Development of Singlet Oxygen Absorption Capacity (SOAC) Assay Method. 3. Measurements of the SOAC Values for Phenolic Antioxidants

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• 作者：Kazuo Mukai ; Aya Ouchi ; Shingo Takahashi ; Koichi Aizawa ; Takahiro Inakuma ; Junji Terao ; Shin-ichi Nagaoka
• 刊名：Journal of Agricultural and Food Chemistry
• 出版年：2012
• 出版时间：August 15, 2012
• 年：2012
• 卷：60
• 期：32
• 页码：7905-7916
• 全文大小：492K
• 年卷期：v.60,no.32(August 15, 2012)
• ISSN：1520-5118

文摘

Measurements of the singlet oxygen (¹O₂) quenching rates (k_Q (S)) and the relative singlet oxygen absortpion capacity (SOAC) values were performed for 16 phenolic antioxidants (tocopherol derivatives, ubiquinol-10, caffeic acids, and catechins) and vitamin C in ethanol/chloroform/D₂O (50:50:1, v/v/v) solution at 35 掳C. It has been clarified that the SOAC method is useful to evaluate the ¹O₂-quenching activity of lipophilic and hydrophilic antioxidants having 5 orders of magnitude different rate constants from 1.38 脳 10¹⁰ M^鈥? s^鈥? for lycopene to 2.71 脳 10⁵ for ferulic acid. The logarithms of the k_Q (S) and the SOAC values for phenolic antioxidants were found to correlate well with their peak oxidation potentials (E_p); the antioxidants that have smaller E_p values show higher reactivities. In previous works, measurements of the k_Q (S) values for many phenolic antioxidants were performed in ethanol. Consequently, measurements of the k_Q (S) and relative SOAC values were performed for eight carotenoids in ethanol to investigate the effect of solvent on the ¹O₂-quenching rate. The k_Q (S) values for phenolic antioxidants and carotenoids in ethanol were found to correlate linearly with the k_Q (S) values in ethanol/chloroform/D₂O solution with a gradient of 1.79, except for two catechins. As the relative rate constants (k_Q^AO (S)/k_Q^伪-Toc (S)) of antioxidants (AO) are equal to the relative SOAC values, the SOAC values do not depend on the kinds of solvent used, if 伪-tocopherol is used as a standard compound. In fact, the SOAC values obtained for carotenoids in mixed solvent agreed well with the corresponding ones in ethanol.

Keywords:

singlet oxygen; quenching rate; endoperoxide; tocopherols; catechins; caffeic acids; carotenoids; SOAC value; kinetic+study&qsSearchArea=searchText">kinetic study; molar extinction coefficient