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:
|Heating in water||40||185||NA|
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.