ISOLATION AND IDENTIFICATION OF PEPTIDES FROM THE DIAFILTRATION PERMEATE OF THE WATER-SOLUBLE FRACTION OF CHEDDAR CHEESE

The water-soluble extract of a mature Cheddar cheese was fractionated by diafiltration using 10 kDa nominal molecular weight cutoff membrane s. The permeate had a savory, cheesy taste, whereas the retentate was bland. The permeate was resolved into nine fractions by gel permeation chromatography on Sephadex G-25. Fractions I-III contained only pepti des, whereas fractions IV-IX comprised mainly free amino acids. Fracti on IV contained a mixture of all amino acids except Phe (fraction V), Tyr (fraction VI), and Trp (fraction IX). Fraction III, which had the savory cheesy taste of the permeate, was dominated by one major peak w ith several minor ones. Fraction III was rechromatographed on a Sephad ex G-25 column, and a number of peptides were isolated from subfractio ns thereof by reversed-phase high-performance liquid chromatography an d characterized by N-terminal amino acid sequencing and mass spectrome try. The results showed that; starter bacteria cell-envelope proteinas e, endopeptidases, and aminopeptidases play an important role in the d egradation of the primary proteolytic products produced by chymosin an d plasmin from alpha(s1)-, alpha(s2)-, and beta-caseins.