Mal d 1, the major apple allergen, is heat labile and easily oxidized. Oxidative reactions catalyzed by polyphenol oxidase (PPO) and/or peroxidase (POD), present in apple, may be involved in decreasing its allergenicity. PPO and POD convert phenolic compounds into o-quinones.In this study the effect of PPO and POD, the polyphenol catechin and the antioxidant DIECA on IgE-binding by Mal d 1 was analyzed. Golden Delicious peel was selected for its high PPO and POD contents. IgE-binding was analyzed by competitive ELISA.IgE-binding by Mal d 1 decreased by adding oxidative enzymes, this decrease was most pronounced when PPO was used. Catechin induced a reduction in IgE binding when POD was used. The combination of catechin and PPO causes the strongest decrease of the allergenicity of Mal d 1. DIECA protected the IgE-binding by the allergen, protection being less strong in the presence of exogenous PPO and POD. The decrease of immunoreactivity is likely to be due to o-quinones, as active species or other intermediates modifying the tertiary structure of the allergens and cross-linking of the proteins, thus reducing their allergenicity.