Solution
The pungency of the condiment mustard results when ground mustard seeds are mixed with water, vinegar, or other liquid (or even when chewed). Under these conditions, a chemical reaction between the enzyme myrosinase and a glucosinolate known as sinigrin from the seeds of black mustard (Brassica nigra) or brown Indian mustard (Brassica juncea) produces allyl isothiocyanate. By distillation one can produce a very sharp-tasting essential oil, sometimes called volatile oil of mustard, containing more than 92% allyl isothiocyanate. The pungency of allyl isothiocyanate is due to the activation of the TRPA1 ion channel in sensory neurons. White mustard (Brassica hirta) does not yield allyl isothiocyanate, but a different and milder isothiocyanate.
Allyl isothiocyanate serves the plant as a defense against herbivores. Since it is harmful to the plant itself, it is stored in the harmless form of a glucosinolate, separate from the myrosinase enzyme. Once the herbivore chews the plant, the noxious allyl isothiocyanate is produced. Allyl isothiocyanate is also responsible for the pungent taste of horseradish and wasabi. It can be produced synthetically, sometimes known as synthetic mustard oil.
Because of the contained allyl isothiocyanate, this type of mustard oil is toxic and irritates the skin and mucous membranes. In very small amounts, it is often used by the food industry for flavoring. In northern Italy, for instance, it is used in the fruit condiment called mostarda. It is also used to repel cats and dogs. It will also denature alcohol, making it unfit for human consumption, thus avoiding the taxes collected on alcoholic beverages.
The CAS number of this type of mustard oil is 8007-40-7, and the CAS number of pure allyl isothiocyanate is 57-06-7.
Read more about this topic: Mustard Oil
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