Selective displacement of caseinate proteins by hens egg yolk lipoproteins at oil-in-water interfaces

Abstract

Competitive adsorption of caseinate and egg yolk lipoproteins has been investigated in triolein or n-tetradecane-in-water emulsions (0.5% w/v protein, 20% v/v oil, pH 7.0). There was a decrease in particle size of the emulsions as the ratio of egg yolk low-density (LDL) or granule lipoproteins (GLP) in the protein solution increased. The reduction in particle size of emulsions was much higher when caseinate was mixed with LDL than GLP. In the mixture of caseinate–LDL, the protein surface coverage was decreased with increase of LDL. The protein concentration per unit of the interface was greater for emulsions containing n-tetradecane than for triolein. In caseinate–GLP mixture, the surface concentration increased in the presence of GLP, suggesting that the adsorption behaviour of GLP is quite different from that of LDL. This may be due to the low solubility of GLP in protein solution. There was great initial increase of droplet size of caseinate emulsions upon addition of GLP, which could disrupted the interfacial caseinate protein film by the adsorbing lipoproteins. SDS-PAGE and time-dependent displacement experiments indicate that β-casein was predominantly displaced by LDL from tetradecane–water interface and by GLP from triolein–water interface. In the mixture of caseinate-lipoproteins, LDL displaced β-casein predominantly, while almost all caseinate proteins were completely displaced by GLP, even at the lowest level (0.1%).