title: Beer thiol-containing compounds and redox stability: kinetic study of 1-hydroxyethyl radical scavenging ability.
abstract: The 1-hydroxyethyl radical is a central intermediate in oxidative reactions occurring in beer. The reactivity of thiol-containing compounds toward 1-hydroxyethyl radical was evaluated in beer model solutions using a competitive kinetic approach, employing the spin-trap 4-POBN as a probe and by using electron paramagnetic resonance to detect the generated 1-hydroxyethyl/4-POBN spin adduct. Thiol-containing compounds were highly reactive toward the 1-hydroxyethyl radical with apparent second-order rate constants close to the diffusion limit in water and ranging from 0.5 × 10⁹ L mol⁻¹ s⁻¹ for the His-Cys-Lys-Phe-Trp-Trp peptide to 6.1 × 10⁹ L mol⁻¹ s⁻¹ for the reduced lipid transfer protein 1 (LTP1) isolated from beer. The reactions gave rise to a moderate kinetic isotope effect (k(H)/k(D) = 2.3) suggesting that reduction of the 1-hydroxyethyl radical by thiol-containing compounds takes place by hydrogen atom abstraction from the RSH group rather than electron transfer. The content of reduced thiols in different beers was determined using a previously established method based on ThioGlo-1 as the thiol derivatization reagent and detection of the derivatized thiols by reverse-phase liquid chromatography coupled to a fluorescence detector. The total level of thiol in beer (oxidized and reduced) was determined after a reduction step employing 3,3',3″-phosphanetriyltripropanoic acid (TCEP) as the disulfide reductant. A good correlation among total protein and total thiol content in different beers was observed. The results suggest a similar ratio between reduced thiols and disulfides in all of the tested beers, which indicates a similar redox state.
authors.affiliation: Department of Food Science, University of Copenhagen , Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark.
authors.forename: Natália E C
authors.initials: NE
authors.lastname: de Almeida
authors.forename: Marianne N
authors.initials: MN
authors.lastname: Lund
authors.forename: Mogens L
authors.initials: ML
authors.lastname: Andersen
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Cardoso
mesh_terms: D001515:Beer / Q000032:analysis*; D002384:Catalysis; D004578:Electron Spin Resonance Spectroscopy; D000431:Ethanol / Q000037:antagonists & inhibitors / Q000737:chemistry; D005513:Food Inspection / Q000379:methods*; D063427:Food Quality; D061353:Food Storage; D016166:Free Radical Scavengers / Q000032:analysis* / Q000737:chemistry; D005609:Free Radicals / Q000037:antagonists & inhibitors* / Q000737:chemistry; D007700:Kinetics; D008956:Models, Chemical; D010084:Oxidation-Reduction; D011725:Pyridines / Q000737:chemistry; D013113:Spin Labels; D019097:Spin Trapping; D013438:Sulfhydryl Compounds / Q000032:analysis* / Q000737:chemistry
chemical_list: D016166:Free Radical Scavengers; D005609:Free Radicals; D011725:Pyridines; D013113:Spin Labels; D013438:Sulfhydryl Compounds; C043438:alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone; C065424:1-hydroxyethyl radical; D000431:Ethanol