For many Americans, nothing is better on a hot day than biting into an ice-cold slice 1 of watermelon. But scientists now say the juicy summer fruit is most nutritious when stored and served at room temperature.

The Study

Researchers compared the levels of key antioxidants in whole watermelons that were either refrigerated or stored at room temperature for two weeks. Ripening watermelon at room temperature increases its nutritional value.

"The amount of lycopene in watermelons increased an average of 20% when we left them out uncut at room temperature, while beta caro tene actually doubled," said study author Penelope Perkins-Veazie, a plant physiologist at the South Central Agricultural Research Laboratory with the USDA Agricultural Research Service in Lane, Oklahoma.

Perkins-Veazie noted that, like tomatoes, the red flesh of watermelons owes its coloring to an abundance of the antioxidant lycopene, an organic pigment from the carotenoid family that ranges in shade from pale yellow to deep red. Beta carotene another carotenoid—is also present in watermelons, although at far lower levels.

Researchers realized that little was known about the impact storage can have after harvesting and packaging and once the heavy fruit is in the kitchen.

The Results

After two weeks, the researchers found that lycopene levels were dependent on storage temperature. Ripening at room temperature increases nutritional value.

Compared with measurements taken at picking, carotenoid levels in melons stored at room temperature (70 degrees F) increased by 11% to 40%, depending on the variety.

The carotenoid level of melons stored at below room temperature, by contrast, did not increase. The researchers posited that a drop in carotenoid activity at the colder temperatures might have halted a ripening process that continues the buildup of beneficial antioxidants.

Food Safety

"But we don't want people to think they can take cut watermelon and just leave it out in room temperature, because that's a safety issue, cautioned Perkins-Veazie.

"If it's cut, you want to leave it in the fridge," she advised. "If it's uncut, it's perfectly all right to leave it on the counter for a day or two."

Lona Sandon, an assistant professor of clinical nutrition at the University of Texas Southwestern Medical Center at Dallas, agreed that food safety takes precedence over antioxidant concerns.

"But you can leave certain fruits sitting out," she added. "In fact, there are several fruits that ripen better when left out-peaches, bananas --that not only end up having better nutrient quality but also perhaps better taste.”

No-Guilt Watermelon Cake

Who thought of watermelons in a cake? Here's a show-stopping dessert perfect for special occasions.


1 watermelon container (8 ounces) fat-free frozen whipped topping, thawed

1 container (8 ounces) nonfat light lemon yogurt

Fresh fruit to decorate cake (strawberries, kiwi fruit, grapes, blueberries)


Select a symmetrical watermelon approximately 7 to 9 inches in diameter. Cut a 3-inch thick cross section from the watermelon. Out 4 slits through rind without cutting flesh. Cut between white rind portion and red flesh to remove rind. Fold together whipped topping and yogurt. Pat watermelon cake dry with paper towel.

Place watermelon cake on flat serving plate. Frost top and sides with whipped topping mixture. Decorate as desired with fresh fruit. Refrigerate until ready to serve. Can be stored several hours or overnight. Cut in wedges to serve.

Servings: Serves 10

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