Changes in composition during ripening and storage of melons

Abstract

The late stages of development and the ripening process in cantaloupes, Honey Dews, Casabas, and watermelons are characterized by the following changes when the fruits remain attached to the plant: progressive increase in per cent of total solids, in total sugar content, in sol. solids, and in sp. gr. of the juice. Reducing sugars, which consist of approx. equal proportions of levulose and dextrose, decrease in amt. during ripening, being partly used in respiration, and partly changed to sucrose. Sucrose increases more rapidly than reducing sugars decrease, showing that sugars are moving into the fruit until the full-ripe stage is reached. The total amt. of pectic substances remains about the same, but the amt. of protopectin, high in unripe melons, decreases rapidly during ripening, with a corresponding increase of pectic substances in sol. form, suggesting that partial disintegration of cell walls is an important part of the ripening process. The flesh becomes progressively sweeter and softer, and the rind turns from green to yellow. Fruits which are picked from the plants in the immature condition show the following changes during the storage at ordinary temps. (70°-75°): little or no increase in sugar content, in the early part of the storage period, and generally a small decrease in sugars, during the latter part of storage, due to the losses occasioned by respiration. Honey Dews and Casabas during storage show the same change in form of sugars as do fruits attached to the plant, i. e., decrease in reducing sugar and increase in sucrose. The total content of pectic substances decreases slightly, and protopectin is changed to pectin, just as in fruit attached to the plant. The flesh becomes softer, but does not gain appreciably in sweetness; hence melons picked very immature, while the sugar content is low, upon artificial ripening become soft and to some extent juicy, but do not attain good flavor because of the lack of sugar. Fruits of Honey Dew and Casaba picked slightly unripe and exposed to ethylene at the rate of 1 pt. to 2000 of air, or 1 pt. to 4000 of air, for 2 to 5 days, show no increase in sugar content, but do show a marked acceleration in the rate of softening, in change from green to yellow color of the rind, and in conversion of reducing sugars to sucrose, compared to similar fruit stored without ethylene treatment. The effects of ethylene upon the ripening process are believed to be due to activation of enzymic reactions, and bring about changes in a short time that would ordinarily require a longer period. [on SciFinder(R)]