Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/2010
Publication Date: 4/28/2010
Citation: Nghiem, N.P., Hicks, K.B., Johnston, D., Senske, G.E., Kurantz, M.J., Li, M., Shetty, J., Janda-Konieczny, G. 2010. Production of ethanol from barley by a conventional process and the EDGE (Enhanced Dry Grind Enzymatic) process. Biotechnology for Biofuels. 3:8. doi:10.1186/1754-6834-3-8.
Interpretive Summary: Interest in renewable liquid fuels, and in particular ethanol, is increasing world-wide. In the U.S., the goal is to replace 30% of the nation’s gasoline consumption by 2030, which will require production of approximately 60 billion gallons per year of ethanol. However, it has been estimated that the maximum quantity of ethanol that can be produced from corn in the U.S. is only about 12 to 15 billion gallons per year, which is well below the national goal. Thus production of ethanol from renewable feedstocks other than corn is needed. Barley is qualified for such an ethanol feedstock. One of the challenges of using barley in fuel ethanol fermentation is the presence of a beta-glucan an ethanol production inhibitor in the grains. In this research we developed the EDGE (Enhanced Dry Grind Enzymatic) process that may improve ethanol yield. Under the optimum conditions established for the new process, ethanol yield of 2.30 gallons/56-lb bushel of barley was achieved. This represents a 1.6% increase than conventional process. The main co-product of ethanol fermentation, which normally is referred to as distillers dried grains with solubles (DDGS), contains very little beta-glucan and therefore is suitable for use in feeds of both cattle and mono-gastric animals such as swine and poultry. This research will benefit enzyme companies, ethanol plant designers and builders, and grower groups outside the Corn Belt who want to build ethanol plants using barley as feedstock.
Technical Abstract: Corn ethanol production is not sufficient to meet the future demand for transportation liquid fuels and lignocellulosic ethanol technology is still not ready for commercialization. Therefore, another starch feedstock for fuel ethanol is needed. Barley is suitable for this role since it can be grown outside the areas currently used for growing corn in the U.S. and it has the potential of producing one to two billion gallons of ethanol per year. On the East coast and in other regions of the country with mild winters, barley is grown as a winter crop and acts as a ground cover to prevent excess nutrients from leaching into watersheds and sensitive areas such as the Chesapeake Bay. Harvest of winter barley in late May/early June allows production of a full soybean crop afterwards in the same crop year. Following the next year with corn and then winter barley, allows a two-year, three-crop rotation. This process results in more grain on the same acreage with less nutrient loss to sensitive waterways, a win/win situation for both renewable fuels and the environment. One problem with using barley in fuel ethanol fermentation is the presence of beta-glucans, which upon solubilization considerably increase the viscosity of the mash. The presence of high levels of beta-glucans in the distillers dried grains with solubles (DDGS) will also make this co-product unsuitable for use in feeds of monogastric animals. In the conventional process for ethanol production from barley, the enzyme beta-glucanase was used to hydrolyze beta-glucans to low molecular weight products, which included glucose and glucose oligomers, and subsequently reduce the viscosity significantly. Using Thoroughbred barley in the conventional process an ethanol yield of 395 L/MT dry solids or 2.26 gallons/56-lb bushel was obtained. A new and improved process, which is called the EDGE (Enhanced Dry Grind Enzymatic) process, was developed for ethanol production from barley. In this new process, in addition to beta-glucanase, a second enzyme was used. The second enzyme was beta-glucosidase, which converted the non-metabolizable oligosaccharides formed in the hydrolysis of beta-glucans to the fermentable sugar glucose. The combined application of the two enzymes allowed ethanol to be produced at 30% total dry solids to reach 15% v/v. Under the optimum conditions established for the newly developed EDGE process, ethanol yield of 402 L/MT (dry basis) or 2.30 gallons/56-lb bushel of barley was achieved. The improvement over the conventional process in a 50 million-gallon-per-year ethanol plant is 880,000 gallons of ethanol per year. The DDGS co-product with high protein and fiber contents and extremely low beta-glucan contents (less than 0.2%) was suitable for use in feeds of both cattle and monogastric animals such as swine and poultry.