Quantifying Polyphenols and Tannins

Determination of Total Polyphenols. The total polyphenol content was determined using the Folin–Ciocalteu reagent, using the method of Lister and Wilson [27 ]. 0.5 ml of each sample was introduced into test tubes, (2.5 ml) of Folin–Ciocalteu's reagent, previously diluted with water (1:10 v/v) and 4 ml (7.5%, (m/v)) of Na₂CO₃ and kept in a water bath (50°C) for 30 minutes. The absorbance of all samples was measured at 765 nm using a spectrophotometer (UviLine 9100-94000UV/Vis). The results are expressed as micrograms gallic acid equivalent per milligram of extract (µg GAE/mg).
Determination of Cathechic Tannins. The quantities of cathechic tannins were estimated using the vanillin method in an acid medium [28 (link)]. A volume of 50 µl of the extract was added to 1.5 ml of the vanillin/methanol solution (4%, m/v) and then mixed using a vortex. Then, 750 µl of concentrated hydrochloric acid (HCl) was added and allowed to react at room temperature for 20 min. Absorbance at 500 nm was measured using a spectrophotometer (UviLine 9100-94000UV/Vis). The concentration of tannins was expressed in micrograms equivalent of the catechin per milligram of extract (µg CE)/mg) from the calibration curve.