“I am testing for bitterness tasting, and I need to know what the difference is between Thiourea and Phenylthiourea (PTC) paper strips. Can you help?”

-Artur

Great question Artur. We get this question a lot, and here’s the short answer, one that you probably won’t like: There has been a fair amount of research into how PTC works to produce a very bitter taste in some people. There appears to be less understanding of how Thiourea and Sodium Benzoate work. See? Not the most helpful response. Let’s dig a little deeper.

The History of PTC

Both Thiourea and PTC are used in education classes to classify people as “supertasters”, “tasters”, and “non-tasters”. In addition, Sodium Benzoate, which can taste bitter, salty, sweet or have no taste depending on the person, is also used in these educational studies.

We found this lab from the University of Vermont that helps illustrate the use of these test strips in the classroom.

Although studies of PTC and taste sensitivity have been going on for many years, beginning in the 1930’s, the discovery of the TAS2R38 gene on human chromosome 7 explaining why humans perceive PTC differently was not discovered until 2003. You can read all about the history of studies involving PTC here, in a great article from Genetics.org. It details the 75-year adventure in Phenylthiocarbamide and genetics.

The point is, PTC in genetics has been studied for quite some time, and there is quite a bit of information on it. There are several known alleles for the PTC gene, but PTC sensitivity is really controlled by two major alleles in humans. PTC paper either tastes bitter or it doesn’t taste like anything at all. Some tasters can taste a very strong bitter taste, while other tasters can taste a mildly bitter taste. Thus, there can be three classifications of phenotypes in a PTC study (strong tasters, mild tasters, and no taste).

Thiourea and Sodium Benzoate

Here’s where the research gets a little fuzzier. And by fuzzier, we mean pretty much non-existent. As the lab from the University of Vermont states, “The genetic variation contributing to phenotypic taste perception of this bitter tastant

[Thiourea] is unknown.” Similar to PTC, it either tastes bitter or it doesn’t taste like anything at all. Again, participants in the study can be classified into three phenotypes, tasters, mild tasters and non-tasters.

Although Thiourea and PTC have the same bitter taste result, PTC tasters may not necessarily be Thiourea tasters, or vice versa.

Sodium Benzoate has different taste perceptions than the other papers. A different pair of alleles determines the ability to taste Sodium Benzoate. It can taste sweet, salty, sour, bitter or tasteless, so this paper is often used in conjunction with another taste test, such as PTC, to characterize taste perception, and break tasters/non-taters into subgroups.

What’s the difference, then?

taste test papers, thiourea, sodium benzoate, ptcSo, in answer to your question Artur, we don’t really know.

There has always been the question of safety using PTC taste test papers, and this may be why some people prefer to use Thiourea. However, our PTC paper is harmless. The quantity of PTC used in a strip is minimal, in fact, it’s less than 0.1%, and if you’d like to double-check us on that, you can check out the SDS on our website.

This lab from the University of Vermont is a great example of how to perform a taste test study using all three strips, but that doesn’t mean you have to use all three. PTC is the most common taste test paper, and for good reason (see all the background and history explaining the science behind it). If you’re simply looking to perform a quick study to group tasters and non-tasters of a bitter substance, you could just use PTC and call it a day.

It’s up to you how you want perform your taste test study, and if you do a quick Google search, you’ll find plenty of examples out there. Sorry we couldn’t provide a better explanation, but hopefully someday, scientists will uncover a bit more about Thiourea and Sodium Benzoate as taste tests.