Comparison of chemical composition, antioxidant and antibacterial activity of Callistemon citrinus skeels (bottlebrush) essential oil obtained by conventional and microwave-assisted hydrodistillation

Abstract Microwave-assisted hydrodistillation and conventional hydrodistillation (MAHD and HD) were used for a comparative study of extraction Callistemon citrinus Skeels leaf essential oils. The time required for a MAHD method is 75 minutes that for HD method is 3.5 hours, so MAHD requires lesser time. The increases in yield of extracted oil by MAHD (0.84%) is found compared oil extracted by HD (0.6%). Essential oils were examined by GC–MS. MAHD extracted essential oils were wealthier in oxygenated molecules. The main constituent was 1, 8-cineole, followed by α-pinene in the case of MAHD. Percentage of the major component increases from 80% to 90% as compared to HD. Their antibacterial activity was examined on ‘Gram-negative’ and ‘Gram-positive bacteria’. In the case of both bacteria, MAHD extracted oil shows better activity than HD extracted one. Antioxidant action was studied by using 2, 2-diphenyl-1-picrylhydrazyl (DPPH•) radical scavenging and β-carotene/linoleic acid assay it is shown that MAHD extract has better activity than HD extract. Surface morphology of Callistemon leaves was studied with scanning electronic microscopy (SEM) which reveals that the MAHD leaves surface undergo major damage to the conventional HD.