KINETICS OF HEAT-INDUCED AGGREGATION OF BETA-LACTOGLOBULIN

Heat-induced aggregation of beta-lactoglobulin was investigated as a f unction of pH, heating temperature, and NaCl concentration by measurem ents of reaction kinetics, differential scanning calorimetry, and ligh t scattering. The aggregation can be well interpreted using a reaction scheme consisting of two steps: a denaturation equilibrium, with a fi rst-order unfolding reaction, followed by second-order aggregation rea ctions. Denaturation becomes rate limiting at high heating temperature , pH values close to the isoelectric point of the protein, and high Na Cl concentration. At neutral pH a maximum is seen in the overall react ion rate as a function of NaCl concentration, which is explained by a stabilizing, salting-cut effect of the salt in combination with an inc rease in the rate of successive aggregation reactions. At high NaCl co ncentrations physical bonding becomes increasingly important; large ag gregates that continue to grow in time are formed, and two phases are distinguished in the aggregation step. The onset time of the secondary aggregation is related to a critical concentration of primary (denatu red or small, aggregated) particles.