Kinetic study of the quenching reaction of singlet oxygen by seven rice bran extracts in ethanol solution. Development of a singlet oxygen absorption capacity (SOAC) assay method

Measurements of singlet oxygen (O2) quenching rates (k_q (S)) and the relative singlet oxygen absorption capacity (SOAC) values were performed for seven rice bran extracts 1-7, which contained different concentrations of antioxidants (AOs) (such as α-, β-, γ-, and δ-tocopherols and-tocotrienols, three carotenoids (lutein, β-carotene, and zeaxan-thin), and γ-oryzanol), in ethanol at 35 °C using UV-vis spectrophotometry. The concentrations of four tocopherols and four tocotrienols, three carotenoids, and γ-oryzanol contained in the extracts were determined using HPLC-MS/MS, UV-HPLC, and UV-vis absorption spectroscopy, respectively. Furthermore, comparisons of k_q (S) (Obsd.) values observed for the above extracts 1-7 with the sum of the product {Σ k^A-O-i_Q (S) [AO-i]} of the k^A-O-i_Q (S) values obtained for each AO-i and the concentration ([AO-i]) of AO-i contained in extracts 1-7 were performed. From the results, it has been ascertained that the SOAC method is applicable to general food extracts to evaluate their ¹O₂-quenching activity.