, we would like to thank all the authors for the magnificent work theydid in making sure that their contributions are timely, easy to read, and most of all,for their time and devotion to details and accuracy of information presented Thehelp of the Marcel Dekker editorial staff is greatly appreciated, with special thanks

to Rod Learmonth and Maria Allegra

Casimir C Akoh David B Min

Preface to the Second Edition

Preface to the First Edition

Contributors

Part I Chemistry and Properties

1 Nomenclature and Classification of Lipids

Sean Francis O’Keefe

2 Chemistry and Function of Phospholipids

Marilyn C Erickson

3 Lipid-Based Emulsions and Emulsifiers

D Julian McClements

4 The Chemistry of Waxes and Sterols

Edward J Parish, Terrence L Boos, and Shengrong Li

5 Extraction and Analysis of Lipids

Fereidoon Shahidi and P K J P D Wanasundara

6 Methods for trans Fatty Acid Analysis

Richard E McDonald and Magdi M Mossoba

7 Chemistry of Frying Oils

Kathleen Warner

Part II Processing

8 Recovery, Refining, Converting, and Stabilizing Edible

Fats and Oils

Lawrence A Johnson

9 Crystallization and Polymorphism of Fats

Patrick J Lawler and Paul S Dimick

10 Chemical Interesterification of Food Lipids: Theory and Practice

De´rick Rousseau and Alejandro G Marangoni

Part III Oxidation

11 Lipid Oxidation of Edible Oil

David B Min and Jeffrey M Boff

12 Lipid Oxidation of Muscle Foods

Marilyn C Erickson

13 Fatty Acid Oxidation in Plant Tissues

Hong Zhuang, M Margaret Barth, and David Hildebrand

14 Methods for Measuring Oxidative Rancidity in Fats and Oils

Fereidoon Shahidi and Udaya N Wanasundara

15 Antioxidants

David W Reische, Dorris A Lillard, and Ronald R Eitenmiller

16 Antioxidant Mechanisms

Eric A Decker

Part IV Nutrition

17 Fats and Oils in Human Health

David Kritchevsky

18 Unsaturated Fatty Acids

Steven M Watkins and J Bruce German

19 Dietary Fats, Eicosanoids, and the Immune System

David M Klurfeld

20 Dietary Fats and Coronary Heart Disease

Ronald P Mensink, Jogchum Plat, and Elisabeth H M Temme

21 Conjugated Linoleic Acids: Nutrition and Biology

Bruce A Watkins and Yong Li

22 Dietary Fats and Obesity

Dorothy B Hausman, Dana R Higbee, and

Barbara Mullen Grossman

23 Lipid-Based Synthetic Fat Substitutes

29 Biosynthesis of Fatty Acids and Storage Lipids in

Oil-Bearing Seed and Fruit Tissues of Plants

Kirk L Parkin

30 Genetic Engineering of Crops That Produce Vegetable Oil

Vic C Knauf and Anthony J Del Vecchio

Casimir C Akoh Department of Food Science and Technology, The University ofGeorgia, Athens, Georgia

M Margaret Barth Redi-Cut Foods, Inc., Franklin Park, Illinois

Jeffrey M Boff Department of Food Science and Technology, The Ohio StateUniversity, Columbus, Ohio

Terrence L Boos Department of Chemistry, Auburn University, Auburn, Alabama

Eric A Decker Department of Food Science, University of Massachusetts, herst, Massachusetts

Am-Anthony J Del Vecchio Monsanto Inc., Davis, California

Paul S Dimick Department of Food Science, The Pennsylvania State University,University Park, Pennsylvania

Ronald R Eitenmiller Department of Food Science and Technology, The versity of Georgia, Athens, Georgia

Uni-Marilyn C Erickson Center for Food Safety, Department of Food Science andTechnology, The University of Georgia, Griffin, Georgia

J Bruce German Department of Food Science and Technology, University ofCalifornia, Davis, California

Barbara Mullen Grossman Department of Foods and Nutrition, The University

of Georgia, Athens, Georgia

Frank D Gunstone Scottish Crop Research Institute, Dundee, Scotland

Dorothy B Hausman Department of Foods and Nutrition, The University of gia, Athens, Georgia

Geor-Dana R Higbee Department of Foods and Nutrition, The University of Georgia,Athens, Georgia

David Hildebrand Department of Agronomy, University of Kentucky, Lexington,Kentucky

Lawrence A Johnson Center for Crops Utilization Research, Department of FoodScience and Human Nutrition, Iowa State University, Ames, Iowa

David M Klurfeld Department of Nutrition and Food Science, Wayne State versity, Detroit, Michigan

Uni-Vic C Knauf Monsanto Inc., Davis, California

David Kritchevsky The Wistar Institute, Philadelphia, Pennsylvania

Patrick J Lawler McCormick and Company Inc., Hunt Valley, Maryland

Shengrong Li Department of Chemistry, Auburn University, Auburn, Alabama

Yong Li Center for Enhancing Foods to Protect Health, Purdue University, WestLafayette, Indiana

Dorris A Lillard Department of Food Science and Technology, The University ofGeorgia, Athens, Georgia

Alejandro G Marangoni Department of Food Science, University of Guelph,Guelph, Ontario, Canada

D Julian McClements Department of Food Science, University of Massachusetts,Amherst, Massachusetts

Richard E McDonald Division of Food Processing and Packaging, National ter for Food Safety and Technology, U.S Food and Drug Administration, Summit-Argo, Illinois

Cen-Ronald P Mensink Department of Human Biology, Maastricht University, tricht, The Netherlands

Maas-David B Min Department of Food Science and Technology, The Ohio State versity, Columbus, Ohio

Uni-Magdi M Mossoba Center for Food Safety and Applied Nutrition, U.S Food andDrug Administration, Washington, D.C

Kumar D Mukherjee Institute for Biochemistry and Technology of Lipids, H P.Kaufmann-Institute, Federal Center for Cereal, Potato, and Lipid Research, Munster,Germany

Sean Francis O’Keefe Department of Food Science and Technology, VirginiaPolytechnic Institute and State University, Blacksburg, Virginia

Edward J Parish Department of Chemistry, Auburn University, Auburn, Alabama

Kirk L Parkin Department of Food Science, University of Wisconsin – Madison,Madison, Wisconsin

Jogchum Plat Department of Human Biology, Maastricht University, Maastricht,The Netherlands

David W Reische The Dannon Company, Inc., Fort Worth, Texas

De´rick Rousseau School of Nutrition, Ryerson University, Toronto, Ontario,Canada

Fereidoon Shahidi Department of Biochemistry, Memorial University of foundland, St John’s, Newfoundland, Canada

New-Elisabeth H M Temme Department of Public Health, University of Leuven, ven, Belgium

Leu-P K J Leu-P D Wanasundara Department of Applied Microbiology and Food ence, University of Saskatchewan, Saskatoon, Saskatchewan, Canada

Sci-Udaya N Wanasundara Pilot Plant Corporation, Saskatoon, Saskatchewan,Canada

Kathleen Warner National Center for Agricultural Utilization Research, tural Research Service, U.S Department of Agriculture, Peoria, Illinois

Agricul-Bruce A Watkins Center for Enhancing Foods to Protect Health, Purdue sity, West Lafayette, Indiana

Univer-Steven M Watkins Lipomics Technologies, Inc., West Sacramento, California

John D Weete West Virginia University, Morgantown, West Virginia

Wendy M Willis Ives’ Veggie Cuisine, Vancouver, British Columbia, Canada

Hong Zhuang Redi-Cut Foods, Inc., Franklin Park, Illinois

Nomenclature and Classification

of Lipids

SEAN FRANCIS O’KEEFE

Virginia Polytechnic Institute and State University, Blacksburg, Virginia

No exact definition of lipids exists Christie [1] defines lipids as ‘‘a wide variety of

natural products including fatty acids and their derivatives, steroids, terpenes, enoids and bile acids, which have in common a ready solubility in organic solventssuch as diethyl ether, hexane, benzene, chloroform or methanol.’’

carot-Kates [2] says that lipids are ‘‘those substances which are (a) insoluble in water;(b) soluble in organic solvents such as chloroform, ether or benzene; (c) containlong-chain hydrocarbon groups in their molecules; and (d) are present in or derivedfrom living organisms.’’

Gurr and James [3] point out that the standard definition includes ‘‘a chemicallyheterogeneous group of substances, having in common the property of insolubility

in water, but solubility in non-polar solvents such as chloroform, hydrocarbons oralcohols.’’

Despite common usage, definitions based on solubility have obvious problems

Some compounds that are considered lipids, such as C1 – C4 very short chain fatty

acids (VSCFAs), are completely miscible with water and insoluble in nonpolar vents Some researchers have accepted this solubility definition strictly and excludeC1 – C3 fatty acids in a definition of lipids, keeping C4 (butyric acid) only because

sol-of its presence in dairy fats Additionally, some compounds that are considered lipids,

such as some trans fatty acids (those not derived from bacterial hydrogenation), are

not derived directly from living organisms The development of synthetic acaloricand reduced calorie lipids complicates the issue because they may fit into solubility-

based definitions but are not derived from living organisms, may be acaloric, andmay contain esters of VSCFAs.

The traditional definition of total fat of foods used by the U.S Food and Drug

Administration (FDA) has been ‘‘the sum of the components with lipid characteristicsthat are extracted by Association of Official Analytical Chemists (AOAC) methods

or by reliable and appropriate procedures.’’ The FDA has changed from a based definition to ‘‘total lipid fatty acids expressed as triglycerides’’ [4], with theintent to measure caloric fatty acids Solubility and size of fatty acids affect theircaloric values This is important for products that take advantage of this, such asBenefat/Salatrim, so these products would be examined on a case-by-case basis Foodproducts containing sucrose polyesters would require special methodology to cal-culate caloric fatty acids Foods containing vinegar (⬃4.5% acetic acid) present a

solubility-problem because they will be considered to have 4.5% fat unless the definition ismodified to exclude water-soluble fatty acids or the caloric weighting for acetic acid

is lowered [4]

Despite the problems with accepted definitions, a more precise working nition is difficult given the complexity and heterogeneity of lipids This chapterintroduces the main lipid structures and their nomenclature

Classification of lipid structures is possible based on physical properties at roomtemperature (oils are liquid and fats are solid), their polarity (polar and neutral lipids),their essentiality for humans (essential and nonessential fatty acids), or their structure(simple or complex) Neutral lipids include fatty acids, alcohols, glycerides, andsterols, while polar lipids include glycerophospholipids and glyceroglycolipids Theseparation into polarity classes is rather arbitrary, as some short chain fatty acids arevery polar A classification based on structure is, therefore, preferable

Based on structure, lipids can be classified as derived, simple, or complex The

derived lipids include fatty acids and alcohols, which are the building blocks for the simple and complex lipids Simple lipids, compose of fatty acids and alcohol com-

ponents, include acylglycerols, ether acylglycerols, sterols, and their esters and waxesters In general terms, simple lipids can be hydrolyzed to two different components,usually an alcohol and an acid Complex lipids include glycerophospholipids (phos-pholipids), glyceroglycolipids (glycolipids), and sphingolipids These structures yieldthree or more different compounds on hydrolysis

The fatty acids constitute the obvious starting point in lipid structures ever, a short review of standard nomenclature is appropriate Over the years, a largenumber of different nomenclature systems have been proposed [5] The resultingconfusion has led to a need for nomenclature standardization The International Un-ion of Pure and Applied Chemists (IUPAC) and International Union of Biochemistry(IUB) collaborative efforts have resulted in comprehensive nomenclature standards[6], and the nomenclature for lipids has been reported [7 – 9] Only the main aspects

How-of the standardized IUPAC nomenclature relating to lipid structures will be presented;greater detail is available elsewhere [7 – 9]

Standard rules for nomenclature must take into consideration the difficulty inmaintaining strict adherence to structure-based nomenclature and elimination of com-mon terminology [5] For example, the compound known as vitamin K1 can be

Table 1 Systematic Names of Hydrocarbons

1920212223242526272829304050607080

NonadecaneEicosaneHenicosaneDocosaneTricosaneTetracosanePentacosaneHexacosaneHeptacosaneOctacosaneNonacosaneTriacontaneTetracontanePentacontaneHexacontaneHeptcontaneOctacontane

described as 2-methyl-3-phytyl-1,4-naphthoquinone Vitamin K1and many other ial names have been included into standardized nomenclature to avoid confusionarising from long chemical names Standard nomenclature rules will be discussed inseparate sections relating to various lipid compounds

triv-Fatty acid terminology is complicated by the existence of several differentnomenclature systems The IUPAC nomenclature, common (trivial) names, and short-hand (␻) terminology will be discussed As a lipid class, the fatty acids are oftencalled free fatty acids (FFAs) or nonesterified fatty acids (NEFAs) IUPAC has rec-ommended that fatty acids as a class be called fatty acids and the terms FFA andNEFA eliminated [6]

In standard IUPAC terminology [6], the fatty acid is named after the parent carbon Table 1 lists common hydrocarbon names For example, an 18-carbon car-boxylic acid is called octadecanoic acid, from octadecane, the 18-carbon aliphatichydrocarbon The name octadecanecarboxylic acid may also be used, but it is morecumbersome and less common Table 2 summarizes the rules for hydrocarbonnomenclature

hydro-Double bonds are designated using the ⌬ configuration, which represents the

distance from the carboxyl carbon, naming the carboxyl carbon number 1 A doublebond between the 9th and 10th carbons from the carboxylic acid group is a⌬9 bond

The hydrocarbon name is changed to indicate the presence of the double bond An

18-carbon fatty acid with one double bond to an octadecenoic acid, one with two double bonds octadecadienoic acid, and so on The double-bond positions are des-

Table 2 IUPAC Rules for Hydrocarbon Nomenclature

1 Saturated unbranched acyclic hydrocarbons are named with a numerical prefix and thetermination ‘‘ane.’’ The first four in this series use trivial prefix names (methane,ethane, propane, and butane), whereas the rest use prefixes that represent the number ofcarbon atoms

2 Saturated branched acyclic hydrocarbons are named by prefixing the side chain

designation to the name of the longest chain present in the structure

3 The longest chain is numbered to give the lowest number possible to the side chains,irrespective of the substituents

4 If more than two side chains are present, they can be cited either in alphabetical order

or in order of increasing complexity

5 If two or more side chains are present in equivalent positions, the one assigned thelowest number is cited first in the name Order can be based on alphabetical order orcomplexity

6 Unsaturated unbranched acycylic hydrocarbons with one double bond have the ‘‘ane’’replaced with ‘‘ene.’’ If there is more than one double bond, the ‘‘ane’’ is replaced with

‘‘diene,’’ ‘‘triene,’’ ‘‘tetraene,’’ etc The chain is numbered to give the lowest possiblenumber to the double bond(s)

Source: Ref 6.

Figure 1 Examples of cis/trans nomenclature.

ignated with numbers before the fatty acid name (⌬octadecenoic acid or simply

9-octadecenoic acid) The⌬ is assumed and often not placed explicitly in structures

Double-bond geometry is designated with the cis – trans or E/Z nomenclature systems [6] The cis/trans terms are used to describe the positions of atoms or groups

connected to doubly bonded atoms They can also be used to indicate relative

po-sitions in ring structures Atoms/groups are cis or trans if they lie on same (cis) or opposite (trans) sides of a reference plane in the molecule Some examples are shown

in Figure 1 The prefixes cis and trans can be abbreviated as c and t in structural

formulas

The cis/trans configuration rules are not applicable to double bonds that are

terminal in a structure or to double bonds that join rings to chains For these

con-ditions, a sequence preference ordering must be conducted Since cis/trans

nomen-Table 3 A Summary of Sequence Priority Rules for E/Z Nomenclature

1 Higher atomic number precedes lower

2 For isotopes, higher atomic mass precedes lower

3 If the atoms attached to one of the double-bonded carbons are the same, proceedoutward concurrently until a point of difference is reached considering atomic massand atomic number

4 Double bonds are treated as if each bonded atom is duplicated For example:

clature is applicable only in some cases, a new nomenclature system was introduced

by the Chemical Abstracts Service and subsequently adopted by IUPAC (the E/Z

nomenclature) This system was developed as a more applicable system to describe

isomers by using sequence ordering rules, as is done using the R/S system (rules to

decide which ligand has priority) The sequence-rule-preferred atom/group attached

to one of a pair of doubly bonded carbon atoms is compared to the preferred atom/group of the other of the doubly bonded carbon atoms If the preferred

sequence-rule-atom/groups are on the same side of the reference plane, it is the Z configuration If they are on the opposite sides of the plane, it is the E configuration.Table 3 sum-

marizes some of the rules for sequence preference [10] Although cis and Z (or trans and E ) do not always refer to the same configurations, for most fatty acids E and trans are equivalent, as are Z and cis.

Common names have been introduced throughout the years and, for certain fattyacids, are a great deal more common than standard (IUPAC) terminology For ex-

ample, oleic acid is much more common than cis-9-octadecenoic acid Common

names for saturated and unsaturated fatty acids are illustrated in Tables 4 and 5

Many of the common names originate from the first identified botanical or zoologicalorigins for those fatty acids Myristic acid is found in seed oils from the Myristi-caceae family Mistakes have been memorialized into fatty acid common names;margaric acid (heptadecanoic acid) was once incorrectly thought to be present inmargarine Some of the common names can pose memorization difficulties, such asthe following combinations: caproic, caprylic, and capric; arachidic and arachidonic;linoleic, linolenic, ␥-linolenic, and dihomo-␥-linolenic Even more complicated is

the naming of EPA, or eicosapentaenoic acid, usually meant to refer to 11,c-14,c-17-eicosapentaenoic acid, a fatty acid found in fish oils However, a dif- ferent isomer c-2,c-5,c-8,c-11,c-14-eicosapentaenoic acid is also found in nature.

c-5,c-8,c-Both can be referred to as ‘‘eicosapentaenoic’’ acids using standard nomenclature

Nevertheless, in common nomenclature EPA refers to the c-5,c-8,c-11,c-14,c-17

iso-Table 4 Systematic, Common, and Shorthand Names of

Saturated Fatty Acids

—Lauric

—Myristic

—PalmiticMargaricStearic

—ArachidicBehenicLignocericCeroticMontanicMelissicLacceroic

Shorthand (␻) identifications of fatty acids are found in common usage The hand designation is the carbon number in the fatty acid chain followed by a colon,then the number of double bonds and the position of the double bond closest to themethyl side of the fatty acid molecule The methyl group is number 1 (the lastcharacter in the Greek alphabet is ␻, hence the end) In shorthand notation, the

short-unsaturated fatty acids are assumed to have cis bonding and, if the fatty acid is

polyunsaturated, double bonds are in the methylene interrupted positions (Fig 2).Inthis example, CH2(methylene) groups at ⌬8 and ⌬11 ‘‘interrupt’’ what would oth-

erwise be a conjugated bond system

Shorthand terminology cannot be used for fatty acids with trans or acetylene

bonds, for those with additional functional groups (branched, hydroxy, etc.), or fordouble-bond systems (ⱖ2 double bonds) that are not methylene interrupted (isolated

Table 5 Systematic, Common, and Shorthand Names of Unsaturated Fatty Acids

—

—Oleic

cis-Vaccenic (Asclepic)

VaccenicElaidicLinoleicRuminicb

Linolenic

␥-Linolenic

StearidonicGondoicGadoleicDihomo-␥-linolenic

Mead’sArachidonicEicosapentaenoic (EPA)Erucic

CetoleicDPADHANervonic (Selacholeic)

One of the conjugated linoleic acid (CLA) isomers.

Figure 2 IUPAC⌬ and common␻ numbering systems

or conjugated) Despite the limitations, shorthand terminology is very popular cause of its simplicity and because most of the fatty acids of nutritional importancecan be named Sometimes the ␻ is replaced by n- (18:2n-6 instead of 18:2␻6).Although there have been recommendations to eliminate ␻ and use n- exclusively [6], both n- and␻ are commonly used in the literature and are equivalent.

be-Shorthand designations for polyunsaturated fatty acids are sometimes reportedwithout the␻ term (18:3) However, this notation is ambiguous, since 18:3 couldrepresent 18:3␻1, 18:3␻3, 18:3␻6, or 18:3␻9; fatty acids, which are completelydifferent in their origins and nutritional significances Two or more fatty acids withthe same carbon and double-bond numbers are possible in many common oils There-fore, the␻terminology should always be used with the ␻ term specified

1 Saturated Fatty Acids

The saturated fatty acids begin with methanoic (formic) acid Methanoic, ethanoic,and propanoic acids are uncommon in natural fats and are often omitted from defi-nitions of lipids However, they are found nonesterified in many food products Omit-ting these fatty acids because they are water soluble would argue for also eliminatingbutyric acid, which would be difficult given its importance in dairy fats The simplestsolution is to accept the very short chain carboxylic acids as fatty acids while ac-knowledging the rarity in natural fats of these water-soluble compounds The sys-tematic, common, and shorthand designations of some saturated fatty acids are shown

inTable 4

2 Unsaturated Fatty Acids

By far the most common monounsaturated fatty acid is oleic acid (18:1␻9), althoughmore than 100 monounsaturated fatty acids have been identified in nature The mostcommon double-bond position for monoenes is ⌬9 However, certain families of

plants have been shown to accumulate what would be considered unusual fatty acid patterns For example, Eranthis seed oil contains⌬5 monoenes and non-methylene-

interrupted polyunsaturated fatty acids containing ⌬5 bonds [11] Erucic acid (22:

1␻9) is found at high levels (40 – 50%) in Cruciferae such as rapeseed and mustardseed Canola is a rapeseed oil that is low in erucic acid (<3% 22:1␻9)

Polyunsaturated fatty acids (PUFAs) are best described in terms of familiesbecause of the metabolism that allows interconversion within, but not among, fam-ilies of PUFA The essentiality of ␻6 fatty acids has been known since the late1920s Signs of ␻6 fatty acid deficiency include decreased growth, increased epi-dermal water loss, impaired wound healing, and impaired reproduction [12,13] Earlystudies did not provide clear evidence that ␻3 fatty acids are essential However,since the 1970s, evidence has accumulated illustrating the essentiality of the ␻3PUFA

Not all PUFAs are EFAs Plants are able to synthesize de novo and interconvert

␻3 and ␻6 fatty acid families via desaturases with specificity in the⌬12 and ⌬15

positions Animals have⌬5, ⌬6, and ⌬9 desaturase enzymes and are unable to

syn-thesized the ␻3 and ␻6 PUFAs de novo However, extensive elongation and

de-Figure 3 Pathway of 18:2␻6 metabolism to 20:4␻6.

saturation of EFA occurs (primarily in the liver) The elongation and desaturation of18:2␻6 is illustrated in Figure 3 The most common of the ␻6 fatty acids in ourdiets is 18:2␻6 Often considered the parent of the ␻6 family, 18:2␻6 is first de-saturated to 18:3␻6 The rate of this first desaturation is thought to be limiting inpremature infants, in the elderly, and under certain disease states Thus, a great deal

of interest has been placed in the few oils that contain 18:3␻6, ␥-linolenic acid(GLA) Relatively rich sources of GLA include black currant, evening primrose, andborage oils GLA is elongated to 20:3␻6, dihomo-␥-linolenic acid (DHGLA).DHGLA is the precursor molecule to the 1-series prostaglandins DHGLA is furtherdesaturated to 20:4␻6, precursor to the 2-series prostaglandins Further elongationand desaturation to 22:4␻6 and 22:5␻6 can occur, although the exact function ofthese fatty acids remains obscure

Figure 4illustrates analogous elongation and desaturation of 18:3␻3 The gation of 20:5␻3 to 22:5␻3 was thought for many years to be via ⌬4 desaturase

elon-The inexplicable difficulty in identifying and isolating the putative⌬4 desaturase led

to the conclusion that it did not exist, and the pathway from 20:5␻3 to 22:6␻3 waselucidated as a double elongation, desaturation, and␤-oxidation

One of the main functions of the EFAs is their conversion to metabolicallyactive prostaglandins and leukotrienes [14,15] Examples of some of the possibleconversions from 20:4␻6 are shown inFigures 5and6[15] The prostaglandins arecalled eicosanoids as a class and originate from the action of cyclooxygenase on 20:

4␻6 to produce PGG2 The standard nomenclature of prostaglandins allows usage

of the names presented in Figure 5 For a name such as PGG2, the PG representsprostaglandin, the next letter (G) refers to its structure (Fig 7), and the subscriptnumber refers to the number of double bonds in the molecule

The parent structure for most of the prostaglandins is prostanoic acid (Fig 7)[14] Thus, the prostaglandins can be named based on this parent structure As well,

Figure 4 Pathway of 18:3␻3 metabolism to 22:6␻3.

they can be named using standard nomenclature rules For example, prostaglandin

E2 (PGE2) is named (5Z,11␣,13E,15S )-11,15-dihydroxy-9-oxoprosta-5,13-dienoic

acid using the prostanoic acid template It can also be named using standard

no-menclature as

7-[3-hydroxy-2-(3-hydroxy-1-octenyl)-5-oxocyclopentyl]-cis-5-hep-tenoic acid

The leukotrienes are produced from 20:4␻6 vis 5-, 12-, or 15-lipoxygenases

to a wide range of metabolically active molecules The nomenclature is shown in

Figure 6

It is important to realize that there are 1-, 2-, and 3-series prostaglandins inating from 20:3␻6, 20:4␻6, and 20:5␻3, respectively The structures of the 1- and3-prostaglandins differ by the removal or addition of the appropriate double bonds.Leukotrienes of the 3-, 4-, and 5-series are formed via lipoxygenase activity on 20:

orig-3␻6, 20:4␻6, and 20:5␻3 A great deal of interest has been focused on changingproportions of the prostaglandins and leukotrienes of the various series by diet tomodulate various diseases

Figure 5 Prostaglandin metabolites of 20:4␻6.

Figure 6 Leucotriene metabolites of 20:4␻6.

Figure 7 Prostanoic acid and prostaglandin ring nomenclature.

3 Acetylenic Fatty Acids

A number of different fatty acids have been identified having triple bonds [16] The

nomenclature is similar to double bonds except that the -ane ending of the parent alkane is replaced with -ynoic acid, -diynoic acid, and so on.

Shorthand nomenclature uses a lowercase a to represent the acetylenic bond; 9c,12a-18:2 is an octadecynoic acid with a double bond in position 9 and the triple

bond in position 12.Figure 8shows the common names and standard nomenclaturefor some acetylenic fatty acids Since the ligands attached to triple-bonded carbonsare 180⬚ from one another (the structure through the bond is linear), the second

representation in Figure 8 is more accurate

The acetylenic fatty acids found in nature are usually 18-carbon molecules withunsaturation starting at⌬9 consisting of conjugated double–triple bonds [9,16] Acet-

ylenic fatty acids are rare

4 transFatty Acids

trans Fatty acids include any unsaturated fatty acid that contains double-bond ometry in the E (trans) configuration Nomenclature differs only from normal cis

ge-fatty acids in the configuration of the double bonds

The three main origins of trans fatty acids in our diet are bacteria, deodorized oils, and partially hydrogenated oils The preponderance of trans fatty acids in our

diets are derived from the hydrogenation process

Hydrogenation is used to stabilize and improve oxidative stability of oils and

to create plastic fats from oils [17] The isomers that are formed during hydrogenationdepend on the nature and amount of catalyst, the extent of hydrogenation, and otherfactors The identification of the exact composition of a partially hydrogenated oil

is extremely complicated and time consuming The partial hydrogenation processproduces a mixture of positional and geometrical isomers Identification of the fatty

Figure 8 Some acetylenic acid structures and nomenclature.

acid isomers in a hydrogenated menhaden oil has been described [18] The 20:1

isomers originally present in the unhydrogenated oil were predominantly cis-⌬11

(73% of total 20:1) and cis-⌬13 (15% of total 20:1) After hydrogenation from an

initial iodine value of 159 to 96.5, the 20:1 isomers were distributed broadly acrossthe molecules from⌬3 to ⌬17 (Fig.9) The major trans isomers were⌬11 and ⌬13,

while the main cis isomers were⌬6, ⌬9, and ⌬11 Similar broad ranges of isomers

are produced in hydrogenated vegetable oils [17]

Geometrical isomers of essential fatty acids linoleic and linolenic were firstreported in deodorized rapeseed oils [19] The geometrical isomers that result fromdeodorization are found in vegetable oils and products made from vegetable oils

(infant formulas) and include 9c,12t-18:2, 9t,12c-18:2, and 9t,12t-18:2, as well as 9c,12c,15t-18:3, 9t,12c,15c-18:3, 9c,12t,15c-18:3, and 9t,12c,15t-18:3 [19 – 22] These trans-EFA isomers have been shown to have altered biological effects and are

incorporated into nervous tissue membranes [23,24], although the importance ofthese findings has not been elucidated

Figure 9 Eicosenoid isomers in partially hydrogenated menhaden oil (From Ref 18.)

trans Fatty acids are formed by some bacteria primarily under anaerobic ditions [25] It is believed that the formation of trans fatty acids in bacterial cell

con-membranes is an adaptation response to decrease membrane fluidity, perhaps as areaction to elevated temperature or stress from solvents or other lipophilic com-pounds that affect membrane fluidity (4-chlorophenol)

Not all bacteria produce appreciable levels of trans fatty acids The producing bacteria are predominantly gram negative and produce trans fatty acids under anaerobic conditions The predominant formation of trans is via double-bond

trans-migration and isomerization, although some bacteria appear to be capable of erization without bond migration The action of bacteria in the anaerobic rumen

isom-results in biohydrogenation of fatty acids and isom-results in trans fatty acid formation in dairy fats (2 – 6% of total fatty acids) The double bond positions of the trans acids

in dairy fats are predominantly in the ⌬11 position, with smaller amounts in ⌬9,

⌬10, ⌬13, and ⌬14 positions [26]

5 Branched Fatty Acids

A large number of branched fatty acids have been identified [16] The fatty acidscan be named according to rules for branching in hydrocarbons (Table 2) Beside

standard nomenclature, several common terms have been retained, including iso-,

with a methyl branch on the penultimate (␻2) carbon, and anteiso, with a methyl

branch on the antepenultimate (␻3) carbon The iso and anteiso fatty acids arethought to originate from a modification of the normal de novo biosynthesis, withacetate replaced by 2-methyl propanoate or 2-methylbutanoate, respectively [16].Other branched fatty acids are derived from isoprenoid biosynthesis including pris-tanic acid (2,6,10,14-tetramethylpentadecanoic acid) and phytanic acid (3,7,11,15-tetramethylhexadecanoic acid)

6 Cyclic Fatty Acids

Many fatty acids that exist in nature contain cyclic carbon rings [27] Ring structurescontain either three (cyclopropyl and cyclopropenyl), five (cyclopentenyl), or six(cyclohexenyl) carbon atoms and may be saturated or unsaturated As well, cyclicfatty acid structures resulting from heating the vegetable oils have been identified[27 – 29]

In nomenclature of cyclic fatty acids, the parent fatty acid is the chain fromthe carboxyl group to the ring structure The ring structure and additional ligandsare considered a substituent of the parent fatty acid An example is given inFigure

10.The parent in this example is nonanoic acid (not pentadecanoic acid, which wouldresult if the chain were extended through the ring structure) The substituted group

is a cyclopentyl group with a 2-butyl ligand (2-butylcyclopentyl) Thus the correctstandard nomenclature is 9-(2-butylcyclopentyl)nonanoic acid The 2 is sometimesexpressed as 2⬘ to indicate that the numbering is for the ring, and not the parent

chain The C-1 and C-2 carbons of the cyclopentyl ring are chiral, and two possibleconfigurations are possible Both the carboxyl and longest hydrocarbon substituentscan be on the same side of the ring, or they can be on opposite sides These are

referred to as cis and trans, respectively.

The cyclopropene and cyclopropane fatty acids can be named by means of thestandard nomenclature noted in the example above They are also commonly namedusing the parent structure that carries through the ring structure In the example in

Figure 11, the fatty acid (commonly named lactobacillic acid or phycomonic acid)

is named 10-(2-hexylcyclopropyl)decanonic acid in standard nomenclature An older

naming system would refer to this fatty acid as cis-11,12-methyleneoctadecanoic acid, where cis designates the configuration of the ring structure If the fatty acid is

unsaturated, the term methylene is retained but the double bond position is noted in

the parent fatty acid structure (cis-11,12-methylene-cis-octadec-9-enoic acid).

Figure 12presents some examples of natural cyclic fatty acids and their trivialand standard nomenclature

7 Hydroxy and Epoxy Fatty Acids

Saturated and unsaturated fatty acids containing hydroxy and epoxy functionalgroups have been identified [1,16] Hydroxy fatty acids are named by means of theparent fatty acid and the hydroxy group(s) numbered with its ⌬ location For ex-

ample, the fatty acid with the trivial name ricinoleic (Fig 13) is named

R-12-hy-Figure 10 Nomenclature of cyclic fatty acids.

Figure 11 Nomenclature for a cyclopropenoid fatty acid

droxy-cis-9-octadecenoic acid Ricinoleic acid is found in the seeds of Ricinus

spe-cies and accounts for about 90% of the fatty acids in castor bean oil

Because the hydroxy group is chiral, stereoisomers are possible The R/S system

is used to identify the exact structure of the fatty acid.Table 6reviews the rules for

R/S nomenclature The R/S system can be used instead of the ␣/␤ and cis/trans

nomenclature systems A fatty acid with a hydroxy substituent in the⌬2 position is

commonly called an␣-hydroxy acid; fatty acids with hydroxy substituents in the⌬3

and⌬4 positions are called␤-hydroxy acids and␥-hydroxy acids, respectively Some

Figure 12 Cyclic fatty acid structures and nomenclature.

common hydroxy acids are shown inFigure 13.Cutins, which are found in the outerlayer of fruit skins, are composed of hydroxy acid polymers, which also may containepoxy groups [16]

Epoxy acids, found in some seed oils, are formed on prolonged storage ofseeds [16] They are named similarly to cyclopropane fatty acids, with the parentacid considered to have a substituted oxirane substituent An example of epoxy fattyacids and their nomenclature is shown inFigure 14.The fatty acid with the common

name vernolic acid is named (using standard nomenclature)

11-(3-pentyloxyranyl)-9-undecenoic acid In older nomenclature, where the carbon chain is carried throughthe oxirane ring, vernolic acid would be called 12,13-epoxyoleic acid or 12-13-epoxy-9-octadecenoic acid The configuration of the oxirane ring substituents can be

named in the cis/trans, E/Z, or R/S configuration systems.

Figure 13 Hydroxy fatty acid structures and nomenclature.

Table 6 A Summary of Rules for R/S Nomenclature

1 The sequence priority rules (Table 3)are used to prioritize the ligands attached to the

chiral center (a > b > c > d ).

2 The molecule is viewed with the d substituent facing away from the viewer.

3 The remaining three ligands (a, b, c) will be oriented with the order a-b-c in a

clockwise or counterclockwise direction

4 Clockwise describes the R (rectus, right) conformation, and counterclockwise describes the S (sinister, left) conformation.

Source: Ref 10.

8 Furanoid Fatty Acids

Some fatty acids contain an unsaturated oxolane heterocyclic group There are morecommonly called furanoid fatty acids because a furan structure (diunsaturated oxo-

lane) is present in the molecule Furanoid fatty acids have been identified in carpus seed oils They have also been identified in plants, algae, and bacteria and

Exo-are a major component in triacylglycerols from latex rubber [1,16] They Exo-are portant in marine oils and may total several percentage points of the total fatty acids

im-or mim-ore in liver and testes [1,30]

Furanoid fatty acids have a general structure shown in Figure 15.A commonnomenclature describing the furanoid fatty acids (as F1, F2, etc.) is used [30] Thenaming of the fatty acids in this nomenclature is arbitrary and originated from elutionorder in gas chromatography A shorthand notation that is more descriptive gives themethyl substitution followed by F, and then the carbon lengths of the carboxyl and

Figure 14 Epoxy fatty acid structures and nomenclature.

terminal chains in parentheses: MeF(9,5) Standard nomenclature follows the sameprinciples outlined in Sec IV.A.6 The parent fatty acid chain extends only to thefuran structure, which is named as a ligand attached to the parent molecule Forexample, the fatty acid named F5 inFigure 15is named 11-(3,4-dimethyl-5-pentyl-2-furyl)undecanoic acid Shorthand notation for this fatty acid would be F5 orMeF(11,5) Numbering for the furan ring starts at the oxygen and proceeds clock-wise

Acylglycerols are the predominant constituent in oils and fats of commercial tance Glycerol can be esterified with one, two, or three fatty acids, and the individualfatty acids can be located on different carbons of glycerol The terms monoacylglyc-erol, diacylglycerol, and triacylglycerol are preferred for these compounds over theolder and confusing names mono-, di-, and triglycerides [6,7]

impor-Fatty acids can be esterified on the primary or secondary hydroxyl groups ofglycerol Although glycerol itself has no chiral center, it becomes chiral if differentfatty acids are esterified to the primary hydroxyls or if one of the primary hydroxyls

Figure 15 Furanoid fatty acid structure and shorthand nomenclature.

Figure 16 Chiral carbons in acylglycerols

is esterified Thus, terminology must differentiate between the two possible urations (Fig 16) The most common convention to differentiate these stereoisomers

config-is the sn convention of Hirshmann (see Ref 31) In the numbering that describes the hydroxyl groups on the glycerol molecule in Fisher projection, sn1, sn2, and sn3

designations are used for the top (C1), middle (C2), and bottom (C3) OH groups(Fig 17).The sn term indicates stereospecific numbering [1].