EFFECT OF TEMPERATURE ON DIACETYL AND ACETOIN PRODUCTION BY LACTOCOCCUS-LACTIS SUBSP LACTIS BIOVAR DIACETILACTIS CNRZ-483

We have investigated the effect of culture temperature on the growth of Lactococcus lactis subsp. lactis biovar diacetilactis, on its acidifying power, on diacetyl and acetoin production, and also on the activities of the principal enzymes involved in the synthesis of these two compounds. The rates of growth and lactic acid production decreased by a factor of similar to 2 when the temperature decreased from 30 to 18 degrees C. At 18 degrees C, the maximal concentration of diacetyl (0.3 mM) was 1.7 times that at 30 degrees C, while that of acetoin was unchanged (5.2 mM). These results are explained by the behaviour of the principal enzymes involved in pyruvate metabolism. The activities of lactic dehydrogenase and acetolactate synthase varied little for culture temperatures between 18 and 30 degrees C. However, the activity of NADH oxidase for a culture temperature of 18 degrees C was 3.7 times that for 30 degrees C, while that of diacetyl reductase for 30 degrees C was 2.7 times that for 18 degrees C. The net effect of temperature on these two activities was an increase in diacetyl production at lower temperature.