Comparison of quercetin and a non-orthohydroxy flavonol as antioxidants bycompeting in vitro oxidation reactions

Two structurally related flavonols, quercetin and morin, along with protoca techuic acid (PA), beta -resorcylic acid (DHBA), and phloroglucinol carboxy lic acid (PCA), which represent quercetin and morin degradation products, w ere assessed with respect to their antioxidant potency by chemical comparis ons in competing oxidation reactions. The measurement of the antioxidant ca pacity was performed with the beta -carotene bleaching method, and the comp ounds were also tested with respect to their abilities to prevent lipid, pr otein, and DNA oxidation. The effect of concentration was also considered. The results obtained strongly suggested that quercetin is a powerful antiox idant in every system used, whereas morin is a much weaker antioxidant and in some cases may also have pro-oxidant action. PA and PCA were always infe rior antioxidants compared to the parent molecule quercetin; DHBA and PCA e xhibited activities comparable to that of morin in reaction comparisons.