Autoxidation of polyunsaturated triacylglycerols. II. Trilinolenoylglycerol

Abstract The hydroperoxides and secondary products formed from trilinolenoylglycerol autoxidized at 40°C were isolated and characterized to clarify the mechanism of oxidative deterioration of polyunsaturated vegetable oils. The products were purified by high performance liquid chromatography (HPLC) and identified either as intact triacylglycerols spectrophotometrically, or after lipolysis (pancreatic lipase) and capillary gas chromatography and gas chromatography‐mass spectrometry. The products included 9‐, 12‐, 13‐, and 16‐mono‐, bis ‐, tris‐hydroperoxy, 9‐ and 16‐hydroperoxy epidioxy, 9‐ and 16‐hydroperoxy bicycloendoperoxy and 9,12‐, 13,16‐, and 9,16‐dihydroperoxy linolenoylglycerols. The mono‐hydroperoxides and sydroperoxy epidioxides were the only main products initially formed at peroxide values (PV) below 30. Bis ‐ and tris‐hydroperoxides were formed consecutively as minor products from the mono‐hydroperoxides at PV's between 31 and 47. Hydroperoxy bicycloendoperoxides and monodihydroperoxides were also formed as minor secondary products at PV's above 75. HPLC analyses show a small preference for the formation of 16‐hydroperoxides on the 1(3)‐position over the 2‐position of trilinolenoylglycerol. However, there was no selectivity for the formation of the 9‐, 12‐ and 13‐hydroperoxides and for the hydroperoxy epidioxides between the 1(3)‐ and the 2‐positions in trilinolenoylglycerol. Mono‐hydroperoxides and hydroperoxy epidioxides of linolenate triacylglycerols may be important precursors of volatile compounds contributing to oxidative deterioration of vegetable oils.