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

A kinetic study of the reaction of singlet oxygen (O) with eight vegetable oils 1-8 containing different concentrations of tocopherols (Tocs) and tocotrienols (Toc-3s) was performed. The second-order rate constants (k) for the reaction of O 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/DO (50:50:1, v/v/v) solution at 35°C using UV-vis spectrophotometry. Furthermore, comparisons of k values determined for the above oils 1-8 with the sum of the product {∑k [AO-i]/10} of the k values obtained for each antioxidant (AO-i) and concentration (in mg/100 g) ([AO-i]/10) of AO-i (Tocs and Toc-3s) contained in the oils 1-8 were performed. The observed k values were not reproduced by the k 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 k values. Recently, the second-order rate constants (k) 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 k values obtained could be well explained as the sum of the product {Σ k [AO-i]/10} of the k and the [AO-i]/10 of AO-i (Tocs and Toc-3s) contained in the vegetable oils.