Sunday, May 22, 2016

Using cilantro's foul flavor to teach my son about human genetics

We are struggling to incorporate variety into the diet of our seven year old, who is not interested in having anything green on his plate. My husband, the cook of the house, has found some ingenious ways to sneak extra veg into dishes (e.g., finely chopped cauliflower disguises itself as meat in chili con carne). My contribution to this effort has been to tackle the problem with a little home-based scientific investigation. (I guess my scientific training is helping my parenting skills as well as my baking skills.) How random genetic variations can affect taste perception was one of the many interesting topics in both Sharon Moalem's Inheritance and Sam Kean's The Violinist's Thumb. Like most couples, my husband and I have some major differences in how some foods taste. This gave me the idea of using these genetic variations to our advantage to talk to our son about human genetics and genetic diversity.

Thamizhpparithi Maari (CC-BY-SA) Wikimedia Commons
I had previously introduced my son to the concept of DNA with Have a Nice DNA, a fun book from Cold Spring Harbor Laboratory Press suitable for elementary-aged children. This set the table for the first experiment: cilantro (or coriander). I find that cilantro tastes a bit soapy, but my husband thinks it tastes great. Before our dinner of black beans and rice with raw cilantro sprinkled on top, I told our son about the differences in how his father and I perceive the taste of this herb. I told him that he would be part of an important experiment to determine whose genes he had inherited. In the spirit of the good nerd we are raising, he was fascinated and curious. The experiment revealed that our son had not inherited my taste perceptions of cilantro. In fact, it made him laugh to hear that I thought it tasted like soap (kids love to see their parents suffer), especially since it was so different from what he thought it tasted like.

Once we learned the outcome, I wanted to teach him more about the genetic basis of this difference. Lucky for me, cilantro is a hot topic on the internet. The prevalence of dislike ranges from 3-21% depending on the ethnic group (21% of east Asians, 17% of Caucasians, 4% Hispanics, and 3% Middle Easterners). While in the minority, the group is quite vociferous in their hatred of the herb. The consumer genetics company 23andme looked at DNA sequence data for ~30,000 users who were asked about their preference for cilantro. Variations in a gene called OR6A2 were linked to differences in cilantro preference. This gene encodes an olfactory receptor that recognizes certain aldehydes, which happen to be the molecular basis of cilantro's smell. Aldehydes are also present in soap. Thus, people with the genetic variant are more likely to sense cilantro's soap-like aldehydes; the sense of smell is a major player in how we perceive flavor. Two other studies found two different explanations for the soapy phenotype (one showed a connection to a different olfactory receptor and the other to a bitter taste receptor); these differences in results could be due to the large variation in the phenotype. My literature searches did not find any more recent stuies in the genetics of cilantro taste perception, suggesting that the work is difficult to fund.

I think my favorite find in my exploration of cilantro was the Gastropodcast, which examined the science behind these differences. Another interesting piece was from New York Times food science writer Harold McGee, who explored the evolutionary basis for taste perceptions. He also discussed how changing the preparation of cilantro can change its flavor; one study showed that crushing cilantro speeds the rate at which plant enzymes break down aldehydes. As a result, fine chopping of cilantro or cooking it a bit can get rid of the soapy flavor for some (this definitely works for me). Based on the success of the cilantro experiment, we will definitely be searching for future food science to explore during family dinners.

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