Australian scientists gather the evidence on the electrochemical pathway that fatty acids set in motion between our tongue and our brain. If confirmed, the textbooks would have to be changed to add a new flavor.
Our language is a sophisticated chemical detection device, capable of distinguishing hundreds of molecules and transmitting the information to the brain. Thanks to these chemical receptors, which insects have on their legs and fish throughout their bodies, we are able to know if something can cause us harm or feel the need to consume food at all costs.
"There is consistent new evidence that fat is the sixth primary flavor."
All these little details have been shaped by evolution. On the tongue of an adult, about 10 centimeters long, there are about 9,000 taste buds that are distributed in various areas. These receptors work as a kind of locks that are activated when molecules with the appropriate shape act as a key and trigger a specific signal. In our case, there are some receptors that are activated by groups called glycophores and that are triggered by sugars and carbohydrates to cause the sensation of sweetness. These receptors occupy a privileged position in the tongue because evolutionarily it compensated us to detect and eat foods with high amounts of energy.
Despite what was believed, the flavors are evenly distributed. Image: Nature
On the tongue we also find papillae that are activated with sodium ions (Na +) and detect the salty taste as well as the receptors that respond to hydrogen ions (acid taste) and alkaloids (bitter taste). Most substances in nature that contain these groups are poisonous, so it is not surprising that the bitter taste is especially unpleasant to us and we instinctively avoid it. Just a few years ago, in 2000, and after decades of discussion, scientists discovered the receptors for a fifth flavor, umami, which is triggered by molecules like glutamate and other amino acids.that indicate the presence of protein and that evoke the feeling that something is "tasty.
Until now it was thought that fat only activated touch receptors.
For a few years, a team of Australian scientists has been investigating the possibility that our language has receptors for a sixth flavor, that of fat. Several studies strongly suggest that fatty acids in chains of different lengths are detectable by humans and these researchers consider that fatty substances can activate regions of the brain in the same way that other flavors do. In a special issue of the prestigious magazine Flavor, researchers Russell Keast and Andrew Costanzo presented a few days ago a compilation of what is known so far about the chemical and electrical pathways that activate fatsin our nervous system in contact with our tongue.
The main difficulty, they explain, is in differentiating the perceptions that activate fat individually and not confusing it with what other flavors cause. Added to this is the fact that fat is not soluble in water and you have to find tricks to emulate its role in food. To verify this, the team of Richard Mattes, from Purdue University, conducted a series of experiments with volunteers who served a kind of custard with different amounts of fat, gum arabic and liquid paraffin to produce similar textures. And they identified two candidate receptors that are activated specifically in the presence of fatty acids and that cause the emission of neurotransmitters that send the signals to the brain.
There is strong evidence for the taste of fat, but there are still steps to be taken.
Although the idea that fat can constitute a new flavor goes back a long way, until recently it was considered that fatty acids only played an important role in defining the texture of a food, that is, that they activated touch receptors present in the mouth but not the chemical receptors that activate the taste. Some preliminary studies, such as those of Oxford University researcher Edmund T. Rollsthey already gave some clues about the role of fat. Specifically, Rolls discovered that even inedible fats, such as paraffin or some saturated hydrocarbons, trigger a pleasure response in the brain. And the food industry, unable to generate fat substitutes that create the same pleasure sensation for the recipient, also suspects that fat could be a flavor.
For Javier Cudeiro, a researcher at the University of a Coruña and an expert in the neuroscience of taste, the data presented in the study "look good and point in the direction that there could be a sixth flavor". Even so, he notes, "there are still important steps to take." "One of them is to identify without a doubt the receptor (or receptors) involved in the transduction," he says. "This involves conducting the definitive electrophysiology experiments, identifying the sensory pathways and nerve centers involved, and eventually cloning the channel." This, Cudeiro recalls, is what has happened over time with the fifth flavor (umami), which was proposed at the beginning of the 20th century but took decades to be demonstrated.
The discovery has implications in the fight against obesity.
To identify a flavor, five criteria must be met and scientists believe they are close to having them all closed. 1) There must be a specific kind of stimulus caused by fatty acids 2) There must be specific mechanisms that translate the chemical signal into electrical impulses 3) A neural signal that reaches the brain after these stimuli must be identified 4) There must be perceptual independence from others flavors and 5) There must be verifiable physiological effects after activation of the taste buds.
To the technical aspects, the cultural difficulties are added to identify the existence of another flavor. We do not have a word in our vocabulary that describes the "fatty" taste, which makes it more difficult to perceive. According to Mattes, people tend to identify these sensations of fatty tastes as bitter, but the stimuli are different. Curiously, remember, it is something similar to what happened with umami a few years ago, that since there was no word, people identified it with the salty taste.
"Now we are taking a step forward and suggesting that fatty acids have their specific receptors that trigger specific physiological responses," says Cudeiro. This is indicated by the authors of the work published in Flavor who argue that "there is new consistent evidence that fat is the sixth primary flavor" and warn that this has some implications that go beyond the merely culinary and could help to understand and fight problems such as obesity.The evidence collected so far shows that people who are not sensitive to fat orally are also not sensitive to the gastrointestinal level and consume too much fatty and energetic food. Understanding these mechanisms could help develop products that satisfy these people and moderate food intake in the future.