Storage Temperature and Ethylene Influence on Ripening of Papaya Fruit

Abstract

The temperature and ethylene response of ripening papaya fruit (Carica papaya L. cv. Sunset) was determined with and without 14 days of storage at 10C. Temperatures at or higher than 30C adversely affected the quality of the ripe papaya. Papayas held at 32.5C for 10 days failed to ripen normally, as evidenced by poor color development, abnormal softening, surface pitting, and an occasional off-flavor. Skin yellowing, fruit softening, and flesh color of papayas exhibited a quadratic response to ripening time within the temperature range of 22.5 to 27.5C. Flesh color development of nonstored fruit did not change significantly during the first 6 days at ripening temperatures, then rapidly increased. Fruit stored for 14 days at 10C exhibited faster ripening rates (e.g., degreening and softening and no delay in flesh color development) than nonstored fruit when removed to other ripening temperatures (17.5 to 32.5 C). Problems of weight loss and development of external abnormalities were more significant at temperatures higher than 27.5C. The optimal temperature range was found to be between 22.5 and 27.5C, with fruit taking 10 to 18 days to reach full skin yellowing from color break, whether or not fruit was stored at 10C. Exogenously applied ethylene (=100 μl·liter-1) stimulated the rate of fruit ripening, as measured by more uniform skin yellowing and rate of flesh softening whether or not the fruit were stored for 14 days at 10C. Ethylene did not ripen immature papayas completely in terms of skin and flesh color development. The outer portion of the flesh of ethylene-treated fruit had a faster rate of ripening, as indicated by carotenoid development and softening rate, while the same area of the flesh was still pale white in nonethylene-treated fruit. Ethylene reduced the coefficient of variation for skin color, softening rate, and flesh color development in treated fruit. Ethylene increased the rate of skin degreening and hastened the rate of carotenoid development and softening in the outer mesocarp, while having little effect on the inner mesocarp.