Sulforaphane Foods: Where It Comes From

Written and reviewed by Dr. Xiaoyan Qiu · July 2026

Broccoli sprouts rank highest, broccoli seeds are close behind, and kale — despite its reputation as a superfood — barely registers. That is the short version of which foods actually deliver sulforaphane, and the full ranking is below. But there is one thing worth knowing before you read the list: almost no food contains sulforaphane directly. What cruciferous vegetables actually store is glucoraphanin, a stable precursor — and sulforaphane is only created when the plant tissue is broken down and an enzyme called myrosinase converts it.^[5] So when people talk about foods high in sulforaphane, they really mean foods rich in glucoraphanin that can convert efficiently. (The conversion step itself is covered in our guide to how glucoraphanin becomes sulforaphane.) This article ranks where that potential is highest, why broccoli sprouts and seeds dominate, whether kale and other crucifers count, and how cooking changes what you actually absorb.

Which Foods Contain Sulforaphane?

Sulforaphane comes almost exclusively from one plant family: the crucifers (Brassicaceae), which include broccoli, broccoli sprouts, cauliflower, cabbage, Brussels sprouts, kale, and watercress.^[3] But not all of them are sulforaphane foods in any meaningful sense. The compound is produced specifically from glucoraphanin, and glucoraphanin is just one of more than 120 glucosinolates found across these plants — each vegetable carries its own characteristic mix.^[3] That is why two equally nutritious crucifers can differ enormously in how much sulforaphane they are able to yield.

The table below ranks common crucifers by their sulforaphane potential — meaning their glucoraphanin content, since that precursor is what determines the ceiling. It is the most useful way to read the question of which foods contain sulforaphane: not “does it have a glucosinolate,” but “does it have this one.” A vegetable can sit high on a general “healthy greens” list and still rank near the bottom here, because its glucosinolates convert to something other than sulforaphane.

Why Broccoli Sprouts and Seeds Are the Richest Source

The single biggest factor in any list of foods highest in sulforaphane is plant age. Young broccoli sprouts — harvested around three to four days after germination — were shown in a landmark study to contain many times the glucoraphanin of the mature vegetable, while occupying a fraction of the volume.^[1] A small handful of sprouts can therefore carry the glucoraphanin of a far larger serving of cooked broccoli, which is why sprouts consistently top the rankings.

Seeds go further still. Across the plant kingdom, glucosinolates are stored at much higher concentrations in seeds than in leaves or stems, approaching ten percent of seed weight in some species.^[3] This is precisely why high glucoraphanin broccoli seeds are the starting material for commercial extraction: they pack the most precursor into the least mass, which makes standardization practical. The trade-off is that seeds are not an everyday food — their value is realized through extraction rather than the dinner plate.

How large is that seed-to-seed gap, concretely? A comparative HPLC study measured the sulforaphane yield obtainable (after hydrolysis) from the seeds of 12 cruciferous species across two genera — Brassica and Raphanus (radish).^[6] The full results, listed from lowest to highest within each genus:

A few notes on the species names above, for anyone cross-referencing the original source: “莲花白” is a regional Chinese common name (used in Sichuan, Yunnan, Shanxi, and Shaanxi) for the same botanical variety already listed above as “head cabbage” — both are Brassica oleracea var. capitata. The two entries in the source table most likely reflect different specific cultivars sampled under their regional names, and the roughly seven-fold gap between them (95.6 vs. 700.1 μg/g) is itself a useful illustration of how much variation exists within a single botanical variety, not just between species. “嫩儿菜” refers to er cai (儿菜), botanically Brassica juncea var. gemmifera — a stem-vegetable variety of mustard grown for its swollen axillary buds rather than its leaves, distinct from the leaf-type mustard greens (芥菜) listed above but part of the same species. And the entry listed as “carrot” sits under the Raphanus (radish) genus in the source table, but true carrot (Daucus carota) belongs to an entirely different plant family (Apiaceae) — this is almost certainly a regional cultivar name for a radish variety rather than actual carrot. We’ve reported the figure as published; formulators sourcing against this specific data point should confirm the cultivar identity against the primary source before relying on it.

Broccoli seed yielded roughly fourteen times more than head cabbage, the next-highest entry in the same genus, and close to seventy times more than the highest-yielding radish sample tested — which is precisely why broccoli seed, not just any crucifer seed, is the standard starting material for commercial glucoraphanin extraction rather than a marketing preference.^[6]

There is a practical catch with sprouts, however. Their glucoraphanin content is highest in the first few days and then falls as the plant grows, so a older, leafier sprout is closer to mature broccoli than to the freshly germinated material the studies measured. Home-grown sprouts also vary with seed batch and growing conditions, and they have a short shelf life. None of this disqualifies them as the best dietary source — it simply means the headline numbers describe an ideal that real kitchens rarely hit consistently.

Does Kale Contain Sulforaphane?

This is one of the most common questions about sulforaphane sources, and the honest answer is: very little. When researchers measured glucosinolates across broccoli, Brussels sprouts, cabbage, cauliflower, and kale, glucoraphanin was the predominant glucosinolate only in broccoli. In kale, the dominant glucosinolate was sinigrin, not glucoraphanin.^[2] Because sinigrin converts to allyl isothiocyanate rather than sulforaphane, kale simply does not produce meaningful amounts of the compound — despite being an excellent vegetable in other respects.

The same logic explains the rest of the family. Cabbage, Brussels sprouts, and cauliflower are also sinigrin- or indole-dominant, and watercress is rich in a precursor that yields a different isothiocyanate entirely.^[2][3] So while many crucifers are loosely described as sulforaphane foods, in practice sulforaphane tracks glucoraphanin specifically — and that points back to broccoli, its sprouts, and its seeds.

It helps to think in terms of precursor-product pairs. Each glucosinolate converts to its own isothiocyanate: glucoraphanin becomes sulforaphane, sinigrin becomes allyl isothiocyanate (the pungent compound behind mustard and horseradish), and gluconasturtiin becomes phenethyl isothiocyanate.^[3] All are studied bioactives, but they are not interchangeable, and only the glucoraphanin route yields sulforaphane. This is why a vegetable can be loaded with glucosinolates yet still be a poor sulforaphane source — the question is never how many glucosinolates a food has, but whether it has this particular one.

How Much Sulforaphane Is in Broccoli and Broccoli Sprouts?

There is no single number, and that is the practical problem. In one survey of 50 broccoli accessions, glucoraphanin ranged from about 0.8 to 21.7 micromoles per gram of dry weight — a more than twenty-fold spread driven by cultivar alone, before cooking or storage enter the picture.^[2] So the honest answer to how much sulforaphane is in broccoli is that it depends heavily on which broccoli, grown how.

Broccoli sprouts sit far above that range on a per-gram basis, which is what makes them the reference point for how much sulforaphane is in broccoli sprouts.^[1] But even here the figure describes potential, not delivered dose: the glucoraphanin still has to be converted, and how much of it you ultimately absorb depends on myrosinase and on your own gut. A high precursor number is the ceiling, not the guarantee.

Put simply, how much sulforaphane in broccoli you get comes down mostly to the cultivar and freshness, while how much sulforaphane in broccoli sprouts you get comes down to how young they were at harvest. Reported precursor figures are also usually given in micromoles per gram of dry weight, so they look larger than the fresh-weight amount on your plate once water content is accounted for. The takeaway is not a single milligram value but a principle: treat any food figure as a range, not a dose, and assume real-world yield lands below the laboratory maximum.

Does Cooking Destroy Sulforaphane?

To a large degree, yes — though it is the enzyme, not the precursor, that suffers. Glucoraphanin is heat-stable, but myrosinase is destroyed by heat, so cooking removes the tool that converts one into the other. In a human cross-over trial, the bioavailability of sulforaphane was about 37% from raw broccoli versus only 3.4% from cooked, and absorption was also markedly delayed when the broccoli was cooked.^[4] That is roughly a ten-fold difference from cooking alone.

For anyone relying on food, the practical takeaways are simple: raw or lightly steamed beats boiled, chopping and then waiting before eating gives the plant enzyme time to work, and pairing cooked crucifers with a raw source of myrosinase can partly rescue the yield. None of this makes food a precise dose, but it does explain why two people eating “broccoli” can end up with very different exposure.

Storage and preparation before cooking matter too. Glucoraphanin is reasonably stable in fresh and frozen vegetables, but commercial freezing usually involves a hot blanching step that inactivates myrosinase, which is why frozen broccoli can be rich in precursor yet yield little sulforaphane unless an enzyme source is added. Prolonged storage and heavy processing chip away further. The compound is, in short, fragile at exactly the points where everyday handling is roughest.

Microwaving is the method people ask about most, and the answer depends on intensity. Brief, gentle microwaving with little water is far kinder to myrosinase than high-power cooking or boiling, where the enzyme is lost quickly and water-soluble glucoraphanin also leaches into the discarded liquid. The general rule holds across every method: the more heat and water, the lower the yield. Gentle and brief preserves the conversion machinery; long and wet destroys it and washes the precursor away.

How to Get the Most Sulforaphane from Food

If whole foods are your route, a few habits meaningfully raise the yield. The foods with sulforaphane worth prioritizing are broccoli sprouts first, then fresh broccoli, eaten raw or only lightly steamed rather than boiled or microwaved to mush. Steaming for just a few minutes is a reasonable compromise: it can soften the texture while leaving more enzyme activity intact than hard boiling does.

Two simple tricks help further. First, chop or blend, then wait roughly forty minutes before heating — this lets myrosinase act while it is still alive, locking in sulforaphane before the heat arrives. Second, when crucifers are already cooked, sprinkle on a pinch of raw mustard seed powder; mustard is a rich myrosinase source and can restore much of the conversion that cooking destroyed. Neither makes intake precise, but together they shift food from a poor converter toward a decent one.

Variety helps as well. Because the active isothiocyanates differ between vegetables, rotating crucifers gives a broader mix of compounds even though only the glucoraphanin route supplies sulforaphane itself. But if maximizing this one compound is the specific goal, the priority order is consistent: fresh sprouts, then raw or barely cooked broccoli, prepared to protect the enzyme. Everything else in the family contributes other isothiocyanates rather than meaningfully adding to the sulforaphane total.

Getting a Consistent Sulforaphane Source

Putting the pieces together, food is a genuinely variable source: cultivar, plant age, storage, cooking method, and individual gut flora all move the final number, often by an order of magnitude. For occasional dietary intake that variability is fine. For a product, a study protocol, or any application that needs a defined and repeatable amount, it is a problem — you cannot build a specification on a vegetable whose precursor content swings twenty-fold.

This is the gap a standardized ingredient fills. A standardized bulk broccoli extract built from high-glucoraphanin seed states its glucoraphanin percentage by HPLC and its myrosinase status per batch, turning a variable food compound into a controllable input. The underlying chemistry is identical to what happens in the kitchen — the difference is that the precursor level and the conversion enzyme are documented rather than left to chance.

For a formulator, that distinction is the whole point. A label claim, a clinical protocol, or a quality specification needs a number it can defend, and “a serving of broccoli” is not that number. Starting from a defined glucoraphanin figure lets the per-serving amount be calculated forward rather than estimated backward from a vegetable, and it makes batch-to-batch consistency a matter of specification instead of harvest luck. Food remains the better answer for everyday eating; a documented extract is the better answer when the amount has to be repeatable and provable.

Frequently Asked Questions

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