title: Effect of l-Cysteine and Transition Metal Ions on Dimethyl Sulfide Oxidation.
abstract: During malt kilning, significant amounts of dimethyl sulfide (DMS) oxidize leading to the formation of dimethyl sulfoxide (DMSO), a precursor of DMS during fermentation. Yet, knowledge regarding reaction mechanisms of DMSO formation during malt production is limited. The role of thiols in sulfide oxidation is unclear as they possess sulfoxide reducing ability as well as pro- and antioxidative properties. This study investigated the effects of the thiol l-cysteine (Cys), molecular oxygen, transition metal ions, and EDTA on DMS oxidation in aqueous model solutions. Highest oxidative DMS consumption was observed when Cys was combined with iron(II) (∼12%) and copper(II) (∼40%). Response surface modeling (RSM) revealed that Cys together with copper(II) had a strictly prooxidative effect and no antioxidative behavior was found. Hydrogen peroxide, as generated via autoxidation of Cys-Cu(I)-Cys complexes, was supposed to be the primary DMS oxidant in this work. Based on redox kinetics, potential reaction mechanisms, and their impact on oxidative processes in thermal food processing, such as malt and beer production, are discussed.
authors.affiliation: Department of Food Technology and Food Chemistry, Chair of Brewing Science, Technische Universität Berlin , Seestrasse 13, 13353 Berlin, Germany.
authors.forename: Matthias
authors.identifier: http://orcid.org/0000-0001-7336-4153
authors.initials: M
authors.lastname: Baldus
authors.affiliation: Department of Food Technology and Food Chemistry, Chair of Brewing Science, Technische Universität Berlin , Seestrasse 13, 13353 Berlin, Germany.
authors.forename: Rüdiger
authors.initials: R
authors.lastname: Klie
authors.affiliation: Department of Food Technology and Food Chemistry, Chair of Brewing Science, Technische Universität Berlin , Seestrasse 13, 13353 Berlin, Germany.
authors.forename: Xi
authors.initials: X
authors.lastname: De
authors.affiliation: Department of Food Technology and Food Chemistry, Chair of Brewing Science, Technische Universität Berlin , Seestrasse 13, 13353 Berlin, Germany.
authors.forename: Frank-Jürgen
authors.initials: FJ
authors.lastname: Methner
mesh_terms: D002384:Catalysis; D003300:Copper / Q000737:chemistry; D003545:Cysteine / Q000737:chemistry*; D006861:Hydrogen Peroxide / Q000737:chemistry; D007501:Iron / Q000737:chemistry; D010084:Oxidation-Reduction; D013438:Sulfhydryl Compounds / Q000737:chemistry; D013440:Sulfides / Q000737:chemistry*
chemical_list: D013438:Sulfhydryl Compounds; D013440:Sulfides; D003300:Copper; D006861:Hydrogen Peroxide; D007501:Iron; D003545:Cysteine; C004784:dimethyl sulfide
keywords: cysteine; dimethyl sulfide; malting and brewing; metal ions; oxidation