Polyols production during single and mixed substrate fermentations in Debaryomyces hansenii

The kinetics of polyols production by Debaryomyces hansenii was studied both on single substrate and mixed substrate-containing media. From the single substrate experiments, polyols (xylitol and arabitol) and ethanol were produced from pentose sugars while ethanol was produced in signi®cant amounts only from glucose-grown D. hansenii. The maximal xylitol volumetric productivity (Qxylitol), 0.28 g lÿ1 hÿ1 was obtained from D-xylose, whereas the maximal arabitol volumetric productivity (Qarabitol), 0.04 g lÿ1 hÿ1 was observed with arabinose. When D. hansenii was cultivated with mixed substrates, a simultaneous sugar consumption pattern occurred both for glucose/arabinose and xylose/arabinose mixtures. The addition of low amounts of xylose to an arabinose medium led to a fourfold increase in the arabitol volumetric productivity: 0.17 g lÿ1 hÿ1. Conversely, glucose addition had no e€ect on arabitol production. Xylitol was the main polyol produced for all tested cultivation conditions by D. hansenii. An enzymatic study of the ®rst two xylose-catabolic enzymes in glucose and xylose-grown D. hansenii revealed that both enzymes were induced by D-xylose. Glucose caused total inhibition of xylitol dehydrogenase, whereas xylose reductase was only partially repressed