Starch to Sugar Conversion in Tsugaru Apples under Ethylene and 1-Methylcyclopropene Treatments

The effects of ethylene and 1-methylcyclopropene (1-MCP) on sugar accumulation during storage of Malus domestica Borkh. cv. "Tsugaru" apples were evaluated. Fruit was harvested and treated with ethylene and 1-MCP at both immature and mature stages. The loss of starch content in immature "Tsugaru" fruit was observed in ethylene-treated fruit at days 7-10, and the total sugar content of all tissue zones only changed slightly following storage. The highest sugar content was of fructose, and the lowest was of sorbitol. The difference in sugar content between ethylene-treated and untreated fruit was observed only after four days of treatment. Other ripening aspects of the immature fruit, such as respiration rate and ethylene production, were not affected by ethylene and 1-MCP. In the mature fruit, the sugar content changed slightly between days 4-7 and then dropped on day 10. Ethylene treatment resulted in an increase in starch hydrolysis and also affected the ripening characteristics of the fruit. However, exogenous ethylene did not seem to induce sugar accumulation in mature "Tsugaru" fruit during storage. Therefore, this study indicates that the accumulation of sugars in the detached ‘Tsugaru’ fruit during storage seems to correlate differently with the ripening properties and starch hydrolysis, depending on fruit maturity at harvest and its storage duration.