Influence of the dry matter on the denaturation kinetics of whey proteins in concentrated sweet whey

Plock, J.; Spiegel, T.; Kessler, H.G.

Milchwissenschaft 53(6): 327-331


The denaturation of alpha-lactalbumin (alpha-Ia), beta-lactoglobulin (beta-Ig) A and B in whey concentrated by evaporation with dry matter concentrations ranging between 5 and 30% was described in terms of reaction kinetics at temperatures of 80 and 110degreeC. For alpha-Ia a reaction order of n = 1.0 was determined, for beta-Ig A n = 1.5 and for beta-Ig B n = 2.0. The reaction orders were independent of the dry matter. The increase in dry matter delays the denaturation at 80degreeC especially of beta-Ig B, whereas beta-Ig A is influenced considerably less and alpha-Ia is not affected at all. By calculating relative rate constants, the deviations in the reaction rate between whey and whey concentrate were able to be quantified. The inhibition of the denaturation of beta-Ig B at increasing dry matter concentration in the low 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 110degreeC, however, ie. in the aggregation-limited temperature range, no influence of the dry matter on the denaturation behaviour of beta-Ig B was ascertained. Thus, the denaturation effect was able to be described approximately by the kinetic data of whey and the actually present concentration of this protein fraction for this temperature.