Optimization of the pretreatment of rice straw hemicellulosic hydrolyzates for microbial production of xylitol

Hemicellulosic hydrolyzate obtained from rice straw was evaluated to determine if it was a suitable fementation medium for the production of xylitol byCandida mogii ATCC 18364. To obtain xylose selectively from rice straw, it is important to establish rapid hydrolysis conditions that yield xylose-rich substrates. The results of hydrolysis experiments indicated that the optimal reaction conditions for the recovery of xylose from rice straw hemicellulose were obtained using a sulfuric acid concentration of 1.5%, a reaction temperature of 130°C, a reaction time of 20 min and a solid to liquid ratio of 1∶10. Because the fermentation of concentrated acid hydrolyzates can be inhibited by compounds present in the raw material or produced during the hydrolysis process, various methods were tested to determine if they could detoxify the hydrolyzates and thus improve xylitol production. The greatest xylitol yield (0.53 g/g) and volumetric productivity (0.38 g/L·h) were obtained when an overlimed hydrolyzate was treated with activated charcoal.