Submitted to: Chemical Engineering Science
Publication Type: Proceedings
Publication Acceptance Date: July 18, 1996
Publication Date: N/A
Interpretive Summary: Corn fiber and corn germ cake are renewable resources available in sufficient quantities from the corn milling industry to serve as potential low cost 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 fiber and germ cake 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. The ethanol yield can be significantly increased if the hemicellulose fraction of the corn kernel is also fermented. The hemicellulose and cellulose fractions are presently marketed as cattle feed. Conversion of the hemicellulose fraction to ethanol is problematic because, in addition to glucose from the residual starch, hydrolysis of the hemicellulose gives a mixture of pentoses (arabinose and xylose) and traditional industrial yeast do not ferment pentoses. We have evaluated non-traditional recombinant microorganisms for conversion of the hemicellulose fractions into ethanol. The hemicelluloses were hydrolyzed with weak acid solutions and resulting sugar mixtures fermented using recombinant Escherichia coli strains KO11 and SL40. Results of the fermentation are discussed in terms of volumetric ethanol production rates, ethanol yields, and effect of inhibitors produced during hydrolysis.