Abstract
The determination of relative astringency (RA) and relative affinity to methylene blue (RMB), based on those of geraniin (RAG and RMBG), shows good reproducibility with small amounts of samples for the estimation of the tannin content of plant extracts, and has been applied to the evaluation of the basal activity of 84 tannins and related compounds. The values obtained for polyphenols of lower molecular weight, which are not regarded as tannins, were zero or almost zero. An increase of these two values of up to about 1.3-1.4 times with increase of molecular weight of polyphenols (particularly such increase due to galloylation) was observed for each type of tannin tested. The RMBG determination gives values somewhat larger than the RAG values for hydrolyzable tannins, and rather smaller than the RAG values for condensed tannins.
