Fifteen years after Glenn Close showed that boiling bunnies is bad for your health, researchers at the University of Warwick have found that the standard British cooking habit of boiling vegetables severely damages the anticancer properties of many brassica vegetables such as broccoli, Brussel sprouts, cauliflower and green cabbage.
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 the vital anti-carcinogen important glucosinolate within the vegetables. The loss of total glucosinolate content after boiling for 30 minutes was: broccoli 77 percent, Brussel sprouts 58 percent, cauliflower 75 percent and green cabbage 65 percent.
Domestic storage of the vegetables at ambient temperature and in a domestic refrigerator showed no significant difference with only minor loss of glucosinolate levels over 7 days.
However the researchers found that storage of fresh vegetables at much lower temperatures such as -85C (much higher than for storage in a refrigerator at 4-8C) may cause significant loss of glucosinolates up to 33 percent by fracture of vegetable material during thawing.
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