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

Abstract

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°C, this strain grew and produced appreciable levels of ethanol at 45°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 ofC. 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.