Effect of pH on the reaction mechanism of thermal denaturation and aggregation of bovine β-lactoglobulin

Abstract

New insights in the aggregation mechanisms of the whey protein β-lactoglobulin were gained by detailed investigation of the denaturation behavior (80–120 °C) at variable pH values (5.1, 6.8, 8.0). Denaturation followed a 1.5 order kinetic and reaction velocity was depending on pH and temperature. Characterization of aggregates formed at 80 °C was correlated to the denaturation progress and comprised particle size measurement, quantification of free thiol groups and analysis of quaternary structures as well as stabilizing forces by various types of gel electrophoresis. Due to low electrostatic repulsion at pH 5.1, a fast and steady aggregate growth was observed, where intermolecular disulfide bonds gain more importance with increasing degree of denaturation. Contrary to that, denaturation at pH 6.8 and 8.0 yielded lower reaction rate constants and a steady increase of the amount of exposed thiol groups, resulting in non-native oligomers which were mainly non-covalently connected to small aggregates.