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

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.