Impact Of By-products In Dilute Acid Hydrolysate Of Corn Stover On Ethanol Fermentation

During the dilute acid pretreatment of corn stover, hemicellulose is hydrolyzed tomonosaccharides, and meanwhile, by-products which may influence ethanol fermentation aregenerated. In this study, five by-products, acetic acid, formic acid, vanillin, furfural and5-hydroxymethylfurfural, were identified by HPLC in the dilute acid hydrolysate of local cornstover. The concentrations of acetic acid and vanillin were higher. Overliming might removesome of the by-products, but no significant influence on the concentrations of carboxylicacids was observed.The work indicated that ethanol production was inhibited by formic acid and acetic acidto a lesser extent than that to the growth of yeast cells, formic acid was shown to be moretoxic than acetic acid, and severe inhibition was observed at the concentration of 1g/L, half ofthe concentration for acetic acid which showed remarkably inhibition effect. Vanillin caused alonger lag-phase for the growth of yeast cells when its concentration was 2g/L, while thelag-phase was not obvious at lower concentrations, and complete inhibition on the ethanolfermentation was observed at the concentration of 6g/L. 5-Hydroxymethylfurfural wasshowed to remarkably inhibit ethanol production, but the biomass yield was a little bit higherthan that of the control experiment. Furfural at 0.5-1.5g/L inhibited the growth of yeast cells,but the ethanol yield was higher. It was found that vanillin, furfural and5-hydroxymethylfurfural could be assimilated and metabolized by S. cerevisiae 6508-127.The synergetic impact of the toxic components on the ethanol fermentation was observed.It was observed that these fermentation inhibitors stimulated the consumption of xylose,improving the ethanol production when their concentrations were low.