Consolidated conversion of hulled barley into fermentable sugars using chemo-, thermo-, and enzymatic (C.T.E.) treatment

Authors: KIM, TAE HYUN - Iowa State University; Nghiem, Nhuan; Taylor, Frank; Hicks, Kevin

Submitted to: Applied Biochemistry and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/28/2010
Publication Date: 1/13/2011
Citation: Kim, T., Nghiem, N.P., Taylor, F., Hicks, K.B. 2011. Consolidated conversion of hulled barley into fermentable sugars using chemical, thermal, and enzymatic (C.T.E.) treatment. Applied Biochemistry and Biotechnology. 164:534-545.

Interpretive Summary: Winter barley is now considered to be a desirable ethanol feedstock for ethanol plants outside the Corn Belt because it is grown on winter-fallow land and doesn't compete with food production. Further, it functions as a winter cover crop and prevents sediment and nutrients from leaching into sensitive waterways. Barley grain contains over 20 percent by weight of non-fermentable, non-starch polysaccharides that simply take up expensive fermentor space during ethanol production. Being able to convert those non-starch polysaccharides into fermentable sugars and ethanol would improve the economics of fuel ethanol. In this study, we developed a novel consolidated chemical, thermochemical, and enzymatic process to convert all the non-starch and starch polysaccharides into fermentable sugars. The process uses dilute acid followed by high temperature and pressure treatment through a flow-through reactor, followed finally by hydrolysis by enzymes into sugars. A provisional patent has been filed on this new process, which will be of interest to all academic and commercial scientists who want to make cellulosic ethanol and starch ethanol in the same processing facility.

Technical Abstract: A novel conversion process of hulled barley into fermentable sugars was developed using chemo-, thermo-, and enzymatic treatment. The purpose of this process is to convert both lignocellulosic polysaccharides and starch in hulled barley into fermentable sugars simultaneously without any hull separation and grinding steps. In this study, whole hulled barley was treated using 0.1 and 1.0 wt. percent of sulfuric acid at various temperatures from 110 deg C to 170 deg C in a 70 ml flow-through stainless steel reactor packed with hulled barley (void percent=50-60percent). After sulfuric acid pretreatment, one step conversion of hulled barley (lignocellulose + starch) into fermentable sugars was performed using an enzyme cocktail. At selected pretreatment conditions, the treated hulled barley, including hull, was completely hydrolyzed into fermentable sugars. The optimum treatment conditions of chemo-, thermo-, and enzymatic (CTE) treatment for maximum fermentable sugars yield were 1.0 wt.% sulfuric acid, 110 deg C, 30 min, 300 psi, 5 mL/min, and 4 mL 1.0 percent H2SO4 per g of barley of liquid throughput. Both starch and non-starch polysaccharides in the pre-treated barley were readily converted to fermentable sugars by incubation at 3 percent solid loading in 0.05 M citrate buffer and 50 deg C, using a cocktail of a-amylase, glucoamylase, cellulase, and ß-glucosidase. Under these conditions, nearly 100 percent of available glucose and xylose were recovered. Treatment at 110 deg C also retained most of the starch and protein in solid form, which is essential for subsequent production of fuel ethanol and high protein Distillers Dry Grains with Solubles co-product.