COMPETITIVE ADSORPTION OF LECITHIN AND BETA-CASEIN IN OIL IN WATER EMULSIONS

Competitive adsorption at the oil-water interface of egg yolk lecithin (L-alpha-phosphatidylcholine) and beta-casein has been studied in n-tetradecane in water and soya oil in water emulsions (0.4 wt % protein, 20 wt % oil, pH 7). With both types of oil phase, the addition of lecithin at high lecithin/protein molar ratios prior to emulsification leads to partial displacement of protein from the interface. Much more lecithin is associated with n-tetradecane droplets than with soya oil droplets, and at low lecithin/protein molar ratios there is substantially more beta-casein adsorbed at the hydrocarbon-water interface than at the triglyceride-water interface. The ability of lecithin to displace beta-casein from the emulsion droplet surface is qualitatively similar to that found previously for a nonionic water-soluble poly(oxyethylene) surfactant.