It is the diversity of phytonutrients in watermelon—and some key players in this group—that make this fruit unique in terms of anti-inflammatory and antioxidant benefits. You will find many different types of phenolic phytonutrients in watermelon, including carotenoids, flavonoids, and triterpenoids. Among these phytonutrients, lycopene (a carotenoid) and cucurbitacin E (a triterpenoid) stand out from a research perspective as being most closely related to this fruit's antioxidant and anti-inflammatory benefits. In the case of lycopene, you can expect to receive an average amount of 4–5 milligrams of lycopene in every 100 grams (approximately two-thirds cup in volume) of red-fleshed watermelon. This amount makes red-fleshed watermelon–on average–more concentrated in lycopene than red tomatoes, which usually contain about 3–4 milligrams per 100 grams (approximately one-half cup in volume). Moreover, the bioavailability of lycopene from red-fleshed watermelon appears to be greater than its bioavailability from red tomato. This greater bioavailability may have to do with the presence of cis-isomeric lycopene in red-fleshed watermelon, which is a more readily available form of this carotenoid. (At WHFoods, our top lycopene sources include not only watermelon and tomato but also papaya and pink grapefruit.) Lycopene is a carotenoid that has been best studied in relationship to cardiovascular disease, where it has repeatedly been shown to lower disease risk through scavenging of lipid peroxyl radicals and reactive oxygen species (ROS). Deficiencies in lycopene over the course of aging have also been associated with increased age-related cardiovascular disease. The lycopene richness in red-fleshed watermelon makes this fruit a logical choice for increased antioxidant protection, particularly as it relates to our cardiovascular system.
We think about cucurbitacin E as a second featured phytonutrient in watermelon that acts to complement the activities of lycopene. Cucurbitacin E is a triterpenoid that is known to lessen unwanted inflammation by inhibiting the activity of the enzyme cyclooxygenase-2 (COX-2). Unlike lycopene, however, it does not appear to be especially effective in the scavenging of ROS. However, it has been shown to be very effective in the scavenging of RNS (which stands for reactive nitrogen species). By combining these two phytonutrients together (lycopene and cucurbitacin E), watermelon is able to provide us with improved scavenging of both oxygen and nitrogen radicals, and to lessen our risk of undesirable oxidative stress or chronic unwanted inflammation.
Within the context of cardiovascular benefits, it's important to recognize a third nutrient in watermelon present in unusual amounts. This nutrient is the amino acid citrulline. While the amount of citrulline in watermelon flesh can vary significantly, the cup of fresh watermelon that we profile on our website is estimated to contain between 200–300 milligrams of citrulline. One primary way in which citrulline can provide us with cardiovascular support is through its role in a metabolic process known as the urea cycle. In this cycle, three amino acids—citrulline, arginine, and ornithine—undergo interconversion. During this interconversion process, a key cell signaling molecule—nitric oxide (NO) —can get produced. NO plays a key role in regulation of blood pressure since it has the ability to increase expansion of our blood vessel diameter, thus lowering the pressure at which our blood flows. Levels of NO have also been determined to play a key role in the regulation of our blood sugar. Since NO is directly produced from the conversion of arginine into citrulline, researchers have long been interested in the degree to which citrulline intake can affect the overall balance of citrulline, arginine, ornithine, and NO in this area of metabolism.
Similarly, researchers have wondered if a citrulline-rich food like watermelon might provide us with potential cardiovascular benefits. One recent study has looked at this exact set of questions in a group of participants who consumed between 3–6 cups of watermelon juice per day over a period of several weeks. What the researchers found was a steady and well-maintained level of citrulline in the bloodstream of the participants, as well as an increased level of arginine. They concluded from these findings that citrulline from the watermelon juice had undergone conversion into arginine, while leaving plenty of citrulline to stabilize blood levels. In other words, the citrulline from watermelon was viewed as improving balance in this area of metabolism. These findings add to the research evidence for watermelon as a fruit that can lower our risk of high blood pressure and type 2 diabetes especially since arginine deficiency—whether chronic and moderate or temporary and serve deficiency—has been linked to increase risk of both health problems.
When considering antioxidant benefits from watermelon, it would be wrong to overlook vitamin C and beta-carotene. In our Food Rating System, watermelon qualifies as very good source of vitamin C, providing about 12 milligrams per fresh cup. Two cups' worth of this delicious fruit means that one-third of our daily recommended vitamin C intake has already been met. Watermelon ranks as a good source of vitamin A in our food rating system, and this rank is largely due to its beta-carotene content. (While watermelon contains a far greater amount of lycopene than beta-carotene, researchers do not take lycopene into account when estimating vitamin A activity since lycopene is a cartenoid that cannot be converted into retinol. Beta-carotene, however, is the best non-retinol form of carotenoids for conversion into vitamin A.) Beta-carotene is typically highest in red-fleshed varieties of watermelon, although amounts can vary greatly, in a range of approximately 5–325 micrograms per 100 grams. But even in the lower half of this range, we are getting valuable antioxidant benefits from the beta-carotene content of watermelon.
We've seen a good bit of animal research on watermelon extracts, watermelon powders, and isolated watermelon phytonutrients (like lycopene, citrulline, or cucurbitacin E) in a variety of other health areas, notably in the area of cancer risk. In this area, watermelon research has often focused on types of cancer called "aerodigestive cancers." These types of cancer include cancers of the oral cavity (mouth), larynx (voice box), pharynx (passageway connecting our nose to our mouth and throat), and esophagus (connecting our mouth to our stomach). Based on the study details that we have seen to date, we would summarize this research as being in the preliminary stages and quite far from being expanded to everyday intake of watermelon in a typical meal plan.
In the context of "other potential health benefits" from watermelon, we also want to mention the seeds of this fruit. Watermelon seeds have been the topic of growing health research and have been studied in their own right for their antioxidant and anti-inflammatory capacity. From a nutrient perspective, watermelon seeds are every bit as nutrient rich as the flesh of this fruit—and perhaps even more so. For example, you will find flavonoids, carotenoids, saponins, phenolic acids, proteins, carbohydrates, and fats in watermelon seeds. For the most part, research on watermelon seeds has focused on the same key areas of potential health benefits as research on the flesh of this fruit, namely, antioxidant, anti-inflammatory, and cardiovascular benefits.
The origins of watermelon have been traced back over 4,000 years to the continent of Africa, with indications of cultivation at least this far back in time based on artifacts and other evidence. Even though this time frame doesn't make the growing of watermelon as "ancient" a practice as the growing of other fruits like figs or grapes, it still qualifies watermelon as one of our most long-enjoyed fruits.
We might not think about watermelon as a fruit with great diversity. But the colors and shapes and sizes of watermelon are far more varied than many people realize. A "personal" size watermelon might only be 6 inches across and weight about 4 pounds. Giant watermelon varieties (for example, Carolina Cross) can frequently weigh more than 100 pounds and extend in length to nearly 3 feet. Four basic categories of identification are typically used to classify watermelon varieties: rind color, flesh color, shape, and seed status (seeded versus seedless). The chart below shows some different possibilities within each of these four categories.
|Categories of Variation in Watermelons||Seed Examples|
|Rind Color Options||light green solid, dark green solid, light green dark stripes|
|Flesh Color Options||yellow, orange, pink, red|
|Shape Options||round/globe, oval, oblong|
|Seed Status Options||seeded, seedless|
When you put all of these categories, you end up with interesting differences in watermelon varieties. Amarillo watermelons, for example, feature yellow, seedless flesh, a light green rind with narrow dark green stripes, and an overall round/globe shape. Varieties like Crimson Sweet feature red, seeded flesh, a dark green rind with broken light green stripes, and an oblong shape. Regardless of their unique combination of features, all varieties of watermelon can make great fruit choices.
Seedless watermelons are a fascinating development in watermelon breeding. (Some observers of the watermelon industry estimate that over three-quarters of all watermelons currently sold in the U.S. are seedless versions.) Given the popularity of seedless watermelons among consumers, we want to provide you with some detailed information on this issue of seeded versus seedless watermelons.
Selective growing and hybridization processes have been used to create watermelons that aren't exactly "seedless" but only contain small, sterile, partly developed soft white seeds that cannot mature into their sturdy black counterparts. Production of seedless watermelons is typically accomplished by planting small seeded watermelons plants (called "plugs" or "starts") among the seedless versions. The purpose of the seeded plants is to provide pollen for the seedless versions. The seeded versions are always planted in a lesser number than the seedless versions (for example, in a ratio of 1:3) and they may be interspersed in the field in a variety of ways. Since the interplanting of seeded versions is carried out exclusively for the purpose of pollination, watermelon varieties called "pollenizer varieties" have been developed specifically for the purpose of growing seedless watermelons.
From a genetic standpoint, overall production of seedless watermelons requires the presence of four watermelon types. Most seeded watermelon varieties contain two sets of chromosomes and are referred to as "2X." Some seeded varieties naturally contain four sets of chromosomes and are referred to as "4X." When a 2X and a 4X variety become parents, each donates one half of its chromosomes to the offspring watermelon, which ends up with 3 sets of chromosomes, making it "3X." This 3X status is what makes the resulting watermelon "seedless." From a commercial production standpoint, however, difficulties in the development of hardy tetraploid (4X) watermelon varieties have resulted in use of colchicine—an alkaloid found in crocus that is known to impact cell division—to trigger genetic changes in 2X seeded varieties that result in a doubling of their chromosome number from 2X to 4X. This step increases the availability of 4X varieties for use in production of seedless 3X watermelons.
Use of colchicine in conversion of 2X into 4X varieties is a practice that some people consider to "cross the line" into genetic modification of food. While we can understand this perspective, we also believe that it is important to point out that this practice would not be classified as genetic modification in a legal sense, nor is it similar to the standard practice that has come to be known as "genetic engineering" (GE). GE involves identification of a gene in one species (called the "donor" species) that does not exist in the species to be genetically modified (called the "recipient" species). Scientists then figure out a way to transfer the new gene from the donor species over into the recipient species. However, in the case of watermelon conversion from 2X into 4X, there is only one species of plant involved and there is no new gene being transferred from one species to another. For these reasons, we don't think about seedless watermelons as GE foods and we don't believe that they need to be avoided for GE-related reasons. But we also understand why some people might conclude otherwise and might want to stick with seeded varieties based on the information described above. In addition, it makes sense to us that some people might want to stick with seeded varieties for yet other reasons (for example the saving, sprouting, and consumption of the seeds, or the saving of the seeds for future planting, or to enjoy this fruit in a way that recognizes seed development as its natural method of reproduction).
All watermelon varieties belong to the same family and genus of plant. Watermelons belong to the Cucurbitaceae family of plants, which is especially well-known for three genera of foods that it contains. Watermelons belong to the Citrullus genus in this family of plants; squashes and pumpkins belong to the Cucurbita genus; and cucumbers and cantaloupes belong to the Cucumis genus. If you think about the overall form of these foods that are all members of the Cucurbitaceae family, their relationship makes practical sense given the location of their seeds and their overall shape. The genus/species name for watermelons is Citrullus lanatus.
Before ending this Description section, we also want to say a few words about the common name for this remarkable fruit. "Watermelon" does indeed point back to the watery content of this fruit's fleshy portion, and anyone who has enjoyed a large-sized slice of watermelon knows just how watery this fruit can be. But it's not so much the percentage of water that makes a watermelon so potentially messy, however, but the matrix of the flesh (and to a certain extent, the way that we cut into it as well). In terms of its overall water percentage, watermelon is indeed on the high side for fruit at approximately 90%. That being said, the weight of all fruits profiled on our website falls between 75-95% water. And in addition, the percent water weight of our WHFoods vegetables falls into this exact same range!
As mentioned in the previous section, watermelons are known to have originated in Africa approximately 4,000–5,000 years ago. The exact location in Africa is much debated, and is thought to have been in areas in the northern, northeastern, and eastern regions of the continent. Over time, however, watermelons became naturalized to other continents, and eventually underwent cultivation in many countries across the globe. At present, major watermelon-producing countries can be found in Asia (China and Vietnam), the Middle East (Iran and Turkey), Africa (Egypt and Algeria), North America (the United States), South America (Brazil), and the Russian Federation. These countries collectively produce over 100 million tons of watermelon, with China producing by far the largest amount.
Within the U.S., Florida, Georgia, California, and Texas are the four largest watermelon-producing states. Other key producers include North Carolina, South Carolina, Arizona, and Indiana. About three-quarters of all watermelon consumed in the U.S. is also grown within the U.S. The other one-fourth is imported primarily from Mexico, Guatemala, Costa Rica, and other Central American countries.
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 that you'll want to evaluate. The first is weight. A more 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 more ripened watermelons will usually be 90% or higher in terms of their water weight. In order to find a watermelon that feels heavy for its size, it can be helpful to lift a couple of different watermelons and compare their relative weights.
A second feature to check over is the "field spot." More ripened watermelons will have sat on the ground for longer periods of time and you'll find evidence of this circumstance on the underside of the watermelon. There will typically be a slightly flattened spot that has developed a creamy yellow color. If this spot is altogether absent, or if the color is more white than cream colored, you are likely to be looking at a watermelon that was picked a little early in the ripening process.
Sometimes the stem end of a watermelon (where it attached to the vine) can provide you with a clue about ripeness. If there is a slight indentation at the stem end, the watermelon was more likely to have ripened more fully and to have detached from the vine more readily. And if you actually find a stem sticking out from the watermelon, it can be an indication that the watermelon was picked prematurely.
Overall "sheen" can also be a good way of distinguishing between degrees of ripeness. A more ripened watermelon will typically have a duller appearance, and a less ripened one will typically appear more glossy.
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 commentators who recommend thumping, most seem to agree that more ripened watermelons will have a deeper, more hollow "bass" sound rather than a solid and shallow "soprano" sound.
Finally, some grocers may be willing to core an uncut watermelon so that you can have an actual taste. If the grocer is confident about being able to sell the watermelon in sliced form should you decide not to purchase it, this step might be one that a grocer is willing to take from a business standpoint and in terms of customer support.
At WHFoods, we encourage the purchase of certified organically grown foods, and watermelon is no exception. Repeated research studies on organic foods as a group show that your likelihood of exposure to contaminants such as pesticides and heavy metals can be greatly reduced through the purchased of certified organic foods, including watermelon. In many cases, you may be able to find a local organic grower who sells watermelon but has not applied for formal organic certification either through the U.S. Department of Agriculture (USDA) or through a state agency. (Examples of states offering state-certified organic foods include California, New York, Oregon, Vermont, and Washington.) However, if you are shopping in a large supermarket, your most reliable source of organically grown watermelon is very likely to be watermelon that displays the USDA organic logo.
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. Remember that we are talking about whole, uncut watermelons here rather than watermelons that have already been sliced open. Like temperatures above 60°F (16°C), temperatures much below 50°F (10°C) are not recommended for storage of uncut watermelons due to increased risk of chilling-type injury that can decrease shelf life and flavor. For these reasons, your refrigerator would not be considered an ideal place for storage of a whole, uncut watermelon.
It's a different story, however, once you've cut into a watermelon. Here we believe that refrigeration is important. The reason being is that watermelons are a very good source of vitamin C, and a good source of both carotenoids and vitamin B6. All three of these nutrients are known to be susceptible to heat, and their loss from food is very likely to be slowed down through refrigeration. When you are storing cut watermelon in your refrigerator, we recommend a sealed container to help keep the flesh moist, to help prevent absorption of odors from other foods, and to lessen exposure to oxygen that could affect nutrients like vitamin C.
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.
If you'd like even more recipes and ways to prepare watermelon the Nutrient-Rich Way, you may want to explore The World's Healthiest Foods book.
Watermelon, diced, fresh
|vitamin C||12.31 mg||16||6.5||very good|
|pantothenic acid||0.34 mg||7||2.7||good|
|vitamin A||43.24 mcg RAE||5||1.9||good|
|vitamin B1||0.05 mg||4||1.6||good|
|vitamin B6||0.07 mg||4||1.6||good|
Density>=7.6 AND DRI/DV>=10%
Density>=3.4 AND DRI/DV>=5%
Density>=1.5 AND DRI/DV>=2.5%