Xylitol production by a newly isolated Candida sp. from enzymatic hydrolysate of xylan from black liquor in pulp and paper industry

Black liquor, the effluent from pulp and paper industry, is an attractive resource for chemical production especially xylose and/or xylitol due to its high content of hemicellulose. In this study, xylan from black liquor was acid extracted and the highest yield at 13.24±0.22 g.L^-1 of black liquor was obtained. The enzymatic hydrolysis of this xylan was carried out. The optimum ratio of xylanase and β-xylosidase producing from Aureobasidium pullulans CU-102 for the hydrolysis of black liquor xylan was analyzed by RSM according to the central composite design. The canonical analysis revealed a maximum amount of xylose at 0.91 g.g^-1 oven dry of xylan (OD) under the optimal concentration of xylanase at 9 U.g^-1 OD and β-xylosidase at 5 U.g^-1 OD. In an attempt to find a more efficient strain for xylitol production, 20 yeast strains were isolated from natural habitats in Thailand based on the ability to produce xylitol from xylose. One strain of Candida sp. was found to have a high xylose consumption rate (12% w/v) and relatively high xylitol yield (0.70 g.g^-1 xylose) in the batch fermentation. Thus, the effective xylitol production from black liquor- derived xylan using a natural isolate of xylitol-producing yeast in Thailand was achieved.