Uv vis spectrophotometer

The power of phenolic extracts to reduce ferric iron (Fe³⁺) present in the potassium ferricyanide complex into ferrous iron (Fe²⁺) was determined according to the method described by Zovko Koncic et al. [68 (link)]. In test tubes, 1 mL of each essential oil of plant was diluted in absolute ethanol at different concentrations (1–20 μL/mL). Then, each tube was mixed with 2.5 mL of a phosphate buffer solution (0.2 M, pH = 6.6) and 2.5 mL of a potassium ferricyanide solution K₃Fe(CN)₆ at 1%. The obtained solution was incubated in a water bath at 50 °C for 20 min. Then 2.5 mL of 10% trichloroacetic acid was added to stop the reaction processes. The whole solution was centrifuged at 3000 revolutions per minute for 10 min. After, 2.5 mL of the supernatant of each concentration was mixed with 2.5 mL of distilled water, and 0.5 mL of the aqueous FeCl₃ solution (0.1%). The absorbance of the reaction medium was measured at 700 nm against a similarly prepared blank, replacing the essential oil with absolute ethanol in order to calibrate the apparatus (UV-VIS spectrophotometer (VWR, Radnor, PA, USA). The positive control was represented by a solution of standard antioxidants; the absorbance of BHA was measured under the same conditions as the samples. An increase in absorbance corresponds to an increase in the reducing power of the tested EOs.