Penelope Perkins-Vazie and Julie Collins of the association's South Central Agricultural Research Laboratory in Lane, Okla. tested several popular varieties of watermelon for levels of carotenoids -- a nutrient that can repair damage from the sun, chemicals, and everyday living -- and the antioxidant lycopene, which may help prevent heart disease and some forms of cancer.
The watermelons were stored for 14 days at 41, 55 and 70 degrees Fahrenheit. The researchers found the fruit actually produced more nutrients after picking, even though the watermelons were selected by commercial growers as "fully ripe when harvested."
However, the study also showed that chilling slowed this process. Watermelons stored at room temperature (70 degrees) contained up to 40 percent more lycopene and 50 to 139 percent more beta-carotene, which the body transforms into vitamin A.
While most people turn to refrigeration to increase the life of perishables, the researchers wrote that watermelons were the exception. "The usual shelf life for watermelons is 14 to 21 days at 55 F after harvest," they wrote. "At refrigerated temperatures, like 41 degrees, watermelon starts to decay and develop lesions after a week."