Autoxidation of polyunsaturated triacylglycerols. I. Trilinoleoylglycerol

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Abstract
The hydroperoxides and secondary products formed from trilinoleoylglycerol autoxidized at 40°C were isolated and characterized to clarify their contribution to oxidative deterioration of vegetable oils. The products were purified by high performance liquid chromatography (HPLC) and identified, as intact triacylglycerols, by ultraviolet, infrared,1H NMR and13C NMR analyses, and after derivatization by lipolysis, gas chromatography, and gas chromatography‐mass spectrometry. The main, primary products included mono‐,bis‐ and tris‐9‐hydroperoxy‐trans‐10,cit‐12‐; 9‐hydroperoxy‐trans‐10,trans‐12; 13‐hydroperoxy‐cis‐9,trans‐11; and 13‐hydroperoxy‐trans‐9,trans‐11‐linolenoyl glycerols. The structures of the minor secondary products analyzed after derivatization were consistent with known oxidative degradation products of linoleate hydroperoxides. HPLC analyses showed that thebis‐ and tris‐hydroperoxides were formed from the mono‐hydroperoxides during autoxidation at peroxide values above 18 and 28 meq/kg. Studies on the further oxidation of the mono‐hydroperoxides support a mechanism for the consucutive formation ofbis‐ and tris‐hydroperoxides from the monohydroperoxides. HPLC analyses showed that no preferential oxidation occurred between the 1(3)‐ and 2‐triglyceride positions. Hydroperoxides of linoleate triacylglycerols may be important precursors of volatile compounds contributing to off‐flavors of vegetable oils.