- Broccoli is a source of sulforaphane which is protective against cancer
- The enzyme myrosinase in broccoli is needed for sulforaphane to form
- But microwaving and boiling destroys myrosinase, meaning sulforaphane doesn’t form – so the vegetable no longer has cancer-fighting properties
- The best way to preserve myrosinase is to steam broccoli for four minutes
Most people would probably admit they eat broccoli more for its health-giving properties than for its flavour.
But new research shows that people who don’t cook it in the right way could be wasting their time.
Scientists found broccoli loses its cancer-fighting properties when it is boiled or microwaved.
The researchers, who presented their findings at the American Institute for Cancer Research Annual Research Conference, found the best way to cook the vegetable is to steam it for three to four minutes.
They say steaming it until it turns a bright green colour can enhance its cancer-fighting compounds.
Broccoli is an excellent source of sulforaphane, a naturally occurring plant compound that has been shown to be protective against cancer.
The enzyme myrosinase in broccoli is needed for sulforaphane to form – so if the myrosinase is destroyed, sulforaphane cannot form.
The researchers found boiling and microwaving broccoli, even for just one minute, destroys most of the myrosinase it contains.
In contrast, they also discovered that steaming it for up to five minutes is the best way to retain the enzyme.
‘Past food processing has tended to focus on improving taste, visuals and microbiological safety,’ said Dr Elizabeth Jeffery, a researcher at the University of Illinois at Urbana-Champaign.
‘Now our task is to go further. Processing can ensure that the bioactives – the cancer protective compounds – arrive in your digestive system in a form the body can use.’
Dr Jeffery also discovered that boiled or microwaved broccoli can still produce sulforaphane if it is eaten with other raw foods that contain myrosinase.
Dr Jeffery asked participants to eat a broccoli supplement with no active myrosinase.
When some participants then ate another item of food which did contain myrosinase, their blood and urine levels of sulforaphane were significantly higher than those who did not eat the second food.
‘Mustard, radish, arugula, wasabi and other uncooked cruciferous vegetables, such as coleslaw, all contain myrosinase, and we’ve seen this can restore the formation of sulforaphane,’ Dr Jeffery said.
This is not the first study to show that the way in which food is prepared can impact how protective it is against cancer.
Previous research has shown that crushing or chopping garlic and then waiting 10 to 15 minutes before exposing it to heat allows its inactive compounds to convert into the active, protective phytochemical allicin.
It has also revealed that cooking tomatoes and other foods that contain lycopene allows the body to more easily absorb the phytochemical.
‘As we’re learning, food processing isn’t just what happens to food before it reach the grocery shelves,’ said American Institute of Cancer Research Associate Director of Nutrition Programmes Alice Bender.
‘This research highlights that what you do in your kitchen can make those fruits and vegetables on your plate even more cancer protective.’