Kinetic Study of the Scavenging Reaction of the Aroxyl Radical by Eight Kinds of Vegetable Oils in Solution

Abstract

A detailed kinetic study was performed for the reaction of the aroxyl radical (ArO • ) with eight vegetable oils 1-8, which contain different concentrations of α-, β-, γ-, and δ-tocopherols and -tocotrienols (-Tocs and -Toc-3s). The second-order rate constants (k s ) and aroxyl radical absorption capacity (ARAC) values for the reaction of ArO • with vegetable oils 1-8 (rice bran 1, perilla 2, rapeseed 3, safflower 4, grape seed 5, sesame 6, extra virgin olive 7, and olive oils 8) were measured in ethanol/chloroform/D 2 O (50:50:1, v/v/ v) solution at 25 C using stopped-flow spectrophotometry. The k s value (16.1 × 10 −3 L g −1 s −1 ) of rice bran oil 1 with the highest activity was 8.0 times larger than that (2.02 × 10 −3 ) of olive oil 8 with the lowest activity. The concentrations (in mg 100 g −1 ) of α-, β-, γ-, and δ-Tocs and -Toc-3s contained in the vegetable oils 1-8 were determined using high performance liquid chromatography-mass spectrometry/mass spectrometry (HPLC-MS/MS). From these results, it was clarified that the ArO • -scavenging rates (k s ) (i.e., the relative ARAC value) obtained for the vegetable oils 1-8 may be well explained as the sum of the product P k AOH-i s AOH-i ½ =10 5 È É of the rate constant (k AOH-i s ) and the concentration ([AOH-i]/10 5 ) of AOH-i (Tocs and Toc-3s) included in vegetable oils. The results suggest that the ARAC assay method might be used in the evaluation of antioxidant activity of general food extracts.

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

“…As the amounts of α-, β-, γ-, δ-Tocs and -Toc-3s contained in the vegetable oils 1-8 differed significantly, different ArO radical-scavenging activities were observed 23 . For example, the k S value of rice bran oil 1 was 8.0 times larger than that of olive oil 8.…”

“…Comparison of the k Q S values observed for the oils 1-8 with the sum of the product ∑ k Q AO-i S AO-i of the k Q AO-i S value obtained for each AO-i and concentration AO-i of AO-i in the oils 1-8 was performed to evaluate the validity of the SOAC method 11,15 . The concentrations of α-, β-, γ-, δ-Tocs and -Toc-3s i.e., AO-i contained in the vegetable oils 1-8 were determined in a previous study 23 and are listed in the Supplementary Information Table S1. The same vegetable oils 1-8 were used to measure 1 O 2 -quenching rates k Q S and k Q t 1/2 and SOAC values in this study.…”

“…k Q and aroxyl radical-scavenging rates k s of the vegetable oils 1-8 Recently, a kinetic study of the scavenging reaction of ArO radical with vegetable oils 1-8 i.e., AOs 1-8, Eq. 3 was performed in mixed solvent at 25 23 . The ArO radical was used as a model of the LOO radical and the rate constants k S were measured using stopped-flow spectrophotometry 27 .…”

“…In a previous study 23 , second-order rate constants k S for the reaction of eight vegetable oils 1-8 AOs, Table 1 with the 2,6-di-t-butyl-4-4-methoxyphenyl phenoxyl abbreviated as aroxyl ArO radical Fig. 1 in Ref.…”

“…1 in Ref. 23 were measured in a mixed solvent, in order to clarify the free radical-scavenging activity of vegetable oils 1-8.…”