Accumulation of Oxygenated Fatty Acids in Oat Lipids During Storage

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 37 degrees C and 65% relative humidity. Steam treatments inactivated lipases, whereas roasting at 106 degrees 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 nonenzymatic mechanisms may also operate. Hydroxy-fatty acids are associated with strongly bitter flavors and are undesirable. Results indicate the importance of enzyme inactivation before storage of processed oat products.