Proteolysis in structural analysis of αs1‐casein adsorbed onto oil surfaces of emulsions and improvement of the emulsifying properties of protein

Abstract

Abstractαs1‐Casein has a unique amphiphilic structure which may provide excellent emulsifying properties. Structural analysis of αs1‐casein adsorbed to emulsified oil globules and improvement of the emulsifying properties of αs1‐casein were undertaken by using proteolysis. Enzymic cleavage of αs1‐casein adsorbed to oil globules of the emulsion was compared with that dissolved in an aqueous solution by using trypsin and chymotrypsin. Thirteen peptide bonds of the adsorbed αs1‐casein in the emulsion were hardly cleaved and were probably among definite regions inaccessible to the proteases. Based on the results, a preliminary model is proposed for the structure of αs1‐casein at an oil/water interface. Emulsifying activity (EA) of αs1‐casein was increased by pepsin digestion. A peptide fraction (PF) separated from the peptic hydrolysate, being composed of αs1‐CN(fl‐23) and a small amount of other peptides, showed an EA similar to that of αs1‐casein at neutral pH. Removal of the small amount of the peptides from PF resulted in a marked decrease of EA. However, the addition of the removed peptides to αs1‐CN(fl‐23) restored the EA. Some synergistic effect between αs1‐CN(fl‐23) and the other peptides in emulsification was suggested.