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Hot and Healthy Wasabi
by author Gina H. Mohammed, PhD

Wasabi, also known as Japanese horseradish, is a pungently flavored condiment used in many Japanese dishes–especially raw fish (sushi and sashimi) and noodle (soba) dishes. Served up as a little green mound of condiment, wasabi is mixed into soy sauce as a dip for the fish, or is mixed directly into a bowl of noodles–with the amount of wasabi determined only by the diner's "heat" tolerance.

This delectable spice is prepared from the wasabi plant, Wasabia japonica (also known as Eutrema wasabi), a Japanese evergreen. It grows naturally in cool mountain river valleys, along stream beds and on river sand bars in Japan. The plant grows about 60 centimetres tall and possesses a thick underground stem, or rhizome, which is the part most frequently used in foods. The rhizome may be grated or ground for fresh use, or it (and other parts) may be prepared as a dehydrated powder for storage. It's not surprising that wasabi is likened to horseradish (Armoracia rusticana), since they are distant relatives. Both belong to the Cruciferae family, along with cabbage, broccoli, brussel sprouts, cress and mustard.

The medicinal value of wasabi has long been acclaimed. Japanese medicinal literature first documented it during the 10th century; it has since been the subject of many modern scientific studies. Chemicals found in wasabi have been reported to possess antibacterial and antifungal properties, to retard platelet aggregation, and to protect against cancer. Researchers at New Zealand's Lincoln University have recently reviewed an impressive body of evidence that supports wasabi's potential as a medicinal plant and as a possible source of pharmaceuticals.

Phytochemical Power

The phytochemicals in wasabi that are particularly interesting are called isolh-iocyanates. These are volatile sulphur-containing compounds that give wasabi its distinctive flavor, as well as many of its medicinal properties.

Recent research shows that certain isothiocyanates from wasabi have potent antibacterial action against the microbes Stapkylococcus aureas and Escherichia culi. Another study found that the vapor from allyl isothiocyanate–the major type in wasabi–can combat 25 strains of yeast, bacteria and mold to varying degrees. The biocidal properties of wasabi may act as an antidote to food poisoning, a possible factor in its traditional use in raw fish dishes in Japan.

Anticoagulative effects of wasabi have also been observed. For example, essential oils prepared from the leaves, petioles, rhizomes and roots of wasabi have been shown to inhibit platelet aggregation. Oils from the root were most effective, followed by the petiole, rhizome and leaf. Although the potency of wasabi extracts was only one-tenth that of aspirin, the isothiocyanates from wasabi had an immediate effect, whereas aspirin needed 30 minutes to work.

This finding raises the prospect that wasabi isothiocyanates may be used to alleviate inflammatory conditions such as asthma or even anaphylaxis. The ability to inhibit platelet aggregation can also be important in treating heart attacks. Dr James Duke, in his book The Green Pharmacy, suggests that a spoonful of wasabi each day may relieve allergies, especially hay fever. Wasabi, like horseradish, is known to be effective in clearing the sinuses.

Wasabi isothiocyanates may be useful in preventing and fighting cancer. Animal studies have shown that wasabi powder may protect against gastrointestinal tumor formation following exposure of animals to chemical carcinogens. Other studies have found that some isothiocyanates can protect against breast, stomach and colon cancers. Scientists aren't certain how, but it may be through activation of the powerful antioxidant glutathione, which may help to detoxify carcinogens.

The value of wasabi in cancer prevention and treatment needs further study, since very high doses of both wasabi (or isolhiocyanate) and carcinogens have been used so far. and these may not accurately portray what would happen at normal levels. Also, there is some evidence to suggest that high doses of certain isothiocyanates, which can prevent tumor initiation, may actually act as tumor promoters if the tumours have already been initated. Wasabi would have to comprise about 20 percent of the diet to provide such high doses.

Could you Grow Your Own?

Bona fide wasabi is not the easiest thing to obtain, as this plant is a rare and difficult plant to grow. Aside from its native Japan, it has been coaxed into cultivation in Taiwan. New Zealand, and parts of the United States (like Oregon), where conditions satisfy wasabi's demand for a cool, wet climate.

The best way to grow wasabi is by water cultivation, typically in gravelly beds along streams. The beds are irrigated by the flowing water, which keeps the roots and rhizome flooded bu! well-aerated. Soil cultivation doesn't produce a particularly good quality rhizome, and hydroponics has not been successful. Wasabi plants take two to three years to reach maturity, or longer if growing conditions are not optimal.

Are you Sure You're Getting the Real Thing?

What about that little dollop of green stuff on your plate of sushi–are you sure it's really wasabi? it may not be. Restaurants commonly use a substitute mixture of regular horseradish powder, mustard powder, cornstarch and artificial color. It's cheaper than wasabi, but tastes nothing like the real thing.

If you make your own Japanese dishes and use wasabi paste from a lube, check the package to see if there's a grade shown. Prepared wasabi from Japan comes in three grades–GTade 1 means it's 100 percent wasabi. Grade 2 has about 25 percent wasabi. and Grade 3 has no real wasabi at all. Grade 1 is hard to find in North America.

Gina Mohammed is a plant physiologist in Sault Ste Marie, ON.

Source: alive #208, February 2000