Tocopherols and Tocotrienols (Vitamin E) – The Lipid Web

Tocopherols and tocotrienols constitute a series of related benzopyranols (or methyl tocols) that are synthesised in plants and other photosynthetic organisms, where they have many important functions. First described in 1922 as a dietary factor essential to prevent fetal reabsorption in rats, it was soon understood that they contained a vitamin (vitamin E) that is essential for innumerable aspects of animal development. Tocopherols are now known to be powerful lipid-soluble antioxidants, but only one isomer, i.e. α-tocopherol, is recognized as having vitamin E activity. In addition, this has regulatory roles in signal transduction and gene expression in animal tissues. Vegetable oils are a major dietary source.

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Kinetic Study of the Quenching Reaction of Singlet Oxygen by Eight Vegetable Oils in Solution

Mukai K, Ohara A, Ito J, Hirata M, Kobayashi E, Nakagawa K, Nagaoka SI

J Oleo Sci. 2019 Jan 1;68(1):21-31. doi: 10.5650/jos.ess18179. Epub 2018 Dec 12.

Abstract

A kinetic study of the reaction of singlet oxygen (1O2) with eight vegetable oils 1-8 containing different concentrations of tocopherols (Tocs) and tocotrienols (Toc-3s) was performed. The second-order rate constants (kQ) for the reaction of 1O2 with vegetable oils 1-8 (rice bran, perilla, rape seed, safflower, grape seed, sesame, extra virgin olive, and olive oils) were measured in ethanol/chloroform/D2O (50:50:1, v/v/v) solution at 35°C using UV-vis spectrophotometry. Furthermore, comparisons of kQ values determined for the above oils 1-8 with the sum of the product {∑kQAO-i [AO-i]/105} of the kQAO-i values obtained for each antioxidant (AO-i) and concentration (in mg/100 g) ([AO-i]/105) of AO-i (Tocs and Toc-3s) contained in the oils 1-8 were performed. The observed kQ values were not reproduced by the kQ values calculated using only the concentrations of the four Tocs and Toc-3s. These results suggest that the contribution of fatty acids contained in the oils 1-8 is also necessary to fully explain the kQ values. Recently, the second-order rate constants (kS) for the reaction of aroxyl radical (ArO・) with the same vegetable oils 1-8 were measured in the same solvent at 25℃ using stopped-flow spectrophotometry (Ref. 23). The kS values obtained could be well explained as the sum of the product {Σ kSAO-i [AO-i]/105} of the kSAO-i and the [AO-i]/105 of AO-i (Tocs and Toc-3s) contained in the vegetable oils.

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