Characterization of two-substrate fermentation processes for xylitol production using recombinant Saccharomyces cerevisiae containing xylose reductase gene

Fermentation characteristics of recombinant Saccharomyces ces cerevisiae co ntaining a xylose reductase gene from Pichia stipitis were investigated in an attempt to convert xylose to xylitol, a natural five-carbon sugar alcoho l used as a sweetener. Xylitol was produced with a maximum yield of 0.95 g g(-1) xylitol xylose consumed in the presence of glucose used as a co-subst rate for co-factor regeneration. Addition of glucose caused inhibition of x ylose transport and accumulation of ethanol. Such problems were solved by a dopting glucose-limited fed-batch fermentations where a high ratio of xylos e to glucose was maintained during the bioconversion phase. The optimized t wo-substrate fed-batch fermentation carried out with S. cerevisiae EH13.15: pY2XR at 30 degrees C resulted in 105.2 g l(-1) xylitol concentration with 1.69 g l(-1) h(-1) productivity. (C) 2000 Elsevier Science Ltd. All rights reserved.