Microbial load of the hemp and of its cannabinoid rich extracts after supercritical and ethanolic extraction: Importance of the hemp moisture

There is great interest in hemp cultivation to obtain an oil rich in cannabinoids. Cannabidiol (CBD) is the most sought after because it has remarkable medicinal properties. But hemp crops are sometimes improperly dried, leading to excessive bacteria and moulds growth during storage, which jeopardizes the microbiological quality of the oil. As a result, the crop must be discarded with a large economic impact. In this work, the microbial load of hemp and the obtained cannabinoid rich oil was assessed after extractions using supercritical CO₂ and with three ethanol-based techniques (maceration, ultrasound, Soxhlet). Extremely high bioburden was found in the hemp, much of it sporulated forms that were difficult to inactivate. The microbial load of the exhausted hemp varied significantly depending on the extraction method, with ethanolic techniques achieving the highest reduction, while supercritical CO₂ ensured the complete elimination of fungi and enterobacteria. A clear relationship was found between higher hemp moisture and increased microbial inactivation during scCO₂ extraction. Fortunately, all extraction techniques yielded sterile extracts. Further, the concentration of cannabinoids, chlorophylls and polyphenols, and the antioxidant capacity of the extracts were evaluated to determine if excessive moisture in the hemp negatively impacted the composition of the oil. On the contrary, the extracts were enriched in cannabinoids. Interestingly, the most concentrated oil (74 % total cannabinoids) was obtained from wet hemp by supercritical extraction. During this latter technique, part of the hemp moisture was removed, and the exhausted hemp was solvent-free, easing its future valorisation. Based on production costs, supercritical extraction was more profitable. Consequently, this work demonstrates that wet, highly biocontaminated hemp could still be a valuable raw material, and that supercritical extraction is the best technique to obtain a CBD oil of high quality from it.