Food Frying E-Book

Alam Zeb

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 986

Veröffentlichungsjahr: 2019

Beschreibung

A wide-ranging exploration of the science and practice of food frying Frying is one of the world's most popular methods of food preparation. Whether using oils or fats, it is valued for the particular flavors and textures it can bring, and represents a multibillion-dollar sector of the global economy. Food Frying: Chemistry, Biochemistry and Safety explores this important cooking technique in its scientific dimensions, charting the relationships between the chemical reactions produced during frying, the changes in food quality that these engender, and associated digestive and health-related issues. By outlining these connections, the author provides an aid to a safer, healthier approach to food frying. Topics covered range from culturally specific forms of frying to detailed analyses of the chemical and biochemical processes involved in its practice. Delivering these insights in a practical and easy-to-follow manner, this unique text includes: * A complete survey of food frying, encompassing cultural, chemical, biochemical, and toxicological concerns * Guidance on the accurate assessment of health, quality, and safety issues associated with food frying Coverage of the latest technologies and methods involved with frying * Information on the possible future development of fried foods Food Frying: Chemistry, Biochemistry and Safety is an invaluable resource for all those who work with fried foods, whether they be food industry professionals, food scientists, or workers in the oil and fat industries.

Leseprobe

Table of Contents

Cover

Foreword

Preface

About the Author

Acknowledgement

Part I: Concept of Food Frying

1 Food Frying

1.1 Introduction

1.2 History of Frying

1.3 Mechanism of Frying

1.4 Why We Fry Foods

1.5 Key Concepts

References

2 Frying Techniques

2.1 Introduction

2.2 Concept of Deep Frying

2.3 Tools Used in Frying

2.4 Optimized Conditions

2.5 Types of Frying

2.6 Tips to Remember During Frying

2.7 Choice of Frying Method

2.8 Key Concepts

References

3 Frying and Culture

3.1 Introduction

3.2 The Common Point

3.3 Frying in American Cuisines

3.4 Frying in European Cuisines

3.5 Frying in Asian Cuisines

3.6 Frying in African Cuisines

3.7 Frying in Middle Eastern Cuisines

3.8 Key Concepts

References

Part II: Chemistry of Food Frying

4 Chemistry of the Frying Medium

4.1 Frying Medium

4.2 Classification and Choice of Frying Medium

4.3 Chemistry of the Frying Medium

4.4 Chemistry of Lipid Oxidation During Frying

4.5 Formation of Volatile Products

4.6 Sterol Oxidation

4.7 Tocopherol Oxidation

4.8 Formation of

Trans

Fatty Acids

4.9 Techniques for Measuring Lipid Oxidation

4.10 Key Concepts

References

5 Chemistry of Fried Foods

5.1 Introduction

5.2 Carbohydrates

5.3 Proteins and Amino Acids

5.4 Lipids

5.5 Micromolecules

5.6 Frying of Carbohydrate‐Rich Foods

5.7 Frying of Protein‐Rich Foods

5.8 Frying of Seafood

5.9 Frying of Vegetables

5.10 Physicochemical Characteristics of Fried Foods

5.11 Improving Product Quality

5.12 Key Concepts

References

6 Chemistry of Interactions in Frying

6.1 Introduction

6.2 Factors Affecting the Frying Medium

6.3 Factors Affecting the Food

6.4 Heat Transfer

6.5 Mass Transfer

6.6 Nutritional Value Retention

6.7 Key Concepts

References

7 Analysis of Frying

7.1 Introduction

7.2 Analysis of Triacylglycerols

7.3 Analysis of FA Oxidation Products

7.4 Analysis of Sterol Oxidation

7.5 Analysis of Sensory Metabolites

7.6 Analysis of Heterocyclic Amines

7.7 Analysis of Acrylamide

7.8 Analysis of Tocopherols

7.9 Analysis of Polyphenolic Compounds

7.10 Analysis of Other Minor Compounds

7.11 Key Concepts

References

Part III: Biochemistry of Food Frying

8 Digestion and Absorption of Fried Foods

8.1 Introduction

8.2 Acceptability of Fried Foods

8.3 Digestion of Fried Foods

8.4 Absorption of Fried Foods

8.5 Excretion of Fried Foods

8.6 Key Concepts

References

9 Nutrition and Metabolism of Fried Foods

9.1 Introduction

9.2 Metabolism of Fried Lipids

9.3 Metabolism of Fried Proteins

9.4 Metabolism of Fried Carbohydrates

9.5 Metabolism of Other Metabolites

9.6 Key Concepts

References

10 Fried Foods in Health and Disease

10.1 Introduction

10.2 Fried Foods and Health

10.3 Fried Foods and Cancer

10.4 Fried Foods and Diabetes

10.5 Fried Foods and Cardiovascular Diseases

10.6 Fried Foods and Aging

10.7 Key Concepts

References

Part IV: Safety in Food Frying

11 Safety Assessment of Food Frying

11.1 Introduction

11.2 Guideline for Assessment

11.3 Quality Indicators for Used Frying Oils

11.4 Physical Assessment

11.5 Chemical Assessment

11.6 Evaluation of Fried Foods

11.7 The Future of Fried Food Safety

11.8 Key Concepts

References

12 Toxicity of Food Frying

12.1 Introduction

12.2 Toxicity of Oxidized Triacylglycerols

12.3 Toxicity of Acrylamide

12.4 Toxicity of Acrolein

12.5 Toxicity of Amines and Alcohols

12.6 Toxicity of Aldehydes

12.7 Pro‐Oxidants

12.8 Disposal of Fried Foods

12.9 Disposal and Use of the Frying Medium

12.10 Key Concepts

References

13 Improving the Quality of Fried Foods

13.1 Introduction

13.2 Improving the Quality of Fried Foods

13.3 Mitigation Strategies for Acrylamide

13.4 Reducing Oil Uptake

13.5 Fortification

13.6 The Role of Natural Antioxidants

13.7 Packaging of Fried Foods

13.8 Quality Control in Frying

13.9 Key Concepts

References

14 The Future of Food Frying

14.1 Introduction

14.2 Current Strategies

14.3 Future Scenarios

14.4 Hurdles

14.5 Key Concepts

References

Index

End User License Agreement

List of Tables

Chapter 1

Table 1.1 Timeline of the frying process.

Table 1.2 Formation of acrylamide during deep frying in various oils.

Table 1.3 Water and fat content in various raw and deep‐fried products.

Chapter 2

Table 2.1 Polyphenol species (mg /100 gpotato) identified and quantified in raw...

Chapter 4

Table 4.1 Typical composition (%) of some important fatty acids (FAs)...

Table 4.2 Triacylglycerol (TAG) composition of some edible oils and f...

Table 4.3 Composition of volatile compounds produced by thermal oxida...

Table 4.4 Mechanisms of volatile formation in heated triolein epoxide...

Table 4.5 Mechanisms of volatile oxidation product formation in heate...

Table 4.6 Phytosterol/stanol profile (μg g

−1

) in commercial sun...

Table 4.7 Distribution of major β‐sitosterol and campesterol oxidation pr...

Table 4.8 Effects of heating on tocopherol degradation.

Chapter 5

Table 5.1 Recent studies on the frying of common carbohydrate‐rich foods.

Table 5.2 Structures and sources of heterocyclic aromatic amines (HAAs) in prote...

Table 5.3 Precursors, sources, matrices, frying conditions, and concentrations o...

Table 5.4 Total polycyclic aromatic hydrocarbon (PAH) compounds (benzo[a]anthrac...

Table 5.5 Effects of animal fats on the formation of polycyclic aromatic hydroca...

Table 5.6 Changes in the FA composition (g kg

−1

) of Mediterranean fish and...

Table 5.7 Classification of common vegetables.

Table 5.8 Changes in the glucosinolate contents of Chinese cabbage and pakchoi d...

Table 5.9 Carotenoid and pigment compositions of selected vegetables leaves.

Table 5.10 Effects on carotenoid, chlorophyll, and α‐tocopherol contents of the ...

Table 5.11 Effects of frying on the formation of Amadori compounds (ACs) (mg kg ...

Chapter 6

Table 6.1 Effects of the addition of α‐tocopherol (α‐T) or δ‐tocopherol (δ‐T) on...

Table 6.2 Texture profile analysis of uncoated and differently coated doughnuts ...

Table 6.3 Changes in the phenolic compounds in watercress leaves during frying a...

Table 6.4 Recent studies on the effects of frying on the carotenoids contents of...

Table 6.5 Different types of organic compounds formed from protein‐rich animal f...

Table 6.6 Formation of HAAs (ng g

−1

) in pork of different shapes fried for...

Table 6.7 Effects of microwave cooking on the formation of PAH (fluorene) in dif...

Table 6.8 Effects of deep frying on the proximate composition of different culti...

Chapter 7

Table 7.1 Analytical methods of triacylglycerol (TAG) determination in differe...

Table 7.2 Thin‐layer chromatographic (TLC) methods for the analysis of oxidize...

Table 7.3 Normal‐phase high‐performance liquid chromatographic (NP‐HPLC) metho...

Table 7.4 Reversed‐phase high‐performance liquid chromatographic (RP‐HPLC) met...

Table 7.5 High‐performance liquid chromatography coupled with mass spectrometr...

Table 7.6 Occurrence of epoxides, alcohols, and ketones in FAME, TAGs, oils, a...

Table 7.7 Gas chromatographic (GC) quantitative methods and corresponding pret...

Table 7.8 Analytical parameters of fast and conventional GC‐MS methods.

Table 7.9 Levels of cholesterol oxidation products (COPs) detected in Cypriot ...

Table 7.10 Analytical chromatographic methods for the determination of vitamin...

Chapter 8

Table 8.1 Average consumer acceptability by attribute of fried salted...

Table 8.2 Faecal fat excretion and fatty acid composition of rats fed...

Chapter 9

Table 9.1 Effect on liver and plasma TAG concentrations of oxidized fat...

Table 9.2 Effects of dietary oxidized lipids on the liver and plasma to...

Table 9.3 Effects of dietary protein oxidation products on specific pat...

Chapter 10

Table 10.1 Range of fat contents in different fried foods.

Table 10.2 Studies investigating the association between a large consumption of ...

Table 10.3 Effects of heated vegetable oils and fats on various cancers.

Chapter 11

Table 11.1 Quality parameters for evaluation of the characteristics o...

Table 11.2 Overview of original and previous independent research on ...

Chapter 12

Table 12.1 Estimated daily dietary intakes of major HAAs (ng person

−1

...

Table 12.2 Epidemiological human studies investigating the effect of ...

Table 12.3 Effects of adsorbent amount on the physical and chemical c...

Chapter 13

Table 13.1 Summary of pretreatment methods applied to different agricul...

Table 13.2 Potential active packaging technologies for food application...

List of Illustrations

Chapter 1

Figure 1.1 Oil content absorbed or remaining on the surface of French fries dur...

Figure 1.2 Frying oil quality curve according to Blumenthal (1991).

Figure 1.3 Scheme of heat and mass transfer during deep frying.

Figure 1.4 Oil content versus moisture loss in French fries during frying at 15...

Figure 1.5 Diagram of oil flowing into a pore.

Figure 1.6 Viscosity changes in fresh and used soybean oils.

Figure 1.7 Important factors involved in the frying operation affecting oil upt...

Chapter 2

Figure 2.1 Schematic representation of the deep frying of foods.

Figure 2.2 Countertop compact electric deep fryer.

Figure 2.3 Automatic industrial multi‐fryer. Firex model No. FAGT 2‐070 with tw...

Figure 2.4 Effect of

carbon dioxide blanketing

(

CDBL

) and

carbon dioxide bubbli

...

Figure 2.5 Trigonal bipyramid model showing the three basic optimizable paramet...

Figure 2.6 Coated and noncoated stainless steel frying pans.

Figure 2.7 Laboratory‐scale vacuum fryer used to produce snacks in the Food Eng...

Figure 2.8 Oil absorption rate of potato chips fried at different frying oil te...

Figure 2.9 Comparison of oil absorption rates for potato chips fried under trad...

Figure 2.10 Diagrammatic representation of an air‐frying system.

Figure 2.11 Microstructure changes in conventional‐fried versus air‐fried potat...

Figure 2.12 Schematic diagram of the steps involved in an industrial frying sys...

Chapter 4

Figure 4.1 Chemical structure of triacylglycerol (TAG). R1, R2, and R3 represen...

Figure 4.2 Structures of homo‐TAGs and hetero‐TAGs.

Figure 4.3 Chemical structures of important polyphenolic compounds in edible oi...

Figure 4.4 Reversed‐phase HPLC‐DAD chromatograms of mustard oil phenolic compou...

Figure 4.5 Structures of squalene and an isoprene unit.

Figure 4.6 Representative structures of carotene (β‐carotene) and xanthophyll (...

Figure 4.7 Chemical structures of cholesterol and phytosterol, with their deriv...

Figure 4.8 Chemical structures of medium‐ to long‐chain fatty alcohols present ...

Figure 4.9 Representative structures of tocopherols and tocotrienols. The R gro...

Figure 4.10 Chemical structures of important phospholipids (phosphatidyl inosit...

Figure 4.11 Chemical structures of important volatile compounds produced during...

Figure 4.12 Effects of thermal oxidation on the formation of hydroperoxides in ...

Figure 4.13 Representative sequence of reactions during frying. These reactions...

Figure 4.14 Representative free radical reaction sequence, showing the steps in...

Figure 4.15 The role of heavy metal ions in the initiation reactions of lipid o...

Figure 4.16 Free radical auto‐oxidation of linolenate. R, CH

3

CH

2−

; R

1

, −(...

Figure 4.17 Formation of hydroperoxy epidioxide from linolenate peroxy radical....

Figure 4.18 Formation of hydroperoxide in the auto‐oxidation of linoleic acid. ...

Figure 4.19 Formation of hydroperoxides of oleic acid. R, CH

3

(CH

2

)

6−

; R

1

Figure 4.20 Formation of epoxides from hydroperoxides of linoleic acid. R, CH

3

C...

Figure 4.21 Mechanism of formation of acrolein from linolenic acid and glycerol...

Figure 4.22 Mechanism of trilinolein auto‐oxidation and the formation of hydrop...

Figure 4.23 Formation of triolein epoxy epidioxides.

Figure 4.24 Chemical structures of oxidized TAGs.

Figure 4.25 Representative sequence of chemical reactions involved in the forma...

Figure 4.26 Hydrolytic reactions of 1,3‐dioleoyl‐2‐linoleoyl glycerol. The reac...

Figure 4.27 Formation of volatile compounds from the decomposition of oleic aci...

Figure 4.28 Mechanism of formation of volatile compounds from hydroxy epidioxid...

Figure 4.29 Formation of cholesterol oxidation products during frying. The chol...

Figure 4.30 Formation of epoxy hydroperoxides of α‐tocopherol in the presence o...

Figure 4.31 Chemical structures of important

trans

fatty acids (TFAs).

Chapter 5

Figure 5.1 Structures of monosaccharide sugars. Aldoses contain aldehyde as a f...

Figure 5.2 Ring structures of monosaccharides. Pyranose is a six‐member ring an...

Figure 5.3 Chemical structures of important disaccharides and trisaccharides.

Figure 5.4 Structures of important polysaccharides present in all foods.

Figure 5.5 Chemical structures of amino acids and their derivatives, peptides a...

Figure 5.6 Important daily sources of food proteins.

Figure 5.7 Contribution of triacylglycerols (TAGs) to the formation of other li...

Figure 5.8 Mechanisms of formation of 5‐

hydroxymethyl‐2‐furfural

(H...

Figure 5.9 HMF is the precursor of several different organic compounds produced...

Figure 5.10 Effects of different temperatures on the formation of HMF and furfu...

Figure 5.11 Effects of different frying times on the formation of HMF and furfu...

Figure 5.12 Mechanism of formation of HMF from glucose and an amino acid.

Figure 5.13 Formation of acrylamide from lipids and amino acids.

Figure 5.14 Mechanism of formation of acrylamide from asparagine.

Figure 5.15 Effects of different temperatures and frying times on the formation...

Figure 5.16 Mechanism of formation of acrolein from glucose.

Figure 5.17 Mechanism of formation of 2‐amino‐1‐methyl‐6‐phenylimidazo[4,5‐b]‐p...

Figure 5.18 Headspace gas chromatography mass spectrometry (GC‐MS) analysis of ...

Figure 5.19 Chemical structures of important polycyclic aromatic hydrocarbons (...

Figure 5.20 Furan (mg kg

−1

) in frozen precooked bread‐coated foods before...

Figure 5.21 Mechanism of formation of different cholesterol oxidation products.

Figure 5.22 Proposed mechanism of degradation and oxidation of β‐carotene durin...

Figure 5.23 Colour differences between products fried under vacuum and in tradi...

Figure 5.24 Correlation of moisture loss with oil uptake during the frying of f...

Chapter 6

Figure 6.1 Classification of interactions during food frying.

Figure 6.2 Schematic representation of several chemical interactions between fo...

Figure 6.3 Changes in important physicochemical characteristics of the frying m...

Figure 6.4 Emission rates of carbonyl compounds from palm oil during continuous...

Figure 6.5 Antioxidant roles of tocopherol and gallic acid, showing the stabili...

Figure 6.6 Degradation of astaxanthin at different temperatures.

Figure 6.7 Effects of astaxanthin and β‐carotene on the formation of hydroperox...

Figure 6.8 Effects of frying on the lipid oxidation parameters (peroxide values...

Figure 6.9 Deep frying of food. Heat transfer and steam are higher in direct he...

Figure 6.10 Effects on the polyphenolic compounds in artichoke of frying at 170...

Figure 6.11 Representative HPLC‐DAD chromatogram of phenolic compounds in water...

Figure 6.12 Representative HPLC‐DAD chromatograms of spinach leaves at 450 nm (...

Figure 6.13 Interactions of carotenoids of spinach leaves during frying in sunf...

Figure 6.14 Effects of frying time on the formation of heterocyclic aromatic am...

Figure 6.15 Correlation of moisture loss with oil uptake during food frying.

Figure 6.16 Changes in TBARS values during the frying of spinach leaves in sunf...

Figure 6.17 Retention of phenolic compounds in virgin olive oil (VOO) (plus a‐T...

Chapter 7

Figure 7.1 Representative electrospray ionization mass spectrometry (ESI‐MS) sp...

Figure 7.2 Reaction of triphenylphosphine with lipid hydroperoxide. This reacti...

Figure 7.3 Fast GC‐MS trace (TIC) of TMS derivatives of a standard COP mixture,...

Figure 7.4 NP‐LC‐APPI‐MS analysis of cholesterol oxidation products. (1) choles...

Figure 7.5 Optimum HPLC chromatographic separation of seven cholesterol oxidati...

Figure 7.6 Derivatization reaction of phytosterols with 4'‐carboxy‐substituted ...

Figure 7.7 (a) Representative

multiple reaction monitoring

(

MRM

) chromatograms ...

Figure 7.8 Schematic representation of an experimental system used in a frying ...

Figure 7.9 HPLC separation of T and T3 isomers at different temperatures with P...

Chapter 8

Figure 8.1 Microstructure of fried rice dough strands prepared with 52% rice fl...

Figure 8.2 True digestibility coefficients (mg fat 100 mg

−1

) of whole unh...

Figure 8.3 Percentage of administrated TAG oligomers, dimers, and polymers foun...

Figure 8.4 Amount (mg) of total oxidized fatty acids (ox‐FA) and ketolinoleic a...

Figure 8.5 Absorption of lipid in the intestinal lumen.

Figure 8.6 Hypothetical transport mechanisms for phenolic compounds (PCs): pass...

Chapter 9

Figure 9.1 Overview of the cellular intake and subsequent metabolism of differe...

Figure 9.2 Effects of a high‐fat diet (HFD) and standard chow diet on the accum...

Figure 9.3 Effects of co‐administration of unoxidized Desi ghee with oxidized g...

Figure 9.4 The most common consequences of the oxidation of proteins.

Figure 9.5 Metabolism of heterocyclic aromatic amines (MeIQx). Most of the end ...

Figure 9.6 Metabolism of acrylamide, indicating the formation of haemoglobin an...

Figure 9.7 Metabolism of hydroxymethyl furfural (HMF).

Figure 9.8 The role of ellagic acid in oxidative stress at different organ site...

Chapter 10

Figure 10.1 Retention and transfer of different nutrients during frying.

Figure 10.2 Effects of frying on

total phenolic contents

(TPC) of watercress le...

Figure 10.3 Repeatedly heated cooking oil emits polycyclic aromatic hydrocarbon...

Figure 10.4 Proposed pathological mechanisms responsible for increased

cardiova

...

Figure 10.5 Genetic associations with body mass index (BMI) according to freque...

Chapter 12

Figure 12.1 Metabolism of acrolein.

Figure 12.2 Effects of 0, 650, 1300, and 2600 ppm oxidized α‐tocopherol on the ...

Chapter 13

Figure 13.1 Classification of frying pretreatment methods.

Figure 13.2 Schematic diagram of a low‐pressure superheated steam dryer and ass...

Figure 13.3 Infrared (IR) heating device used by Huang (2004).

Figure 13.4 Formation of polymers (POL) and loss of tocopherols (TOC) in high l...

Chapter 14

Figure 14.1 Effects of dietary oxidized lipids on the fat deposition in rabbits...

Guide

Cover

Table of Contents

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Food Frying

Chemistry, Biochemistry, and Safety

Alam Zeb

University of Malakand,Khyber Pakhtunkhwa, Pakistan

This edition first published 2019© 2019 John Wiley & Sons Ltd

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Library of Congress Cataloging‐in‐Publication Data

Names: Zeb, Alam, 1979– author.Title: Food frying : chemistry, biochemistry and safety / Alam Zeb, University of Malakand, Khyber Pakhtunkhwa, Pakistan.Description: Hoboken, NJ, USA : Wiley, [2019] | Includes bibliographical references and index. |Identifiers: LCCN 2018042187 (print) | LCCN 2018042489 (ebook) | ISBN 9781119468486 (Adobe PDF) | ISBN 9781119468394 (ePub) | ISBN 9781119468516 (hardcover)Subjects: LCSH: Fried food. | Food–Analysis. | Biochemistry–Industrial applications. | Frying–Safety measures.Classification: LCC TX689 (ebook) | LCC TX689 .Z43 2019 (print) | DDC 641.7/7–dc23LC record available at https://lccn.loc.gov/2018042187

Cover Design: WileyCover Image: © LauriPatterson / Getty Images

ToMy Mother (BIBI NASEEBA, died on Friday, 13 October 2017):A teacher and most precious gift of my life.Your true love, purity, and affections for me will always be missed.

Foreword

The process of deep fat frying has been in use for nearly 4000 years, and today it is one of the most popular ways to prepare food, with an increasing market worldwide. Reasons for this success are that the process is relatively cheap, fast, and easy to use, and imparts good taste and smell characteristics to the product. Although the process itself is very simple, involving immersing the product into hot oil or fat and waiting for some time, deep fat frying is an art, with many pitfalls that must be taken into consideration in order to produce high‐quality tasty products that are attractive to the consumer. In addition, the health aspect is coming more and more into focus.

The process occurring in the fryer is very complex and dynamic, with numerous different reactions taking place at the surface of the food and in the oil. Fatty acids are degraded to volatile aroma‐active compounds; triacylglycerols are cross‐linked, resulting in an increase of viscosity; the polarity of the oil changes due to degradation of triacylglycerols, inducing foaming; and the properties of the product change. The factors that make deep fat frying a complex process include not only temperature and time but also the type of fryer, oil, or food being fried, the use of additives, the amount of frying medium being used, the temperature profile, cleaning of the fryer, and the type of heat transfer employed. Even today, the interplay of these factors and the consequences for the process are not fully understood.

People who are involved in the frying process, such as processors, restaurant operators, and suppliers to these industries (including oil producers, food and ingredient suppliers, equipment manufacturers, and the service trade) should have an advanced and comprehensive knowledge of the dynamics of frying. Food Frying: Chemistry, Biochemistry, and Safety by Professor Alam Zeb gives a very good overview of the different aspects of this complex process. The frying process is comprehensively presented in 14 chapters, divided into 4 parts covering the concept of frying, the chemistry of frying, the biochemistry of frying, and the safety of frying.

When a new book on deep fat frying is published, the question arises whether it is needed or not. There are already some standard reference works on the subject, but the content of this book shows that the author has approached the topic in great detail and included many new aspects. That makes it a comprehensive source for information about the frying process. It discusses not only the chemistry of frying but also the analysis and evaluation of used frying oils, the biochemical effects and health‐related issues important for the evaluation of the frying process, and issues of food safety, which is one of the most important topics today. The book gives the reader advice on how to protect the consumer from potential health drawbacks of eating fried food. It provides information for persons working in the food production industry, restaurant operations, the basic sciences, official and commercial laboratories, marketing, service provision, and the supply chain who are involved in the production of fried food, research on the frying process, or the assessment of used frying oils, or who are interested in deep fat frying in general.

I believe that this new book on deep fat frying is a wonderful enrichment of the list of existing books on frying and I wish it the success it deserves.

Bertrand MatthäusMax Rubner‐InstitutFederal Research Institute of Nutrition and FoodDepartment of Safety and Quality of CerealsWorking Group of Lipid ResearchDetmoldGermany

Preface

Food frying is a traditional and widely used method of preparation of a variety of foods. Food is fried in edible oils or fats for the purpose of obtaining a characteristic flavour, texture, and acceptability. A wide range of vegetables, meat, fish, snacks, and other products are prepared using frying. Fried foods contribute a huge market worth billions of dollars to the world economy and thus demand continuous research and development. The use of new technologies for the extraction and purification of edible oils and the production of fried foods of the highest quality is evolving daily, and there is a general interest in understanding the process of food frying. Thus, this is a comprehensive book that provides information on all the latest scientific research on the chemistry, biochemistry, and safety of food frying.

The frying of foods involves complex chemical reactions that produce several biochemical changes upon ingestion of the fried product. This book aims to cover them in four main parts. Part I explains the basics of food frying. It consists of three chapters, on food frying, frying techniques, and frying in different cultures. Part II covers the important chemistry of food frying in terms of composition, reactions, and consequent changes in the quality of fried foods. It consists of four chapters giving details of the chemistry of the frying medium and of fried foods and presenting a clear explanation of the fundamental chemical reactions and interactions that take place during frying. This part will be especially helpful for readers in the food industries or academia. Part III covers the biochemical effects and health‐related issues of food frying. It consists of three main chapters dealing with the digestion, absorption, metabolism, and health aspects of food frying. It also discusses up‐to‐date knowledge of the biochemical effects associated with food frying. Part IV covers the topic of food safety, which is one of the key topics of modern food research. It consists of four chapters, which cover the safety assessment of food frying, the toxicity of frying, how to improve the quality of fried foods, and the future of this area.

The book is organized in such a manner as to provide a smooth flow of scientific knowledge from chemistry to biochemistry to safety, while allowing each chapter to be read alone. It should serve as the latest reference resource for food scientists, technologists, food chemists, biochemists, nutritionists, and health professionals working in academia, scientific labs, and industry. It provides fundamental and applied information to benefit those with different backgrounds in science. It can also be used as a textbook for undergraduate, graduate, and postgraduate students in the relevant disciplines.

About the Author

Dr Alam Zeb is a Professor of Biochemistry at the Department of Biotechnology, University of Malakand, Pakistan. He has served for the last 16 years at this university, while teaching chemistry and biochemistry courses to undergraduate, graduate, and postgraduate students of biotechnology. Dr Zeb received his PhD with distinction from the Institute of Biochemistry, Technical University of Graz, Austria in 2010, funded by the Higher Education Commission (HEC) of Pakistan. During his studies at Graz, he also taught practical food chemistry courses to postgraduate students. He is one of Pakistan’s highest‐funded research project winners in the field of food science and technology. Dr Zeb has published more than 100 research articles regarding the subject of food science in various international peer‐reviewed journals. He has supervised several PhD and MPhil research students during his service at the University of Malakand. He is a member of the editorial board of several international journals, including Frontiers in Chemistry, and Frontiers in Nutrition. Dr Zeb has been enlisted as Productive Scientist of Pakistan since 2009, and has received research productivity awards from the Pakistan Council for Science and Technology for the last seven consecutive years, representing his potential and enthusiasm for research in the field of food biochemistry.

Acknowledgement

This work would not have been possible without the help of some important people. Dr Francisco J. Morales and Dr Marquez‐Ruiz of the Institute of Food Science, Technology and Nutrition (ICTAN), Spanish National Research Council (CSIC), Spain are highly acknowledged for providing the original copyrighted data used to produce high‐quality figures in Chapter 5. Similarly, Prof Dr Michael Murkovic of the Institute of Biochemistry, Technical University of Graz, Austria is thanked for providing an original copyrighted figure for Chapter 5, and support at the university. I am grateful to the Ernst Mach‐Nachbetreuungsstipendium (EZA) Fellowship, OeAD Austria for providing an opportunity to complete this work in Graz, Austria. I am also thankful to the University of Malakand for supporting me in finalizing this book, while doing research at the Technical University of Graz.

Finally, I acknowledge my wife, son (Umar Alam Khan), and a daughter (Haya Bibi) for missing me at home, while I was completing this work in Graz.

Part IConcept of Food Frying

1Food Frying: The Concept

1.1 Introduction

Frying is a food preparation technique that involves foods and hot oil or fats. It is one of the fastest and simplest techniques for cooking food with pleasant, attractive properties. The food frying process consists of four main components: first, specific conditions such as temperature and pressure; second, a utensil or fryer; third, foods; and fourth, frying oil (referred to as ‘frying medium’ from this point onward). The fryer may be a simple pan or a complex industrial technology. The frying medium is usually an oil or an animal‐derived fat. The temperatures used for frying are in the 150–200 °C range. High temperatures promote reactions between food components like proteins and carbohydrates, surface dehydration of the crust, and oil uptake (Gertz 2014). In contrast to boiling in hot water, the heating of foods at elevated temperatures provides a desirable appearance (colour), texture (crispness), flavour, and taste (Perkins 2007). Frying is a more efficient process than other cooking methods, and has gained great popularity in both restaurants and industry because of its speed and operational simplicity.

Even though deep frying is an old and very popular process, it is still poorly understood. Proper frying practice and the most appropriate frying oil are generally determined by experience. Good understanding of the frying process helps in optimizing the manufacturing processes with regard to the quality of the food, the use life of the fat, and energy consumption. To guarantee a good quality of the fried end product, it is necessary to install a management system which includes all critical points of the frying process (Gertz 2014).

1.2 History of Frying

Food frying is one of oldest known food preparation techniques. However, the exact date of its invention and who first used it is hard to trace. Some authors propose that it was invented by the ancient Chinese (Rossell 2001). The third book of the Old Testament, Leviticus, chapter 2, verses 4–7, written c. 600 BCE, distinguishes between bread baked in an oven and that cooked on the griddle or in the pan. Pliny (c. 1st century CE) provides a prescription for spleen disease that involves frying eggs in vinegar (Morton 1998). Knowledge of frying was common in the fourteenth century, but scientific writing on the subject was still rare. Table 1.1 provides a brief history and timeline of the frying process (Stier 2004). The German Fat Society, ‘Deutsche Gesellschaft fuer Fettwissenschaft’ (DGF) may be considered a pioneer of fat science and frying. The DGF held symposia on frying fats in 1973 and 1979. The first conference on the subject, ‘The Frying of Foods’, was held in Madrid in 1986. These conferences and symposia were considered the prime motivator for attracting scientists' attention to frying science and technology. The European Society for Lipid Science and Technology has contributed much to the understanding of frying. In recent times, significant scientific breakthroughs have occurred, resulting in a huge sum of knowledge on frying that it is not possible to accommodate in a single book.

Table 1.1 Timeline of the frying process.

Source: Modified and reproduced with kind permission of John Wiley & Sons (Stier 2004).

Year

Event

3000 BCE

Chinese frying of meat

1300 BCE

Hebrews fry flat breads

1537 CE

Potatoes introduced in Europe

1600–1700

French fried potatoes emerged

1853

Potato chip invented in Saratoga Springs, NY by George Crum

1890s

Potato chip industry begins in the United States

1897

Hydrogenation of edible oils invented

1906

Commercial oil roasting of shelled peanuts by Planters

1908

J. P. Dushesues founds Leominster Potato Chip Company

1926

Laura Scudder develops first potato chip bag of waxed paper

1927–1930

Cellophane begins to be used for potato chip bags

1929

Clarence Birdseye develops new commercial freezing technologies

1932

First tortilla chips (Doolin and Filler) produced in San Antonio, TX

1933

Dixie wax paper introduces pre‐printed glassine bag. Cracker barrel marketing of chips comes to an end

1930–1935

National Potato Chip Institute tells consumers that chips are not fattening if eaten in small amounts

1938

H. W. Lay Co. founds Lay's Potato Chip Company in Atlanta, GA

1946

First automatic packaging machine for chips developed

1945–1950

Extruded snacks introduced. MacBeth introduces continuous immersion cookers

1950

Under‐pan fired cookers introduced

1950–1952

Fryers with external heat exchangers with oil circulation introduced; Pork rinds introduced

1950–1955

Laminate bags with polypropylene/cellophane and polypropylene glassine introduced

1953

Simplot scientists develop a technique for par‐frying potato slices

1957

Heat & Control introduces ‘Big Goose’, a 1600 lb. capacity continuous system

1958

Urshel develops new slicers for potato chip manufacture

1961

Frito‐Lay merger

1969

Potato chip controversy develops with the introduction of Pringles and Chippos

1970–1975

7000 lb. capacity fryers introduced

1973

1st DGF Symposium. Germany proposes regulations based on oxidized fatty acids for restaurant frying oil

1979

2nd DGF Symposium. Polar materials provides index of restaurant frying oil quality

1987

Blumenthal publishes surfactant theory of frying

2000

3rd DGF Symposium. Principle quality index should be sensory parameters of food being fried

2004

4th DGF Symposium

2004

4th International Symposium on Deep‐Frying

2011

6th International Symposium on Deep‐Frying, Germany

2013

7th International Symposium on Deep‐Frying, United States

2015

8th International Symposium on Deep‐Frying

2016

1st International Symposium on Lipid Oxidation and Antioxidants, Portugal

2017

9th International Symposium on Deep Frying, China

1.3 Mechanism of Frying

Frying involves essential components such as foods and frying medium. As a general rule, frying medium is initially preheated to about 160–200 °C and then desired foods are either kept in it or immersed in it. Several physical and chemical reactions occur that result in the formation of fried foods. Figure 1.1 shows the experimental results of oil distribution during the frying and cooling of a potato slice. During frying, a small amount of oil is absorbed by the potato, while during cooling, the internal oil content increases at a fast rate for the first minute, while surface oil decreases until an equilibrium is reached after 4 minutes. In order to understand the fundamentals of frying, the following concepts are important.

Figure 1.1 Oil content absorbed or remaining on the surface of French fries during frying (170 °C) and cooling (20 °C).

Source: Reproduced with kind permission of John Wiley & Sons (Gertz 2014).

1.3.1 Heat and Mass Transfer

Foods can be prepared at an elevated temperature in different ways, such as by pan frying, shallow frying, or deep frying, while temperatures of 100–103 °C can be achieved when cooking in water. With the use of fat or hot air as a heating medium, a higher temperature can be generated without exceeding the boiling temperature of the water inside the food (Vitrac et al. 2000). As the temperature difference between the heating medium and the food increases, the heat transfer within the cooking process runs much faster. Simultaneous with the heat transfer, mass is transferred from the food to the frying medium and vice versa (Gertz 2014).

A food is a solid body with holes and pores filled with water and air. Immediately after its immersion in hot oil, traces of free water at the surface evaporate very rapidly, causing a violent bubbling and drying of the surface. When the vaporization of water is faster than the ability of the surrounding oil to remove the steam by convection, the heat transfer rate from oil to food surface is zero, due to the heat resistance of the steam evaporating from the surface. The introduction of the food into the hot oil and the sudden evaporation of moisture from the food cause a violent bubbling. Bubbling enlarges the contact area between air and oil. Thus, the heat transfer rate between oil and air increases, accelerating the oxidative degradation of the oil (Costa et al. 1999). By lowering the oil temperature, reducing the quantity of food to be fried, or pre‐drying the food, rapid evaporation of the water from the surface of the food and intense bubbling can be avoided (Sobukola et al. 2010). With increasing frying time, the bubbling becomes less intense and the evaporating water steam has a more protective effect (Dana et al. 2003), creating a steam blanket above the oil surface and reducing the headspace air flow, providing protection against oxidation by avoiding contact with air.

The heat is transferred by convection from the oil to the surface of the product and by conduction to the centre of the product. The water inside the product is heated to boiling point, resulting in an increased pressure. As a consequence, water at the surface leaves the product and that in the interior of the food migrates from the central position radially outward to the walls (Vitrac et al. 2000). This water transport is responsible for providing cooling in the external region of the product after the first period of frying, ensuring that the food is not burnt or charred. The moisture in the inner part of the food is heated to boiling, inducing gelatinization of starch and denaturation of proteins (Gertz 2014).

It has been shown by Manglik (2006) that by adding small quantities of surface‐active soluble agents, the interfacial tension and surface tension (oil–solid interfacial, oil–vapour tension) can be altered and the heat transfer improved. A simple practical test at 170 °C with 10 × 10 × 500 mm potato pieces demonstrates the heat transfer capacities of different oils (Table 1.2). The measured times till the central temperature reaches 100 °C are all different due to the different physical and chemical properties of the oils. In frying tests, it has been observed that potatoes fried in beef tallow and palmolein contain higher amounts of acrylamide than those fried in sunflower or rapeseed oil for the same period, due to the accelerated heat transfer (Gertz et al. 2003).

Table 1.2 Formation of acrylamide during deep frying in various oils.

Source: Reproduced with kind permission of John Wiley & Sons (Gertz 2014).

Time needed to reach 100 °C in the score

FOS‐unit

Acrylamide level (µg kg

−1

) of French fries (40 g) prepared in oil (fryer capacity: 2 l); heating time: 3, 5 min, 170 °C

Palmolein

65

3.5

594

Beef tallow

74

2.5

301

Sunflower oil

80

0.8

205

Rapeseed oil

80

0.5

203

Groundnut oil

82

0.4

190

Groundnut oil hardened

84

0.0

192

Palmolein and beef tallow contain more polar components, such as mono‐ and diacylglycerols and medium‐chain triacylglycerols (TAGs), than do oils such as rapeseed oil, sunflower oil, and groundnut oil. To compare the relative polarities, fresh oils were measured with FOS (Food Oil Sensor). The reading units of the FOS measurements are related to their dielectric constants and polarity (Wegmuller 1994). It is possible that these more polar compounds reduce the surface tension between oil and food surface or oil and water steam; however, Gil and Handel (1995) have not observe any effect of diacylglycerols or fatty acids on the surface tension in frying oils. Blumenthal (1991) published a monograph proposing a surfactant theory of frying. As oil degrades, more surfactant materials are formed, causing increased contact between oil and food. Those materials cause a better heat transfer at the oil–food interface and reduce the initially high surface tension between these two immiscible zones. The so‐called ‘Frying Oil Quality Curve’ (Figure 1.2) demonstrate the relationship between the degradation of frying oil and the chemical changes in the oil. This curve shows five stages of oil degradation, and relates them to food quality. The goal must be to extend the optimum frying window.

Figure 1.2 Frying oil quality curve according to Blumenthal (1991).

Source: Reproduced with kind permission of John Wiley & Sons (Gertz 2014).

After the external zone is dehydrated, the crust–crumb interface starts moving towards the centre from the food. This porous dried region (crust) is created and continues to increase in size as long as water is migrating from the central position of the food radially outward to the surface. The temperature profile in the crust is a function of oil temperature, whereas the evolution of the core temperature is independent of the oil temperature so long as water is transferred from the inner part of the food to the surface (Figure 1.3); it cannot be changed to accelerate the frying process.

Figure 1.3 Scheme of heat and mass transfer during deep frying.

Source: Reproduced with kind permission of John Wiley & Sons (Gertz 2014).

The thickness of the crust increases with frying time up to about 0.3–2.0 mm (Ngadi et al. 1997; Gertz 2014). When frying potato chips (crisps), the crust region enlarges quickly and the core zone disappears. The low thickness, lack of liquid water to be evaporated, falling pressure, and high heat transfer raise the temperature of the material above 100 °C very quickly.

Models developed to calculate the transient temperature, moisture content, and oil content during the frying process use many simplifying assumptions. Dincer (1996) propose a single‐phase model using a discretization of heat and mass transfer. To simplify the calculations, it is assumed that there is no effect of mass transfer on heat transfer and vice versa. Farid and Chen (1998) found a good agreement between the predicted and experimental temperature distribution, except at the end of the frying period, where the central temperature of the potato chips exceeded the boiling temperature of water.

A two‐phase or moving‐boundary model has been proposed to describe the mechanism of heat and mass transfer during frying by Farkas et al. (1996), among others. These authors proposed the existence of two regions, separated by an interface: the core (unfried) and the crust (fried) regions. During immersion frying, heat is transferred from the frying oil to the core via the crust region. Water is evaporated at the moving boundary at 100 °C. The heat conduction equation was used to describe the heat transfer in this region. The temperature difference is the driving force of heat transfer. The changing physical properties due to increasing fat degradation made the system too complex for a realistic model to be developed. Also, the effects of crust formation on physical properties were neglected. This model is comprehensive and helps to explain the frying process. The simplified scheme of heat and mass transfer during the actual frying of food is depicted in Figure 1.3.

1.3.2 Oil Uptake

During the frying process, food takes up oil contents. Oil uptake seems to be independent of frying temperature, but is significantly affected by frying time, moisture loss, and the structure of the products to be fried (Gamble et al. 1987; Alvarez et al. 2000). The initial moisture content of food can be reduced by pre‐treatments such as pre‐drying at temperature 70–75 °C, air or vacuum drying (Mariscal and Bouchon 2008), osmotic dehydration (Bunger et al. 2003) and blanching (Sobukola et al. 2010), or else in combination with a post‐treatment (Mariscal and Bouchon 2008). In the food industry, the use of hydrocolloids such as carboxymethylcellulose, pectin, sodium alginate, powdered cellulose, and modified starch is very common to retard the moisture loss (Holikar et al. 2005; Saha and Bhattacharya 2010; Gertz 2014).

The initial superficial vaporization and subsequent in‐depth vaporization create a porous, dried, and overheated region which is generically called ‘crust’. The pores can be small voids, molecular interstices, or large caverns which are filled with water and air. They may be interconnected or nonconnected. The water should be able to travel throughout the entire porous structure, as if it were a network of pipes. For this reason, it is important not to overheat the product when food is immersed into hot oil. A good structured crust helps to retard the loss of moisture; otherwise, the pores will be too large or will be destroyed due to the high vapour pressure. When the porosity of the material is low, the increase in pressure can significantly reduce the drying rate. For materials with weak structures due to high water content and/or the absence of cell structure, water transport can be so intense that liquid water escapes the surface without vaporization (Gertz 2014).

Fried foods like yeast‐raised doughnuts have more oil accumulated at the surface due to their thin crust layer. Unlike in deep frying, these foods float on the surface during frying (i.e. shallow frying). The heated water in the core starts boiling and increases the volume of the food. Only a little water finds its way through the crust. For this reason, the crust is very thin. Another effect is that volatiles remain in the hot oil, producing off‐flavours like rancidity, because not enough steam is leaving the crust and stripping them off (Gertz 2014).

1.3.3 Mechanism of Oil Absorption

Oil uptake is a complex mechanism that is still not clearly understood. The initial product structure, the various interchanges between the product and the heating medium, and the variations of product and oil properties are the factors which complicate this phenomenon (Ziaiifar et al. 2008).

1.3.3.1 Water Escape and Oil Uptake

Most authors agree that during frying, heat and mass transfer are controlled by heat transfer at the surface of the product. The rate of vaporization is proportional to the temperature difference between the oil and the boiling point of water (Vitrac et al. 2002). Numerous works propose a simple description based on a convective mass transfer approach that is too simple. Farkas et al. (1996) were the first scientists to propose a physical description of frying. They stated that this process should be described as a complex Stephan problem, because of the coupled heat and mass transfer resulting in the displacement of a moving vaporization front that separates two dynamic regions: a dehydrated crust and a humid core. As the crust presents low thermal conductivity, it affects heat, and mass transfer and is partly responsible for the decrease in the dehydration rate.

In general, we can say that the more the water is removed from the surface, the more the oil is absorbed. Figure 1.4 plots the relationship between oil content and moisture loss. When mass transfers in deep fat frying are studied, the escape of water is usually linked to oil absorption. Indeed, Gamble et al. (1987) found that moisture loss and oil uptake were inter‐related and were both linear functions of the square root of frying time. They hypothesized that the oil entering the slice would lie in the voids left by the escaping water. Hence, in addition to quantitative aspects, water loss can become an explanatory variable for transformation and especially oil uptake, because water escape is at the origin of very diverse material phenomena such as the creation of cavities (Vitrac et al. 2000). Indeed, as dehydration occurs at a temperature above 100 °C, water steam finds selective weaknesses in the cellular adhesion that lead to the formation of capillary pathways, increasing surface porosity. Furthermore, some of this vapour may be trapped within the pores as a result of restrictive intercellular diffusion and expand, becoming superheated, distorting the pore walls, and contributing to product porosity. Accordingly, some studies have examined the increase of porosity during frying and correlated it to the amount of oil uptake (Pinthus and Saguy 1994; Moreira et al. 1997). Characterization of the product microstructure thus appears to be a determining factor in the description of transfers at the macroscopic scale, such as oil uptake.

Figure 1.4 Oil content versus moisture loss in French fries during frying at 155 °C.

Source: Reproduced with kind permission of John Wiley & Sons (Ziaiifar et al. 2008).

1.3.3.2 Capillary Pressure and Oil Uptake

Moreira et al. (1999) introduced a physical relation between oil absorption and porosity, stating that the mechanism of oil uptake may be caused by capillary forces. Indeed, when a fluid displacement such as oil absorption occurs in microcanals like crust pores, surface phenomena such as viscosity or capillary forces become very important. Capillarity is the ability of a narrow pore to draw a liquid upwards. It occurs when the adhesive intermolecular forces between a liquid and a solid are stronger than the cohesive intermolecular forces in the liquid. This causes a concave meniscus to form where the liquid is in contact with the vertical surface. This phenomenon creates a difference of pressure between the two sides of the curbed interface, as expressed by the Laplace law (Figure 1.4):

(1.1)

where Pi is the pressure at the point i (Pa), γ is the surface tension of the oil (N m−1), ϑ is the wetting angle between the oil and the solid (rad), and r is the pore radius (m).

In addition, P2−P3 = −ρgh, according to the hydrostatic pressure difference (Figure 1.5), where ρ is the oil density (kg m−3), g is the acceleration gravity (m s−2), and h is the height of the capillary motion (m).

Figure 1.5 Diagram of oil flowing into a pore.

Source: Reproduced with kind permission of John Wiley & Sons (Ziaiifar et al. 2008).

Therefore, the pressure difference ΔP at the two points 1 and 3 of the pore is:

(1.2)

Oil absorption is therefore dependent on pore radius. Small pores cause higher capillary pressures and thus higher oil content (Moreira et al. 1997). In addition, the lower the contact angle between the oil and the product surface, the higher the adhesion forces and the oil uptake. Finally, the higher the surface tension of the liquid, the higher the oil uptake. Moreira and Barrufet (1998) stated that γ decreases with increasing temperature, resulting in a capillary pressure reduction. This fact contributes to limiting oil uptake during frying.

The main difficulty with capillarity motion determination at the end of frying is the determination of pore radii that are nonhomogenous in shape. Furthermore, pores can be filled with liquid, water vapour, or air depending on the conditions at the end of frying. Thus, the wetting property of oil towards the solid matrix is nonhomogenous and difficult to determine in such complex and multiple fluid phase systems. Moreover, capillary motion equations are mostly used in their static form, resulting in the expression of the equilibrium positions of fluids. This simplification comes from the fact that other forces, such as vacuum effect and the weight of absorbed oil, are involved in oil absorption.

1.3.3.3 Vapour Condensation and Vacuum Effect

During frying, intense drying occurs at a temperature greater than the temperature of water ebullition. The solid matrix of the food is an obstacle to water bubble growth, leading to a pressure gradient in the food. Overpressure was evaluated in an experimental work by Vitrac et al. (2000), who measured an inner overpressure of 45 kPa during the frying of an alginate gel containing 10% starch. Overpressure depends on the initial structure of the material. Indeed, the more resistant the structure is towards fluid dilatation, the higher the pressure inside the material. However, some structures are not sufficiently resistant to pressure and can break, allowing liquid water to escape. This phenomenon of water loss in both steam and liquid forms was observed during the deep fat frying of apple slices (Vitrac et al. 2003).

Consequently, during frying, when the product still presents high free water content susceptible to evaporate, the escape of water and the associated overpressure in the material is an obstacle to oil absorption. In opposition, when the product is removed from the fryer, the core temperature decreases, steam condenses, and the pressure in the product abruptly decreases. As a consequence, the important difference between the inner and outer pressures creates a ‘vacuum effect’, resulting in the penetration of the surface oil into the product (Gamble and Rice 1987). Moreover, Vitrac et al. (2000) found the depression in a food model gel to be 35 kPa a few seconds after the product had been removed from the oil bath; they therefore stated that this vacuum is the most important force acting on oil uptake in the porous media.

1.3.3.4 Adherence and Drainage of Oil

Oil absorption involves a balance between adhesion forces (capillary and water condensation) and drainage of oil during the cooling period (Ufheil and Escher 1996