Enhanced enzymatic conversion with freeze pretreatment of rice straw

Production of bioethanol by the conversion of lignocellulosic waste has attracted much interest in recent years, because of its low cost and great potential availability. The pretreatment process is important for increasing the enzymatic digestibility of lignocellulosic materials. Enzymatic conversion with freeze pretreatment of rice straw was evaluated in this study. The freeze pretreatment was found to significantly increase the enzyme digestibility of rice straw from 48% to 84%. According to the results, enzymatic hydrolysis of unpretreated rice straw with 150 U cellulase and 100 U xylanase for 48 h yielded 226.77 g kg(-1) and 93.84 g kg(-1) substrate-reducing sugars respectively. However, the reducing sugar yields from freeze pretreatment under the same conditions were 417.27 g kg(-1) and 138.77 g kg(-1) substrate, respectively. In addition, hydrolyzates analysis showed that the highest glucose yield obtained during the enzymatic hydrolysis step in the present study was 371.91 g kg(-1) of dry rice straw, following pretreatment. Therefore, the enhanced enzymatic conversion with freeze pretreatment of rice straw was observed in this study. This indicated that freeze pretreatment was highly effective for enzymatic hydrolysis and low environmental impact. (C) 2010 Elsevier Ltd. All rights reserved.