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-1(2)) with eight vegetable oils 1-8 containing different concentrations of tocopherols (Toes) and tocotrienols (Toc-3s) was performed. The second-order rate constants (k(Q)) for the reaction of O-1(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/D2O (50:50:1, v/v/v) solution at 35 degrees C using UV-vis spectrophotometry. Furthermore, comparisons of k(Q) values determined for the above oils 1-8 with the sum of the product {Sigma k(Q)(AO-i) [AO-i]/10(5)} of the k(Q)(AO-i) values obtained for each antioxidant (AO-i) and concentration (in mg/100 g) ([AO-i]/10(5)) of AO-i (Toes 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 Toes 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 center dot) with the same vegetable oils 1-8 were measured in the same solvent at 25 degrees C using stopped-floe spectrophotometry (Ref. 23). The k(s) values obtained could be well explained as the sum of the product {Sigma k(s)(A)(O-i) [AO-i]/10(5)} of the k(s)(AO-i) and the [AO-i]/10(5) of AO-i (Toes and Toc-3s) contained in the vegetable oils.