Accumulation of Oxygenated Fatty Acids in Oat Lipids During Storage

Authors: Doehlert, Douglas; ANGELIKOUSIS, STEVEN - North Dakota State University; Vick, Brady

Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/19/2010
Publication Date: 12/1/2010
Citation: Doehlert, D.C., Angelikousis, S., Vick, B.A. 2010. Accumulation of Oxygenated Fatty Acids in Oat Lipids During Storage. Cereal Chemistry. 87(6):532–537.

Interpretive Summary: When food products made from oats are stored, their fats (also called lipids) can react with oxygen to produce compounds that detract from the flavor of the oats. In this study, we have identified the chemical compounds produced in oats when their fats react with oxygen and we show how treatments, like steaming the grain before processing, can prevent the production of these oxygenated products. Most of oxidation of fats appears to be catalyzed by enzymes in the oats, called lipoxygenase. Lipoxygenase along with other enzymes called lipoperoxygenase insert oxygen into the fat structure and convert it into compounds called hydroxy- and epoxy- fatty acids. These compounds have very bitter taste and can make oat products unpalatable. Steaming of the grain inactivates these enzymes. Our results indicate that these treatments prevent the accumulation of these oxygenated fatty acids, whereas untreated oats will accumulate high levels of these unpalatable compounds. Our results indicate the importance of enzyme inactivation prior to storage of processed oat products.

Technical Abstract: Oxygenated fatty acids were identified in oat grain by gas chromatography - mass spectrometry. We hypothesized that most of these were the results of lipoxygenase activity. This hypothesis was tested by measuring concentrations of these compounds after hydrothermal treatments and storage of oat groats or oat flour for 22 weeks at 37o C and 65% relative humidity. Steam treatments inactivated lipases, whereas roasting at 106o C did not. Free fatty acids accumulated quickly in untreated or roasted flour, but not in steamed flour or groats. A total of six hydroxy and epoxy fatty acids were identified. Oxidized fatty acids were found in both esterified lipids and free fatty acids, indicating that lipase action was not necessary for lipid oxidation. More oxidation products were found in flour than in groats, and less were found in the steamed treatments. Lipoperoxygenase appeared to be involved in the formation of oxidation products, although non-enzymatic mechanisms may also operate. Hydroxy-fatty acids are associated with strongly bitter flavors and are undesirable. Results indicate the importance of enzyme inactivation prior to storage of processed oat products.