Enhanced Production of Bioxylitol from Corn Cobs by Candida magnoliae

An effective microbial process using Candida magnoliae was developed for xylitol production from xylose obtained from corn cob. The hydrolysate containing approximately 25 g-xylose/L and 3.0 g-glucose/L was obtained from 100 g-corn cobs/L by 1.0-3.0% sulfuric acid with 60 min of hydrolysis time. The corn cob hydrolysate was then treated by charcoal pellets which selectively removed more than 90% of inhibitors without affecting xylose concentration. Using the hydrolysate medium treated with the charcoal pellets, xylitol production using C. magnolia was successfully performed, resulting in a final production of approximately 18 g-xylitol/L from 25 g-xylose/L within 36 h. In total, 15-18 g xylitol could be produced from 100 g of corn cobs. From the batch experiments operated under strictly controlled oxygen supply conditions, it was found that the successful xylitol production occurred at the narrow range of the oxygen transfer rate (OTR) from 0.8 mmol-O-2/L.h to 4.7 mmol-O-2/L.h. A two-step fermentation consisting of the cell growth step using normal hydrolysate medium and the xylitol production step using the concentrated corn cob hydrolysate was effective to avoid serious inhibitory effect and to realize a high concentration of xylitol production (approximately 49 g/L).