[NAFEX] Watermelons Are Healthier When Served Warm
Sam.Brungardt at state.mn.us
Mon Jul 31 11:12:16 EDT 2006
Watermelons Are Healthier When Served Warm
07.31.06, 12:00 AM ET
MONDAY, July 31 (HealthDay News) -- For many Americans, nothing is
better on a hot day than biting into an ice-cold slice of watermelon.
But scientists now say the juicy summer fruit is most nutritious when
stored and served at room temperature.
Reporting in the Aug. 9 issue of the Journal of Agriculture and Food
Chemistry, the researchers based their premise on a tally that compared
the levels of key antioxidants in whole watermelons that were either
refrigerated or stored at room temperature for two weeks.
"What we found was very surprising," said study author Penelope
Perkins-Veazie, a plant physiologist at the South Central Agricultural
Research Laboratory with the USDA Agricultural Research Service in Lane,
"The amount of lycopene in watermelons went up about an average of 20
percent when we left them out uncut at room temperature, while beta
carotene actually doubled," she said.
Perkins-Veazie noted that, like tomatoes, the red flesh of watermelons
owes its coloring to an abundance of lycopene, an organic pigment from
the carotenoid family that ranges in shade from pale yellow to deep red.
Beta carotene -- another carotenoid -- is also a nutritional feature of
watermelons, although at far lower levels.
Antioxidants gobble up cancer-causing free radical molecules that can
While it is known that light, temperature and moisture changes which
occur during harvesting and packaging can alter a watermelon's lycopene
content by 10 percent to 20 percent, the researchers realized that
little was known about the impact storage can have once the heavy fruit
is in the kitchen.
To fill in the blanks, Perkins-Veazie and her USDA colleague Julie K.
Collins focused on three popular seeded and seedless varieties of
All were described by their Oklahoma harvesters as "fully ripe" when
acquired. Whole, uncut samples of each of the melons were kept in a
cooler for one night at 68 degrees Fahrenheit (F) before being cut up
and sampled for color, condition and carotenoid content.
Twenty samples of each melon variety were then weighed and stored in
coolers set at either 41, 55, or 70 degrees F.
After two weeks, the researchers found that lycopene levels were
dependent on storage temperature.
Compared to measurements taken at picking, carotenoid levels in melons
stored at room temperature were up between 11 percent and 40 percent,
depending on the variety.
As visual proof of this biochemical development, the authors observed
that, after the 14 days of storage, the flesh of all three varieties of
watermelons kept at room temperature was darker than they had been when
they were freshly picked -- a sign of increased pigmentation from the
These room-temperature melons also had thinner rinds, a sign of
The flesh of melons stored at either of the below-room temperature
levels, by contrast, had not experienced any gains in carotenoids.
Such melons either lost color or maintained the same color as when
picked, with no change in rind thickness.
The researchers posited that a drop in carotenoid enzyme activity at the
colder temperatures might have halted a ripening process that continues
the build-up of beneficial antioxidants.
"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,"
"If it's cut, you want to leave it in the fridge," she advised. "If it's
uncut, it's perfectly alright to leave it on the counter for a day or
two, and if you like cold watermelon -- which a lot of people do -- it's
perfectly alright to put it in the fridge to let it cool down a little
before eating it."
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. "If you're
not going to eat it right away, they don't have to be taking up space in
your fridge. 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."
Connie Diekman, director of nutrition at Washington University in St.
Louis, did not think the study considered all the nutritional factors
related to the temperature issue.
"I could not find where they looked at some of the water-soluble
nutrients in the melon which we know are very sensitive to light and
air," Diekman said. "So, I would be curious to know if there were
changes to any of those on a negative side that might have offset this
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