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

摘要

Characteristics of astringency removal in persimmon cv. Saijo fruits treated with 80% CO2 and ethanol vapour (EtOH) were investigated in relation to acetaldehyde production. Soluble tannin concentration in the flesh decreased rapidly with exposure to acetaldehyde vapour. A decrease in soluble tannin content in the flesh treated with CO2 coincided with an increase in acetaldehyde content to 0.15μl/g FW. EtOH treatment, which also resulted in a decrease in soluble tannin content simultaneously caused an accumulation of acetaldehyde to only 0.025μl/g but an accumulation of EtOH to 8.0μl/g. Thus, whether acetaldehyde 'triggered' the tannins to polymerize is questionable. Acetaldehyde evolution from flesh discs incubated with ethanol or pyruvic acidsolution was determined before, and 2 days after, CO2 and EtOH treatments. Flesh discs treated with CO2 and incubated with pyruvic acid yielded nearly 5 nl of acetaldehyde/g, whereas those treated with CO2 + EtOH yielded only 0.25 nl acetaldehyde after6 h. Ethanol treatment reduced acetaldehyde evolution in the discs incubated with ethanol, whereas the level was not affected by incubation with pyruvic acid. Increases in alcohol dehydrogenase (ADH) and pyruvate decarboxylase (PDC) activities were detected in the flesh following CO2 treatment. EtOH treatment did not affect PDC activity in the flesh but decreased ADH activity. The results demonstrate that EtOH treatment results in the removal of astringency in Saijo fruits, but EtOH may act independently of the accumulation of acetaldehyde in the tissue.