Competitive adsorption of hen's egg yolk granule lipoproteins and phosvitin in oil-in-water emulsions

Competitive adsorption of egg-yolk granule lipoproteins and phosvitin in oil-in-water emulsions was investigated at pH 4.0, 7.0, and 9.0. Protein solutions contained different ratios of granule proteins to pure phosvitin. The droplet size of the pH 4.0 emulsions was higher than the values obtained for the pH 7.0 and 9.0 emulsions at all of the different combinations of granule and pure phosvitin. Unlike the pH 7.0 and 9.0 emulsions, the amount of phosvitin bound to the oil-water interface at pH 4.0 increased with increase in weight ratio of added pure phosvitin. Time-dependent exchange experiments showed that displacement of phosvitin from the interface by granule lipoproteins was higher and more rapid at pH 7.0 than at pH 4.0, suggesting that the reduction in negative charges of phosvitin molecules at pH 4.0 increases its affinity to the interface. There was an initial increase in droplet size of the phosvitin emulsions upon addition of a granule preparation, which was probably as a result of bridging flocculation of the emulsions by the adsorbing lipoproteins. The results suggest that granule lipoproteins are more surface active than phosvitin and that protein mixtures containing lipoproteins and pure phosvitin would stabilize food emulsions better at pH 7.0 and 9.0 than at pH 4.0.