Antioxidant mechanism of flavonoids. Solvent effect on rate constant for chain-breaking reaction of quercetin and epicatechin in autoxidation of methyl linoleate.
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 degrees C, k(inh) had values of 4.3 x 10(5) M(-)(1) s(-)(1) for quercetin and 4.2 x 10(5) M(-)(1) s(-)(1) for epicatechin, respectively. In the hydrogen-accepting "water-like" solvent tert-butyl alcohol, the values were 2.1 x 10(4) and 1.7 x 10(4) M(-)(1) s(-)(1), respectively. The solvent effect (factor of 20) is more significant than for alpha-tocopherol (factor of 4), and the two flavonoids have efficiencies comparable to that of alpha-tocopherol in scavenging peroxyl radicals in the nonpolar solvent but not in the hydrogen-bonding solvent.
Pedrielli
P
P
Food Chemistry, Department of Dairy and Food Science, Royal Veterinary and Agricultural University, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark.
Pedulli
G F
GF
Skibsted
L H
LH
D000975:Antioxidants / Q000737:chemistry*; D002392:Catechin; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D005419:Flavonoids / Q000737:chemistry*; D007700:Kinetics; D008041:Linoleic Acids; D010100:Oxygen; D011794:Quercetin; D012997:Solvents / Q000494:pharmacology*
D000975:Antioxidants; D005419:Flavonoids; D008041:Linoleic Acids; D012997:Solvents; C005575:methyl linoleate; D002392:Catechin; D011794:Quercetin; D010100:Oxygen