Production of diacetyl-acetoin, lactic acid and cell mass by L. plantarum strains ATCC 8014, ATCC 14431, ATCC 4008 and ATCC 8041 were examined in the growth medium of Craig and Snell (J. Bacteriol. 61:283,1951) containing glucose, lactose, citrate or pyruvate as substrates. The yield coefficient, μM lactate produced per mg cell dry weight, averaged 73.4 for glucose-grown cells and 64.9 for lactose-grown cells with no significant inter-strain difference. Strains that produced higher lactic acid concentrations did so because they produced more cell mass. Glucose and lactose reduced diacetyl-acetoin synthesis in all strains except 8041. Diacetyl-acetoin synthesis doubled when strains 14431 and 8014 were grown in medium containing 20 mM citrate, but was not markedly affected in strains 4008 and 8041. Pyruvate stimulated diacetyl-acetoin synthesis in all four strains 10- to 20-fold. Conversion of pyruvate to diacetyl and acetoin was ⩾30% of the theoretical molar yield for strains 8014, 8041 and 14431 grown in the presence of 20 mM pyruvate.

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The influence of pH on the type and concentration of metabolites produced from pyruvate by Lactobacillus plantarum ATCC 8014 was examined in pH-controlled fermentors at pH values of 4.5 to 6.5. Specific growth rates, cell dry weights, and diacetyl concentrations were highest at pH 5.5, with values of 0.78 h-1, 190

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