EFFECT OF SURFACTANT ON SOME PHYSICOCHEMICAL PROPERTIES OF DAIRY OIL-IN-WATER EMULSIONS

Droplet size, fraction of protein adsorbed, and protein surface concen tration in dairy oil-in-water emulsions were studied as a function of the surfactant-to-protein molar ratio. Emulsions were made by homogeni zing skim milk (96 g/100 g) with anhydrous milk fat (4 g/100 g); the p rotein content in emulsions was 3.2g/100 g. Two nonionic surfactants w ere considered: glycerol monolinoleate (oil-soluble) and Tween 20 (wat er-soluble). The latter emulsifier was added before or after emulsific ation. Droplet size, measured in a dissociating medium was not affecte d by the amount of surfactant. Some significant droplet aggregation oc curred in the presence of glycerol monolinoleate at surfactant-to-prot ein molar ratio >16. Tween 20 prevents the formation of aggregates whe n present during emulsification whereas aggregates were not completely disrupted when Tween 20 was added after emulsification. In the absenc e of surfactant, 20% of protein present adsorbed at the oil-water inte rface and this fraction decreased with increasing amounts of surfactan t. A subsequent decrease in surface protein concentration was observed . Provided it was not added in too large amounts to the emulsion, the incorporation of glycerol monolinoleate led to a partial protein displ acement from the interface without inducing some resulting droplet agg regation.