Abstract: Fermentabilities of four strains, Candida shehatae NLP21, Pichia stipitis NLP22, NLP23 and NLP31 on 30 g/L xylose or mixture sugars (glucose 15 g/L and xylose 15 g/L) of the fermentation medium, and on the fermentation medium of the concentrations of the nitrogen sources reduced to 1/2 and 1/10 of its original were studied. The results showed that the mass concentrations of ethanol produced by NLP23 and NLP31 were the highest, (11.14±0.13) and (11.15±0.08) g/L respectively, when they were fermented on the fermentation medium with 30 g/L xylose. When four strains fermented on the fermentation medium with 15 g/L glucose and 15 g/L xylose, the mass concentration of ethanol produced by NLP31 was the highest, (10.91±0.12) g/L. The fermentability of NLP23 was the same as NLP31 when the concentration of nitrogen sources was reduced to 1/2 of its original, but NLP31 produced more xylitol. The fermentabilities decreased step by step with the fermentation batch increasing when the mass concentration of nitrogen sources was reduced to 1/10 of its original, because the mass concentration of the nitrogen source was too low.

Key words: xylose, glucose, fermentation, fuel ethanol