Solvent extraction of Cannabis sativa under cryogenic conditions

Abstract

Extraction of natural products using safe, selective and green solvents is of major importance for their use as ingredients in foods, beverages, cosmetics and pharmaceutical products. In the particular case of cannabis, ethanol at ambient conditions has been found to be very effective in the extraction of cannabinoids, terpenoids, and other valuable metabolites; however, it also extracts chlorophyll, vegetable oils and waxes. Alternatively, the selectivity towards cannabinoids could be increased by operating at lower temperatures. In this regard, this work focused on the cryogenic extraction of leaves and flowers of Cannabis sativa L. with ethanol. Extractions were carried out in a rotary tumbler under batch operation at different temperatures (−80 °C to 20 °C) and solvent:solid ratios (4:1 to 25:1 mL/g). The content of cannabinoids in samples was measured via U-HPLC under isocratic elution using a mixture of a 0.1% wt. formic acid aqueous solution and pure acetonitrile, using a diode array detector at 280 nm, and with an external standard method. Terpenes were quantified by GC using headspace injection, FID detection, and using external standards for calibration. The yields with respect to dry biomass were in-between 0.43% and 4.22% wt. The corresponding cannabinoids content with respect to dry material ranged from 0.25% to 2.67% wt., and these mainly corresponded to cannabidiol and cannabinol. The content of terpenoids was in between 0.01 and 1% wt., and the major fraction corresponded to monoterpenes d-Limonene, β-Myrcene, α-Terpinene, Terpinolene, and p-Cymene. Cryogenic extracts were characterized by a translucent aspect with minor content of coloring compounds and other impurities. Preferred operating conditions corresponded to −20 °C and a solvent:solid ratio of 16:1 mL/g; under these conditions and with respect to dry biomass, the extraction yield was 3.47% wt., the cannabinoids content was 0.67% wt., and the CBD content was 0.59% wt.