A Model Experiment for Elucidating the Mechanism of Astringency Removal in Persimmon Fruit Using Respiration Inhibitors.

Japanese persimmon fruits, such as cvs. 'Hiratanenashi', 'Atago', and 'Yokono', have remarkable astringency even at a mature stage, so it is only edible after removal of the astringency. Postharvest treatments for removing astringency from astringent cultivars of persimmon fruits, without concomitant softening, include alcohol vapor, carbon dioxide, and warm water. The mechanism of such artificial de-astringency is still obscure.Two chemicals (0.1% dinitrophenol and 1.0% arsenic trioxide), which inhibit aerobic respiration, caused de-astringency in astringent persimmon fruits held in a normal atmosphere. The tissues which absorbed these chemicals showed no abnormal softening. These treatments induced accumulation of ethanol and acetaldehyde at high concentrations in the tissues. However, malonic acid (10 mM), which induced ethanol and acetaldehyde accumulation at lower levels, was not effective in removing astringency from the fruit.An experiment using heated fruit (75°C for 15 min) with a high quantity of soluble kakitannin showed that acetaldehyde reacted with kakitannin, causing it to be insolubilized in the fruits, but ethanol did not.We conclude that removal of astringency from persimmons is the result of a direct reaction between acetaldehyde, produced during anaerobic respiration, and soluble kakitannin, forming an insoluble, non-astringent product.