High pressure liquid chromatography of autoxidized lipids: II. Hydroperoxy‐cyclic peroxides and other secondary products from methyl linolenate

Abstract

Abstract A previous study of autoxidation products by high pressure liquid chromatography (HPLC) of methyl oleate and linoleate was extended to methyl linolenate. Autoxidized methyl linolenate was fractionated by HPLC either after reduction to allylic alcohols on a reverse phase system, or directly on a micro silica column. Isolated oxidation products were characterized by thin layer and gas liquid chromatography and by ultraviolet, infrared, nuclear magnetic resonance and mass spectrometry. Secondary products from the autoxidation mixtures (containing 3.5–8.5% monohydroperoxides) included epoxy unsaturated compounds (0.2–0.3%), hydroxy or hydroperoxy‐cyclic peroxides (3.8–7.7%), epoxy‐hydroxy dienes (<0.1%), dihydroxy or dihydroperoxides with conjugated diene‐triene and conjugated triene systems (0.9–2.9%). Cyclization of the 12‐ and 13‐hydroperoxides of linolenate would account for their lower relative concentration than the 9‐ and 16‐hydroperoxides. Dihydroperoxides may be derived from the 9‐ and 16‐linolenate hydroperoxides. Cyclic peroxides and dihydroperoxides are suggested as important flavor precursors in oxidized fats.