Oil polyunsaturated fatty acid composition but not tocopherol levels determine oxylipin formation in plant and algae oils during pan-frying

The oxidation of linoleic acid (LA) and α-linolenic acid (ALA) in plant oils results in primary oxidation products known as oxylipins. It is not known whether the mechanisms of oxidation are driven primarily by oil polyunsaturated fatty acid (PUFA) composition (i.e., more double bonds resulting in more rapid oxidation) or antioxidant (tocopherol) content. The present study addressed this unknown by measuring the effects of pan-frying on LA and ALA-derived oxylipin concentrations in plant and algae oils with different baseline fatty acid and tocopherol concentrations. Oxylipins, free fatty acids and tocopherols were quantified in algae, olive, corn, canola, and soybean oils before and after 30 minutes of pan-frying. Fatty acid epoxides and hydroxides of LA or ALA were significantly elevated after pan-frying, whereas fatty acid diols were reduced. The level of change in oxylipins was lower in low-PUFA algae and extra virgin olive oils compared to soybean, canola and corn oils (high in PUFAs). Tocopherols decreased significantly after 30 minutes of pan-frying, particularly in oils with low PUFA composition. Minor changes were observed in free fatty acids. Our findings demonstrate that oil PUFA composition is a greater determinant of lipid oxidation than tocopherol content, and that PUFAs in high LA or ALA oils may spare tocopherol oxidation by acting as free radical scavengers.