APTITUDE OF CHEESE BACTERIA FOR VOLATILE S-METHYL THIOESTER SYNTHESIS.2. COMPARISON OF CORYNEFORM BACTERIA, MICROCOCCACEAE AND SOME LACTIC-ACID BACTERIA STARTERS

Various strains of coryneform bacteria, Micrococcaceae and commercial starters of Lactococcus lactis and Leuconostoc were compared for their aptitude to form S-methyl thioesters. Resting cells were incubated wi th methanethiol alone at pH 7 and in conjunction with a mixture of str aight, branched and hydroxy short-chain fatty acids up to C-6 at pH 7 and 5. Results showed that all the strains synthesized at least S-meth yl thioacetate, with strains that were low and high producers in each group. This is the only thioester formed in small amount by Leuconosto c. Brevibacterium linens (six strains) and Micrococcaceae (five strain s) were able to form branched-chain thioesters especially from their i ntracellular fatty acids at neutral pH, and straight-chain thioesters mostly from exogenous fatty acids at acid pH. Coryneform bacteria othe r than B. linens (four strains) and L. lactis (four starters) synthesi zed thioesters up to S-methyl thiobutyrate from endogenous or exogenou s fatty acids but not branched-chain ones, except for one starter whic h formed a very little thioisovalerate. Some particular effects of pH and added fatty acids revealed differences between species or strains in their specific enzymatic systems.