Journal of Nutrition & Food Sciences
Open Access

Flavonoid Content

The concentration gradient of Gallic acid was prepared as standard solution (0–200 g/ml), and calibration curve was established using Gallic acid. The free phenol samples of bulbs, leaves, and flowers were diluted with deionizer water as sample solutions, in which bulbs and leaves samples were diluted to 20‐fold and flowers were diluted to 80‐fold. The 400 μl of deionizer water and 100 μl of sample or standard solution was added to 5‐ml centrifuge tube and mixed well. The diluted extract or Gallic acid was added to 0.2 ml Folin–Ciocalteu reagent and mixed for 6 min, followed by the addition of 2 ml of 20% sodium carbonate and 800 μl deionizer water. The content of total flavonoids was investigated using the sodium borohydride/chloroquinone method. Catechin standard solution (0–6 mM) was prepared with tetrahydrofuran/ethanol (1:1, v/v). The 2 ml sample was taken in 10‐ml glass tubes and dried by fluxing nitrogen. Then, it was dissolved in 3 ml tetrahydrofuran/ethanol (1:1, v/v). The mixture of 1 ml this solution, 0.5 ml sodium borohydride(50 mM), and 0.5 ml aluminum dichloride (74.6 mM) were shaken for 15 min at room temperature. Then, 0.5 ml sodium borohydride was further added to each test tube and shaken for 30 min at room temperature. Cold acetic acid solution was added into each tube, and the solution was kept in the dark for 15 min. Then, 1 ml of 20 mM chloranil was added and heated at 95°C. The reaction solutions were cooled, and the final volume was diluted to 4 ml with methanol.