Fragmented proteins as food emulsion stabilizers: A theoretical study

Using a model based on the primary structure of αs1 -casein, the colloid stabilizing ability of fragmented protein and that of the intact chains are compared. We perform self consistent field (SCF) calculations to obtain the induced interaction potentials between the oil droplets, resulting from the overlap of adsorbed protein layers in each case. For the intact αs1 -casein, we confirm the known result, that the mediated interparticle interaction potential develops a deep attractive energy minimum at high salt concentrations and pH values close to the isoelectric point of the protein. The same does not occur for the appropriately fragmented systems, with improved emulsion stability predicted as a result, even at pH values close to pI. It is shown that this superior performance, for the case considered, is due to the diblock-type behavior of one of the fragments. However, it is well known that αs1 -casein more closely resembles the less favorable triblock structure. However, it is also demonstrated that the presence of a "diblock" like fragment by itself may not always be enough to produce a better emulsion stabilizer. It is seen that the hydrolysis of some peptide bonds may indeed lead to a suitable polypeptide, but that this is displaced from the interface by the structurally less desirable ones, also generated by the fragmentation process. The displacement occurs due to the competitive adsorption between different fragments. The removal of the undesirable fragments from the solution is found to greatly enhance the predicted colloid stabilizing ability of the remaining polypeptide.