Studies on the Removability of Astringency in Japanese Persimmon Fruits

I. “On-Tree Removal” of Astringency by Ethanol Treatment (Part I)

Abstract

Experiments were carried out using a method of applying ethanol to remove astringency from the fruits of Japanese persimmon while still on the tree. The effects of treatments on other characteristics of these fruits were also observed.
1. Astringent fruits were enclosed in polyethylene bags containing small amount (usually 2-5mls) of 5% to 20% ethanol, and kept on the tree. The ethanol vapors penetrated the flesh of the fruits, primarily through the skin, and successfully removed the astringency. The time required for complete loss of astringency varied with time of treatment, fruit size, concentration and amount of ethanol employed, and cultivar. For example, in the case of Hiratanenashi cultivar, only two days were required when the fruits were treated at the end of July with 5mls of 20% ethanol, whereas more than a week were required when they were treated in September with 4mls of 10% ethanol. The average time required was usually within five days. No substantial drop of fruits resulted from the treatment.
2. The ease of astringency removal by this method was compared among 10 cultivars. Hiratanenashi and Sakushu-Mishirazu were the easiest, followed by Seishu-Mukaku, Atago, Shimpei, Saijo, Shakoku, Gionbo, Hagakushi and Yokono in that order; the astringency being very difficult to remove in the latter four.
3. Hiratanenashi fruits were thus treated at half-monthly intervals from the middle of July to the end of September. After the loss of astringency was complete, the bags were removed and the fruit were allowed to remain on the tree until harvest time. Astringency, once removed, did not reappear. The treatment had no effect on fruit size except for July treated fruit, in which it was slightly depressed.
The non-astringent fruits showed earlier coloration and had higher contents of reducing sugars (glucose and fructose) and malic acid, compared with the astingent ones.
There was no difference in flesh firmness at harvest between astringent and non-astringent fruits.
The most characteristic phenomenon associated with the loss of astringency was the browning reaction of the flesh tissue. In treated fruits, brown flecks appeared in two weeks, increasing gradually until the entire flesh became brown. However, fruit with slight astringency remaining did not develop brown coloring of the flesh. The degree of flesh browning was greater at earlier times of treatments and at higher concentrations employed.
The browning phenomenon was observed in fruits only when they remained on the tree; it was not observed in fruits detached and stored for one month.