Ultrasonic-Assisted Extraction of Cannabidiolic Acid from Cannabis Biomass

Summary

Ultrasonic-assisted extraction (UAE) increases extraction efficiency of solvents and when applied to Cannabis spp. biomass it reduces the time required for extraction. This decreases the cost and potential cannabinoid loss due to degradation. Additionally, UAE is considered a green method due to low solvent use.

Abstract

Industrial hemp (Cannabis spp.) has many compounds of interest with potential medical benefits. Of these compounds, cannabinoids have come to the center of attention, specifically acidic cannabinoids. The focus is turning toward acidic cannabinoids due to their lack of psychotropic activity. Cannabis plants produce acidic cannabinoids with hemp plants producing low levels of psychotropic cannabinoids. As such, utilization of hemp for acidic cannabinoid extraction would eliminate the need for decarboxylation prior to extraction as a source for the cannabinoids. The use of solvent-based extraction is ideal for obtaining acidic cannabinoids as their solubility in solvents such as supercritical CO₂ is limited due to the high pressure and temperature required to reach their solubility constants. An alternative method designed to increase solubility is ultrasonic-assisted extraction. In this protocol, the impact of solvent polarity (acetonitrile 0.46, ethanol 0.65, methanol 0.76, and water 1.00) and concentration (20%, 50%, 70%, 90%, and 100%) on ultrasonic-assisted extraction efficiency has been examined. Results show that water was the least effective and acetonitrile was the most effective solvent examined. Ethanol was further examined since it has the lowest toxicity and is generally regarded as safe (GRAS). Surprisingly, 50% ethanol in water is the most effective ethanol concentration for extracting the highest amount of cannabinoids from hemp. The increase in cannabidiolic acid concentration was 28% when compared to 100% ethanol, and 23% when compared to 100% acetonitrile. While it was determined that 50% ethanol is the most effective concentration for our application, the method has also been demonstrated to be effective with alternative solvents. Consequently, the proposed method is deemed effective and rapid for extracting acidic cannabinoids.

Introduction

Industrial hemp (Cannabis spp.) produces acidic cannabinoids in various plant tissues (flowers, leaves, and stems), with the highest concentration found in the flower¹. The Cannabis industry utilizes several methods to extract these compounds. One such method is solvent extraction that utilizes a non-polar and/or polar solvent, of which ethanol is the most commonly used. However, solvent extraction alone is limited in its ability; therefore, augmentative extraction techniques, such as microwave-assisted extraction (MAE) and ultrasonic-assisted extraction (UAE), are designed to increase the yield. In addition, high concentratio....

Protocol

1. Plant material preparation

1. Obtain Cherry Wine inflorescences from plants grown in the field, planted in a south-to-north configuration, with plants 1 m apart in center and rows 1.2 m apart (cultivation located in Longmont, Colorado, USA).
2. Air-dry the inflorescences at 35 °C for 48 h. Grind the inflorescences using a grinding machine set a 177 µm.
3. Pass the pulverized material through the No. 80 mesh sieve. Store the resulting powder in a sealed bag at room temperature for future use.

2. Ultrasound extraction

1. Weigh 0.5 g of the Cannabis ....

Results

The solvents utilized range from the middle of the polarity index (0.460 - ACN) to polar (1.000 - water). From Table 2, it can be seen that water did not make an effective extractant for cannabinoids, which is not unexpected, as cannabinoids have limited solubility in water due to their hydrophobicity¹³. In contrast to water, the other solvents had similar extracted values of CBD and CBDA, with the least polar solvent acetonitrile (ACN) having higher extraction when compared to th.......

Discussion

The polarity of a solvent plays a critical role in the effective extraction of compounds. Since acidic cannabinoids are slightly polar in nature, due in large part to the carboxylic acid moiety, it was assumed that a polar solvent such as methanol or ethanol would be most effective. Garrett and Hunt¹⁹, in their study using THC, demonstrated that solubility in aqueous ethanol was based on percent ethanol in the solution and ionic strength of the solution. While ionic strength was not examined in th.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Acetonitrile	J.K.Baker	9017-88	solvent
Cannabichromene	Cerilliant	C-143	Cannabinoids standard
Cannabidiol	Cerilliant	C-045	Cannabinoids standard
Cannabidiolic acid	Cerilliant	C-144	Cannabinoids standard
Cannabidivarin	Cerilliant	C-140	Cannabinoids standard
Cannabigerol	Cerilliant	C-141	Cannabinoids standard
Cannabinol	Cerilliant	C-046	Cannabinoids standard
Centrifuge	Hanil Scientific Inc	Supra 22K	Centrifuge
Cherry Wine hemp	CFH, Ltd.	-	Flower extraction material
Distilled water	TEDIA	WS2211-001	solvent
Ethanol	TEDIA	ES1431-001	solvent
Filter paper	Whatman	#2	Filtering
Grinder	Daesung Artlon	DA280-S	Milling
HPLC	Shimadzu	LC-10 system	Analysis of Cannabinoid
Methanol	TEDIA	MS1922-001	solvent
Minitab 16.2.0	Minitab Inc.
Syringe filters	Whatman	6779-1304	Filtering
Tetrahydrocannabivarin	Cerilliant	T-094	Cannabinoids standard
Trifluoroacetic acid	Sigma-aldrich	302031-1L	HPLC flow solvent
Untrasonic bath	Jinwoo	4020P	Ultrasonic extraction
Zorbax Eclipse plus C18 HPLC column	Agilent	9599990-902	HPLC column
Δ8 - Tetrahydrocannabinol	Cerilliant	T-032	Cannabinoids standard
Δ9 - Tetrahydrocannabinol	Cerilliant	T-005	Cannabinoids standard
Δ9 - Tetrahydrocannabinolic acid	Cerilliant	T-093	Cannabinoids standard