Continuous fermentation of L-lactic acid by the mold Rhizopus oryzae

The continuous fermentation of L-lactic acid by Rhizopus oryzae AHU6537 was attempted with dilution rate of 0.02 h(-1) and feed glucose rate of 2.0 kg/(m(3) (.) h) in an airlift bioreactor. As a result, stable operation could be carried out over a long time without immobilizing cells. When the optimum amount of yeast extract in batch culture was added to the starting medium, the cells formed spherical pellets, and the fermentation rate was improved. Further, to investigate the influence of glucose and lactic acid concentration, when the dilution rate and glucose concentration in feed medium were controlled in continuous fermentation, it was found that R. oryzea was strongly inhibited by the lactic acid produced. When the effect of lactic acid inhibition was analyzed according to a Michaelis-Menten mechanism with uncompetitive inhibition and the fermentation rate at the steady state was simulated, the calculated lines agreed well with experimental values.