Hot Water Kills Broccoli's Benefits
Boiling, Blanching Can Cause Veggies to Lose Antioxidants
Oct. 17, 2003 -- Too much water may spoil a cook's best efforts
to eat healthy. Two new studies show that using a lot of water to cook
vegetables can cause them to lose much of their cancer-fighting
Researchers found blanching, boiling, or microwaving vegetables
in water caused antioxidants to leak out of the vegetables and into the cooking
water. But streaming them preserved most of these valuable nutrients.
Flavonoids, an antioxidant, are nutrients that are found
naturally in many vegetables. They're thought to have a variety of healthy
effects in the body by helping to protect cells from free radicals (unstable
compounds that damage cells).
The results appear in the November issue of the Journal of
the Science of Food and Agriculture.
Beware of Boiling Broccoli
The first study compared the effects of various cooking methods
on the antioxidant content of fresh broccoli. Researchers tested high-pressure
boiling, low-pressure (conventional) boiling, steaming, and microwaving about 5
ounces of broccoli using about two-thirds of a cup of water.
They found that microwaving the broccoli in the water for five
minutes at full power produced the greatest nutrient loss, and the microwaved
broccoli lost 74% to 97% of three key antioxidants. Boiling also led to a
significant loss of these antioxidants.
In contrast, steaming broccoli over the water for three and a
half minutes caused only minimal loss of the three antioxidants (0% to
"Most of the bioactive compounds are water soluble; during
heating they leak in a high percentage into the cooking water, reducing their
nutritional benefits in the foodstuff," says researcher Cristina
Garcia-Viguera, of the department of food science and technology at CEBAS-CSIC
in Murcia, Spain, in a news release. "Because of this, it is recommended to
cook vegetables in the minimum amount of water (as in steaming) in order to
retain their nutritional benefits."
Beware of Blanching Before Freezing
In the second study, researchers looked at the effects of
blanching 20 different types of vegetables before freezing and storing
They found that blanching (briefly immersing them in rapidly
boiling water) of vegetables prior to freezing caused a loss of up to one-third
of their antioxidant content, including vitamin C. Slight additional losses
were detected during freezer storage.
Folic acid was also very sensitive to the effects of blanching
and more than half of this vitamin was lost during blanching.
Researchers say these effects varied greatly depending on the
particular vegetable, but in general vitamins and antioxidants were much more
sensitive to processing and storage than fiber content, which was not affected
and even increased slightly after blanching and freezing in some cases.