Cellulase-added cassava ethanol process boosts ethanol titer and reduces glycerol production

Abstract

Cassava is a widely used raw material for bioethanol production. In addition to starch, there is about 4–5 % (w/w) cellulose in cassava tuber, which is not utilized in current cassava ethanol process. Here, a bolt-on cellulase-added ethanol process was developed to realize the in situ conversion of cellulose in cassava tuber. As a result, the final ethanol titer increased from 127.94 g/L to 131.84 g/L, with 57.17 % cellulose and some recalcitrant starch additionally hydrolyzed. Moreover, the titer of glycerol, a main by-product of ethanol fermentation, decreased from 10.78 g/L to 9.95 g/L and the ratio of ethanol/glycerol increased from 11.87 to 13.25. To investigate the reason for the decreased glycerol production in this cellulase-added cassava ethanol process, the effect of medium viscosity on glycerol production was extensively investigated, which indicated, for the first time, that the reduction of glycerol biosynthesis was due to decreased viscosity aroused by the cellulase addition. Overall, this cellulase-added cassava ethanol process not only realized the conversion of cassava cellulose and higher ethanol titer, but also reduced the production of glycerol.