Comprehensive analysis of Callistemon citrinus and essential oils using 2-D GCxGC-TOF/MS

Abstract: The study was aimed at extracting essential oils from Callistemon citrinus and Cymbopogon citratus, performing extensive characterisation of the extracted oils and investigating their antimicrobial effects against a batch of pathogens. These two plants are commercially known as Lemon bottlebrush tree and Lemon grass, and were chosen because of their documented history in having bioactive properties such as antioxidant, anti-inflammatory, anti-cancer, antibacterial, and their beneficial effects particularly in the cosmetics, pharmaceutical and food industry. Plant samples were prepared by extracting the oils from the plant materials using various solvents by means of a soxhlet extraction method. Upon selecting three different solvents for the extraction, the procedure was based on phytochemical isolation. Dichloromethane, a polar solvent was used for extracting phyto-constituents such as alkaloids, terpenoids, fatty acids, flavonoids. Ethanol, a semi –polar solvent was used for extracting alkaloids, tannins, polyphenols, flavonols, terpenoids and sterols. Lastly hexane, a non-polar solvent used to extract terpenoids, tannins, polypeptides, anthocyanin. All these solvents were used selectively and after completion, the extracted materials/essential oils were air dried and diluted with different solvents for further analysis. GCxGC-TOF/MS was the selected separation technique to confirm that indeed the secondary metabolites found had bioactive properties. A biological test was conducted as well to confirm the bioactive properties by testing the essential oils against 11 common pathogens namely Bacillus subtilis, Klebsiella oxytoca, Proteus mirabilis, Staphylococcus aureus, Mycobacterium smegmatis, Enterobacter cloacae, Staphylococcus epidermidis, Enterococcus faecalis, Proteus vulgaris, Escherichia coli and Klebsiella pneumonia. Analysis of the oils by GCxGC TOF/MS revealed the presence of a total of 300 compounds in Cymbopogon citratus and Callistemon citrinus. Neral (Citral) was found to be a major compound in Callistemon citrinus oil and Mycrene was found to be a major compound in Cymbopogon citratus oil. Compounds like sulcatone, linalool, ocimene, citronellol, geraniol and eucalyptol were also common in the oils...M.Sc. (Chemistry