The polyunsaturated fatty acids (PUFA) linoleic acid and α-linolenic acid in plant oils are precursors for a multitude of fatty acid oxidation products, so-called oxylipins. The oxylipin pattern of an oil is a complex picture of both, the enzymatic activity of fatty acid oxidizing enzymes in the oil seed and (non-enzymatic) oxidation during oil production, storage and processing. The presence and concentrations of specific oxylipins thus depend on the origin of an oil and the processing conditions and may allow to draw conclusions about the quality and authenticity of oils.

Screening of different plant oil revealed that the widely known autoxidation- and lipoxygenase-derived products occurred in relevant concentration; however, in rapeseed and flaxseed oil, other oxylipins dominated which were so far almost unknown in edible oils. A deeper insight in the oxylipin patterns of oils by non-targeted LC-HRMS screening unveiled several new, in part highly abundant hydroxy-PUFA and a new possible formation pathway of oxylipins in seeds.

Processing of plant oils such as storage, strong heating or refining had a strong impact on oxylipin patterns. Storage of freshly pressed oils revealed a rather low lipid peroxidation in flaxseed oil despite the high PUFA content, while autoxidation was massive in rapeseed oil. High temperatures such as during deep-frying promote the formation of E,E-hydro(per)oxy-PUFA as well as of trans-epoxy-PUFA, while the refining process caused a distinct hydrolysis of epoxy-PUFA to the corresponding dihydroxy-form.

Thus, the oxylipin pattern of oils were found to be specific for the oil source as well as the pressing and processing conditions and might help to answer urgent questions of food fraud.