Characterization of an ethanol producing yeast isolate and optimization of ethanol fermentation

Abstract

Bioethanol or biofuel as an alternative to fossil fuels has been expanded in the last few decades in the whole world. Saccharomyces cerevisiae is the choice of organism for ethanol production. Characterization of an ethanol producing ability and to optimization of ethanol production by a laboratory strain of yeast was attempted in the present study. Based on morphological and physiochemical characters, the yeast strain was identified to be Saccharomyces cerevisiae. The strain was moderately thermotolerant and ethanol tolerant as well as osmotolerant. It was resistant to cycloheximide at 0.0015g/100ml concentration but growth was inhibited in presence of Hydrogen peroxide. Ethanol producing capability of the Saccharomyces cerevisiae strain was studied using sugarcane molasses as substrate. The reducing sugar was estimated by DNS method and ethanol was estimated by redox titration. Fermentation was optimized with respect to temperature, reducing sugar concentration and pH. Analysis of fermentation characteristics under different substrate and environmental conditions, it was observed that reducing sugar concentration of 5%-6%, temperature of 30°Cand pH 6.0 were optimum for fermentation with maximum yield of ethanol. Maximum ethanol production was 11 % by free cells using the initial reducing sugar concentration 5.50% at 48 hrs under shaking condition. Immobilized yeast cells showed significant improvement of ethanol production. Under shaking condition, 12% ethanol was produced by immobilized cells using the reducing sugar concentration 6% at 48 hrs. Ethanol production was higher in shaking condition than that in stationery non shaking condition using the same environmental condition. Influence of boron, chromium, copper, magnesium chloride was investigated on ethanol production. Only chromium was found to show stimulatory effect on ethanol production. This selected strain could be potential strain for ethanol production from cane molasses.