THE OILY PRESS

Written by Edwin N. Frankel. Published 2005.
ISBN-13: 978-0-9531949-8-8 (ISBN-10: 0-9531949-8-1).

On this page you can read the Author's Preface and reviews of this book written in the scientific literature. For more details of the chapters and to buy the book, please see the main Lipid Oxidation web page.

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Preface | Reviews

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After more than six decades, the field of lipid oxidation continues to be very active and has expanded into broad areas of food science and technology, free radical chemistry, nutrition, biochemical and biomedical interests. Although there have been significant advances in this challenging field, many important problems remain unsolved. This second edition follows the example of the first edition in offering a summary of the many unsolved problems that need further research. New developments in lipid oxidation research and technology and new dietary guidelines have resulted in difficult and challenging problems of control with nutritional and biological implications. Various processed foods have been reformulated with oils rich in long-chain polyunsaturated fatty acids because of their recognized nutritional benefits, but lipid oxidation has seriously limited their utilization. Because partial hydrogenation produces trans fatty acids now considered nutritionally harmful, much effort has been made in developing alternate methods for the preparation of oxidatively stable oils. To avoid hydrogenation, special plant breeding has been used to develop several high-oleic and low-linolenic acid oils, and has improved their oxidative stability and nutritional value. In the last decade, enormous worldwide attention has been given to natural phenolic antioxidants, including flavonoids and various phytochemicals found in many fruits and vegetables and beverages. Although some new knowledge has been acquired about the absorption of these antioxidants in humans, their in vivo activity is still not well understood. The development of reliable biomarkers that can be better related to degenerative disease presents one of the most difficult challenges in this field.

The second edition includes important developments in the characterization by capillary gas chromatography-olfactometry of aroma and flavor impact of volatile decomposition products from polyunsaturated fatty acids and esters. Discussions are included on various mechanisms for the formation from linoleate of 4-hydroxy-2-nonenal, which has received much attention in the biochemical literature because of its cytotoxic properties, and its occurrence in oxidized LDL and in vegetable oils heated at frying temperatures. Some of the volatiles produced from fish oils are responsible for major problems in their utilization, because they produce very powerful ‘fishy’ odors and flavors perceptible at extremely low levels of oxidation.

This second edition offers new material on methods of sensory detection (nasal: through the nose) or (retronasal: through the mouth and back of the oral cavity), different flavor release phenomena in the headspace versus the mouth, and matrix in flavor release from oils compared to emulsion systems. Advanced gas chromatographic methods are included, such as solid phase microextraction for the volatile analyses in foods and vegetable oils, gas chromatography-olfactometry, and aroma extraction dilution analyses.

A number of advanced instrumental methods have emerged for analysing mixtures of complex products of lipid oxidation. The second edition has a new chapter that examines these research methods, and how they provide new information on the stereochemistry of hydroperoxides from oleate and linoleate, polyunsaturated phospholipids and triacylglycerols, oils extracted from fried foods and their decomposition products (Chapter 6). The formation of the nonconjugated bis-allylic 11-hydroperoxide intermediate from linoleate was established unambiguously for the first time using alpha-tocopherol acting as hydrogen donor. Conjugated linoleic acid (CLA) has been claimed to be bioactive and to have beneficial nutritional effects. The mechanism of CLA autoxidation is discussed, together with the complex isomeric mixtures of endoperoxides and thromboxanes (prostaglandin-like compounds) produced from arachidonic acid, phospholipids and cholesterol. Many of these new research methods are useful for the direct mass spectral identification of intact labile polyunsaturated hydroperoxides and other oxidation products without the necessity of derivatization, but their quantitation has not been achieved without the availability of authentic standards. This new chapter includes important advances in the development of very sensitive methods for the analysis of volatile flavor compounds, linking their relative release to sensory perception in foods.

A new section in the chapter on Stability Methods (Chapter 7) covers electron spin resonance spectrometry and spin-trapping for measuring the tendency of foods to form radicals during early stages of oxidation, and a discussion on its merits and pitfalls. The chapter on Control Methods (Chapter 8) has new material on physical refining, and soft column deodorization, more structural details of oxidative deterioration compounds formed during refining of different vegetable oils obtained by high performance size exclusion chromatography, and trans isomers of polyunsaturated fatty acids, oxidized sterols and cyclic monomers. Novel processing technology includes special membranes for the separation of impurities in crude oil extracts and for refining oils, cold pressing and hot expeller-pressing oils that have attracted interest for environmental reasons as they avoid the use of chemical solvents in the extraction of seeds. There is also information on high-oleic and midoleic canola and sunflower oils now commercially available as substitutes for partially hydrogenated oils, and an expanded section on packaging.

Chapter 9 on Antioxidants presents more detailed information on metal vii PREFACE inactivators including ethylenediamine tetraacetic acid (EDTA), new material on lactoferrin, an expanded discussion of synergism, problems with methodology to evaluate antioxidants in multi-phase systems, and more on the mechanism of rosemary antioxidants at elevated temperatures. A new section on the evaluation of natural antioxidants in plants was motivated by the explosion of published research on the antioxidant properties of phytochemicals, including new tables comparing free radical trapping methods and lipid oxidation methods for the evaluation of natural antioxidants.

Chapter 10 on Multiphase Systems includes the effects of food proteins that can inhibit oxidation of oil-in-water emulsions by several mechanisms and how pH affects their activity. The metal complexing activity of bovine lactoferrin in inhibiting oxidation in emulsions and liposome systems is compared with that of EDTA. Antioxidants are greatly influenced by the colloidal properties of lipid systems. Interactions of emulsifiers with antioxidants, hydrogen bondings, interphase transport and surface access are important parameters determining their activity in lipid-containing systems differing in their colloidal characteristics. Proteins have strong binding properties with flavonoid antioxidants in foods and biological systems, and generally increase the oxidative stability of liposomes. The partitioning behavior of different phenolic antioxidants in emulsions is greatly affected by interactions between oils and emulsifiers that determine their solubilization and their activity in inhibiting lipid oxidation.

There is an expanded discussion in Chapter 11 on Foods on the interactions between metmyoglobin, deoxyhemoglobin and deoxymyoglobin and their mechanism of initiating lipid oxidation in meat and fish. The antioxidant properties produced by the Browning products are discussed, together with the methodology problems involved with model systems generally used in the literature. New information is added on the structure of volatile compounds and their impact on the flavor of cooked meat. The effect of thermal processing of foods and beverages (tomato juice, wine, coffee and tea) are subject to complex interactions between lipid oxidation and reducing browning reaction products, proteins, phospholipids, and phenolic antioxidants that are influenced by multifactorial changes during processing and storage. The methodological problems of using simplistic model systems and unidimensional methods to evaluate antioxidants in foods are discussed here and throughout the second edition. New material addresses the problems of iron supplementation in infant formulas and the control of oxidation by lactoferrin and EDTA, and the relative oxidative stability of long chain polyunsaturated fish and algae oils and emulsions, including the antioxidant activity of roasted foods.

Chapter 12 on Frying contains new material on complex interaction compounds produced by non-enzymatic browning reactions between thermally oxidized lipids and amines, amino acids and proteins. This chapter also discusses the new varieties of vegetable oils containing higher levels of oleate and lower levels of linolenate being used for frying, because partial hydrogenation produces trans fatty acids, which are now considered nutritionally undesirable. New tables include aroma extraction dilution analysis of volatiles from French fries; analyses of total polar compounds and tocopherol in frying oils versus fried potatoes; fatty acid composition of new varieties of soybean, sunflower, and canola oils suitable for frying without partial hydrogenation.

The controversial subject of whether or not natural antioxidants can account for the strong epidemiological evidence that fruits and vegetable consumption is associated with reduced coronary heart disease, cancer and other diseases is covered in Chapter 13 on Biological Systems. The absorption of antioxidants in human blood as metabolites, their molecular mechanisms of protection in vivo, and of disease intervention are under intensive investigation around the world. Important developments are included in discussions of new pathways of LDL oxidation, the metabolic interactions between LDL and HDL on cholesterol transport mechanisms, new evidence on the role of antioxidant enzymes in HDL, which can break down oxidized lipids and neutralize their proinflammatory effects, and the close link between the oxidation and inflammation hypotheses of cardiovascular disease. The new evidence of core aldehyde formation in oxidized LDL is examined, together with the bioactivity of oxidized phospholipids on the surface of LDL particles that are recognized by macrophages. More information is discussed on the cyclic oxidation products of arachidonate described as isoprostanes in biological samples as an index of oxidative status.

Important nutritional topics have been added to the second edition, including the significant role of docosahexaenoic acid (DHA) in neural membrane phospholipid metabolism, immune responses and the aging process. The difference in antioxidant testing results between animal and human studies and between in vitro and in vivo effects is discussed in terms of different end-points of oxidation. This chapter concludes with seven important unsettled nutritional questions that need future research. With so many unanswered questions, the conclusion is drawn that it would be imprudent to make dietary recommendations to the public before the mechanisms of polyunsaturated lipid nutrition, in vivo activity of antioxidants, and in vivo lipid peroxidation are better understood.

The author gratefully acknowledges the invaluable editorial work of Bill Christie and Frances Daniel.

Edwin N. Frankel

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Anon, in Oils & Fats International, May 2006, pp.44–45.

"After more than six decades, lipid oxidation continues to be a very active field of study...It is timely, therefore, that The Oily Press has now published - as Volume 18 in its Lipid Library series - the second edition of this very useful book.... Fully updated with new knowledge gleaned over the intervening years, the second edition includes important new information on analytical developments, the reformulation of food products and other aspects of this vast and complicated subject, such as how nutritional benefits of lipid products can be limited by the phenomenon of lipid oxidation."

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Dr Neil MacFarlane, DSM Nutritional Products, Heanor, UK, writing in Lipid Technology, 2005, Vol.17, pp.165–166.

The first edition of this book, published in 1998, became an industry standard text and an essential reference for anyone working in the field of lipid oxidation. Now, some 7 years later, a much expanded second edition of this book appears. During this time considerable interest has developed in the challenge of incorporating long-chain polyunsaturated fatty acids into foods, in reformulating oils and fat products to low levels of trans acids, the emergence of high-oleic and low-linolenic acid food oils and natural phenolic antioxidants.

The second edition maintains the structure of the original book but each chapter is expanded considerably to take account of new developments and a new chapter on research methods for lipid oxidation is added. The book highlights that the human nose is extremely sensitive to secondary oxidation products, with examples given for many oils and fats. Traditional wet chemical methods are too insensitive for analysis of these sensory compounds, so the book describes well the many methods now available for volatile sensory analysis. Below are some new additions to the second addition.

Chapter 1, on free radical oxidation, is unchanged but Chapter 2 on hydroperoxide formation adds new material on cholesterol oxidation. Hydroperoxide decomposition includes more details on oleate, linoleate and linolenate decomposition products. ‘Methods to determine extent of oxidation’ is much expanded over the first edition with reference to advanced GC methods for detection of volatiles. This is amplified considerably with a completely new chapter on ‘Research methods for lipid oxidation’ and covers new advances in both LC-MS and GC-MS and front-end sampling. At the same time, older LC and counter-current methods are presented. It is fascinating to see how well a counter-current experiment conducted some 45 years ago and taking several weeks to execute stacks up against the newest analytical toys.

The chapter on ‘Stability methods’ now has a new section which includes electron spin resonance, and ‘Control of oxidation’ includes expanded discussion of processing, blending with monounsaturated oils, and packaging methods. A number of free radical trapping methods are shown and their merits discussed. ‘Oxidation in multiphase systems’ has become more important during the last seven years with more emphasis being placed on the polarity paradox and how to select the most suitable antioxidant system for the food. Extensive examples are given of many multiphase systems and how different antioxidants partition between the phases.

The chapter on ‘Foods’ looks in greater detail at how food components interact and either stimulate or protect against oxidation, and a much-expanded section has been included for fish, fish oils and foods enriched with fish oil to take account of the many recent developments in this food sector. ‘Frying fats’ now looks at the uptake of fats by fried foods and more recent data on the health effects of different fractions of heated frying fat.

‘Biological systems’ now includes material on the pathways and products of low-density lipoprotein (LDL) oxidation and the role of high-density lipoprotein (HDL) in protection against atherosclerosis.

The amount of work put into this second edition by the author is impressive and the publisher is to be congratulated on the print quality. Tables and figures from the original edition have been replaced, when necessary, with more recent and topical information. As usual, Dr Frankel is provocative in his definition of unsettled questions and future research, and his views on the limited value of some current methodologies of lipid oxidation (e.g. thiobarbituric acid value and `Rancimat') are well aired.

Perhaps the most important aspect of this book is the sheer breadth and expertise of coverage of lipid oxidation. There is something here for everyone working in the lipid field. While departmental libraries should contain this volume, it should also be available in the lab and on the desk for immediate reference.

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Dr William E. Artz, University of Illinois Urbana-Champaign, Illinois, USA writing in INFORM, 1999, Vol.10, No.5, p.527.

The emphasis throughout the text is on the chemistry of lipid oxidation. The text opens with a very brief introduction to lipid chemistry and structure. This is followed by an extensive and well-written discussion of the reactions involved in autoxidation and photooxidation, including the differences among various substrates, the kinetics involved, the effects of complicating factors, such as transition metals, and the volatile and nonvolatile oxidation products produced from a variety of fatty acid sources.

There is a very informative chapter on free radical chemistry and the mechanism of oxidation, followed by chapters on hydroperoxide formation and decomposition. E.N. Frankel published much of the work summarized in the text, and his comprehensive knowledge of the discipline is apparent in his concise and accurate description of the chemistry involved in those reactions. The next chapter focuses on the numerous methods used to monitor lipid oxidation in foods and biological systems. The weaknesses and strengths of several methods are presented.

The next two chapters are on the control of oxidation. A brief discussion of the various methodologies available, from hydrogenation to the appropriate packaging, is presented. The second chapter on that topic covers antioxidants, including their mechanism of action, the effect antioxidant structure has on that mechanism, the kinetics involved, and the differences between synthetic and natural antioxidants, ending with the use of antioxidant enzymes.

Lipid oxidation in a variety of systems is discussed in depth and there are chapters on multiphase systems, food products, and frying fats. The chapter on food products includes raw materials and processed foods, including milk, meat, fish, and cereals. There is a lengthy chapter at the end of the text on biological systems that includes discussion of coronary heart disease.

The text makes good use of figures, particularly to illustrate many of the key reactions involved in lipid oxidation. It is relatively easy to read, if one assumes the reader is well versed in lipid chemistry. While some chapters have relatively few references, many chapters have a substantial list of references, but certainly the key ones are included for each topic. Anyone seriously interested in the chemistry of lipid oxidation would be well advised to obtain the text. In my opinion, it is must reading for graduate students and others beginning work in this area. For food scientists combating the effects of excessive lipid oxidation, as well as academicians and research scientists interested in this area, it provides an accurate and excellent synopsis of much of the research done over the past 20 years or so. It should prove to be a very useful addition to the reference text library of anyone working in this area.

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Dr Youlin G.L. Yiong, University of Kentucky, Kentucky, USA, writing in J. Food Biochem., 1999, Vol.23, No.6, pp.651-652.

Oxidation of lipids is a complex process which involves the reactions of unsaturated hydrocarbons with free radicals, active oxygen species, and various other oxidizing compounds. Oxidation occurs ubiquitously in systems that contain lipids, and is a leading cause for quality deterioration in foods during processing and storage. Because of its importance to food quality, lipid oxidation has been subjected to extensive research for many decades, and has been a major topic of discussion in many research journals and magazines as well as books. However, none of the previous books or reviews has as thoroughly dealt with the subject of lipid oxidation as the book, Lipid Oxidation.

This book provides a comprehensive review of various fundamental and many applied aspects of lipid oxidation. It is not simply a summary of past and current literature of the topic, it gets into in-depth discussion, in a highly organized and systematic way, of the mechanism of lipid oxidation. A large portion of the discussion is convincingly propped by the firsthand results generated in the authors's own research laboratory. Hence, the book lends itself a unique, insightful perspective on the complex process of lipid oxidation. The aim of the book is to integrate a large body of interdisciplinary information on the oxidation of unsaturated lipids in order to develop the basic principles involved in the methodology and mechanisms of free radical oxidation. This is achieved by developing 12 chapters, beginning with the basics of free radicals and hydroperoxide chemistry, progressing into topics related to the control of lipid oxidation, such as methodology and use of antioxidants, and ending with discussion on oxidation in exemplary food systems.

There is an introductory preview, preceding Chapter 1, that provides background information about lipids, e.g., classification, nomenclature, general reactions of unsaturated fatty acids, and impact of lipid oxidation on human health. Chapter l reviews the classical mechanism of lipid oxidation via free radical chain reactions. Additionally, it describes the kinetics of hydroperoxide formation, the relative rates of different unsaturated fatty acids, and metal catalysis. Chapter 2 presents specific examples of detailed mechanisms for autoxidation of four major unsaturated fatty acids, i.e. oleate, linoleate, linolenate, and arachidonate, as well as a brief summary of oxidation of other polyunsaturated fatty acids and their acylglycerols. Chapter 3 is devoted to photooxidation of unsaturated fats, such as singlet oxygen-dependent formation of hydroperoxides. This is followed by Chapter 4, which describes detailed accounts for the decomposition of hydroperoxides and the various resulting degradation products. Chapter 5 evaluates some of the most commonly used methods for measuring lipid oxidation, including sensory panel analysis, tests for peroxides, conjugated dienes, carbonyls, and TBARS, along with chromatographic and several less used methods.

In Chapter 6, techniques for assessing the oxidative stability of unsaturated lipids are introduced. This leads to Chapter 7, which describes the methods to control oxidation, i.e., metal chelation, processing, hydrogenation, genetic modification, and packaging, and to Chapter 8, which describes the various synthetic and natural antioxidants and their mechanisms. Chapter 9 deals with oxidation in multiphase systems, notably emulsions. Chapter 10 addresses oxidation and resulting quality changes in foods, both raw and processed, including milk, meat, poultry, fish, and cereal products. Chapter 11 describes the complex chemistry of frying fats, and Chapter 12, the last chapter of the book, presents contemporary views on the impact of oxidized lipids on human nutrition and health with emphasis on the relationship between oxidation of plasma lipoproteins and coronary heart disease.

The book is conspicuously well conceived, arranged, and written. Clarity is a particular strength of the book and each paragraph contains important, some essential, messages. The numerous reactions and equations are drawn with highly legible lines and fonts. The book is also well meshed with graphs and figures. Furthermore. the subject index seems to be thoroughly prepared making the different subjects and topics easy to locate in the text. The only inadequacy of the book is that the titles of some of the chapters are not descriptive enough and sometimes ambiguous. Overall, however, this is an outstanding book, perhaps the best of the kind, which address lipid chemistry in foods. The author's writing style and the inclusiveness of the various topics make the book readily adaptable as a textbook for graduate level lipid oxidation courses. My graduate students who have had the opportunity to read this book are also of a high opinion on the book especially with regard to the lecture-style writing. No doubt, industrial scientists will equally find this book an invaluable reference source.

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Dr Michael H. Gordon, University of Reading, Reading, UK, writing in Lipid Technology, 1999, Vol.11, No.2, p.47

Ed Frankel has been at the forefront of developments in lipid oxidation for over 40 years. He has contributed to understanding of mechanisms, and analytical techniques for assessment of oxidation in edible oils and fats, and in recent years he has been involved in fruitful collaborations with biochemists and physiologists in applying methods to the assessment of oxidative deterioration and resistance to oxidation in low-density lipoproteins. He is thus uniquely placed to write this book which describes many aspects concerned with lipid oxidation.

The book comprises 12 chapters covering mechanisms and kinetics of lipid oxidation and hydroperoxide formation; photoxidation of unsaturated fats; hydroperoxide decomposition; methods to determine the extent of oxidation and the oxidative stability of oils; control of oxidation and antioxidants, and a discussion of oxidation in multiphase systems, foods, frying fats and biological systems.

Despite the vast amount of literature on lipid oxidation, some of the work is apparently contradictory due to variations in substrate, medium, experimental conditions or methods of monitoring oxidation. Frankel makes a valuable contribution to the literature by clearly describing many concepts that help the reader to understand the processes that contribute to many of the differences that are observed.

He has strong views about some of the procedures used for assessment of lipid oxidation or antioxidant activity including the limitations of accelerated test methods at elevated temperatures and the use of fatty acid micelles and azo initiators, and he argues these points forcibly. In many cases his arguments are convincing, although I feel that accelerating oxidation by the use of azo initiators does provide information relevant to the properties of antioxidants in foods. However, uncritical extrapolation of data from one system to another can certainly lead to erroneous conclusions. Although many references are given, some statements are also made without supporting references, and this can be frustrating at times.

A few errors are present in the book such as the statement on page 53 that cold-pressed virgin olive oil and unprocessed vegetable oils obtain their colour from carotenoids.

Despite these qualifications, this is an excellent book, and it will be essential reading for all scientists involved in research into lipid oxidation or antioxidants, or development of new food systems in which lipid oxidation may occur.

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