INCREASE OF XYLITOL PRODUCTION-RATE BY CONTROLLING REDOX POTENTIAL INCANDIDA-PARAPSILOSIS

The effect of redox potential on xylitol production by Candida parapsi losis was investigated. The redox potential was found to be useful for monitoring the dissolved oxygen (DO) level in culture media, especial ly when the DO level was low. An increase in the agitation speed in a 5 L fermenter resulted in an increased culture redox potential as well as enhanced cell growth. Production of xylitol was maximized at a red ox potential of 100 mV. As the initial cell concentration increased fr om 8 g/L to 30 g/L, the volumetric productivity of xylitol increased f rom 1.38 g/L.h to 4.62 g/L.h. A two-stage xylitol production strategy was devised, with stage 1 involving rapid production of cells under we ll-aerated conditions, and stage 2 involving cultivation with reduced aeration such that the culture redox potential was 100 mV. Using this technique, a final xylitol concentration of 180 g/L was obtained from a culture medium totally containing 254.5 g/L xylose in a 3,000 L pilo t scale fermenter after 77 h fermentation. The volumetric productivity of xylitol during the fermentation was 2.34 g/L.h. (C) 1998 John Wile y & Sons, Inc.