When you chew broccoli, its cells rupture, releasing an enzyme that produces a class of chemicals called sulphoraphanes. Nathan Matusheski, a researcher at the University of Illinois at Urbana-Champaign, crushed raw broccoli in the lab to mimic chewing, and tested the resulting mush.
Matusheski told ACS delegates that in common supermarket broccoli, 20 per cent of the sulphoraphanes are the anti-carcinogenic kind, which have an extra sulphur atom in each molecule. The rest lacks this crucial sulphur and has no cancer-fighting capability. But when he tested broccoli that had been heated to 60°C, he found the relative levels were reversed, favouring the anti-cancer compound.
A protein in broccoli called ESP plays a role in pushing the balance towards the sulphur-poor sulphoraphane. Matusheski confirmed that heating the broccoli destroys the ESP, tipping the balance in favour of the beneficial sulphoraphane. But cooking broccoli conventionally does not help, as the enzyme that produces sulphoraphanes in the first placed is also destroyed.
One way to ensure high levels of the beneficial compound may be to eliminate the genes that code for the ESP protein. This could be done by making hybrids with wild strains, says Matusheski, who prefers this approach on an ethical basis. Another method would be gene silencing.
"This is one of many studies that will build our knowledge" of immune-enhancing foods, says Sara Risch, a food technology adviser with the Chicago-based food science consultancy Science by Design. At the ACS, chemists also probed the alleged immune effects of cranberries and soybeans, with less conclusive results. "But this broccoli research identifies something that could be taken to the plant breeders," says Risch.
The story was reported by Celeste Biever from The 225th National Meeting of the American Chemical Society in New Orleans, Louisiana, 23-27 March
New Scientist issue: 5 April 2003
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