Tannin in Persimmon (Diospyros Kaki L.) Fruits

II. Volatile Compounds and Soluble Tannin of the Fruits in the Course of Removal of Astringency

Abstract

Using four astringent cultivars of persimmon (Diospyros Kaki L.) fruits, changes in contents of soluble tannin and some volatile compounds were determined in relation to the process of removal of astringency. While various treatments have been known to be effective for removing astringency, the methods used in this study were as follows; drying at an ambient temperature after peeling, dipping in warm water of 40°C for 24 hours, freezing at -30°C for two months, and storing at room temperature for sufficient days to ripen to a soft consistency.
When the fruits were softening and losing their astringency during the treatments, except for frozen ones, soluble tannin content decreased rapidly, and alcohols and acetaldehydes content showed an increase. About the time when the contents of these volatiles reached maximum the fruits became non-astringent. In the fruits which had their astringency been removed, contents of tannin cells were already coagulated and shrunk easily. The production of alcohols preceded that of acetaldehyde and was dominant in quantity among the volatiles. Ethanol was applied to pulpslice or squeezed-juice and the reaction was observed microscopically, but no coagulating effect was found even when there was a high concentration of alcohol. Therefore it is unlikely that the alcohols have a direct effect, and an accumulation of acetaldehyde even at a low level would play an important role in coagulation of tannin and thus removal of astringency as reported previously.