Humans have bitter taste receptors to taste bitterness in plants that we eat. Also for humans a bitter taste can indicate that the food should not be eaten as bitterness under certain circumstances is associated with toxins.
Domestic cats are, as we know, strict meat eaters and it has puzzled scientists as to why they have seven functional bitter taste receptors with distinct receptor ranges. These receptors are similar to human bitter receptors. Cats probably taste bitterness as well as us.
A study suggested that the existence of these receptors in the domestic is to detect the presence of bitter compounds in invertebrate and vertebrate prey. They may also play a role in “non-oral perception”.
I’m not quite sure what “non-oral perception” means except to think that receptors which detect bitterness may exist outside of the mouth of the domestic cat but that seems improbable. I think it means detecting bitterness inside the body: in the heart and lungs as a means to detect infections.
One aspect of the study (published on Plos One) which may have been omitted is the fact that both domestic and wild cats do eat a certain amount of plant life and if some plants contain poisonous compounds then the ability to detect bitterness would help the cat to survive. However, domestic cats can and do sometimes eat poisonous houseplants which confuses the theory — or do they? Perhaps cats avoid poisonous house plants. Cats eat grass containing folic acid which I presume the cat detects as a bitter taste but a safe substance.
In addition animals which are prey to the domestic cat may have ingested plants which contain bitter, poisonous compounds. The domestic cat is able to detect these when eating prey and leave behind the poisonous compounds.
In addition, there may be certain parts of the anatomy of prey items such as bile which the cat does not wish to ingest. Bile is produced in the liver of most vertebrates and aids in digestion. The domestic cat does not wish to ingest bile because it serves no purpose to eat it and because it is inedible.
Dr Gary Beauchamp of the Monell Centre in the US, suggest that the receptors may help to protect cats from an internal toxin. I believe that what he means is there may be animal-based toxins within prey which the cat needs to avoid. I have already referred to bile which may be a mild toxin. Bile acid is probably toxic to a cat if ingested because it is a substance which should be used in a certain way inside the body and not ingested through the mouth and then into the stomach. There are probably other bitter toxins in prey which the cat needs to avoid.
Conversely to bitterness, domestic cats don’t taste sweetness.
P.S. Some companies add a bittering agent to anti-freeze to prevent cats ingesting it. Most don’t however which I think is irresponsible.