Distribution of S-alk(en)ylcysteine sulfoxides in some Allium species. Identification of a new flavor precursor: S-ethylcysteine sulfoxide (ethiin)

The content of S-alk(en)ylcysteine sulfoxides, important nonvolatile flavor precursors, was determined in 15 different Allium species by means of gas chromatography. The method employed is based on derivatization of S-alk(en) ylcysteine sulfoxides with ethyl chloroformate followed by their reduction with sodium iodide. The total content of S-alk(en)ylcysteine sulfoxides var ied considerably in the wide range between 0.02 and 1.3% fresh weight. Not only the total content but also relative proportions of individual derivati ves varied to a great extent. A novel S-alkylcysteine derivative, S-ethylcy steine sulfoxide (ethiin), not previously reported to occur in Allium speci es, was found in most of the samples examined in trace amounts. None of the other S-alk(en)ylcysteine sulfoxides, for example, isopropyl, (Z)-1-propen yl, butyl, or pentyl, were detected in any of the samples analyzed, limitin g possible levels of each of these components to less than or equal to 1 pp m in fresh weight.