Statistical optimization of xylitol production from corncob hemicellulose hydrolysate by Candida tropicalis HDY-02.

The statistical experimental designs were adopted to optimize the culture medium in xylitol production by Candida tropicalis HDY-02 with corncob hemicellulose hydrolysate as substrate. In the first step, Plackett-Burman design was used for screening the important variables. KH(2)PO(4), yeast extract, (NH(4))(2)SO(4) and MgSO(4)·7H(2)O were found to significantly affect xylitol yield. In the second step, central composite design (CCD) was used to determine the optimum level of each of the significant variables. A second-order polynomial was determined by the multiple regression analysis of the experimental data. The interactive effects of yeast extract and MgSO(4)·7H(2)O on xylitol yield of C. tropicalis HDY-02 were determined to be significant. The validation experimental was consistent with the prediction model. The optimum combinations for xylitol yield were 5 gl(-1) (NH(4))(2)SO(4), 1.3 gl(-1) KH(2)PO(4), 4.6 gl(-1) yeast extract and 0.6 gl(-1) MgSO(4)·7H(2)O. Under these optimal conditions, the continuous fed-batch experiments could produce xylitol of 58 gl(-1) with a yield of 0.73 g g(-1) xylose.