Overcooking broccoli can kill the vital enzyme it contains

Adding radishes, rocket or wasabi, a form of Japanese horseradish, can have the same effect.

But overcooking the broccoli can kill the vital enzyme it contains. Steaming it quickly for just two to four minutes is the best way to preserve its well-known health benefits, say US scientists.

Elizabeth Jeffery, a professor of nutrition at the University of Illinois, said: “Broccoli, prepared correctly, is an extremely potent cancer-fighting agent. Three to five servings a week are enough to have an effect.”

An enzyme called myrosinase must be present for sulforaphane, broccoli’s cancer-preventing component, to form in the vegetable.

Broccoli sprouts, which are young plants just three to four days old, contain myrosinase in abundance.

Researchers found that myrosinase from the young sprouts enhances the levels of sulforaphane formed and absorbed from the broccoli when the two are eaten together.