This 2020 Chinese/USDA study investigated effects on sulforaphane amount from heating broccoli in water and microwaving at different power settings to different temperatures:
“Microwave treatment causes a sudden collapse of cell structure due to the increase in osmotic pressure difference over vacuole membrane. Mild heating could increase SFR [sulforaphane] level, possibly explained by the increased activity of MYR [the enzyme myrosinase] which can hydrolyze GLR [glucoraphanin] into SFR at high temperature (up to 60°C).
Microwave‐cooked broccoli had higher levels of these two compounds compared to broccoli heated in water. The broccoli sample without cooking as a control showed the least amount of GLR, indicating that microwave heating did help to release more GLR from the cell.
In the temperature range of 50–60°C, a positive correlation was observed between GLR or SFR contents and temperature. However, these two physiochemical contents were negatively correlated with temperature when it increased to 70°C.
The glucoraphanin (GLR) and sulforaphane (SFR) contents (μmol/g DW) in florets of broccoli during microwaving at 40, 50, 60, and 70°C using low power level (LL) or high power level (HL). Data are reported as the mean ± SD (n = 3). Values with different letters are significantly (p < .05) different.
[For example, sulforaphane levels of the control (raw), LL40, LL70, and HL40 conditions weren’t significantly different, and the HL70 level was significantly lower than those levels]. The microwave using high level at 60°C showed the greatest SFR level (2.45 µmol/g DW).”
Table S1 from the supporting material:
| Temperature
(°C) |
Time
(S) |
Power level
|
|
| Heating in water | 40 | 185 | NA |
| 50 | 230 | ||
| 60 | 262 | ||
| 70 | 290 | ||
| Microwave (HL) | 40 | 65 | 950 |
| 50 | 90 | ||
| 60 | 108 | ||
| 70 | 120 | ||
| Microwave (LL) | 40 | 115 | 475 |
| 50 | 148 | ||
| 60 | 178 | ||
| 70 | 200 |
https://onlinelibrary.wiley.com/doi/10.1002/fsn3.1493 “Microwave cooking increases sulforaphane level in broccoli”
The researchers demonstrated a more effective method of increasing sulforaphane than did the cited and widely discussed 2004 Heating decreases epithiospecifier protein activity and increases sulforaphane formation in broccoli (not freely available). The older study methods were difficult to implement in kitchens, and evaluated heating temperature as the only factor.
The present study added microwave power level irradiation effects as a factor, and simplified heating temperature implementation. People can use Table S1 to maximize broccoli floret sulforaphane content in their kitchens. See Week 2 of Changing an inflammatory phenotype with broccoli sprouts for changes.
The study provided an optimal sulforaphane end result of “(2.45 µmol/g DW)”. I asked a study author for additional data, and they replied:
“The control GLR and SLR amount was 2.18 and 0.22 µmol/g DW, respectively, while the HL60 GLR amount was 2.78 µmol/g DW.”
Microwaving 10 grams of broccoli florets to 60°C (140°F) increased the sulforaphane amount by 1,114% (2.45 / .22)! That also increased the glucoraphanin amount by 27% (2.78 / 2.18) for further processing into sulforaphane after eating.
I replied: That’s an exciting result, increasing sulforaphane more than 11 times, while also increasing glucoraphanin! I haven’t found similar experiments with broccoli sprouts. Would you expect similar results?
The study author responded:
“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. Further studies are being carried out.”
The study also measured broccoli stems:
“GLR and SFR were hardly detected in stems. Less than 52% of GLR was detected in the [50/50] mixture of florets and stems compared to florets.
Microwaved at 60°C, the florets had a concentration of GLR and SFR at 2.78 and 2.45 µmol/g DW, respectively, which was significantly higher than the levels detected in mixture of florets and stems (1.21 and 0.82 µmol/g DW, respectively).”
The 50% florets / 50% stems mixture’s glucoraphanin amount of 1.21 µmol was roughly comparable with the 1.08 µmol glucoraphanin amount of mature broccoli extract in item 2 below.
Reminders from Eat broccoli sprouts today:
- A 1 mg sulforaphane weight equals a 5.64 μmol sulforaphane amount.
- “Content of glucoraphanin in extract from broccoli sprouts was 16.6 μmol per gram of fresh weight. In contrast, mature broccoli extract contained 1.08 μmol per gram of fresh weight.”
- The bioavailability of sulforaphane in a broccoli sprout extract with the myrosinase enzyme 100 μmol gelcap was 36.1% which weighed 6.4 mg.
- The question of how much sulforaphane is suitable for healthy people remains unanswered.
Surface Your Real Self 
It looks like this study compared two types of heating: (1) via microwave; and (2) via a pot containing water and broccoli . Do you have any idea (or have there been any studies) as to the effects of oven cooking (e.g., no water added) of broccoli and/or broccoli sprouts?
So, as an example, put broccoli sprouts on a tray and put the tray in an oven that is pre-heated to 140F. Broccoli sprouts are left in for 5 mins or so. Same result?
Thanks for your comment!
I believe the differences between the two microwave levels in the above chart demonstrated that microwave power level irradiation effects were the dominant factor that increased sulforaphane. High power had better results than low power at the same temperatures because it was more disruptive: “Microwave treatment causes a sudden collapse of cell structure due to the increase in osmotic pressure difference over vacuole membrane.”
I’d guess the study authors were obligated to replicate findings of previous experiments for heating-by-itself in water to increase sulforaphane.
Great answer and great blog, thank you!
Do you have a current best practice for what you do with your sprouts after they’re done growing?
For example, I’ve seen one or more of the following steps: (1) rinse sprouts; (2) chop/crush sprouts and let them sit for 30 mins; (3) heat the sprouts (e.g., via microwave, boiling, oven, etc.) to ~160F for a few mins; (4 – optional) add mustard powder (or mustard seed) to heated sprouts; and finally (5) eat (or refrigerate or freeze, depending on needs) the sprouts.
That’s just one example I saw, but you would know better as to what is the best practice given the research. Keep up the great work!
Thanks!
I follow the 3-day-old broccoli sprouts have the optimal yields study and stop them at the 3-day-old point. That study evaluated six broccoli cultivated varieties’ seeds and sprouts at the 3, 5, and 7-day points past germination. Five of the varieties’ sprouts had the most sulforaphane after 3 days, with one cultivar most at the 5-day-old point.
Those researchers processed the sprouts through multiple steps in order to evaluate them. It’s hard to say that people would get the same absolute results, but easier to guess that 3-day-old sprouts would probably have more sulforaphane content than 7-day-old sprouts. Then I microwave them per Week 6 of changing an inflammatory phenotype with broccoli sprouts to no more than 60°C (140°F).
Do your broccoli seeds specify their cultivar? I don’t see any cultivars disclosed on the labels of the ones on Amazon.
Thank you! My seeds (from true leaf) do not seem to specify the cultivar. I will stick to 3 days (instead of 4 or 5 days) based on that study.
Do you have any concerns about foodborne illness when eating your sprouts? That is my only concern. Obviously the health benefits far outweigh the risks, but I wish that there was a way to easily negate any risk of illness.
Broccoli seed suppliers are missing a marketing opportunity by not specifying their cultivars. They could be advertising specific benefits, etc. The 3-day-old broccoli sprouts have the optimal yields study showed that broccoli cultivars’ sulforaphane contents vary widely.
I wonder why batches don’t always have consistent yields although I treat each of them consistently. Bacteria could be a possible explanation. My kitchen isn’t a laboratory.
See Week 7 of changing to a youthful phenotype with broccoli sprouts for the cause of poor yields! You may be surprised.