Oxidative stress imposed by increased concentration of free radicals, particularly, Reactive Oxygen Species (ROS) has been known to contribute to the initiation and progression of several diseases. Plant derived antioxidants can counteract oxidative stress and are capable of reducing the risk of developing these diseases. In the present study, the methanolic extracts of five medicinal plants were tested for their antioxidant capacities using different antioxidant assays. The total flavonoid and phenolic contents of the extracts were determined and a correlation was established between antioxidant capacities and total phenol/flavonoid content. Among the tested extracts, the highest amount of total phenolic and total flavonoid content was found in methanol extract of KUPS_1(Rheum australe) with TPC value of 249.58 ± 7.73 Gallic acid equivalent µg/mg and TFC value of 480.84 ± 8.81 Rutin equivalent µg/mg. All the samples showed 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2-azino-bis-(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) and Ferric Reducing Activity Potential (FRAP) antioxidant activities at different levels. Highest DPPH radical scavenging was shown by KUPS_1(Rheum australe) (IC50 = 3.47 ± 0.09), ABTS radical were most efficiently quenched by KUPS_5(Bergenia ciliata) (IC50 = 3.82 ± 0.63) and the highest reducing potential was shown by KUPS_2(Nirbikhi) (FRAP = 61.76 ± 2.29 equivalent µg Fe2+/ml). A significant correlation was found between the antioxidant activity of extracts and their total phenolic and total flavonoid contents.
We would like to acknowledge University Grants Commission (UGC), Sanothimi, Nepal for providing Collaborative Research Grant to accomplish this work.