food emulsifiers and their applications

Food Emulsifiers and Their Applications


Edited by

Gerard L. Hasenhuettl Kraft Foods

Richard W. Hartel University of Wisconsin

SPRINGER-SCIENCE+BUSINESS MEDIA, B.V.

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Library of Congress Cataloging-in-Publication Data Food emulsifiers and their applications/edited by Gerard L.

Hasenhuettl and Richard W. Hartel. p. em.

Includes bibliographical references and index. ISBN 978-1-4757-2664-0 ISBN 978-1-4757-2662-6 (eBook) DOI 10.1007/978-1-4757-2662-6 1. Food additives. 2. Dispersing agents.

II. Hartel, Richard W., 1951-TP455.F667 1997 664'.06-dc21

I. Hassenhuettl, Gerard L., 1944-

97-1647 CIP

British Library Cataloguing in Publication Data available

To our wives and children

Contents

Contributors

Preface

ONE

Overview of Food Emulsifiers Gerard L. Hasenhuettl

1.1 Introduction

1.2 Emulsifiers as Food Additives 1.3 Emulsifier Structure 1.4 Emulsifier Functionality

References

TWO

Synthesis and Composition of Food-Grade Emulsifiers

R. J. Zielinski

2.1 Introduction

2.2 Mono- and Diglycerides

2.3 Propylene Glycol Monoesters 2.4 Lactylated Esters

2.5 Polyglycerol Esters

vii

xiii XV

1

1

2 5 7

9

11

11

13

15 18 23

viii Food Emulsifiers and Their Applications

2.6 Sorbitan Esters 2. 7 Ethoxylated Esters 2.8 Succinylated Esters 2.9 Fruit Acid Esters 2.10 Acetylated Monoglycerides 2.11 Phosphated Esters 2.12 Sucrose Esters

References

THREE

Analysis of Food Emulsifiers Gerard L. Hasenhuettl

3.1 Introduction 3.2 Thin-Layer and Column Chromatography 3.3 Wet Chemical Analysis 3.4 Physical Methods 3.5 Instrumental Methods 3.6 Setting Specifications for Food Emulsifiers

References

FOUR

26 26 29 31 33 36 36 38

39

39 40 43 52 54 62 63

Carbohydrate/Emulsifier Interactions 67 Lynn B. Deffenbaugh

4.1 Introduction 67 4.2 Inclusion Complexes of Starch 68 4.3 Effects of External Lipid Materials on

Starch Properties 69 4.4 Factors Affecting Complex Formation 81 4.5 Physical Properties of Starch/Emulsifier Complexes 85 4.6 Summary 90

References 90

Contents ix

FIVE

Protein/Emulsifier Interactions Martin Bos, Tommy Nylander, Thomas Arnebrant,

and David C. Clark

5.1 Introduction

5.2 Protein Stability

5.3 Protein/Surfactant Interactions

5.4 Protein/Phospholipid Interactions

95

95

97

98

120 5.5 Protein/Emulsifier Interactions-Food Applications 132

References 137

SIX

Physicochemical Aspects of an Emulsifier Functionality 147

Bjorn Bergenstahl

6.1 Introduction

6.2 Surface Activity 6.3 Solution Properties of Emulfiers 6.4 The Use of Phase Diagrams to

Understand Emulsifier Properties

6.5 Examples of the Relation between Phase Diagrams and Emulsion Stability

6.6 Some Ways to Classify Emulsifiers

6.7 The Emulsifier Surface

References

SEVEN

Emulsifiers in Dairy Products and Dairy Substitutes

Stephen R. Euston

7.1 Introduction

7.2 Ice Cream

147

148

149

153

154 161

167

171

173

173

174

X Food Emulsifiers and Their Applications

7.3 Whipped Cream and Whipping Cream 183 7.4 Whipped Toppings 187 7.5 Cream Liqueurs 191 7.6 Creams and Coffee Whiteners 194 7. 7 Processed Cheese 197 7.8 Recombined, Concentrated and Evaporated Milks 199 7.9 Other Dairy Applications of Emulsifiers 202 7.10 Summary 203

References 204

EIGHT

Applications of Emulsifiers in Baked Foods

Frank T. Orthoefer

211

8.1 Introduction 211 8.2 History of Emulsified Shortenings 211 8.3 Emulsifier Function in Baked Goods 213 8.4 Role of the Shortening 215 8.5 Role of the Emulsifier 216 8.6 Emulsifier Interaction with Bakery Components 221 8. 7 Applications in Baked Goods 225 8.8 Summary 233

References 234

NINE

Emulsifiers in Confectionery Mark Weyland

235

9.1 Introduction 235 9.2 Emulsifiers in Chocolate and Compound Coatings 236 9.3 Antibloom Agents in Chocolate and

Compound Coatings 244 9.4 Other Emulsifiers Used in Coatings 248 9.5 Emulsifiers in Nonchocolate Confectionery 249

Contents xi

9.6 Processing Aids 252

References 253

TEN

Margarines and Spreads Eric Flack

10.1 Introduction 10.2 Early Development

10.3 Yellow-Fat Consumption

10.4 Definitions and Descriptions

10.5 Structure and Raw Materials

10.6 Fat Crystallization

10.7 Emulsifiers 10.8 Processing

10.9 Reduced- and Low-Fat Spreads

10.10 Oil-in-Water Spreads

10.11 Liquid Magarine

10.12 Summary References

ELEVEN

Emulsifier Trends for the Future Gerard L. Hasenhuettl

11.1 Globalization in the Food Industry

11.2 Nutritionally Driven Changes in Food

11.3 Trends toward Safer Emulsifers

11.4 Emulsifer Structure and Interactions

with Other Ingredients

11.5 Enzymatic Synthesis of Food Emulsifiers

References

Index

255

255 256 257 258 262 263 267 270 274 278 278 279 279

281

282 282 283

284 285 286

287

Contributors

Thomas Arnebrant

Department of Pharmaceutical Analysis

Ferring AB Box 30047

S-216 13 Malmo, Sweden

Bjorn Bergenstahl Institute for Surface Chemistry

P.O. Box 5607

S-114 86 Stockholm, Sweden

Martin Bos

TNO Nutrition & Food Research Institute

P.O. Box 360

3700 AJ Zeist, The Netherlands

David C. Clark

DMV International

NBC-Iaan 80

P.O. Box 13 5460 BA Veghal, The Netherlands

xiii

xiv Contributors

Lynn B. Deffenbaugh

Hill's Pet Nutrition

Science & Technology Center

P.O. Bo.c 1658

Topeka, KS 66601-1658

Stephen R. Euston

New Zealand Dairy Research Institute

Private Bag 11029

Palmerston North, New Zealand

Eric Flack

Danisco Ingredients, Ltd.

North Way

Bury St. Edmonds Suffolk, 1P32 6NP, United Kingdom

Gerard L. Hasenhuettl Kraft Foods, Inc.

801 Waukegan Rd.

Glenview, IL 60025

Tommy Nylander University of Lund, Chemical Center Department of Physical Chemistry P.O. Box 124 S-22100 Lund, Sweden

Frank T. Orthoefer

2004 Me Cracken St.

Stuttgart, AR 72160

Mark Weyland

Quest International

5115 Sedge Blvd.

Hoffman Estates, IL 60192

Richard J. Zielinski Quest International Joliet Technical Center 24 708 Durke Dr.

Joliet, IL 60410-5249

Preface

Food emulsions have existed since long before people began to process foods for

distribution and consumption. Milk, for example, is a natural emulsion/colloid in

which a nutritional fat is stabilized by a milk-fat-globule membrane. Early

processed foods were developed when people began to explore the art of cuisine.

Butter and gravies were early foods used to enhance flavors and aid in cooking.

By contrast, food emulsifiers have only recently been recognized for their abil

ity to stabilize foods during processing and distribution. As economies of scale

emerged, pressures for higher quality and extension of shelf life prodded the de

velopment of food emulsifiers and their adjunct technologies. Natural emulsifiers,

such as egg and milk proteins and phospholipids, were the first to be generally

utilized. Development of technologies for processing oils, such as refining,

bleaching, and hydrogenation, led to the design of synthetic food emulsifiers.

Formulation of food emulsions has, until recently, been practiced more as an

art than a science. The complexity offood systems has been the barrier to funda

mental understanding. Scientists have long studied emulsions using pure water,

hydrocarbon, and surfactant, but food systems, by contrast, are typically a com

plex mixture of carbohydrate, lipid, protein, salts, and acid. Other surface-active

ingredients, such as proteins and phospholipids, can demonstrate either syner-

XV

xvi Preface

gistic or deleterious functionality during processing or in the finished food.

The formulator of food emulsions has therefore traditionally been an experi

enced individual who reasoned by analogy to obtain desired technical effects

in the new food products. Recent impressive progress has been made in under

standing the physical chemistry of food emulsions, dispersions, and foams by

application of sophisticated instrumentation and computing power. An appre

ciation of ingredient interactions has also been developed, as many of the ref

erences in this book bear testimony. However, a coherent work focusing on the

design of emulsifiers for food applications has been notably absent.

In this volume, we have attempted to collect material that clarifies the process

of designing a commercially viable emulsifier system for new products or im

provement of existing foods. The process begins with an understanding of the

role and possibilities of the emulsifier to not only stabilize emulsions but also to

provide critical secondary functionalities. Manufacturing technology is de

scribed and analytical tests that ensure the quality of the emulsifier ingredient

are presented. Interactions of food emulsifiers with carbohydrates, proteins, and

water are significant in their use and are extensively discussed. Applications of

emulsifiers in the dairy, bakery, confectionery, and margarine industries demon

strate the reasoning process used to develop emulsion-based products. It is our

hope that this effort will stimulate further innovation directed at increasing the quality and reducing the expense of processed food products.

Acknowledgments The editors express their apprec1atwn to Barbara Bagnuolo and Julie

Hasenhuettl for typing and proofreading large portions of the manuscript.

Gerard L. Hasenhuettl Richard W. Hartel

ONE

Overview of Food Emulsifiers

Gerard L. Hasenhuettl

1.1 Introduction Food emulsions, colloids, and foams have their origins in the evolution of ani

mal species. Milk has a naturally occurring membrane that allows the disper

sion of fat droplets into an aqueous environment. Early food formulations to

produce butter, whipped cream, cheese, and ice cream built upon the natural

emulsifiers present in the system. The development of mayonnaise in France

as a cold sauce utilized the natural egg phospholipids to disperse a liquid oil

into an acidified aqueous phase. The emulsifying power is still very impressive

by today's standards since it allowed up to 80% oil to be dispersed without in

version to an oil-continuous emulsion. The invention of margarine by the

French chemist Hippolyte Mege-Mouries in 1889 utilized the solid fat of tal

low to produce a stable oil-continuous emulsion to serve as a low-cost substi

tute for butter. In this case, the emulsion had to be stable temporarily only

until the product was chilled.

Synthetic emulsifiers have come into common use only in the latter half of

the twentieth century. Their development was driven by the emergence of the

processed food industry, which needed technology to produce and preserve

quality products that could be distributed through mass market channels. A

key technical hurdle was to maintain product stability over an extended shelf

1

2 Food Emulsifiers and Their Applications

life. With small amounts of emulsifier, for example, salad dressings can be

stored on a shelf for more than a year without visible separation. Now, other

factors such as the development of rancidity limit consumer acceptance of ag

ing products.

Detailed knowledge of the physical chemistry of emulsions is best obtained

when pure oil, water, and surfactants are used. Food emulsions, by contrast, are

extraordinarily complex systems. Commercial fats and oils are complex mixtures

of triglycerides that also contain small amounts of highly surface-active materi

als (Friberg and Larsson, 1990). Salt content and pH in food emulsions vary

widely enough to have significant effects on their stability. Natural and commer

cial emulsifiers are often complex mixtures that vary in composition between dif

ferent manufacturers. Other food ingredients, such as proteins and particulates,

contribute surface activity that may dramatically alter the character of the emul

sion. Because of all these complex relationships, the formulation of food emul

sions grew up as an art, dominated by individuals having a great deal of

experience. The gradual development of sophisticated techniques such as elec

tron microscopy, nuclear magnetic resonance, and chromatography/mass spec

trometry has solidified the art with a scientific dimension.

The subject of food emulsions has been extensively reviewed by Friberg

and Larsson (1990), Krog et al. (1985), and Jaynes (1985). This book will be

oriented to the design, manufacture, and use of food emulsifiers as ingredients

to improve the quality and economy of processed foods.

1.2 Emulsifiers as Food Additives Approximately 500,000 metric tons of emulsifiers are produced and sold

worldwide. However, since the value/volume ratio of these products is low,

very little truly global trade has yet developed. In the United States, food

emulsifiers fall into two categories: substances affirmed as GRAS (21CFR184)

and direct food additives (21CFR172). Substances that have been affirmed as

GRAS (generally recognized as safe) usually have less stringent regulations at

tached to their use. However, Food and Drug Administration Standards of

Identity may preclude their use in certain standardized foods. In comparison,

direct food additives may be allowed only in certain specific foods at low max

imum allowable levels. The method of manufacture and analytical constants

may also be defined. The most commonly used food emulsifiers are listed in

Tables 1.1 and 1.2.

Overview of Food Emulsifiers 3

Table 1.1 Emulsifiers affirmed as GRAS

2ICFR Typical Emulsifier No. Functionalities applications

Lecithin 184.1400 Coemulsifier, viscosity Margarines, chocolate reducer products

Monoglycerides 184.1505 Emulsifier, aerator, Margarines, whipped crystal stabilizer toppings, peanut

butter stabilizers

Diacetyltartaric acid 184.1101 Emulsifier, film former Baked goods, esters of confections, dairy monoglycerides product analogs

Monosodium salt of 184.1521 Emulsifier, lubricant, Dairy products, analogs, phosphated release agent soft candy monoglycerides

The European Economic Community (EEC) has also developed regulations

for food additives that may be utilized within the member nations. Substances

are divided into four annexes that have some resemblance to United States

regulations. Annex I is similar to the GRAS list (2ICFRI82). These additives

may be used anywhere except in natural or standardized processed foods.

Annexes 2 and 3 resemble direct food additive regulations. A separate listing

for solvents and solubilizing agents is contained in Annex 4, which is not sep

arated in FDA regulations. Although the additive regulations are similar, great

care must be taken in trade between the United States and the EEC because

some specific emulsifiers are defined differently. For example, emulsifiers de

rived from polyglycerols up to decaglycerol are permitted in the United States,

but they are limited to tetraglycerol or lower in the EEC.

Other parts of the world have not developed into trading blocks with defined

regulations. Each country may have a unique perspective on which emulsifiers

may be allowed in food products. The problem is compounded by the fact that

regulations are written in the national language, requiring extensive and careful

translation. Some major differences in technology may develop because of a

country's unique specifications. For example, polysorbates have not been per

mitted as food additives in Japan. As a result, technology for production of

higher cost polyglycerol and sucrose esters has been widely developed there.


Table 1.2 Emulsifiers classified as direct food additives

21CFR Typical Emulsifier No. Functionalities applications

Lactylated 172.850 Emulsifier, plasticizer, Baked products,

monoglycerides surface-active agent whipped toppings

Acetylated 172.828 Film former, moisture Fruits, nuts, pizza

monoglycerides barrier

Succinylated 172.830 Emulsifier, dough Shortenings, bread

monoglycerides strengthener

Ethoxylated 172.834 Emulsifier, stabilizer Cakes, whipped

monoglycerides toppings, frozen

desserts

Sorbitan 172.842 Emulsifier, rehydrating Confectionery

monostearate agent coatings, yeast,

cakes, icings

Polysorbates 172.836 Emulsifier, opacifier, Salad dressings,

172.838 solubilizer, wetting agent coffee whiteners,

172.840 gelatins, ice cream

Polyglycerol esters 172.854 Emulsifier, aerator, cloud Icings, salad oils,

inhibitor peanut butter,

fillings

Sucrose esters of 172.859 Emulsifier, texturizer, Baked goods, fruit

fatty acids film former coatings,

confectionery

Calcium and sodium 172.844 Emulsifier, dough Bread, coffee

Stearoyllactylates 172.846 conditioner, whipping whiteners, icings,

agent dehydrated

potatoes

Propylene glycol 172.858 Emulsifier, aerator Cake mixes,

esters whipped toppings


As with any other totally new food additive, the need to prove safety of the

product in foods at high levels of consumption requires extensive toxicity studies

and enormous documentation. The consequent financial and time commitments

make development of totally new emulsifiers unattractive for emulsifier manu

facturers. A somewhat easier development approach is to petition for expanded

use (new applications or higher permitted levels) of emulsifiers that are already

approved. However, even this tactic may require several years of review.

In addition to national regulations, many food processors require their in

gredients, including food emulsifiers, to be kosher so that their products are

acceptable to Jewish and many Islamic consumers. For emulsifiers to be

kosher, they must be produced from kosher-certified raw materials. This re

quirement precludes the use of almost all animal fats. This is not much of a

problem since emulsifiers are easily produced from vegetable fats that can be

blended to give similar fatty acid compositions. The major concern in kosher

certification is to determine in advance whether the customer's rabbinical

council recognizes the Hekhsher (kosher symbol) of the producer's rabbi.

Products labeled as "all natural" must contain ingredients that have not

been chemically processed or modified. Only lecithin or other naturally occur

ring materials such as proteins would be acceptable for these products.

1.3 Emulsifier Structure Surface-active compounds (surfactants) operate through a hydrophilic head

group that is attracted to the aqueous phase, and an often larger lipophilic tail

that prefers to be in the oil phase. The surfactant therefore positions itself at

the air/water or oil/water interface where it can act to lower surface or interfa

cial tension, respectively. Figure l.l shows some typical hydrophilic and

lipophilic groups. Lipophilic tails are composed of Cl6 (palmitic) or longer

fatty acids. Shorter chains, such as Cl2 (lauric), even though they can be ex

cellent emulsifiers, can hydrolyze to give soapy or other undesirable flavors.

Unsaturated fatty acids are Cl8 molecules having one (oleic) or two (linoleic)

double bonds. Linoleic acid is usually avoided since it is easily oxidized and

may produce an oxidized rancid off-flavor in the finished food. Fats may be hy

drogenated to produce a mixture of saturated and unsaturated fatty acids.

Emulsifiers produced from these fatty acids may have an intermediate consis

tency (often referred to as "plastic") between liquid and solid. These products


Lipophilic end Hydrophilic end

-OH

Saturated; palmitate or stearate

H H

Unsaturated; oleate

Unsaturated; linoleate

Figure 1.1 Typical hydrophilic and lipophilic groups.

also contain measurable concentrations of trans (E) fatty acids that have higher

melting points than the cis (Z) fatty acids.

Polar head groups may be present in a variety of functional groups. They

may be incorporated to produce anionic, cationic, amphoteric, or nonionic sur

factants. Mono- and diglycerides, which contain an -OH functional group, are

the most widely used nonionic emulsifiers. Lecithin, whose head group is a

mixture of phosphatides, may be visualized as amphoteric or cationic, depend

ing on the pH of the product.

Proteins may also be surface active due to the occurrence of lipophilic

amino acids such as phenylalanine, leucine, and isoleucine. lnterfacially ac

tive proteins will fold so that lipophilic groups penetrate into the oil droplet

while hydrophilic portions of the chain extend into the aqueous phase.

Proteins in this configuration may produce a looped structure that provides

steric hindrance to oil-droplet flocculation and coalescence. Charged proteins

may also stabilize emulsions due to repulsion of like charged droplets.

Proteins may also destabilize water-in-oil emulsions, such as reduced fat mar

garines, by causing the emulsion to invert.

Food emulsifiers may be thought of as designer molecules because the

structure and number of heads and tails may be independently varied. A very

useful conceptual tool is hydrophile/lipophile balance (HLB). The topic has

been extensively reviewed by Becher, so only a brief description will be pre

sented here. The number and relative polarity of polar groups in a surface-ac-


tive molecule determine whether the molecule will be water- or oil-soluble (or

-dispersible). This concept has been quantitated by calculation of an HLB

value to describe a given emulsifier. High-HLB values are associated with

easy water dispersibility. Since conventional practice is to disperse the surfac

tant into the continuous phase, high-HLB emulsifiers are useful for preparing

and stabilizing oil-in-water (0/W) emulsions. Low-HLB emulsifiers are useful

for formulation of water-in-oil (W/0) emulsions, such as margarine. Extreme

high or low values are not functional as emulsifiers since almost all of the mol

ecule will be solubilized in the continuous phase. They would, however, be

very useful for full solubilization of another ingredient, such as a flavor oil or

vitamin, in the continuous phase. At some intermediate values of HLB, the

molecule may not be stable in either phase and will result in high concentra

tion at the interface.

1.4 Emulsifier Functionality In addition to their major function of producing and stabilizing emulsions, food

emulsifiers contribute to numerous other functional roles, as shown in Table

1.3. Some foods, notably chocolate and peanut butter, are actually dispersions

Table 1.3 Other functions offood emulsifiers

Emulsifier frmction

Whipping (aerating) agent

Dispersant

Dough conditioner

Defoamer

Starch complexer

Crystallization inhibitor

Antistaling agent

Antis ticking agent

Antispattering agent

Freeze-thaw stabilizer

Gloss enhancer

Cloud formers

Hydrating agents

Encapsulating agents

Dispersion stabilizers

Example(s)

Whipped toppings

Flavors, vitamins

Bread, buns, rolls

Yeast and sugar manufacturing

Macaroni, pasta

Salad oil

Yeast-raised baked goods

Candy, chewing gum

Margarines, frying shortenings

Frozen toppings and coffee

Whiteners

Confectionery coatings

Beverages

Powdered milk drinks

Flavors, aromas

Peanut butter


of solid particles in a continuous fat or oil phase. Chocolate viscosity is controlled by the addition of soy lecithin or polyglycerol ricinoleate (PGPR). Oil separation in peanut butter is prevented by use of a monoglyceride or highmelting fat. In some cases the secondary effect may be of greater concern than formation of the emulsion. Strengthening of dough and retardation of staling are vital considerations to processors who bake bread.

A common practice in the food industry is to use two- or three-component emulsifier blends to achieve multiple functionalities. In a cake emulsion, for example, aeration to produce high volume, foam stabilization, softness, and moisture retention are achieved by using an emulsifier blend. One useful statistical method to optimize emulsifier blends is the full factorial experimental design using a zero or low level of each emulsifier and a higher level of each emulsifier. The major advantage of this design is that it will detect two- and three-factor interactions that are not uncommon in complex food systems.

Small-molecule emulsifiers (e.g., monoglycerides) may exert their effect by partially or totally displacing proteins from an oil/water interface. This replacement is entropically favored because of the difference in size and mobility of the species. Direct interaction of emulsifiers and proteins may be visualized through electrostatic and hydrogen bonding, although it is difficult to observe in a system that contains appreciable amounts of oil. Chapter 5 on emulsifier/protein interactions will elaborate on these concepts.

Emulsifier suppliers generally employ knowledgeable technical service professionals to support their customers product development efforts. Their experience in selecting emulsifiers for a functional response is a valuable initial source of information. However, food processors may want to develop unique

products that have no close relationship to a product currently in commerce. In this case, the supplier may have some general ideas for emulsifier selection. However, it may be necessary for product developers to define their own criteria for emulsifiers based on critical functions required in the product.

Statistical experimental design is a very useful tool to optimize food emulsifiers and their concentrations. For example, a full factorial design (Krog et al., 1985; Jaynes, 1985) may be used to determine the levels of three emulsifiers to obtain an optimum product. Response surface methodology (RSM) and fractional factorial designs are very useful techniques because they reduce the number of experiments necessary to obtain optimal concentrations. However, since synergistic and antisynergistic effects are often observed between emulsifiers, care should be taken to design the experiments so that two-factor inter-


actions are not confounded. Robust design is also highly recommended so that

the food product has minimal sensitivity to uncontrolled noise factors.

The objective of this book is to provide the food industry professional or inter

ested technical professional with an overview of what emulsifiers are, how they

are prepared, and how they are utilized in food products. Although in many

senses food emulsifiers have become commodity ingredients, sophisticated un

derstanding and application in processed foods is likely to continue to advance.

References Friberg, S., Larsson, K. (eds.) (1990). Food Emulsions, Marcel Dekker, New York.

Jaynes, E. {1985). "Applications in the food industry, II," in Encyclopedia of Emulsion Technology {ed. P. Becher), Vol. 2, Marcel Dekker, New York, 1985, pp. 367--85.

Krog, N., Rilson, T.H., Larsson, K. (1985). "Applications in the food industry, " in

Encyclopedia of Emulsion Technology (ed. P. Becher), Vol. 2, Marcel Dekker, New

York, pp. 321-66.

TWO

Synthesis and Composition of Food-Grade Emulsifiers

R.J. Zielinski

There are a number of families of food-grade emulsifiers, which may be classi

fied as

Mono- and diglycerides

Propylene glycol monoesters

Lactylated esters

Polyglycerol esters

Sorbitan esters Ethoxylated esters

Succinylated esters

Fruit acid esters

Acetylated mono- and diglycerides

Phosphated mono- and diglycerides

Sucrose esters

In this chapter the general methods of preparing these food-grade emulsifiers

and some of the characteristics of each group of esters will be discussed.

2.1 Introduction The food-grade emulsifiers are generally esters composed of a hydrophilic (wa

ter-loving) end and a lipophilic (fat-loving) end. In general, the lipophilic end

is composed of stearic, palmitic, oleic, or linoleic acid or combinations of these

fatty acids. The hydrophilic end is generally composed of hydroxyl or carboxyl

11


groups. The melting point of the various esters within each family will be determined by the melting point of the fatty acids used to prepare the emulsifier. The melting points of the common fatty acids are given in Table 2.1. When stearic and palmitic acids dominate, the ester will be solid and relatively high-

Table 2.1 Melting points of fatty acids

Acid CMP eC) C8:0 Caprylic acid 16.3 CIO:O Capric acid 31.5

Lauric acid 44.2 Cl4:0 Myristic acid 56.4 Cl6:0 Palmitic acid 62.9 Cl8:0 Stearic acid 69.6 Cl8:1 Oleic acid 14 Cl8:2 Linoleic acid -6

melting; when oleic and linoleic acids dominate, the ester will be low-melting and could be a liquid at room temperature. The fatty acids present in an emulsifier may be obtained from either a fat or oil or a fatty acid source. All fats and oils are triglycerides, and the fatty acids can be obtained from the triglycerides by a hydrolytic process followed by fractional distillation. Generally, either natural or fully hydrogenated fats and oils are split to obtain the fatty acids. This process is illustrated in Equation 1.

0 II

CH2-0-C-R CH2-QH + R--cOOH

I 0 I II CH-o--c-R1 + 3H20 CH-QH + R1--cOOH

I I CH2-0-C-R CH2-0H + R2--cooH

II 0

Triglyceride Glycerine Fatty acids

(R = saturated or unsaturated alkyl chain)

(1)

where R, R1, and R2 are the alkyl portion of fatty acid groups.

Synthesis and Composition of Food-Grade Emulsifiers 13

Kosher oleic acid may be obtained from high-oleic safflower and high-oleic

sunflower seed oils. It may also be obtained from a specially purified tall oil

from pine trees. Commercial stearic acid may be of three types: (i) a mixture of

about 90% stearic acid and 10% palmitic acid, (ii) a mixture of about 70%

stearic acid, 30% palmitic acid, or (iii) a mixture of about 50% palmitic acid

and 50% stearic acid; all are known as stearic acid. Generally, partially hydro

genated fats and oils are used to prepare plastic-type emulsifiers.

2.2 Mono- and Diglycerides The mono- and diglycerides are the most widely used food-grade emulsifiers.

They may be esters that are solid and high-melting, esters that are liquid at

about room temperature, or a plastic-type ester. There are a variety of mono

and diglycerides commercially available at the present time. These are com

monly designated as (i) 40% a-monoglycerides, (ii) 50% a-monoglycerides,

and (iii) 90% monoglycerides. Monoglycerides are commonly composed of a

number of components, as indicated in Figure 2.1.

These components are present in different amounts in the commercially

available esters. The various types of commercial compositions are described

in the following discussion.

The mono- and diglycerides may be prepared by either an interesterifica

tion process with glycerine and triglycerides or a direct esterification process

with fatty acids. These processes are illustrated in Equation 2. In the latter

case, water of esterification is formed and removed during the process step.

0 0 0 II II II

CH2-0H CH-C-R CH2-0-C-R CH2-0-C-R

I I I 0

I 0

II II CH-OH CH-OH CH-0-C-R CH-0-C-R

I I I I 0 II

CH2-0H CH-0-H CH2-0H CH2-0-C-R

Glycerine Monoglyceride Diglyceride Triglyceride

Figure 2.1


0 II

CH2-0H CH2-0-c-R CH2-0H CH-OH

I I 0 I I II heat CH-QH + CH-0-C-R CH-OH + CH-QH

I I 0 catalyst

I I 0 II II

CH2-0H CH2-0-C-R CH2-0H CH-Q-C-R

Glycerine Triglyceride Glycerine Monoglyceride

0 II

CH2-0H CH2-0H CH2-D-c-R

I heat I 0 I 0 II II

CH-OH + R-cOOH CH-O-c-R + CH-0-C-R

I I 0 I 0 II II

catalyst

CH2-0-C-R CH2-D-C-R

Glycerine Diglyceride Triglyceride

(2)

The catalysts commonly used in these processes are sodium hydroxide or hy

drated lime (calcium hydroxide); the temperatures involved range from 200 to

250°C. The proportions of each of the products-free glycerine, monoglyceride,

diglyceride, and triglyceride-are purely dependent on the molar ratio of glycer

ine and oil or glycerine and fatty acid used. The overall composition can be ap

proximated using a random distribution of the free hydroxyl group and fatty acid

groups (Feuge and Bailey, 1946). The various fatty acid groups from the oil or

fatty acid are also assumed to he randomly distributed in the final product.

Once the desired ratio of oil or fatty acid and glycerine has been chosen to

yield the desired monoglyceride content, a number of different types of mono

glyceride compositions are still potentially available. For example, if a 40%

monoglyceride composition is desired, then (i) the catalyst may be neutralized,


generally by phosphoric acid; (ii) the catalyst may be not neutralized; (iii) the

reaction mixture may be cooled to a determined temperature and the glycerine

that is insoluble in the final composition removed by decantation type process;

and (iv) the excess free glycerine may be removed from the reaction products

by vacuum distillation. A 40% monoglyceride prepared by a decantation-type

process (iii) may contain about 4% free glycerine, while a 40% monoglyceride

prepared by a vacuum-stripping process will typically contain less than 1%

free glycerine. A stripped 40% monoglyceride will typically be composed of

about 46% monoglyceride, 43% diglyceride, 10% triglyceride, and 1% glycer

ine. Similarly, a 50% monoglyceride may be prepared by decantation from in

soluble glycerine or by a vacuum-stripping process. A vacuum-stripped 50%

monoglyceride will typically contain about 55% monoglyceride, 38% diglyc

eride, 5% triglyceride, and 2% free glycerine.

Under the conditions of high temperature, very low pressure, and an ex

tremely short path, monoglycerides may be distilled and thus concentrated and

purified. This process is known as "molecular distillation." Typically, a 40%

monoglyceride mixture is subjected to molecular distillation to yield mono

glycerides of over 90% purity. The nondistilled portion is recycled for an addi

tional interesterification process to yield another 40% monoglyceride-type

composition for use as the feedstock.

As previously mentioned, either nonhydrogenated or partially hydrogenated

triglycerides, or saturated or unsaturated fatty acids, may be used to prepare

solid, plastic, or liquid monoglyceride mixtures.

The mono- and diglycerides have a generally recognized as safe (GRAS)

FDA status.

2.3 Propylene Glycol Monoesters Propylene glycol or 1,2-propanediol is a food-allowed, dihydroxy polyol that is

used to prepare a variety of food-grade emulsifiers. The 1,3-propanediol is not

allowed in preparing food-grade emulsifiers. There are two methods of prepar

ing food-grade propylene glycol monoesters (PGME): (i) interesterification of

propylene glycol with triglycerides and (ii) direct esterification with fatty acids.

In contrast to the mono- and diglycerides, both procedures do not yield the

same compositions. When an interesterification process is used, the final com

position contains mono-, di-, and triglycerides in addition to propylene glycol

mono and diesters. This is illustrated in Equation 3.


CH2-QH

I CH-OH

I CH3

Propylene glycol

CH2-QH

I CH-QH

I CH3

Propylene glycol

+

+

0 II

CH2-0-c-R

I ~ heat CH-O-C-R

I 0 catalyst

II CH2-0-c-R

Triglyceride

0 0 II II

CH2-o-c-R CH2-0-c-R

I I ~ CH-OH + CH-0-C-R

I I CH3 CH3

Propylene Propylene glycol glycol monoester diester

0 0 II II

CH2-0-c-R CH2-Q-C-R

I I 0 II

CH-QH + CH-0-C-R

I I CH-QH CH2-QH

Monoglyceride Diglyceride

(R = saturated or unsaturated alkyl chain)

CH2-0H

I + CH-OH +

I CH2-QH

Glycerine

0 II

CH2-o-c-R

I 0 II

+ CH-o-c-R

I 0 II

CH2-o-c-R

Triglyceride

(3)


Basic catalysts such as sodium hydroxide or hydrated lime (calcium hydroxide)

are used in the interesterification process. Generally, the excess propylene glycol

and the glycerine formed during the reaction are removed by a vacuum distillation

process. The basic catalyst is neutralized prior to the distillation process to prevent

disproportionation of the products during the distillation process; the most com

monly used acid is 85% phosphoric acid. The composition of the final product is

controlled by the molar ratio of propylene glycol to triglyceride in the starting reac

tion mixture. The approximate final concentrations of propylene glycol monoester

and monoglyceride may be determined by assuming that a random distribution oc

curs during the reaction process (Feuge and Bailey, 1946). By controlling the mo

lar ratio of propylene glycol to triglyceride, propylene glycol monoester contents

ranging from about 13 to 70% may be obtained. Generally, most commercial com

positions contain 50 to 70% propylene glycol monoester.

Commercial products containing propylene glycol monoesters of greater

than 90% are produced by means of a molecular distillation process similar to

that employed for the production of distilled monoglycerides. In the PGME

case, an interesterification mixture containing a high concentration of PGME

is used as a feedstock for the distillation process. Small amounts of distilled

monoglycerides may co-distill with the propylene glycol monoester.

The direct esterification of propylene glycol with fatty acids yields a mix

ture of free propylene glycol, propylene glycol monoester, and propylene glycol

diester, as illustrated in Equation 4.

The residual propylene glycol is generally removed by a vacuum steam

stripping process. The amount of propylene glycol monoester ranges from 45

to 70% in commercially available compositions prepared by direct esterifi

cation of propylene glycol with fatty acids. The amount of monoester can be

approximated by assuming a random distribution with various molar ratios of

propylene glycol to fatty acid (Feuge and Bailey, 1946). A basic catalyst

such as sodium hydroxide or hydrated lime is generally used during the es

terification step to avoid the formation of dipropylene glycol esters. The ba

sic catalyst is neutralized with an acid, usually 85% phosphoric acid, prior

to the steam-stripping step to avoid a disproportionation of the monoester

during the stripping step.

If a strong acid is used as a catalyst during the direct esterification step,

then the distinct possibility of the self-condensation of propylene glycol to the

dimer or trimer followed by esterification of the dimer or trimer exists. Thus,

acid-catalyzed esterifications can contain dipropylene glycol monoesters and


0 II

CH2-0H CH2--o-c-R

I heat I CH-OH + R-cOOH CH-OH +

I catalyst

I CH2 CH3

0 II

CH2-0-c-R

I ~ CH2-0-C-R

I

(4)

tripropylene glycol monoesters. These esters are not allowed by the FDA as direct food additives.

The FDA regulations for propylene glycol monoesters allow the use of all edible oils and edible fatty acids. However, the majority of the propylene glycol monoesters commercially available contain very high percentages of palmitic acid and stearic acid that are saturated fatty acids. Few unsaturated propylene glycol monoesters are available at this time.

2.4 Lactylated Esters Lactic acid, 2-hydroxypropanoic acid, is a bifunctional acid. As illustrated in Figure 2.2, fatty acid esters may be prepared by reaction with either the hydroxyl group or the fatty acid group. Lactic acid can also self-react to form polymeric (dimer, trimer, etc.) chains. These polymers can also react with fatty acid moieties. This is also illustrated in Figure 2.2.

This self-condensation reaction cannot be avoided, and all lactic acid emulsifiers contain mixtures of monomer, dimer, and trimer esters.


OH f--- R-COOH

I CH3-c-COOH f--- R-QH

I H

Lactic acid

Figure2.2

/R-COOH

OH

I 0 CH3

II I CH3-C-c-o-cOOH f--- R-OH

I H

Dilactic acid

2.4.1 Reaction at the Hydroxyl Group

Two broad categories of food-grade emulsifiers that are prepared by the reaction

of the hydroxyl group of lactic acid with either fatty acids or fatty acid chlorides

are commercially available: (i) the lactylic esters of fatty acids and (ii) partial

metal salts of lactylic esters of fatty acids. Each will be discussed in tum.

2.4.1.1 Lactylic &ters of Fatty Acids. Two types of lactylic esters of fatty acids

are commercially available. One composition contains approximately 60%

monomer, 10% dimer and trimer, 30% free fatty acid, and 3% free polylactic

acid. The second composition contains approximately 42% monomer, 16%

dimer and trimer, 30% free fatty acid, and 12% polylactic acid. Three methods

are available to prepare a lactylic ester with a 60% monomer content. The first is

the reaction of lactic acid of known monomer content with a fatty acid chloride

with or without the presence of a weak base to capture the hydrogen chloride

generated (Thompson and Buddemeyer, 1956). This method uses a costly acid

chloride and an extensive purification process. The second method involves the

direct esterification of about a 1:1 molar ratio of sodium lactate and fatty acid,

followed by acidification with mineral acid and isolation of the fatty lactylic ester

(Eng, 1972). A third method of preparing a lactylic ester with a 60% monomer

content is to react lactic acid with acetic anhydride to form the lactyl acetate.

The lactyl acetate is then subjected to an acidolysis reaction with fatty acids in

the presence of a sodium base under high-vacuum conditions. The mixture is

then acidified with mineral acid and the fatty lactylic esters isolated.

The lactylic ester with about 42% monomer and 16% dimer and trimer


acids most probably is prepared by the direct esterification of lactic acid with

fatty acid in about a 1:1 molar ratio (Thompson et al., 1956). A high free poly

lactic acid content (see Chapter 3 for analytical procedure) indicates that the

product has not been water-washed.

There are no restrictions on the lactic acid content of the lactylic esters of

fatty acids in the FDA regulations (21CFR172). There are no FDA restrictions

on the edible fatty acids that may be used in the preparation of the lactylic es

ters of fatty acids; however, the stearate esters are most commonly produced.

2.4.1.2 Metallic Salts of Lactylic Esters of Fatty Acids. There are two metal

lic salts of lactylic esters of fatty acids that are used in the food industry: cal

cium salt and sodium salt. The calcium salt was commercialized first, as a

dough conditioner for bread, and is known as calcium stearoyl-2-lactylate.

The 2 indicates that 2 moles of lactic acid were used in its preparation. The

sodium salt, which was commercialized later, is known as sodium stearoyl-2-

lactylate, sodium stearoyllactate, or simply "SSL." It is used extensively in

many food applications.

Both esters can be prepared by the same process, the direct esterification of the partial salt of lactic acid with a fatty acid in about a 2: l molar ratio of lac

tic acid to fatty acid (Thompson et al., 1956). Both esters have a monomer con

tent of about 40%, a polymeric content of about 31%, and a polylactic acid

content of about 6%.

Care must be taken to use high-quality starting materials to avoid excessive

darkening during the reaction process. The color of the final product can be re

duced by the use of hydrogen peroxide as a bleaching agent.

The amounts of lactic acid and metal ion content of both esters are regulated

by the FDA and are about 34% and 4.5%, respectively. Only the use of specified

grades of stearic acid is permitted by the FDA regulations for the products.

2.4.2 Reaction at the Carboxylic Acid Group

2.4.2.1 Lactylated Monoglycerides. The carboxylic acid group of lactic acid

can react with the hydroxyl group of other fatty acid-derived compositions to

yield emulsifiers that are useful in many food products. One of the most common

fatty acid compositions used is a reaction product with a monoglyceride to form a

lactylated monoglyceride identified in the FDA regulations as glycerol-lacto es

ters of fatty acids. The overall simplified reaction is illustrated in Equation 5.

As can be seen from Equation 5, the number of hydroxyl groups remain the

+

Monoglyceride


OH

I CH -C-COOH

3 I ____.

H

Lactic acid

0 OH II I r,--o--c -c -cH,

CH-OH

I

Lactylated monoglyceride

+ Hp

(5)

same in the reaction product as in the starting monoglyceride and a methyl

group is introduced. This has the net effect of lowering the melting point and

increasing the fat solubility of the lactylated monoglyceride compared to the

starting monoglyceride.

As previously discussed, lactic acid can homopolymerize; therefore, dilac

tate and trilactate esters of monoglycerides can and will be formed during the

esterification reaction.

A major variable in the formation of lactylated monoglycerides is the compo

sition of the monoglyceride that is reacted with lactic acid. For example, Barsky

(1950) disclosed the use of shortening compositions containing lactylated mono

glyceride made by two different methods. The first lactylated monoglyceride was

prepared by the reaction of l mole of oleic acid with l mole of glycerine; then the

reaction product was reacted with 33% of 88% lactic acid. The second mono

glyceride was prepared by the interesterification of 100 parts of partially hydro

genated oil with 25 parts of glycerine; then the reaction product was reacted with

29.5% of anhydrous lactic acid. In both cases, about a nominal 40% monoglyc

eride intermediate composition was made, and about 7% of free glycerine could

be expected to be present in the monoglyceride mixture. The free glycerine can

react with lactic acid to yield water-soluble, oil-insoluble, glycerol lactates.


These glycerol lactates can be removed by water-washing or can be steam

stripped from the reaction mixture under reduced pressure.

A distilled monoglyceride could also be used as a reacting monoglyceride

composition. However, during the reaction with lactic acid, the distilled mono

glyceride could totally or partially disproportionate to yield free glycerine and

a mixture of mono-, di-, and triglycerides. Thus, the benefit of using a distilled

monoglyceride could be lost.

Other possibilities of starting monoglycerides are an unstripped intermedi

ate monoglyceride with an a-mono content of 28 to 40%, a 40% U-monoglyc

eride that has been vacuum-stripped to remove the free glycerine, or a 50%

monoglyceride type that has or has not been vacuum-stripped to remove the

free glycerine before reaction with lactic acid. Of course, any diglycerides pre

sent in the monoglyceride mixture can also react with lactic acid.

Another variable in the production of lactylated monoglycerides is the

amount of lactic acid reacted with the monoglyceride intermediate. In theory,

a monoglyceride can react with 2 moles of lactic acid to yield the dilacty

lated monoglyceride ester. Commercially, lactylated monoglycerides are

available that contain either about 15% or 22% lactic acid. There is an ana

lytical constant known as WICLA (see Chapter 3), which stands for water-in

soluble combined lactic acid, used by some companies to characterize

lactylated monoglycerides. This value will give an estimation of the amount

of active functional lactylated monoglyceride present in the commercial

product as opposed to a total lactic acid value that is a summation of the

WICLA value and the amount of lactic acid present in a water-soluble form,

such as glycerol lactates.

Because of the wide range of possible starting monoglycerides and the reac

tion conditions chosen, all commerciallactylated monoglyceride compositions

may not be compositionally the same, and possibly, differences in functionality

can exist between products with a similar lactic acid content.

The FDA regulations for lactylated mono- and diglycerides permit the use

of any edible fat or oil or edible fatty acids to be used in their manufacture.

There are no restrictions on the amount of lactic acid that can be present in the

lactylated mono- and diglycerides.

2.4.2.2 Lactylated Fatty Acid Esters of Glycerol and Propylene Glycol. Another

emulsifier, prepared from lactic acid by the reaction of the carboxylic acid

group of the lactic acid with the hydroxyl groups of glycerol and propylene gly-


col monoesters, is the lactylated fatty acid esters of glycerol and propylene gly

col. In this type of emulsifier, propylene glycol is interesterified with an edible

fat or oil to yield a mixture of mono- and diglycerides and propylene glycol mo

noesters. The reaction mixture is then reacted with lactic acid. As with the

lactylated mono- and diglycerides, a great variety of propylene glycol mo

noester and monoglyceride mixtures could be used to react with lactic acid to

yield a final composition. In addition, lactic acid can react with any free propy

lene glycol and free glycerine initially present or formed by a disproportiona

tion of the starting propylene glycol monoesterlmonoglyceride composition.

These propylene glycol lactates and glycerol lactates are removed by water

washing or vacuum distillation of the reaction product. Obviously a complex

composition is produced.

It should be noted that only propylene glycol esters prepared by an inter

esterification process may be used. Propylene glycol mono- and diesters pre

pared by a direct fatty acid esterification route are not allowed under the

pertinent FDA regulation (21CFR172.850). The FDA regulation further speci

fies the WICLA content of the final ester composition to be 14 to 18%.

2.5 Polyglycerol Esters Polyglycerol esters have been commercially available to the food industry for

over 25 years, but they have been known in the nonfood industry for many

more years. The polyglycerol alcohols are most often prepared by the poly

merization of glycerine with an alkaline catalyst at elevated temperatures

(Harris, 1941; Babayan and Lehman, 1973). The polymerization is a random

process and a number of different polyglycerols are produced. This is illus

trated in Equation 6.

The extent of polymerization is followed by refractive index, viscosity, or

hydroxyl value. When the theoretical hydroxyl value for a diglycerol is ob

tained, the polyglycerol could be called diglycerol. When the hydroxyl value

for triglycerol is obtained, the polyglycerol could be called a triglycerol, etc.

The hydroxyl values for di- to decaglycerol are summarized in Table 2.2. The

theoretical molecular weight of each polyglycerol is also given in Table 2.2.

In general, no effort is made to separate the various polyglycyerols, and the

entire reaction mixture that contains a distribution of polyglycerols is used to

prepare polyglycerol esters. At lower degrees of polymerization, higher con

centrations of lower poyglycerols are present; at higher degrees of polymeriza-


heat

catalyst

OH OH OH

I I I CH2-cH-cH2-0-CH2-CH-CH2-0H Diglycerol

OH OH OH OH

I I I I CH2-CH-(H2-0-CH2-(H-(H2-0-cH2-CH-CH2-0H Triglycerol

OH OH OH OH OH

I I I I I CH2-CH-cH2-G-CH2-CH-CH2-0-CH2-CH-CH2-0-CH2-CH-CH2-0H

Tetragl ycerol

and so on, up to decaglycerol + (n- 1) H20 (6)

Table 2.2

Theoretical Theoretical Polyol hydroxyl value molecular weight

Glycerine 1839 92 Diglycerol 1352 166 Triglycerol 1169 240 Tetraglycerol 1072 314 Pentaglycerol 1012 338 Hexaglycerol 971 462 Heptaglycerol 942 536 Octaglycerol 920 610 Nonaglycerol 902 684 Decaglycerol 888 758


tion, higher concentrations of higher polyglycerols are present. The number of

possible esterification sites in a polyglycerol is the nominal polyglycerol plus

2(n + 2). Thus, a triglycerol has 5 possible esterification sites and an octa

glycerol has lO possible esterification sites.

The polyglycerol esters may be prepared from the polyglycerols by either a

direct esterification with fatty acids or an interesterification with triglycerides.

When a fatty acid process is used, the theoretical molecular weight of the

polyglycerol is used with the molecular weight of the fatty acids to calculate

the reaction charge. Generally, if low degrees of esterification are used, the re

action product is neutralized and allowed to "phase out" at about l00°C. The

free polyol is separated and the emulsifier is filtered and packaged. If higher

degrees of esterification are used, then no polyol will phase out and the prod

uct, neutralized or not neutralized, is filtered and packaged.

If an interesterification process is used, then additional glycerine from the

fat or oil is introduced into the reaction mixture. This additional glycerine will

modify the polyol distribution of the final product compared to the polyol dis

tribution of the starting polyglycerol. Additional mono- and diglycerides will

be produced compared to a direct esterification process, and distribution of

fatty acids ester will be different than if a direct esterification process were

used. Esters prepared by an interesterification process are still identified by

the polyol that was initially used.

It is obvious that even if a single fatty acid were used to make polyglycerol

esters that the number of compositions possible are very numerous and com

plex. Since mixtures of fatty acids are used, this makes the polyglycerol es

ters even more complex. Thus, a triglycerol monostearate polyglycerol ester

is a mixture of the stearate and palmitate esters of glycerine, diglycerol,

triglycerol, tetraglycerol, pentaglycerol, hexaglycerol, heptaglycerol, oc

taglycerol, nonaglycerol, and decaglycerol, while a decaglycerol tristearate is

a mixture of the stearate and palmitate esters of the same polyglycerols but in

different proportions.

A wide range of polyglycerol esters are commercially available from liquid

esters such as hexaglycerol dioleate to plastic esters like triglycerol mono

shortening to solid esters like decaglycerol decastearate.

FDA regulations permit the use of edible hydrogenated or nonhydro

genated nonlauric oils and the edible fatty acids derived from them as well

as oleic acid from tall oil to prepare polyglycerol esters up to and including

decaglycerol.


2.6 Sorbitan Esters Only one sorbitan ester is currently approved in the FDA regulations as a di

rect food additive in the United States: sorbitan monostearate. However, a

GRAS petition has been filed to permit the use of sorbitan tristearate in con

fectionery coatings (Federal Register, 1988). The FDA, as of 1996, has not

acted on this petition. The most commonly used process for the production of

sorbitan esters is the direct fatty acid esterification of sorbitol with stearic acid

(Brown, 1943; Japanese Patent, 1974). Generally, the stearic acid used is

about a 50:50 mixture of stearic and palmitic acids. The overall reaction is

shown in Equation 7.

Sorbitan is a monoanhydro sorbitol and sorbide (or isosorbide) is a dianhy

dro sorbitol, as illustrated in Equation 7. Commercial sorbitan monostearate is

the stearate, palmitate ester of a mixture of about 1 to 12% sorbitol, 65 to 72%

sorbitan, and 16 to 32% isosorbide. It can be demonstrated that the amount of

sorbitan is fairly constant but that the amount of linear sorbitol and isosorbide

can vary among manufacturers.

The use of an acidic catalyst during the esterification of sorbitol promotes

the cyclization of sorbitol to the mono- and dianhydro forms. The use of a basic

catalyst promotes the esterification reaction at the expense of color formation.

It is possible that each commercial supplier has its own blend of acidic and

basic catalysts to generate the ratio of sorbitan esters required to meet tight

FDA specifications for hydroxyl number, saponification number, and acid

number while minimizing color degradation of the product. Hydrogen peroxide

can be used to reduce the color of a sorbitan monostearate.

Stockburger (1981) has patented a process for preparing sorbitan esters in

which sorbitol is first dehydrated with an acid catalyst to the desired ratio of

sorbitol, sorbitan, and sorbide polyols. The mixture of polyols is then reacted

with fatty acids and a basic catalyst to yield the desired sorbitan ester with an

improved light color. The use of sorbitan monostearate in foods is highly regu

lated. The reader is referred to 21CFR172.842 for further details on where sor

bitan monostearate can be used in food products, and for the required

analytical constants.

2.7 Ethoxylated Esters Four ethoxylated fatty acid esters have FDA approval for use as direct food ad

ditives. These are ethoxylated sorbitan monostearate, ethoxylated sorbitan

CH2-DH

I CH-OH

I CH-OH +

I CH-OH

I CH-DH

I CH2-0H

Sorbitol


catalyst R-COOH

CHI

L<JH I I o

r-<JH I CH_j

I CH-OH

I

Sorbitan monoester

+

CH2-0H

I CH-OH

I CH-OH

I CH-OH

I CH-OH

I 0 II

CH2-0-C-R

Linear sorbitol monoester

0

+

J=l I 0

r_j CH

I CH-OH

I ~ CH2-0-C-R

I

Sorbide monoester

(7)


monooleate, ethoxylated sorbitan tristearate, and ethoxylated saturated mono

and diglycerides. The base ester that has been ethoxylated is sorbitan mono

stearate, sorbitan monooleate, sorbitan tristearate, and a 28% monoglyceride,

respectively. For each of these esters the same basic reaction is involved, the

reaction of a hydroxyl group with ethylene oxide. This reaction is illustrated in

Equation 8 for a monoglyceride.

A basic catalyst such as potassium hydroxide is used during the ethoxyla

tion process (Egan and Lampost, 1969). The ethoxylation process is a highly

exothermic reaction and adequate cooling must be available to control the re

action temperature. The ethoxylated esters are highly complex in composition,

and the actual components of the ethoxylated sorbitan or monoglyceride esters

have not been defined. Ethylene oxide itself is a highly explosive compound

under certain conditions. Safety instructions on the handling of ethylene oxide

must be read and understood before an ethoxylation process is undertaken.

Another name for ethoxylated compositions is polyoxyethylene (20) sorbitan

CH2-0H 0

I I \ CH-QH + CH2-CH2

I 0

II CH2-0-C-R

Monoglyceride Ethylene oxide

CH2-0-CH2-CHpH

I CH-O-CH2-CH2-0H

I

CH2-0-CH2-CHpH 0

I 1\ catalyst CH2-CH2

CH-OH

I CH -C-R

2 II 0

IH2-0-CH2-CH2 -O-CH2-CH2-0H

CH-Q-CH -CH -OH I 2 2

CH -O-C-R 2 II

0

(8)


monostearate, for example. Polyoxyethylene refers to the ethylene oxide poly

meric chain and the (20) indicates that approximately 20 moles of ethylene oxide

have been reacted with one average molecular weight of the starting fatty acid

ester. Other more common names for these products are polysorbate 60 for

ethoxylated sorbitan monostearate, polysorbate 80 for the oleate, polysorbate 65

for the tristearate, and polyglycerate 60 for the saturated monoglyceride.

The polyoxyethylene group is a hydrophilic, or water-loving, group. By the

introduction of the polyoxyethylene group, the starting fatty acid ester is made

more hydrophilic and the final composition has excellent water solubility or

dispersibility. The melting point of each of the starting esters is decreased and

the ethoxylated esters are liquids or soft pastes at room temperature.

The use of the ethoxylated esters in food products is highly regulated, and

the reader is referred to 21CFR172.834, 21CFR172.836, 21CFR172.832, and

21CFR172.840 for details of where and how much polyglycerate 60, polysor

bate 60, polysorbate 65, and polysorbate 80, respectively, may be used.

2.8 Succinylated Esters Succinylated esters of monoglycerides and propylene glycolesters are permit

ted as direct food additives. The essential step in the preparation of succiny

lated esters is the reaction of a hydroxyl group with succinic anhydride. This is

illustrated in Equation 9 for a monoglyceride.

0 II

CH,--c~

+ 0 -------+

CH -0-C-R 2 II

CH--c/ 2 II

0 0

Monoglyceride Succinic anhydride

0 II

CH2-0-C-CH2-CH2-COOH

I CH-OH

I CH -0-C-R

2 II 0

Succinylated monoglyceride

(9)


Freund (1966) patented the manufacture of succinyl monoglycerides; in

this patent he also describes the production of succinyl propylene glycol mo

noesters. Martin (1968) has patented stearoyl and behenoyl propylene glycol

hydrogen succinate. The succinylation reaction is carried out under anhydrous

conditions with or without a catalyst such as potassium carbonate by the reac

tion of a distilled monoglyceride or distilled propylene glycol monoester with

succinic anhydride above the melting point of the fatty acid ester and below

the melting point of succinic anhydride. Care must be exercised when han

dling succinic anhydride because it is an irritant and is sensitive to moisture.

Generally, a reaction temperature of around ll0°C is used. If a catalyst is

used, it is generally not removed and is left in the final composition. Care must

be taken to avoid the reaction of the carboxylic acid group of the succinyl

group with other available hydroxyl groups to form polymeric materials. This

polymeric condensation reaction will take place easier in the presence of a

catalyst and at temperatures above 170°C. In the determination of the extent of

completion of the succinylation reaction, a nonalcoholic solvent should be

used for an acid number determination. For, if a solvent such as ethyl alcohol

is used, then the alcohol will react with the succinic anhydride, in a fashion

similar to the monoglyceride, and a false indication of the completeness of re

action will be obtained.

While it is possible to react 2 moles of succinic anhydride with 1 mole of

monoglyceride, the most functional results have been found with between

about 0.75 to 1.1 moles of succinic anhydride per mole of distilled monoester,

either monoglyceride or propylene glycol monoester.

The current FDA regulations for succinylated monoglycerides permit any

edible oil or edible fatty acid to be used as a source of the monoglyceride in

termediate. However, restrictions are placed on the succinic acid content, acid

number, and melting point of the final composition. Restrictions have been

placed on the use of succinyl monoglycerides in food products; see

21CFR172.830. In contrast, only saturated edible oils predominantly C16 and

C18 in chain length may be used in the preparation of the propylene glycol

monoester intermediate. Regulation 21 CFR172. 765 specifies the acid number,

hydroxyl number, and degree of succinylation of the succistearin (stearoyl

propylene glycol hydrogen succinate). The emulsifier can be used in many ap

plications with good manufacturing practice.


2.9 Fruit Acid Esters There are two fruit acids used to make food-grade emulsifiers: tartaric acid and

citric acid. Tartaric acid-derived esters have been used extensively in Europe,

but they have not been used very much in the United States. One of the fore

most uses of tartaric acid-derived esters is a dough conditioner; in the United

States other dough-conditioning agents are used in place of tartaric acid esters.

The tartaric acid esters used are the mono- and diglycerides of diacetyl tartaric

acid (DATEM esters). The synthesis of these esters is shown in Equation 10.

COOH

I HO-CH

I HO-CH

I COOH

Tartaric acid Acetic anhydride

Diacetyl tartaric anhydride

Acetic acid

(lOa)


CH -0-C-R 2 II

0

/

COOH

II 0

H3C-c-O-CH

0 II

H3c-c-o-cz o

""II c-o CH2

I CH-QH

I DATEM

(lOb)

The DATEM esters have FDA GRAS status under 21CFR184.ll0l.

However, the regulation states that the DATEM esters must meet the specifica

tions of the Food Chemicals Codex (1981). The Food Chemical Codex specifies the tartaric acid content, the acetic acid content, the total fatty acid

content, the glycerine content, the acid value, and the saponification value of

the DATEM ester. Thus, while DATEM esters have a GRAS status, their com

position is limited in the United States.

The acid group of the DATEM esters makes them somewhat sensitive to


pH; if the food product is basic, the DATEM ester can be converted to the an

ionic form. The two acetyl groups are somewhat liable to hydrolysis, which

yields acetic acid. These esters should not be used in aqueous systems that are

expected to have a long storage life.

Two different types of citric acid-based emulsifiers are permitted as direct

food additives: stearyl monoglyceride citrate (21CFR172.755) and monoglyc

eride citrate (21CFR172.832). The monoglyceride citrate is restricted to use in

antioxidant solutions. It is prepared by the reaction of glycerol monooleate

with citric acid. The final product has an acid number of 70 to 100 and has a

14 to 17% total citric acid content.

Stearyl monoglyceride citrate is prepared by the reaction of citric acid,

monoglycerides, and stearyl alcohol to yield a composition with an acid num

ber of 40 to 52, a saponification number of 215 to 255, and a total citric acid

content of 15 to 18%. The expected reaction is shown in Equation 11.

As can be seen, the reaction products are quite complex. Both saturated and

unsaturated monoglycerides may be used. This type of ester is used in shorten

ings containing other emulsifiers and is not used extensively in the food industry.

2.10 Acetylated Monoglycerides Another food-grade additive that is formed by the reaction of an acid anhy

dride with a hydroxyl group is the acetylated monoglycerides. This reaction is

illustrated in Equation 12.

The starting monoglyceride may be saturated or unsaturated and is of mole

cularly distilled type. 21CFR172.828 permits the use of a non-food-grade cat

alyst or a food-grade catalyst in the acetylation reaction. The acetic acid

byproduct and any excess acetic anhydride or formed triacetin are removed by

vacuum distillation. Since the acetic anhydride is monofunctional, there is no

danger of polymers being formed.

The acetylated monoglycerides may also be formed by an interesterification

process. In this case, triacetin is interesterified with a suitable mixture of edi

ble fats or oils and glycerol, as illustrated in Equation 13.

In this case, the composition of the final mixture can be calculated using a ran

dom distribution (Feuge and Bailey, 1946). The final reaction mixture is sepa

rated by means of steam-stripping and molecular distillation. Any unreacted

triacetin is removed by the vacuum steam-stripping process, and the desired

acetylated monoglycerides are concentrated by the molecular distillation process.


CH2-COOH

I HQ-C-COOH +

I CH2-COOH

Citric acid

CH-QH

I CH-QH

I 0 II

CH-0-C-R

Monoglyceride

+

Stearyl alcohol

(ll)

Note that in direct reaction acetylation, the hydrophilic hydroxyl group is re

placed by a lipophilic acetyl group; thus, if a fully acetylated ester is prepared, the product is no longer an emulsifier since it has no hydrophilic groups. In the

interesterification process both fully esterified and partially esterified compositions can also be formed, depending on the amount of glycerine used.

The more fully esterified compositions are useful for their film-forming and moisture barrier properties.

FDA regulation 21CFR172.828 specifies that the final composition have a Reichert-Meiss! value of 75 to 200 and an acid value under 6. The Reichert-


0 0 II II + CH3-c-o-c-c-CH3 ------+

CH -0-C-R 2 II

0

Monoglyceride

CH2-0H

I CH-OH + I

CH2-0H

Acetic anhydride

0 II

CH2-0-C-cH3

I 0 II

CH-O-C-cH3

I 0 II

CH2-0-C-cH3

0 II

CH2-0-C-CH3

I ~ CH-O-C-CH3

I

0 II

CH2-0-c-R

I ~ + CH-Q-C-R

I

0 II

CH2-0-C-cH3

I 0 II

+ CH-0-C-R

I 0 II

CH2-0-C-R

+

+

CH -0-C-R 2 II

0

(12)

catalyst

+

0 II

CH2-Q-C-R

I CH-OH

I CH -0-C-CH

2 II 3

0

+ other

compounds

(13)


Meissl number determines the amount of short-chain fatty acids in the final

composition, and this is a measure of the degree of acetylation (see Chapter 3

for methodology). The degree of acetylation in commercially available acety

lated monoglycerides ranges from 50 to 90%.

2.11 Phosphated Esters Information on the synthesis of phosphate esters is sparse. However, Harris

(1939a, b) suggests that they can be prepared by the reaction of a mono- and

diglyceride intermediate with phosphorus pentoxide at 50 to 125°C in a two

step reaction. The reaction mixture is then neutralized with sodium carbonate

to produce the desired product.

The monosodium phosphate derivative of mono- and diglycerides of edible

fats or oils or edible fat-forming fatty acids is recognized as GRAS by the FDA.

These emulsifiers are available in a solid, liquid, or paste form. Typically, the

phosphorus content of these compositions ranges from 3.5 to 5.5%, and their pH

ranges from 6.0 to 7.5. They have found some applications in the confectionery

industry as viscosity reducers analogous to lecithin (Chapter 9).

2.12 Sucrose Esters The newest family of emulsifiers to obtain FDA approval for use as direct food

additives is the sucrose esters. This occurred in 1982 (47FR5547). The su

crose esters permitted as additives under 21CFR172.859 are the mono-, di-,

and triesters. This regulation does not relate to the fully esterified sucrose es

ters that have been promoted as nonabsorbable fat and oil replacements. These

esters are a mixture of the octa-, hepta-, and hexaesters of sucrose.

The main method of preparing sucrose monoesters is by means of an inter

esterification process between sucrose and methyl esters of fatty acids. The ba

sic process is illustrated in Equation 14.

Sucrose and the methyl esters of fatty acids are very insoluble in one an

other. In addition, sucrose darkens and carmelizes on heating to temperatures

around 150°C. This insolubility and darkening of the sucrose has led to the

use of organic solvents such as N,N-dimethylformamide (DMF) or dimethyl

sulfoxide (DMSO) and reduced pressure in the preparation of the sucrose

mono-, di-, and triesters (Haas, 1959). The use of DMSO as a solvent was al

lowed in 1987 (52FR10883).

HO

Sucrose


HOCH2

0 H

H

0

H OH OH

RCOOCH2

HO 0

H OH

Sucrose monoester

0 H

H

0

OH H

H

+

0 II

R-C -OCH3 _______.

Methyl esters

Methyl alcohol

(14)

Another interesterification process used to prepare the sucrose monoesters

under vacuum is known as the "microemulsion process," or the "transparent

emulsion process." In this process edible propylene glycol is utilized as a sol

vent and reactant (Osipow and Rosenblatt, 1969). In an improvement on the

original microemulsion process, it was found that water could be used under

carefully controlled reaction conditions in place of the propylene glycol (Osipow

and Rosenblatt, 1972; Yamagishi et al., 1974). In the microemulsion process, a

very high amount of a sodium or potassium salt of a carboxylic acid is used to


produce an emulsion particle size less than one-quarter the wavelength of light,

in contrast to other emulsions in which particle sizes are greater than the wave

length of light. This particle is so small the emulsion appears transparent.

However, the use of the high amount of the metal salts of the fatty acids and un

reacted sucrose leads to difficult purification and separation procedures. In gen

eral, solvents such as ethyl acetate, methyl ethyl ketone, or isobutyl alcohol are

used during the purification process. FDA rule 21CFII 72.859 specifies the

amount of these solvents that can be in the final sucrose ester. A patent has been

issued regarding the purification of the sucrose ester reaction mixture (Mizutani

et al., 1973), but many other purification processes are possible. Overall, the

production of the sucrose monoesters is a more complicated process than the

production of the other food-grade emulsifiers.

References Babayan, V.K., Lehman, H. (1973). U.S. Patent 3,637,774, January 25. Barsky, G. (1950). U.S. Patent 2,509,414, May 30. Brown, K.B. (1943). U.S. Patent, 2,322,820, June 29. Egan, R.R., Lampost, S.B. (1969). U.S. Patent, 3,433,645, March 18. Eng, S. (1972). U.S. Patent 3,636,017, January 18. Federal Register, 53, 40808, December, 1988. Feuge, R.O., Bailey, A.E. (1946). Oil and Soap, 23, 259. Food Chemical Codex (1981). 3d ed., pp. 98-99. Freund, E.H. (1966). U.S. Patent 3,293,272, December 20. Harris, B.R. (1939a). U.S. Patent 2,177,983, October 31. --(1939b). U.S. Patent 2,177,984, October 31. --(1941). U.S. Patent 2,258,892, October 14. Hass, H.B. (1959). U.S. Patent 2,893,990, July 7. Japanese Patent Publication (1974). No. 15246, April13. Martin, J.B. (1968). U.S. Patent 3,375,262, March 26. Mizutani, N., et al. (1973). U.S. Patent 3,798,324, July 24. Osipow, L.l., Rosenblatt, W. (1969). U.S. Patent 3,480,616, November 25. --(1972). U.S. Patent 3,644,333, February 22. Stockburger, G.J. (1981). U.S. Patent 4,297,290, October 21. Thompson, J.B., Buddemeyer, B.D. (1956). U.S. Patent 2,744,825, May 8. Thompson, J.B., eta!. (1956). U.S. Patent 2,733,252, January 31. Yamagishi, F., eta!. (1974). U.S. Patent 3,792,041, February 12.

THREE

Analysis of Food Emulsifiers


3.1 Introduction Analytical methods for food emulsifiers are closely associated with or derived

from methods commonly used for fats and oils (Sonntag, 1982; Karleskind,

1996). Test methods are of several types and are carried out for a variety of

reasons. Analysis ensures that the composition of the emulsifier is correct and

that it has not seriously degraded during processing. Often the composition

and distribution of homologs has implications for the utility of the emulsifier in

the individual food product (see, for example, Halkier, 1980). The final level of

testing is often a measurement of performance in the food system itself.

Specifications are negotiated and agreed upon between the producer and the

customer (usually a processed food manufacturer). Analytical tests are carried

out on the process line or control laboratory of the supplier, who then provides

a certificate of analysis to the customer. The customer may then check the

analysis as part of the receiving procedure and accept or reject the shipment.

Disputes may be settled by submitting a sample to an independent laboratory.

Quality assurance testing is also necessary to ensure that foods conform to

39


standards set by government regulatory agencies. The U.S. Food and Drug

Administration (FDA), the European Economic Community (EEC), and the

regulatory agencies of individual countries have limits on the maximum con

centration of emulsifiers or other food additives allowed in specific products.

This topic has been reviewed by several authors (Kroeller, 1966, 1968;

Gernert, 1968; Amano, 1979). Professional organizations, such as the

Association of Official Analytical Chemists (AOAC), the American Oil

Chemists' Society (AOCS), International Union of Pure & Applied Chemistry

(IUPAC), Leatherhead Food Research Association, and the National Academy

of Sciences (Food Chemicals Codex), have compiled lists of official methods

that are used for fats, oils, and emulsifiers (Cunniff, 1995; Firestone, 1990;

Paquot and Hauffen, 1987; Slack, 1987; Taylor, 1996).

To determine emulsifiers in intact food products, the fats and emulsifiers must

first be extracted. Fats and oils are soluble in nonpolar solvents, such as hexane

or toluene. However, emulsifiers are amphiphilic and more polar and tend to

be less soluble in cold hexane or petroleum ether, particularly when emulsifier

concentration is high compared to total lipid level. Chloroform or chlorofonn/

methanol mixtures (Flor and Prager, 1980) are sufficiently polar but also suffi

ciently immiscible to allow for extraction from aqueous food systems. In cases

where total lipid content is high compared to emulsifier concentration,

Halverson and Qvist (1974) have reported extracting total lipids with refluxing

hexane followed by extraction with acetonitrile. Solid foods samples (e.g., cake,

coffee whitener) are conveniently extracted using a Soxhlet extraction apparatus.

Liquid samples (e.g., milk, ice cream mix) are usually separated in a separatory

funnel or countercurrent distribution apparatus. Another factor complicating ex

traction from foods is that lipids may be tightly complexed by starches or pro

teins or may simply be encapsulated in a biopolymeric matrix. Jodlbauer (1976)

has demonstrated the use of an amylase enzyme to release lipids from a pasta

product so that they are more easily extracted.

3.2 Thin-Layer and Column Chromatography After lipids have been extracted, the emulsifiers may be isolated from the non

polar lipids by simple thin-layer or column chromatography. For example, on a

silica gel column, triglycerides may be eluted with hexane followed by diglyc

erides with 5% diethyl ether, and monoglycerides in 10% ether/hexane.

Dieffenbacher et al. (1988, 1989) have described a one-step extraction and

Analysis of Food Emulsifiers 41

purification process using a Celite/sodium sulfate column. Fractions from

these separations may be quantitated gravimetrically and/or subjected to fur

ther analytical testing.

Thin-layer chromatography (TLC) and paper chromatography have been

used for detection of food emulsifiers. The method was a simple, rapid, and

reasonably reliable means to test for the presence of emulsifiers in lipid com

ponents (Murphy and Hibbert, 1969; Wurziger, 1968). Mono- and diglycerides

are readily separable on a boric acid-impregnated silica gel plate. Spots can

be visualized by spraying with dichlorofluorescein and identified by their Rf

values. Schmid and Otteneder (1976) utilized a petroleum ether, diethyl ether,

and acetic acid solvent system to identify monoglycerides in alimentary pastes.

Kanematsu and coworkers (1972) separated monoglycerides from propylene

glycol fatty acid esters in shortenings using a chloroform/acetone solvent sys

tem. Thin-layer chromatography was also used by Paganuzzi (1987) to separate

lipids for further analysis by gas-liquid chromatography.

Because of their importance in lipid metabolism and as components of lipid

membranes, phospholipids have been widely studied and analyzed. TLC has

been reported as a method of separation and analysis of phospholipids from

fish and oilseeds (Erdahl et al., 1973; Vyncke and Lagrou, 1973; Kimura et al.,

1969; El-Sebaiy et al., 1980; Lendrath et al., 1990; Biacs et al., 1978).

Watanabe and coworkers (1986) have reported a two-dimensional TLC proce

dure on silica gel that uses acidic and basic solvent systems. The method was

applied to soy and egg lecithins. Detection of phospholipids may be accom

plished by conventional nonselective stains, such as sulfuric acid. However,

the compound class may be distinguished from other lipids by phosphorus de

tection, by either selective reagents or spectroscopy (Senelt et al., 1986).

Experimental design can also be used to optimize separation of phosphorus

containing lipids (Olsson et al., 1990).

Monoglycerides can be further derivatized with organic acids to produce

new emulsifiers with unique functionalities (see Chapter 2 for synthesis).

Compounds such as lactylated, succinylated, and diacetyltartaric esters

(DATEM) monoglycerides may be determined by TLC (Bruemmer, 1971;

Yusupoca et al., 1976; Jodlbauer, 1981). These methods deal with the com

plexity of separating derivatives from unreacted monoglycerides. In some

cases, synthesized authentic standards were used to confirm identification of

the spots. Calcium and sodium stearoyllactylates, also widely used in bakery

products, are also capable of being determined by TLC. Regula (1975) carried


out the separation on Kieselgel G using a hexane/acetone/acetic acid solvent

system. Spots were visualized by spraying with bromocresol green. Kroeller

(1969) used starch paper impregnated with mineral oil as the stationary phase.

Methyl red was used to visualize the top half of the chromatogram, and potas

sium hexacyanoferrate was used on the bottom.

One of the major drawbacks to the routine use of TLC in lipid analysis has

been the difficulty of obtaining quantitative rather than qualitative results.

This problem has been addressed by the development of a unique chromato

graphic system that uses a coated rod rather than a plate. After development,

the rod is placed in a scanning-flame ionization detector that transforms spots

into peaks on an x-y plot. Determinations of monoglycerides (Takagi and

ltabashi, 1986; Ranny et al., 1983), phospholipids (Tanaka et al., 1979), and

sucrose esters (Rios et al., 1994) have been reported using this technique.

Duden and Fricker (1977) have described the detection of monoglycerides and

lecithin using a fluorescence reagent in a chromatogram spectrophotometer.

Despite these improvements, TLC is being rapidly replaced by gas-liquid

chromatography (GLC) and high-performance liquid chromatography. These

methods offer the convenience of autosampling, which translates into im

proved productivity for routine analyses.

Historically, the first methods developed for testing fats, oils, and emulsi

fiers were wet methods; that is, they involved the use of solutions and chemical

reactions. Procedures used to define these tests often involved separations and

structure determination of the products through chemical degradation. Tests to

measure the melting properties of these materials were spawned in the early

1900s as an adjunct technology of catalytic hydrogenation. With the develop

ment of gas-liquid chromatography and high-performance liquid chromatogra

phy, instrumental methods have often replaced older, more labor intensive wet

methods. Automated sampling served to increase analytical productivity even

further. Perhaps the ideal model of a control lab is a clinical chemistry facility.

Automated sampling, fluid transfer, reactions, determination, and reporting of

results have virtually eliminated repetitive procedures.

The major problem with control testing has been that it occurs after the

emulsifier has been produced. The results then compel the quality control

manager to accept or reject the product. Modem quality practices are incorpo

rating analytical measurements directly into the process stream or chemical

reactor. In-process analysis allows rapid correction before the product is pro

duced, resulting in less scrap and rework.


3.3 Wet Chemical Analysis Wet analysis describes a determination that uses solvents and chemical reagents

to determine an aspect of emulsifier composition. An example would be titration

of free fatty acid with alcoholic potassium hydroxide. Wet methods have been

standard practice for many years. However, a large analysis volume in laborato

ries poses the problem of disposal or recycling of reagents and/or spent solvents.

For this reason, the current trend is to replace the wet method with instrumental

or physical measurements that supply related or equivalent information. Some of

the most widely used methods for emulsifiers are described next.

3.3.1 a-Monoglyceride t

Monoglycerides may exist as alpha, the most predominant form, which has the

fatty acid esterified in the 1 or 3 positions of the glycerol head group, or beta,

where the substitution is at the 2 position. The alpha isomer has adjacent hy

droxyl groups in the 1, 2 or 2, 3 positions. The isomer is determined by titration

with periodic acid resulting in cleavage, as shown in the following equation:

The analysis is carried out by dissolving the sample (extracted lipid or pure

OH

I

OH 0-1-1

C17H35 + HI04 ----+ 0

0 II

CH -c-c ~ 2 H I

0 -~-~ C17H35 + HI04 + HI03 + Hp

0

(15)

t Cunniff (l995a); Firestone (l990n).


emulsifier) in a solvent and reacting with an excess of periodic acid dissolved

in 95% methanol. Potassium iodide is then added, and liberated iodine is

titrated with standard arsenite solution. An aqueous solution of periodic acid

is used to determine free glycerine. The result for monoglyceride is then cor

rected for the amount of periodic acid consumed by free glycerine. For many

years, chloroform, a potential carcinogen, was the solvent used in this test.

Since about 90% of the monoglyceride is alpha, this determination is an ac

cepted approximation of the total monoglyceride concentration. Due to the

problem of solvent disposal and the fact that the method is labor intensive, it

has been largely supplanted by gas-liquid chromatography (Firestone, l990g)

(see Section 3.5, Instrumental Methods). AOCS has classified the test as a sur

plus (obsolete) method.

3.3.2 Acid Value/Free Fatty Acid t

Fatty acids may occur during the preparation of many common food emulsi

fiers. They may be present as residues from direct esterification reactions or

may be due to hydrolysis of glycerides. Fatty acids may act as antiemulsifiers

in some systems. They also make a system sensitive to pH, since alkali trans

forms fatty acids into soaps, which are powerful anionic surfactants. Attempts

are therefore made to keep free fatty acids in mono/diglycerides as low as pos

sible. Other emulsifiers, such as sodium stearoyl lactylate and lactylated

monoglycerides have high acid values that must fall in a range defined by the

FDA or other regulatory body.

Acid value is determined by dissolving a weighed sample of the emulsifier

in an isopropanol/toluene or ethanol/diethyl ether solvent and titrating with a

standard potassium hydroxide solution to a phenolphthalein endpoint. In cases

where the acid value is used to track the progress of reactions using anhy

drides, such as in production of DATEM and acetylated monoglycerides, an

aprotic solvent rather than an alcohol must be used. Alternatively, the sample

solution may be titrated potentiometrically to the equivalence inflection point.

The latter method is particularly useful for dark-colored samples where a vi

sual endpoint is difficult to observe. The acid value is defined as the number of

milligrams of potassium hydroxide necessary to neutralize the free fatty acid

per gram of sample and is determined by the formula

+Cunniff (l995c); Firestone (1990k).


(A- B)(N)(56.1)

w

where A mL standard alkali used in titration

B = mL standard alkali used to titrate blank

N = normality of standard alkali

W = g of sample

Free fatty acid percentage can be determined by dividing the acid value by

a factor characteristic of the fatty acid present. Values for this factor are C12

(lauric)= 2.81, C16 (palmitic)= 2.19, and C18 (stearic or oleic)= 1.99.

3.3.3 Iodine Valuet

Emulsifiers may be prepared from saturated or unsaturated (mainly oleic) acid

or from partially hydrogenated triglycerides. Unsaturated emulsifiers are more

susceptible to oxidative rancidity than those derived from saturated fats or

fatty acids. Titration with reagents that add across the carbon-carbon double

bond have been utilized to determine unsaturation since the early days of or

ganic chemistry. Two common methods have gained common acceptance. (i)

The Wijs method reacts the sample dissolved in carbon tetrachloride with an

iodine monochloride solution in glacial acetic acid; excess reagent is then

titrated with standard sodium thiosulfate solution. (ii) The Hanus method is almost identical but uses iodine monobromide as the reagent. Because of the

high toxicity of carbon tetrachloride, a modified method has been developed

that substitutes cyclohexane. Iodine value is expressed as the number of centi

grams of iodine absorbed per gram of sample (same as % iodine absorbed) and

is calculated using the formula

where s B

N

w

=

=

=

=

(S- B)(N)(l2.69)

w mL used to titrate sample

mL used to titrate blank

normality of thiosulfate solution

weight of sample

t Cunniff (1990e); Firestone (l990f).


In this test, when reporting the value, it is important to also identify the

method by which the value was determined.

Iodine value may also be calculated from the fatty acid composition (FAC) of

fats, oils, and fatty acids through gas-liquid chromatography (GLC)(Firestone,

1990h). The same method may be used for food emulsifiers, but new conversion

factors would probably need to be developed to translate GLC peaks to iodine

values. Near infrared reflectance (NIR) has also been developed as a rapid

method to determine unsaturation by measurement of the carbon-carbon double

bond absorbance peak. However, a great deal of work is necessary up front to as

semble a calibration curve to relate the measured absorbances to traditionally

measured values.

3.3.4 Peroxide Valuet

As mentioned before, unsaturated fatty acids can undergo oxidation to produce

off-flavors characteristic of rancidity. Autoxidation occurs through a free radical

chain reaction that produces hydroperoxides as an early intermediate. The hy

droperoxide can react further to produce aldehydes, ketones, and hydrocarbons.

Detection of hydroperoxides in food ingredients is therefore a necessary precau

tion to ensure that the product does not become rancid during its normal shelf life.

Peroxides and hydroperoxides may be determined by the reaction of a solu

tion of the sample in acetic acid and chloroform with potassium iodide.

Liberated iodine is then titrated with standardized sodium thiosulfate solution

using a starch indicator. Precautions need to be taken to avoid the presence of

residual oxidizing or reducing agents on glassware. Also, strong ultraviolet

light must be avoided, since it forms peroxides by a photochemically induced

oxygen addition. Peroxide is defined as the number of milliequivalents of per

oxide (AOAC uses the term "active oxygen") per 1000 g of sample that oxidize

potassium iodide. The exact value is obtained from the following formula:

(V)(T) (1000) m

where V = volume of titration

T = normality of thiosulfate solution

m = wt in g of sample

t Cunniff (l995g); Firestone (1990s).


Since the practicing formulator needs to minimize the peroxide content of in

gredients, the lower the peroxide value, the less is the risk of developing rancidity.

Special surveillance should be maintained on materials that have higher iodine

values (higher unsaturation). Of course, other materials that catalyze oxidation,

such as iron, copper, and lipoxygenase enzymes, must also be considered.

Recently, peroxides have been determined utilizing high-performance liq

uid chromatography (HPLC) (Yang, 1992; Yang et al., 1991). A sample is sep

arated on a column and fractions then pass through a post-column reaction

chamber where they are mixed with a luminescence reagent. Light emitted

from the chemiluminescence reactions is then measured by a special photo

chemical detector. The method is fairly rapid and requires only small amounts

of sample. An additional advantage is that different peroxide species may be

measured separately, which may indicate where oxidation is occurring. The

major disadvantage is the capital cost of the equipment and the high cost of the

luminescence reagent.

3.3.5 Saponification Numbert

Reaction of a fat, oil, or emulsifier with hot alcoholic potassium hydroxide

causes the cleavage (saponification) of fatty acids from the polyol portion of the

lipid. The extent of this cleavage can be measured by back titration with dilute

hydrochloric acid with a phenolphthalein indicator. Alternatively, the titration

can be potentiometric, and the endpoint determined by observation of the in

flection point. This procedure is especially convenient for dark samples where

the phenolphthalein endpoint is difficult to see. Saponification value is the

number of milligrams of potassium hydroxide required to saponify one gram of

fat and is determined by the formula

where B =

s = N =

w =

(B- S)(N) (56.1)

w

mL used to titrate blank

mL used to titrate sample

normality of standard alkali

wt of sampling

t Cunniff (1995d); Firestone (1990j).


This value is sensitive to both the degree of esterification and the chain

length of the substituent fatty acid. Higher degrees of esterification and shorter

chain lengths are reflected by higher saponification values. Conversely, longer

chain lengths and lower degrees of substitution are reflected in lower saponifi

cation values.

3.3.6 Hydroxyl Valuet

Free hydroxyl groups may be determined by reaction of the emulsifier with

acetic anhydride in the presence of pyridine. Water is then added and heated

to hydrolyze excess acetic anhydride to acetic acid (as well as mixed anhy

drides to acetic and fatty acids). The mixture is then titrated with standard al

kali to determine residual acetic (and fatty) acid. The hydroxyl value is

determined by the formula

_(5_6._1 )_(7)_(V._0 -_V_) + A V

m

where T = normality of standard alkali solution

V0 = mL of standard alkali to titrate blank V = mL of standard alkali to titrate sample

w = wt of sampling

AV = acid value of sample

It is recommended that the value be obtained by averaging duplicates. In a

sense, the hydroxyl value provides inverse information to the saponification

value. High saponification value indicates a high degree of substitution, while

high hydroxyl values are indicative of low degrees of substitution.

Major difficulties with the hydroxyl method are (i) a great deal of operator

skill and experience is required, (ii) the method is very time-consuming and

labor intensive, and (iii) results are often inconsistent due to the differential

reactivity of primary and secondary hydroxyl groups. A near infrared re

flectance (NIR) method that uses the hydroxyl-stretching frequency is an at

tractive alternative. It requires only 5 to 10 minutes to obtain a value and is

therefore more adaptable to process control than the titrimetric method. The

only drawback is the necessity of constructing a calibration curve when setting

t Cunniff (1995!); Firestone (19901).


up the determination. Hydroxyl values are used mainly to specify and control

polyglycerols and polyglycerol esters.

3.3.7 Lactic Acid Analysest

Monoglycerides and fatty acids may be reacted with lactic acid to produce

lactylated derivatives that are useful emulsifiers. Lactic acid may be present as

esterified or free lactic acid. In addition, lactic acid has both a carboxyl func

tion and can self-condense to produce small polymers. The total lactic acid

present in a sample encompasses all these species and is indicative of the lac

tic acid/lipid ratio in the production batch. In this test, a sample is boiled with

alcoholic potassium hydroxide followed by addition of hydrochloric acid solu

tion. Lipid material is separated by exhaustive extraction with diethyl ether.

The aqueous phase is then titrated with standard potassium hydroxide solution

to the phenolphthalein endpoint.

Free lactic acid is determined by dissolving the sample in benzene and ex

tracting the solution with water. Free lactic and poly lactic acids are then quan

titated by titration with standard potassium hydroxide. An obvious problem

with this test is the use of benzene, which is a carcinogen.

Water-insoluble combined lactic acid (WICLA) is determined by dissolving a

sample in benzene and extracting the sample as described in the previous test. The

benzene layer (or upper phase from the previous test) is evaporated to dryness. The

residual solid is then heated with alcoholic potassium hydroxide neutralized and

titrated in the same manner as carried out in determination of total lactic acid.

The above methods suffer from the disadvantage of using a toxic, carcino

genic solvent and laborious phase-separation procedures. Franzke and Kroll

(1977) recommend the use of chloroform and petroleum ether for the determi

nation of free and total hydroxy acids, respectively. The authors report the

analysis of lactic, citric, and tartaric acid in emulsifiers. They have also re

ported the use of an enzymatic method for determination of total lactic acid

(Franzke and Kroll, 1980).

3.3.8 Reichert-Meiss! Valuet

This method is specific for determination of acetic and short-chain fatty acids that

have been esterified to mono- or diglycerides. The method involves (i) cleavage of

t Taylor ( l996a).


the short-chain acid in alkali followed by neutralization with dilute sulfuric acid,

(ii) distillation of the liberated acetic (or other short-chain) acid, and (iii) determi

nation of the condensed acid by titration with standard base to the phenolphthalein

endpoint. The method is therefore equipment intensive (the condensing unit must

be replaced or cleaned between samples) and time-consuming.

3.3.9 Moisture

Moisture is generally undesirable in food emulsifiers because it is a diluent and

it represents a potential problem for microbial growth. Some exceptions are the

polysorbates that require a small amount of water to provide clarity and prevent

phase separation, and emulsifier hydrates where gel phases are preformed for

specific applications. Several methods for moisture have been developed through

the history of oil processing. The distillation method uses a toluene solvent to as

sist distillation of water from a large sample through a condenser and into a grad

uated separation tube (Firestone, l990i). The water is quantitated by volume.

The method is equipment intensive because of the need to clean and replace the

distillation apparatus between samples. The distillation method is most

amenable where the water concentration is about 0.5% or higher.

Lower levels of moisture are readily analyzed by reaction with Karl Fischer

reagent. The procedure is amenable to lecithin as well as other emulsifiers that

can be solubilized for the analysis (Firestone, l990p). Instruments are cur

rently available that allow repetitive determinations without the necessity of

disassembly and cleaning between samples.

3.3.10 Color

Color of emulsifier is a reflection of the quality of starting lipid in its manufac

ture and/or manufacturing conditions. Thermal abuse of fats and emulsifiers

are well known to produce dark colors. In many cases, oxidized tocopherols

are thought to be the chromatic impurities. Dark-colored emulsifiers may de

tract from the appearance of finished food products where they are used in

high concentrations (e.g., cake icings). However, color evidence that an emul

sifier has been abused also suggests that pro-oxidants may be present that may

adversely affect the flavor of the product. Emulsifiers would therefore be

processed to produce the lightest color possible.

t Firestone (l990m).


Color is most commonly determined by comparison with a set of standards,

such as colored glass. The most common example is the Lovibond method (also

known as the Wesson method) in which a column ofliquid (or molten) emulsifier

is compared to a set of colored standards (Firestone, l990b). Two values are ob

tained for red (R) and yellow (Y) colors. These are the most common colors en

countered in thermally abused emulsifiers. A related method, which reports only

one value, is the Gardner method (Firestone, l990t). The method is most com

monly used for measurement of color in lecithin, but otherwise is widely applied

to nonedible products. Spectrophotometric methods, such as ultraviolet absorp

tion, have not been widely accepted, probably because the information they pro

vide is ambiguous. Many constituents commonly found in lipids can absorb in

the ultraviolet region. Spectrophotometry is useful in determination of green pig

ments such as chlorophyll (Cunniff, l995b; Firestone, l990c). Since spectropho

tometric methods are most amenable to adaptation for on-line process control, it

is likely that their use will increase as processing becomes more advanced.

3.3.11 Fatty Acid Soaps

Although the official AOCS method has been classified as a surplus method

(obsolete), residual soap remains an important process check in emulsifier pro

duction. Many emulsifiers are produced by interesterification using alkaline

catalysts (see Chapter 2). The catalyst is neutralized at the end of the process

prior to removal of excess polyol by distillation. In batch processes, if the al

kali is not properly neutralized, disproportionation (reverse reactions) can oc

cur, resulting in emulsifiers that are out of specification. Analysis of soap

(alkali) is used to assess proper neutralization.

The determination is carried out by dissolving an emulsifier sample in a

suitable organic solvent/water mixture and titrating with standard hydrochloric

acid. Bromophenol blue or phenolphthalein may be used as indicators. The

method may also be adapted for potentiometric titration. Another method for

assessing the extent of neutralization is to measure the pH. A 5% solution of

emulsifier in isopropanol/water is equilibrated to room temperature and the pH

is read using a standard electrode. A pH reading of 6.5 to 6.8 indicates that

soap is absent and the emulsifier has been properly neutralized.

3.3.12 Phosphorus and Other Lecithin Procedures

Soy lecithin, which is widely used as an emulsifier in food products such as

chocolate and margarine, is obtained by degumming of soybean oil. Purity of


the lecithin obtained in this way is therefore a major concern. Its chemical

structure is that of a phospholipid where phosphoric acid is esterified to a glyc

erol molecule and an organic base. Total phosphorus in the sample may be de

termined by a laborious process in which the sample is saponified, phosphorus

is separated by precipitation with molybdate solution, the precipitate is dis

solved in base, and excess base is titrated with standard nitric acid (Firestone,

1990r). Tamanaka and Kudo (1991) have reported a rapid method where phos

phorus precipitated by molybdate is determined spectrophotometrically. A

much simpler, albeit less precise, procedure is to determine lecithin content as

acetone-insoluble material based on the principle that neutral lipids are solu

ble in acetone while phospholipids are not (Firestone, 1990g). This principle

was used by Goldstein (1984) to develop a method for determination of lecithin

in oils. The oil sample was dispersed in acetone and lecithin was quantitated

by measurement of the turbidity.

Individual phosphatides, such as phosphatidylcholine and phos

phatidylethanolamine may also be determined by HPLC (see Section 3.5,

Instrumental Methods). Combinational measurements have been reported for

separation and phospholipid class identification in commercial soy lecithin

(Lendrath et al., 1991) and in egg yolk (Holopainen, 1972). Individual phos

pholipids of soybean and rapeseed were separated by micellar electrokinetic

capillary chromatography (lngvardsen and Michaelsen, 1994).

Determining the presence and composition of phospholipids in foods is an

exercise in separation followed by measurement. Wewala and Baldwin (1982)

describe a procedure for the analysis of lecithin in instant milk powders.

Ugrinovits (1983) described determination oflecithin in cocoa powders.

3.4 Physical Methods Physical properties of emulsifiers are often critical to their functionality and

subsequent consumer acceptance of finished food products. The next chapter

will explore this topic in some detail. In this section we will discuss analytical

procedures for a few routinely measured properties.

3.4.1 Melting Point

The temperature at which an emulsifier melts may have a substantial impact on a

food-processing operation. For example, the melting point of a peanut butter sta

bilizer must be matched to the fill temperature of the peanut butter to prevent oil


separation. Several methods are commonly used to determine melting points of

fats and emulsifiers. Unlike pure chemical compounds these materials exhibit

broad melting ranges rather than sharp melting points. To further complicate the

situation, phases may melt and then recrystallize as polymorphic forms undergo

transitions in the system. Techniques such as differential scanning calorimetry

and programmed-temperature x-ray diffraction are necessary to study these

polymorphic transitions, but they will not be discussed here.

Capillary melting points, widely used for other substances, are sometimes

utilized. The range is usually observed as an initial softening progressing grad

ually to complete liquefaction. The melting point is defined as the temperature

at which the sample first becomes a clear liquid (Firestone, l990a).

Shortcomings of this method are that it is subjective, it is susceptible to varia

tions in heating rate, and dispersed inorganic material interferes with observa

tion of the clear liquid. Softening point, also referred to as the slip point, has

been used to determine melting behavior of fats and oils. The procedure is

similar to capillary melting point, except it uses an open capillary, and the

endpoint is the temperature at which the sample runs out of the tube. However,

collaborative studies have found it to be unsuitable for emulsifiers. The con

geal point (Firestone, l990d) is determined by cooling a relatively large sam

ple of fat to a first crystallization temperature. A temperature curve is then

constructed as a crystallization exotherm is observed. The maximum tempera

ture of the curve is defined as the "congeal point." This method is less sensi

tive to insoluble impurities but is time-consuming when performed manually.

Wiley melting point is a long accepted method for emulsifiers as well as for

fats and oils. The measurement involves suspending a disc of material at an in

terface of unmixed water and ethanol. Heating and gentle stirring with a ther

mometer are applied. When the disc melts and becomes spherical, the

temperature is read and reported. Definition of the exact temperature where

the solid becomes a sphere is somewhat operator-dependent and the method is

also time-consuming. AOCS has classified the method as surplus (obsolete).

Mettler dropping point also starts with a disc of emulsifier that is placed in

a disc holder. The disc is heated in an instrument at a specified rate. When the

disc melts, it drops out of the holder and breaks an electric eye circuit and the

temperature is recorded. Advantages of this method over other techniques are

(i) it is unaffected by operator variability in determining the endpoint, (ii) the

measuring process can be left unattended, and (iii) output can be recorded into

a computer control chart thus eliminating transcription errors.


3.4.2 Viscosity/Consistency

Viscosity is a property of an emulsifier that is important to processing and transfer

of material, such as pumping through product feed lines. Measurements are not

generally made routinely. A viscosity/temperature profile is usually constructed,

and acceptable ranges are defined for processing operations. Some classes of

emulsifiers, such as polyglycerol esters, are very thick and have to be heated to be

pumped through heat-traced lines. Sucrose stearate poses a problem since it de

composes when heated too high and is therefore preferred as a powder form.

Viscosity of lecithins had been measured by a procedure known as the "bub

ble time" method (Firestone, l990v) that was also used widely in the paint indus

try. A clear liquid sample is placed in an ASTM tube in a constant-temperature

bath. The tube is inverted to produce a bubble at the bottom of a column ofliquid.

The time for the bubble to reach the top is measured and recorded. The value in

poise is obtained by comparison with standard samples. Viscosity may also be de

termined directly using a Brookfield viscometer (Firestone, 1990u). In the latter

case, it is not as critical that the samples be clear.

Rheological properties are most often determined when emulsifiers are incor

porated into foods and ingredients such as shortenings. Consistency (Firestone,

l990e) may be measured using a penetrometer, such as an lnstron or Stevens

texture analyzer. The method measures the distance a probe penetrates into a

sample at a given force, temperature, and time. This property is critical to perfor

mance when the product is mechanically incorporated into a food product. An

example is dough-sheeting to produce Danish pastries or pizza crust.

3.4.3 Refractive Index

Production of some emulsifiers is controlled by refractive index measurement.

For emulsifiers, in most cases, the measurement is correlated to some other

property. For example, in the preparation of polyglycerol, refractive index in

creases with the degree of polymerization. The method is rapid and much more

convenient than a wet chemical method such as hydroxyl number. Since many

food emulsifiers are solids, it is convenient to maintain the refractometer at a

temperature of 60°C for all measurements.

3.5 Instrumental Methods There has been little recent effort toward development of new wet methods for

analysis of food emulsifiers. Studies that are carried out in this area have fo-


cused almost exclusively on elimination of toxic solvents or substitution with a

more benign solvent. Instrumental methods that provide a rapid unattended

process are attractive areas of investigation. In addition, some of the more so

phisticated terchniques can separate lipid classes and even distinct com

pounds. The disadvantage of instrumental methods is the high capital cost and

maintenance of sophisticated instruments. In this section, we will provide an

overview of a number of instrumental methods for characterizing emulsifiers.

3.5.1 Gas-Liquid Chromatographyt

Volatile compounds may be easily separated and detected using a gas-liquid

chromatograph. However, food emulsifiers and lipids in general are non

volatile. To usefully apply this analytical technique, emulsifiers must be de

rivatized to increase their volatility. Structural information may also be

obtained by cleavage of the emulsifier followed by derivatization and analysis

of its subunits.

The most common GLC analysis performed on lipids is the fatty acid com

position (FAC). In this test, fatty acids are cleaved from their glycerol or other

polyol backbone and converted to a volatile derivative, most often methyl es

ters. The sample is injected and separated on a packed or capillary column

and detected on a flame ionization or thermal conductivity detector. Fatty

acids are well separated primarily by chain length and secondarily by unsatu

ration. Peaks are identified by their retention times as previously established

by a standard. Concentration is determined by peak height or area corrected

by response factor as a percentage of the total fatty acids.

Monoglycerides and propylene glycol esters of fatty acids can be deter

mined directly by derivatization of the dry sample by hexamethyldisilazane

and chlorotrimethylsilane in the presence of pyridine (Nakanishi and Tsuda,

1983). Dieffenbacher has suggested the use of N,N-bis(trimethylsilyl)trifluo

roacetamide (BSTFA) in a 3:1 ratio with chlorotrimethylsilane (Brueschweiler

and Dieffenbacher, 1991). Lee and coworkers (1988) have formed propyl de

rivatives of mono- and diglycerides and determined them by GC/MS. After

separation of the sample, peaks are quantitatively determined by reference to

an internal standard. Monoheptadecanoylglycerol (monomargarine) had been

traditionally used but it is difficult to synthesize. Solutions of this standard are

not stable and must be periodically prepared. Butyl alcohol, which has the

t Christie (1989).


same molecular weight as monomargarine, is commercially available at a rea

sonable cost and stable to 1,2-acyl shifts (Hasenhuettl, 1990). Cholesteryl ac

etate has also been utilized as an internal standard (Blum and Koehler, 1970).

Collaborative studies have been conducted with the objective of developing a

uniform method for AOCS, AOAC, and IUPAC (Brueschweiler and

Hautefenne, 1990; Firestone, 1994). Figure 3.1 shows the separation of propy

lene glycol esters and monoglycerides by GLC.

Polyol distributions of other food emulsifiers can be determined by cleav

age of fatty acids, as for fatty acid distribution. The residual polyol can be pu

rified and converted to a volatile trimethylsilyl derivative that is analyzed by

GLC. Use of this technique provides structure information on the underlying

polyol. Percentages of sorbitan, sorbitol, and isosorbide present in sorbitan

mono- or tristearate can be determined using this procedure (Murohy and

Grisley, 1969; Tsuda et al., 1984). Polyols from polysorbates are detectable by

GLC, but under conditions reported by Lundquist and Meloan (1971), they are

eluted as a single peak. Detection of 1,4-dioxane, a carcinogenic byproduct of

ethoxylation reactions, may also be determined in polysorbates by GLC (Birkel

et al., 1979). Polyol distribution from diglycerol through dodecaglycerol are

obtainable for polyglycerol esters (Schuetze, 1977; Sahastrabudhe, 1967).

Polyglycerol polyricinoleate (PGPR), which has been extracted from chocolate

products, has also been determined by gas-liquid chromatography (Dick and

Jmcmal Standard Internal Standard

PGMS

PGMP

PGMS GMO&GMS

GMS

12 15 18 21 24

Time (min) Time (min)

Figure 3.1 GLC separation of monoglycerides and propylene glycol ester emulsifiers. (a) Commercial emulsifier; (b) in shortening. (Hasenhuettl et al., 1990.)


Miserez, 1976). Although fatty acid esters of saccharides, such as galactose,

xylose, and sucrose, are unstable to high temperatures, volatile derivatives of

these esters have been determined by GLC (Tsuda and Nakanishi, 1983;

Fregapane et al., 1992). Calcium stearoyl lactylate has also been analyzed

(Yukawa and Hanada, 1982). The number of lactic acid residues esterified to

stearic acid in calcium or sodium stearoyllactylate may also be analyzed using

this procedure.

3.5.2 High-Performance Liquid Chromatography (HPLC)

As previously discussed, thin-layer and column chromatography have been

useful in the separation and analysis of lipids. HPLC may be viewed as a logi

cal extension of these techniques. Small amounts of lipid are introduced onto a

solid or reverse phase column and the column is developed using a solvent as

a moving (mobile) phase. As peaks are eluted, they are observed and quanti

tated by a detector. Modern HPLC units collect data on a digital computer.

This method of analysis has an advantage over GLC because nonvolatile lipids

can be separated without the necessity of forming volatile derivatives.

However, lipids as a class pose some disadvantages for HPLC. Saturated lipids

do not absorb UV light except at short wavelengths where some useful solvents

are not transparent. Derivatives of lipids that contain chromophores can be

prepared but this negates a major advantage of HPLC. Refractive index detec

tion may be used for detection of peaks. The analyst is then limited to an iso

cratic solvent system because gradient elution causes drift of the IR detector.

Recently, an evaporative light-scattering detector (ELSD) has been developed

to overcome these technical problems for lipids (Christie, 1992; Bruns, I 988;

Lee et al., 1993). Figure 3.2 shows a separation of phospholipids using the

ELSD detector. HPLC can also be interfaced with an MS instrument to give

both separation and identification of peaks.

The most commonly reported separations of food emulsifiers under a pot

pourri of columns, solvents, and detectors have been monoglycerides (Filip

and Kleinova, 1993; Takagi and Ando, 1994; Renger and Wenz, 1989; Tajano

and Kondoh, 1987; Martin et al., 1989; Rilsom and Hoffmyer, 1978;

Brueschweiler, 1977) and phospholipids of soy (Melton, 1992; Sotirhos et al.,

1986; Hurst and Martin, 1984; Huyghebaert and Baert, 1992; Tumanaka and

Fujita, 1990; Rhee and Shin, 1982) and egg (Hsieh et al., 1981; Kaitaranta

and Bessman, 1981). Hurst and Martin (1980) have also employed HPLC to

determine phosphatidylcholine in chocolate. Separation of phospholipids has


Phospholipids Class Standards

Column:

Mobile Phase: Gradient:

Sample: Flowrate: Detector: Drift Tube Temp: Gao Flow:

1. Cholesterol 2. PalmHic acid 3. Phosphatidylethanolamine 4. Phosphatidylserine 5. Phosphatidylcholine 6. Sphingomyelin

12 16

Spherisorb Silica, 3jlm, 100x 4.6nvn

2DIIin.

A: IPA, 8: Hexane, C: Waler Time 0 7 15 A 58 52 52 8 40 40 40 c 2 8 8 Phospholipids Class Slandards 1.25mllmin ELSD Mark IIA, 105'C 50mm

Egg Yolk Phospholipids

Column:

Mobile Phase: Gradient:

Saf111le: Flowrate: Detector: Drift Tube Temp: Gaa Flow:

1. Cholesterol 2. Phosphalidylethanolamine 3. Phosphalidylcholine

3 4. Sphingomyelin

12 16 2D Min.

Spherisorb Silica, 3~m. 100x4.6mm A: IPA, 8: Hexane, C: Waler Time o 7 15 A 585252 8 404040 c 2 8 8 Egg Yolk Phospholipids 1.25mUmin ELSD Mark IIA, 105'C 50mm

Figure 3.2 HPLC separation of phospholipids using an evaporative light-scattering detector. (Courtesy of Alltech Associates, Inc.)

also been reviewed by Christie (1996). Garti and Aserin (1981) reported the

separation of polyglycerol mono- and polyesters by HPLC on a LiChrosorb col

umn. Sorbitan esters of fatty acids could also be separated on the same station

ary phase (Garti and Aserin, 1983). Murakami and coworkers (1989)

described the separation of sucrose esters by preparing their 3,5-dinitroben

zoyl derivatives. This technique was used to determine sucrose esters in a

wide range of food products.

The development of facile extraction and rapid sample prepurification

methods as well as autosampling technology will undoubtedly encourage more

widespread use of HPLC.

3.5.3 Spectroscopic Methods

As previously mentioned with respect to HPLC detectors, saturated lipids do

not contain chromophores that absorb in the UV range, except at short wave-


lengths. The short-wavelength region is not selective enough to allow determi

nation of lipids in the presence of other organic compounds. However, com

plexes of emulsifier functional groups have been widely utilized to analyze

emulsifiers colorimetrically. A diagnostic qualitative analysis for ionic surfac

tants was developed by Lew (1975). Methylene blue was used to analyze for

anionic surfactants at 650 nm while cationic compounds were determined with

Orange 2 at 485 nm.

Several determinations of phospholipids rely on complexation of the choline

moiety of phosphatidylcholine. Molybdenum blue (Hartman et al., 1980),

dipicrylamine (Mueller, 1977), and Reinecke's salt (Moelering and Bergmeyer,

1974) were used to determine lecithins in a variety of food products.

Polyoxyethylene chains in food emulsifiers can complex with cobalt thiocyanate

or Dragondorff's reagent to produce a colored complex. This method has been

used to detect polysorbates in instant noodle soup (Saito et al., 1987; Tonogau et

al., 1987) and in salad dressings (Daniels et al., 1982). Shmidt (1979) reported a

procedure for determination of DATEM esters by mixing saponified lipid with

sodium metavanadate solution and measurement of the absorption at 490 nm.

Infrared spectroscopy is applicable to the functional groups present in the

common food emulsifiers. The emergence of Fourier transform infrared spec

troscopy (FTIR) makes rapid detection of functional groups possible. The tech

nique could therefore be used to monitor manufacturing processes. Given

these capabilities, it is somewhat surprising that little work has been done to

measure emulsifiers. Ingber utilized near infrared (NIR) reflectance to deter

mine monoglyceride concentration and determine the hydroxyl value in poly

glycerols and polyglycerol esters (N. Ingber, personal communication).

Spectrophotometric analysis has also been utilized to measure impurities in

food emulsifiers. Fujita and Yamanaka (1991) measured the absorbance of io

dine liberated from an iodide solution from reaction with lipid peroxides. This

technique yields equivalent information to the peroxide method described pre

viously. Infrared absorption at 1675 cm·1 was utilized to determine residual di

methylformamide in sucrose esters (Jakubska, 1977). However, this method is

inadequate to determine the solvent at ppm levels.

3.5.4 Nuclear Magnetic Resonance (NMR)

Nuclei of atoms having an odd atomic number may be measured in terms of

their chemical shifts. This measurement is carried out in an instrument that

places a sample in a magnetic field and then scans the radio frequency to ob-


tain signals. These signals are dependent on the environment of the nuclei and

are therefore useful for determining functional groups and chemical structure.

Relaxation time of the signal is useful to determine the physical state of a mol

ecule. Wide-line NMR is widely used to measure the amount of solid fat or

solid fat content (SFC) in a sample. However, this technique is rarely used for

food emulsifiers and is not included here. Chemical shifts have been utilized

to determine the mesomorphic form of emulsifiers in aqueous systems, which

is likewise beyond the scope of this chapter. The reader is referred to

Lindblom (1996) for a thorough treatment of this subject. Mesomorphic phase

behavior in food emulsions will be discussed in Chapter 6.

Proton (1 H) NMR is the oldest technique. However, because of the large num

ber of similar protons in alkyl chains of emulsifiers, this technique has not shown

widespread utility. Press and coworkers (1981) observed the protons on choline at

3.3 ppm to determine phosphatidylcholine content in lecithin. Sheeley et al.

(1986), in the same laboratory, proposed that the vinylic protons at 5.3 ppm could

serve as an alternative measurement of the iodine value, discussed earlier.

Chemical shifts of carbon (13C) are useful for determination of the func

tional environment of the carbon atom being observed. Since lipids have significantly fewer carbons than hydrogen atoms, the problem of spectra

interpretation is more tractable. Gunstone (1993) has recently reviewed the

field of 13C NMR of lipids. Chemical shifts of isopropylidene derivatives of

monoglycerides have been reported by Dawe and Wright (1988). Sacchi and

coworkers (1990) utilized the shifts of glyceryl and carbonyl carbons to mea

sure the levels of monoglycerides, diglycerides, and free fatty acids in olive oil.

Chemical shifts for glyceryl carbon atoms are listed for monoglycerides, propy

lene glycol esters, acetylated monoglycerides, phosphatidylcholine, and phos

phatidylethanolamine in Table 3.1.

Chemical shifts of phosphorus atoms (31 P) are of great utility in determining

the structure and concentration in phospholipids. Since there is only one phos

phorus atom per lipid molecule, assignment is more straightforward than for 1 H or 13C NMR. However, this is somewhat offset by the numerous types of

phospholipid molecules found in natural samples, such as egg. Glonek and

Merchant (1996) have recently reviewed this method.

3.5.5 Mass Spectrometry

Mass spectrometry has long been used to elucidate the structures of organic

molecules. The molecular ion is an accurate indicator of the molecular weight


Table 3.1 13C chemical shifts for some food emulsifiers

Emulsifier structure Gl-1 Gl-2 GL-3 N-CH2 O-CH2

Soy phosphatidylcholine 63.01 70.51 63.33 66.26 59.34

Egg yolk phosphatidylcholine 62.94 70.63 63.78 66.62 59.32

Soy phosphatidylethanolamine 62.81 70.59 64.07 40.69 62.08

Egg yolk phosphatidylethanolamine 62.81 70.55 64.07 40.59 62.13

1-Monoglyceride 65.04 70.27 63.47

1,2-Diglyceride 65.04 72.25 61.58

!-Propylene glycol monoester 69.46 66.13 19.2 (CH3)

2-Propylene glycol monoester 65.92 71.77 16.25 (CH3)

Propylene glycol diester 65.42 67.98 16.5 (CH3)

Monoacetylated monoglyceride:

a 62.07 72.39 61.40

~ 63.00 68.19 65.26

Diacetylated monoglyceride 62.00 69.16 62.33

of the compound, while the fragmentation pattern is an indication of carbon

chain (or daughter) structure and associated functionality. Lipids and food

emulsifiers are usually nonvolatile complex mixtures of molecules of highly

varying molecular weights. Therefore, great confusion is encountered trying to

determine which species are molecular ions and which are fragmentation

peaks. New techniques such as direct sample introduction, fast atom bombard

ment (FAB), chemical ionization (CI), and negative ion mass spectrometry

have made analysis of lipids and emulsifiers more feasible. Tandem mass

spectroscopy (MS/MS) allows an ion peak to be further fragmented to smaller

peaks. Insight on molecular structure is therefore increased dramatically. Le

Quere (1993) has reviewed the apparatus, methodology, and application to

lipids of this technique.

Integration of chromatographic techniques, such as GLC and HPLC, can

simplify mass spectra by enabling analysis of compounds that are present in

high concentration. Application to food emulsifiers is expected to occur

rapidly as instrument and detector technology are improved.

Fast atom bombardment was utilized to analyze complex mixtures of phos

pholipids present in egg yolk (Traitler and Nikiforov, 1984). Protonated molecu

lar ions (MH+) could be readily resolved and identified. Negative (OH-) chemical

ionization mass spectrometry was used to characterize polysorbates in foods

(Daniels et al., 1985). Two peak series were attributed to polyoxyethylene chains

alone and linked to sorbitans. Fatty acids attached to the sorbitans could also be


identified from the spectra. An electrospray technique has also been found to be

useful for analysis of sucrose fatty acid esters (Schuyl and van Platerink, 1994).

This technique showed a series of molecular ions that corresponded to the de

gree of substitution of fatty acids onto the sucrose molecule.

3.6 Setting Specifications for Emulsifiers The practice of setting specifications for a food ingredient may be a matter of

custom, such as adoption of the manufacturer's values, or it may be a carefully

reasoned approach based on functionality. When food processors are making

commodities or products very similar to those on the market, the first approach

may be quite adequate and even time-saving. Emulsifier producers are very

likely to have an understanding of what the customer needs for an emulsifier to

function properly in the food system. Sometimes, however, the food processor

may develop a "new to the world" product that has no close relative in current

commerce. In this case a well-reasoned logical approach is necessary.

A logical specification approach starts with selection of an emulsifier sys

tem that imparts functionality to the finished or in-process food product. This

selection has most likely resulted from a careful regulatory and technical eval

uation of possible emulsifier(s) system. During the process, the most critical

functional responses such as emulsion stability, aeration, or viscosity should

have been defined.

As a second step, each emulsifier in the system should be correlated to

each functional response.

Third, critical analytical values need to be selected for each emulsifier.

Most of these tests have been discussed, but which of them show a correlation

with functionality is not always clear. A factorial design may be constructed for

each analytical constant and each emulsifier as measured by the critical re

sponse function. Emulsifiers having a range of analytical values should be

tested. If a wide range is not available, an approximation could be obtained us

ing a low and high lot and preparing blends to represent values in the middle.

Based on the analytical constant correlation with function, a range of values

is selected that give acceptable functional response. A statistical safety factor

should be defined and specifications appropriately tightened.

As a reality check, the emulsifier manufacturer and food processor should eval

uate the specifications to determine whether they can realistically be met. If not,

further experimental design may be necessary to arrive at a more robust system.


Finally, appropriate purity analyses should be defined. These are analyses

such as color, odor, and peroxide value that can influence the appearance, fla

vor, and shelf stability of the finished food product. For example, an unsatu

rated monoglyceride may need to have a low peroxide value to keep it from

acting as a pro-oxidant in a susceptible product.

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Kyokai, 59-74. Biacs, 0., et al. (1978). Acta Aliment. Acad. Sci. Hung., 7(3):181-93, CA 89:213672. Birkel, T., et al. (1979). ]. Assoc. Off. Anal. Chem., 62(4):931--6. Blum, J., Koehler, W. (1970). Lipids, 5(7):601--6. Bruemmer, J.M. (1971). Brot Gebaeck, 25(11):217-20. Brueschweiler, H. (1977). Mitt. Geb. Lebensmittelunters. Hyg., 68(1):46-63. --, Dieffenbacher, A. (1991). Pure Appl. Chem., 63(8):1153--62. --, Hautefenne, A. (1990). Pure Appl. Chem., 62(4):781-93. Bruns, A. (1988). Fett Wiss. Technol., 90(8):289-91. Christie, W.W. (1996). "Separation of phospholipid classes by high performance liquid

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-- (1989). Gas Chromatography and Lipids: A Practical Guide, The Oily Press, Ayr, Scotland.

Cunniff, P. (ed.) (1995.) Official Methods of Analysis of AOAC International, 16th ed., AOAC International, Arlington, VA.

Ibid. (1995a). 41.1.63 Method 969.34. Ibid. (1995b). 41.1.60 Method 942.19. Ibid. (l995c). 41.1.20 Method 940.28. Ibid. (1995d). 41.1.18 Method 920.160. Ibid. (1995e). 41.1.15 Method 993.20. Ibid. (19951). 4l.l.l2 Method 965.32. Ibid. (1995g). 4l.l.l6 Method 965.33. Daniels, D.H., et al. (1985). ]. Agric. Food Chem., 33(3):368-72. --(1982). ]. Assoc. Off. Anal. Chem., 65(1):162-5. Dawe, R.G., Wright, J.L.C. (1988). Lipids, 23(4):355-8. Dick, R., Miserez, A. (1976). Mit. Geb. Lebensmittelunters Hyg., 67(4):472-87. Dieffenbacher, A., et al. (1988). Rev. Fr. Corps. Gras, 35(12):495-9 --(1989). Rev. Fr. Corps. Gras, 36(2):64. Duden, R., Fricker, A. (1977). Fette Seifen Anstrichm., 79(12):489-91. El-Sebaiy, L.A., eta!. (1980). Food Chem., 5(3):217-28. Erdahl, W.L., et al. (1973). ]. Amer. Oil Chemists Soc., 50(12):513-15.


Filip, V., Kleinova, M.(l993). Z. Lebensm.-Unteres. Forsch., 196(6):532-5. Firestone, D. (1994). ]. Assoc. Off. Anal. Chem., 77(3):677-80. -- (ed.) (1990). Official Methods and Recommended Practices of the American Oil

Chemists' Society, 4th ed., American Oil Chemists' Society, Champaign, IL. Ibid. (1990a). Method Cc 1-25. Ibid. (1990b). Method Cc 13b. Ibid. (1990c). Method Cc 13d-55. Ibid. (1990d). Method Cc 14--59. Ibid. (1990e). Method Cc 14--59. Ibid. (1990f). Methods Cd 1-25, Cd 1b-97. Ibid. (1990g). Method Cd 1b--9l. Ibid. (1990h). Method Cd 1c-85. Ibid. (1990i). Methods Cd 2a-45, Ja 2a-46. Ibid. (1990j). Methods Cd 3-25, Cd 3b--76, Cd 3c9l. Ibid. (1990k). Methods Cd 3a-63, Cd 2d-63, Ja 6-55. Ibid. (19901). Method Cd 4-40. Ibid. (1990m). Method Cd 5-40. Ibid. (1990n). Method Cd 11-57. Ibid. (1990o). Method Ce 1b-89. Ibid. (1990p). Method Ja 2b-87. Ibid. (1990q). Method Ja 4-46. Ibid. (1990r). Method Ja 5-55. Ibid. (1990s). Method Ja 8-87. Ibid. (1990t). Method Ja 9-87. Ibid. (1990u). Method Ja 10-87. Ibid. (1990v). Method Ja 11-87. Flor, R.V., (1980). Prager, M.J., ]. Assoc. Off Anal. Chem., 63(1):22-6. Franzke, C., Kroll, 1. (1980). Nahmng, 24(1):89-90. -- (1977). Z. Lebensm.-Unters. Forsch., 163(3):206-7. Fregapane, G., et al. (1992). Prog. Biotechnol., 8:563-8. Fujita, M., Yamanaka, K. (1991). Yakagaku, 40(1):20-3. CA ll4:100052. Garti, N., Ascerin, A. (1983). ]. Am. Oil Chem. Soc., 60(6):1151-4. -- (1981). ]. Liq. Chromatogr., 4(7):1173-94. Gernert, G., (1968). Z. Lebensm.-Unters. Forsch., 138(4): 216-220. Glonek, T., Merchant, R.E. (1996). "31 P nuclear magnetic resonance profiling of phos

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Comprehensive Treatise, Vol. 2, Chap. XIV, Lavoisier Publishing, Paris. Kimura, S., et al. (1969). Nippon Shokuhin Kogyo Gakkai-Shi, 16(9):425-9. Kroeller, E. (1969). Fette Seifen Anstrichm., 71(10):896---8. --(1968). Fette Seifien Anstrichm., 70(6): 431-33. --(1966). Fette Seifen Anstrichm., 68(12): 1066---68. Lee, T., et al. (1993). ]. Am. Oil Chem. Soc., 70(4):343-7. -- (1988). ]. Assoc. Off Anal. Chem., 71(4):785-8. Lendrath, G., et al. (1991). Fett Wiss. Technol., 93(2):53-61. --(1990). ]. Chromatogr., 502(2):385-92. Le Quere, J.L. (1993). "Tandem mass spectrometry in the structural analysis of lipids,"

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FOUR

Carbohydrate/Emulsifier Interactions

Lynn B. Deffenbaugh

4.1 Introduction Many different types of emulsifiers are used in food products. The inclusion rate is

usually low, < 3%. Composition and characteristics of emulsifiers used in foods

are discussed in other chapters. Emulsifiers often function indirectly in foods by

modifying the properties of major components such as carbohydrates, protein, or

fat. This chapter discusses the impact of emulsifiers on carbohydrates.

Carbohydrates are a large group of diverse food components. Carbohydrates

can be classified into three categories based on degree of polymerization: mono

and disaccharides, oligosaccharides, and polysaccharides. Polysaccharides

are further divided into starch and nonstarch fractions. The nonstarch polysac

charides are plant cell wall materials that contribute dietary fiber to foods.

Mono-, di-, and oligosaccharides and nonstarch polysaccharides (fiber) inter

act minimally with emulsifiers from the perspective of food-product character

istics. Starches, however, form complexes with emulsifiers that significantly

alter the characteristics that the starches provide in foods. Emulsifiers that

complex with starch are notably different in function and usage from protein

complexing emulsifiers discussed in the next chapter.

This chapter discusses how complexes form between starches and emulsi-

67


fiers, and how starch properties are affected by complex formation. Understanding the effects of emulsifiers on carbohydrates is dependent on measurement of physical properties of starch/emulsifier complexes, which are also discussed.

4.2 Inclusion Complexes of Starch The interaction between emulsifiers and starches is primarily formation of an inclusion or clathrate complex. Linear sections of starch molecules can form a helix into which a fatty adjunct can enter. The lipophilic portion of an emulsifier is often a fatty acid chain connected to a hydrophilic portion via an ester linkage. The fatty acid chain can serve as the fatty adjunct in an inclusion complex with starch.

Starches are composed of linear molecules (amylose), and branched molecules (amylopectin). In an inclusion complex with amylose, the amylose exists as a left-handed helix with 6 glucosyl residues per turn and 0.8 nm between helices (Mikus et al., 1946). The branch points of amylopectin intercept helix formation and limit complex formation. Monoglycerides, one of the most commonly used types of emulsifiers, are known to bind with amylopectin at much

lower levels than with amylose (Hahn and Hood, 1987; Lagendijk and Pennings, 1970; Twillman and White, 1988).

In general, a complexing agent can be any hydrophobic molecule with a rodlike shape and a diameter less than the 4.5 to 6 A-wide internal core of a starch helix (Rutschmann and Solms, 1989). Complexing agents include iodine (asP-), fatty acids, hydrocarbon chains of emulsifiers, and various organic molecules (i.e., n-butyl alcohol, t-butyl alcohol, dimethyl sulfoxide, and a-naphthol). Organic aroma compounds have been shown to form thermostable inclusion complexes with amylose (Maier et al., 1987; Schmidt and Maier, 1987).

Amylose alone exists in solution as a random coil. In the presence of complexing agents, energy minimization drives amylose into a helix configuration (Neszmelyi et al., 1987). Hydrocarbon chains of fatty acids or hydrophobic complexing adjuncts are attracted into the hydrogen-lined, hydrophobic core of an amylose helix (Krog, 1971). Once formed, the complex is stabilized by dipolar interactions (Mikus et al., 1946) and fulfillment of hydrophobic solvation requirements of the helix (Krog, 1971). Computer-derived models of amylose complexes with stearic acid and iodine have been derived on the basis of the energy minimization concept (Neszmelyi et al., 1987).

Carbohydrate/Emulsifier Interactions 69

The long axis of complexing agents is internal and parallel to the long axis

of the amylose molecule (Mikus et al., 1946; Rundle and French, 1943a, b).

Complexing agents interchange reversibly, competing for the same space in

the amylose helix (Mikus et al., 1946; Schoch and Williams, 1944). The unit

cell packing size and distance between starch helices are not altered by the

type of complexing agent (Raphaelides and Karkalas, 1988).

Lipid chains usually occupy the helix as paired dimers linked by hydrogen

bonds at the carboxyl groups in fatty acids or glycerol in monoglycerides

(Raphaelides and Karkalas, 1988). The hydrocarbon chains in complexes are so

highly ordered that they have been reported to be crystalline (Carlson et al., 1979).

Amylose helices induced by complexation aggregate into partially crys

talline structures that exhibit a V-type x-ray diffraction pattern (Szczodrak and

Pomeranz, 1992) and are insoluble. These insoluble complexes consist of

lamellar crystals with the helix perpendicular to the lamella (Raphaelides and

Karkalas, 1988). Amylose and amylopectin complexes can be differentiated by

their physical properties. Amylopectin emulsifier complexes are more soluble

than amylose complexes. The insolubility of the fatty acid/amylose complex

has long been used as a means to selectively precipitate amylose, but not amy

lopectin, from solution (Schoch and Williams, 1944). Complexes cannot al

ways be assumed to be insoluble, however, since the degree of insolubility

varies with the surfactant (Kim and Robinson, 1979). The complex between

starch molecules and iodine is used to differentiate and quantitate the amylose

fraction, which forms a blue complex, and the amylopectin fraction, which

forms a red-purple complex.

4.3 Effects of External Lipid Materials on Starch Properties 4.3.1 General

Either native or external lipid materials can interact with starch. The mechan

isms and effects of the interactions are qualitatively similar but much larger in

magnitude for external lipids such as emulsifiers added to foods. While native

lipids significantly affect starch properties, the presence and level is not dis

cretionary in product development. The effect of emulsifiers on starch proper

ties in food is especially relevant because use of emulsifiers provides choice

and control in product development. This chapter focuses on the effects of ex

ternally added emulsifiers on starch properties.


Many food emulsifiers function by interacting with the starch component of food. Emulsifiers were first used as crumb softeners in breads and were shown to interact with starch but not gluten (Favor and Johnston, 1947; Strandine et al., 1951). Starch-complexing emulsifiers are used to retard firming or staling in bread, prevent stickiness in instant mashed potatoes, and control texture in

extruded products.

Specific effects of emulsifiers and various fatty adjuncts on starch properties are described in the accompanying tables. Data for nonwaxy "normal" starches are summarized in Table 4.1, and data for waxy, high amylopectin starches are summarized in Table 4.2. These data from many sources are consistent overall and support general conclusions about starch/emulsifier interactions, as discussed below.

4.3.2 Iodine-Binding Capacity

Emulsifiers or externally added fatty adjuncts repress iodine binding capacity (IBC) of nonwaxy starches (Table 4.2). This effect on IBC is caused by the reversible exchange between the adjunct and J3- within the starch helix.

No or only slight reduction of IBC with waxy starches or amylopectin have been reported (fable 4.2). The average length of amylopectin branches is 20 to 26 residues. Fatty acids require 3 turns of a starch helix with 6 residues per tum to form a complex, and thus can interact with amylopectin (Rundle and French, 1943b). The IBC of amylopectin is low compared to normal or high amylose starches, and starch-complexing agents decrease IBC of waxy maize starch slightly (Figure 4.1). Formation of weak or unstable complexes between amylopectin and emulsifiers may significantly modify the starch properties, but IBC is not a sensitive method to predict or monitor the interaction.

4.3.3 Starch-Pasting

Starches and starch-containing ingredients provide many of the physical and organoleptic properties of foods. Dramatic changes occur in starches and starch-containing products when processed. When starches are cooked in the presence of water, starch granules absorb water and swell to many times their original size. Amylose, the linear fraction of starch, leaches from the granules. A hot starch paste is a mixture of swollen granules, granule fragments, and colloidally and molecularly dispersed starch molecules (Olkku and Rha, 1978). The viscosity increases greatly as this hot paste matrix forms. The fragile, swollen granules will eventually disintegrate, especially when shear is ap-

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& R

obin

son,

197

9

Kro

g, 1

971

Kro

g &

Nyb

o Je

nsen

, 19

70

Moo

rthy

, 19

85

Osm

an e

t al

., 19

61

Bou

rne

et a

l., 1

960

Eli

asso

n, 1

986b

Ghi

asi

et a

l.,

l98

2a

Hoo

ver

& H

adzi

yev,

198

1

Kim

& R

obin

son,

197

9

Kro

g, 1

971

Mer

cier

et

al.,

1980

Moo

rthy

, 19

85

Osm

an e

t al

., 19

61

Str

andi

ne e

t al

., 19

51

Roa

ch &

Hos

eney

, 19

95a,

b

van

Lon

khuy

sen

& B

lank

esti

jn,

1974

.....

Tabl

e 4.1

co

ntin

ued

I()

Eff

ect

of

com

ple

xat

ion

S

tarc

h

Co

mp

lex

ing

o

n s

tarc

h p

rop

erti

es

typ

e/fr

acti

on

ag

ent

Ref

eren

ce(s

)

Incr

ease

gra

nule

sw

elli

ng;

Mai

ze,

pota

to,

whe

at

SDS,

an

anio

nic

surf

acta

nt

Eli

asso

n, 1

986b

m

ake

gela

tini

zati

on o

ccur

earl

ier

Des

tabi

lize

gra

nule

and

T

apio

ca

SLS,

an

anio

nic

surf

acta

nt

Moo

rthy

, 19

85

incr

ease

pas

te v

isco

sity

D

ecre

ase

star

ch t

hick

enin

g W

heat

D

AT

EM

, M

G,

SSL

E

vans

198

6 po

wer

< 8

5°C

(bef

ore

Whe

at

GM

S, S

SL

Ghi

asi

et a

l.,

1982

d ge

lati

niza

tion

) P

otat

o M

G

Hoo

ver

& H

adzi

yev,

198

1 D

elay

los

s of

W

heat

S

ucro

se m

onoe

ster

s B

ourn

e et

a!.

, 19

60

bire

frin

genc

e W

heat

sta

rch

Suc

rose

mon

oest

ers

Ebe

ler

& W

alke

r, 1

984

Whe

at

MG

,SS

L

Eli

asso

n, 1

985

Mai

ze,

pota

to, w

heat

G

MS,

SD

S, S

SL

Eli

asso

n, 1

986b

W

heat

M

G,

SSL

G

hias

i et

a!.

, 19

82a,

b W

heat

flo

ur

Suc

rose

mon

oest

ers

Pom

eran

z et

a!.

, 19

69

Pot

ato

MG

R

ilso

m e

ta!.

, 19

84

Var

ious

M

G

van

Lon

kyhu

ysen

&

Bla

nkes

tijn

, 19

74

Incr

ease

ini

tial

pas

ting

M

aize

, po

tato

, tap

ioca

, w

heat

S

ucro

se e

ster

D

effe

nbau

gh,

1990

a te

mpe

ratu

re, h

ot p

aste

W

heat

sta

rch

Suc

rose

mon

oest

ers

Ebe

ler

& W

alke

r, 1

984

visc

osity

, te

mpe

ratu

re o

f W

heat

SS

L

Eli

asso

n, 1

983

peak

vis

cosi

ty W

alke

r, 19

84

Pot

ato,

whe

at

SSL

E

lias

son,

198

6b

(i.e

., am

ylog

raph

or

RV

A),

Whe

at

DA

TE

M,

MG

, SS

L

Eva

ns,

1986

de

lay

gela

tini

zati

on

Non

wax

y P

OE

MS

F

avor

& J

ohns

ton,

194

7 M

aize

M

G

Kro

g, 1

971

Mai

ze,

pota

to,

tapi

oca,

whe

at

DA

TE

M,

MG

, SS

L

Kro

g, 1

973

.....

w

Sta

bili

ze p

asti

ng v

isco

sity

and

prev

ent

long

coh

esiv

e te

xtur

e

Dec

reas

e pe

ak v

isco

sity

Dec

reas

e ge

lati

niza

tion

ent

halp

y

Incr

ease

set

back

vis

cosi

ty

Incr

ease

set

back

vis

cosi

ty (

gela

tion

)

Dep

ress

ed G

' and

G";

inc

reas

ed

tem

pera

ture

of G

' and

G";

incr

ease

d vi

scou

s pa

rt o

f

visc

oela

stic

res

pons

e

Indu

ced

gela

tion

(in

crea

sed

rigi

dity

of f

resh

sta

rch

gels

)

Dec

reas

ed g

el v

olum

e of

heat

ed s

tarc

h

Dec

reas

e co

ld p

aste

vis

cosi

ty

Dec

reas

e re

trog

rada

tion

of

star

ch

Pea

flou

r

Whe

at f

lour

Pot

ato

Mas

a ha

rina

flou

r

Tap

ioca

wax

y m

aize

, po

tato

Mai

ze,

pota

to,

tapi

oca,

whe

at

Def

fenb

augh

, 19

90a

Pota

to,

whe

at

Mas

a ha

rina

flou

r

Mai

ze,

pota

to,

tapi

oca,

whe

at

Mai

ze,

pota

to,

whe

at

Mai

ze,

pota

to, w

heat

Whe

at

Mai

ze,

pota

to,

tapi

oca,

whe

at

Mai

ze

Pot

ato

Pota

to

Am

ylos

e/am

ylop

ecti

n m

ixtu

res

SSL

Suc

rose

mon

oest

ers

MG

MG

GM

S, S

LS

PO

EM

S

Suc

rose

est

er

C'fA

B,

sat'd

MG

, SD

S, S

SL,

Lec

ithi

n, l

ysol

ecit

hin

MG

Suc

rose

est

er

GM

S, S

LS

CSL

, G

MS

MG

, SS

L

PO

EM

S

MG

MG

MG

CT

AB

, SD

S

Lin

et

al.,

1990

Pom

eran

z et

a!.

, 19

69

Rii

som

et

a!.,

1984

Tw

illm

an &

Whi

te,

1988

Moo

rthy

, 19

85

Fav

or &

Joh

nsto

n, 1

947

Eli

asso

n, 1

986a

Tw

illm

an &

Whi

te,

1988

Def

fenb

augh

, 19

90a

Eli

asso

n, l

98

6b

Con

de-P

etit

and

Esc

her,

199

4

Eli

asso

n, 1

985

Fav

or &

Joh

nsto

n, 1

947

Kro

g, 1

971

Osm

an &

Dix

, 19

60

Hoo

ver

& H

adzi

yev,

198

1

Rii

som

eta

!.,

1984

Gud

mun

dsso

n &

Eli

asso

n, 1

990

Kro

g &

Nyb

o-Je

nsen

, 19

70

Lag

endi

jk &

Pen

ning

, 19

70

.... ~ Ta

ble

4.1

cont

inue

d

Eff

ect

of

com

ple

xat

ion

S

tarc

h

Co

mp

lex

ing

o

n s

tarc

h p

rop

erti

es

typ

e/fr

acti

on

ag

ent

Ref

eren

ce(s

)

Ric

e D

AT

EM

, M

G, S

SL,

Miu

ra e

t al.,

199

2 S

ucro

se e

ster

s D

ecre

ase

amyl

opec

tin

Mai

ze

Suc

rose

est

ers

Mat

suna

ga &

Kai

num

a, 1

986

recr

ysta

lliz

atio

n

Dec

reas

ed f

orm

ulat

ion

of

Bar

ley,

mai

ze, w

axy

mai

ze

EM

G,

DA

TE

M,

MG

, SS

L

Szcz

odra

k &

Pom

eran

z, 1

992

resi

stan

t st

arch

R

educ

ed g

el b

reak

ing

stre

ngth

M

aize

, pot

ato,

whe

at

CS

L,G

MS

C

onde

-Pet

it a

nd E

sche

r, 1

994

Red

uced

sta

rch

extr

udat

e T

apio

ca

MG

M

erci

er e

t al

., 19

80

solu

bili

ty a

nd r

etro

grad

atio

n P

otat

o an

d m

aize

C

SL,

MG

S

taeg

er e

t al

., 19

88

Red

uced

in

vitr

o en

zym

olys

is

Pot

ato

MG

, SS

L

Ghi

asi

et a

l., i

982

with

B-a

myl

ase

Pot

ato

amyl

ose

EM

G,

poly

sorb

ate

60

Kim

& R

obin

son,

197

9 R

educ

ed i

n vi

tro

amyl

oglu

cosi

dase

A

myl

ose

MG

E

lias

son

& K

rog,

198

5 di

gest

ion

Red

uced

in

vitr

o a-

amyl

ase

Am

ylos

e M

G

Eli

asso

n &

Kro

g, 1

985

dige

stio

n P

otat

o am

ylos

e L

ysol

ecit

hin

Hol

m e

t al

., 19

83

Dec

reas

ed g

luco

amyl

ase

Mai

ze, p

otat

o, t

apio

ca, w

heat

S

ucro

se e

ster

D

effe

nbau

gh,

1990

a di

gest

ibil

ity

Pot

ato

amyl

ose

Lys

olec

ithi

n H

olm

et a

l., 1

983

Slow

ed r

ate

of in

viv

o a-

amyl

ase

Pot

ato

amyl

ose

Lys

olec

ithi

n H

olm

et

al.,

1983

di

gest

ion

CSL

= ca

lciu

m s

tear

oyl-

lact

yl-2

-lac

tyla

te;

CTA

B =

cety

ltri

met

hyla

mm

oniu

m b

rom

ide;

DA

TE

M =

diace

tyl

tart

aric

aci

d es

ters

of

mon

ogly

lcer

ides

; E

MG

= eth

oxyl

ated

m

onog

lyce

ride

s; G

MP

= gly

cero

l m

onop

alm

itat

e; G

MS

= gly

cero

l m

onos

tear

ate;

MG

= mo

nogl

ycer

ides

; PO

EM

S = p

olyo

xyet

hyle

ne s

tear

ate;

SD

S = s

odiu

m d

odec

yl

sulf

ate;

SL

S = s

odiu

m I

aury

! su

lfat

e; S

SL =

sodi

um s

tear

oyl-

2-la

ctyl

ate.

.......

Ul

Tabl

e 4.

2 E

ffec

t o

f em

ulsi

fier

s an

d c

ompl

exin

g ag

ents

on

pro

per

ties

of

wax

y st

arch

Eff

ect

of

com

ple

xat

ion

o

n s

tarc

h p

rop

ert

ies

Sli

ght

redu

ctio

n io

dine

-

1970

bind

ing

capa

city

N

o re

duct

ion

in i

odin

e

bind

ing

capa

city

No

effe

ct o

n sw

elli

ng

Sli

ght d

elay

in

peak

vis

cosi

ty

Vis

cosi

ty p

rofi

le n

ot a

ffec

ted

Dec

reas

ed h

ot p

aste

vis

cosi

ty

Dep

ress

ed G

' an

d G

"; s

ligh

tly

incr

ease

d te

mpe

ratu

re o

f G'

and

G";

sli

ghtl

y in

crea

sed

visc

ous

part

of v

isco

elas

tic

resp

onse

Inso

lubl

e co

mpl

ex p

reci

pita

ted

No

extr

udat

e co

mpl

ex f

orm

ed

No

com

plex

det

ecte

d by

x-r

ay

diff

ract

ion

or D

SC

Sta

rch

ty

pe/

frac

tio

n

Am

ylop

ecti

n

Wax

y m

aize

Pot

ato

amyl

opec

tin

Pot

ato

amyl

opec

tin

Wax

y m

aize

Am

ylop

ecti

n

Wax

y m

aize

Wax

y m

aize

Wax

y ba

rley

Pot

ato

amyl

opec

tin

Am

ylop

ecti

n

Wax

y m

aize

Wax

y m

aize

Co

mp

lex

ing

ag

ent

MG

Suc

rose

est

ers

Suc

rose

mon

oste

arat

e

Suc

rose

mon

oste

arat

e

Suc

rose

est

ers

MG

DA

TE

M,

MG

, SS

L

PO

EM

S

GM

S, S

LS

Suc

rose

mon

oste

arat

e

MG

CSL

, M

G

Suc

rose

est

ers

Ref

eren

ce(s

)

Kro

g, 1

971;

Kro

g &

Nyb

o-Je

nsen

,

Def

fenb

augh

, 19

90a

Bou

rne

et a

l.,

1960

Bou

rne

et a

l.,

1960

Def

fenb

augh

, 19

90a

Hoo

ver

& H

adzi

yev,

198

1

Eva

ns,

1986

Fav

or &

John

ston

, 19

47

Eli

asso

n, 1

986b

Bou

rne

et a

l.,

1960

Bat

res

& W

hite

, 19

86

Sta

eger

et

al.,

1988

Def

fenb

augh

, 19

90a

~

Tabl

e 4.

2 co

ntin

ued

Eff

ect

of

com

ple

xa

tio

n

on

sta

rch

pro

per

ties

Wea

k co

mpl

ex s

ugge

sted

by

gluc

oam

ylas

e di

gest

ion,

vis

cosi

ty

prof

iles

, hi

gh-p

erfo

rman

ce s

ize

excl

usio

n ch

rom

atog

raph

y,

and

NM

R

Com

plex

con

firm

ed b

y D

SC

and

x-ra

y di

ffra

ctio

n

Red

uced

am

ylop

ecti

n

retr

ogra

dati

on

Sta

rch

ty

pe/

fra

ctio

n

Wax

y m

aize

Pot

ato

amyl

opec

tin

Wax

y m

aize

, am

ylop

ecti

n

Pot

ato

amyl

opec

tin

Co

mp

lex

ing

a

gen

t

Suc

rose

est

ers

CT

AB

, SD

S

CT

AB

, un

sat'd

MG

CT

AB

, SD

S

Ref

eren

ce(s

)

Def

fenb

augh

, 19

90a

Gud

mun

dsso

n &

Eli

asso

n, 1

990

Eli

asso

n, 1

988

Gud

mun

dsso

n &

Eli

asso

n, 1

990

CSL

= c

alci

um s

tear

oyl-

lact

yl-2

-lac

tyla

te;

CT

AB

= c

etyl

trim

ethy

lam

mon

ium

bro

mid

e; D

AT

EM

= d

iace

tyl

tart

aric

aci

d es

ters

of m

onog

lyce

ride

s; G

MS

= gl

ycer

ol

mon

oste

arat

e; M

G =

mon

ogly

ceri

des;

PO

EM

S=

pol

yoxy

ethy

lene

ste

arat

e; S

DS

=so

dium

dod

ecyl

sul

fate

; SL

S =

sod

ium

Iaur

y! s

ulfa

te; S

SL =

sodi

um s

tear

oyl-

2-la

cty

late

.

.--.. ...:::: () L.. 0 ..... en 0>

E IJ") ...._,

E c:

0 0 tO ..... 0

en ..0 <(

1.0

0.8

0.6

0.4

0.2

0.0


•--•Hylon VII o--oWheat A--A Maize c--o Potato o--oTapioca v--vWaxy Maize

T--------v-----~v------------------------------v

0 2 3 4 5 % SE (starch wt. basis)

Figure 4.1 Iodine-binding capacity of starches measured in the presence of a sucrose ester emulsifier. (From Deffenbaugh, 1990a.)

plied. This relative decrease in viscosity after time and application of shear

defines a peak viscosity.

The process whereby the ordered structure of the starch granule is lost is

called "gelatinization." The transition is a first-order water-mediated melting

of crystalline regions in the starch granule (Donovan, 1979; Zobel, 1984).

Maximum solubilization and swelling occur when excess (> 5 times) water is

present, typical of sauces, gravies, and puddings. In lower moisture systems,

such as baked or extruded products, granule swelling can be limited by mois

ture content. Extremely high viscosities result because diluent is limited.

Uses and functions of starches are multiplied by modifying properties with

emulsifiers. For example, time of addition and/or time for diffusion of fatty ad

juncts into starch granules are processing parameters than can be varied to

produce substantially different properties in cooked starch or cereal grain

products (Lund, 1984). If added before starch gelatinization, monoglycerides

penetrate the granule, form molecular complexes, and reduce starch swelling

power. Addition of monoglycerides after gelatinization enhances granule sta

bility (van Lonkhuysen and Blankestijn, 1974). The function of starch-com

plexing emulsifiers is primarily due to formation of starch/emulsifier

complexes. The magnitude of the effect of starch/emulsifier complexes on

starch cooking properties varies with starch type, emulsifier type, and process

ing conditions.


Emulsifier and starch molecules must have access to each other to interact.

Starch-complexing emulsifiers must be soluble enough or in a phase that

yields monomers (see Section 4.4.4). Starch molecules have limited availabil

ity until gelatinization begins. Emulsifiers adhere to the granule surface before

gelatinization, and they begin to form insoluble starch/emulsifier complexes as

soon as the granule begins to swell and amylose begins to solubilize. These in

soluble complexes near the surface stabilize the granule. The rate of further

swelling and amylose leaching are slowed. Gelatinization temperature is in

creased because more energy is required to cook or swell the stabilized gran

ule. Some emulsifiers, such as polysorbate 60, may cover the starch surface

with a film, increase hydrophobicity, and inhibit water transfer into the granule

(Kim and Walker, 1992c).

The effect of emulsifiers on starch gelatinization is detected in many ways

(Table 4.1). When starch pastes were made with SSL or GMS, changes in vis

coelastic properties of the paste were coincident with reduced granule swelling

(Eliasson, 1986b). The granules were less deformable (stiffer), as indicated by

an increase in the temperatures where peaks in storage (G') and loss (G") mod

ule were reached. Pasting temperature, hot viscosity, and temperature of peak

viscosity of most normal starches are increased in the presence of emulsifiers

that have a fatty adjunct that can form inclusion complexes with starch.

According to Mitchell and Zillman (1951), the increase in starch paste viscos

ity in the presence of complexing agents is a result of the increased ability of

granules to absorb and hold water without rupturing.

Gelatinization, the melting of crystalline regions in the granule, causes loss

of birefringence and disappearance of a starch x-ray diffraction pattern

(Eliasson, 1986a). When emulsifiers delay gelatinization, the loss of birefrin

gence is delayed (see Table 4.1).

Some emulsifiers with a fatty acid chain adjunct do not form complexes

with starch. Anionic surfactants, such as sodium lauryl sulfate (SLS) and

sodium dodecyl sulfate (SDS), destabilize the granule because of its highly

negative charge (Eliasson, 1986b; Moorthy, 1985). The destabilization leads to

rapid, complete swelling of the granules, and a rapid increase in viscosity

early in the pasting (cooking) cycle. Loss of granule integrity will subsequently

lead to a dramatic loss in viscosity after peak. This is undesirable if the starch

is being utilized for its thickening, texturizing abilities. In the selection of an

emulsifier for product development applications, charge as well as chemical

composition need to be considered when effect on starch is important.


4.3.4 Starch Paste Gelation

The formation of a composite starch gel is responsible for the texture and

structure of many food systems. A starch gel formed from a paste is a compos

ite of swollen starch granules embedded in and reinforcing the amylose gel

matrix (Ring, 1985). As a starch paste cools, molecules become less soluble

and aggregate, and a three-dimensional gel forms (Osman, 1967). The consis

tency increases because molecular associations form a cross-linked network

that increases the resistance of the paste to deformation (Zobel, 1984).

Gelation is initiated by rapid precipitation of amylose in solution, while amy

lopectin gels much slower and requires higher concentrations. Amylose serves

as (i) the chief material for formation of a gel network to entrap unabsorbed wa

ter and (ii) a binding material to link intact or fragmented swollen granules.

In starch gels made with emulsifiers, the insoluble complex produced will

form a gel (Conde-Petit and Escher, 1992). The formation of complexes be

tween amylose and emulsifiers accelerates gelation in the first few hours of ag

ing after gelatinization compared to starch gels made without emulsifiers

(Conde-Petit and Escher, 1994). The gelation of maize, potato, tapioca, and

wheat starch during cooling is responsible for the setback viscosity of profiles

shown in Figure 4.2 (Deffenbaugh, 1990a). A sucrose ester emulsifier in

creased setback viscosity due to complex formation that accelerated gelation.

Gelation can be induced and controlled by use of emulsifiers in starch-con

taining foods (Conde-Petit and Escher, 1992).

4.3.5 Retrogradation

The primary reasons for using emulsifiers are modification of finished product

characteristics. Retrogradation in starch-containing foods impairs texture and

taste, and emulsifiers inhibit this retrogradation.

Retrogradation is the formation of ordered, partially crystalline sites within

a cooled starch paste or gel. The recrystallization of starch is a long-term

process that occurs during the hours and weeks after pasting and gelation.

Amylose retrogrades so fast that it is often complete before the food is con

sumed. Retrogradation of amylopectin occurs more slowly and affects the tex

ture and taste offoods throughout shelf life (Miles et al., 1985).

Emulsifiers decrease the rate of retrogradation of starch gels mainly through

emulsifier/starch-complex formation (Miura et al., 1992). The helix structure of

starch in a complex prevents side-by-side stacking of starch molecules and,


100 - M•In -·· l S Sit -·2!1. 5I pp u Sl

];-

'§ 60

5 • 40

~ ~ 20

0 ~~--~-+--~~-+_,

120

100

0 4 6 B I 0 IZ I< 16 18 20 Time (n1in)

I5>0°CI H.ot to g~0c I c~ lo S0°C

100

gao 1;-

·e 60

5 Ill 40 . -~ 0 ~ 20

100

200

-P•hl• ···· I:IL $(

-·1"-H -- ~il n

16 IB 20

I /-·-·-•-•-·-•

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g eo ~: :: ~~ h ;~\:.. . ~~/-·-·--~ 1:-8 60

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5 ;.\ \ \.. //1 j \~:~ .. ]!

Q 40 .'-

• 40 ... 0 0 ~ 20 : 20

1 i: I i:

0~~-+--~+--l~r--~--· 0 8 10 IZ 14 16 18 20

Time (min} I50°CI Heat to 95°C I Cool to ~C

,_{.~-!:,'

8 10 12 14 IG 18 20 Timl!!(mln}

Heat to 95°C I Cool lo .50°C

Figure 4.2 Rapid Visco Analyzer viscosity profiles of maize, potato, tapioca, and wheat starches with 0, 1, 2, or 5% (starch wt basis) of a sucrose ester emulsifier. (From Deffenbaugh, J990a .)

thus, reduces nucleation sites for retrogradation or recrystallization (Matsunaga

and Kainuma, 1986).

Amylopectin retrogradation plays an important role in the shelf life of

foods. The increase in firmness and loss of flavor in staled bread is caused by

the retrogradation of the amylopectin fraction of starch (Schoch and French,

194 7). Controlling or modifying amylopectin retrogradation through use of

emulsifiers is of practical significance.

The interaction between emulsifiers and amylopectin is harder to prove

than the interaction between emulsifiers and amylose. In the literature, indi

rect or inconclusive evidence of amylopectin/emulsifier interactions have been reported by various authors (Kugimiya et al., 1980; Evans, 1986; Eliasson and

Ljunger, 1988). For example, formation of insoluble complexes between a

monoglyceride and amylopectin has been reported (Batres and White, 1986).


A weak, limited interaction between amylopectin and a sucrose ester emulsi

fier was observed with various methods (Deffenbaugh, 1990a). IBC and glu

coamylase digestion of waxy maize starch were slightly reduced by the

emulsifier. Delay in development of viscosity during gelatinization of waxy

maize starch also suggested that the emulsifier interacted with amylopectin.

Conclusive data describing direct and indirect effects of emulsifiers on amy

lopectin retrogradation are now available (Gudmundsson and Eliasson, 1990).

Emulsifiers were found to be most effective at directly inhibiting amylopectin ret

rogradation at very high, near 100%, amylopectin levels. Amylopectin/emulsifier

complexes were responsible for this direct effect. In the presence of amylose,

amylopectin will cocrystallize with amylose, which forms nuclei. When amylose

and amylopectin are present together, ligands will preferentially complex with

amylose. The amylose then cannot co-crystallize with amylopectin, and the emul

sifier's effect on amylopectin is indirect. In addition, when the amylose compo

nent complexes with emulsifiers, less emulsifier is available to interact with

amylopectin, and direct amylopectin/ emulsifier-complex formation is reduced.

4.3.6 Enzymolysis

Complex formation interferes with the ability of enzymes to digest starch molecules

(see Table 4.1). Kinetics of glucoamylase, which cleaves successive glucose units

from the nonreducing end of starch chains, were not directly affected by a sucrose

ester emulsifier (Deffenbaugh, 1990a). Reduced digestibility of normal starches in

the presence of an emulsifier were due to decreased availability of the starch sub

strate. Precipitation of the complex and reduced steric compatibility of helical

starch with the active site of the enzyme reduced the starch substrate availability.

Glucoamylase digestion of waxy maize starch was not inhibited by a su

crose ester (Deffenbaugh, 1990a). If a complex formed in the outer branches, it

was not stable enough or strong enough to inhibit glucoamylase.

The inhibition of starch enzymolysis by emulsifiers is analytical evidence of

complex formation. It should be noted however, that emulsifier/starch-complex

formation does not have a significant effect on overall extent of digestibility of

starch in vivo as shown in rats (Holm et al., 1933).

4.4 Factors Affecting Complex Formation 4.4.1 Adjunct Properties

Binding of saturated fatty acids and monoglycerides increases as chain length

increases (Hahn and Hood, 1937; Gray and Schoch, 1962). Maximum binding


has been reported with 18-carbon saturated fatty acids (Hahn and Hood, 1987)

and 14- to 16-carbon fatty acids on monoglycerides (Hoover and Hadziyev,

1981; Krog, 1971; Lagendijk and Pennings, 1970). Geometrical structure as

well as chain length and molecular weight will influence the ability of the lig

and to penetrate the starch helix (Miura et al., 1992). If chain length as well as

helix conformation are known, the fatty acid to amylose ratio required to

achieve saturation of the amylose helix is predictable from stoichiometric rela

tionships (Karkalas and Raphaelides, 1986).

Solubility of the adjunct affects the equilibrium between complex formation

and concentration of the adjunct in solution. The lower solubility of fatty acids

versus monoglycerides in aqueous systems drives fatty acids into the lipophilic

core of the amylose helix more than monoglycerides.

Increased unsaturation in free fatty acids or fatty acid chains of monoglyc

erides reduces the ability of the adjunct to bind with starch (Hahn and Hood,

1987; Krog, 1971; Lagendijk and Pennings, 1970). The 30° bend at cis bonds

inhibits rotation and causes steric hindrance. In addition, lower solubility of sat

urated fatty acids will favor complex formation with the hydrophobic helix core.

Steric hindrance from bulky groups on emulsifiers and surfactants interferes

with the ability of the adjuncts to form complexes with starch (Gray and Schoch,

1962). Monoglyceride binding is less than binding of fatty acids of the same

chain length because steric hindrance of the glycerol group interferes with com

plex formation (Hahn and Hood, 1987). Propylene glycol esters of fatty acids,

with a particularly bulky polar group, have lower complexing ability than emul

sifiers with smaller polar groups (Krog, 1971). In addition to steric hindrance,

hydrophilic polar groups are not compatible with the hydrophobic helix core.

The higher the proportion of the polar group to the overall molecule, the less

compatible the molecule is with the hydrophobic interior of the helix.

4.4.2 Starch Granule

The starch granules may also sterically hinder starch complexation with ad

juncts in solution. Monoglycerides exist in micelles in solution and attach to

the starch granule surface simply by adsorption at low temperatures ( < 50°C)

(van Lonkhuysen and Blankestijn, 1974). As the temperature increases, the

monoglycerides penetrate swollen granules to complex with amylose. Other

workers measured strong surfactant/starch complexes at temperatures as low

as 60°C, where only slight disorganization (gelatinization) of the starch granule

has occurred (Ghiasi et al., 1982c). The amount of the insoluble, possibly crys-


talline complex, increased when held at 60°C for 1 hour. These authors con

cluded that the surfactants do enter the granule and complex with amylose be

fore gelatinization.

4.4.3 Starch Type

The source of starch in part determines its functionality in foods, and different

starches will be affected by emulsifiers in different ways and to varying ex

tents. GMS restricted swelling of potato starch granules more than it did maize

or wheat starch granules (Eliasson, 1986b). Some methods of analysis, such as

iodine-binding capacity and glucoamylase digestion, are less sensitive to the

unique reaction of different starches in the presence of an emulsifier

(Deffenbaugh, 1990a). Other methods, such as viscoelastic properties of starch

gels (Eliasson, 1986b) and viscosity profiles (Deffenbaugh, 1990a) do differen

tiate the response of different starches in the presence of emulsifiers.

Viscosity parameters of various starches in the presence of a sucrose ester

emulsifier are shown in Table 4.3 (Deffenbaugh, 1990a). Time to peak viscos

ity was changed more in tapioca than in maize, wheat, and potato starches. The

emulsifier changed peak viscosity most in potato starch, and changed setback

viscosity most in wheat starch. Potato and tapioca granules were stabilized by

complex formation so that granule swelling and disintegration were more grad

ual. Moorthy (1985) also reported that starch-complexing emulsifiers stabi

lized the pasting viscosity of tapioca starch. Viscosity profiles are a

convenient, easy way to study complex interactions between components in

food systems.

4.4.4 Environmental Conditions

Iodine and fatty acid-binding capacity of amylose decrease with increasing

temperature (Banks and Greenwood, 1975; Hahn and Hood, 1987). Thermal

stress reduces the strength of interactions holding the complex together, and

the helix becomes more disorganized as temperature increases.

Binding of some fatty acids is affected by pH via changes in protonation of

the carbonyl group (Hahn and Hood, 1987). Palmitic or stearic acid form dimers

near or below the pKa (pH 4. 7 to 5.0) where the carbonyl groups are partially

protonated. It is assumed that dimers form by parallel alignment, the double hy

drocarbon chain cannot fit into the amylose helix. Above the pK"' dimers disso

ciate and complex formation with single fatty acid chains occurs. pH does not

affect binding of fatty acids, such as lauric or myristic acid, that do not form


Table 4.3 Viscosity profile parameters of starches with 0, 1, 2, or 5% (starch wt basis) sucrose ester emulsifier. (From Deffenbaugh, 1990a.)

T'lllle to peak (min)

Starch 0% SE 1% SE 2% SE 5% SE

Maize 5.431 5.962 6.723 7.724

Potato 3.031 3.642 4.083 5.154

Tapioca 3.671 4.262 7.233 8.334

Wheat 7.321 8.082 8.453 8.844

Waxy maize 3.451 3.541 3.862 4.163

Peak viscosity (%)

Starch 0% SE 1% SE 2%SE 5% SE

Maize 57.91 77.22 74.32 65.93

Potato 2561 2322 2263 183.64

Tapioca 113.21 104.92 99.63

101.322•3

Wheat 78.41 80.11 81.21 81.61

Waxy maize 88.81 101.62 98.02 89.83

Maximum setback viscosity (%)

Starch 0% SE I% SE 2% SE 5% SE

Maize 55.01 86.02 93.83 97.43

Potato 83.91 83.91 110.32

Tapioca 61.51 68.12 84.83 118.04

Wheat 78.811 90.92 129.!3 166.64

Waxy maize 50.21 51.01 52.61 51.31

I, 2, 3, 4 These numbers indicate significant difference (P < 0.05) within starch type.

dimers at lower pH. pH does not affect binding of monoglycerides because the

carbonyl group of the fatty acid is involved in the ester linkage to glycerol.

Amylose-complexing ability of compounds containing hydrocarbon chains

is significantly affected by the phase behavior of the lipid material (Larsson,

1980). The most effective amylose-complexing emulsifiers have a high degree

of molecular freedom in an aqueous phase and exhibit lyotrophic mesomor

phism. Micelles or liposomes of emulsifiers are the most effective polymorphs

for providing lipid monomers, and as a result, are more effective complex for

mers than lipids in other polymorphic states (Riisom et al., 1984; Eliasson,

1986a). Lysolecithin, a native lipid in cereal starches, complexes readily with


amylose because it exists as micelles in solution with a high equilibrium con

centration of monomers readily available for interaction (Takahashi and Seib,

1988). Crumb softeners are added to bread dough as J3-crystal monoglycerides

that convert into an a-crystalline state during baking that readily complex with

starch (Krog, 1981; Krog and Nybo-Jensen, 1970). Blends of emulsifiers that

form an emulsion in solution will be less effective starch-complexing agents

than pure monoglycerides.

4.5 Physical Properties of Starch/Emulsifier Complexes Physical characterization of starch/emulsifier complexes has provided infor

mation on the functionality of emulsifiers in starch systems. Techniques such

as differential scanning calorimetry, nuclear magnetic resonance, and electron

spin resonance spectroscopy have been especially useful.

4.5.1 X-Ray Diffraction Pattern

X-ray diffraction was one of the first methods used to identify and study inclu

sion complexes with starch (Mikus et al., 1946). X-ray diffraction provides infor

mation on the crystallinity of starches. A clathrate (inclusion) complex is

indicated when powder diffractograms of starch have a so-called V-type pattern.

X-ray diffraction has been used to confirm the presence of inclusion complexes

when an aqueous starch system has been heated in the presence of native lipids

or fatty adjuncts (Biliaderis et al., 1986; Deffenbaugh, 1990a; Eliasson, 1988;

Eliasson and Krog, 1985; Hanna and Lelievre, 1975; Hoove~ and Hadziyev,

1981; Kugimiya et al., 1980; Osman et al., 1961; Rutschmann and Solms, 1990).

The helical conformation of amylose within the complex has also been shown us

ing x-ray diffraction (Rutschmann and Solms, 1990). X-ray diffraction data does

suggest V-type complex specifically between amylopectin and lipid ligands

(Gudmundsson and Eliasson, 1990). It appeared important that "free" amy

lopectin was used, whereas amylopectin in waxy maize granules did not complex

(Eliasson and Ljunger, 1988; Evans, 1986; Kugimiya et al., 1980)

X-ray diffraction measurements have indicated that the cell dimension of

the helix is essentially the same for complexes with various emulsifiers con

taining one fatty acid moiety. Emulsifiers with two or more fatty acids are ster

ically excluded from the helix and complex formation is inhibited (Osman et

al., 1961). Most V complexes have a pitch of approximately 0.8 nm, indicating


that the coils of the helix are in contact with each other (French and Murphy,

1977). Jane and Robyt (1984) studied the lamella-like organization of V-type

complexes and concluded that starch chains were folded such that the chain

axes were perpendicular to the surface of the lamella.

4.5.2 Infrared Spectroscopy

Infrared spectroscopy has confirmed the presence of the carboxyl (Bates and

White 1986; Osman et al., 1961), methyl (Bates and White, 1986), or carbonyl

(Hahnel et al., 1995) group of complexing agent inside the starch helix in a

complex. A positive shift in the carbonyl IR absorption peak for GMS in a

starch complex has been measured (Hahnel et al., 1995). The strength of the

carbonyl group double bond increased because of the additional electron den

sity of the starch complex.

4.5.3 Electron Spin Resonance

Stable free radical spin probes of fatty acids are used to study the interaction be

tween the fatty acid and starch using electron spin resonance (ESR). Changes in

probe motion, reflected as changes of spectral line shape, occur when the probe

is adsorbed or in a highly viscous medium compared to measurements of the

probe in a solvent. The motion of a spin probe of stearic acid was greatly slowed

in the presence of wheat, high amylose maize, and waxy maize starches (Pearce

et al., 1985, 1987a). Binding was weaker in waxy maize than in the other

starches (Pearce et al., 1987b). The interactive moiety of the probe was shown to

be the fatty acid. Results were similar at room temperature or after heating to

95°C and cooling back to room temperature. Binding was thought to occur

throughout the interior of the granule since surface absorption could not account

for the amount of probe bound. The presence of water-facilitated binding, pre

sumably by enhancing solvent penetration into the granule (Nolan et al., 1986;

Pearce et al., 1985). Similar results were reported by Nolan et al. (1986) for

probe binding to maize starch at room temperature. Johnson et al. (1990) also

measured spin probe binding by regular and waxy maize starches at room tem

perature after heating to 95°C. Heating was found to decrease the strength of the

complex formed after cooling, most likely because of altered molecular confor

mation. Spin probe penetration into the granule increased upon heating, due

both to increased granular surface area and increased accessibility of the interior

of the granule to the fatty acid probe.

Additional ESR analysis indicated that the fatty acid spin probe was slowly


released during heating of starch to 95°C as the complex dissociated upon

melting (Pearce et al., 1987a, b). Upon cooling, the probe was immobilized

again indicating reformation of the complex.

4.5.4 Nuclear Magnetic Resonance

Nuclear magnetic resonance (NMR) can measure changes in the environment

of food components on a molecular basis. 13C NMR can detect changes in the

environment of carbon atoms in starch induced by complex formation with

emulsifiers (Deffenbaugh, 1990a; Jane et al., 1985).

Jane et al. (1985) reported a downfield shift in resonances of all starch car

bons, but especially Cl and C4, in preformed inclusion complexes with amy

lodextrin. Deshielding of Cl and C4, the carbons in the glycosidic linkage, was

indicated by the downfield shift. Rotation about the CO bonds of the glycosidic

linkage must have occurred upon formation of a helix from a random coil. In so

lution state, l3C NMR, Cl and C4 of maize starch, experienced a downfield shift

in the presence of complexing agents during gelatinization between 55 to 75°C

(Deffenbaugh, 1990a). No effect was seen > 70°C in solution state. The com

plexes were forming during gelatinization but could not be detected in solution

state 13C NMR after precipitation of the starch/emulsifier complexes. Formation

of complexes with amylopectin in waxy maize starch was also detected.

Proton NMR has also been used to understand starch/ligand-complex forma

tion. Signal intensity from amylose protons was reduced when Na palmitate was

added, an effect attributed to the loss of conformational mobility upon complex for

mation leading to extreme line broadening (Bulpin et al., 1982). The signal was re

stored upon heating to 90°C, apparently due to dissociation of the thermally

reversible complex. Resonances of protons 3 and 5 of the glucosyl residues in cy

cloheptaamylose shifted upfield in the presence of lysolecithin (Kim and Hill,

1985). These changes indicated that these protons, directed toward the interior of

the molecule, were in a more hydrophobic environment upon inclusion of the

lysolecithin. No band shifts were found for amylopectin protons upon formation of

amylopectin/monoglyceride complexes (Batres and White, 1986).

4.5.5 Differential Scanning Calorimetry

Differential scanning calorimetry (DSC) data defines the temperature and en

thalpy of thermal transitions. Gelatinization of starch is a water-mediated, en

dothermic melting phenomenon. Complexes between starches and emulsifiers

form exothermally (i.e., crystallize) during heating of starches with the emulsifier


and water (Kugimiya et al., 1980). The net enthalpy of starch gelatinization en

dotherm is reduced in the presence of external lipids due to simultaneous,

exothermic crystallization of starch/lipid complexes (Biliaderis et al., 1986;

Deffenbaugh, 1990a; Eliasson, 1983; Eliasson, 1986a; Eliasson and Ljunder,

1988; Eliasson et al., 1988; Evans, 1986; Kugimiya et al., 1980). Data is given

in Table 4.4 showing the effect of a sucrose ester emulsifier on gelatinization

temperature and enthalpy of various starches (Deffenbaugh, 1990a). Microscopy

and viscosity profile measurements, discussed previously, also detect a delay in

gelatinization of normal starches in the presence of emulsifiers. Depending on

moisture and emulsifier levels, DSC may not be sensitive enough to detect the

delay in starch gelatinization caused by emulsifiers (Deffenbaugh, 1990a; Kim

and Walker, 1992b). See Table 4.4.

Table 4.4 DSC parameters of starch gelatinization endotherm from thermograms of starch with 0, I, 2 or 5% (starch wt basis) sucrose ester emulsifier. (From Deffenbaugh, l990a.)

To eq Starch 0% SE 1% SE 2% SE 5% SE

Maize 66.661 66.531 66.491 66.421

Potato 59.741 59.831 59.751 59.611 Tapioca 63.541 63.971 64.03 I 63.901

Wheat 58.701 59.101 58.421 59.021

Waxy maize 69.031 68.401 68.401 68.131

Tpeq Starch 0% SE 1% SE 2% SE 5% SE

Maize 72.831 72.591 72.691 72.661

Potato 64.751 64.751 64.891 64.601

Tapioca 70.191 70.641 70.821 70.311

Wheat 63.691 63.721 63.301 63.671

Waxy maize 74.751 74.171 74.291 74.241

MI (J/g)

Starch 0% SE 1% SE 2% SE 5% SE

Maize 13.441 11.5()2 10.612 10.662 Potato 16.931 16.641 16.261·2 15.372

Tapioca 18.191 15.282 13.773 11.834

Wheat 10.611 9.581·2 9.332 8.782

Waxy maize 16.901 17.011 16.961 16.831

12 3 4 Different numbers indicate significant difference (P- 0.05) within starch type.


Starch crystallites in most starches melt or gelatinize between 60 and 80°C

in a first-order melting process. The insoluble starch/lipid complexes that form

during gelatinization typically melt between 100 to ll5°C. At high moisture

levels, melting of the complexes is highly cooperative and only a single en

dotherm is observed.

The gelatinization endotherm is not observed in DSC rescans of starch sam

ples because gelatinization is irreversible. Starch inclusion complexes melt

and recrystallize reversibly and, thus, occur in rescans. Identification of starch

complex-melting endotherms in first and subsequent DSC scans of starch sam

ples is used to confirm the presence of starch/lipid complexes (Deffenbaugh,

1990a; Eliasson et al., 1988; Hoover and Hadziyev, 1981; Kugimiya et al.,

1980; Staeger et al., 1988; Szczodrak and Pomeranz, 1992).

DSC can be used to measure the relative thermal stabilities of starch inclu

sion complexes. The stability of the complex depends on the type of starch and

emulsifier, and is important because complex stability affects the rheological

changes during gelatinization (Eliasson, 1986b). Thermal stability (Tg) and

complex-melting enthalpy (All) decrease when a fatty acid chain is interrupted

with cis unsaturation (Eliasson and Krog, 1985; Stute and Konieczny-Janda,

1983; Raphaelides and Karkalas, 1988). Chain length of the lipid moiety has

no effect on ~and may or may not affect Tg (Hoover and Hadziyev, 1981;

Eliasson and Krog, 1985; Raphaelides and Karkalas, 1988; Stute and

Konieczny-Janda, 1983). GMS forms a very stable complex with starch and

has some of the most profound effects on gelatinization properties.

Physical properties of starch/emulsifier complexes will depend on conditions

during crystallization. Multiple-melting endotherms for starch/emulsifier com

plexes or shifting of endotherms upon rescanning indicates the presence of dif

ferent crystal polymorphs (Kugimiya et al., 1980; Biliaderis and Galloway, 1989;

Eliasson, 1988; Biliaderis et al., 1986; Bulpin et al., 1982; Paton, 1987). At the

onset of gelatinization, association of the amylose chain with a ligand provides

the conformational order (helicity) for nucleation that precedes crystallization.

Complexation during the first heating may be incomplete due to restricted mobil

ity of amylose during gelatinization (Kugimiya and Donovan, 1981).

Small, imperfect crystals formed during gelatinization may have individual

helical segments distributed randomly without crystallographic register. An

annealing process occurs between Tg, amorphous glass transition temperature,

and Tm, crystallite melting temperature. Partial melting of less stable crystals

allows sufficient chain mobility for growth of more stable crystals. The melt-


ing/recrystallization process yields a more dense crystal composed of crystallites embedded in and molecularly continuous with disordered chain segments. Annealing of polymorphs as the temperature increases or during rescans will increase crystallite melting temperature.

Different polymorphs of starch/emulsifier complexes may also exist within a larger crystal that has folded onto itself (Eliasson, 1988). Complexes in folds or at the surfaces of crystals would have a lower melting temperature than complexes further inside the crystal.

4.6 Summary It is ironic that the interaction between emulsifiers and starches is "simply" based on one phenomenon-the formation of inclusion complexes between starch helices and fatty adjuncts. The amount of research devoted to understanding the interaction between starches and emulsifiers is daunting. Many methods and measurements are used in these studies because each provides a different perspective to understanding the extent and nature of the interaction.

The physical and sensory characteristics of many foods are largely defined by starches. New and improved foods are developed because emulsifiers can be used to modify the characteristics of starches in foods. Reduction of stickiness in reconstituted potatoes is an example. The food industry is also dependent on emulsifiers to improve shelf life of foods. The economic advantage of increasing shelf life of bread with anti staling emulsifiers outweighs the cost of the emulsifier by manyfold. Applications for starch-complexing emulsifiers will continue to expand as the properties of the interaction are better understood.

Acknowledgment The author acknowledges with great appreciation the assistance of Mrs. Teresa Booher in preparation of the manuscript.

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FIVE

Protein/Emulsifier Interactions

Martin Bos, Tommy Nylander, Thomas Arnebrant, and David C. Clark

5.1 Introduction

Many food emulsions are more complex than the traditional definition of an

emulsion: a colloidal dispersion of liquid droplets in another liquid phase.

This is mainly because the dispersed phase is often partially solidified or the

continuous phase may contain crystalline material, as in ice cream. However,

one characteristic that all emulsions have in common is that they are (thermo

dynamically) unstable. The four main mechanisms that can be identified in the

process of breaking down an emulsion are creaming, flocculation, coalescence,

and Ostwald ripening. There are two ways in which the process of breakdown

of an emulsion can be influenced. First, use of mechanical devices to control

the size of the dispersion droplets and second, the addition of stabilizing

chemical additives like low molecular weight emulsifiers and polymers to keep

it dispersed. The main purpose of the latter is to prevent the emulsion droplets

from fusing together (coalescence), often achieved by repulsive droplet/droplet

interactions. These interparticle interactions are determined mainly by the

droplet surface, which is coated with emulsifiers, often biologically surface-ac

tive components like proteins, mono- and diglycerides, fatty acids, or phospho

lipids. The forces most commonly observed are electrostatic double layer, van

95


der Waals, hydration, hydrophobic, and steric forces. They are responsible for many emulsion properties including their stability.

The complex mechanisms involved in formation, stabilization, and destabilization of emulsions make fundamental studies on applied systems difficult. One approach has therefore been to clarify the basic physical and chemical properties of emulsions by the study of simpler model systems. The adsorption behavior of single-emulsion components like proteins, fatty acids, surfactants, or phospholipids at liquid/air or liquid/liquid interfaces have given information about surface activity, adsorbed amounts, kinetics, conformation, and surface rheology. The development of experimental techniques has made it possible to extend these studies to multicomponent systems. This has provided further information concerning competitive adsorption, displacement, and complex formation, which can be related to emulsion and foam stability.

For further information concerning the physicochemical factors affecting the emulsion structure as well as characterization of food emulsion stability, the reader is referred to the reviews of Dickinson (1987a; 1988), Dickinson and Stainsby (1982), and Tadros and Vincent (1983), and for the principles of emulsion formation to the review of Walstra (1983) along with the other chapters in this book. In this chapter we will focus on the molecular interactions between proteins and other surface-active components present at the interface of the emulsion droplets that prevent the droplets from fusing together. Understanding the interaction between these emulsifier components is the key to increase the emulsion stability as well as to be able to tailor the structure of these systems. Various surface-active components like lipids, low molecular weight (LMW) surfactants, and even phospholipids will be regarded as emulsifiers. We will first discuss the stability of the protein in liquid solutions, which is an important factor for their behavior in emulsion systems. Although the behavior at liquid/liquid and liquid/air interfaces can be best compared with the situation in an emulsion or foam, we will also discuss some relevant studies concerning the solid/liquid interface as well as the effect of emulsifiers on the solution behavior of proteins. A number of techniques can be used to study protein/emulsifier interactions, including surface film balance, ellipsometry, Brewster angle microscopy (BAM), circular dichroism (CD), differential scanning calorimetry (DSC), surface rheology, fluorescence spectroscopy, and neutron reflectivity. It is beyond the scope of this chapter to discuss these techniques in detail, but when necessary a brief explanation will be given.

The link between the molecular interactions between emulsifier compo-

Protein/Emulsifer Interactions 97

nents and the properties of food emulsions will be discussed in the last section

of this chapter.

5.2 Protein Stability A protein molecule can interact with other molecules and surfaces in many

ways. This is mainly due to the complexity of the surface of the protein mole

cule, which comprises positive and negative charges, groups with hydrogen

bonding capability, and nonpolar regions. Intermolecular and surface forces

can thus occur via electrostatic interactions, hydration forces, acid/base inter

actions, hydrogen bonding, and the van der Waals forces. The hydrophobic and

ionic interactions together with the gain in entropy due to conformational

changes are often regarded as the driving forces for protein adsorption (Norde,

1986; Haynes and Norde, 1994). The orientation of the protein may affect its

interfacial properties (Bos and Kleijn, 1995a, b). Proteins can be classified as

"soft" when they have low internal stability and consequently can change their

conformation upon adsorption, and "hard" if the protein has a high internal

stability (Arai and Norde, 1990a, b; Norde et al., 1991). However, from this

simplified description it is impossible to generalize the behavior of proteins at

interfaces, due to their difference in size, shape, and flexibility and their sus

ceptibility to changes in solution conditions and properties of the interface.

One important aspect regarding emulsifying properties is the stability of a

protein in solution. It is important to distinguish the conformational stability of

the protein from protein aggregation or precipitation due to reduced solubility

at pH close to the isoelectric point, at high ionic strength, and/or through the

binding of ions or lipids. Note that aggregation or precipitation can occur with

out any conformational changes of the protein (Tanford, 1967), although the

two types of instability relate to each other. Information about conformational

stability of a protein can be obtained from circular dichroism measurements

(Townend, 1969), compressibility measurements (Gekko, 1986), and calorime

try (Privalov, 1979; 1988) and has been extensively reviewed by several au

thors (Privalov, 1979, 1982; Dill, 1990; Creigton, 1990).

Here, we will focus only on some important aspects. The amino acid se

quence of the peptide chain determines its folding into ordered structural mo

tifs (a helix, ~ sheets, etc.) that in turn associate to form tertiary and

quartenary structure. Introducing disulfide bridges will also increase the sta

bility. As a result, the interior of globular proteins is very densely packed, with


a mean packing density of 0.74, which is comparable with the values found for

crystals and organic molecules (Richards, 1977). In this densely packed envi

ronment, short-range forces like van der Waals interactions and hydrogen

bonding play an important role (Privalov, 1978). In addition, the hydrophobic

interactions contribute significantly in stabilizing the structure, as first pointed

out by Kauzmann (1959). Accumulation of hydrophobic residues in the core of

the molecule leads to a strong folding force. In contrast, the polar groups prefer

the outside of the protein molecule due to their solvent affinity.

Due to the delicate balance of forces mentioned above, the protein is margin

ally stable (Pace, 1981; Privalov, 1988; Dill, 1990). Changing one amino acid

residue might stabilize or destabilize the protein (Matsumura et al., 1988).

Binding of a lipid, surfactant, or another protein molecule can also have the

same effect. For instance, it has been shown that at low surfactant-to-protein ra

tios, the binding can stabilize the protein against thermally induced unfolding,

as observed for the interaction between fatty acids or sodium dodecylsulfate

(SDS) and bovine serum albumin (Gumpen et al., 1979), as well as SDS and~

lactoglobulin (Hegg, 1980). On the other hand, increasing the surfactant-to-pro

tein ratio above lO moles of SDS per mole serum albumin or 1 mole of SDS per

mole of J3-lactoglobulin monomer causes unfolding of the protein. Creamer

(1995) observed similar stabilization of ~-lactoglobulin against urea induced un

folding at 1:1 molar ratios between the protein and SDS as well as palmitate. In

many emulsions involving proteins and emulsifiers, the interaction could take

place at the interface. The proximity of an interface might disturb the stability

force balance of the protein, resulting in unfolding of the protein. The unfolding

of proteins upon adsorption is entropically favored (Dill, 1990; Norde, 1986) and

might be the driving force for adsorption where the contact between the hy

drophobic domains and the aqueous environment are minimized by proper ori

entation of the molecule (Haynes and Norde, 1994).

5.3 Protein/Surfactant Interactions 5.3.1 Protein/Surfactant Interactions at Solid Surfaces

Protein/surfactant interactions of solid surfaces have been studied with the aim

of estimating the protein attachment strength to surfaces, for optimizing deter

gency processes, and for avoiding undesired adsorption in medical applications.

The major part of the work has been carried out with the purpose of characteriz

ing the protein binding to the surface rather than the protein/surfactant interac-


tion. Due to this fact, many studies referenced below are concerned with the de

gree of removal, or elution, of adsorbed protein by surfactant. We have, however,

included these data in this review and tried to evaluate them in connection with

the sparse data that allow understanding on a molecular level. Even if the data

mainly refer to solid surfaces, the basic principles are also valid at liquid inter

faces such as those of the emulsion droplet. Since the process of surfactant inter

action with proteins at interfaces is determined by the surfactant/protein, the

surfactant/surface and protein/surface interactions, the following brief introduc

tion is intended to provide a background on surfactant association and adsorp

tion, and on surfactant/protein interactions in solution.

The polarized structure of surfactants derives from the hydrophilic head

group and a hydrophobic, usually hydrocarbon, part that promotes interaction

with each other, other molecules, and surfaces by the hydrophilic head as well

as the hydrophobic moieties. These interactions can be expected to be of elec

trostatic or polar, steric, and hydrophobic type, and the total interaction is

often a sum of or a balance between two or more of these forces. As a conse

quence of the strong tendency for the hydrophobic chains to avoid contact with

water, self-association will take place both in solution and at interfaces (see

Section 5.4.4). The monomer concentration in solution will be strongly depen

dent on the association pattern and thus have a pronounced effect on the inter

facial behavior (Lindman and Wennerstrom, 1980; Israelachvili, 1992).

The general features of surfactant adsorption are

l. At high surfactant concentrations [around the critical micelle concentra

tion (erne)], the adsorption rate is fast.

2. For water-soluble surfactants, the adsorption is reversible upon dilution.

3. Usually a plateau in the adsorption isotherm is reached in the range of

the erne.

4. As a rule surfactants adsorb at hydrophobic surfaces. The amounts ad

sorbed are in the range of, or below, those corresponding to a monolayer.

5. In the absence of specific chemical interactions, ionic surfactants adsorb

only onto hydrophilic surfaces of opposite charge (Amebrant et al., 1989).

These aspects of surfactant adsorption are illustrated in Figure 5.1 for the

adsorption of dodecyl trimethyl ammonium bromide (DTAB) onto methylated

silica and in Figure 5.2, where a schematic adsorption isotherm is shown.

There is a vast literature concerning the association of surfactants at

solid/aqueous interfaces (Somasundaran and Kunjappu, 1989; Pashley and


~ 0.05

t "'s u

~ooooosoo8~ 'bn 0.04 6 § 0.03

~ 0

0 § s 0 «< 0.02 § "a

Q)

-€

\ 0 0.01 Ul

"a <:t;

_Q 0.00

0 1800 3600 Time (s)

Figure 5.1 The adsorption of DTAB (2 X erne in phosphate-buffered saline pH 7, I= 0.17) onto methylated silica; rinsing took place after 1800 seconds of adsorption (Wahlgren, 1992). (Reprinted with kind permission of the American Chemical Society, Washington, DC)

r iv

ii

c

Figure 5.2 A schematic illustration of an isotherm for adsorption of ionic surfactants to hydrophilic surfaces (Somasundaran and Kunjappu, 1989). Different stages of the isotherm are labeled (I) to (IV), and schematic drawings of possible structures that exist in these regions are presented in Figure 5.3. (Reprinted with kind permission of the American Chemical Society, Washington, DC.)

lsraelachvili, 1981; Scamehorn et al., 1982; Tiberg, 1994; Wangerud, 1994). The structure of the surface aggregates at the plateau has been debated, and surface micelles, finite bilayers, or infinite bilayers have been suggested for hydrophilic surfaces. Indications of complete bilayers (Pashley and lsraelachvili, 1981) or interpenetrating hydrocarbon chains (Somasundaran and Kunjappu, 1989) have been found. Figure 5.3 is an illustration of possible


association behavior of surfactants in the different regions found in the adsorp

tion isotherm, as shown in Fig 5.2. The upper drawings correspond to a hy

drophilic surface, the lower to a hydrophobic surface.

5.3.1.1 Interaction of Surfactants with Adsorbed Proteins. The removal of

preadsorbed proteins by surfactant has been extensively studied by Horbett and

coworkers (Bohnert and Horbett, 1986; Rapoza and Horbett, 1989, 1990b; Ertel

et al., 1991) in investigations into the adsorption strength of blood plasma pro

teins, particularly fibrinogen. They introduced the term "elutability" to describe

the degree of removal. The surfactant elutability of proteins is affected by factors

that are known to influence the binding strength of a protein to a surface. Thus,

surfactant elutability has been found to decrease with conditions favoring confor

mational changes, i. e., decreasing protein concentration (Rapoza and Horbett,

1989, 1990a), increasing temperature (Bohnert and Horbett, 1986; Rapoza and

Horbett, 1990a), time of adsorption or "residence time" (Rapoza and Horbett,

1989; Ertel et al., 1991), and decreasing stability of the protein (McGuire et al.,

1995a, b; Wahlgren et al., 1993). However, surfactant elutability will be influ

enced not only by protein properties but also by the type of surfactant (Welin

Klintstrom et al., 1993; Wahlgren et al., 1993a, b; Wahlgren and Amebrant,

1991) and surface (Wahlgren et al., 1993, 1994; Elwing and Colander, 1990), as

further discussed next.

11-111 IVa ivb

Figure 5.3 An illustration of probable arrangements of adsorbed surfactant molecules at different degrees of surface coverage. Adsorption to hydrophilic surfaces (upper panels) and hydrophobic ones (lower panels). The illustrations are drawn to represent structures having minimal water contact with the hydrophobic parts of the molecules. The labels (I) to (IV) refer to structures that may exist in different regions of the isotherm shown in Figure 5.2. The figures should be considered as schematic and other structures, especially for ii to iii, have been suggested. (Reprinted with kind permission of the American Chemical Society, Washington, DC.)


Influence of protein properties. Even though ionic surfactants may inter

act, more or less specifically with charged residues of proteins, especially so at

low concentrations (see Section 5.3.1.2), no clear relation could be established

regarding the influence of protein net charge on the interaction with ionic sur

factants at high surfactant concentration (Wahlgren et al., 1993; Wahlgren and

Amebrant, 1991; McGuire et al., 1995c). This might, of course, be related to

the fact that in principle all proteins contain both negative and positive

charges except at extreme pH. In an effort to determine key protein parameters

for their interaction with surfactants, Wahlgren and coworkers studied the

DTAB-induced removal of six adsorbed proteins: cytochrome c, bovine serum

albumin, a-lactalbumin, ~-lactoglobulin, lysozyme, and ovalbumin from silica

and methylated silica surfaces (Wahlgren et al., 1993). For silica surfaces, it

was found that the removal of the proteins that were still adsorbed after rinsing

with buffer, increased with decreasing molecular weight, adiabatic compress

ibility [a measure of conformational stability (Gekko and Hasegawa, 1986)],

and increasing thermal denaturation temperature (Wahlgren et al., 1993). In

the case of hydrophobic (methylated silica) surfaces, differences between the

proteins were smaller. However, increasing molecular weight and shell hy

drophobicity of the protein seemed to reduce the degree of removal. It was also

found that the removal did not relate to the degree of desorption of proteins

upon rinsing with buffer, indicating that the mechanisms for the two processes

are different. Recent experiments on stability mutants of bacteriophage T4

lysozyme show a convincing relationship between DTAB-mediated elutability

and the difference in free energy of thermal unfolding of the protein in compar

ison with the wild type (McGuire et al., 1995a). Thus it can be concluded that

factors relating to the structural stability of the protein are of major importance

and that an increased conformational stability increases the degree of elution.

Influence of surfactant properties. Wahlgren and coworkers studied the

influence of different surfactant head groups on the desorption of adsorbed

lysozyme (Wahlgren, 1992; Wahlgren et al., 1993; Wahlgren and Amebrant,

1991) by surfactants at concentrations above the erne (an exception was trieth

ylene glycol n-dodecyl ether [C12E3, which does not form micelles (Mitchell et

al., 1986)]. The difference between the effect of sodium dodecylsulfate (SDS)

and cationic and nonionic surfactants on protein adsorption to hydrophilic sur

faces was found to correlate to the strength of binding to protein in solution.

This suggests that above the critical association concentration (cac), complex


formation between surfactant and protein is involved in the removal mecha

nism of proteins from hydrophilic surfaces. In the case of hydrophobic sur

faces, the removal processes of protein by the different surfactants, including

non-micelle-forming ones, are in general more similar than for the hydrophilic

surfaces. This might be expected, due to the different orientation of the surfac

tant, and suggests a replacement mechanism, due to higher surface activity of

the surfactant (Wahlgren, 1992). Blomberg and coworkers used the interfero

metric surface force technique (lsraelachvili and Adams, 1978) to study the

interaction between lysozyme adsorbed on mica and SDSo (sodium dodecane

sulfonate) and SDS. They found that SDSo, which has a Krafft temperature

above room temperature and hence does not form micelles, had a minor effect

on the interaction between adsorbed lysozyme layers on mica (Tilton et al.,

1993), and from the small change in surface potential, they concluded that few

surfactant molecules were bound to the adsorbed protein. SDS showed a simi

lar low binding to lysozyme on mica at low concentrations (up to 0.5 erne) but

caused a collective desorption of the protein at the erne of the surfactant, indi

cating that the cac to adsorbed lysozyme is in the range of its self-association

limit in solution (erne) (Blomberg, 1992). These studies show that anionic sur

factants bind to an adsorbed layer of lysozyme, which is almost neutral after

binding of the positively net-charged protein to the negative mica surface. The

binding of surfactant thus leads to an increased negative charge of the layer, which in the case of SDS finally leads to desorption of the protein. It is likely

that this is due to electrostatic repulsion between the negatively charged sur

face and the protein/surfactant complexes.

Nonionic surfactants are generally found to be ineffective in removing pro

tein from hydrophilic surfaces (Wahlgren, 1992; Elwing et al., 1989). As men

tioned above, these surfactants bind to a very low extent to protein in solution

(except when specific binding sites or pockets are present) and to the protein

covered surface. At hydrophobic surfaces, however, they usually have a con

siderable effect (Elwing et al., 1989; Wannerberger et al., 1994). This was

elegantly demonstrated in a study of surfactant interactions with proteins ad

sorbed at a surface with a gradient in wettability (Elwing et al., 1989).

The effect of chain length of alkyltrimethylammonium surfactants on the

elutability of fibrinogen at concentrations above their erne was found to be

small at both silica and methylated silica surfaces (Wahlgren, 1992). Rapoza

and Horbett (1988, 1990a) did not find any effects of chain length of sodium

alkyl sulfates on the elutability of fibrinogen and albumin down to a chain


length of 6 carbon atoms. However, they found, as expected, that the chain

length did influence the surfactant concentration at which the onset of protein

removal was initiated. The trend was similar to the one observed for the onset

of other cooperative binding events (e.g., micelle formation).

Rapoza and Horhett (1990h) found that surfactants with large head groups

such as Tween 20 gave rise to lower fibrinogen elutahility levels than other sur

factants at polyethylene surfaces. Welin-Klintstrom et al. (1993) found that the

elutahility of fibrinogen adsorbed at surfaces with a wettahility gradient de

creased with the bulkiness of the hydrophobic part of the surfactant. In this con

nection it was also found that nonionics showed an increased removal of

fibrinogen into the more hydrophilic region of the gradient surface when the

cloud point (phase separation temperature) was approached (Wahlgren et al.,

1995). These general observations of removal efficiency are in line with the find

ings of Backstrom and coworkers (Backstrom, 1987; Lindman et al., 1988), who

studied the removal of fat by different surfactants and found a maximum at con

ditions corresponding to an optimum in the packing of surfactant molecules at a

flat interface and those of Malmsten and Lindman (1989), who investigated,

among other variables, the effect of temperature on cleaning of hard surfaces.

Thus, it may be concluded that at high surfactant concentrations, head group

effects are, as expected, most pronounced at hydrophilic surfaces hut less impor

tant at hydrophobic ones. In addition, it appears that principles for detergency in

general, involving the packing efficiency of molecules at interfaces, are applica

ble to qualitatively describe the removal of proteins from the surface.

Influence of suiface properties. As previously described, the adsorption

and orientation of surfactants are dependent on the type of surface, and it is

therefore natural to expect that the way in which surfactants interact with pro

teins should be influenced by the characteristics of the surface as well.

Horhett and coworkers (Bohnert and Horhett, 1986; Rapoza and Horhett,

1989) studied the elutahility of fibrinogen and albumin at different polymeric

surfaces and found that the elutahility and the change in elutahility with time

differed between surfaces. These differences could not, however, he correlated

to surface energetics in terms of their critical surface tension of wetting.

Investigations into the elutahility of lysozyme and ~-lactoglobulin from methy

lated silica (hydrophobic) and oxides of silicon, chromium, and nickel by SDS

and cetyltrimethylammonium bromide (CTAB) showed that it did not follow

any rules relating to the charge of the surface. Instead, elutahility of ~-lac-

Protein/Emulsifer Interactions 1 05

toglobulin and lysozyme decreased roughly in the order silica > chromium ox

ide > nickel oxide (Wahlgren and Arnebrant, 1991). The similarity between

the behavior of the two oppositely charged surfactants indicates that the re

movability of protein in these cases mainly reflects the binding mode of the

protein to the surface.

Elwing et al. (1989, 1990) studied the surfactant elutability of proteins ad

sorbed to a surface containing a gradient in hydrophobicity and found large

differences in the amounts removed from the hydrophilic and hydrophobic

ends. In the case of a nonionic surfactant (Tween 20), the elutability was

largest at the midpoint of the gradient, which can be attributed to enhanced

conformational changes of the adsorbed protein at the hydrophobic end, in

combination with a lower efficiency of removal by nonionics at hydrophilic

surfaces. At hydrophobic surfaces the removal is generally high (Elwing et al.,

1989; Wannerberger et al., 1994). However, this may not be considered as evi

dence for weak binding of the proteins to the surface, but rather as an indica

tion of the strong interaction between the surfactants and surface.

Simple models. The observed effects of surfactants on adsorbed proteins

can be classified into two types of behavior, a short description of which fol

lows (see Figure 5.4):

l. Complex formation between surfactant and protein that leads to desorp

tion of protein from the surface. In this case the surfactant does not have

to adsorb at the surface, but it has to interact with the adsorbed protein.

2. Replacement of protein by surfactant. This implies that the interaction

between the surfactant and the surface has to be stronger than the inter

action between the protein or the surfactant/protein complex and the

surface. Adsorption of the surfactant to the surface is essential in this

connection, but binding of surfactant to protein may not be required.

Of course, the surfactant might bind to the surface and/or to the adsorbed

protein without any net effect on the amount of protein adsorbed. A partial re

moval according to mechanisms (1) or (2) as illustrated in Figure 5.4 may be

the most common observation and has previously been suggested as one indi

cation of the presence of multiple adsorption states of the protein (Horbett and

Brash, 1987).

It is important to note that surfactant can remove proteins without binding to

the surface [case (1), left side of Figure 5.4]. This could be described as a solubi-


• ~·

Figure 5.4 An illustration of surfactant-protein interactions at solid interfaces. The top drawing schematically shows an adsorbed layer of protein consisting of a removable (type 1) and a nonremovable (type 2) fraction. The differences might be due to, e.g., conformational and/or orientational aspects. The bottom-left drawing illustrates formation of desorbing complexes of surfactant and protein (solubilization), and replacement of protein by surfactant is shown to the right.

lization of the proteins by the surlactant. An interesting question is whether the

replacement of proteins by surlactant in case (2) (right side of Figure 5.4) is first

initiated by solubilization followed by surlactant adsorption. Nonionic surlac

tants interact to a very low extent with soluble proteins (Tanford, 1980), as for ex

ample can be concluded from the low amounts adsorbed to the adsorbed protein

layer (Wahlgren, 1992). These surlactants still remove proteins from hydropho

bic surlaces, and it is thus evident that in this case it occurs through replace

ment of adsorbed protein molecules by surlactant.

5.3.1.2 Adsorption from Mixtures of Proteins and Surfactants. Proteins and

surlactants can interact in solution to form surlactant/protein complexes that

may have different properties from those of the pure protein (Tanford, 1980;

Ananthapadmanabhan, 1993). Ionic surlactants are known to interact with

proteins in solution, and the interaction is generally stronger for SDS than for

cationic surlactants (Nozaki et al., 1974; Subramanian et al. , 1986;

Ananthapadmanabhan, 1993). Nonionic surlactants are known to generally in

teract poorly with soluble proteins (Tanford, 1980) unless specific hydrophobic

binding sites exist. Three types of interactions are observed:

l. Binding of the surlactant by electrostatic or hydrophobic interactions to

specific sites in the protein, such as for ~-lactoglobulin (Tanford, 1980;


Jones and Wilkinson, 1976; Coke et al., 1990: Frapin et al., 1990;

O'Neill and Kinsella, 1987; Kresheck et al., 1977; Clark et al., 1992;

Creamer, 1995), serum albumin (Tanford, 1980; Nozaki et al., 1974;

Brown, 1984; Ericsson and Hegg, 1985), and specific lipid-binding pro

teins such as puroindoline from wheat (Wilde et al., 1993).

2. Cooperative adsorption of the surfactant to the protein without gross con

formational changes.

3. Cooperative binding to the protein followed by conformational changes

(Few et al., 1955; Subramanian et al., 1986; Su and Jirgensons, 1977;

Nelson, 1971).

These different interactions can occur in the same system upon increasing the

surfactant concentration. The conformational changes that occur in case (3)

can involve changes in secondary structure (Nozaki et al., 1974; Subramanian

et al., 1986; Su and Jirgensons, 1977). Several models for the protein/surfac

tant complexes have been suggested, e.g.: rigid rod (Reynolds and Tanford,

1970), pearl and necklace ( Shirahama et al., 1974), and flexible helix model

(Lundahl, 1986). In the cooperative region (2 and 3), above the critical associ

ation concentration ( cac ), the interaction is mainly one of hydrophobic charac

ter (Tanford, 1980; Subramanian et al., 1977; Nelson, 1970).

The adsorption from surfactant/protein mixtures to hydrophobic solid sur

faces is to some extent analogous to the adsorption at air/water or oiVwater in

terfaces, which have been the subject of frequent studies (Courthaudon et al.,

1991a, b; Clark et al., 1994). Competitive adsorption between proteins and

surfactants at these interfaces has recently been reviewed by Dickinson and

Woskett (1989). They conclude that, as expected, small surface-active compo

nents above a certain critical concentration will dominate over proteins at

these interfaces, since such components normally have higher surface activity

(superiority in lowering interfacial tension).

Experimentally it is observed that the presence of surfactants in protein so

lutions may influence the amount of proteins adsorbed to solid surfaces in

three different ways (Wahlgren 1992; Wahlgren and Arnebrant, 1991, 1992;

Wahlgren et al., 1993, 1995):

l. Complete hindrance of protein adsorption

2. Reduced amounts of adsorbed protein compared to adsorption from pure

protein solution

3. Increased amounts adsorbed


The complete lack of adsorption in case (1) could be explained by complex for

mation with a surfactant resulting in an entity that has no attraction to the surface

or direct/preferred surfactant adsorption, due to their higher surface activity and

diffusivity, unpending adsorption of proteins, or protein/surfactant complexes. In

cases (2) and (3), the formation of complexes in solution leads to a decrease or in

crease in the amounts of protein adsorbed, respectively. The presence of surfactant

influences the total amount of protein adsorbed by steric effects or changes in the

electrostatic interaction between complexes as opposed to native protein. In addi

tion, the complex may adsorb in a different orientation than the pure protein, re

sulting in a positive or negative effect on the adsorbed amount.

Due to the different shapes of the adsorption isotherms of surfactants and pro

teins, the interaction with the interface is of course, as for protein mixtures,

strongly dependent on the relative concentration of the components. The special

character of the surfactant adsorption isotherms featuring the sharp increase in ad

sorbed amount in the range of their critical association concentration will influence

these events in a very pronounced way. Studies regarding these surfactant/protein

"Vroman effects" have been reported; for example, adsorption of fibrinogen from

mixtures containing Triton X-100 passes through a maximum (Slack and Horbett,

1988). The adsorption from ~-lactoglobulin/SDS mixtures at different degrees of

dilution was studied by Wahlgren and Amebrant (1992) (see Figure 5.5). At con

centrations above the erne for the surfactant, the amount adsorbed corresponded to

a layer of pure surfactant and was found to increase after rinsing. At lower concen

trations, the adsorbate prior to rinsing appeared to be a mixture of protein and sur

factant, and the total amount adsorbed passes through a maximum. The

composition of the adsorbate after rinsing is most likely pure ~-lactoglobulin, since

interactions between the surface or protein and SDS are reversible.

At high degrees of dilution of the mixture, the absence of surfactant adsorp

tion to the methylated silica, the nonreversible adsorption of ~-lactoglobulin,

and the observed partial desorption of the adsorbate from the mixture imply

that some SDS molecules are bound to ~-lactoglobulin molecules with a higher

affinity than to the surface (see Figure 5.5). The amount of protein adsorbed is

larger, even after rinsing, than for adsorption from pure ~-lactoglobulin solu

tions, and it can be concluded that SDS binding in this case facilitates the ad

sorption of protein.

Conclusions. Generally, it can be concluded that surfactants may interact with

interfaces through solubilization or replacement mechanisms, depending on sur-

Protein/Emulsifer Interactions 1 09

0.18

0 ......-: --..-...: .-- .

0.12

0.06

0

1000 100 10 Degree of dilution

Figure 5.5 The amounts adsorbed to a methylated silica surlace as a function of degree of dilution for a mixture of ~-lactoglobulin and SDS (0.2 w/w), in phosphate buffered saline pH 7, I= 0.17. The figure shows the adsorbed amount (!lg/cm2) after 30 minutes of adsorption (e) and 30 minutes after rinsing(+). In addition, the figure shows the adsorption of pure ~-lactoglobulin, after 30 minutes of adsorption (•) and 30 minutes after rinsing (x). Finally, the adsorption isotherm of SDS is inserted (0). (From Wahlgren and Arnebrant, 1992.)

factant surface interactions and surfactant/protein binding. Solubilization re

quires complex formation between protein and surfactant, and replacement re

quires adsorption of the surfactant to the surface. As for protein adsorption, one of

the most important protein properties affecting surfactant-induced desorption ap

pears to be conformational stability. Differences between a competitive situation

and addition of surfactant after protein adsorption may derive from the alteration

in surface activity of protein/surfactant complexes formed in solution compared to

pure protein, the difference in diffusivity of surfactants and proteins affecting the

"race for the interface," and time-dependent conformational changes resulting in

"residence time" effects.

The effects observed at low surfactant concentration, below the erne, m

volve the specific binding of surfactant to some proteins and are not fully un

derstood. Further, the exact prerequisites for solubilization versus replacement

as well as detailed information on molecular parameters such as aggregation

numbers are not known.


5.3.2 Protein/Surfactant Interactions at Liquid/Air and Liquid/Liquid Interfaces

Interactions between proteins and surfactants at air/water and oil/water inter

faces has attracted considerable study in recent years because the conse

quences of competitive adsorption of these two species at these interfaces can

often strongly influence dispersion (foam or emulsion) stability against coales

cence. The majority of proteins have high affinity for interfaces, which they

saturate at comparatively low concentrations compared to low molecular

weight (LMW) surfactants (Dickinson and Woskett, 1989; Coke et al., 1990).

Thus, on a mole for mole basis at low concentrations, proteins reduce the sur

face tension to a greater extent than LMW surfactants. However, the opposite

effect is observed at high concentrations, because at saturation coverage with

LMW surfactants, the interfacial tension of the interface is usually lower than

that achieved by proteins, and as a result, the latter molecules will be dis

placed from the interface. The region where the two different components co

exist in the interfacial layer is of greatest interest, since it is in this region that

the stability of the system to coalescence is most greatly affected. A clearer

understanding of this has emerged from direct study of the structures that separate the dispersed-phase of foams or emulsions, under conditions of high dis

persed-phase volume (i.e., foam or emulsion thin films). Such structures form

rapidly in foams following limited drainage but may occur only in emulsions

after creaming of the dispersed phase.

5.3.2.1 Foam and Emulsion Film Stabilization. Thin films are stabilized by

two distinct mechanisms; the one that dominates is dependent upon the molec

ular composition of the interface (Clark, 1995). Low molecular weight surfac

tants such as food emulsifiers or polar lipids congregate at the interface and

form a fluid-adsorbed layer at temperatures above their transition temperature

(see Figure 5.6a). When a surfactant-stabilized thin film is stretched, local

thinning can occur in the thin film. This is accompanied by the generation of a

surface-tension gradient across the locally thin region. Surface tension is high

est at the thinnest point of the stretched film, due to the local decrease in the

surface concentration of emulsifier in the region of the stretch. Equilibrium

surface tension is restored by adsorption of surfactant from the interlamellar

liquid, which is of very limited volume in a drained thin film. This process is

called the "Gibbs effect." Alternatively, migration of the surfactant by lateral

diffusion in the adsorbed layer toward the region of highest surface tension


may also occur (Clark et al. 1990a). Here, the surfactant drags interlamellar

liquid associated with the surfactant head group into the thin region of the film

and contributes to the restoration of equilibrium film thickness. This process is

often referred to as the "Marangoni effect" (Ewers and Sutherland, (1952).

In contrast, the adsorbed layer in protein-stabilized thin films is much

stiffer and often has viscoelastic properties (Castle et al., 1987). These derive

from the protein/protein interactions that form in the adsorbed layer (see

Figure 5.6b). These interactions result in the formation of a gel-like adsorbed

layer, recently referred to as a "protein-skin" (Prins et al., 1995), in which lat

eral diffusion of molecules in the adsorbed layer is inhibited (Clark et al.,

l990b). Multilayer formation can also occur and serves to further mechani

cally strengthen the adsorbed layer (Coke et al., 1990). When pure protein

(o) Syrfnctnru-alonc (b) Pmtein-olpne

h igh mobility

~ Film sttetchiog ~

rapid ~ ~Protcin diffusion~ ~ dcfonnntion

""' (c) Mixed mlem /

rc:duc:ed mobility ·

Slow diffusion

-

Pilm stretching

J P'lm ruilre .

-i

no int.emct.i:ons

No Protein defonnation

Figure 5.6 Schematic diagram showing the possible mechanisms of thin-film stabilization. (a) The Marangoni mechanism in surfactant films; (b) the viscoelastic mechanism in protein-stabilized films; (c) instability in mixed component films. The thin films are shown in cross section and the aqueous interlamellar phase is shaded. (Reprinted with kind permission of the Royal Society of Chemistry, London.)


films are stretched, the change in interfacial area is dissipated across the film,

due to the cohesive nature of the adsorbed protein layer and possibly the de

formability of the adsorbed protein molecules.

Thin-film instability can result in systems that contain mixtures of proteins

and low molecular weight surfactants (Coke et al. 1990; Clark et al., 1991a;

Sarker et al., 1995), as is the case in many foods. The origin of this instability

rests in the incompatibility of the two stabilization mechanisms: the Marangoni

mechanism relying on lateral diffusion, and the viscoelastic mechanism on im

mobilization of the protein molecules that constitute the adsorbed layer. One

can speculate that in a mixed system, competitive adsorption of low molecular

weight surfactant could weaken or interfere with the formation of protein/pro

tein interactions in the adsorbed layer and destroy the integrity and viscoelas

tic properties of the adsorbed layer (see Figure 5.6c). This could be a

progressive process, with the presence of small quantities of adsorbed surfac

tant initially introducing faults or weaknesses in the protein film. Adsorption

of more surfactant could induce the formation of protein "islands" in the ad

sorbed layer. These structures could be capable of slow lateral diffusion but

would be too large to participate in Marangoni-type stabilization. Indeed, they

could impede surfactant migration in the adsorbed layer. Adsorption of pro

gressively more surfactant would reduce the size of the protein aggregates still

further until the adsorbed protein was in its monomeric form. Ultimately, all

the protein would be displaced from the interface by the surfactant.

Two types of interaction are shown in the schematic diagram of the mixed sys

tem. First, there is an interactive process associated with the coadsorption or

competitive adsorption of the two different species at the interface. Second, many

of the functional proteins used in food production have physiological transport ac

tivities and therefore possess binding sites, which may allow the formation of

complexes with surfactants. Let us consider each of these processes in tum. The

transition in adsorbed-layer structure at the air/water and oil/water interface

caused by competitive adsorption between protein and emulsifiers has been stud

ied in detail. Oscillatory surface shear (Kragel et al., 1995) and dilation (Clark et

al., 1993: Sarker et al., 1995) measurements have been carried out at the air/wa

ter interface and show an emulsifier-induced reduction in surface shear viscosity

and surface dilational elasticity at critical emulsifier/protein ratios. This is consis

tent with the cartoon depicted in Figure 5.6, where at a specific molar ratio the

emulsifier will break down protein/protein interactions in the adsorbed layer, re

sulting in a reduction in surface shear viscosity and dilational elasticity. Similar


observations have been made at the oil/water interlace under conditions of con

stant shear in experiments where both components were present in solution when

the interlace was formed (Courthaudon et al., 1991) and when the competing sur

factant was added subsequent to formation of the protein-adsorbed layer (Chen

and Dickinson, 1995). Direct measurements of changes in adsorbed-layer rheo

logical properties in foam and emulsion films is possible using the fluorescence

recovery after photobleaching (FRAP) technique (Clark et al., 1990a; Clark,

1995). This method relies on the positioning of a fluorescent reporter molecule in

the adsorbed layer either by covalent labeling of the protein of interest with a flu

orescent moiety such as fluorescein isothiocyanate (FITC) or by use of an amphi

pathic fluorescent molecule [e.g., 5-N-(octadecanoyl)amino fluorescein, ODAF] at

low (submicromolar) concentrations that are insufficient to alter adsorbed-layer

structure. FRAP allows direct measurement of the lateral diffusion coefficient of

the fluorophore in the adsorbed layer of the thin film. The presence of an exten

sive network of protein/protein interactions in the adsorbed layers arrests lateral

diffusion of the probe molecule, as is the case in all films stabilized by protein

alone (Clark et al., 1990b). This situation persists in the presence of emulsifier

until a critical ratio of emulsifier/protein is achieved. This is marked by the onset

of surlace lateral diffusion in the adsorbed layer. The technique serves as a useful

means of (i) comparing the resistance of different proteins to emulsifier-induced

adsorbed layer disruption, (ii) evaluating the effectiveness of protein modification

strategies at improving the resistance of proteins to competitive displacement,

and (iii) investigating the usefulness of natural food ingredients as crosslinkers of

proteins in the adsorbed layer.

5.3.2.2 Specific Binding of Proteins and Emulsifiers. Let us now consider the

effects of specific binding of emulsifiers by food proteins on adsorbed-layer

properties at the air/water and oil/water interlace. There are many examples of

proteins that possess binding activity, including bovine serum albumin and ~

lactoglobulin (see Section 5.3.1.2). Investigation of the binding properties of

these proteins has been generally confined to studies in bulk solution. For ex

ample, the presence of a fluorescent tryptophan residue in the hydrophobic

cleft of ~-lactoglobulin (Papiz et al., 1986) has facilitated the study of emulsi

fier binding by fluorescence titration. Subsequent analysis of binding by con

ventional methods such as that of Scatchard (1949) allows determination of the

dissociation constant (Kd) of the complex formed. Typical examples of KJs for

~-lactoglobulin are shown in Table 5.1. The effect of complex formation can


usually be detected by shifts in the surface-tension (y) curve (Dickinson and

Woskett, 1988). An example of this is shown for Tween 20 and ~-lactoglobulin

in Figure 5.7 (Coke et al., 1990). Surface-tension/concentration (y-c) curves

for Tween 20 alone and in the presence of a fixed concentration of ~-lactoglob

ulin (0.2 mglml; 10.9 J1M) are shown.

Table 5.1 Typical dissociation constants of emulsifier/P-lactoglobulin complexes

Dissociation Emulsifier constant Reference

Tween 20 4.6 j.iM Wilde and Clark, 1993

L-a lysophosphatidyl- 166.J.!M Sarker et al., 1995

choline, palmitoyl Sucrose monolaurate 11.6 j.iM Clark et al., 1992

Sucrose monostearate 1.02 j.iM Clark et al., 1992

Sucrose monooleate 24.8 j.iM Clark et al., 1992

Sodium stearoyl 0.26 j.iM Clark, unpublished

lactylate, pH 7.0 Sodium stearoyl 0.30 j.iM Clark, unpublished lactylate, pH 5.0 Lauric acid 0.7 j.iM Frapin et al., 1993 Palmitic acid 0.1 j.iM Frapin et al., 1993

The general features described earlier are evident with a comparatively low

concentration of protein causing a significant reduction in y. In the absence of

protein, yreduces gradually with increasing Tween 20 concentration. The gradi

ent of the reduction in surface tension reduces at higher Tween 20 concentra

tions (> 30 J1M) but doesn't become completely flat due to failure to attain

equilibrium y, possibly due to the presence of a mixture of surface-active species

in the Tween-20 sample. In contrast, the curve in the presence of protein main

tains a relatively steady surface-tension value of about 50 mN/m up to Tween-20

concentrations of 25 j.iM due to adsorption of the protein. This means that the

curve for the sample containing protein crosses that of Tween 20 alone. This is

strong evidence for complex formation between the two components, since the

curves cross due to a reduction in the concentration of free emulsifier in solution

due to that which interacts with the protein to form the complex.

Thus, great care must be taken when considering the surface properties of


80

70

~ 5 60 ~ 0 ·u.; ~ Q) ~

Q) <..>

50 $ .... ;::l

r:n. 40

30 0 20 40 60 80 100

Figure 5.7 Surface tension isotherm for Tween 20 in the absence (e) and presence (•) of 0.2 mg/mL ~-lactoglobulin. The data were recorded after 20 minutes adsorption and are therefore not at equilibrium.

solutions containing mixtures of interacting components. In the simplest case

of a single binding site, the two-component system becomes a three-compo

nent system comprising free emulsifier, free protein, and emulsifier/protein

complex. The relative proportions of the components present can be calculated

in the following manner (Clark et al., 1992). In the simplest case, the interac

tion of an emulsifier (E) with a protein (P) can be described by the expression

P+E~PE (l)

where PE is the emulsifier/protein complex. Thus the dissociation constant

(Kd) for the complex can be expressed as

[P] [E]

[PE] (2)

where the square brackets indicate molar concentrations of the different

species. It is also the case that


[P] = [P101] - [PE] (3)

[E] = [E101] - [PE] (4)

where [P101] and [E101] are the total protein and emulsifier m the system. Substituting (3) and (4) in (2) gives

which can be solved for [PE] and can be used to calculate the relative concentrations of the three components. In addition, the binding data, which may comprise a change in a parameter (e.g., intrinsic fluorescence) caused by formation of the complex may be fitted using this equation, provided there is a single active binding site and the titration is carried out to saturation. Alternatively, it is possible to determine the dissociation constant and number of binding sites from the Scatchard (1949) equation

v (6)

[E]

where v is the fraction of protein with occupied sites (i.e., [PE]/[P101]). If the Scatchard plot of v against v/[E] gives a straight line, it indicates the presence of only one class of binding site. The gradient of this line is -l!Kd, and the intercept on the xaxis gives the number of binding sites, n. If the Scatchard plot does not give a straight line, then the shape of the curve obtained can be used to identify if the observed binding is positively or negatively cooperative or the presence of multiple independent sites. In the former case the Hill equation can be used to determine the Kd and a cooperativity coefficient (Hill, 1910).

Evidence for the formation of a specific complex in solution by direct measurement or by crossovers in surface-tension/concentration isotherms is not sufficient to allow the conclusion that intact complex adsorbs directly at the air/water or oil/water interface. There are few studies that provide convincing data that support such a hypothesis, and that which is provided often only indirectly points toward the presence of adsorbed complex at the interface. One of the best understood systems is that of Tween 20 and ~-lactoglobulin (Coke


et al, 1990; Wilde and Clark, 1993), which are known to interact in solution

to form a 1:1 complex characterized by a Kd = 4.6 ~' which has an in

creased hydrodynamic radius of 5. 7 nm compared to 3.5 nm for P-lactoglobu

lin alone (Clark et al., 1991b ). Detailed measurements of the properties of

foam films formed from a constant concentration of 0.2 mg/mL mixed native

and fluorescein-labeled P-lactoglobulin as a function of increasing Tween-20

concentration (Wilde and Clark, 1993; Clark, 1995) have been reported. This

study revealed that between molar ratios (R) of Tween 20 to P-lactoglobulin of

0.2 to 0.9, there was a progressive increase in the thickness of the foam films

and a corresponding decrease in the amount of adsorbed protein to an inter

mediate level of approximately 50% of that which was originally adsorbed

(see Figure 5.8). These changes occurred prior to the onset of surface diffu

sion of the labeled protein as determined by the FRAP technique at R = 0.9

(Coke et al., 1990). The increase in foam-film thickness was unexpected since

protein displacement by the Tween 20 should have reduced the thickness of

the thin film. One persuasive interpretation of the data is that coadsorption or

trapping of the Tween-20/P-lactoglobulin complex in the adsorbed multilay

ers could account for adsorbed-layer thickening (Clark et al., 1994), since the

complex is known to have an increased hydrodynamic radius (Clark et al.,

1991b). Calculations reveal that this is a distinct possibility, since 16 to 49%

of the P-lactoglobulin present in solution will be in the complexed form in the

R-value range, 0.2 to 0.9. Further confirmation of this explanation comes from

measurements of foam-film thickness at different P-lactoglobulin concentra

tions but at constant R value. Film thickness data for P-lactoglobulin at 0.2

and 1.0 mg/mL are also shown in Figure 5.8. The completely different thick

nesses observed at the two protein concentrations can be rationalized in terms

of the amount of Tween-20/P-lactoglobulin complex formed. The sharp reduc

tion in film thickness observed in the 0.2 mg/mL P-lactoglobulin sample at R

= 0.9 occurs when there is 5.41-LM complex present in the sample. An equiv

alent amount of complex is present in the 1 mg/mL sample at R = 0.1 and

could account for the immediate reduction in film thickness observed with the

1 mg/mL P-lactoglobulin sample and the complete absence of a film thicken

ing step at low R values.

Further evidence supporting direct adsorption of the complex formed be

tween ~-lactoglobulin and Tween 20 comes from dynamic surface-tension

(Ydyn) measurements performed using the overflowing cylinder apparatus

(Clark et al., 1993). The Yclvn isotherm for Tween 20 showed classical sig-


40

0 0 ,._, --Cl) _.., ~ ;::S

30 0 u OJ u

43 ... ;::S

CIJ

8 -E 20 Cl)

Cl) OJ

];a u

~

4 Molar ratio (R)

Figure 5.8 A comparison of foam-film thickness and surface concentration data for ~lactoglobulin samples as a function of Tween 20 concentration. Surface concentration of FITC/~-lactoglobulin (0.2 mg/mL) as determined by fluorescence counts (.&); foamfilm thickness for samples containing 0.2 mg/mL (•) and l.O mg/mL (e) ~-lactoglobulin. R refers to the molar ratio of Tween 20: ~-lactoglobulin.

moidal behavior hut was shifted to increased surfactant concentration by ap

proximately 2 orders of magnitude compared to the static measurements.

Inclusion of ~-lactoglobulin (0.4 mg/mL) in the initial solutions caused only a

small reduction in the measured Ydyn to 71 mN/m. This remained unaltered in

the presence of Tween 20 up to a concentration of 15 f.!M. Above this concen

tration a small hut significant further reduction in Ydyn was observed. The ef

fect resulted in a small inflection in the Ydyn curve in the region corresponding

to 15 to 40 J.LM Tween 20. At higher Tween-20 concentrations, the curve for

the mixed system followed that of Tween 20 alone. The inflection in the Ydyn

isotherm observed for the mixed system at concentrations of Tween 20 greater

than lO JlM could not he due to adsorption of Tween 20 alone since under the

prevailing conditions, the concentration of free Tween 20 was reduced by its

association with ~-lactoglobulin. Using Equation (5) it can he shown that the

Tween-20/~-lactoglohulin complex is the dominant component in solution in

the Tween-20 concentration range of 15 to 35 flM (Clark et al., 1993). Indeed,

the Ydyn isotherm indicates that there is very little difference between the sur-


face activity of the three components present in solution, Tween 20, ~-lac

toglobulin, and the complex, since 'Ydyn behavior is dominated by the compo

nent present in the highest concentration. Such observations provide

important evidence for direct adsorption of intact complex, and in this partic

ular case provides evidence that the observed "induction period" in static y isotherms could be due to the formation of protein islands (de Feijter and

Benjamins, 1987) and can be abolished if interactions between the adsorbed

protein molecules can be prevented, as is the case with the Tween-20/~-lac

toglobulin complex.

Direct adsorption of complex at the air/water interface also appears to have

importance in functional properties of certain lipid-binding proteins from

wheat called "puroindolines" (Blochet et al., 1991; Wilde et al., 1993). These

proteins show unusual behavior in the presence of lipids that they bind, in

that their foaming properties are generally unaltered and in some cases en

hanced. A systematic study of the influence of interaction with lysophos

phatidyl cholines (LPC) of different acyl chain lengths has been completed

(Husband et al., 1995) and has produced persuasive evidence of the impor

tance of the complex on foaming activity. First, two isoforms of the protein

were investigated, puroindoline-a and -b (the b form has also been referred to

as "friabilin"). Puroindoline-b has a significantly increased Kd for LPC com

pared to puroindoline-a (i.e., 20-fold weaker binding) and the enhancement

of foaming properties is correspondingly reduced in the b form. Further stud

ies of the binding of LPC to the a form revealed that the binding became

tighter with increasing acyl chain length, and higher concentrations of the

short-chain-length LPC are needed to achieve optimal foam stability en

hancement. One interesting observation was that the micellar form of LPC

was the species that bound to the protein. This finding emerged from the ob

servation that lauryl-LPC showed no interaction with the puroindoline-a until

the levels present exceeded the critical micelle concentration of 400 ~·

This indicates a cooperative binding since it takes place in this concentration

range, and any of the suggested structures for the protein/surfactant com

plexes described in Section 5.3.1.2, e.g., the pearl and necklace structure,

could be applicable. It seems increasingly likely that the functional proper

ties of the puroindolines are linked to a role in the transport and spreading of

lipid at the air/water interface analogous to the role of amphipathic lung sur

factant proteins such as SP-B, with which they have striking structural homol

ogy (Hawgood and Clements, 1990).


5.4 Protein/Phospholipid Interactions Introduction. In this section we will discuss the interaction between phos

pholipids and proteins. Both proteins and phospholipids are major components

of biological membranes, and therefore it is not surprising that a vast number

of publications concerning protein/phospholipid interactions are related to un

derstanding the biomembrane processes. This aspect has recently been re

viewed in a book by Watts (1993).

In pharmaceuticals, phospholipids are often used as colloidal drug carriers

in drug delivery systems in various physical forms like liposomes or emul

sions. These drug delivery systems are cleared from the circulation (blood

stream) by the reticuloendothelial system. It is believed that this clearance is

triggered by adsorption of serum proteins on the phospholipid interface and

will depend on the properties of both the protein and the phospholipid (Eidem

and Speiser, 1989; Tabata and lkada, 1990; Patel, 1992).

In untreated milk the fat globule is stabilized by a lipid membrane, composed

mainly of sphingo- and phospholipids. Homogenization of milk results in a total

area increase of the fat globules by some 6- to 10-fold, where the increased surface

is stabilized by proteins adsorbed from milk during the process. Phospholipids,

particularly phosphatidyl-choline Oecithin), are added to various processed foods,

where they act as emulsifiers alone or together with proteins. Therefore, proteins

and phospholipids, separately as well as in complexed form, contribute signifi

cantly to the physical properties of many systems of technological interest (e.g.,

emulsions and foams). The intention of this section is to emphasize the diverse na

ture of phospholipid/protein interaction and to point to some implications of this for

the physicochemical as well as the biological properties of phosholipidlprotein sys

tems. It is also our intention to point at some of the major forces involved in phos

pholipid/protein interactions. We will highlight only some properties of importance

for the understanding of phospholipid/protein interactions. Therefore the classifi

cation of interactions made in this section, when the lipid is dispersed in solution,

at different interfaces and with lipid phases, is arbitrary. Assignment according to

polar/nonpolar, anionic/cationic, or soluble/insoluble phospholipids could also

have been possible.

5.4.1 Protein/Phospholipid Interactions in Dispersed Systems

Many proteins have the biological role of transporting molecules with hydropho

bic properties, which are bound to a hydrophobic pocket in the protein. ~

Lactoglobulin is thought to transport retinol (Papiz, 1986; Sawyer, 1987; North,


1989) but has also been shown to have high affinity for phospholipids, fatty

acids, and triglycerides (Diaz de Villegas, 1987; Creamer, 1995; Sarker et al.,

1995; Kristensen, 1995). An important application of lipid/protein interactions

was reported by Kurihara and Katsuragi (1993), who found that a lipid/protein

complex, formed between ~-lactoglobulin and phosphatidic acid, could mask

bitter taste. This property was suggested to be specific for phosphatidic acid

since no effect was observed for mixtures of ~-lactoglobulin and phosphatidyl

choline, triglycerides, and diglycerides. Differential scanning calorimetry mea

surements confirm the presence of a specific interaction between phosphatidic

acid and ~-lactoglobulin since the presence of distearoylphosphatidic acid

(DSPA) as well as dipalmitoylphosphatidic acid (DPPA) thermally stabilized the

protein, which was not observed when the protein was mixed with phosphatidyl

choline, phosphatidylethanolamine, or phosphatidylglycerol (Kristensen et al.,

1995). No interaction could be observed if the lipid contained unsaturated fatty

acid residues or if it was mixed in the gel state with the protein. Thus, the results

show that the interactions between ~-lactoglobulin and phospholipids are

strongly dependent on the acyl chain as well as the head group. This is not sim

ply a question of having a negatively charged head group since no interaction

was observed for phosphatidylglycerol.

The influence of protein structure on lipid/protein interactions has been

demonstrated by Brown et al. (1983), who observed that native ~-lactoglobulin

is unable to bind to phosphatidylcholine vesicles. However, if the protein was

dissolved in a-helix-forming solvent, binding to the phospholipid was ob

served. Brown suggested that the acyl chains of the lipid interact with the hy

drophobic interior of the a helix, while the polar head group is likely to

interact with the hydrophilic exterior of the protein (Brown, 1984). The par

tially unfolded proteins formed during food processing may give helix struc

tures when interacting with the lipids and these lipid/protein complexes can

improve the emulsification process (Brown, 1984; de Wit, 1989).

5.4.2 Protein/Phospholipid Interactions at Solid Surfaces

A few studies have demonstrated the use of deposited phospholipid layers, de

posited via the Langmuir-Blodgett technique or by spin coating, to follow the

interaction between proteins and phospholipids in situ by using ellipsometry

(Malmsten, 1994, 1995; Corselet al., 1986; Kop et al., 1984). This approach

can also be used to analyze the kinetics of interaction (Corsel et al., 1986; Kop

et al., 1984). The work of Malmsten (1994, 1995) showed that the interaction


of human serum albumin, lgG, and fibronectin from human plasma with phos

pholipids spin-coated onto methylated silica surfaces depends on the phos

pholipid head group. He found no interaction of proteins with phospholipids

that have no net charge or shielded charges like phosphatidylcholine, phos

phatidylethanolamine, sphingomyelin, and phosphatidylinositol, whereas in

teraction was observed with the phospholipid surfaces containing unprotected

charges like phosphatidic acid, diphosphatidylglycerol, and phosphatidylser

ine. No differences in adsorption behavior were found for spin-coated surfaces

and Langmuir-Blodgett -deposited phospholipid layers.

The consequences of nonspecific interactions with negatively charged di

oleoylphosphatidylserine (DOPS) bilayzrs observed for fibrinogen and albumin

in contrast to the specific ones observed for prothrombin have been demon

strated by Corsel et al. (1986). By analyzing their data in terms of intrinsic

binding and transport rate, they found that the initial rate of adsorption of pro

thrombin was transport-limited, whereas the rate-determining step for the al

bumin interaction was the binding. The adsorption rate of fibrinogen was either

transport-limited or controlled by the binding, depending on pH and ionic

strength. Since the DOPS bilayer contained biological binding sites for pro

thrombin, the interaction was completely reversible. However, the interaction

of fibrinogen and albumin with the bilayer probably induced conformational

changes of the proteins and as a consequence the interaction was irreversible.

Kop et al. (1984) found that a high density of DOPS in the bilayer was needed

for the high-affinity binding of prothrombin. Consequently, an introduction of

dioleoylphosphatidylcholine (DOPC) into the bilayer markedly decreased the

affinity for binding.

5.4.3 Protein/Phospholipid Interactions at liquid/air Interfaces

Electrostatic interactions between protein molecules and lipid monolayers

have been shown to be important for phospholipid/protein interactions at the

liquid/air interface. A model food emulsion was used to study the interaction

between nitroxide homologs of fatty acids and milk proteins by following the

mobility of the nitroxide radicals using electron spin resonance (Aynie,

1992). It was found that at pH 7 the lipid/protein interaction was correlated

with the number of positive charges on the protein. Thus, the importance of

the interaction in the emulsions was found to decrease in the order <X51-casein

> ~-lactoglobulin > ~-casein, suggesting that the interaction was of electro

static nature. The work of Quinn and Dawson (1969a, b) concerning the inter-


action between cytochrome c (positive net charge below pH 10) and phospho

lipids from egg yolk also suggest that it is determined by electrostatics. Their

results show that the limiting pressures for penetration are 20 and 24 mN/m

for phosphatidylcholine and phosphatidylethanolamine, respectively, whereas

penetration into the phosphatidic acid and diphosphatidylglycerol (cardi

olipin) monolayers occurred up to pressures (< 40 mN/m) close to the col

lapse pressure of the film. Furthermore, the presence of sodium chloride

decreased the interaction. Later, Kozarac et al. (1988) confirmed the findings

of Quinn and Dawson with their reflection spectroscopy results. Cornell

(1982) observed a specific interaction between ~-lactoglobulin and egg yolk

phosphatidic acid (e-PA) in spread mixed films at low pH (1.3 and 4) where

~-lactoglobulin carries a positive net charge. No interaction was observed in

the neutral pH range or for egg yolk phosphatidyl choline, (e-PC). ~-lac

toglobulin, adsorbing from solution into a spread monolayers of palmitoy

loleoylphosphatidylcholine (POPC) and palmitoyloleoylphosphatidylglycerol

(POPG), was found to interact with the lipids only in the acid pH range

(Cornell and Patterson, 1989). The highest amounts of ~-lactoglobulin

(Cornell and Patterson, 1989), a-lactalbumin, or BSA (Cornell et al., 1990)

bound to mixed monolayers of POPC and POPG were observed below the iso

electric point of the protein, when the lipid layer and the proteins carry an op

posite net charge, whereas less was adsorbed around and almost nothing

above the isoelectric point. The interaction was also found to be reduced in

the presence of calcium as well as if sodium chloride was added (Cornell et

al., 1990). Bos and Nylander (1995) used the film balance to study the incor

poraffon of ~-lactoglobulin into monolayers of distearoylphosphatidic acid

(DSPA), distearoylphosphatidylcholine (DSPC), and dipalmitoylphosphatidic

acid (DPPA) and some of their results are shown in Figure 5.9. The highest

rate of incorporation was observed for ~-lactoglobulin into the negatively

charged DSPA monolayer. The rate also increases with ionic strength of the

subphase, which probably is due to a decrease of the repulsion within the

phosphatidic acid protein monolayer. The incorporation into the zwitterionic

DSPC monolayers is, as expected, less salt-dependent. The importance of

electrostatic interactions for the incorporation of proteins and peptides in

lipid layers have also been reported for a number of non-food-related systems

like adsorption of SecA (Breukink et al., 1992), actin (Grimard et al., 1993),

IgG (Lu and Wei, 1993), and opioid peptides and opiate drugs (Bourhim et

al., 1993) into phospholipid monolayers.


DSPC

. I , I

-3 [t

(j) -3.5

~ t -4 r

''I' 'I

DPPA

0_0

-4.5

0 5 1 0 15 20 25 30

ri (mN/m)

Figure 5.9 The rate of incorporation of P-lactoglobulin into monolayers of dis

tearoylphosphatidic acid (DSPA), distearoylphosphatidylcholine {DSPC), and dipalmi

toylphosphatidic acid (DPPA) versus surface pressure (II). The data were recorded at

constant surface pressure by measuring the area increase of the lipid monolayer

spread on a protein solution containing 1.15 mg/L in 10 11M phosphate buffer pH 7,

with 0 11M (e), 50 11M (•), or 150 11M (A) sodium chloride. The rate in mg/m2 was

calculated from the area increase using the IT-area isotherm of spread monolayers of

P-lactoglobulin. Data adopted from Bos and Nylander (1995), where the experimental

details are also given.

Besides electrostatic interactions, hydrophobic interactions (based on the

hydrophobic effect (Tanford, 1980) between protein and phospholipid are also

important. Para-K-casein, a product of the cleavage of K-casein, retains its

ability to interact with DMPC monolayers due to its more hydrophobic nature,

whereas the macropeptide does not (Griffin et al., 1984). The adsorption of~-


lactoglobulin into phosphatidic acid monolayers (Bos and Nylander, 1995)

showed that incorporation was faster into a distearoyl monolayer than into a di

palmitoyl monolayer, especially at higher surface pressures (see Figure 5.9).

This shows that the incorporation also is dependent on hydrophobic interac

tions. Bougis et al. (1981) showed that for the incorporation of snake venom

cardiotoxins into lipid interfaces, not only electrostatic interactions but also

hydrophobic interactions are important.

5.4.3.1 Structure of Protein/lipid Monolayers. The structure of mixed protein/

phospholipid films depends on both the properties of the components and their

interaction. It has been shown that conformational changes of the proteins during

or after the adsorption at the liquid/air and liquid/liquid interfaces influence the

properties of the protein film (Graham and Philips, 1979; Mitchell, 1986;

Dickinson and Stainsby, 1982). Circular dichroism spectra of ~-lactoglobulin

bound to phospholipid monolayers were found to be similar to those recorded in

solution, indicating that the conformation of the protein did not change signifi

cantly when interacting with the lipid monolayer (Cornell and Patterson, 1989;

Cornell et al., 1990). Katona et al. (1978) showed that the~ form of a hydrophobic

myelin protein was more able to interact with sphingomyelin than the <X form, in

dicating that the phospholipid is able to recognize different conformations of the

protein. Furthermore, the physical state of the phospholipid phase is important for

the interaction between protein and lipid. Fidelio et al. (1986) reported a more fa

vorable interaction between melittin and phospholipids when the lipid film was in

a more liquid expanded state. This might be related to the fact that the protein is

able to penetrate into the phospholipid layer (more hydrophobic interactions).

Interaction (adsorption) of proteins with lipids might also occur at higher surface

pressures, where the lipids are in the condensed or crystalline phase. The protein

then is not able to intercalate the phospholipid monolayer, but might bind to it

forming a second layer, like actin does on negatively charged liposomes through

electrostatic interactions (Grimard et al., 1993).

Another interesting point for discussion is the homogeneity of the mixed

phospholipid/protein film. The homogeneity of mixed protein/lipid films has

been studied by, for instance, electron microscopy of films transferred to a solid

support by Cornell and Carroll (1985). They found that only lipids with the

chains in liquid state, e-PA, dioleoylphosphatidylcholine, and dioleoylphos

phatidylethanolamine, formed homogenous films with ~-lactoglobulin, whereas

DPPA and DSPC formed heterogeneous layers. Cornell and Patterson (1989) and

Cornell et al. (1990) observed penetration of ~-lactoglobulin, a-lactalbumin, or


BSA into mixed monolayers of POPC and POPG at such high lipid pressure that

they found it unlikely that the proteins could penetrate into a protein layer of

their own at this pressure. Thus, they concluded that the formation of pure pro

tein patches is unlikely and that portions of the protein is suggested to be inter

calated in the lipid monolayer. Fluorescence microscopy together with the

surface-film balance technique has also been used to study the structure of

mixed phospholipid cytochrome c and b films (Heckl et al., 1987). It was found

that proteins were located mainly in the fluid membrane phase that coexisted

with solid lipid domains without protein. The penetration in the lipid monolayer

was reduced with increasing pressure. Cytochrome c (positively charged) was

found to interact with dimyristoylphosphatidic acid (DMPA) mono layers but not

with dipalmitoylphosphatidylcholine (DPPC) layers, from which it was con

cluded that the interaction was largely of electrostatic nature. The effect of dif

ferent proteins on the organization of lipid monolayer has been demonstrated by

Aynie et al. (1992). Their results indicate that the IX8ccasein in contrast to ~-lac

toglobulin and ~-casein, probably due to the stronger lipid/protein interaction,

induce an ordering of a monolayer of nitroxide fatty acids on the surface of an

emulsion droplet.

5.4.4 Effect of Lipid Phase Behavior on Protein/Lipid Interactions

As discussed previously, the interaction between surfactants and proteins usually takes place via monomers in the specific binding regime, whereas the co

operative association usually takes place in the range of the erne. However, in the case of lipids with low aqueous solubility, the association structures are

generally already present when the lipids are mixed with the protein. Thus, the

formation of these structures has a profound impact on protein/lipid interac

tions. It is therefore important to be familiar with the phase behavior of the

particular lipid under investigation and often seemingly conflicting results can

be derived from differences in the phase structure of the lipids. For instance,

we have observed that the interaction between ~-lactoglobulin and phospha

tidic acid occurred only when the lipids were present as a dispersion, but not

when they were mixed in the gel state with the protein (Kristensen et al., 1995). Hence, we will briefly discuss lipid phase behavior, although a more

detailed description is given elsewhere (see Larsson, 1994).

5.4.4.1 Polar Lipid Phase Behavior. The polar lipids, having large charged or

uncharged polar groups, have an amphiphilic nature and will thus associate in


aqueous systems. The common feature for this self-association is the formation

of a polar interface, which separates the hydrocarbon and water regions. An

overview of some of the main types of structures is given in Figure 5.10. The

hydrocarbon chains can exist either in a fluid state, as in liquid crystalline

phases, or in a solid state, as in the lipid gel phases (Larsson, 1994).

Polar lipids can be further divided into two classes on the basis of their in

teraction with water:

l. Lipids and synthetic analogs that are water-soluble in monomeric and

micellar form, i.e., surfactants.

2. Lipids with very low water solubility, but with the ability to swell into liq

uid crystalline phases.

The water-soluble polar lipids (e.g., ionized fatty acids, bile salts, and syn

thetic surfactants, charged or uncharged) have monomeric solubility in the mil

limolar range and form micelles at higher concentrations. The critical micelle

concentration (erne) is considered to be a narrow concentration range, within

which aggregates start to form by a strong cooperative process (Lindman and

Wennerstrom, 1980). The driving force for micelle formation is the hydrophobic

interaction (see Tanford, 1980). For ionic amphiphiles, erne also depends on the

ionic strength, since addition of salt reduces the electrostatic repulsion between

the charged head groups. At low water content an inverse micellar structure, the

1 2 phase, is formed in which the hydrocarbon chains form the continuous

medium and the aqueous medium is present within the micelles.

A common feature of the two classes of polar lipids is the tendency to form

lyotropic liquid crystalline phases (see Figure 5.10). The main features of the

most commonly found mesophases were determined by Luzatti and coworkers

in the early 1960s by x-ray diffraction [reviewed by Luzatti in 1968 (Luzatti,

1968)]. Later spectroscopy studies have given a considerable number of con

tributions to the understanding of the dynamic nature of these phases. The

lamellar phase (La) consists of stacked infinite lipid bilayers separated by wa

ter layers, while the hexagonal phases consist of infinite cylinders, having ei

ther a hydrocarbon core (H1) or a water core (Hu)· The cubic phases have been

shown to exist in a number of lipid systems (Fontell, 1990) and their possible

role in biological systems has been discussed by Larsson (1989). Since the cu

bic phases are isotropic and highly viscoelastic, they can be hard to analyze

and to handle. Different structures of the cubic phases have been suggested,

which depend on the particular lipid system (Larsson, 1989; Lindblom and


Reversed micelles (L2)

(Solid) (Melt) <-Cubic

z Reversed hexagonal 0 i= (HII) <1:: a: f-

"Water-in-oil" z w u <-Cubic (Q) z 0 u f-z I"Mirror plane" I Lamellar <1::

(La) f-u <1:: LL. a: ::l <-Cubic (/) "Oil-in-water" c w (/) <1::

Hexagonal w a: (Hi) u ~

<·Cubic

(H20) e Micelles (L1)

Figure 5.10 Commonly formed association structures by polar lipids. Phase transitions can be induced by changes in water content, temperature, or interaction with other solution components, like proteins. The lamellar liquid crystalline phase (LJ , can be regarded as the mirror plane, where the aggregates are of the "oil-in-water" type on the water-rich side and of the "water-in-oil" type on the water-poor side (Fontell, 1992). On both the water-rich and water-poor sides of the L" there are two possible locations for cubic phases. Other "intermediate phases" may also occur.

Rilfors, 1989; Fontell, 1992). One type of cubic structure, consisting of rod

like aggregates, has been proposed by Luzatti et al. (1968). The two polar rod

like networks formed in this way give two continuous and unconnected systems of fluid hydrocarbon chains. The other main type of cubic phases, ob

served for water-insoluble lipids, are bicontinuous and based on curved nonin

tersecting lipid bilayers, which are organized to form two unconnected continuous systems of water channels (see Lindblom et al., 1979; Larsson,

1989). If an interface is placed in the gap between the methyl end groups of

Protein!Emulsifer Interactions 129

the lipid, it will form a plane that can be described as a minimal smface

(Andersson et al., 1988; Larsson, 1989). A minimal surface has zero average

curvature at any point on the surface; that is, in all points the surface is as con

cave as it is convex. A minimal surface exhibiting periodicity, as in the cubic

lipid aqueous phase, is termed an "infinite periodic minimal surface" (IPMS),

and three types of IPMS, with different geometry, have been shown to be im

portant in lipid systems (Andersson et al., 1988; Larsson, 1989).

With decreasing water content, the phase behavior of the polar lipids often

follows this sequence: hexagonal phase (HJ ~ lamellar phase (LJ for water

soluble lipids and lamellar phase (LJ ~ reversed hexagonal phase (H1J for

lipids with low water solubility. Cubic liquid crystalline phases (Q) often occur

in between these. Phase transitions can also occur with changes in tempera

ture; with increasing temperature the sequence of thermal transitions is usu

ally the same as with decreased water content.

In nature and in many technical applications the aggregates consist of a

mixture of different lipids, which either exist in a homogenous mixture or sep

arate into domains. As discussed in the review by Raudino (1995), the lateral

distribution in these mixed aggregates is influenced by a number of factors like

ionic strength, presence of polymers/proteins, as well as the composition of the

lipids; thus it is hard to give any general rules to predict when phase separa

tion will occur.

5.4.4.2 Some Aspects of the Interaction between Proteins and Lipid Structures.

Interactions between proteins and lipid structures are of fundamental importance

in biological membranes, as well as in food emulsions. Our aim is to give some ex

amples of the effects the interaction can have on the lipid phase behavior as well

as on the protein structure. The same type of molecular forces, as discussed in

previous sections, are responsible for the interaction.

Much of the work on lipid phase transitions induced by proteins and pep

tides has been focused on intrinsic and peripheral membrane proteins. Many

of these proteins carry a positive net charge at neutral pH, and most biological

membranes are neutral, zwitterionic, or negative under physiological condi

tions (Sankaram and Marsh, 1993). Binding of these proteins generally takes

place via direct electrostatic interaction between basic residues, like lysine

and arginine, and the opposite charges on the lipids. However, other effects

like hydrophobic interaction and steric factors can contribute significantly.

Gramicidin, an uncharged and hydrophobic pentadecapeptide, favors the tran-


sition lamellar phase --treversed hexagonal phase (Hu) in phosphatidylcholine

and phosphatidylethanolamine systems (Chupin et al., 1987). It was suggested

that the ability of the peptide to promote cylindrical (curved) structures, like

the hexagonal phase, is due to its conical shape and strong intermolecular at

tractive forces. An example of protein/lipid interactions that promote the re

verse transition has been presented by Fraser et al. (1989). They found that

myelin basic protein could, due to its flexible structure and proper charge dis

tribution, interact through electrostatic as well as nonpolar interactions with

PE and mixed PE/PS hexagonal phase and thereby promote the formation of

lamellar phase. It was proposed that the properties of myelin basic protein in

stabilizing the lamellar structure could be related to the stability of myelin

sheath multilayers (Fraser et al., 1989). Heimburg et al. (1991) reported that

binding of cytochrome c did not promote inverted hexagonal phase of DMPG

alone or in mixtures with neutral lipids. On the other hand, the recorded data

suggested the formation of an isotropic phase, with increased curvature of the

lipid layer. Our recent work on the interaction between cytochrome c and

monoolein in the cubic phase shows that the transition of cubic to inverted

hexagonal phase occurred at a much lower temperature at high protein content

than without protein being present (Razumas et al., 1995).

The NMR studies by Spooner and Watts (1991a, b) show that the interac

tion between cardiolipin bilayers and cytochrome c appears to cause extensive

unfolding of the protein. Similar observations have been made by Heimburg et

al. (1991), who reported that cytochrome c binds to bilayers of phosphatidyl

glycerol and mixtures between neutral and anionic lipids in two forms:

l. Close to the native conformation in solution

2. Unfolded with the heme crevice opened.

It was observed that in the fluid state of pure DMPG and DOPG, the bound

protein existed in the more unfolded form (II), whereas in the gel state of

DMPG the native form (I) prevailed. When DOPG, was mixed with nonionic

(DOG) or zwitterionic (DOPC), the bound fraction of the native form (I) in

creased with the content of neutral lipids.

The work of Minami et al. (1995), in which incorporation of P-lactoglobulin

and P-lactalbumin with negative net charges and lysozyme with positive net

charge at neutral pH, into a sphingomyelin/palmitate gel phase, was studied

found no correlation with the protein net charge. Instead, the amount of pro

tein, which could be dissolved in the thin aqueous layer of the gel phase was


suggested to be limited by the dimension of the layer. This is likely to be re

duced as a consequence of the osmotic stress exerted by the "outside" solution

phase at high enough protein concentration (Minami et al., 1995).

The lateral phase separation of vesicle bilayers, containing a mixture of

phosphatidic acid and phosphatidylcholine, in the presence of lysozyme has

been followed by differential scanning calorimetry (Raudino and Castelli,

1992). The protein/lipid interaction, which was shown to be dependent on

electrostatic forces, thermally stabilized the protein. As discussed by Raudino,

the lateral phase separation occurring when protein binds to heterogeneous hi

layers can eventually lead to the formation of defective lamellar phases, so

called ribbon phases, where the broken lamellae are limited by curved rims

(Raudino, 1995).

It has been shown that a number of proteins can be entrapped in the cubic

monoolein/water phase (Ericsson et al., 1983; Razumas et al., 1994; Razumas

et al., 1995). Not only can enzymes up to 590 kD be entrapped in the cubic

phase but also their activity is retained for a longer time compared to when

they are in bulk solution (Razumas et al., 1994).

How will the structure of the cubic phase be affected by the entrapment of a

protein? It seems that properties like viscoelasticity, microscopic appearance,

and the nature of x-ray diffraction pattern are basically the same as for a pure

monoolein/water phase (Ericsson et al., 1983; Portmann et al., 1991; Landau

and Luisi, 1993; Razumas et al., 1994; Razumas et al., 1995). However, there

are some important differences, indicating that the amount of protein as well

as the amount of water determines the phase behavior (Ericsson, 1986). The

study of Razumas et al. (1995) of the cubic monoolein/cytochrome c aqueous

phase also confirms this and points to the influence of electrolyte present.

Differential scanning calorimetry and enzyme activity measurements show that

lysozyme retains its conformation and activity in the cubic phase (Ericsson et

al., 1983). Similarly, it has been observed by circular dichroism measurements

that bacteriorhodopsin and melittin (Landau and Luisi, 1993) as well as a

chymokypsin (Portmann et al., 1991) retain their native conformation. On the

other hand, differential calorimetry data, and other observations on cy

tochrome c entrapped in the cubic phase, suggested some interactions that af

fect the thermal stability of the protein as well as of the cubic phase (Razumas

et al., 1995). Razumas et al. (1994) used a cubic monoolein-aqueous-phase

containing enzyme as the biocatalytic layer in amperometric and potentiomet

ric biosensors. They observed large differences in the stability, which


decreased in the order lactate oxidase > creatinine deiminase > glucose oxi

dase > urease, and corresponded to the order of increasing molecular weight.

Further investigations have shown that the introduction oflecithin in the cubic

phase can increase the stability of entrapped glucose oxidase (Nylander et al.,

1995). The mobility of the entrapped enzyme is limited in the cubic phase

compared to bulk solution (1995), whereas the diffusion measurements of

Mattisson et al. (1995) show that a typical substrate molecule, like glucose,

can move relatively freely into the cubic phase. These studies point to an im

portant potential application of cubic lipid phases as a flexible and biocompat

ible matrix for the immobilization of enzymes for synthesis as well as for

analytical applications. The cubic monoglyceride phases also have the ability

to solubilize lipophilic proteins as well as relatively large amounts of mem

brane lipids. Larsson and Lindblom (1982) have reported the solubilization of

a-gliadin, which is a hydrophobic wheat protein fraction, into a cubic 1-

monoolein aqueous phase, with the same characteristics as a binary cubic 1-

monoolein phase. In this case, the proteins most probably are dispersed in the

lipid bilayer region of the cubic phase.

5.5. Protein/Emulsifier InteractionsFood Applications In the previous sections we have treated various aspects of intermolecular

forces that have to be considered for the understanding of protein/emulsifier

interactions. Most of the results that have been presented have been obtained

from well-defined model systems. It should be born in mind that in an applied

system, we often have to consider one or several types of molecular interac

tions, that work either synergistically or antagonistically. We will present some

observations where the versatile nature of protein/emulsifier interactions are

demonstrated. In the last section we will give a brief summary of the principles

given in this chapter.

5.5.1 Lipolytic Enzymes and Protein/Lipid Interactions

The action of lipolytic enzymes is of importance in a number of food applica

tions or related areas, ranging from their use in detergents, as tools in modify

ing lipids for the breakdown of acylglycerides both as unwanted side effects, to

the naturally occurring process in the human intestine. It is well known that li

pases work mainly at an interface and thus they are an important example of


lipid/protein interactions at interfaces. Excellent reviews regarding lipase ac

tion have been written by Verger and Pattus (1982) and Pieroni et al. (1990),

but we will highlight only some aspects in relation to the mechanisms of pro

tein/lipid interactions. There are several types of lipases that act on phospho

lipids and triglycerides, but we will mainly discuss lipases catalyzing the

hydrolysis of the ester bonds of triacylglycerols. The enzymatic activity is de

termined by the concentration of lipolytic enzymes associated with the lipid

film and can be inhibited by various proteins (Gargouri et al., 1984).

Experiments carried out with mixed protein/dicaprin films transferred over

pure buffer yielded evidence that inhibition of hydrolysis was caused by pro

teins bound to the dicaprin film rather than by a direct interaction between

protein and lipase in the bulk phase (Gargouri et al., 1985). Furthermore,

since some lipases were inhibited by adsorption of proteins at the lipid layer,

whereas other lipases were still able to hydrolyze a mixed protein/phospho

lipid layer, indicating that the inhibition of some lipases cannot be attributed

merely to steric effects hindering accessibility to dicaprin molecules within

the film. Surface concentration measurements of inhibitory proteins showed

that only 5 to 9% of the area of a mixed lipid/protein film was covered by in

hibitory proteins, implying that long-range electrostatic forces are likely to be

involved in the inhibition as well as parameters such as surface viscosity and

surface potential. However, similar inhibitory effects caused by melittin (pi > 10) and 13-Iactoglobulin A (pi = 5.2) at pH 8.0 strongly suggest that the nature

of the inhibition is· not an electrostatic phenomenon, but might be assigned to

the effect on the properties of the hydrocarbon moiety of the lipid (Gargouri et

al., 1987, 1989; Pieroni et al. 1990). This is supported by the finding that there

is a correlation between inhibition of lipase activity and the ability of the in

hibitory protein to penetrate into the phospholipid monolayer.

The necessary interface can also be provided by a particular lipid structure,

e.g., the cubic lipid aqueous phase. In a simple experiment, Wallin and

Arnebrant (1994) demonstrated that a cubic phase was decomposed much

faster by the action of lipase from Humicola lanuginosa than the oil phase in a

reference sample consisting of triolein and aqueous phase. This was attributed

to the much larger interfacial area of the cubic phase. In an in vitro study of

lipolysis of triglycerides in a intestinal-like environment, Patton and Carey

(I 979) observed, along with the initial crystalline phase, a viscous isotropic

phase composed of monoglycerides and fatty acids, which is identical to the

one formed in monoglyceride systems.


5.5.2 Emulsion Properties and Protein/Emulsifier Interactions

The formation of the interfacial layer on the emulsion droplet is strongly linked

to the properties of the aqueous environment as well as to the properties of the

oil phase. An example of the former has been provided by Chen and Dickinson

(1995a-c), who showed that the addition of an anionic surfactant, sodium lau

ryl sulfate (SLES), can introduce flocculation of a gelatin stabilized oil-in-wa

ter emulsion at sufficient surfactant concentrations. An increase of the SLES

concentration led to a restahilization of the flocculated emulsion. This could he

related to the hulk behavior, where the anionic surfactant will neutralize the

positively charged gelatin and cause precipitation of the protein. As more sur

factant is added, the solubility of the protein increases due to binding of sur

factant that increases the protein net charge, and finally the precipitate is

redissolved. Measurements of the composition of the interfacial layer reveal

(Chen and Dickinson, 1995c) that gelatin is initially replaced by SLES, hut as

the surfactant concentration increases, more gelatin can he accommodated at

the interface due to partial neutralization of the gelatin at the interface. This

will eventually cause flocculation to occur (Chen and Dickinson, 1995a). A

further increase of surfactant concentration leads to a decrease in gelatin surface concentration (Chen and Dickinson, 1995c) and a restabilization of the

emulsion (Chen and Dickinson, 1995a). It is noteworthy that an emulsion sta

bilized by P-lactoglohulin, which was negatively charged under the prevailing

experimental conditions, did not show any signs of flocculation upon addition

of SLES, although a complex was formed in the hulk solution.

Several examples of how the properties of the oil phase composition can affect the structure of the adsorbed layer of protein on the emulsion droplet, and

hence the stability of the emulsion, have been studied. For instance, the work

of Leaver and Dagleish (1992) on the structure of adsorbed layers of ~-casein

on emulsion droplets, where it was found that the cleavage of the protein on

the oil-droplet surface by trypsin gave different products depending on

whether a triglyceride oil or tetradecane, was used. This demonstrates that the

structure of the adsorbed layer depends on the composition of the oil.

Furthermore, it was shown by Heertje et al. (1990) that if a monoglyceride was

dissolved in the oil phase, the displacement of caseinate from the oil/water in

terface was correlated to the interfacial concentration of monoglyceride. They

also found that at high monoglyceride concentration in the oil phase, the

amount of saturated (monostearoylglycerol) lipid adsorbed at the interface was


larger than that of the unsaturated (monooleoylglycerol) one, which also led to

more extensive displacement of caseinate.

We have in the foregoing section mainly been concerned with the binding of

emulsifiers to proteins, but one can also think of cases where there is a repul

sion between the lipid and head group and the protein. In this way the struc

ture of the adsorbed protein layer, and hence the properties of the emulsion,

can be changed. This has been demonstrated by Brookbanks et al. (1993), who

found that the thickness of adsorbed layers of milk proteins was significantly

greater when the protein was adsorbed onto negatively charged phosphatidyl

glycerol (PG) liposomes. The more extended structure was attributed to charge

repulsion between the negatively charged lipid surface and the negatively

charged surface domains of the protein.

5.5.3 Conclusion

The interaction between emulsifiers and proteins is to a larger extent driven by

electrostatic or hydrophobic interactions, or in many cases it is a combination

of the two. Thus, it is commonly observed that ionic emulsifiers interact more

strongly with proteins than nonionic ones. For emulsifiers with low water solu

bility, e.g., polar lipids, the interaction with proteins is largely dependent on

the phase structure upon addition. The binding can, depending on the type of

emulsifier, lead to stabilization of the protein structure at low-surfactant-to

protein ratios. However, an increase in surlactant concentration can induce

unfolding of the protein and in some cases precipitation of the protein.

We have seen that the stability of emulsions and foams is determined by in

terfacial processes, which are affected by the properties of the interface as well

as the interactions occurring in bulk solution.

When no emulsifier/protein interactions are present, the composition of the

interfacial film is determined by only the surface activity and concentration of

the components. In the case of reversibility the "race for the interface" is won

by the most surface-active and/or abundant molecule, and in the case of irre

versibility the transport rate might also play a role. In this context it has to be

born in mind that proteins can change their conformations (sometimes in a

time-dependent way) at the interface. This may lead to a strong interaction be

tween the protein and the surface, which can hamper the displacement of a

protein by more surface-active emulsifiers.

The presence of protein/emulsifier interactions can have pronounced im

pact on the interfacial behavior of the components. In cases where the emulsi-


fier binding induces protein unfolding, exposure of hydrophobic domains of

the protein, or precipitation at the interface due to charge neutralization, the

surface activity of the complex is increased compared to the native protein. On

the other hand, if the protein is more soluble or stabilized by the emulsifier in

teraction, the complex has less tendency to adsorb at the interface.

Precipitation of the complex in the bulk can cause loss of surface-active mate

rial and hence a decrease of the surface concentration. The emulsifier/protein

interactions at interfaces can give more efficient packing and thus a higher to

tal surface concentration. If protein/protein interactions take place at the inter

face, they may be disrupted by protein/emulsifier interactions.

Although emulsions and foams are stabilized by the same mechanisms,

there are marked differences. First, there are profound differences between the

two types of liquid interfaces: the liquid/air and the one between two con

densed media. The oil/aqueous interface allows hydrophobic residues to be

come dissolved in and interact favorably with the oil phase, which is not

possible at the air/water interface. It should be noted that unfolding of the pro

tein induced by action of emulsifiers or by the presence of an interface gener

ally leads to exposure of hydrophobic residues; that is, the unfolded protein is

more "oil soluble" than the native one. Second, in the stabilization of foams

the viscoelastic properties of the surface film as well as the thin aqueous film

has large effects. This means that protein/protein interactions in protein-stabi

lized foams are important, and the addition of surfactants can disrupt these in

teractions and lead to the collapse of the foam. Furthermore, they can also be

stabilized by low molecular weight emulsifiers by means of Gibbs and

Marangoni effects.

Steric and/or repulsive forces are important for stabilization of emulsions.

Therefore, the mixed-protein/emulsifier layer should be optimized with respect

to charge and/or by segments in the surface layer protruding into the aqueous

environment to give a hairy structure that will sterically stabilize the emulsion.

This chapter has shown the enormous variety in emulsifier/protein interac

tions that can occur in food emulsions and foams. Each protein/emulsifier

combination is unique and its behavior specific when applied in a particular

foam or emulsion, where other ingredients are present. However, we have

demonstrated that it is possible to establish certain principles for

protein/emulsifier interactions. These principles based on mechanisms at the

molecular level have also to be transferred to processes of manufacturing, stor

age, and distribution of food products based on emulsions and foams. The

Protein/Emu1sifer Interactions 137

challenge is to increase the resistance of microbial growth without excessive

use of antimicrobial substances, control digestion of the product, and achieve

controlled release of flavors as well as design new functional ingredients based

on natural products.

Acknowledgement Thomas Arnebrant thanks the Swedish Research Council for Engineering

Sciences (TFR) and Martin Bos acknowledges the EU Human Capital and

Mobility program (ERBCHRXT930322) for their financial support. Tommy

Nylander acknowledges the Swedish Council for Forestry and Agricultural

Research. David Clark acknowledges the support of the Biotechnology and

Biological Sciences Research Council.

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Protein/Emu1sifer Interactions 145

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SIX

Physicochemical Aspects of an Emulsifier Functionality

Bjorn Bergenstahl

6.1 Introduction The characteristic property of all emulsifiers is their surface activity. Surface

activity is the ability to form a surface excess at interfaces. The formation of

adsorbed layers at interfaces are displayed in a change of a range of easily ob

servable and technically important properties.

l. The surface tension is reduced.

2. The lifetimes of bubbles are increased. (Only very pure water displays a

very short lifetime, a few seconds, of bubbles created by shaking.

Normal standard "pure water," double distilled, usually displays a bub

ble lifetime of about 20 to 30 seconds.)

3. The emulsifiability of oils in water is enhanced. Smaller drops with a

longer lifetime are formed with less stirring.

4. The aggregation rate of dispersed particles is changed. Surface-active

additives may induce or prevent flocculation of disperions.

5. The sediment volume of settling particles is influenced. Surface addi

tives inducing adhesive may create a loose or compact sediment.

6. Crystallization properties are changed. This may include crystallization

rate and crystal shape.

147


This chapter aims to discuss the principal physical origin of the various func

tionalities of typical lipid food emulsifiers. Aspects on the functionality under

very different conditions in various foods will be discussed. I will try to show how

we may select emulsifiers on the basis of their fundamental properties. ·

6.2 Surface Activity When an additive is added to a solution, the gain of entropy is very large at low

concentrations. If the additive displays surface activity and adsorbs at an in

terface, the system loses entropy, which has to be balanced by a gain in free

energy due to the adsorption. At very low concentrations the solubility always

prevails, but when the concentration is increased, more and more of the avail

able surfaces will be covered by the adsorbed molecules. To display surface

activity, the emulsifier needs to have certain properties:

1. It has to form a noncrystalline form t in contact with water.

2. It should have a reduced solubility in water due to a large hydrophobic part.

3. It has to interact with water through polar interactions.

4. It should have a significant molecular weight to reduce the effect of the reduced entropy when it adsorbs.

5. It has to have a reduced solubility in an oil environment due to large size and

the presence of polar groups at the interface.

High-melting emulsifiers do not display surface activity when dispersed in wa

ter until a critical temperature, the Krafft temperature, has been reached. At this

temperature the emulsifier solubility in the solution has reached a sufficient con

centration to allow for a significant formation of adsorbed layers at the interfaces.

The presence of hydrophobic parts of the molecules increases the energy

gain due to adsorption. In aqueous environments most emulsifiers tend to ag

gregate in micelles at a critical concentration, erne (critical micelle concentra

tion), or to precipitate as liquid crystals. Above the aggregation concentration

all properties depending on the chemical potential, for instance the adsorption

properties, are more or less constant. The aggregation is mainly driven by the

presence of the hydrophobic parts of the molecules (Tanford, 1973).

t Several lipid emulsifiers are exceptions and are applied in a hydrated gel form (a crystals).

However, this crystal form resembles the liquid crystalline form in terms of interactions with

both phases and spreadability over the interfaces.


A polar part of the molecule is necessary to avoid the formation of a sepa

rate oil phase. The type of aggregates formed during the adsorption will reflect

the balance between the polar part and the hydrophobic part of the molecule.

The free-energy gain at adsorption is mainly proportional to the molecular

weight, while the entropy loss due to the demixing is independent of molecular

weight. Hence, small molecules, for instance lower alcohols, do not form ad

sorbed layers at hydrophobic surfaces in contact with water solutions, while

pronounced layers are formed with additives of higher molecular weights, for

instance monoglycerides. Proteins display a much higher surface activity than

protein hydrolysates.

In an oil environment, solvophobic effects are absent and the adsorption

has to be generated by polar interactions between the second phase and the

surface-active molecule.

The interaction between particles is influenced when the particles are cov

ered by an adsorbed layer of an emulsifier. The change in the interaction

strongly influences the macroscopic properties of the dispersions (Table 6.1).

Table 6.1 Effects of changes in the interactions on the macroscopic properties of dispersions

Interaction

Attraction

Repulsion

Stability

Flocculation Stable

Sedimentation

Large sediment volume Small sediment volume

The solution properties of emulsifiers are determined for the surface activ

ity of the emulsifiers. In addition, the ability to generate repulsive interactions

is also reflected in the solution properties of emulsifiers.

6.3. Solution Properties of Emulsifiers When water is added to a surfactant system, the solubilization in the system

may in principle pass through a series of aggregation structures and phases in

a particular sequence. The sequence is: reversed micelles ~ reversed hexago

nal phase ~ lamellar phase ~ hexagonal phase ~ micellar solution ~ mole

cular solution (Fontell, 1978) (Figure 6.1).

The free energy of solubilization, LlG,oluhilization' can be described as a sum of


Krafft point

hexagonal , phase :micelles

' '

reversed micelles

reversed hexagonal

lamellar phase phase

Melting point M---

Emulsifier

Figure 6.1 A typical sequence of liquid-crystalline phases and solution phases formed in a binary emulsifier mixture. (Modified after Fontell, 1978.)

free energy contributions in the process by the expression: emulsifier phase + water ~ more solubilized phase:

L\Gphase transformation + .L\.Gmixing + .AGpolar group/water interaction + .L\.~ydrophobic

where .ilGmixing is negative when changing from large aggregates to small ag

gregates (micelles and molecular solutions).

ilGhydrophobic is positive and equal to Ahydrocarbonlwater 'Y hydrocarbon/water· The hydrophobic effect is the driving force for the aggregation and gives the upper

limit of the molecular solubility for amphiphilic molecules (critical micelle

concentration) .

.ilGpolar group/water is negative. This term consists mainly of the work released

when more water allows a larger separation between repelling aggregates or

molecules:

l next aggregate }

LlGpolar group/water = L I F(l) dl all neighbors aggregate

where l is the average distance between the polar groups and F(l) is the inter

action.

The area per molecule in the aggregates is given by the balance between

the interfacial tension of the oil/water interface and of the space needed for the


polar group itself and the space generated by repulsive interactions between

the emulsifier head groups at the interface.

The area per molecule expands in the series A reversed micelles < Areversed hexagonal

< A lamellar A hexagonal < Amicelles" At a specific ratio of water and emulsifier, the system's tendency is to obtain

aggregates as small as possible to maximize the AG mixing and the AG polar group/water·

The lower limit in aggregate size is given by the increased hydrophobic contact

between the exposed hydrocarbon/water interface.

The interesting result of this exercise is that the area per molecule is to a

large extent a measure of the ability to generate repulsive interactions.

In the solubilization sequence, reversed aggregates ~ lamellar phase ~

hexagonal phase~ micellar solution~ molecular solution, the area per mol

ecule of the surfactant/water interface increases. Depending on the packing

constraints given by the hydrophobic moiety in the aggregates, the range of the

repulsive interaction on the polar side of the molecule, and the molecular

weight, this process has to proceed more rapidly or more slowly (Israelachvili

et al., 1976, 1977). Hence, the packing constraints of the hydrocarbon chain

are an important link between properties and aggregation.

The ratio of the actual area A, as it is created by the repulsive interactions,

to the theoretical area of a saturated hydrocarbon chain, A0 (23 A2) enforces

different geometries (Israelachvili et al., 1976, 1977) due to the different ratio

of volume to area of different aggregates, as shown in Table 6.2.

The successive solvation of surfactants in Table 6.2 correspond to a suc

cessive change into aggregates that correspond to a more long-range interac

tion. If there is an upper limit for the repulsion, the solvation series is

terminated at that stage. Hence, the maximum solvated aggregate formed at a

surplus of water is a measure of the ability of the emulsifier to generate re

pulsive interactions.

The area of the molecule is a measure of the interaction when water is

available, and may be generalized as the hydrophilicity of the molecule. The

spatial requirement of the hydrophobic part of the molecule is of course a mea

sure of the hydrophobicity of the molecule. Consequently, there is a close link

with the classical view of emulsifiers as molecules with a balance between the

hydrophobic and the hydrophilic properties, as they are expressed in the HLB

numbers, proposed by Griffin (1949, 1979).


Table 6.2 The geometries of different aggregates

Area/volume

Sphere (micellar solution) 2

2 1tr

(4/3)1tr 3

2

T

Rods (hexagonal phase)

2r1tl 2

n. /z T

Bilayers (lamellar phase)

l

T

Reversed rods (reversed hexagonal phase)

2

Packing constraint t (A0 = 23A2 for a saturated hydrocarbon tail)

3 • Vhydrophoh = 3Ao rhydrophob

2 • vhydrophob - 2A - 0

rhydrophob

l · Vhydrophoh _ A - 0

rhydrophob

T radius of the aggregate, usually limited by the length of molecule

= a fictitious length of the aggregate

vhydrophob

rhydrophob

Ao

A

= volume of the hydrophobic part of the molecule

the maximum length of the hydrophobic moiety

area of a cylindrical packing of the hydrophobic moiety

(= V hydrophob 1 rhydrophob or 23 A2 per hydrocarbon chain)

area per molecule at an average water/amphiphilic interface

t The packing constraint is here defined as the necessary cross section of an amphiphilic molecule in the aggregate at the oil/water interface. This definition is Aofpacking parameter according to Israelachvili et al. (1992, 1976, 1977).


6.4 The Use of Phase Diagrams to Understand Emulsifier Properties Friberg and coworkers (Wilton and Friberg, 1971; Friberg and Mandel, 1970b;

Friberg and Rydhag, 1971; Friberg and Wilton, 1970; Rydhag, 1979; Rydhag

and Wilton, 1981; Friberg et al., 1969; Friberg and Mandel, 1970a; Friberg,

1971) have investigated phase diagrams and emulsion stability extensively.

They concluded that the optimum composition for a stable emulsion should be

that at which the lamellar phase, the oil phase, and the water phase are in

equilibrium in the corresponding phase diagram (Figure 6.2).

The relation between the formation of lamellar phases and emulsion stabil

ity is basically of an empirical nature. The emulsifiability is enhanced at cer

tain compositions (Friberg and Mandel, 1970b; Friberg and Rydhag, 1971;

Friberg and Wilton, 1970), and the formation of crystalline phases corresponds

to an observed destabilization (Wilton and Friberg, 1971). The formation of

multilayers around the emulsion droplets under certain conditions has also

been shown (Friberg, 1990).

It was suggested that the formation of a multilayer of a lamellar liquid-crys-

Micellar solution and oil phase

lamellar micellar solution and oil phase

Water

p- Xylene

1 2 3 4 5

Nonylphenoi-E09

Figure 6.2 Emulsion experiments in the phase diagram of an ethoxylated nonyl-phenol and xylene. Systems with compositions corresponding to the position in the phase diagram were weighed into flame-sealed ampoules. The emulsifiability of the systems was tested by shaking the ampoules. The stability of the emulsions formed was observed the emulsification. (Modified from Friberg et al., 1969; Friberg and Mandell, 1970a.)


talline phase coating the droplet surface reduces the van der Waal's attraction

and that this was an important contribution to the observed effects in the emul

sification experiments (Friberg, 1971). However, this explanation is not a use

ful general explanation since the emulsifier concentration in optimized food

emulsions rarely is high enough to allow for multilayer adsorption (Walstra,

1988; Dickinson, 1986). Obviously, this observation is contradictive to the

need for a separate phase of liquid-crystalline material around the droplet.

However, a correlation between the presence of, or the possibility to form, liq

uid-crystalline phases and emulsion stability is still experimentally observed

in several systems. To stabilize an dispersion, the emulsifier should:

l. Contribute to the repulsive interactions between the droplets

2. Contribute to the interfacial viscosity

3. Be well anchored to the interface

These properties are reflected in the formation of various liquid-crystalline

phases (Table 6.3). These aspects are illustrated by a few examples.

Table 6.3 The relation between the function of an emulsifier to stabilize an emulsion and its ability to form various aggregation structures

Stabilizing property aggregates Micelles Bilayers Reversed

Water-continuous emulsions

Repulsive interactions

Interfacial viscosity

Anchoring

Repulsive interactions

Interfacial viscosity

Anchoring

Optimal

Weak Optimal

Too water-soluble

Intermediate

Weak

Optimal

Oil-continuous emulsions

Weak

Weak

Acceptable

Intermediate

Optimal

Optimal

6.5 Examples of the Relation between Phase Diagrams and Emulsion Stability 6.5.1 Monoglycerides

Weak

Acceptable

Optimal

Weak

Too oil-soluble

A technical monoglyceride at room temperature remams m a nonhydrated

crystalline phase (~ phase) in equilibrium with a surplus of water. Above


40°C, the monoglyceride takes up water and a lamellar phase is formed

(Wilton and Friberg, 1971). The lamellar phase coexists with a surplus of wa

ter (no micelles are formed). When the lamellar phase is cooled, a semicrys

talline phase, termed "a phase," is formed. This phase is metastable below

30°C and converts only slowly into an aqueous and a ~ phase.

The swelling of the lamellar and a phases indicates the existence of a strong

repulsive hydration force. This force has been measured by the osmotic stress

technique (Figure 6.3). In contrast, no hydration force strong enough to separate

the bilayers is present in the ~ phase. The hydration force between emulsion

droplets coated with this emulsifier depends on the liquid-crystalline state of the

adsorbed emulsifier film in the same way. This explains why monoglycerides ap

pearing in the ~form are inactive as emulsifiers, and why a monoglyceride-stabi

lized emulsion rapidly destabilizes when the monoglyceride converts from

lamellar or a into~ phase (Wilton and Friberg, 1971). In technical systems, it is

important that the conversion of a phase into ~ phase is delayed. An a phase

can be stabilized by the presence of ionic charges (soap) (Larsson and Krog,

1973) or by a wide distribution of the fatty acid-chain composition. The solution

properties of a range of food emulsifiers are summarized in Table 6.4.

6.5.2 Lecithins

Lecithin is one of the most commonly used food emulsifiers, and its popularity

can be expected to grow even further due to its natural origin. Technical

lecithins, usually soybean lecithin, are always natural mixtures of various

phospholipids. The most frequent one is phosphatidylcholine (PC). The second

'" 4 0..

_§ • • Lamellar phase 60 C .. s 3 • .5 c c Gel phase 23 C

" 2 ccccc • • '" ;:; c£ c 00

" '" 0..

" c c > ·:n 0 • :; 0.. • " ~ -1

0 5 10 15 dw(A)

Figure 6.3 The hydration repulsion between bilayers of monopalmitin in the liquidcrystalline and gel states. (Redrawn from Pezron et al., 1991.)


Table 6.4 Formation of liquid-crystalline phases by lipid emulsifiers

Fatty Liquid-crystalline Upper swelling Emulsifier acid phases formed at limit (at 25°C)

Monoglycerides:

Distilled saturated C18-16 Lamellar phase at 50°C 50% Krog, 1990

Cubic at 70°C

Distilled unsaturated Cl8:l-2 Cubic< 20°C 35% Krog, 1990

Reversed hexagonal at 55°C

Monoolein C18:1 Cubic< 20°C 40% Krog, 1990

Reversed hexagonal at 90°C

Tetraglycerolesters:

Tetraglycerol C12 Lamellar < 20°C 55% Krog, 1990t

monolaurin Fluid isotropic 40°C

Organic acid esters:

Diacetyl tartaric acid C16-l8 Lamellar 45°C 55% Krog, 1990

monoglyceride ester

Sodium steraoyllactylate:

pHS C18 Reversed hexagonal at 45°C 40% Krog, 1990 pH7 C18 Lamellar at 42°C 60% Krog, 1990

Sorbitan esters:

Polyoxyethylene (20) C18:1 Hexagonal phase (up to 30°C) sorbitan monooleate aud micellar solution Hall, Pethica, 1967 Polyoxyethylene (20) C18 Hexagonal phase (30 to 50°C)

sorbitan monostearate and micellar solution Hall, Pethica, 1967

above 30°C

Sorbitan stearate C18 Lamellar above 50°C - Hall, Pethica, 1967

tThe data are extracted from a review of several original sources.

is phosphatidylethanolamine (PE). Phosphatidylinositol (PI) and phosphatidic

acid (PA) are usually present at intermediate levels, and phosphatidyl serine

(PS), lysophosphatides (LPC and LPE), etc., at low levels. Nonphosphatides

such as steroids, vitamin E, and free fatty acids are usually also present in

technical products. The properties of lecithins reflect some type of average

properties of the mixture. This section will first describe the characteristic

Physicochemical Aspects of an Emulsifier Functionality 15 7

properties of the most common phosphatides and then discuss the properties of

various mixtures.

6.5.3 Phosphatidylcholine

The phase diagram of a typical unsaturated phosphatidylcholine is displayed

in Figure 6.4. The phase diagram is characterized by a large swelling lamellar

phase. Saturated phosphatidylcholines have a phase transition temperature up

to about 40°C, whereas the corresponding temperature for unsaturated

lecithins is well below 0°C. The phase diagram of soybean PC is described in

Bergenstahl and Fontell (1983) and is rather similar to the phase diagram of

dioleoyl PC.

6.5.4 Phosphatidylethanolamine

Phosphatidylethanolamine is less hydrophilic than PC. The saturated

ethanolamines form lamellar phases that swell less than the corresponding PC

species. The phase transition temperature is about lO to 40°C above the corre

sponding temperature of the phosphatidylcholine (Figure 6.5). The more lim

ited ability to create long-range repulsive interactions, and thereby to defend a

large molecular area, is displayed in the tendency to form reversed hexagonal

phase with unsaturated PE species, as shown in Table 6.5.

200

~ 150

l 8 100 ~

50

0 Water

Lamellar phase

Reversed Hexagonal

Cubic

Crystalline phase

Dioleoylphosphatidylcholine

Figure 6.4. The phase diagram of water and dioleoylphosphatidylcholine. (From

Bergenstahl and Stenius, 1987.)


90 [J

G 70 [J •

~ 50 • c. [J • E 30 ~ •

10 •

- 1 0 10 12 14 1 6 1 8 20 22

Chain length

Figure 6.5 The main transition temperature for phosphatidylcholine (PC) (•) and phosphatidylethanolamine (PE) (D) as a function of chain length. The sources of data are given in Table 6.4.

6.5.5 Phosphatidylinositol

The phase diagram of soybean PI and water has been determined by the author

(1991) and by Soderberg (1990). The diagram is characterized by a large

lamellar phase with an unlimited swelling. The liquid-crystalline phase is

formed below room temperature.

6.5.6 Phosphatidic Acid

The phase diagram of the sodium salt of dioleoylphosphatidic acid has been de

termined by Lindblom et al. (1991). The phase diagram is characterized by a

lamellar phase that transforms to a reversed hexagonal phase at about 30% of

water. This transformation occurs although there is an ionic charge on the mole

cules and despite the small head group. A possible explanation, supported by

evidence from NMR measurements, is that this is due to ion condensation.

6.5.7 Lysophosphatides

The phase diagrams of a series of different lysophosphatides has been investi

gated by Arvidsson et al. (1985). Lysophosphatidylcholine has the same hy

drophilic polar group as the ordinary PC but only one of the two fatty acids.

This reduces the volume demand of the aggregate, and the packing constraint

allows for the formation of micelles and hexagonal phases.

6.5.8 The Properties of Mixtures of Phosphatides

Technical phosphatides are always mixtures. Their properties reflect some

type of average that the mixture develops. One way to investigate this is to de-


Table 6.5 The formation of liquid-crystalline phases by various phospholipids

Fatty Liquid-crystalline Phospholipid acids phases formed at

Phosphatidylcholine:

Distearoyl CIS Lamellar phase at 55°C Dipalmitoyl CI6 Lamellar phase at 4I °C Dimyristoyl CI4 Lamellar phase at 23 C Dioleoyl CIS:! Lamellar below 0°C Egg PC CI6-IS:I Lamellar at 2°C Soybean PC CIS:I-2 Lamellar below 0°C

Phosphatidyletanoleamine:

Dipalmitoyl CI6 Lamellar phase at 68°C Reversed hexagonal at S4°C

Dioleoyl C1S:l Lamellar below 0°C Reversed hexagonal at 5°C

Soybean PE CIS l-2+ Reversed hexagonal above 0°C

Phosphatidylinositol:

Soybean PI C1S:I-2+ Lamellar below 0°C

Phosphatidic acid:

Dioleoyl ClS:l Lamellar below 0°C

Lyso PC:

Palmi toy! CI6 Micellar solution below 0°C

iThe data are extracted from a review of several original sources. +Mainly.

Upper swelling limit (at 25°C)

Small, I9S6t

36% Insko & Matsui,I97S 40% Janiak et al., I97S 42% Bergenstahl & F ortell, I9S7 44% Small, I9S6 35% Bergenstahl & Fortell, I9S7

20% Caffrey, I9S5

20% Gawrish et al, 1992

30% Bergenstahl, 1991

Unlimited Bergenstahl, 1991 Soderberg, 1990

Unlimited Lindblom et al., I99I

Unlimited Eriksson et al., I9S7

terrnine the type of liquid-crystalline phase that develops when different phos

phatides are allowed to interact together with water. Figure 6.6 shows the

phase diagram of dioleoyl PC and dioleoyl PE in 40% water (Eriksson et al.,

1985). The figure shows that a lamellar phase is formed when the system con

tains mainly PC, but that about 60% PE nonlamellar phases start to form. This

change is enhanced at high temperatures. Between the hexagonal phase and

the lamellar phase is an area in which a cubic phase appears (above 50°C).


100

80

G ~ 60 e ::l ~ '" <l.l 0., a 40 ~

20

0

100% DOPE

Reversed hexagonal phase

Cubic phase

Lamellar phase

50150

Composition

100% DOPC

Figure 6.6 The phase diagram of dioleoyl PC and dioleoyl PE with 40% water. (Redrawn after Eriksson et al., 1985.)

The more highly unsaturated soybean PE and soybean PC display a similar

aggregation pattern, but the temperature at which the system changes from

lamellar to nonlamellar phases is lower (Figure 6. 7), and the phase diagram is

dominated by the hydrophobic properties of the PE up to fairly high concentra

tions of PC. A mixture of PI and PC displays the extreme swelling properties of

ionically charged emulsifiers at an early stage. This was indeed also expected

since a similar pattern was observed when a small amount of ionically charged

detergents was added to the lamellar phase formed by monoglycerides

(Larsson and Krog, 1973). When PI and PE are mixed, the properties of the

mixture are dominated by the hydrophilic PI up to quite a high PE:PI ratio.

A preliminary conclusion from this work is that the properties of phos

phatide mixtures are determined by the ratio of anionic (particularly PI) phos

phatides to PE rather than by the PC:PE ratio.

Technical soybean lecithin contains a mixture of different phospholipids

(Rydhag, 1979). In most cases, the weakly hydrophilic phospha

tidylethanolamine dominates, and this type of lecithin is suitable for inverse

emulsions such as in margarine. More hydrophilic soybean lecithins suitable


Water PC Water

PI

Water

Figure 6.7 The phase diagram of soybean PC, soybean PE, and water; of soybean PC, soybean PI, and water; and of soybean PI, soybean PE, and water. (Redrawn after

Bergenstahl, 1991.) The cubic phase was not included in the original drawing, but it is a possible interpretation of the x-ray peaks included in the paper. It is also supported by the data from the study by Eriksson eta!. (1985).

for oil-in-water emulsions are obtained by partial hydrolysis to form

lysolecithins (Emulfluid E). t It is also possible to increase the effective hy

drophilicity of the PE by making the polar head group larger through acetyla

tion (Emulfluid A).

6.6 Some Ways to Classify Emulsifiers

A common problem in industrial development work is the choice of suitable

surfactants to obtain the desired results. In the literature a number of different

methods of making a fast preliminary selection of suitable emulsifiers have

been proposed. The most common methods and concepts are discussed here

and are compared with the function of the emulsifier in the emulsion.

6.6.1 The Solubility Concept

One of the first ideas, proposed by Bancroft (1913) at the beginning of the cen

tury, was that the solubility of the emulsifier determines the type of emulsion

that is formed. An oil-soluble emulsifier will create an oil-continuous ernul-

t Emulfluid™, Lucas Meyer, Elbdeich 62, Hamburg, Germany


sion, and a water-soluble emulsifier will tum the emulsion into a water-contin

uous one. This is true for low molecular emulsifiers with a high solubility (usually in micellar aggregates), but it is also valid for polymers. However, most likely, the concept can also, to some extent, be expanded to include emulsifiers with just a dispersibility in either one of the phases (for instance lecithin). Experience in this direction is exemplified in Table 6.6. However, the Bancroft rule provide us just with the first very general directions. To proceed further we

need possibilities to rank emulsifiers quantitatively.

Table 6.6 Emulsifiahility compared with solubility according to the Bancroft rule. (Ostberg et al., 1995.)

Emulsifier Soluhility/dispersihility Type of emulsion

Sorbitan esters Oil-soluble Oil-continuous (Span)

Etoxylated sorbitan Water-soluble Water-continuous esters (Tween) Hydrophobic lecithin Oil-dispersible Oil-continuous (normal technical lecithin) Hydrophiliclecithin Water-dispersible Water-continuous (high LPC or low PE) Proteins Water-soluble Water-continuous Fat crystals Oil-dispersible Oil-continuous

6.6.2 The Phase Inversion Concept

Ethoxylated surfactants have a tendency toward declining hydrophilicity with in

creasing temperature. This leads to a change from water solubility at low temper

atures to oil solubility at higher temperatures. According to the Bancroft rule,

this will cause a given system to switch from being water-continuous to being oil

continuous. The hydrophilicity can be viewed as a property that is gradually lost

with increasing temperature. The distance from the breakeven point, the phaseinversion temperature (PIT), is then a measure of the strength of the hydrophilicity. Shinoda claims that the best stability of an oil-in-water emulsion is obtained at 30°C below the PIT and for a water-in-oil emulsion at about 20°C above the PIT. However, the droplet size obtained directly after the homogenization (by shaking) reach a minimum at the PIT. Consequently, Shinoda suggests that the emulsifier should be chosen so that the emulsification can be performed at a PIT


about 20 to 30°C above the final storage temperature [emulsification by the PIT

method (Shinoda and Saito, 1968)].

Shinoda and coworkers (Shinoda and Saito, 1968; Shinoda and Kunieda,

1983; Kunieda and Ishikawa, 1985, reviewed in Shinoda and Friberg, 1986)

have worked according to this concept and characterized a number of different

ethoxylated emulsifiers in combination with various solvents. They then found

that the PIT depends not only on the number of ethoxy groups but also on the oil

phase, indicating the importance of the solubility properties for the stability.

Emulsification experiments performed with a range of different oil-to-water

ratios show that the emulsion type is determined mainly by the emulsifier

properties and is for many systems (pure solvents!) very insensitive to the

phase ratio (Shinoda and Friberg, 1986).

It is obvious that this says a lot about the properties of ethoxylated surfactants

but its applicability to food emulsions is very limited for two main reasons:

1. The concept is based on strongly temperature-dependent properties of

the emulsifiers. This excludes ionic emulsifiers (less important for the

food industry), and it also excludes the most commonly used polyhy

droxy and nonionic zwitterionic emulsifiers as they display a very weak

temperature dependence of their hydrophilicity.

2. The solvent properties are important in the PIT concept. However, food

emulsions are made almost solely from triglyceride oils and water that will

behave differently due to the large molecular weight of the oil molecules.

6.6.3 The HLB (Hydrophilic/Lipophilic Balance) Concept

Emulsifiers are molecules with a duality in their properties. The balance be

tween the hydrophobic and hydrophilic properties of the molecules should

then determine the performance, for instance to the type of emulsion formed. If

the emulsifier is changed from being hydrophobic to hydrophilic, the emulsion

formed changes from oil-continuous to water-continuous. The balance of the

emulsifier is recorded as a number, the HLB value. When this concept was in

troduced by Griffin (1949), the HLB value of unknown emulsifiers was deter

mined by comparing the emulsification properties in a predetermined system

of a mixture of hydrophobic and hydrophilic emulsifiers with a predefined

HLB number.

The important development of the HLB system came when the group con

tribution system was constructed by Davies (195 7), and it became possible to


estimate an HLB value of an unknown emulsifier from the molecular formula (Table 6.7). The advantage of the HLB concept is that it makes it possible to characterize numerous emulsifiers and emulsifier blends (it is usually assumed that it is possible to calculate an average HLB value from the w/w composition). Large tables of data for commercial emulsifiers are also available.

The limitation of the HLB value is that it provides a rather one-dimensional description of the properties (molecular weight and temperature dependence are omitted). It is also difficult to calculate useful HLB values for several important food emulsifiers, for instance phospholipids. The HLB values do not include the important crystallization properties of monoglycerides and modified monoglycerides.

Table 6.7 Calculation of HLB numbers according to Davies (1957). The table is modified according to Davies (1957). HLB = 7+L group contributions. (From Bergenstahl and Claesson, 1990.)

Group

Carboxylic acid soap Sorbitan ester

Glyceryl ester

Ester

Carboxylic acid

Alcohol

Ether

EO group

CH3 , CH2 , CH

Group contribution

212 6.8 5.25 2.4 2.1 1.9 1.3 0.33 -0.475

6.6.4 A Comparison between the HLB and the Geometry of the Molecule

There is an obvious analogy between the idea of a hydrophilic lipophilic balance and that of a balance in the molecules that are appearing in the packing constraints creating the different association structures (Figure 6.8). Griffin (1978) has also suggested a relationship between various solution properties and the HLB number. Transforming these descriptions into various aggregation structures, a clear relation between the molecular packing and the HLB value is obtained.


Aggregate

~>t· ..,.,--. Micelles

Lamellar phase

Reversed aggregates

Shape Character in solution

Clear solution

White dispersion

Milky appearance

Lumps of emulsifier

HLB

> 13 >2

7-10 l-2

<7 <1

Figure 6.8 A comparison between molecular aggregation, solution characteristics, AIA0, and the packing parameter. (Modified from Bergenstiihl and Claesson, 1990.)

This result shows that the ability to form liquid-crystalline phases corre

sponds to the traditional HLB characterization of the emulsifiers.

6.6.5 The Role of the Emulsifier in Homogenization

The discussion so far has been dealing mainly with the situation when droplets

are protected by a layer of emulsifier. However, the emulsifiers also have a cru

cial role during the emulsification that usually is included in all empirical

tests that are the bases for the rules.

When an emulsion is created from a large and homogeneous oil phase, the

emulsifier should support two different processes: the formation of new droplets

and protection against recoalesce. The emulsifier acts according to both static

and dynamic (diffusion-induced) interactions (Walstra, 1983) (Table 6.8).

Table 6.8 The role of the emulsifiers during the formation of emulsions

Static Dynamic

Destabilize the Interfacial Diffusion to and

interfaces tension across the interfaces

Stabilize the Repulsive Diffusion to the

droplets surface forces the interfaces


The principal role of the intenacial tension is obvious. The presence of emulsifiers lowers the intenacial tension from about 30 mN/m for a triglyceride/water system to between 1 and lO mN/m. Nonionic emulsifiers close to the PIT create densely packed intenaces with very low intenacial tensions. However, the effects of the intenacial tension itself are not very large. Walstra (1983) has shown that the droplet size is only weakly dependent on the intenacial tension.

During the homogenization, new intenaces are formed. The emulsifiers have to diffuse to the intenaces to lower the intenacial tension during the events when the droplets are formed. This process must be rapid to be successful, as rapid as the time scale for the formation of the droplets. For geometrical reasons, the diffusion from the surrounding phase of the droplet is much more rapid than the diffusion from the internal liquid. This is one important contribution to the validity of the solution rules (Bancroft, PIT, HLB, and phase diagrams).

During the homogenization, the water-soluble substances in the oil phase diffuse over to the water phase. These types of diffusion across the intenaces create disturbances that contribute to the emulsification. In many systems, this effect gives an increased efficiency if the emulsifier is added to the oil phase before the emulsification. For dispersible emulsifiers (phospholipids) there are also other reasons why it is more efficient to add the emulsifier to the oil phase instead of the water phase. During the homogenization, phospholipids tend to form stable liposomal dispersion in competition to the emulsification of the oil phase. Westesen has indeed observed that a significant fraction of the phospholipids in a commercial phospholipid emulsion for paranteral use is lost in liposomal aggregates (Westesen and Wehler, 1992).

Emulsification involves an intensive shear. The shear by itself causes a high frequency of recoalescence events. If the emulsification is to be successful the formed droplets have to be protected. The repulsive interactions generated by the emulsifiers create a static protection.

The hydrodynamic interaction is crucial for the result of a collision due to shear. The hydrodynamic interactions depend on the existence of an intenace with an intenacial viscosity and elasticity. During the collision event, the intenace close to the approaching droplet is depleted of emulsifiers due to the streaming ofliquid. The sunactant-depleted zone will then have a higher interfacial tension than the surrounding emulsifier-covered areas of the droplets. This leads to sunace diffusion in the direction opposite to the liquid flow and ensures the hydrodynamic resistance. If the emulsifier is oil-soluble, emulsi-

Physicochemical Aspects of an Emulsifier Functionality 16 7

fier from the internal part of the droplet will diffuse to the depleted area and

thereby reduce the hydrodynamic protection of the droplet.

The discussion in this section has been very qualitative, but an important

point is that the emulsifiers contribute to the emulsification as well as to the

stabilization. The role of the emulsifier for the stabilization is usually difficult

to identify in the simple type of shaking experiments that are the main back

ground to the HLB, the PIT, and the phase diagram concepts. This type of sim

ple, and thereby effficient, experiment provides information about both the

emulsifiability and the stability with a certain emulsifier.

6.7 The Emulsifier Surface The ability of various food emulsifiers to generate adsorbed layers influencing

the interparticle interactions has been discussed. The type and magnitude de

pend on the composition of the surface generated from the adsorption process.

Foods usually are complex mixtures. They may contain both low molecular sur

face-active lipids and a versatile range of more or less surface-active proteins

and polysaccharides. The actual chemical composition of the emulsion droplet

surface is then the key factor that determines most of the surface interactions.

In systems containing several surface-active components, three types of ad

sorbed layers can be identified based on how the layers are formed. In reality,

the differences between the three adsorption structures discussed below are

not sharp, but this simplified description can provide a base when the proper

ties of complex systems are discussed.

l. Competitive adsorption. A monolayer containing one predominant type of

molecule at the interface builds up through competition with other less

surface-active components that may be replaced in the interface.

2. Associative adsorption. An adsorbed layer containing a mixture of several

different surface-active components is formed.

3. Layer adsorption. One component adsorbs on top of the other.

6.7.1 Competitive Adsorption

In a system with several surface-active components, a homogeneous monolayer

is formed by the most surface-active component. The adsorption depends on the

main driving force for adsorbtion, mainly the hydrophobic interaction. Hence,


from a mixture of two emulsifiers, the most hydrophobic emulsifier will have the

strongest affinity to the interface. A consequence is that under competitive ad

sorption the component with the lowest water solubility will dominate the inter

face [e.g., the lowest critical micelle concentration (Kronberg, 1983)].

The character of the adsorbed layer, for instance its ability to generate re

pulsive interactions, is determined by the dominating compound. The struc

ture of the layer depends on the geometrical shape of the molecules and on

lateral interactions between the molecules in the layer. Nonionic surfactants

may form very dense layers due to head-group attraction. Ionic surfactants are

able to form extremely loose layers due to inter-head-group repulsion.

An interesting experimental observation in agreement with this relation is

that the concentration of emulsifier necessary to obtain an emulsion is much

lower for ionic emulsifiers than for nonionic emulsifiers.

In a series of emulsions, we have studied the efficiency of the emulsification

(Ostberg et al., 1995) by droplet size measurements after homogenization. The

results show that for several emulsifiers very small droplets are obtained

(about 0.2 to 0.4 Jlm). The particle size obtained depends on the concentration

of emulsifier. The nonionic emulsifiers leads to a constant particle size down to

a critical concentration below which the ability to form emulsions is strongly

reduced. The critical concentration can be compared with the thickness of the

emulsifier layer on the emulsion droplet. The apparent thickness of the emulsi

fier layer can be estimated from the particle size and the concentration of

emulsifier (counted on the dispersed phase), if we assume that all emulsifier is

adsorbed to the interface. The apparent thickness gives the upper limit for the

adsorbed layer rather than the correct value:

volume of emulsifier Thickness of emulsifier layer =

emulsion droplet area

0 = cern Vemulsion droplet

A emulsion droplet

where cern is the emulsifier concentration (v/v) in the disperse phase.

6

The critical thickness (the thickness of the emulsifier layer at the critical

concentration) of the emulsifier layer can be compared with the size of the mol

ecule. The results show a thickness of about 60% of the theoretical length of

the molecule for nonionic emulsifiers. Hydrophobic emulsifiers are less effi

cient during the emulsification and give very high values of the apparent thick-


ness. The properties of the ionic emulsifiers are different. These emulsifiers

are able to emulsify the emulsions down to extremely low concentrations corre

sponding to very low surface concentrations (thin layers).

6.7.2 Associative Adsorption

In associative adsorption, a mixed surface is formed. The properties displayed

by the surface are some sort of average properties.

A typical associative system may be a long alcohol (for instance decanol)

and charged surfactants (for instance soaps). The alcohol acts as a spacer be

tween the charged groups, which decreases the head-group repulsion within

the layer and reduces the surface energy. This increases the adsorption and

enhances the surface activity. Similarly, a lamellar phase is formed in the cor

responding three-component phase diagram: water/sodium caprylate/deeanol

(Fontell, et al., 1968). Mixed layers are commonly formed due to associative

adsorption with natural and technical emulsifier blends. This is also a neces

sary requirement of the common assumption that an average HLB value should

describe the properties of an emulsifier blend (Davies, 1957). A common sys

tem assumed to act in this way is a mixture of sorbitan esters and ethoxylated

sorbitan esters where the smaller sorbitan esters can use the space between

the bulky ethoxylated esters (Boyd et al., 1976).

In the case of associative adsorption, both components are expected to be

present in the surface. If this situation is to be stable, the adsorption of the sec

ond component should be either enhanced by the presence of the first compo

nent or at least not influenced by it. The total amount of adsorbed material

should be greater than or equal to the sum of the two components.

6.7.3 Layered Adsorption

Adsorption in layers is possible when different classes of surface-active com

ponents are present in a mixture. See Table 6.9. The two components must be

very different in character to give a structure with a layered character rather

than a mixed layer. The second component adsorbs to a particle displaying the

characteristic properties of the primary adsorbing emulsifier. This usually

means a more hydrophilic surface, which can be expected to reduce the ad

sorbed amount. However, in some eases, the presence of certain groups in

creases the adsorption of specific substances.

The effects of the emulsifiers on protein adsorption is essential in most

emulsifier applications in the food industry.

Ethoxylated surfaetants usually give a strong reduction of protein adsorp-


Table 6.9 The apparent emulsifier layers for various emulsifiers estimated from equation. (From Ostberg et al., 1995.)

Emulsifier cone (%)1

Radius (Jlm)2

Dodecylbenzenesulfate

0.1 0.47

Emulsifier-layer thickness (1)3

1.6

Fatty acid monoethanolamid ethoxylate (7EO)

10 0.27 90

Curve shape4

Fatty acid monoethanolamid ethoxylate (l3EO)

7 0.20 45

Fatty acid monoethanolamid ethoxylate (l8EO)

lO 0.23 59

1 The emulsifier concentration calculated on the oil phase. 2 The radius is shown as D(3, 2)/2.

Estimated length of the emulsifier (1)5

15

54

75

93

3 The apparent emulsifier layer, estimated assuming that all emulsifier is estimated at the interface. 4 The curve shape shows the dependence for the apparent emulsifier layer of the emulsifier concentration. 5 The estimated length of the emulsifier molecule is estimated from the chemical formula or from measurements in the corresponding lamellar phase.

tion. Courthaudon et al. (1991b) have shown C12E08 totally displace all ad

sorbed ~-casein from an emulsion system. Similar effects have also been obtained with emulsions formed with polysorbates (Dickinson and Tanai, 1992)

and with monoglycerides (Hall and Pethica, 1967). On the other hand, egg

yolk PC did not reduce the the adsorbed amount of ~-casein more than about

20% (Courthaudon et al., 1991a).

The adsorption of a range of plasma proteins at various phospholipid sur-


faces has been characterized using ellipsometry (Malmsten, 1995). A large

variation of the adsorbed amount was obtained, depending on the combination

of protein and phospholipid. Purified PC and PE gave low adsorbed amounts,

while phosphatidic acid enhanced the adsorption of fibrinogen with a factor of

5 compared to a bare hydrophobic surface.

References Arvidsson, G., et al. (1985). Eur. ]. Biochem, 152, 753-9. Bancroft, W.D. (1913).]. Phys. Chem., 17, SOl. Bergenstahl, B. (1991). In Food Polymers, Gels, and Colloids (ed. E. Dickinson), Royal

Society of Chemistry London, pp. 123-131. ---, Claesson, P. M. (1990). In Food Emulsions (eds. K. Larsson, S. Friberg),

Marcel Dekker, New York. --, Fontell K. (1983). Prog. Call. Pol. Sci., 68, p. 48-52. --, Stenius P.J. (1987). Phys. Chem., 91, 5944-48. Boyd, J. V., et al. (1976). In Theory and Practice of Emulsion Technology (ed. A. L.

Smith), Academic, London. Caffrey, M. (1985). Biochemistry, 24, 4826--44. Courthaudon, J. L., et al. (1991a).]. Agr. Food Chem., 39, 1365. --et al. (1991b).]. Colloid Interface Sci., 145, 390. Darling, D., Birkett, R. J. (1987). In Food Emulsions and Foams (ed. E. Dickinson),

Royal Society of Chemistry, London. Davies, J. T. (1957). Proc. Intern. Congr. Surf. Activity, 2d, London, 1, 426. Dickinson, E. (1986). Food Hydrocolloids, 1, 3. ---, Tanai S. (1992). Food Hydrocolloids, 6, 163-71. --et al. (1991). Food Hydrocolloids, 4, 403-14. Eriksson, P. 0., et al. (1987). Phys. Chem., 91, 846-63. --et al. (1985). Chem. Phys. Lipids, 37, 357-71. Fontell, K. (1978). Progr. Chem. Fats Other Lipids, 16, 145-62. --- et al. (1968). Acta Polytechnica Scandinavica, Chapter 2, Chemistry Series III,

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Cosm., 85, 27-30. --et al. (1969). ]. Colloid Interface Sci., 29, 155-6. Gawrish, K., et al. (1992). Biochemistry, 31, 2856-64. Griffin, W. C. (1979). In Kirk-Othmer Encyclopedia of Chemical Technology, Wiley, New

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lnoko, Y., Mitsui, T.J. (1978). Phys Soc. ]ap., 44, 1918. lsraelachvili, J. (1992). Intermolecular and Surface Forces, Academic, London. --eta!. (1977). Biochim. Biophys. Acta, 470, 185-201. ---eta!. (1976). ]. Chem. Soc. Faraday Transactions II, 72, 1525. Janiak, M.J., eta!. (1979). ]. Biol. Chem., 254, 6068-78. Krog, N. (1990). In Food Emulsion (eds. K. Larsson, S. Friberg), Marcel Dekker, New

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161-71. Pezron, 1., eta!. (1991).]. Colloid Interface Sci., 144, 449-57. Rydhag, L. (1979). Fette Seifen Anstrichm., 81, 168-73. --,Wilton, I. (1981). ]. Assoc. Off. Chem. Soc., 58, 830-7. Shinoda, K., Friberg, S. (1986). Emulsions and Solubilization, Wiley, New York. ---, Kunieda H. (1983). In Encyclopedia of Emulsion Technology, Vol. 1 (ed. P

Becher), Marcel Dekker, New York. ---,Saito, H. (1968). ]. Colloid Interface Sci., 30, 258-63. Small, D. M. (1986). Handbook of Lipid Research: Physical Chemistry of Lipids,

Plenum, New York. Soderberg, I. (1990). Structural Properties of Monoglycerides, Phospholipids and Fats

in Aqueous Systems, PhD Thesis, University of Lund, Sweden. Tanford, C. (1973). In The Hydrophobic Effect, Wiley, New York. Walstra, P. (1983). In Encyclopedia of Emulsion Technology, Vol. 1 (ed. P. Becher),

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emulsions,]. Assoc. Off. Chem. Soc., 48, 771-4.

SEVEN

Emulsifiers in Dairy Products and Dairy Substitutes

Stephen R. Euston

7.1 Introduction Bovine milk has been an important source of food for human beings for thou

sands of years. Not only is milk a very nutritious food in its own right, but it is

also a very versatile starting point for many other dairy products.

Milk is a complex food emulsion and colloidal sol. Table 7.1 gives the compo

sition of whole cow's milk. The emulsion component is composed of fat droplets

dispersed in an aqueous phase containing protein. The protein is in the form of

both casein micelles, which are themselves colloidal particles, and free in solu

tion as whey protein. A considerable reserve of knowledge has been assembled

on the structure and properties of the milk proteins (Swaisgood, 1992). The fat

droplets are stabilized by an adsorbed layer of protein and phospholipid called

the "milk fat globule membrane" (MFGM), which is distinct from the aqueous

phase protein (Walstra and Jenness, 1984). The average composition of the

MFGM has been estimated to be about 48% protein, 33% phospholipid, and

ll% water, with the remainder made up of other minor lipid components

(Walstra and Jenness, 1984). The phospholipid fraction of the membrane is com

posed of lecithin, phosphatidyl ethanolamine, phosphatidyl serine, phosphatidyl

inositide, plasmalogens, and sphingomyelin. Phospholipids are important food

173


Table 7.1 Approximate composition of bovine milk. (From Walstra & Jenness, 1984, Dairy Chemistry and Physics. Copyright © 1984, Wiley-lnterscience. Reprinted by permission of John Wiley & Sons, Inc.)

Average content Average dry Component (wt%) Range (wt%) matter (%)

Water 87.3 85.5-88.7

Solids, nonfat 8.8 7.9-10.0 69.0

Fat in dry matter 32.0 21.(}.-38.0

Lactose 4.6 3.8--5.3 36.0

Fat 3.9 2.4--5.5 31.0

Protein 3.25 2.3-4.4 26.0

Casein 2.6 1.7-3.5 20.0

Mineral substances 0.65 0.53-0.80 5.1

Organic acids 0.18 0.13-0.22 1.4

Miscellaneous 0.14 l.l

emulsifiers in their own right. The contribution that they make to the stability of

the milk fat globule is not well understood, but their use as food-grade emulsi

fiers has been the subject of extensive fundamental research (Courthaudon et al.,

1991; Dickinson et al., 1993a; Dickinson and Iveson 1993).

Until this century the conversion of milk to butter, cream, ice cream, and

various types of cheese had been more of a craft than a science. It is only rela

tively recently that an albeit incomplete understanding of these processes has

been available. It is now understood that the formation of these milk-based

products is a consequence of either the destabilization of the dispersed-phase

fat droplets (as in butter, ice cream, and whipped cream) or of the dispersed

aqueous-phase proteins (as in cheese). Emulsifiers play an important role in

the formation of structure in many dairy products.

In the following pages, the major emulsifier-containing dairy and imitation

dairy products will be reviewed. A brief description of their production will be

given where relevant, with emphasis on the role that emulsifiers play in the

formation and stability of the product.

7.2 Ice Cream Ice cream is probably the most complex food that we encounter. It is both a

foam and an emulsion, and it contains ice crystals and an unfrozen aqueous

Emulsifiers in Dairy Products and Dairy Substitutes 175

phase whose freezing point is depressed by freeze concentration of salts, sug

ars, and polysaccharide stabilizers. Despite its obvious complexity, ice cream

has been widely studied, and much is known about the formation of its struc

ture and the role that low molecular weight emulsifiers play in this (Covin and

Leeder, 1971; Lin and Leeder, 1974; Goff, 1988; Krog and Barfod, 1990;

Barfod et al., 1991). A typical ice cream formulation is shown in Table 7.2.

Table 7.2 A representative composition of ice cream. (Based on Rosentahl, 1991, Milk and Dairy Products Properties and Processing.)

Constituent

Fat Milk solid, nonfat Sugar Stabilizer Emulsifier Water

Weight percent in ice cream

10.0

11.0

13.0

0.2

0.5

65.3

Ice cream manufacture is a relatively simple process. The ingredients are

mixed, heated to destroy pathogens, and then homogenized. The homogeniza

tion step is included to reduce the fat droplet size so that churning of the fat

does not occur upon whipping. An in-line pasteurization step is then carried

out prior to cooling to 4°C and aging of the mix at this temperature for at least

4 hours. During this time milk proteins are able to redistribute between the fat

surface and the aqueous phase and fat crystallization occurs. The ice cream

mix is then aerated and frozen in a continuous freezer. Freezing is completed

by hardening the packed ice cream at minus 18°C initially, and finally at mi

nus 25°C (Arbuckle, 1986; Rosentahl, 1991; Varnan and Sutherland, 1994).

An acceptable ice cream product can be made without the addition of low

molecular weight emulsifiers. It has been known for several years, however,

that incorporation of emulsifiers into ice cream results in a product that whips

more easily, is drier (a necessary requirement in molded products), has im

proved melt-down resistance, and has a smoother body and texture (Arbuckle,

1986). In addition to this, the ice cream has a higher overrun, the air is more

finely dispersed, and the foam structure is more stable if emulsifiers are pre

sent (Keeney, 1982). An understanding of the mechanism by which emulsifiers

change these properties has emerged over the past few years (Goff, 1988; Krog


and Barfod, 1990; Barfod et al., 1991). Before describing the role of emulsi

fiers in ice cream structure formation, it is pertinent to consider the structure

of the adsorbed layer formed around the fat droplet in the ice cream premix

emulsion. During the homogenization stage the ice cream mix is subject to

high shear. This results in the disruption of the fat phase into small droplets.

Surface-active components of the mix will adsorb onto the nascent-oiVwater

interface, lowering the interfacial tension and thus stabilizing the emulsion

droplets. The exact composition of the interfacial layer will depend on the pro

portions of each type of surface-active component and their relative surface

activities. Recent research has thrown light on the competitive adsorption be

tween different milk proteins (Dickinson, 1986; Dickinson et al., 1988b;

Dickinson et al., 1989a; Dickinson et al., 1989c; Euston, 1989; Dickinson et

al, 1990b; Dickinson, 1992), milk proteins and emulsifiers (Dickinson and

Woskett, 1988a; Dickinson et al., 1990a; Dickinson, 1992; Euston et al.,

l995a; Euston et al., 1995b), and on the cooperative adsorption between pro

teins and polysaccharide stabilizers (Dickinson and Euston, 1990; Dickinson,

1992; Dickinson, 1993). These studies have identified that, in general, the

more surface-active component will predominate at the fat-droplet interface.

Thus the more surface-active protein in a mixture will dominate the adsorbed

layer initially, low molecular weight emulsifiers will, generally, displace pro

tein from the surface with time, and under certain conditions polysaccharides

can interact with proteins and/or emulsifiers to contribute to the structure of

the adsorbed layer (Bergenstahl et al., 1992). The adsorbed layer of the ice

cream emulsion will be a composite of these functional ingredients.

The key to the formation of ice cream structure is the formation of a stable

foamed product. In ice cream this is achieved in two ways. The foam in ice

cream is not a typical protein-stabilized foam, where air bubble stabilization is

achieved by protein adsorption at the air/water interface. The initial stabiliza

tion of the foam network may indeed proceed by this mechanism, but prior to

freezing, the foam structure is stabilized primarily by the partial coalescence

of emulsion fat droplets at the air bubble interface. Figure 7.1 is a cryo-SEM

micrograph of ice cream. Adsorption of fat globules at the air bubble surface is

clearly visible. For this to be able to occur, the emulsion must be relatively un

stable to the shearing forces exerted on the mix during air incorporation.

Several workers have attempted to demonstrate the link between emulsion co

alescence stability and the mechanical or viscoelastic properties of the ad

sorbed protein layer (Doxastakis and Sherman, 1984; Rivas and Sherman,


1984; Dickinson and Stainsby, 1988; Dickinson et al., 1988a). Dickinson et al.

(1988a) have shown a correlation between the surface shear viscosity of ad

sorbed layers of various proteins at the planar oil/water interface, and the coa

lescence stability of emulsions made with these proteins. The higher the

interfacial viscosity, the more stable the resultant emulsion under perikinetic

conditions. It has also been demonstrated that the orthokinetic stability of pro

tein-stabilized emulsions (stability under turbulent or shearing conditions) is

reduced by the presence of low molecular weight emulsifiers (Chen et al.,

1993; Dickinson et al., 1993; Dickinson and Williams, 1994). The explanation

for this lies in the ability of the low molecular weight emulsifier to displace

protein from the fat-droplet smface, thus reducing the mechanical strength of

the adsorbed layer. Emulsifiers present at concentrations too low to cause sig

nificant protein displacement can interfere with interprotein interactions

within the adsorbed layer and reduce the interfacial viscosity in this way

(Dickinson et al., 1990a).

Figure 7.1 Cryo scanning electron micrograph of ice cream. Note the partial coverage of the air bubble (AB) surface by fat globule (FG) and the partially coalesced fat globules (PC) in the foam lamellae. (Courtesy of A.B. McKenna.)


Emulsifiers that have an improving effect on the structure of ice cream do so because they are able to aid in the destabilization of the milk protein-stabilized ice cream emulsion. Emulsifiers commonly used in ice cream mix such as glycerol monostearate (GMS) and polysorbates, destabilize the emulsion by displacing protein from the fat-droplet surface. This is a result of their greater surface activity than milk proteins. Several studies have shown that the surface activity of emulsifiers is strongly temperature-dependent. Studies on model systems (Dickinson and Tanai, 1992) and in ice cream mix (Krog and Barfod, 1990; Barfod et al., 1991) indicate that displacement of protein from the oiVwater interface by emulsifiers is at a maximum at temperatures between 4°C and l0°C. This observation provides an explanation for the improvement in ice cream structure and stability imparted by the aging process. It is during the aging step at 4°C in ice cream manufacture that the displacement of the majority of the protein occurs. Krog and Barfod and coworkers (Krog and Barfod, 1990; Barfod et al., 1991) have investigated the aging effect in ice cream emulsions and have shown that whereas protein displacement does occur during aging in the absence of emulsifiers, displacement is greater when GMS is present, and greater still when glycerol monooleate has been added (Figure 7.2).

The temperature dependence of emulsifier surface activity can be explained in terms of the phase behavior in aqueous solution. In the bulk phase, monoglycerides exhibit a phase behavior similar to that of triglycerides (Krog, 1990). That is, they can exist in two polymorphic forms, the a. and ~forms, that differ in the way the molecules pack in the crystal structure. When cooled from a random molten state, a metastable crystalline structure termed the a.' state is formed. Further cooling leads to a transition to the ~ state. The most stable ~-crystalline structure will form if the a.' state is stored at ambient temperature. Lutton et al. (1969) proposed that the temperature dependence of GMS surface activity can be explained by either the formation of a condensed crystalline monolayer at the oiVwater interface at 5°C or by micelle formation close to the surface. The possibility that both mechanisms contribute to the increased surface activity on cooling cannot be ruled out.

Monoglycerides, and indeed other emulsifiers, have also been shown to exhibit a complex liquid-crystalline phase behavior in aqueous solution (Krog, 1990). Under certain conditions, the ~-crystal form of a monoglyceride will interact with water to form a lamellar liquid crystal. On cooling, this can transform to a so-called a.-gel phase (Krog, 1990). It has been hypothesized that


30

Q) rJ) cc

..r:: c. - 20 cc ..... c c Q) -0 .... c.

eft-Q)

10 > ·;:; cc Q)

a:

0 2 3 4 5 6 24

Aging time at 5°C

Figure 7.2 Changes in amount of protein adsorbed to fat globules in an ice cream mix

during the aging period at 5° C. The amount of protein bound in the fat phase is calcu

lated relative to the total protein in the mix. (From Krog, N., Barfod, N.M., AIChE Symposium Series, 86, 1-6. Reproduced with permission of the American Institute of Chemical Engineers.© 1990 A!ChE. All rights reserved.)

phase transformations between different crystalline and/or liquid-crystalline

forms of the adsorbed monoglycerides are important in protein displacement

(Berger, 1990). During homogenization the temperature of the ice cream mix is

high (80°C). Protein and emulsifier will both occupy the surface, with the

emulsifier having a relatively small effect on the protein surface coverage. As

the mix is cooled for aging, it is possible that a water-containing lamellar liq

uid-crystalline phase of the emulsifier is formed, which subsequently trans

forms into the a-gel phase. This latter transformation is accompanied by the

uptake of large quantities of water. At a later stage the more stable ~-crys

talline state may be formed. Berger (1990) believes that the two transforma

tions, lamellar to a gel, and a gel to ~ crystal, will play a role in protein

displacement. The change from lamellar to a gel phase results in a decrease in

surface area of about 30%, and formation of the ~-crystal structure releases

large amounts of water (Berger, 1990). Darling and Birkett (1987), however,


believe that in ice cream insufficient emulsifier is present in the system for liq

uid-crystalline phases to form. For this to occur the emulsifier must be ad

sorbed on the fat droplet surface at a concentration far greater than that

required for monolayer surface coverage. This is not the case in ice cream

emulsions (Darling and Birkett, 1987).

Once the emulsion has been destabilized in the freezer, partial coales

cence of the fat droplets has to occur at the air/water interface to partially

stabilize the foam structure prior to freezing. Research (Boode, 1992; Boode

and Walstra, 1993) has indicated that the crystal structure of the fat in emul

sion droplets is important in determining their susceptibility to partial coa

lescence. Van Boekel (1980) has shown that when fat crystals form at the

surface of emulsion droplets, and are large enough to penetrate the adsorbed

layer, a lipid bridge can form between two droplets that are in contact with

each other. The proportion of solid fat in emulsion droplets is important in

determining instability (Walstra, 1987). If the majority of the fat is solid, coa

lescence, or partial coalescence will not occur, and the droplets will be sta

ble. Similarly, if the droplets contain a very low proportion of solid fat,

coalescence can occur. If the solid fat content is in the approximate range 10

to 50%, partial coalescence is possible. A proportion of the emulsion droplet

is required to be in the form of liquid fat for partial coalescence to occur.

Walstra (1987) envisages a partial coagulum offat droplets as being held to

gether by necks of liquid oil.

When fat crystallizes in dispersed emulsion droplets, considerable super

cooling can be observed. Crystallization of fats occurs at nucleation points that

already exist in the fat phase. These nucleation points occur relatively infre

quently in emulsion droplets where the fat is dispersed into a large number of

small droplets. Consequently, in dispersed systems the triglyceride needs to be

cooled below its bulk phase freezing point before crystallization is initiated.

Emulsifiers in adsorbed monolayers can act as templates for the surface crys

tallization of triglycerides. Emulsifiers containing saturated hydrocarbon

chains have been shown to be good initiators of fat crystallization, whereas

those with unsaturated hydrocarbon chains are not as good (Berger, 1990;

Barfod et al., 1991). Figure 7.3 gives the solid fat content (SFC) as a function

of time for model ice cream emulsions stored at 5° C. Both saturated (GMS) and

unsaturated (GMO) emulsifiers initiate crystallization compared to control

emulsions with no emulsifier, but the SFC of GMS-containing emulsions is al

ways greater than for those containing GMO.


100

..... c:

80 Q) ..... c: 0 u ..... 60 co ..... "0

0 40 Cll

~

20

0 2 3 4 24

Hours at 5°C

Figure 7.3 Recrystallization of fat phase of ice cream emulsions without emulsifier (control) or with saturated (GMS) or unsaturated (GMO) monoglycerides after cooling to 5°C and aging. (From Barfod et al., 1991, and reproduced with permission.)

Darling and Birkett (1987) point out that in a mixed triglyceride system,

such as is found in milk fat, single discrete crystals are unlikely to form under

the rapid cooling conditions used in ice cream manufacture. They have shown

that in a cooled vegetable oil emulsion, concentric layers of triglyceride crys

tals are formed at the surface of oil droplets. These contain imperfections that

may be due to dislocations or recrystallization processes, and these are likely

to cause the destabilizing effect.

The ability of triglyceride crystals to penetrate the adsorbed layer depends

on a number of factors. The surface tension between crystal and oil, crystal

and water, and oil and water will determine how far into the oil phase the crys

tal will penetrate (i.e., if it is preferentially wetted by the oil or water phase).

Emulsifiers, by way of their surface activity, will alter these surface tensions,

and this may result in the crystals being able to penetrate further into the

aqueous phase. This would lead to a decrease in emulsion stability. The des

orption of protein by emulsifier also aids destabilization by reducing the thick

ness of the layer through which fat crystals have to penetrate. The polymorphic

form of the fat crystal will also play a role in fat-droplet instability.

Triglycerides can exist in three general polymorphic forms, the a, ~. and W polymorphs. When cooled from a melt, triglycerides will generally form a-type


crystals. These are not stable (Larrson and Dejmek, 1990) and will transform

into a W polymorph and subsequently to the stable ~ polymorph. Having been

formed at lower temperature, a crystals contain triglyceride in a more disor

dered liquid-like arrangement. These disordered crystals are softer and are

able to deform and follow the contours of the fat droplet more easily.

Consequently, they are less likely to penetrate the adsorbed layer. The ~-crys

talline structure is more solid-like, with the triglyceride molecules arranged in

ordered arrays. The ~ crystals have a greater mechanical strength and are un

able to deform to the shape of the fat droplets. This leads to their bursting out

of the droplet into the aqueous phase (Darling, 1982).

In practice, two types of emulsifier are commonly used in ice cream: mono

and diglycerides and polyoxyethylene derivatives of glycol or glycol esters, for

example polysorbates (Keeney, 1982). Sucrose esters have also been evaluated

and have been found to be suitable as ice cream emulsifiers (Buck et al.,

1986). Mono- and diglycerides and polysorbates are usually all found in cur

rent ice cream emulsifier blends. The explanation for this lies in the relative

abilities of polysorbates and mono- and diglycerides as emulsion destabilizers,

or as foam-forming agents. Polysorbates are far more efficient at displacing

protein from the oiVwater interface than are mono- and diglycerides and thus

are better emulsion destabilizers (Keeney, 1982). Mono- and diglycerides are

better foaming agents and thus are able to aid the formation of the initial foam

prior to fat-droplet agglomeration at the air/water interface (Keeney, 1982). A

second factor is the differing abilities of emulsifiers to influence fat crystalliza

tion. Figures 7.2 and 7.3 show that whereas GMO is able to displace more pro

tein from the fat globule surface during aging than does GMS, GMS initiates

more fat crystallization than GMO. Use of a mixed emulsifier system would

also allow optimum protein displacement combined with optimum fat crystal

lization.

In summary, nonprotein emulsifiers are important in ice cream in several

respects:

l. They promote protein desorption from the surface of fat droplets, both by

their higher relative surface activity and the possible formation of liq

uid-crystalline mesophases.

2. They can act as nucleation points for surface crystallization of triglyc

erides.

3. They may promote fat crystal penetration of the adsorbed protein layer by

alteration of the surface tension between various phases.


4. They may help in the initial formation and stabilization of the ice cream

foam prior to partial fat-globule coalescence and freezing. Monoglycerides

are particularly good at this function.

7.3 Whipped Cream and Whipping Cream The distinction between whipped cream and whipping cream is one of colloidal

state. Whipping cream is an oil-in-water emulsion stabilized by adsorbed milk

protein and (where added) low molecular weight emulsifier. Whipping cream can

be made by concentration of the milk fat globules found naturally in milk, or by

a recombination process where amorphous milk fat is homogenized with milk

proteins and emulsifiers. The fat content of whipping cream is about 35% by

weight. Unlike ice cream emulsion, which only has to be stable enough to be

aged for a few hours before processing into ice cream, whipping cream emulsion

has to be stable enough to allow storage for several weeks at ambient tempera

tures, if UHT processed, without appreciable loss of stability.

Whipped cream is formed from whipping cream when air is incorporated

into the emulsion to form a foam. The structure of whipped cream resembles

that of ice cream in some ways. The foam is stabilized, initially by adsorbed

protein and any added emulsifier. Prolonged whipping of the cream leads to

partial agglomeration of fat globules at the air/water interface. Whereas in ice

cream the final structure is partially stabilized by fat-globule adsorption at the

air bubble surface, but mostly by freezing of the aqueous phase, in whipped

cream the higher dispersed-phase fat content (35 wt% compared to about 10

wt% in ice cream) leads to a higher degree of fat-particle coalescence at the

air/water interface. This greater fat adsorption leads to formation of a stable

foam without the need for freezing. Figure 7.4 is a cryo-SEM micrograph show

ing fat-globule adsorption at the air/water interface in whipped cream.

Comparing this to Figure 7.1, a cryo-SEM micrograph of ice cream, it is appar

ent that structural similarities exist, but that the degree of fat-globule adsorp

tion appears to be less in ice cream. The adsorbed fat globules contribute to

the rheological properties of the foam. By influencing drainage in the aqueous

lamellae between air bubbles, the partially coalesced, adsorbed fat globules

impart a small but finite yield stress on the whipped product (Dickinson and

Stainsby, 1982). This allows whipped cream to "stand up" under its own

weight even at ambient temperature.


Figure 7.4 Cryo scanning electron micrograph of whipped cream. Note the greater coverage of the air bubble (AB) surface by adsorbed fat globules (FG) than occurs in ice cream (Figure 7.1). (Courtesy of A.B. McKenna.)

Nonhomogenized cream separated from milk will whip satisfactorily with

out addition of emulsifiers. If the cream is homogenized prior to whipping and

the mean fat-globule size is reduced, emulsifiers have to be added to aid desta

bilization. Anderson and Brooker (1988) have attributed the differences in

whipping ability of homogenized and nonhomogenized cream to the differ

ences in interfacial composition of the emulsion droplets in these systems.

Nonhomogenized cream contains fat droplets stabilized by native MFGM. The

composition of this has been described earlier (Section 7.1). After homoge

nization, the particle size is reduced, interfacial area is increased, and conse

quently, native MFGM is insufficient on its own to stabilize the newly formed

interface. A combination of increased interfacial area and competitive adsorp

tion between MFGM material and cream serum proteins means that proteins

from the aqueous phase (caseins and whey proteins) contribute to the interfa-


ciallayer. The adsorbed layer in homogenized cream has been found to consist

mainly of caseins, with smaller amounts of ~-lactoglobulin and ~-lactalbumin

(Anderson et al., 1977; Darling and Butcher, 1978; McPherson et al., 1984).

This is consistent with the available data on competitive adsorption between

casein and whey proteins in model systems (Euston, 1989; Dickinson et al.,

1990b). In the early stages of whipping, before fat-globule adsorption and par

tial coalescence occurs to any great extent, the air bubbles are stabilized by

adsorbed milk serum proteins. Since this air/water interface is composed of the

same proteins that surround the fat/water interface in homogenized cream, the

difference in interfacial tension between the two interfaces is not very great

(Anderson and Brooker, 1988). Interfacial tension differences have already

been put forward as a driving force for fat-globule adsorption at the air/water

interface in ice cream (Section 7.2). Because of the small interfacial tension

differences between fat globule and air bubble in homogenized cream, the dri

ving force for fat-globule adsorption is low. In nonhomogenized milk the inter

facial tension differences between a fat globule stabilized by MFGM and an air

bubble stabilized by cream serum proteins are sufficient to act as the driving

force for fat-globule adsorption at the surface of air bubbles. Of course, this is

also aided by the presence of fat crystals at the fat-globule surface and by the

shearing forces introduced during whipping.

The importance of the fat phase manifests itself in two ways. As in ice

cream (Section 7.2), fat crystals are known to be important in the shear-in

duced coalescence of the fat globules (Darling, 1982), and the presence of a

certain amount of liquid fat is a prerequisite for good whipping properties.

Bucheim (1986) put forward the idea that the interfacial layer surrounding the

fat droplets ruptures when they collide during agitation. The subsequent

spreading of liquid fat is the first stage in destabilization by aggregation of ad

jacent droplets. The importance of the solid fat content of the fat globules has

been demonstrated by Darling (1982), who observes a direct correlation be

tween the SFC and whipping time in natural cream.

Recombining technologies are becoming an increasingly important process

for making whipping cream bases. These would encounter the same problems

as homogenized cream (i.e., the similarity in composition and interfacial ten

sion between air/water and oil/water interfaces), if they were formulated with

milk protein as the only surface-active material. For this reason, recombined

whipping creams, and indeed homogenized natural creams contain added low

molecular weight emulsifiers. These will alter the composition of the fat-


droplet surface, thus changing the interfacial tension. Addition of an optimum concentration of emulsifiers results in an oil/water interface composed of protein and emulsifier differing sufficiently from the air bubble interface for fatglobule adsorption to occur on whipping. For similar reasons to those proposed for ice cream (Section 7.2), whipping cream emulsifiers are usually a combination of two types. There is often a lipophilic emulsifier such as GMS, or one of its derivatives, and a water-soluble polyoxyethylene derivative such as one of the Tweens. Thome and Eriksson (1973) have shown that the amphoteric phospholipids are good emulsifiers in whippable emulsions when used in combination with monoglycerides. This is a significant observation when the trend toward natural, nonsynthetic emulsifiers is considered. Phospholipids are a natural component of milk fat and can be produced as a byproduct when milk is processed into, for example, butter. This can explain the increasing use of buttermilk powders as combined emulsifier/protein systems in whipped emulsions (Vodickova and Forman, 1984).

The structure of the composite fat-globule surface layer in homogenized and recombined dairy whipping cream is not known for certain. Two theories have been put forward. One theory (Krog, 1977) maintains that a primary layer of emulsifier adsorbs at the fat-droplet surface, and that a secondary layer of protein is attached to this primary layer through relatively weak cooperative hydrogen bonding. When the cream is whipped this protein layer is removed from the fat globule relatively easily, and the emulsion destabilized in this way. Doxastakis and Sherman {1984), however, have evidence that the protein and emulsifier form a mixed interface where both are adsorbed through hydrophobic interaction with the interface. It is speculated that this can lead to local

ized differences in the interfacial tension at the fat-droplet surface (i.e., between protein-rich and emulsifier-rich regions of the adsorbed layer), which helps to drive fat-globule adsorption and partial coalescence. Whichever of these theories is correct, the elements are also relevant to the destabilization of ice cream emulsion when it is frozen and whipped.

A stable whipped cream can be formed from whipping cream that has been held at room temperature for some time. However, a superior product is obtained if the cream is aged for several hours at low temperature prior to whipping. This, as in ice cream, is a consequence of increased emulsifier surface activity at low temperature.

It would appear, therefore, that the functions of emulsifiers in whipping cream are essentially the same as for ice cream, i.e.,


l. They destabilize the cream through their ability to displace protein from

the oil/water interface. This changes the adsorbed layer composition

and interfacial tension of the fat droplet.

2. They may destabilize the emulsion through their ability to form lyotropic

liquid-crystalline mesophases and the subsequent phase transforma

tions that occur to form stable crystalline forms.

3. They may participate in the initial foam stabilization.

4. They aid in the formation of fat crystals at the fat-droplet surface, which

crystals are essential for fat-globule partial coalescence.

This last point is reinforced by electron microscopic studies of emulsifier

containing whipping creams. Figure 7.5 is a cryo-TEM micrograph of a whip

ping cream containing Tween 80. The large needle-like crystals that emanate

from the fat droplet are, apparently, typical of those formed in Tween-contain

ing systems (McKenna, 1995 personal communication). The bridging of two fat

droplets by these needle-like crystals is clearly visible.

7.4 Whipped Toppings Whipped toppings, usually made with hydrogenated (hardened) vegetable oils,

have been a popular dairy analog product for several years. Table 7.3 gives a

typical composition for a whipped topping powder.

Si (1991) lists the types of emulsifier used in whipped toppings as propy

lene glycol esters of monoglycerides, acetic acid esters of monoglycerides, or

lactic acid esters of monoglycerides.

In whipped toppings, as in dairy whipping creams, the emulsifiers appear to

Table 7.3 Typical whipped topping powder composition. (From Si, 1991. Reprinted by permission of the Society of Dairy Technology.)

Ingredient

Hardened coconut or

palm kernel oil

(melting point 3l-36°C)

Maltodextrin

Sodium caseinate Emulsifiers

Composition (%)

52.0

32.0

8.0 8.0


Figure 7.5 Cryo transmission electron micrograph of whipped cream containing Tween 80 as emulsifier. A partial agglomerate of fat globules is shown. The spikes emanating from the fat globule (FG) are fat crystals (FC) and can clearly be seen to bridge between two fat droplets (B). These spikes are, apparently, features of Tween-containing systems. (Courtesy of A.B. McKenna.)

be important in the destabilization of the emulsion, while the protein is impor

tant in giving initial stability to the oil-in-water emulsion. The mechanism by

which emulsion destabilization is achieved, however, is different. Whereas

whipped dairy creams and whipped imitation creams are stabilized by par

tially coalesced, relatively intact fat globules adsorbed at the air/water inter

face, whipped toppings are stabilized by crystalline fat at the air bubble surface. Krog and coworkers (Barfod and Krog, 1987; Bucheim et al., 1985; Krog et al., 1986) have carried out extensive studies of the factors that effect structure formation in whipped toppings. They have shown (Barfod and Krog, 1987) that part of the fat in spray-dried topping powders is in a supercooled state. When these topping powders are reconstituted in water at low temperature, they show large structural changes that determine whipping characteris-


tics and foam structure. The emulsion becomes unstable due to spontaneous

recrystallization of the supercooled fat. The destabilization of the emulsion is

probably promoted by the temperature-dependent desorption of protein from

the surface, followed by coalescence. This makes crystallization of the super

cooled fat more likely, due to the increased probability of nucleation sites

(Bucheim et al., 198S).

Scanning electron microscopy studies (Bucheim et al., 198S) show that the

final structure of the aerated whipped topping is stabilized by a layer of crys

talline fat of about 0.1jlm thickness. The aqueous phase lamellae between air

bubbles also contains large proportions of crystalline fat, with smaller propor

tions of relatively intact fat globules.

The kinetics of fat crystallization and emulsion destabilization depend on

the type of emulsifier used in the formulation. Bucheim et al. (198S) have in

vestigated the effect of distilled propylene glycol monostearate (PGMS), dis

tilled unsaturated monoglycerides (glycerol monooleate, GMO), and distilled

saturated monoglycerides (glycerol monostearate, GMS) on the structure of

whipped toppings. Only PGMS is typically used in commercial formulations.

Figure 7.6 shows that all the emulsifiers promote fat crystallization when com

pared to toppings without added emulsifier. The effect of PGMS and GMO,

however, was greater than for GMS. The increased emulsion destabilization

caused by the enhanced fat recrystallization led to PGMS- and GMO-contain

ing whipped toppings being more stable than those made from GMS-contain

ing emulsions (Bucheim et al., 198S). The GMS-containing reconstituted

topping emulsion is too stable to allow consequent stabilization of incorporated

air (whipping).

The importance of protein desorption on the whipped topping structure and

stability has been demonstrated by Krog and coworkers (Krog et al. 1986;

Barfod and Krog, 1987). Table 7.4 gives the percentage protein contents of the

fat and aqueous phases of whipped topping powders reconstituted at soc and

30°C, and containing PGMS, GMS, or no added emulsifier. At soc in the ab

sence of emulsifier, almost one-quarter of the protein is associated with the fat

phase. This falls to 1.3% when PGMS is present and 7.7% with GMS added.

The temperature dependence of protein displacement is also evident. At 30°C,

over 40% of the protein is in the fat phase when emulsifier is absent, but this

drops to about 33.7% in the presence of PGMS and 12.3% when GMS is in

cluded in the formulation (Krog et al., 1986). The GMS-containing reconsti

tuted toppings have a significant proportion of protein still associated with the


40

~ ..... c Q) ..... c 0 30 u ..... Ctl ......

"0

0 (/)

20

... ... ...

10

0 10 20 30

Time (min) at 15°C

Figure 7.6 Crystallization of supercooled lipid fractions in topping emulsions with different surfactants, reconstituted (I :3) in deuterated water (D20), measured by pulsedNMR at l5°C. e GMO (Dimodan 0), • PGMS (Promodan SP), o GMS (Dimodan PV), A no surfactant added. [From Bucheim et al. (1985). Reprinted by permission of Scanning Microscopy International.]

Table 7.4 Distribution of protein between the fat cream phase and the water phase of centrifuged topping emulsion. (From Barfod and Krog, 1987. Reprinted by permission of the American Oil Chemists Society.)

After I hour After I hour After I hour After I hour at S°C at S°C at 30°C at 30°C %protein in %protein in %protein in %protein in

Surfactant fat phase water phase fat phase water phase

l0%PGMS 1.3 98.7 33.7 66.3 l0%GMS 7.7 92.3 12.3 87.7 None 24.0 76.0 41.7 58.3

fat-droplet surface, even after aging of the emulsions at 5°C. This is obviously enough to form an adsorbed layer strong enough, in combination with the lower

degree of fat recrystallization, to prevent stabilization of the incorporated air

bubbles. This is in contrast to the situation in ice cream and whipping cream,

where GMS is capable of destabilizing the fat emulsions to a degree that par

tial coalescence can occur. Darling and Birkett (1987) point out that the level


of emulsifiers in whipped toppings is sufficient to allow the formation of emul

sifier adsorbed layers of far greater than monolayer coverage. They suggest that

the formation of liquid-crystalline mesophases, and the a.-gel phase of the ad

sorbed emulsifier, is a possibility. Westerbeek et al. (1991) have shown that a

common emulsifier used in whipped toppings, glycerollactopalmitate (GLP),

is capable of forming the a.-gel phase at oil/water interfaces, and this may con

tribute to emulsion destabilization.

The present understanding of the formation of structure in whipped top

pings suggests the following mechanism for emulsion destabilization and for

mation of the foam structure:

1. The powdered, dried topping emulsion is stable.

2. When reconstituted at low temperature, protein desorption is initiated and

is aided by added emulsifiers such as PGMS. The mechanism of protein

desorption will be similar to that already described for ice cream. There is

an almost total desorption of protein from the fat droplet surface.

3. Coalescence of fat droplets can occur during whipping, due to the pres

ence of a liquid fat produced by supercooling.

4. Coalescence leads to a recrystallization of the supercooled fat, which is

again aided by the presence of emulsifiers.

5. A continuous phase of elongated fat crystals is formed, resulting in an in

creased viscosity of the whip, which is capable of stabilizing dispersed

air bubbles.

As in ice cream, the functions of emulsifiers in whipped toppings are to pro

mote protein desorption and fat crystallization.

7.5 Cream Liqueurs Cream liqueurs are dairy emulsions of high added value. The combination of

milk protein-stabilized cream emulsion and high alcohol content make cream

liqueurs unique among dairy emulsions. Table 7.5 gives a typical range of

compositions for cream liqueur. In practice many commercial formulations

also have small amounts of GMS added.

The production of cream liqueurs is governed by the relative poorness of

the alcoholic aqueous phase as a solvent for proteins and sugars. Two commer

cial processes are in common use (Banks and Muir, 1988), namely, the single-


Table 7.5 Range of compositions of a standard cream liqueur. (Reprinted from Banks et al., 1981, with permission.)

Component

Milk fat Added sugars Sodium caseinate Nonfat milk solids Ethanol Water

Composition (wt%)

12-16 15-20 2.6-3.5 l.0-3.5 14 46-51

stage process and the two-stage process. Figure 7. 7 presents flowcharts for

both processes. The main difference between the two processes lies in the

stage at which the alcohol is added. In the single-stage process this is prior to

homogenization, whereas in the two-stage process it is after homogenization.

Banks and Muir (1988) found that homogenization in the presence of alcohol

leads to the formation of fewer large fat globules, and as such is preferable in

terms of emulsion stability. A characteristic of cream liqueur production is the harsh homogenization conditions used (two passes at 300 bar). This results in a product in which more than 97% of the fat droplets have a diameter less than 0.8 f..Lm. A second factor favoring formation of smaller fat droplets is the significant lowering of interfacial tension observed at the oil/water interface when alcohol is added to the aqueous phase (Bullin et al., 1988; Dickinson and Woskett, 1988; Burgaud and Dickinson, 1990). As a result of the very fine droplet size, the protein in the added cream has to be supplemented by sodium

caseinate (to a fat-to-caseinate ratio of approximately 5:1) to provide adequate

coverage of the newly formed fat surface by protein (Banks et al., 1981). The

fine particle size of the dispersed fat droplets gives the product an excellent

stability with respect to creaming. Banks et al. (1981) have noted no signs of

creaming in liqueurs with a composition within the range quoted in Table 7.5

after 12 months storage. The high level of added sodium caseinate, however,

leads to cream liqueur emulsions being unstable in acid environments. This means that they are not suitable for combination with acidic beverage mixers

such as lemonade. A cream liqueur that is stable in an acid environment can

be made by replacing the sodium caseinate with GMS. The emulsifier replaces

milk protein as the primary emulsion stabilizer at the oil/water interface, and the nonadsorbed protein is unable to aggregate the fat droplets when exposed


Single-Stage Process

Water Caseinate Sugar Cream Citrate

Cream Base Alcohol

I I Homogenize

Product 2 x 300 bar, 55"C

Two-Stage Process

Cream Base Homogenize 2 x 300 bar, 55"C coolto<21rC

Homogenized Base

Gentle mixing

Alcohol

Product

Figure 7.7 Flow diagrams for the process of manufacture of a cream liqueur in (a) a single stage and (b) two stages. (From Banks and Muir, 1988. Reprinted by permission of Elsevier Applied Science Publishers.)

to acidic surroundings (Banks and Muir, 1988). Acid stability in this type of

product is gained at the expense of emulsion stability and shelf life. In prac

tice, legal limits in some countries set the concentration of GMS at no more

than 0.4 wt%, and so total replacement of caseinate by GMS is not feasible.

Many manufacturers add low concentrations of GMS as well as sodium ca

seinate to cream liqueur formulations. Dickinson and coworkers (1989b) have

shown that, in addition to displacing some, but not all of the milk protein from

the fat droplet surface, which presumably infers some acid stability on the

product, GMS also improves the creaming stability of a model cream liqueur.

When model cream liqueurs were stored at room temperature for 12 weeks, no

creaming was observed with added GMS concentrations above 0.5 wt%. Below

this level of added GMS a reduced degree of creaming was observed compared

to control samples with no emulsifier (Dickinson et al., 1989b). The increased

creaming stability was associated with rheological changes in the emulsifier

aqueous phase. At low CMS concentrations the emulsions exhibit Newtonian

behavior, whereas above 0.5 wt%, a clear yield stress is found. Dickinson et al.


(1989b) postulate the formation of a weak gel-like network in the continuous

phase formed by interaction of caseinate with GMS. It is also likely that inter

action between caseinate and GMS at the oil/water interface plays a role in the

creaming stability. Evidence for interactions between adsorbed caseinate lay

ers and GMS has been reported by Doxastakis and Sherman (1984), who in

vestigated the surface rheological properties of mixed caseinate GMS systems.

An apparent contradiction in the work of Dickinson et al. (1989) is that al

though creaming stability is enhanced at GMS levels above 0.5 wt%, the shelf

life, as tested using an accelerated method at 45°C, decreases in this region

(Figure 7.8). Dickinson et al. (1989) point out that whereas weak gels are able

to prevent formation of a substantial cream layer, they are also prone to slow

150 .------------------------------,

0

0 2

GMS concentration (wt%)

Figure 7.8 Effect of GMS on the shelf life of simulated cream liqueurs on storage at 45°C. The time for serum separation to first become visible is plotted against the GMS concentration. Different symbols refer to separate experiments.(Based on Dickinson et al., 1989. Reprinted by permission of the Institute of Food Technologists.)


syneresis when stored for any length of time. This leads to separation of the

aqueous phase and formation of a distinct, clear serum layer at the bottom of

the sample container. Whether this syneresis will occur at room temperature is

not certain, and Dickinson et al. (1989b) stress that a correlation between the

shelf life at 45°C and that at room temperature may not follow. Cream liqueurs

stored under ambient conditions can have shelf lives of several years. Clearly

these are likely to be consumed before serum separation becomes evident.

Since the legal limits on the amount of emulsifier that can be added are set at

about 0.4 wt%, the problem of gel syneresis is unlikely to be encountered. At a

level of 0.4 wt% added GMS, creaming under gravity would not be eliminated

completely, but would be reduced to a level acceptable to the consumer

(Dickinson et al., 1989b).

7.6 Creams and Coffee Whiteners Cream products containing 10 to 20% fat have been popular as coffee cream

ers for over 50 years (Abrahamson et al., 1988). Coffee creamers and whiteners

perform several functions: they give coffee a white color, reduce bitter taste by

complexation of the tannic acids with milk proteins, give the coffee a cream

like flavor, and give body to the coffee (Sims, 1989).

Traditionally, coffee cream is produced by simple concentration of milk up

to the required fat content. The cream is usually heat treated using a UHT

process, homogenized either before or after heating, and packed aseptically to

give a long shelf life. Emulsifiers are not usually added to this product. More

recently, with the advent of recombining technology and with the preference of

some consumers for vegetable oil-based products over those containing milk

fat, new products have appeared that require the addition of emulsifiers to

their formulations. If a recombined coffee cream is produced, the formulation

is more complex than for coffee cream. Table 7.6 gives a typical formulation

for a recombined coffee cream containing 19% milk fat, as suggested by

Zadow (1982).

The recombining process involves a two-stage homogenization with an 18-

MPa first stage and a 3-to-4-MPa second stage. Presumably the emulsifiers are

added to aid in the homogenization process by reducing the energy required to

form the fat/water interface. It may also be assumed that since in natural coffee

creams the milk fat is already in a dispersed state, the energy required to re

duce the particle size is less, and so emulsifiers are not needed. However,


Table 7.6 Typical formulation for a recombined coffee cream. (From Zadow, 1982. Reprinted by permission of the International Dairy Federation.)

Ingredient Composition (wt%)

Skim milk powder 3.0 Buttermilk powder 4.5 Anhydrous milk fat 19.0 Carrageenan 0.03 GMS 0.05 Tween 60 0.1 Water 73.32

Zadow (1982) states that emulsifiers and stabilizers are required only if the

product is to be given a high heat treatment (a UHT process or steam injec

tion). This may indicate a role for the emulsifiers in protecting the protein or

emulsified fat from heat damage. Evidence exists to support this hypothesis

and will be dealt with in more detail in Section 7.8.

Whereas coffee cream and recombined cream are used in a liquid form, coffee whiteners based on vegetable fat are also popular in dry powder form. Typical

formulations for liquid and dry powder coffee whiteners are given in Table 7.7.

Table 7.7 Typical formulations for liquid and powdered coffee whiteners. (From Si, 1991. Reprinted by permission of the Society of Dairy Technology.)

Ingredient Composition ( wt%)

Liqnid Powder

Fat 10.0 30.0 Sodium caseinate l.O 4.0 Maltodextrin (DE28) 10.0 62.0 Monoglycerides 0.2 -1.5 Tartaric acid esters 0.2 0.5 of monoglycerides Carrageenan 0.05 Sodium alginate 0.05 K2HP04 0.2 1.5 Flavor 300 ppm lOOOppm Water to 100%


Other water-soluble surfactants, such as Tween 60, are commonly used in

place of the tartaric acid esters of monoglycerides. Si (1991) states that the func

tion of the emulsifiers in coffee whitener is to improve whitening ability and to

aid powder dispersibility in coffee. Knightly (1969) has found that GMS is more

effective in improving powder dispersibility, whereas Tween 60 is better at im

proving the rate of solution of the powder. Optimum whitening ability is attrib

uted to small fat globules and a narrow particle-size range, and its attainment in

coffee whitener has been attributed to the presence of the GMS and its deriva

tives (Si, 1991). Whitening power in a dispersion is related to the surface area of

the disperse particles. The higher the surface area the greater the light re

flectance from the dispersion and thus the greater the whitening effect. This is

true for both dairy coffee creams and nondairy coffee whiteners. Leo and

Betscher (1971) have noted that there is an optimum particle-size range for opti

mum optical density and whitening power of the dispersion. Overhomogenization

of a coffee whitener formulation is known to result in a loss of whitening power.

The emulsifiers added to powdered formulations prior to spray drying are

capable of stabilizing the emulsion in the liquid form. Sodium caseinate is

usually required to give stable fat droplets in the dried powder (Sims, 1989),

since an adsorbed proteinaceous layer is better able to withstand the extreme

conditions in the drier. Because sodium caseinate is used at high concentra

tion (typically in the range 3 to 15%), ways of reducing the amount in coffee

whitener have been sought. One way of doing this is to use sodium (or calcium)

stearyl lactylate or sodium stearyl fumarate as an emulsifier. Miller and

Werstak (1983) have used 2.5% monoglycerides plus sodium stearyl-2-lacty

late (SSL) in the approximate ratio of 7.3:1. They claim a reduction of sodium

caseinate to 60% of that required in normal formulations. The function of SSL

appears to be through its ability to form a complex with sodium caseinate (Leo

and Betscher, 1971). It is likely that this interaction results in improved fat en

capsulation in the dried state through increased interfacial rigidity of the ad

sorbed layer. This is analogous to the increased emulsion coalescence stability

observed when GMS complexes with protein adsorbed at the oil/water-emul

sion interface (Doxastakis and Sherman, 1984; Rivas and Sherman, 1984).

7.7 Processed Cheese Processed cheese manufacture dates back approximately 100 years.

Originally, it was used as a way of increasing the shelf life of cheese and of uti-


lizing lower quality cheese (Carie et al., 1985). To manufacture processed

cheese, the cheese raw material (a mixture of rennet and fresh cheeses) is first

cleaned, chopped, and heated at 70 to 82°C with emulsifying salts and other

additives. Heating and water addition are often combined by using direct

steam injection. The pH of the mix is lowered to 5.6 to 5.8 using organic acids

such as citric or lactic, and the product is then extruded into packages

(Rosenthal, 1991). Alternatively, the correct pH can be obtained by careful se

lection of a blend of polyphosphate emulsifying salts, which have some buffer

ing capacity in this application (Lee, S.K., 1995 personal communication). The

final product can have 15 to 25% fat and up to 58% water.

The structure of processed cheese is one of fat droplets dispersed in a concen

trated, gelled protein network. Emulsion stability in the fat droplets is controlled,

primarily, by adsorbed caseins or hydrolyzed casein fractions. Some manufactur

ers add mono- and diglycerides as emulsifiers. The structure and texture of

processed cheese is closely linked with the size and distribution of fat globules in

the cheese (Thomas et al., 1980; Shimp, 1985).lf the fat in a processed cheese is

weakly homogenized and large fat droplets are formed, the cheese is soft and

melts easily. lf the fat droplets are small, the cheese is hard and nonmelting.

To control the structure of processed cheese, so-called emulsifying salts such

as polyphosphates are added. Although these are not surface active they play an

important role in modifying the emulsifying activity of the surface-active ca

seins. Caseins bind calcium, and this has the effect of reducing their solubility,

and thus their emulsifying activity. Through their ability to chelate calcium more

strongly than the caseins, emulsifying salts are able to improve the solubility and

emulsifying properties of the caseins. Emulsifying salts are of two types: those

that bind calcium relatively weakly and those that bind calcium more strongly.

Weak emulsifying salts have a modest effect on the emulsifying properties of the

caseins and lead to the formation of a soft cheese with relatively large fat

droplets. Strong emulsifying salts give a greater improvement in the emulsifying

capacity and result in a hard cheese with smaller fat droplets.

The use of low molecular weight, surface-active emulsifiers (Tweens and

Spans) was first investigated in the 1950s (Holtorff et al., 1951). They are not

as good as emulsifying salts in promoting structure formation in processed

cheese, and in some cases they act to destabilize the fat emulsion by protein

displacement from the surface.

Concern has been expressed over the nonnutritional effect of forming a

phosphorus/calcium complex. The supplementation of emulsifying salts by


monoglycerides has been investigated as a way of reducing the concentration

of emulsifying salts. Gavrilova (1976) produced processed cheese of improved

rheology and shelf life using an emulsifying salt/monoglyceride mixture.

Zakhorova et al. (1979a, b) achieved a 50% reduction in the concentration of

emulsifying salts required by adding 1% monoglyceride to the cheese. The

processed cheese produced was reported to be of good quality and to have im

proved hydrophilic properties.

Lee et al. (1995) have studied the effect of adding small concentrations of

low molecular weight surfactants as coemulsifiers in combination with emulsi

fying salts in a model processed cheese. The surfactants used were sodium do

decyl sulphate (SDS, an anionic surfactant), cetyl-trimethyl ammonium

bromide (CTAB, a cationic surfactant), lecithin (a zwitterionic surfactant), and

GMS (a nonionic lipophilic surfactant). Although the addition of surfactant

was observed to result in a reduction in fat-droplet size, the degree of unifor

mity of the dispersion differed between emulsifiers. In contrast to previous re

ports that smaller more evenly dispersed fat droplets gave firmer cheeses

(Thomas et al., 1980; Shimp, 1985), Lee et al. (1995) found no relationship be

tween processed cheese hardness and emulsion structure in the presence of

emulsifiers. They concluded that electrostatic interactions between the emulsi

fier and the protein played the major role in determining the rheological prop

erties of the cheese. The anionic surfactant SDS gave the softest cheese, the

cationic surfactant CTAB the hardest. GMS and lecithin gave cheeses with

rheological properties little different from the control with no added emulsifier.

In the future, low molecular weight emulsifiers may play a greater role in con

trolling the texture of processed cheese.

7.8 Recombined, Concentrated, and Evaporated Milks Recombined and concentrated milk products are produced for economic rea

sons. The cost effectiveness of transporting milk products that have been con

centrated by removal of a proportion of the water phase, and the associated

changes in shelf life, make milk concentration a viable process. Similarly, it is

cost effective to transport dehydrated ingredients for recombination into milk.

The function of emulsifiers in these products is, primarily, to aid in the forma

tion and stabilization of the emulsions. A secondary function, which is claimed

by many manufacturers of emulsifiers, is the effect that emulsifiers have on the

heat stability of milks and milk proteins.


7.8.1 Recombined Milk

Recombination of dairy ingredients into milk products is a popular and viable al

ternative to the export/import of fresh dairy products. It is particularly important

in countries where, for various reasons (e.g., transport delays, high temperatures),

the shelf life of fresh products prohibits their importation or local production.

In such cases, dried dairy ingredients are recombined close to the point of

sale, so as to reduce these problems.

Two approaches to recombining of whole milk can be used:

l. Recombination of anhydrous milk fat (AMF), skim milk powder (SMP),

and water

2. Reconstitution of whole milk powder (WMP) with water

In the past the latter process was, generally, less popular because of prob

lems with the oxidative stability of the fat in the powder during storage.

Advances in gas packing of powders, more regular shipping, and use of cooler

storage facilities have removed this obstacle. Zadow (1982) noted that the

choice of whether to recombine or reconstitute WMP depends on the export

strategy of a particular manufacturer. During the late 1970s, an increase in the

production of reconstituted WMP was seen. This corresponded to a change

from a butter!SMP-orientated export industry to a cheese/WMP-orientated ex

port strategy in countries such as New Zealand and Australia (Zadow, 1982).

In the recombination process, AMF, SMP, and water are recombined to give

a product with the same fat and protein content as whole milk.

The recombination process has been described by Kieseker (1983). The skim

milk powder is dissolved in the water at 40 to 55°C. The fat is added in a molten

state, and the mixture is homogenized at 14.0 to 17.5 MPa for the first stage and

at 3.5 MPa at 55 to 60°C in the second stage. The milk is then subjected to one

of three heat treatments: pasteurization at 72.2°C for 15 seconds; UHT process

ing at 135 to 150°C for 2 to 5 seconds; or in-can sterilization (e.g., 120°C for lO

minutes). UHT processing can be by either direct steam injection for rapid heat

ing or indirect heating in a plate or tubular heat exchanger.

Many manufacturers add low molecular weight emulsifiers to the formulation,

particularly mono- and diglycerides (Zadow, 1982; Kieseker, 1983; Sjollema,

1987). Emulsifiers in the form of phospholipids can also be added through the

practice of replacing up to 20% of the SMP with buttermilk powder (BMP)

(Zadow, 1982; Kieseker, 1983; Sjollema, 1987) to give an improved taste.

It is claimed that emulsifiers aid in the formation of the milk fat emulsion


during homogenization. Recent research by Mayhill and Newstead (1992), how

ever, suggests that little benefit in terms of emulsion formation and stability is

gained by their addition. In the case of mono-/diglyceride emulsifiers, it appears

that tradition dictates their presence in the formulation. It is possible that any re

duction in creaming due to reduced fat-droplet size in the presence of emulsifier

is cancelled out by reduced emulsion stability caused by protein displacement.

7.8.2 Evaporated and Concentrated Milks

Evaporated and concentrated milks are produced by removal of water from nat

ural or recombined milks. The technology used to make these products includes

evaporation under reduced pressure, reverse osmosis, ultrafiltration, and freeze

concentration (Knipschildt and Anderson, 1994; Varnan and Sutherland, 1994).

These concentrated milk products are more susceptible to heat coagulation,

when UHT processed or sterilized, than are normal concentration milks.

It has been known for some time that the heat stability of skim milk can be

altered by surfactant molecules (Singh and Creamer, 1992). Anionic surfac

tants such as SDS have been shown to shift the maximum in the heat stabil

ity/pH profile of skim milk to more acidic values and to give a marked increase

in maximum heat stability (Fox and Hearn, 1978). Cationic surfaetants such as

CTAB move the maximum heat stability to more alkaline values and give only

a slight improvement in heat stability at the maximum (Pearce, 1978; Shalabi

and Fox, 1982). The mechanism by which these changes occur is not known

for certain. It has been suggested that binding of the surfactant to casein mi

celles alters the surface charge, which leads to changes in heat stability (Fox

and Hearn, 1978; Pearce, 1978; Shalabi and Fox, 1982). This view is sup

ported by the fact that nonionie surfaetants such as Triton X and Tween 80

have no effect on the heat stability of skim milk (Fox and Hearn, 1978).

Research into the effect of addition of SDS and CTAB on the heat stability of

milk proteins is useful only in helping to understand the process of heat coag

ulation. These surfactants cannot be added to milk products. In addition to

this, in most concentrated milk products and in whole milk, the fat globules

play a role in heat stability. Surfaetants would interact with both the fat-droplet

surface and the milk proteins. This makes the process of heat coagulation in

fat-containing milks more complicated than in skim milk.

The milk fat globule membrane is known to play a role in the heat stability of

milk. In nonhomogenized whole milk the fat globules have little effect on heat

stability (Singh and Creamer, 1992). However, after homogenization the heat eo-


agulation time decreases with increasing homogenization pressure (Singh and

Creamer, 1992). Obviously, this is an important observation since homogeniza

tion of milk is often essential so as to give adequate creaming stability.

It has been known for some time that lecithin can be used to increase the

heat stability of homogenized and concentrated milks (Maxcy and Sommer,

1954; Leviton and Pallansch, 1962; Hardy et al., 1985; Singh and Tokley,

1990; Singh et al., 1992). The mechanism oflecithin action has as yet not been

elucidated. Lecithin is known to displace protein from the fat-droplet surface

(Courthaudon et al., 1991; Dickinson et al., 1993a; Dickinson and lveson,

1993) and to complex with milk proteins (Barratt and Rayner, 1972; Korver

and Meder, 1974; Hanssens and van Cauwelaert, 1978). Hardy et al. (1985)

and McCrae and Muir (1992) believe that lecithin is incorporated into the ad

sorbed layer during and after homogenization. McCrae and Muir (1992) also

believe that lecithin/protein interactions play a role in heat stability of concen

trated milks. Singh et al. (1992) have put forward the view that lecithin may

promote the formation of a complex between K-casein in the micelles and ~

lactoglobulin. The formation of the same complex can be promoted by preheat

ing concentrated milks prior to the main heat treatment. This has been shown

by Newstead et al. (1977) to have a stabilizing effect on the heat stability of re

combined evaporated milk. It is interesting to note that, despite evidence of

lecithin/protein interactions, Singh et al. (1992) have shown that the heat sta

bility of skim milk is unaffected by lecithin addition. This is powerful evi

dence for the main stabilizing effect being fat-droplet based.

7.9 Other Dairy Applications of Emulsifiers Emulsifiers have been added to other dairy products to exploit functional prop

erties not normally associated with such emulsifiers. In recombined butter,

phospholipids are added as antispitting agents, to prevent fat spitting during

heating, and monoglycerides have been claimed to provide better "stand-up"

properties during storage (Kieseker, 1983).

Both sucrose esters and glycerol esters of fatty acids (monoglycerides) are

finding a wide range of novel uses. In addition to being good emulsifiers for use

in ice cream (Bucket al., 1986), they are known to improve the mouthfeel in

yoghurt (Farooq and Haque, 1992), inhibit microbial growth (Conley and

Kabara, 1973; Kato and Shibasaki, 1975; Shibasaki, 1979; Beuchat, 1980;

Kabara, 1983; Tsuchido et al., 1987), enhance the thermal death rate of bacte-


ria and bacterial spores (Tsuchido et al., 1981; Tsuchido et al. 1983), and in

crease the heat stability of bovine serum albumin (Makino and Moriyama,

1991 ). It appears that these functions are a result of their ability to bind to pro

teins (Clark et al., 1992; Fontecha and Swaisgood, 1994).

7.10 Summary Emulsifiers are very versatile food additives. They can be used as aids to

emulsion formation (e.g., in coffee whiteners/creamers and recombined prod

ucts), or in contrast, as emulsion destabilizers as in ice cream, whipping

cream, and whipped toppings. These two functions rely on the classical ability

of emulsifiers to act as surface-active agents. In this way they can influence the

formation and stabilization of the fat-droplet adsorbed layer and the composi

tion of this layer. This ability of emulsifiers to displace protein from the fat

droplet surface also, probably, accounts for the increase in heat stability of

concentrated milks when phospholipids are added.

In a similar vein, displacement of adsorbed caseinate by GMS in cream

liqueurs can be used to give increased acid stability to these products. A sec

ondary function of the GMS in cream liqueurs is its ability to interact with pro

teins, thereby forming a weak gel in the aqueous phase. The associated increase

in viscosity gives improved creaming stability. The ability of the emulsifier SSL

to interact with the proteins in caseinate is also exploited in coffee whiteners.

The replacement of sodium caseinate in powdered coffee whitener is achieved

by using SSL. It has been hypothesized (Leo and Betscher, 1971) that this is pos

sible because of the increased mechanical strength of a protein/SSL adsorbed

layer caused by emulsifier/protein interactions.

In processed cheese, the ability of charged emulsifiers to interact with proteins

in the cheese matrix may prove a useful way of controlling cheese texture. This

would introduce a way of reducing the concentration of emulsifying salts such as

mono- and polyphosphates. The final, but very important, function of some emul

sifiers is their ability to act as initiators of fat crystallization. This is a particularly

important function in whipped products, and in combination with protein dis

placement forms the basis of the formation of the whipped foam structure.

A wide range of emulsifiers allowed for food use can be added to achieve the

above effects. Of late, consumer opinion has been focused on the "unnatural"

nature of synthetic emulsifiers. There is a slow push toward the replacement of

synthetic emulsifiers with natural emulsifiers such as milk and soy phospho-


lipids, and milk fat-derived mono- and diglycerides. The future may see a large

increase in the use of products such as BMP, which is rich in natural milk phos

pholipids as well as protein, and milk fat that has been enriched in mono- and

diglycerides by processes such as controlled glycerolysis of triglycerides.

Acknowledgments I would like to thank the following people: Drs. Jeremy Hill, Peter Munro, and

Mike Boland (NZDRI) and Dr. Susan Euston (Massey University) for proof

reading this manuscript; Dr. David Newstead (Milk Powder Technology

Section, NZDRI) for valuable discussion and comments on UHT fouling and

heat stability of concentrated milks; Dr. Siew-Kim Lee (Cheese Technology

Section, NZDRI) for comments on and suggestions for the section on processed

cheese; Mr. Bing Soo (Food Systems Section, NZDRI) for supplying informa

tion on coffee whitener/creamer; Mr. Tony McKenna (Food Science Section,

NZDRI) for supplying the electron micrographs used in Figures 7.1, 7.4, and

7.5; Vanessa Ellery (Graphics Unit, Information Centre, NZDRI) for prepara

tion of Figures 7.2, 7.3, 7.6, and 7.7. Finally, I would like to thank the New

Zealand Dairy Board for permission to publish this work.

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EIGHT

Applications of Emulsifers in Baked Foods

Frank T. Orthoefer

8.1 Introduction The development of emulsifiers or surfactants for bakery products has followed

the development of shortenings. The term "shortening" was initially used to re

fer to the fats used to "shorten" or tenderize baked foods. The composition of

shortening has progressed from natural fats to blends of oils, hydrogenated

fats, and hard fats. Shortenings may include additives such as emulsifiers, an

tioxidants, antifoams, and metal scavengers. In addition to their tenderizing

function, the shortening affects structure, stability, flavor, storage quality, eat

ing characteristics, and eye appeal of baked foods. Many of the functional ef

fects are due to or enhanced by the emulsifier added via the shortening. This

chapter will concentrate on the role of the emulsifier in baked foods.

8.2 History of Emulsified Shortenings Historically, animal fats were used for bakery products because of their natural

plasticity and flavor (O'Brien, 1996). Lard was the preferred animal fat for its

pleasing flavor. Faced with excess supplies of cottonseeds and cottonseed oil,

vegetable shortenings were invented by the cottonseed industry early in this

211


century. Initially, cottonseed oil was blended with lard as a "lard compound"

or simply compound shortening. Hydrogenation as a process was invented in

1910. This new process allowed the development of substitutes for the semi

solid (plastic) animal fats and permitted the creation of products with im

proved functional properties.

Along with this modification technique came improved methods for pro

cessing the oil, including refining, bleaching, and deodorization. The products

possessed improved oxidative stability, uniformity, and enhanced perfor

mance. With the development of lipid chemistry came methods for alcoholysis,

esterification, interesterification, and isomerization. These advances in lipid

chemistry brought new emulsifiers and shortening formulations. High-ratio

shortenings were introduced about 1933. These contained mono- and diglyc

erides that brought about finer dispersion of fat particles in the dough, giving

strengthened cake batters. These finer particle dispersions allowed higher

sugar levels, with increased water added, to produce sweeter tasting and more

tender cakes. High-ratio shortenings possessed excellent creaming properties.

Moist, higher volume, fine-grained, even-extured cakes were produced. Icings

were improved as well (Hartnett, 1977).

Emulsifier development also proceeded as well in the 1930s (Stauffer, 1996).

Specialty shortenings were the result. Commercial layer cakes, pound cakes,

cake mixes, creme fillings, icings, whipped toppings, bread, and sweet dough

shortenings were created. The development of specialty products resulted in im

provements in processing and improved product performance for the retail, food

service, and food-processing industries. In addition to the traditional plastic

shortenings, liquid shortenings, fluid shortenings, and powdered products were

produced. All these shortenings involved formulation with emulsifiers.

The terms emulsifiers and emulsifying agents, surfactants and surface-ac

tive agents are used interchangeably in the literature. The terms "emulsifier"

and "emulsifying agents" are, strictly speaking, chemicals or compounds ca

pable of promoting emulsification or stabilization of emulsions by their effect

on interfacial tension. Surfactants for foods may include not only emulsifiers

but also compounds with other functions such as protein or starch interaction.

In most cases, the terms are used interchangeably.

The role of the emulsifier and that of the shortening are intimately bound in

bakery products. Generally, the food emulsifiers for bakery products supple

ment and improve the functionality of a properly developed shortening.

Emulsifiers act as lubricants, emulsify fat in batters, build structure, aerate,

Applications of Emulsifiers in Baked Foods 213

improve eating quality, extend shelf life, modify crystallization, prevent stick

ing, and retain moisture. A list of emulsifiers commonly used in shortenings is

given in Table 8.1. The selection of or addition of an emulsifier to a shortening

base may significantly change the application of the shortening (Table 8.2).

Table 8.1 Emulsifiers used in shortenings

Mono- and diglyceride Lecithin Lactylaled monoglyceride Calcium stearyllactylate Sodium stearoyllactylale Propylene glycol monoesters Diacetyl tartaric monoglycerides Ethoxylaled monoglycerides

Sorbilan monostearate Polysorbate 60 Polyglycerol esters Succinylated monoglycerides Sodium stearoyl fumarale Sucrose esters Stearoyllactylate

Table 8.2 Examples of nonemulsulfied and emulsified shortenings

N onemulsified

All-purpose Puff pastry Pie crust Cookie Danish roll-in Donut fry

Emulsified

Cake and icing Household Filling Cake mix Yeast raised Specialty cake

8.3 Emulsifier Function in Baked Goods Baked goods without emulsifiers have been described as tough, dry, stale,

leathery, or tasteless (Brandt, 1996). Current processing, distribution, and

storage of baked goods requires the use of additives that maintain quality and

freshness. Emulsifiers are commonly used in many food products. These sup

plementary materials or food additives are used to

• Compensate for variations in raw materials

• Guarantee constant quality

• Produce attractive products

• Preserve freshness and eating properties

• Facilitate processing (Schuster and Adams, 1984)


Emulsifiers in nearly all applications refers to their ability to emulsify oil in water. This is also true in some bakery applications. However, emulsification is often of secondary importance. Activity as surface-active agents is most desirable. Starch complexing, protein strengthening, and aeration are the primary functions. Fat sparing effects are also of importance. The average composition

of wheat flour is

Fraction Percent

Starch 70.0-75.0 Protein 11.5-12.5 Pentosan 2.0-2.5 Lipid l.0-1.5 Crude fiber 0.2 Ash 05

The interactions between proteins, carbohydrates, and lipids are significant for the processing of wheat flours. The interactions between emulsifiers and flour components are multifaceted and account for the improved functionality and performance of baked products.

Surfactants used in bakery products are regulated in most countries. Each country may differ in their regulations but the usage level and applications are well defined. European Economic Community (EEC) number and U.S. FDA Code of Federal Regulation (21CFR) for the most common food emulsifiers are shown in Table 8.3. The specification and assay procedures of all emulsifiers presented in this chapter are published in the Food Chemicals Codex (Organization of the Food Chemicals Codex 1981).

Baked products are the largest users of food emulsifiers. Yeast-raised and chemically leavened products are the most important segments. Other uses include cookies, crackers, pasta, and snacks. Recent figures indicate that about 400 million pounds of emulsifiers are used in the food industry. The bakery industry accounts for 50% of the total food emulsifier market (Brandt, 1996). Annual growth in the production of food emulsifiers is estimated at about 3%.


Table 8.3 Regulatory status of emulsifiers. (From O'Brien, 1996, p. 517.)

U.S. FDA EEC Emulsifier (2ICFR) nlllllber

Monoglycerides and diglycerides (GRAS) 182.4505 E47l Succinyl monoglyceride 172.830

Lactylated monoglyceride 172.852 E472 Acetylated monoglyceride 172.828 E 472

Monoglyceride citrate 172.832 E472 Monoglyceride phosphate (GRAS) 182.4521

Stearyl monoglyceride citrate 172.755 E472

Diacetyl-tartrate ester of monoglyceride (GRAS) 182.4101 E472 Polyoxyethylene monoglyceride 172.834

Propylene glycol monoester 17.854 E477

Lactylated propylene glycol monoester 172.850 Sorbitan monostearate 172.842 E491

Polysorbate 60 172.836 E435

Polysorbate 65 172.838 E 436

Polysorbate 80 172.840 E433

Calcium stearoyllactylate 172.844 E 482

Sodium stearoyllactylate 172.846 E 481

Stearoyllactylic acid 172.848 Stearyl tartrate E483

Sodium stearyl fumarate 172.826

Sodium Iaury! sulfate 172.822 Dioctyl sodium sulfosuccinate 172.810

Polyglycerol esters 172.854 E 475 Sucrose esters 172.859 E 173

Sucrose glycerides E474 Lecithin (GRAS) 184.1400 E322 Hydroxylated lecithin 172.814 E322 Triethyl citrate (GRAS) 182.1911

8.4 Role of the Shortening A shortening when mixed into a dough interupts the development of the gluten

structure. Literally, the structure is "shortened" and the baked product is ten

der. Overall, the shortening also contributes to the quality of the finished prod

uct by imparting a creamy texture and rich flavor, tenderness, and uniform

aeration for moisture retention and size expansion. Fat-based products are for

mulated and processed for plasticity to allow spreadability and to disperse


thoroughly and uniformly in a dough, icing, or batter over a wide temperature

range. The ability of the fat to disperse in streaks and films helps to lubricate

the structure of the dough during mixing and thereby prevents the starch and

protein components from compacting into a dough mass.

The characteristics of the fat that are important for shortening formulations

include melting point, stability, solid fat index, and plasticity. Plasticity is used

to define the characteristics of shortening that are functionally most important.

Shortenings are processed to various plasticity ranges (Weiss, 1981).

Narrow-plastic-range products have a steep solids profile and melt rapidly.

These are commonly used in cream icing products or as filler fats for hard

cookies where melting near body temperature is required. Wide-plastic-range

shortenings contain 15 to 30% solids over a broad temperature range, and re

sist breakdown during creaming. Their plastic nature enables them to spread

readily and combine thoroughly with the other solids or liquids without crack

ing, breaking, or having liquid oil separating from the crystalline fat.

Commercial products are prepared by carefully cooling, plasticizing, and tem

pering correctly formulated blends of melted fats and oils.

Crystal size has a major influence on the rheological properties of plastic shortenings. A small crystal size with a large surface area is required to effec

tively bind the liquid oil present in a shortening formulation. Typical crystal

sizes are from 5 to 9Jlm (P. Chawla and J.M. deMan, 1990).

Crystal size is controlled by source of the oil (O'Brien, 1996). The smaller crys

talline form is referred to as W and the larger form is ~- Plastic shortenings in the W configuration consist of small, uniform, needle-like crystals with a smooth tex

ture and the ability to aerate well, and they have excellent creaming properties.

8.5 Role of the Emulsifier The emulsification of the shortening in bakery products is promoted with the

addition of surface-active agents (surfactants, emulsifiers). Much of the work

on shortenings has centered on the addition of an emulsifier or emulsifier sys

tem to an all-purpose shortening base, although specialty liquid, narrow-plas

tic-range, and special-purpose emulsified products have been produced.

Emulsifiers are used extensively in bakery products, especially breads and

cakes. Some of the benefits are

l. Increased shelf life

2. Imparted tenderness and improved flavor release


3. Reduced mixing time and improved mixing tolerance

4. Improved machinability

5. Improved gas retention

6. Improved water absorption

7. Improved volume

8. Improved hydration rate of flour and other ingredients

9. Better texture and symmetry

10. Reduced egg and shortening usage

8.5.1 Monoglycerides and Derivatives

Monoglycerides are prepared by reacting glycerine with edible fats and oils or

fatty acids in the presence of a catalyst (Henry, 1995). The important charac

teristics are melting point and monoglyceride content. The monoglyceride con

tent varies from 40 to 95%. Two crystalline forms are generally present: alpha

and beta. The alpha form is the most functional in bakery products. The major

variables involved in the production of monoglycerides are source of the fat,

monoglyceride content desired, iodine value or degree of unsaturation, and

fatty acid composition. Approximately 40 million pounds (18 million kg) of

monoglycerides are used in the United States in yeast-raised bakery products

(WH. Knightly, 1988). An equal amount was believed to be used in cakes, ic

ings, and other applications. In addition to the improved aeration and sugar

holding capacity of cakes formulated with monoglycerides, breads were found

to have an improved shelf life due to retarded staling rate. Various techniques

were applied to improve monoglyceride formulations including other emulsi

fier types. Today, plastic, hydrated, powdered, and distilled monoglycerides

are used in bakery applications.

In addition to their antistaling effects, monoglycerides in bakery products

result in

• Reduction of interfacial tension

• Improved dispersion of ingredients

• Increased aeration

• Greater foam stability

• Modification of fat crystals

Several derivatives of monoglycerides are prepared for bakery applications

(Figure 8.1). These are of two general types. One is considered as dough


When R equals

HO-

CH CH-C00-

31

OH

CH3 -coo-

OOCCH

I -QOC-cH-CH-COQ-

1 OOCH3

H-

Emnlsifier

Glycerol monosterate (GMS)

Succinyl monoglyceride (SMG)

Lactylated monoglyceride (LacGM)

Acetylated monoglyceride (AcMG)

Diacetyl-tartaric acid ester of

monoglyceride (DATEM)

Polyoxyethylene monoglyceride or

ethyoxylated monoglyceride

(EMG)

Propylene glycol monoester

(PGME)

Figure 8.1 Monoglycerides and derivatives.


strengtheners and includes SMG (succinylated monoglycerides), EMG

(ethoxylated monoglycerides), and DATEM (diacetyl tartaric acid esters of

monoglycerides). They also are used as emulsifiers, starch- and protein-com

plexing agents, and foam stabilizers. The other is the alpha-tending emulsifiers

and includes GMS (glycerol monosterate), LacGM (lactylated monoglycerides),

AcMG (acetylated monoglycerides), and PGME (propylene glycol monoesters).

The alpha-tending emulsifiers, normally used in cake production, contribute to

the emulsification of the shortening in the water phase as well as incorporating

air into the fat phase. These are believed to form a solid film at the oil/water in

terface resulting in a stable emulsion and preventing the liquid oil from inter

fering with aeration during cake batter mixing.

8.5.2. Sorbitan Emulsifiers

Sorbitan monostearate is an oil-soluble, low-HLB nomomc emulsifier.

Reaction of the sorbitan esters with ethylene oxide results in the formation of

the polyoxyethylene sorbitan monostearate or polysorbate emulsifiers (Figure

8.2). Sorbitan esters are excellent emulsifiers for icings, improving aeration,

gloss, and stability. They function as emulsifiers, aerating agents, and lubri

cants in cakes, toppings, cookies, and crackers. The polysorbate 60 emulsifier

is used as a dough strengthener at about 0.2% of flour weight. Polysorbate 60

is also used in combination with glycerol monostearate and propylene glycol

monostearate in fluid cake shortenings.

8.5.3 Anionic Emusifier

The anionic emulsifiers include SMG, DATEM (see (Figure 8.1), and other lac

tic acid derivatives (Figure 8.3). Sodium stearoyl lactylate (SSL) is the most

widely used in the United States. The calcium version, insoluble in water, is

also widely used. Both are dough strengtheners.

SSL may be added as a stabilizer to hydrated monoglyceride preparations.

Other benefits from the lactic acid emulsifiers are antistaling, aeration, and

starch and protein complexing.

8.5.4 Polyhydric Emulsifiers

The polyhydric emulsifiers include the polyglycerol esters and sucrose esters

(Figure 8.4). Both have multiple applications as emulsifiers for foods in gen

eral and in bakery products, particularly the sucrose esters. The sucrose esters

are common food emulsifiers in Japan. They provide emulsifying, stabilizing,


Where

R1 = H (CH2CH20)n

R2 = H

R3 = H

Sorbitan monostearate

Polyoxyethylene (20) sorbitan monostearate

(Polysorbate 60)

R1 = H(CH2CH20)n- Polyoxyethylene (20) sorbitan tristearate R2 and R3 = H3C (CH2)16CO- (Polysorbate 65)

Figure 8.2. Sorbitan esters and derivatives.

and conditioning effects in baked goods. Eight hydroxyl groups that may be es

terified are present in sucrose. As expected, the degree of esterification affects

the hydrophylic lipophilic balance (HLB) of the sucrose ester (Table 8.4). The

product is considered a noncaloric fat substitute when six or more of the hy

droxyls are sterified (Olestra™ by Proctor & Gamble).

8.5.5 Lecithin

Lecithin is a coproduct of soybean oil and, to a limited extent, of other vegetable oil refining (com oil and rapeseed oil). It is obtained by water-washing crude vegetable oil and separating and drying the hydrated gums. The crude material is very dark colored and viscous, consisting of a variety of phospholipids (Figure 8.5). In addition to the phospholipids, these are also present


CH3

Sodium stearyllactylate (SSL) {also in calcium form)

0 0 II II _

H C (CH ) -0-c -CH-CH-C -o8NJ±) 3 2 17

Sodium stearyl fumarate

Sodium lauryl sulfate (SDS)

Figure 8.3. Anionic surfactants.

triglycerides, tocopherols, and glycolipids. Various purified grades are pro

duced by bleaching and fractionating as well as by chemical modification

(Schmidt and Orthoefer, 1985). Commercial lecithin products are specified

based on their acetone-insoluble fraction (a measure of the phospholipid con

tent), viscosity, and color. Lecithin is present in other sources such as egg yolk,

butter, beans, nuts, etc. Lecithin is usually the least expensive emulsifier.

8.6 Emulsifier Interaction with Bakery Components

Emulsification and lubrication by the emulsifiers accounts only partially for

the beneficial effects observed when they are added to baked products.

Proteins and lipids also contribute to the functional properties of the flour.

Emulsifiers have been shown to interact with the various components present

as well as with added ingredients.


HO

Figure 8.4

8.6.1 Starch

OH

I CH2-CH-cH3

I [0-CH -CH-CH -OJ 2

1

2 n

0 II

OH

0-H C-HC-CH 2 I 2

OH

Polyglycerol monostearate

CH2-0-C -(CH3)16CH3

0 0

H OH OH H

Sucrose diester

H

Starch exists in a helical, coiled configuration with about six residues per tum.

This structure is basically a hollow cyclinder that has a hydrophyllic outer sur

face and a hydrophobic inner core. The inner space is about 45 nm in diame

ter. Straight-chain, alkyl molecules such as stearic acid will fit in the inner

Applications of Emulsifiers in Baked Foods

Table 8.4 Sucrose ester surfactants. (From Stauffer, 1996, p. 576.)

Percent Percent Percent Percent monoester diester triester tetraester

71 24 5 0 61 30 8 1 50 36 12 2 46 39 13 2 42 42 14 2 33 49 16 2

CH2-0-R1

I

r~~ CH -0-P-Q-R

2 lb 3

a

(R 1 and R2 are fatty acids)

If R2 = Choline ethanolamine inositol serine

Then Phosphatidylcholine

Phosphatidylethanolamine

Phosphatidyl inositol

Phosphatidylserine

Figure 8.5. Lecithin.

HLB

15 13 ll 9.5 8

6

223

space. The n-alkyl portion of emulsifiers such as present in GMS form a com

plex with the helical regions of the starch. It is this complex that is thought to

retard starch crystallization in bread, often called "retrogradation," slowing

the staling process.

The influence of emulsifiers on starch consists of (i) affect on the rate of

gelatinization, the gelatinization temperature, the peak viscosity, and the gel


strength and (ii) complex formation by the starch molecules. In studies of

starch pastes with monoglycerides, the maximum complexation occurs with

monopalmitin (Lagendijk and Pennings, 1970). Longer and shorter saturated

fatty acid monoglycerides reacted to a lesser extent. Unsaturated fatty acid

monoglycerides react to a lesser extent because of the bend in the fatty acid

chain due to the unsaturated linkage (Hahn and Hood, 1987).

Surfactants modify the gelatinization behavior of starch. DATEM is gener

ally found to be less interactive than GMS or SSL. GMS raises the swelling

temperature and results in increased paste viscosity. SSL also increases paste

viscosity (Schuster and Adams, 1984). Overall the interaction between emulsi

fier and starch takes place at the surface of the granule, and the starch/surfac

tant complex apparently stabilizes the granule, retarding water penetration and

swelling as the temperature is increased.

During breadmaking, only small amounts of emulsifiers are bound to starch

in the sponge stage and during mixing. Binding does not occur until the tem

perature is increased to near the gelatinization temperature. The formation of

starch complexes is ascribed principally to the amylose portion of the starch.

Both the degree of interaction and solubilities of the complexes are dependent

upon the emulsifier type.

8.6.2 Protein

The wheat flour proteins, gliadin and glutenin, form a viscous, colloidal com

plex known as "gluten" when mixed into a dough. Lipids are also involved in

the formation of the gluten complex. The properties of the gluten are influ

enced by the lipids and the emulsifiers present. Lipophilic parts of surfactants

interact with hydrophobic regions of proteins, contributing to unfolding or de

naturation of the protein. Generally, surfactants contribute to protein denatura

tion, enhancing interfacial absorption and emulsion stabilization.

Most dough strengtheners are anionic surfactants. The association of the

lipophilic portion to the hydrophobic protein portion incorporates the negative

charge into the complex, promoting aggregation in the dough. The overall ef

fect is aggregation of the gluten protein and an increase in dough strength.

The ionic surfactants induce protein insolubilization, resulting in increased

viscosity and elasticity of the dough. Nonionic surfactants disrupt the hy

drophobic portion of the protein, leading to reduced dough viscosity and elas

ticity and increased protein extractability. A blend of emulsifiers generally

provides the best dispersibility and functionality.


8.6.3 Lipids

Wheat flour contains 1.4 to 2.0% lipids divided into free (0.8 to 1.0%) and

bound (0.6 to 1.0%) forms. They may be further divided into nonpolar (50.9%)

and polar (49.1 %) forms. The bound lipids exist as starch inclusion com

plexes. The nonstarch lipids, about 85% of the total, participate in the chemi

cal, physical, and biochemical processes important for the preparation of

baked goods. The nonstarch lipids consist of glycolipids, phospholipids, and

stearyl esters. Interaction between nonstarch lipids and emulsifiers is limited.

Likely, added lipids merely influence or substitute for each other.

Non-polar-lipid addition to untreated flour gives a deterioration of baking

properties (Schuster and Adams, 1984). Addition of polar lipids to untreated

flour increases loaf volume in breadmaking. The improvement is likely based

on the effects of galactolipids and phospholipids. Emulsifiers may interact with

the water phase of the dough, forming associated lipid-water structures with

free polar flour lipids (Krog, 1981). Emulsifiers may compete with naturally

occurring lipids in wheat flour for the reactive groups of the wheat flour dough.

Their effect on protein components was modulated as a consequence.

8.7 Applications in Baked Goods 8.7.1 Yeast-Raised Products

The functions of emulsifiers in yeast-raised products are dough conditioning

and strengthening as well as crumb-softening. Emulsifiers are also used.

8.7.1.1 Dough Conditioning. There is no precise definition of dough condi

tioners. The term is commonly used to describe adjuncts that aid in the devel

opment of less tacky, more extensible doughs that are processed through

machinery without tearing or sticking or that result in a product of finer crumb

structure and improved volume and symmetry. These may be summarized as

• Increased mixing and machining tolerance of the dough

• Increased tolerance to ingredient variations

• Diminished knockdown during handling

• Assists maximum dough absorption

• Reduced shortening requirements

• Improved loaf volume, structure, texture, and other quality characteristics


• Extended keeping quality

• Facilitates variety bread production

In the production of yeast-raised products, the mixing of the dough results

in gluten/gluten bonding through disulfide linkages. Development of the link

ages is often incomplete, resulting in a weak dough structure. Gas that is pro

duced by the yeast escapes through the weak portion of the gluten films. Cells

having weak gluten walls have a tendency to collapse.

Dough-strengthening emulsifiers increase the degree of gluten/gluten binding

sites and/or bridges that supplement disulfide linkages. This results in stronger,

developed gluten films. As a result the benefits from dough conditioners are

• Improved tolerance to variation in flour quality

• Drier doughs with greater resistance to abuse

• Improved gas retention giving lower yeast requirements, shorter proof times,

and greater finished product volumes

• Uniform internal grain, stronger side walls, and reduction of "cripples"

• Reduced shortening requirements without loss of volume, tenderness, or

slicing ease

The dough conditioners recognized as highly functional dough strengthen

ers are calcium stearoyl lactylate, ethoxylated monoglycerides (EOM), poly

oxyethylene sorbitan monostearate (PS 60), succinylated monoglycerides

(SMG), and sodium stearoyl lactylate (SSL) (Tenny,l978). Comparative loaf

volumes found for the various conditioners are shown in Figure 8.6, for fully

proofed dough shocked to mimic abuse in production.

Dough conditioners are available in plastic, powdered, and liquid forms

that may he added to the sponge, brew, or dough. The use levels are normally

in the range of 0.25 to 0.5% of flour weight. Often the dough conditioners are

combined with crumb softeners. For example, EOM, PS 60, and SMG are

blended with monoglycerides, a crumb softener.

8.7.1.2 Crumb-Softening. Emulsifiers that complex with starch are referred

to as "crumb softeners." Although there is a controversy over the mechanism of

activity, evidence exists that a primary effect is to complex with amylose, the lin

ear starch fraction. The staling phenomena is generally believed to result from

amylose crystallization. Amylose leaches from the starch granule during dough

preparation and baking. The amylose polymers associate upon cooling, forming a

rigid gel within lO to 12 hours. Amylopectin, the branched chain starch fraction,

2900

2800

2700

2600

_fl

- 1- - '-.:

2500

00 .10 .25 .50 NO CSL

ADD


r----- f-----

- :-- f- 1--

I

~l - :'- r--: :-I!

. 10 .25 .50 .10 .25 .50 .10 .25 .50 EOM PS-60 SMG

%Flour, wt

~ r---:

•

.10 .25 .50

SSL

1-

f-

f-

1---

Figure 8.6 Comparative loaf-volume response produced on abused dough by CSL, EOM, PS-60, SMG, and SSL. (From Tenney, 1978.)

crystallizes more slowly, resulting in firming of the bread in 3 to 6 days. Crumb

softeners tend to result in less free amylose from the baking process; therefore,

less free amylose is avaliable to form a rigid gel. The emulsifier "softens" the ini

tial crumb. No change occurs with the amylopectin fraction with softener addi

tion. It gradually crystallizes to form a firmer texture. Treated bread stales at the

same rate as untreated bread in the case of amylopectin.

Comparison of softeners as a function of compressibility after 96 hours of

storage is shown in Figure 8. 7. The most effective softeners are the lactylates

and SMG. Plastic mono- and diglycerides and hydrated distilled monoglyc

erides are also effective. The polysorbate, EOM, and lecithin had little starch

complexing ability. There is an apparent dual functionality of conditioner and

softener for the lactylates and SMG.

Use levels of softeners vary with the market. The most commonly used crumb

softeners are the water emulsions, or hydrates, of mono-/diglycerides. The hy

drates contain 22 to 25% solids and are used from about 0.5 to l% of flour weight.

The hydrates are significantly more functional. Water-dispersible distilled mono

glycerides are also sold. These blends use sufficient unsaturated monoglycerides

to promote rapid hydration in the water of the sponge, brew, or dough.


180

170

160

150

140

130

12 o_

Crumb compressibility (0.1 mm)

I n ~ n 1 11 ~!I_ _Jl ~J- r-~ r-J r---. ; r---

j Jl JJ - ~- ~ r--- r--- -

NO ADD

.10 .25 .50

CSL

10.25.50

EOM

.10 .25 .50

PS-60

.10 .25 .50

SSL

10.25 .50

SMG

%Flour, wt

.10 .25 .50

Mo-Di

.10 .25 .50

LSC

.10 .25 .50 1.0

Dis. M . H.

Figure 8.7 Relative crumb-softening effect in bread by CSL, EOM, PS-60, SSL, SMG, Mo-Di (54% mono- and diglyceride), LEC (lecithin), and Dis. M.H. (22% solids distilled monoglyceride hydrate). (From Tenney, 1978.)

8.7.1.3 Emulsifier Blends. Lecithin has been used in breads and baked

goods longer than any other emulsifier. It was shown to give higher ductility

through interaction with the gluten. Other activity from the lecithin is delayed

staling and shortening reduction. A synergistic effect also occurs with lecithin

and monoglycerides. The monoglycerides produce better crumb grain, softer

bread, and higher loaf volumes. Ethoxylated monoglycerides with monoglyc

eride is an effective dough conditioner. The negative effects of liquid oils in

place of shortening in bread preparation is overcome with the combination.

DATEM also acts as a dough conditioner, shortening saver, and antistaling

agent in combination with glycerol monostearate. Others include SMG, su

crose esters, polysorbate 60, SSL, and CSL. The SSL and CSL can form com

plexes with gluten acting as a dough strengthener.

The direct and indirect action of the emulsifier begins with dough prepara

tion and ends with oven baking and storage (Figure 8.8). The first stage begins


Improvement of wettability Stabilization of distributed phases Mixing

Fermentation Scaling, kneading,

moulding

Baking

Storage

Decrease of mixing time and mixing speed Reducing shortening levels Improvement of mixing tolerance Improvement of machinability

Improvement of gas-retaining properties Shorter fermentation Greater shock-tolerance

Improvement of gas-retaining properties Improved loaf volume Better texture Better crumb grain Better uniformity Decrease of water loss

Improvement for crumbsoftness Longer shelf life

Figure 8.7 Influence of emulsifiers on production and quality of baked products. (From Schuster arul Adams, 1984.)

with wetting, and dispersing activity then follows with interactions with flour

components during mixing and in the baking process itself.

8.7.2 Chemically Leavened Products

8.7.2.1 Cakes. The role of emulsifiers in layer cakes or snacks cakes is di

verse. They include aeration, emulsification, and crumb-softening.

The aerated structure of batters depend on whipped-in-air and carbon diox-


ide from the leavening agent. The use of emulsifiers lowers the surface tension

of the aqueous phase, improving the amount of air that can be whipped into the

batter. Large amounts of finely divided air cells are important for development

of uniform grain (Randleman et al.,1961). The dissolved C02 evolves at air

cell sites and does not spontaneously form bubbles. If the original batter con

tains many small air cells, the final cake will have a larger volume and fine

(close) grain. The creaming of the sugar and shortening have a major influence

on air incorporation. The incorporation of monoglycerides in the plastic short

ening (2 to 5% alpha-monoglycerides) ensures numerous small air cells being

created during beating or creaming.

Cake batter is, of course, an aerated emulsion. The integrity of the air cells

determines cake volume and uniformity. Shortening is an antifoam that disrupts

foam cells. Emulsifiers, however, coat the exterior of the fat particles protecting

the integrity of the air cell (Wooten, 1967). Proper emulsifier selection has per

mitted the use of liquid oil where only shortening could previously be used.

Light, tender, moist cakes are preferred by the consumer. Emulsifiers pro

vide the desired aeration, emulsification, and crumb-softening. Crumb-soften

ing in cakes is a function of moisture retention, shortening activity, and

starch-complexing. The starch-complexing is the same as for breads. The

emulsifiers complex with the starch to soften the product.

Several types of emulsifiers are used in cakes. Propylene glycol monoester

(PGME) is utilized at 10 to 15% of the shortening. Monoglycerides and mix

tures of lactated monoglycerides with PGME are also used in cake mixes.

In bakers' cakes, a large number of emulsifiers are used, depending on the for

mula, production equipment, and labeling requirements. With soybean oil as the

shortening, a hydrated blend of emulsifiers such as PS 60, SSL, sorbitan mono

stearate, and distilled monoglycerides work well. Fluid shortenings are produced

containing lactated monoglycerides. The traditional bakers' -cake system is a plas

tic shortening with 5 to 10% monoglycerides (3% alpha-monoglyceride content).

Packaged cake mixes often use emulsified PGME at 10 to 15% of the oil. The

cakes are unusually tender and are not suitable for commercial cake production.

Emulsified cake shortenings are also used for cake donuts. The degree of air

entrapment during the creaming phase determines the grain in the final donut.

8.7.2.2 Cookies and Crackers. Although emulsifiers are used to only a limited

extent in cookies and crackers, they play a significant role in (i) controlling

spread, (ii) improving cutting and appearance, and (iii) improving texture. The


limited use probably stems from the reluctance to change the successful for

mulas in this segment of the baking industry. New products utilizing emulsi

fiers are receiving greater acceptance since they have been shown to play

functional roles.

Certain emulsifiers have the ability to change the degree of spreading of

cookie dough as it is baked (Table 8.5). The effect likely occurs because of al

tering of the viscosity of the dough. Cookie dough with SSL shows increased

spread compared to a nonemulsified control (Rusch, 1981). The SSL may in

teract with the starch granule, delaying hydration of the granule and subse

quent gelatinization (Tsen et al., 1973).

Lecithin may be used to produce a drier dough that machines better and

that improves release from the rotary die surface. Use is from 0.25 to 0.7% of

the flour. Part of the effect may simply be reduction of available water because

of lecithin hydration.

Lecithin that is highly fluidized with other oils or fatty acids is widely used

as release agents in cookie baking due to improved release from rotary dies.

Heat-resistant lecithins such as those modified with acetic anhydride are espe

cially adaptable to the application. Lecithin is used in cookie and cracker for

mulations at 0.25 to 1.0% of flour weight. It may be added with the shortening

at the creaming stage or simply combined with the shortening when rotated.

Antistaling is of less significance in cookies and crackers since they are of

Table 8.5 Spread ratios of cookie doughs with different emulsifiers. (From Tsen et al., l973.)

Spread 0.5% additive ratio

Monoglyceride 8.3

Ethoxylated monoglyceride 8.8

Sodium stearoyl fumararale 10.4

Sodium stearoyllactylate 10.0

Sucrose monopalmitate 9.8

Sucrose mono- and distearate 9.6

Sucrose distearate 9.7

Sorbitan monostearate 9.2

Polyoxylated (20) sorbitan 9.3

monostearate Succinylated monoglycerides 9.2


lower moisture content. The greasiness of high shortening levels is reduced by

the addition of small amounts of lecithin. Lecithin in general gives a "drier"

dough with equivalent moisture and shortening levels. The drier dough is more

machinable. Other benefits attributed to lecithin are reduced mixing times and

dough development with more tender cookies.

SSL is promoted to improve the efficiency of shortening in cookie or cracker

formulations. SSL when incorporated into dough at 0.25% of the flour pro

duces a finer grained, more uniform pattern of surface cracks. The resistance

to shear (firmness) decreases, with improved eating quality, and permits short

ening reduction (Tenney, 1978). Levels are 0.25% SSL in cookies and 0.1% in

crackers based on flour weight.

8.7.3 Extruded Snacks/Cereals

Extrusion-cooked snacks, pastas, and cereals often include emulsifiers in the

formula. Gelatinization of the starch occurs during the cooking/extrusion step.

Monoglycerides and SSL have been found to reduce the energy required for

the extrusion and to obtain a desirable texture in the final product. When

monoglycerides are added, they influence the appearance and properties of the

extrudate such as smoothness of the extrudate surface and fine pore structure.

Use levels are typically 0.25 to 0.5% of the starch weight and is added at the

dough makeup stage.

8.7.4 Cream Icings

Cream icings are prepared by creaming sugar with fat, then adding flavor, egg

white, and perhaps a small amount of water. The emulsified shortening gener

ally contains 2 to 3% alpha-monoglyceride. Polyoxyethylene sorbitan mono

stearate at 0.5% is included in some icings to assist in air incorporation.

Propylene glycol esters when incorporated into the shortening produce icings

with excellent gloss and gloss retention.

8.7.5 Fat-Free Bakery Products

The fat-free or low-fat foods are marketed in almost every segment of the food

industry. In most instances, there is no one solution for removal of fats from the

formulation. Skillful formulation using fat replacers, emulsifiers, bulking

agents, flavors, and other ingredients has been applied to fat replacement.

Low-fat and fat-free cakes have been produced using additional emulsifiers

in conjunction with starch-based fat replacers and gums or hydrocolloids for


moisture retention and functionality. PGME and DATEM products have as

sisted in formula development.

Emulsifiers are not generally regarded as fat substitutes or replacers.

Emulsifiers affect the texture and mouthfeel by their effect on surface interac

tions. The caloric value of emulsifiers varies depending on their actual compo

sition and digestibility. They tend to have fat-like properties through their

hydration, water-binding, and dispersing effects in processed foods. The gen

eral functions of emulsifiers in low-fat or no-fat applications are to

• Prevent separation of components

• Reduce size of fat globules and improve dispersion of remaining fat

• Provide a fat-sparing action

• Provide texture perception of higher fat levels

• Texturize, provide lubricity

• Complex starches and proteins

Mono- and diglycerides are the most used emulsifiers. Distilled monoglyc

erides have a caloric advantage over the lower mono-containing preparations.

Other emulsifiers in reduced fat products include the polysorbates, polyglyc

erol esters, and sorbitan monoesters.

Many noncaloric fats have been synthesized. Sucrose polyesters (Olestra TM

from Proctor & Gamble) is probably the best known. Emulsifier use in prod

ucts utilizing the noncaloric, synthesized fat replacers is very likely similar to

that utilizing the traditional caloric version.

8.7.6 Release Agents

A separate application of emulsifiers in bakery products, although not incorpo

rated into the dough, is release agents or pan sprays. Lecithin is the primary

emulsifier used. Often the pan sprays are formulated with an oil in combina

tion with mold inhibitors and lecithin. One to 6% lecithin is added. Modified

lecithins that exhibit improved heat stability may used. The pan spray may

simply be brushed or sprayed to achieve a thin film promoting easy release of

baked products from pans or belts.

8.8 Summary The market for emulsifiers in bakery products continues to grow. Reduced-fat

products have provided the more recent surge in utilization. Producers of


emulsifiers as well as bakeries themselves, as with many of our industries,

have undergone consolidation. Fewer producers have placed new require

ments on the final product that is transferred to the ingredient supplier, in this

case the supplier of the emulsifier. The function of the emulsifier is even of

greater importance. Growth in food service furthers the need for bakery prod

ucts having desirable sensory characteristics and meeting the demands of to

day's marketplace.

References Brandt, L. (1996). Emulsifiers in baked goods, Food Product Design, Feb., pp. 64-76. Chawla, P., deMan, J.M. (1990). ]. Am. Oil Chem. Soc., 67, 329. Hahn, D.E., Hood, L.F. (1987). Factors influencing com starch lipid complexing, Ger.

Chem., 64,81-85. Handleman, A.R., et al. (1961). Bubble mechanisms in thick foams and their effect on

cake quality, Ger. Chem., 38, 294. Hartnett, D.I. (1977). ]. Am. Oil Chem. Soc., 54, 557. Henry, C. (1995). Monoglycerides: the universal emulsifier, Ger. Foods World, 40(10),

734-738. Knightly, W:H. (1988). Ger. Foods World, 33,405-412. Krog, N. (1981). Theoretical aspects of surfactants in relation to their use in breadmak

ing, Ger. Chem., 58, 158--164. Lagendijk, J., Pennings, H.J. (1970), Ger. Sci. Today, 15, 354-356, 365. O'Brien, R.D. (1996). Shortening: types and formulations, in Bailey's Industrial Oil and

Fat Products (ed. Y.H. Hui), 5th ed., Vol. 3, pp. 161-193, Wiley, New York. Rusch, D.T. (1981). Emulsifiers: uses in cereal and bakery foods, Ger. Foods World,

26(3), 1ll-ll5. Schmidt, J.C., Orthoefer, F. (1985). Modified lecithins, in Lecithins (eds. B.F. Szuhaj

and G.List), Chap.lO, pp. 203-213, Am. Oil Chern. Soc., Champaign, IL. Schuster, G., Adams, W.F. (1984). Emulsifiers as additives in bread and fine baked

products, in Advances in Cereal Science and Technology (ed. Y. Pomeranz), Chap. 4, pp. 139-242, Am. Assoc. Cer, Chern. Inc., St. Paul, MN.

Stauffer, C.E. (1996). Emulsifiers for the food industry, in Bailey's Industrial Oil and Fat Products, 5th ed., Vol. 3, pp. 483-516, Wiley, New York.

Tenney, R.J. (1978). Dough conditioners/bread softeners, Baker's Digest, 52 (4), 24. Tsen, C.C., et al. (1973). High protein cookies I. Effect of soy fortification and surfac

tants, Baker's Digest, 47(4); 34-39. Weiss, T.J. (1983). Food Oils and Their Uses, AVI, Westport, CT. Wooten, J.C., et al. (1967). The role of emulsifiers in the incorporation of air into layer

cake batter systems, Ger. Chem., 44, 333.

NINE

Emulsifiers in Confectionery

Mark Weyland

9.1 Introduction The use of emulsifiers in both chocolate confectionery and sugar confectionery

has been established for many years. They are useful functional additives

without which many candy products would be impossible to make. In this

chapter, an outline of the range of emulsifier functionalities will be presented,

but since it is a very diverse field, it is not possible to cover every application

or use. A bibliography is provided for further study, which is recommended.

Emulsifiers act in multiphase confectionery systems in two main ways. The

first is as an emulsifying agent to enable two distinct phases to be combined in

a stable quasi-homogeneous state for an indefinite length of time. The two or

more phases involved in most food products may be selected from a list that in

cludes oil, water, protein, carbohydrates, and air. These phases have a natural

tendency to repel each other and form discrete layers within a food product. In

most food products this tendency to separate into phases is undesirable and

must be controlled by a suitable blend of processing techniques and carefully

selected emulsifying agents. Furthermore, even if the food product is satisfac

tory at the time of production, it must still withstand the rigors of distribution

and storage on the shelf, such that at the point of consumption by the con-

235


sumer the product has an acceptable taste, appearance, and texture. These

qualities in modern food products are often critically dependent on the type

and level of emulsifiers used in the product.

The second function of an emulsifier is often to act as a surfactant. In these

cases the role of the emulsifier is to modify the behavior of the continuous

phase of a food product so as to bring about a specific effect or benefit. The

most common example of this in confectionery is the use of lecithin in choco

late to reduce the viscosity of the product and improve the ease of handling

and processability.

Many of the classes of emulsifiers described in this book have also found

their way into confectionery products. These include lecithin and modified

lecithins such as YN and phosphated monoglycerides, glycerol monostearate,

polyglycerol esters including polyglycerol polyricinoleate (PGPR), sorbitan es

ters, polysorbates, lactic acid and tartaric acid derivatives of monoglycerides,

acetylated monoglycerides, sucrose esters, and propylene glycol monoesters.

All these compounds have a common feature that makes them suitable as

emulsifying agents: they are ambiphilic, possessing both lipophilic and hy

drophilic properties. The nature of this property is often expressed as hy

drophilic/lipophilic balance or HLB. The HLB number is an indication of the

properties of an emulsifier and is usually on a scale of 0 to 20. An emulsifier

with a low HLB will tend to be more oil-like and will therefore have a greater

affinity for the oil phase of a confectionery product. Lecithin, for example, has

an HLB of 4 and has a great affinity for the oil phase in chocolate. Polysorbate

60, by contrast, has an HLB of 15 and is quite soluble in water and therefore

has an affinity for the syrup phase in toffees and caramels.

It is often the case in food products, and in confectionery too, that a combi

nation of two emulsifiers in a recipe or formula containing two distinct phases

will result in the longer lasting and more uniform product. In these cases, com

binations oflow- and high-HLB emulsifiers give the best results.

In the remainder of this chapter, a number of the more common confec

tionery types using emulsifiers are described, along with a review of the avail

able knowledge relating to the most optimal emulsifier types and their benefits.

9.2 Emulsifiers in Chocolate and Compound Coatings The use of emulsifiers in chocolate and compound coatings is perhaps the best

documented in the literature of any of the applications of these ingredients in

Emulsifiers in Confectionery 237

confectionery. The recent changes in the Standard of Identity for chocolate

products (1993) has led to the possibility of using any safe and suitable food

grade emulsifier in chocolate. A number of emulsifiers used in compound or

vegetable fat coatings with advantage can now also be used in chocolate. Other

emulsifiers not available for use in the United States at this time are used in

the EC and can bring particular benefits to the chocolate and compound coat

ing user. These will also be described later, but first there follows a description

of the most widely used emulsifier, soy lecithin.

9.2.1 Lecithin

Chocolate and compound coatings are dispersions of solid particles in a con

tinuous fat phase. The solid particles are composed of sugar granules, milk

solids, and cocoa solids. In chocolate the fat is cocoa butter and comes directly

from the crushing of cocoa nibs, but in compound coatings the fat comes from

vegetable oils added to the formula to give the same fat content as chocolate

overall. Moisture is also present in the coating, introduced indirectly via the

sugar or other solid ingredients. It is the presence of these solid particles and

moisture that causes chocolate and compound coatings to deviate from true

Newtonian viscosity behavior. The solid particles tend to abrade each other,

and the resultant internal friction causes the viscosity of the material to vary

according to the applied shear stress.

Viscosity is very important when considering how chocolate and compound

coatings are used, because they always have to flow to either fill a mold without

defects or air bubbles or cover a candy piece with a thin, even coat. These

properties are controlled almost completely by the rheological behavior of the

coating, which in turn is dependent on the nature of the continuous liquid

phase, that is, the fat and fat-soluble ingredients. Considering the flow proper

ties of molten chocolate, the two most important parameters are plastic viscos

ity and yield value. "Plastic viscosity" is defined as the force required to keep

liquid chocolate flowing once it has started moving, whereas "yield value" is

the force required to start the mass of liquid chocolate moving. Both plastic

viscosity and yield value can be decreased by the use of specific surfactants,

and this enables the chocolate manufacturer to have greater control of cocoa

butter levels. Plastic viscosity and yield value are often combined in a value

called "apparent viscosity," but it is important to understand that chocolates

with equal apparent viscosities can have different yield values and different

plastic viscosities.


Coatings can always be made more fluid for better control by adding more

cocoa butter or vegetable fat to the mix, but since these are the more costly in

gredients in coatings, this is often an unattractive solution. Better by far is to

add a surfactant like lecithin to reduce coating viscosity. It is possible to add

0.5% lecithin to a coating to have the same viscosity reduction effect as the

addition of 5% cocoa butter or vegetable fat (Minifie, 1980). Lecithin allows

coating users to operate efficiently at much lower fat contents than would oth

erwise be the case (Figure 9-1).

Lecithin is commercially extracted from the soybean by solvent extraction

and precipitation. It is a light brown fluid that contains approximately 65%

acetone-insoluble phosphatides and 35% soybean oil. An oil-free product is

also available that is in the form of granules. The chemical composition of soy

lecithin is as follows (Minifie, 1980):

Soybean oil 35%

Phosphatidyl choline 18

Phosphatidyl ethanolamine 15 Phosphatidyl inositol 11

Other phosphatides and polar lipids 9 Carbohydrates, e.g., sterols 12

39

38

L. Q) 37 ~ ::I .0 36 co 0 (.)

35 0 (.)

'#- 34

33

1\ \

"" ~ .......... ['...

~ -32

0.1 0.2 0.3 0.4 0.5 0.6 0.7

% lecithin (soya)

Figure 9.1 Effect of addition of lecithin on the fat content in dark enrobing chocolate. Curve represents chocolate formulas of equal viscosity. (Minifie, 1980.)


A structure for lecithin is given in Figure 9.2.

Lecithin exhibits both lipophilic and hydrophilic properties. A possible ex

planation of the mechanism by which lecithin reduces intraparticle friction is of

fered by Harris (1968). Moisture present in chocolate and compound coatings

adher-es to the surface of sugar particles and gives them a syrupy, tacky surface

that in tum increases friction between the sugar grains. When lecithin is intro

duced the hydrophilic functional group in lecithin attaches itself to the sugar

surface while the lipophilic group is left to project out into the surrounding oil

phase. This enables the particles to slip more easily over each other, reducing

the viscosity. This effect is demonstrated in Figure 9.3, in which the viscosity-re

ducing effect of lecithin is seen only where sugar is present in the formula.

Lecithin is usually added late in the chocolate or compound-making

process since it can be adsorbed by cocoa particles during grinding and mix

ing, thereby losing its effectiveness. In some cases a small amount of lecithin

is added to the mixed ingredients prior to roller refining to aid in the grinding

process, but the remaining portion is added just before the end of the conching

process. This provides the maximum liquification of the chocolate or com

pound coating at minimum fat content.

Lecithin also has the benefit of protecting coatings against moisture inva

sion and sugar granulation, which may occur at above 60°C when stored in

bulk form. Lecithin used in excessive amounts will not further reduce viscosity

of chocolate or compound coatings but will produce certain negative effects

such as softening of chocolate and increase of crystallization time (Jeffrey,

1991). This is because the chemical structure of lecithin is very different from

cocoa butter or vegetable fats, and this can interfere with the crystallization

0 II

CH2-o-c-R

I ?! CH-0-C-R

I 0 II

lipophile

hydrophilic

CH2-o-P-O-cH2-CH2-N-(CH3) 3

II II OH OH

Figure 9.2 Chemical structure of soy lecithin. (Woods, 1976.)


100

90

80

[',_

1'---~

I I ~Cocoa/Fat r--__

1---~-- ---- - -

70 c--·- --

--: 60 "' u tJ

~ 50 >. -.. 0 40 u

"' >

!\

\ \\ -·· - - t---- -

\ l \

' Chocolate I .........

I'-. 30

20 "" I 1'--.:_ugor I Fat

10

0 .1 0 .2 0 .3 0.4 0.5 0 .6 0 .7

"I• Lecithin (Soya)

Figure 9.3 Influence of lecithin on viscosity measured using a Redwood viscometer. (Minifie, 1980.) (In this viscosity measurement method, the time taken for a known amount of chocolate to drain through a hole in a cup is measured using a stopwatch. This value in seconds gives an empirical value for chocolate consistency.)

process in the fat phase. Levels of over l% in typical 30% fat coatings should

not be used.

9.2.2 Synthetic Lecithin

These products are used in chocolate and compound coatings outside the

United States and are made by reacting mono-, di-, and triglycerides of par

tially hydrogenated rapeseed/canola oil or other liquid vegetable oil with phos

phorus pentoxide to produce phosphatidic acids. Neutralization with ammonia

or caustic soda results in an ammonium or sodium salt. These surfactants are

often given the name synthetic lecithins or sometimes YN lecithin. They have


a neutral flavor and can be used at higher dosage levels than natural lecithin

without the negative impact on viscosity (Bonekamp-Nasser, 1992; Klienert,

1976; Nakanishi, 1971). See Figure 9.4.

YN is also claimed to reduce the thickening of chocolate and compound

coatings due to moisture and overheating (Bradford, 1976). A comparison be

tween lecithin at 0.3%, YN at 0.3%, and cocoa butter added at 5% to choco

late gave the same similar overall viscosity readings (see Figure 9.5), but a

calculation of the Casson yield values showed that YN produced significantly

lower values than with the other systems. The viscosity reducing effect of YN

is reportedly less in milk-free coatings than with milk coatings (Klienert,

1976; Hogenbirk, 1989). Milk coatings have generally higher viscosities than

milk-free coatings due to the effect of milk solids/fat/emulsifier interactions.

150

140

130

120

110

100

.... 90 ~

~ 1 RP.M.

~\ - Soya lecithin

~\ ---·YN -

RPM. : Rate of shear -\\ \\

--r--------

\"' --

------g tl ao "' 0 ?- 70

' "" ' ..............

--' r--'

~

"' 60 0

..... ..........

... u

"' > 50 "0

u 40 ~ 0 0 30 L.

cD

... '-..5 R.P.M. ... ... '~ --.. _

'<" r::--.......... ..... .......... ... -r---20

10

20 R.P.M. ~ .... --1-----~-- --- -------

0 0.1 0.2 0.3 04 0.5

0/o Lee ith 1 n

Figure 9.4 Brookfield viscosity measurements of milk chocolate at three levels of shear. Comparison of effeet of soya lecithin and YN lecithin. (Minifie, 1980.)


700 c:;- 5% cocoa butter E

..s?. 600 -Ul Q) 0.3% lecithin c: > 500 ~ --+-Ul 0.3% YN Ul Q) 400 .... __.._ +' Ul .... ctl 300 Q)

..c: (/)

200 0 10 20 30 40 50

Shear rate (s-1)

Figure 9.5 Viscosity plot comparing lecithin, YN, and cocoa butter. (Bradford, 1976.)

These interactions result in higher viscosities compared to coatings containing

only cocoa solids and sugar for surfactant adsorption. Details of how these interactions occur are absent from the literature.

9.2.3 Polyglycerol Polyricinoleate (PGPR)

PGPR is a surfactant used in the chocolate and compound industries in

Europe and other parts of the world, excluding the United States. It has a

unique role to play in modifying the viscosity behavior of chocolate coatings. It

is made by reacting polyglycerol with castor oil fatty acids under vacuum. The

resultant material is a colorless, free-flowing fluid with little or no odor. PGPR

is also claimed to he a moisture scavenger in chocolate and compound coat

ings, preventing thickening of coatings over time (Application Notes Admul

WOL, Quest International).

Its chemical structure is, in general form,

where R= H or a fatty acyl group derived from poly condensed ricinoleic acid

and n is the degree of polymerization of glycerol.


A number of studies have been published that compare the effects of PGPR

with lecithin and YN. Most conclude that PGPR, when added to chocolate or

compound coatings at 0.5% or less, can reduce the coating yield value to al

most zero (Application Notes Admul WOL, Quest International; Bamford,

1970). The practical benefit of such a feature is that in a chocolate bar molding

operation, PGPR addition would allow the chocolate to flow easily into even

complicated mold shapes without entrapping air bubbles and also to flow

around inclusions. Furthermore, the opportunity exists to reduce the fat con

tent of the chocolate as well as the coat of chocolate formulations.

A typical comparison of lecithin and PGPR additions to a milk and to a

dark chocolate using a Rotovisco viscometer is given in Tables 9.1 and 9.2

(Application Notes Admul WOL, Quest International).

The values in Tables 9.1 and 9.2 indicate that in milk chocolate it is possi

ble to reduce the yield value to almost zero. The presence of lecithin in the

emulsifier mix allows the plastic viscosity to be minimized, and this blend pro-

Table 9.1 Casson plastic viscosities and yield values of a milk chocolate when cocoa butter, lecithin, and PGPR are added

Casson plastic Casson yield value Addition Amount viscosity (poise) (dynes/cm2)

Cocoa butter 0.0 45 llO l.O 29.8 97 2.0 26.5 62 4.0 16.3 58 5.0 15.3 58

Lecithin 0.05 30.0 79 0.1 26.7 54

0.2 20.0 40

0.4 15.6 37

PGPR 0.075 30.0 86 0.175 29.2 38.5

0.3 26.8 22

0.5 30.5 2.5

0.6 32.0 2.0

Lecithin + PGPR 0.1 14.1 34

0.2 13.4 32

0.3 12.7 29


Table 9.2 Casson plastic viscosities and yield values of a dark chocolate when cocoa butter, lecithin and PGPR are added

Casson plastic Casson yield Addition Amount viscosity (poise) value (dynes/cm2)

Lecithin 0.3 18.5 155 0.7 17.1 221 0.97 14.4 297 1.3 12.4 285

PGPR 0.0 12.9 199 0.1 12.5 151 0.2 14.8 82 0.5 14.9 13 1.0 15.9 0

vides the optimum solution. In dark or semisweet chocolate the effect of PGPR

on plastic viscosity is small, while it can reduce yield values to very low values

at 0.5% addition. The mechanism by which PGPR affects yield value is not

understood but its practical benefits are widely reported.

PGPR is also claimed to be advantageously used in ice cream coatings since

it allows low apparent viscosities in the presence of low levels of moisture

(Bamford, 1970). Also claimed is PGPR's beneficial effect on fat-phase crystal

lization leading to easier tempering, improved texture, and longer shelflife of

coatings (Application Notes Admul WOL, Quest International.). The author has

found that the viscosity-reducing properties of PGPR does lead to significantly

reduced viscosity at temper and a level of temper, as measured by a temperme

ter, which is easier to maintain over long periods in an enrober without signifi

cant recirculation of chocolate via melt-out and retempering circuits.

PGPR's most recognized benefit remains that of fat reduction, and manufac

turers claim that a blend of 0.5% lecithin and 0.2% PGPR allows cocoa butter

reductions of approximately 8%.

9.3 Antibloom Agents in Chocolate and Compound Coatings There are many references in the literature to uses of emulsifiers as additives

to influence the physical appearance and texture of chocolate and compound

coatings. One of the main problems to be overcome when making cocoa but-


ter-based chocolate is to ensure that the cocoa butter crystallizes in the cor

rect crystal form or polymorph. Cocoa butter has several different polymorphic

forms that have melting points ranging from 17 to 35°C. The forms are repre

sented by the greek letters y, a, pt, and~· As the polymorphic form increases

in stability it also increases in melting point. To make chocolate in the familiar

glossy, fast-melting form with good snap, it is necessary to crystallize the cocoa

butter in the highest melting polymorph, which is ~· This form of cocoa butter

is also needed to ensure good contraction in molded products and the long

bloom-free shelf life expected for good quality chocolate goods. Bloom is the

phenomenon in which liquid fat is forced to the surface of a product and spon

taneously crystallizes there as a grayish layer that looks to the uninformed con

sumer as if the product has gone moldy. The liquid fat is forced out to the

surface in this way by the following mechanisms:

l. Chocolate is not preconditioned (tempered) correctly such that insuffi

cient concentration of seeds in the ~ form is present in the crystallizing

chocolate mass. This leads to a higher level of less stable W forms in the

chocolate mass that later transform to the more stable ~ form. This

transformation causes the chocolate coating or bar to contract and

squeeze liquid fat to the surface. Chocolate contains liquid fat even at

room temperature, where cocoa butter attains a maximum solid fat con

tent of approximately 85%. This liquid fat at the surface crystallizes in

an uncontrolled fashion and is a mixture of ~' W, and even possibly

some a forms.

2. Chocolate is tempered correctly, but in storage or distribution the prod

uct is subjected to wide temperature variations, resulting in partial

melting and resolidification of the chocolate. Under these conditions

uncontrolled recrystallization takes place and extensive bloom can oc

cur. This kind of change is often referred to as "heat damage" and the

product is classified as not heat resistant.

3. In molded bars that contain peanuts or other nutmeats as solid inclu

sions, or in enrobed products that have centers containing quantities of

soft vegetable oil or dairy butter oil, this oil can "migrate" from the cen

ter to the chocolate shell. The soft oil will cause the chocolate to become

soft and cocoa butter will dissolve. This will cause severe damage to the

product due to physical handling prior to consumption or due to discol

oration and bloom of the chocolate shell, which will now be far more

heat-sensitive.


4. Long-term changes in cocoa butter crystal structure via ~(V) to ~(VI)

transitions can also be a cause of bloom in some cases, although this

may not be as common as the mechanisms above. In this scenario cocoa

butter in the stable ~ state can exist in two forms, given the nomencla

ture V and VI. At the time of manufacture only the form V can he

formed. Form VI has a slightly lower energy than form V, but the trans

formation from one to the other takes place at a very slow rate because

there is a significant kinetic harrier to he overcome. This bloom mecha

nism occurs only in solid dark (milk-fat-free) chocolate bars. Milk fat

present at low levels (2%) in chocolate will prevent this type of bloom.

(See also the reference to STS as a bloom inhibitor in Section 9.3.1.)

In all the cases above, the negative impact of uncontrolled crystallization is

discoloration and bloom. This phenomenon is also seen in compound coatings

based on other vegetable fats, hut since they are not polymorphic in the same

way as cocoa butter, the mechanism of bloom formation is different. Problems

of discoloration tend to stem from types 2, 3, and 4 above rather than type l.

The final result is, however, the same, with an unattractive dull finish becom

ing apparent on the coating surface.

Emulsifiers can have a role in helping control the rate of crystallization of

cocoa butter and other vegetable hard butters both at the time of production

and during subsequent storage and distribution. This in turn can promote

bloom prevention.

9.3.1 Sorbitan Tristearate (STS)

STS is an emulsifier often associated with bloom prevention; it is claimed that

when added to chocolate in the liquid state at 2% it slows down the crystalliza

tion rate of cocoa butter, thereby reducing the concentration of the most unsta

ble a form. The more stable W form is still produced hut this transforms into

the~ form thus deterring bloom (Anon., l99la). In this way STS behaves as a

crystal modifier.

The situation is further complicated, however, because there exists not one

hut two ~ forms of cocoa butter, usually referred to as forms V and VI. In this

classification system the W form is called form IV and transitions from form IV

to form V, the stable form, occur via the liquid phase only. The transformation

of form V to form VI takes place only via the solid phase and can take many

months to occur. Also, identification of form VI is difficult and requires spe

cialized x-ray diffraction techniques. However, this ~transformation is also as-

Emulsifiers in Confectionery 24 7

sociated with bloom in solid chocolate that has been well tempered. Work done

by Garti et al. (1986) has indicated that STS is particularly effective at block

ing this V to VI transformation and, hence, preventing bloom even after exten

sive temperature cycling between 20 and 30°C.

Other emulsifiers studied by Garti included sorbitan monostearate and

Polysorbate 60, but these were only half as effective as STS. STS is a high

melting-point emulsifier (approximately 35°C} whose structure is more closely

related to cocoa butter triglycerides than to most other emulsifier types. It is

speculated that it is due to this similarity that STS co-crystallizes with cocoa

butter from the melt and, due to its rigid structure, binds the lattice in form V.

Other more liquid or less triglyceride-like emulsifiers tend to depress the melt

point of crystallized cocoa butter, increasing liquidity and promoting form IV

to V transformations in preference.

This is presumably why STS is a more effective antibloom agent in solid

chocolate than in enrobed chocolate items, where soft center oils can soften

cocoa butter crystals via migration and lead to type IV-V bloom occurring (see

type 3 bloom previously mentioned). Krog (1987), however, claims that STS

locks fats in the less stable W form and prevents the transformation to ~

Berger (1990) also claims that STS performs well as a bloom inhibitor or gloss

enhancer in palm kernel oil-based compound coatings used to enrobe cakes

by stabilizing the W form of the vegetable fat, a situation also observed by the

author in several practical cases using lauric coating fats but with much less

reliability when using domestic fats such as soybean or cottonseed-based coat

ing fats. Such products tend to have longer bloom-free shelf lives in many

cases so that the need for antibloom additives is not so imperative.

The use of STS in food in the United States is limited to chocolate and com

pound coatings for which there is a petition pending for acceptance by FDA as

a food additive. This uncertain status has not deterred United States food com

panies from enjoying the benefits that STS can bring to coating appearance.

STS is, however, more widely accepted as an additive in EC countries.

9.3.2 Sorbitan Monostearate (SMS) and Polysorbate 60

SMS and polysorbate 60 [also known as polyoxyethylene (Player, 1986) sorbi

tan monostearate] are also used as antibloom agents, especially in compound

coatings based on vegetable butters. They are not as effective as STS, but they

have the advantage of being already accepted by FDA as food-grade emulsi

fiers. They are usually used in combination, where the SMS acts as a crystal


modifier and the polysorbates act as hydrophilic agents to improve emulsifica

tion with saliva and aid flavor release (Dziezak, 1988; Lees, 1975). SMS can

also be used at high levels in coatings to increase heat resistance due to its

high melt point, 54°C; unfortunately, the addition of SMS also causes the coat

ing to become waxy.

Up to 1% of this combination can be added to coatings to improve initial

gloss and bloom resistance. The optimum ratio of SMS to polysorbate 60 is

60:40 (Woods, 1976). These emulsifiers are claimed to function by forming

monomolecular layers of emulsifier on the surface of sugar and cocoa particles,

thereby inhibiting the capillary action that causes liquid fat to migrate to the

surface and cause bloom. Lecithin is still needed in these systems to control

coating viscosity and reduce fat content.

In another nomenclature system, SMS is also called Span 60 and polysor

bate 60 is called Tween 60 (Lang, 1974). Spans and Tweens are also claimed to

reduce the rate of fat crystallization; therefore, to develop proper crystal size a

suitable tempering system needs to be employed. They are employed in both

chocolate and compound coatings and may be used with advantage iffast crys

tallization of the coating would be disadvantageous.

9.4 Other Emulsifiers Used in Coatings Mono- and diglycerides are also used as additives to chocolate and compound

coatings, often as their purified or distilled forms. They can act as seeding

agents especially when in high-melting-point forms such as glycerol mono

stearate (GMS). They are more commonly used as antibloom agents in lauric

type palm kernel oil compound coating to extend useful shelf life. A typical

usage level would be 0.5%. Berger (1990) claims good results in hydrogenated

palm kernel oil coatings when using glyceryllacto palmitate at 1 to 5% as a

gloss improver; the application was as a coating for a baked product. Moran

(1969) found that a polyglycerol ester of stearic acid reduced the viscosity of

fat sugar systems better than lecithin as well as retarded crystallization, im

proved gloss, and better demolding.

Lactic acid esters of monoglycerides have also been used to control gloss in

compound coatings (Hogenbirk, 1989; Dziezak, 1988) and to improve demold

ing performance (Anon., 1991b). Woods (1976) describes the use of triglycerol

monooleate in compound coating chocolate to improve initial gloss and gloss

retention, and triglycerol monostearate as a whipping agent to aerate coatings


giving them a lighter texture for filling applications. Herzing (1982) describes

in detail the types of polyglycerol esters needed to optimize the glossy proper

ties of lauric and nonlauric compound coatings: triglycerol monostearate, oc

taglycerol monostearate, and octaglycerol monooleate. These emulsifiers are

added to the coating fat at up to 6% by weight.

Polyglycerol esters have also been claimed to speed up the setting time of

chocolate panning coatings when used at levels of 0.4 to 0.6% (Player, 1986).

Hogenbirk (1989) has found advantages of viscosity reduction to some degree

with examples of mono- and diglycerides, diacetyl tartaric acid esters of mono

glycerides (DATEM), acetylated monoglycerides, and propylene glycol mo

noesters. Musser (1980) has published results showing the benefits of adding

up to 1.5% DATEM to chocolate and compound coatings to modify viscosity

properties and to improve the rate of crystallization of coating fat phases. In a

series of experiments, Musser found that the addition of DATEM to fully

lecithinated milk and dark chocolates, and dark sweet coatings, could further

reduce the viscosity of the coatings as measured by a Brookfield viscometer. At

the same time Musser found that the DATEM was acting as a seeding agent in

chocolate systems, improving the speed of crystallization and resulting in a

finer grain and better gloss in molded bars. Musser's conclusions relative to the

effect of DATEM on viscosity is supported by the author's own published study

on chocolate viscosity and emulsifiers (Weyland, 1994).

9.5 Emulsifiers in Nonchocolate Confectionery Unlike in chocolate and compound coatings, the continuous phase of sugar

confectionery is not oil or fat but is either sugar or a sugar syrup (in this case

"sugar" means any nutritive carbohydrate sweetener). For this reason the role

of an emulsifier in sugar confectionery is to enable small quantities of

lipophilic material to be finely dispersed within a sugar matrix to achieve a de

sired effect. This effect may involve the dispersion of color, flavor, or some

other fat-soluble ingredient, or the direct physical interaction of the emulsifier

with the sugar phase to achieve the desired textural properties.

A major factor in consumer acceptance is the mouthfeel of a confection.

Vegetable fats and emulsifiers are used to improve texture and lubricate the

product to achieve better chewing characteristics. A well-chosen surface-active

agent can improve this aspect as well as slow down the release of added flavor

ings. They will affect the viscosity characteristics of the sweet and influence the


crystal shape present in grained confections. The improvement in fat dispersion

throughout the confection will slow the rate at which the ingredient becomes ran

cid as the amount presented or migrating to the surface is lessened.

For the purposes of this review I will divide the use of emulsifiers into the

following categories: (i) chewing gum; (ii) caramels, toffee, and fudge; and (iii)

jellies and gums.

9.5.1 Chewing Gum

Chewing gums contain fats and emulsifiers that act as softening agents or plas

ticizers to the gum base. In this role, emulsifiers can also act as carriers for

colors and flavor aiding in the dispersion of these important ingredients within

the gum base. Up to 1% lecithin can be used to soften chewing gum to the de

sired consistency (Patel et al., 1989) and can be hydrated or mixed with a veg

etable oil or suitable fatty emulsifier such as mono- and diglycerides, to aid in

dispersion within the chewing gums. Chewing gums prepared in this way have

the desirable soft, chewy properties popular in today's top products.

Other emulsifiers are also used in chewing gum to provide suitable textural

and antistick properties to the chewing gum base; and these include monoand diglycerides, glyceryl lacto palmitate, sorbitan monostearate, triglycerol

monostearate, triglycerol monoshortening, and polysorbates 60, 65, and 80.

Lecithin is also used to provide a protective coating to chewing gum pieces

prior to a hard panning process (Dave et al., 1991). Normally, only hard chewing

gums can be hard panned in this way, but by using a hydrated lecithin coating it

is possible to candy coat the gum and then allow the lecithin to soften the chew

ing gum in storage prior to consumption. By this technique the emulsifier coat

ing, when set, forms a suitable base for syrup-based candy coatings.

9.5.2 Caramels, Toffee, and Fudge

Emulsifiers acting as surface-active agents increase the resistance of caramels

and similar fat-containing confections to stick on cutting knives or to oil out due

to manipulation in the process. The use of glycerol monostearate (GMS) and sim

ilar products such as mono- and diglycerides do produce an improvement in low

fat products such as in toffee and nougat. It is also claimed that the addition of

these agents can help bind the oil and oil-based flavoring into a confection, re

ducing sweating and problems with rancidity. One property of emulsifiers that is

particularly important is the improvement in emulsification in high-fat-content


confections such as butterscotch and caramels. During the manufacturing

process, a high-sugar-content syrup is produced in which fat globules are dis

persed. The finer these globules are the better will be the eating qualities.

Consumer acceptance is based on flavor, appearance, texture, and chew.

The last two factors are influenced directly by the number and size range of fat

globules present in the product. The lower the size and the more even the dis

persion of fat globules, the smoother the confection. Fat-containing products of

this type exhibit non-Newtonian flow with a yield stress, which means that it is

necessary to apply a sufficient level of stress to cause flow. Fat makes a minor

contribution to the viscosity in relation to that due to the milk protein, but its

presence is extremely important for lubrication. The higher the level of water

left in a confection of this type, the higher the danger of stickiness and grain

ing. GMS is a highly effective emulsifier to ensure maximum fat dispersion and

minimum stickiness, but glycerol monooleate and lecithin are also quite effec

tive. A usage level of 0.25 to 0. 7% is normal.

Fudges are fondants that contain milk protein and fat having a flavor char

acteristic of toffee and caramel. Its texture can vary widely from a hard product

often sold as a cut tablet to a soft form used in starch-molded products. In

fudgemaking, an emulsified milk phase is prepared consisting of sweetened

condensed milk, vegetable fat such as hardened palm kernel oil, and an emul

sifier, usually GMS. The fat is emulsified into the syrup solution in a high

speed mixer at 120 to l40°F. Without GMS present the fat is more likely to

separate during the subsequent cooking and working process or during the

storage life of the fudge. This emulsified milk phase is added to a sugar/corn

syrup mix and cooked to the desired moisture content of 8 to 15%. During this

cooking process the characteristic Maillard or caramelized flavors develop.

Finally, fondant is added during the cooling stage to provide the correct

level of sugar seeds to make the desired sugar crystal size in the fudge. The

fudge is then sheeted, deposited, or extruded.

9.5.3 Jellies and Gums

Some emulsifiers and surface-active agents such as GMS and saturated

ethoxylated monoglycerides or polyglycerate 60 are adsorbed onto starch gran

ules. This property can be used to modify the texture of starch-based sugar

confectionery. Gel formation in starch-based jellies and gums is mainly due to

the water-soluble fraction of starch, the amylose. Interaction between amylose


and emulsifiers creates a water-insoluble helical complex and creates an irre

versible textural effect. This interaction was quantified by Krog (1977) using

the amylose-complexing index or ACI. The ACI is defined as the percentage of

amylose precipitated at 60°C after l hour and after reacting 5 mg of the emul

sifier with 100 mg of amylose in solution. See Table 9.3.

Table 9.3 ACI values of some food emulsifiers

Glycerol monostearate (85%) 87 Glycerol monooleate {45%) 35 Mono- and diglycerides (50% monoester) 42 DATEM 49 Sorbitan monostearate 18 Lecithin 16 Polysorbate 60 32 Acetylated monoglycerides 0

To be an active amylose-complexing agent an emulsifier must have a high

level of saturated monoglycerides and some degree of water dispersability. An

example of the use of emulsifiers in starch-based confectionery is in the making

of Turkish delight, where it is possible to use emulsifiers with high ACI values

(GMS) to avoid pastiness or cheesiness. Usage levels are typically 0.025%.

9.6 Processing Aids Emulsifiers are sometimes used in small amounts in confectionery products ei

ther to control aeration or to prevent product sticking to machinery and pack

aging. They can also be used to displace starch from starch-molded jellies and

gums and provide a shiny attractive appearance as well as a barrier to degra

dation from atmospheric oxygen and moisture.

Aeration of protein systems containing small amounts of fat, such as

nougats, can be facilitated by the addition of triglycerol monostearate. Liquid

fat or lipophilic emulsifiers such as GMS or acetylated monoglycerides usually

tend to destabilize forms and cause deaeration.

Emulsifiers are also useful release agents providing barrier properties be

tween product and molds, tables, metal, conveyor belts, utensils, and machin-


ery, especially on cooling. Release agents must be food-grade materials and

have high stability to resist oxidation and hydrolysis.

Acetylated monoglycerides are used as release agents or as oiling and pol

ishing agents because they form stable films on the surface of confectionery

items. They have a-crystalline stability, plastic, nongreasy texture, and neu

trality of flavor, color, and odor. They reduce shrinkage, harden through mois

ture loss, and prevent fat degradation and mold growth. They retain moisture

and other desirable properties of the foodstuff and prevent contamination by

moisture or dust. They are usually applied directly to the confectionery prod

uct by spraying. Melting points used are in the range 30 to 46°C. Typical ap

plications include nuts and dried fruits and certain panned confectionery

items. Lower melting-point forms (l0°C) can be sprayed directly onto convey

ers and molds to release goods with high sugar contents such as fondant

creams and jellies.

Another release agent used often on chocolate-enrobing tunnels is a mix

ture of lecithin and cocoa butter. This is sprayed onto the band before the

candy center is deposited to ensure clean separation of the centers from the

band prior to chocolate-enrobing.

References Anon. (199la). Confectionery Production, 57(2), 136-7, 140. --- (l991b). Confectionery Production, 57(6), 451-2. Bamford, H.F., eta!. (1970). Rev. Int. Choc. (RIC), 25, 6. Berger, K.G. (1990). World Conference on Oleochemicals into the 21st century, AOCS,

Champaign, IL, pp. 288-91. Bonekamp-Nasser, A. (1992). Confectionery Production, 58(1), 66, 68. Bradford, L. (l976).Int. Flavors Food Addit., 7(4), 177-9. Dave, ].C., eta!. (1991). U.S. Patent 5,135,761, March 28. Dziezak, J.D. (1988). Food Techno!., 42(10), 171-86. Garti, N., eta!. (1986). ]. Assoc. Off. Chem. Soc., 63(2) 230-236. Gregory, D.H. (1982). Confectionery Production, 48(10), 437-9. Harris, T.L. (1968). Surface Active Lipids in Foods, Monograph No. 32, Society of

Chemical Industry, England. Herzing, A.G., eta!. (1982). U.S. Patent 4,464,411, November 5. Hogenbirk, G. (1989). Confectionery Production, 55(1), 82-3. Jeffrey, M.S. (1991). Manufacturing Confectioner, 71(6), 76-82. Klienert, J. (1976). Rheol. Texture Food Qual., pp. 445-73, AVI, Westport, CT. Krog, N. (1977). ]. Assoc. Off. Chem. Soc., 54(3), 124--31. Lang, M. (1974). Confectionery Manufacturing and Marketing, 11(2), 3-5, 13. Lees, R. (1975). Confectionery Production, 41(6), 296,298, 304.


Minifie, B.W. (1980). Manufacturing Confectioner, 60(40), 47-50. Moran, D.P.J. (1969). Rev. Int. Choc. (RIC), 24,12. Musser, J.C. (1980). 34th PMCA Production Conference, Lancaster, PA. Nakanishi, Y. (1971). Rev. Int. Choc. (RIC), 26, 8. Patel, M.M. et al. (1989). U.S. Patent 5,041,293, December 28. Player, K. (1986). Manufacturing Confectioner, 66(10), 61-5. Weyland, M. (1994). Manufacturing Confectioner, 74(5). Woods, L.C. (1976). Gordian, 76(2), 53-7.

TEN

Margarines and Spreads

Eric Flack

10.1 Introduction The invention of margarine in the 1860s is attributed to the French chemist

Hippolyte Mege Mouries, in response to a competitive challenge initiated by

the French Government under Napoleon III for a less expensive and less per

ishable substitute for butter.

Mege had already undertaken research in this field at the Imperial farms,

where he had observed that although underfed or hungry cows lost weight, they

still produced milk, though of lower than normal yield, and that the milk con

tained fat. Thus, he deduced that milk fat was derived from normal body fat,

i.e., tallow. However, since tallow itself does not possess the melting property

of milk fat, he construed that through some metabolic process, a fractionation

of the fat occurred, the lower melting fractions of which were transported to the

mammary glands of the udder whereby, through the enzymatic action of

pepsin, it became transformed to butter fat and dispersed as an emulsion in

the milk plasma, while the harder fractions were utilized by the animal as a

source of energy (Andersen and Williams, 1954).

Having arrived at these conclusions, Mege set out to imitate this natural

process by carefully rendering fresh tallow at body heat (about 45°C) using ar-

255


tificial gastric juices to facilitate separation of tissue from pure fat and then,

following crystallization at 25 to 30°C, extracting under pressure about 60% of

a soft semifluid fraction-oleomargarine-and about 40% of a hard white

fat-oleostearine. The softer fraction had a melting point similar to butter fat,

a pleasant flavor not unlike melted butter fat, a pale yellow color, and could

easily be plasticized, and although different in fatty acid composition from but

ter fat, it offered a useful basis for the production of a substitute. He assumed,

therefore, that this new butter fat substitute consisted of glycerides of margaric

and oleic acids (the former then considered to be a C17 homolog of the satu

rated fatty acids, although now known to be a eutectic mixture of palmitic and

stearic acids) that solidified in crystals having a pearly luster. The name mar

garine was derived from the Greek word "margarites," meaning pearl and thus

is pronounced with a hard "g" according to its derivation.

Mege's process was to take a proportion of the soft fat with appropriate

quantities of milk and water, into which a small amount of udder extract was

stirred. Following agitation, a stable emulsion similar to thick butter cream

formed that, on further churning, thickened to resemble butter. While this

process may now sound rather rudimentary, it nonetheless comprised all the

elements of margarine production as we know them today.

10.2 Early Development Mege took out patents in France and England, but the next major development

took place in Holland when, in 1871 in the absence of patent law in Holland at

that time, he sold his invention to the butter merchants Johannes and Anton

Jurgens in the village of Oss. Also in the same locality was another family of

butter merchants-Simon and Henry Van den Bergh-who were to commence

production shortly afterward and who later were to join forces with the Jurgens

and eventually become the largest margarine manufacturers in the world

(Schwitzer, 1956).

Production followed in most countries in Europe-Austria (1873/4), Italy

(1874), Germany (1874), Norway (1876), and Denmark (1883), which was later

to become the largest per capita consumer of margarine. Mege applied for a

United States patent that was granted in 1874.

Many variations were developed in the following years and patents on new

formulations and processes were taken out. At the same time there was strong

opposition to the introduction of margarine into the market by the farming

Margarines and Spreads 257

community, and in some places antimargarine legislation was introduced.

Opposition from such quarters continued well into the twentieth century and is

not entirely unknown today.

10.3 Yellow-Fat Consumption Despite the restrictions encountered in some countries, the consumption of

margarine has continued to grow, and in many cases has overtaken the con

sumption of butter. Consideration of available statistics may be complicated

since they do not always distinguish between the use of products for spreading,

baking, or frying. Nonetheless, the variation in consumption of spreads, espe

cially before, during, and after the Second World War, is clearly marked. In

the United States, according to the National Association of Margarine

Manufacturers, the change in comparative levels of consumption of margarine

versus butter is significant. See Table 10.1.

Table 10.1 United States-Average con-sumption of butter and margarine (lb per capita)

Year Butter Margarinet

1930 17.8 2.8 1935 17.6 3.0 1940 17.0 2.4

1945 10.9 4.1

1950 10.7 6.1

1955 9.0 8.2

1960 7.5 9.4

1965 6.5 9.9

1970 5.3 11.0

1975 4.7 11.0

1980 4.5 11.2

1985 4.9 10.8

1990 4.4 10.9

1991 4.2 10.6

1992 4.2 11.0

1993 4.5 10.8

1994 4.8 9.9

t From 1975; includes spread products.

Source: USDA Economic Research Service.


A similar development has been seen in Europe (Table 10.2), where in re

cent years (and also forecast to continue) the trend is for a reduction in yellow

fat consumption generally, with small reductions in both butter and margarine

in the order of 4 to 5% and an increase in spreads of 17 to 19% by 1997.

Table 10.2 Europe-Average consumption of butter, margarine, and spreads (kg per capita)

1987 1992 (Est.)

Country Butter Margarine Spreads Butter Margarine Spreads

Belgium/ Luxembourg 8.3 12.8 3.2 7.4 11.7 5.1 Denmark 10.2 16.9 3.5 9.0 14.4 6.2 France 8.8 3.9 0.4 8.2 3.4 0.9 Germany 8.3 7.7 0.3 6.7 8.0 0.9 Greece 0.9 1.4 0.1 1.0 1.4 0.2 Ireland 5.8 4.5 3.4 3.1 4.2 6.8 Italy 2.3 1.2 1.9 1.3 Netherlands 4.1 13.7 3.3 3.4 11.9 4.0 Portugal 0.8 3.4 0.1 1.0 3.0 0.3 Spain 0.5 1.6 0.8 0.5 2.2 1.6 UK 4.9 7.5 0.6 3.9 6.1 2.4 Total EC 5.1 5.4 0.7 4.5 5.1 1.4

Source: Food Source '92 (1992), Frost & Sullivan, New York.

The reason for the change in consumption patterns in recent years-which

is expected to continue into the future-is principally related to concerns over

health following recommendations to reduce overall fat consumption and espe

cially saturated fats from many authorities, for example, the National Academy

of Sciences in the United States and the Committee on Medical Aspects of

Food Policy (COMA) in the UK. Reduction in the consumption may also be

due to factors such as the decline in bread consumption.

There have also been significant structural changes within the markets, as

will be discussed later.

10.4 Definitions and Descriptions The name and basic composition of margarine, or oleomargarine, has been

more or less established since Mege's original formulation-that is, it should


be similar to butter. However, with the new developments during more recent

years involving different components and varying combinations of vegetable

oils, animal fats, and milk fat, a range of new descriptions have come into be

ing such as low-fat spreads, low-calorie spreads, and yellow-fat spreads. In

1993, Moran listed the varieties then available, as shown in Table 10.3.

Table 10.3 Some current spreads

High-fat spreads

Low-fat spreads

Source: Moran (1993).

Butter

Approx. fat content(%)

80

Margarine: Packet 80

Soft 80

Polyunsaturated fatty acids

(PUFA) spreads 80

Vegetable/butter-fat

blended spreads

Vegetable fat spreads

Vegetable/butter-fat

blended spreads

Butter-fat spreads

Very low-fat spreads Water-continuous spreads

80

70

60 40 70

40 40 20-30 15 9

5

In Europe, the adoption of Council Regulation (EC) No. 2991/94 of 5

December 1994 brought all products, including butter, under the one descrip

tion, "Spreadable Fats" and described them as "products in the form of a solid,

malleable emulsion-with a fat content of at least 10% but less than 90% by

weight. The fat content, but excluding salt, must be at least two-thirds of the dry

matter." These terms are further qualified as "products which will remain solid

at a temperature of 20°C and which are suitable for use as spreads."

The definitions and sales descriptions are detailed in Table 10.4.

Clause 2 of Article 3 of this regulation states that the sales descriptions

"minarine" and "halverine" may be used in place of "half-fat margarine."

10

g Ta

ble

10.4

D

efin

itio

ns a

nd

des

crip

tio

ns

for

spre

adab

le f

ats

Fat

-gro

up

def

init

ion

s

A.

Milk

fat

s

Pro

duct

s de

rive

d ex

clus

ivel

y fr

om m

ilk

and/

or c

erta

in m

ilk

prod

ucts

for

whi

ch f

at

is t

he e

ssen

tial

con

stit

uent

of v

alue

B.

Fat

s

Pro

duct

s de

rive

d fr

om s

olid

and

/or

liqu

id

vege

tabl

e an

d/or

ani

mal

fat

s su

itab

le

for

hum

an c

onsu

mpt

ion,

wit

h a

mil

k-fa

t

cont

ent

mor

e th

an 3

% o

f the

fat

con

tent

C.

Fat

s co

mpo

sed

of p

lant

and

/or

anim

al p

rodu

cts

Pro

duct

s de

rive

d fr

om s

olid

and

/or

liqu

id

vege

tabl

e an

d/or

ani

mal

fat

s su

itab

le f

or

hum

an c

onsu

mpt

ion,

wit

h a

mil

k-fa

t

cont

ent

of b

etw

een

10 a

nd 8

0%

Sal

es d

escr

ipti

on

l. B

utte

r

2. T

hree

-qua

rter

-fat

but

ter

3. H

alf-

fat

butt

er

4. D

airy

spr

ead

xo/o

l. M

arga

rine

2. T

hree

-qua

rter

-fat

mar

gari

ne

3. H

alf-

fat

mar

gari

ne

4. F

at s

prea

ds xo

/o

l. B

lend

2. T

hree

-qua

rter

-fat

ble

nd

3. H

alf-

fat

blen

d

4. B

lend

ed s

prea

d xo

/o bu

t no

t m

ore

than

Sour

ce:

Offi

cial

Jou

rnal

of t

he E

urop

ean

Com

mun

ities

, 13

16, V

ol. 3

7,9/

12/1

994.

Pro

du

ct

cate

go

ries

(a

dd

itio

nal

des

crip

tio

n w

ith

in

dic

atio

n o

f% f

at c

on

ten

t b

y w

eig

ht)

Mil

k-fa

t co

nten

t no

t le

ss t

han

80%

but

les

s th

an 9

0%.

Max

. w

ater

16%

; m

ax.

dry

nonf

at m

ilk

mat

eria

ls 2

%

Mil

k-fa

t co

nten

t no

t le

ss t

han

60%

but

not

mor

e th

an 6

2%

Mil

k-fa

t co

nten

t no

t le

ss t

han

39%

but

not

mor

e th

an 4

1%

Pro

duct

s w

ith

mil

k-fa

t co

nten

t:

• L

ess

than

39%

•

Mor

e th

an 4

1 %

; le

ss t

han

60%

• M

ore

than

62%

; le

ss t

han

80%

V

eget

able

and

/or

anim

al f

ats

not

less

tha

n 80

%;

less

tha

n 90

%

Not

les

s th

an 6

0%; l

ess

than

62%

Not

les

s th

an 3

9%;

mor

e th

an 4

1%

Pro

duct

s w

ith

fat

cont

ent:

• L

ess

than

39%

•

Mor

e th

an 4

1 %

; le

ss t

han

60%

•

Mor

e th

an 6

2%;

less

tha

n 80

%

Pro

duct

from

a m

ixtu

re o

f veg

etab

le a

nd/o

r an

imal

fat

s

wit

h fa

t co

nten

t of

not

les

s th

an 8

0% b

ut n

ot m

ore

than

90%

N

ot l

ess

than

60%

; no

t m

ore

than

62%

N

ot l

ess

than

30%

; m

ore

than

41%

Pro

duct

s w

ith

fat

cont

ent:

• L

ess

than

39%

• M

ore

than

41

%;

less

tha

n 60

%

• M

ore

than

62%

; le

ss t

han

80%


Whether the listed descriptions will gain greater prominence other than as

the required secondary descriptions is doubtful since consumers, presumably,

will prefer to favor the brand names that have been applied to the broad range

of products now available.

Fat spreads falling outside these standards, for instance those with fat con

tents below 10% and concentrated products with fat contents of 90% or more,

will not be classed as spreadable fats.

EC legislation does not specify vitamin fortification, which is left for deci

sion at the national level. However, in the UK the requirement will remain as

previously specified in the Margarine Regulations (Sl 1867) 1967. That is,

each 100 g of margarine shall contain 800 to 1000 mg of vitamin A and 7.05 to

8.82 mg of vitamin D. This does not apply to other spreads, so that vitamin for

tification in these cases is a matter for individual decision by the manufactur

ers and/or retailers.

Legislation in the United States and Canada is currently less detailed than

in Europe, but both require a minimum of 80% fat. In the United States, FDA

§156.110 describes margarine (or oleomargarine) as "food in plastic form or

liquid emulsion" containing not less than 80% fat and describes a method for

fat determination. It specifies vitamin A fortification to be not less than 15,000

I.U. per pound but leaves vitamin D as an optional ingredient while stating not

less than 1500 I.U. per pound. While spreads are not specified in the legisla

tion, low-fat spreads were stated in 1990 as the fastest growing category, with

spreads from 20 to 72% fat on the market (Borwanker and Buliga, 1989).

The National Association of Margarine Manufacturers of the United States

describes spreads as having fat contents ranging from 18 to 79%. Details of

market shares in the United States are shown in Table 10.5.

Table 10.5 United States retail market share of margarine and spread products

Type 1980 1990

Stick margarine 65 44 Soft margarine 19 l3

Liquid margarine 1 2

Low-fat vegetable oil spreads 15 41 Total retail market 100 100

Source: National Association of Margarine Manufacturers.


Canadian Standard B.09.016 states that margarine shall be "a plastic or

fluid emulsion of water in fat, oil or fat and oil that are not derived from milk"

and shall contain not less than 80% fat and not less than 3300 I.U. vitamin A

and 530 I.U. of vitamin D.

Calorie-reduced margarine is specified in Standard B.09.0l7 as containing not

less than 40% fat and having 50% of the calories normally present in margarine.

The conversion of International Units of vitamins A and D to microgram

equivalents is complicated in the case of vitamin A since it depends upon the

origin of the fat. Thus, to convert vitamin A from I. U. to f..Lg retinol in foods of

animal origin, the I.U. of retinol should be multiplied by 0.3. However, for

foods of plant origin, the I.U. of beta-carotene should be divided by 10. This

arises because l I.U. of vitamin A is equivalent to 0.3 f..Lg retinol or 0.6 f..Lg

beta-carotene. The conversion of the units for vitamin D is straightforward, i.e.,

li.U. vitamin D = 0.025f..Lg.

10.5 Structure and Raw Materials Margarine is a water-in-oil (W/0) emulsion; that is to say, the water (the disperse

phase) is distributed as droplets within the oil (the continuous phase). In mar

garine, the levels of each largely simulate that found in butter and are regulated

in most places by legislation, viz., minimum 80% fat, maximum 16% water, the

remainder consisting of salts, proteins, emulsifiers, vitamins, colors, and flavors.

Whereas production initially was based upon the use of fractionated animal

fats such as tallow and lard, these were later superseded by vegetable oils and,

for a period, marine oils, both of which offer a much greater flexibility in phys

ical characteristics and economy.

Being the main and most expensive ingredient, the fat blend is also the

most important factor in the formulation of margarine. As oil prices fluctuate, it

is essential to have a fat blend providing the desired quality at minimum cost.

Thus, it is vital to be able to utilize alternative formulations based on prevail

ing price conditions while still maintaining quality. Therefore, a full under

standing of the physical characteristics of the individual oils composing the

blend is critical. In this respect, factors of importance for the fat phase include

the solid/liquid fat ratio, crystallization rate, and melting properties.

In the early days of margarine production, large quantities of milk and wa

ter in almost equal proportions were used for emulsification with the fat, with

much of the excess water being pressed out during kneading to arrive at a final


moisture content of 16% or lower. Nowadays, the aqueous phase is added at

optimum levels and usually consists of a simple solution of skim milk powder

or whey powder in water, with the addition of salt and the pH adjusted to 5.5 to

6.0 by using, for instance, citric acid.

10.5.1 Oils and Fats

Oils and fats, otherwise known as triglycerides, are esters of glycerol and fatty

acids having a basic formula

where R1, R2, and R3 are the fatty acid residues, which may be the same but,

invariably, are different according to the source of the fat. Examples of the

variations in fatty acid compositions of different oils and fats are shown in

Table. 10.6.

Modification of the fat by, for instance, hydrogenation, whereby some of the

unsaturated links (double bonds) become saturated (for instance oleic C18:1 to

stearic CIS) offer the opportunity of considerable variation in the melting points of fats, especially the liquid vegetable oils. The exact physical character

of a fat depends upon that of the constituent fatty acids that can vary widely in

melting point, as illustrated in Table 10.7.

10.6 Fat Crystallization Variations in the crystallization properties of fats and differences between

batches of a similar origin may cause problems in production even though pro

cessing techniques are fully controlled and highly automated (Madsen, 1983).

The crystallization rates of some individual and blended fats are shown in

Table 10.8

Oils and fats are polymorphic and can crystallize in more than one form,

which can differ in terms of melting point, density, heat of fusion, and rate of

crystallization. The three crystal forms are commonly known as alpha (a), beta

prime (W), and beta (~), with the a form having the lowest values, the W inter-

~

Tabl

e 10

.6

Fat

ty a

cid

com

posi

tion

s o

f oil

s an

d f

ats

(%m

/m)

""' L

ow-

Bee

f G

rou

nd

-P

alm

er

uci

c S

un

-F

atty

aci

d ta

llow

L

ard

C

oco

nu

t n

ut

Pal

m

ker

nel

ra

pes

eed

S

oy

a fl

ower

C-1

0 &

low

er;

--

-13

-17

capr

ic, e

tc.

C12

laur

ic

0.2

0.2

45.9

-50.

3 -

tr

43.6

-51.

4 -

tr

C14

myr

istic

3

-4

1.6

16.8

-19.

0 tr

0.

8-1.

3 15

.3 1

7.2

tr

tr

tr

C14

:1 m

yris

tole

ic

0.5-

1 tr

-

-tr

C

16 p

alm

itic

2

6-2

8

25

-30

7.

7-9.

7 9.

2-13

.9

43.1

-46.

3 7.

2-10

.0

3.4

-6

9.9-

12.2

5.

6-7.

4 C

16:1

pal

mit

olei

c 2

-3

2.5-

3.5

-tr

tr

-

0.2-

0.6

tr

tr

C18

ste

aric

2

3-2

7

15

-25

2.

3-3.

2 2.

2-4.

4 4.

0-5.

5 1.

9-3.

0 l.

l-2

.5

3.6-

5.4

3.0-

6.3

C18

:1 o

leic

3

0-3

5

35

-45

5.

4-7.

4 36

.6-6

5.3

36.6

-65.

3 11

.9-1

8.5

52-6

5.7

17.7

-25.

5 14

.0-3

4.0

C18

:2 l

inol

eic

1-1.

5 7-

12

1.3-

2.1

15.6

-40.

7 9.

4-11

.9

1.4-

3.3

16.9

-24.

8 50

.5-5

6.8

55.5

-73.

9 C

18:3

lin

olen

ic

0-1

0.

5-1

tr

tr

0.1-

0.4

tr

6.5-

14.1

5

5-9

5

tr

C20

& h

ighe

r 4

-8

1-4

tr

2

-8

[xx]

1 [x

x]1

1-6

[x

x]l.

5 [x

x]l.

5

Iodi

ne v

alue

t 4

5-5

7

59

-70

7.

5-10

84

-105

5

0-5

4

16

-19

10

9-12

6 12

5-13

6 85

tiodi

ne v

alue

is a

mea

sure

of t

he d

egre

e of

uns

atur

atio

n of

the

fat.

Table 10.7 The melting points of fatty acids

Fatty acid No. of double bonds

C12lauric

C 14 myristic

C 14: 1 myristoleic

C16 palmitic

C16:1 palmitoleic

C18 stearic

C18:1 oleic

C18:2 linoleic

C18:3linolenic

C20 arachidic

1

1

1 2

3

Source: Andersen and Williams (1954).

Table 10.8 The crystallization rates of fats

Fat (0 C) Time (min)

Coconut 3

Coconut/palm 1:1 4

Coconut/palm, interesterified 5 Palm-hardened 5

Palm-hardened/palm 2:1 8 Lard 14

Lard/palm 1:1 15 Palm 27

Sheafat 45

Source: Madsen (1983).


M.P. eC)

44.2

54.4

Liquid

62.9

Liquid

69.6

16.2

Liquid

Liquid

74.4

Temp.

20

15

18

17

13 lO

10

lO

10

mediate, and the most stable ~ form the highest values. Transition from one form

to another is from a ~ W ~ ~ and is not reversible without remelting the fat.

The polymorphism of crystalline fats may cause problems with the consistency

of margarine and spreads. During production, the fats initially crystallize in the a form and normally will rapidly transform to the W form. This is the desirable form

for spread production since the small needle-shaped W crystals (about l!lm long)

impart good plasticity. Should the crystals transform from W form to the much

larger p form (> 20 Jlm) they will give the spread a grainy consistency known as

"sandiness," as can be seen in Figure 10.1 (Madsen and Als, 1968).


(a) (b)

Figure 10.1 Fat crystals in (a) normal margarine with good consistency and (b) a margarine with large ~crystals causing a "sandy" texture. (Magnification 200x.) (Courtesy of Danisco Ingredients, Denmark.)

Concurrently, the specific area of the crystal surface will decrease, allowing

the liquid oil to penetrate to the surface of the margarine, which may then lead

to oiling out, especially if the margarine comes under pressure. Some veg

etable oils such as partially hardened sunflower or low erucic rapeseed are

particularly prone to form ~ crystals and thus can cause sandiness in spreads.

In this case, sorbitan tristearate at 0.3% of the fat has been found to inhibit the

transition from the W to the ~ form

The crystal-modifying effect of a range of emulsifiers-sorbitan esters,

ethoxylated sorbitan esters, ethoxylated fatty alcohols, citric acid esters of

monoglycerides (Citrem), diacetyl tartaric acid esters of monoglycerides

(DATEM), sucrose monostearate, sodium stearoyl lactylate, and polyglycerol

esters- has been investigated on the polymorphism of tristearin (glyceryl tris

tearate) (Garti et al. , 1982).

In these trials it was found that sorbitan monostearate and Citrem (Cl6/Cl8

fatty acids) were the most effective in preventing the recrystallisation (from a to ~ form) of tristearin.

It should be noted that when used in emulsions, surface-active materials will

Margarines and Spreads 26 7

be adsorbed at the oil/water interface and that only lipophilic emulsifiers with

high solubility in the oil phase can perform as crystal inhibitors in emulsions. Varying the level of saturated fat affects the degree of crystallinity of the oil

phase (Borwanker and Buliga, 1989). Spreads with 40% fat were made using

oil phases of varying crystallinity by blending either liquid soyabean oil or stick margarine oil with soft margarine oil. The textures of the spreads made with these blends were visibly very different, increasing in softness in the

same direction as the oil itself. As a consequence of increased firmness, the

stability of the resulting spread was expected to increase with increasing crystalinity in the oil phase. A centrifugation procedure was used to measure the stability of the emulsions (Figure 10.2). The higher amount of water and/or oil

(especially water) released corresponds to a less stable emulsion.

10.7 Emulsifiers The main function of emulsifiers in processed foods is to reduce the interfacial

tension between the phases of an emulsion-usually oil and water. In such two-phase systems, one phase is dispersed as large droplets within the other.

"0 +-'Cil c Ul Cll co u Cll .... -Cll Cll .s-.: >.0

.. ~I... ==o ..c.._ co Cll +-'+J CJ)co

3:

60

50 ""' 40 '"--30 " 20

-a...___ -~ 10

~

0

4.5 6.3 8.6 10.4

Crystallinity (enthalpy, J/g)

50 Soft 50 liquid

75 25

Soft 75 25

~

13.0

50 Soft 50 Stick

O Oil

O Water

Figure 10.2 Effect of the degree of crystallinity on the emulsion stability of 40% fat spreads as measured by ultracentrifugation. (From Borovanker and Buliga, 1989.)


They are either oil-in-water (0/W) emulsions, where the continuous phase is

water (such as in milk or ice cream) or water-in-oil (W/0), where the continu

ous phase is oil (as in butter and margarine).

The stability of two-liquid phase emulsions is kinetic stability, i.e., the system

is not thermodynamically stable (Friberg et al., 1990). Thermodynamically sta

ble emulsions would spontaneously reform following separation by, for instance,

centrifugation, while experience shows that an emulsion that has separated re

mains so unless mixed by some external action. In reality, the two separated

phases are in the most stable state to which all emulsions will tend. Thus, a sta

ble emulsion is one in which this inevitable trend has been retarded so that it is

not noticeable during the normal life of the product--even if it be several years.

Margarine is a water-in-oil emulsion in principle only because, in reality, it is

a dispersion of water droplets in a semisolid fat phase, containing fat crystals

and liquid oil (Krog et al., 1983). Preparation of the emulsion requires consider

able energy to reduce the droplet size of the disperse phase, thereby creating an

increase in the surface area between the two immiscible phases.

The initial water-in-oil emulsion is prepared in mixing tanks with vertical or

horizontal stirrers to ensure emulsification but without incorporating too much air.

It is rather coarse in water-droplet size and fairly unstable if not kept agitated.

In modern continuous production, the emulsion exists for only a brief pe

riod before passing into the chilling unit where final emulsification and crys

tallization of the fat phase take place. Thus, the emulsion need not be very

stable against coalescence as the water droplets become fixed within the semi

solid phase. However, the droplet size is important when considering flavor re

lease and microbiological spoilage. Thus, emulsifiers are used to lower the

interfacial tension between the oil and water phases, which will generally re

sult in a smaller water-droplet size. Distribution of the water droplets in the

range 2 to 4 11m will give better stability against deterioration such as mold

growth. However, it is still desirable for some of the water droplets to be larger

in size-10 to 20 11m-to give a better flavor release in the mouth.

For these purposes, therefore, lipophilic emulsifiers such as mono-/diglyc

erides of long-chain fatty acids (C16-C18) are used at levels of 0.1 to 0.3%, often in combination with 0.05 to 0.1% refined soya lecithin.

Comparisons of the water-droplet distribution in margarine emulsion and in

finished margarine are shown in Figure 10.3. Droplet size in the emulsion is

further reduced during the cooling and kneading processes in the tube chiller.

The water droplets in finished margarine are stabilized by adsorbed fat


(a) (b)

Figure 10.3 Water-droplet size distribution in (a) margarine emulsion and (b) the finished margarine. (Magnification 200x.) (Courtesy of Danisco Ingredients, Denmark. )

crystals, as seen in Figure 10.4 showing the microstructure of margarine by

freeze-fracture transmission electron microscopy. It is clearly seen that the wa

ter droplets are covered by fat crystals, oriented flatly along their surface.

Margarine is frequently used for frying when it is especially important that

it does not spatter. Spattering is caused when the margarine melts in the frying

pan, the emulsion breaks, and the coalesced water droplets, due to gravity,

form a film of water covered with molten fat on the frying pan. When the tem

perature reaches boiling point, the increase in vapor pressure will cause spat

tering-sometimes explosive-of the water phase.

It is desirable, therefore, that the margarine allow gradual evaporation of

the water from the small water droplets and the formation of a fine, golden

brown sediment that does not adhere to the frying pan. Both formulation and

processing play important roles in reducing the tendency to spatter. The pres

ence of salt and milk are desirable as is a high pH, up to say 6, while sugars

and starches will increase the tendency to spatter. The selection and addition

of the emulsifier is of considerable importance in producing a margarine with

good frying properties.

While a combination of mono-/diglycerides and lecithin will have only a


Figure 10.4 Freeze fracture electron micrograph showing the microstructure of margarine. Water droplets (w) are covered with fat crystals. (Bar: l!lm.) (Courtesy of Dr. W. Buchheim, Keil.)

limited effect in reducing spattering in low-salt margarine, there are other

emulsifiers that, either alone or with lecithin, will help prevent coalescence of

water droplets during frying. In this respect, citric acid esters of mono- and

diglycerides (Citrem), polyglycerol esters, and thermally oxidized soybean oil

interacted with mono- and diglycerides used at 0.3 to 0.4%, together with soya

lecithin can be very effective.

10.8 Processing Typical modern processing involves the separate processing of the oil and wa

ter phases. The oils and fats are kept in storage tanks at temperatures just ade

quate to maintain them at the required fluidity. Preferably, they should be

bottom fed to avoid splashing and aeration. It is essential that the plant, i.e.,

tanks, pipes, and pumps, be entirely free from copper or copper alloys to avoid

the high risk of oxidation.

The final oil blend together with oil-soluble components such as emulsi

fiers, colors, flavors, and vitamins, is prepared separately from the water phase


that may contain milk components such as whey powder, skim milk powder, or

sodium caseinate and also salt, gelatin, or thickener, water-phase flavors where

appropriate, and preservatives such as potassium sorbate for low-fat products.

Modern methods involve the feeding of the phases by computer-controlled

load cells, which ensures fast throughput and constant composition.

A second emulsion tank is used for maintaining quantities of finished emul

sion for feeding the cooling and kneading equipment. Cooling and kneading

can be carried out by either of two different methods: (i) tube chiller or (ii)

chilling drum-complector.

In the former, cooling and kneading take place in a closed system and in a

single process. In the latter, the cooling and kneading are carried out sepa

rately-cooling on the chilling drum and kneading in the complector. The ad

vantage of the chilling drum-complector method is that it allows the product to

rest between cooling and kneading, which is important with formulas based on

slower crystallizing fats, for instance, puff pastry margarine. By comparison,

the tube chiller is relatively more compact considering throughput, is easy to

operate, and reduces the possibility of spoilage.

Most types of margarine can be made very satisfactorily using the tube

chiller method, although in some cases extra working units (pinning machines)

may prove advantageous. However, the chilling drum-complector has been the

preferred method for puff pastry margarine, although tube chillers are now

· widely used, and is perfectly satisfactory for normal table margarine and for

cake margarine. The suitability of both methods is summarized in Table 10.9.

Table 10.9 Comparison of processing methods

Type

Block/stick margarine Soft table margarine Low-fat spread Cake and creaming margarine Puff pastry margarine Shortening W/0 emulsion with high water content

Tube chiller

XXX

XXX

XXX

XXX

XX

XXX

XXX

XXX = Excellent; XX = acceptable; X = poor.

Source: Madsen (TPlOl).

Chilling drum-complector

XXX

X

X

XXX

XXX

X

X


The comparative merits of the two methods were investigated using four differ

ent fat combinations (see Table 10.10) in puff pastry margarines that were then

evaluated by various parameters including a "finger" judgement (see Table

10.11) of plasticity after one week (Madsen, TPlOl).

Table 10.10 Dilatation, iodine value, and melting points of fat blends used for comparison of puff pastry margarines

Solid fat index

Iodine Fat blend so 10° 15° 20° 25° value

l. l8°Ct animal 37 37 34 27 22 67

2. 18°Ct vegetable 40 40 36 31 24 7l

3. 12°Ct animal 43 42 37 29 23 66 4. soct animal 37 35 31 25 19 74

tThe figures indicate storage and rolling temperature of the puff pastry margarine. Source: Madsen (fPlOl).

Table 10.11 Plasticity judgement by finger method

Fat blend Method Plasticity judgment

l. l8°C animal Chilling drum Fine plasticity Tube chiller Lumpy/gritty, a little firm,

becoming slack and very

greasy when worked

2. 18°C vegetable Chilling drum Good plasticity, tending to

become greasy

Tube chiller Gritty, firm, becoming slack

and greasy when worked

3. 12°C animal Chilling Fine plasticity

Drum

Short and gritty, very,

Tube chiller firm, becoming soft and

greasy when worked 4. soc animal Chilling drum Fine plasticity

Tube chiller Short and gritty, very firm,

becoming soft and greasy

when worked

Source: Madsen, TPlOl.

M.P. eq 37

37

41

37

Score

5

0

4

1

5

0

5

0


Similar results were found when the same products were judged after 3

weeks' storage.

This rather critical evaluation did not fully take into account the differ

ences that might result from the use of varying techniques possible with tube

chillers, which was investigated separately.

Table 10.12 Plasticity judgment by means of the finger method in puff pastry margarines made on tube chiller with varying production techniques

Production Plasticity judgment Points technique Fat blend after I week at l8°C

l. Normal Animal Lumpy and gritty, a little firm but 0

becomes slack and greasy when worked Vegetable Gritty, firm but becomes slack and l

greasy when worked 2. Intermediate Animal A little lumpy and soft, very greasy 1

crystallizer when worked Vegetable A little firm but becomes soft and 2

greasy when worked 3. Pinning machine Animal A little lumpy and fairly soft; very l

greasy when worked Vegetable Becomes easily soft and greasy when 2

worked

4. Resting tube + Animal Soft and greasy 0 pinning machine

Vegetable Too soft and very greasy l 5. Low capacity Animal Fine homogeneity but too soft, fairly 3

good plasticity Vegetable Fine homogeneity, a little too soft, 4

fairly good plasticity

Source: Madsen, TPlOl.

The important issue relates to the postcrystallization of the fats, which was

further investigated (Madsen, 1981 ). A good plastic puff pastry margarine can

be bent without breaking and the plasticity evaluated by repeated handwork

ing to check stability, firmness, and greasiness (Figure 10.5).

In the case of cake margarine, the most important points are that the fat

blend is soft and easy to incorporate into the batter and has good creaming

properties. This, therefore, suggests the use of lauric fats (coconut, palm ker

nel) that crystallize quickly and, thereby, facilitate creaming.


Figure 10.5 Evaluation the plasticity of puff pastry margarine by hand. (Courtesy of Danisco Ingredients, Denmark.)

10.9 Reduced- and Low-Fat Spreads As has been previously highlighted, low-fat spreads have been the only growth

area in a gradually declining market. They can have fat contents from lO to

79% and, except in the case of very low-fat spreads, are W/0 emulsions.

However, with low-fat products, it is necessary to strike a balance between sta

bility and mouthfeel, which can be affected both by the composition and the

method of processing.

Margarine is essentially a stable product and the appropriate fat blend and the

combination of milk proteins, lecithins, and/or saturated mono- and diglycerides

used in production ensure both stability and the desired eating characteristics

(Flack, 1992). However, in reduced- and low-fat spreads in which the dispersed

phase (aqueous) can exceed the phase volume of the continuous (fat) phase, prob

lems can arise with stability, meltdown, and flavor release (Moran, 1993).

While milk proteins are in high-fat products to improve mouthfeel and fla

vor, they also act as hydrophilic 0/W-emulsion stabilizers, and thus their use

in low-fat products, together with the considerable energy input needed, could

result in phase inversion.

These problems can be overcome by a combination of formulation and pro

cessing. Important factors in the formulation include the melting characteristics


of the fat blend, the type and level of emulsifier, and the addition of thickeners

such as gelatin, sodium alginate, pectin, and carrageenan to the aqueous phase.

Low levels of whey protein may be used to improve flavor release with the further

advantage that the pH of the aqueous phase can be lowered to improve keeping

properties because, unlike casein, whey proteins do not precipitate at low pH.

The speed of processing, i.e., the rate of throughput and the emulsion tempera

ture, are also important factors in the stability of the spread.

Examples of the effect of various types of emulsifiers on the stability of low

fat spreads with fat contents of 40% and 20% are shown in Tables 10.13 and

10.14, respectively.

Table10.13 Effect of types and blends of emulsifiers on the stability of a 40% fat spread

Levels Water separation % after

of use Types of emulsifier 5 min 10 min 15 min 20 min

0.6% Distilled monoglyceride from

vegetable oil. IV approx. 80

0.6% Distilled monoglyceride from

plus

0.2%

vegetable oil. IV approx. 80

Polyglycerol ester of fatty

acids. IV approx. 80

Distilled monoglyceride from

1.6

0

0.4% plus

0.2%

vegetable oil. IV approx. 80 0

Polyglycerol ester of interesterified

ricinoleic acid. IV approx. 85

IV = Iodine value.

Formulation of spread:

Water phase 56.4% water

pH 4.5 1.5% gelatin

Fat phase


0.5% whey powder

1.5% salt

0.1% potassium sorbate

39.2-39.4% fat blend

0.{H).8% emulsifier (as above)

4 ppm beta-carotene

2.6 9.5 15.8

l.O 2.6 6.3

0 0 0


Table 10.14 Effects of types and blends of emulsifiers on the stability of a 20% fat spread

Levels and types of emulsifiers

0.8 % distilled monoglyceride from

sunflower oil. IV approx. lOS

O.S % distilled monoglyceride from

sunflower oil. IV approx. lOS

plus

O.S% polyglycerol ester of

interesterified ricinoleic acid. IV

approx 8S

IV = Iodine value.

Formulation of spread:

Water phase 69.9% water

Results

Emulsion split into separate

phases in tube chiller

Produced a fine, stable spread

with good spreadability and

mouthfeel

pH6.8

4.0% skim milk powder

3.0% gelatin

Fat phase


l.S% sodium alginate

1.5% salt

0.1% potassium sorbate

19.0-19.2% fat blend

0.8--1.0% emulsifier (as above)

8 ppm beta-carotene

The trial batches in both cases were made on a three-tube Perfector pilot

plant using a fat blend composed of

60 parts soya oil

30 parts partially hydrogenated soya oil

lO parts coconut oil

Both examples indicate the potential instability of these emulsions and the

variation in the stabilizing effects of different emulsifier blends even when used

at low dosage levels. These results suggest that emulsifier structure at the inter

face plays a critical role in retarding water-droplet flocculation and coalescence.

While the evaluation of spreads by measuring water separation provides

quantifiable results, a quicker and more practical evaluation of the stability of


spreads can be made by spreading a sample with a knife on cardboard, as

shown in Figure 10.6, where the desired qualities of good spreadability and

low moisture loss are shown in the right-hand photograph. A rheological mea

surement to obtain quantitative data could also be carried out.

It is rather more difficult to produce low-fat butter spread from butter oil

due to the relative hardness of the fat at low temperatures. Nonetheless, spread

with a butter fat content of about 40% has been produced using 5% sodium ca

seinate plus 2% sodium alginate in the water phase and 0.5% distilled mono

glyceride, IV approximately 55, in the fat phase.

Figure 10.6 Evaluating margarine by spreading on cardboard. (Courtesy of Danisco Ingredients, Denmark.)

However, in this case it is not possible to lower the pH of the aqueous phase

without precipitating the caseinate, which will reduce its emulsifying proper

ties, and therefore, the keeping properties of the spread will be limited.

However, a satisfactory low-fat butter spread can be produced from dairy

cream, using a distilled monoglyceride with high iodine value (80 to 105) in

the cream and a thickener such as sodium alginate. In this case, phase inver

sion from 0/W to W /0 can be achieved in the tube chiller, using normal or

slightly reduced cooling and operating at 40 to 50% of the usual capacity. To

obtain a satisfactory working effect, a high rotor speed in the tube chiller cool

ing cylinder would be preferable (Madsen, 1989).

Factors that may affect the efficiency of phase inversion in low-fat emul

sions are listed in Table 10.15.


Table 10.15 Factors promoting the inversion of oil-in-water emulsions

l. Increased rotor speed 2. Controlled temperature (maintenance of optimum fat solids level) 3. Use oflow-HLB emulsifiers 4. Increased oil-droplet size entering unit

Source: Moran (1993).

Most of these factors concern the increase in rate of collision of oil droplets

upon which the rate of coalescence is dependent (Moran, 1993). The emulsi

fier(s) likely provide steric hindrance to keep droplets separated.

10.10 Oil-in-Water Spreads According to Moran (1993), the advantages of 0/W spreads over the more con

ventional W/0 spreads may be attributed to

• Product structure not dependent on the type of fat used

• Any level of fat can be used from 1% to more than 50%

• High levels of protein are possible

• Processing is easier and cheaper

• Flavor release is quicker on the palate

Against this, however, one major drawback is that unless products are pre

pared at comparatively low pH, then ultra-high-temperature processing and

possibly an aseptic filling procedure must be followed if shelf lives comparable

to conventional spreads are required.

Oil-in-water spreads remain a relatively unexplored area of the spreadable

fats market, possibly due to the problem of microbiological deterioration, but

may offer a potential for future expansion in markets where adequate levels of

preservatives are permitted. In contrast to W /0 emulsions, these systems

would utilize high-HLB emulsifiers to stabilize the water-continuous emulsion.

10.11 Liquid Margarine Liquid margarine is used primarily for frying and is available particularly in

markets such as the United States, Germany, and Sweden, where butter or

margarine are normally used for frying (see Table 10.5).


In markets such as the UK that have traditionally used solid fats like lard or

cooking fat or, more recently, liquid vegetable oils, there is less interest in us

ing liquid margarine.

A typical composition has a fat phase of about 82% based on soya or sun

flower oil, in which emulsifiers perform two functions. First, an emulsifier such

as citric acid ester of monoglyceride (Citrem) at, say, 0.4% plus 0.2% soya

lecithin produces a stable water dispersion with limited spattering during fry

ing; and second, a selected mono- and diglyceride blend prevents oiling out on

storage and thus gives a homogenous product with low viscosity. If the mar

garine is not intended for frying, the Citrem can be replaced with 0.2% dis

tilled monoglyceride. The water phase may contain proportions of skimmed

milk powder and salt as well as a preservative such as potassium sorbate.

Flavoring may be added to both phases.

The aqueous phase should be adjusted to 4.5 to 6.5 pH and pasteurized at

80°C. The fat phase should be tempered to about 60°C and the emulsifiers

melted into a small amount of the liquid oil to a temperature of 65 to 70°C,

which is then stirred into the main part of the fat phase. The water phase is

added to the fat phase under continuous agitation before cooling through the

tube chiller with an outlet temperature of approximately 5 to 7°C.

The emulsion should be rested for 2 hours to allow proper fat crystal forma

tion and then stirred vigorously for 15 minutes before topping off for packaging.

10.12 Summary Standard margarines containing 80% fat are, under normal conditions, rela

tively stable, requiring minimal quantities of lecithin and/or mono- and diglyc

erides over and above the quantities of milk proteins usually present.

However, where the margarine is required for special purposes, i.e., cake

making or frying and particularly in products with reduced fat levels, emulsi

fiers specific to the unique functional requirements of the application should

be selected (see Chapter 8 for applications of emulsifiers in baking products).

References Andersen, A.J.C., Williams, P.N. (1954). Margarine, 2d ed., Pergamon, Oxford. Borwanker, R.P., Buliga, G.S (1989). Emulsion properties of margarines and low fat

spreads, in Proc. Food Emulsions and Foams-Theory and Practice (eds. P.G. Wan eta!.), San Francisco, pp. 44-52.


Flack, E. (1992). The role of emulsifiers in reduced fat and fat free foods, in Food Technology International Europe (ed. A. Turner), Sterling Publications, London, pp. 179-181.

Friberg, S.E. et al. (1990). Emulsion stability, in Food Emulsions (eds. K. Larrson and S.E. Friberg), Marcel Dekker, New York, pp. 1-40.

Garti, N., et al. (1982).]. Am. Oil Chem. Soc., 59, 181. Krog, N., et al. (1988). Applications in the food industry, in Encyclopaedia of Emulsion

Technology, Vol. 2: Applications of Emulsions (ed. P. Becher), Marcel Dekker, New York, p. 321.

Madsen, J. Puff Pastry Margarine: A Comparison of the Chilling Drum and Tube Chiller Methods of Production, TP101, Grinds ted, Denmark.

--- (1981). Post-Crystallisation in Puff Pastry Margarine, at 11th Scandinavian Symposium on Lipids, Bergen, Norway.

--- (1983). Product Formulation and Processing of Margarine and Yellow Fat Spreads, at Margarine and Yellow Fat Seminar, Coventry, England.

--- (1989). Low Calorie Spread and Melange Production in Europe, at World Conference on Edible Oils and Fats Processing, Maastricht, Holland.

--- , Als, G. (1968). Sandiness in Table Margarine and the Influence of Various Blends of Triglycerides and Emulsifiers Thereon, at /Xth Int. Soc. of Fat Research Congress, Rotterdam.

Moran, D.P.J. (1993). Reduced calorie spreads, in Porim Technology, No. 15., Feb '93, Palm Oil Research Institute of Malaysia.

Schwitzer, M.K. (1956). Margarine and Other Food Fats, Leonard Hill, London.

ELEVEN

Emulsifier Trends for the Future


As in many other industries, forecasting the future is usually done by examin

ing the trends of the past and extrapolating the changes for several years into

the future. While this works well for continuous functions, discontinuous

events often produce dramatic changes in market structures. Forecasting tech

nology is essentially an observation of technical events, extrapolating the

trends, and trying to estimate which technologies are about to jump to the next

S curve. Food technology abhors radical change. Development of new crops is

contingent on being able to diffuse the crop into the massive agronomic supply

chain. Issues such as cross-pollination and identity preservation may pose sig

nificant problems. When a new product is brought to market, it needs to be

thoroughly tested or examined for its safety. Programs like HACCP are aimed

at institutionalizing safety into the industry. Even if the government is assured

of a product's safety, consumer acceptance is by no means assured.

Controversies around genetically engineered and irradiated foods are testi

mony to this principle.

As we stated in Chapter l, development of totally new emulsifiers is un

likely because of the time and cost involved with regulatory approval.

However, this by no means sounds a death rattle for innovations in the field of

281


food emulsifiers. Some social, demographic, and technical developments may

cause discontinuities in the underlying science involving food emulsions. A

few of these trends will be examined.

11.1 Globalization in the Food Industry The food industry has traditionally been multidomestic. A number of factors

such as local taste, perishability, and low value-to-volume ratios in shipping

were responsible. However, counter trends such as increased income in develop

ing nations, more international communication and travel, and increased consol

idation in the processed food industry are exerting globalization pressures.

Development of food products for the global market will change some of the

rules for higher value products. Emulsions will require more microbiological

and physical stability to withstand shipping long distances and the absence of

refrigerated storage in some countries. Some lessons may be learned from the

pharmaceutical and cosmetic industries that are further advanced in the appli

cation of emulsifiers to produce long shelf lives.

One example of a new global product might be a margarine that is stable

without refrigeration. In addition to a higher melting fat, a more robust emulsi

fier system will be required because coalescence of water droplets could cause

separation into a phase that would be vulnerable to microbial growth.

As global population continues to explode, food emulsifiers will also need

to adapt to new lower cost sources of protein, carbohydrate, and fat emulsions

formed at lower temperature and mechanical shear can also contribute to en

ergy savmgs.

11.2 Nutritionally Driven Changes in Foods Nutritional studies in the area of diet and health or the counterpart, diet and

disease, are continually being carried out and reported, often with apparently

contradictory interpretations. Assessing trends in this area can be confusing

unless one stays with a few areas where there is general consensus.

Saturated fat has been long associated with its ability to raise serum choles

terol, notably LDL. The FDA's NLEA regulations recognized this consensus by

requiring labeling of saturated fat for all packaged foods. Food processors have

therefore been making a substantial effort toward substitution of solid fats with

liquid oils. This poses a formidable challenge in some products where solid fat is

Emulsifier Trends for the Future 283

part of the physical structural or primary functionality of food. For example, the

development of high liquid-oil margarines will require an emulsifier that can sta

bilize a W/0 emulsion where the continuous phase is liquid. Adjunct technolo

gies, such as the development of molecular networks to thicken the oil phase can

make a significant contribution to providing structure to the processed food.

Solid fat is implicated in such functions as aeration of whipped toppings and for

mation of evenly dispersed air cells in cakes. Replacement with liquid oil places

more of a functional burden on the emulsifier system.

Health authorities have recommended that total dietary fat should not ex

ceed 30% of calories. Some consensus is also building that some forms of can

cer may correlate to total caloric consumption. Since fat represents 9 cal/ gram,

cutting fat consumption will also reduce total calories (if the same weight of

food is consumed). If consumers respond to these recommendations, pressures

for availability of reduced-fat and fat-free foods will continue or even increase.

Elimination of fats from products normally containing high levels creates enor

mous challenges to maintain texture and flavor. Flack (1992) has speculated

that emulsifiers can play an important role in reclaiming some of these quali

ties. Structured emulsifier phases have been patented as the basis for forma

tion of a pseudo-fat phase (Heertje, et al., 1994; Kleinherenhrink et al., 1995).

This trend toward replacement of fat functionality with emulsifiers will un

doubtedly continue.

11.3 Trends toward Safer Emulsifiers Interest in natural and minimally processed foods has waned and resurged

many times over the last half century. As previously mentioned, phospholipids

and proteins are the only "all natural" emulsifiers. The discovery and elimina

tion of dioxane in polysorhates illustrates many of the concerns voiced about

synthetic food additives. Testing and surveillance of additives will continue

and more definitive assays will he developed to assure their safety.

Toxicological evaluations are also becoming more sophisticated and spe

cialized. For example, Larsson (1994) has described a model that tests the ef

fects of surfactants on gastric and intestinal lumina cells. Concerns about

penetration of single-chain food emulsifiers, such as lysophosphatidylcholine

and sodium stearoyllactylate, have been expressed.

Microbes have long been used in the food industry to produce cultured

products such as cheese and yogurt. Microbes have also been used to produce


very efficient surfactants for application such as enhanced oil recovery and oil

spill control. A logical extension of these technologies would be to develop

food-grade organisms that produce natural surfactants. However, extensive

evaluation would still be essential to ensure the safety of these products when

consumed in processed foods.

11.4 Emulsifier Structure and Interactions with Other Ingredients Chapter 6 of this book has discussed the formation of mesophases of food

emulsifiers in aqueous environments. Although this property has been known

for a few decades, functional implications are just beginning to emerge

(Heertje et al., 1994; Kleinherenbrink et al., 1995). lsraelachvili (1985) has

described mesophase formation as a function of intermolecular forces. He pro

poses a model, shown in Figure 11.1, where a free energy minimum is

achieved by formation of a structure that balances attractive forces of hy

drophobic alkyl chains and the repulsive forces between polar head groups.

The author has calculated a "critical packing parameter" from the effective

head group area, length of the alkyl chain, and volume of the cone defined by

the previous two factors. Table 11.1 lists the structures expected for ranges of

critical packing parameters. The significance of this technology is that once

Interfacial (hydrophobic) attraction ,.--/Head-group (hydrophilic) repulsion

~ Volume v ·-._ \

Area a0

Figure 11.1 Determination of critical packing parameter {lsraelachvili, 1985).

Emulsifier Trends for the Future 285

Table 11.1 Amphiphilic packing of surfactants. (From lsraelachvili, 1985.)

Lipid type

Single-chain lipids with large head group areas Single-chain lipids with small head group areas Double-chain lipids with large head group areas Double-chain lipids with small head group areas Double-chain lipids with small head group areas

Critical packing shape

< l/3

l/3-l/2

l/2-l

-l

>l

Critical packing parameter (VIaJ.)

Cone

Truncated cone

Truncated cone

Cylinder

Inverted truncated cone

Structures formed

Spherical micelles

Cylindrical micelle (hexagonal)

Flexible bilayers, vesicles

Planar bilayers (lamellar)

Inverted micelles

the functional role of a mesophase is defined, rational design of head and tail

groups can he accomplished and the emulsifier synthesized by techniques de

scribed in Chapter 2.

Emulsifiers may he viewed as one class of functional food ingredients. As

Chapters 4 and 5 have pointed out, these ingredients may interact with carbo

hydrates and proteins to produce a number of technical effects. The area of in

gredient interactions is the subject of a recent book by Gaonkar (1995). New

experimental techniques such as scanning tunneling microscopy and interfa

cial rheology have the potential to provide greater understanding of these in

teractions. Emulsifiers can then be designed to form more selective interactive

structures that may result in improved or entirely new functionalities.

11.5 Enzymatic Synthesis of Food Emulsifiers Production of emulsifiers involves contacting lipid and polar phases that are

mutually insoluble. To achieve homogeneity, temperatures as high as 500°F

are applied and held until reaction is complete.


A consequence of this drastic processing is the production of undesirable

and often unidentified byproducts from side reactions. These byproducts can

impart metallic, soapy, or bitter off-flavors in finished food products. For exam

ple, high temperatures cause caramelization of sucrose esters. To avoid this

problem, solvents such as dimethyl sulfoxide and dimethyl formamide have

been used. However, removal of these solvents from the product poses another

serious problem.

An alternative approach is to catalyze esterification or interesterification reac

tions with enzymes such as lipase or esterase. Since these reactions are carried

out at much lower temperatures, formation of odors and off-flavors can be signifi

cantly reduced. This is particularly advantageous for unsaturated fatty acids that

can be oxidized by high temperatures and small quantities of air. Another poten

tial advantage for enzyme synthesis would be the ability to produce high concen

trations of monoesters without the need for short path distillation. To accomplish

this, the reaction could be carried out at a temperature just below the melting

point of the monoester. As the reaction proceeds and monoester selectively pre

cipitates, the equilibrium will shift to produce more monoesters.

Examples of emulsifier synthesis are recent works of Vulfsen (1993) as well

as Arcos and Otero (1996). Shah and coworkers (1994) have studied lipase

catalyzed reactions in monolayers and microemulsions. The major disadvan

tages of enzyme-catalyzed interesterification are high enzyme cost (relative to

sodium or calcium hydroxide catalysts), longer reaction times, and the ten

dency of enzymes to denature. However, the problems are surmountable and

the use of enzyme technology is expected to increase.

References Arcos, J.A., Otero, C. (1996). ]. Am. Oil Chem. Soc., 73:673-82. Flack, E. (1992). Food Techrwlogy International-Europe, 79-81. Gaonkar, A. (ed.) (1995). Ingredient Interactions: Effects on Food Quality, Marcel

Dekker, New York. Heertje, 1., et al. (1994). European Patent 0 558 523 Bl, July 13. lsraelachvili, J.N. (1985). Intermolecular and Surface Forces: With Applications to

Colloidal and Biological Systems, Academic, New York, pp. 246--62. Kleinherenbrink, F.A., et al. (1995). International Patent Application WO 95/35035,

December 28. Larsson, K. (1994). Lipids-Molecular Organization. Physical Functions and Technical

Applications, The Oily Press, Ayr, Scotland, pp. 156--62. Shah, D.O., et al. (1994). ]. Am. Oil Chem. Soc., 71:1405-9. Vulfsen, E.N. (1993). Trends Food Sci. & Techno!., 4:209.

Index

A acetylated diglycerides, 33 acetylated monoglycerides, 33, 44,

60,253 preparation of, 33-36

acetylated monoglyceride citrate, 33-36

preparation of, 33-36 acid value/free fatty acid, 44 adsorbed proteins:

binding strength of, 101

interactions of surfactants, 101

influence of, 102 adsorbed surfactant molecules, 101

adsorption, emulsifier:

associative, 167 competitive, 167 layer, 167 surface, 167-169

aeration, bakery products, 214, 217 aggregation structures:

association structures, 151, 152

289

hydrocarbon chain packing, 151 thermodynamics, 150

albumin, 102

"all natural" ingredients, 5

amino acid, peptide chain, 97 amphiphilic packing of surlactants,

285 ampoules, flame-sealed, 153 amylopectin molecules, 68, 79, 80

amylose-complexing index, ACI, 252 amylose molecules, 68, 79 amylose leaches, 226 amylopectin, 226 anionic emulsifier:

sodium stearollactylate, 219 anionic surfactants, 221 AOAC, Association of Official

Analytical Chemists, 40, 56

method, 51 AOCS, 56 association structures, 154-155

associative adsorption, 167, 169

290 Index

B

baked products: cream icings, 232 crumb-softening, 226 emulsifiers, 216

applications, 225 extruded snacks/cereals, 232 fat-free products, 232 dough conditioning, 225 monoglycerides in, 217, 218 production influences, 229 shortening, 215 yeast in, 217

Bancroft rule, 162, 166 birefringence, loss of, 78 bovine milk, 173

composition of, 174 bovine serum albumin 98 102 113

' ' ' ' 126

bread dough, 85

Brewster angle microscope (BAM), 96

Brookfield viscosity measurements 241

'

butter, 1, 174, 202, 257, 259 butter and margarine consumption:

content of, 259, 260 in Europe, 258

market share of, 261 in the U.S., 257

butterscotch, 251

c cake batters, 212, 230 calcium stearoyl-2-lactylate, 20, 57 calcium hydroxide, 17 capillary melting point, 53

carboxylic acid group reaction, 20 caramels, 251 casein, 122, 124, 126, 134, 170

micelles, 173 caseinate, 134 casson viscosities, yield values:

chocolate, 243, 244 cationic surfactant (CTAB), 199 cetyl-trimrthyl ammonium bromide

CTAB, 199 cheese, 174

manufacture, processed, 198 chemically leavened products, 229

cookies, crackers, 230 layer and snacks cakes, 229 spread ratios, 231

chewing gum, 250 lecithin, 250

mono- and diglycerides, 250 chocolate, 7

antibloom agents, 248--249 bloom, 245--248 coatings, viscosities, 244 compound coatings:

antibloom agents, 244--248 confectionery, 236 lecithin, 237-242

crystallization, 248--249 diglycerides, 248 fat, crystallization of, 244 milk, 241, 243

monoglycerides, 248

plastic viscosity, 237 polyglycerol polyricinoleate,

PGPR, 242-244 polysorbate 60, 24 7 sorbitan:

tritearate, STS, 246--24 7 monostearate, 24 7

synthetic lecithin, 240

'

viscosity, 8, 237, 241, 243, 248--

249

viscosity, apparent, 237

yield value, 237

chromatography/mass spectrometry, 2

circular dichroism, CD, 96

clathrate complex, starch, 68

coalescence, 95

cocoa butter:

antibloom agents, 248--249

crystallization rate, 246-24 7

polymorph, 245-24 7

coffee creamers, 195

column chromatography, 40-42

competitive adsorption, 167

hydrophoblic interaction, 167

critical micelle concertration, 168

ionic surfactants, 168

nonionic surfactants, 168

compound coatings:

antibloom agents, 248--249

gloss, 248

crystallization, 248--249 viscosity, 248-249

confectionery emulsifiers, 235-236

chocolate, 235, 236

compound coatings, 236

sugar, 235 concentrated milk, 199-202

production of, 201

products, 199

congeal point, 53

critical micelle concentration (erne),

148,167

cream, 174

fat globule coalescence, 183

destabilized, 187

recombined whipping, 185-186,

186

stabilization, 187

Index 291

whipped, whipping, 183-187

cream liqueurs, 191-195

composition of, 192

cream stability, 192-195

manufacture of, 193

production of, 191

shelf life, 194

cream, coffee whiteners, 195-

197

recombined, 195-196

formulation, whiteners, 196

cream icings, 232

citric acid esters, monoglycerides,

266

cubic phase, monoolein/water, 131

cubic monoglyceride phase, 132

crystal size of shortenings, 216

cryo scanmng:

ice cream, 177

whipped cream, 184, 188

crystals (see also crystallization):

fat, bakery products, 217

fat, margarine, 266 fat, effect, emulsifiers, 266-267

crystallization:

effect on margarine, 267

fat, confectionery, 239

fat, chocolate, 248

fat, margarine, 265

cytochrome c, 102, 123, 126, 130

0

dairy applications, emulsifiers, 202

decaglycerol decastearate, 25

decaglycerol tristearate, 25

derivatives, bakery products, 217

diacetyl tartaric acid esters of:

monoglycerides (DATEM)

292 Index

diacetyl tartaric acid esters (continued) esters, 31, 32, 44, 59,228, 233,249,266

differential scanning calorimetry

(DSC),53,87,96,131 diglycerides, 6, 15, 23, 25, 33, 40,

41,49,55,60,182,198, 200,204,212,227,240, 249,250,268,274,279

hydroxyl values, 23, 24 interesterification process, 15, 17 diacetyl tartaric acid, 31

dimyristoylphosphatidic acid, 126 dioleoyl PC, PE, 160 dioleoylphosphatidylserine, DOPS, 122 dioleoylphosphatdylcholine, 125 dioleoylphosphatidylethanolamine, 125 dipalmitoylphosphosphatidic acid, 121 diphosphatidylglycerol, 122 dipalmitoylphosphatidic acid, DPPA,

123 dipalmitoylphosphatdylcholine, 126 distearoylphosphatidic acid, 121, 123 DMPG, 130 dodecyl sulfate, SDS, 78 DOPG, 130 DTAB, adsorption, 100

E

egg yolk, 123 electron microscopy, 2, 266, 269, 270 ellipsometry, 121, 171 emulsifiers:

anionic, 219 analytical methods for, 39 baked foods, 211-216 bakery products, role of, 212-214 breakdown, process of, 95

bilayers, 154 binary mixture, liquid-crystalline,

150 carbohydrate interactions, 67 l3C chemical shifts, 61 chocolate confectionery, 235, 236 classified as, ll

classification, 161 coalescence, 6, 176 color of, 50 compound coatings confectionery,

236 consistency, 54 crumb softeners in bread, 70 dairy applications, other, 202 determination of, 40--52 destabilization, whipped toppings,

189 dispersion, stabilize, 154 emulsifier/starch-complex forma-

tion, 69, 79 enzyme synthesis, 286 fat, crystal structure of, 180 flocculation, 6

food additives, 2-5 functionality, 7-9 future trends, 281-286 hexagonal phase, 149 high-melting, 148 ice cream, 175 instrumental methods, 54--62 interaction, ingredients, 284--285 interfacial viscosity, 154 lactoglobulin, 114 lamellar phase, 149 margarine, function of, 267-270 melting point of, 52-54 mesophases, 284--285 micelles, 149, 154

molecular solution, 149 nonchocolate confectionery, 249 nutritional studies, 282 phase diagrams, 153-156 properties of, 96, 153, 154 properties, physical, 52 polyhydric, 219 polysorbate 60, 219 processing aids, 252-253 shortenings, 211-213 solution properties of, 149 solubilization sequence, 149 sorbitan, icings, 219 specification for, 62 starch, characterization of, 85 starch-complexing, 77-78, 83

structure, S--7, 61 sugar confectionery, 235, 249 surface activity, 147-149,230

surfactants, 212 synthetic, 1

testing and surveillance of, 283

regulatory status, FDA, EEC, 215 whipped toppings, 190

emulsifier classification:

geometry of molecule, 164 homogenization role, 165 hydrophilic/lipophilic balance,

163-164 layers for, 170 phase inversion, 162 solubility, 161

emulsifier interaction, bakery compo-

nents, 221 emulsifier surface, 16 7-169 emulsion stability, 154--155 emulsion phase diagrams, 154--155

entropy, gain of, 148 enzymatic synthesis, food, 285

Index 293

enzymolysis in starches, 81 ethoxylated esters, 11, 26, 169, 266

sorbitan monostearate, 26 sorbitan monoolate, 27-28 sorbitan tristearate, 28 mono- and diglycerides, 28 surfactants, 169 preparation of, 28--29 polyoxyethlene (20) sorbitan, 28

ethoxylated fatty alcohols, 266 ethoxylated monoglycerides, 228 ethoxylated nonyl-phenol and xylene,

153 evaporated milk, 201

European Economic Community

(EEC), 40 baked goods in, 214

extruded snacks/cereals, 232

F

fat content, solid, SFC, 180 crystallization:

margerine, 263-267 polymorphic, 263-265 whipped toppings, 189

fat:

crystals of:

bakery products, 217 margarine, 266 effect of emulsifiers on,

266-267 crystallization:

confectionery, 239 chocolate, 248 margarine, 265

fat, yellow, consumption, 257 fat-free baked products, 232

294 Index

fat plasticity, 272, 274 fat spreads, 274

stability of, 275-276 spreadability of margarine, 277

fatty acids, 12 composition of, 264 lactylic esters, 19 metal salts of, 19, 20 melting points of, 265 soaps, 51 sorbitan esters, 58

fibrinogen, adsorption of, 108

flocculation, 95 fluorescence recovery after photo

bleaching, FRAP, 113 fluorescence microscopy, 126 Food and Drug Administration

(FDA), 40 regulatons of, 40

baked goods, 214 GRAS status, DATEM esters,

32 hydroxyl, 26 propylene glycol, 18 sorbitan monostearate, 26 succinylated monoglycerides,

30 Reichert-Meiss! value, 34

form stability, bakery products, 217 Fourier transform infrared spec

trosopy, FTIR, 59 food emulsifiers, solution properities,

155-156 free fat acids, 60

measuring, in olive oil, 60 freeze fracture, margarine, 270 fruit acid esters, 11, 31-33

tartaric acid-derived esters, 31 fudge, 251-252

G

gas-liquid chromatography GLC), 46, 55-57

Gibbs effect, 110

performed on lipids, 55 GLC, 56 gliadin, 132 glyceryl monostearate (GMS), 86,

197 gelatin, 134 gelatinization, 78, 89 gelatinization endotherm of starches,

88

globalization, food industry, 282 globular proteins, interior, 97

hydrogen bonding, 98 hydrophobic interreaction of, 98 van der Waals interaction, 98

gluten structure, 215 gluten proteins, 224 glycerollactopalmitate (GLP), 191, 250 glycerol monostearate (GMS), 178,

180-18,189,236,248, 250,251,252

glycerol monooleate, 189 GRAS, 2-3, 15, 26

monosodium phosphate, 36 status of, 32

gums, 251

H

helix starch, structure of, 79 hexaglycerol dioleate, 25 hydroxyl value, 48 high-performance liquid chromatogra

phy (HPLC), 47, 52,57-58 detectors of, 58

separations of phospholipids, 58 homogenization, 166

hydrated distilled monoglycerides, 227 hydrodynamic interactions, 166

hydrophile/lipophile balance (HLB),

6-8,151,163-164,169,

220,236

hydrophilic, 5, 11, 100 hydrated lime, 17 hydration:

force, emulsion droplets, 155 repulsion, monopalmitin, 155

ice cream, 95, 17 4-183 aging of, 178 composition of, 175 coalesence stability of, 176 cryo scanning of, 1 77

emulsifiers, 175, 178

fat globles in, 179 fat crystallization in, 180-182

interfacial viscosity, 177

manufacture of, 175 orthokinetic stability, 177

inclusion complexes, starch, 68 interesterification process, 17 interfacial tension, role, 165-166

in bakery products, 217

iodine

dilation value, margarine, 272

melting point, fat blends, 272

value, 45--46 binding of starches, 77

ionic surfactants, 100

isotherm adsorption, 100 isotherm surface tension, 115 IUPAC, 56

Index 295

J jellies, 251

ACI values, 252

K

kosher, 5, 13

Krafft temperature, 148

L

lactic acid, 236 analyses of, 49 water-in-soluble combined,

(WICLA), 22 esters of:

glycerol, 22 monoglycerides, 187, 248

propylene glycol, 22 lactalbumin, 102, 123, 125, 130, 185 lactoglobulin, 102, 104, 106, 109,

113-114,117, 118, 120-121,122,124,125, 126,130,133,134,185

lactylated esters, 18-23, 41 hydroxyl group reaction, 19 fatty acids of, 19 metal salts of, 19, 20 preparation of, 19-23

lactylated monoglycerides, 20-22, 23,44,227,230

preparation of, 20-22 lamellar liquid-crystalline phase,

emulsifiers of, 153

lamellar phase, monoglycerides, 154 Langmuir-Blodgett technique, 121

layer adsorption, 167, 169, 171

296 Index

layer adsorption, (continued) surface, protrin, 171 phospholipid, 171 ellipsometry, 171

lecithin, 42, 50, 60, 120, 155-161, 173,199,202,220,223, 228,231,233,236, 238-239,248,250,253, 268,274

phosphorus, procedures for, 51-52 phosphatidyl, 171 phosphatidylcholine content in,

60,155 soy lecithin, 51, 239 synthetic, 240 viscosity, 54

linear molecules, starches, 68 lipid emuisifiers, liquid-crystalline,

156 lipid fractions, topping emulsions,

190 lipid materials, effects of 69, 96 lipid/protein interaction, 122 lipid structures, 129, 133 lipids in baked foods, 225 lipophilic, 5, ll lipolytic emzymes, 133 liposomes, 84 liquid chromatography, 42 liquid-crystaline mesophases,

whipped toppings, 191 liquid margarine, 278-279 low-fat spreads, 274-278 low molecular weight (LMW), 96 lysolecithin, 84 lysophosphatidyl cholines (LPC),

119,159,283 lysophosphatides (LPC), (LPE), 156,

158 lysozyme, 102, 104

M

Marangoni effect, Ill margarine, l, 255, 258-279

emulsifiers, 267-270 liquid margarine, 278 low-fat spreads, 274-276 market share, United States, 261 oil-in-water (0/W) spreads, 7, 278 phase inversion, 277-278 processing, 270-27 4 puff pastry margannes, 272-27 4

plasticity, 272-427 reduced fat spreads, 6, 274 spreadability, 277 structure, 262

fat crystallization, 263, 265-266 fat melting points, 272

polymorphism, 263-265 oils and fats, 263-426

melting points, 265 raw materials, 262 water-droplet distribution,

268-269 water-in-oil (y//0) emulsion, 7,

268,274,277-278 mass spectrometry, 60 mayonnaise, l

melting point, 12, 52-53 melittin interactions, 125 Mettler dropping point, 53 micelles, 84, 148, 165 microemulsion process, 37 milk, l, 173

composition of bovine milk, 17 4 concentrated, 199-202 fat globule membrane (MFGM),

173,184,185 proteins, 122, 135 recombined, 199-201

shelf life, 200 minarine, 259 moisture, 50 molded products, 175 molecular aggregation, 165 molecular distillation, 15, 17 monoglycerides, 3, 6, 8, 11, 13-15,

21-22,25,40-44,55-57, 59--61, 134, 149, 154--156, 178, 182, 198--200, 202, 212, 217-219,227,230--1240, 248--250,252,268--270, 274,279

acetic acid esters of, 187, 236, 249,252-253

acetylated, 33, 44, 60 preparation of, 33-36

citric acid esters of (CITREM),

266,270,279 diacetyltartaric acid esters of

(DATEM), 3, 31-33, 41, 44,59,228,249,252,266

distilled, 22, 30, 233

distilled saturated, 156 distilled unsaturated, 156 ethoxylated, 231, 250 lactic acid esters of, 20--22, 44,

187,230,236,248 phase behavior, 178 phases of:

cubic phase, 156 lamellar phase, 156 reversed hexagonal, 156

phosphated, 3, 11, 236 propylene glycol esters of, 60, 187 stearyl monoglyceride citrate, 33 succinylated (SMG), 30, 213, 227,

278,231 tartaric acid esters of, 197, 236

Index 297

yeast-raised bakery products, 217 monoglyceride citrate, 33 monomargarine, 55, 56 monoolein, 130, 156 monopalmitin, 155, 224 monostearate, 231

cubic, water phase, 131 mouthfeel, 249 myelin protein, 125

N

near infrared reflectance (NIR), 46, 48,59

nougat, 250 nuclear magnetic resonance (NMR),

2,59,60

0

oil-continuous emulsions, 154 oleic acids, 11-13, 256 oleomargarine (see margarine) oleostearine, 256 organic acid esters, 156

diacetyl tartaric acid, 156 monoglyceride ester, 156

orthokinetic stability, 177

Oswald ripening, 95 olalbumin, 102

p

packing parameter, 165 palmitic acids, 11-13, 256 palmitoyloleoylphosphatidylcholine,

123

298 Index

palmitoyloleoylphosphatidylglycerol,

123 para-K-casein, 124 peanut butter, 7

penetrometer, 54 pentosan, 214 peptide chain, 97 peroxide value, 46, 4 7

phase diagrams, 153, 166 emulsion stability, 154 lamellar liquid crystalline phase,

153 water and dioleoylphosphatidyl

choline, 157 phase inversion, concept, 162 phase inversion temperature (PIT),

162 phosphated esters, 36

monosodium phosphate, 36 preparation of, 36

phosphatides, mixtures of, 158 phosphatidic acids, 122, 158, 240

dioleoyl, 159 lysophosphatidylcholine (lyso PC),

159 phosphatidylglycerol, 135 phosphatidylcholine (PC), 52, 57-61,

122,130,155,157-159 dimyristoyl, 159 dioleoyl, 159 dipalmitoyl, 159 distearoyl, 159 egg, 159 soybean, 159 transition temperature for, 158

phosohatidylserine, 122 phosphatidylethanolamine (PE), 52,

60, 61, 122, 130, 156-159,173

dioleoyl, 159

dipalmitoyl, 159 soybean, 159

phosphatidylinositide, 173 phosphatidylinositol (PI), 122, 156,

158,159 soybean, 159

phosphatidyl serine (PS), 156, 173 phospholipids, 41, 42, 52, 57-61,

159,166,171,173,186, 200,202

liquid-crystalline phases, 159 phosphoric acid, 15, 17 phosphorus pentoxide, 240 photobleaching, fluorescence

recovery, 113

polar lipid:

classes, 127 cubic phase, 127 lamellar phase (LJ, 127 liquid crystalline phase, 127 hexagonal phase, 127 hydrophobic interaction, 127 micelle concentration ( cnc ), 127 phase behavior, 126 surfactants, 127 structure, 128, 129

plasmalogens, 173 plasticity, 5

polyglycerate 60, 251 polyglycerol, 59 polyglycerol esters, 3, 11, 23, 54, 58,

59,213,233,249,266, 270

of stearic acid, 248 preparation of, 23-25

polyglycerol polyricinoleate (PGPR), 8,56,236,242-244

polyhydric emulsifiers, 219 polyglycerol esters, 219 sucrose esters, 219

polylactic acid, 20 polymerization, 242 polymorphic form, 245, 246 polyoxyethylene (20), sorbitan mono-

stearate, 28, 29, 114, 115, 118,156,182,220,232

polyoyl, 56 polyphosphates, 198 polysorbates, 3, 29, 59, 61, 178, 182,

219,236,250 polysorbate 60, 29, 213, 220, 227,

230,233,236,247-248, 250,252

processed cheese, 197-199 manufacture of, 198

programmed temperature x-ray dif

fraction, 53 propylene glycol, 17 propylene glycol esters, 15, 17, 23,

55,232 propylene glycol lactates, 23 propylene glycol monoesters

(PGME), 11, 17, 18, 22-23,213,230-232, 236,249

prepartion of, 15 propylene glycol monostearate

(PGMS), 15, 189-191 proteins, 162, 69, 71, 89

adsorption, 169 desorption, 189 strenghthening, 214

protein complexes in baked foods,

224 protein/emulsifier:

interactions, 95-135 food applications, 132 lipolytic enzymes, 132, 133 lipid structure, 133

protein stability, adsorption, 97

Index 299

protein, lipid:

interactions, 126 monolayers, 125

protein hydrolysates, 149 protein/phospholipid interactions, 120

dispersed systems, 120, 121 solid surface interactions, 121

protein stability, 97 protein/surfactant interactions, 98--119

adsorption:

binding to, 107 competive, 111 cooperative, 107 isotherm, 99 mixtures of, 106

adsorbed:

surface properties, 103 complex formation, 105 replacement of, 105

binding, protein and emulsifiers,

113 coadsorption, 112 dissociation constant (Kd),113 emulsifier properties, 134 foam, emulsion stabilization, 110 hydrophobic surfaces, 103 hydrophilic surfaces, 103 Krafft temperature, 103 liquid air, 110 liquid/liquid interfaces, 110 lactoglobulin, 117 electrostate repulsion, 103 monolayer of, 99 nonionic surfactants, 106 interactions, solid interfaces, 106 ionic surfactants, 99, 106 solid surfaces, 98 solution influence, 107 micelles, critical concentration of,

99

300 Index

protein properties of, 102

surface tension, llO protein/phospholipid interactions,

122 protein/protein interactions, ll2 puddings, 77

puroindolines, ll9

R

refractive index, 54 regulatory agencies, 40 Reichert-Meiss! value, 34, 49 reverse osmosis, 201 reversed aggregates, 165

s saponification number, 26, 4 7

sauces, 77 Scatchard equation, ll6 shelf life, 200

milk, 200

salad dressings, 2

shortening, 2ll-216 emulsified, 2ll-213 fluid, 230 melting point, 216 nonemulsified, 213 plasticity, 216 solid-fat index, 216

sodium caseinate, 192 sodium dodecylsulfate, SDS, 98 sodium hydroxide, 17 sodium lauryl sulfate (SLS), 78, 134 sodium hydroxide, 17

Sodium caseinate, 192 sodium stearoyl fumarate, 197, 213,

221,231 sodium stearoyllactylate (SSL), 20,

41,42,44,156,197,203, 213,219,221,224,227, 228,230-232,266,283

softening point, 53 solubility, 161

Bancroft rule, 162 sorbide, 26

polyoyls, 26 sorbitan, 26

polyoxylated (20), 231 monostearate (SMS), 26, 56, 219,

230,231,247,248,250, 252

tristearate (STS), 56, 246, 24 7, 266

sorbitan esters, ll, 26, 162, 164, 169,220,233,266

ethoxylated, 26, 28, 266 production, 26 polyxyethylene (20), 156 sorbitan monooleate, 156 sorbitan monostearate, 156, 24 7 sorbitan stearate, 156

soy lecithin, 8

soybean phospholipids, 161 phase diagram, 161

spectroscopy, 59 sphingomyelin, 125, 173 spread ratios of cookie dough, 231 spreadable fats, 259, 260 starch:

complexes, in baked foods, 222 complexing, 77, 214 differential scanning calorimetry, 85

inclusion complexes of, 68

iodine binding capacity, 77

composition of, 68

gelatinization of, 85, 86 temperature, Tlf Tm, 89 glass transmission, 89 crystallite melting, 89

granule, 82--83 lysolecithin, 85 nuclear magnetic resonance, 85 properties:

amylose helix, 82 effects of lipid materials, 69 fatty acids, 81 gelatinization, 77

module, 78 monoglyceride binding, 82 pasting, 70 retrogradation, 79, 80, 223 viscosity, 70, 77, 79

saturated fatty acid monoglyc-

erides, 224 types of, 83 viscosity profile, 83 emulsifier complexes, 77, 78, 79,

83,85-90 electron spin responce, 85 infrared spectroscopy, 85 pH effects, 83 temperature, 83

paste gelation, 79 unsaturated fatty acid monoglyc

erides, 224 waxy, table of, 75

starch/emulsion complexes:

V-type x-ray diffraction pattern, 69 statistical experimental design, 8

fractional factorial, 8

Index 301

response surface methodology

(RSM), 8 staled bread, 80 stearic acids, 11-13, 26, 256 stearoyllactylate, 213 succinylated esters, 11, 29

preparation of, 29, 30 sucrose esters, 3, 11, 42, 58, 59, 182,

213,227,236 preparation of, 36--38

sucrose monopalmitate, 231 sucrose monostearate, 231 sucrose distearate, 231 sucrose monostearate, 266 sucrose polyesters, 233

Olestra ™, 233 surface activity, 148, 167

components, 167 polar interactions, 148 surfactants, 5

surface tension, emulsifiers, 147, 227

surfactants, 168, 199, 201, 212 anionic, 199, 201, 224

cationic, 199 cetyl-trimethyl ammonium

bromide (CTAB), 199 ionic, 99, 100, 168 interaction of, 101 lecithin, 199 molecules, arraingments of, 101

nonionic, 168, 201, 224 properties, 102

sodium dodecyl sulphate (SDS),

199,201 solidlaqueos interfaces, 99 sucrose ester, 223 zwitterionic, 199

302 Index

T

tetraglycerolesters, 156

monolaurin, 156 tetraglycerol, 156

thin film stabilization, 111, 112

tocopherols, 50 toffee, 250 triglycerides, 2, 12-5, 17, 204, 240,

263 glycerolysis of, 204

triglycerol, 23 triglycerol monooleate, 248

triglycerol monoshortening, 250

triglycerol monostearate, 248, 252

triglycerol monoshortening, 25

triglycerol monostearate polyglycerol

ester, 25 tripropylene glycol monoesters, 18

u ultrafiltration, 201

v van der Waals interaction, 98

vesicle bilayers, 131

viscosity, 8, 54,177,237,241-244,

248 apparent, 237 interfacial, 177 plastic, 237, 243, 244

vitamin fortification, 261

Vroman effects, 108

w water-continuous emulsions, 154

water-insoluble combined lactic acid

(WICLA), 49

waxy starch table, 75

wet chemical analysis, 43-50

titration, 43-49 wheat flours, 214

whipped cream, whipping cream,

183,185

electron micrograph, 188

recombined, 185, 186

whipped toppings, 187

emulsion destabilization, 189

fat crystallization, 189 powder composition, 187 protein desorption, 189

Wiley melting point, 53

y

yeast-raised products, 225

crumb-softening, 225--227

dough conditioning, 225

dough strenghthening, 225, 226

emulsifier functionality during

processing, 227

yield value, 237 yoghurt, 202

food emulsifiers and their applications

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