Hot Water Kills Broccoli's Benefits

Boiling, Blanching Can Cause Veggies to Lose Antioxidants

Medically Reviewed by Brunilda Nazario, MD on October 29, 2003
From the WebMD Archives

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 antioxidants.

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 11%).

"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 vegetables.

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.

Show Sources

SOURCES: Vallejo, F. Puuppoponen-Pimiä, R. Journal of the Science of Food and Agriculture, November 2003; vol 83: pp 1511-1516, 1389-1402. News release, John Wiley & Sons, Inc.

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