A Melon for Dieters and Diabetics

August 1, 2007 at 2:03 am

Mention watermelon and people immediately think of sweet, juicy, crimson-colored fruit. But watermelons didn’t start that way, notes Angela R. Davis of the U.S. Agricultural Research Service. Wild watermelons in their native Africa are white fleshed, the size of softballs, and “hard like softballs,” she notes. Bitter and anything but sweet, watermelons hardly started as dessert.

LOOKS THE SAME, BUT. . . These melons may resemble the conventional supermarket versions, but they’re far less sweet. That means they would fit well into sugar- or calorie-paring diets. Davis

LYCOPENE SOURCE. These reduced-sugar melons may not be terribly sweet, but they remain rich in lycopene, a potentially healthful plant pigment. As their slightly lighter color suggests, the lower-sugar melons (top) are also lower in lycopene than the moderately-sweet types (bottom). Davis

On the other hand, U.S. domesticated watermelons are so sweet that they tend to be off-limits to most of the nation’s 20 million people with diabetes. People adhering to low-carb diets also shun the fruit. So, Davis, a melon geneticist and enthusiast, embarked on developing a low-sugar alternative to the standard U.S. supermarket melon. She started by screening a host of noncommercial melons, including many that retained some of their wild traits.

“The project took a lot longer than we expected,” she says. “Because there’s a correlation between color and sugar content,” low-sugar variants that the researchers initially found—including some wild varieties—had unappetizingly white flesh inside. However, Davis’ team eventually ran across one melon that bore yellow flesh and little sugar. Seven generations of crossbreeding progeny of this melon yielded two lines of fruit whose seeds now uniformly grow into pink, low-sugar melons. Another, even redder line produces melons with midlevel sugar content.

Davis’ group, based in Lane, Okla., describes these new melons in a pair of papers slated to be published later this year in HortScience.

The new melons may not start out sweet enough to satisfy everyone’s taste. However, adding a dash of artificial sweetener usually takes care of the problem, Davis finds. Indeed, in one taste test her group conducted, people eating the melons actually preferred a low-sugar watermelon treated with an artificial sweetener over a conventional supermarket melon.

Lots of lycopene

A natural plant pigment, lycopene, imparts the carmine hue found in most commercial watermelons. This same phytochemical is responsible for much of a tomato’s red color. However, lycopene is more than a food coloring. A carotenoid in the beta-carotene family, it’s an established antioxidant, able to quash biologically damaging chemical reactions by agents known as free radicals.

Several studies have tentatively linked diets high in lycopene with a reduced risk of cancer (see Looking for Lycopene? Tomatoes Are Okay, But . . . ). On the other hand, a Food and Drug Administration review recently reported finding “no credible evidence to support an association between lycopene intake and a reduced risk of prostate, lung, colorectal, gastric, breast, ovarian, endometrial, or pancreatic cancer.” Meanwhile, other research suggests that diets rich in the pigment reduce an individual’s risk of sunburn (see Dietary Protection against Sunburn).

With all that, breeders would like to retain a watermelon’s bounty of lycopene while offering a low-sugar alternative. And Davis’ group succeeded. The typical watermelon today has 40 to 46 micrograms of lycopene per gram (µg/g) of fruit—although some small melons can reach 120 µg/g. The new bright-red, medium-sugar melon developed at the Oklahoma lab averages 66 µg/g, Davis notes, and develops about 8.5 percent sugar by volume. That’s roughly 40 percent less sugar than is typical in a commercial melon. Her team’s low-sugar lines possess only about 25 µg/g lycopene and about half the sugar of a supermarket watermelon. How sweet is that? “About as sweet as a cucumber,” Davis says.

All the new melons have the typical elliptical shape of conventional watermelons and weigh in at about 10 to 12 pounds.

The Oklahoma team will now turn its experimental melons over to seed companies, which Davis expects to further change the fruit for greater disease resistance, or perhaps to create a cultivar with a somewhat different shape, size, or color than the reduced-sugar melons that the researchers starting with.

Consumer appeal

Davis’ group teamed up with some other Oklahoma researchers for a series of taste tests in a Native American community plagued by a high incidence of diabetes. The researchers recruited 125 middle school and high school students. Another 41 adult volunteers ranged in age from 20 to 90.

Each individual was offered two types of watermelon—a regular-sugar variety and a low-sugar fruit sweetened with sucralose, an artificial sugar that is sold in the United States under the trade name Splenda. The researchers chose sucralose because it’s some 600 times as sweet as natural sugar and has little or no unpleasant aftertaste.

“Overall, there was a significant preference for the artificially sweetened watermelons compared with the conventional watermelons,” the researchers reported last year in the International Journal of Food Sciences and Nutrition. On a six-as-highest scale, the testers ranked the conventional melon’s taste at about 4.4 and the low-sugar melons at 4.9 and 5.5, depending on how much sweetener had been added. Davis’ team concluded “that a low-sugar watermelon is a palatable fruit choice to individuals who must restrict sugar or total carbohydrate intake—with the added benefits of lycopene.”

I routinely eat my watermelon slices well into the white flesh of the rind, where I find the fruit refreshing. Davis says that one of her lab’s medium-sweet melons should satisfy me—offering a succulent snack with only a fraction of the normal calories. Yum.

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