Formation and stability of sodium caseinate emulsions: influence of retorting (121°C for 15 min) before or after emulsification

Oil-in-water emulsions containing 30% soya oil and various concentrations of sodium caseinate were prepared in a two-stage valve homogenizer. The emulsions were sealed in glass bottles and then heated at 121°C for 15 min in an autoclave. In some experiments, the caseinate solutions were heated at 121°C for 15 min first, mixed with soya oil (to give 30% oil in the final emulsion) and then homogenized. Heat treatment (121°C for 15 min) of either sodium caseinate emulsions or sodium caseinate solutions prior to emulsion formation, at all caseinate concentrations used, resulted in an increase in surface coverage, an increase in creaming stability and a change in the proportions of individual caseins at the droplet surface. Heat treatment of sodium caseinate solutions resulted in the formation of several new peptides, due to protein degradation, as well as polymerization of casein molecules, as revealed by SDS–PAGE. Both the polymerized caseinate material and degradation products were adsorbed efficiently during emulsification; the degradation products were more readily adsorbed than the parent protein. Experiments on heated emulsions indicated that the adsorbed caseinate molecules were more susceptible to degradation during heating than those in solution.