Effect of apolar phase dielectric constant on interfacial properties of β-lactoglobulin (dielectric constant and interfacial properties of β-lactoglobulin)

In this work, we hypothesized that the difference in the dielectric constant value existing between two non-miscible phases such as oil and water could be partially responsible for both protein unfolding and reorganization of the protein structure at the interface. So, we replaced the oil phase, whose dielectric constant value is 2, by organic solvents chosen for both their non-miscibility with water and their range of dielectric constant values higher (range 6.1-7.2) than that of oil. Using a dynamic drop tensiometer, we studied both surface activity and viscoelastic properties of the milk protein at various interfaces. The aqueous phase (pH7; 25 °C) contained the compact globular β-lactoglobulin at a concentration of 11 mg l−1. Compared to lipid phase (dielectric constant=2), the use of apolar phase with a higher permittivity value (7.2) resulted in an increase in both the surface activity of β-lactoglobulin and viscoelastic parameters of the interfacial film. Moreover, the interfacial water organization would appear as determinant as dielectric constant value, in the increase in surface pressure due to increase in protein concentration at the interface.