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The Science of Taste

How Do We Taste Food? | Vermont Public Radio

By Debolina Datta

Cooking  food isn’t easy. It involves a lot of hard work and years of experience to present that perfect plate of food, that perfect balance of taste, texture, appearance and smell. But what if I were to say that the taste of a particular food item doesn’t have much to do with what a good chef you are but by the sensitivity of neurons in your guest’s brain? That if a guest complains of a particular dish being too salty, it does not really have much to do with your skills but with the threshold point of sodium ions in your guest’s body? A little disheartening? Maybe. But that is exactly how this well-engineered machine called the human body works.

In humans, the taste receptor cells are grouped together on the tongue and back of the mouth in taste buds. Vertebrate taste receptor cells are epithelial sensory cells that synapse onto terminals of cranial sensory neurons, which then carry the signals to taste centres in the brain. For years together, people were very well versed with the concept of the taste map which states that sweet is at the front of the tongue, bitter is at the back, and salty and sour at the sides. Unfortunately this concept has been disproven as different tastes are sensed by taste buds which are distributed all over the tongue. Although the tongue map doesn’t exist, there may indeed be a taste map in the brain. A region called the gustatory cortex has been reported to contain clusters of neurons that are specialized to respond to individual basic tastes.  Mammals have six distinct tastes which are normally present in all foods. Now the distinct transduction mechanisms appear to be separately localized in different taste receptor cells. Scientists have made great progress in identifying taste receptors and genes that code for them but they are far from recognising the exact way in which in functions.

1402 The Tongue.jpg
Components of taste buds. Creative Commons

A striking feature is that our taste cells actually last only for a few days! They keep getting replaced by a special layer of stem cells in the taste buds. These stem cells divide to repopulate the taste cells and keep the machine functioning. Humans in general have been engineered to have an aversion or affinity for a particular kind of food based on conditioning. For example, humans tend to prefer sweet foods as opposed to bitter ones. This can very easily be observed while feeding a child who will be delighted to eat something that has a high sugar content as opposed to food items which are bitter. Now there is a very simple explanation behind the same which can be traced back to our ancestors, who would simply eat fruits because of its availability and high energy content. This affinity has stuck in our genes over the years. On the other hand, anything that might be bitter was a direct indication of toxic materials present in it thereby making it unfit for consumption. A trigger or warning sign to avoid these made us naturally averse to this flavour. Of course, there are arguments to these hypotheses as well and research is still ongoing on the evolution of taste perception.

Accounting for taste - Curious
Basic types of taste. Australian Academy of Science

Interestingly enough, the food that we eat and the perception of taste cannot solely be attributed to the taste buds present in the tongue. In fact, the major sensation of taste comes from the odour receptors in the nasal cavity, more commonly known as retro nasal olfaction. The brain being as ingenious as it is, is also capable of distinguishing between the odours that we sniff through our nostrils and those that reach the nasal cavity from behind as we eat. The same receptors are responsible to detect smell from both sources, thereby enhancing each sensation as we eat. It is a combination of the efforts of both the taste buds and odour receptors that our food might seem delicious or disgusting. The absence of any of the senses would simply spoil the dining experience. 

The sensations that we have on a daily basis are nothing but the action of sequential and coordinated firing of a number of neurons. There are pathways that neurons take up to the taste centre of the brain and recent evidence suggests intercommunication at many of these layers. Scientists believe that due to the combinations and permutations of the different pathways and receptors being activated, the depth of perception is enhanced. And because each human being has a different composition and physiology, the way we perceive food and the vast variety of things around us changes.

It just gets you thinking about the complexity and excellence of the perfectly developed human body. And how efficiently it works to make our experiences and sensations so intense and profound.

Wine Tasting - de Panky/ from Panky

References

  1. Melis, M., & Tomassini Barbarossa, I. (2017). Taste Perception of Sweet, Sour, Salty, Bitter, and Umami and Changes Due to l-Arginine Supplementation, as a Function of Genetic Ability to Taste 6-n-Propylthiouracil. Nutrients9(6), 541.
  2. Bradbury J (2004) Taste Perception: Cracking the Code. PLoS Biol 2(3): e64.

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