title: Nonvolatile S-alk(en)ylthio-L-cysteine derivatives in fresh onion (Allium cepa L. cultivar).
abstract: The L-cysteine derivatives (R)-2-amino-3-(methyldisulfanyl)propanoic acid (S-methylthio-L-cysteine), (R)-2-amino-3-(propyldisulfanyl)propanoic acid (S-propylthio-L-cysteine), (R)-2-amino-3-(1-propenyldisulfanyl)propanoic acid (S-(1-propenylthio)-L-cysteine), and (R)-2-amino-3-(2-propenyldisulfanyl)propanoic acid (S-allylthio-L-cysteine) were prepared from 3-[(methoxycarbonyl)dithio]-L-alanine, obtained from the reaction of L-cysteine with methoxycarbonylsulfenyl chloride. The occurrence of these S-(+)-alk(en)ylthio-L-cysteine derivatives in onion (Allium cepa L.) was proven by using UPLC-MS-ESI(+) in SRM mode. Their concentrations in fresh onion were estimated to be 0.19 mg/kg S-methylthio-L-cysteine, 0.01 mg/kg S-propylthio-L-cysteine, and 0.56 mg/kg (S-(1-propenyllthio)-L-cysteine, concentrations that are about 3000 times lower than that of isoalliin (S-(1-propenyl-S-oxo-L-cysteine). These compounds were treated with Fusobacterium nucleatum, a microorganism responsible for the formation of mouth malodor. These L-cysteine disulfides were demonstrated to predominantly produce tri- and tetrasulfides. Isoalliin is almost entirely consumed by the plant enzyme alliin lyase (EC 4.4.1.4 S-alk(en)yl-S-oxo-L-cysteine lyase) in a few seconds, but it is not transformed by F. nucleatum. This example of flavor modulation shows that the plant produces different precursors, leading to the formation of the same types of volatile sulfur compounds. Whereas the plant enzyme efficiently transforms S-alk(en)yl-S-oxo-L-cysteine, mouth bacteria are responsible for the transformation of S-alk(en)ylthio-L-cysteine.
authors.affiliation: Corporate R&D Division, Firmenich SA, P.O. Box 239, CH-1211 Geneva 8, Switzerland. Christian.starkenmann@firmenich.com
authors.forename: Christian
authors.initials: C
authors.lastname: Starkenmann
authors.forename: Yvan
authors.initials: Y
authors.lastname: Niclass
authors.forename: Myriam
authors.initials: M
authors.lastname: Troccaz
mesh_terms: D013437:Carbon-Sulfur Lyases / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D003545:Cysteine / Q000031:analogs & derivatives* / Q000032:analysis / Q000378:metabolism; D004220:Disulfides / Q000378:metabolism; D016967:Fusobacterium nucleatum / Q000378:metabolism; D009055:Mouth / Q000382:microbiology; D009812:Odorants; D019697:Onions / Q000737:chemistry*; D018517:Plant Roots / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization; D013457:Sulfur Compounds / Q000378:metabolism; D055549:Volatile Organic Compounds / Q000378:metabolism
chemical_list: D004220:Disulfides; D013457:Sulfur Compounds; D055549:Volatile Organic Compounds; C006453:alliin; D013437:Carbon-Sulfur Lyases; C019243:alliin lyase; D003545:Cysteine