Diversity of amino acid converting enzymes in wild lactic acid bacteria

A total of 156 lactic acid bacteria isolates belonging to the genera Lactococcus, Lactobacillus and Leuconostoc were analysed for the amino acid converting enzymes aminotransferases, glutamate dehydrogenase, and α-ketoisovalerate decarboxylase. All isolates showed aminotransferase activity towards phenylalanine (substrate for the aromatic aminotransferase AraT) and isoleucine (substrate for the branched-chain aminotransferase BcaT). Although there was a high variability inter- and intra-species, the lactococcal strains showed the highest values for both aminotransferase activities. Moreover, α-ketoisovalerate decarboxylase (Kivd) activity was only found in lactococcal isolates, although at low relative numbers (16%). On the other hand, glutamate dehydrogenase (Gdh) activity values were highest in facultative heterofermentative lactobacilli (FHL) and the activity was found at high relative numbers (50%) in leuconostocs. Results showed a high variability in amino acid convertase activities within the wild LAB isolates assayed, therefore the utilisation in the dairy industry of new strains with high flavour-forming abilities could be a powerful tool to enhance cheese aroma development.