Two isolates of ethanol producing yeasts were isolated and identified as Clavispora lusitaniae Gr45 and Saccharomyces cerevisiae B1, then tested for improving its ethanol productivity by changing some nutritional and environmental conditions using YFM medium by static culture technique. Among different sources of nitrogen, ammonium sulfate give slight increase in many of measured factors than other sources with both strains, and it was found that 0.1% of ammonium sulfate is the best concentration. Determine the best carbon source, glucose was the obvious choice as the most appropriate sugar substrate for ethanol production by both strains, and by examining the effect of its concentration, increasing glucose concentration more than 5 % resulted in decreasing the ethanol concentration (gl-1) and ethanol yield (%) by both strains , record the lowest value at 30% glucose. There are significant effect on the growth and ethanol production by Cl. lusitaniae Gr 45 and Sacch. cerevisiae B1 on glucose concentrations ranged from 5 to 30 % and from 5 % to 25 %, respectively. The optimum environmental conditions which gave the highest ethanol productivity were: initial pH values 6.2, incubation temperature 30oC, inoculum size 10% and fermentation period 72h. |
