Occurrence and formation of oxidized fatty acids in edible oils and their use as novel parameters to evaluate oil quality and authenticity

eng: Plant oils consist of a large amount of oleic acid, linoleic acid (LA) and -linolenic acid (ALA). They are precursors for a multitude of fatty acid oxidation products. Their pattern in plant oils is a complex picture of the 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 depends on the oil source and the processing conditions. In order to address this hypothesis, analytical methods for quantification of oxylipins and fatty acids using liquid chromatography-mass spectrometry (LC-MS) were developed. Analysis of oxylipins in freshly pressed virgin flaxseed, rapeseed and sunflower oil showed that the widely known autoxidation- and lipoxygenase-derived products occurred in relevant concentrations; however, in rapeseed and flaxseed oil, 15-OH-LA and 15(16)-epoxy-ALA - being so far almost unknown in plant oils - dominate with concentrations up to 0.1 g/100 g. A non-targeted LC-MS screening of oils unveiled several new hydroxy fatty acids, and the involvement of fatty acid desaturase 3 in oxylipin formation. Their concentrations were specific for the oil source and the pressing conditions and thus might be a new potential marker to evaluate authenticity. Storage of plant oils revealed a rather low lipid peroxidation in flaxseed oil despite the high polyunsaturated fatty acid (PUFA) content, while in rapeseed oil, the increase in E,Z-hydro(pero)xy-PUFA and in the peroxide value was massive. High temperatures such as during deep-frying promote the formation of E,E-hydro(pero)xy-LA as well as of trans-epoxy fatty acids. Refined oils can be distinguished from virgin oils by low E,Z-hydroxy- and cis-epoxy-PUFA as well as high dihydroxy-PUFA levels. Thus, the oxylipin pattern can be used to assess high temperature application which not ++

eng: only interesting for the evaluation of frying oil quality but also of the authenticity of virgin oils.