Protein/surfactant interfacial interactions Part 2. Electrophoretic mobility of mixed protein + surfactant systems

摘要

Protein-protein and protein-surfactant interactions have been investigated in bulk aqueous solution and in oil-in-water emulsion systems by electrophoretic mobility measurements. The interaction between oppositely charged β-lactoglobulin and gelatin has been studied under neutral pH conditions. The addition of cationic gelatin to a β-lactoglobulin-stabilized emulsion induces flocculation and charge neutralization of the emulsion droplets. The procedure of mixing the gelatin solution with the ?-lactoglobulin-stabilized emulsion has no significant effect on the observed mobility behaviour of the emulsion droplets. Binding of the anionic surfactant sodium lauryl ether sulphate (SLES 2EO) to β-lactoglobulin and gelatin was observed under neutral pH conditions. The charge neutralization line for gelatin + SLES 2EO complexes in distilled water appears consistent with its maximum precipitation line. However, the charge neutralization line of gelatin + SLES 2EO at pH 7.0 occurs at slightly lower surfactant concentrations compared to the maximum precipitation line. The addition of SLES 2EO to a gelatin-stabilized emulsion causes a change in calculated zeta potential of the emulsion droplets and a partial charge neutralization for the flocculated emulsion droplets. Electrophoretic mobility measured in solutions of β-lactoglobulin + gelatin + SLES 2EO shows that the three-component complexes (or precipitates) are negatively charged. Various possible interaction mechanisms are discussed taking account also of results obtained on the same systems by other complementary techniques.