Ultrasound-assisted Extraction of Cannabinoids: Double the Yield in Half the Time
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A simple strategy for enhancing the efficacy of alcohol-based cannabis extraction has been described by a team of researchers based at Sopron University in Hungary. This is certainly not the first-time researchers have assessed and extolled the virtues of ultrasound-based extraction for botanicals but, does make a significant contribution to the fairly limited literature available specifically on its use for cannabis extraction. The goal of the study was to assess the effects of time, input power and solvent composition on extract properties to identify the optimal conditions for extracting compounds from the hemp plant matrix. Their findings were published in The Journal of Food Science.
Enhancing cannabis alcohol extraction
Many cannabis extraction methods exist for creating marijuana concentrates. From the ancient craft of creating hashish to modern approaches like supercritical CO2 and hydrocarbon solvent extraction, each technique has its own benefits and pitfalls. Despite the myriad of methods and setups, simple alcohol-based extraction continues to prove popular for producers of all sizes. Extractors opt for alcohols like ethanol because they are cheap, safe, easy to handle and very effective at extracting desirable compounds from plant material. That’s not to say that alcohol extraction is without it’s challenges. It’s polarity, for example, means that it mixes with water and dissolves water-soluble molecules like chlorophyll which must then be removed to avoid creating a bitter extract. As with any extraction process, there is always a demand to reduce costs and runtime and improve the extraction of desirable compounds. The team at Sopron University set out to take a simple alcohol extraction setup and enhance its performance with the addition of an ultrasonicator.
Corresponding author Professor Levente Csoka of the Institute of Wood Based Products and Technologies explained “Ultrasonication is a relatively inexpensive and simple technique to use considering the small amounts of solvents needed for extraction. We believe it can be used to reduce runtime and the energy required compared to other conventional techniques such as Soxhlet extraction, maceration and hydro-distillation, which are both laborious and time-consuming.” In simple terms, ultrasonication aids extraction via the rapid formation of microbubbles which then violently collapse. Known as cavitation, this causes tiny localised hotspots with temperatures of the order of 104 K and pressures as high as 103 bar. These extreme conditions disrupt the cell wall and allow target compounds to dissolve into the solvent more readily.
Prof. Csoka went on to say “Ultrasonic-based extraction techniques have already been applied to a number of plants, such as Curcuma amada, Ocimum tenuiflorum and vanilla pods, as well as bioproducts such as strawberries, citrus peels and carrot residues. As far as cannabis is concerned, a few reports are available on its ultrasonic extraction, but extraction from inﬂorescence has not been considered .”
The idea behind this research was to enable the transfer of a well-established extraction technique for other botanical products into the cannabis industry.
Developing an ultrasonic extraction method
The end goal of the research was to identify the optimal setup for ultrasound-assisted extraction. This hinged on testing the impact of adjusting three independent factors, namely time, input power and solvent concentration. Methanol was selected as the solvent due to its compatibility with the desired extract components. Professor Csoka explained “The polarity of the solvent significantly affects the extraction process. Methanol is a proven solvent for the extraction of polyphenols, flavones, terpenoids, etc. But, it would be interesting to study the influence of changing the extraction solvent to see what affect it has on the properties of the extract.” In this case the team opted to test their technique on industrial hemp which has a very low concentration of the main psychoactive component of cannabis, ∆9-THC. But, they were keen to highlight that this technique can just as easily be applied to any cannabis chemotype.
Focusing on the highlights of the study, ultrasonication was found to have a significant beneficial impact on extraction across the board. Demonstrating the potential of this approach, ultrasonic extraction done for just 15 minutes doubled extraction efficiency compared to a 30 minute control extraction. In particular, the extraction of cannabinoids was enhanced considerably - as confirmed by high-performance liquid chromatography coupled to diode array and mass spectrometry detectors (HPLC-DAD MS/MS) analysis.
In summary of their findings and the benefits of ultrasonication, the team said “What we have found can be attributed to more effective mixing, faster energy transfer and reduced thermal gradients during the process. As added benefits, the equipment size is small compared to other extraction techniques, responds rapidly to changes to process parameters and is quick to start up - all leading to increased production and the elimination of process steps.”
At this stage though, not everything is clear. The potential negative impacts of ultrasonic must also be considered. Professor Csoka explained “The thermal stability of the compounds of interest must be considered. As for cannabinoids, the acidic ones are more susceptible to degradation than the neutral ones. At high ultrasonic powers and long sonication times, degradation of these thermolabile compounds may occur considering the extremely high temperatures attained inside the cavitation bubble. On the other hand, there may be compounds, which require the kind of extreme conditions of ultrasound to be separated from the plant matrix and dissolved into the extraction solvent.”
Meeting the global demand for cannabis extracts
The team at Sopron are now planning to build on this initial success. This was in fact their first foray into botanical extraction and cannabis research – usually they focus on cellulose composites and their functional modifications. Prof. Csoka said “For us, the next step may be to look into the applications of the extracted cannabinoids by their separation and immobilization into a suitable matrix or, by using them as a green chemical (reducing agents) to create nanoparticles.”
With the rapid increase in demand for cannabis extracts, this paper highlights a real opportunity for the optimization of alcohol-based extraction in a growing global market. Simplicity and ease of use may prove to be big draws for this technology. The major operating parameters time/temperature, power/amplitude, frequency, solvent composition and solute to solvent ratio can all be easily tuned as required, thus making this a very accessible solution. However, whether this approach can be scaled up to mass production quantities remains to be seen.