A Scheme for the Fractionation of Cheese Nitrogen and Identification of Principal Peptides

A four-step fractionation scheme for the isolation of peptides from cheese was investigated. The, first three steps involved water extraction, ultrafiltration and gel filtration; water was used as solvent which renders the fractions suitable for sensory assessment. In the last step, gel filtration. fractions were applied to a Sep-pak reverse phase C-18 cartridge from which individual peptides were eluted by using increasing concentrations of acetonitrile. The two principal peptides in the ultrafiltrate permeate of water soluble extract were isolated and identified by amino acid sequencing and mass spectroscopy as alpha(s1)-CN f1-9 and alpha(s2)-CN f1-13. These peptides may have been produced by the combined action of chymosin and PI-type cell wall-associated proteinase of the Lactococcus spp. starter.