Sunday, April 29, 2007

Effect of supplemental hemicellulase on enzymatic hydrolysis and ethanol fermentation of softwood pretreated by ball milling

Hiroyuki Inoue, Shinichi Yano, Osam Takimura, Katsuji Murakami, Akinori Matsushika, Kenichiro Tsukahara, and Shigeki Sawayama. Biomass Technology Research Center, National Institute of Advanced Industrial Science and Technology, 2-2-2 Hiro-suehiro, Kure, Japan

Lignocellulosic biomass, such as wood and agricultural residues, is an attractive material for fuel ethanol production since it contains large amounts of potentially fermentable sugars in the form of cellulose and hemicelluloses. The interest of using hemicellulose as a resource for the efficient production of ethanol is currently increasing. Softwood is a promising feedstock, since its principal hemicellulose component, O-acetyl galactoglucomannan, gives readily fermentable mannose as the major sugar after hydrolysis. This is advantageous over hardwood hemicellulose hydrolyzed to unfermentable xylose.

In this study, we investigated the enzymatic hydrolysis and the subsequent ethanol fermentation of two kinds of softwood (Japanese cypress, Douglas fir) pretreated by ball milling (BM). Acremonium cellulase was used as the commercial cellulase. This enzyme has been developed in Japan and is suitable for ethanol production since its beta-glucosidase activity is higher than that of conventional cellulase from Trichoderma species. BM treatment significantly improved the yield of glucose with low cellulase loading (4-8 FPU/g dry wood). However, hemicellulase activity contained in the cellulase appeared to be insufficient for the hydrolysis of glucomannan backbone. The mannose yield from the BM-treated softwood was evaluated using Acremonium cellulase supplemented with some commercial hemicellulases. The results indicated that the presence of additional hemicellulolytic activities was essential for an efficient hydrolysis of BM-treated softwood. Consecutive hydrolysis and fermentation of BM-treated Japanese cypress showed that approximately 240 and 210 g ethanol /kg dry wood were produced from hydrolysate treated by Acremonium cellulase supplemented with and without hemicellulase, respectively.