Interfacial and Molecular Properties of High-Pressure-Treated ß-Lactoglobulin B

Interfacial properties of β-lactoglobulinBsubjected to hydrostatic pressures up to 400MPawere studied by measuring surface pressure at the air/water interface and the elastic interfacial shear modulus at the oil/water interface.Thesurface hydrophobicity of pressurized β-lactoglobulin was determined byan1-anilinonaphthalene-8-sulfonate assay and exposure of free thiol groups using the Ellman assay. The molar mass of pressure-induced oligomers was measured using a combination of size exclusion chromatography, light scattering, and refractive index measurements. High-pressure treatment of β-lactoglobulin increased the surface pressure growth rate and its final level at the air/water interface. After high-pressure treatment, the maximum interfacial elasticity at the oil/water interface increased, and the time lag before growth of the interfacial elasticity decreased. Up to 200 MPa, large amounts of monomeric β-lactoglobulin were formed with increased exposure of thiol groups and increased surface hydrophobicity compared to unpressurized β-lactoglobulin. At a pressure higher than 200 MPa, surface hydrophobicity continued to increase, while exposure of thiol groups decreased, the latter due to the formation of covalently linked oligomers. We have shown that surface hydrophobicity rather than thiol exposure is important for the pressure-induced increase in growth rate and the final level of surface pressure at the air/water interface and in interfacial elasticity at the oil/water interface.