THE OILY PRESS

Written by Edwin N. Frankel, University of California, USA. Published 2007, ISBN-13: 978-0-9552512-0-7 (ISBN-10: 9552512-0-6).

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 Antioxidants in Food and Biology: Facts and Fiction web page.

Go to main Antioxidants in Food and Biology: Facts and Fiction web page

---

Preface | Reviews

The field of antioxidants has expanded over the past six decades into a wide variety of multidisciplinary areas that affect foods and health. This book conveys the complexity of antioxidant chemistry by providing an appreciation of the various phenomena that affect oxidation and its inhibition in foods and biological systems. By emphasizing mechanistic aspects of antioxidants and lipid oxidation, this book also attempts to sort out facts from fiction, by identifying the many problem areas requiring further research to improve our understanding of complex antioxidant effects and to stimulate better designed methodology and dietary studies for the future.

The introductory Chapter 1 provides an overview of past, present and future aspects to initiate readers into the broad interdisciplinary fields of antioxidants in foods and biology. There is a vast basic literature on how antioxidant structures affect activity in solutions, but our knowledge on how these structural effects apply to multiphase foods and biological systems is limited. Knowledge on the sites of antioxidant action in foods and biological systems is necessary for a better understanding of their effects on their stability and susceptibility to oxidation. In foods, the activities of antioxidants are often difficult to predict and control, because their interactions with metal-protein complexes may either inhibit or promote oxidation. In biology, the activity of antioxidants is even more difficult to predict on the basis of in vitro studies, because interfacial interactions occur between different cellular sites and the complex effects of enzyme cofactors and inhibitors, and immune systems.

Chapter 2 deals with the classical chemistry necessary to understand more fully how antioxidants operate and the main aspects of the mechanisms of lipid oxidation and antioxidants. In addition to inhibiting the initiation and the propagation of oxidation, other multiple effects of antioxidants are discussed, including inhibiting the decomposition of hydroperoxides, inactivating prooxidant metals, reducing hydroperoxides and scavenging oxygen. Due to the multiplicity of factors influencing antioxidants' activities in complex foods and biological systems, the common use of artificial and non-relevant azo initiators to evaluate antioxidants is discouraged, because it may be misleading.

Chapter 3 presents details on how the activity of antioxidants is affected at the interface of complex multiphase lipid systems. This chapter introduces the concept of interfacial antioxidation that depends on the partition of antioxidants between the aqueous phase, lipid phase and surfactant-enriched interface in foods and biological systems, and the colloidal chemistry of different types of emulsions affecting activity. Knowledge on the sites of antioxidant and prooxidant actions in multicomponent systems is essential to predict more successfully their activity in complex foods and biological systems.

Chapter 4 discusses the problems of evaluating the activities of antioxidants in foods and biological systems. Because antioxidant activity is strongly affected by the physical composition of the target systems, valid methods to evaluate antioxidants require the control of a multitude of parameters. A judicious choice of several methods is also necessary to determine the effects of different products of lipid oxidation. The many important questions are discussed for the careful choice of antioxidant protocols in foods and biological systems. This chapter ends with recommended protocols based on several substrate properties for valid antioxidant evaluations.

Chapter 5 on antioxidants in different foods deals with their interactions between food lipids, proteins and sugars, synergistic effects of phospholipids, and plant and beverage sources of phenolic compounds. This chapter includes information on the natural antioxidants in vegetable oils, milk, meat, fish and cereal products, special foods, herbs and spices. Plant polyphenols constitute the most important dietary antioxidants evaluated by a multitude of in vitro tests. The many analytical problems are discussed regarding the widespread use of one-dimensional methods to evaluate multifunctional food and biological antioxidants, and the caution required in making nutritional recommendations based on the so-called antioxidant capacity values of foods.

Chapter 6 covers extensive worldwide research on biological antioxidants, generally based on the hypothesis that the health of an individual is influenced by the efficiency of various protection systems against oxidant damage. The nutritional approach to antioxidant therapy is, however, poorly understood due to the multiple interacting factors that relate degenerative diseases to diet and to oxidation. Because of a lack of reliable biomarkers of oxidative stress, animal and human feeding studies have produced controversial and mixed results. Although there is extensive evidence that diets high in fruits and vegetables rich in phenolic antioxidants are associated with a lower incidence of cardiovascular disease, very few studies have shown that flavonoids are directly responsible for health effects in the diet. Because of complexities in the behavior of natural phenolic antioxidants in different systems, the true impact of oxidation processes in biological tissues is controversial. Results of most in vitro and in vivo studies to assess the effects of phenolic antioxidants in biological systems are extremely difficult to interpret, because questionable methodology has been used to measure oxidation and the oxidative susceptibility of polyunsaturated lipids and other biological targets. The chapter ends with the many questions that remain to be researched to understand and predict the effectiveness of phenolic antioxidants better in various biological systems.

Chapter 7 covers the renewed attention in biochemistry on the Maillard browning reaction, developed early in food chemistry, and on the interactions of reducing sugars, proteins and lipid secondary oxidation products. The complex biological modification of proteins by glucose in blood known as glycation and glycosylation involves oxidative and non-oxidative processes, producing low-molecular weight aldehydes that may initiate cardiovascular diseases and are implicated in age-related chronic diseases, including obesity, diabetes and renal disorders. The cross-linking between proteins and carbohydrates generates lifelong products of advanced glycation end products (AGEs) at later stages of the Maillard reactions, contributing to tissue degeneration. Advanced glyco-sylation has been shown to affect a number of proteins and has been implicated in the pathogenesis of several diabetes and age-related diseases. Glycation products that are formed in heated foods and a number of recently developed inhibitors are discussed in detail to control their formation in biological systems.

The final chapter, Chapter 8, addresses the important question that concerns food scientists and nutritionists today, as to whether additional or more effective natural phenolic antioxidants are needed in our diet to reduce oxidative stress from dietary and environmental factors, and the risk of cardiovascular disease. There is much in vitro evidence supporting a possible beneficial role for polyphenols in preventing cardiovascular disease and cancer. Because oxidative damage is involved in atherosclerosis and other degenerative diseases, antioxidants have been generally thought to contribute to cardiovascular protective effects. However, intervention trials with vitamin E and different phytochemicals produced confusing results. The beneficial nutritional effects of fruits and vegetables have been tied up to increased levels of antioxidants in the body. However, very few studies provide direct evidence that the benefits of eating fruits and vegetables are actually due to in vivo antioxidant activity. Many phenolic compounds recognized for their antioxidant activity in vitro might have different and additional in vivo properties. Discussions include the evidence for several non-antioxidant activities of vitamin E, flavonoids and other phenolic compounds. Looking at future research, the nutritional and health properties of plant foods are examined, with a list of the many unsettled questions that deserve additional research using more relevant and reliable bioassays for clarification of the interactions between dietary polyphenols and health effects. Another section discusses recent claims for the health benefits of organic compared to conventional plant foods. These claims have been difficult to prove due to the complex environmental and agricultural factors known to influence the contents of phenolic compounds in plants, and because very little reliable data have been published on their corresponding antioxidant activity. A final section deals with nanotechnology, a new development in food technology that deals with extremely small structures that have unique, novel and potentially useful functional properties caused by modified interfacial phenomena with potential applications for antioxidants.

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

Edwin Frankel, University of California Davis, California, USA

To return to the top of the page.

Dr Neil Macfarlane, DSM Nutritional Products, Kaiseraugst, Switzerland, writing in the November 2007 issue of Lipid Technology (2007, vol.19, No.11, p.266)....

The `Preface' provides a succinct and well written overview of the book content, its objectives and aims warning the reader of the complexity of antioxidant chemistry in model systems, oils, emulsions, foods and biological systems. The book is going to be controversial, attempting to sort out facts from fiction highlighting problem areas for future research and suggesting better designed methodology for future studies.

The roller coaster begins with Chapter 1, `Introduction to antioxidants', and draws our attention to modern trends of trying to incorporate potentially unstable long-chain polyunsaturated fatty acids into foods, of restricting our use of synthetic antioxidants in favour of natural antioxidants, of fortifying foods with pro-oxidant iron and of drastic reductions in the use of hydrogenation to provide stable and not just textural food attributes. All of these trends challenge food science to minimize undesirable lipid oxidation and the complexities of this potential oxidation in biological systems are not well understood.

`Chemistry of Antioxidation' provides a brief overview of lipid oxidation mechanisms and how different antioxidants can be beneficial in slowing or changing the oxidation profiles of lipids. Professor Frankel reminds us that azo dyes which are often used to study model systems are of little or no value in the study of food systems and to evaluate antioxidants kinetically their use may be misleading. `Antioxidant action in multiphase systems' teaches us that antioxidants behave quite differently depending on their location in the multiphase so antioxidants which are good at stabilizing oil might not be ideal for an emulsion or complex multiphase food. Much future research is required to position antioxidants better where they are needed rather than in the wrong phase and to pick the most appropriate antioxidants in each phase.

`Antioxidant protocols for foods and biological systems' addresses the essential tools required to assess the performance of antioxidants. Again the validity of many of the currently used tools and experimental conditions is questioned and suggests that much of the data we have for decision-making is irrelevant. The chapter concludes with Professor Frankel's recommendations for study protocols. I highly appreciate the recommendation to study at low levels of oxidation, particularly for the long-chain polyunsaturated fatty acids where minute levels of secondary oxidation produce such an unpleasant taste sensation that the food or multiphase would be deemed unacceptable were the oxidation to continue further.

`Food antioxidants' provides a brief review of how synthetic and natural antioxidants can help to preserve different foods (oils, milk products, meat, fish products, cereals and others) and of how many additional components within the food itself can have antioxidant or synergistic properties (e.g. Maillard products, phospholipids and flavanoids). We are reminded that whilst the flavanoids can perform spectacularly as antioxidants in vitro, their in vivo benefits are less clear. `Antioxidants in biology' draws our attention to wondering how well these nutritional lipids perform once eaten and whether the antioxidant knowledge we have for the oil and food is relevant in vivo. Particular focus is given to the antioxidant benefits of eating fruit and vegetables but of the difficulties in interpreting in vivo data largely because there is no consensus for reliable in vivo testing protocols. `Browning and glycation reaction products in biology' revisits the subject introduced in `Food antioxidants'.

The final chapter, `Future perspectives' is where Professor Frankel puts over 50 years of his lipid expertise on the table and draws up a comprehensive list of questions which are as yet unanswered. He provides his thoughts on how these questions might be approached for future solution. This is a rich hunting ground for future PhD students and shows us that Lipid Science in both food and biology has a bright future.

I have no hesitation in recommending this volume to libraries, students and teachers alike both in the food and the pharma sectors.

---

Professor Jan Pokorny, Institute of Chemical Technology, Prague, Czech Republic, writing in the October 2007 issue of European Journal of Lipid Science and Technology (2007, vol.109, No.10, p.1045)....

Lipid oxidation and antioxidants are very important topics both for lipid scientists and biologists oriented on lipid metabolism. Professor Frankel is a well known expert of high reputation on both lipid oxidation and antioxidants. He published a monograph on Lipid Oxidation in 1995 (the Second Edition in 2005), where he has already included his important observations on antioxidants. He has now published a logical continuation of his previous work - a monograph on lipid antioxidants.

The book starts with a brief introduction to the general mechanisms of antioxidant activity (Chapter 1). The mechanisms are relatively simple in bulk lipids (Chapter 2). But they become substantially more complicated in multiphase systems, such as lipid emulsions (Chapter 3), where the partition of antioxidants between the oil and the aqueous phases affects the activity. Many synergistic, antagonistic and other active components interfere in real foods.

Original papers dealing with the activities of antioxidants sometimes do not define the exact experimental conditions and purpose of the respective study. It is very easy to study interactions between very stable synthetic radicals such as DPP* and antioxidants, but such experiments do not reflect the real activity with relatively unstable lipid oxy or peroxy radicals (Chapter 4). The author therefore criticizes antiradical methods, defining the antioxidant activity on the basis of their reaction with stable nitrogen-containing free radicals. The determination is very fast and simple, but it does not give any accurate information on the antioxidant activity in real foods or in the body. Several other methods are critically reviewed from the standpoint of their applicability; methods approaching real storage or heating conditions are preferred.

In Chapter 5 applications of natural antioxidants from various natural sources are reviewed, not only in vegetable oils and other plant materials, but also for the stabilization of meat, dairy, fried and bakery products.

Additions of antioxidants for inactivation of free radicals in vivo are often discussed, just now as they probably initiate the development of some chronic diseases. Therefore, antioxidants are recommended as components of main meals, e.g. fruit, vegetables and red wine consumption (Chapter 6). The in vivo activity of antioxidants depends, however, on their bioavailability as they are partially decomposed after ingestion. The importance of phenolic antioxidants in human metabolism is still not fully understood, and more research on the subject is necessary. More research would also be welcome on metabolites of phenolics. As the intake of phenolics is relatively high, non-antioxidant activities of phenolics should not be neglected.

The antioxidant activity of non-enzymatic browning products have been been discussed during the last few decades, not only in relation to food products, but mainly because of their effect in human metabolism (Chapter 7). Inhibition of advanced glycation end products (AGE) is very important.

The final parts of each chapter should be studied with particular interest as the author, on the basis of his profound experience, explains not only what has been achieved on the topic, but also what are the most frequent erroneous opinions, what should be solved, and what is still open or not finally evident. Future research predictions are also based on Frankel's deep knowledge of the subject (Chapter 8). It would consist of intensive research in several areas, such as the role of antioxidants in nutrition, their activity in specific food materials, and activities other than inhibition of lipid oxidation. The definition of antioxidants is very precise among food scientists, but rather loose among biologists so that the term is often used incorrectly. Unsettled questions on antioxidants are listed, and priorities of further research emphasized.

The book is written in clear language and thus can be easily understood even by non-English speaking coleagues and students. The book offers excellent information to food scientists, biologists, researchers, medical experts, teachers and advanced students. Many figures, graphs, tables, and references will invite for further study. I warmly recommend the book for all colleagues interested in lipid antioxidants.

---

Dr William E. Artz, Associate Professor Food Science and Human Nutrition, University of Illinois at Urbana-Champaign, Illinois, USA, writing in the August 2007 issue of the American Oil Chemists' Society's magazine Inform (page 557)....

This book is another well-written text by E.N. Frankel with an extensive set of excellent references. He continues to provide texts that prove very helpful for those of us involved in food lipid oxidation research and for those of us trying to minimize oxidation in food products and other biological systems. The text provides not only a wealth of information on lipid oxidation but also insightful evaluative comments on various areas of oxidation and antioxidant (AO) research.

His comments, for example, on how AO affect transition metal activity regarding oxidation are very interesting. His discussion on individual analyses for determining the extent of oxidation or analyses for evaluating AO activity is an excellent and useful resource for researchers in this area. It should help investigators select the best analyses for their particular food or biological system. It should be a "must read" for scientists beginning research in this area.

Chapter 1 starts with a very brief section on past aspects of antioxidants, followed by a longer section on present aspects, such as interfacial phenomena, phytochemicals, etc. The chapter ends with a short future-aspects section suggesting areas that need further investigation. Chapter 2 covers the chemistry of autoxidation, from the familiar group of free radical reactions to AO classes, and how their structure affects activity. Synergistic AO systems, as well as oxidation inhibition in various biological systems, are discussed.

Chapter 3 is a discussion of AO activity in multiphase colloidal systems, including an examination of which AO work best in these systems (based on referenced research results). It also includes a discussion of metal catalysts and the effect of proteins. A variety of emulsion systems are discussed. The chapter contains over 60 references, primarily from E.A. Decker's group and from work done at U.C. Davis under the direction of J.B. German and E.N. Frankel.

Before beginning any research on AO activity, particularly on AO that have not been well defined, an investigator should carefully consider Chapter 4. The chapter provides an interesting discussion on the questions that need to be answered when conducting research in this area, as well as the strengths and weaknesses of the various analyses available for quantifying AO activity. The end of the chapter provides a useful outline of recommended protocols that should be considered before beginning experiments on AO activity. The chapter contains more than 100 references.

Chapter 5 is on food antioxidants, with discussions on the amount of specific AO present and added to various foods and food systems, such as fish oils, meat, olive oil, frying oils, milk products, fish products, and cereal products.

Chapter 6 is a long chapter (with more than 130 references) on AO in biology, which begins with AO enzymes, oxidation of low-density lipoproteins, in vitro vs. in vivo studies, plus a section on the pro-oxidant chemistry of phenolic AO. There is a large section on the "bioavailability, absorption and pharmacokinetic studies" of several different AO. The chapter ends with a section on dietary recommendations, although no specific recommendations are given other than that consumption of fruits and vegetables high in AO from normal sources is advised, since the highdose experiments have typically had negative results.

Chapter 7 discusses browning and glycation reaction products in biology, including the formation of these compounds in food and their relationship to aging. The AO activity of Maillard reaction products is included. The accumulation, inhibition, and effects of AGE, or advanced glycation reaction end products, are discussed.

The final chapter is titled "Future perspectives". The discussion in the chapter includes two important groups of AO: tocopherols and flavonoids. The chapter provides an evaluation of previous studies, and the author suggests additional research that should be done, as well as how previous studies could be improved. The final section in the chapter (approximately eight pages titled "Future research") contains specific research questions that should be addressed, including questions on protocol improvements, improvements in bioassays for AO, questions of processing and improved bioavailability, questions of the needs of various groups (e.g., adolescents, adults, etc.) regarding AO, plus several more.

This is a well written and informative text by one of the top investigators in the field of food lipid oxidation. It would be a nice addition to any food scientist's library, especially those scientists with a substantial interest in lipid oxidation. It would also be a useful ancillary reference text for a graduate course in food lipid chemistry.

---

To return to the top of the page.

PJ Barnes & Associates, PO Box 200, Bridgwater TA7 0YZ, UK
Tel: +44-1823-698973
Fax: +44-1823-698971
E-mail: sales@pjbarnes.co.uk
Web site: www.pjbarnes.co.uk

Please contact us if you have any problems using this web site. Thank you.
©Copyright 2007 PJ Barnes & Associates

Home page | News | Buy books | Search | Contact us