Composition and oxidative stability of crude oil extracts of corn germ and distillers grains

Abstract

The fatty acid composition, Acid Value, and the content and composition of tocopherols, tocotrienols, carotenoids, phytosterols, and steryl ferulates were determined in corn germ oil and four post-fermentation corn oils from the ethanol dry grind process. The oxidative stability index at 110 °C was determined for the five oils, and four oils were compared for their stability during storage at 40 °C as determined by peroxide value and hexanal content. The fatty acid composition of all five oils was typical for corn oil. The Acid Value (and percentage of free fatty acids) was highest (28.3 mg KOH/g oil) in corn oil extracted centrifugally from a conventional dry grind ethanol processing facility and for oil extracted, using hexane, from distillers dried grains with solubles (DDGS) from a raw starch ethanol processing facility (20.8 mg KOH/g oil). Acid Value was lowest in two oils extracted centrifugally from thin stillage in a raw starch ethanol facility (5.7 and 6.9 mg KOH/g oil). Tocopherols were highest in corn germ oil (∼1400 μg/g), but tocotrienols, phytosterols, steryl ferulates, and carotenoids were higher in all of the post-fermentation corn oils. Hexane extracted oil from DDGS was the most oxidatively stable as evaluated by OSI and storage test at 40 °C, followed by centrifugally extracted thin stillage oil from the raw starch ethanol process, and centrifugally extracted thin stillage oil from the conventional dry grind ethanol process. Corn germ oil was the least oxidatively stable. When stored at room temperature, the peroxide value of centrifugally extracted thin stillage oil from the raw starch ethanol process did not significantly increase until after six weeks of storage, and was less than 2.0 mequiv. peroxide/kg oil after three months of storage. These results indicate that post-fermentation corn oils have higher content of valuable functional lipids than corn germ oil. Some of these functional lipids have antioxidant activity which increases the oxidative stability of the post-fermentation oils.