Chemical composition, antimicrobial and free- radical scavenging activity of essential oils from Khaya senegalensis (Desr) A. Juss

Investigations were conducted to evaluate the chemical composition, free-radical scavenging activity and the antimicrobial efficacy of essential oils obtained from the leaf and stem bark of Khaya senegalensis (Desr) A. Juss.  The plant materials (leaf and stem bark) were dried under shade, blended and sieved to obtain their respective powders. The essential oils obtained by subjecting the powders to hydro distillation method for 3hr in a Clevenger type apparatus were then investigated using standard methods.  The average percentage yields of the oils were 0.85± 0.01%) and 0.50± 0.00% for the leaf and stem bark respectively. The major constituents of the essential oils were khayasinine (39.11%), 7-diacetyl-7oxogedunine (27.09%) and methyl- angolensate (11.51%) for the leaf oil and ivorenolide (28.77%), khivorine (16.33) and 3-diacetyl khivorine (16.10%) for the stem oil. The inhibitory concentration (IC50) of the free radical scavenging activity of the oils were 1.40± 0.29 and 1.00± 0.02 for the leaf and stem oils respectively. The mean diameter of the zones of inhibition exhibited by the oils at 50 µg/ml was between 7.67± 0.67mm and 16.33 ±0.33mm while the MIC was between 5 µg/ml and 40µg/ml for the plant materials. The plant oils remarkably inhibited the growth of Bacillus subtilis ATCC6633, Candida albicans ATCC10231, Escherichia coli, Klebsiella pneumoniae and Staphylococcus aureus. The activity of the plant oils compared favourably with the antibiotics used as positive control.  The demonstration of significant antimicrobial and high free radical scavenging activities in addition to the presence of bioactive compounds in the plant materials could explain the basis for the use of K. senegalensis in the traditional treatment of diseases caused by the test microorganisms.