Influence of Protein Interfacial Composition on Salt Stability of Mixed Casein Emulsions

The influence of casein surface composition on the stability toward flocculation by sodium chloride has been investigated for oil-in-water emulsions (20 vol % oil, 1 wt % total protein) prepared with a mixture of alpha(s1)-casein + beta-casein. It has been observed that the poor salt stability of emulsions containing 100% alpha(s1)-casein is greatly enhanced by the replacement of about one-third of the alpha(s1)-casein by beta-casein. With around half of the adsorbed protein layer consisting of beta-casein, emulsions remain stable at ionic strengths of 2 M NaCl in the presence or absence of calcium ions (5 mM). At the point of droplet flocculation in these emulsions, most of the casein present is associated with the surface of the droplets. These results provide definitive evidence for the important influence of the compositional balance in sodium caseinate on the colloidal stability behavior of casein-based emulsions.