Volatile compounds thermally generated from S-propylcysteine and S-propylcysteine sulfoxide aroma precursors of Allium vegetables

Two nonvolatile flavor precursors occurring in Allium vegetables, S-propyl- L-cysteine and its sulfoxide, were heated in closed model systems at differ ent temperatures (from 80 to 200 degrees C) in the presence of variable amo unts of water (0-98%) for 1-60 min. It seems to be indisputable that therma lly generated breakdown products of both S-propyl-L-cysteine and particular ly S-propyl-L-cysteine sulfoxide can significantly participate in the aroma formation of culinary processed Allium vegetables. Dipropyl disulfide, dip ropyl trisulfide, propylthiol, and dipropyl thiosulfonate were identified a s the predominant volatile compounds generated by thermal degradation of S- propylcysteine sulfoxide. Dipropyl disulfide and 2-(propylthio)ethylamine w ere the major breakdown products formed from S-propylcysteine. Substantial amounts of various alkyl- and alkylthio-substituted pyridines were also gen erated from both S-propylcysteine and its sulfoxide.