Amino acid catabolism in cheese-related bacteria: selection and study of the effects of pH, temperature and NaCl by quadratic response surface methodology

Aims: To screen the cystathionine lyase and l-methionine aminotransferase activities of cheese-related bacteria (lactococci, non-starter lactobacilli and smear bacteria) and to determine the individual and interactive effects of temperature, pH and NaCl concentration on selected enzyme activities. Methods and Results: A subcellular fractionation protocol and specific enzyme assays were used, and a quadratic response surface methodology was applied. The majority of the strains, 21 of 33, had detectable cystathionine lyase activity which differed in the specificity. Aminotransferase activity on l-methionine was observed in only three strains. The cystathionine lyase activities of Lactobacillus reuteri DSM20016, Lactococcus lactis subsp. cremoris MG1363, Brevibacterium linens 10 and Corynebacterium ammoniagenes 8 and the l-methionine aminotransferase activity of Lact. reuteri DSM20016 had temperature and pH optima of 30–45°C, and 7·5–8·0, respectively. As shown by the quadratic response surface methodology these enzymes retained activities in the range of temperature, pH and NaCl concentration which characterized the cheeses from which the bacteria originated. Conclusions: The enzyme activities may have a role in flavour development during cheese ripening. Significance and Impact of the Study: The findings of this work contribute to the knowledge about the amino acid catabolic enzymes in order to improve cheese ripening.