Allyl isothiocyanate is the volatile oil in mustard and is formed from the hydrolysis of sinigrin by the enzyme myrosin. Allyl isothiocyanate is extremely toxic and is a very powerful irritant that will blister skin. It has strong antimicrobial activity and, when diluted, is used as a counterirritant. Allyl isothiocyanate is used as a flavoring ingredient in many types of foods (e.g., frozen dairy products, meats, baked foods) but because of its toxicity, it is only used in very small amounts.
Leung, Albert Y. 1980. Encyclopedia of Common Natural Ingredient used in Food, Drugs and Cosmetics. John Wiley and Sons, N Y. 409 pp.