Location: Bioenergy Research Unit
Title: Influence of Stenocarpella maydis infected corn on the composition of corn kernel and its conversion into ethanol Authors
Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 6, 2012
Publication Date: January 31, 2012
Citation: Dien, B.S., Wicklow, D.T., Singh, V., Moreau, R.A., Moser, J.K., Cotta, M.A. 2012. Influence of Stenocarpella maydis infected corn on the composition of corn kernel and its conversion into ethanol. Cereal Chemistry. 89:15-23. Interpretive Summary: Stenocarpella is a leading cause of ear rot within the United States Corn Belt and is increasing in prevalence. Despite the rapid growth in corn ethanol production, nothing is known regarding the effect of processing infected kernels into ethanol. Corn was harvested from an infected field and sorted by the extent of infection. The classification was validated by measuring ergosterol, a sterol associated with the fungal infection. The corn samples were analyzed for bulk and chemical properties. The infection was associated with drastic decreases in kernel size and bushel test weights. Corn oil contents also declined with increased infection. Notably, starch content on a weight basis was unaffected. The samples were next converted to ethanol using a laboratory protocol that models the corn dry grind process, which is the dominant corn ethanol industrial process. Corn ethanol yield was unaffected. However, the animal feed co-produced with the corn ethanol (Distillers’ Dried Grains with Solubles (DDGS)) was altered; most significantly it was lowered in oil content. Stenocaprella infected corn is not considered a risk for feeding to production animals. Therefore, Stenocarpella infected corn will not alter ethanol yields but may lower DDGS oil contents. Corn producers and corn ethanol processers will find these results of interest.
Technical Abstract: Widespread epidemics of Stenocarpella ear rot (formerly Diplodia ear rot) have occurred throughout the central U.S. Corn Belt in recent years, but the influence of S. maydis infected grain on corn ethanol production is unknown. In this study, S. maydis infected ears of variety 'Heritage 4646' were hand-harvested in 2010 from a production field in central Illinois and segregated into 1 of 5 levels of ear rot severity based upon visual symptoms. The concentration of ergosterol, a sterol produced by fungi but not plants, was observed to increase with the severity of ear rot (127-306.5 µg/g) and none was detected in the control corn. Corn test weight declined with progression of the disease and was 42.6% lower for the most severely rotted grain from ears infected early in their development. Accompanying changes in composition were also apparent. Oil content decreased (4.7 to 1.5%) and fiber increased (6.6 to 9.6%) but starch content remained largely invariant. Oil composition also varied among the infected samples. Corn samples were converted to ethanol using a laboratory scaled corn dry grind ethanol process. Ethanol yields were similar on an equivalent weight basis (2.77-2.85 gal/bu). However, Distiller’s Dried Grains with Solubles (DDGS) composition was modified and significantly reduced in oil content (10.9 to 3.8%). Based upon these results, we conclude that Stenocarpella ear rot will affect DDGS composition but not ethanol yield on an equivalent weight basis.