Rheology and texture of fermented milk products

Abstract

© 2015 Nova Science Publishers, Inc. Rheology is a branch of science which defines the relation between forces exerted on a material and the ensuing deformation or flow of the material as a function of time. Food is usually neither liquid nor solid, but has viscoelastic characteristics. Viscoelastic materials reveal a combination of viscous (liquid) and elastic (solid) behavior. Yoghurt is among the most popular fermented milk products. Yoghurt is a protein network formed by casein micelles entrapping serum and fat globules. The distribution of the other components has an important effect on the rheological behavior of yoghurt. It is a typical example of weak viscoelastic gel. Dynamic rheological measurements of yoghurt are of interest as they are directly related to its viscous and solid properties. Viscosity measurements can be used to confirm the stability of the fermented milk products. Basically, the viscosity of fermented milk products can be measured by using different types of rheometers: Ostwald, Hoppler, Brookfield and Haake Rheostress ones. Textural properties (firmness, consistency, cohesiveness, and index of viscosity) of fermented milk products are usually analyzed by Texture Analyzer apparatus. Viscosity, structure, and textural characteristics of the gel are influenced by several factors, including protein concentration, milk fat content, heat treatment of milk, acidity, type of a starter culture, incubation temperature, and addition of flavorings or other functional ingredients. In the case of low-fat products, behavior of proteins during the gelation process is of particular importance. However, these products somewhat lack the textural and sensory attributes of their full-fat counterparts.