The tube of wasabi you pick up at the supermarket and the fresh wasabi a restaurant grates in front of you are both called "wasabi." Yet they may come from entirely different plants, and from different parts of those plants.
Nowhere does this difference matter more than for hexaraphane (6-MSITC), a compound derived from Japanese wasabi. This publication has covered research on the compound several times before. Here, however, the question is not what it does, but something more basic: which wasabi actually contains hexaraphane? In particular, how much can be expected from the shelf-stable tube wasabi commonly found in supermarkets?
To put the conclusion first: hexaraphane is found in Japanese wasabi, and within the plant it is most abundant in the rhizome. Horseradish has been reported to contain low levels, and in processed wasabi products the content varies widely depending on factors such as the proportion of Japanese wasabi rhizome used. Ordinary shelf-stable tube wasabi, some of which is made mainly from horseradish, is therefore difficult to regard as a source of hexaraphane.
What this article covers
- How Japanese wasabi and horseradish differ
- Which part of Japanese wasabi contains the most hexaraphane
- Why shelf-stable tube wasabi is an unlikely source of hexaraphane
- What to look for on the ingredient label when choosing wasabi
How do Japanese wasabi and horseradish differ?
Both Japanese wasabi and horseradish belong to the Brassicaceae family, and grating either one releases a sharp, pungent bite. In that sense they resemble each other, but botanically they are different species.
Japanese wasabi is native to Japan
Japanese wasabi is Eutrema japonicum, a perennial native to Japan that many people picture growing in clear running water or in wasabi fields. The part most familiar as food is the "rhizome," which thickens near the soil surface.
Finely grating this rhizome brings out not only pungency but also a bright aroma and a faint sweetness, giving a clean, refined flavor.
- Rhizome
- a stem that grows horizontally underground or near the soil surface. It looks like a root, but botanically it is a stem.
Horseradish is also known as Western wasabi
Horseradish, in turn, is Armoracia rusticana. Although it belongs to the same Brassicaceae family, the part used as food is mainly the thick root.
Horseradish also has a distinct pungency, and its price is relatively stable. Because it is easy to process, it is often used as a raw material for tube wasabi and powdered wasabi. The two plants share some pungent compounds, but the types and composition of the isothiocyanates that create their aromas are not the same. 1
- Isothiocyanates
- a group of compounds found in Brassicaceae plants such as wasabi and broccoli. They are generated when the plant tissue is grated or chopped, and they give rise to pungency and aroma.
Japanese wasabi and horseradish at a glance
In everyday conversation, calling both of them "wasabi" is perfectly sufficient. When the subject turns to hexaraphane, however, it makes sense to treat them separately.
Hexaraphane is most abundant in the rhizome of Japanese wasabi
Hexaraphane, which appears regularly in this publication, is formally named 6-methylsulfinylhexyl isothiocyanate (6-MSITC).
The functions under investigation are covered in detail in "Why hexaraphane (6-MSITC) from Japanese wasabi is attracting attention." Rather than repeat that discussion, this article looks only at where the compound is found and in what amounts.
The rhizome contained the most in all five cultivars
A study published in 2004 measured hexaraphane content in the rhizome, root, stem, and leaf of five cultivars of Japanese wasabi. The pattern was consistent: in every cultivar the rhizome contained the most, followed by the root, the stem, and the leaf. 2
Even among Japanese wasabi, cultivar differences were observed. Comparing the cultivar with the highest rhizome hexaraphane content with the one with the lowest, the difference was approximately 1.6-fold. 2 In other words, it cannot be assumed that all Japanese wasabi is equivalent.
Hexaraphane content in horseradish was low
The same study also measured hexaraphane in horseradish, and the reported content was low. 2
Horseradish certainly has a firm pungency. However, the main contributor to that sharp bite is a different isothiocyanate, allyl isothiocyanate (AITC), which is common to both Japanese wasabi and horseradish. 1 Hexaraphane is less a driver of pungency than a compound that is abundant in the rhizome of Japanese wasabi.
Pungency and hexaraphane content are not the same thing, so a strong sensory kick does not necessarily indicate a high hexaraphane content.
Why ordinary shelf-stable tube wasabi is difficult to regard as a source
With these differences in mind, it becomes clearer why the shelf-stable tube wasabi lined up on supermarket shelves is difficult to regard as a source of hexaraphane. There are three main reasons.
Reason 1: Some products are made from horseradish
Tube wasabi is a single name for many different formulations. Some products use only Japanese wasabi, others use horseradish, and others blend the two.
Since the hexaraphane content of horseradish has been reported to be low, products in which horseradish predominates are unlikely to provide intake comparable to Japanese wasabi rhizome. 2
Reason 2: Even with Japanese wasabi, the plant part and proportion differ
The same study also measured hexaraphane content in 25 commercially available processed wasabi products. Here the content varied widely by manufacturer and product type. 2
The research team attributed that variation to the proportion of Japanese wasabi raw material used, particularly the proportion of rhizome, which is rich in hexaraphane. 2 That analysis dates from 2004, however, and does not directly indicate the formulation or content of individual products sold today, so current products need to be checked against the latest ingredient labels and product information.
In short, a label stating "Japanese wasabi" is not enough on its own to infer how much hexaraphane is present. It depends on how much Japanese wasabi is used, and which part of the plant.
Reason 3: "Tube wasabi" is not a single category
The shape of the container says nothing about what is inside. Some products can be stored at room temperature before opening, while others are refrigerated or frozen types that use a large proportion of Japanese wasabi.
That said, it would be equally inaccurate to conclude that "anything in a tube contains no hexaraphane." It should also be noted that the study referenced here did not examine whether room-temperature storage itself reduces hexaraphane. What the study supports is that hexaraphane content in processed wasabi products varies widely, and that the proportion of Japanese wasabi rhizome is an important factor. 2
A familiar analogy: a drink labeled "contains fruit juice" is not the same product at 10% juice as it is at 100%. Wasabi is similar. Even when the label says "wasabi," the contents differ according to the ratio of Japanese wasabi to horseradish and the plant parts used.
If hexaraphane matters to you, what should you look for on the label?
So what should you actually check when choosing wasabi? Here are a few points of reference.
Check whether it is Japanese wasabi or horseradish
Start with the ingredient label to see which of the two is used. If it lists "horseradish" or "Western wasabi," that is a different plant from Japanese wasabi. When several ingredients are listed, the order of listing is also a clue. Even so, a label alone cannot tell you the precise hexaraphane content.
Incidentally, the vivid green color of tube wasabi is not a way to tell Japanese wasabi from horseradish. Both are pale when freshly grated, and the green color of commercial products generally comes from added coloring. Checking the ingredient label is more reliable than judging by the intensity of the color.
Check the plant part and the proportion of Japanese wasabi
If the product description states something like "made with Japanese wasabi rhizome" or "100% Japanese wasabi," that offers a clue about the raw material. The difficulty is that the phrase "made with Japanese wasabi" alone reveals nothing about the proportion of rhizome. If hexaraphane is a consideration, whether the compound is standardized to a defined amount is another point to look for.
Wasabi as a food and standardized ingredients are different things
The rhizome of Japanese wasabi does contain hexaraphane, but it is intensely pungent and is not eaten in large amounts at once. Because content also varies with cultivar and plant part, the amount obtained from food inevitably varies.
In research settings, by contrast, wasabi extracts or standardized ingredients with a defined hexaraphane content are sometimes used. Enjoying wasabi as a condiment at the table and consuming a defined amount in a study are best considered separately.
For a fuller picture of hexaraphane, see "Why hexaraphane (6-MSITC) from Japanese wasabi is attracting attention," which reviews the research as a whole.
Summary
- Japanese wasabi and horseradish belong to the same Brassicaceae family but are different plants
- Within Japanese wasabi, hexaraphane (6-MSITC) is most abundant in the rhizome
- The hexaraphane content of horseradish has been reported to be low
- Hexaraphane content in processed wasabi products varies widely with factors such as the proportion of Japanese wasabi rhizome
- Ordinary shelf-stable tube wasabi is an unlikely source of hexaraphane
- This does not mean that every tube contains none; the raw material, plant part, and storage format are what matter
The tube wasabi used without a second thought and a freshly grated Japanese wasabi rhizome are not the same thing, even when the pungency feels similar. When hexaraphane is on your mind, look beyond whether the label says "wasabi" and consider which plant, which part, and how much of it is actually used.
References
- Sultana T, Savage GP, McNeil DL, Porter NG, Martin RJ, Deo B. Comparison of flavour compounds in wasabi and horseradish. Journal of Food, Agriculture and Environment. 2003;1(2):117-121. ↩
- Murata M, Uno M, Nagai Y, Nakagawa T, Okunishi I. Content of 6-methylsulfinylhexyl isothiocyanate in wasabi and processed wasabi products. Journal of the Japanese Society for Food Science and Technology (Nippon Shokuhin Kagaku Kogaku Kaishi). 2004;51(9):477-482. (In Japanese) ↩
