3.6.3. Hydroxyl Radical Scavenging Activity

Hydroxyl radical scavenging activity is an important indicator of the antioxidant activity of health products and medicines [49]. In the method, the hydroxyl radicals were produced by the Fenton reaction between H₂O₂ and Fe²⁺, and the Fe²⁺ in the aqueous solution of o-phenanthroline-Fe²⁺ was oxidized to Fe³⁺, resulting in a decrease in absorbance at 536 nm [54]. The degree of inhibition of the 536 nm absorbance decline rate of the sample reflected the hydroxyl radical scavenging activity of the samples [55]. According to the measuring principle, 1 mL of o-phenanthroline absolute ethanol solution (1.5 mM o-phenanthroline in absolute ethanol) was mixed with 1 mL of PBS buffer (pH 7.4), and 1 mL of sample solution was added. Mixing thoroughly, 1 mL of FeSO₄ solution (1.5 mM) was added and the solution was mixed again. Then 1 mL of H₂O₂ (0.02%, v/v) was added to the solution. After reacting for 60 min in a constant temperature water bath at 37 °C, the absorbance value of the sample mixed solution measured at 536 nm was A_S. Ultrapure water was used instead of H₂O₂ as the control group, and its absorbance value A_n was measured. Ultrapure water was used instead of the sample as the blank group, and its absorbance value A₀ was measured. The hydroxyl radical scavenging rate of the antioxidant was calculated according to Equation (6).