Submitted to: Cereal Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/14/2006
Publication Date: 9/1/2006
Citation: Wu, X., Zhao, R., Wang, D., Bean, S., Seib, P.A., Tuinstra, M.R., Campbell, M., O'Brien, A. 2006. Effects of amylose, corn protein and corn fiber contents on production of ethanol from starch-rich media. Cereal Chemistry. 83(5):569-575. Interpretive Summary: Little is currently understood about the biochemical components of grain that determine the amount of ethanol that can be produced. Once the relationships between grain composition and ethanol production are understood, cereal grains, such as sorghum, with the right components can be selected for by breeders. A model system made of various ratios of amylase, amylopectin, fiber, and protein was used to study the impact of these factors on fermentation yields and efficiency. The amount of amylose present in the samples was found to have a significant effect on fermentation efficiency. Testing of cereal grains from wheat, corn, and sorghum with various amylose levels confirmed the findings of the model system. The selection of grains with improved ethanol production could lead to improved production of fuel ethanol and add value to U.S. crops such as sorghum.
Technical Abstract: The effects of amylose: amylopectin ratio, and protein and fiber contents on ethanol yields were evaluated by using artificially formulated media made from commercial corn starches with different contents of amylose, corn protein, and corn fiber, as well as different cereal sources, including corn, sorghum, and wheat with differing amylose contents. Second-order response-surface regression models were used to study the effects and interactions of amylose: amylopectin ratio, and protein and fiber contents on ethanol yield and conversion efficiency. The results showed that the amylose content of starches had a significant (P<0.001) effect on ethanol conversion efficiency. Neither the effect of protein and fiber contents, nor the interactions among amylose, protein, and fiber were significant at P=0.05 level. Conversion efficiencies increased as the amylose content decreased, especially when the amylose content was less than 35%. The reduced quadratic model fits the conversion efficiency data better than the full quadratic model does. Fermentation tests on mashes made from corn, sorghum, and wheat samples with different amylose contents confirmed the adverse effect of amylose content on fermentation efficiency. High-temperature cooking with agitation significantly increased the conversion efficiencies on mashes made from high-amylose (35-70%) ground corn and starches. A cooking temperature of 160 °C or higher was needed on high-amylose corn and starches to obtain a conversion efficiency equal to that of normal corn and starch.