Physical Characterization of Milk Fat and Milk Fat-Based Products

Abstract

This chapter describes the fundamental principles of physical methods for measuring important properties of milk fat and milk fat-based products and aims to give examples illustrating the efficacy of these methods in practice. The sensory properties of products such as butter, cream, cheese, ice cream and milk chocolate are largely dependent on product physical properties, especially properties governed by the fat’s phase change behaviour. 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 term physical 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). Techniques for measuring phase change behaviour are described first. These are grouped, somewhat loosely, under the heading Thermal Properties, together with techniques for measuring milk fat critical temperatures. Second, three highly specialized techniques – Light Spectroscopy, Nuclear Magnetic Resonance (NMR) relaxometry and spectroscopy, and Ultrasound – are described in turn. Third, the measurement of rheological properties and density – mechanical properties – are discussed under the headings Rheological Techniques and Density. Then, methods for measuring refractive index, colour, dielectric properties and electrical conductivity are described under the heading Electromagnetic Properties. Optical methods for investigating phase change are covered under Thermal Properties rather than here. The last main section, Functional Properties, comprises descriptions of techniques, often empirical, for measuring “ingredient properties” and “end-use properties” of milk fat and milk fat-based products. The measurement techniques described in the chapter are those of greatest importance and utility in the physical characterization of milk fat and milk fat-based foods for research and food industry purposes. Many are becoming increasingly sophisticated in terms of capability and usefulness.