What Is Myrosinase The Enzyme Behind Sulforaphane?

Myrosinase is an enzyme found in certain plants — most notably broccoli, Brussels sprouts, cabbage, and other cruciferous vegetables. It is the enzyme that converts glucoraphanin, a compound stored in those plants, into sulforaphane. Without myrosinase, that conversion does not happen.

The two substances are kept apart inside the plant’s cells. Glucoraphanin sits in the cell fluid. Myrosinase is stored separately. When the plant’s tissue is damaged — by chopping, chewing, or blending — the two meet and the reaction begins. This is a defense system the plant uses against insects and other threats. For humans, it is the reason raw or lightly cooked broccoli can produce sulforaphane in the body, while heavily boiled broccoli often cannot.

How Does Myrosinase Turn Glucoraphanin Into Sulforaphane?

The process is a two-step chemical reaction that happens within seconds of cell damage. When myrosinase contacts glucoraphanin, it removes the sugar portion of the molecule. The result is an unstable intermediate compound. That intermediate then rearranges on its own into sulforaphane, or into related compounds called isothiocyanates, depending on conditions.

This reaction is fast. In damaged plant tissue, much of the conversion occurs within minutes. The enzyme does not need heat, acid, or any added cofactor to work. It simply needs water and contact with its target molecule.

What matters for the reader is this: sulforaphane is not present in meaningful amounts in intact broccoli. It is created after the plant is disrupted. The enzyme is the switch.

Why Does Cooking Destroy Myrosinase?

Myrosinase is a protein, and like most proteins it is sensitive to heat. When cruciferous vegetables are cooked, the enzyme can lose its shape and stop working. This process is called denaturation, and it is the same reason an egg white turns solid when heated.

The temperature threshold and the time needed vary. Steaming briefly, stir-frying quickly, or blanching for a short time tends to preserve more enzyme activity than boiling for several minutes. Boiling is the most damaging method because heat transfers efficiently through water and the enzyme is exposed on all sides.

This is one of the more useful things to understand about cruciferous vegetables. A long boil can leave the glucoraphanin largely intact but remove the enzyme needed to convert it. The result is a vegetable that still contains the raw material but has lost the tool that turns it into sulforaphane.

Does Raw Broccoli Produce More Sulforaphane Than Cooked?

Yes, in general. Raw broccoli retains active myrosinase, so chopping and chewing it sets the reaction in motion. Cooked broccoli that has been heated enough to denature the enzyme produces little sulforaphane on its own.

But this is not the full picture. The human gut contains bacteria that can also convert glucoraphanin to sulforaphane, though the amount they produce varies widely between people and is generally lower than what plant myrosinase achieves. So cooked cruciferous vegetables are not useless. They still supply glucoraphanin, fiber, vitamins, and other compounds.

There is a practical trick supported by some research: adding a small amount of raw cruciferous vegetable — like a pinch of raw mustard powder, raw radish, or a few shreds of raw cabbage — to cooked broccoli can reintroduce myrosinase and restore some conversion. Mustard seeds and horseradish also contain the enzyme. The evidence for how much this boosts sulforaphane levels in the body is limited, but the underlying chemistry is sound.

How Does Chewing and Chopping Affect Sulforaphane Formation?

Mechanical damage is what starts the reaction. The more thoroughly the plant tissue is broken down, the more myrosinase contacts glucoraphanin. Chewing does this naturally. Chopping, slicing, and blending do it in the kitchen.

Timing matters here. If you chop broccoli and let it sit for a few minutes before cooking, some sulforaphane forms during that resting period. Once formed, sulforaphane is more heat-stable than the enzyme itself. So a brief rest after chopping, followed by cooking, can preserve more of the final compound than cooking immediately.

Some research suggests that letting chopped cruciferous vegetables rest for several minutes before heating helps. The exact optimal time is not firmly established, and different studies use different methods. What is clear is the general principle: damage first, then heat, is better than heat alone.

Is Myrosinase the Same in All Cruciferous Vegetables?

The enzyme is broadly similar across the cruciferous family, but the amount and the specific compounds it acts on differ by plant.

• Broccoli and broccoli sprouts are rich in glucoraphanin, the precursor to sulforaphane.
• Brussels sprouts, cabbage, and kale contain myrosinase but different glucosinolate profiles, leading to different isothiocyanates.
• Mustard seeds, horseradish, and wasabi are especially high in myrosinase activity.
• Broccoli sprouts contain far more glucoraphanin by weight than mature broccoli, though the exact amounts vary by growing conditions.

This matters because sulforaphane is not the only beneficial isothiocyanate. Other cruciferous vegetables produce different end products with their own studied effects. The enzyme is the shared mechanism, but the output depends on the starting material.

What Does the Evidence Say About Sulforaphane and Health?

Sulforaphane has been studied for its effects on inflammation, oxidative stress, and certain cellular processes. Laboratory and animal studies have shown a range of biological activities. Human trials are fewer and often small.

Some human research has looked at sulforaphane’s effects on markers of inflammation and on detoxification enzymes. Results have been mixed, and study designs vary. No large human trial has confirmed that eating broccoli or taking sulforaphane supplements prevents cancer or treats any specific disease.

This is an area where marketing often runs ahead of the science. Broccoli sprout extracts and sulforaphane supplements are sold with claims that go beyond what human evidence supports. The honest position: sulforaphane is a biologically active compound with plausible mechanisms and early human data, but it is not an established treatment for any condition.

Eating cruciferous vegetables is associated with health benefits in observational studies. Whether sulforaphane specifically is responsible, and to what degree, is not settled. Vegetables contain many compounds that could contribute.

Do Supplements Contain Active Myrosinase?

It depends on the product. Some supplements provide glucoraphanin alone, without myrosinase. Others include both, or provide sulforaphane directly. The formulation matters because without the enzyme or a substitute, glucoraphanin may not convert efficiently in the body.

Gut bacteria can convert some glucoraphanin, but the efficiency varies from person to person. A supplement that supplies only glucoraphanin may produce less sulforaphane than expected.

There is no standard for how these supplements are made, and testing has found that label claims do not always match contents. Anyone considering a supplement should know that regulation of dietary supplements in the US is less strict than for medications, and that no supplement has been proven to treat or prevent disease.

Key Takeaways

Myrosinase is the enzyme that makes sulforaphane possible. It is stored separately from glucoraphanin inside cruciferous plants, and it acts when plant cells are damaged. Heat can destroy it, which is why cooking method affects how much sulforaphane forms. Raw or lightly cooked cruciferous vegetables retain more enzyme activity. Adding a small amount of raw mustard, radish, or cabbage to cooked broccoli may help restore some conversion, though the human evidence is limited. Sulforaphane is a studied compound with promising early findings, but it is not a proven treatment for any disease.