CHEMICAL EVIDENCE FOR THE DE-ASTRINGENCY (INSOLUBILIZATION OF TANNINS) OF PERSIMMON FRUIT

After artificial removal of the astringency from persimmon fruit by treatment with ethanol, thiol-promoted degradation of the insolubilized proanthocyanidin polymers with 2-sulfanylethanol yielded 4 beta-(2-hydroxyethylsulfanyl)-6- and -8-[1-(2-hydroxyethylsulfanyl)ethyl]-flavan-3-ols 9-14. Furthermore, when deuteriated. ethanol was used for de-astringency, the deuterium atoms were incorporated into the C-2 unit attached to the A-ring of these compounds. These findings evidently show that acetaldehyde important role in polymerization (insolubilization) of water-soluble proanthocyanidins, causing the loss of astringency.