Spectrophotometric Determination of Antioxidant Reducing Power

RP of S. aureus samples was determined according to the method reported by Ding et al. [42 (link)], with slight modification as described by Łopusiewicz et al. [43 (link)]. 0.5 mL of the suspension (1A–C) was mixed with 0.5 mL of water:methanol (8:2, v:v) solution and 0.5 mL of 1% potassium ferricyanide (Sigma-Aldrich, Darmstadt, Germany) and incubated at 50 °C for 20 min. After cooling, 1 mL of this mixture was transferred to 1 mL of 0.1% ferric chloride (Sigma-Aldrich, Darmstadt, Germany), and the absorbance was measured at 700 nm using a spectrophotometer (Evolution 220 UV-Visible spectrophotometer, Thermo Fisher Scientific Inc., Waltham, DE, USA). Experiments were performed in triplicate. The RP was calculated according to Equation (2): $\mathrm{Reducing} \mathrm{power} (\%)=\frac{{\mathrm{A}}_{\mathrm{control}}{ - \mathrm{A}}_{\mathrm{sample}}}{{\mathrm{A}}_{\mathrm{control}}}\times 100$