The chemical composition and antibacterial activities of the essential oils from three Aframomum species from Cameroon, and their potential as sources of (E)-(R)-nerolidol

Abstract

Essential oils obtained by hydrodistillation of seeds, pericarps, leaves and rhizomes of Aframomum dalzielii, A. letestuianum and A. pruinosum grown in Cameroon were analyzed by GC-FID and GC-MS. The seed oils of the three species were characterized by a high content of (E)-(R)-nerolidol (>88.0%), which was fully characterized by NMR spectroscopy and chiral GC analysis. The main constituents of the pericarp and rhizome oils were monoterpene hydrocarbons, mainly β-pinene (0.8%-22.9%) and sabinene (29.0%-42.3%), along with 1,8-cineole (4.5%-23.7%); leaf oils were characterized by sesquiterpenes, namely (E)-β-caryophyllene (18.4%-82.4%) and caryophyllene oxide (4.5%-23.7%). The antibacterial activities of these essential oils and of nine pure compounds (sabinene, β-pinene, 1,8-cineole, linalool, racemic (E)-nerolidol, (E)-(R)-nerolidol, (E)-β-caryophyllene, α-humulene and caryophyllene oxide) were assessed against Micrococcus luteus and Escherichia coli. The strongest activities were observed against E. coli. The seed essential oils and their major component, (E)-(R)-nerolidol, exhibited the lowest MIC values (0.19-0.39 μL/mL), justifying their traditional use and their potential application as natural food preservatives.