Chemical composition and bioactivity studies of Alpinia nigra essential oils

• β-Caryophyllene with 62 compounds were detected in A. nigra essential oils (EOs).
• All EOs showed strong free radical scavenging activity like butylated hydroxyl toluene.
• Rhizome EO was found most active against Yersinia enterocolitica.
• Compromised and damaged bacterial cells were confirmed.
• Weak biting deterrent and larvicidal activity was found against Aedes aegypti.

Free radical scavenging, bactericidal and bitting deterrent properties of Alpinia nigra essential oils (EOs) were investigated in the present study. Chemical composition of the EOs was analyzed using GC–MS/GC–FID which revealed the presence of 63 constituents including β-caryophyllene as major component. All the EOs were found to possess notable antioxidant activities as determined using methods for scavenging of 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical. Rhizome essential oil (REO) exhibited best effective free radical scavenging activities among other EOs compared to the standard antioxidant, butylated hydroxyl toluene. The efficacy of A. nigra EOs was tested against three Gram positive and four Gram negative bacteria. Flow cytometry, field emission scanning electron microscopy and transmission electron microscopy studies revealed the bacterial cell membrane damage and disintegration when they are treated with REO. Further, all EOs showed weak biting deterrent and larvicidal activity against the blood-feeding female adults and 1 day old Aedes aegypti larvae except flower essential oil which was inactive at 125 ppm. Current investigation highlights the detailed chemical composition and bioactive potential of A. nigra EOs for the first time.

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