The pungency of mustard seeds is primarily due to secondary metabolites such as isothiocyanate and nitrile. The pungency is usually felt only when the seeds are crushed. This is because of
- the coat of the intact seeds blocks the pungent volatiles from being released
- the pungent chemicals are stored as inactive conjugates and compartmentalized from the enzymes that convert them into active chemicals
- the pungent chemicals are formed only after the reaction with atmospheric oxygen
- the pungent chemicals are formed only after the reaction with atmospheric carbondioxide