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

Abstract

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 ( Y P/S) of 0.54 g g −1. This strain was cultivated batch-wise at variable starting concentrations of xylose ( S o) and biomass ( X o) 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 ( S o = 53 g L −1, X o = 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 Y P/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.