We investigated the removal of astringency and changes in ethanol and acetaldehyde concentrations in 'Hiratanenashi' and 'Denkuro' persimmon (Diospyros kaki Thunb.) fruits by applying an ethanol patch treatment or enclosing them in a polyethylene bag with a cube containing ethanol on-tree and after harvest. Treatments for removing astringency from on-tree or harvested fruit included i) patch treatment, where a silica ethanol patch was attached to the peel of individual fruits, and ii) bag treatment, where individual fruits without calyx lobes was enclosed in a polyethylene bag with a cube containing ethanol. In 'Hiratanenashi' fruit in both on-tree and after harvest treatments with the ethanol patch, ethanol penetrated into the fruit and was accumulated in fruit flesh immediately after the start of the treatment. This was followed by acetaldehyde accumulation. Additionally, soluble tannin concentration was decreased. The trends in ethanol and acetaldehyde accumulation and the decrease in soluble tannin concentration in the on-tree and postharvest bag treatments were quite similar to those receiving the patch treatment. However, the penetration of ethanol from a silica ethanol patch into fruit was not evenly distributed, and the rate and the amount of ethanol decreased as the distance between the flesh and the patch increased. The amount of acetaldehyde was small and the decrease in soluble tannin concentrations was lower in parts of the flesh that were not near the patch, resulting in imperfect removal of astringency. 'Denkuro' fruit, which usually remains astringent even with ethanol treatment, did not lose its astringency in patch treatment although the ethanol accumulation in the flesh was greater than that of the 'Hiratanenashi' fruit. From these results, we determined that penetration of ethanol followed by acetaldehyde accumulation in the flesh leads to a loss of astringency in persimmons with either patch or bag treatment. Thus, we found that it is important to create a large enough accumulation of acetaldehyde in the flesh around the entire fruit to thoroughly remove the astringency from persimmon fruits.
