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Diabetes Developments - A blog on latest developments in diabetes by David Mendosa

Microwaving Veggies

May 3rd, 2009 · 6 Comments

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Imagine my surprise when I read a new research report that the healthiest methods for cooking veggies seem to be microwaving or cooking on a flat metal surface without any oil. After all, on the Internet we can find thousands of diatribes on the dangers of microwave cooking. Several of my friends have junked their microwaves or given them away to people they don’t like.

Researchers at the University of Murcia and Madrid’s University of Complutense in Spain examined how six different cooking methods affected the antioxidant activity of 20 different vegetables. We get most of our nutritional antioxidants from vegetables and fruit. They may prevent cancer and other diseases.

The six cooking methods were boiling, pressure-cooking, baking, microwaving, frying, and cooking without oil, which they called griddling. The vegetables were artichokes, asparagus, beets (beetroot), fava beans (broad beans), broccoli, Brussels sprouts, carrots, cauliflower, celery, corn (maize), eggplant, garlic, green beans, leeks, onions, peas, green peppers, spinach, Swiss chard, and zucchini.

The Spanish scientists published their findings as “Influence of Cooking Methods on Antioxidant Activity of Vegetables” in the April 2009 issue of the Journal of Food Science, a publication of the Institute of Food Technologists. The free full-text of the article is online.

“Depending on the vegetable in question, griddling and microwave cooking produced the lowest losses, while pressure-cooking and boiling lead to the greatest losses,” the study concluded. “In short, water is not the cook’s best friend when it comes to preparing vegetables.”

Cooking anything at more than about 115 to 118 degrees destroys their enzymes, according to many raw food fans. So you can imagine my further surprise when I read in this new study that some of the vegetables that they cooked actually increased their antioxidant levels.

The safest vegetable to cook is the artichoke. No matter what cooking method the Spanish scientists subjected this tasty thistle to they couldn’t detect any loss of nutrients.

In fact, all cooking methods increased antioxidant levels of celery and carrots. All methods except boiling increased antioxidant levels of green beans.

The scientists tested their fat-soluble (lipoperoxyl) and water-soluble (hydroxyl) radical scavenging capacity. Vegetable have both types of antioxidant compounds, which function synergistically.

In terms of fat-soluble radical scavenging, microwave cooking works best for eggplant, corn, pepper, and Swiss chard, all of which significantly increase their capacity. Artichoke, asparagus, garlic, onion, and spinach keep the same capacity that they have in raw form. Fava beans and beets lose 5 percent and 30 percent of their fat-soluble scavenging capacity respectively. The worst vegetable to microwave in terms of fat-soluble radical scavenging is cauliflower, which loses more than half of its capacity.

In terms of water-soluble radical scavenging, microwave cooking works best for celery, which significantly increases its capacity. Beets, broccoli, carrots, eggplant, garlic, green beans, leek, corn, and peas keep essentially the same capacity that they have in raw form. The worst vegetables to microwave in terms of water-soluble radical scavenging are peppers and Swiss chard, which lose 30 percent or more of their capacity.

Those of us who have diabetes and know that we need the best possible nutrition will appreciate these new findings. But don’t expect the scaremongers on the Web to write about this study any time soon. This news is just too good for them to like.

This is a mirror of one of my articles that Health Central published. You can navigate to that site to find my most recent articles.

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6 responses so far ↓

  • 1 Sarah // Jun 3, 2009 at 7:20 am

    I wonder, if you cook the vegetables in water but eat the water (i.e., soup, fat-free stir fry), if the scenario improves. It sounds as if peppers and swiss chard are bad to microwave when it comes to water soluble “radical scavenging” because they lose so much juice — but is the goodness still there in the juice?

  • 2 David Mendosa // Jun 3, 2009 at 7:29 am

    Dear Sarah,

    Good questions. But I would be surprised if anyone knows the answers yet.

    Best regards,

    David

  • 3 Wendell // Jun 9, 2009 at 2:22 pm

    So, so, close. This was shaping up to be the most definitive look at an often debated subject. While the study is extremely useful, it falls short. Where is steaming? We are often told that steaming is the best method to cook vegetables. We are often told this without any scientific proof at all. I, and the millions of uninformed would have liked to get an answer on this. Seriously…pressure cooking was one of the methods but not steaming? When was the last time you went to someone home for dinner and they pulled out the pressure cooker?

  • 4 David Mendosa // Jun 9, 2009 at 4:56 pm

    Dear Wendell,

    I agree.

    I followed up. But the correspondence was less than satisfactory. My first message to the lead author was:

    “Great research! I just reviewed it.

    “But why you didn’t include steaming as a seventh way of cooking? You mention steaming in passing, but that’s all. I personally have always thought that steaming was the best way to cook vegetables.”

    She replied, “Thank you very much for your message. The steaming is included in the paper.”

    Then, I wrote again, “Dear Professor Murcia,

    “I appreciate your reply. Thank you.

    “But in the paper AS PUBLISHED at http://www3.interscience.wiley.com/cgi-bin/fulltext/122267406/HTMLSTART the word steam or steamed or steaming appears only one time. It is in this sentence:

    “Because modern day consumers seek to avoid aggressive cooking methods which may affect the functionality of foods, there is growing interest in the phytochemical profiles and antioxidant activities of cooked (boiled, microwaved, steamed, griddled, fried, and baked) vegetables.

    “When you list the cooking treatments they are:

    “Boiling Pressure-cooking Microwave cooking (medium power) Baking (200 °C) Griddling Frying

    “Steaming — at least in this country — is quite different from pressure cooking, which you define as, “Pressure-cooking: vegetables (500 g) were placed in a pressure cooker (stainless steel, 22 cm diameter, Magefesa®, Zaragoza, Spain), containing water (300 mL) and a pressure valve for high pressure-cooking.”

    “A pressure cooker does, of course, use steam. But steaming, as we do it here, is not under pressure.

    “Wikipedia has a good article about steaming at http://en.wikipedia.org/wiki/Steaming (and a different article about pressure cooking).

    “Is steaming as such not used in Spain?”

    I sent that to her days ago, and she did not reply. Sorry.

    Best regards,

    David

  • 5 marcus // Jun 19, 2009 at 12:06 am

    Sarah, I know that vitamins and minerals lost can be recovered in the juice, but I’m not sure about antioxidants. A chemist should know that answer. Based on what I say below I believe that the antioxidants can be recovered from the juice.

    Enzymes and antioxidants are different things. Enzymes are proteins and, similar to meat protein, they cook and loose their functionality when heated. Antioxidants are different, many are molecules which are smaller than proteins and aren’t effected negatively by cooking temperatures. Since the antioxidants aren’t destroyed by cooking, they probably just follow the water out of the vegetable via osmosis.

    I hope that helps you understand whats happening a bit more.

  • 6 marcus // Jun 19, 2009 at 12:12 am

    I’m going to predict that steaming will create more losses in most vegetables than microwaving or griddling. This is because steaming uses hot water vapor to cook and as that water condenses on the vegetables and heats them, some of the nutrients and antioxidants are going to seep into that water, and the water with this good stuff is going to drip off the vegetables into the water below. Certainly since the vegetable isn’t submerged in the water it won’t loose nearly as much as boiling of pressure cooking however.

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