PROTEIN/SURFACTANT INTERFACIAL INTERACTIONS .3. COMPETITIVE ADSORPTION OF PROTEIN PLUS SURFACTANT IN EMULSIONS

We present results of competitive adsorption between proteins and surfactant (nonionic Tween 20 or anionic sodium lauryl ether sulphate SLES 2EO) in various oil-in-water emulsions. The addition of gelatin to a beta-lactoglobulin-stabilized emulsion results in secondary layer adsorption of gelatin. The condition of half-coverage of gelatin correlates with the maximum degree of bridging flocculation. The amount of nonionic surfactant (Tween 20) required for complete displacement of gelatin from the oil/water interface is found to be higher than that required for displacement of beta-lactoglobulin. The mixed proteins are less easy for the nonionic surfactant to displace from the oil/water interface. The addition of anionic surfactant (SLES 2EO) to a gelatin-stabilized emulsion leads to co-operative adsorption as well as competitive adsorption. The co-operative adsorption induces a higher gelatin surface concentration which correlates with enhanced emulsion flocculation. In emulsions containing the mixed proteins (beta-lactoglobulin + gelatin), added anionic surfactant SLES 2EO is unable to displace proteins completely from the droplet surfaces and the protein surface concentration behaviour shows a consistent trend to that found in separate emulsion flocculation studies.