Dried mustard seeds or powders are not very pungent because the drying process halts enzyme activity. However, once hydrated with water, the enzymes are able to produce allyl isothiocyanate, leading to the pungency that you associate with mustard. It can, however, take several minutes to hours for the enzymes to make enough of the isothiocyanate for detection. For example, if mustard is mixed with an acidic solution such as a citric acid or vinegar, the enzymes will function, but at a much slower rate, leading to a less pungent dish. In addition, isothiocyanates are fairly unstable and break down quickly. Although the addition of acid reduces the rate at which the enzymes produce isothiocyanate, the lower pH substantially prevents the allyl isothiocyanate from breaking down in your recipe.
Extended exposure of the isothiocyanates to heat also increases breakdown and formation of a non-pungent product. What is to be learned from this discussion? The cook who thrives on the preparation and consumption of pungent dishes should wait until the end of the cooking period to add the mustard or horseradish.
The second group of chemical structures that define the pungent family of flavors is the alkaloids. Alkaloids are a large diverse family of carbon‐based compounds that contain a nitrogen base. In plants, alkaloids are important in the development of the plant, fruit, and seed.