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Inhibitory Mechanisms of Quercetin Against Hemoglobin-mediated Lipid Oxidation in Washed Muscle Model

Lipid oxidation in fresh and further processed meat facilitates quality deterioration during storage, including loss of color, flavor, and in some cases nutritional value. Flavonoids are found ubiquitously in plants as a member of polyphenolic compounds and have received considerable attention for their antioxidant properties. Numerous studies have demonstrated that free radical scavenging and metal chelation could be the key factors responsible for the antioxidative activities of flavonols. In our previous work, a fraction isolated from cranberry juice powder was an effective inhibitor of lipid oxidation in mechanically separated turkey (MST) and washed cod muscle. The compound responsible for the inhibitory activity was then identified as quercetin. However, the mechanisms by which quercetin inhibits lipid oxidation due to heme proteins present in muscle foods has received little attention. With this background, we studied the antioxidant effect of quercetin on hemoglobin(Hb)-mediated lipid oxidation and the mechanisms involved in washed cod muscle model. Quercetin strongly inhibited Hb-mediated lipid oxidation in washed muscle. Quercetin showed effective hydroxyl radical scavenging ability similar to butylated hydroxytoluene (BHT). Quercetin reduced metHb resulting in formation of oxyHb. Bound quercetin decreased heme dissociation from metHb. Conversion to oxyHb and decreased heme dissociation represent routes to limit Hb-mediated lipid oxidation. Electrospray ionization mass spectrometry (ESI-MS) indicated one molecule of quercetin was covalently bound to Hb α-chain. Quercetin quinone docked 3.3 Å from the thiol of αCys(H15) but not near any other Cys residues of turkey Hb. At the docking site, hydrogen bonding between quercetin quinone and amino acids of α- and β-chain was demonstrated. This represents a path by which quercetin became covalently bound to α-chain. Molecular docking of heme proteins to polyphenols provides a template to better understand antioxidant interactions in muscle foods.