Formation of Epoxy Fatty Acids in Triacylglycerol Standards during Heating.

Epoxy fatty acid formation during heating was estimated using triolein (OOO) and trilinolein (LLL). Epoxy octadecanoic acids were found in heated OOO, while epoxy octadecenoic acids were found in heated LLL. The content of epoxy fatty acids increased with heating time, and trans-epoxy fatty acids were formed significantly more than cis-epoxy fatty acids. A comparison between OOO and LLL indicated that epoxy fatty acid formation was higher in the OOO than that in the LLL. Heating tests in the presence of α- tocopherol suggested that the formation of epoxy fatty acids could be suppressed by antioxidants.

Comparison of the Catabolic Rates of Linoleic and Oleic Acid Hydroperoxides Using 13CO2 Expired from Mice.

Unsaturated fatty acids, such as oleic and linoleic acids, are easily oxidized by exposure to temperature and light in the presence of air to form unsaturated fatty acid hydroperoxides as primary oxidation products. However, the catabolic rates of unsaturated fatty acid hydroperoxides in the human body remain unknown. In this study, ethyl esters of 13C-labeled linoleic acid (*C18:2-EE) and oleic acid (*C18:1-EE) and their hydroperoxides (*C18:2-EE-OOH and *C18:1-EE-OOH, respectively) prepared by the photo-oxidation of *C18:2-EE and *C18:1-EE, respectively, were administered to mice and their catabolic rates were determined by measuring the expired 13CO2 levels. *C18:2-EE-OOH and *C18:1-EE-OOH were ß-oxidized faster than *C18:2-EE and *C18:1-EE, respectively. Notably, rapid ß-oxidation of *C18:2-EE-OOH and *C18:1-EE-OOH was similar to that of medium-chain fatty acids, such as octanoic acid. Then, degradation products of C18:2-EE-OOH and C18:1-EE-OOH were analyzed under gastric conditions by gas chromatography/mass spectrometry. Major decomposition products of C18:2-EE-OOH and C18:1-EE-OOH were medium-chain compounds, such as octanoic acid ethyl ester, 9-oxo-nonanoic acid ethyl ester, and 10-oxo-8-decenoic acid ethyl esters, indicating that C18:2-EE-OOH and C18:1-EE-OOH isomers formed during photo-oxidation were decomposed under acidic conditions. These findings support previous reports that dietary lipid hydroperoxides are not absorbed into the intestine as lipid hydroperoxides but as degradation products. This is the first study to suggest that dietary lipid hydroperoxides decompose during gastric digestion to form medium-chain compounds that are directly absorbed into the liver via the portal vein and rapidly catabolized via ß-oxidation.