Flavonoid Analysis

2.7.3.1. (C) Test for flavanoids ( Sofowara, 1993; Harbrone, 1973): Three methods were used to determine the presence of flavonoids in the plant sample.5 ml of dilute ammonia solution were added to a portion of the filtrate of each plant extract followed by addition of concentrated H2SO4. A yellow colouration observed in each extract indicated the presence of flavonoids. The yellow colouration disappeared on standing. Few drops of 1% aluminium solution were added to a portion of each filtrate. A yellow colouration was observed indicating the presence of flavonoids. A portion of the powdered plant sample was in each case heated with 10 ml of ethyl acetate over a steam bath for 3 min. The mixture was filtered and 4 ml of the filtrate was shaken

The reaction mixture contained 100 µl of each of the extract solution in separate tubes (1 mg/ml) to which was added 0.5 ml of Folin-Ciocalteu phenol reagent, 1.5 ml of 20% (w/v) sodium carbonate and 10 ml of distilled water. After 2h of reaction at ambient temperature, the absorbance was measured at 765 nm and used to calculate the phenolic contents, using gallic acid as a standard. All experiments were performed thrice and the results were averaged and reported in the form of mean ± S.D.Then the total phenolic contents were expressed in term of gallic acid equivalents (mg GAE/g dry extract)

About 0.1 ml of the sample extract was added to a volumetric flask (10 ml) containing 7.5 ml of distilled water and 0.5 ml of Folin-Ciocalteu phenol reagent, 1 ml of 35 % Na2CO3 solution and dilute to 10 ml with distilled water. The mixture was shaken well and kept at room temperature for 30 min. A set of reference standard solutions of gallic acid (20, 40, 60, 80 and 100 μg/ml) were prepared. Absorbance for test and standard solutions were measured against the blank at 725 nm with an UV/Visible spectrophotometer. The tannin content was expressed in terms of mg of GAE /g of extract