Kinetic study of the quenching reaction of singlet oxygen by α-, β-, γ-, δ-tocotrienols, and palm oil and soybean extracts in solution

Abstract

Measurements of the singlet oxygen ( 1 O 2 ) quenching rates (k Q (S)) and the relative singlet oxygen absorption capacity (SOAC) values were performed for 11 antioxidants (AOs) (eight vitamin E homologues (α-, β-, γ-, and δ-tocopherols and -tocotrienols (-Tocs and -Toc-3s)), two vitamin E metabolites (α-and γ-carboxyethyl-6-hydroxychroman), and trolox) in ethanol/chloroform/D 2 O (50:50:1, v/v/v) and ethanol solutions at 35°C. Similar measurements were performed for five palm oil extracts 1-5 and one soybean extract 6, which included different concentrations of Tocs, Toc-3s, and carotenoids. Furthermore, the concentrations (wt%) of Tocs, Toc-3s, and carotenoids included in extracts 1-6 were determined. From the results, it has been clarified that the 1 O 2 -quenching rates (k Q (S)) (that is, the relative SOAC value) obtained for extracts 1-6 may be explained as the sum of the product {Σ k Q AO-i (S) [AO-i]/100} of the rate constant (k Q AO-i (S)) and the concentration ([AO-i]/100) of AO-i (Tocs, Toc-3s, and carotenoid) included.

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

“…3.1 UV-Vis absorption spectra of vegetable oils 1-8 in ethanol/chloroform/D 2 O solution The UV-vis absorption spectra were measued for vegetable oils 1-8 in the mixed solvent, by varying the concentration of oils 1-8, where the concentration was defined as gram per liter g/L . As reported in a previous study 18 , eight vitamin E homologues 4 Tocs and 4 Toc-3s show UV absorption maxima at λ max 292.5 -298.5 nm in the mixed solvent. All the vegetable oils 1-8 contained vitamin E homologues see Table S1 , and UV absorption attributable to Tocs and Toc-3s were observed for oils 1-8, as shown in Fig.…”

“…On the other hand, as expected, the k Q S values of vegetable oils 1-8 were by two orders of magnitude smaller than those 3.18 10 4 -1.60 10 4 L g 1 s 1 of vegetable extracts such as tomato, carrot, and red paprika , which include high concentrations of carotenoids. The k Q S value 7.32 10 3 L g 1 s 1 of crude palm oil extract was also larger than those of vegetable oils 1-8 18 .…”

“…Recently, measurements of the 1 O 2 -quenching rate constants k Q AO-i S of AOs 4 Tocs and 4 Toc-3s were performed in the mixed solvent 16,18 . The k Q AO-i S values of these AOs are listed in Table 2.…”

“…The concentrations in mg/100 g of α-, β-, γ-, δ-Tocs and -Toc-3s in vegetable oils 1-8 were determined using HPLC-MS/MS, in a previous study 18 . Furthermore, comparison of the k S values observed for the above oils 1-8 with the sum of the product ∑k S AO-i AO-i /10 5 of the k S AO-i values obtained for each AO-i 4 Tocs and 4 Toc-3s and the respective concentrations AO-i /10 5 of AO-i in the vegetable oils was performed 23,24 .…”

“…vegetable, fruit, and palm oil extracts 11,18 . From these results, a new assay method that could quantify the singlet oxygen absorption capacity SOAC of AOs, including natural AOs and food extracts, was proposed 15 .…”