Physical properties, fats texture

Pastry, Cake, and Biscuit Products. In general, fats play several essential nutritional, technological, functional, and organoleptic roles in most all-bakery applications. As a result of its physical properties, fat plays a major part in the production of the majority of items in the pastry, cake, biscuit, and chocolate confectionery sector for example, in the preparation of pastry cream and in the desired appearance and texture of the end product. These physical properties include, above all, the rheological properties (consistency, plasticity, texture, etc.), and the properties of fusion and crystallization depend on the type of fat, the temperature, and the working conditions of the product. 

A constitutively hydrophobic food fat is called upon to perform in a hydrophilic environment, suggesting the most important physical property to be its emulsifying capacity. Simultaneously, the fat is ingredient-compatible, heat-stable, and confers a smooth oral sensation. The basic assignment of a fat replacer is to mimic these properties through substitution for the fat s viscosity, texture, and the slippery, creamy, lubricious mouthfeel (Glicksman, 1991). One of the earliest fat substitutes to perform thus was Simplesse (Roller and Jones, 1996), a protein perceived to be of a creamy texture due to inherent 0.1-3.0-pm-diameter microparticles (Thayer, 1992). 

Fat and fat structure development in ice cream and related frozen dairy desserts are critical for optimal structure and physical properties, stability, flavor and texture. This chapter will present a brief review of the functionality of fat in ice cream, with citations of the most recent and most pertinent references. In particular, readers are referred to Berger (1997), Golf (1997, 2002, 2003), Buchheim (1998), Marshall et al. (2003) and Golf and Tharp (2004) for more detailed information. 

The sensory properties, especially texture and appearance, of milk fat-based products such as butter, cream, cheese, ice cream and milk chocolate are largely dependent on the physical properties of the product, especially properties governed by the phase change behavior of the fat, used here to mean melting and crystallisation behavior, crystal polymorphism and microstructure (Birker and Padley, 1987 O Brien, 2003). The same may be said of the functional properties of milk fat, milk fat fractions and milk fat-based products when these are used as food ingredients. 

Fats provide fundamental structural and textural attributes to a wide range of consumer products, including lipstick, chocolate, and everyday products such as butter and margarine (1, 2). Within these fat-based products, certain textural properties are required to meet desirable sensory attributes to gain consumer acceptance (3). This has led to an increase in research efforts on the physical properties of fats, particularly their rheology. 

The Science of Ice Cream begins with an introductory chapter on the history of ice cream. Subsequent chapters outline the physical chemistry underlying its manufacture, describe the ingredients and industrial production of ice cream and ice cream products respectively, detail the wide range of different physical and sensory techniques used to measure and assess ice cream, describe its microstructure (i.e. ice crystals, air bubbles, fat droplets and sugar solution), and how this relates to the physical properties and ultimately the texture that you experience when you eat it. Finally, some suggestions are provided for experiments relating to ice cream and ways to make ice cream at home or in a school laboratory. 

Rousseau, D and Marangoni, AG (1998c) Tailoring the textural attributes of butter fat/canola oil blends via Rhizopus arrhizus lipase-catalyzed interesterification. 2. Modification of physical properties. J. Agric. Food Chem., 46, 2375-2381. 

Proper control of the crystalline microstructure leads to products with the desired textural properties and physical characteristics. For example, tempering of chocolate prior to molding or enrobing is designed to control crystallization of the cocoa butter into a large number of very small crystals that are aU in the desired polymorphic form. When controlled properly, the cocoa butter crystals in chocolate contribute to the desired appearance (shine or gloss), snap, flavor release, meltdown rate upon consumption, and stability during shelf life (fat bloom). Similar... 

The dispersion of the crystalline fat phase in a material determines the physical and textural properties of a lipid-based product. For example, the hardness, snap, and glossy appearance of chocolate is caused by crystallization of cocoa butter in the form of numerous, very small (1 pm or less) crystals of the most stable polymorph (p form). The size distribution (mean size and range of sizes), polymorphic form, and shape of the fat crystals, as well as the network formed among the crystals, all play important roles in determining physical attributes of lipid-based products. 

Figure 1.1 showed the links between the formulation, the process and the texture. The first step is to understand how the formulation and process affect the microstructure. This requires microscopy techniques to visualize the ice crystals, air bubbles, fat droplets and matrix and image analysis to quantify their sizes, shapes and locations. The next step is to measure the mechanical, rheological and thermal properties and to relate them to the microstructure. The final stage is to relate these physical measurements to the sensory properties. This chapter describes the techniques used to make these measurements. 

The microstructure of ice crystals, air bubbles, fat droplets and matrix is central to the physical and hence sensory properties of ice cream. Considering the components separately is sufficient for some properties, but for many others it is impossible to treat one component in isolation from the rest. Many mechanical, thermal and rheological properties depend on the whole microstructure this necessitates a materials science approach. Furthermore, the texture experienced during consumption depends on the manner in which the product is eaten, and the way in which the microstructure breaks down. Only when all these factors are combined is it possible for the ice cream scientist to link the ingredients and the process through the microstructure to the texture. However, the current understanding of these links is far from complete and this remains an active area of research. This chapter is only a short overview of a very complex subject, and interested readers are referred to the Further Reading for more detailed treatments. 

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