Characterization of yeasts for ethanolic fermentation of molasses with high sugar concentrations.

Abstract

Five yeast isolates obtained from molassess (1,3A and 3B) or jaggery (Gl and G2) and three Saccharomyces cerevisiae strains, S. cerevisiae MTCC 172, S. cerevisiae MTCC 174, and S. cerevisiae HAU-11 were examined for theirethanol production ability in molasses with high sugar concentrations and other desirable fermentation characteristics. Four strains, isolate 3B, S. cerevisiae HAU-11, S. cerevisiae MTCC 174 and S. cerevisiae MTCC 172, gave high efficiency of ethanol production, i.e., 71.0, 67.0, 66.7, and 61.5 per cent, respectively, in concentrated molasses (40 per cent sugars). Viability of the yeast strains was quite high in diluted molasses but decreased drastically with increase in concentration of sugars in the medium and also by prolonged incubation. The four superior strains (3B, S. cerevisiae MTCC 172, S. cerevisiae MTCC 174, and S. cerevisiae HAU-11) showed viability between 57 to 71 per cent in molasses with sugar concentration of 35- 40 per cent. Although isolates Gl and 3A produced maximum biomass but they were poor ethanol producers, while the four strains (3B, S. cerevisiae MTCC 172, S. cerevisiae MTCC 174, and S. cerevisiae HAU-11) produced less biomass but yielded higher ethanol content. Further, these strains adapted faster in fermentation media with high sugar concentrations as compared to other yeast cultures. These 4 strains were found to be highly ethanol tolerant (16 per cent, v/v), while rest of the strains could not grow in the presence of ethanol content of more than 10 per cent. None of the yeast strains studied showed high flocculence, it varied between 1 to 4.