Composition and biological assays of the leaf essential oil of Asparagus flagellaris (Kunth) Bak

Abstract

Abstract Background Asparagus flagellaris leaves are ethnomedicinally used to treat syphilis, gonorrhea and other sexually transmitted diseases (STDs), with no reports on the volatile constituents. This study was aimed to quantitatively and qualitatively characterise the composition of essential oil, evaluates the free radical scavenging and antimicrobial capacity of the essential oil. Methods The essential oil was isolated by hydrodistillation method using all-glass Clevenger-type apparatus, while the identification and quantification of constituents were performed by gas chromatography-mass spectrometry (GC-MS) technique. The antioxidant activity on 2, 2-diphenyl-1-picrylhydrazyl (DPPH) was evaluated and the oil was also tested against 10 strains of microorganisms consisting of 6 bacteria: Escherichia coli, Salmonella typhi, Klebsiella pneumonia, Pseudomonas aeruginosa, Staphylococcus aureus and Bacillus subtilis and 4 fungi: Candida albicans, Penicillium notatum, Aspergillus niger and Rhizopus spp. using broth dilution and surface plate methods, respectively. Results A pale yellow essential oil with a characteristic scent was obtained, with a yield of 0.80% (w/w). A total of 28 compounds accounting for 97.41% of the total oil contents were identified. The oil was predominated by Thymol and its derivatives, accounting for 57.48%. The most abundance (% area) constituents of the essential oil were 5-Thymyl tiglate (18.49%), Thymyl-2-methyl butyrate (17.34%), Thymol hydroquinone dimethyl ether (10.52%), Thymol methyl ether (9.42%) and 5-Propyl-1, 3-benzodioxole (4.59%). The essential oil showed a significant free radical scavenging activity compared to the standard antioxidant drugs used in this study, with % inhibition varying from 88.06 ± 0.0001 to 93.05 ± 0.0006. The leaf essential oil exhibited antimicrobial activity on all the tested organisms at 500–125 μg/mL, with an 18–10 mm inhibitory zone. Conclusion The leaf essential oil of A. flagellaris contains notable chemical compounds responsible for its antioxidant and antimicrobial activities.

Keywords

• Antioxidant
• Antimicrobial
• Asparagus flagellaris
• Chemical constituents
• Thymol derivatives