Many epidemiological studies have
concluded that a diet rich in fruits and vegetables reduces the incidence of
heart disease and cancer in humans. Scientists have found that lycopene in the
diet correlates with reduced incidence of certain types of cancer. And lycopene
levels in fat tissuean indicator of lycopene consumptionhave been
linked with reduced risk of myocardial infarction (heart attack).
Most clinical research dealing with lycopene has used tomatoes as the food
source. But Agricultural Research
Service scientists at the South Central Agricultural Research Laboratory
(SCARL) in Lane, Oklahoma, and at the Phytonutrients Laboratory in Beltsville,
Maryland, are working to determine lycopene levels in varieties of watermelon.
They also want to assess its bioavailability, that is, how well the human body
digests and uses it. Funds for the studies were provided in part by the
National Watermelon Promotion Board.
A trio of ARS scientistsplant physiologist Penelope Perkins-Veazie,
food technologist Julie K. Collins, and entomologist Sam D. Pair, research
leader at SCARLgrew, evaluated, and analyzed 13 watermelon cultivars at
the Oklahoma laboratory to establish the relative effect of genetic background
on lycopene content. The 13 cultivars included 11 red-fleshed and 2
yellow-fleshed types as well as seedless, open-pollinated, and hybrid types
representing seasonal production periods.
The researchers used tristimulus colorimeter readingsa relatively
inexpensive method to measure visible color in the cut melonsand compared
the measurements to the amounts of lycopene extracted from the melons. Lycopene
content varied widely among cultivars and types, but the seedless ones tended
to have more. Results showed that watermelon has as much or more lycopene as
raw tomatoes and that the amount depends on both variety and growing
But Can We Digest and Use It?
In late summer of 2000, ARS nutritionist Beverly A. Clevidence and chemist
Alison J. Edwards of the Phytonutrients Laboratory began a 19-week study of 23
healthy adults to assess the bioavailability of lycopene from watermelon.
The scientists used tomato juice as the known benchmark for judging the
relative bioavailability of lycopene.
Twelve female and 11 male, nonsmoking adults, ages 36-69, participated in
the study. All ate a controlled weight-maintenance diet along with watermelon
juice at the study facility during the three treatment periods. The watermelon
juice was prepared at ARS' Citrus and Subtropical Products Laboratory in Winter
Haven, Florida. The juice was bottled and frozen immediately without
pasteurization and defrosted just before it was consumed. The scientists then
analyzed the lycopene content of the juice.
Blood and fecal samples were collected at the study's onset and then weekly
during each treatment period.
Participants completed three 3-week regimens, each preceded by a washout
period during which they received a minimal amount of dietary lycopene. In a
random order, all volunteers received the W-20 treatment (20 milligrams of
lycopene a day from watermelon juice) and the C-0 treatment (control, no
juice). In addition, they received either the W-40 treatment (40 milligrams of
lycopene a day from watermelon juice) or the T-20 treatment (20 milligrams of
lycopene a day from tomato juice).
The investigators found that all juice treatments increased the plasma
concentration of lycopene. Lycopene concentration was similar regardless of
whether subjects consumed 20 milligrams of lycopene from tomato juice or from
watermelon juice, which was not heat-processed.
The investigators had expected lycopene availability to be greater from
tomato juice because it had received heat treatment, which is believed to
improve lycopene bioavailability.
"To our knowledge, this is the first study to show that lycopene from
watermelon is bioavailable," says Clevidence. "Next, we would like to
find out if plasma lycopene levels are higher when people eat watermelon with a
meal containing fat than when they eat it by itself."
Hooray for Watermelon!
Watermelon is fat free and is a source of vitamins A, B6, C, and thiamin.
Studies have shown that a cup and a half of watermelon contains about 9 to 13
milligrams of lycopene. On average, watermelon has about 40 percent more
lycopene than raw tomatoes. Red, ripe flesh is the best indicator of the
sweetest and most nutritious watermelon, though it's hard to choose the ripest
melon when it's uncut.
"We think there are a lot of potential uses for watermelon that are
just beginning to be explored," says Perkins-Veazie. "It can be a
so-called functional foodone that can help prevent certain
There is commercial interest in producing watermelon juice. A company in
California has perfected a great-tasting, all-natural version that is already
selling in California and Oregon.By Jennifer
Arnold, formerly with ARS.
This research is part of Human Nutrition (#107) and New Uses of Plant
Products (#106), two ARS National Programs described on the World Wide Web at
Julie K. Collins, and
Sam D. Pair are with the USDA-ARS
South Central Agricultural Research
Laboratory, Hwy. 3 West, Lane, OK; phone (580) 889-7395, fax (580)
Beverly A. Clevidence and
Alison J. Edwards are with the
Laboratory, 10300 Baltimore Blvd., Bldg. 308, Room 114, Beltsville, MD
20705-2350; phone (301) 504-8396 [Clevidence], (301) 504-8430 [Edwards], fax