Cannabis Terpenes: Getting into the Weeds

Fig. 3 from Booth, et al., 2017

The volatile chemical components in cannabis are well known: they consist mainly of terpenes. The aroma profile of cannabis, in contrast, has yet to be nailed down with standard sensory methods. As a result, we have no data-based description of how the various strains smell. Between the chemical cornucopia and the sensory desert lies a largely unexplored zone: the biochemical. It consists of the metabolic means by which the plant produces its characteristic (yet highly variable) smell.

Thanks to three researchers at the University of British Columbia, we finally have some insight into the biochemistry of terpene production in cannabis. Their study, published two months ago in PLoS ONE, is fascinating but it’s not an easy read. In addition to chemical analysis, it involves cDNA cloning, plasmid-transformed E. coli cells, expression vectors, and gene sequence analysis. It’s a dense paper but one that is worth unpacking given the many possibilities it holds for the breeding, cultivation, and commercialization of cannabis.

Let’s start with the basics. The plant, and especially the resin produced in the glandular trichomes of the female flowers, contains a highly variable mix of terpenes. Terpenes are a class of organic molecular structures built from isoprene units (C5H8). Monoterpenes contain two isoprene units (C10H16), sesquiterpenes contain three (C15H24). Among the monoterpenes frequently found in cannabis are α-pinene, β-pinene, limonene, myrcene, β-ocimene, and terpinolene. Cannabis sesquiterpenes include alloaromadendrene, β-caryophyllene, α-humulene, farnesol, and valencene. These are all familiar molecules to fragrance chemists—they show up in all sorts of floral and citrus notes.

This array of cannabis terpenes is produced via two well-known biosynthetic pathways known as MEP and MEV. Each step in these pathways is enabled by one or more enzymes, known as terpene synthases (TPS). These enzymes are coded for by a large gene family found in plants generally; enzymes in the TPS-b gene subfamily produce monoterpenes, while TPS-a enzymes mostly make sesquiterpenes.

What the UBC team has done is identify the enzyme genes active at each step of terpene creation in cannabis. This is a significant achievement. Because terpenes “are responsible for much of the scent of cannabis flowers and contribute characteristically to the unique flavor qualities of cannabis products” we can now begin to understand how and why a particular strain of cannabis smells the way it does.

What the UBC study makes clear is that strain-specific terpene production is complicated. For example, two strains rich in α-pinene may create it using different enzymes. Conversely, the same enzyme may yield different terpenes in different strains. There are probably additional factors in the mix, as “terpene profiles showed considerable variations between individual plants.”

Nevertheless, the pieces are now in place for breeders to select for and genetically manipulate the terpene profiles of a given strain. The authors note:

“Knowledge of the genomics and gene functions of terpene biosynthesis may facilitate genetic improvement of cannabis for desirable terpene profiles.”

Toward the end of the paper the UBC team throws in another fascinating phrase:

The present study highlights the large number of CsTPS genes and the diverse products of the encoded TPS enzyme activities, which contribute to the complex terpene profiles of cannabis. The knowledge of multigene nature of the CsTPS family and the often multiple products of the encoded enzymes will be critical when selecting or breeding, or improving plants by genome editing, for particular terpene profiles for standardized cannabis varieties.

“Standardized cannabis varieties” is an interesting concept. Right now, cannabis cultivation is a farrago of strains and hybrids, raised under an varying greenhouse practices and post-harvest treatments (drying and trimming). Although impressively technological in some respects, the industry presents as a hippie-dippie craft aesthetic with cute varietal names and limited (possibly unrepeatable) production runs. In order for the industry to scale up, it will have to produce enormous volumes of cannabis using strains that respond consistently to uniform growing conditions and handling, a possibility UBC co-author Jonathan Page (who is also CEO of Anandia Labs in Vancouver, B.C.) raises in a new interview.

To me, “standardized cannabis varieties” conjures up more intriguing possibilities, such as branded fragrance and flavor profiles aimed at different segments of the recreational market. Large-scale production will require strains that have consistent aroma, flavor, and potency. Some will no doubt view this as sell-out to corporate agribusiness, a betrayal of traditional cannabis folkways. But it will also bring economies of scale and the high level of safety and quality that consumers expect in branded products. Dedicated hemp-heads will always appreciate the boutique hybrid strain, but a national market will also need to appeal to the casual user who wants a reliable product.

UPDATE June 5, 2017
Beer guru Stan Hieronymus quotes this post, noting that terpenes link hops and cannabis.

The study discussed here is “Terpene synthases from Cannabis sativa,” by Judith K. Booth, Jonathan E. Page, & Jörg Bohlmann, published in PLoS ONE 12(3): e0173911, 2017.