Preliminary Evaluation for Comparative Antioxidant Activity in the Water and Ethanol Extracts of Dried Citrus Fruit (Citrus unshiu) Peel Using Chemical and Biochemical in Vitro Assays

Comparative antioxidant activities of the water and ethanol extracts obtained from dried citrus fruit (Citrus unshiu) peel were determined using chemical and biochemical in vitro assays. Chemical assays were used for evaluation of 1,1-diphenyl-2-picryl hydrazyl (DPPH) radical scavenging, hydrogen peroxide scavenging, and reducing power of both extracts and their total phenolic, flavonoid and tannin contents and antioxidant activities were investigated. Biochemical assays were performed to evaluate the inhibition activities of AAPH-induced rat RBC hemolysis and Fe-induced lipid peroxidation using rat brain tissue cells. Linear correlation between the antioxidant activities of both extracts were determined by chemical assays, and total phenolic, flavonoid and tannin contents was observed in concentration-dependent mode. Both extracts showed >95% DPPH radical scavenging and >85% hydrogen peroxide scavenging, and higher reducing capacity at the same level of 3200 ppm. In the inhibition activity of AAPH-induced hemolysis, water extracts showed a strong activity in concentration-dependent mode up to 1600 ppm with no statistical difference found between 1600 and 3200 ppm (P > 0.05). In the inhibition activity of Fe-induced lipid peroxidation, ethanol extracts showed the higher inhibition percentage of lipid peroxidation than those of water extracts at the same concentration with no significant difference (P > 0.05) found in the range of 800 to 3200 ppm. The extracts of dried Citrus unshiu peel may be considered as potential antioxidant ingredients of functional food depending on the conditions at which reactive oxygen species are implicated.