KINETIC-MODEL OF GROWTH AND LACTIC-ACID PRODUCTION FROM LACTOSE BY LACTOBACILLUS-BULGARICUS

Batch and continuous fermentation kinetics of Lactobacillus bulgaricus were examined in detail. The batch kinetic model includes the effect of pH, lactate and substrate. The effect of pH on the enzyme beta-gala ctosidase is reflected in the value of mu(max), the Monod's growth con stant. Empirical expressions to estimate model parameters based on pH were established. These were further used to estimate the cell mass an d lactic acid concentration for the fermentation proceeded with no pH control. At high pH lactic acid was mostly formed by growth associated mechanisms and at low pH it was due to the cell maintenance. The rela tionship between ATP concentration and cell mass in a batch fermentati on could be approximated by a Leudeking-Piret like relationship. The c ontinuous fermentation was studied with varying pH and initial substra te conditions. A maximum productivity of 6.2 g/litre per hour was obta ined at pH 5.6 for the CSTR system, which was three times the producti vity obtained for a batch system at the same pH. The CSTR system had a high productivity over a very small range of retention times. Three s tages were found to be sufficient to utilize completely the lactose, b ut at the cost of decreasing the productivity to 4.8 g/litre per hour.