title: Photooxidative degradation of beer bittering principles: a key step on the route to lightstruck flavor formation in beer.
abstract: Isohumulones, dihydroisohumulones, tetrahydroisohumulones, and humulinones, important hop-derived bittering compounds in beer, were shown to give rise to reactive triacylmethyl radicals on interaction with triplet-excited riboflavin after spin trapping by 5,5-dimethyl-1-pyrroline N-oxide or 2-methyl-2-nitrosopropane, followed by electron paramagentic resonance spectroscopy combined with spectral simulation. Electron abstraction from the ionized beta-tricarbonyl chromophore, which is common to all five-membered ring hop derivatives, is the initial event on photoinduced degradation. Radicaloid decomposition of isohumulones leads to precursors for 3-methylbut-2-ene-1-thiol, the lightstruck constituent in beer. Interaction of reduced derivatives of isohumulones with triplet-excited riboflavin furnished radical precursors of volatile aldehydes, which may lead to the development of unpleasant stale or cardboard flavors.
authors.affiliation: Faculty of Pharmaceutical Sciences, Laboratory of Pharmacognosy and Phytochemistry, Harelbekestraat 72, Ghent University, B-9000 Ghent, Belgium.
authors.forename: Kevin
authors.initials: K
authors.lastname: Huvaere
authors.forename: Mogens L
authors.initials: ML
authors.lastname: Andersen
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 / Q000032:analysis*; D003517:Cyclopentanes / Q000032:analysis / Q000737:chemistry; D008027:Light; D010084:Oxidation-Reduction; D010777:Photochemistry; D013649:Taste
chemical_list: D003517:Cyclopentanes; C081209:isohumulone