Short communication Changes in unreacted starch content in corn during storage Benjamin M. Plumier, Mary-Grace C. Danao * , Kent D. Rausch, Vijay Singh Department of Agricultural and Biological Engineering, University of Illinois, Urbana, IL, 61801, USA article info Article history: Received 21 September 2014 Received in revised form 9 November 2014 Accepted 10 November 2014 Available online 25 December 2014 Keywords: Resistant starch Dry grind ethanol Distillers dried grains with solubles (DDGS) Storage temperature Storage time abstract In the dry grind process, corn is ground, mixed with process water and cooked; starch is enzymatically hydrolyzed to sugars, and subsequently fermented to ethanol by yeast. The conversion of starch into ethanol, however, is not complete as distillers dried grains with solubles (DDGS) often contain more than 5% starch. The amount of unreacted starch represents inefficiencies in the process and reducing this amount is important to improving profitability of the ethanol industry. Additionally, dry grind facilities have reported seasonal variation in ethanol yields. In order to minimize variation in ethanol yields and the amount of unreacted starch in DDGS, it is important to understand the effects that storage tem- perature and time have on the digestibility of the corn starch. While starch quality is largely controlled by genetics and growing conditions, postharvest practices (handling, storage, and processing conditions) also affect starch composition and structure. In this study, changes in unreacted starch content of corn during storage were monitored to provide an explanation for the seasonal variation in ethanol yields observed by dry grind facilities. Yellow dent corn was harvested in 2011 and 2012 and stored indoors, outdoors, and under refrigeration for 5e12 mo. Results with the 2011 harvest corn showed unreacted starch content ranging from 2.17 to 14.1% over a 48 wk period. Unreacted starch was more influenced by storage time, initially decreasing at a rate of 0.31% per wk during the first 10 wk and steadily increased at an average rate of 0.16% per wk for the duration of storage. Results with the 2012 harvest corn, however, showed a higher average unreacted starch content of 13.0% during 20 wk of storage and no appreciable change in unreacted starch content regardless of storage temperature. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Production of ethanol from corn has become an essential fuel industry in the U.S. With the goal of producing 36 billion gallons of ethanol from corn and biomass sources by 2022 (Schnepf and Yacobucci, 2010), the ethanol industry is clearly of great economic importance. Greater process efficiency could lead to increased production so it is important to understand and be able to monitor corn quality and how it changes over time. The most common method used for converting corn into ethanol is the dry grind process, which is responsible for 86% of domestic production (Mueller, 2010). The dry grind ethanol process involves grinding corn, producing a slurry, then breaking down starch molecules with alpha amylase in the presence of heat and water. Glucoamylase is added to further break down the starch into glucose so that it can be consumed by yeast and converted into ethanol. A strong correlation between starch content and ethanol yield would be expected; however, Singh and Graeber (2005) found that there was a lack of correlation among final ethanol concentration, starch extractability, and starch content for 18 hybrids of yellow dent corn. The lack of correlation may be due to a number of factors e non- extractable starch is converted into ethanol due to the physical separation (milling), thermal treatment (cooking), enzymatic re- actions (liquefaction and saccharification); other micronutrients present in the corn are required by the yeast during fermentation (Ingledew, 2009); and a certain amount of starch that is resistant to enzymatic hydrolysis is physically extracted during milling but does not ferment to ethanol. Several researchers have noted the chemical composition of the starch, specifically, its amylose to amylopectin ratio, had a significant effect on the efficacy of enzy- matic hydrolysis (Jane, 2009; Ji et al., 2003; Murthy et al., 2011; Sharma et al., 2007). Resistant, or unreacted, starch in corn is highly correlated with amylose levels (Berry, 1986). Yangcheng et al. (2013) reported average starch to ethanol conversion effi- ciency of 93.0% for waxy corn, which has low amylose to amylo- pectin ratio, compared to that of regular corn (88.2%). * Corresponding author. E-mail address: gdanao@illinois.edu (M.-G.C. Danao). Contents lists available at ScienceDirect Journal of Stored Products Research journal homepage: www.elsevier.com/locate/jspr http://dx.doi.org/10.1016/j.jspr.2014.11.006 0022-474X/© 2015 Elsevier Ltd. All rights reserved. Journal of Stored Products Research 61 (2015) 85e89