Effect of redox potential on stationary-phase xylitol fermentations using Candida tropicalis.
Redox potential was used to develop a stationary-phase fermentation of Candida tropicalis that resulted in non-growth conditions with a limited decline in cell viability, a xylitol yield of 0.87 g g(-1) (95% of the theoretical value), and a high maximum specific production rate (0.67 g g(-1) h(-1)). A redox potential of -100 mV was found to be optimum for xylitol production over the range 0-150 mV [correction]. A shift from ethanol to xylitol production occurred when the redox potential was reduced from 50 mV to 100 mV as cumulative ethanol (Y(ethanol)) decreased from 0.34 g g(-1) to 0.025 g g(-1) and Y(xylitol) increased from 0.15 g g(-1) to 0.87 g g(-1) (alpha=0.05). Reducing the redox potential to 150 mV did not improve the fermentation. Instead, the xylitol yield and productivity decreased to 0.63 g g(-1) and 0.58 g g(-1) h(-1) respectively and cell viability declined. The viable, stationary-phase fermentation could be used to develop a continuous fermentation process, significantly increasing volumetric productivity and reducing downstream separation costs, potentially by the use of a membrane cell-recycle reactor.
Kastner
J R
JR
Department of Biological and Agricultural Engineering, Driftmier Engineering Center, The University of Georgia, GA 30602, Athens, USA. jkastner@engr.uga.edu
Eiteman
M A
MA
Lee
S A
SA
D019149:Bioreactors; D041022:Candida tropicalis / Q000254:growth & development / Q000378:metabolism*; D005285:Fermentation; D010084:Oxidation-Reduction; D014993:Xylitol / Q000378:metabolism*; D014994:Xylose / Q000378:metabolism*
D014994:Xylose; D014993:Xylitol