ULTRASONIC-ASSISTED EXTRACTION IN CANNABIS
INDEX
1. Cannabis components 3
2. The extraction process 4
3. Extraction using sonication 4
4. Advantages and Disadvantages of ultrasonic extraction 5
1. Cannabis components
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Cannabis contains over 500 distinct compounds, which include cannabinoids,
terpenoids, flavonoids, and omega fatty acids. Terpenoids are the responsible
for the aroma of cannabis and other flowering plants. Cannabinoids are
compounds unique to cannabis, the most well known is THC (C 21H30O2), and
also the CBD (C21H26O2). The both of them can be obtain by using supercritical
process.
The major active principle in all cannabis products is Δ 9- tetrahydrocannabinol
(Δ9-THC or simply THC), also known by its International Non-Proprietary Name
(INN) as dronabinol. The unsaturated bond in the cyclohexene ring is located
between C-9 and C-10 in the more common dibenzopyran ring numbering
system. There are four stereoisomers of THC, but only the (–)-trans isomer
occurs naturally (CAS-1972-08-03).
The fully systematic name for this THC isomer is (−)-(6aR,10aR)-6,6,9-
trimethyl-3-pentyl- 6a,7,8,10a-tetrahydro-6H-benzo[c]chromen-1-ol. Two related
substances, Δ9- tetrahydrocannabinol-2-oic acid and Δ9-tetrahydrocannabinol-4-
oic acid (THCA), are also present in cannabis, sometimes in large amounts.
During smoking, THCA is partly converted to THC. The active isomer Δ 8-THC,
in which the unsaturated bond in the cyclohexene ring is located between C-8
and C-9, is found in much smaller amounts. The molecular formula of the THC
is C21H30O2.
In the plant, cannabinoids are synthesized and accumulated as cannabinoid
acids, but when the herbal product is dried, stored and heated, the acids
decarboxylize gradually into their proper forms, such as CBD or d-9-THC [De
Meijer et al. 2003]. Originally it was thought that CBD was the metabolic parent
to d-9-THC, but it was later found that its biosynthesis occurs according to a
genetically determined ratio [Russo and Guy, 2006]. Even though the chemical
structures of all four compounds are similar, their pharmacological effects can
be very different. The most researched compounds of the plant are d-9-THC
and CBD.
Other closely related substances that occur in cannabis include cannabidiol
(CBD) and, in aged samples, cannabinol (CBN), both of which have quite
different pharmacological effects to THC. Other compounds include the
cannabivarins and cannabichromenes; they are all collectively known as
cannabinoids. Unlike many psychoactive substances, cannabinoids are not
nitrogenous bases.
Terpenes are volatile organic compounds formed by the union of hydrocarbon
of 5 carbon atoms, known as isoprene. The smallest and most volatile
compounds are monoterpenes, which are biosynthesised by the union of two
isoprene molecules. The biggest and least volatile are biosynthesised by the
union of three or more isoprene molecules. The sesquiterpenes are next in the
chain, which are formed by the union of three isoprene molecules. Terpenes are
secondary metabolites, which provide the plant with its organoleptic
characteristics (aroma and flavour) and that constitutes most of the essential oil
produced by aromatic plants. Terpenes and cannabinoids share their
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biosynthetic pathways and, in fact, cannabinoids are terpeno-fenolic
compounds.
2. The extraction process
Liquid-liquid extraction is a unit operation frequently employed in the industry,
for recovery and purification of a desired ingredient from the solution in which it
was prepared. This process can also be used to eliminate impurities of the
streams.
Extraction is the removal of a soluble constituent from one liquid into another.
By convention, the first liquid is the feed (F) which contains the solute at an
initial concentration Xf The second liquid is the solvent (S) which is at least
partially immiscible with the feed (Todd, 2007).
According to David Todd, in his book “Fermentation and Biochemical
Engineering Handbook Principles, Process Design, and Equipment”, the solvent
does the extraction, so the solvent-rich liquid leaving the extractor is the extract
(E). With the solute partially or completely removed from the feed, the feed has
become refined so the feed-rich liquid leaving the extractor is the raffinate (R).
3. Extraction using sonication
This technique relies on the phenomenon of bubble formation and their violent
collapse called cavitation, which results in local hotspots with temperature of the
order of 104 K and pressure as high as 103 bar (Iskalieva et al., 2012). It allows
the target compounds to dissolve in the solvent by disrupting the cell wall, thus
enhancing yield in much lesser time (Shirsath, Sonawane, & Gogate, 2012).
ultrasonication facilitates faster mass and energy transfer, uniform mixing and
reduced thermal gradients, thus leading to shorter extraction times at lower
temperatures. Temperature, time, solvent, power, and frequency are the main
parameters affecting the efficiency of ultrasonication (Azmir et al., 2013). The
time and temperature can have either positive or negative impact on extraction
and hence, should be considered cautiously. Longer sonication time may result
in the degradation of some thermolabile compounds due to higher temperature.
Additionally, it also increases the energy and operational costs (Tomsik et al.,
2016).
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.
The technology behind ultrasonic extraction is anything but easy to understand.
In essence, sonication relies on ultrasonic waves. A probe is inserted into a
solvent mixture, and the probe then emits a series of high and low-pressure
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sound waves. This process essentially creates microscopic currents, eddies,
and pressurized streams of liquid, forming a particularly harsh environment.
These ultrasonic sound waves, which emit at a speed of up to 20,000 per
second, create an environment that breaks through cellular walls. The forces
which typically work to hold the cell together are no longer viable within the
alternating pressurized atmosphere created by the probe.
Millions upon millions of tiny bubbles are created, which subsequently pop,
leading to the complete breakdown of the protective cell wall. As the cell walls
break down, the inner materials are released directly into the solvent, thus
creating a potent emulsion.
4. Advantages and Disadvantages of ultrasonic extraction
Advantages:
A 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
It is a much more environmentally friendly extraction method that does
not rely on harsh solvents to extract the cannabinoid.
The extraction method can work with a variety of substances such as
ethanol, CO2, H2O, olive oil, coconut oil, and many others.
Preserves the integrity and concentration of the cannabinoids and
terpenes. Ultrasonic extractors do not require heat or pressure at all.
Disadvantages:
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
