Submitted to: Biotechnology Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 13, 2005
Publication Date: January 19, 2006
Citation: Saha, B.C., Cotta, M.A. 2006. Ethanol production from alkaline peroxide pretreated enzymatically saccharified wheat straw. Biotechnology Progress. 22:449-453. Interpretive Summary: Ethanol is a renewable bio-based oxygenated fuel. Wheat straw contains about 70% carbohydrates that can serve as a low cost feedstock for conversion to fuel ethanol. Research needs to be carried out to develop an efficient pretreatment method which can help enzymes break down the complex carbohydrates to simple sugar mixtures without generating compounds inhibitory to fermentative microorganisms. The efficient utilization of all these sugars is essential for cost-effective production of ethanol from wheat straw. Research was conducted to break down wheat straw using alkaline peroxide as a pretreatment option and commercially available enzymes followed by fermentation of the sugars by an ethanol producing recombinant bacterium. This research demonstrates that wheat straw can be easily broken down to sugars completely after pretreatment with alkaline peroxide and enzymatic hydrolysis. The method does not generate any common fermentation inhibitors. The bacterium is able to ferment the sugars efficiently to ethanol. The results will greatly aid in developing bioprocess technologies for conversion of wheat straw to fuel ethanol.
Technical Abstract: Wheat straw used in this study contained 44.24 ± 0.28% cellulose and 25.23 ± 0.11% hemicellulose. Alkaline H2O2 pretreatment and enzymatic saccharification were evaluated for conversion of wheat straw cellulose and hemicellulose to fermentable sugars. The maximum yield of monomeric sugars from wheat straw (8.6%, w/v) by alkaline peroxide pretreatment (2.15% H2O2, v/v; pH 11.5; 35 deg C; 24 h) and enzymatic saccharification (45 deg C; pH 5.0; 120 h) using cellulase, beta-glucosidase, and xylanase was 672 ± 4 mg/g (96.7% yield). During the pretreatment, no measurable quantities of furfural and hydroxymethyl furfural were produced. The yield of ethanol (per L) from alkaline peroxide pretreated enzyme saccharified wheat straw (66.0 g) hydrolyzate by recombinant Escherichia coli strain FBR5 at pH 6.5 and 37 deg C in 48 h was 18.9 ± 0.9 g with a yield of 0.46 g per g available sugars (0.29 g/g straw). The ethanol yield was 15.1 ± 0.1 g with a yield of 0.23 g/g straw in the case of simultaneous saccharification and fermentation by the E. coli strain at pH 6.0 and 37 deg C in 48 h.