Degradation and debittering of a tryptic digest from β-casein by aminopeptidase N from Lactococcus lactis subsp. cremoris WG2

Abstract

The mode of action of purified aminopeptidase N from Lactococcus lactis subsp. cremoris Wg2 on a complex peptide mixture of a tryptic digest from bovine β-casein was analyzed. The oligopeptides produced in the tryptic digest before and after aminopeptidase N treatment were identified by analysis of the N- and C-terminal amino acid sequences and amino acid compositions of the isolated peptides and by on-line liquid chromatography- mass spectrometry. Incubation of purified peptides with aminopeptidase N resulted in complete hydrolysis of many peptides, while others were only partially hydrolyzed or not hydrolyzed. The tryptic digest of β-casein exhibits a strong bitter taste, which corresponds to the strong hydrophobicity of several peptides in the tryptic digest of β-casein. The degradation of the 'bitter' tryptic digest by aminopeptidase N resulted in a decrease of hydrophobic peptides and a drastic decrease of bitterness of the reaction mixture.