Salt stability of casein emulsions

We present a comparison of the salt stability of oil-in-water emulsions prepared separately with alpha(s1)-casein, beta-casein and sodium caseinate at low protein/oil ratios. Measurements have been made of changes in average droplet sizes, creaming rates, and bulk and interfacial rheology over the pH range 5.5-7.0 and ionic strength range 0.01-0.20 M. Static light-scattering has also been used to determine second virial coefficients in dilute casein solutions under similar conditions of pH and ionic strength. It has been demonstrated that alpha(s1)-casein emulsions become flocculated at ionic strengths of 0.1 M and above, whereas emulsions made with beta-casein or sodium caseinate remain stable. The emulsion stability behaviour is interpreted in terms of (i) recent theoretical calculations of interactions between adsorbed casein layers and (ii) the experimentally determined thermodynamic interaction parameters of the caseins in bulk solution. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.