Dr. Nari Nayini, Vu Lam, George Wharam, Derek Moy, Zachary Eisenberg
- Thermal rather than photodegradation was the more significant pathway for reduced potential THC.
- The most significant reductions in potential THC occurred in the first 30 days, regardless of storage conditions.
Cannabis (Cannabis sativa L) is an agricultural commodity that secretes a resin containing a specific class of terpenophenolic compounds called cannabinoids. Cannabinoids are relatively unstable and are known to change or degrade over time — however, limited research exists to determine the rate at which this occurs under different storage conditions. [1-5]
The most common cannabinoid produced in raw cannabis plants is tetrahydrocannabinolic acid (THCA), which has no intoxicating effects in and of itself when orally consumed. However, through a thermal and time dependent process called decarboxylation, THCA converts to tetrahydrocannabinol (Δ9-THC), a compound that provides the euphoric and intoxicating properties commonly associated with cannabis.
As with any agricultural consumable, cannabis has a limited shelf-life that is dependent on environmental factors during production, processing, packaging, storage, and distribution. The conversion of THCA to Δ9-THC is not necessarily problematic as this happens naturally when the plant is combusted and/or decarboxylated. But the degradation of Δ9-THC into cannabinol (CBN) and other degradants does reduce the ‘potency’ and thus, the value of the plant material.
Currently, shelf-life testing of cannabis products is not required by most regulatory bodies in the US. The California Department of Cannabis Control (DCC) permits cannabinoid label claim variance of 12% for edible products and 10% for flowers and other manufactured goods. However, these limits only apply to compliance batch testing performed prior to sale to the general public — a static point in time — and do not take into consideration the time or environmental effects the product will be subjected to prior to actual consumption.
Anresco designed this study to investigate the influence of temperature, light, and time on cannabinoid concentrations in cannabis trim. The THCA-dominant trim material was sourced locally from a San Francisco cannabis cultivator. All precautions were taken to create a homogeneous mix of the trim which was then split into 100-gram portions and packaged into two types of glass jars with screw caps — clear and amber. The jars were stored at three different temperatures: refrigerated (~4°C); ambient (~22°C); and high/abuse (~30°C). The samples were stored for seven durations of time: 0, 30, 60, 90, 150, 210, and 360 days. Triplicate sample jars of each type/temperature were analyzed at each of those time points — the average of which is reported in this study.
The 100-gram trim samples were homogenized using dry ice. Samples were ground to a powder which was transferred back to the original jar. After sublimation of the dry ice, a 0.50 mg sample was weighed into a 50-mL centrifuge tube, to which a 40 mL of 9:1 (v/v) methanol/chloroform extraction solvent was added. The centrifuge tube was vortexed for 10 seconds followed by sonication for 20 min at 50°C. Samples were allowed to equilibrate to room temperature for further serial dilutions of (1:10 dilution – 100 µL of extracted sample + 900 µL acetonitrile, for 1:100 dilution take 100 ul of 1:10 diluted sample + 900 µL of acetonitrile).
Chemicals and Reagents
Reference Materials for the below cannabinoids were purchased from Cayman Chemicals, Restek, Sigma Aldrich, and Cerilliant.
- ∆8 THC (delta-8-tetrahydrocannabinol)
- ∆9 THC (delta-9-tetrahydrocannabinol)
- THCA (tetrahydrocannabinolic acid)
- CBD (cannabidiol)
- CBDA (cannabidiolic acid)
- CBN (cannabinol)
- CBG (cannabigerol)
- CBC (cannabichromene)
Extraction reagents used (methanol, chloroform) were ACS grade or equivalent.
A run sequence for the LC-DAD (liquid chromatography with diode array detector) was set up in the following order:
- A mixed 5 ppm standard was used for conditioning.
- A five-point calibration curve was developed starting with the lowest concentration standard and followed by the subsequent standards of increasing concentrations of (1.0, 5.0, 10.0, 25.0, and 50.0 ug/mL for each compound).
- Blanks were used after concentrated samples to clean the column before the next sample.
- The standards were at least checked at 5, 10, 25 or 50 ppm at a minimum between every 10 samples.
A Shimadzu iNexera was used with a Restek Raptor C18 150mm x 4.6 x 2.7 um @ 40°C (VL 3/17/19). Sampling was performed using a Shimadzu LC-2040 Autosampler and the detector used was a Shimadzu LC-2040 Photo Diode Array set at 228 nm wavelength.
The mobile phase was: A) water with 0.1% formic acid + 0.5 MM ammonium formate and B) acetonitrile with 0.1% formic acid. Flow rate was Isocratic with a B concentration of 75%.
Identification and Quantification
Confirmation of identity requires that the retention time of the sample is within +/- 5% of the standard. The appropriate retention times and elution order for the cannabinoid compounds were:
|Cannabinoid||Retention Time (min)|
Figure 1: THCA Concentration, Storage Days, and Storage Temperatures (4, 20, 30°C) in both clear (upper panels) and amber (lower panels) vials.
THCA decreased over time in all storage conditions and temperatures. (Figure 1) The decarboxylation of THCA to Δ9-THC is temperature dependent and, as expected, the most rapid degradation of THCA was observed at the highest storage temperature of 30°C. At lower temperatures, the largest declines occurred in the first 30 days (~20% on average), followed by more modest declines over subsequent time intervals. Samples held at 4°C remained relatively stable (<25% degradation) until 210 days, regardless of jar storage. Samples held at 20°C, however, only remained stable until day 60 in clear jars and day 150 in amber jars.
Figure 2: Δ9-THC Concentrations, Storage Days, and Storage Temperatures (4, 20, 30°C)
Δ9-THC concentrations first increased and then decreased in all jar types and temperature conditions. (Figure 2) This phenomenon was most pronounced in samples held at higher temperature conditions — likely the result of initial decarboxylation of THCA to Δ9-THC, followed by degradation of Δ9-THC into CBN and other compounds.
Storage in amber jars resulted in significantly better retention of Δ9-THC irrespective of storage temperatures. In fact, the Δ9-THC concentrations in amber jars were positive relative to T=0 in all storage conditions except one (360 days, 4°C) and were 11.6% higher on average than the concentrations in clear jars.
Figure 3: CBN Concentration, Storage Days, and Storage Temperatures (4, 20, 30°C)
CBN content increased significantly over time and at a marginally higher rate in clear jars as compared to amber jars. (Figure 3) At higher temperatures the CBN increased significantly more compared to lower temperatures (~3x at 30°C and ~1.5x at 20°C relative to 4°C), showing that the degradation process of Δ9-THC to CBN is predominantly thermal and time dependent.
Figure 4: Total Potential THC Concentration, Storage Days, and Storage Temperatures (4, 20,30°C)
Total potential THC was calculated using the formula: Total THC = (0.877 * THCA) + Δ9-THC. On average samples held in amber jars degraded 2.6% less than those stored in clear jars. Samples stored at 4°C degraded 1.5% less than samples stored at 20°C and 3.5% less than samples stored at 30°C. Relative to time, however, these differences were trivial. By day 30, samples degraded 11.8% on average, and by day 360, samples degraded 34.6% on average.
The degradation of the original cannabinoid profile varied depending on how the samples were stored and for what duration of time.
Temperature strongly influenced the degradation of THCA to Δ9-THC, yet that did not materialize into statistically significant deviations in total potential THC through 90 days. (Figure 4) After 90 days, Δ9-THC degraded into CBN at a significantly higher rate in samples held at higher temperatures. In the final 3 testing periods, samples held at 4°C retained an average of 3.2% more total potential THC than samples held at 20°C, and 14.1% more total potential THC than samples held at 30°C.
Samples held in amber jars marginally reduced the rate of degradation of THCA to Δ9-THC, as well as the degradation of Δ9-THC to CBN. By day 360, samples held in amber jars retained 2.56% higher total potential THC than those held in clear jars.
Time was the most significant driver of potency degradation. By day 30, total potential THC decreased by an average of 11.83%, and by day 60 degradation of total potential THC exceeded 12.5% for every temperature and container condition. Again, for context, the California DCC requires relabeling of all products whose tested values exceed 10% variance from what is listed on its packaging.
If the value of a plant is defined by its concentration of total potential THC, it is best to sell/distribute/consume the material as soon as possible and within 30 days. If the material is to be stored for a significant amount of time, reduced temperature and exposure to light will slow the degradation pathways and provide increased retention of total potential THC.
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