Composite Blends from Heat-Denatured and Undenatured Whey Protein: Emulsifying Properties

A solution of commercial whey protein isolate was heat-denatured (DWPI) and combined in various ratios with undenatured whey protein isolate (WPI). Emulsions with an oil volume fraction varying from 0.05 to 0.26 were prepared from these mixtures using a lab scale valve homogenizer. The protein content of the aqueous phase was standardized to 3%. The emulsifying activity index of the protein mixtures was determined and the emulsions were analysed for resistance to stirring-induced coalescence, separation stability, viscosity and age thickening. Higher levels of DWPI in the protein blend and higher oil volume fractions of the emulsion increased emulsifying activity, emulsion viscosity and stability. However, these emulsions showed evidence of age thickening. Resistance to stirring-induced coalescence was improved by increasing the proportion of DWPI in the blend and by reducing the oil content of the emulsion. The roles of heat-denatured and undenatured whey proteins in emulsified systems appeared complementary.