Simultaneous saccharification and fermentation of cellulose to lactic acid

Batch experiments were carried out for conversion of cellulose to lactic acid by simultaneous saccharification and fermentation (SSF) at different pH values. Saccharification was carried out with a cellulase enzyme preparation from T. reesei and fermentation was by L. bulgaricus. A kinetic model was developed to simulate SSF by incorporating cellulase enzyme kinetics with growth kinetics of L. bulgaricus. The enzyme kinetics were fitted by a Michaelis-Menten type equation, while the growth kinetics of L. bulgaricus were represented by a cybernetic-type model incorporating lactate and undissociated lactic acid inhibition term. The saccharification of cellulose was rate-limiting above pH 5, while lactic acid fermentation was rate limiting below pH 5. The glucose concentration in the fermentation broth was lower than that in simple saccharification (SS) at all pH values. Lactic acid productivity (0.45 g/l/h) was maximum at pH 5 and was higher than that of lactic acid productivity by SS followed by fermentation. The kinetic model was able to predict the performance of SSF quite well.