Green extraction of hemp (Cannabis sativa L.) using microwave method for recovery of three valuable fractions (essential oil, phenolic compounds, and cannabinoids): a central composite design optimization study.

Industrial hemp (Cannabis sativa L.) is an herbaceous plant with a characteristic scent that has been used for over 5000 years for its various properties. In particular, hemp essential oil can be used in pharmaceutical, cosmetic, and nutraceutical fields. In this work, hemp Futura 75 was processed with an innovative and green extraction method, namely Microwave-Assisted Extraction (MAE) [1], using a Design of Experiment (DoE) approach [2]. After the essential oil distillation, two valuable byproducts, namely the residual biomass and water enriched in hydrophilic compounds, were recovered and analyzed. The design variables analyzed were the microwave irradiation power (W/g), the extraction time (min), and the amount of water added to hemp samples (%). This research aimed to evaluate how these experimental parameters can affect the EO yield and composition together with the yield and antioxidant properties of the aqueous residue. Total phenolic and flavonoid content (TPC, TFC) and antioxidant activity (DPPH) were calculated through spectrophotometric UV-Vis experiments [3-4]; whereas phenolics and cannabinoids in the residual water and biomass, respectively, were determined by HPLC-MS analysis. GC-MS analysis was performed to study the chemical composition of essential oils obtained by MAE. At the same time, GC-FID was used to quantify the essential oil constituents and the CBD content in the residual biomass. Regarding the essential oil analysis, the responses yield and content of some compounds were well described by the mathematical models applied. In addition, in the case of the aqueous residues, the yield, polyphenols, and flavonoids content and antioxidant activity, as the four responses analyzed, suitably fit the models. On the other hand, there were no relationships between the CBD content in the residual biomass and the MAE experimental conditions, probably due to the samples' intrinsic variability. A multiple optimizing procedures based on desirability approach was employed to identify the most suitable experimental parameters able to maximize all the satisfactory responses simultaneously. In particular, high microwave power and long extraction times are needed to enhance the yield and chemical profile of essential oil, along with a medium-high amount of water, required to improve the aqueous extract yield and antioxidant capacity. HPLC-MS analysis put in evidence the abundance of flavone glycosides and CBD in the residual water and biomass, respectively. Our work showed that hemp biomass is a multipurpose matter able to provide different fractions employable in several fields such as nutraceuticals, pharmaceuticals, cosmetics, and pest science.