Development of a Singlet Oxygen Absorption Capacity (SOAC) Assay Method. Measurements of the SOAC Values for Carotenoids and alpha-Tocopherol in an Aqueous Triton X-100 Micellar Solution

作者：Mukai Kazuo^*; Ouchi Aya; Azuma Nagao; Takahashi Shingo; Aizawa Koichi; Nagaoka Shin ichi

来源：Journal of Agricultural and Food Chemistry, 2017, 65(4): 784-792.

DOI：10.1021/acs.jafc.6b04329

• singlet oxygen
• quenching rate
• carotenoids
• alpha-tocopherol
• SOAC value
• kinetic study
• micellar solution
• endoperoxide

Recently, a new assay method for the quantification of the singlet oxygen absorption capacity (SOAC) of antioxidants (AOs) and food extracts in homogeneous organic solvents was proposed. In this study, second-order rate constants (k(Q)) for the reaction of singlet oxygen (O-1(2)) with eight different carotenoids (Cars) and alpha-tocopherol (alpha-Toc) were measured in an aqueous Triton X-100 (5.0 wt %) micellar solution (pH 7.4, 35 degrees C), which was used as a simple model of biomembranes. The k(Q) and relative SOAC values were measured using ultraviolet visible (UV-vis) spectroscopy. The UV-vis absorption spectra of Cars and alpha-Toc were measured in both a micellar solution and chloroform, to investigate the effect of solvent on the k(Q) and SOAC values. Furthermore, decay rates (k(d)) of O-1(2) were measured in 0.0, 1.0, 3.0, and 5.0 wt % micellar solutions (pH 7.4), using time-resolved near-infrared fluorescence spectroscopy, to determine the absolute k(Q), values of the AOs. The results obtained demonstrate that the k(Q) values of AOs in homogeneous and heterogeneous solutions vary notably depending on (0 the polarity [dielectric constant (epsilon)] of the reaction field between AOs and O-1(2), (ii) the local concentration of AOs, and (iii) the mobility of AOs in solution. In addition, the k(Q) and relative SOAC values obtained for the Cars in a heterogeneous micellar solution differ remarkably from those in homogeneous organic solvents. Measurements of k(Q), and SOAC values in a micellar solution may be useful for evaluating the O-1(2) quenching activity of AOs in biological systems.

• 出版日期2017-2-1