STABILIZATION OF THE PRUSSIAN BLUE COLOR IN THE DETERMINATION OF POLYPHENOLS

A stabilized reagent for the determination of total polyphenols by the Prussian blue method was developed. H3PO4 complexed with excess Fe3+ in the mixture, stopping the reaction. Gum acacia, a protective colloid, prevented precipitation by impeding the coalescence of the colloidal particles formed. Efficiency of chelating agents tried was H3PO4 (A) > Na4EDTA (B) > sodium hexametaphosphate (C). Effectiveness of protective colloids was gum acacia (D) = Reten (an anionic polyacrylamide) (E) > Methocel 60 HG (F) > phosphomannan 2448 (G) > starch (H) > polysaccharide B 1828 (I). Both the chelating agent and the protective colloid must be added to effect stabilization. Effectiveness of combinations was (A + D or E) > (B + D) > (A + F) > (A + G) > all other combinations. (A + D) prevented change in color density and prevented precipitation for up to 60 h with catechin as the polyphenol.