Dehydrogenase Activity of Lactic Streptococci

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Abstract
Single-strain cultures of Streptococcus lactis, S. diacetilactis and S. cremoris were incubated in nonfat milk medium at temperatures of 21, 30 and 38 C for 14 and 36 hr. At the end of the incubation period, the quantities of ethanol and acetaldehyde produced by each culture were determined by a gas-liquid chromatographic technique. A significant difference in ethanol production was noted between strains within a species. Higher levels of acetaldehyde were usually retained by organisms which produced lower levels of ethanol. Addition of 100 ppm of acetaldehyde to newly inoculated cultures resulted in marked increases in the level of ethanol at the end of the incubation period. The 3 species were also capable of reducing propanal to n-propanol.