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Scientists Discover the Origin of Cannabis’ Distinctive Skunk-like Odor

By Alexander Beadle

Published: Nov 24, 2021   
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Scientists at ABSTRAX Tech, a California-based terpene research and product development company, have identified the chemicals that cause cannabis’ distinctive skunk-like aroma.

While the majority of cannabis’ scent profile is known to be a result of the terpene compounds present in a given strain, these terpenes were unable to explain the skunk-like or gasoline-like smell that is attributed to some cannabis strains. Now, ABSTRAX researchers have discovered a number of key volatile sulfur compounds (VSCs) – volatile organic compounds that contain sulfur – which directly explain this pungent odor given off by some cannabis strains.

Their research, which has been peer-reviewed and published in ACS Omega, also suggests that these VSCs could have additional medicinal properties, as their chemical structures strongly resemble a number of compounds in garlic that are known to improve cardiovascular health.

New VSCs explain distinctive cannabis odor

To unravel cannabis’ scent profile, the ABSTRAX Tech scientists focused on investigating VSCs for two reasons. Firstly, since cannabis smells are often described as skunk-like, it would make sense to screen them for compounds that are also present in skunk’s aerosol spray. And since VSCs are already known to exist in other pungent plants like hops, it would be unsurprising to find the same compounds in cannabis plants.

In order to screen cannabis samples for known and unknown VSCs, the scientists employed the use of a custom-built two-dimensional gas chromatography (2DGC) system with three detectors running simultaneously: a time-of-flight mass spectrometer (TOF-MS), flame ionization detector (FID), and a sulfur chemiluminescence detector (SCD). The use of two-dimensional gas chromatography provides better separation efficiency than traditional one-dimensional analysis, with the combination of sulfur chemiluminescence, mass spectrometry, and flame ionization, giving researchers the means to detect, identify, and quantify very low concentrations of any VSCs present in the samples.

“The combination of multiple detectors, in tandem with 2DGC to analyze cannabis, gave us the tools needed to parse through data and identify trends between certain compounds and the aromas of various cannabis cultivars,” lead study author Dr Iain Oswald, explained in a statement. “Our data conclusively establishes a link between this new family of VSCs in cannabis and its pungent aroma.”

The study identified a family of seven VSCs present in cannabis, some of which had not been previously identified in nature. Five of these compounds contained a prenyl functional group in their chemical structure and are believed to contribute to cannabis’ unique skunk-like smell. Further tests identified the compound 3-methyl-2-butene-1-thiol as the primary component of this aroma.

“Much like cannflavins are prenylated flavonoids found specifically in cannabis, some of these newly discovered ‘cannasulfur compounds’ also appear to be highly specific prenylated VSCs to cannabis,” said Oswald. “It is interesting to see a common chemical theme within entirely different classes of compounds produced by this plant.”

The medicinal potential of cannabis VSCs

Possibly the most important impact of the study is the discovery that the VSCs found in cannabis are structurally very similar to other VSCs found in garlic.

Cannabis VSCs vs garlic VSCs. Image credit: Alexander Beadle.

Allyl thiol, which is the allylic analog of the most prominent cannabis VSC, is known to be a powerful histone deacetylase (HDAC) inhibitor. HDAC inhibitors have been shown to inhibit the growth of cancerous tumors both in vitro and in vivo, and so this may provide a new dimension for cannabis anti-cancer research. Diallyl disulfide has also been shown to benefit cardiovascular health and protect against colorectal cancer, and so there is the potential for its cannabis counterpart to do the same.

“I have suspected for years now that we were missing something in our understanding of this plant,” study co-author Josh Del Rosso, said in a statement. “Although terpenes have been hailed as the major source of the pungent scent of cannabis, we now know that it is this new class of VSCs.”

“I hope our results can act as a springboard to help other researchers determine if these compounds endow cannabis with even more medicinal properties than we ever imagined.”

VSCs can translate into extract products, but have a short shelf-life

Interestingly, when the researchers screened three brands of butane hash oil concentrates for the VSCs detected in cannabis, they found measurable concentrations of the major VSC found in cannabis flower, 3-methyl-2-butene-1-thiol, in all three extracts. Additionally, a second VSC found in cannabis flower, 3-methyl-2-butenyl acetothioate, was observed in higher concentrations than the 3-methyl-2-butene-1-thiol in two of these samples.

After an olfactory testing panel, it was found that high levels of these two compounds were correlated with higher scores for extract pungency. The fact that these volatile compounds can be retained throughout the extraction process appears to be one of the reasons why these extracts can still carry such a strong cannabis-like aroma. But if these compounds are confirmed to have medicinal benefits, this could be a significant finding for the industry.

“We confirmed that cannabis extracts can indeed contain these compounds in reasonable concentration if processed correctly,” said Kevin Koby, CSO of ABSTRAX, in a statement. “Their high volatility makes them prone to volatilization, so we weren’t sure how they would translate into cannabis extracts. We were pleasantly surprised to see high levels in the sample we measured, especially if these compounds possess beneficial medicinal properties.”

Lastly, the ABSTRAX scientists set out to determine when these VSCs appear in the cannabis, and when their concentrations are at a peak. By sampling small clippings from cannabis plants being grown in a hydroponic greenhouse system and continuing to take measurements after harvesting and curing, the researchers found that the VSCs in cannabis arise very late in the growth cycle of the plant. VSCs were first detected seven weeks after the cannabis clones were planted, at which point the smell of the plants in the greenhouse also became more noticeably pungent.

Peak VSCs concentrations were recorded at the end of the curing and drying process, but when remeasured after ten days of storage, the levels of almost every VSC had fallen off significantly.

“These results prove that cannabis producers are racing against time when it comes to getting quality products into customers’ hands,” said Koby. “Hopefully our results will establish a new standard for cultivators and distributors to help preserve and protect these key compounds – regardless of the rigors of processing, packaging, and time on shelf. Most importantly, it will help brands maximize their products and literally push cannabis quality to the next level.”


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