Fats in Food Technology

Kanes K. Rajah

• Publisher: Wiley-Blackwell
• Year: 2014
• Print ISBN: 9781405195423
• eBook ISBN: 9781118788769
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

Fats are present in some form in the vast majority of processed foods we consume, as well as in many 'natural' products. Changes in consumer behaviour, centered around an increased emphasis on healthy food consumption, mean that it is more important than ever for food scientists to understand the properties, roles and behaviours that fats play in food and in diets.

Fats in Food Technology, Second Edition is an in-depth examination of the roles and behaviours of fats in food technology and the benefits that they impart to consumers. It considers both fats that are naturally present in foods (such as milk fat in cheese) and fats that have been added to improve physical, chemical and organoleptic properties (like cocoa butter in chocolate). Newly revised and updated, the book contains useful information on the market issues that have driven change and the disciplines that have helped to regulate the trade and use of fats and oils in food technology. Drawing on the recent literature as well as the personal R&D experiences of the authors, the book highlights those areas where potential efficiencies in processing and economy in the cost of raw materials can be made. Issues concerning health, diet and lifestyle are covered in dedicated chapters.

This book will be useful to anyone in industry and research establishments who has an interest in the technology of fat-containing food products, including scientists in the dairy, spreads, bakery, confectionery and wider food industries, as well those involved in the production of edible oils.

Chapter 1

Physical properties of fats in food¹

Kiyotaka Sato and Satoru Ueno

Laboratory of Food Biophysics, Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, Japan

1.1 Introduction

Oils and fats are important ingredients in a wide variety of manufactured foods, and constitute a significant part of food recipes. The major foods in which they are used are all discussed in detail in this volume. However, it is important to note that the forms in which oils and fats are made available to food manufacturers have changed significantly over the years, particularly since the 1960s, largely because of the major shifts that have taken place in consumer lifestyles and the increasing concerns with health, food safety and a balanced diet. Many of the food products that are now available to consumers reflect this new direction. Important examples arising out of the lipid research that has followed are trans-free fatty acids, reduced high-melting, in particular saturated, fats, very-low-yellow fat emulsions, spreadable butter, aerated fats, structured oils, molecularly designed structured fats with new nutritional advantages, and so on. All these initiatives have required an in-depth understanding of the behaviour of the fats concerned so that they can be used effectively as ingredients in food. Consequently, the study of their physical properties is of major interest and is covered in this chapter.

In general, fats form networks of crystal particles, maintaining specific polymorphic forms, crystal morphology and particle–particle interactions (Marangoni, 2005). The control of the physical properties of food fats has therefore been of importance in research efforts and can be considered under five headings:

• clarification of molecular and crystal structures of triacylglycerols (TAGs) with different fatty-acid moieties (Kaneko et al., 1998; Kaneko, 2001);
• crystallisation and transformation mechanisms of TAG crystals (Sato, 1996, 1999; Sato and Koyano, 2001; Sato and Ueno, 2005);
• clarification of formation mechanisms of mesoscale and macroscale fat crystal network starting from nanoscale primary fat crystals (Acevedo et al., 2011);
• rheological and texture properties that are dominated mainly by fat crystal networks (Boode et al., 1991; Marangoni and Hartel, 1998; Marangoni et al., 2012; Walstra et al., 2001);
• influences of external factors such as shear, ultrasound irradiation, minor lipids on fat crystallisation kinetics (Martini et al., 2008; Mazzanti et al., 2011; Smith et al., 2011; Wright et al., 2000).

The first topic is of an introductory nature and so will not be elaborated in this chapter (for more details, see the cited references). The remaining four topics are related to observed systems of food fats, with which this chapter is mainly concerned.

The chapter begins with a brief review of the three basic physical properties of fats by collecting together recent work on the crystallisation and transformation of the fats in bulk and in emulsion states. We will then focus on fundamental aspects of the crystallisation and transformation of fats employed in real food systems, through describing the use of important examples, such as cocoa butter, palm oil and palm mid-fractions. Since these natural fats are multi-TAG systems, knowledge of the fundamental properties of pure TAGs composing the natural fats may be necessary, as will be argued. Those who wish to compare real fats with pure fats are directed to the literature (Himawan et al., 2006; Sato, 1996; Sato and Koyano, 2001; Sato and Ueno, 2001; Sato et al., 1999).

1.2 Basic physical properties of fat crystals

The physical properties of the food fats are influenced primarily by three factors: (1) polymorphism (structural, crystallisation and transformation behaviour); (2) the phase behaviour of fat mixtures; and (3) the rheological and textural properties exhibited by fat crystal networks. In this section we cover the fundamentals and look at recent research work on these three properties.

1.2.1 Polymorphic structures of fats

Polymorphism is defined as the ability of a chemical compound to form different crystalline or liquid crystalline structures. The melting and crystallisation behaviour will differ from one polymorph to another.

Table 1.1 summarises the basic physical properties of the three typical polymorphic modifications of α, β′ and β. Polymorph α is least stable, easily transforming to either the β′ form or the β form, depending on the thermal treatment. Polymorph β′, the meta-stable form, is used in margarine and shortening because of its optimal crystal morphology and fat crystal networks, which give rise to optimal rheological and texture properties. The most stable β form tends to form large and plate-like crystal shapes, resulting in poor macroscopic properties in shortening and margarine.

Table 1.1 Three typical polymorphic forms of fats and their main physical properties.

The three main polymorphs, α, β′ and β of fats, are defined in accordance with subcell structure: α polymorphs have a hexagonal subcell (H); β′ polymorphs have an orthorhombic–perpendicular subcell (O_⊥); and β polymorphs have a triclinic–parallel subcell (T_//) (Larsson, 1966; see Figure 1.1 (a)). The subcell structures can be determined most clearly by measuring X-ray diffraction (XRD) short spacing patterns of poly-crystalline samples.

Figure 1.1 Polymorphic structures of three typical forms of triacylglycerol (TAG). (a) Subcell structures and (b) chain length structures.

Figure 1.1 (b) shows the chain-length structure, illustrating the repetitive sequence of the acyl chains involved in a unit cell lamella along the long-chain axis (Larsson, 1972). A double chain-length structure (DCL) is formed when the chemical properties of the three acid moieties are the same or very similar. In contrast, when the chemical properties of one or two of the three chain moieties are largely different from those of the moieties, a triple chain-length (TCL) structure is formed because of chain sorting. The relevance of the chain-length structure is revealed in the mixing phase behaviour of the different types of the TAGs in the solid phase: when the DCL fats are mixed with the TCL fats, phase separation readily occurs. The chain length structures can be determined solely by measuring the XRD long spacing patterns of the poly-crystalline samples.

In food fats, transformation from polymorph β′ to polymorph β often causes deterioration of the end product, mostly because of changes in the crystal morphology and network, as indicated in Table 1.1. The β-type polymorph is found in confectionery fats made of cocoa butter (Timms, 2003). There are two β-type crystals: a meta-stable β₂ form is more useful than the more stable β₁ form (Sato and Koyano, 2001; Van Mechelen et al., 2006a, 2006b). Atomic-level structure analyses of the TAGs have been attempted to resolve the microscopic mechanism of the polymorphic β′–β transformation. Results were reported first for the β forms (as reviewed for the β forms in Kaneko, 2001), and have been reported for the β′ form (Sato et al., 2001; van Langevelde et al., 2000). Mechanistic processes of solid-state transformation from β′ to β forms in trilauroyl-glycerol crystals were observed by a cutting-edge method with synchrotron radiation microbeam XRD (SR-μ-XRD) (Ueno et al., 2008), as will be presented below.

As the physical properties of food fats are greatly influenced by fat polymorphism, it is a prerequisite for those who are engaged in the material production of oils and fats to know how the fatty-acid composition influences the fat polymorphism. Two categories of fatty-acid composition may be considered: (1) mono-acid TAGs in which the three fatty-acid moieties of the TAG are of the same type; and (2) mixed-acid TAGs in which different fatty-acid components are connected to three different glycerol carbons on the TAG. The following diversity in fatty-acid composition of TAGs can be found:

• Mono-acid TAGs:
  • the acids may be saturated;
    • the number of carbon atoms in the fatty-acid chain, N_c, may be odd or even;
  • the acids may be unsaturated.
    • the number of carbon atoms in the fatty-acid chain, N_c, may be odd or even;
    • there may be a cis or a trans conformation around the double bond;
    • the number of double bonds may vary;
    • the position of the double bonds may vary.
• Mixed-acid TAGs:
  • there may be three saturated acids with different chemical species;
  • there may be three unsaturated acids with different chemical species;
  • there may be three acids containing saturated and unsaturated species;
  • the different fatty acids may be connected to carbon atoms of different stereo-specific number (sn).

In 1988, Hagemann summarised the melting behaviour of TAGs with different combinations of fatty-acid moieties with different chemical species (Hagemann, 1988). Hagemann showed a general tendency in the melting behaviour of mono-acid TAGs to be as follows:

• In saturated mono-acid TAGs, the melting points of the α, β′ and β forms increase when N_c is increased from 8 to 30. With respect to the quantitative dependence of the melting point of the polymorphs on N_c, the melting points of the α form increase smoothly with N_c, whereas the melting points of the β′ and β forms increase in a ‘zig-zag’ manner with N_c odd or even.
• In the mono-unsaturated mono-acid TAGs, the melting points of the β forms are available, showing specific dependence on double-bond conformation and on the position of the double bond. For example, trans unsaturated TAGs showed higher melting points than those of cis unsaturated TAGs at every double-bond position.

Since 1988, much work has been done on the polymorphic behaviour of mixed-acid TAGs. It is important to understand such behaviour as natural oils and fats contain these mixed-acid TAGs (for reviews, see Larsson et al., 2006; Sato et al., 1999; Sato and Ueno, 2001; Sato and Ueno, 2005).

The fatty-acid compositions of TAGs are closely related to β′-tending properties. TAGs containing different types of ...

Table of contents

• Cover
• Title Page
• Copyright
• List of Contributors
• Preface
• Chapter 1: Physical properties of fats in food1
• Chapter 2: Bakery fats1
• Chapter 3: Water continuous emulsions
• Chapter 4: Oil modification processes
• Chapter 5: Fats for chocolate and sugar confectionery1
• Chapter 6: Spreadable products
• Chapter 7: Emulsifiers and stabilisers1
• Chapter 8: Food safety and quality issues of dairy fats
• Chapter 9: Culinary fats: solid and liquid frying oils and speciality oils1
• Appendix: Nomenclature for fatty acids and triglycerides
• Index