Miraculin Totally Explained

Everything about Miraculin totally explained

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 isn't 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 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.

Glycoprotein structure

Miraculin was first sequenced in 1989 and was found to be a glycoprotein consisting of 191 amino acids and some carbohydrate chains.
Miraculin occurs as a tetramer (98.4 kDa), a combination of 4 monomers group by dimer. Within each dimer 2 miraculin glycoproteins are linked by a disulfide bridge.

SIGNAL (29) MKELTMLSLS FFFVSALLAA AANPLLSAA

1-50 DSAPNPVLDI DGEKLRTGTN YYIVPVLRDH GGGLTVSATT PNGTFVCPPR

51-100 VVQTRKEVDH DRPLAFFPEN PKEDVVRVST DLNINFSAFM PNPGPETISS

101-150 WCRWTSSTVW RLDKYDESTG QYFVTIGGVK FKIEEFCGSG FYKLVFCPTV

151-191 CGSCKVKCGD VGIYIDQKGR GRRLALSDKP FAFEFNKTVY F

Amino acids sequence of glycoprotein miraculin unit adapted from Swiss-Prot biological database of protein sequences.

The molecular weight of the glycoprotein is 24.6 kDa including 3.4 kDa (13.9% of the weight) of sugar constituted (on molar ratio) of glucosamine (31%), mannose (30%), fucose (22%), xylose (10%) and galactose (7%).

Sweetness properties

Miraculin, unlike curculin (another taste-modifying agent), isn't sweet by itself, but it can change a sour beverage into a sweet beverage, even for a long period after consumption. The anti-sweet compound, Gymnemic acid suppresses the sweet taste of miraculin, like it does for sucrose.
The duration and intensity of the taste-modifying phenomena depends on various factors—miraculin concentration, duration of contact of the miraculin with the tongue, and acid concentration. Maximum sweet-induced response has been shown to be equivalent to the sweetness of 17% sucrose solution.
Glycoprotein is sensitive to heat, when heated over 100ºC miraculin loses its taste-modifying property. Miraculin activity is inactivated at pH below 3 and pH above 12 at room temperature. The sweet modifying effect stays at pH 4 (in acetate buffer), for 6 months at 5ºC.
The detailed mechanism of the taste-inducing behaviour 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. It is believed that miraculin has 2 active sites. One site maintains the sweet protein attached to the membranes while the other (Xylose or Arabinose) active the sweet receptor membrane in acid solution. The presence of positively charged ions (Ca²⁺ and/or Mg²⁺) interferes with the binding of the active sugar of miraculin to the sweet receptor and therefore inactive sweet taste.

As a Sweetener

As miraculin is a readily soluble protein and relatively heat stable, it's a potential sweetener in acidic food (for example soft drinks). Japanese researchers' more or less successful attempts to mass produce it are focused on recombinant technology. 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.
Miraculin was denied approval for use as a sweetener by the United States Food and Drug Administration (FDA).
Miraculin has no legal status in the European Union. However it's approved in Japan as a harmless additive, according to the List of Existing Food Additives published by the Ministry of Health and Welfare (published by JETRO).

Further Information

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