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: June 8, 2011
Publication Date: January 6, 2012
Citation: Dien, B.S., Wicklow, D.T., Singh, V., Moreau, R.A., Winkler-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(1):15-23. Technical Abstract: Stenocarpella ear rot (formerly Diplodia ear rot) is resurfacing as a concern in the central United States Corn Belt. There are reports of some fields containing more than 50% mummified ears. Ears infected within two weeks of silking may be completely mummified with white to grayish brown mycelium covering light-weight, shriveled, and lusterless light-brown kernels. The severity of ear rotting decreases sharply with later infection dates during kernel development. Ears infected later in the growing season may appear normal with disease symptoms seen as discolored kernel embryos after the ear is broken in the middle. It is notable that the feeding of Stencoarpella corn to animals is not considered a risk. The influence of S. maydis infected grain on corn ethanol production is unknown. This is of significant concern because the U.S. corn ethanol processes 40% of the domestic corn harvest and generates 12 bn gal of fuel ethanol per year. For this study, Stenocarpella infected corn was manually harvested from a Central Illinois Farm in 2010 and the corn graded into five categories; an uninfected control was also included. The corn ears were graded based upon visual criteria designed to fractionate the corn from early to late infection after planting. The visual selection criteria were validated by measuring ergosterol. This fungal associated sterol is not produced by plants and is often used as an indicator of fungal infection in grain. Ergosterol concentrations were observed to increase with severity of infection (Figure 1). No ergosterol was detected in the uninfected control. The mildest infected corn is often referred to as “hidden” Stenocarpella because the infection is only noticeable as a discoloration of the kernel tip ends. It is notable that this sample was stille determined to have significant ergosterol content. To our knowledge there are no published data on the affect of ear rot infection on corn ethanol production. The majority of corn is converted to ethanol in the dry grind process. For this study, the fate of corn was modeled from arriving at the factory gate through the production of ethanol and dried distillers grains and soluble (DDGS). When corn first arrives, it is analyzed for bushel test weight, moisture, and chemical composition. The later is measured using near infrared spectroscopy (NIR). The corn is next processed into ethanol using one of two schemes. Corn starch can be either liquefied and simultaneously saccharified and fermented (SSF) to ethanol using a combination of alpha and gluco amylase enzymes or it can be directly treated by SSF using the newer granular starch amylase. Following fermentation the ethanol is removed from the beer and the spent grains dried and marketed as DDGS. DDGS is used as animal feed, especially for beef and dairy production. For this study, the set of six corn samples described above were compared for bulk and chemical properties. Chemical composition was independently determined by the wet chemistry and NIR methods. The corn was subsequently converted to ethanol using both processes and evaluated for ethanol productivities and yields. Finally, the spent grains, generated by the traditional method, were processed to DDGS, which was analyzed for composition.