title: Reaction Mechanisms of Metals with Hydrogen Sulfide and Thiols in Model Wine. Part 1: Copper-Catalyzed Oxidation.
abstract: Sulfidic off-odors as a result of hydrogen sulfide (H2S) and low-molecular-weight thiols are commonly encountered in wine production. These odors are usually removed by the process of Cu(II) fining, a process that remains poorly understood. The present study aims to elucidate the underlying mechanisms by which Cu(II) interacts with H2S and thiol compounds (RSH) under wine-like conditions. Copper complex formation was monitored along with H2S, thiol, oxygen, and acetaldehyde concentrations after the addition of Cu(II) (50 or 100 μM) to air-saturated model wine solutions containing H2S, cysteine, 6-sulfanylhexan-1-ol, or 3-sulfanylhexan-1-ol (300 μM each). The presence of H2S and thiols in excess to Cu(II) led to the rapid formation of ∼1.4:1 H2S/Cu and ∼2:1 thiol/Cu complexes, resulting in the oxidation of H2S and thiols and reduction of Cu(II) to Cu(I), which reacted with oxygen. H2S was observed to initially oxidize rather than form insoluble copper sulfide. The proposed reaction mechanisms provide insight into the extent to which H2S can be selectively removed in the presence of thiols in wine.
authors.affiliation: Department of Food Science, The Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: Gal Y
authors.initials: GY
authors.lastname: Kreitman
authors.affiliation: 44 Sandwich Road, Ash, Canterbury, Kent CT3 2AF, United Kingdom.
authors.forename: John C
authors.initials: JC
authors.lastname: Danilewicz
authors.affiliation: School of Agriculture, Food and Wine, Waite Research Institute, The University of Adelaide , PMB 1, Glen Osmond, South Australia 5064, Australia.
authors.forename: David W
authors.initials: DW
authors.lastname: Jeffery
authors.affiliation: Department of Food Science, The Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: Ryan J
authors.initials: RJ
authors.lastname: Elias
mesh_terms: D002384:Catalysis; D003300:Copper / Q000737:chemistry*; D003545:Cysteine / Q000737:chemistry; D006862:Hydrogen Sulfide / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D014920:Wine / Q000032:analysis*
chemical_list: D013438:Sulfhydryl Compounds; D003300:Copper; D003545:Cysteine; D010100:Oxygen; D006862:Hydrogen Sulfide
keywords: H2S; copper; oxidation; reaction mechanism; thiols; wine aroma