2.6.3. Hydroxyl Radical Scavenging Assay

The hydroxyl radical (•OH) scavenging rates of the strains were determined, and all steps were performed following the method described by Wang et al. [26]. In brief, an aliquot (0.1 mL) of sample PBS (0.2 M, pH 7.4), 1.0 mL of O-phenanthroline (0.1%, w/v), 1.0 mL of 2.5 mM FeSO₄, and 0.5 mL of samples were mixed to obtain a homogeneous mixture; an aliquot (1.0 mL) of 20 mM H₂O₂ was reacted with the mixture to trigger the reaction at 37 °C. After 1.5 h, the mixture was centrifuged (10,000× g, 10 min), and the absorbance (A_s) of the supernatant was read at 536 nm. The following formula was adopted to calculate the scavenging rates (%):

where A_s represents the absorbance of the reaction mixture, A₀ represents the absorbance of the reaction mixture without sample, and A represents the absorbance of the reaction mixture in the absence of H₂O₂.