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%.