Peroxidatic Step in Oxidation of Beers. Lucien Chapon and Sylvette Chapon, Laboratoire de Chimie Biologique II, U.E.R. Alimentation & Nutrition, Université de Nancy I, Nancy, France. J. Am. Soc. Brew. Chem. 37:0096, 1979.

The formation of H₂O₂ in the oxidation of primary reducers by O₂ is well known. The reactions to which H₂O₂ can lead were studied on model solutions at pH 4, first under strict exclusion of O₂, then in its presence. This type of oxidation was called peroxidatic and studied by injecting progressively H₂O₂ into an aqueous solution of ascorbic acid (AH₂) as a hydrogen donor, in the presence of various catalysts and of some typical substrates of coupled oxidation (ethanol, catechin, glutathione, sulfite). The more active catalysts are iron complexes. The phenomena can be satisfactorily explained by assuming a chain mechanism initiated by hydroxyl radicals formed in a FENTON reaction between H₂O₂ and the reduced forms of the catalysts. The role of AH₂ seems to be limited to bringing the catalyst back to its reduced form. Ethanol is the main substrate of coupled oxidation. It leads to ethanal. Polyphenols are not completely protected by ethanol. They polymerize to tannoids. Sulfhydryl compounds act as radical scavengers. In beer the result of manifold reactions of activation and inhibition of peroxidatic catalysts is observed.

Keywords: Activators, Ascorbic acid, Inhibitors, Oxidation, Peroxidatic catalysts, Substrates.