A colorimetric method described by Ren et al. (2020) (link) was used to analyze total flavonoid content with rutin solutions (4, 8, 12, 16 and 20 μg/mL) serving as standards. Briefly, powdered samples were extracted with 50% (v/v) methanol in an ultrasonication bath (VCX600, Sonics and Materials Inc., Newtown, CT, USA) for 90 min at room temperature, then centrifuged at 12,000 rpm for 20 min. The supernatant was collected and used to measure absorbance at 360 nm with a UV-6000 spectrophotometer. The calibration standard was 50% (v/v) methanol.
Free full text: Click here