Chemical composition, and antibacterial and antioxidant activities of essential oils from Laggera tomentosa Sch. Bip. ex Oliv. et Hiern (Asteraceae)

Authors: TOKUMA GETAHUN, VINIT SHARMA, DEEPAK KUMAR, NEERAJ GUPTA

Abstract: Laggera tomentosa Sch. Bip. ex Oliv. et Hiern (Asteraceae), an endemic Ethiopian medicinal plant, is traditionally used to treat various ailments. Previously, the chemical constituents of the essential oil (EO) of its leaves and inflorescence were documented. However, no data about the chemical compositions of other parts of the EOs of the plant have been reported to date. Moreover, there are no previous biological activity reports on any parts of the EOs of this plant. Thus, in this study, the EOs were isolated from the stem bark and roots of this plant by hydrodistillation and analyzed using gas chromatography-mass spectrometry to identify their components. In addition, antibacterial potentials of the oils were evaluated using the disc diffusion and minimal inhibitory concentration (MIC) methods. 2,2-diphenyl-1-picrylhydrazyl (DPPH) and hydrogen peroxide methods were also employed to assess their antioxidant properties. Oxygenated monoterpenes (71.82% and 77.51%), of which 2,5-dimethoxy-p-cymene (57.28% and 64.76%) and thymol methyl ether (9.51% and 8.93%) were identified as major components in the EOs of stem bark and roots of L. Tomentosa and the oils, were the most potent in the DPPH (IC₅₀, 0.33 ± 1.10 and 0.39 ± 0.97 mg/mL) assay, respectively. Moreover, the EOs demonstrated appreciable activity towards the gram+ (S. aureus and B. Cereus) bacteria. Among these oils, the oil of the stem bark showed the greatest activity to the gram+ (MIC = 0.625 mg/mL) bacteria. Therefore, the overall results suggested that the EOs of L. Tomentosa may be a promising prospect for pharmaceutical, food, and other industrial applications.

Keywords: Laggera tomentosa, essential oils, 2,5-dimethoxy-p-cymene, thymol methyl ether, antibacterial and antioxidant activities

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