Antioxidant Mechanism of Flavonoids. Solvent Effect on Rate Constant for Chain-Breaking Reaction of Quercetin and Epicatechin in Autoxidation of Methyl Linoleate

• Published in: Journal of agricultural and food chemistry Vol. 49; no. 6; pp. 3034 - 3040
• Main Authors: Pedrielli, Pamela, Pedulli, Gian F, Skibsted, Leif H
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.06.2001
• Subjects: Analytical, structural and metabolic biochemistry; Antioxidants - chemistry; Aromatic and heterocyclic compounds; Biological and medical sciences; Catechin; Electron Spin Resonance Spectroscopy - methods; Flavonoids - chemistry; Fundamental and applied biological sciences. Psychology; General pharmacology; Heterocyclic compounds, pigments; Kinetics; Linoleic Acids; Medical sciences; Other biological molecules; Oxygen; Pharmacognosy. Homeopathy. Health food; Pharmacology. Drug treatments; Quercetin; Solvents - pharmacology; Flavanol; Polyunsaturated fatty acid; Lipids; Antioxidant; Flavonoid; Radical scavenger; Biological activity; Free radical; Linoleic acid; Autoxidation; Polyphenol; Quercetin; Oxidation; Kinetic parameter
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/jf010017g

The rate of oxygen depletion, as measured by electron spin resonance spectroscopy (oximetry using a spin probe), in a homogeneous solution of peroxidating methyl linoleate (initiated by an azo initiator) in the presence or absence of antioxidants was converted to second-order rate constants for the inhibiting reaction of quercetin and epicatechin. In the non-hydrogen-bonding solvent chlorobenzene at 50 °C, k inh had values of 4.3 × 105 M-1 s-1 for quercetin and 4.2 × 105 M-1 s-1 for epicatechin, respectively. In the hydrogen-accepting “water-like” solvent tert-butyl alcohol, the values were 2.1 × 104 and 1.7 × 104 M-1 s-1, respectively. The solvent effect (factor of 20) is more significant than for α-tocopherol (factor of 4), and the two flavonoids have efficiencies comparable to that of α-tocopherol in scavenging peroxyl radicals in the nonpolar solvent but not in the hydrogen-bonding solvent. Keywords: Quercetin; epicatechin; antioxidant mechanism; hydrogen atom transfer; solvent effect