Submitted to: World Journal of Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 18, 1996
Publication Date: N/A
Interpretive Summary: Corn hulls and corn germ meal are renewable resources available in sufficient quantities from the corn milling industry to serve as potential feedstocks for production of fuel alcohol. A wide variety of schemes have been used for converting woody feedstocks into free sugars suitable for fermentation. We have digested the corn hulls and germ meal by mixing them with weak acid solutions and heating the solutions to a high temperature. However, the resulting products were a mixture of primarily three sugars, two of which traditional microorganisms used for industrial fermentation cannot use. So, instead we fermented the sugar mixtures with two genetically engineered bacteria. Both bacteria fermented the sugars from the feedstocks within 48 h and gave good ethanol yields. However, both bacteria left some of the sugars unconsumed. Further work is needed to develop a novel fermentation scheme that ensures all the sugars are converted into alcohol.
Technical Abstract: Most of the fuel ethanol produced in the United States is derived from corn starch. Fuel ethanol production can be significantly increased if the fibrous fractions of the corn kernel (corn hulls and de-oiled germs) were also fermented. Currently, these are mixed with corn steep liquor and ethanol fermentation bottoms (if available) and marketed as cattle feed. Conversion of these fractions into ethanol is problematic because hydrolysis of the hemicellulose gives a mixture of pentoses (arabinose and xylose) in addition to glucose. The yeast strains used to ferment the hydrolyzed starch do not ferment pentose. We have evaluated non-traditional recombinant microorganisms for conversion of the corn fiber hemicellulose fractions into ethanol. The hemicelluloses were hydrolyzed by treating with weak acid solutions. The resulting sugar mixtures were fermented extensively using recombinant Escherichia coli strains K011 and SL40. Fermentation results are discussed in terms of the volumetric ethanol rates and ethanol yields.