The ability to distinguish between different tastes has been crucial to the survival of Homo sapiens.
Well developed ‘gustation’ allowed our hunter gatherer ancestors to distinguish between nutritional and toxic foods. We have evolved to enjoy the taste of food that is good for us and avoid food that harms us.
Our brains have evolved in such a way that if we think food tastes good we want to eat more. We enjoy foods that are good for our health.
We like the taste of fish, vegetables, bread and milk. These foods are often full of proteins, fibre and carbohydrates and have a pleasant, savory taste. We call savory tastes ‘umami’ (うま味) – a word of Japanese origin.
We enjoy foods that taste sweet; it is the sweet foods that are full of the sugars that give us energy.
We have a craving for food that tastes salty; among other things salt ensure that our muscles work properly and stops us dehydrating.
Recent research has shown that we may also gain pleasure from the taste of fats in foods; amongst other things dietary fats are essential to help keep our bodies warm and support cell growth.
When we eat something ‘hot’ such as chillis we often describe this as as ‘taste’. The ability to taste ‘heat’ on our tongues has nothing to do with taste and is just a pain signal sent by our oral nerves to the brain.
We have evolved to dislike foods that are bitter or sour; it is the harmful toxins in plants that have a bitter or sour taste. The ability to detect bitter and sour tastes gives us a natural defense against eating these harmful toxins.
We do not like foods that taste acidic; it is the acidic foods that have gone bad and could poison us.
In total, Homo sapiens can detect combinations of five difference tastes. These different tastes include detecting foods that are bitter, sour, salty, sweet and savory (umami). Some scientists think we can detect the taste of ‘fat’ in our food; that would make ‘fat’ our sixth taste.
A human tongue has up to 4,500 visible bumps and grooves called papillae.
Four different types of papilla are located on different parts of the human tongue.
If you examine the cross section below you will notice how ‘taste buds’ are located in the side walls of the papillae.
Look closely and you will see that one type of papilla, the ‘filiform’ papilla, has no taste buds in its side walls.
Another difference is that the filiform papillae have microscopic ‘hair-like’ extensions called microvilli at their apex. The microvilli increase the tongue’s friction to help move food toward the throat after it has been eaten.
Whereas the microvilli of human filiform papillae can only be seen using a microscope, those of cats are easily visible to the naked eye.
Taste buds are the ‘houses’ which contain our taste receptor cells. The elongated taste receptor cells are specialised cells which detect tastes. One taste bud typically contains between 10 and 50 taste receptor cells.
Each taste bud contains a combination of receptor cells and support cells. The support cells provide structural support to the taste bud ‘house’ but have no role in determining taste. It is the receptor cells which identify how food ‘tastes’.
Each receptor cell specialises in identifying a single taste whether bitter, sour, salty, sweet or ‘umami’. A single taste bud typically houses some or all of the different types of specialist taste receptor cells.
A receptor cell can respond to other tastes, but it responds strongest to one particular taste.
Receptor cells live for only 1 to 2 weeks and are then are replaced by new receptor cells. In elderly people taste receptor cells are not replaced as fast as in younger people; that is why the elderly cannot taste as well as the young.
Taste receptors housed in taste buds can be found everywhere on a human tongue.
It used to be though that different regions of the tongue specialised in detecting different tastes, but we now know that not to be the case.
Humans have approximately 10 000 taste buds. Most are located on our tongues with some located in other places, including the oral cavity.
After chewing a bar of chocolate, ‘sugar’ molecules are released into your mouth and dissolve in your saliva.
Saliva is more than 99% water; it is the water in your saliva that delivers the dissolved (water-soluble) ‘sugar’ molecules onto the microvilli of your taste receptors.
The microvilli enlarge the surface area of individual taste receptor cells so more tastes can be sampled.
The saliva containing the dissolved sugar molecules builds up in the grooves between the papillae.
Sweet receptor cells detect the dissolved sugar molecules that wash over the microvilli in saliva. After identifying the presence of sugar molecules the ‘sweet’ receptor cells transmit electro chemical signals to our brain through nerve fibres.
Our brains then tell us, ‘you are eating sugar!’
When we say ‘that food tastes delicious!’ what we really mean is that it has a ‘great flavor’. A combination of taste and smell can be equated to ‘flavor’.
If you have a bad cold or put a peg on your nose while you are eating, your food completely loses its ‘flavor’.
It is flavor, that combination of taste and smell, which drives our appetite.
Our ability to detect five different tastes ( six if you include the ‘fat’ taste) reflects our omnivorous ancestry and the wide variety of food that we are able to eat.
However many organisms, with their more restricted diets, have either lost or never evolved the ability to detect such a wide variety of tastes as we can.
For instance cats, with their preference for eating meat, have only 500 taste buds and have no ‘sweet’ taste receptors.
Mallard ducks have 400 taste buds on their beaks, but none on their tongues. Their taste buds are located on the upper and lower parts of their beaks. It is the moment when they grasp and hold food with their beaks that they decide if it is safe to swallow.
Cows have 25,000 taste buds; they have so many because they need to quickly identify which plants and grasses contain dangerous poisons before eating them.
Catfish are the champions when it comes to taste buds! They have an amazing 25,000 taste buds located all over their bodies…
but no taste buds on their tongues!
With ineffective eyesight and living in muddy water, it is the taste buds on their bodies that allows catfish to identify if food is safe to eat. Catfish do not have scales; they are covered with tissue that is more like skin.