Wondering if microwaving alters a food’s nutritional state?

Multiple studies have shown that the cooking method used in food preparation directly impacts the quality of nutrients. Don’t believe it!?

Let’s consider broccoli as an example. Why?

1. Because vegetables are great for you! In fact, there’s strong evidence that regular consumption of Brassica foods, like broccoli, is associated with a decreased risk for certain chemically induced cancers. This is probably due to their phenolic compounds and glucosinolate content. [1, 2]

2. More importantly, there are real research studies with accurate data compiled on the nutritional state of broccoli in various cooking states.

Before we get to cooking methods, one more note on how great broccoli is for you!

Several studies demonstrated that Brassica vegetables contain a wide range of natural antioxidants, vitamins and phenolic compounds [8–10]. These dietary antioxidants, in addition to protecting against free radicals in the human body [11] and are related to a reduced risk of several chronic diseases [12] including cancers and heart diseases [13]. Broccoli was specifically noted for its strong antioxidant activity compared to other vegetables.

For reference, what is Brassica food you ask? Kale, cabbage, collard greens, broccoli, cauliflower, kai-lan, Brussels sprouts, kohlrabi, tender greens, mustard spinach, among others.

Back to cooking methods!

So, you believe in the benefits of vegetables, painstakingly took the time to hit up a farmers market for organic produce, and now, you’re going to microwave it!?

Here’s what you need to know!

One study [21] showed that microwaving and even conventional cooking affected the antioxidant composition and in vitro activity of nutrients found in broccoli.

Yet another study [10] established that after microwaving and conventional cooking, the total antioxidant activity remained relatively unchanged.

It can get confusing, so let us explain what’s going on. The controversy could be partially explained due to the different conditions of time, added water, and microwave power.

A group of researchers from Spain set out to find out exactly this. They looked at duration of cooking, power (1000, 700, and 500 W microwaves), and various amounts of water added.

Vitamin C – is sensitive to cooking

In general, Vitamin C in cooked broccoli showed a decrease of 20-60% in comparison to uncooked.

Researchers found that vitamin C was significantly affected by every factor involved separately: power, cooking time, and volume of cooking water.

Nevertheless, the combination of power × time caused the greatest loss, followed by the combination of higher water volume and cooking time at any given power set. Obviously best for Vitamin C and Protein, don’t cook it at all!

Phenolic compounds – Can handle short cooking times

The microwave cooking using short cooking times and no-contact-with-cooking-water combinations were better in terms of favoring the retention of phytochemicals in broccoli, but were all significantly affected.

Glucosinolates – the cancer fighting benefit is lessened with every minute-watt

The total content of intact glucosinolates was significantly affected by the cooking parameters power, time, and added water and the combination of the three parameters [power × time × water.

Vallejo et al. [15] previously found 75% loss in total glucosinolate content, particularly when water was used to cook and water vapor was noted during the cooking process. This is in comparison to only 18% decrease otherwise.

Minerals – Are the survivors

Cooking conditions did not significantly affect the mineral content (magnesium, manganese, sodium, calcium, zinc, and copper) in broccoli from under different conditions, and the level of retention of minerals was always high for almost all the analyzed mineral elements.

Conclusion and Advice – What’s the take away anyway?

In general, Vitamin C seemed to be the bioactive phytochemical most affected by the microwave cooking. You aren’t going to get very much of it from a cooked vegetable, whether microwaved or not. Consider getting enough raw fruits and vegetables to keep your daily needs, or supplementation when you are under stress (see Vitamin C article).

On the other hand, the most stable phytonutrients were the minerals. So even if you are cooking your broccoli well done, rest assured, you are likely getting your minerals.

Now when it comes to phenolic compounds and glucosinolates, which are typically the compounds that we attribute the cancer busting disease fighting health benefits of greens, well, they tend to be very sensitive to cooking. Try to use setting with the lowest power for the lowest duration or time that will allow you to consider you broccoli, and veggies in general, edible.

Very importantly, minimize the water used in cooking, many nutrients, including vitamins, phenols, and glucosinolates, are all leached into the water. If you do use water, try to use settings that minimize water vaporization, and we highly recommend consuming the actual water in addition to the cooked veggies.

Best of all, eat the veggie raw, although yes, we know, you didn’t want to hear it.

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References:

(1) Zareba, G.; Serradelf, N. Chemoprotective effects of broccoli and other Brassica vegetables. Drug Future 2004, 29 (11), 1097–1104.

(2) Zhang, Y.; Munday, R. E. X.; Jobson, H. E.; Munday, C. M.; Lister, C.; Wilson, P.; Fahey, J. W.; Mhawech-Fauceglia, P. Induction of GST and NQO1 in cultured bladder cells and in the urinary bladders of rats by an extract of broccoli (Brassica oleracea italica) sprouts. J. Agric. Food Chem. 2006, 54 (25), 9370–9376.

(8) Podsedek, A.; Sosnowska, D.; Redzynia, M.; Anders, B. Antioxidant capacity and content of Brassica oleracea dietary antioxidants. Int. J. Food Sci. Technol. 2006, 41, 49–58.

(9) Podsedek, A. Natural antioxidants and antioxidant capacity of Brassica vegetables: A review. LWT-Food Sci. Technol. 2007, 40 (1), 1–11.

(10) Turkmen, N.; Sari, F.; Velioglu, Y. S. The effect of cooking methods on total phenolics and antioxidant activity of selected green vegetables. Food Chem. 2005, 93 (4), 713–718.

(11) Nilsson, J.; Stegmark, R.; Akesson, B. Total antioxidant capacity in different pea (Pisum satiVum) varieties after blanching and freezing. Food Chem. 2004, 86 (4), 501–507.

(12) Knekt, P.; Kumpulainen, J.; Jarvinen, R.; Rissanen, H.; Heliovaara, M.; Reunanen, A.; Hakulinen, T.; Aromaa, A. Flavonoid intake and risk of chronic diseases. Am. J. Clin. Nutr. 2002, 76 (3), 560– 568.

(13) Duthie, G. G.; Duthie, S. J.; Kyle, J. A. M. Plant polyphenols in cancer and heart disease: Implications as nutritional antioxidants. Nutr. Res. ReV. 2000, 13 (1), 79–106.

(14). Zhang, D. L.; Hamauzu, Y. Phenolics, ascorbic acid, carotenoids and antioxidant activity of broccoli and their changes during conventional and microwave cooking. Food Chem. 2004, 88 (4), 503–509.

(15) Vallejo, F.; Tomas-Barberan, F. A.; Garcia-Viguera, C. Glucosi- nolates and vitamin C content in edible parts of broccoli florets after domestic cooking. Eur. Food Res. Technol. 2002, 215 (4), 310–316. 


(16) Carmen Lopez-Berenguer, Micaela Carvajal, Diego A. Moreno, Christine Garcia-Viguera “Effects of Microwave Cooking Conditions on Bioactive Compounds Present in Broccoli Inflorescences” Food Science and Technology Department and Plant Nutrition Department, CEBAS-CSIC, P.O. Box 164, Espinardo, Murcia, Spain; Journal of Agricultural and Food Chemistry 2007, 55, 10001–10007

General Disclaimer: All information here is for educational purposes only and is not meant to cure, heal, diagnose nor treat. This information must not be used as a replacement for medical advice, nor can the writer take any responsibility for anyone using the information instead of consulting a healthcare professional. All serious disease needs a physician.