Quantifying Terpenes: An Introduction into Botanical Flower Metrics

It's a unique plant in its ability to produce aromas and flavors with remarkable depth and complexity.  Because of this, many different strains with incredibly diverse aromas have evolved over time due to the diligent work of cultivators around the world. Although the aroma properties of cannabis have been investigated to some degree in the past, there is a lack of understanding on the origins of many from a chemistry standpoint. We aim to bridge this gap and relate our discoveries in easy-to-understand metrics that will help guide users and cultivators alike.

Our Terpene Technology

Abstrax tech has ignited an effort to comprehensively understand the aroma properties of cannabis and the chemical compounds leading to specific scents and effects. To this end, we have invested heavily in research and development analytical equipment, including a 2-dimensional gas chromatographic system coupled with mass spectrometry (Figure 1). This instrument can measure the aromas of cannabis, determine what they are, and how much are present.

 Figure 1. Abstrax Tech Instrument room housing 2-dimensional gas chromatographic system.

Compared with traditional 1-dimensional gas chromatography – a method commonly used in analytical labs – 2-dimensional gas chromatography (2DGC) allows for much better separation of compounds (Figure 2), a requirement to correctly identify and quantify them. In short, the operating principle in 2DGC is to first separate compounds by molecular size (x-axis in Figure 2, right) followed by separation of these compounds further by polarity (y-axis in Figure 2, right). This allows for much easier and more accurate identification of each compound compared with a simple 1-dimensional chromatogram (Figure 2, left). We can then analyze the 2D data in 3D to determine how much of each compound exists (Figure 2, bottom): The size of a peak corresponds to the quantity of a given compound.

Figure 2. Left: chromatogram obtained from traditional 1-dimensional gas chromatography. Right: Chromatogram obtained from 2-dimensional gas chromatography. Each spot represents an individual compound. Over 300 compounds have been found in some cannabis strains, highlighting the complexity of the plants aromas.

With this powerful analytical technique, we have discovered numerous important compounds in cannabis that have never been reported. However, the most exciting aspect of this research has been the direct correlation of certain compounds with desirable aromas in cannabis. Below we describe the science behind how we uncovered these compounds, as well as how we relate them in a user-friendly way by developing proprietary metrics. These metrics are based entirely on the chemistry of cannabis, with minimal bias or subjectivity.

Finding the gas and understanding the gas factor

TL;DR: We discovered what compounds give cannabis its gassy scent. We then created a numerical metric from 0 – 100 to rate how gassy a strain is based on its chemistry.

We have identified the compounds contributing to the ‘gassy aroma’ of cannabis. These compounds were confirmed by conducting two separate experiments: (1) A statistical experiment and (2) A time dependent experiment. In the former, we measured cannabis strains with varying degrees of gas. We identified clear trends in specific compounds: non-gassy strains have very low amounts, while gassy strains have significantly higher amounts. Figure 3 shows the 1-D chromatographic views of these compounds, showing clear differences between some gassy and non-gassy stains. After narrowing down the list of suspected compounds, we conducted a series of time dependent experiments on two highly gassy strains and measured the aroma compounds over time. We found significant decreases in the suspected gassy compounds compared to majority of other compounds as shown in Figure 3.

Figure 3: 1-D chromatograms showing differences in response in gassy and non-gassy strains. Arrows indicate peaks related to gassy compound (Prenyl mercaptan); Higher peaks indicate higher amounts of gassy compounds.

After confirming the chemical composition of the gassy aroma, we developed a metric, the Gas Factor, to easily quantify how gassy a strain is. We did this by having 5 cannabis experts rate strains based on gassiness. These data form an S-shaped curve, as shown in Figure 4 as the orange circles, which can be fitted using a modified generalized logistic function that yields the black line.

Figure 4: Time dependent experiments show significant decreases over time in amount of gassy compound annotated by the arrow in two different gassy strains.

We can thus calculate the Gas Factor by simple knowing the concentrations of compounds associated with the gas and compare between strains – the first time to quantify based solely on the chemistry of cannabis. This metric allows one to directly compare strains to one another, as well as definitively answer the question, “Which strain is the gassiest out there?”

We note the following empirical observations about these data:

• The shape of the curve is non-linear, most likely due to how the human nose senses these compounds.
• There is a threshold concentration around 50 ng where gassiness becomes apparent.
• Once a strain is at a certain “gassiness” (linear region over ~100 ng), it becomes difficult to differentiate gassiness levels.
• The Gas Factors we report are typically measured on samples < 2 weeks old. Therefore, strains consumed after this time may have gas levels lower than expected.
  
  

Figure 5. Graph showing experimental data (orange circles) and fitted lines used to calculate the Gas Factor for strains.

Finding the Fruity components and understanding the Fruit Factor

TL;DR: We discovered what compounds give cannabis its fruity, sweet scent. We then created a numerical metric from 0 – 100 to rate these scents based on the chemistry of the strain

In addition to the gassy aroma in cannabis, we have found over 20 compounds contributing to fruity, sweet aromas that have previously been overlooked or undiscovered. We determined which compounds relate to these aromas by again looking for trends between strains while also cross referencing their known aroma description and potency. Many of these compounds are described as, “fruity, sweet, dairy, cheesy, apple, banana, pear”, as well as other fruit-like descriptors. We then fit these data similarly to how we did for the Gas Factor, using a generalized logistic function to most accurately represent the Fruit Factor (Figure 6). This allows us to obtain a value to express the ‘fruity’, or exoticness of a given strain.

Figure 6. Graph showing experimental data (orange circles) and fitted lines used to calculate the Fruit Factor for strains.

We note the following regarding the fruit factor:

• As the Fruit Factor is calculated using a multitude of compounds, there exist many permutations of this scent.
• To date, the fruit factor is a general category for these aromas. However, we are currently investigating how to adapt this metric to more specifically capture the wide ranging fruity, sweet aromas in cannabis.
  
  

Strain Balance: Understanding how compounds relate to one another

TL;DR: We developed a metric to explain how the major compounds of a strain relate to one another. This allows for understanding how complex a given strain aroma may present itself.

The aroma of cannabis can not only be potent, but extremely complex and difficult to describe. We find that in general, strains with a small number of compounds accounting for a high percentage of the total aroma concentration lead to less complex, more targeted aromas. Conversely, strains that have more diversity in their highest concentration compounds often have more nuanced, complex aroma profiles. To approximate this, we introduce the Balance metric. This metric relates the top aroma compound concentrations to quantify how complex a strain profile is. This is calculated by conducting statistical analysis on the dominant terpenes and normalizing from 0 – 100. Figure 7 shows how different the relative amounts of the top 20 terpenes can be between high balance (top) and low balance (bottom) strains.

Figure 7. Graphs showing top 20 terpenes for two different strains. Top: Low balance, targeted strain dominated by a few compounds. Bottom: High balance, complex strain with similar concentrations of top compounds.

Conclusions and Outlook

This guide was written to help explain to the public how Abstrax Tech metrics were calculated and can be used. We are currently developing other metrics to help relate other aspects of the aroma of cannabis in a quantifiable way. We believe that these metrics are the first truly quantitative approaches in the cannabis community to relate the aroma characteristics of this unique plant, allowing for the direct comparison of different strains with minimal personal bias. We remind the reader that having higher values for these metrics is not necessarily better, but rather a guide to help decide what aromas and flavors one prefers. We envision the wider cannabis community adopting these metrics to allow greater transparency as well as the ability to compare strains to one another. This will help both the end users as well as cultivators alike. In the words of Thomas Hobbes, “Scientia potentia est”.