Introduction Flavonol quercetin (Q) (3,5,7,3′,4′-pentahydroxyavone) (Scheme 1) due to its phenolic structure is a strong antioxidant and free radical scavenger . Oxidation of quercetin during its antioxidative functions is usually accompanied by the production of the quercetin radical anion, superoxide, and hydrogen peroxide . Quercetin undergoes autoxidation-the nonenzymatic reaction with atmospheric
oxygen. Also, it is known that one-electron oxidation of quercetin is catalyzed by dierent peroxidases like lactoperoxidase (LPO)  and horseradish peroxidase (HRP) [4-7] in the presence of H2O2.