Studies on the Tannin of Fruits and Vegetables

Part VIII. Precipitation of tannin with synthetic polyethers

Abstract

As the previous report, that tannin was precipitated by methyl cellulose, expected the similar effect with other polyethers, the precipitation of tannin with soluble and synthetic polyethers, i.e. polyethyleneglycol (M.W. 200-20, 000), polypropyleneglycol (M.W. 400-2, 000), polypropyleneglycol ether of trimethylolpropan (M.W. 300-4, 000) and glycerin (M.W. 3, 000), and some surface active agents were studied.
The effects of pH, temperature, and co-existence of other substances on the precipitation with polyether are similar with case of metyl cellulose. The precipitation is under the rule of concentration ratio of tannin to polyether. The heigher the molecular of tannin is, the lower the molecular of polyethyleneglycol need to precipitate and the larger precipitation ratio with same polyether is. Among many polyethers, polyethyleneglycol have the strongest activity of precipitation.
Therefore, the precipitation ratio with polyethyleneglycol (M.W. 1, 000) is in the proportion to the molecular of tannin. Polyether did not precipitate low molecular polyphenolics, catechin, chlorogenic acid, and anthocyanin, but was able to remove completely the astringent tannin from fruit and vegetable juices. Among surface active agents, Tween which contained polyethyleneresidue, also precipitated tannin.