Ocimene

Super Q (80/100 mesh) was purchased from Alltech (PA, USA). n-Hexane (95%, for pesticide residue analysis) was purchased from Fisher Scientific (Loughborough, Leicestershire, UK). (Z)-3-Hexenyl acetate (98%) were purchased from Alfa Aesar (Heysham, UK). Limonene (97%), cis-jasmone (92%) and linalool (96%) were purchased from TCI America (Portland, USA). α-Pinene (98%), camphene (90%), 6-methyl-5-hepten-2-one (98%), methyl salicylate (99%), ocimene (90%) (mix of (E) and (Z)-isomers), (E)-caryophyllene (80%), benzothiazole (96%), indole (98%), myrcene (97%), octanal (99%), undecane (99%), tridecane (99%), pentadecane (99%), nonanal (95%) and decanal (98%) were purchased from Sigma Aldrich (Steinheim, Germany). Geranylacetone (96%) was purchased from TCI (Tokyo, Japan). (E,E)-α-Farnesene was synthesized in three steps from isoprene and sulfur dioxide (Hassemer et al. 2016 (link)). (E)-4,8-Dimethyl-1,3,7-nonatriene (DMNT) and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene (TMTT) were synthesized from geraniol and (E,E)-farnesol, respectively (Leopold 1990 ).

The separation was achieved on a Perkin Elmer Elite-5-MS fused-silica capillary column (30 m × 0.25 mm, film thickness 0.25 µm), using helium as carrier gas at a standard flow rate of 1.1 mL/min. The temperature of the injector was adjusted at 250 °C with an initial temperature of 50 °C, initial hold 5 min, and ramp 4.0 °C/min to 280 °C. The total running time was 62.50 min and the solvent delay was from 0 to 4.0 min. MS scan time was from 4 to 62.5 min, covering mass range 50.00 to 300.00 m/z. The chemical ingredients of the EO were characterized by comparing their mass spectra with the reference spectra in the MS Data Centre of the National Institute of Standards and Technology, and by matching their Kovats and retention indices with values reported in the literature [29 (link),30 (link)]. In addition, the EOs Kovats and retention indices with values were compared with 20% of HPLC grade of reference EOs including α-pinene, eucalyptol, caryophyllene, γ-terpinene, ocimene, endo-borneol, α-terpineol, jasmone, α-cadinene, p-menthane that were purchased from Sigma-Aldrich, Hamburg, Germany) [31 (link)].

Twenty-four SPME fibers (DVB/CARBOXEN/PDMS 50/30 μm, Supelco^TM, Bellefonte, PA) were cleaned by heating in a gas chromatograph injector at 250°C for five minutes with helium as the carrier flow. Cleaning efficiency had been previously checked in similar conditions: blank analyses confirmed that there was no carryover from the previous analysis. Fibers were controlled by GC-MS analysis after incubation in a headspace vial containing a mixture of the standard compounds ocimene, limonene, methyl salicylate caryophyllene and farnesene (Sigma-Aldrich, Saint-Quentin Fallavier, France). The variability expressed as the ratio between the mean and the standard deviation of compounds’ areas were 41, 13, 9, 22 and 30% respectively. Fibers were then wrapped in aluminum foil and stored in individual screw-capped Pyrex glass tubes until use.