What Chemicals Are in Horseradish and What Do They Do?

December 13, 2025 •

4 min read

Horseradish contains up to 10 times more of the powerful cancer-fighting compound glucosinolates than its cruciferous cousin, broccoli. These are the foundational chemicals in horseradish that, when the root is grated, react with enzymes to create the volatile, sinus-clearing intensity it is famous for. Understanding these chemical reactions reveals the science behind this potent condiment.

Quick Summary

The pungency of horseradish is caused by isothiocyanates, particularly allyl isothiocyanate, which are formed when the root is crushed. This reaction is initiated by the enzyme myrosinase breaking down glucosinolates like sinigrin. Horseradish also contains various antioxidant compounds and the enzyme horseradish peroxidase.

Key Points

Spiciness Origin: The fiery sensation of horseradish comes from allyl isothiocyanate (AITC), a volatile compound released when the root is crushed.
Enzymatic Reaction: AITC is formed by the reaction between the stored compound sinigrin and the enzyme myrosinase upon cell damage, such as grating.
Volatile Nature: Horseradish's heat is felt in the sinuses because AITC is highly volatile, unlike the capsaicin in chili peppers, which primarily affects the mouth.
Antimicrobial Properties: The isothiocyanates found in horseradish have demonstrated antimicrobial effects, which contribute to its traditional medicinal uses.
Antioxidant Content: Besides the pungent compounds, horseradish is rich in vitamin C and other antioxidants like flavonoids that offer health-promoting benefits.
Preservation Chemistry: Prepared horseradish stays consistent in heat because vinegar is added to halt the chemical reaction that produces the volatile isothiocyanates.
Scientific Applications: The enzyme horseradish peroxidase (HRP) is a separate and significant chemical in the root, used extensively in laboratory and diagnostic testing.

The Core Chemical Reaction: From Precursor to Pungency

The characteristic heat of horseradish is the result of a chemical reaction that occurs when the root is damaged. This reaction involves the glucosinolate sinigrin and the enzyme myrosinase, which are stored separately in the intact root. When the root is grated or chewed, these substances mix, and myrosinase breaks down sinigrin into allyl isothiocyanate (AITC). AITC is a volatile compound responsible for the strong, pungent flavor and the sensation of heat in the sinuses and eyes. This process is similar to the reactions in mustard and wasabi. The volatility of AITC means its potency decreases over time, explaining why fresh horseradish is hotter than bottled varieties, which often contain vinegar to stabilize the reaction.

Other Notable Compounds and Their Functions

Horseradish contains a variety of other phytochemicals in addition to the primary pungency-causing compounds.

Other Glucosinolates and Isothiocyanates

While AITC is dominant, other related compounds are present. These include gluconasturtiin, which hydrolyzes into phenethyl isothiocyanate (PEITC), another pungent compound found in higher concentrations in some horseradish types. Trace amounts of other isothiocyanates may also be present.

Antioxidants and Nutrients

Horseradish is a source of antioxidants and nutrients. It is particularly rich in vitamin C. Flavonoids like kaempferol and quercetin, known for antioxidant and anti-inflammatory properties, have been identified. Phenolic acids also contribute to its antioxidant activity.

The Enzyme Horseradish Peroxidase (HRP)

Horseradish roots also contain the enzyme horseradish peroxidase (HRP). This enzyme is important in biochemistry and molecular biology for amplifying signals in laboratory tests.

A Comparison of Horseradish Compounds


Compound	Type	Function in Plant	Flavor/Sensation	Human Health Impact	Notes
Sinigrin	Glucosinolate	Precursor to AITC	Odorless	Potential anticancer, antimicrobial via breakdown	Key building block for heat.
Myrosinase	Enzyme	Catalyzes glucosinolate hydrolysis	None	Aids in releasing bioactive compounds	The catalyst.
Allyl Isothiocyanate (AITC)	Isothiocyanate	Defense against herbivores	Pungent, volatile heat in sinuses	Antimicrobial, potential anti-cancer	Main compound for heat.
Phenethyl Isothiocyanate (PEITC)	Isothiocyanate	Defense against pests	Less volatile, contributes to heat	Potential anti-cancer	Secondary spicy contributor.
Horseradish Peroxidase (HRP)	Enzyme	Plant defense	None	Used in diagnostic tests	Biochemical research tool.
Vitamin C	Nutrient	Antioxidant	None	Immune support, antioxidant	Nutritional value.
Flavonoids (e.g., Kaempferol)	Antioxidant	Plant defense	None	Anti-inflammatory properties	Health-promoting profile.

Factors Affecting Horseradish Chemistry

The chemical composition and intensity of horseradish are influenced by genotype, growing conditions, and processing. The volatility of AITC means potency fades with time and exposure; vinegar in prepared horseradish stabilizes the flavor. Different varieties of horseradish can have varying levels of volatile compounds. Colder storage also helps preserve the heat.

The Potential Health Implications of Horseradish Chemicals

Research suggests potential health benefits from horseradish compounds, particularly isothiocyanates, which show antimicrobial and anticancer properties in studies. They can fight bacteria like E. coli and Salmonella. Glucosinolates and isothiocyanates may also inhibit some cancer cell growth. The antioxidants provide support against cell damage.

Potential Side Effects

Consuming large amounts of horseradish can cause digestive irritation. It may also affect thyroid function if consumed in very high quantities.

Conclusion: A Chemical Powerhouse

Horseradish's pungency is a result of a specific chemical reaction creating allyl isothiocyanate. Along with other glucosinolates, antioxidants like vitamin C and flavonoids, and the enzyme HRP, it possesses a complex chemical profile. Its intense flavor and potential health benefits make it a noteworthy root. Processing methods like adding vinegar are used to stabilize these powerful chemicals.

Note: This information is for informational purposes only and does not constitute medical advice. Consult a healthcare professional before using horseradish as a treatment for any condition.

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What are the main chemicals that give horseradish its spicy flavor?

Allyl isothiocyanate (AITC) is the main chemical that produces horseradish's spicy flavor and the intense, nasal-clearing sensation. It is created when the enzyme myrosinase interacts with the precursor compound sinigrin after the root is grated or cut.

Is the heat from horseradish the same as chili peppers?

No, the heat is different because it comes from different chemicals. Chili peppers contain capsaicin, which activates pain receptors on the tongue. Horseradish contains volatile isothiocyanates, which are sensed by nerve endings in the sinuses and nasal passages, causing the signature upward burn.

What is the function of the chemicals in horseradish in nature?

The potent chemicals in horseradish, particularly the isothiocyanates like allyl isothiocyanate, act as a natural defense mechanism for the plant. The sharp taste and irritant effect repel pests and grazing animals, protecting the plant from being eaten.

How does processed horseradish differ chemically from fresh horseradish?

Processed horseradish, which is mixed with vinegar, is chemically stabilized. Vinegar halts the enzymatic reaction that creates allyl isothiocyanate, preserving the spice level at the time of processing and preventing it from dissipating over time. Fresh horseradish is much more volatile and loses its heat rapidly.

Does cooking destroy the chemicals in horseradish?

Yes, cooking horseradish significantly reduces its pungency. Heat degrades the volatile isothiocyanates, leading to a milder flavor. This is why horseradish sauces and dishes that are cooked tend to be much less spicy.

What is horseradish peroxidase used for?

Horseradish peroxidase (HRP) is an enzyme found in the root that is widely used in scientific research. It is a valuable tool in molecular biology and biochemistry for its ability to amplify signals in a variety of diagnostic assays, such as ELISA and Western blotting.

Are there any other health-promoting compounds in horseradish?

Yes, in addition to glucosinolates, horseradish contains antioxidants such as vitamin C and flavonoids like kaempferol. These compounds offer antioxidant and anti-inflammatory benefits that contribute to overall health.

Frequently Asked Questions

The primary chemical that gives horseradish its spicy flavor is allyl isothiocyanate (AITC), a volatile compound released when the root is grated or crushed.

Horseradish affects your nose and sinuses because allyl isothiocyanate is a volatile compound that evaporates and travels up into your nasal passages, irritating the nerve endings there.

Adding vinegar to grated horseradish stops the enzymatic reaction that creates allyl isothiocyanate. This preserves the horseradish's flavor and heat at that specific intensity, preventing it from losing its pungency over time.

The isothiocyanates that cause the spiciness are also responsible for some of horseradish's potential health benefits, including antimicrobial and antioxidant effects. However, excessive consumption can cause digestive irritation.

Yes, cooking horseradish significantly diminishes its heat. The volatile isothiocyanates are easily destroyed by heat, which is why a dish with cooked horseradish is much milder than one with fresh or prepared horseradish.

True wasabi is from a different plant but belongs to the same family and contains similar chemicals. However, most 'wasabi' paste sold commercially is just horseradish that has been dyed green, since true wasabi is very expensive and rare.

Glucosinolates are sulfur-containing compounds found in cruciferous vegetables like horseradish. They are the precursor molecules that release pungent isothiocyanates when the plant tissue is damaged.