3.3. Evaluation the cofermentation process to produce ethanol
When the hydrolysate mixture contain 41.2 g/L glucose and 21.4 g/L xylose was fermented by P. stipitis, it produced 26.8 g/L ethanol at 54 h with a yield of 0.47 g/g, which is corresponding to a 92% of conversion. Both glucose and xylose in hydrolysate mixture were completely utilized to produce ethanol. This result has proved that the hydrolysate mixture was more suitable for ethanol fermentation by P.stipitis. Particularly, none of extra nutritional supplementation was preformed during hydrolysate fermentation. It means that the nutrient in the hydrolysate may be provided through the acid hydrolysis in pretreatment and was sufficient to support the need in fermentation by P. stipitis. In comparison with synthetic medium fermentation, the fermentation of rice straw hydrolysate by P. stipitis usually gave a higher ethanol yield with a relatively lesser rate in ethanol production and sugar consumption. This indicated that the hydrolysate overall gave a positive effect on fermentation by P. stipitis.
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