Competitive adsorption between a dry-heated soy protein–dextran mixture and surface-active materials in oil-in-water emulsions

Competitive adsorption between the protein of a dry-heated soy protein isolate (SPI)–dextran mixture and Tween 40, glycerol monosteareate (GMS) or bovine serum albumin (BSA) in oil–water (o/w) emulsions was studied at various protein/surfactant or BSA weight ratios. Soy protein molecules of the mixture were displaced to some extent from the interface, as a result of competitive adsorption with the small-molecule surfactant or BSA. Complete displacement at weight ratios as high as 2 was not observed and, additionally, a significant proportion of the conjugate remained at the interface conferring stability to the system against creaming, with the exception of GMS. In this case, soy protein displacement is believed to lead to enhancement of protein–protein interactions, bridging flocculation, creaming of oil-droplet flocks and serum separation.