PHYTOCHEMICAL SCREENING AND IN-VITRO STUDIES OF ANTIOXIDANT AND ANTIMICROBIAL ACTIVITY OF EXTRACTS OF DRIED STEVIA REBAUDIANA LEAVES

The present study is based on the comparative evaluation of preliminary phytochemical screening and in vitro antimicrobial activity of methanolic and ethanolic extracts of Stevia rebaudiana leaves. The crude extracts of S. rebaudiana leaves were subjected to phytochemical screening tests by using standard procedures for the detection of the presence or absence of eight major secondary metabolites. The free radical scavenging activity of both the extracts was measured by using the 1,1- diphenyl-2-picrylhydrazyl (DPPH) assay. The dose dependent increase was observed in DPPH activity of methanolic and ethanolic extracts (10, 20, 40, 50, 100 µg/ml), and the range was 28.65 – 64.35 % and 28.15 – 61.57 % as compared to ascorbic acid 30.15 – 85.99 %. The antibacterial activity of S. rebaudiana leaves was tested by agar-well diffusion assay. The plant extracts of four different concentrations (25, 50, 75 and 100 mg/mL) were prepared in DMSO and tested against eight bacterial strains and was compared with that of standard drug tetracycline (10 µg/mL). The results of preliminary phytochemical screenings showed the presence of different kinds of phyto-constituents in methanolic and ethanolic extracts of S. rebaudiana leaves and the most abundant compounds were phenols followed by phytosterols, tannins, saponins, glycosides and flavonoids. Out of the two extracts, methanolic extract showed higher antibacterial activity at 100 mg/mL with inhibition zone of 25.93 ± 0.16 mm on Zymomonas spp. The results signified the effective therapeutic potential of S. rebaudiana.