Lactobacillus casei and Lactobacillus plantarum initiate catabolism of methionine by transamination

Aims: To study the ability of Lactobacillus casei and Lact. plantarum strai ns to convert methonine to cheese flavour compounds. Methods and Results: Strains were assayed for methionine aminotransferase a nd lyase activities, and amino acid decarboxylase activity. About 25% of th e strains assayed showed methionine aminotransferase activity. The presence of glucose in the reaction mixture increased conversion of methionine to 4 -methylthio-2-ketobutanoate (KMBA) and 4-methylthio-2-hydroxybutanoate (HMB A) in all strains. The methionine aminotransferase activity in Lact. planta rum and Lact. casei showed variable specificity for the amino group accepte rs glyoxylate, ketoglutarate, oxaloacetate and pyruvate. None of the strain s showed methionine lyase or glutamate and methionine decarboxylase activit ies. Conclusions: The presence of amino acid converting enzymes in lactobacilli is strain specific. Significance and Impact of the Study: The findings of this work suggest tha t lactobacilli can be used as adjuncts for flavour formation in cheese manu facture.