Simultaneous saccharification and fermentation of cellulose: effect of β- d-glucosidase activity and ethanol inhibition of cellulases

Compared with saccharification in the absence of yeast, simultaneous saccharification and fermentation (SSF) using Trichoderma cellulases and Saccharomyces cerevisiae enhanced cellulose hydrolysis rates by 13–30%. The optimum temperature for SSF was 35°C. The requirement for β- d-glucosidase (β- d-glucoside glucohydrolase, EC 3.2.1.21) in SSF was lower than for saccharification: maximal ethanol production was attained when the ratio of the activity of β- d-glucosidase to filter paper activity was ∼1.0. Ethanol inhibited cellulases uncompetitively, with an inhibition constant of 30.5 gl −1, but its effect was less severe than that of an equivalent concentration of cellobiose or glucose. No irreversible denaturation of cellulases [1,4-(1,3;1,4)-β- d-glucan 4-glucanohydrolase, EC 3.2.1.4] by ethanol was observed .