Does frozen broccoli contain glucoraphanin?

Yes, in good proportion. Blanching before freezing inactivates myrosinase but does not destroy glucoraphanin. Frozen broccoli provides glucoraphanin, but its conversion to sulforaphane depends on gut microbiota, which is less efficient than active plant myrosinase.

Are glucoraphanin supplements equivalent to eating broccoli?

It depends on the supplement. If it contains active myrosinase, the conversion can be efficient. If it only contains pure glucoraphanin without the enzyme, the bioavailability of sulforaphane can be 3–4 times lower than that of fresh sprouts. The label should explicitly state whether active myrosinase is present.

Does kale have as much glucoraphanin as broccoli?

No. Kale of the species Brassica oleracea has glucoraphanin in a lower proportion than broccoli; its dominant glucosinolates are gluconapin and glucobrassicin. Kale has other compounds of nutritional interest, but it is not the best source of glucoraphanin specifically.

Do all broccoli sprouts have the same glucoraphanin content?

No. The concentration varies depending on the variety, germination time, growing conditions, and storage. The range of 10–100 times more than mature broccoli comes from laboratory-selected cultivars. Commercial sprouts have variable but generally high concentrations.

Where is glucoraphanin concentrated? Best dietary sources

💡 Key Takeaways

Glucoraphanin is not found in all vegetables: it is a compound exclusive to cruciferous vegetables, and among them, broccoli is the most concentrated and documented source. However, the concentration varies greatly depending on the variety, stage of development, and preparation.

Glucoraphanin is present only in cruciferous vegetables; broccoli is the most concentrated and documented source
Concentration varies up to 27 times between broccoli varieties of the same species
3-day-old broccoli sprouts concentrate 10–100 times more glucoraphanin than mature broccoli (selected cultivars)
Kale, cauliflower, and Brussels sprouts contain glucoraphanin but in smaller proportions than broccoli
Cooking does not destroy glucoraphanin but it does destroy myrosinase, drastically reducing the conversion to sulforaphane

This article includes a comparative table of 8 glucoraphanin sources with concentration data and practical observations, based on Kushad et al. (1999), Fahey et al. (1997), and Bouranis et al. (2023).

Table of Contents

If glucoraphanin is the precursor to sulforaphane, the practical question is obvious: what foods contain it and in what quantity? The answer is more nuanced than most articles suggest.

Only in cruciferous vegetables, not all vegetables

Glucoraphanin belongs to the family of glucosinolates, compounds synthesized only by plants of the Brassicaceae family. It is not found in tomatoes, spinach, carrots, or legumes. It is an exclusive territory of cruciferous vegetables.

Within cruciferous vegetables, glucoraphanin is not the only glucosinolate present, nor is it predominant in all species. Kale, for example, has more gluconapin and glucobrassicin than glucoraphanin. Broccoli is the exception: glucoraphanin is its dominant glucosinolate, making it the most relevant source for those specifically seeking this precursor.

Variation among species and varieties

Kushad et al. (1999) analyzed 65 accessions of Brassica oleracea grown under uniform conditions. The concentration of glucoraphanin in broccoli varied from 0.8 to 21.7 µmol/g dry weight—a difference of more than 27 times between the poorest and richest varieties (DOI: 10.1021/jf980985s). In Brussels sprouts, cauliflower, and kale, sinigrin and glucobrassicin predominated over glucoraphanin.

Source	Glucoraphanin	Observation
Mature broccoli	0.8–21.7 µmol/g DW	Large variation among cultivars
Broccoli sprouts (3 days)	10–100× more than mature broccoli	Data from selected cultivars (Fahey 1997)
Broccoli microgreens (7–14 days)	Comparable to sprouts; documented bioavailability in humans	Bouranis et al., Foods 2023
Broccoli seeds	Very high	Mainly used as a supplement
Cauliflower	Present, lower than broccoli	Dominant glucosinolate: sinigrin
Kale (B. oleracea)	Low compared to broccoli	Predominant glucosinolates: gluconapin, glucobrassicin
Brussels sprouts	Present alongside sinigrin	Mixed profile
Radish	Glucoiberin and glucoraphanin in root	Main isothiocyanate different from sulforaphane

Sprouts and microgreens: the highest accessible concentration

Fahey et al. (1997) documented that 3-day-old broccoli sprouts contain 10 to 100 times more glucoraphanin than mature broccoli of the same variety, in selected cultivars (DOI: 10.1073/pnas.94.19.10367). This range does not automatically apply to all commercially available sprouts, where variety and growing conditions yield more variable results.

Broccoli microgreens (7–14 days germination) have shown a glucoraphanin concentration comparable to younger sprouts, with sulforaphane bioavailability in humans similar to that documented for sprouts (Bouranis et al., Foods 2023, DOI: 10.3390/foods12203784). A practical advantage of microgreens is that they are more tender and easier to incorporate into regular diet.

How preparation affects available glucoraphanin

Glucoraphanin is heat-stable: it resists cooking better than myrosinase. Boiling broccoli does not destroy glucoraphanin—it remains present in the cooked tissue—but it does destroy the enzyme that converts it to sulforaphane.

It is also water-soluble: part of the glucoraphanin passes into the cooking water when boiled. Prolonged boiling reduces the glucoraphanin content in the tissue through this mechanism. Brief steaming preserves more glucoraphanin than boiling because there is less contact with water.

Industrial freezing includes a blanching step that inactivates myrosinase, although it preserves a good portion of glucoraphanin. Frozen broccoli has available glucoraphanin, but its conversion to sulforaphane depends on colonic microbiota, not plant myrosinase.

→ Why cooking drastically reduces available sulforaphane: Broccoli sprouts: glucoraphanin, myrosinase, and why the form matters

Conclusion

Broccoli and its young forms—sprouts, microgreens—are the most concentrated sources of glucoraphanin in a regular diet. Cauliflower, kale, and Brussels sprouts contain glucoraphanin but in smaller proportions and with other predominant glucosinolates. Variety within broccoli matters: concentration can vary more than 27 times between cultivars. And preparation determines how much of that glucoraphanin can be converted to sulforaphane.

→ Why broccoli concentrates so much glucoraphanin compared to other vegetables: Glucoraphanin in broccoli: variety, cultivation, and actual concentration