Submitted to: Enzyme and Microbial Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/18/2007
Publication Date: 5/1/2007
Citation: Saha, B.C., Cotta, M.A. 2007. Enzymatic saccharification and fermentation of alkaline peroxide pretreated rice hulls to ethanol. Enzyme and Microbial Technology. 41:528-532. Interpretive Summary: Rice hulls, a complex lignocellulosic material, contain 47% carbohydrate that has the potential to be converted to fuel ethanol. Research needs to be carried out to develop an efficient pretreatment method which can help enzymes breakdown the complex carbohydrate to simple sugars. Research has been conducted to evaluate alkaline peroxide as a pretreatment option for rice hulls, enzymatic breakdown of the pretreated rice hulls followed by fermentation of the sugars by an ethanol producing recombinant bacterium. This research demonstrates that the rice hulls can be brokendown to sugars completely after pretreatment with alkaline peroxide and enzymatic hydrolysis, and the generated sugars are fermented to ethanol with a very good yield. The results will greatly aid in developing bioprocess technologies for conversion of any lignocellulosic biomass to fuel ethanol.
Technical Abstract: Rice hulls used in this study contained 35.62 +/- 0.12% cellulose and 11.96 +/- 0.73% hemicellulose. Alkaline H2O2 pretreatment and enzymatic saccharification methods were evaluated for conversion of rice hull cellulose and hemicellulose to simple sugars. The yield of sugars from diluted alkaline peroxide pretreated (7.50% H2O2, v/v; pH 11.5; 35 deg C; 24 h) rice hulls (15.0%, w/v) after enzymatic saccharification (45 deg C, pH 5.0, 72 h) by three commercial enzyme preparations (cellulase, beta-glucosidase, and xylanase) using 0.12 ml of each enzyme preparation per g straw was 428 +/- 12 mg/g (90% yield). During the pretreatment, no measurable furfural and hydroxymethyl furfural were produced. The almost complete conversion (96%) of rice hulls to sugars was achieved by saccharifying the liquid and solid fractions separately after alkaline peroxide pretreatment. The concentration of ethanol from alkaline peroxide pretreated, enzyme saccharified rice hull (39 g) hydrolyzate by recombinant Escherichia coli strain FBR5 at pH 6.5 and 35 deg C in 24 h was 8.2 +/- 0.2 g per L with a yield of 0.49 g/g available sugars (0.21 g/g hulls). The ethanol concentration was 8.0 +/- 0.2 g per L with a yield of 0.20 g/g hulls in the case of simultaneous saccharification and fermentation by the E. coli strain at pH 6.0 and 35 deg C in 48 h.