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Microwaving Destroys Antioxidants in Foods like Broccoli
Various references, see article
A study in the November 2003 Journal of the Science of Food and Agriculture caused a stir because it found that microwaved broccoli loses much of its nutritional punch. The researchers steamed, pressure-cooked, boiled, and microwaved about 2 cups of the vegetable with 10 tablespoons of water and then compared the flavonoid content by cooking method. Flavonoids are substances in fruits and vegetables with antioxidant properties that may lower your risk for heart disease, stroke, and some cancers. Steamed broccoli lost 11% of its flavonoids; pressure-cooked, 53%; boiled, 81%; and microwaved, a whopping 97%.

Heat from any sort of cooking lowers the levels of some vitamins. But water exposure is another major factor. Many nutrients dissolve in it, so when vegetables are prepared in water, some of the healthful elements leach out and get thrown away with the (veggie) bath water. That's probably why steamed broccoli, which didn't come into direct contact with water, came out on top.

But you don't have to microwave broccoli in 10 tablespoons of water, as the researchers in this study did. Just a couple will do — and frozen vegetables don't need any extra water. You can have your microwave and get most of your veggie nutrients, too.
- Copyright © 2004 Harvard Health Publishing - June 2004

Total flavonoid and individual hydroxycinnamoyl derivative (sinapic and caffeoyl-quinic acid derivative) contents were evaluated in the edible portions of freshly harvested broccoli (cv Marathon inflorescences) before and after cooking and in the cooking water. High-pressure boiling, low-pressure boiling (conventional), steaming and microwaving were the four domestic cooking processes used in this work. The predominant sinapic acid derivatives were identified as 1,2,2′-trisinapoylgentiobiose and 1,2′-disinapoyl-2-feruloylgentiobiose. In addition 1,2-diferuloylgentiobiose and 1-sinapoyl-2,2′-diferuloylgentiobiose were also identified in broccoli inflorescences. The results showed large differences among the four treatments in their influence on flavonoid and hydroxycinnamoyl derivative contents in broccoli. Clear disadvantages were detected when broccoli was microwaved, namely high losses of flavonoids (97%), sinapic acid derivatives (74%) and caffeoyl-quinic acid derivatives (87%). Conventional boiling led to a significant loss of flavonoids (66%) from fresh raw broccoli, while high-pressure boiling caused considerable leaching (47%) of caffeoyl-quinic acid derivatives into the cooking water. On the other hand, steaming had minimal effects, in terms of loss, on both flavonoid and hydroxycinnamoyl derivative contents. Therefore we can conclude that a greater quantity of phenolic compounds will be provided by consumption of steamed broccoli as compared with broccoli prepared by other cooking processes.
- Copyright © 2003 Society of Chemical Industry