Why is wasabi so hot?

by Wendy Sadler
Sushi with wasabi. CC-BY-SA Alpha.

Sushi with wasabi. CC-BY-SA Alpha.

A mouth-watering piece of fresh salmon sat smothered in green wasabi. You taste it and suddenly your head starts to itch and your sinuses go berserk. It’s an incredible zingy, fresh feeling but why on earth should a plant based food make your body react so strangely?

Wasabi comes from the root of a cabbage-type plant that has evolved to try and protect itself from being eaten by generating an unpleasant reaction for those trying to eat it. It is actually really rare to find genuine wasabi outside of Japan as it’s so difficult to grow and harvest.

Wasabi roots. Public domain.

Wasabi roots. Public domain.

When we’re served wasabi, most of us are instead eating a mixture of horseradish, mustard and green food colouring. The important bit of both horseradish and wasabi is a chemical called allyl isothiocyanate, and this is what makes your wasabi receptors go into overdrive!

A receptor is something that sits on a cell in your body and tells the cell to behave in certain ways in reaction to the substrate binding to the receptor, for example the wasabi chemical. The reaction to allyl isothiocyanate can make your body sting, burn, cough, choke or stimulate tears because your body is not used to this chemical. Sometimes your body can create multiple reactions if the sensors are flooded and you might generate an itch in addition to the more normal burning reaction.

The wasabi receptor responsible for your reaction is known by the catchy name of ‘TRPA1’ which is a relative of another receptor – ‘TRPV1’ – which responds to the spice in chilli peppers. Capsaicin is the chemical inside chillis that gives them spice, and the capsaicin receptor responds to hot temperatures, spice in chilli peppers and – weirdly – spider venom!

A 3D picture of TRPA1, the wasabi receptor. This sits in the cell membrane and substrates travel from the top (outside the cell) to the bottom (inside the cell). Paulsen CE, Armache JP, Gao Y, Cheng Y, and Julius D. UCSF.

A 3D picture of TRPA1, the wasabi receptor. This sits in the cell membrane and substrates travel from the top (outside the cell) to the bottom (inside the cell). Paulsen CE, Armache JP, Gao Y, Cheng Y, and Julius D. UCSF.

The capsaicin from chillis is larger than the chemical found in wasabi. Where capsaicin causes a reaction through contact with the tongue, the smaller wasabi chemical tends to vaporise and go up your nose where it meets hundreds of wasabi receptors resulting in the slightly addictive wasabi brain rush (accompanies sometimes by the weird itching sensation).

TRPA1 receptors are really important parts of how our bodies perceive pain and other irritating things. They respond to stuff like onions, mustard, tear gas, cigarette smoke and car exhausts – and of course, wasabi. Scientists from the University of California have been researching the structure of the wasabi receptor using super powerful microscopes and have developed beautiful 3D models to show how they behave. They hope that understanding the process better will lead to more effective pain relief for chronic pain sufferers.

 

Amazingly the smell of wasabi has been shown to be the most effective at waking you up quickly, which is why a Japanese company have developed it into a new type of smoke alarm for the deaf! A mist of wasabi is sprayed when fire is detected and the irritation of allyl isothiocyanate wakes up the inhabitants so they are alerted to the fire. This fire alarm even won the Annals of Improbable Research’s Ig Nobel Prize in Chemistry in 2011. Ig Nobel Prizes are a parody of the Nobel Prizes and are given to honour achievements that “first make people laugh, and then make them think”.

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Posted in Biology, Exploring Science