Chemical Composition, Antioxidant, and Antibacterial Properties of <i>Solanecio gigas</i> Leaf Essential Oil and Extracts

Objectives The objective of this study was to examine the chemical composition and antibacterial and antioxidant properties of essential oil (EOs) and solvent extracts from the leaves of Solanecio gigas , a medicinal plant that has long been used in Ethiopian traditional medicine but has received little scientific attention. Methods Gas chromatography–mass spectrometry (GC–MS) was used to analyse the EOs obtained by hydrodistillation. Soxhlet extraction was used to create solvent extracts using methanol, ethyl acetate, and chloroform. To find the main classes of compounds, phytochemical screening was done. Utilizing the 22-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay, antioxidant activity was assessed. The agar diffusion method was used to test the antibacterial activity against Staphylococcus aureus, Streptococcus pyogenes, Escherichia coli , and Klebsiella pneumoniae . The microdilution assay was used to determine the minimum inhibitory concentrations (MICs). Colourimetric techniques were used to quantify the total phenolic and flavonoid contents. Results The essential oil contained 15 compounds, as determined by GC-MS analysis, with the main constituents being, Sabinene (38.909%), and α-Pinene (18.20%). The highest levels of flavonoids (130.10 ± 0.08 μg CE/mg) and phenolics (110.2 ± 0.03 μg GAE/mg) were found in the methanolic extract. Compared with the essential oil (IC₅₀ = 10.2 ± 0.22 μg/mL), the methanolic extract showed superior antioxidant activity (IC₅₀ = 2.1 ± 0.11 μg/mL). At concentrations of 25–200 mg/mL, the EOs demonstrated strong antibacterial activity with inhibition zones ranging from 7.1 ± 0.15 mm to 24.1 ± 0.40 mm, especially against K. pneumoniae and E. coli . The MIC range was 80.25 to 250.3 μg/mL. Conclusion The antibacterial and antioxidant qualities of S. gigas essential oil and extracts offer scientific support for the plant's traditional medicinal uses. The EOs demonstrated strong antibacterial activity against both Gram-positive and Gram-negative bacteria, while the methanolic extract, rich in phenolic and flavonoid compounds, showed the strongest antioxidant activity.