Estimation of the degree of polymerization of condensed tannins of some wild fruits of Zimbabwe (Uapaca kirkiana and Ziziphus mauritiana) using the modified vanillin-HCl method

Abstract

Methanol and glacial acetic acid were compared for their effect in the vanillin assay for tannins. The time taken for the development of colour was followed using a spectrophotometer. By reacting vanillin and condensed tannins in the presence of acetic acid, the time for the development of the chromogenic substance was reduced approximately threefold compared with the time taken in the presence of methanol. The degree of polymerization was followed by reacting a catechin standard, the tannin of the Uapaca kirkiana and Ziziphus mauritiana, with vanillin in acetic acid medium at 30°C and measuring absorbance at intervals. The values obtained suggested between 4 and 10 monomer units of catechin per polymer of tannins for the different portions of the two fruits. © 2005 Society of Chemical Industry.