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 o f Lactococcus lactis subsp. lactis biovar diacetilactis, on its acidif ying power, on diacetyl and acetoin production, and also on the activi ties of the principal enzymes involved in the synthesis of these two c ompounds. 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 unc hanged (5.2 mM). These results are explained by the behaviour of the p rincipal enzymes involved in pyruvate metabolism. The activities of la ctic dehydrogenase and acetolactate synthase varied little for culture temperatures between 18 and 30 degrees C. However, the activity of NA DH oxidase for a culture temperature of 18 degrees C was 3.7 times tha t 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 t emperature.