Polyols production during single and mixed substrate fermentations in Debaryomyces hansenii

The kinetics of polyols production by Debaryomyces hansenii was studied bot h on single substrate and mixed substrate-containing media. From the single substrate experiments, polyols (xylitol and arabitol) and ethanol were pro duced from pentose sugars while ethanol was produced in significant amounts only from glucose-grown D. hansenii. The maximal xylitol volumetric produc tivity (Q(xylitol)), 0.28 g l(-1) h(-1) was obtained from D-xylose, whereas the maximal arabitol volumetric productivity (Q(arabitol)), 0.04 g l(-1) h (-1) was observed with arabinose, When D. hansenii was cultivated with mixe d substrates, a simultaneous sugar consumption pattern occurred both for gl ucose/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 l(-1) h(-1). Conversely, glucose addition had no effect on arabitol production. Xylitol was the main polyol produced for all tested cultivation conditions by D. hansenii. An enzymatic study of the first two xylose-catabolic enzymes in glucose and xylose-grown D. hans enii revealed that both enzymes were induced by D-xylose. Glucose caused to tal inhibition of xylitol dehydrogenase, whereas xylose reductase was only partially repressed. (C) 1999 Elsevier Science Ltd. All rights reserved.