The kinetics of the fieat-induced irreversible denaturation of p-lactoglobulins (p-LG) A and B and of cy-lactalbumin ((U-LA) in milk were examined over a wide temperature/time range (70-15O"C, 2-5400 set). Denaturation of P-LG was best described with an apparent reaction order of 1.5 ((U-LA; first order). The abrupt changes in the temperature dependence of the rate constants (P-LG at 9O"C, IX-LA at 80°C) were interpreted in terms of the different activation energies and entropies occurring in the two temperature ranges. By using the kinetic parameters for calculating lines of equal degrees of denaturation in a plot of log-time versus l/absolute temperature it was possible to predict the effect of different heat treatments on the denaturation of individual proteins.

Skim milk powder (SMP), a whey protein concentrate (WPC) and fat globules with modified membranes were used for the fabrication of mixed and filled dairy gels. Firmness and syneresis of pure gels varied broadly with pH and total solids (TS). Mixing SMP and WPC at 10% TS showed synergistic effects on gel firmness, particularly for 5050 blends, and addition of fat provided further reinforcement. Syneresis of gels and their appearance changed from high and clear to low and turbid, respectively, as the WPC content was increased. Microstructural studies revealed the porous structure of the parent gels, compatability between both protein sources and between fat globules and the protein matrix.

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The effects of heating and storage conditions on the chemical changes in milk which are unaffected by the oxygen content, such as the loss of thiamin and lysine and the formation of hydroxymethylfurfural, were investigated and the kinetics of the reactions worked out. All changes could be described by one equation which was valid over a surprisingly wide range of times and temperatures (from 1 set up to 1 yr, from 4°C up to 160°C) and which gave straight lines in the Arrhenius plot log time = f (l/absolute temperature). Because of this it is possible to optimize product quality, heating processes, and storage conditions.

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