Potent antioxidant and radical-scavenging activity of Chenpi--compensatory and cooperative actions of ascorbic acid and citric acid.

Dried peels of Satsuma mandarin (Citrus unshiu Marcov.) have been used as traditional Chinese and Japanese medicine, which are called 'Chenpi'. In our present study, cold and hot water extracts of Chenpi exhibited a strong inhibitory activity against linoleic acid peroxidation and 1,1-diphenyl-2-picryl-hydrazyl (DPPH) radical-scavenging activity compared with o-methanol extract. When these extracts were separated into ethanol-soluble(ES) and ethanol-precipitable fractions, the dominant antioxidant and radical-scavenging activities were detected in the ES fractions, which suggests that these antioxidant and radical-scavenging activities are responsible for water-soluble and low-molecular-weight substances. As possible active principles for antioxidant activities in the water extracts, the contents of ascorbic acid and citric acid in these extracts were measured, and the antioxidant and radical-scavenging activities of these substances were assayed at various concentrations. The experimental results indicate that the antioxidant activity against lipid peroxidation in the water extracts is dominantly associated with citric acid, and the DPPH radical-scavenging activity of the water extracts is majorly responsible for ascorbic acid, suggesting a compensatory action of ascorbic acid and citric acid in expression of the antioxidant and radical-scavenging activities of Chenpi.