Broccoli in a Cancer Prevention Diet: Microwaving? Freezing?

Broccoli and other cruciferous vegetables provide many vital nutrients, as well as a unique group of compounds called glucosinolates, which may help reduce cancer risk. In Part 1 of my interview with Elizabeth Jeffery, PhD, we heard her advice that to maximize cancer-fighting “punch” of these vegetables, it’s best to blanch them briefly and serve “raw”, or cook them by steaming three to four minutes. In Part 2 of the interview, Dr. Jeffery noted that since research has not yet resolved questions about how stir-frying and roasting rate for delivering glucosinolate compounds along with the enzyme that makes the active protective form available, it’s smart to serve these along with some form of raw cruciferous vegetable or condiment.

In this final 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, addresses the big questions about microwaving broccoli and differences between fresh and frozen forms.

Microwaving Your Veggies

One of the questions that commonly comes up in Q&A sessions when I am speaking – whether to the general public, to cancer survivors or to health professionals – relates to microwave cooking, including for vegetables. Some people are afraid that microwaving food produces unsafe radiation, which is not true. Periodically warnings circulate against microwaving based on media reports of some study in which flavonoids (healthful phytochemicals) or vitamins like vitamin C are shown largely lost after microwaving. However, it’s important to look at how microwaving was done in this research.

The studies that I have seen showing such results microwaved the vegetables in a large amount of water. Results in the headlines or brief summary abstracts of such studies are misleading; cooking in a large amount of water – whether on the stove or in a microwave — leads to loss of water-soluble vitamins, minerals and phytochemicals. Actually, studies support the value of microwaving – as long as properly done with little or no added water. Research involving peas, spinach, green beans, beets, carrots and more has shown excellent retention of nutrients such as vitamin C and folate, as well as carotenoid and flavonoid compounds when cooked properly in the microwave.

Broccoli and other cruciferous vegetables are unique. The apparently cancer-fighting glucosinolate compounds in these vegetables are water-soluble. If you cook them by any method in a large amount of water, the compounds are largely lost. As long as they are cooked in a microwave with little or no added water, the glucosinolates are still there; the problem is that after about one minute, the enzyme that creates the actively protective form is destroyed. So if you do cook them in a microwave, go back to the advice Dr. Jeffery shared in Part 2 of this interview, to include in the meal another source of active myrosinase (such as coleslaw or raw cabbage, radishes, or some mustard or wasabi as a condiment). On the other hand, if instead you steam these cruciferous vegetables for one to four minutes, you both prevent loss of nutrients leaching into the cooking water and preserve the vital enzyme.

What about Frozen Broccoli?

Frozen vegetables in general are a great choice. Research has repeatedly shown that folate, beta-carotene and vitamin C are well maintained in frozen vegetables. You help retain vitamin C by cooking directly from the freezer without thawing first. Frozen spinach and other vegetables are easy to keep on hand, and provide an easy way to boost nutrition in soup, chili, pasta sauce, eggs and casseroles.

Once again, cruciferous vegetables such as broccoli are unique. Commercially frozen broccoli is blanched more extensively than the 20 to 30 seconds Dr. Jeffery discussed in Part 1 of our interview as a helpful way to maximize formation of protective compounds compared to serving broccoli raw. This commercial blanching means that if you do use frozen broccoli or kale, you’ll get more of that cancer-prevention power by including another raw cruciferous vegetable in the meal so that its myrosinase enzyme can also support formation of active isothiocyanate compounds from the glucosinolates in your frozen cruciferous vegetable.

Bottom Line:  A wide range of cruciferous vegetables offers a bevy of health-protecting nutrients and unique cancer-protective compounds. To maximize this cancer-fighting potential, blanch 20 to 30 seconds and serve “raw”, or steam for three to four minutes to serve cooked. If you prefer to microwave, roast, stir-fry or cook frozen forms by any means, add a raw crucifer like cabbage, arugula, watercress or radish; or flavor with some mustard or wasabi.

This concludes my interview with Dr. Jeffery. Please share links to this post via email to friends and family, or through Twitter, Facebook, or other social media.

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References

Moreno DA et al. Effects of stir-fry cooking with different edible oils on the phytochemical composition of broccoli. J Food Sci. 2007 Jan;72(1):S064-8.

Palermo M, Pellegrini N, Fogliano V. The Effect Of Cooking On Phytochemical Content In Vegetables: A Review. J Sci Food Agric. 2013 Nov 14. doi: 10.1002/jsfa.6478. [Epub ahead of print]

Rungapamestry V, et al. Changes in glucosinolate concentrations, myrosinase activity, and production of metabolites of glucosinolates in cabbage (Brassica oleracea Var. capitata) cooked for different durations. J Agric Food Chem. 2006; 54(20):7628-34.

Song L and Thornalley PJ. Effect of storage, processing and cooking on glucosinolate content of Brassica vegetables.  Food Chem Toxicol. 2007 Feb;45(2):216-24.

Wang GC, Farnham M, Jeffery EH. Impact of Thermal Processing on Sulforaphane Yield from Broccoli ( Brassica oleracea L. ssp. italica). J Agric Food Chem. 2012. 60(27):6743–6748.