Variations in phytochemical content and composition in distillers corn oil from 30 U.S. ethanol plants

Authors: Moser, Jill; Hwang, Hong-Sik; BYARS, JEFFREY; VAUGHN, STEVEN; AURANDT-PILGRIM, JENNIFER - MARQUIS INCORPORATED; KERN, OLIVIA - TRUCENT

Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/6/2022
Publication Date: 12/22/2022
Citation: Moser, J.K., Hwang, H., Byars, J.A., Vaughn, S.F., Aurandt-Pilgrim, J., Kern, O. 2022. Variations in phytochemical content and composition in distillers corn oil from 30 U.S. ethanol plants. Industrial Crops and Products. 193. Article 116108. https://doi.org/10.1016/j.indcrop.2022.116108.
DOI: https://doi.org/10.1016/j.indcrop.2022.116108

Interpretive Summary: Biofuels including bioethanol and biodiesel are used as alternatives to petroleum-based fuels. They are highly valued because they are renewable, can reduce greenhouse gas emissions, and reduce dependence on imported petroleum-based fuels. Carbon dioxide, distillers dried grains with solubles (DDGS) and distillers corn oil (DCO), which is extracted from the corn after the starches have been fermented into ethanol, are the main coproducts of bioethanol. Finding value-added uses for these coproducts may help to improve the sustainability and profitibability of this industry. DCO is currently used both as a feed additive in animal production, and as a feedstock for biodiesel. However, DCO contains valuable phytochemical lipids that could be used as food or industrial antioxidants and food supplements or ingredients, including tocopherols, tocotrienols, phenolic compounds, carotenoids, and phytosterols. However, not much is known about how the content of these components varies among different DCO sources. In addition, there was little previously known about the oxidative stability and presence of phenolic compounds in DCO. If these phytochemicals could be separated from DCO they could represent an additional valuable coproduct of ethanol, while the remaining oil could still be used for feed and fuel. In this study we analyzed these components in DCO from 30 ethanol plants throughout the United States to determine the average content and composition of fatty acids and lipid phytochemicals. We found that the fatty acid composition of the DCO was very similar across the thirty samples. There was higher variability among tocopherols, tocotrienols, carotenoids, but the average content of these components was still relatively high. DCO was especially rich in phytosterols. In addition, the DCO samples had higher oxidative stability compared to commercial corn oil. DCO from the dry grind ethanol process may be a sustainable feedstock for bioactive lipids for foods, dietary supplements, and industrial use.

Technical Abstract: Distillers corn oil (DCO) is a coproduct of bioethanol production. In the dry-grind ethanol process, DCO is extracted post-fermentation by the centrifugal separation of oil from the aqueous thin-stillage or whole stillage, and is a valuable coproduct currently used in animal production as a feed additive or as a feedstock for biodiesel production. This study analyzes the variability in the fatty acid profiles and the content and composition of bioactive components in DCO for thirty bioethanol plants in the United States. The fatty acid profiles of the DCO samples were similar to commercial corn oil with an average of 55.8% linoleic acid (C18:2), 28.0% oleic (C18:1), 11.7% palmitic (C16:0), 1.5 % stearic (C18:0), and 1.3 % linolenic (C18:3). There was very low variability in fatty acid composition among the samples, with all major fatty acids having = 3.5% coefficient of variation (CV). Average tocopherols were 1022.7 mg kg-1 comprised of gamma-, delta-, and alpha-tocopherols, with CV’s ranging from 20.8%-57.8%. The mean gamma- and delta-tocotrienols contents were 347.6 mg kg-1, with CV’s ranging from 18.8-71.7%. Carotenoids comprised of lutein, zeaxanthin, beta-cryptoxanthin, and alpha- and beta-carotenes were 239 mg kg-1, with CVs ranging from 19.7-39.6%. Total phytosterols were 19,360 mg kg-1, while a class of phytosterols, ferulate phytosterol esters, were 4626 mg kg-1. There was lower variation in phytosterol content, with CVs ranging from 9-13%. Methanol extracts from DCO contained 242.0 mg total phenolics (gallic acid equivalents) kg-1, with a 27.9 % CV. The antioxidant activity of methanol extracts, measured by diphenyl picrylhydrazyl radical scavenging activity, was 3.83 µmol Trolox equivalents kg-1 (CV = 19.9 %). The oils had an average oxidative stability index (OSI) at 110 °C of 11.8 hr. The OSI of the oils were significantly correlated with lutein, delta-tocopherol, and phytosterols including stigmasterol and campesterol. The results indicate that there was a higher amount of variation between plants in the content and composition of tocopherols, carotenoids, and total phenolics than for fatty acids composition and phytosterols. However, DCO from the dry grind ethanol process may be a sustainable feedstock for bioactive lipids for foods, dietary supplements, and industrial use.