Screening a yeast of utilizing xylose and studying its fermentation characteristics to ethanol

In order to obtain efficient xylose-fermentation strains, a microbial strain which can convert xylose to ethanol was screened from dejecta of flocks and herds. According to the physiological, biochemical character and 26S ribosomal DNA partial sequences of strain, the strain was identified as Candida tropicals. The strain was cultured for the purpose of ethanol production with the method of increasing xylose concentration in substrates. A xylose utilization rate of 65.2% and a ethanol recovery of 21.9% (vs theory data) were obtained by the cultured strains (Candida tropicals) at the xylose concentration of 7%. The technological parameters in the process of converting xylose to ethanol were optimized. The yield of ethanol of 37.7% and 79.2% (vs theory data) by xylose and glucose were respectively obtained based on the optimal selected fermentation medium, when xylose and glucose were used as mixed carbon source, pH was 5.5, temperature was at 35°C, inoculum solution 10% and were fermented in anaerobic condition for 96 h. At the same time, the xylitol of 30.2 g/L was got. The results show that the strain is a glucose/xylose co-utilizing natural strain and can effectively co-ferment both glucose and xylose simultaneously to ethanol.