The Flavor of Physics

I do need a breather from the flavors of entanglement ~Alanis Morissette

Today, I get to combine my love of physics with my oral fixation. You have no idea how happy this makes me, sweet galleons.

A team of neurobiology researchers at the University of Southern California [Fun Fact: When I was in high school and began receiving mailings from the various universities that wanted me to attend their institution, USC’s was one of the ones that really stood out in terms of creativity. It consisted of a handful of cards instead of a brochure, and the graphic design work on them was top-notch. When the time came to actually start applying and I dumped out the two banana boxes of mailings I had shoved under my bed, USC made the first cut based on their mailing alone… in retrospect, I didn’t really have a very good system in place for selecting a university.] made an interesting discovery about how protons affect the taste system.

We’ve touched on taste buds as chemoreceptors in a previous post, but what we didn’t get into then is how those chemoreceptors work. The chemoreceptors for each individual type of flavor (sweet, bitter, etc.) respond a bit differently. And, while we have a decent handle on most of them, the workings of the sour chemoreceptors haven’t been terribly well understood.

Until now.

The sour sensation is evoked by acidic substances. And I’m referring to the low pH acids like those found in lemons and pickles, not necessarily the “burn your face off” acids and certainly not the “tripping balls” kind of acid.


But the whys in reference to acidic substances tasting sour have been a bit murky. We knew that acids release protons. And it is these protons that activate the taste system. How? We had no fucking clue.

What we did know, however, was that if you were to somehow shrink yourself way down and actually lick a proton, it would taste sour.


I'z gunna lick you, proton. I'z gunna lick you GOOD.

Perhaps it’s just me, but the idea of a subatomic particle having a flavor is ridiculously awesome. Maybe it’s just because I never entertained the notion before.

Science is fucking delicious.

Anyway, to get back on track, our USC team decided to figure out exactly how those pesky protons were stimulating the taste system. To do this, our team was going to need to get creative. As Emily Liman, a professor of neurobiology at USC, stated:

“In the past, it’s been difficult to address this question because the taste buds on the tongue are heterogeneous. Among the 50 or so cells in each taste bud there are cells responding to each of the five tastes. But if we want to know how sour works, we need to measure activity specifically in the sour sensitive taste cells and determine what is special about them that allows them to respond to protons.”

To do this, Liman and her team genetically modified mice, marking their sour receptor cells with a yellow fluorescent protein. They then recorded the electrical responses from those cells alone.

The results surprised them.

The team expected to find those released protons binding to the outside of the cells, opening a pore in the membrane to allow sodium to enter the cell. The entry of the sodium would send an electrical signal to the brain, and we would perceive the taste as sour.

However, what our USC team actually found was that these protons (which can also be considered hydrogen ions that have lost their one electron… most references to this USC study refer to our renegade protons as hydrogen ions… personally, I think it’s just to make the protons feel fancy) were entering the cells and stimulating the electrical responses directly.

And now we know.

I feel I have to include this quote of Liman’s, simply because it made me roll my eyes and mutter an irritated “no shit” when I read it:

“This mechanism is very appropriate for the taste system because we can eat something that has a lot of protons and not much sodium or other ions, and the taste system will still be able to detect sour. It makes sense that nature would have built a taste cell like this, so as not to confuse salty with sour.”

I suppose, instead of mocking her, maybe I should take the advice of my favorite Kids in the Hall sketch:


And now, for a tale of disappointment. Disappointment in people and their tenuous grasp on science and health news. The disappointment, naturally, is mine.

Someone I know was recently lauding the fact that soy milk is delicious (which I agree with, though I know the substance is much maligned… to each their own) on the Facebooks. He was promptly referred to an article about the phytoestrogens (plant-derived estrogen-like compounds) in soy products by another. And while there have been studies that have found rather substantial amounts of phytoestrogens in soy products, they are not, by any means, the only food-type substance containing these chemicals. Many legumes, seeds, nuts, cereals, and *le gasp!* alcoholic beverages also contain phytoestrogens.

In my mind, if you’re going to make the argument against a food or beverage based on a chemical component, you should be willing to make the same argument against every other food or beverage containing said chemical. However, people like beer. Most people do not like soy milk.

In conclusion, my helpful nudge toward the broader collection of phytoestrogen containing foods was summarily ignored. Apparently, like Christians do with the Bible, it’s perfectly acceptable to only cite specific studies in order to make your point. And, when presented with an argument based in your own canon… you should ignore the hell out of it.

Good times.

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