Saturday, May 8, 2021

Yeah, About That TPS Report Cover Sheet . . .


Unlike ex-Initech employee Peter Gibbons, I’m a fan of TPS reports. That is to say, studies of terpene synthases (TPS) in cannabis. These are the plant enzymes that turn precursor molecules into the various fragrant terpenes behind each strain’s aroma profile. Some TPS enzymes convert geranyl diphosphate into a slew of monoterpenes, while others convert farnesyl diphosphate to a bunch of sesquiterpenes.

Identification of cannabis terpene synthases and the genes that produce them is a relatively new field. Canadian researchers led by Judith K. Booth at UBC in Vancouver were early leaders in this effort and last fall they published another study. This one, in Plant Physiology, was the subject of a “news and views” piece in the same issue, written by Marc-Sven Roell at the Heinrich-Heine University in Düsseldorf.

Like Bill Lumbergh, I have some issues with Roell’s TPS report cover sheet. Specifically, with his claims about what is required for future cannabis breeding efforts aimed at fragrance and flavor.

To predict and design cannabis smell and taste to meet consumer demands, two milestones have to be reached. First, a comprehensive understanding of terpene composition is required, which can be achieved by using quantitative terpene profiling in existing cultivars. Second the underlying molecular and biochemical mechanisms leading to these distinct profiles need to be understood.

Roell insists that we must first know everything about terpenes in all cultivars—their complete chemical composition plus their physiological means of production—before we can get around to breeding hybrids with specific consumer appeal.

Notice anything missing? How about sensory evaluation of the smell and taste of the existing cultivars? And how about relating perceived aroma to differences in terpene composition?

Roell no doubt expects to find cultivar to cultivar differences in terpene composition, which he assumes will equate to differences in aroma and flavor. But differences in chemical composition don’t necessarily translate into perceptible differences in aroma, much less differences that are meaningful to cannabis consumers. So his strategy of starting with comprehensive knowledge of terpene composition will be enormously inefficient.

This objection also cuts in the opposite direction. As a plant physiologist, Roell ought to know that even within genetically identical clones, terpene composition can vary with growing conditions. Thus, it is possible that within-clone variation could result in perceptible aroma differences.

So either way you look at it, Roell’s insistence that baseline chemical data is an absolute prerequisite for breeding better smelling cannabis is pretty weak, especially when he totally neglects sensory measurement.

In fact, I’d argue that the best way to assist breeding efforts is begin with quantitative sensory evaluation of a range of existing cultivars. Next, cross-tabulate aroma profiles with sales and consumer preference data to obtain a ranking of most-valued sensory traits. Go back to your list of cultivars and start hybridizing for likely winners. It’s the purely phenotypic selection method that worked very well for Luther Burbank in the days before gene sequencing and gas chromatography. This approach would get the program going a lot faster than Roell’s “study the hell out of everything before making a move” strategy. I think he has it totally backwards—sensory analysis should precede chemical analysis.

“Hello Marc-Sven, what’s happening?

We have sort of a problem here. Yeah, you apparently didn’t include sensory analysis in your new cover sheet on the TPS report.

Did you see the memo about this?

Yeah, if you could just go ahead and make sure you do that from now on that would be great. 

And I’ll go ahead and make sure you get another copy of that memo.”

The study discussed here is “Terpenes in Cannabis: Solving the puzzle of how to predict taste and smell,” by Marc-Sven Roell, published in Plant Physiology 184:8-9, 2020.

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