Valorizing industrial hemp (Cannabis sativa L.) by-products: Cannabidiol enrichment in the inflorescence essential oil optimizing sample pre-treatment prior to distillation

Byproducts of industrial hemp (Cannabis sativa L.), including inflorescences, represent an exploitable material to produce niche products for the pharmaceutical, nutraceutical, cosmetic and pesticide industry. One of them is the essential oil, whose composition can be properly modulated on an industrial level by optimizing the extractive conditions and sample pretreatment. This allows to achieve high concentrations of bioactive compounds, such as cannabidiol (CBD) and sesquiterpenes [e.g. (E)-caryophyllene]. In the present work, we evaluated the effects of type of distillation apparatus, status of conservation of the plant material, grinding and sample-pretreatment with microwave and heat, on the hemp essential oil chemical profile obtained from the monoecious cultivar Felina 32. Seven marker compounds, including the monoterpenes α-pinene, myrcene and terpinolene, the sesquiterpenes (E)-caryophyllene, α-humulene and caryophyllene oxide, and the cannabinoid CBD were quantified in the different hemp essential oil samples by gas chromatography-flame ionization detection (GC-FID) analysis, whereas the overall chemical profiles were achieved by gas chromatography-mass spectrometry (GC–MS) analysis. Results showed that hydrodistillation (HD) in comparison with steam distillation (SD) gave a higher content of cannabinoids. Drying was fundamental to induce decarboxylation of cannabinoid acids to the relative alcoholic forms, coupled with an increase of the sesquiterpene fraction. The optimization of sample pretreatments pointed out that the exposure of dry inflorescences to microwave heating at 900 W power for 1 min was the best method to increase the abundance of bioactive compounds in the essential oil, with special reference to CBD, (E)-caryophyllene and caryophyllene oxide. Overall, these results give new insights into the exploitation of hemp byproducts in different fields such as pharmaceuticals, nutraceuticals and eco-friendly insecticides.