Myrosinase & Sulforaphane: The Enzyme That Controls Conversion

Myrosinase is the conversion engine behind most glucoraphanin-based sulforaphane strategies. If a food or supplement supplies glucoraphanin but little active myrosinase, the amount of sulforaphane that ultimately reaches the body can fall sharply and become more variable.

That makes myrosinase one of the most important—and most misunderstood—words on a sulforaphane supplement label.

What is myrosinase?

Myrosinase is an enzyme naturally present in cruciferous plants. In intact plant tissue it is separated from glucosinolates such as glucoraphanin. Chopping, chewing or crushing damages cells and allows enzyme and precursor to interact.

In the sulforaphane pathway, myrosinase hydrolyzes glucoraphanin and enables formation of sulforaphane. If plant myrosinase is absent or inactive, gut microbes can perform some conversion, but human exposure is generally lower and more variable.

Why myrosinase matters in humans—not just in chemistry

The importance of myrosinase is supported by multiple human pharmacokinetic models rather than one isolated experiment.

Native myrosinase vs added myrosinase

Native myrosinase is the enzyme already present in broccoli, sprouts and related plants. It works well when preserved through handling and preparation.

Added myrosinase comes from another source—commonly mustard seed in research formulations—and is intentionally paired with glucoraphanin to improve conversion.

Biochemically, the goal is the same: place enough functional enzyme in contact with the precursor to generate sulforaphane efficiently.

Cooking can turn an enzyme-rich food into a precursor-heavy food

Heat can deactivate broccoli's endogenous myrosinase. A small human crossover study illustrates the consequence: estimated sulforaphane bioavailability was about 37% from raw broccoli but only 3.4% from cooked broccoli, despite the same 200 g food amount.^[5]

That does not mean glucoraphanin disappears. It means the rapid conversion system has been impaired.

Why mustard seed keeps appearing in sulforaphane research

Mustard seed is a concentrated practical source of active myrosinase. It has been used in human studies both to enhance conversion from cooked broccoli and to improve bioavailability from glucoraphanin-rich broccoli seed extract.

The 2026 crossover trial is especially useful because it tested the enzyme question directly in a supplement-like system: the added mustard-seed myrosinase increased average bioavailability from 18.6% to 39.8%.^[3]

Does active myrosinase survive the stomach?

Not perfectly—and this is where the story becomes more interesting than “enzyme present = problem solved.”

A human pharmacokinetic pilot using a glucoraphanin-rich extract with active myrosinase found that omeprazole administration and enteric coating changed glucoraphanin-to-sulforaphane conversion.^[6]

The study suggests that gastric acidity and release location can influence enzyme performance. You should not take a proton-pump inhibitor to improve sulforaphane absorption; the editorial lesson is that finished-product delivery design matters beyond the ingredient list.

What happens without active myrosinase?

Gut bacteria can convert some glucoraphanin, so a precursor-only product is not necessarily inactive. The problem is efficiency and variability.

Human studies repeatedly find lower and less predictable exposure when active plant myrosinase is absent. That means two people can swallow the same precursor dose and generate meaningfully different internal sulforaphane exposure.

Does every “broccoli sprout extract” contain active myrosinase?

No. Extraction, drying, heating and other processing can inactivate enzymes. A product can truthfully contain broccoli sprout or seed material without retaining enough functional myrosinase to reproduce fresh-plant conversion.

Useful labels should therefore distinguish:

• total broccoli extract weight;
• defined glucoraphanin content;
• whether active myrosinase is present;
• the source of myrosinase when added; and ideally
• finished-product conversion or yield information.

Do direct sulforaphane products need myrosinase?

No. Preformed or stabilized sulforaphane has already bypassed the glucoraphanin-conversion step. The formulation challenge shifts from enzymatic conversion to chemical stability, delivery and tolerability.

This is why “must contain myrosinase” is only correct for precursor-based formulations, not every possible sulforaphane product.

Does better conversion guarantee better clinical outcomes?

No. Myrosinase can improve the probability that a glucoraphanin dose becomes measurable sulforaphane exposure. It cannot guarantee that a disease endpoint, longevity marker or symptom will improve.

That distinction is essential. Pharmacokinetic evidence answers “Did more sulforaphane reach the body?” Clinical trials answer “Did that exposure change an outcome that matters?” Those are different questions.

Bottom line

For a glucoraphanin-based sulforaphane supplement, active myrosinase is one of the strongest evidence-backed formulation features you can look for. Human studies show better conversion when native enzyme is preserved or external enzyme is added, and they also show that cooking and gastrointestinal delivery can change how well the system works.

Evaluate myrosinase as part of a complete delivery system—not as a magic badge. For the chemistry, see sulforaphane vs glucoraphanin; for the broader buying framework, see the sulforaphane supplement guide.