Kinetic study of β-lactoglobulin thermal aggregation at low pH

Kinetics of β-lactoglobulin (β-lg) thermal aggregation at pH 3.35, 85 °C, and 2–8% w/w protein concentration was studied using high performance liquid chromatography (HPLC) coupled with multi-angle laser light scattering (MALS) and rheology. Rate of β-lg aggregation was found to be of first order with respect to the initial protein concentration, and the conversion of native-like β-lg monomers/dimers (<36 kDa) to aggregates increased with initial concentration and heating times. The size of the aggregates formed during heating was dependent on the initial protein concentration. A simple nucleation and growth model was described for the β-lg aggregation at pH 3.35, where nucleation was found to be a rate limiting step below the previously identified critical concentration, Cc ∼ 6.4% protein. Above the Cc, nucleation occurred quickly and was not rate limiting. Critical size of the nucleus varied with protein concentration, with larger critical size needed at lower protein concentrations.

► Kinetics of β-lg thermal aggregation at low pH as affected by protein concentration.
► Molar mass distribution of β-lg aggregates and viscosity data analyzed.
► Bimodal distribution of β-lg aggregates observed after heating at pH 3.35.
► Nucleation and growth mathematical model fitted experimental data suitably.
► Nucleation was not rate limiting at higher (∼ 8% w/w) protein concentrations.