Kinetic study of the quenching reaction of singlet oxygen by eight vegetable oils in solution

Abstract

�A kinetic study of the reaction of singlet oxygen ( 1 O 2 ) with eight vegetable oils 1–8 containing different concentrations of tocopherols (Tocs) and tocotrienols (Toc-3s) was performed. The second-order rate constants (k Q ) for the reaction of 1 O 2 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/D 2 O (50:50:1, v/ v/v) solution at 35℃ using UV-vis spectrophotometry. Furthermore, comparisons of k Q values determined for the above oils 1-8 with the sum of the product {∑k QAO-i [AO-i]/10 5 } of the k QAO-i values obtained for each antioxidant (AO-i) and concentration (in mg/100 g) ([AO-i]/10 5 ) of AO-i (Tocs and Toc-3s) contained in the oils 1-8 were performed. The observed k Q values were not reproduced by the k Q 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 Q values. Recently, the second-order rate constants (k S ) 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 S values obtained could be well explained as the sum of the product {Σ k SAO-i [AO-i]/10 5 } of the k SAO-i and the [AO-i]/10 5 of AO-i (Tocs and Toc-3s) contained in the vegetable oils.