Changes in corn protein content during storage and their relationship with dry grind ethanol production

Authors: RAMCHANDRAN, DIVYA - University Of Illinois; Hojilla-Evangelista, Milagros - Mila; MOOSE, STEPHEN - University Of Illinois; RAUSCH, KENT - University Of Illinois; TUMBLESON, M - University Of Illinois; SINGH, VIJAY - University Of Illinois

Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/3/2018
Publication Date: 5/31/2018
Citation: Ramchandran, D., Hojilla-Evangelista, M.P., Moose, S.P., Rausch, K.D., Tumbleson, M.E., Singh, V. 2018. Changes in corn protein content during storage and their relationship with dry grind ethanol production. Journal of the American Oil Chemists' Society. 95(8):923-932. https://doi.org/10.1002/aocs.12070.
DOI: https://doi.org/10.1002/aocs.12070

Interpretive Summary: Seasonal variation in ethanol yields causes enormous economic losses for dry grind ethanol plants. In this research, we determined the influence of corn long-term storage conditions and soluble protein fractions on the inconsistency of ethanol yields from the dry grind process. There is little published information on these factors in relation to variations in dry grind ethanol yields. For this work, we stored corn for one year at ambient and refrigerated conditions. We then took corn samples every four weeks, from which we produced ethanol using a lab-scale dry grind method and measured the ethanol yields. We found that temperature had no major effect on ethanol yields based on similar results for both storage conditions. We also evaluated the effects of postharvest storage on protein quality (soluble protein contents) and their relationship to ethanol concentrations. We sampled stored corn at periodic intervals, extracted separately the four major soluble protein fractions, and calculated their amounts. We observed that water-soluble albumin decreased by half and the ethanol-soluble prolamin (zein) increased by 43% in corn stored from 2 to 10 months. Our calculations also show that ethanol yields measured at 24 hours increased with prolamin content, but decreased with higher amounts of alkali-soluble glutelin. This result indicated that zein and glutelin could influence ethanol yields and their amounts in stored corn may be used as indicators of the extent of variability in ethanol concentration.

Technical Abstract: Changes in corn grain during storage can cause variations in dry grind ethanol yields. The first objective of this study was to determine the effects of postharvest storage on dry grind ethanol concentrations. Ethanol concentrations for corn stored under ambient and refrigerated conditions were measured every 4 weeks for 1 year. Ethanol concentrations had a decreasing trend for corn stored from 0 to 16 weeks and an increasing trend from week 16 to 24. These trends were similar for corn stored at refrigerated and ambient conditions. The effects of postharvest storage on soluble protein content and their relationship with ethanol concentration were also evaluated. Stored corn was sampled at weeks 0, 8, 16, 24, and 40. Soluble proteins were extracted using a sequential extraction procedure and expressed with respect to the total crude protein of corn, and the total values were not affected by storage temperature (ranging from -7 to 23 deg. C). During 8 to 40 week storage at ambient and refrigerated temperature, the albumin content of corn decreased by 43.6% and 48.5% while the prolamin content increased by 37.9% and 43.0%, respectively. Ethanol yield at 72 hours of fermentation had no correlation with soluble protein content; however, ethanol yield at 24 hours correlated negatively with glutelin (r = -0.76) and positively with prolamin (r = +0.74) contents.