Essential Oil Characterization and Biological Activities of Millettia thonningii (Schumach. & Thonn.) Baker Leaf, Stem and Root

Abstract

Millettia thonningii has been used in folk medicine for centuries to treat pains, pathogenic diseases, and radical-induced aliments. Essential oils (EOs) are a source of bioactive compounds, and their potential application as an alternative to synthetic products in the treatment of infectious diseases and oxidative stress has been validated. Leaf, stem and root EOs of M. thonningii were obtained by hydro-distillation and characterized by Gas Chromatography-Mass Spectrometry (GC-MS) technique. Antioxidant activity was evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical while antibacterial activity was assessed using agar well diffusion and broth micro-dilution techniques. EOs yields obtained were 0.18, 0.20 and 0.27% for the leaf, stem and root, respectively. Seventeen (leaf), twenty-two (stem) and fifteen (root) compounds were identified in EOs representing 96.3, 98.2 and 91.0% of the whole composition, respectively. Two major constituents in leaf essential oil (EO) were β-atlantol (23.6%) and β-caryophyllene (22.7%); β-caryophyllene (54.3%) was the most abundant in stem EO followed by caryophyllene oxide (11.4%) and α-humulene (7.2%) while epicedrol (57.1%) was the major compound in the EO followed by cedrol (10.6%) and β-cedrene (9.8%). α-Humulene, caryophyllene oxide, cedrol and isolongifolen-9-one were common in the three parts. Stem EO showed the highest antioxidant activity among others (IC50 = 259.76 µL/mL). However, the leaf, stem and root EO showed strong inhibition on the growth of Escherichia coli, Pseudomonas aeruginosa, Salmonella typhi and Streptococcus pneumoniae (14.0 - 20.0 mm and 5 - 20 µL/mL). This research further justified the ethnomedicinal uses of M. thonningii against pathogenic disorders and radical-induced aliments.