Surface protein composition and concentration of whey protein isolate-stabilized oil-in-water emulsions: effect of heat treatment.

The heat-induced changes in the surface protein compositions and concentrations of whey protein isolate (WPI)-stabilized emulsions were examined. With increasing heating temperature, the amount of adsorbed beta-lactoglobulin (beta-lg) increased whereas the amount of adsorbed alpha-lactalbumin (alpha-la) decreased. In emulsions formed with 0.5 wt% WPI, the adsorbed alpha-la almost disappeared from the interface of the emulsion droplets after heating at 121 degrees C. With heat treatment at 90 degrees C, adsorbed beta-lg increased but adsorbed alpha-la decreased in the first 5 min, and then changed slightly with increasing heating time. This change in the proportions of beta-lg and alpha-la at the interface may have arisen from the displacement of alpha-la from the interface by beta-lg in the aqueous phase. The addition of NaCl resulted in an increase in the total surface protein concentration during heat treatment, but the competition between beta-lg and alpha-la at high temperatures was eliminated. The emulsions lost stability because bridging flocculation of the emulsion droplets occurred during heat treatment in the presence of NaCl (>50 mM).