Competitive adsorption of β-casein and nonionic surfactants in oil-in-water emulsions

Abstract

Competitive adsorption of β-casein and three nonionic surfactants has been investigated in hydrocarbon oil-in-water emulsions (0.4 wt% protein, 20 wt% oil, pH 7). Addition of a water-soluble surfactant, C12E8 (octaethylene glycoln-dodecylether) or Tween 20 (polyoxyethylene sorbitan monolaurate), after emulsion formation leads to a complete displacement of protein from the oil-water interface at surfactant-to-protein molar ratios in excess of 17:1. Addition of the oil-soluble surfactant C12E2 (diethylene glycoln-dodecylether) prior to emulsification leads to reduction in droplet size but no protein displacement. Addition of C12E8 prior to emulsification leads to a slightly greater reduction in droplet size and partial protein displacement at high surfactant-to-protein ratios. The competitive displacement of β-casein from the emulsion droplet surface by C12E8 is broadly consistent with interfacial tension data for C12E8 + sodium caseinate at the hydrocarbon oil-water interface. © 1991 Academic Press, Inc.