Abstract
Characteristics of removal of astringency in Japanese persimmon 'Saijo' fruit 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 coincided with an increase in acetaldehyde content to 0.15μl/gFW. EtOH treatment, which also resulted in a decrease of soluble tannin content simultaneously caused an accumulation of acetaldehyde to only 0.025μl/gFW but an accumulation of EtOH to 8.0 μl/gFW. Thus, acetaldehyde 'triggered' the tannins to polymerize is questionable. Acetaldehyde evolution from the flesh discs incubated with ethanol or pyruvic acid solution 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/gFW, whereas those treated with CO2+EtOH yielded only 0.25 nl acetaldehyde after 6 hr. Ethanol treatment reduced acetaldehyde 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 (PDC) 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 astringency of 'Saijo' fruit, but EtOH may act independently of the accumulation of acetaldehyde in the tissue.
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