Miraculin

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Miraculin is a glycoprotein extracted from the miracle fruit plant, a shrub native to West Africa (Synsepalum dulcificum or Richadella dulcifica). Local names for the plant include taami, asaa, and ledidi. Miraculin itself is not sweet, but the human tongue, once exposed to miraculin, perceives ordinarily sour foods, such as citrus, as sweet for up to an hour afterwards. This small red berry has been used in West Africa to improve the taste of acidic foods.

Because the miracle fruit itself has no distinct taste, this taste-modifying function of the fruit had been regarded as a miracle. The active substance, isolated by Prof. Kenzo Kurihara, a Japanese scientist, was named miraculin after the miracle fruit when he published his work in Science in 1968. Miraculin was first sequenced in 1989 and was found to be a glycoprotein consisting of 191 amino acids and some carbohydrate chains.

The detailed mechanism of the taste-inducing behavior is still unknown. It has been suggested that the miraculin molecule can change the structure of taste cells on the tongue. As a result, the sweet receptors are activated by acids, which are sour in general. This effect remains until the taste buds return to normal.

While attempts to express it in E. coli bacteria have failed, Japanese researchers have succeeded in preparing genetically modified plants, such as lettuce, that express miraculin. This efficient method to produce miraculin might be able to be applied to create a new sugar-free sweetener.