Fermentation of xylose and rice straw hydrolysate to ethanol by Candida shehatae NCL-3501

Candida shehatae NCL-3501 utilized glucose and xylose efficiently in batch cultures. The specific rate of ethanol production was higher with mixtures of glucose and xylose (0.64-0.83 g g(-1) cells d(-1)) compared to that with individual sugars (0.38-0.58 g g(-1) cells d(-1)). Although the optimum temperature for growth was 30 degrees C, this strain grew and produced appreciable levels of ethanol at 45 degrees C. A stable ethanol yield (0.40-0.43 g g(-1) substrate utilized) was obtained between 10 g L(-1) and 80 g L(-1) of initial xylose concentration. Conversion efficiency was further improved by immobilization of the cells in calcium alginate beads. Free or immobilized cells of C. shehatae NCL-3501 efficiently utilized sugars present in rice straw hemicellulose hydrolysate, prepared by two different methods, within 48 h. Ethanol yields of 0.45 g g(-1) and 0.5 g g(-1) from autohydrolysate, and 0.37 g g(-1) from acid hydrolysate were produced by free and immobilized cells, respectively.