Constituents of Geranium thunbergii SIEB. et Zucc. III. Application of Determination Methods of Tannin Activity with Hemoglobin and of Ellagitannin with Nitrous Acid

The factors which might cause errors upon the relative astringency (RA) determination with hemoglobin, and the ellagitannin determination (RE determination) by coloring with nitrous acid, were examined to establish facile determination methods for tannin. Comparison of the first method with the hide powder method was also carried out. The RA and RE determinations were then applied to the tannin of Geranium thunbergii, and of four other species of Geranium, and also to geraniin, the pure ellagitannin obtained from the formerly reported tannin 1, to give following results : The main constituents of the tannin in these plants are ellagitannins, and the ratios of ellagitannin to the whole tannin in these plants are generally analogous. G. thunbergii collected periodically exhibited the largest amount of tannin in summer, and almost the same ratio of ellagitannin to the whole tannin in this plant all the time. There was practically no difference of the results between this plant of white flower and that of red flower by the two methods. The RA and RE values decrease markedly when G. thunbergii was dried and stored. RA and RE values of geraniin, and of G. thunbergii extract, in boiling water vary only to a small extent within 2 hr.