CONTINUOUS ENZYMATIC PRODUCTION OF XYLITOL WITH SIMULTANEOUS COENZYMEREGENERATION IN A CHARGED MEMBRANE REACTOR

We have developed a new process for the production of xylitol from D-x ylose by enzyme technology. An NADH-dependent xylose reductase (XR) fr om Candida tenuis catalyzes the reduction of xylose, which is coupled to enzymatic oxidations of D-glucose or D-xylose by glucose dehydrogen ase from Bacillus cereus to make achievable an up to 10,000-fold regen eration of NADH per cycle of discontinuous conversion. Using a simple kinetic model as a tool for process optimization, suitable conditions with regard to performance and stability of the multicomponent reactio n system were established, and 300 g/L of substrate could be converted in yields above 96% in one single batch reaction. Due to selective an d over 98% complete retention of the native coenzyme by negatively cha rged nanofiltration membranes used in a continuously operated enzyme r eactor, a specific productivity of 80 g xylitol per liter, day, and ki lounit of XR was maintained over the 150-h reaction time with only a s ingle dosage of NADH. (C) 1996 John Wiley & Sons, Inc.