Inhibited autoxidation linoleic acid

The effects of flavonoids on in vitro and in vivo lipid peroxidation have been thoroughly studied [123]. Torel et al. [124] found that the inhibitory effects of flavonoids on autoxidation of linoleic acid increased in the order fustin < catechin < quercetin < rutin = luteolin < kaempferol < morin. Robak and Gryglewski [109] determined /50 values for the inhibition of ascorbate-stimulated lipid peroxidation of boiled rat liver microsomes. All the flavonoids studied were very effective inhibitors of lipid peroxidation in model system, with I50 values changing from 1.4 pmol l-1 for myricetin to 71.9 pmol I 1 for rutin. However, as seen below, these /50 values differed significantly from those determined in other in vitro systems. Terao et al. [125] described the protective effect of epicatechin, epicatechin gallate, and quercetin on lipid peroxidation of phospholipid bilayers. 

In our system, the rate of autoxidation of linoleic acid, is essentially zero in the absence of the initiator. (Notice the flatness of the oxygen trace at the far left in Figure 1 before the initiator is added.) Our system produces classical inhibition kinetics. Initiator can be injected into the bulk aqueous phase and the autoxidation starts instantly. When the vitamin E is injected, it also produces an instantaneous effect. The rate of autoxidation before the vitamin E is added, Roxi> is also observed after all the... 

During the inhibited self-initiated autoxidation of methyl linoleate by a-Toc in solution, Niki and coworkers made the interesting observation that a-Toc acts as an antioxidant at low concentrations, but high concentrations (up to 18.3 mM) actually increased hydroperoxide formation due to a pro-oxidant effect. The pro-oxidant effect of a-Toc was observed earlier by Cillard and coworkers in aqueous micellar systems and they found that the presence of co-antioxidants such as cysteine, BHT, hydroquinone or ascor-byl palmitate inverted the reaction into antioxidant activity, apparently by reduction of a-To" to a-Toc . Liu and coworkers ° found that a mixture of linoleic acid and linoleate hydroperoxides and a-Toc in SDS micelles exhibited oxygen uptake after the addition of a-Toc. The typical ESR spectrum of the a-To" radical was observed from the mixture. They attributed the rapid oxidation to decomposition of linoleate hydroperoxides, resulting in the formation of linoleate oxy radicals which initiated reactions on the lipid in the high concentration of the micellar micro-environment. Niki and coworkers reported pro-oxidant activity of a-Toc when it was added with metal ions, Fe3+25i Qj. jjj (jjg oxidation of phosphatidyl choline liposomes. a-Toc was found... 

Walnuts are the seeds of Juglans regia L. (Juglandaceae) and are highly nutritious. They are rich in oil that is composed of unsaturated fatty acids that are susceptible to oxidation, such as linoleic acid and oleic acid. Despite the low content of a-tocopherol (an antioxidant) in walnuts, as compared to other types of nut,"" walnuts are fairly stable when preserved this implies that an unknown antioxidant(s) within walnuts inhibits lipid autoxidation. Indeed, an aqueous ethanol extract from commercially available walnuts showed marked superoxide dismutase (SOD)-like... 

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