The anti-cancer properties of Brassica vegetables, namely broccoli, cabbage, cauliflower and Brussels sprouts, are well-known. However, boiling such vegetables severely impairs their potential
health benefits, as a new UK study has reported.
Researchers from Warwick University purchased a selection of Brassica vegetables and evaluated the impact of different storage and different cooking methods on concentrations of glucosinolates.
These are constituents of Brassica vegetables which are metabolised in the body to become substances known as isothiocyanates. These substances are thought to reduce the risk of some cancers.
The results showed that boiling the vegetables for 30 minutes reduced levels of glucosinolates by 58% to 77%, depending upon the vegetable. Steaming, stir frying or microwaving the vegetables
had a negligible effect on levels of glucosinolates. Storing vegetables at ambient or refrigeration temperatures resulted in minor losses of glucosinolates. Freezing had a more severe impact,
due to the thawing process.
It was concluded that people should avoid boiling vegetables in order to gain the maximum nutritional benefits (although 30 minutes seems a long time to boil vegetables!)
For more information, see
Song & Thornalley (2007). Effect of storage, processing and cooking on glucosinolate content of Brassica vegetables. Food Chemistry and Toxicology, Vol 45, pg 216-24.