Production of detoxified sorghum straw hydrolysates for fermentative purposes

Abstract

Sorghum straw can be hydrolysed to obtain monosaccharide solutions, mainly containing xylose. The usual biotechnological application of xylose is its bioconversion to xylitol. The global process from straw to xylitol can give an added value to the sorghum straw. The process has the following sequential steps: reduction of size, acid hydrolysis, neutralization, detoxification, fermentation, recovery and purification. This work deals with the optimization of the detoxification process of sorghum straw hydrolysates with activated charcoal. The variables evaluated were pH (1-5), contact time (20-60 min) and activated charcoal charge (20-33 g kg −1 ). Mathematical models were obtained through a factorial experimental design. The models suggest that optimal conditions for detoxification are pH 1, contact time of 29 min and a charcoal charge of 33 g kg −1 . These conditions allowed hydrolysates with 54.2 g xylose L −1 , 13.5 g glucose L −1 , 12 g arabinose L −1 , 0.2 g furfural L −1 and 0.0 g acetic acid L −1 to be obtained. The results suggest that performing the detoxification step before the neutralization step gave the best outcome. Fermentations by Candida parapsilosis NRRL Y-2315 were performed and it was confirmed that the treated hydrolysate is suitable for xylitol production, yielding up to 17 g L −1 of this polyol.