What is Myrosinase and Why Does it Matter?
Myrosinase is a family of enzymes responsible for catalyzing the hydrolysis of a class of compounds called glucosinolates. When these two are mixed, they produce biologically active compounds known as isothiocyanates, which are responsible for the pungent flavor of many cruciferous foods. This enzymatic reaction is part of a sophisticated plant defense mechanism known as the "mustard oil bomb," designed to deter herbivores and pathogens. For humans, this process is highly beneficial, as these isothiocyanates, particularly sulforaphane derived from broccoli, are associated with various health benefits, including cancer chemoprevention. Understanding where is myrosinase found is key to preserving its activity and maximizing these nutritional benefits in your diet.
Primary Plant Sources: The Cruciferous Family
The most significant source of myrosinase for human consumption is the plant family Brassicaceae, commonly known as cruciferous vegetables. The enzyme is stored in special cellular compartments, keeping it separate from glucosinolates until the plant tissue is damaged by chopping, chewing, or processing.
Vegetables and Sprouts
- Broccoli and Broccoli Sprouts: These are exceptionally rich sources of both glucoraphanin (a glucosinolate) and active myrosinase. Research has shown that eating raw broccoli or broccoli sprouts maximizes the conversion to sulforaphane, a potent health-promoting compound. Mild cooking methods can enhance sulforaphane yield by inactivating other proteins that compete with myrosinase, but high-heat cooking destroys myrosinase entirely.
- Cabbage and Cauliflower: Both of these widely consumed cruciferous vegetables contain myrosinase. Similar to broccoli, their myrosinase activity is greatest when consumed raw, as in coleslaw, or lightly cooked.
- Horseradish and Wasabi: The distinct pungency of horseradish and wasabi is a direct result of myrosinase acting on glucosinolates when the root is crushed. The resulting allyl isothiocyanate is a potent compound that serves as a deterrent to herbivores.
- Mustard Seeds: Myrosinase was first discovered in mustard seeds. The enzyme is highly concentrated in the seeds and is what gives mustard its characteristic flavor when ground and mixed with liquid.
- Other Sources: Other cruciferous plants like radishes, arugula, daikon, watercress, and kale also contain myrosinase and can contribute to your dietary intake of this enzyme.
The Microscopic World: Myrosinase in Other Organisms
While plants are the main source, myrosinase activity has also been identified in other organisms that have evolved in relation to glucosinolate-containing plants.
- Insects: Certain insects, like the cabbage aphid, have evolved their own myrosinase-like enzyme. This allows them to effectively utilize the plant's own defense system against their own predators, earning them the moniker "walking mustard oil bombs".
- Bacteria and Fungi: Myrosinase has also been isolated from various microorganisms. A marine bacterium, Shewanella baltica, for instance, was found to produce a novel myrosinase with potential biotechnological applications. Some endophytic fungi found in horseradish roots also possess glucosinolate-decomposing activity.
- Human Gut Microbiota: For cooked cruciferous vegetables where the plant's own myrosinase has been denatured by heat, gut bacteria play a crucial role in converting glucosinolates into isothiocyanates. However, this microbial conversion is less efficient and more variable than the plant's native enzymatic process.
Cellular Compartmentalization: The "Mustard Oil Bomb"
The glucosinolate-myrosinase system is a classic example of plant chemical warfare. In the plant's intact cells, myrosinase is sequestered in specialized cells called myrosin cells (or idioblasts) and stored in protein bodies or vacuoles, while glucosinolates are housed in adjacent but separate S-cells. Only when tissue is damaged does the enzyme come into contact with its substrate, triggering the defense reaction.
How Processing Affects Myrosinase Activity
The way food is prepared dramatically affects myrosinase activity. Because the enzyme is heat-sensitive, high-temperature cooking, such as boiling or prolonged microwaving, will inactivate it. Eating vegetables raw or minimally processed is the best way to retain myrosinase activity. For those who prefer cooked vegetables, chopping them first and waiting about 40 minutes before cooking can still yield good results, as this allows the reaction to occur before the heat destroys the enzyme. Adding a source of active myrosinase, such as powdered mustard seed or fresh broccoli sprouts, to cooked vegetables is another effective strategy to restore enzyme activity and boost beneficial compound formation.
Comparison of Myrosinase Sources and Processing Methods
| Source | Myrosinase Activity | Bioavailability of Products | Notes |
|---|---|---|---|
| Raw Broccoli | High | High | Contains active, heat-sensitive enzyme for potent conversion. |
| Cooked Broccoli | Low to None | Low (unless reconstituted) | Heat inactivates myrosinase, requiring gut bacteria or exogenous enzyme for conversion. |
| Mustard Seed Powder | Very High | Variable (depends on use) | Extremely high enzyme concentration; can be added to cooked cruciferous vegetables to restore activity. |
| Freeze-Dried Sprouts | High | High | Gentle processing preserves the active enzyme; effective way to supplement. |
| Gut Microbiota | Variable and Less Efficient | Variable and Lower | Converts glucosinolates when plant myrosinase is absent but is highly dependent on individual gut flora. |
Conclusion
In summary, myrosinase is an enzyme predominantly found in the Brassicaceae family of plants, including familiar items like broccoli, mustard, and cabbage. Its presence is not limited to plants, extending to certain insects and microbes. Inside plants, myrosinase and its substrates are stored separately, only reacting when the plant tissue is damaged to produce health-promoting isothiocyanates. Crucially, myrosinase is sensitive to heat, meaning consumption of raw, lightly cooked, or freeze-dried cruciferous vegetables is the most effective way to harness its power and maximize the bioavailability of beneficial compounds. For those who prefer their vegetables cooked, adding an external source of myrosinase, such as mustard seed powder, is an excellent workaround.
[FoundMyFitness: Stability and heat sensitivity of myrosinase enzyme in cruciferous vegetables (https://www.foundmyfitness.com/episodes/stability-heat-sensitivity-myrosinase-cruciferous-vegetables)]
