Semiquantitative analysis of 3-butenyl isothiocyanate to monitor an off-flavor in mustard seeds and glycosinolates screening for origin identification.

The present paper describes the development of an analytical method for the semiquantitative analysis of 3-butenyl isothiocyanate in mustard seeds, this compound being linked to an undesirable (at least for the European palate) off-flavor. 3-Butenyl isothiocyanate is one of the enzymatic degradation products of gluconapin, a member of the glucosinolate family of compounds. A headspace-gas chromatography-mass spectrometry (HS-GC-MS) method has been developed for the rapid analysis of 3-butenyl isothiocyanate in mustard seeds. The cross-check of this HS-GC-MS method has been made on the basis of the analysis of the native gluconapin using liquid chromatography coupled to time-of-flight mass spectrometry (LC-TOF-MS). Both techniques gave comparable results. The HS-GC-MS method was kept as the method of choice as it is rapid and solvent-free. Because yellow mustard seeds do not normally contain gluconapin, its presence in such seeds above the limit of detection was already considered as a criterion for potentially problematic mustard batches. However, "organoleptically" acceptable brown mustard seeds already contained measurable amounts of gluconapin and had to be differentiated from mustard seeds containing nonacceptable levels of gluconapin, as it is typically the case for brown mustard originating from the Indian subcontinent. Thus, a 3-butenyl isothiocyanate content "cut point" has been established to discriminate between batches. This limit could then be applied for the acceptance or rejection of mustard seed batches. In addition, LC-TOF-MS screening of mustard seeds from different geographic origins showed the heterogeneity of the glucosinolate profile and the difficulty to find good origin markers.