芥菜
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.