Enhancement of Xylitol Yield by Xylitol Dehydrogenase Defective Mutant of Pichia stipitis
2000
Kim Min-Soo | Ryu Yeon-Woo Ajou University, Suwon (Korea Republic)
In order to produce xylitol with high yield, experiments were carried out to develope xylitol dehydrogenase (XDH) defective mutant from Pichia stipitis and to investigate the xylitol fermentation characteristics of mutant strain. After treatment of P. stipitis with EMS, mutant PXM-4 was selected based on the XDH activity and xylitol production capability. Among the tested cosubstrates, galactose was selected as an adequate cosubstrate on xylitol production of mutant PXM-4. With the increase of galactose concentration, xylitol production was decreased because the transport of xylose into cell was inhibited by galactose. The optimal concentration of galactose for the production of xylitol using 20 g/L xylose was 20 g/L. Under this condition, maximum concentration of xylitol and yield were 14.4 g/L and 97%, respectively. In order to prevent the inhibitory effect of xylose transport by galactose, galactose was fed with low concentration and the concentration of xylitol produced was increased up to 25 g/L. In the fermentation of corn cob hydrolyzate by mutant PXM-4, xylose was completely converted to xylitol with a 100% yield in 4 days culture.
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