ELECTRON-SPIN-RESONANCE SPIN-TRAPPING IDENTIFICATION OF RADICALS FORMED DURING AEROBIC FORCED AGING OF BEER

Using 2-methyl-2-nitrosopropane, 5,5-dimethyl-1-pyrroline N-oxide (DMP O), phenyl-N-tert-butylnitrone, and 4-pyridyl-1-oxide-N-tert-butylnitr one as spin traps, spin adducts of free radicals formed in beer under aerobic conditions have been characterized by ESR spectroscopy. The 1- hydroxyethyl radical is found to be the quantitatively most important radical, while the hydroxyl radical is trapped only by DMPO and only a t high concentrations (0.5 M). Fenton-like oxidation processes in beer thus involve reaction of the 1-hydroxyethyl radical in an important r eaction with oxygen, converting it to hydroperoxyl radicals.