According to a report in the New Scientist, chewed raw broccoli contains small quantities of a strong chemical that slows the enzymes which damage DNA and have the potential to cause cancer.

By chewing broccoli, its cells rupture and release an enzyme that produces sulphoraphanes, researchers at the University of Illinois have found.

In most commercially grown broccoli, 20 per cent of the sulphoraphanes are anti-carcinogenic and have an extra sulphur atom in each molecule, but by heating the broccoli, the relative levels are reversed.

There is a protein in broccoli known as ESP which edges the balance towards the sulphur-poor sulphoraphane. Heating the broccoli destroys this. One way to ensure high levels of the beneficial compound may be to eliminate the genes that code for the ESP protein by making hybrids with wild strains or by gene silencing.

This research could ultimately help plant breeders in developing broccoli with even greater cancer-fighting powers.