Model compound studies: influence of aeration and hemicellulosic sugars on xylitol production by Candida tropicalis.

Abstract

The influence of other hemicellulosic sugars (arabinose, galactose, mannose, and glucose), oxygen limitation, and initial xylose concentration on the fermentation of xylose to xylitol was investigated using experimental design methodology. Oxygen limitation and initial xylose concentration had strong influences on xylitol production by Candida tropicalis ATCC 96745. Under semiaerobic conditions, xylitol yield was highest (0.62 g/g), whereas under aerobic conditions volumetric productivity was highest (0.90 g/[L x h]). In the presence of glucose, xylose utilization was strongly repressed and sequential sugar utilization was observed. Ethanol produced from the glucose caused a 50% reduction in xylitol yield when the ethanol concentration exceeded 30 g/L. When complex synthetic hemicellulosic sugars were fermented, glucose was initially consumed followed by a simultaneous uptake of the other sugars. The highest xylitol yield (0.84 g/g) and volumetric productivity (0.49 g/[L x h]) were obtained for substrates containing high arabinose and low glucose and mannose contents.