Influence of cultivation conditions on xylose-to-xylitol bioconversion by a new isolate of Debaryomyces hansenii

About 270 yeast isolates were screened for xylitol production using xylose as the sole carbon source. The best isolate, Debaryomyces hansenii UFV-170, released 5.84 g L−1 xylitol from 10 g L−1 xylose after 24 h, corresponding to a yield of xylitol on consumed substrate (YP/S) of 0.54 g g−1. This strain was cultivated batch-wise at variable starting concentrations of xylose (So) and biomass (Xo) and agitation intensity, in order to improve xylitol production and to evaluate, through simple carbon balances, the influence of these conditions on xylose metabolism. Under the best microaerobic conditions (So = 53 g L−1, Xo = 1.4 g L−1, 200 rpm), xylitol production reached 37.0 g L−1, corresponding to xylitol volumetric productivity of 1.0 g L−1 h−1, specific productivity of 0.22 g g−1 h−1 and YP/S = 0.76 g g−1. Almost 83% of xylose was consumed for xylitol production, the rest being consumed for growth, while respiration was negligible. The new isolate appeared to be a promising alternative for industrial xylitol bioproduction.