α-Tocopherol-dependent occurrence of linoleic acid 11-hydroperoxide in triacylglycerol: what it signifies in food oxidation and quality

Although α-tocopherol (α-Toc) suppresses lipid oxidation overall, during linoleic acid oxidation it can paradoxically facilitate the formation of a unique hydroperoxide isomer bearing a hydroperoxyl group at the C11-position. Whether this isomer occurs in real foods and what it signifies in food oxidation and quality have remained unknown. Here, we initially applied a newly developed isomer-selective liquid chromatography–tandem mass spectrometry method to intact triacylglycerol autoxidized in the presence of α-Toc and identified the isomer within the triacylglycerol molecule. Interestingly, its formation coincided with the emergence of the pro-oxidant properties of excess α-Toc, pointing to its potential as an indicator of pro-oxidative conditions. The isomer was scarcely detected in commercial oils, whereas the external addition of excess α-Toc enhanced its formation, suggesting that such pro-oxidative conditions were not prevalent in the examined oils. As an additional perspective on its decomposition, gas chromatography–mass spectrometry analysis revealed a range of volatiles, with heptanal and heptanoic acid as key compounds whose generation has long remained uncharacterized in linoleic acid oxidation. Together, these findings position the isomer as both a candidate marker of pro-oxidative conditions in foods and a possible contributor to food flavor, suggesting its significance for guiding food quality improvement.