Variation in aminopeptidase and aminotransferase activities of six cheese related Lactobacillus helveticus strains

Aminopeptidase and aminotransferase activities of six Lactobacillus helveticus strains grown in milk and in a peptide rich glucose based medium de Man Rogosa Sharpe (MRS) were examined. The strains had similar specificity for ten aminopeptidase substrates but some significant (P < 0.05) strain differences in activity levels. Higher aminopeptidase activity was found after growth in milk against almost all substrates. Aminotransferase activity was detected against 13 amino acids. All strains had highest activity against aromatic amino acids followed by branched-chain amino acids. Five strains had activity against Met. Activity against Asn, Asp, Lys, Gln, His and Pro was detected among four strains but only after growth in MRS. Significantly (P < 0.05) higher activity against aromatic amino acids was found after growth in MRS. No obvious differences were found in activities against branched-chain amino acids and Met because of growth medium. These results may offer potential to choose strains that accelerate amino acid release in cheese with or without introducing new aroma notes during ripening.