We all know that the taste of sweetness is given by the carbohydrates, also known as sugars or glucides.
But the sensation of sweet is given by taste sensors, and like every sensor, they can be tricked.
That's why the sweetest taste in nature comes not from sugars, as you could see, but from other substances.
In fact, the artificial sweeteners use the same principle.
The miracle fruits (photo above), which are the small red berries of Richardella dulcifica (Synsepalum dulcificum), a shrub indigenous to tropical West Africa, have long been known for their taste properties to improve acidic foods.
These berries have the property of modifying the taste of sour foods and dilute mineral and organic acids into a sweet taste after the fruit pulp has been chewed.
This modifying effect lasts for some time, usually for 1-2 h.
This is due to a glycoprotein named miraculin, made of 191 amino acids and some sugar chains.
Miraculin itself is tasteless, but the human tongue, once exposed to miraculin, perceives ordinarily sour foods, such as citrus, as sweet for up to an hour afterwards.
One thousandth part of a gram of miraculin is enough for making you eat a lemon like a sweet apple.
Some researchers believe that the miraculin molecule can change the structure of taste sensors on the tongue for sweet, becoming activated by acids, which are sour in general.
Japanese geneticists have achieved through genetic engineering plants, like lettuce, producing miraculin.
Miraculin might be used as a sugar-free sweetener, without bringing the side effects of the artificial ones, supposed to be carcinogenic.
From the aril of the katemfe fruit (or Sudan miracle fruit) (photo center) (Thaumatococcus daniellii), found also in West Africa, is extracted thaumatin, a low-calorie (virtually calorie-free) protein sweetener and flavor modifier.
The substance is often used for its flavor, not exclusively as a sweetener.
The thaumatins were first found as a mixture of proteins, but some of them are about 2000 times sweeter than sugar.
But thaumatin's taste is markedly different from sugar's: its sweetness is felt very slowly and for long time, it leaves a liquorice-like aftertaste at high usage levels.
Thaumatin is highly water-soluble and stable to heating under acidic conditions and its synthesis is induced in katemfe in response to an attack upon the plant by viruses and fungi.
The thaumatin protein is considered a prototype for a pathogen-response protein domain, found also in rice and some worms.
Within West Africa, the katemfe fruit is cultivated for some time, and thaumatin has been approved as sweetener in European Union (E957), Israel, Japan and US.
Another proteic sweetener was found in the serendipity berry (photo bellow), the drupe of the shrub Dioscoreophyllum cumminsii, also from West African.
Its protein, called monellin, is 3000 to 5000 times sweeter than sugar; some say 70,000 (this means one monellin molecule: one sugar molecule or 1000 times more on gram to gram comparison).
Instead, monellin is sensitive to high temperatures.
In South America (Paraguay and Southern Brazil), Guarani Indians used for centuries the leaves of the shrub named sweet grass (Stevia rebaudiana) as sweetener in mate beverage.
The sweet taste of the plant is given by two glycosides: stevioside and rebaudioside.
These chemicals are 250-300 times sweeter than sugar, heat stable, acidity stable, and non-fermentable.
Since early 1970s, Japan is the biggest cultivator and consumer of stevia as an alternative to artificial sweeteners but the plant is also cultivated in China, Korea, Taiwan, Thailand, Malaysia and Israel (outside South America).
A 1985 study points steviol, a breakdown product from stevioside and rebaudioside, as mutagen but this is disputed and human clinic results do not enhance this.