Since the reddish color of cyanidin can interrupt the visible detection, the concentrations of cyanidin must be considered.Herein 3 samples of extracted cyanidin (0.8 mg (A), 1.6 mg (B)
and 3.3 mg (C)) were dissolved in 5 mL of MeOH and allowed to form complex under the optimum of qualitative determination. It was found that the absorbance of all complexes was directly proportional to cyanidin concentrations. However, the absorbance were rapidly decreased at the beginning and then stable in a few minutes as shown in Fig. 5.