Furfural and glucose can enhance conversion of xylose to xylitol by Candida magnoliae TISTR 5663

- Furfural (300 mg/L) reduced xylose conversion to xylitol in the absence of glucose.
- The suppressory effect of furfural was reversed by adding glucose (3 g/L).
- With added glucose and furfural, xylitol productivity exceeded 1.0 g/L h.
- Glucose and furfural together enhanced xylitol production relative to control.
- A final xylitol concentration of nearly 28 g/L was obtained with furfural present.

Xylitol production from xylose by the yeast Candida magnoliae TISTR 5663 was enhanced by supplementing the fermentation medium with furfural (300 mg/L) and glucose (3 g/L with an initial mass ratio of glucose to xylose of 1:10) together under oxygen limiting conditions. In the presence of furfural and glucose, the final concentration of xylitol was unaffected relative to control cultures but the xylitol yield on xylose increased by about 5%. Supplementation of the culture medium with glucose alone at an initial concentration of 3 g/L, stimulated the volumetric and specific rates of xylose consumption and the rate of xylitol production from xylose. In a culture medium containing 30 g/L xylose, 300 mg/L furfural and 3 g/L glucose, the volumetric production rate of xylitol was 1.04 g/L h and the specific production rate was 0.169 g/g h. In the absence of furfural and glucose, the volumetric production rate of xylitol was ∼35% lower and the specific production rate was nearly 30% lower. In view of these results, xylose-containing lignocellulosic hydrolysates contaminated with furfural can be effectively used for producing xylitol by fermentation so long as the glucose-to-xylose mass ratio in the hydrolysate does not exceed 1:10 and the furfural concentration is ≤300 mg/L.