Monday, May 4, 2009
9-12
Simple process for production of ethanol from soybean hulls while maintaining protein value
Jonathan R. Mielenz, Bioconversion Science and Technology, Oak Ridge National Laboratory, Bethel Valley Rd, PO Box 2008, Oak Ridge, TN 37831, John S. Bardsley, Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, and Charles Wyman, Center for Environmental Research and Technology, Bourns College of Engineering, University of California, Riverside, 1084 Columbia Avenue, Riverside, CA 92521.
Soybeans are grown for their protein value and are one of the largest commodity crops in the United States . The soybean hull itself contains cellulose, hemicellulose, pectin, uronic acid and approximately 10% protein by weight. Our research shows the soybean hulls are a source of fermentable carbohydrates for ethanol production. Saccharomyces cerevisiae as well as recombinant ethanologenic bacteria readily ferment soybean hulls carbohydrates to ethanol in simultaneous saccharification fermentation mode using commercial cellulase, beta-glucosidase and pectinase enzymes but importantly requiring no pretreatment. Bench-scale fermentation process used only non-recombinant Saccharomyces cerevisiae yeast and high substrate loading up to 20% w/w. Results showed a significant proportion of carbohydrate fibers are removed by conversion to ethanol while the protein remains intact. Protein and amino acid analysis before and after fermentation revealed up to 2.5X higher concentration of protein with yeast cells accounting for only about 10% of the remaining protein. Among the more than dozen amino acids assayed there was essentially an identical amino acids profile for substrate and product. The U.S., and Brazil plus Argentina each produced about 90 million metric tons of soybeans in 2005, which potentially could yield up to 550 million gallons of ethanol and nearly 3 million ton of higher value protein feed from fermentation of the resulting soybean hulls worldwide, not accounting for the growing market in China . By elimination of the cellulosic fiber matter, the resulting fermentation residues should be suitable for feed for monogastric animals, pigs and chickens, which represent the fastest growing livestock market.