Computer Simulation of the Pre-Heating, Gelation, and Rheology of Acid Skim Milk Systems - Food Colloids: Self-Assembly and Material Science - page 269

Chapter 18

Computer Simulation of the Pre-Heating,
Gelation, and Rheology of Acid Skim Milk
Systems

Joost H. J. van Opheusden

MATHEMATICAL AND STATISTICAL METHODS GROUP,
BIOMETRIS, WAGENINGEN UNIVERSITY, BORNSESTEEG 47, 6708
PD WAGENINGEN, THE NETHERLANDS

18.1 Introduction
Milk is, and has been for maybe half a billion years, an essential consumption
product. Breast-feeding of sucklings is natural behaviour among mammals, and
in human culture animal milk is considered a valuable element of the diet for
people of all ages. Whether intended for direct consumption or further process-
ing, milk is routinely pasteurized to reduce microbial contamination. Different
heat-treatment procedures are used, depending on the final consumption
product intended. 1 As well as enhancing the safety of the product, the heat
treatment also changes milk's properties, such as the taste. But even more
important for the production of secondary milk products, such as cheese,
yoghurt, and butter, are the heat-induced microscopic changes.
Milk is a very stable colloidal system of fat globules and proteins dispersed in
water. A substantial part of the protein content ( 3 wt%) is present in the

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form of casein micelles of size 100 nm; the casein micelles also contain

substantial amounts of calcium phosphate. The smaller whey proteins (3 nm)
constitute a minor fraction (

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0.5 wt%). Skim milk is prepared by removing the

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large fat globules ( 1 mm) from the suspension.

In this modelling study, we first concentrate on the description of skim milk
samples during heat treatment at slightly different levels of acidity. Small
differences in acidity of milk occur mainly due to seasonal variation. For
different temperatures and different pH values, there are changes in the
properties of the casein micelles and the whey proteins, as well as in their
mutual interaction. At high temperatures the denaturation of whey proteins
leads to destabilization, but the casein micelles themselves are not so much
affected by heat treatment. 2 Denaturated whey proteins can bind with each

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