Vol.2 No.4 2010

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Research paper−270−Synthesiology - English edition Vol.2 No.4 pp.270-281 (Feb. 2010) 2 Knowing wood and celluloseThe pretreatment technology for enzymatic saccharification that we developed is a method that utilizes the structural characteristics of wood and cellulose. Therefore, the structures of wood and cellulose will be outlined since they are important for developing this technology.2.1 The basis of celluloseThe main components of wood are cellulose, hemicellulose, and lignin. The molecules of cellulose and hemicellulose are composed of sugars while lignin is a complex aromatic compound. In wood, the percentage of cellulose is highest at about 40~50 %. Cellulose is a biological macromolecule where the glucose is chain-linked, and the nature of cellulose in wood is an assembly of cellulose molecules called the cellulose microfibril. When the cellulose molecules are biosynthesized, they self-assemble regularly like stacked boards to form cellulose microfibrils of 3~5 nm width (Fig. 1, right bottom). This microfibril is the main body of the cellulose crystal, and it does not dissolve in water or ordinary organic solvents since it is extremely stable. However, the assembly forces of the cellulose molecules are the intermolecular force and the hydrogen bond that are generally considered weak. Although the component sugar is glucose, amylose in starch has different chemical and physical properties from cellulose and dissolves in hot water. Therefore, enzymatic saccharification by amylase occurs quickly, and bioethanol can easily be produced.2.2 Wood structure is nanostructureAs shown in Fig. 1 right top, the “wood fiber” is composed of nanosize “cellulose microfibrils” held together using hemicellulose and lignin as adhesives, and the “wood structure” is formed by laying the vessels and tracheids that 1 IntroductionRecently, the interest in bioethanol as automobile fuel has risen from the perspectives of measures for global warming and energy security. In the United States and Brazil, over 20 million kiloliters per year are produced. However, since the raw materials are food biomass such as corn and sugar cane, the increased price of foods and feedstuff in competition to the mass production of bioethanol has become an issue. Therefore, it is essential to establish a technology that allows use of nonfood biomass (cellulosic biomass) such as wood, straw, pasture grass, and others. Compared to the starch biomass such as corn, the cellulosic biomass is thought to be more effective in reducing carbon gas in terms of total life cycle assessment (LCA) from the production of raw material to the use of bioethanol[1].In general, bioethanol is produced by fermenting the sugar obtained from the raw materials, using yeasts. Therefore, it is necessary to hydrolyze (saccharify) the cellulose in wood to glucose. Currently, enzymatic saccharification method is drawing attention. Here, the pretreatment to enhance the enzyme reactivity of wood and cellulose is important.Milling has been known as a highly effective pretreatment for enzymatic saccharification despite its high cost. Therefore, in developing the new pretreatment technology, by reinvestigating the milling process that is known to be effective, we clarified the mechanism by which milling enhanced the enzyme saccharification property of cellulose, using some new analysis methods. Next, we developed the new technology based on the findings obtained, and were able to construct an efficient and economically feasible pretreatment technology based on the new concept.- Pretreatment for enzymatic saccharification using natural structure of cellulose -Takashi EndoBiomass Technology Research Center, AIST 2-2-2 Suehiro, Hiro, Kure 737-0197, Japan E-mail : Original manuscript received September 1, 2009, Revisions received October 13, 2009, Accepted October 14, 2009Bioethanol production from woody biomass by enzymatic hydrolysis of cellulosic components and fermentation has attracted much attention. In this process, pretreatment is important to improve enzymatic degradability of cellulose. A milling process is one of the most effective methods for pretreatment, but its high cost has been a problem. Recently we have developed the economically feasible wet-mechanochemical process as milling pretreatment, which can unravel cellulosic components into nanoscale fibers. Thus-obtained nanofibrous product showed a high enzymatic accessibility, while keeping the cellulose crystalline structure and the lignin content. This process is based on the understanding of the nanoscopic structural characteristics of wood and cellulose.Bioethanol production from woods with the aid of nanotechnologyKeywords : Bioethanol, enzymatic saccharification, pretreatment, mechanochemical treatment, nanofiber[Translation from Synthesiology, Vol.2, No.4, p.310-320 (2009)]

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