Gekkeikan* General Research Institute developed a new production technology of bioethanol. The institute enabled to produce ethanol from inedible plant materials such as chaff and paddy straw by using "super yeast," sake yeast genetically modified with koji mold (aspergilli) genes.
*Gekkeikan Sake Co Ltd is a brewing maker in Japan.
The new method pretreats plants for fermentation with high-temperature and pressure water, not with chemical agents.
The research was conducted as a part of the "Innovative Technology Development Research Project," which was established by Japan Science and Technology Agency (JST), with the help of researchers from Kobe University, Kyoto University and Tohoku University. The results of the research will be announced at the annual meeting of JSBBA (Japan Society for Bioscience, Biotechnology, and Agrochemistry) 2008, which will take place March 28, 2008.
Plant cellulose, a raw material for bioethanol, has a chemically-stable and robust structure. So, the strength of the structure is weakened by the method called "subcritical water treatment" to be ready for fermentation.
In a subcritical region, water is at a high temperature and pressure (150-370°C) and acidic. But when the temperature and pressure decline, it quickly becomes neutral. Plant cellulose can be pretreated with a devise simpler than the one used for supercritical water (above 374°C and 22.1MPa).
From the perspectives of environmental load and safety, the new method is superior to the existing pretreatment method that uses chemical agents such as sulfuric acid.
To produce super yeast, which makes alcohol, koji mold's genes that produce cellulolytic enzymes were incorporated in sake yeast so that the enzymes are densely arranged on the surfaces of the yeast cells like the hands of a multiarmed deity.
In normal sake brewing, alcohol is produced by two processes: Koji mold dissolves rice starch into sugar, and yeast ferments the sugar. However, because super yeast has the functions of koji mold, it can produce ethanol by itself from cellulose pretreated with subcritical water.
The subcritical water treatment and the super yeast realized clean and easy pretreatment and simple and efficient ethanol production. Therefore, it is now possible to build a small-scale plant in each place where plant materials are produced.
Gekkeikan General Research Institute has already confirmed in the experiment that chaff and paddy straw can be used to produce ethanol. And the institute will advance the research to improve the yield of alcohol, aiming at the practical use of the technology.
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