HEAT-INDUCED AGGREGATION OF BETA-LACTOGLOBULIN STUDIED BY DYNAMIC LIGHT-SCATTERING

The in situ heat-induced aggregation of commercial beta-lactoglobulin as such, or after further purification, was followed to a z-average hy drodynamic diameter of 15-20 nm at 59-63 degrees C by dynamic light sc attering. In this temperature range, measurable increase of hydrodynam ic diameter occurred after an apparent lag period, which was strongly dependent on heating temperature, pH and initial protein concentration . The changes in time scale of the aggregation process agreed with cha nges in amount of unfolded beta-lactoglobulin, assuming a two-state mo del of the denaturation. The pH dependence reflected the midpoint unfo lding temperature and not the sulphydryl group reactivity, suggesting that this reactivity was not rate limiting in the aggregation. The agg regation process was modelled numerically with Fuchs-Smoluchowski kine tics. (C) 1996 Elsevier Science Ltd