Role of whey components in the kinetics and thermodynamics of β-Lactoglobulin unfolding and aggregation

The optimisation of dairy unit operations involving heat transfer requires the control of fouling and aggregation phenomena following the denaturation of thermosensitive proteins, in particular β-lactoglobulin (β-lg). This study intends to give a better view of the influence of whey components (whey proteins, lactose, and minerals such as calcium) on β-lg denaturation through a combined kinetic and thermodynamic approach. β-lg denaturation in model solutions of increasing complexity (pure β-lg solution, whey protein solution, and two model wheys differing in mineral content) was characterised at temperatures ranging from 64.5 to 98 °C by following the evolution of soluble β-lg concentration with HPLC. It was demonstrated that whatever the model solution composition, a two-step mechanism (unfolding followed by aggregation) of 1.5-order kinetics could be adopted to describe β-lg denaturation reaction, as the temperature dependence of the denaturation reaction rate was properly fitted by Arrhenius equation. The dependency of kinetic and thermodynamic parameters on solution composition indicated that the presence of whey proteins enhanced β-lg aggregation, whereas lactose showed a small protective effect against β-lg unfolding. Additionally, minerals, especially calcium, tended to stabilise β-lg native state while increasing β-lg aggregation rates. However, at high mineral content, calcium influence could be hindered or even reversed, presumably owing to a lower bioavailability due to complexation with anions such as inorganic phosphates.