Quantification of Flavonoids in Plants

The aluminum chloride colorimetric method was used for the determination of the total flavonoid content of the sample [21 –24 ]. For total flavonoid determination, quercetin was used to make the standard calibration curve. Stock quercetin solution was prepared by dissolving 5.0 mg quercetin in 1.0 mL methanol, then the standard solutions of quercetin were prepared by serial dilutions using methanol (5–200 μg/mL). An amount of 0.6 mL diluted standard quercetin solutions or extracts was separately mixed with 0.6 mL of 2% aluminum chloride. After mixing, the solution was incubated for 60 min at room temperature. The absorbance of the reaction mixtures was measured against blank at 420 nm wavelength with a Varian UV-Vis spectrophotometer (Cary 50 Bio UV-Vis Spectrophotometer, Varian). The concentration of total flavonoid content in the test samples was calculated from the calibration plot (Y = 0.0162x + 0.0044, R² = 0.999) and expressed as mg quercetin equivalent (QE)/g of dried plant material. All the determinations were carried out in triplicate.