Study of Antioxidant and Mushroom Tyrosinase Inhibitory Activities of Selected Medicinal Plants of Nepal

Phytochemicals are naturally occurring chemical compounds present in plants. It includes glycosides, alkaloids, tannins, saponins, phenols, flavonoids, carbohydrates, etc. Among them, some of them possess antioxidant property, which is responsible for regulation of free radicals in the body and tyrosinase inhibitory activity that results in the reduction in melanin synthesis. In addition, phytochemicals provide different health benefits to humans. Thus, the aim of the study was to determine antioxidant and tyrosinase inhibitory activities of some selected medicinal plants of Nepal.

Phytochemical screening of methanolic extracts of test samples was performed with various reagents and the phenol and flavonoid contents were also determined. Antioxidant activity was carried out by DPPH free radical scavenging method and tyrosinase inhibitory activity was performed by mushroom tyrosinase inhibitory method. The presence of phytochemicals was confirmed by the visual color change upon addition of test reagents. The higher phenol and flavonoid contents among the selected plants were found to have better antioxidant and tyrosinase inhibitory activities.

Among the selected plants, Diploknema butyraceae had the highest phenol content (665.33 ± 0.0 mg GAE/g dry extract weight) and flavonoid content (728 ± 0.3 mg quercetin/g dry extract weight) and showed similar DPPH free radical scavenging activity (IC50 value 6.012 μg/ml) to standard ascorbic acid (IC50 value 4.73 μg/ml). In addition to this, mushroom tyrosinase inhibition was also found highest in the same plant (31.07 ± 2.13 %) followed by Jatropha curcas (17.51± 0.49 %), Woodfordia fruticosa (16.95 ± 2.24 %) and least in Crateva unilocularis (1.41 ± 2.13%).

The results above showed some probability of Diploknema butyraceae with potential tyrosinase inhibitory property. Therefore, further studies should be focused on isolation of active constituents responsible for tyrosinase inhibitory activity.