Colourless, tasteless liquid. Need help!

[Jayemm]

Hi!

I'm trying to remember the name of a liquid we used in an experiment at school (over twenty years ago, mind!).

It was colourless and tastless to the majority of people, but apparently pregnant women report that it tastes of grapefruit to them.

I can't remember the name of this liquid or it's purpose. can anyone help?

[Catso]

I remember something like that.

Though as I remember it (perhaps it was different liquid) it tasted absolutely vile to the majority, but some people found it tasteless. Might have been known by some abbreviation, like TCP?

[Jayemm]

Thanks for the reply, but I think we are remembering different liquids. There is probably a whole slew of experiments out there relating to taste perception.

I just remembered that this experiment came about the same time that we were doing stuff on colour blindness. The point was obviously to learn about things that were perceived differently according to the individual.

The liquid I am trying to remember was definitely tasted by pregnant women. We did the experiment only being told to record what we tasted - when we had handed in our reports she remarked that she would be able tot ell if any of us were pregnant by what we had written. There were a few scared looking girls in the class that, I can tell you!!

Initials ring a bell though, not 'TCP' itself, but the liquid going by a set of initial ... hmm might have to start googling again.

Thanks again Catso, I appreciate you taking time to respond.

[Catso]

Yes, the reasons we had it were as yours - the start of genetics & inherited characterisics.

No, I know it wasn't TCP! That was just a for instance.

[theprof]

I can't be certain of the chemical involved here as there is more than one possibility.

My first choice would be phenylthiocarbamide (PTC), which fits in with what Catso said. PTC powder can be either tasteless or very bitter to those genetically predisposed. PTC is soluble in water and polar organic solvents and you may have tasted the powder dissolved in water. Pregnancy however, is not a factor in the ability to taste the chemical.

Another good contender is 6-n-propylthiouracil (PROP) which has the novel property of being able to distinguish between "tasters" and "supertasters". This substance in solution can either taste very acrid or be as tasteless as water depending on a person's genetic profile. Supertasters usually have an aversion to grapefruit juice.

Naringin, which is the bitter component of grapefruit juice, also has similar properties in the pure form - it's taste can vary between slightly bitter to horrendously acrid.

There are also some other more obscure chemicals with similar properties.

Research has shown that the ability to taste these substances during the first trimester of pregnancy may have helped women avoid certain harmful foods. Scientists have found that more women than men can detect the bitter taste of PROP and other chemicals with similar properties. As many substances that are potentially harmful to the foetus (but not an adult), are bitter or acrid in taste, nature may be minimising the risks involved.

As far as the pregnancy issues mentioned by Jayemm go -sorry, it sounds a very useful test, but your teacher was having you on. It's purely a matter of genetics.

[theprof]

Incidentally, PTC is more commonly known as Phenythiourea in the UK.

You asked about it's purpose? Well, it's used in medicine, but it has also been used as a very effective rodenticide!

[Jayemm]

Many thanks to you - your reply has been very educational. It does seem that my teacher was 'messing with our heads' !

I very much appreciate both of you taking time to respond.

[theprof]

My pleasure and thanks.