Quantifying Tannins in Vernonia guineensis

The Folin–Ciocalteu method described by Govindappa et al. [36 ] was used to determine the total tannin content in Vernonia guineensis extract. The mixture consisting of extract (100 µl, 2 mg/ml), Folin–Ciocalteu reagent (500 µl, diluted 10 times in water), sodium carbonate (1000 µl, 35%), and distilled water (8.4 ml) was shaken, incubated (room temperature, 30 minutes), and the absorbance (700 nm, spectrophotometer) was read. The various concentrations of tannic acid (100 to 500 µg/ml) were used to draw the standard curve which made it possible to calculate the content of total tannins in the extract.