Selection and identification of thermotolerant ethanol producing yeast strains

Abstract

The supply of non-renewable energy sources from fossil fuel is depleting day by day and it has become one of the greatest challenges to find the alternative sources. Bioethanol as an alternative biofuels has stimulated the worldwide interest. The use of bioethanol as a fuel will minimize the amounts of fossil-derived carbon dioxide (CO2) to the Earth's atmosphere. Yeast is the most acceptable of all organisms for ethanol production because of its diverse substrate specificity and ease of production of ethanol. Temperature is one of the most important environmental factors affecting microbial activity and production cost. The main objective of this research work was to isolation, characterization and process optimization of ethanol producing thermotolerant yeast strains. In total 5 yeast isolates have been characterized on the basis of morphological and physico-chemical characters. Most of the strains were thermotolerant, ethanol tolerant, pH tolerant, as well as osmotolerant. All the strains were formed psedomycelium under stress condition. They were resistant to chloramphenicol but growth was inhibited in the presence of 1% acetic Acid. The strains C and E showed good Invertase activity and all the strains were capable of fermenting glucose, fructose, sucrose, maltose and amylose among 10 carbohydrates. Ethanol producing capability of the strains was studied using sugarcane molasses as substrate. Productivity was observed at different incubation temperature, pH and reducing sugar concentration. After fermentation at different condition, at temperature 35°C, pH 6.0, reducing sugar concentration 6.0% and shaking condition (115 rpm) found to be optimum for ethanol production by both C and E strains. The C and E strains produced maximum 11.25 % and 13.20% respectively at 48 hours under optimum condition. Pilot scale (5 L) production by both strains was found 9.55% and 11.50% under optimum condition. These strains could be potential for ethanol production from cane molasses in commercial scale.