| Abstract
| - Isohumulones, dihydroisohumulones, tetrahydroisohumulones, and humulinones, important hop-derived bittering compounds in beer, were shown to give rise to reactive triacylmethyl radicals oninteraction with triplet-excited riboflavin after spin trapping by 5,5-dimethyl-1-pyrroline N-oxide or2-methyl-2-nitrosopropane, followed by electron paramagentic resonance spectroscopy combinedwith spectral simulation. Electron abstraction from the ionized β-tricarbonyl chromophore, which iscommon 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, thelightstruck constituent in beer. Interaction of reduced derivatives of isohumulones with triplet-excitedriboflavin furnished radical precursors of volatile aldehydes, which may lead to the development ofunpleasant stale or cardboard flavors. Keywords: Isohumulones; lightstruck flavor; EPR spectroscopy; photooxidation; beer
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