Kinetics of Heat-Induced Aggregation of β-Lactoglobulin

Heat-induced aggregation of β-lactoglobulin was investigated as a function of pH, heating temperature, and NaCl concentration by measurements of reaction kinetics, differential scanning calorimetry, and light scattering. The aggregation can be well interpreted using a reaction scheme consisting of two steps: a denaturation equilibrium, with a first-order unfolding reaction, followed by second-order aggregation reactions. Denaturation becomes rate limiting at high heating temperature, pH values close to the isoelectric point of the protein, and high NaCl concentration. At neutral pH a maximum is seen in the overall reaction rate as a function of NaCl concentration, which is explained by a stabilizing, salting-out effect of the salt in combination with an increase in the rate of successive aggregation reactions. At high NaCl concentrations physical bonding becomes increasingly important; large aggregates 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 (denatured or small, aggregated) particles. Keywords: Whey; β-lactoglobulin; aggregation; kinetics; light scattering