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 hydrodynamic diameter of 15-20 nm at 59-63 degrees C by dynamic light scattering. In this temperature range, measurable increase of hydrodynamic 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 changes in amount of unfolded beta-lactoglobulin, assuming a two-state model of the denaturation. The pH dependence reflected the midpoint unfolding temperature and not the sulphydryl group reactivity, suggesting that this reactivity was not rate limiting in the aggregation. The aggregation process was modelled numerically with Fuchs-Smoluchowski kinetics. (C) 1996 Elsevier Science Ltd