SURFACE COVERAGE OF BETA-LACTOGLOBULIN AT THE OIL-WATER INTERFACE - INFLUENCE OF PROTEIN HEAT-TREATMENT AND VARIOUS EMULSIFIERS

Competitive adsorption of beta-lactoglobulin and small-molecule emulsifiers has been compared at room temperature and at 70 degrees C in oil-in-water emulsions (0.4 wt % protein, 20 wt % n-tetradecane, pH 7). Protein heat treatment leads to a higher protein surface coverage, and the coverage increases steadily with increasing emulsion storage time. Heat-treated protein is more difficult to displace from the oil-water interface by water-soluble nonionic surfactant Tween 20, as confirmed by complementary surface shear viscosity measurements. In emulsions containing anionic surfactant DATEM, the surface coverage of beta-lactoglobulin is only slightly affected by the presence of emulsifier at 70 degrees C. Surface shear viscosity measurements are suggestive of an interfacial complex between beta-lactoglobulin and DATEM. Monoglyceride present in corn oil-in-water emulsions leads to an increase in protein surface concentration at low emulsifier concentrations but a reduction at higher concentrations in agreement with earlier work. Diglyceride has no effect on the measured beta-lactoglobulin surface coverage.