EMULSIFYING PROPERTIES OF WHEY-PROTEIN AND CASEIN COMPOSITE BLENDS

Fluid emulsions containing 30% fat were produced with various ratios of casein and whey protein. The effects of adding commercial monoglycerides to the oil phase and of heat treating protein solutions before emulsion formation were also investigated. Interfacial pressure and protein load detemination both indicated preferential adsorption of casein over whey proteins. The addition of monoglycerides reduced the amount of protein adsorbed, except for emulsions produced from heated protein solutions containing high proportion of whey protein, for which an increasing trend was observed. Resistance to stirring-induced coalescence decreased with an increasing proportion of whey in the mixture except for emulsions from heated pure whey protein solution with added monoglycerides, which improved the resistance. Emulsions containing casein showed extensive creaming and coalescence upon storage. Heat treatment reduced creaming and coalescence but induced slight sedimentation. Monoglycerides were also effective in reducing coalescence of emulsions containing casein. Pure whey protein emulsions showed no coalescence but considerable creaming upon storage. Creaming was inhibited by heating whey protein solution, which produced viscous emulsions. Conflicting results between stirring-induced coalescence and storage coalescence suggest important changes in membrane properties during storage.