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The ability of a protease added during mashing in a pilot-scale brew to release protein-derived thiols as antioxidants and thereby improve flavor stability during storage was investigated. The protease treatment resulted in increased protein-derived thiol concentrations in fresh beer produced at a pilot scale compared with a control beer without protease treatment, and electron spin resonance lag phase analysis also demonstrated improved oxidative stability of the protease-treated beer. However, the protease treatment also resulted in high sulfite levels and, therefore, it was not possible to conclude that the improvement in oxidative stability was solely a direct effect of increased levels of protein-derived thiol concentrations. The development of papery character and volatile linear aldehydes was inhibited when the protease-treated beer was stored at 35°C but the protease treatment also resulted in increased concentrations of free amino acids in beer, resulting in a more fruity aged or vinous character of the beer during storage due to increased formation of Maillard reaction products. Thiols were found to be irreversibly oxidized during storage, which indicates that thiols cannot be regenerated during storage; and, if thiols are to act as antioxidants in beer, increased concentrations must be present in the fresh beer. Keywords: Antioxidants, Flavor stability, Mashing, Proteases, Protein thiols, Storage
