Volatile Decomposition Products in the Air Oxidation of Triolein and Trilinolein

Purified triolein (TO) and trilinolein (TL) were oxidized by introducing oxygen at 75°C into the same apparatus as employed previously. In each oxidized sample, volatile decomposition products, especially aldehydes (as the origin of rancid odor), were identified by gas chromatography mass spectrometry, comparing with the products from the corresponding fatty acid methyl-ester.It was observed that heptane and octane as hydrocarbons, 1-heptanol and 1-octanol as alcohols, and heptanal, octanal, nonanal, decanal, 2-decenal and 2-undecenal as aldehydes were formed from TO, while pentane as a hydrocarbon and hexanal, heptanal, 2-heptenal, 2-octenal and 2, 4-decadienal as aldehydes were obtained from TL. The precursors of those products, the monohydroperoxides (MHP), and cleavage positions were discussed in comparison with those of methyl-esters. The formation mechanism of the above products could be explained except for heptanal from TO and 2-heptenal from TL (these were assumed to be secondary oxidation products). Further, 3-nonenal (or 2-nonenal), which was expected to be formed from TL, was not found. In the oxidation of TL, formation of 11-MHP was found in addition to 9-MHP and 13-MHP.The relative percentages of peak area were calculated from a gas chromatogram of volatiles derived from TO, and aldehydes accounted for about 67% of the area. The odor of octanal was the strongest. In the oxidation of TL, 2, 4-decadienal accounted for 42% of the total area, and the odor of hexanal was the strongest at each stage of oxidation.