Simultaneous saccharification and co-fermentation (SSCF) of AFEXTM pretreated corn stover for ethanol production using commercial enzymes and Saccharomyces cerevisiae 424A(LNH-ST)

Xylose consumption by Saccharomyces cerevisiae 424A(LNH-ST) during simultaneous saccharification and co-fermentation (SSCF) of AFEXTM pretreated switchgrass was inhibited by unhydrolyzed solids. Such inhibitory effects were not found in unhydrolyzed solids from AFEXTM pretreated corn stover (AFEXTM-CS). However, the xylose consumption was still unsatisfactory during 6 h pre-hydrolysis SSCF. By extending the pre-hydrolysis time to 24 h or longer, the xylose consumption was improved significantly. In order to better understand the reasons for such improvement, the hydrolysate slurries after 6 h pre-hydrolysis and 24 h pre-hydrolysis were studied and compared. We found that the glucose concentration after pre-hydrolysis was the critical factor that determined cell viability and hence xylose consumption during SSCF. Low temperature (30 °C) and ethanol inhibition were shown to be the factors limiting hydrolysis rate and hence productivity during SSCF.