Influence of retorting (121 °C for 15 min), before or after emulsification, on the properties of calcium caseinate oil-in-water emulsions

Oil-in-water emulsions, containing 30% soya oil and various concentrations of calcium 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 in an autoclave, and then mixed with soya oil (to give 30% oil in the final emulsion), followed by homogenization. Heat treatment (121 °C for 15 min) of calcium caseinate emulsions or heat treatment of calcium caseinate solutions prior to emulsion formation, at all caseinate concentrations, resulted in an increase in surface coverage and altered the proportions of individual caseins at the droplet surface. Heat treatment of calcium caseinate solutions at 121 °C for 15 min resulted in the formation of several new peptides, due to protein degradation, and polymerization of casein molecules, as revealed by SDS-PAGE. Both the polymerized caseinate material and degradation products were adsorbed onto the droplet surface efficiently during emulsification; the degradation products were more readily adsorbed than the parent protein. Creaming stability of calcium caseinate emulsions, after storage at 20 °C for 24 h, increased with an increase in caseinate concentration. Creaming stability of these emulsions improved further when the emulsions were retorted or when emulsions were made using retorted calcium caseinate solutions.