Straw Hemicellulosic Hydrolysate Research Articles

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, with 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.

Effect of inoculum level of xylitol production from rice straw hemicellulose hydrolysate by Candida guilliermondii.

The effect of inoculum level on xylitol production by Candida guilliermondii was evaluated in a rice straw hemicellulose hydrolysate. High initial cell density did not show a positive effect in this bioconversion since increasing the initial cell density from 0.67 g L-1 to 2.41 g L-1 decreased both the rate of xylose utilization and xylitol accumulation. The maximum xylitol yield (0.71 g g-1) and volumetric productivity (0.56 g L-1 h-1) were reached with an inoculum level of 0.9 g L-1. These results show that under appropriate inoculum conditions rice straw hemicellulose hydrolysate can be converted into xylitol by the yeast C. guilliermondii with efficiency values as high as 77% of the theoretical maximum.

Bioconversion of rice straw hemicellulose hydrolysate for the production of xylitol

Xylitol production by the yeast Candida guilliermondii was evaluated in a rice straw hemicellulose hydrolysate under different conditions of initial pH and nitrogen source. Xylitol production was significantly affected (p < 0.05) by the nitrogen source, pH, and the interaction between these factors. The best yield and productivity were observed at initial pH of 5.3 in medium containing ammonium sulfate as nitrogen source. Under these conditions, the xylitol yield factor (Y p/s ) was 0.68 g/g and volumetric productivity (Q p ) was 0.51 g/L.h.

Influence of media composition on xylitol fermentation by Candida guiliiermondii using response surface methodology

The bioconversion of xylose to xylitol by the yeast Candida guilliermondii FTI 20037 was evaluated under different nutritional conditions using rice straw hemicellulose hydrolysate. Statistical designs were used to determine the fermentation medium composition. Ammonium sulfate and rice bran have been identified as required nutrients in the hydrolysate since there was a significant interaction between them. In the presence of both nutrients, the xylitol yield factor (Yp/s) and volumetric productivities (Qp) were 0.68 g/g and 0.54 g/L.h, respectively.