Changes in milk on heating: viscosity measurements

Abstract

SummarySkim milk was heated at 85 °C for different holding times. As a result of such heating, whey proteins, in particular β-lactoglobulin, denatured and associated with casein micelles. This led to an increase in size of the casein micelles but also to a different interaction between them. Both these changes could be described by using a quantitative model which was developed for the viscosity of so-called adhesive hard spheres. We applied the model successfully to skim milk and were able to describe on a quantitative basis the changes due to the heat treatment of milk. It was shown that after heating the casein micelles became larger and acquired a mutual attraction. The unfolding of the whey proteins and their subsequent association with the casein micelles appeared to be responsible for these changes. How this reaction influences the fouling of heat exchangers is discussed.

Dairy Systems

“…The viscosity of skim milk does not change much after heat treatment at 60 • C, which is lower than the denaturation temperature of whey protein (70 • C), but increases significantly after heat treatment at 90 • C (Jeurnink and de Kruif, 1993). The effect of heat treatment on skim milk viscosity becomes less significant after removal of whey proteins, suggesting the enhancing effects are attributed to heat-denatured whey proteins, especially β-lactoglobulin aggregates (Jeurnink and de Kruif, 1993).…”

“…Relative viscosity has been used not only to determine the effects of milk composition on viscosity but also the effects of other factors such as heat treatment. Jeurnink and de Kruif (1993) studied the effect of heat treatment on skim milk viscosity using an Ubbelohde capillary viscometer. The U-tube viscometer is a convenient and inexpensive method to measure and compare the apparent viscosity of milk products.…”

“…When milk is heated, denatured whey proteins can form whey protein aggregates as well as associate with casein micelles. Interactions between whey proteins and casein produce two different changes in casein micelles: (i) The micelle grows in size, and (ii) the interaction between micelles is altered (Jeurnink and de Kruif, 1993). Anema et al (2004) indicated that viscosity changes in reconstituted skim milk after heat treatment were related to a change in volume fraction of the casein micelles, which was correlated with the amount of denatured whey protein associated with casein micelles.…”

Dynamic footprint of sequestration in the molecular fluctuations of osteopontin

“…It should be noted that S 2 predicted using DynaMine are on an absolute scale, allowing for comparison between predictions for different proteins. [61]. By comparison, the hydration level used in this experiment is considered appropriate.…”

Phase Stability of Concentrated Dairy Products

“…Evaporation leads to increased concentrations of both the casein micelles and the fat globules. In Table 1, the approximate fat and casein contents of these products are compared (Snoeren et al, 1984;Walstra and Jenness, 1984;Jeurnink and de Kruif, 1993). The calculation of the volume fractions of casein micelles in these products was made as described for a solution of skim milk powder and is explained in the Materials and Methods section of this paper.…”