Alongside of tomatoes, watermelon has moved up to the front of the line in recent research studies on high-lycopene foods. Lycopene is a carotenoid phytonutrient that's especially important for our cardiovascular health, and an increasing number of scientists now believe that lycopene is important for bone health as well. Among whole, fresh fruits that are commonly eaten in the U.S., watermelon now accounts for more U.S. intake of lycopene (by weight of fruit eaten) than any other fruit. Pink grapefruit and guava are two other important fruit sources of lycopene, although in the U.S., these fruits are more often consumed in the form of juice.
Health scientists are becoming more and more interested in the citrulline content of watermelon. Citrulline is an amino acid that is commonly converted by our kidneys and other organ systems into arginine (another amino acid). The flesh of a watermelon contains about 250 millligrams of citrulline per cup. When our body absorbs this citrulline, one of the steps it can take is conversion of citrulline into arginine. Particularly if a person's body is not making enough arginine, higher levels of arginine can help improve blood flow and other aspects of our cardiovascular health. There's also some preliminary evidence from animal studies that greater conversion of citrulline into arginine may help prevent excess accumulation of fat in fat cells due to blocked activity of an enzyme called tissue-nonspecific alkaline phosphatase, or TNAP.
If you've gotten used to thinking about the juicy red flesh at the center of a watermelon as its only nutrient-rich area—and far more nutrient-rich than the more lightly-colored flesh that is farther out near the watermelon rind—it is time to change your thinking. In a recent study, food scientists compared the nutrient content of flesh from different parts of a watermelon: flesh from the center, the stem end, the blossom end (opposite from the stem), and the periphery (the part nearest to the rind). What they've discovered were impressive concentrations of phenolic antioxidants, flavonoids, lycopene, and vitamin C in all of these different areas. The exact distribution of nutrients was also highly dependent on the variety of watermelon. But there was no area in any of the watermelon varieties that came out badly in terms of nutrients, and in many of the watermelon varieties, the flesh's outer periphery contained impressive concentrations of most nutrients.
Recent studies have confirmed the nutritional importance of allowing a watermelon to fully ripen. For example, research has shown that the biggest jump in lycopene content occurs at the time when a watermelon's flesh turns from white-pink to pink. Yet when that flesh continues to ripen, resulting in a color change from pink to red, the lycopene content becomes even more concentrated. Prior to ripening, when the flesh of a watermelon is primarily white in color, its beta-carotene content is near zero. Even when allowed to ripen to the white-pink stage, a watermelon still contains very little of its eventual beta-carotene content. But as it moves from white-pink to pink to red, the beta-carotene content of a watermelon steadily increases. Like lycopene and beta-carotene, total phenolic antioxidants in a watermelon also increase consistently during ripening, all the way up until the appearance of fully red flesh. The bottom line: eating a fully ripe watermelon can really pay off in terms of nutrient benefits. Please see our section called "How to Select and Store" to learn about determining a watermelon's ripeness before you purchase it.
If you have ever tasted a watermelon, it is probably no surprise to you why this juicy, refreshing fruit has this name. Watermelon has an extremely high water content, approximately 92%, giving its flesh a juicy and thirst-quenching texture while still also subtly crunchy. As a member of the Cucurbitaceae family, the watermelon is related to the cantaloupe, squash, pumpkin, cucumber, and gourd that grow on vines on the ground. Watermelons can be round, oblong, or spherical in shape and feature thick green rinds that are often spotted or striped. (Many people report, however, that they like the taste and predictable ripeness of a watermelon best if the watermelon is symmetrical in shape.) Watermelons range in size from a few pounds to upward of ninety pounds. Between 600–1,200 different varieties of watermelon exist worldwide, but all of these varieties belong to the same scientific genus and species of plant, called Citrullis lanatus.
While we often associate a deep red/pink color with watermelons, there are many varieties that feature orange, yellow, or white flesh. These varieties are typically lower in the carotenoid lycopene than red/pink varieties.
A good bit of controversy has arisen over the exact nature of seedless watermelons. Contrary to some information that you will find on various websites, seedless watermelons are not the result of genetic engineering. Seedless watermelons are the result of hybridization. By crossing a diploid watermelon (with two sets of chromosomes) and a tetraploid watermelon (with four sets of chromosomes), it is possible to produce a watermelon that contains triploid seeds (with three chromosomal sets). When planted, these triploid seeds will grow into seedless watermelons. Seedless watermelons will typically appear to contain some white seeds even though they are labeled as seedless. These white seeds are not actually seeds, but only empty seed coats.
Ten years ago, it was somewhat rare to find seedless watermelons in the marketplace. Today, up to 85% of all watermelons produced in the U.S. are estimated to be seedless. This great increase in the availability of seedless watermelons is due to the vastly increased use of "non-bearing pollinators" by watermelon growers. Previously, growers were required to interplant rows of acreage with seeded, fruit-bearing watermelons in order to pollinate their seedless varieties. Today, they are able to pollinate with plants that produce flowers needed by bees, but yield no fruit. These non-fruit-bearing plants allow pollination to continue, but in a less time-consuming and space-consuming way. It's possible to grow seedless watermelons most anywhere that seeded watermelons will grow. Some of the more common seedless varieties include Fandango, Super Cool, Honeyheart, King of Hearts, Queen of Hearts, Crimson Trio, Scarlet Trio, and SuperSweet.
Some common varieties of seeded watermelon include Jubilee, Royal Jubilee, Royal Sweet, Crimson Sweet, Sangria, Fiesta, Sugar Baby, Baby Doll, and Charleston Gray. A 15–20 pound diploid, seeded watermelon will typical contain hundreds of seeds.
History Watermelons are generally believed to have originated in Africa several thousand years ago and to have traveled over time from Africa to Asia to Europe to North America. Their arrival in Asia and the Middle East is believed to date back to approximately 900–1,000 A.D., and their arrival in Europe is estimated to have occurred in 1300–1400 A.D. It was not until Europeans began to colonize North America that watermelons arrived in what is now the U.S.
Today, over four billion pounds of watermelon are produced each year in the U.S. About 85% of watermelons are purchased in fresh form by consumers. Although there is some watermelon production in virtually all states, about three-fourths of all U.S. watermelons are grown in Florida, California, Texas, Georgia, and Indiana. On an average, per person basis, we eat over 15 pounds of fresh watermelon each year.
On a global basis, China is by far the largest watermelon-producing country and accounts for over half of all world production. The European Union countries, Iran, Turkey, Egypt, Brazil, and the United States are the next largest watermelon producers, but each produces less than 5% of the world total.
How to Select and Store If you are purchasing a pre-cut watermelon that has already been sliced into halves or quarters, choose the flesh that is deepest in color and lacks any white streaking. If the watermelon is seeded, the seeds should also be deep in color, or white.
When purchasing a whole, uncut watermelon, there are several features to you'll want to evaluate. The first is its weight. A fully ripened watermelon will feel heavy for its size. Heaviness in a watermelon is a good thing because the water content of a watermelon will typically increase along with ripening, and a fully ripened watermelon will be over 90% water in terms of weight, and water is one of the heaviest components in any food
Second, look for a watermelon with a relatively smooth rind that is slightly dulled on top. The top and the bottom of a watermelon are worth determining and examining on a watermelon. The bottom or "underbelly" of a watermelon is the spot where it was resting on the ground. If that "ground spot" is white or green, the watermelon is unlikely to be fully ripe. A fully ripened watermelon will often have a ground spot that has turned creamy yellow in color. Opposite from the ground spot will be the top of the watermelon. In a fully ripened watermelon, that spot will typically not be shiny but somewhat dulled. The green color may appear in many different shades, however, from light green to deeper shades.
Perhaps most controversial about ripeness testing of a watermelon is whether or not to give it a thump. We've read many arguments both pro and con. However, among experts who recommend thumping, most seem to agree that a fully ripened watermelon will have a deeper, hollower "bass" sound rather than a solid and shallow "soprano" sound.
Finally, some grocers will be willing to core an uncut watermelon so that you can have an actual taste. (If you decide not to purchase the melon, the grocer can slice it up and sell it in sliced form.) So consider requesting this if you are uncertain as to the quality.
Uncut watermelons are best stored at temperatures of 50-60°F (10–16°C). In many regions, room temperatures will typically be warmer than 60°F and may be less than ideal for whole watermelon storage due to increased risk of decay. Better storage temperatures will typically be found in cellars or basements that are partly or completely below ground level. While we've seen one study showing increases in lycopene content when whole watermelon was stored at a temperature of 68°F (20°C), we believe that a fully-ripe or close-to-fully-ripe melon will already have outstanding lycopene content and that it would be better for you to err on the safe side in terms of decay risk if you are planning to wait several days before slicing open your watermelon.
Like temperatures above 60°F (16°C), temperatures much below 50°F (10°C) are not recommended for storage of uncut watermelons. This is due to increased risk of chilling-type injury that can decrease shelf life and flavor. (Therefore, the refrigerator would not be a good place for you to store a whole, uncut watermelon for this reason.)
With uncut, whole watermelon, one final storage precaution would be the avoidance of contact with high ethylene-producing foods like passion fruit, apples, peaches, pears, and papaya. Watermelons are ethylene-sensitive fruits that may become overly ripe too quickly under these circumstances.
Once cut, watermelons should be refrigerated in order to best preserve their freshness, taste, and juiciness. Store your cut watermelon in a sealed, hard plastic or glass container with a lid.
Tips for Preparing WatermelonWash the watermelon before cutting it. Due to its large size, you will probably not be able to run it under water in the sink. Instead, wash it with a wet cloth or paper towel.
Depending upon the size that you desire, there are many ways to cut a watermelon. The flesh can be sliced, cubed, or scooped into balls. Watermelon is delicious to eat as is, while it also makes a delightful addition to a fruit salad.
While many people are just accustomed to eating the juicy flesh of the watermelon, both the seeds and the rind are also edible and nutrient-rich. (In fact, in many parts of the world, watermelon seeds are widely enjoyed as a snack and pickled watermelon rind has a rich culinary tradition.) If you choose to eat the rind, we recommend purchase of certified organic watermelon. (The reason for this suggestion is an increased risk of unwanted contaminants like pesticide residues on the outer skin of non-organic watermelon.)
How to EnjoyA Few Quick Serving Ideas
Purée watermelon, cantaloupe and kiwi together. Swirl in a little plain yogurt and serve as refreshing cold soup.
In Asian countries, roasted watermelon seeds are either seasoned and eaten as a snack food or ground up into cereal and used to make bread.
A featured item of Southern American cooking, the rind of watermelon can be marinated, pickled, or candied.
Watermelon mixed with thinly sliced red onion, salt and black pepper makes a great summer salad.
Watermelon is a wonderful addition to fruit salad. And fruit salad can be made days ahead since cut fruit, if chilled, retains its nutrients for at least 6 days.