Characteristics of acetaldehyde accumulation and removal of astringency with ethanol and carbon dioxide treatments in 'Saijo' persimmon fruit

Characteristics of removal of astringency in Japanese persimmon 'Saijo' fru it with 80% carbon dioxide (CO2) and ethanol vapor (EtOH) were investigated in relation to acetaldehyde production. Soluble tannin concentration in the flesh decreased rapidly by exposure to an acetaldehyde vapor. A decrease in soluble tannin content in the flesh treated with CO2 was coin cided with an increase in acetaldehyde content to 0.15 mu l/gFW. EtOH treat ment, which also resulted in a decrease of soluble tannin content simultane ously caused an accumulation of acetaldehyde to only 0.025 mu l/gFW but an accumulation of EtOH to 8.0 mu l/gFW. Thus, acetaldehyde 'triggered' the ta nnins to polymerize is questionable. Acetaldehyde evolution from the flesh discs incubated with ethanol or pyruv ic acid solution was determined before and 2 days after CO2 and EtOH treatm ents. Flesh discs treated with CO2 and incubated with pyruvic acid yielded nearly 5 nl of acetaldehyde/gFW, whereas those treated with CO2 + EtOH yiel ded only 0.25 nl acetaldehyde after 6 hr. Ethanol treatment reduced acetald ehyde evolution in the incubated discs with ethanol, whereas the evolution level with pyruvic acid was not affected. The increases in alcohol dehydrogenase (ADH) and pyruvate decarboxylase (PD C) activities were detected in the flesh with CO2 treatment. EtOH treatment did not affect PDC activity in the flesh but decreased ADH activity. Our results demonstrate that EtOH treatment result in the removal of astrin gency of 'Saijo' fruit, but EtOH may act independently of the accumulation of acetaldehyde in the tissue.