Cascade hydrolysis and fermentation of corn stover for production of high titer gluconic and xylonic acids.

Simultaneous saccharification and fermentation (SSF) is an efficient fermentation operation in lignocellulose biorefining. However, SSF may not be applicable when the pH values of hydrolysis and fermentation do not match, or the strong intermediate inhibitors on cellulase activity are generated. This study proposed a cascade hydrolysis and fermentation (CHF) process for cellulosic gluconic acid fermentation to overcome the inhibition of the intermediate glucono-γ-lactone on cellulase activity. The pretreated and detoxified corn stover feedstock was enzymatically hydrolyzed into hydrolysate slurry, then gluconic acid and xylonic acid fermentations were directly conducted by inoculating Gluconobacter oxydans strain without solid/liquid separation. The sugar loss and energy consumption were effectively avoided by moving the solid/liquid separation into the fermentation stage. The experiments and the techno-economic analysis show that the CHF is simple and cost effective fermentation operation when SSF is not applicable.