Studies on the antioxidant properties of some phytoestrogens

Isoflavones genistein and daidzein are nonsteroidal phytoestrogens occurring mainly in soybean foods. These phytoestrogens possess estrogenic properties and show a variety of health benefits as anti‐inflammatory agents. However, the mechanism of their action has not been identified in detail. The aim of this study is to characterize the antioxidant powers of genistein, daidzein and daidzein metabolite–equol through their activities to scavenge superoxide anion radical (O^?₂^?), hydroxyl radical (HO^?), 2,2–diphenyl–1‐picrylhydrazyl radical (DPPH^?) and hydrogen peroxide (H₂O₂) using chemiluminescence and spectrophotometry techniques. Potassium superoxide in dimethyl sulphoxide (DMSO) and 18‐crown‐6 ether were used as a source of O^?₂^?. Hydroxyl radicals were produced using the Fenton reaction. In free radical assays, genistein had the IC₅₀ values (an amount of antioxidant concentration required to decrease the initial radical concentration by 50%) 0.391 ± 0.012 mM for O^?₂^?, 0.621 ± 0.028 mM for HO^? and 1.89 ± 0.16 mM for DPPH^?. The IC₅₀ values for daidzein for these free radicals were 1.924 ± 0.011 mM, 0.702 ± 0.012 mM and 2.81 ± 0.03 mM, respectively. Equol was the most active the free radical scavenger with IC₅₀ = 0.451 ± 0.018 mM for HO^? and IC₅₀ = 1.36 ± 0.11 mM for DPPH^?. All tested compounds exerted a significant effect on the H₂O₂: IC₅₀ = 18.1 ± 1.1 μM for genistein, IC₅₀ = 2.1 ± 0.5 μM for daidzein, and IC₅₀ = 1.06 ± 0.2 μM for equol. These findings show that genistein, daidzein and equol are effective free radical scavengers and possess high antioxidant power in vitro. Copyright © 2016 John Wiley & Sons, Ltd.