Enhanced Xylitol Production from Statistically Optimized Fermentation of Cotton Stalk Hydrolysate by Immobilized Candida tropicalis

Q. Zhang, Y. Li, L. Xia, Z. Liu and Y. Pu

Abstract
Dilute-acid hydrolysate of cotton stalk was prepared for the xylitol production, immobilized Candida tropicalis was used as the fermentation inoculum. The fermentative conditions were selected by single factor experiments, three factors were chosen as main conditions from five parameters to design the response surface test using a central composite design. Regression equation and analysis of variance were proposed with regard to the effects of reducing sugar concentration, initial pH value and inoculation ratio of yeast. The results showed that the correlation between actual and predicted values were significantly predicted by the model, the optimized fermentative conditions were determined as follows: reducing sugar concentration of hydrolysate was 94 g L–1, inoculation ratio of the immobilized Candida tropicalis was 5.7 % (w/v), initial pH value was 5.1. Under the optimal conditions, the experimental concentration of xylitol was 13.02 ± 1.10 g L–1, which was close to the theoretical predicted value, and shows that the model is feasible.

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Keywords
xylitol, response surface methodology, cotton stalk hydrolysate, immobilized Candida tropicalis, optimisation