Abstract
Astringent persimmons (Yokono cv.) were peeled and then sun-dried under usual weather conditions. The mechanism of astringency removal was examined, with particular attention given to the relation between gas exchange and the insolubility of soluble tannin in fruit. The amount of soluble tannin in persimmons decreased markedly during seven to nine day′s drying and the organoleptic test for astringency was almost negative. The fruit weight decreased about 45% during this period.
1. The amounts of oxygen intake and carbon dioxide production from dried persimmons decreased markedly from the third to ninth days, after which the decrease was more gradual. On the other hand, in astringent persimmons dried with peels, in which astringency did not disappear, the amount of the above gases remained nearly constant through nineteen days of drying.
2. Alcohols (containing both of methanol and ethanol) increased in percentage by weight as the persimmon dried, but the percentage remained almost constant when calculated relative to the original fresh fruit weight. The alcohol content was considerably greater than that of aldehyde from the beginning of the drying period. It is concluded that these alcohols do not affect the removal of astringency.
3. Acetaldehyde was small in quantity in the fresh fruit, but during the first four weeks of drying it increased considerably to a value equal to that of the original fresh fruit weight.
4. From these results, it can be concluded that the removal of persimmon astringency by sun drying is due to the reaction between soluble tannin and acetaldehyde which is formed by incomplete respiration due to the membrane formed on the fruit surface during drying and to the degradation of fruit tissues.
