The science of taste is confusing. We think of certain foods as having certain tastes. By extension, we think those foods represent those tastes. But our taste buds do not react to foods, they react to food compounds. To explain further, here is my informal answer to a related Quora question: “How do artificial sweeteners trick our taste receptors into thinking they’re sugar?”
The Simplified Science of Sweetness
Artificial sweeteners do not trick our sweet taste buds into thinking they are sugar. We do not have taste receptors that detect sugar. We have taste receptors that detect sweetness. So, in other words, our sweet taste receptors do not think artificial sweeteners are sugar, they only think they are sweet (of course they can’t think at all, it’s all just chemical reactions).
The taste cells responsible for detecting sweetness contain receptor proteins that bind to sweet ligands and this causes a signal from activated synapses to sensory nerve fibers that carry the signal to the brain, where the “sweet” taste is processed.
A “sweet ligand” is a molecule that binds to and activates human sweet taste receptors. These types of molecules are not only sugars, but can be many other compounds. Even some amino acids are sweet. For example, glycine is sweet. You can use glycine powder to sweeten your coffee. Some proteins can also be sweet. And, of course, artificial sweeteners are sweet.
Here is a more formal explanation of this process:
Binding of a [sweet] ligand to the sweet taste receptor leads to activation of the heterotrimeric G-protein α-gustducin. Phospholipase C β2 is subsequently stimulated, leading to release of intracellular Ca2+ and activation of the transient receptor potential cation channel M5 (TRPM5). This sequence results in the release of ATP, which can then activate adjacent sensory afferent neurons that send signals to brain centers involved in taste perception. 1Lee AA, Owyang C. Sugars, Sweet Taste Receptors, and Brain Responses. Nutrients. 2017 Jun 24;9(7):653. doi: 10.3390/nu9070653. PMID: 28672790; PMCID: PMC5537773.
This can be confusing and the science of taste is confusing. Something that is sweet is something that binds to our sweet taste detectors. We think of sugar as the definition of sweet. But we only perceive it as sweet because it binds to these proteins in our sweet taste cells. When other compounds bind to them, they are detected as sweet as well. A compound does not have to be like sugar to do this. Instead, a wide range of compounds are able to bind to the sweet taste receptors and many of these are chemically unrelated to sugars or even carbohydrates in general. Some artificial sweeteners were discovered to be sweet by accident.
For example, when James Schlatter discovered the artificial sweetener aspartame, he wasn’t trying to make an artificial sweetener. He was trying to make an ulcer drug. As the story goes, he accidentally got some of the compound on his fingers and when he licked his fingers to pick up a piece of paper he noticed a very sweet taste. Wala! A new artificial sweetener (in time).
Here are some sweet compounds:
- Glucose, fructose, sucrose, maltose.
- Artificial sweeteners: Saccharin, aspartame, cyclamate.
- Sweet amino acids: D-tryptophan, D-phenylalanine, D-serine.
- Sweet proteins: Monellin, brazzein, thaumatin.
Of course, some compounds are sweeter than others. For example, fructose is sweeter than glucose or sucrose (sucrose, or table sugar, is half fructose and half glucose).
And, it may interest you to know that the sweetest compound is a protein called thaumatin (or talin). It comes from the katemfe plant (Thaumatococcus daniellii) in West Africa, and it is around 3,250 times sweeter than sugar. Can you imagine?
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