Effect of Postharvest Heat Treatment and Storage on Sugar Metabolism in Polyethylene-wrapped Muskmelon Fruit

Postharvest sugar content and activities of four enzymes of sucrose metabolism were followed in the edible mesocarp tissue of the netted muskmelon ( Cucumis melo L., var. reticulatus, cv Magnum 45). Melons harvested at full-slip were shrink film-wrapped to inhibit water loss and/or heated to 45°C for 3 hr before storage at 4°C for up to 18 days. Sucrose content of edible mesocarp remained constant between harvest and 12 days of storage. The sucrose content of nonheated fruit declined between 12 and 18 days of storage, but there was no coincident increase in glucose or fructose. There was little acid invertase activity. Neutral invertase activity did not vary significantly with storage, but was slightly higher in heated, wrapped fruit than in nonheated, wrapped fruit. Sucrose synthase activity increased with storage, and was higher in heated than nonheated fruit. There was no discernible pattern of sucrose-phosphate synthase activity. No enzyme activity was correlated with the content of any sugar.