Formation of triacylglycerol core aldehydes during rapid oxidation of corn and sunflower oils with tert-butyl hydroperoxide/Fe2+.

Abstract

The lipid ester core aldehydes formed during a rapid oxidation (7.8 M tert-butyl hydroperoxide, 90 min at 37 degrees C) of the triacylglycerols of purified corn and sunflower oils were isolated as dinitrophenylhydrazones by preparative thin-layer chromatography and identified by reversed-phase high-performance liquid chromatography with on-line electrospray ionization mass spectrometry and by reference to standards. A total of 113 species of triacylglycerol core aldehydes were specifically identified, accounting for 32-53% of the 2,4-dinitrophenylhydrazine (DNPH)-reactive material of high molecular weight representing 25-33% of the total oxidation products. The major core aldehyde species (50-60% of total triacylglycerol core aldehydes) were the mono(9-oxo)nonanoyl- and mono(12-oxo)-9,10-epoxy dodecenoyl- or (12-oxo)-9-hydroxy-10,11-dodecenoyl-diacylglycerols. A significant proportion of the total (9-oxo)nonanoyl and epoxidized (12-oxo)-9,10-dodecenoyl core aldehydes was found in complex combinations with hydroperoxy or hydroxy fatty acyl groups (6-10% of total triacylglycerol core aldehydes). Identified were also di(9-oxo)nonanoylmonoacylglycerols (0.5% of total) and tri(9-oxo)nonanoylglycerols (trace). The identification of the oxoacylglycerols was consistent with the products anticipated from tert-butyl hydroperoxide oxidation of the major species of corn and sunflower oil triacylglycerols (mainly linoleoyl esters). However, the anticipated (13-oxo)-9,11-tridecadienoyl aldehyde-containing acylglycerols were absent because of further oxidation of the dienoic core aldehyde. A significant proportion of the unsaturated triacylglycerol core aldehydes contained tert-butyl groups linked to the unsaturated fatty chains via peroxide bridges (2-9%). The study demonstrates that rapid peroxidation with tert-butyl hydroperoxide constitutes an effective method for enriching natural oils and fats in triacylglycerol core aldehydes for biochemical and metabolic testing.