Gelation of whey protein induced by proteolysis or high pressure treatment

A proteolytic enzyme from Bacillus licheniformis, specific towards cleavage of peptide bonds with glutamic or aspartic acid, can be used to hydrolyse whey proteins and cause gelation. Combination of heat and proteolysis provi des the possibility of producing a variety of gels with different rheologic al and microstructural properties ranging from weak, opaque gels to strong, almost transparent gels. Thus, pre-denaturation prior to addition of enzym e enhances the gelation properties, and gelation proceeds by a different me chanism compared to unheated whey protein. Hydrolysis prior to thermal gela tion reduces the gel strength, whereas simultaneous hydrolysis and thermal treatment results in gels with a microstructure dependent on the temperatur e. Gels composed of aggregates formed at 40 to 60 degrees C exhibit an open structure and large pores, whereas at higher temperatures a more fine stra nded structure is formed. Purified alpha-lactalbumin forms strong, transpar ent gels when hydrolysed with the enzyme, High pressure is able to make whe y proteins gel, but the practical application is hindered by the presence o f non-incorporated liquid. High pressure is perhaps more useful in selective hydrolysis of beta-lactog lobulin, for improving the foaming properties or for manipulation of casein micelles.