Digestive System > Pregastric Physiology

Sweet Proteins: Miraculin, Monellin, Curcuin, Thaumatin, ...

Several proteins have been isolated and characterized that taste sweet, often thousands of times sweeter than sucrose on a molar basis. These proteins are all the products of plants and have been avidly pursued as non-carbohydrate sweeteners with significant commercial potential as sugar substitutes with virtually no caloric burden. Because purification of these proteins from their natural sources is expensive, several have been expressed in other transgenic plants or bacteria.

Each of these proteins appears to interact with and stimulate activation of the human sweet taste receptor (hT1R2-hT1R3) on taste receptor cells, but the precise mechanisms of those interactions remain only partially characterized.

Proteins that Taste Sweet

Well known proteins that intrinsically taste sweet include:

West Africa is clearly a sweet place to be. It seems likely that these plants evolved sweet proteins in seeds and fruit to appeal to animals and enhance their dispersal.

Miraculin: A Protein that Modulates the Sweet Taste

In contrast to the intrinsically sweet-tasting proteins described above, miraculin is a protein that is said to modify the sense of sweet taste. This protein is present in the berries of Synsepalum dulcificum, the miracle fruit, again from West Africa.

At neutral pH, miraculin does not taste sweet, but it binds to sweet taste receptors and blocks several artifial sweeteners from binding, thereby acting as an antagonist. Most interestingly, when acidic solutions are subsequently introduced into the oral cavity, the structure of miraculin changes and it becomes an agonist and activates the sweet receptor. In other words, if you ingest miraculin and then consume something sour (e.g. citric acid), the normally sour material tastes sweet. This effect lasts roughly an hour after eating miracle berries.

References and Reviews

Pregastric Digestion: Index

Send comments to Richard.Bowen@colostate.edu