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With the determination of tea tannin by the Lowenthal method and the colorimetric method using ferrous tartrate, the extraction rates of tannin in the green tea with several solvents, the temperature effect on the extraction of catechin fractions, and the reduction of tannin content by the filtration of infusion were investigated.The preparations of determining solutions were carried out as follows: in the Lowenthal method, 500 mg. of powdered tea was infused with ca. 70ml. of hot water for 90 min. and in the colorimetric method, 100 mg. of sample was treated in the same way for 30min. After cooling, both infusions were filled up to 100 ml. and filtered, then the tannin content in the filtrates was determined.Tea tannin, especially ester-type catechins, most of which consisted of (-)-epi-gallocatechin gallate, were less extractable in hot water than in aq. acetone and other organic solvents.The infused tannin content increased as the extraction temperature rose till 60°C., then reached almost a constant level.At a low temperature, the extraction rate of ester-type catechins was remarkably small, however, at a high temperature (over 80°C.)pyrogallol-type catechins seemed to be decomposed yielding gallic acid and (±)-gallocatechin.The tannin content was considerably lower in the first 20 ml. of filtrate through. several filter papers than in the succeding 20-40ml.

Fluctuations of Tannin Content due to the Preparation of Sample Solution in the Determination of Tea Tannin