debittering of tryptic digests from β-casein and enzyme modified cheese by x-prolyl dipeptidylpeptidase from lactobacillus casei ssp. casei. llg

the proline-rich β-casein was digested in vitro with trypsin, and the oligopeptides producedwere then isolated by rp-hplc and subsequently identified by amino acid analysis and ion massspectrometry. the peptide fractions from the complete digestion were then treated with purified x-prolyldipeptidyl peptidase (x-pdp) extracted from lactobacillus casei ssp. casei llg. two bitter peptides (f53-97and f203-209) containing x-pro-y-pro in their amino acid residues were completely hydrolyzed by x-pdp,while several peptides with a high degree of hydrophobicity were also decreased in a peak area. thedebittering effect of x-pdp from lactobacillus casei ssp. casei llg on enzyme modified cheese (emc) wasalso investigated by both subjective and objective methods. the bitterness of cheddar cheese slurriessupplemented with neutrase® 0.5 l was completely eliminated after treatment with crude enzyme extractfrom lactobacillus casei ssp. casei llg. two hydrophobic peptides in emc with ala-pro-phe-pro-glu-valand phe-leu-leu residues were hydrolyzed by crude enzyme extract. the rp-hplc, and subsequently, ionmass spectrometry analysis have shown that the debittering effect on emc was due partially to the presenceof x-pdp.