Submitted to: Journal of Chemical Technology & Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/4/2007
Publication Date: 9/3/2007
Citation: Saha, B.C., Cotta, M.A. 2007. Enzymatic hydrolysis and fermentation of lime pretreated wheat straw to ethanol. Journal of Chemical Technology and Biotechnology. 82:913-919. Interpretive Summary: Wheat straw contains about 70% complex carbohydrate 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 breakdown the carbohydrates to simple sugars 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. Native wheat straw is very resistant to breakdown by enzymes. Research has been conducted to evaluate various pretreatment options for wheat straw. In this research, lime pretreatment has been evaluated for its effectiveness in the enzymatic breakdown of the carbohydrate to sugars and fermentability of the sugars to ethanol by an ethanol producing recombinant bacterium. The results are important in choosing a suitable pretreatment option for 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. Lime pretreatment and enzymatic saccharification methods 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 lime pretreatment (100 mg g**-1 straw, 121 deg C, 1 h) and enzymatic hydrolysis (45 deg C, pH 5.0, 120 h) using a cocktail of 3 commercial enzyme preparations (cellulase, beta-glucosidase, and xylanase) at the dose level of 0.15 ml of each enzyme preparation per g**-1 straw was 568 +/- 13 mg/g g**-1 (82% yield). During the pretreatment, no measurable quantities of furfural and hydroxymethyl furfural were produced. The concentration of ethanol from lime pretreated enzyme saccharified wheat straw (78 g) hydrolyzate by recombinant Escherichia coli strain FBR5 at pH 6.5 and 35 deg C in 24 h was 22.5 +/- 0.6 g l**-1 with a yield of 0.50 g g**-1 available sugars (0.29 g g**-1 straw). The ethanol concentration was 20.6 +/- 0.4 g l**-1 with a yield of 0.26 g g**-1 straw in the case of simultaneous saccharification and fermentation by the E. coli strain at pH 6.0 and 35 deg C in 72 h.