Submitted to: Applied Biochemistry and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 23, 1996
Publication Date: N/A
Interpretive Summary: In the United States, 60% of all fuel alcohol is produced by fermentation of corn starch from the corn wet-milling industry. Corn fiber is a co-product of wet-milling and is marketed in animal feeds, with the income used to offset the costs of alcohol production. Since future uses of these animal feeds are questionable, we have examined methods for converting corn fiber into sugars for alcohol production. Corn fiber was subjected to high pressure ammonia treatment and then digested with various commercial enzyme mixtures. The results showed that corn fiber was only partially digested to sugars, indicating current enzyme digestion methods have major limitations for converting corn fiber or other biomass materials (corncobs, corn stover, straws) to sugars for alcohol production. Further studies will examine ways to overcome these limitations and will involve the use of microorganisms that naturally digest corn fiber and ferment it to alcohol.
Technical Abstract: Corn fiber is a co-product produced during the corn wet-milling process and is a potential fermentation feedstock for conversion into biofuels. Corn fiber was subjected to ammonia-explosion (AFEX) treatment and then enzymatically digested with a combined mixture of commercial amylase, xylanase, and cellulase enzyme preparations. While the starch and cellulose components were converted solely to glucose, oligosaccharides represented 30-40% of the xylan degradation products. This enzyme mixture also produced substantial oligosaccharides with xylans purified from corn fiber, corn germ, beechwood, oatspelt, or wheat germ. Commercial xylan-degrading enzyme preparations were then used alone or in varying combinations to attempt to maximize degradation of these isolated xylans of differing chemical compositions. The results showed that oatspelt and beechwood xylans were degraded most extensively (40-60%) with substantial amounts of xylose, xylobiose, and xylotriose as products, depending on the enzyme combination that were used. Corn fiber and wheat germ xylans were poorly degraded and only small amounts of arabinose and xylose and large amounts of pentamer or longer oligosaccharides were produced by enzymatic degradation. The data suggest that while enzymatic digestion of biomass hemicellulose does not produce toxic products, the process is not effective in producing a suitable fermentable substrate stream due to the low levels of monosaccharides and high levels of oligosaccharides produced. Alternative processes include dilute acid hemicellulose hydrolysis or direct fermentation of the untreated biomass by native or genetically-modified xylanolytic microorganisms.