Migration of Highly Unsaturated Fatty Acid Methyl Ester Peroxyl Radicals from Lipid Core to Aqueous Surface Lowers the Oxidizability of Highly Unsaturated Lipids in Aqueous Micelles

摘要

The rates of aerobic oxidation of polyunsaturated fatty acid methyl esters (PUFA) such as lino1eate, alpha-linolenate, gamma-linolenate, arachidonate, eicosapentaenoate and docosahexaenoate were compared in homogeneous chlorobenzene solution and Triton X-100 aqueous micelles at 37 deg. C. The rate of disappearance of PUFA increased in homogeneous solution but decreased in aqueous micelles with an increasing number of unsaturation. Peroxyl radicals derived from highly unsaturated fatty acid methyl esters such as eicosapentaenoate and docosahexaenoate are considered to be more polar than those from linoleate because the ratio of oxygen uptake to substrate consumption increased from 1 to 3.4 with an increasing number of unsaturation. In the oxidation of a 1:1 mixture of linoIeate and other PUFA in aqueous micelles, the rates of disappearance PUFA and linoleate, (-d[PUFA]/dt)/(-d[1inoleate]/dt) increased while the total rates of disappearance of substrates, -dllinoleate +PUFA]/dt, decreased with an increasing number of unsaturation, indicating polar peroxyl radicals from highly unsaturated lipids not to propagate the chain oxidation. The rate of disappearance of butyl hydroxytoluene situated in the core of micelles decreased with an increasing number of unsaturation during the oxidation of PUFA. All of the data support the idea that polar peroxyl radicals from highly unsaturated fatty acid methyl ester migrate from the core to the micelle surface with consequent reduction in rates of oxidation by enhancing the rates of termination and reducing the rates of propagation.