For gas chromatography, the extracted oil samples were diluted (10 L of oil in 1 mL methyl tertbutyl ether) and then analyzed using an Agilent 6890 Series FID, GC System equipped with an Agilent DB-5 bonded fused silica capillary column (5% phenyl/95% methyl silicone; 30 m x 0.25 mm i.d.). Helium was used as the carrier gas at a column pressure of 16.2 psi (0.112 MPa). The oven temperature was held at 60oC for 2 min and then programmed to increase at 4oC/min to 200oC, split ratio of 50:1 at a flow rate of 1 mL min-1. The injector temperature and detector temperatures were 180oC and 220°C,respectively. Separation and identification of known samples of oil constituents (p-cymene, 1,8-cineole terpinen-4-ol, methyl chavicol, geraniol, thymol,
eugenol, methyl eugenol and β-caryophyllene) were used to confirm constituent separation.