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

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• 作者：Kazuo MukaiAya Ouchi ; Nagao Azuma ; Shingo Takahashi ; Koichi Aizawa ; Shin-ichi Nagaoka
• 刊名：Journal of Agricultural and Food Chemistry
• 出版年：2017
• 出版时间：February 1, 2017
• 年：2017
• 卷：65
• 期：4
• 页码：784-792
• 全文大小：504K
• ISSN：1520-5118

文摘

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 (¹O₂) with eight different carotenoids (Cars) and α-tocopherol (α-Toc) were measured in an aqueous Triton X-100 (5.0 wt %) micellar solution (pH 7.4, 35 °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 α-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 ¹O₂ 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 (i) the polarity [dielectric constant (ε)] of the reaction field between AOs and ¹O₂, (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 ¹O₂ quenching activity of AOs in biological systems.