May 16, 2007
Boiling Vegetables Reduces Anti-Cancer Benefits
Steaming, microwaving, and stir-frying are all much better than boiling.
The researchers, Prof Paul Thornalley from Warwick Medical School at the University of Warwick and Dr Lijiang Song from the University of Warwick’s Department of Chemistry bought Brassica vegetables, (broccoli, Brussel sprouts, cauliflower and green cabbage) from a local store and transported them to the laboratory within 30 minutes of purchasing. The effect of cooking on the glucosinolate content of vegetables was then studied by investigating the effects of cooking by boiling, steaming, microwave cooking and stir-fry.
Boiling appeared to have a serious impact on the retention of those important glucosinolate within the vegetables. The loss of total glucosinolate content after boiling for 30 minutes was: broccoli 77%, Brussel sprouts 58%, cauliflower 75% and green cabbage 65%.
The effects of other cooking methods were investigated: steaming for 0–20 min, microwave cooking for 0–3 min and stir-fry cooking for 0–5 min. All three methods gave no significant loss of total glucosinolate analyte contents over these cooking periods.
I'm big on eating raw cabbage as cole slaw. Stir-frying seems like the most attractive way to prepare the other Brassica (aka cruciferous) vegetables.
Who boils vegetables for 30 minutes?
No kidding; The only time I boil vegetables for 30 minutes is when I'm making *soup*. So I guess the question is, does the glucosinolate end up in the broth, or is it destroyed by the prolonged heat?
Dennis is right. Boiling vegetables for 30 minutes makes them inedible.
Cabbage is good in stir-fries as well as raw.
C'mon, a long simmer makes for a tasty stew, or have you never had borscht? The trick is to make sure it's just hot enough to denature enzymes as you add each vegetable. Those otherwise, in a long stew, destroy substantially all the nutrients (and can lead to off flavors as well). As a result I'm a fan of blanching, wilting or otherwise quick-heating vegetables. What you do after depends on the effect you want (cf borscht above), but there is a whole world of vegetable food out there that doesn't equate to salad. I love salad, but in moderation.
I will say one thing, though: despite loving broccoli and cabbage in almost any form, including raw and completely unseasoned, despite tolerating cauliflower except when deeply overcooked, I simply loathe Brussels sprouts. They have a special flavor all their own that I cannot stand. I can eat almost anything else.
An earlier study found that microwaving did more to destroy flavonoids and some other phytochemicals than boiling:
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.
From "Phenolic compound contents in edible parts of broccoli inflorescences after domestic cooking"
published in the 15 Oct 2003 issue of Journal of the Science of Food and Agriculture. Abstract at
The new study examines a different class of chemicals, so it may not actually be inconsistent with the older study.
Also, the full text of the 2003 study is not available online, so it is hard to tell if the experimental procedures