An assessment of the phytochemical constituents, antimicrobial and antioxidant activities of Juniperus macropoda Boiss

Abstract

Juniperus macropoda Boiss. (Himalayan Pencil Cedar) is utilized as an incense, sacred and medicinal plant by inhabitants of the Lahaul-Spiti district, found in the cold desert areas of the western Himalayan region. The medicinal plants contain diverse varieties of bioactive compounds that may combat the increased threat of antimicrobial resistance and oxidative stress. In the presented study, the phytochemical constituents as well as the antimicrobial and antioxidant activities of the selected plant part have been screened. After extracting plant material (twigs with appressed leaves) in acetone and methanol solvents, the phytocomponents were initially studied by preliminary tests and later by estimating total phenol content, total flavonoid content and total tannin content. The gas chromatography-mass spectrometry (GCMS) analysis of both extracts and the liquid chromatography mass spectrometry (LC/MS) of methanol solvent extract were also conducted. The dried extracts of the plant material dissolved in dimethyl sulfoxide were screened for their antimicrobial activity by adopting disk diffusion and broth microdilution assays against four bacteria and one fungus. Further, the antioxidant potential of both extracts was screened by following 1,1-Diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging and reducing power assays. In the results, preliminary tests for phytocomponents revealed the presence of alkaloids, flavonoids, tannins and terpenoids. A little higher contents of phenol, flavonoid and tannin were recorded in acetone extract than methanol. Also, GCMS revealed a higher percentage of Abietol, Abietal < 4-epi > and 1 H-3a,7-Methanoazulen-6-ol, octahydro-3,6,8,8-tetramethyl-,[3R-(3.α.,3a.β.,6.α.,7.β.,8a.α.)] in both extracts. The presence of phenolics and flavonoids was also supported by LC/MS. Furthermore, for the disk diffusion method, both extracts of the selected plant displayed the highest zones of inhibition (ZOI) against Bacillus cereus, while both extracts displayed the least activity against Escherichia coli. However, in the results of the broth microdilution method, the highest antimicrobial activity, with the least minimum inhibitory concentrations (MIC), was recorded against Pseudomonas putida, and again, the highest MIC values were documented against Escherichia coli. Thus, the E. coli was found to be least sensitive to both extracts. For DPPH free radical inhibition, acetone extract displayed an IC₅₀ (half inhibitory concentration) value of 434.10 µg/mL and methanol extract displayed 390.83 µg/mL, while for the reducing power method, acetone extract displayed an effective concentration (EC) value of 1245.00 µg/mL and methanol displayed 1260.75 µg/mL for reduction of iron. Overall, plant extract displayed some extent of antimicrobial activity against B. cereus and P. putida. However, it remained inactive against E. coli. Also, plant unveiled antioxidant potential, which may be attributed to the phytocomponents recorded in both extracts.