roccoli and other cruciferous vegetables of the Brassica family such as radishes, rape seed, water cress, kale, sprouts, turnips and cauliflower contain glucosinolates. Metabolites of glucosinolates, the isothiocyanates, are implicated in protection from cancer because they induce phase II detoxification and inhibit phase I detoxification, which decreases the formation of carcinogens. In order to receive the anti-cancer protective effects of broccoli, the glucosinolates must be converted to isothiocyanates, but humans do not possess the thioglucosidase enzyme for this process. However, within cruciferous plants, an enzyme called myrosinase is able to cleave glucosinolates to isothiocyantes when broccoli is eaten. Broccoli must be cooked, because the myrosinase is stored in vacuoles and heating breaks down the plant cells allowing the enzymes to come into contact with the glucosinolates. The trouble is, too much heat denatures myrosinase which subsequently prevents this conversion. Light cooking or steaming should therefore optimise the anti-cancer effect of broccoli by breaking the cell walls, while sparing some of the myrosinase from being denatured.
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