This 2019 USDA study investigated representative broccoli cooking methods for their impact on kaempferol and quercetin levels:
“Understanding cooking effects on flavonoids is crucial to accurately estimate their daily intake and further investigate their health benefits. The purpose of this study was not to compare different conditions of each cooking methods, but to focus on retentions of individual flavonoids under common cooking conditions in the US:
- For boiling, we chose to use 85 seconds.
- A 5-minute steaming time was used.
- Microwave treatment was carried out in a 1200W microwave at full power for 1 minute.
Seven kaempferol (Km) glycosides and one quercetin (Qn) glycoside were identified and quantified in raw and cooked broccoli by HPLC-MS:
Boiling resulted in significant loss of all flavonoids, while steaming and microwaving led to minor losses or even increases of flavonoids.
Microwaving without water or with small amount of water tended to retain or increase total phenolics and/or flavonoids. When a large amount of water was added during microwaving, to some extent resembling boiling, total phenolics and/or flavonoids decreased.
Different agriculture practices may affect flavonoids’ existence and their interactions with other compounds, which in turn alter their sensitivity to heat treatments.
Retention of nutrients in cooked foods can be calculated as apparent retention (AR) based on dry form, or true retention (TR) based on fresh/wet form. TR represents actual consumption forms and also takes weight change after cooking into consideration.
The possible explanation for TR over 100% is that thermal processing may increase extractability and/or release from binding to other compounds as a result of matrix softening.”
https://www.cell.com/heliyon/fulltext/S2405-8440(19)30568-7 “Effects of domestic cooking on flavonoids in broccoli and calculation of retention factors”
The Material and methods section didn’t state that heated products’ temperatures were measured. So there wasn’t sufficient evidence for a solely thermal explanation of only microwaving achieving percentages over 100 per:
“The possible explanation for TR over 100% is that thermal processing..”
A more plausible explanation similar to Microwave broccoli to increase sulforaphane levels may account for microwaving’s increased percentages:
“Microwave treatment causes a sudden collapse of cell structure due to the increase in osmotic pressure difference over vacuole membrane.
We didn’t expect this result, and think microwave irradiation might help to release more conjugated forms of glucosinolates and then get hydrolyzed by released myrosinase.”
I immerse 3-day-old broccoli sprouts in 100 ml distilled water, then microwave them on 1000W full power for 35 seconds to ≤ 60°C (140°F). After microwaving I transfer broccoli sprouts to a strainer, and allow further myrosinase hydrolization of glucoraphanin and other glucosinolates into sulforaphane and other healthy compounds.
Myrosinase deactivation above 60°C wasn’t a consideration, since boiling, steaming, and a 1200W microwave on full power for one minute may have produced temperatures above 60°C. I’ll guess that an active enzyme wasn’t a requirement for flavonoid contents of broccoli purchased in a Beltsville, Maryland, grocery store.
The microwave tests used:
“Broccoli florets (150 g) were put in a microwave safe bowl with a 1 tablespoon [15 ml] of water.”
- A lesser weight of 3-day-old broccoli sprouts;
- A greater volume of distilled water;
- A less powerful microwave operated on full power for a lesser duration.
Before microwaving, I would expect a estimated 134 mg total flavonoids from eating 3-day old broccoli sprouts every day. This study’s findings lead me to expect that current practices with microwaving would improve flavonoid levels.
4 thoughts on “Microwave broccoli to increase flavonoid levels”
Excellent blog posts! I started to consume broccoli sprouts oriented on your regime just recently. However, I have a few questions left:
1. I’ve read that you can also freeze broccoli sprouts to increase sulforaphane levels. Would it be adequate to first store the sprouts in the freezer, and then microwave it to 60 c right before consumption, or is it better the other way around? Does the order matter? (I’m a little worried I might accidentally decrease sulforaphane content). After microwaving, I usually chop the sprouts, wait a little bit, and then eat them.
2. Is it possible to guess the sulforaphane based on taste? With my first test batch, I consumed three and 4-day broccoli sprouts and found that the older ones taste like mustard. However, I felt much more alert when I ate the younger ones, which were delicious.
3. How’s your hair doing? 🙂
Best wishes Katrin
Thanks for commenting Katrin!
1. Good question! Could you point me to what you’ve seen? I haven’t looked into freezing.
Studies often do what this study did and freeze-dry (lyophilize) their samples after experimental conditions and before analysis. I’d guess that wouldn’t have the same effects as regular freezing, though.
2. Good stuff! Maybe it could be done by taste if each batch were consistent?
I have batch effects, such that each one is a little bit different taste, volume, etc. although they’re the same age. I try to treat them equally, but my kitchen isn’t a laboratory, so I don’t.
3. Hard to find an impartial observer. 🙂 Dr. Greg Fahy has another clinical trial in progress, and since his presentation was my starting point, before and after hair color could be something they’ll measure.
Hi Gettingwell4, thank you for your reply:) So I did not freeze-dry but just froze the broccoli sprouts. Interestingly, I didn’t feel an “effect” so to say, and I didn’t feel more energetic when I consumed the “dumb-freeze” sprouts. In fact, I even poured away the excess water, so I guess the batch was pretty much useless – And so it felt!
I found this Youtube video with Rhonda Patrick and Dr. Fahey very interesting: https://www.youtube.com/watch?v=-PqziTSrKaU
My best anecdotal results have been with fresh, 3-day old sprouts eaten right away (that was my first try).
I feel that I can’t get the microwaving right. Why do you put water in it, and do you throw the water away after microwaving?
Interesting video Katrin, thanks! Dr. Jed Fahey has certainly done a lot of work in this area.
The 2018 Dutch review Isothiocyanates from Brassica Vegetables-Effects of Processing, Cooking, Mastication, and Digestion covered freezing. What do you think?
I immerse broccoli sprouts in water because that’s what Microwave broccoli to increase sulforaphane levels did with broccoli florets. After microwaving to 60° C I transfer broccoli sprouts to a strainer, and allow further myrosinase hydrolization of glucoraphanin and other glucosinolates into sulforaphane and other healthy compounds.
Most of the broccoli sprout compounds released by microwaving are water-soluble. Enhancing sulforaphane content showed an example of how they leach out if left in water after achieving 60° C.