Bioethanol Production from Rice Straw in the MAFF Research Project, Japan
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1219-AA02-01
Bioethanol Production from Rice Straw in the MAFF Research Project, Japan
Ken Tokuyasu Food Resources Division, National Food Research Institute, National Agriculture and Food Research Organization, 2-1-12 Kannondai, Tsukuba, Ibaraki 305-8642, JAPAN
ABSTRACT Rice straw is among the most abundant herbaceous biomass, and regarded as the central feedstock for bioethanol production in Japan. We found that significant amounts of soft carbohydrates (SCs), defined as carbohydrates readily recoverable by mere extraction from the biomass or brief enzymatic saccharification, exist in rice straw in the form of free glucose, free fructose, sucrose, starch, and β-1,3-1,4-glucan. Based on the finding, we proposed a simple method for bioethanol production from rice straw samples with SCs, by a heat treatment for sterilization and starch gelatinization, followed by simultaneous saccharification/fermentation with Saccharomyces cerevisiae. This method would offer an efficient process for bioethanol production without the aid of harsh thermo/chemical pretreatment step. INTRODUCTION Bioethanol industry is growing in both developing and developed countries, in parallel with the increase in the needs of sustainable supply of energies and materials by environmentally friendly systems. In the industry, lignocellulosic biomass has been regarded as an alternative source of fermentable monosaccharides to corn starch or sugarcane juice. However, no bioethanol-production systems from lignocellulosic feedstocks can run economically independently, mainly due to a high cost for monosaccharide extraction from rigid lignocellulose, a high cost for saccharification enzymes, and inefficient fermentation of pentoses such as D-xylose and L-arabinose [1]. From Fy 07, the ministry of agriculture, forestry and fisheries, Japan (MAFF) started a five year research project named “Development of biomass conversion technologies as a way of vitalizing areas.” The ministry set two kinds of agricultural waste (rice straw and wheat straw), as well as five herbaceous energy crops (sugar beet, potato, sorghum, sweet potato, and sugarcane) as feedstock for bioethanol production. In order to develop breakthrough methods for efficient bioethanol production without competition with food/feed production, our group has been studying a synthetic method for conversion of these herbaceous feedstocks into ethanol. Among the herbaceous feedstocks for bioethanol, rice straw is the most abundant in Japan and some parts in Asia. In the MAFF project, we could find that significant amounts of soft carbohydrates (SCs), defined as carbohydrates readily recoverable by mere extraction from the biomass or brief enzymatic saccharification, exist in rice straw in the form of free glucose, free fructose, sucrose, starch, and β-1,3-1,4-glucan. In this paper we introduce a simple method for bioethanol production from rice straw samples with SCs, by a heat treatment for sterilization and starch gelatinization, followed by simultaneous saccharification/fermentation with Saccharo
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