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

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