Improvement for Oxidative Flavor Stability of Beer—Role of OH-Radical in Beer Oxidation

The development of a method for determining an endogenous antioxidant activity of beer provides a new technique that allows prediction of the oxidative flavor stability of beer. Free radicals in beer were detected during an oxidative forcing test using a spin trapping method with electron spin resonance spectroscopy. The detected free radicals were identified as hydroxyl radical (OH-radical) by analyzing hyperfine structures of spin adducts of α-phenyl-N-t-butylnitrone and 5,5′-dimethyl-l-pyrroline-N-oxide and by investigating the effect of various reagents on the free radical generation during the oxidative forcing test. By monitoring in detail the progress of OH-radical generation, it was found that the OH-radical was not always generated just after starting the forcing test, but was generated after a definite time period, which we called the “lag time,” of OH-radical generation. The “lag time” was considered to be related to the endogenous antioxidant activity of beer. The mechanism of OH-radical generation is also discussed.