Studies on Tannins of Fruits and Vegetables

Factors affecting the precipitation of protein with tannin were studied. Formation of the preciptate was influenced not only by pH but also by the kinds of buffer solution, proteins, and tannins. The amount of precipitate became maximum at pH 4.5-5.0 and also in the case where the ratio of gelatin to tannin was 10 to 3-4. The solubility of precipitates with tannins increased with the rise of temperature. The precipitation with tannins except tannic acid was scarcely affected by the presence of inorganic salts, sugars, and ethyl alcohol. The deproteining activities of several tannins, expressed as the ratio of precipitated gelatin to tannin at pH 4.5 and at 10°C, were as follows; tannic acid 2.11, acorn tannin 2.65, chestnut tannin 3.15, lotus root tannin 3.05, perssimon tannin 3.45, apricot tannin 3.19, apple tannin 2.80, and Japanese pear tannin 2.21.