Wasabi ワサビ is King of Herbs and part of Japanese culture. This herb known as Wasabia japonica is associated with the Brassicaceae family of crops, including brussels sprouts, cauliflower, cabbage, broccoli watercress, horseradish, bok choy and black mustard.

Wasabi was first mentioned in the famous Japanese herb dictionary called the Honzowamyo – Names of Living Things. This collection of 18 chapters contains descriptions of 1,025 types of plants including animals and minerals.  This 2 volume dictionary was compiled in 918 by the court physician Sukehito Fukane, who served Emperor Daigo during 901 to 923 in the Heian period (794-1185).

The entry described wasabi as a medicinal plant and was known as wild ginger. Since then, Wasabi cultivation in Japan has continued over the last millennium.

During the Keicho period (1596-1615), wasabi cultivation was primarily focused along the Abe River in the Shizuoka prefecture of central Japan. In this period wasabi was consumed by the Japanese elite and supplies were controlled by Shogun Tokugawa Ieyasu (1543-1616) the governor of the prefecture.

Today, the cultivation of wasabi in Japan extends from Sakhalin Island which is located in the North Pacific Ocean to the northern region of Hokkaido reaching out to Kyushu. The highest producing region of wasabi rhizomes is found in the Shimane prefecture. Outside Japan, they are grown in other countries including Taiwan, Korea, New Zealand, Iceland, Thailand, Columbia, Israel, Brazil, Canada, USA and the United Kingdom.

Wasabi was first mentioned in the famous Japanese herb dictionary called the Honzowamyo – Names of Living Things. This collection of 18 chapters contains descriptions of 1,025 types of plants including animals and minerals.  This 2 volume dictionary was compiled in 918 by the court physician Sukehito Fukane, who served Emperor Daigo during 901 to 923 in the Heian period (794-1185).

The entry described wasabi as a medicinal plant and was known as wild ginger. Since then, Wasabi cultivation in Japan has continued over the last millennium.

During the Keicho period (1596-1615), wasabi cultivation was primarily focused along the Abe River in the Shizuoka prefecture of central Japan. In this period wasabi was consumed by the Japanese elite and supplies were controlled by Shogun Tokugawa Ieyasu (1543-1616) the governor of the prefecture.

Today, the cultivation of wasabi in Japan extends from Sakhalin Island which is located in the North Pacific Ocean to the northern region of Hokkaido reaching out to Kyushu. The highest producing region of wasabi rhizomes is found in the Shimane prefecture. Outside Japan, they are grown in other countries including Taiwan, Korea, New Zealand, Iceland, Thailand, Columbia, Israel, Brazil, Canada, USA and the United Kingdom.

 

Wasabia Japonica Varieties

The wasabi rhizome, which is a swollen stem takes two years to mature.  During the growing cycle, several petioles produce deep green heart-shaped leaves which contain some of the zingy taste associated with wasabi.

Today, Japan cultivates several varieties of rhizomes and they include Mazuma, Daruma, Midori, Sanpoo, Izawa, Medeka Takai and Shimane.  This wasabi produce is mostly supplied from the Shizuoka and Shimane prefectures including Nagano. In addition, the Hangen wasabi is grown in the Kanagawa prefecture.

Medicinal properties of wasabi

Wasabi contains volatile naturally occurring organosulphur compounds called isothiocyanates (ITCs): these provides the zingy taste.  During the grating of a wasabi rhizome, the volatile ITCs are released from the plant tissues facilitated by the enzyme myrosinase.  The ‘free’ ITCs are not present in the wasabi plant but are released from Sinigrin (glucosinolates) which are abundant within the cell vacuoles of Brassicaceae plants.  These ITCs are the result of mechanical damage to the plant tissue and the myrosinase degrades sinigrin to generate allyl isothiocyanate (AITC).  This volatile compound is responsible for the zingy taste of wasabi.  Interestingly, myrosinase is a member of the glycoside hydrolase family and has the ability to cleave the thio-linked glucose in the glucosinolates to produce glucose and an aglucone.

The aglucone is unstable and undergoes a Lossen rearrangement to produce sulphate and several other products. These ITCs are produced from Sinigrin under neutral and alkaline conditions. 

The allyl isothiocyanate (AITC) is mostly concentrated in the rhizome part of the plant.  However, the compounds  6-methylthiohexyl-ITC and 7-methylthioheptyl-ITC contribute to the fresh flavour of wasabi. Therefore, a combination of ITCs is present in various amounts and this contributes to the wasabi kick.

Wasabi Kick

A large concentration of wasabi receptors are located in the nasal passages and are known as TRPA1 (Transient receptor potential cation channel subfamily A member 1) receptors.  These TRPA1 receptors are related to the TRV1 (transient receptor potential cation channel subfamily V member 1) receptors and often referred to as the capsaicin receptor.

The primary function of the capsaicin TRV1 receptors is to react with the exothermic heat generated from hot chilli peppers. However, wasabia TRPA1 receptors have a broader scope than capsaicin receptors in the zingy taste of foods stuffs.

This effect is also experienced in the grating of the wasabi rhizome which releases the volatile allyl isocyanates and travels up the nose causing an activation at the TRPA1 receptor to initiate the Wasabi Kick. 

Consequently, wasabia japonica and horseradish have quite different taste profiles: since whilst consuming the compound in horseradish 2-phenylethyl isothiocyanate is released. This compound is not present in wasabia japonica.

The wasabi kick is the result of myrosinase acting on sinigrin to give aglycone. This aglycone undergoes a Lossen rearrangement to allow an amount of volatile allyl isothiocyanate (AITC) in the mouth. After 20 minutes the wasabi kick starts to diminish at room temperature due to the deactivation of myrosinase enzymes in wasabi. To partly revive the kick, the myrosinase enzymes can be reactivated in wasabi using lemon juice.

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