Food emulsions : principles, practice, and techniques

366 Pages·1999·13.992 MB·English

by  D J McClements

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Table of Contents
Preface
The Author
Chapter 1 CONTEXT AND BACKGROUND
1.1. Emulsion Science in the Food Industry
1.2.General Characteristics of Food Emulsions
1.2.1.Definitions
1.2.2Mechanisms of Emulsion Instability
1.2.3.Ingredient Partitioning in Emulsions
1.2.4.Dynamic Nature of Emulsions
1.2.5.Complexity of Food Emulsions
1.3.Emulsion Properties
1.3.1.Dispersed-Phase Volume Fraction
1.3.2.Particle Size Distribution
1.3.3.Interfacial Properties
1.3.4.Droplet Charge
1.3.5.Droplet Crystallinity
1.4.Hierarchy of Emulsion Properties
1.5.Investigation of Emulsion Properties
1.6.Overview and Philosophy
Chapter 2MOLECULAR INTERACTIONS
2.1.Introduction
2.2.Forces of Nature
2.3.Origin and Nature of Molecular Interactions
2.3.1.Covalent Interactions
2.3.2.Electrostatic Interactions
2.3.3.van der Waals Interactions
2.3.4.Steric Overlap Interactions
2.4.Overall Intermolecular Pair Potential
2.5.Bond Strengths and the Role of Thermal Energy
2.6.The Structural Organization of Molecules in Liquids
2.6.1.Thermodynamics of Mixing
2.6.2.Potential Energy Change on Mixing
2.6.3.Entropy Change on Mixing
2.6.4.Free Energy Change on Mixing
2.6.5.The Properties of More Complex Systems
2.7.Molecular Interactions and Conformation
2.8.Higher Order Interactions
2.8.1.Hydrogen Bonds
2.8.2.Hydrophobic Interactions
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2.9.Computer Modeling of Liquid Properties
2.9.1.Monte Carlo Techniques
2.9.2.Molecular Dynamics Techniques
Chapter 3COLLOIDAL INTERACTIONS
3.1.Introduction
3.2.Colloidal Interactions and Droplet Aggregation
3.3.van der Waals Interactions
3.3.1.Origin of van der Waals Interactions
3.3.2.Interdroplet Pair Potential
3.3.3.Hamaker Function
3.3.4.Electrostatic Screening
3.3.5.Retardation
3.3.6.Influence of an Interfacial Layer
3.3.7.General Features of van der Waals Interactions
3.4.Electrostatic Interactions
3.4.1.Origins of Surface Charge
3.4.2.Ion Distribution Near a Charged Surface
3.4.3.Electrostatic Interactions Between Charged Droplets
3.4.4.Ion Bridging
3.4.5.General Features of Electrostatic Interactions
3.5.Polymeric Steric Interactions
3.5.1.Polymeric Emulsifiers
3.5.2.Interdroplet Pair Potential
3.5.3.Distance Dependence of Polymeric Steric Interactions
3.5.4.Optimum Characteristics of Polymeric Emulsifier
3.5.5.General Features of Polymeric Steric Stabilization
3.6.Depletion Interactions
3.6.1.Origin of Depletion Interactions
3.6.2.Interdroplet Pair Potential
3.6.3.General Features of Depletion Interactions
3.7.Hydrophobic Interactions
3.8.Hydration Interactions
3.9.Thermal Fluctuation Interactions
3.9.1.Protrusion Interactions
3.9.2.Undulation Interactions
3.10.Hydrodynamic Interactions and Nonequilibrium Effects
3.11.Total Interaction Potential
3.11.1.van der Waals and Electrostatic
3.11.2.van der Waals, Electrostatic, and Steric
3.11.3.van der Waals and Steric
3.11.4.van der Waals, Electrostatic, and Hydrophobic
3.11.5.van der Waals, Electrostatic, and Depletion
3.12.Predicting Colloidal Interactions in Food Emulsions
Chapter 4EMULSION INGREDIENTS
4.1.Introduction
4.2.Fats and Oils
4.2.1.Molecular Structure and Organization
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4.2.2.Bulk Physicochemical Properties
4.2.3.Fat Crystallization
4.2.4.Chemical Changes
4.3.Water
4.3.1.Molecular Structure and Organization
4.3.2.Bulk Physicochemical Properties
4.4.Aqueous Solutions
4.4.1.Interaction of Water with Ionic Solutes
4.4.2.Interaction of Water with Dipolar Solutes
4.4.3.Interaction of Water with Nonpolar Solutes: The Hydrophobic Effect
4.5.Surfactants
4.5.1.Molecular Characteristics
4.5.2.Functional Properties
4.5.3.Surfactant Classification
4.6.Biopolymers
4.6.1.Molecular Characteristics
4.6.2.Molecular Basis of Conformation and Aggregation
4.6.3.Functional Properties
4.6.4.Modification of Biopolymers
4.6.5.Ingredient Selection
Chapter 5INTERFACIAL PROPERTIES AND THEIR
CHARACTERIZATION
5.1.Introduction
5.2.Molecular Basis of Interfacial Properties
5.2.1.Interfaces Between Two Pure Liquids
5.2.2.Interfaces with Adsorbed Emulsifiers
5.3.Thermodynamics of Interfaces
5.3.1.Gas–Liquid Interface in the Absence of an Emulsifier
5.3.2.Gas–Liquid Interface in the Presence of an Emulsifier
5.3.3.Liquid–Liquid Interface
5.3.4.Measurement of the Surface Excess Concentration
5.4.Properties of Curved Interfaces
5.5.Contact Angles and Wetting
5.6.Capillary Rise and Meniscus Formation
5.7.Adsorption Kinetics
5.7.1.Movement of Molecules to an Interface
5.7.2.Incorporation of Emulsifier Molecules at an Interface
5.8.Common Types of Interfacial Membranes
5.9.Interfacial Composition and Competitive Adsorption
5.10.Measurement of Surface and Interfacial Tensions
5.10.1.Du Nouy Ring Method
5.10.2.Wilhelmy Plate Method
5.10.3.Sessile- and Pendant-Drop Methods
5.10.4.Drop-Volume Method
5.10.5.Spinning-Drop Method
5.10.6.Maximum Bubble Pressure Method
5.10.7.Oscillating Jet Method
5.10.8.Capillary Wave Method
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5.11.Interfacial Rheology
5.11.1.Measurement of Interfacial Shear Rheology
5.11.2.Measurement of Interfacial Dilatational Rheology
5.12.Characterization of Interfacial Structure
5.13.Practical Implications of Interfacial Phenomena
Chapter 6EMULSION FORMATION
6.1.Introduction
6.2.Overview of Homogenization
6.3.Physical Principles of Emulsion Formation
6.3.1.Droplet Disruption
6.3.2.Droplet Coalescence
6.3.3.The Role of the Emulsifier
6.4.Homogenization Devices
6.4.1.High-Speed Blenders
6.4.2.Colloid Mills
6.4.3.High-Pressure Valve Homogenizers
6.4.4.Ultrasonic Homogenizers
6.4.5.Microfluidization
6.4.6.Membrane Homogenizers
6.4.7.Homogenization Efficiency
6.4.8.Comparison of Homogenizers
6.5.Factors Which Influence Droplet Size
6.5.1.Emulsifier Type and Concentration
6.5.2.Energy Input
6.5.3.Properties of Component Phases
6.5.4.Temperature
6.6.Demulsification
6.6.1.Nonionic Surfactants
6.6.2.Ionic Surfactants
6.6.3.Biopolymer Emulsifiers
6.6.4.General Methods of Demulsification
6.6.5.Selection of Most Appropriate Demulsification Technique
6.7.Future Developments
Chapter 7EMULSION STABILITY
7.1.Introduction
7.2.Energetics of Emulsion Stability
7.2.1.Thermodynamics
7.2.2.Kinetics
7.3.Gravitational Separation
7.3.1.Physical Basis of Gravitational Separation
7.3.2.Methods of Controlling Gravitational Separation
7.3.3.Experimental Measurement of Gravitational Separation
7.4. Flocculation
7.4.1.Physical Basis of Flocculation
7.4.2.Methods of Controlling Flocculation
7.4.3.Structure and Properties of Flocculated Emulsions
7.4.4.Experimental Measurement of Flocculation
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7.5.Coalescence
7.5.1.Physical Basis of Coalescence
7.5.2.Methods of Controlling Coalescence
7.5.3.Influence of Emulsifier Type and Environmental Conditions
7.5.4.Experimental Measurement of Droplet Coalescence
7.6.Partial Coalescence
7.6.1.Physical Basis of Partial Coalescence
7.6.2.Methods of Controlling Partial Coalescence
7.6.3.Experimental Measurement of Partial Coalescence
7.7.Ostwald Ripening
7.7.1.Physical Basis of Ostwald Ripening
7.7.2.Methods of Controlling Ostwald Ripening
7.7.3.Experimental Measurement of Ostwald Ripening
7.8.Phase Inversion
7.8.1.Physical Basis of Phase Inversion
7.8.2.Methods of Controlling Phase Inversion
7.8.3.Experimental Measurement of Phase Inversion
7.9.Chemical and Biochemical Stability
Chapter 8EMULSION RHEOLOGY
8.1.Introduction
8.2.Rheological Properties of Materials
8.2.1.Solids
8.2.2.Liquids
8.2.3.Plastics
8.2.4.Viscoelastic Materials
8.3.Measurement of Rheological Properties
8.3.1.Simple Compression and Elongation
8.3.2.Shear Measurements
8.3.3.Empirical Techniques
8.4.Rheological Properties of Emulsions
8.4.1.Dilute Suspensions of Rigid Spherical Particles
8.4.2.Dilute Suspensions of Fluid Spherical Particles
8.4.3.Dilute Suspensions of Rigid Nonspherical Particles
8.4.4.Dilute Suspensions of Flocculated Particles
8.4.5.Concentrated Suspensions of Nonflocculated Particles in the
Absence of Colloid Interactions
8.4.6.Suspensions of Nonflocculated Particles with Repulsive Interactions
8.4.7.Concentrated Suspensions of Flocculated Particles
8.4.8.Emulsions with Semisolid Continuous Phases
8.5.Major Factors that Determine Emulsion Rheology
8.5.1.Dispersed-Phase Volume Fraction
8.5.2.Rheology of Component Phases
8.5.3.Droplet Size
8.5.4.Colloidal Interactions
8.5.5.Particle Charge
Chapter 9APPEARANCE AND FLAVOR
9.1.Introduction
9.2.Emulsion Flavor
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9.2.1. Flavor Partitioning
9.2.2. Flavor Release
9.2.3. Measurements of Partition Coefficients and Flavor Release
9.3. Emulsion Appearance
9.3.1. Interaction of Light Waves with Emulsions
9.3.2. Overall Appearance
9.3.3. Experimental Techniques
Chapter 10 CHARACTERIZATION OF EMULSION PROPERTIES
10.1. Introduction
10.1.1. Research and Development
10.1.2. Quality Control
10.2. Testing Emulsifier Efficiency
10.2.1. Emulsifying Capacity
10.2.2. Emulsion Stability Index
10.2.3. Interfacial Tension
10.2.4. Interfacial Rheology
10.3. Microstructure and Droplet Size Distribution
10.3.1. Microscopy
10.3.2. Static Light Scattering
10.3.3. Dynamic Light Scattering
10.3.4. Electrical Pulse Counting
10.3.5. Sedimentation Techniques
10.3.6. Ultrasonic Spectrometry
10.3.7. Nuclear Magnetic Resonance
10.3.8. Neutron Scattering
10.3.9. Dielectric Spectroscopy
10.3.10. Electroacoustics
10.4. Dispersed-Phase Volume Fraction
10.4.1. Proximate Analysis
10.4.2. Density Measurements
10.4.3. Electrical Conductivity
10.4.4. Alternative Techniques
10.5. Droplet Crystallinity
10.5.1. Dilatometry
10.5.2. Nuclear Magnetic Resonance
10.5.3. Thermal Analysis
10.5.4. Ultrasonics
10.6. Droplet Charge
10.6.1. Electrophoresis
10.6.2. Zetasizer©
10.6.3. Electroacoustics
REFERENCES
©1999 CRC Press LLC
Preface
As one strolls along the aisles of a supermarket, one passes a wide variety of food products,
both natural and manufactured, which exist either partly or wholly as emulsions or which
have been in an emulsified form sometime during their production. Common examples
include milk, flavored milks, creams, salad dressings, dips, coffee whitener, ice cream, soups,
sauces, mayonnaise, butter, margarine, fruit beverages, and whipped cream. Even though
these products differ widely in their appearance, texture, taste, and shelf life, they all consist
(or once consisted) of small droplets of one liquid dispersed in another liquid. Consequently,
many of their physicochemical and sensory properties can be understood by applying the
fundamental principles and techniques of emulsion science. It is for this reason that anyone
in the food industry working with these types of products should have at least an elementary
understanding of this important topic.
The primary objective of this book is to present the principles and techniques of emulsion
science and show how they can be used to better understand, predict, and control the
properties of a wide variety of food products. Rather than describe the specific methods and
problems associated with the creation of each particular type of emulsion-based food product,
I have concentrated on an explanation of the basic concepts of emulsion science, as these are
applicable to all types of food emulsion. Details about the properties of particular types of
food emulsion are described in the latest edition of an excellent book edited by S.E. Friberg
and K. Larsson (Food Emulsions, 3rd edition, Marcel Dekker, New York, 1997), which
should be seen as being complementary to this volume.
It is a great pleasure to acknowledge the contributions of all those who helped bring this
book to fruition. Without the love and support of my best friend and partner Jayne and of my
family, this book would never have been completed. I also thank all of my students and co-
workers who have been a continual source of stimulating ideas and constructive criticism and
my teachers for providing me with the strong academic foundations on which I have at-
tempted to build. Finally, I thank all those at CRC Press for their help in the preparation of
this book.
©1999 CRC Press LLC
The Author
Dr. David Julian McClements has been an Assistant Pro-
fessor in the Department of Food Science at the University
of Massachusetts since 1994. He received a B.S. (Hons) in
food science (1985) and a Ph.D. in “Ultrasonic Character-
ization of Fats and Emulsions” (1989) from the University
of Leeds (United Kingdom). He then did postdoctoral re-
search at the University of Leeds, University of California
at Davis, and the University College Cork in Ireland, be-
fore joining the University of Massachusetts. Dr.
McClements’ research interests include ultrasonic charac-
terization of food emulsions, food biopolymers and col-
loids (focusing on emulsions, gels, and micellar systems),
protein functionality, and physicochemical properties of
lipids.
Dr. McClements has co-authored a book entitled Ad-
vances in Food Colloids with Professor Eric Dickinson and co-edited a book entitled Devel-
opments in Acoustics and Ultrasonics with Dr. Malcolm Povey. In addition, he has published
over 100 scientific articles as book chapters, encyclopedia entries, journal manuscripts, and
conference proceedings. Dr. McClements recently received the Young Scientist award from
the American Chemical Society’s Division of Food and Agriculture in recognition of his
achievements.
©1999 CRC Press LLC