INFLUENCE OF PH AND HEATING ON PHYSICOCHEMICAL PROPERTIES OF WHEY PROTEIN-STABILIZED EMULSIONS CONTAINING A NONIONIC SURFACTANT

The influence of polyoxyethylene sorbitan monolauarate (Tween 20) on d roplet flocculation in 20 wt % soybean oil-in-water emulsions stabiliz ed by whey protein isolate (WPI) was investigated by light scattering, rheology, and creaming measurements. In the absence of Tween 20, emul sions were prone to droplet flocculation near the isoelectric point (p I) of the proteins (4 < pH < 6) but were stable at higher and lower pH values. Flocculation led to an increase in emulsion particle size, vi scosity, and creaming index. Addition of Tween 20 at low concentration s (R < 0.1, where R is the surfactant/protein molar ratio) had little effect on emulsion properties, but at higher concentrations (R > 5) it decreased the amount of flocculation and shifted it to lower pH value s. The higher concentrations of Tween 20 also reduced the extent of dr oplet flocculation in emulsions heated at 78 degrees C for 30 min in t he presence of 100 mM NaCl. The results are explained in terms of comp etitive adsorption, protein-surfactant interactions, and colloidal int eractions. This study shows that the physicochemical properties of pro tein-stabilized emulsions can be controlled by adding nonionic surfact ants.