Antioxidant, antimicrobial and phytochemical analysis of three endemic Rhododendron spp. of Sikkim Himalaya

Abstract

• Phytochemicals screening of R. dalhousiae, R. ciliatum and R. maddenii was performed. • Total flavonoids and phenols content were found maximum in methanol extracts of Rhododendron spp . • HPLC analysis identified the presence of various phenolic compounds in Rhododendron spp . • Among three species, high anti-oxidative potential was recorded for R. dalhousiae . • Rhododendron spp . exhibited antibacterial potential against pathogenic bacteria. The genus Rhododendron (family: Ericaceae), distributed mostly in the higher altitude of the Indian Himalayan Region (IHR), has great ecological significance and economic importance. In the present study, three endemic species of Rhododendron viz., R. dalhousiae, R. ciliatum and R. maddenii were investigated for antioxidant, antimicrobial activity and phenolic compounds. Five different solvents viz., methanol, ethanol, ethyl acetate, dichloromethane and hexane were used for the extraction. The highest total phenolic and flavonoid contents were found in the methanolic extracts of all the examined Rhododendron spp . The 2, 2-diphenyl-1-picrylhydrazyl (DPPH) and 2, 2-azinobis-3-ethylbenzothiazoline-6 sulfonic acid (ABTS) free radical scavenging potential were found maximum in the methanolic extract of R. dalhousiae with IC 50 values of 13.58 ± 1.81 µg ml −1 and 11.21 ± 1.88 µg ml −1 , respectively. High performance liquid chromatography (HPLC) analysis showed the presence of various phenolic acids namely gallic acid, ferulic acid, vanillic, caffeic acid, catechin, p-coumaric and m-coumaric acid in the plant extracts. The Rhododendron spp. leaf extracts also exhibited antimicrobial potential against both gram-positive and gram-negative bacteria. R. dalhousiae leaves extracted with n-hexane and methanolic solvents showed better antibacterial response against gram-positive bacteria namely Bacillus subtilis and B. megaterium . The results of this preliminary study suggest that the studied endemic Rhododendron spp. are potential source of natural antioxidant and antimicrobial compounds which can be further used as pharmacological agents.