November 2013 update: Please read the groundbreaking news about crucifers!
Cruciferous veggies may seem tough on the outside, but as we talked about in the first post on these anti-cancer wonders, they’re highly sensitive to boot. If you don’t handle them properly, their magic powers could literally evaporate.
University of Warwick scientist Dr. Paul Thornalley explains: Crucifers contain compounds called glucosinolates that, when mixed with an enzyme (myrosinase), get converted to another compound (isothiocyanates )with high cancer prevention activity. Talk about a mouthful…
Thornalley has some astute advice for you cooks:
• Juicing raw crucifers (kale juice, for example): Use a high speed juicer with a strong motor. A juicer that blends the pulp with the juice (a Vitamix or the like) is excellent. If you use one that separates the pulp, make sure that the vegetable material gets broken down into very small pieces, “leaving a smooth mixture with no lumps or unbroken fibres. This will have broken most of the plant cells and released their contents into the juice. The glucosinolates, myrosinase and isothiocyanates are then in the juice.”
The beneficial health effects will be preserved as long as you don’t heat the juice or leave it at a warm room temp for more than 2-3 hours. If you refrigerate it, Thornalley says, isothiocyantes may last in the juice for several days.
• Shredding raw crucifers (salads and cole slaw): If you’re shredding crucifers finely and plan to eat them raw, don’t leave them sitting on the counter for too long. Eat them within 2 to 3 hours of shredding –or stick them in the fridge, where the magic compounds should last for several days. If you keep the cut to greater than a centimetre, you will be more likely to preserve the anti-cancer compounds.
And chew raw veggies well. “Research has shown that intestinal bacteria also convert glucosinolates to isothiocyanates in the gut.” (Not to mention, it will help with the gas.)
• Buying crucifers already cut or shredded: You are risking glucosinolate loss. Freezing and thawing fresh vegetables can cause this. So does sitting around at room temp after being cut.
• Cooking crucifers: Again, don’t cut them too finely; instead cut or tear them into pieces larger than 1 centimetre (for the leaves) or 1 millilitre (for the flowers). Then steam the veggies lightly, using a steamer and a small amount of water, or stir fry them, using olive oil and a low to medium heat. Don’t boil them; if you do, the healthy glucosinolates will end up in the water. (Well, couldn’t we drink the water, Dr. T?) Microwaving is ok if you don’t use a lot of water and don’t use a high heat.
What about baking—say baking cabbage, for example? Thornalley has not personally investigated this, but he and others suggest that very high temperatures for prolonged periods will likely destroy glucosinolates.
Mashing crucifers after cooking (mashed cauliflower)? Steam large pieces of cauliflower in a steamer, then mash. Throw the cooking water into the mixture. Eat and then refrigerate, and you should be good to go for several days.
Thanks, Dr. Thornalley, for your helpful advice. Isn’t it great when scientists are so consumer-friendly?