An environmentally friendly and efficient method for xylitol bioconversion with high-temperature-steaming corncob hydrolysate by adapted Candida tropicalis

This study reports a new process to prepare corncob hemicellulose hydrolysate through high temperature steaming (HIS) for xylitol bioconversion by adapted Candida tropicalis. Under the optimal corncob hydrolysis conditions of 160 degrees C and 120 min, the maximum xylose yield was more than 20%. The optimal fermentative parameters from the HTS hydrolysate is as follows: initial xylose concentration of 140 gl(-1), initial pH 6.0, initial cell concentration of 1.2 gl(-1) and 30 degrees C using a two-step dissolved oxygen process with a rotary shaker speed at 200 rpm for the first 24-26 h and then at 150 rpm until 48 h of fermentation. The highest xylitol yield (71.4%) and volumetric productivity (2.12 gl(-1) h(-1)) were obtained from the HTS hydrolysate, which were 158% and 149%, respectively, higher than the results obtained from the acid hydrolysate. Additionally, the amount of inhibitors produced by the HIS hydrolysis and the burden of ion exchange purification after fermentation with HIS hydrolysate were much lower compared with the acid hydrolysate. Therefore, fermentation with corncob HIS hydrolysate is an environmentally friendly and efficient method to produce xylitol, demonstrating a wide potential application in xylitol bioconversion. (C) 2011 Elsevier Ltd. All rights reserved.