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Methyl linoleate was allowed to autoxidize in bulk phase at 50 C in the presence of either synthetic phospholipids consisting of saturated fatty acids or egg yolk phospholipids to estimate the effect of base group and fatty acid moiety of phospholipids on oil autoxidation. Dipalmitoyl phosphatidylcholine (DPPC) and dipalmitoyl phosphatidylethanolamine (DPPE) exhibited poor antioxidant activity at 50 C and showed no synergistic effect with α‐tocopherol. The addition of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) of egg yolk accelerated the oxidation of methyl linoleate. However, egg yolk PC and PE collected at various stages of heating at 180 C inhibited hydroperoxide formation at the initial stage of oxidation. This effect could be attributed to the browning products formed during heating reaction. Thus, browning color products formed from unsaturated phospholipids at high temperatures may influence oil stability, although the base group of phospholipids did not exert any significant effect.

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Abstractα‐Tocopherol at high concentration (1.25×10−4M) exhibited a prooxidant effect during autoxidation of linolenic and arachidonic acids. This prooxidant activity involved a significant increase of the conjugated diene level, especially with linolenic acid. High performance liquid chromatographic evaluation of malondialdehyde, a by‐product of the hydroperoxides of polyunsaturated fatty acids, showed that malondialdehyde was not increased during prooxidant effect ofα‐tocopherol. Thus, malondialdehyde does not seem to be a good indicator for the manifestation of the prooxidant activity ofα‐tocopherol.