Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2010
Publication Date: 9/18/2010
Citation: Moreau, R.A., Liu, K., Moser, J.K., Singh, V. 2011. Changes in lipid composition during dry grind ethanol processing of corn. Journal of the American Oil Chemists' Society. 88:435-442.
Interpretive Summary: Most of the approximately 11 billion gallons of ethanol produced in the US in 2009 was made via the dry grind ethanol process, where ground corn is fermented and the major co-product is an animal feed called distillers dried grains with solubles. These studies demonstrated that the 10-15% free fatty acids known to occur in distillers dried grains with solubles originate in both the particulate (distillers grains) and soluble (thin stillage) centrifugation fractions of the dry grind ethanol process. This study concluded that yeast sterols and other yeast lipids were not detected at any stage during the dry grind ethanol process. This report also confirms that most of the potentially valuable corn phytosterols, tocopherols, and tocotrienols are retained during the dry grind ethanol process and serve as antioxidants in the corn oil or they could be removed and sold for separate applications.
Technical Abstract: During the dry grind ethanol process, ground corn is fermented and the major co-product is a feed called distillers dried grains with solubles (DDGS). This study investigated the changes that occur in the composition of corn oil during the dry grind ethanol process. In the first part of this study, samples of distillers dried grains (DDG), thin stillage, distiller solubles (also called syrup or concentrated thin stillage), and DDGS were obtained from 7 dry grind ethanol plants. The levels of deleterious free fatty acids were high (>7%) and those of valuable total phytosterols were also high in all fractions (>2%). In the second part of this study changes in fatty acid composition and contents of crude oil, phytosterols, tocopherols and tocotrienols were quantitatively analyzed in nine dry grind process fractions from three commercial ethanol plants. Fatty acid and phytosterol composition remained nearly constant in all nine fractions, although some significant variations in phytosterol composition existed among the fractions. Examination of the tocopherols and tocotrienols revealed that gamma-tocopherol was the most abundant tocol in ground corn but an unknown tocol became the predominant tocol after fermentation and persisted in the remaining processing fractions and in the final DDGS product.