Chemists Uncover the Source of Cannabis’s Unpleasant Odor
Chemists in the United States have identified the structure of the compounds responsible for the smell of cannabis. It turns out that, as with many other aromatic plants, volatile sulfur-containing compounds are the main contributors to the plant’s unpleasant odor. The researchers also tracked how cannabis synthesizes these compounds at different stages of its growth. The study was published in the journal ACS Omega.
The flowers of certain strains of cultivated cannabis (Cannabis sativa) have an unusual smell, similar to the liquid that skunks release from their scent glands when threatened. Although scientists have already identified about 200 different compounds responsible for the various nuances of cannabis’s aroma, the source of its sharp and unpleasant scent had remained a mystery until now.
A team of chemists led by Iain W. H. Oswald from the research division of Abstrax Tech set out to determine which organic compounds are responsible for this pungent odor. They hypothesized that it likely comes from organosulfur compounds, since sulfur-containing organic molecules are known to give many plants their strong smells.
To find the mysterious sources of the sharp aroma, the researchers used two-dimensional gas chromatography. This analytical method allows for the separation of very small amounts of substances: the solution of the compounds being studied is vaporized at high temperature, and all the substances sequentially pass through two columns with a solid carrier. In each column, compounds with different structures are retained for different amounts of time, resulting in a graph where each compound is represented by two retention times. Using this method, the chemists detected seven different sulfur-containing compounds, whose structures they identified using mass spectrometry data.
To determine which of the discovered molecules contributed most to the cannabis smell, the chemists conducted olfactory tests with different strains of the plant. They found that the most important compound was likely VSC3 (3-methyl-2-butene-1-thiol), while the others only slightly modified or enhanced its aroma. To confirm this hypothesis, the chemists prepared two solutions containing these compounds. One solution included all the identified substances, including VSC3, while the other did not contain VSC3. It turned out that only the first solution had the characteristic cannabis smell.
Next, to study at what stage of development the plant produces these aromatic compounds, the chemists grew their own cannabis plants. Each week, they measured the concentration of the aromatic compounds using gas chromatography. They discovered that cannabis begins to actively synthesize these substances in the seventh week of flowering. As soon as the peaks of these compounds appeared on the chromatograms, the researchers also noticed the familiar cannabis smell, further confirming their hypothesis.
In conclusion, the chemists successfully identified the compounds responsible for the smell of cannabis. Many of these were discovered for the first time as plant metabolites, and their biosynthesis and potential therapeutic properties remain to be studied, the authors note.