Fermentation of D-xylose and mixtures of D-xylose and glucose by Candida shehatae

andida shehatae, was used to ferment D-xylose to ethanol. A process was developed to ferment mixtures of D-xylose and D-glucose. C. shehatae cells, pre-grown on D-xylose, simultaneously fermented D-xylose and D-glucose. This fermentation method eliminated the lag in D-xylose consumption, increased D-xylose utilization, and reduced fermentation times. Since D-glucose did not severely repress D-xylose metabolism, chemostat studies of sugar mixtures were performed. C. shehatae completely utilized a mixture of D-xylose and D-glucose (50% each) over a dilution rate of 0.15 hr;A two-phase (fully aerobic to anaerobic), single-stage fed-batch fermentation method was developed to increase final ethanol levels and decrease fermentation times. This method increased final ethanol levels to 45 g/L, compared to 30 g/L in batch D-xylose fermentations, and decreased fermentation times by 44 hours. The method also improved mixed sugar fermentations. Ethanol levels were increased to 50 g/L, compared to 25 g/L in batch, mixed sugar fermentations, and simultaneous fermentation of D-glucose and D-xylose occurred.;Unlike most D-xylose fermentation studies reported in the literature, cell viability was measured to depict fermentation performance. Added ethanol of 25 g/L and 50 g/L terminated cell growth, caused a decline in cell viability, and caused a decrease in cell size. The rate of decline in cell viability was proportional to the concentration of ethanol. Also, cell viability was higher at higher fermentation pH, and the ethanol yield was increased and the xylitol yield decreased when the medium pH was increased from 2.5 to 6.0. The availability of oxygen also had a direct effect on cell viability. Following a switch from aerobic to anaerobic conditions, cell growth ceased and cell viability declined. The specific death rate was...