SELF-CONSISTENT-FIELD MODELING OF ADSORBED CASEIN INTERACTION BETWEEN2 PROTEIN-COATED SURFACES

The equilibrium distribution of polymer segments and the interaction f ree energy between hat hydrophobic surfaces covered with the individua l milk proteins, alpha(s1)-casein and beta-casein, have been calculate d over the pH range 5.5-7.0 using Scheutjens-Fleer self-consistent-fie ld theory. The interaction potential between the beta-casein layers is predicted to be repulsive at all ionic strengths, whereas that betwee n the alpha(s1)-casein layers has an attractive well above a certain i onic strength (ca. 0.05 M). The strong repulsion between beta-casein l ayers is attributed to combined steric and electrostatic interaction i nvolving the charged dangling tail of adsorbed beta-casein. The attrac tion between alpha(s1)-casein layers is attributed to extensive bridgi ng of chains between the opposite surfaces. These predictions are cons istent with the poorer stability of a,,-casein emulsions towards flocc ulation by salt.