Microbial xylitol production from culm of Sasa kurilensis using the yeast Candida magnoliae

A sugar solution containing 31 g l-1 xylose was prepared from the culm of Sasa kurilensis by hydrolysis with 2% sulfuric acid with a liquor-to-solid ratio of 6 (g g-1) at 121°C for 1 h. During acid hydrolysis, also some byproducts were generated, such as acetic acid, furfural, 5-hydroxymethylfurfral, and low molecular weight phenolics, which inhibit bioconversion of xylose to xylitol. Except for acetic acid, these inhibitors were successfully removed from the hydrolysate by contacting with a steam-activated charcoal (15 g l-1 dose) for 24 h. Bioconversion of the detoxified hydrolysate to xylitol by the yeast, Candida magnoliae, was investigated under various microaerobic conditions. The oxygen transfer rate (OTR) varied from 8.4 to 27.6 mmol-O2 l-1 h-1. The maximum xylitol yield (0.62 g-xylitol g-xylose-1) was attained at the OTR of 1.2 mmol-O2 l-1 h-1. An additional increase in the OTR brought about cell growth, which consumed xylose. A proper control of the oxygen supply is necessary to produce efficiently xylitol from the culm hydrolysate.