Cruciferous vegetables such as broccoli provide a variety of nutrients and natural compounds for a healthy diet, including a unique group called glucosinolates, which may have specific effects for a cancer prevention diet. In Part 1 of my interview with Elizabeth Jeffery, PhD, we learned that the surest way to get these special compounds is to blanch first and serve “raw”, or steam them three to four minutes to serve cooked.
What about other delicious ways of preparing cruciferous vegetables like broccoli, Brussels sprouts and cauliflower? How do stir-frying and roasting rate for delivering glucosinolate compounds along with the enzyme that makes the active protective form available to us? In this portion of our video interview, Dr. Jeffery, Professor Emerita in the Department of Food Science and Human Nutrition at the University of Illinois at Urbana-Champaign, expands on her previous explanations.
After you watch the video interview, scroll down for more of what Dr. Jeffery shared off-camera, along with some practical ideas for taking this research on cruciferous vegetables “from daunting to doable”.
(Email subscribers, click here to go to my Smart Bytes® blog to view the video.)
Dr. Jeffery is primarily discussing broccoli in our video interview, and broccoli and broccoli sprouts are the subjects of much of the research regarding glucosinolates. Yet the cruciferous vegetable family includes many different choices, including others that form heads, such as cauliflower and Brussels sprouts, as well as dark green leafy vegetables types like kale and collard greens – known as the “headless crucifers”. These cruciferous vegetables all contain slightly different glucosinolates, which in turn are broken down to slightly different isothiocyanate and indole compounds. Should we assume that the findings about maintaining myrosinase activity to get maximum isothiocyanates apply not just to broccoli, but to other crucifers, too? Dr. Jeffery says yes, because the enzyme appears to change very little across varieties.
So What about Roasting & Stir-Frying?
Roasting is one of my favorite ways to prepare Brussels sprouts and cauliflower. The good news is that there’s no loss of water-soluble compounds like vitamin C, flavonoids or glucosinolates due to leaching into cooking water. However, in our video interview you heard Dr. Jeffery say that effects on myrosinase when roasting vegetables are not yet known.
What about stir-frying, one of the ways I love to fix broccoli and bok choy? Based on a limited amount of research, glucosinolate content seems to remain unchanged. The question is whether the myrosinase enzyme remains viable, however, and Dr. Jeffery says that we have no data on this. Stir-frying tends to be quick, but temperatures are high.
Since glucosinolates tend to be relatively stable in heat, and there’s no loss into cooking water, most of the glucosinolates themselves should still be in broccoli and other cruciferous vegetables cooked by either of these methods. If the myrosinase enzymes have been destroyed, then you won’t get the full quota of protective isothiocyanate compounds you would have otherwise. However, although a much smaller amount, the healthful bacteria in your colon will form some isothiocyanates from the glucosinolates that travel through the digestive tract intact. Individuals seem to vary widely in how much they produce, based on differences in colon microbiota. You’ll also still get plenty of other nutrients from these vegetables when roasted or stir-fried, too.
Oven roasted cauliflower is a long-time favorite. One trendy variation, known as cauliflower steaks, involves cutting the whole cauliflower head into1-inch thick slices top-to-bottom. Save the small end florets for another use, and roast the “steaks” on a cookie sheet. Brush both sides with olive oil, perhaps containing some chopped garlic, and bake at 450° for about 25 minutes, gently turning over halfway through. (These can also be prepared on the stove top if you prefer.)
Tip 1: Add Another Cruciferous Vegetable
Since it’s not clear how roasting and stir-frying affect myrosinase enzymes needed to convert the original cruciferous compounds (“glucosinolates”) into the unique “isothiocyanates” and “indoles” with active effects, how about some insurance? One option Dr. Jeffery suggests is to include somewhere in the meal another cruciferous vegetable that can supply this vital enzyme.
Cruciferous vegetables include a wide range of options, including several that could fit this bill nicely:
♦ Raw cabbage (green or red) – Serve a small side of slaw or cabbage salad, one of Dr. Jeffery’s favorite strategies.
♦ Radishes – Use one or two as a colorful edible garnish for a meal, or slice into a salad.
♦ Daikon radishes – Slice or shred these standbys of Asian cuisine (which look a bit like white carrots) into salads or just munch a few slices raw. One study suggests that to get myrosinase, you should wash, but not peel, daikon, as the enzyme is located only in the outer skin in at least some varieties.
♦ Watercress – Add a few sprigs of watercress to your salad.
♦ Arugula – Enjoy an arugula salad, or add a few leaves to a mixed salad for a peppery taste that’s a traditional part of Mediterranean cuisine.
♦ Kohlrabi and Turnip – slice raw bulbs for dipping just as you would use jicama, or julienne or shred them to add to a salad or garnish a dish.
If slaw is your option, one quick and easy shortcut is to use the pre-shredded cabbage mix available in grocery stores. However, some research notes pre-shredded products may lose up to 75 percent of their glucosinolates. Does it reflect true loss of the compounds, or is this actually ok, reflecting myrosinase action initiated by the shredding process, breaking the glucosinolates down to isothiocyanates? When I asked Dr. Jeffery about this, she said that she has not tested this food, but can speculate that the glucosinolates may have been broken down to isothiocyanates (ITC); yet because ITC are not stable, they could then break down or bind to other compounds before they had a chance to reach target areas in our bodies. Of course, regardless of whether pre-shredded cabbage is a good source of glucosinolates, it could still be a viable source of the myrosinase enzyme. Bottom line: to get the most all-over benefit, shred your own cabbage for slaw (it’s much quicker than it seems, unless you’re feeding a crowd), but as an easy source of myrosinase to break down glucosinolates from roasted or stir-fried vegetables, it could be a reasonable choice.
Tip 2: Flavor with Mustard or Wasabi
Mustard as a condiment – an English style or stone ground brown mustard with the bit of a “bite” that indicates isothiocyanates have formed – complements not only the nutrition but also the flavor of many cruciferous vegetables. Dry mustard powder that you mix as an ingredient in a sauce or dressing, as Dr. Jeffery’s mother used to do, is another option for getting this source of myrosinase enzyme.
A simple and delicious way to include mustard is with this easy sauce: for four cups of vegetables, combine 1 tablespoon of olive oil, 1 tablespoon of balsamic vinegar, 1 to 2 tablespoons of mustard and 2 minced or pressed garlic cloves; add 2 tablespoons of chopped fresh parsley, thyme or other herbs if you like. Here are some examples of using mustard as a flavoring that would also work to provide the myrosinase enzyme for breaking down glucosinolates in cruciferous vegetables in case it was lost if you roasted or stir-fried the vegetable:
Wasabi, commonly offered with sushi, can add a spicy, extremely hot horseradish-like flavor to a variety of foods. If you like “heat”, a dab of this and nobody will say vegetables are dull!
What’s next? Come back for the third and final portion of my interview with Dr. Jeffery, when she discusses how use of frozen broccoli and microwave cooking affect the cancer-fighting isothiocyanates you get.
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