SIMULTANEOUS SACCHARIFICATION AND FERMENTATION OF CELLULOSE TO LACTIC-ACID

Batch experiments were carried out for conversion of cellulose to lact ic acid by simultaneous saccharification and fermentation (SSF) at dif ferent pH values. Saccharification was carried out with a cellulase en zyme preparation from T. reesei and fermentation was by L. bulgaricus. A kinetic model was developed to simulate SSF by incorporating cellul ase enzyme kinetics with growth kinetics of L. bulgaricus. The enzyme kinetics were fitted by a Michaelis-Menten type equation, while the gr owth kinetics of L. bulgaricus were represented by a cybernetic-type m odel incorporating lactate and undissociated lactic acid inhibition te rm. The saccharification of cellulose was rate-limiting above pH 5, wh ile 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 (0.4 5 g/l/h) was maximum at pH 5 and was higher than that of lactic acid p roductivity by SS followed by fermentation The kinetic model was able to predict the performance of SSF quite well. (C) 1997 Elsevier Scienc e Ltd.