In the industrial methods of removing astringency in the astringent persimmons, several treatments have been used : such as treatments with distilled spirits, drying and others. Soluble tannins cause astringency in persimmons. The removal of astringency is considered to be due to the conversion of the soluble tannins to insoluble compounds. Acetaldehyde is responsible for insolubility of the tannins, and it might be produced by the action of the enzyme, such as pyruvate decarboxylase (PDC) or alcohol dehydrogenase (ADH) in persimmons.
The contents of the soluble tannins and the activities of PDC and ADH were determined during the growing and ripening period of both the astringent and sweet persimmon, and it was found that the amounts of the soluble tannins decreased and the activities of both enzymes were always present during these periods. Even a sweet persimmon was astringent in the growing period and it contained much soluble tannins, but later the content of soluble tannins decreased to less than 0.1%, and at this level the astringent taste was not detectable. Both alcohol and drying treatment on the astringent persimmons were effective for removing astringency, and the activities of PDC were present in all the samples, but the dried samples showed no activity of ADH.