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Title: Characterization of normal and waxy corn starch for bioethanol production

item YANGCHENG, HANYU - Iowa State University
item JIANG, HONGXIN - Iowa State University
item Blanco, Michael
item JANE, JAY-LIN - Iowa State University

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/16/2012
Publication Date: 1/16/2013
Citation: Yangcheng, H., Jiang, H., Blanco, M.H., Jane, J. 2013. Characterization of normal and waxy corn starch for bioethanol production. Journal of Agricultural and Food Chemistry. 61:379-386.

Interpretive Summary: Substantial effort is devoted to improve bioenergy production to reduce the nation's dependence on foreign oil. Bioethanol is widely used as a transportation fuel in the United States, which provides more than 60% of the world’s ethanol production, most of which is currently produced by corn starch fermentation. Production of ethanol requires enzymatic conversion of starch to glucose (sugar), which is then fermented by yeast to produce ethanol. Since this is an energy demanding process, improving starch conversion efficiency reduces the cost and energy requirements of producing ethanol. One approach to improve ethanol yield and conversion efficiency is to develop corn hybrids with genetic potential for improved ethanol yield and/or conversion efficiency. In this study, a diverse set of eight corn races were studied that produce two different types of starch. Waxy type starch consists primarily of branched chains of amylose (starch) molecules, and differs from normal corn starch which has mostly unbranched starch structure. The results from this research indicated that waxy corn had 5 to 8% better conversion efficiency than starch obtained from normal corn. This was due to improved enzymatic conversion of starch to ethanol which resulted from the differenct starch structure. Knowledge about starch structural variation may help breeders identify corn germplasm with improved starch conversion efficiency and/or greater ethanol yield. This germplasm can be incorporated into breeding programs to develop hybrids with greater bioenergy potential.

Technical Abstract: The objectives of this study were to: 1) Compare the differences of ethanol production between normal and waxy corn representing a diverse set of racial germplasm using a cold-fermentation process; 2) Understand the effects of starch structure and properties on ethanol production. Ethanol yields positively correlated with kernel starch content of the normal and waxy corn. In a two year study, average starch-ethanol conversion efficiency of the waxy corn (93.2%, 2009; 93.0%, 2010) was substantially greater than that of the normal corn (88.0%, 2009; 88.4%, 2010). Starches of the selected lines were isolated for characterization, including amylose content, amylopectin branch-chain-length distributions, thermal properties, and enzymatic hydrolysis of raw starch. Starch hydrolysis of uncooked dry-grind corn showed that > 90% of starch in the waxy corn was hydrolyzed, whereas < 80% of starch in the normal corn was hydrolyzed. This indicated that normal corn contained a significant portion of starch that was less readily hydrolyzed by the enzymes, which reduced the conversion efficiency.