Rice straw with altered carbohydrate content: Feedstock for ethanol production

Rice straw is a potential feedstock for cellulosic ethanol, since it is the most abundant agricultural waste in the world and contains starch. The structural configuration of starch makes it easy to hydrolyze, which consequently could increase ethanol yields. In this study, effects of starch in rice straw on ethanol production were investigated. A transgenic rice straw with high vegetative starch content and conventional rice straw were pretreated using dilute acid, hot water, or ammonium hydroxide. To evaluate starch solubility during the pretreatments, pretreated samples were either washed or unwashed prior to enzymatic hydrolysis. Starch or cellulose were solubilized and hydrolyzed during all three pretreatments. As a result, unwashed samples showed up to 60% and 79% higher glucose yield and ethanol yield, respectively, than washed samples. In addition, greater starch content in transgenic rice straw led to increased ethanol yields compared to control rice straw. Unwashed transgenic samples pretreated with dilute acid, hot water, or ammonium hydroxide achieved ethanol yields of 17.5%, 14.9%, and 20.4% g g^-1 biomass, respectively.