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

Droplet size, fraction of protein adsorbed, and protein surface concentration in dairy oil-in-water emulsions were studied as a function of the surfactant-to-protein molar ratio. Emulsions were made by homogenizing skim milk (96 g/100 g) with anhydrous milk fat (4 g/100 g); the protein content in emulsions was 3.2g/100 g. Two nonionic surfactants were considered: glycerol monolinoleate (oil-soluble) and Tween 20 (water-soluble). The latter emulsifier was added before or after emulsification. Droplet size, measured in a dissociating medium was not affected by the amount of surfactant. Some significant droplet aggregation occurred in the presence of glycerol monolinoleate at surfactant-to-protein molar ratio >16. Tween 20 prevents the formation of aggregates when present during emulsification whereas aggregates were not completely disrupted when Tween 20 was added after emulsification. In the absence of surfactant, 20% of protein present adsorbed at the oil-water interface and this fraction decreased with increasing amounts of surfactant. 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 displacement from the interface without inducing some resulting droplet aggregation.