The cross : Are we still discovering new flavors?
Thierry Thomas-Danguin: It all depends on what you consider a “flavor”. Scientifically, there are five categories: sweet, salty, bitter, sour, and umami. The latter was highlighted twenty years ago and uses glutamate, for example the taste of Parmesan or soy sauce.
A flavor corresponds to the activation of a receptor in the taste buds. Each receptor is specialized: the one for the sweet will only smell that. And contrary to popular belief, there is no “flavor card” on the tongue. Each taste bud has receptors for all flavors. That said, we can see “nuances” within the flavors.
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That is to say ?
T. T.-D. : For example, stevia causes, in the scientific sense, a sweet flavor even if some consumers will report a less sweet or more “liquorice” sensation. We very often discover new molecules with a whole range of sweet or bitter tastes, because our physiology is more sensitive to these flavors.
Conversely, the salty taste receptor is very specific to a handful of molecules: sodium ions (classic salt), potassium ions (diet salt) and lithium ions (toxic, not used in food).
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Certain sensations such as astringency or fat raise the question of possible undefined flavors. For astringency, research indicates that it is more likely to be sensations related to touch than a flavor in the strict sense. Ditto for the mustard that stings the nose, a spiciness that depends on a sensation conveyed by the trigeminal nerve and not by the taste buds.
Are there flavors that humans cannot perceive, much like we cannot see infrared light?
T. T.-D. : Hard to say. What is certain is that animals do not perceive flavors the same way we do. The cat, for example, does not have a receptor for sweet, because its carnivorous diet makes the perception of this kind of flavor unnecessary.
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Many Covid-19 patients have lost their taste or smell, sometimes both. What do these pathologies teach us about taste?
T. T.-D. : Already, the difficulty of compensating by the other senses, especially when the sense of smell is affected. 80% of the information on the identity of a food comes from olfaction. As unbelievable as it may sound, blind tasting and odorless a wedge of Granny Smith apple and a wedge of white onion: it is very difficult to tell them apart by taste alone.
This does not mean that taste is less important than smell in everyday life. Some cancer patients, for example, see their perceptions altered, with a metallic taste in the mouth which handicaps them. Several studies are now focused on these physiological and pathological damage to taste.