Production of xylitol by Saccharomyces cerevisiae using waste xylose mother liquor and corncob residues

Exorbitant outputs of waste xylose mother liquor (WXML) and corncob residue from commercial-scale production of xylitol create environmental problems. To reduce the wastes, a Saccharomyces cerevisiae strain tolerant to WXML was conferred with abilities to express the genes of xylose reductase, a xylose-specific transporter and enzymes of the pentose phosphate pathway. This strain showed a high capacity to produce xylitol from xylose in WXML with glucose as a co-substrate. Additionally, a simultaneous saccharification and fermentation (SSF) process was designed to use corncob residues and cellulase instead of directly adding glucose as a co-substrate. Xylitol titer and the productivity were, respectively, 91.0 g l-1 and 1.26 ± 0.01 g l-1  h-1 using 20% WXML, 55 g DCW l-1 delignified corncob residues and 11.8 FPU gcellulose-1 cellulase at 35° during fermentation. This work demonstrates the promising strategy of SSF to exploit waste products to xylitol fermentation process.