|Li, Xin Liang|
|O Bryan, Patricia|
Submitted to: Enzyme and Microbial Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 20, 2006
Publication Date: June 1, 2006
Citation: Dien, B.S., Li, X., Iten, L.B., Jordan, D.B., Nichols, N.N., O Bryan, P.J., Cotta, M.A. 2006. Enzymatic saccharification of hot-water pretreated corn fiber for production of monosaccharides. Enzyme and Microbial Technology. 39:1137-1144. Interpretive Summary: Corn fiber is a high-fiber low-value byproduct of wet-milling. Corn fiber is also considered a good source of biomass for conversion to ethanol because it contains a lot of carbohydrates and is present at facilities that often times have ethanol production facilities on site. In this paper, we looked at a new technology for converting corn fiber to ethanol. Corn fiber was heated in hot water (160 deg C for 20 min), the recovered material converted to monosaccharide sugars and fermented using a recombinant strain engineered for ethanol production. The enzyme mixture used to digest the hot-water treated corn fiber contained enzymes produced by growing fungi on corn fiber, as well as, commercial preparations. The resulting enzymes were 80% efficient at extracting the carbohydrates as monosaccharides, and the material produced was readily fermentable to ethanol by the bacterial strain FBR5. This work should be of interest to those working in the fuel ethanol and corn wet milling industry.
Technical Abstract: Corn fiber, currently produced at wet milling facilities, is readily available and a potential feedstock for ethanol fermentation. In this study, corn fiber is converted to ethanol at the laboratory scale using a novel process. The corn fiber was first destarched by treating with glucoamylase. The partially destarched corn fiber (DSCF) was pretreated with hot-water, enzymatically saccharified using a custom blend of hydrolytic enzymes, and fermented to ethanol with recombinant Escherichia coli FBR5, which has been engineered for producing ethanol at high yields. Treating DSCF with hot-water (HW-DSCF) at 160 deg C for 20 min was found to solubilize 58% of the solids and 75% of the xylan and produced very low levels of furfural inhibitors. Enzymes were used to complete hydrolysis. Enzymes were prepared by culturing Trichoderma reesei Rut C30 and Aspergillus niger NRRL 2001 strains separately on HW-DSCF. The preparations had very different enzyme profiles, and it was further discovered, when combined, the preparations were significantly more effective for saccharifying HW-DSCF than either added alone. The maximum sugar yields were 74% and 54% for arabinose and xylose, respectively, at a loading of 0.6 mg protein/g DSCF of each enzyme preparation. The yields were further increased to 80% by increasing the pretreatment time to 30 min and adding a commercial cellobiase. HW-DSCF was fermented to ethanol by a separate saccharification and fermentation scheme, albeit at lower enzyme loadings than used for earlier saccharification tests. The DSCF derived sugars were found to be readily fermentable by E. coli FBR5, and the ethanol yield was 50% (maximum) based upon the beginning loading of DSCF and 101% based upon sugars recovered during the saccharification step.