Friday, January 26, 2018

How strong is the smell of new-mown grass to you?

When grass is cut, a chemical called leaf alcohol (chemically speaking 3-cis-hexen-1-ol or (Z)-3-hexenol) is released into the air. It's the plant's way of signaling that it has been injured. Tea leaves do the same thing. You're probably not surprised to find out, then, that the chemical is particularly prominent in green teas, but it's present in most other teas as well.*

According to The Good Scents Company, the taste (= flavor) of this chemical is "Fresh, green, raw, fruity with a pungent depth." In other words, it activates not just your odor receptors but also your cool/cold receptors, hence "fresh," "raw," and "pungent."

Turns out that to some people the smell of leaf alcohol is more intense than it is to others. People who are more sensitive tend to consume cucumbers a little more often, perhaps because for them cucumbers are more flavorful?** Here's the graph:

The difference looks slight, but it turns out that statistically it is quite significant.

The odor receptor for cis-3-hexen-1-ol is named OR2J3. Changes in the structure of this receptor lead to a 25% decrease in the ability to smell this chemical!***

There a single genetic change that is in strong linkage disequilibrium with these changes in OR2J3. Linkage disequilibrium means that if you have a version of the gene change in one place in your DNA, you are very likely to have a gene change in another location in your DNA. You can find this linked genetic change in your raw DNA report from both Ancestry DNA and 23andme, at rs7766902.

I've included rs7766902 in my survey on tea preferences and genetic changes. If you have done either 23andme or Ancestry DNA, would love to have you take the survey so we can find out whether a change in rs7766902 leads to preferences in tea just as it does for cucumbers!

Here's the link to the survey:

Be ready to take a few minutes to find your raw data, but I think finding out why you like what you like will be worth it!

Thanks so much --

* Chi-Tang Ho, Xin Zheng, Shiming Li. Tea aroma formation. Food Science and Human Wellness 4 (2015) 9–27.

** S.R. Jaeger, B. Pineau, C.M. Bava, K.R. Atkinson, J.F. McRae, L.G. Axten, S.L. Chheang, M.K. Beresfor*d, M. Peng, A.G. Paisley, H.C. Reinbach, S.A. Rouse, M.W. Wohlers, Y Jia, R.D. Newcomb. Investigation of the impact of sensitivity to cis-3-hexen-1-ol (green/grassy) on food acceptability and selection. Food Quality and Preference 24 (2012) 230–242.

*** Jeremy F. McRae, Joel D. Mainland, Sara R. Jaeger, Kaylin A. Adipietro, Hiroaki Matsunami, Richard D. Newcomb; Genetic Variation in the Odorant Receptor OR2J3 Is Associated with the Ability to Detect the “Grassy” Smelling Odor, cis-3-hexen-1-ol. Chemical Senses 37 (2012) 585–593.

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