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Chemical structures of caffeic acid and its related compounds.
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Figure 1: Chemical structures of caffeic acid and its related compounds.

Mentions: Chlorogenic acid is an ester of caffeic acid with quinic acid (Fig. 1). It is found naturally in various agricultural products such as coffee beans, potatoes and apples. Ferulic acid (Fig. 1) occurs in rice, wheat, olives, citrus fruits and leaves and many other plants. Thus, it is of interest to examine the influence of the polyphenols on the formation of reactive oxygens by UVA in view of their widespread occurrence in food products.

Antioxidant Activity of Caffeic Acid through a Novel Mechanism under UVA Irradiation

Mori H, Iwahashi H - J Clin Biochem Nutr (2009)

Bottom Line: Caffeic acid inhibited the formation of hydroxyl radicals.Caffeic acid hardly scavenged both hydroxyl radicals and superoxide radicals under conditions employed in this paper in spite of its ability to act as a hydrogen donor or a reagent for the aromatic hydroxylation, because high concentration of DMPO trapped hydroxyl radicals overwhelmingly.Thus, the inhibitory effect of caffeic acid seems to occur in the standard reaction mixture under UVA irradiation through a novel antioxidation activity, i.e., ability to quench the exited xanthone.

Affiliation: Department of Chemistry, Wakayama Medical University, 580 Mikazura, Wakayama 641-0011, Japan.

ABSTRACT
Effect of caffeic acid on the formation of hydroxyl radicals was examined during xanthone-mediated photosensitization. The reaction was performed on irradiation (lambda = 365 nm) of the standard reaction mixture containing 15 microM xanthone, 0.1 M 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and 20 mM phosphate buffer (pH 7.4) using electron paramagnetic resonance (EPR) with spin trapping. Caffeic acid inhibited the formation of hydroxyl radicals. Caffeic acid hardly scavenged both hydroxyl radicals and superoxide radicals under conditions employed in this paper in spite of its ability to act as a hydrogen donor or a reagent for the aromatic hydroxylation, because high concentration of DMPO trapped hydroxyl radicals overwhelmingly. Furthermore, caffeic acid inhibited the formation of hydroxyl radicals in the standard reaction mixture with EDTA under UVA irradiation. Accordingly, the inhibitory effect of caffeic acid on the formation of hydroxyl radicals in the standard reaction mixture under UVA irradiation is not due to its ability to chelate iron. Thus, the inhibitory effect of caffeic acid seems to occur in the standard reaction mixture under UVA irradiation through a novel antioxidation activity, i.e., ability to quench the exited xanthone.

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