Gallic acid solution

The total phenolic content of P. odora EO was evaluated using a modified colorimetric method described previously by Singleton and Rossi 10 . 0.50 mL of (1mg/mL) of the oil in methanol was mixed with 0.25mL of Folin-Ciocalteau reagent after that 3.0mL of distilled water was added. Immediately, 0.75mL of sodium carbonate NaCO3 (20%) and 0.95 mL of distilled water was added. The mixture was shaken well and incubated in the dark for 30 min at 37ºC for the development of color. The absorbance was read at 765 nm. The measurement was compared to a standard curve prepared with a gallic acid solution (Sigma Chemical). The total phenolic content in the plant oil was expressed as milligrams of gallic acid equivalent per gram of dry weight (mg GAE/ g DW).

For the phytochemical characterization of biologically active compounds from beetroot, peels were used: ethanol of HPLC purity, ethanol, citric acid, Folin-Ciocâlteu reagent, and gallic acid solution were obtained from Sigma Aldrich (St. Louis, MO, USA).