Broccoli & Pressure: the untold story of the better cooking method

Broccoli Pressure Cooker /Instant Pot Nutriton

The 2007 study from the Italian Universita’ Degli Studi in Potenza evaluated how much vitamin C and Sulforaphane – the most powerful antioxidant you never heard of – were retained from farm to table, and this is how they did it.

Although I already made a quick reference to this broccoli study in the past, I wanted to revisit it in detail to share more about it.  There are lots of interesting tidbits, there, including data that’s been hidden by omission by myself and just about anyone else who has cited this study to promote the nutritional benefits of pressure cooking.

Aren’t you curious about their findings, now?!? Ok, first let’s find out what, exactly, was measured…

hip info: measured antioxidants

Vitamin C – also known as L-ascorbic acid, is a water-soluble vitamin that is naturally present in some foods, added to others, and available as a dietary supplement. Humans, unlike most animals, are unable to produce their own vitamin C and the body needs it to build collagen, metabolize protein to protect against cardiovascular diseases and stimulate the immune system.

Sulforaphane – Sulforaphane is a phenolic phytonutrient with beneficial antioxidative properties. Broccoli and other cruciferous vegetables don’t already contain it. This compound is actually produced when the vegetable is damaged by either chewing, addition of liquid or processing. There’s is evidence of possible benefits for the treatment of osteoarthritis, certain cancers, respiratory illnesses and skin and blood disorders.

the method

The study tracked the antioxidant content of broccoli from harvest, through storage (refrigerator and freezer) and then after five different cooking methods (boiling, steaming, microwaving, pressure cooking and microwave pressure cooking).

The broccoli was trimmed, washed and transported to the lab via a refrigerated van within two hours of harvest.  The experiments and measurements began immediately after the vegetables arrived at the lab.

Nordicware Tender Cooker (Microwaveable pressure Cooker)

The refrigerated (chilled) broccoli was stored in a climatic chamber to simulate refrigerator temperatures. The frozen broccoli was steam-blanched blanched, cooled down in water, drained and dried prior to being packed in freezer bags and stored in a deep chest domestic freezer.

When boiled, broccoli was added to boiling tap water in a ratio of1:8 by weight (approx 750g of broccoli in 6L of water) and then cooked for 15 min. The steamed broccoli was cooked for 23 min with a broccoli/tap water ratio of 1:2. The pressure cooked broccoli was treated for 2 min (broccoli/tap water 2:1 b.w.). When the broccoli was microwaved it was zapped for 11 min at 600 W using a domestic microwave oven (Panasonic) with the broccoli/tap water ratio of 6:1.  And when they used the microwave pressure cooker for the broccoli it was zapped 7 min using a 14:1 broccoli/water ratio using a Nordicware microwaveable pressure cooker.

the findings

Get fresh broccoli and cook ’em right away!

While the broccoli used in this study were harvested just two hours prior to the testing, broccoli you find in the supermarket have been picked, shipped to a reseller, then to a distribution center, then to the supermarket and sat on a shelf waiting for you to come and buy them. So, they could have been picked days, maybe even a weeks before you actually bring them home. Even if you’re lucky enough to buy your broccoli at the farmer’s market their Vitamin C will slowly deteriorate while sitting in the fridge. The exact amount of nutrient loss will vary between cultivars and time of harvest, according to the authors who compared their results with similar research.

In this study, the vitamin C decreased by 18% after a week in the fridge, and an additional 20% after three weeks – with a total vitamin loss of 38% compared to fresh broccoli!

Sulforaphane concentration went downhill during storage, too,  with a recorded final loss of 29% after four weeks of storage.

Freezing broccoli stops nutrient loss but…

The pre-freeze blanching was to blame for a 32% Vitamin C loss. Once the broccoli was frozen, the nutritional properties did not decrease any further for up to two months – which is the last measure for this study.  The nutrient reduction is actually similar to what was measured in steamed broccoli (details further down) – even though that broccoli was steamed for a longer amount of time.

Pressure cooker wins, but microwave pressure cooker wins more

In the past, when sharing results from this study, for myself and others, the focus has always been on how pressure cooking shines compared to conventional cooking methods – but the real untold story, here, is how microwaveable pressure cookers perform.

Vitamin C and Sulforaphane Retention in Broccoli

Cooking MethodVitamin C RetentionSulforaphane Retention  
Boiling65.8%0%
Steaming77.6%0%
Pressure Cooking92.4%83.2%
Microwave90.6%61.1%
Microwave Pressure99.6%97.3%
Adapted from “The Influence of Processing and Preservation on the Retention of Health-Promoting Compounds in Broccoli,” by F. Galgano et. al, 2007, JOURNAL OF FOOD SCIENCE—Vol. 72, Nr. 2, 2007, page 134. Copyright Year by "© 2007 Institute of Food Technologists".

The researchers concluded that both the pressure cooker and microwaveable pressure cooker are good tools for cooking broccoli:

In particular, boiling and steaming caused vitamin C losses of 34.2% and 22.4%, respectively, which were significantly different from those observed for all the other cooking methods (P < 0.05). Conversely, the other heat treatments (pressure, microwave, and pressure/microwave cooking) did not cause any significant loss of vitamin C in comparison with the fresh reference sample.

In the present research, microwave cooking determined a 39% reduction of sulforaphane in broccoli, similarly to what reported by Howard and others (1997) in an analogous study. Pressure cooking determined a 16.8% reduction of sulforaphane, while pressure combined with microwave cooking did not cause any deleterious effect (P < 0.05) (Table 1 [excerpted above] ).

So, even though the pressure cooker beats steaming, boiling and microwaving in nutrient retention – the real shocker is that using a microwave pressure cooker the researchers saw a previously unheard-of nearly complete retention of Vitamin C and Sulforaphane compared to fresh broccoli.

I’ve never personally tried a microwaveable pressure cooker (I don’t have a microwave) but, at least for broccoli, they make a compelling case for nutrient preservation.

Do you have a microwaveable pressure cooker?  Comment, below.

now, pressure cook that broccoli!

If you have a microwaveable pressure cooker, you can make hip recipes, too. If a browning step is called-for simply do it in another pan before transferring the food into the microwaveable pressure cooker and then cook for the time recommended by the manufacturer of the microwaveable pressure cooker.

References:

Galgano, F., Favati, F., Caruso, M., Pietrafesa, A. and Natella, S. (2007), The Influence of Processing and Preservation on the Retention of Health-Promoting Compounds in Broccoli. Journal of Food Science, 72: S130–S135. doi: 10.1111/j.1750-3841.2006.00258.x

Vitamin C Fact Sheet for Health Professionals, NIH Office of Dietary Supplements, Retrieved from https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/

What is Sulforaphane? Boots Web MD – Partners in Health, retrieved from http://www.webmd.boots.com/healthy-eating/sulforaphane