On determination conditions for total polyphenols in fruits and its derived products by Folin phenol methods
Determination methods (Folin Denis method and Folin Ciocalteus method) of total polyphenols in fruit and its derived products were studied. Folin Ciocalteus method was more suitable to be used than Folin Denis method in stability, sensitivity, and accuracy. After a series of optimization experiments, the best determination procedure of Folin Ciocalteus method was put forward, that is, 5.0 mL water, 1.0 mL coloration reagent, and 3.0 mL 7.5% sodium carbonate solution are orderly added into 1.0 mL extract of samples, then blend it, and measure its optical density at 765 nm after coloration for 2 hours. Under this procedure, average recovery rate of gallic acid in 6 materials (including apple, pear, banana, persimmon, grape and wine) is 77.2% to 112.1% relative deviation of the method is 0.8% to 5.7%