MadSci Network: Biochemistry
Query:

Re: Why does fresh hot mustard burn the back of your nose when you chew ?

Date: Thu Jun 17 19:57:51 2004
Posted By: Samuel Conway, Product Chemistry Supervisor
Area of science: Biochemistry
ID: 1078532123.Bc
Message:

The material in question is called ALLYL ISOTHIOCYANATE.  Roughly, it looks
like this:

CH2==CH-CH2-N==C==S

It is usually found in "hot" mustard and in horseradish.  It is an oily
compound that vaporizes rather easily (vapor pressure 5 mm Hg at 25 deg C).
 Like the "hot oils" found in peppers, which are generally capsaicins and
related compounds, allyl isothiocyanate is very irritating to mucous
membranes, and for some reason many of us like it.  The difference, though,
is in its volatility, which is to say, how fast it vaporizes on your tongue.

When you chew spicy food the oil is released.  Capsaicins are not very
volatile and thus tend to stick to your tongue.  That is why Mexican food
and other pepper-spicy foods mostly burn the tongue and throat.  Allyl
isothiocyanate evaporates more readily on your tongue and floats its way up
into your sinuses (yes, as a gas), which is why both your mouth and nose
burn when you eat something with horseradish or mustard in it.  It is also
why the burn from these foods tends to fade after a few seconds, while the
burn from Mexican food can stay with you for a good long time.

And that is why I'll take Japanese wasabi over jalapenos any day!



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