Abstract
The precipitation of tannin with soluble polyvinylpyrrolidone (PVPs, MW 40, 000 and 360, 000) was scarcely affected by pH in acid solution but not developed in alkaline solution. The production of precipitate was prevented by the presence of borate ion, Na2SO4, and ethanol, and decreased with the rise of temperature. The ratio of removal tannin to original one changed under the control of the concentration ratio of tannin to PVPs and when PVPs was 2.9 times as much as tannic acid, the precipitate became greatly soluble. Among several polyphenolics, only high molecular tannin was precipitated. These results show that the tannin precipitation activity of PVPs is resemble to the case of methyl cellulose.
