ABSTRACT
BACKGROUND: US legislation requires the use of advanced biofuels to be made from non-food feedstocks. However, commercialization of lignocellulosic ethanol technology is more complex than expected and is therefore running behind schedule. This is creating a demand for non-food, but more easily converted, starch-based feedstocks other than corn that can fill the gap until the second generation technologies are commercially viable. Winter barley is such a feedstock but its mash has very high viscosity due to its high content of beta-glucans. This fact, along with a lower starch content than corn, makes ethanol production at the commercial scale a real challenge. RESULTS: A new fermentation process for ethanol production from Thoroughbred, a winter barley variety with a high starch content, was developed. The new process was designated the EDGE (enhanced dry grind enzymatic) process. In this process, in addition to the normal starch-converting enzymes, two accessory enzymes were used to solve the beta-glucan problem. First, beta-glucanases were used to hydrolyze the beta-glucans to oligomeric fractions, thus significantly reducing the viscosity to allow good mixing for the distribution of the yeast and nutrients. Next, beta-glucosidase was used to complete the beta-glucan hydrolysis and to generate glucose, which was subsequently fermented in order to produce additional ethanol. While beta-glucanases have been previously used to improve barley ethanol production by lowering viscosity, this is the first full report on the benefits of adding beta-glucosidases to increase the ethanol yield. CONCLUSIONS: In the EDGE process, 30% of total dry solids could be used to produce 15% v/v ethanol. Under optimum conditions an ethanol yield of 402 L/MT (dry basis) or 2.17 gallons/53 lb bushel of barley with 15% moisture was achieved. The distillers dried grains with solubles (DDGS) co-product had extremely low beta-glucan (below 0.2%) making it suitable for use in both ruminant and mono-gastric animal feeds.
