Cannabis is the genus of a plant that belongs to the Cannabaceae family, it has been used for medicinal purposes for millennia, its first use being described by the Chinese. The recent discovery of the endocannabinoid system has provided increased knowledge of the actions of Cannabis compounds in the human body. Endocannabinoids seem to act to control pain, muscle tone, inflammation, appetite, among other effects.
Cannabis contains over 100 different cannabinoid compounds and has the capacity for analgesia through neuromodulation of pain, for neuroprotection and anti-inflammatory mechanisms. Studies have shown the positive effects of different cannabinoids - Δ9-tetrahydrocannabinol (THC), cannabidiol (CBD), cannabinol (CBN), cannabichromene (CBC), cannabigerol (CBG) and cannabidivarin (CBDV) - of cannabis on human health. In addition, the entourage effect of cannabinoids associated with terpenes (α-pinene, β-pinene, β-myrcen, limonene, terpinolene, linalool, α-terpineol, β-, α-caryophylene humolene, caryophyllene oxide) existing in the plant, has also been the object of studies for presenting synergistic effects and superior performance than a single compound.
Extraction is essentially the first step in analyzing chemical compounds in plants. This step is necessary to extract the desired chemicals from plant materials for later use. Proper extraction must be carried out to ensure that the plant's chemical compounds are not destroyed during the extraction process.
Extraction processes have several applications in the chemical engineering, food and pharmaceutical industries, being mainly used in the recovery, isolation and separation of important components from a plant source, in addition to removing contaminants or unwanted compounds.
Studies show that extracts obtained from different subspecies of the Cannabis plant can lead to different effects on the health of the same individual. Studies also show that in addition to cannabinoid composition, plant subspecies also differ in relation to terpenes.
Regarding the extraction techniques commonly and currently used to obtain bioactive extracts from Cannabis plants, the following techniques stand out: hydrodistillation; steam distillation or water vapor drag distillation of essential oils; the extraction of organic compounds by organic solvent; extraction with cold fat (enfleurage); the maceration; microwave extraction; supercritical fluid extraction; extraction by mechanical stirring with a heating plate; extraction by winterization with reactors; percolation extraction; extraction by infusion and boiling; extraction by rotaevaporators; glycerin extraction; extraction through percolation using a heating plate and solvent; extraction via centrifugal partition chromatography; extraction by decoction using a hot plate with aqueous solvent until boiling and infusion and extraction assisted by ultrasound.
The most traditional and simplest method of extracting active compounds from herb species involves steeping in water until most of the ingredients are dissolved. For cannabinoid compounds, it is necessary to use alternative methods, employing organic solvents instead of water for the extraction, since the solubility of the main compounds is very low in polar solvents. The most commonly used solvents are organic substances such as ethanol, ether, chloroform, hexane and methanol.
When organic solvents are used for extraction, the product obtained consists of a combination of several compounds, including some undesirable substances that dissolve together with the cannabinoids. Furthermore, high boiling or extraction temperatures often lead to degradation of compounds that are sensitive to heat. These procedures can cause decarboxylation or degradation reactions and also the loss of terpenes.
Ultrasonic Assisted Extraction (UAE) uses ultrasound energy and solvents to extract specific compounds from various plant matrices. The ultrasound technique consists of mechanical waves with a frequency range (> 20 kHz) higher than the audible frequency range of human hearing (20 Hz to 20 kHz). These waves consist of a series of compression and rarefaction cycles that can be propagated through a solid, liquid or gaseous medium, inducing the displacement and removal of molecules from their original positions.
UAE is a process that uses acoustic energy and solvents to extract the compounds of interest from various plant matrices. Increased mass transfer is caused by liquid-induced acoustic cavitation, which is one of the beneficial effects of this technology.
Variables associated with UAE, such as frequency, potency, duty cycle, temperature, extraction time, the right type of solvent and the correct liquid-solid ratio, need precise control for an optimal extraction to be carried out. This can be a disadvantage in using UAE as a technique for extracting Cannabis components. The localized heating provided by this technique can lead to loss of terpenes.
Microwave Assisted Extraction (MAE) is a conventional technique for extracting active components from medicinal plants, which uses microwave energy to heat the solvents containing the samples to be analyzed, partitioning the analytes from the analyzed matrix. MAE's main advantage is its ability to rapidly heat the sample solvent mixture, resulting in its wide applicability for rapid analyte extraction.
Factors that affect the effectiveness of MAE techniques include time, temperature, the dielectric properties of the sample mixture, and the types of solvents used. Among other disadvantages of the MAE technique, we can also highlight the need for special equipment, the low selectivity and the inevitable reactions that occur at high temperatures, especially the loss of terpenes.
Hydrodistillation is an extraction method widely used in laboratories, where the Clevenger system is used. This system consists of immersing all the vegetable raw material in the solvent. The extraction, in turn, takes place at a temperature below 100ºC, which can make it slow, with lower yield, but avoids the loss of compounds sensitive to high temperatures. This method calls for the use of a hot plate. The biggest disadvantages of this technique are the long extraction time and the amount of solvents used.
Steam distillation or water vapor drag distillation of essential oils is a distillation that uses water vapor in immiscible substances, in general organic compounds, with the advantage that the mixture to be distilled boils below 100 °C. This method calls for the use of a hot plate. It also has the disadvantage of extraction time.
Cold fat extraction (enfleurage) is a cold extraction technique that involves placing layers of fresh flowers on wax on a glass plate. Every day this layer of flowers is replaced by new ones and, slowly, the wax extracts these aromatic components, being later filtered and distilled at a low temperature. As a disadvantage of this technique, the slowness of the extraction process stands out.
Medical Cannabis is consumed by patients using a wide variety of methods, including smoking, vaporizing and consuming infused oils or other edible products. One of the problems associated with smoking or vaporization is that the dose the patient receives is unreliable due to the variability of the plant product and the way patients inhale and retain the vapor. The use of steam and/or smoking also has a number of well-known negative health effects and is particularly undesirable for young patients. For this reason, the production of an extract that can be formulated in a variety of ways is becoming more popular.
Cannabinoids are non-polar compounds with low water solubility and can be extracted using a wide variety of different organic solvents, including hydrocarbons (e.g., ethyl ether) and alcohols (e.g., ethanol). Extractions using these solvents can be efficient, but depending on the final product, they may violate individual country regulations and may require additional testing. For example, residual solvents should be defined for drugs in accordance with good manufacturing practices (GMP).
These solvents can also be expensive and, due to their toxicity, environmental risk and flammability, are less desirable when extractions are conducted on a large scale.
Supercritical fluid extraction (SFE) can eliminate the need for these organic solvents when manufacturing medical cannabis extracts. Carbon dioxide (CO2) is the main solvent in SFE. It has GRAS status (generally recognized as safe) and evaporates from the extract when exposed to normal atmospheric conditions.
Carbon dioxide is non-flammable, relatively inert, plentiful and inexpensive. It can be kept in a liquid state even when its temperature is increased to a limit point called the critical point. Beyond this point, condensation is not possible, even with increasing pressure to extremely high values. The fluid assumes the so-called supercritical state (SCF). SCFs have greater compressibility than liquids but have similar densities to liquids.
The concept of critical temperature is defined as a temperature above which a substance in a gaseous state cannot be liquefied by compression. This concept was described experimentally nearly two centuries ago. It was later discovered that by increasing the temperature of these substances to values equal to or above their critical temperature and pressure, they could be used as sophisticated solvents for extracting and fractionating complex mixtures. An attractive feature of SCFs over conventional solvents is that solvent power can be varied by manipulating temperature and pressure above the critical point. In particular, CO2 has a critical temperature of 31.1 °C and a critical pressure of 73.7 bar. These conditions are experimentally easy to achieve.
In CO2 supercritical fluid extraction, the fluid mainly extracts the essential oils from Cannabis, in a similar way to what organic solvents do. This method is unique as it has the characteristics of a supercritical fluid that has liquid and gaseous properties. In this technique, the extracts are left with more terpenes (up to 10%).
CO2 has selectivity in the extraction of non-polar compounds, being the most suitable for obtaining terpenes and cannabinoids. Another important point that should be highlighted is the possibility of modulating the extraction conditions to obtain fractions of specific extracts, that is, by changing the process pressure and temperature conditions we can obtain extracts rich in different compounds, such as terpenes, fatty acids, chlorophyll and cannabinoids (CBD, CBDA, CBG, CBGA, CBN and THC).
Due to the fact that it does not use organic solvents and because it presents a higher yield in the concentration of terpenes, the extraction by supercritical fluid CO2 has become the most sought-after extraction technique today. In this sense, the company Piauhy Labs, which is a company based in Portugal, has as purpose the development and commercialization of personalized bioactive extracts of Cannabis through the extraction with supercritical CO2, where we will have a higher concentration of terpenes in the extracts obtained from the extractions. We will also research terpenes that have a lower intensity in the plant and identify them. Subsequently, Piauhy Labs intends to obtain a Certification of compliance with Good Laboratory Practices, in accordance with the principles of the OECD, for the pharmaceutical area, so that the results obtained from its research are properly used for the granting of licenses or for the registration of pharmaceutical products, including medicines for human use and similar products. As a result of the intended investigation and extraction processes, Piauhy Labs intends to create patents and originate intellectual property, with the ultimate goal of producing innovative medicines. medicines that improve the quality of life of patients, medicines that improve the health of the population in general.
Elmo Resende, Ph.D
Director of R&D
Piauhy Labs
References
Aladic, K. et al. Cold Pressing and Supercritical CO2 Extraction of Hemp (Cannabis sativa) Seed Oil. Chem. Biochem. Eng. Q. 28, 481–490, 2014.
Bojczuk, M.; Żyżelewicz, D. and Hodurek, P. Centrifugal partition chromatography – a review of recent applications and some classic references. Journal of Separation Science 40(7), 1597-1609, 2017.
Citti, C.; Linciano, P.; Russo, F. et al. A novel phytocannabinoid isolated from Cannabis sativa L. with an in vivo cannabimimetic activity higher than Δ9-tetrahydrocannabinol: Δ9-Tetrahydrocannabiphorol. Sci Rep 9, 20335, 2019.
Da Porto, C.; Decorti, D. and Natolino, A. Separation of aroma compounds from industrial hemp inflorescences (Cannabis sativa L.) by supercritical CO2 extraction and on-line fractionation. Industrial Crops and Products 58, 99–103, 2014.
Franco, R.; Rivas-Santisteban, R.; Reyes-Resina, I.; Casanovas, M.; Perez-Olives, C.; Ferreiro-Vera, C.; Navarro, G.; de Medina, V. S. and Nadal, X. Biological potential of varinic-, minor-, and acidic phytocannabinoids. Pharmacological Research, 2000.
Hazekamp, A.; Simons, R.; Peltenburg‐Looman, A.; Sengers, M.; Zweden, R. V. and Verpoorte, R. Preparative Isolation of Cannabinoids from Cannabis sativa by Centrifugal Partition Chromatography. Journal of Liquid Chromatography & Related Technologies, 27:15, 2421-2439, 2004.
Jone, O.; Maitane, O.; Mikel, A. and Etxebarria, N. Optimisation and characterisation of marihuana extracts obtained by supercritical fluid extraction and focused ultrasound extraction and retention time locking GC-MS. Journal of Separation Science 36(8), 1397–1404, 2013.
K. ALADIĆ et al., Cold Pressing and Supercritical CO2 Extraction of Hemp (Cannabis sativa) seed Oil. Chem. Biochem. Eng. Q. 28 (4) 481–490, 2014.
Micalizzi, G.; Vento, F.; Alibrando, F.; Donnarumma, D.; Dugo, P. and Mondello, L. Cannabis Sativa L.: a comprehensive review on the analytical methodologies for cannabinoids and terpenes characterization. Journal of Chromatography A, 1637, 461864, 2021.
Monton, C.; Madaka, F.; Settharaksa, S.; Wunnakup, P.; Suksaeree, J. and Songsak, T. Optimal condition of cannabis maceration to obtain the high cannabidiol and Δ9 -tetrahydrocannabinol content. An. Acad. Bras. Cienc. 91: e20190676, 2019.
Perrotin-Brunel, H.; Perez, P. C.; Roosmalen, M. J. E. V.; Spronsen, J. V.; Witkamp, G. J. and Peters, C. J. Solubility of Δ9-tetrahydrocannabinol in supercritical carbon dioxide: Experiments and modeling. The Journal of Supercritical Fluids 52(1), 6–10, 2010.
Ramirez, C. L. [Studies in Natural Products Chemistry] Volume 61, Cannabinoids: Extraction Methods, Analysis, and Physicochemical Characterization, 143–173, 2018.
Rožanc, J.; Kotnik, P.; Milojevi´c, M.; Gradišnik, L.; Hrnˇciˇc, M. K.; Knez, Ž. and Maver, U. Different Cannabis sativa Extraction Methods Result in Different Biological Activities against a Colon Cancer Cell Line and Healthy Colon Cells. Plants 10, 566, 2021.
Ternelli, M.; Brighenti, V.; Anceschi, L.; Poto, M.; Bertelli, D.; Licata, M: and Pellati, F. Innovative methods for the preparation of medical Cannabis oils with a high content in both cannabinoids and terpenes. Journal of Pharmaceutical and Biomedical Analysis 186, 113296, 2020.
Cannabis is the genus of a plant that belongs to the Cannabaceae family, it has been used for medicinal purposes for millennia, its first use being described by the Chinese. The recent discovery of the endocannabinoid system has provided increased knowledge of the actions of Cannabis compounds in the human body. Endocannabinoids seem to act to control pain, muscle tone, inflammation, appetite, among other effects.
Cannabis contains over 100 different cannabinoid compounds and has the capacity for analgesia through neuromodulation of pain, for neuroprotection and anti-inflammatory mechanisms. Studies have shown the positive effects of different cannabinoids - Δ9-tetrahydrocannabinol (THC), cannabidiol (CBD), cannabinol (CBN), cannabichromene (CBC), cannabigerol (CBG) and cannabidivarin (CBDV) - of cannabis on human health. In addition, the entourage effect of cannabinoids associated with terpenes (α-pinene, β-pinene, β-myrcen, limonene, terpinolene, linalool, α-terpineol, β-, α-caryophylene humolene, caryophyllene oxide) existing in the plant, has also been the object of studies for presenting synergistic effects and superior performance than a single compound.
Extraction is essentially the first step in analyzing chemical compounds in plants. This step is necessary to extract the desired chemicals from plant materials for later use. Proper extraction must be carried out to ensure that the plant's chemical compounds are not destroyed during the extraction process.
Extraction processes have several applications in the chemical engineering, food and pharmaceutical industries, being mainly used in the recovery, isolation and separation of important components from a plant source, in addition to removing contaminants or unwanted compounds.
Studies show that extracts obtained from different subspecies of the Cannabis plant can lead to different effects on the health of the same individual. Studies also show that in addition to cannabinoid composition, plant subspecies also differ in relation to terpenes.
Regarding the extraction techniques commonly and currently used to obtain bioactive extracts from Cannabis plants, the following techniques stand out: hydrodistillation; steam distillation or water vapor drag distillation of essential oils; the extraction of organic compounds by organic solvent; extraction with cold fat (enfleurage); the maceration; microwave extraction; supercritical fluid extraction; extraction by mechanical stirring with a heating plate; extraction by winterization with reactors; percolation extraction; extraction by infusion and boiling; extraction by rotaevaporators; glycerin extraction; extraction through percolation using a heating plate and solvent; extraction via centrifugal partition chromatography; extraction by decoction using a hot plate with aqueous solvent until boiling and infusion and extraction assisted by ultrasound.
The most traditional and simplest method of extracting active compounds from herb species involves steeping in water until most of the ingredients are dissolved. For cannabinoid compounds, it is necessary to use alternative methods, employing organic solvents instead of water for the extraction, since the solubility of the main compounds is very low in polar solvents. The most commonly used solvents are organic substances such as ethanol, ether, chloroform, hexane and methanol.
When organic solvents are used for extraction, the product obtained consists of a combination of several compounds, including some undesirable substances that dissolve together with the cannabinoids. Furthermore, high boiling or extraction temperatures often lead to degradation of compounds that are sensitive to heat. These procedures can cause decarboxylation or degradation reactions and also the loss of terpenes.
Ultrasonic Assisted Extraction (UAE) uses ultrasound energy and solvents to extract specific compounds from various plant matrices. The ultrasound technique consists of mechanical waves with a frequency range (> 20 kHz) higher than the audible frequency range of human hearing (20 Hz to 20 kHz). These waves consist of a series of compression and rarefaction cycles that can be propagated through a solid, liquid or gaseous medium, inducing the displacement and removal of molecules from their original positions.
UAE is a process that uses acoustic energy and solvents to extract the compounds of interest from various plant matrices. Increased mass transfer is caused by liquid-induced acoustic cavitation, which is one of the beneficial effects of this technology.
Variables associated with UAE, such as frequency, potency, duty cycle, temperature, extraction time, the right type of solvent and the correct liquid-solid ratio, need precise control for an optimal extraction to be carried out. This can be a disadvantage in using UAE as a technique for extracting Cannabis components. The localized heating provided by this technique can lead to loss of terpenes.
Microwave Assisted Extraction (MAE) is a conventional technique for extracting active components from medicinal plants, which uses microwave energy to heat the solvents containing the samples to be analyzed, partitioning the analytes from the analyzed matrix. MAE's main advantage is its ability to rapidly heat the sample solvent mixture, resulting in its wide applicability for rapid analyte extraction.
Factors that affect the effectiveness of MAE techniques include time, temperature, the dielectric properties of the sample mixture, and the types of solvents used. Among other disadvantages of the MAE technique, we can also highlight the need for special equipment, the low selectivity and the inevitable reactions that occur at high temperatures, especially the loss of terpenes.
Hydrodistillation is an extraction method widely used in laboratories, where the Clevenger system is used. This system consists of immersing all the vegetable raw material in the solvent. The extraction, in turn, takes place at a temperature below 100ºC, which can make it slow, with lower yield, but avoids the loss of compounds sensitive to high temperatures. This method calls for the use of a hot plate. The biggest disadvantages of this technique are the long extraction time and the amount of solvents used.
Steam distillation or water vapor drag distillation of essential oils is a distillation that uses water vapor in immiscible substances, in general organic compounds, with the advantage that the mixture to be distilled boils below 100 °C. This method calls for the use of a hot plate. It also has the disadvantage of extraction time.
Cold fat extraction (enfleurage) is a cold extraction technique that involves placing layers of fresh flowers on wax on a glass plate. Every day this layer of flowers is replaced by new ones and, slowly, the wax extracts these aromatic components, being later filtered and distilled at a low temperature. As a disadvantage of this technique, the slowness of the extraction process stands out.
Medical Cannabis is consumed by patients using a wide variety of methods, including smoking, vaporizing and consuming infused oils or other edible products. One of the problems associated with smoking or vaporization is that the dose the patient receives is unreliable due to the variability of the plant product and the way patients inhale and retain the vapor. The use of steam and/or smoking also has a number of well-known negative health effects and is particularly undesirable for young patients. For this reason, the production of an extract that can be formulated in a variety of ways is becoming more popular.
Cannabinoids are non-polar compounds with low water solubility and can be extracted using a wide variety of different organic solvents, including hydrocarbons (e.g., ethyl ether) and alcohols (e.g., ethanol). Extractions using these solvents can be efficient, but depending on the final product, they may violate individual country regulations and may require additional testing. For example, residual solvents should be defined for drugs in accordance with good manufacturing practices (GMP).
These solvents can also be expensive and, due to their toxicity, environmental risk and flammability, are less desirable when extractions are conducted on a large scale.
Supercritical fluid extraction (SFE) can eliminate the need for these organic solvents when manufacturing medical cannabis extracts. Carbon dioxide (CO2) is the main solvent in SFE. It has GRAS status (generally recognized as safe) and evaporates from the extract when exposed to normal atmospheric conditions.
Carbon dioxide is non-flammable, relatively inert, plentiful and inexpensive. It can be kept in a liquid state even when its temperature is increased to a limit point called the critical point. Beyond this point, condensation is not possible, even with increasing pressure to extremely high values. The fluid assumes the so-called supercritical state (SCF). SCFs have greater compressibility than liquids but have similar densities to liquids.
The concept of critical temperature is defined as a temperature above which a substance in a gaseous state cannot be liquefied by compression. This concept was described experimentally nearly two centuries ago. It was later discovered that by increasing the temperature of these substances to values equal to or above their critical temperature and pressure, they could be used as sophisticated solvents for extracting and fractionating complex mixtures. An attractive feature of SCFs over conventional solvents is that solvent power can be varied by manipulating temperature and pressure above the critical point. In particular, CO2 has a critical temperature of 31.1 °C and a critical pressure of 73.7 bar. These conditions are experimentally easy to achieve.
In CO2 supercritical fluid extraction, the fluid mainly extracts the essential oils from Cannabis, in a similar way to what organic solvents do. This method is unique as it has the characteristics of a supercritical fluid that has liquid and gaseous properties. In this technique, the extracts are left with more terpenes (up to 10%).
CO2 has selectivity in the extraction of non-polar compounds, being the most suitable for obtaining terpenes and cannabinoids. Another important point that should be highlighted is the possibility of modulating the extraction conditions to obtain fractions of specific extracts, that is, by changing the process pressure and temperature conditions we can obtain extracts rich in different compounds, such as terpenes, fatty acids, chlorophyll and cannabinoids (CBD, CBDA, CBG, CBGA, CBN and THC).
Due to the fact that it does not use organic solvents and because it presents a higher yield in the concentration of terpenes, the extraction by supercritical fluid CO2 has become the most sought-after extraction technique today. In this sense, the company Piauhy Labs, which is a company based in Portugal, has as purpose the development and commercialization of personalized bioactive extracts of Cannabis through the extraction with supercritical CO2, where we will have a higher concentration of terpenes in the extracts obtained from the extractions. We will also research terpenes that have a lower intensity in the plant and identify them. Subsequently, Piauhy Labs intends to obtain a Certification of compliance with Good Laboratory Practices, in accordance with the principles of the OECD, for the pharmaceutical area, so that the results obtained from its research are properly used for the granting of licenses or for the registration of pharmaceutical products, including medicines for human use and similar products. As a result of the intended investigation and extraction processes, Piauhy Labs intends to create patents and originate intellectual property, with the ultimate goal of producing innovative medicines. medicines that improve the quality of life of patients, medicines that improve the health of the population in general.
Elmo Resende, Ph.D
Director of R&D
Piauhy Labs
References
Aladic, K. et al. Cold Pressing and Supercritical CO2 Extraction of Hemp (Cannabis sativa) Seed Oil. Chem. Biochem. Eng. Q. 28, 481–490, 2014.
Bojczuk, M.; Żyżelewicz, D. and Hodurek, P. Centrifugal partition chromatography – a review of recent applications and some classic references. Journal of Separation Science 40(7), 1597-1609, 2017.
Citti, C.; Linciano, P.; Russo, F. et al. A novel phytocannabinoid isolated from Cannabis sativa L. with an in vivo cannabimimetic activity higher than Δ9-tetrahydrocannabinol: Δ9-Tetrahydrocannabiphorol. Sci Rep 9, 20335, 2019.
Da Porto, C.; Decorti, D. and Natolino, A. Separation of aroma compounds from industrial hemp inflorescences (Cannabis sativa L.) by supercritical CO2 extraction and on-line fractionation. Industrial Crops and Products 58, 99–103, 2014.
Franco, R.; Rivas-Santisteban, R.; Reyes-Resina, I.; Casanovas, M.; Perez-Olives, C.; Ferreiro-Vera, C.; Navarro, G.; de Medina, V. S. and Nadal, X. Biological potential of varinic-, minor-, and acidic phytocannabinoids. Pharmacological Research, 2000.
Hazekamp, A.; Simons, R.; Peltenburg‐Looman, A.; Sengers, M.; Zweden, R. V. and Verpoorte, R. Preparative Isolation of Cannabinoids from Cannabis sativa by Centrifugal Partition Chromatography. Journal of Liquid Chromatography & Related Technologies, 27:15, 2421-2439, 2004.
Jone, O.; Maitane, O.; Mikel, A. and Etxebarria, N. Optimisation and characterisation of marihuana extracts obtained by supercritical fluid extraction and focused ultrasound extraction and retention time locking GC-MS. Journal of Separation Science 36(8), 1397–1404, 2013.
K. ALADIĆ et al., Cold Pressing and Supercritical CO2 Extraction of Hemp (Cannabis sativa) seed Oil. Chem. Biochem. Eng. Q. 28 (4) 481–490, 2014.
Micalizzi, G.; Vento, F.; Alibrando, F.; Donnarumma, D.; Dugo, P. and Mondello, L. Cannabis Sativa L.: a comprehensive review on the analytical methodologies for cannabinoids and terpenes characterization. Journal of Chromatography A, 1637, 461864, 2021.
Monton, C.; Madaka, F.; Settharaksa, S.; Wunnakup, P.; Suksaeree, J. and Songsak, T. Optimal condition of cannabis maceration to obtain the high cannabidiol and Δ9 -tetrahydrocannabinol content. An. Acad. Bras. Cienc. 91: e20190676, 2019.
Perrotin-Brunel, H.; Perez, P. C.; Roosmalen, M. J. E. V.; Spronsen, J. V.; Witkamp, G. J. and Peters, C. J. Solubility of Δ9-tetrahydrocannabinol in supercritical carbon dioxide: Experiments and modeling. The Journal of Supercritical Fluids 52(1), 6–10, 2010.
Ramirez, C. L. [Studies in Natural Products Chemistry] Volume 61, Cannabinoids: Extraction Methods, Analysis, and Physicochemical Characterization, 143–173, 2018.
Rožanc, J.; Kotnik, P.; Milojevi´c, M.; Gradišnik, L.; Hrnˇciˇc, M. K.; Knez, Ž. and Maver, U. Different Cannabis sativa Extraction Methods Result in Different Biological Activities against a Colon Cancer Cell Line and Healthy Colon Cells. Plants 10, 566, 2021.
Ternelli, M.; Brighenti, V.; Anceschi, L.; Poto, M.; Bertelli, D.; Licata, M: and Pellati, F. Innovative methods for the preparation of medical Cannabis oils with a high content in both cannabinoids and terpenes. Journal of Pharmaceutical and Biomedical Analysis 186, 113296, 2020.