Ethanol Production by Xylose Fermenting Yeast Cultures Using a Mixture of Dextrose and Xylose

Abstract

Ever-increasing demand for motor fuels has led to the search for alternate sources of energy world over. Lignocellulosic biomass is the most abundant, renewable source which is being replenished through photosynthesis. In many developed countries, a number of “Biorefineries” have been set up to produce ethanol from plant biomass. However, ethanol productivities are still low. Moreover, distiller’s ethanologenic yeast Saccharomyces cerevisiae cannot utilize pentoses, with the result that about 30% sugar is left unutilized. Although recombinant technology is being used for genetic improvement of yeasts for formation of a mixture of sugar, in genetically engineered yeast strains, xylose fermentation is slow as compared to dextrose fermentation. Studies are being conducted in laboratories to isolate xylose fermenting yeast culture from natural sources. A number of promising yeast cultures were isolated, which could produce ethanol both in dextrose and xylose medium. A number of combinations of mixture of dextrose and xylose were used as substrate to produce ethanol by xylose fermenting yeast isolate. Yeast isolate F produces maximum ethanol in a mixture of dextrose and xylose in 72 h of fermentation.