DEBITTERING OF TRYPTIC DIGESTS FROM B-CASEIN AND ENZYME MODIFIED CHEESE BY X-PROLYL DIPEPTIDYLPEPTIDASE FROM LACTOBACILLUS CASEI SSP. CASEI. LLG

The proline-rich B-casein was digested in vitro with trypsin, and the oligopeptides produced were then isolated by RP-HPLC and subsequently identified by amino acid analysis and ion mass spectrometry. The peptide fractions from the complete digestion were then treated with purified x-prolyl dipeptidyl peptidase (X-PDP) extracted from Lactobacillus casei ssp. casei LLG. Two bitter peptides (f53-97 and 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. The debittering effect of X-PDP from Lactobacillus casei ssp. casei LLG on enzyme modified cheese (EMC) was also investigated by both subjective and objective methods. The bitterness of cheddar cheese slurries supplemented with Neutrase ® 0.5 L was completely eliminated after treatment with crude enzyme extract from Lactobacillus casei ssp. casei LLG. Two hydrophobic peptides in EMC with Ala-Pro-Phe-Pro-Glu-Val and Phe-Leu-Leu residues were hydrolyzed by crude enzyme extract. The RP-HPLC, and subsequently, ion mass spectrometry analysis have shown that the debittering effect on EMC was due partially to the presence of X-PDP.