Photooxidative degradation of beer bittering principles: a key step on the route to lightstruck flavor formation in beer.
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.
Huvaere
Kevin
K
Faculty of Pharmaceutical Sciences, Laboratory of Pharmacognosy and Phytochemistry, Harelbekestraat 72, Ghent University, B-9000 Ghent, Belgium.
Andersen
Mogens L
ML
Skibsted
Leif H
LH
Heyerick
Arne
A
De Keukeleire
Denis
D
D001515:Beer / Q000032:analysis*; D003517:Cyclopentanes / Q000032:analysis / Q000737:chemistry; D008027:Light; D010084:Oxidation-Reduction; D010777:Photochemistry; D013649:Taste
D003517:Cyclopentanes; C081209:isohumulone