This 2021 review evaluated effects on glucoraphanin and sulforaphane content of cooking broccoli and other Brassica vegetables:
“The amount of glucosinolates (GLS) in brassica vegetables can be affected significantly during processing and cooking, depending on their specific conditions and types:
- Microwaving can retain or even increase content of glucoraphanin (GLR), and can increase production of sulforaphane (SLR) within a short time;
- Fermentations generally decrease content of GLR;
- Short-time steaming may promote formation of SLR; and
- Short-time microwaving may promote formation of SLR from GLR better than fermentation and steaming.
Other processing and cooking effects include:
- Packaging and freezing can reduce loss of GLR content. Freezing treatment promotes hydrolysis of GLS to form SLR, and freezing stress may lead to GLS degradation;
- Boiling and blanching result in the largest loss of GLR from broccoli, as loss of GLR content is mainly due to its leakage into the water; and
- Stir-frying may be a suitable and healthful cooking option to prevent loss of GLR, but contents of GLR and SLR were still influenced due to different factors.
It is better for consumers to microwave or steam brassica vegetables before consumption to obtain greater health benefits.”
https://www.sciencedirect.com/science/article/abs/pii/S030881462101013X “The effect of processing and cooking on glucoraphanin and sulforaphane in brassica vegetables” (not freely available). Thanks to Dr. Jing Sun for providing a copy.
This review found mainly negative effects of cooking Brassica vegetables with boiling, stir frying, blanching, or high pressure on glucoraphanin and sulforaphane content. Previously curated studies cited were:
- Microwave broccoli to increase sulforaphane levels;
- Enhancing sulforaphane content; and
- Sorting out the Value of Cruciferous Sprouts as Sources of Bioactive Compounds for Nutrition and Health.
Blue heron on its way to the breakfast buffet