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Ultrasound-Assisted Extraction is Ideal to Prepare Solid Edibles For Testing, Study Finds

By Alexander Beadle

Published: Sep 30, 2022   

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Use ultrasound-assisted extraction to prepare solid edibles for analysis, and use solid-phase extraction for beverages, scientists recommend.

In a new study, currently available in pre-proof in the Journal of Food Composition and Analysis, researchers from European University Cyprus and the University of Cyprus tested a variety of common extraction methodologies used to prepare cannabis edibles for analysis.

In contrast to previous work endorsing the use of Soxhlet extraction, this new study found that ultrasound-assisted extraction (UAE) recovered the greatest yields in samples of cannabis chocolate, hemp tea, and hemp seeds. For cannabis beverages, including cannabis beer and energy drink, solid-phase extraction (SPE) was just as effective as UAE.

The researchers also report a faster method for liquid chromatography-mass spectroscopy (LC-MS) for the quantitative analysis of seven important cannabinoids in cannabis edibles, which can be completed within ten minutes and used in tandem with the UAE and SPE extraction procedures.

Analyzing edibles

Being able to accurately quantify the levels of cannabinoids present in edible cannabis products is an important element of regulating this emerging sector. While cannabis-infused foods are still prohibited in many jurisdictions, those that do allow them often impose certain limits on the levels of THC that are allowed to be present.

To make sure that these products are complying with regulation, scientists need to be able to effectively extract and quantify cannabinoids of interest from these edible foodstuffs. Separating out the mostly nonpolar cannabinoids from matrices that can include nonpolar fats, as well as other sugars, flavorings, or milk solids, is understandably a difficult task.

Currently, there is no standardized method for such extractions on cannabis foods, though supercritical fluid extraction (SFE), Soxhlet extraction, microwave-assisted extraction, ultrasound-assisted extraction (UAE), and solid-phase extraction (SPE) are all in use to some degree. In terms of analysis, LC-MS is a common approach.

UAE for solid samples

To evaluate the effectiveness of Soxhlet extraction and UAE in solid samples of cannabis-infused chocolate, hemp seeds, hemp tea, and cannabis-based coffee, the researchers spiked samples of each with an internal standard solution containing seven well-known cannabinoids.

In the Soxhlet technique, the spiked samples were placed in a refluxing methanol solvent for fourteen hours. The resulting extract was dried, redissolved in methanol, filtered, and then injected into the fast LC-MS system for analysis.

For UAE, standard-spiked samples were mixed with methanol and placed in a vial in an ultrasonic bath. This ultrasonic bath was used in a pulse-mode for a total of 40 minutes (15 minutes of pulsing, a 10 minute break, and a final 15 minutes of pulsing) before the contents of the vial were prepared similarly for LC-MS.

The researchers found that higher recoveries were obtained using UAE (between 70-110%) than the Soxhlet (40-93%) method. The researchers attribute the recoveries greater than 100% to the thermal and mechanical effects of acoustic cavitation, where microbubbles form and collapse when liquid is irradiated by intense ultrasound.

They also found that the UAE method was able to recover six of the seven cannabinoids contained in the internal standard mixture for the chocolate and tea samples and four in the hemp seed samples. In contrast, Soxhlet extraction recovered four cannabinoids in one chocolate sample and two cannabinoids in another. For the hemp seed samples, the Soxhlet technique actually recovered five cannabinoids compared to UAE’s four, however the actual percentage recovery was significantly lower across all standards.

Analyze beverages using SPE

In the liquid samples of cannabis beer and energy drink, UAE was compared against SPE.

For this SPE procedure, samples were passed through a commercially available SPE cartridge that had been activated by washing with methanol, water, and ammonium acetate. After this, samples of beer and energy drink were spiked with internal standards, loaded into the column, and passed through the cartridge. To remove unwanted substances, the cartridge was washed with hydrochloric acid, with methanol used to elute the final extract.

Once again, ultrasonication treatment with UAE performed well, recovering six cannabinoids in the energy drink samples and four in the beer samples, all with recovery values of around 85%.

The SPE procedure also demonstrated recovery values of up to 85%. However, SPE was able to recover all seven cannabinoids from the energy drink samples and five from the beer.

“Considering all the above, it was concluded that UAE was the most appropriate method for extracting cannabinoids from solid food matrices. On the other hand, the SPE procedure proved to be more suitable for the preparation of liquid samples,” the researchers wrote.

“Unfortunately, the recovery values obtained using the Soxhlet apparatus were extremely low (in many cases they even reached ~40.0%), proving its ineffectiveness in processing cannabis-based products.”

Real-world sample tests reveal concerns over THC content

To confirm the results seen in these experiments, and to determine the real cannabinoid content in the un-spiked versions of products used in this study, the researchers also carried out a series of tests using a previously described high performance liquid chromatography-mass spectrometry (HPLC-MS) method, UAE, and SPE.

They found that CBD was the most abundant cannabinoid found in these products, followed by CBG. Delta-9 THC was found in five of the cannabis-based products tested, despite the suppliers of these products all claiming that the products were free from this intoxicating cannabinoid.

“In some cases, the Δ9-THC content exceeded the maximum permissible value set by EFSA [European Food Safety Authority] and the Government of Cyprus and, therefore, the ‘THC-free’ label, found on hemp-based food products, can often mislead the consumer,” the researchers wrote.

There was a notable absence of delta-9 THC in any of the cannabis beer or energy drink samples, and in the coffee beans. The lack of THC in the beverages could be explained by the fact that these products tend to only contain cannabis aroma compounds, the researchers suggest, and are not infused with cannabis oil or mixed with plant leaves.

 

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