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 a ctivities 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 enzy me assays were used, and a quadratic response surface methodology was appli ed. The majority of the strains, 21 of 33, had detectable cystathionine lya se activity which differed in the specificity. Aminotransferase activity on L-methionine was observed in only three strains. The cystathionine lyase a ctivities of Lactobacillus reuteri DSM20016, Lactococcus lactis subsp. crem oris MG1363, Brevibacterium linens 10 and Corynebacterium ammoniagenes 8 an d the L-methionine aminotransferase activity, of Lact. reuteri DSM20016 had temperature and pH optima of 30-45 degreesC, 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 ch aracterized the cheeses from which the bacteria originated. Conclusions: The enzyme activities may have a role in flavour development d uring 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.