Studying a chaperone-like effect of beta-casein on pressure-induced aggregation of beta-lactoglobulin in the presence of alpha-lactalbumin

Abstract Protein aggregation can be used to improve functionality in certain food systems, especially in gelled systems. However, in beverages application, this phenomenon is generally undesirable since it is usually related to protein insolubility and turbidity. Nonetheless, some research has demonstrated a molecular chaperone-like property of certain milk proteins that helps avoid protein aggregation. Here, we investigated the effect of beta-casein (β-CN) on pressure-induced aggregation of beta-lactoglobulin (β-lg) in whey solution using various qualitative and quantitative analyses (turbidity, SDS-PAGE, HPSEC and TEM). Protein model solutions containing different ratios of alpha-lactalbumin (α-la), β-lg and β-CN were pressurized by high hydrostatic pressure (HHP). Pressure treatment of β-lg alone generated a highly turbid solution containing large aggregates while the addition of both proteins (α-la and β-CN) at different ratios led to a drastic decrease in turbidity, despite the presence of larger aggregates. In fact, TEM analysis showed larger and amorphous aggregates for β-lg with α-la and β-CN, and globular, denser aggregates for β-lg alone. Further analysis of these aggregates by fractionation (HPSEC) followed by SDS-PAGE showed no β-CN directly involved in β-lg aggregation, suggesting a chaperone-like effect of β-CN under HHP. Our experiments, performed on model dairy solutions, demonstrated that α-la and β-CN inhibits the formation of insoluble aggregates (decreases turbidity) under HHP treatment of β-lg that could be relevant in milk protein fortified beverages.