Physical characterization of milk fat and milk fat-based products

Abstract

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. The termphysical properties is used here to mean both physical properties as such (e.g., density) and characteristics that can be measured by physical means (e.g., polymorph type). The measurement of physical properties is essential for the proper understanding and control of processing operations and of the sensory properties, functionality and shelf stability of the Wnal product (Birker and Padley, 1987; Rajah, 2002; O'Brien, 2003). Techniques for measuring phase change behavior are described Wrst. These are grouped, somewhat loosely, under the heading thermal properties, together with techniques for measuring milk fat critical temperatures. Second, the measurement of rheological properties and of density is described under these headings. Then, methods for measuring refractive index, color, dielectric properties and electrical conductivity are described under the heading electromagnetic properties. These headings are not mutually exclusive. Optical methods for measuring phase change behavior are included under thermal properties rather than under electromagnetic properties. Rheological methods of particular use for measuring phase change behavior are also included under thermal properties, but are described in more detail under rheological properties. The last main section, functional properties, comprises descriptions of techniques for measuring "ingredient properties" and "end use properties" of milk fat and milk fat-based products. The measurement techniques described in this chapter are those of greatest importance and utility for the physical characterization of milk fat and milk fat-based foods for research and food industry purposes.