INFLUENCE OF THE DRY-MATTER ON THE DENATURATION KINETICS OF WHEY PROTEINS IN CONCENTRATED SWEET WHEY

The denaturation of alpha-lactalbumin (alpha-la), beta-lactoglobulin ( beta-lg) A and B in whey concentrated by evaporation with dry matter c oncentrations ranging between 5 and 30% was described in terms of reac tion kinetics at temperatures of 80 and 110 degrees C. For alpha-la a reaction order of n = 1.0 was determined, for beta-lg A n = 1.5 and fo r beta-lg B n = 2.0. The reaction orders were independent of the dry m atter. The increase in dry matter delays the denaturation at 80 degree s C especially of beta-lg B, whereas beta-lg A is influenced considera bly less and alpha-la is not affected at all. By calculating relative rate constants, the deviations in the reaction rate between whey and w hey concentrate were able to be quantified. The inhibition of the dena turation of beta-lg B at increasing dry matter concentration in the lo w temperature range is not to be explained by the enhanced viscosity. On the contrary, it is due to a conformation-stabilizing effect of the environmental medium concerning the unfolding reaction. Upon heating to 110 degrees C, however, ie. in the aggregation-limited temperature range, no influence of the dry matter on the denaturation behaviour of beta-lg B was ascertained. Thus, the denaturation effect was able to be described approximately by the kinetic data of whey and the actuall y present concentration of this protein fraction for this temperature.