Oxylipin formation in commercial vegetable oils: A novel approach to monitoring oxidative stability and shelf-life indicators

Oxylipins are bioactive lipid molecules produced from oxygenation of polyunsaturated fatty acids and play key roles in inflammation and immunity. While they are typically generated through enzymatic pathways in biological tissues, non-enzymatic oxidation of linoleic acid(LA) and alpha-linolenic acid(ALA) in vegetable oils also leads to the formation of oxylipins.

In this study, we investigated commercial corn and soybean oils stored at 55°C, monitoring lipid hydroperoxide formation by UV-VIS spectroscopy, hexanal and propanal levels by GC/FID, tocopherol degradation by HPLC, and oxylipin generation by LC/MS. The oils were selected for their comparable LA content (~54%), with soybean oil containing an additional 5% ALA, which promotes formation of additional ALA-derived oxylipins.

LC/MS analysis revealed elevated concentrations of LA-derived oxylipins, including 9-OXO-ODE, 13-OXO-ODE (ketones), 9-HODE, 13-HODE (alcohols), and 9,10-EpOME, 12,13-EpOME (epoxides) following storage of both oils. Additionally, soybean oils showed increases in ALA-derived oxylipins such as 9-OXO-OTrE, 13-OXO-OTrE (ketones), 9-HOTrE, 13-HOTrE (alcohols), and 9,10-EpODE, 12,13-EpODE (epoxides). The formation pathways of these compounds differ: alcohols form through tocopherol-mediated free radical scavenging, while ketones result from hydrogen abstraction from radicals.

Our findings revealed that oxylipin concentrations increased consistently with prolonged oxidation, with formation occurring earlier than lag phases of hexanal and propanal. This supports the idea that oxylipins are generated prior to β-scission reactions that lead to rancid aldehyde production. Hydrolyzed oils exhibited significantly higher oxylipin levels compared to non-hydrolyzed oils, suggesting these compounds are embedded within triacylglycerol structures. No fatty acid diols were detected, as they require enzymatic activity, absent in commercial oils.

These findings propose that monitoring oxylipin levels during the storage of commercial bulk oils could serve as an innovative approach to assessing the extent of oxidation. Furthermore, oxylipins may act as early indicators of shelf-life degradation, as they are generated prior to the emergence of rancid secondary oxidation products.