TEMPERATURE-DEPENDENCE OF THE COMPETITIVE DISPLACEMENT OF PROTEIN FROM THE EMULSION DROPLET SURFACE BY SURFACTANTS

The surface coverage of beta-casein in soya oil-in-water emulsions (0.4 wt% protein, 20 wt% oil, pH 7) has been determined at temperatures in the range 0-20-degrees-C from an analysis of the aqueous phase after centrifugation. The presence of glycerol monostearate dissolved in the oil phase is found to greatly enhance the competitive displacement of protein from the triglyceride-water interface by water soluble surfactants (C-12E8 or Tween 20) added after emulsification. There is a minimum in protein surface concentration at a temperature of 5-10-degrees-C in the presence or absence of surfactants. We discuss the relevance of the results to the competitive displacement of milk protein during the ageing of ice-cream mix.