Partial identification of peptides from the water-insoluble fraction of cheddar cheese

Proteolysis is regarded as the most important biochemical event during the ripening of Cheddar cheese (Fox et al. 1994). Although schemes have been developed for the fractionation of peptides in cheese (see McSweeney&Fox, 1993), relatively few peptides have, as yet, been isolated from cheese and identified. Most workers have concentrated on fractionation of water-soluble peptides from cheese, and little attention has been focused on the water-insoluble peptides. Primary proteolysis in Cheddar cheese results from the actions of chymosin (EC 3.4.23.4) and plasmin (EC 3.4.21.7), the specificities of which in solution have been established (see Fox et al. 1994), but the extent to which these results can be extrapolated to cheese is not clear. The objectives of this study were to isolate and identify peptides in the water-insoluble fraction (WISF) of cheese and to establish the extent to which the results of casein (CN) hydrolysis studies in solution can be extrapolated to Cheddar cheese.