Production of Ethanol from Rice Straw using Xylose Fermenting Yeast Isolates

Abstract

With increasing energy demand world-over, there is a need to develop cost effective technologies for the production of bio fuels using renewable sources such as lignocellulosic biomass. However, ethanol productivity is still low and the process is not economically viable. The major limiting factors include the complex and highly crystalline structure of lignocellulosics, low loading rate during saccharification and low amount of hexose and pentose sugars generated during saccharification. Distiller’s ethanologenic yeast Saccharomyces cerevisiae cannot utilize pentoses; with the result about 30% sugar is left unutilized. Studies were conducted in our laboratory to isolate xylose fermenting yeast cultures. A number of promising yeast cultures were isolated, which could produce ethanol both in dextrose and xylose medium. Enzyme hydrolysate of rice straw contained a mixture of glucose, cellobiose and xylose. Various parameters were optimized to maximize ethanol production by xylose fermenting yeast isolates X-1, X-3, and isolate F. Yeast isolate X-3 produced maximum ethanol in rice straw hydrolysate in 72 h of fermentation.