成熟段階の異なるカキ‘平核無’果実のアルコール脱渋に伴う軟化と呼吸量及びエチレン生成量の関係

Abstract

′Hiratanenashi′ is the most important cultivar of Japanese persimmon (Diospyros kaki Thunb.). Because of its astringency, fruits are marketed after treating with 30-40% ethanol to remove astringency. However, a large problem is that fruits soften rather easily after alcohol treatment.To gain a better understanding of this phenomenon, fruits were harvested and treated with alcohol vapour at various stages of development from July to December. The rates of fruit softening, calyx dropping, respiration and ethylene production were studied.After harvest, respiration and ethylene production rates of nontreated fruits were high in unripened stages, but became low in ripened stages. Immature fruits softened more rapidly than mature fruits.Further experiments on physiological changes after alcohol treatment were conducted with fruits harvested at short intervals between stage II and III (from immature to mature). Respiration and ethylene production of the fruits were rapidly reduced within one or two weeks. When the rate of ethylene production was high, at the immature stage, calyx dropping and rapid fruit softening were also observed, but at the mature stage, when the rate of ethylene production was low, calyx dropping was not observed and fruit softening rates were reduced correspondingly.At the mature stage, from early October till early November, later harvesting of fruits reduces the rate of fruit softening after alcohol treatment. However, when fruits are harvested and treated with alcohol in early October, there is a risk of abrupt fruit softening. Consequently, if harvesting is delayed until at least 120 days after full bloom (about October 10), the occurrence of abrupt fruit softening in Yamagata prefecture may be avoided.