Episode 30: Why do some people taste soap when they eat cilantro?

For this episode, we dove back into the culinary world. In Episode 9 we examined the mechanisms of umami flavor and in Episode 18 we learned about thirst. For this episode we asked why some people love cilantro while others simply taste soap.

It turns out that the disagreement about cilantro – whether it is delicious or disgusting – is not a new one. The first documented reference comes from Pliny a 1st century Roman naturalist. He referred to cilantro as having “cooling and refreshing properties”.  Pliny clearly was in the “loves cilantro” camp.

Conversely, John Gerard, a 16th century herbalist, called cilantro a “stinking herb with venomous quality”. His French contemporary, Olivier de Serres, said it “smells like stinkbugs”. 

These differences in experience with cilantro persist to this day. Based on a population study from 2012 published in the journal Flavour about 10-15% of people overall dislike cilantro. And there is an inverse relationship between rates of reported dislike of cilantro and how prominently cilantro features in that culture’s cuisine. More cilantro in the diet equaled less dislike.

The Good & Bad of Aldehydes

To understand the differences in our experience with cilantro, we must review a little bit of biochemistry. Specifically, we need to review aldehydes. Aldehydes are carbon molecules that contain a functional group with the structure CHO, where the carbon is double-bonded to oxygen.

It turns out that aldehydes are the main source of cilantros pungent, fragrant flavor. There are lots of different aldehydes contained in cilantro but one seems to be key to our question of the love hate relationship: trans-2-decenal.

On the surface there doesn’t seem to be anything unique about this particular aldehyde. But, in a genome-wide association study, those who taste and smell soap with cilantro have a specific polymorphism of the OR6A2 olfactory receptor. OR6A2 is an aldehyde receptor that binds trans-2-decenal. This strongly suggests that variations in OR6A2 and the ability to bind trans-2-decenal, are the source of cilantro hatred. You can even get commercial genetic testing kits that will tell you your genotype for this gene.

Recall that the 16th century French scientist Olivier de Serres said that cilantro smelled like stink bugs. Turns out they are actually a real type of insect called the marmorated stinkbug or Halyomorpha halys. When threatened H. halys releases a pungent odor from its abdomen that has been described as cilantro-like. And, as you might imagine, the defensive odor is comprised of trans-2-decenal!

But why soap?

A question remains: how does the above explain a soapy taste? Saponification (i.e., soap production) involves hydrolysis of lipids in the presence of heat and sodium hydroxide, which produces the fatty acid salts that comprise soap. Aldehydes, including trans-2-decenal, are byproducts of this saponification reaction and are the reason that soap has distinct aromas. 

What this means is that when someone says that cilantro tastes like soap they actually are indeed tasting soap.

For those looking for a way to minimize this effect dicing, grinding up, or food processing the leaves activates an aldehyde reductase enzyme in the leaf itself. This aldehyde reductase breaks down aldehydes like trans-2-decenal to less aromatic compounds. Theoretically this should reduce the soapy flavor.  

Take Home Points

1. Dichotomous, love-hate responses to cilantro result from different sensitivity to the aldehyde trans-2-decenal.
2. This difference in sensitivity results from genetic variations in the OR6A2 olfactory receptor.
3. Trans-2-decenal is also a byproduct of saponification, and those who taste soap w/ cilantro are actually tasting soap.
4. Grinding up or dicing cilantro activates an aldehyde reductase enzyme which breaks down trans-2-decenal and theoretically may make it more palatable for those who taste soap.

CME/MOC

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Listen to the episode

https://oembed.libsyn.com/embed?item_id=19877855

Credits & Citation

◾️Episode written by Avi Cooper
◾️Show notes written by Tony Breu and Avi Cooper
◾️Audio edited by Clair Morgan of nodderly.com

Cooper AZ, Abrams HR, Breu AC. Why do some people taste soap when they eat cilantro? The Curious Clinicians Podcast. July 21, 2021

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Image credit: Source: https://www.scientificpsychic.com/etc/timeline/atmosphere-composition.html