Oregano essential oil (OEO): extraction and chemical composition

Leaves of oregano (O. vulgare spp.) were collected from the experimental area of Facultad de Ciencias Agropecuarias, Universidad Nacional de Córdoba (FCA-UNC), Argentina (April 2016), and an exemplar was deposited in the ACOR herbarium (FCA-UNC). OEO was obtained by hydrodistillation and stored with sodium sulphate in a glass vial at − 18 °C until use (Olmedo et al. 2015).

OEO composition was determined using a Perkin-Elmer^® Clarus 600 gas chromatography-mass spectrometry (GC–MS) instrument equipped with a DB-5 capillary column (30 m × 0.25 µm). The following conditions were used: helium as carrier gas with a 0.9 mL/min flow rate; temperature program: 40 °C for 5 min, then ramped at 10 °C/min until 100 °C, and finally, ramped at 15 °C/min until 245 °C; detector and injector temperatures set at 280 and 260 °C, respectively; electron impact ionisation at 70 eV; mass spectral data acquired in scan mode (mass interval m/z 35–450). The compounds were identified by comparing the retention time (Adams 1995) and mass spectra of the main components available in NIST libraries with the injection of standards (Sigma^®, St. Louis, MO, USA). Results were expressed as g/100 g, from triplicate analyses (Olmedo et al. 2014).