Relationship between Differences in the Ease of Removal of Astringency among Fruits of Japanese Persimmon (Diospyros kaki Thunb.) and Their Ability to Accumulate Ethanol and Acetaldehyde.

Abstract

The relationship between the accumulation of ethanol and acetaldehyde in the flesh of five Japanese persimmon cultivars and the ease of removal of astringency after harvest with ethanol vapor and carbon dioxide treatment was investigated. The degree of softening of the flesh during the ethanol treatment varied with the cultivar. Likewise, the rate of decrease in soluble tannins differed among cultivars with either treatment, fruits of some cultivars remained astringent even after treatment. The amount of ethanol and acetaldehyde which accumulated in the flesh varied from one cultivar to another depending on the treatment. The rate of decrease of soluble tannins was closely related to the levels of acetaldehyde that accumulated in the flesh. The coagulation response time of fruit juices to acetaldehyde vapor was about the same in the five cultivars. These results suggest that tannin polymerize readily in those cultivars which accumulate acetaldehyde rapidly to a relatively high levels, and they explain why the amount of soluble tannins decreases slowly when ethanol slowly penetrates the fruit skin and/or if the absorbed ethanol is not rapidly metabolized to acetaldehyde.