Effects of α‐ and γ‐tocopherols on formation of hydroperoxides and two decomposition products from methyl linoleate

Abstract The antioxidant effects of α‐and γ‐tocopherols (at 0, 10, 100, 500, and 1000 ppm) were evaluated in a model system based on the autoxidation of methyl linoleate in bulk for 4 d at 40°C. Samples were collected every 24 h and analyzed for the 9 cis,trans , 9 trans,trans , 13 cis,trans , and 13 trans,trans isomers of hydroperoxide, hydroxy, and ketodiene oxidation products by high‐performance liquid chromatography. Results showed that both α‐ and γ‐tocopherols are effective hydrogen donors as evidenced by their abilities to inhibit the formation of hydroperoxides, hydroxy compounds, and ketodienes and the cis,trans to trans,trans isomerization of hydroperoxides. Compared with γ‐tocopherol, α‐tocopherol was a more efficient antioxidant at very low concentrations (10 ppm) but a less efficient antioxidant at the high concentrations (100–1000 ppm). This paradoxical behavior is explained on the basis of differences in ease of hydrogen donation between the two tocopherol homologs. Although α‐tocopherol shows some loss of efficiency with increasing concentration, it is not a prooxidant when compared to the control void of antioxidants.