Fuel Ethanol Production from Molasses by Indigenous Yeast Isolates

A total of 14 newly isolated, indigenous yeast strains from molasses and grapes, along with the control yeasts D1-D3, were investigated for ethanol production abilities and related parameters like ethanol and sugar tolerance. Strains M1, M5, M9, M12 and M15 were found ethanol resistant up to 12 % ethanol and yeast strains G1, G2, M1, M5, M6, M11, M12 and M15 showed resistance up to 20 % (w/v) glucose concentration. Among new isolates M12 gave maximum alcohol, [9.13 % (v/v)] with pure glucose followed by M15 [8.43 % (v/v)], M1 [7.37 % (v/v)] and M6 [7.26 % (v/v)] in 72 h. Ethanol productivity, after 24 h, was found to be maximum in case of M12, M3, M6, M5 and M15, in reducing order, ranging from 1.08 to 1.37 g(ethanol)/100 g(substrate)/h and ethanol yield after 72 h was maximum in case of M12, M15, M1 and M6 ranging from 38.15 to 47.97 g(ethanol)/100 g(substrate). All the newly isolated strains lag behind control strains D1-D3 in productivity (1.32-1.98 g(ethanol)/100 g(substrate)/h) as well as in yield (47.55-47.92 g(ethanol)/100 g(substrate)). Sugarcane molasses medium having 15-16 % fermentable sugars along with other yeast nutrients, was further tested for alcohol production at 30 degrees C under stationary conditions, by selected yeast strains M1, M5-M7, M12 and M15, added at 0.25 % (w/v) on wet weight basis. Except M1, M5 and M12, all the strains, including control strains, produced considerable amount of alcohol ranging from 8.12 to 9.14 % (v/v) in 48 h but, simultaneous generation of high yeast biomass calls for optimization of fermentation parameters, especially aeration and agitation, for improved ethanol production.