Kinetic Study of Singlet-Oxygen Quenching and Aroxyl-Radical Scavenging Activities of Vitamin E Homologs and Fatty Acids Present in Vegetable Oils

Recently, singlet-oxygen (O-1(2)) quenching and aroxyl-radical (ArO center dot) scavenging rates (k(Q) and k(s), respectively) of eight vegetable oils were measured in the ethanoUchloroform/D2O solution. Furthermore, the k(Q) and k(s) values and concentrations of four tocopherols and four tocotrienols contained in the vegetable oils were measured. In this study, the concentrations of nine fatty acids (including stearic, oleic, linoleic, and linolenic acids) comprising the above-mentioned eight vegetable oils were determined by gas chromatography. The k(Q) and k(s) values for ethyl stearate, ethyl oleate, ethyl linoleate, methyl linolenate, and glyceryl trioleate in the ethanol/chloroform/D2O solution were measured by UV-vis spectrophotometry. Based on the results obtained for the above-mentioned fatty acid esters, the k Q and k s values were estimated for nine fatty acids. Furthermore, comparisons of k Q values observed for the vegetable oils with the sum of the product {Sigma k(Q)(AO-i) [AO-i)} of the k(Q)(AO-i) values obtained for each antioxidant-i (AO-i) and the concentrations ([AO-i]) of AO-i (Le., four tocopherols (& four tocotrienols) and nine fatty acids) contained in vegetable oils were performed. Based on the results, a detailed comparison of the contributions of the tocopherols (and tocotrienols) and the fatty acids to the O-1(2)-quenching rate constants (k(Q)) was performed. This indicated that both the tocopherols (and tocotrienols) and the fatty acids contribute to the O-1(2) quenching. A similar comparison was conducted for the ArO center dot-scavenging rate constants (k(s)). The results suggested that only the tocopherols (and tocotrienols) contained in the oils contributed to the ArO center dot-scavenging, with negligible contribution from the fatty acids.