The ability of Lactobacillus casei subsp. pseudoplantarum to produce acetoin and diacetyl (AD) was evaluated in succinate buffer (initial pH 4.4) containing sodium pyruvate, at 30°C. Cells grown in MRS broth containing pyruvate produced AD more rapidly than did an equal number of cells either grown in broth without pyruvate or even stored, after harvesting during logarithmic growth, in MRS broth in the presence of pyruvate for 120 minutes. One or more of the enzymes catalyzing formation of AD appears to be formed originally during growth in the presence of pyruvate. The rate of AD production by pyruvate-grown cells was exponential, being 0.08 μmoles mg dry wt−1 ml−1 min−1 during the first 30 min of the reaction. Storage of pyruvate grown cells at 7°C for 6 h in 0.3 mmol/L KH2PO4 buffer, pH 7.0 resulted in 77% loss of activity. Inclusion of 0.5 ml of MRS broth in the assay mixture led to a considerable increase in AD production by both cells grown in the absence and presence of pyruvate. Lactose slightly stimulated AD production in cells grown on lactose, whereas glucose had practically no effect on glucose-grown cells. Acetate and acetaldehyde reduced AD production. The effect varied with the compound used and strain studied. Of 7 concentrations of cetylpyridinium chloride tested for their effect on AD production, the least and most inhibitory concentration were 1 and 10 μg ml−1 of assay mixture.

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