Optimization of the microwave-assisted extraction 185 (MAE) of the Cannabis sativa inflorescences to get a CBD-rich essential oil

The essential oil obtained from industrial hemp (Cannabis sativa L.) represents a potential candidate for the pharmaceutical, nutraceutical, cosmeceutical and pesticide science. In the present work, the microwave-assisted extraction (MAE) was performed to enrich the hemp essential oil in bioactive compounds, especially cannabidiol (CBD), using the dry inflorescences of the Italian variety CS (Carmagnola Selezionata) (Fig. 1). For this purpose, an optimization of the operative conditions to increase the essential oil yield and CBD content, namely the microwave irradiation power (W/g), extraction time (min) and water added to the plant matrix after moistening (%), was carried out through a central composite design (CCD) approach (Fig. 2). The conventional hydrodistillation (HD) for 240 min was used for comparative purposes. The chemical constituents of essential oils (Fig. 3) obtained by MAE and HD were identified by GC-MS, whereas the quantitative detection of CBD and main terpenoids (α-pinene, β-pinene, myrcene, limonene, terpinolene, (E)-caryophyllene, α-humulene and caryophyllene oxide) was achieved by GC-FID. Moreover, chiral chromatography was used to obtain the enantiomeric distribution of the chiral components (α-pinene, β-pinene, limonene, (E)-caryophyllene and caryophyllene oxide). Results showed that the MAE process, using high irradiation power and relatively long extraction times, increased significantly the concentration of CBD in the essential oil while maintaining high oil yield values when compared with conventional HD. The (+)-enantiomers of three chiral monoterpenes (α-pinene, β-pinene and limonene) were predominant, while (E)-caryophyllene and caryophyllene oxide were enantiomerically pure. In conclusion, the MAE was successfully applied to hemp dry inflorescences in order to get an essential oil enriched in CBD, which may be exploited in several industrial applications.