title: Radicaloid-type oxidative decomposition of beer bittering agents revealed.
abstract: trans-Isohumulones, dihydroisohumulones, tetrahydroisohumulones, and humulinones, which are important hop-derived flavor components of beer, were found, by using electrolysis of organic solutions, to be stable against oxidation, like weak acids; however, they are readily oxidized in their anionic forms as present in beer. Oxygen- and carbon-centered radicals were formed by oxidation and identified by using spin trapping under aerobic and anaerobic conditions, followed by EPR (electron paramagnetic resonance) spectroscopy. Generated radicals were reactive, most likely degrading into products lacking the tricarbonyl chromophore; this is typical of five-membered-ring hop derivatives. Thus, flavor-active beer constituents may degrade oxidatively in the absence of oxygen, thereby leading to reaction products that escape UV detection.
authors.affiliation: Faculty of Pharmaceutical Sciences, Laboratory of Pharmacognosy and Phytochemistry, Harelbekestraat 72, Ghent University, 9000 Ghent, Belgium.
authors.forename: Kevin
authors.initials: K
authors.lastname: Huvaere
authors.forename: Mogens L
authors.initials: ML
authors.lastname: Andersen
authors.forename: Karsten
authors.initials: K
authors.lastname: Olsen
authors.forename: Leif H
authors.initials: LH
authors.lastname: Skibsted
authors.forename: Arne
authors.initials: A
authors.lastname: Heyerick
authors.forename: Denis
authors.initials: D
authors.lastname: De Keukeleire
mesh_terms: D001515:Beer; D003517:Cyclopentanes / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D005421:Flavoring Agents / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry; D027582:Humulus / Q000737:chemistry; D010084:Oxidation-Reduction; D013649:Taste
chemical_list: D003517:Cyclopentanes; D005421:Flavoring Agents; D005609:Free Radicals; C081209:isohumulone