Mustard is a condiment added to a variety of foodstuffs and a frequent cause of food allergy. A new strategy for the detection of mustard allergen in food products is presented. The methodology is based on liquid chromatography analysis coupled to mass spectrometry. Mustard allergen Sin a 1 was purified from yellow mustard seeds. Sin a 1 was detected with a total of five peptides showing a linear response (lowest LOD was 5ng). Sin a 1 was detected in mustard sauces and salty biscuit (19±3mg/kg) where mustard content is not specified. Sin a 1, used as an internal standard, allowed quantification of this mustard allergen in foods. A novel LC/MS/MS SRM-based method has been developed to detect and quantify the presence of mustard. This method could help to detect mustard allergen Sin a 1 in processed foods and protect mustard-allergic consumers.Depto. de Bioquímica y Biología MolecularFac. de Ciencias QuímicasTRUEpu