McKenna Texture in Food

Semi-Solid Foods
1. Auflage 2003
ISBN: 978-1-85573-708-2
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: Adobe DRM (»Systemvoraussetzungen)

E-Book, Englisch, 448 Seiten

Reihe: Woodhead Publishing Series in Food Science, Technology and Nutrition

Texture is one of the most important attributes used by consumers to assess food quality. This quality is particularly important for the growing number of semi-solid foods from sauces and dressings to yoghurt, spreads and ice cream. With its distinguished editor and international team of contributors, this authoritative book summarises the wealth of recent research on what influences texture in semi-solid foods and how it can be controlled to maximise product quality.Part one reviews research on the structure of semi-solid foods and its influence on texture, covering emulsion rheology, the behaviour of biopolymers and developments in measurement. Part two considers key aspects of product development and enhancement. It includes chapters on engineering emulsions and gels, and the use of emulsifiers and hydrocolloids. The final part of the book discusses improving the texture of particular products, with chapters on yoghurt, spreads, ice cream, sauces and dressings.With its summary of key research trends and their practical implications in improving product quality, Texture in food Volume 1: semi-solid foods is a standard reference for the food industry. It is complemented by a second volume on the texture of solid foods. - Summarises the wealth of recent research on what influences texture in semi-solid foods and how it can be controlled to maximise product quality - Reviews research on the structure of semi-solid foods and its influence on texture, covering emulsion rheology, the behaviour of biopolymers and developments in measurement - Considers key aspects of product development and enhancement and includes chapters on engineering emulsions and gels and the use of emulsifiers and hydrocolloids

Autoren/Hrsg.

McKenna, B M

Inhaltsverzeichnis

1;Front Cover;1
2;Semi-Solid Foods;4
3;Copyright Page;5
4;Table of Contents;6
5;Contributors;12
6;Introduction;16
7;Part I: Food structure and texture;18
7.1;Chapter 1. The rheology of emulsion-based food products;20
7.1.1;1.1 Introduction;20
7.1.2;1.2 General characteristics of food emulsions;21
7.1.3;1.3 Rheological properties of dilute emulsions;26
7.1.4;1.4 Rheological properties of concentrated emulsions;32
7.1.5;1.5 Measuring the rheological properties of emulsions;39
7.1.6;1.6 Factors controlling emulsion rheology;41
7.1.7;1.7 Future trends;47
7.1.8;1.8 Sources of further information and advice;48
7.1.9;1.9 References;49
7.2;Chapter 2. Phase transitions, food texture and structure;53
7.2.1;2.1 Introduction;53
7.2.2;2.2 Rheological techniques for studying phase transitions;56
7.2.3;2.3 Starch gelatinization;58
7.2.4;2.4 Food polymer gels;62
7.2.5;2.5 Phase transitions in fats;71
7.2.6;2.6 Crystallization kinetics;72
7.2.7;2.7 Structural and textural changes due to glass transition;73
7.2.8;2.8 Future trends;75
7.2.9;2.9 Sources of further information and advice;75
7.2.10;2.10 References;75
7.3;Chapter 3. Phase separation in foods;80
7.3.1;3.1 Introduction;80
7.3.2;3.2 Properties of mixed biopolymer systems;81
7.3.3;3.3 Mechanisms of phase separation;82
7.3.4;3.4 Controlling biopolymer systems;88
7.3.5;3.5 Future trends;96
7.3.6;3.6 References;97
7.4;Chapter 4. The structure and texture of starch-based foods;103
7.4.1;4.1 Introduction;103
7.4.2;4.2 The rheological properties of starch;103
7.4.3;4.3 Starch in multi-component food systems;109
7.4.4;4.4 Future trends;118
7.4.5;4.5 Sources of further information and advice;119
7.4.6;4.6 References;120
7.5;Chapter 5. Biopolymer systems for low-fat foods;126
7.5.1;5.1 Introduction;126
7.5.2;5.2 Measuring the structure of biopolymer systems;128
7.5.3;5.3 Understanding and controlling the microstructure of biopolymer systems;136
7.5.4;5.4 Conclusions;141
7.5.5;5.5 Acknowledgements;142
7.5.6;5.6 References;143
7.6;Chapter 6. Introduction to food rheology and its measurement;147
7.6.1;6.1 Introduction;147
7.6.2;6.2 Relevance of rheological properties of foods;148
7.6.3;6.3 Basic rheology;151
7.6.4;6.4 Measurement systems;157
7.6.5;6.5 On-line measurement systems;172
7.6.6;6.6 Instrument selection;173
7.6.7;6.7 References;175
7.7;Chapter 7. In-line and on-line rheology measurement of food;178
7.7.1;7.1 Introduction;178
7.7.2;7.2 Requirements of an in-line or on-line sensor;180
7.7.3;7.3 In-line rheometry;181
7.7.4;7.4 In-line viscosity measurements;183
7.7.5;7.5 Capillary (or tube) viscometers;184
7.7.6;7.6 Rotational viscometers;189
7.7.7;7.7 Vibrational viscometers;192
7.7.8;7.8 High-frequency rheometry;195
7.7.9;7.9 Summary;196
7.7.10;7.10 References;196
8;Part II: Product development;200
8.1;Chapter 8. Engineering food emulsions;202
8.1.1;8.1 Introduction;202
8.1.2;8.2 Energy density and emulsion formation;205
8.1.3;8.3 Emulsion formation, microstructure and properties;205
8.1.4;8.4 Emulsion stability;206
8.1.5;8.5 Emulsion formulation in practice: a case study;207
8.1.6;8.6 Future trends;215
8.1.7;8.7 Sources of further information and advice;215
8.1.8;8.8 References;215
8.2;Chapter 9. The creation of new food structures and textures by processing;218
8.2.1;9.1 Introduction: processing, microstructure and gel formation;218
8.2.2;9.2 Selecting process conditions;220
8.2.3;9.3 Process-induced structures;221
8.2.4;9.4 Structure-related rheological properties;226
8.2.5;9.5 Conclusions;228
8.2.6;9.6 Acknowledgements;231
8.2.7;9.7 References;231
8.3;Chapter 10. Using emulsifiers to improve food texture;233
8.3.1;10.1 Introduction;233
8.3.2;10.2 The chemistry of emulsifiers;233
8.3.3;10.3 Association structures with water;242
8.3.4;10.4 Interfacial properties of emulsifiers;248
8.3.5;10.5 Emulsifier–carbohydrate interactions;259
8.3.6;10.6 Emulsifier–fat interactions;260
8.3.7;10.7 Future trends;264
8.3.8;10.8 References;265
8.4;Chapter 11. The use of hydrocolloids to improve food texture;268
8.4.1;11.1 Introduction;268
8.4.2;11.2 The range and choice of hydrocolloids;270
8.4.3;11.3 Thickening characteristics;271
8.4.4;11.4 Gelling characteristics;273
8.4.5;11.5 Structure and properties of individual hydrocolloids;276
8.4.6;11.6 The health benefits of hydrocolloids;287
8.4.7;11.7 Future trends;290
8.4.8;11.8 Bibliography;291
8.5;Chapter 12. Developing new polysaccharides;292
8.5.1;12.1 Introduction;292
8.5.2;12.2 Developing new polysaccharides: key issues;296
8.5.3;12.3 Producing stable polysaccharides;310
8.5.4;12.4 Producing functional polysaccharides;314
8.5.5;12.5 Applications;319
8.5.6;12.6 Future trends;324
8.5.7;12.7 Sources of further information and advice;325
8.5.8;12.8 Acknowledgements;325
8.5.9;12.9 References;325
8.6;Chapter 13. The rheology and textural properties of yoghurt;338
8.6.1;13.1 Introduction;338
8.6.2;13.2 The principles of yoghurt manufacture;339
8.6.3;13.3 The main factors affecting yoghurt texture;343
8.6.4;13.4 Measuring the rheological and textural properties of yoghurt;349
8.6.5;13.5 Future trends;357
8.6.6;13.6 Sources of further information and advice;359
8.6.7;13.7 References;359
8.7;Chapter 14. Controlling the texture of spreads;367
8.7.1;14.1 Introduction;367
8.7.2;14.2 Emulsion microstructure: ingredients;369
8.7.3;14.3 Emulsion microstructure: processing;374
8.7.4;14.4 Spread stability during transport and storage;381
8.7.5;14.5 Analysing spread texture;382
8.7.6;14.6 Future trends;386
8.7.7;14.7 References;387
8.8;Chapter 15. Factors affecting texture of ice cream;390
8.8.1;15.1 Introduction: the structure of ice cream;390
8.8.2;15.2 Influences on textural properties: ice crystallization;391
8.8.3;15.3 Influences on textural properties: foam stability and melting behaviour;397
8.8.4;15.4 Future trends;402
8.8.5;15.5 Sources of further information and advice;403
8.8.6;15.6 References;403
8.9;Chapter 16. Controlling textures in soups, sauces and dressings;406
8.9.1;16.1 Introduction;406
8.9.2;16.2 Defining the product;407
8.9.3;16.3 Ingredient and product classification;412
8.9.4;16.4 Texturising requirements;417
8.9.5;16.5 Texturising ingredients;422
8.9.6;16.6 Achieving the right texture;430
8.9.7;16.7 Improving texture and the use of new texturising agents;434
8.9.8;16.8 Future trends and conclusions;435
8.9.9;16.9 Sources of further information and advice;436
8.9.10;16.10 Acknowledgements;437
8.9.11;16.11 References;437
9;Index;439

Leseproben

1 The rheology of emulsion-based food products
D.J. McClements    University of Massachusetts, USA 1.1 Introduction
Many familiar foods exist as emulsions at some stage during their production (Dickinson and Stainsby, 1982; Dickinson, 1992; Friberg and Larrson, 1997; McClements, 1999). These foods include natural products such as milk, and processed foods such as cream, butter, margarine, fruit beverages, soups, cake batters, mayonnaise, cream-liqueurs, sauces, desserts, salad cream, ice cream and coffee whitener (Swaisgood, 1996; Stauffer, 1999). The overall quality of a particular emulsion-based food product is determined by a combination of physicochemical and sensory characteristics, such as appearance, aroma, taste, shelf-life and texture. This chapter focuses primarily on the textural attributes of emulsion-based food products. Food emulsions exhibit a great diversity of rheological characteristics, ranging from low-viscosity Newtonian liquids (e.g. milk, fruit beverages), to viscoelastic materials (e.g. salad dressings, heavy cream) to plastic materials (e.g. butter, margarine). This diversity is the result of the different sorts of ingredients and processing conditions used to create each unique type of product. The creation of a food emulsion with specific quality attributes depends on the selection of the most appropriate raw materials (e.g. water, oil, emulsifiers, thickening agents, minerals, acids, bases, vitamins, flavors, colorants) and processing conditions (e.g. mixing, homogenization, pasteurization, sterilization) for that particular product. A better understanding of the fundamental principles of emulsion rheology would help to improve the economic production of high-quality products (Race, 1991; Barnes, 1994; Rao, 1995). This chapter aims to present the conceptual and theoretical framework required by food scientists to understand and control the rheological properties of emulsion-based food products. 1.2 General characteristics of food emulsions
1.2.1 Classifications and definitions
An emulsion consists of two immiscible liquids (oil and water), with one of the liquids dispersed as small spherical droplets in the other (Friberg and Larrson, 1997; McClements, 1999) (Fig. 1.1). In foods, the diameter of these droplets typically ranges between about 0.1 and 100 µm. A system that consists of oil droplets dispersed in an aqueous phase is called an oil-in-water (or O/W) emulsion, e.g. milk, cream, mayonnaise, soft drinks, soups and sauces. A system that consists of water droplets dispersed in an oil phase is called a water-in-oil (or W/O) emulsion, e.g. margarine, butter and some spreads. The material within the droplets is referred to as the dispersed, discontinuous or internal phase, whereas the material that makes up the surrounding liquid is called the continuous or external phase. It is also possible to create multiple emulsions, which can be either of the oil-in-water-in-oil type (O/W/O) or the water-in-oil-in-water type (W/O/W) (Dickinson and McClements, 1995; Garti and Benichou, 2001). The process of converting bulk oil and bulk water into an emulsion, or of reducing the size of the droplets in an existing emulsion, is known as homogenization (Walstra, 1993; Walstra and Smulders, 1998). In the food industry, homogenization is usually achieved by applying intense mechanical agitation to a liquid using a mechanical device known as a homogenizer, e.g. a high-speed blender, a high-pressure valve homogenizer, a colloid mill or an ultrasonic homogenizer (McClements, 1999). Fig. 1.1 Schematic representation of a polydisperse oil-in-water emulsion, consisting of oil droplets dispersed in an aqueous phase. Emulsions are thermodynamically unstable systems because the contact between oil and water molecules is unfavorable, and so they tend to break down with time (Dickinson, 1992; Friberg, 1997; Walstra, 1996a; McClements, 1999). The preparation of emulsions that are kinetically stable over a time period that is of practical use to the food industry (e.g. a few days, weeks, months or years) requires the incorporation of substances known as emulsifiers and/or thickening agents. An emulsifier is a surface-active substance that adsorbs to the surface of emulsion droplets to form a protective coating that prevents the droplets from aggregating with one another, e.g. certain proteins, polysaccharides, phospholipids, small molecule surfactants and solid particles (Stauffer, 1999). An emulsifier also reduces the interfacial tension and therefore facilitates the disruption of emulsion droplets during homogenization, which aids in the formation of emulsions containing smaller droplets (Walstra and Smulders, 1998). A thickening agent is a substance that either increases the viscosity of the continuous phase or forms a gel network within the continuous phase, thereby slowing down the movement of droplets due to gravity or Brownian motion, as well as providing the product with characteristics textural attributes (Imeson, 1997). Many types of polysaccharide and protein are suitable for use as thickening agents in food emulsions (Imeson, 1997). 1.2.2 Instability mechanisms
A number of physicochemical mechanisms may be responsible for the breakdown of food emulsions (Dickinson, 1992; Walstra, 1996a; Friberg, 1997; McClements, 1999), the most important being gravitational separation, flocculation, coalescence, partial coalescence, Ostwald ripening and phase inversion (Fig. 1.2). Creaming is the process whereby droplets move upwards due to gravity because they have a lower density than the surrounding liquid. Sedimentation is the process whereby droplets move downwards due to gravity because they have a higher density than the surrounding liquid. Flocculation is the process whereby two or more droplets ‘stick’ together to form an aggregate in which the droplets retain their individual integrity. Coalescence is the process whereby two or more droplets merge to form a single larger droplet. Partial coalescence is the process whereby two or more partly crystalline droplets merge to form a single irregularly shaped aggregate due to the penetration of solid fat crystals from one droplet into a fluid region of another droplet. Ostwald ripening is the process whereby larger droplets grow at the expense of smaller droplets due to mass transport of dispersed phase material through the continuous phase. Phase inversion is the process whereby an oil-in-water emulsion changes to a water-in-oil emulsion, or vice versa. It should be noted that partial coalescence and phase inversion are integral parts of many food processing operations, such as the production of butter, margarine, ice cream and whipped cream (Dickinson and Stainsby, 1982; Berger, 1997; Buchheim and Dejmek, 1997; Walstra, 1996b). Generally, the term ‘emulsion stability’ refers to the ability of the emulsion to resist changes in its physicochemical properties over time. Nevertheless, it is always important to identify clearly the most important physical and/or chemical mechanisms responsible for the instability of a particular emulsion, since this will determine the most effective strategy to improve its stability. Fig. 1.2 The different physiochemical processes that can cause food emulsions to break down. 1.2.3 Colloidal properties
The rheological properties of food emulsions are strongly influenced by their colloidal nature, i.e. by the size, concentration, interactions and interfacial properties of the emulsion droplets (McClements, 1999). It is therefore useful to review briefly the colloidal characteristics of emulsions before discussing their rheological characteristics. Droplet concentration The concentration of droplets in an emulsion is usually characterized in terms of the dispersed phase volume fraction (?) which is equal to the volume of emulsion droplets (VD) divided by the total volume of emulsion (VE): ? = VD/VE. Practically, it is often more convenient to express the composition of an emulsion in terms of the dispersed phase mass fraction (?m), which is equal to the mass of emulsion droplets (mD) divided by the total mass of emulsion (mE): ?m = mD/mE. The relationship between ?m and ? is given by the following equations: m=??+1-??1?2-1   [1.1a] =?m?m+1-?m?2?1-1   [1.1b] where ?1 and ?2 are the densities of the continuous and dispersed phases, respectively. When the densities of the two phases are equal, the mass fraction is equivalent to the volume fraction. The droplet concentration may also be represented as either a dispersed phase volume percentage (= 100 ?) or disperse phase mass percentage (= 100 ?m). It is particularly important to convert the droplet concentration to the appropriate units when comparing experimental work with theoretical predictions. Droplet size When all the droplets in an emulsion have the same size, the emulsion is referred to as ‘monodisperse’,...