beta-casomorphin 4 from milk fermented by a mutant of Lactobacillus helveticus

Hydrophobic peptides were isolated from milk fermented by a wild-type strain and a mutant strain of Lactobacillus helveticus L89 deficient in X-prolyl-dipeptidyl aminopeptidase (X-PDAP, EC.3.4.14.5) which is specific for peptide bonds on the carboxyl side of proline residues. Peptides were fractionated by RP-HPLC. Chromatogram profiles showed differences in peptide elution time, concentration and number. An opioid peptide, beta-casomorphin 1-4 (60-63), was detected in a peptide extract derived from milk fermented with an X-PDAP-deficient mutant of L. helveticus. The molecular weight of this tetrapeptide was confirmed by mass spectrometry. A tetradecapeptide present in the wild-type culture (beta-cas 106-119) was absent in the mutant strain culture after 24 h of fermentation with the pH controlled at 6. (C) Published by Elsevier Science Ltd