Self-consistent-field modelling of casein adsorption - Comparison of results for alpha(s1)-casein and beta-casein

The theoretical adsorption behaviour of the milk proteins, alpha(s1)- and beta-casein, has been studied using a self-consistent-field (SCF) model. Previously published results for beta-casein on the effects of ionic strength and pH on protein conformation are compared with those for alpha(s1)-casein. We find a lower adsorbed amount for alpha(s1)-casein, and a more complex adsorbed conformation because of its more heterogeneous primary structure. The predominant conformation appears to involve a substantial loop for alpha(s1)-casein, producing a thinner adsorbed layer than is predicted for beta-casein, which has, predominantly, a long tail extending away from the surface into the aqueous region. The overall layer structure for both proteins is shown to consist of a combination of many coexisting protein conformations. The relative proportion of the different conformations controls the overall layer properties and their variation with pH and ionic strength.