Self-consistent-field modelling of adsorbed casein Interaction between two protein-coated surfaces

Abstract

The equilibrium distribution of polymer segments and the interaction free energy between flat hydrophobic surfaces covered with the individual milk proteins, α _s1 -casein and β-casein, have been calculated over the pH range 5.5–7.0 using Scheutjens–Fleer self-consistent-field theory. The interaction potential between the β-casein layers is predicted to be repulsive at all ionic strengths, whereas that between the α _s1 -casein layers has an attractive well above a certain ionic strength (ca. 0.05 M). The strong repulsion between β-casein layers is attributed to combined steric and electrostatic interaction involving the charged dangling tail of adsorbed β-casein. The attraction between α _s1 -casein layers is attributed to extensive bridging of chains between the opposite surfaces. These predictions are consistent with the poorer stability of α _s1 -casein emulsions towards flocculation by salt.