Kinetic Study of the Quenching Reaction of Singlet Oxygen by Carotenoids and Food Extracts in Solution. Development of a Singlet Oxygen Absorption Capacity (SOAC) Assay Method

Abstract

A kinetic study of the quenching reaction of singlet oxygen (1O2) with eight kinds of carotenoids and α-tocopherol was performed in ethanol/chloroform/D2O (50:50:1, v/v/v) solution at 35 °C. The overall rate constants, kQ (=kq+kr, physical quenching+chemical reaction), for the reaction of carotenoids with 1O2 were measured, using the competition reaction method, where endoperoxide was used as a singlet oxygen generator, 2,5-diphenyl-3,4-benzofuran (DPBF) as an UV-vis absorption prove, and α-tocopherol as a standard compound. The rate constants, kQ (S) and kQ (t1/2), were determined by analyzing the first-order rate constant (S) and the half-life (t1/2) of the decay curve of DPBF with carotenoids, respectively, showing good accordance with each other. Similar measurements were performed for tomato and carrot extracts. From the results, a new assay method that can quantify the singlet oxygen absorption capacity (SOAC) of antioxidants, including carotenoids, α-tocopherol, and vegetable extracts, has been proposed.

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

“…The UV spectrum of EP indicates that the commercially available EP includes 95% EP and 5% EP-precursor unreacted. 29) Fig. 1.…”

“…[26][27][28] Recently, kinetic studies of the quenching reaction of 1 O 2 with natural antioxidants (AOs) (such as carotenoids, tocopherol homologues (Tocs), catechins, and caffeic acids) were performed in ethanol/chloroform/ D 2 O (50:50:1, v/v/v) (hereafter abbreviated as "mixed solvent") and ethanol solutions at 35°C. [29][30][31] The overall rate constants, k Q (=k q + k r , physical quenching + chemical reaction), for the reaction of AOs with 1 O 2 were measured, using the competition reaction method, where endoperoxide was used as a singlet oxygen generator and 2,5-diphenyl-3,4-benzofuran (DPBF) as an UV-vis absorption probe (Scheme 1). [29][30][31] 1 O 2 þ AO À!…”

“…[29][30][31] The overall rate constants, k Q (=k q + k r , physical quenching + chemical reaction), for the reaction of AOs with 1 O 2 were measured, using the competition reaction method, where endoperoxide was used as a singlet oxygen generator and 2,5-diphenyl-3,4-benzofuran (DPBF) as an UV-vis absorption probe (Scheme 1). [29][30][31] 1 O 2 þ AO À! k Q physical quenching ðk q Þ þ chemical reaction ðk r Þ…”

“…α-Toc was used as a standard compound. 29) As described above, development of the SOAC assay method was performed. However, the examples of food extracts investigated are only three and limited to vegetable extracts.…”

“…From the results, a new assay method, which can quantify the singlet oxygen absorption capacity (SOAC) of antioxidants, including carotenoids, phenolic antioxidants, and vegetable extracts, was proposed. [29][30][31] Relative SOAC value was defined in the following way:…”