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Antioxidants in the Microwave
Blanching and Freezing also Robs Them, Study
By Amanda Gardner, HealthDay Reporter
THURSDAY, Oct. 16 (HealthDayNews) -- Getting the necessary
nutrients from vegetables may be even harder than you thought.
New research shows that different ways of preparing,
storing and processing vegetables can affect how good they are for
Broccoli, for instance, can lose as much as 97 percent
of some antioxidants, or cancer-fighting compounds, when it is zapped
in the microwave.
Vegetables that are blanched before freezing (a common
processing technique) can lose up to one third of their antioxidants.
Frozen storage can also cause losses, albeit much smaller ones.
Two studies detailing these findings appear in the November
issue of the Journal of the Science of Food and Agriculture.
Antioxidants are plentiful in vegetables and work to
eliminate free radicals, which can damage cell DNA and contribute to
various diseases. That's why eating fiber, fruits, and vegetables,
all of which contain antioxidants, can help prevent cancer and cardiovascular
As it turns out, though, that protective effect is most
pronounced when the vegetable is in its natural state.
The first study found that the simplest cooking method
was also the worst when it came to preserving nutrients. Broccoli lost
97 percent of flavonoids, 74 percent of sinapics and 87 percent of
caffeoyl-quinic derivatives (three different types of antioxidants)
when it was microwaved.
When boiled the conventional way (i.e., not in a pressure-cooker),
this green lost 66 percent of its flavonoids; when tossed in a pressure
cooker, broccoli lost 47 percent of its caffeoyl-quinic acid derivatives.
Steamed broccoli, on the other hand, lost only 11 percent,
0 percent and 8 percent, respectively, of flavonoids, sinapics, and
The advantage of steaming vs. conventional boiling is
that you're "not using water directly in contact with the vegetable.
The nutritional compounds don't go into the water," says Cristina
Garcia-Viguera, lead author of this paper. "Once the compounds
are in the water, the temperature destroys them much easier."
A microwave wreaks havoc because it heats the inside
of the vegetable. That, combined with the fact that you normally use
water when microwaving, causes the destruction of valuable nutrients.
Even reheating steamed broccoli in a microwave would
probably have the same effect, Garcia-Viguera says, although she did
not specifically examine this in her research.
The findings can probably be extrapolated to many other
vegetables but, again, the researchers did not specifically address
The second study looked at the effects of blanching and
freezing and of long-term freezer storage on more than 20 common vegetables.
As it turned out, different species showed different effects from these
In general, dietary fiber components were not affected
or even went up slightly. Mineral content, also, tended to remain stable.
On the other hand, antioxidant activity went down 20
percent to 30 percent during blanching.
Carrots, peas, and broccoli lost 30 percent of their
vitamin C during blanching/freezing, while green beans lost 10 percent
and spinach lost 40 percent (with an additional 30 percent lost during
deep frozen storage).
Spinach also lost almost 40 percent of its potassium
and 70 percent of its folic acid during blanching.
Don't despair just yet, says Samantha Heller, a senior
clinical nutritionist at New York University Medical Center in New
The use of these vegetables in the studies meant they
were nutritious in the first place, she says. "Then I'm still
reaping the benefits even if they're losing some of their qualitative
values," she says.
Moreover, Heller points out, not all of the healthy properties
of vegetables are being eliminated. "You're still getting plenty
of healthy compounds as well as fiber, so there's absolutely no reason
not to eat vegetables -- although, of course, the fresher the better," she
"If people are willing to have vegetables anyway,
shape or form, even if they are going to nuke then, I'd rather have
them do that,"
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