Sesquiterpene hydrocarbon rich essential oils of Caryopteris odorata (D. Don) Robin.: Chemical composition, antioxidant and antimicrobial activity

The stem, leaf and flower essential oils of Caryopteris odorata (D. Don) Robin. were analyzed by gas chromatography (GC) and GC-mass spectrometry (GC-MS). A total of forty-two compounds were identified, comprising 97.8% of stem, 99.8% of leaf and 94.9% of flower oil. All three oils were found to be dominated by sesquiterpene hydrocarbons. Interestingly, isomeric longipinenes, which occur rarely in the lower plants, were the major constituents of stem and flower oils. The in vitro antioxidant potential of stem, leaf and flower oils was assessed by DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging, iron chelating and reducing power methods. Leaf oil showed good reducing power (ascorbic acid equivalent, ASE 2.2 +/- 0.0) and good DPPH radical scavenging activity (IC50 1.1 +/- 0.8). Antimicrobial activity of stem, leaf and flower oils was tested against one Gram-positive, four Gram-negative bacteria and two fungal strains at different concentrations using the well diffusion method. The zone of inhibition and minimum inhibitory concentration values of the oils for all microorganisms were in the range 1.7 +/- 0.6 to 16.7 +/- 0.6 mm and 5-70 mu L/mL, respectively.