Miraculin itself does not taste
sweet. When
taste buds are exposed to miraculin, the protein binds to the sweetness receptors. This causes normally sour-tasting acidic foods, such as
citrus, to be perceived as sweet.[2][3] The effect can last for one or two hours.[4][5]
History
The sweetening properties of Synsepalum dulcificum berries were first noted by des Marchais during expeditions to West Africa in the 18th century.[6] The term miraculin derived from experiments to isolate and purify the active
glycoprotein that gave the berries their sweetening effects, results that were published simultaneously by Japanese and Dutch scientists working independently in the 1960s (the Dutch team called the glycoprotein mieraculin).[7][8] The word miraculin was in common use by the mid-1970s.[9][10][11]
Glycoprotein structure
Miraculin was first sequenced in 1989 and was found to be a 24.6
kilodalton[2] glycoprotein consisting of 191
amino acids[12] and 13.9% by weight of various sugars.[2]
The
native state of miraculin is a
tetramer consisting of two
dimers, each held together by a
disulfide bridge.[14] Both tetramer miraculin and native dimer miraculin in its crude state have the taste-modifying activity of turning sour tastes into sweet tastes.[15] Miraculin belongs to the
Kunitz STI protease inhibitor family.
Sweetness properties
Miraculin, unlike
curculin (another taste-modifying agent),[16] is not sweet by itself, but it can change the perception of sourness to sweetness, even for a long period after consumption.[4] The duration and intensity of the sweetness-modifying effect depends on various factors, such as miraculin concentration, duration of contact of the miraculin with the tongue, and acid concentration.[3][4] Miraculin reaches its maximum sweetness with a solution containing at least 4*10−7mol/L miraculin, which is held in the mouth for about 3 minutes. Maximum is equivalent in sweetness to a 0.4 mol/L solution of
sucrose.[17] Miraculin degrades permanently via
denaturation at high temperatures, at
pH below 3 or above 12.[18]
Although the detailed mechanism of the taste-inducing behavior is unknown, it appears the sweet receptors are activated by acids which are related to sourness, an effect remaining until the
taste buds perceive a neutral pH.[3][4] Sweeteners are perceived by the human sweet taste receptor, hT1R2-hT1R3, which belongs to
G protein-coupled receptors,[4] modified by the two
histidine residues (i.e. His30 and His60) which participate in the taste-modifying behavior.[19] One site maintains the attachment of the protein to the membranes while the other (with attached
xylose or
arabinose) activates the sweet receptor membrane in acid solutions.[14]
As a sweetener
As miraculin is a readily soluble protein and relatively heat stable, it is a potential
sweetener in acidic food, such as
soft drinks. While attempts to express it in
yeast and
tobacco plants have failed, researchers have succeeded in preparing
genetically modifiedE. coli bacteria that express miraculin.[20]Lettuce and
tomato have also been used for mass production of miraculin.[21][22]
The use of miraculin as a food additive was denied in 1974 by the United States
Food and Drug Administration.[23] Since 2011, the FDA has imposed a ban on importing Synsepalum dulcificum (specifying 'miraculin') from its origin in
Taiwan, declaring it as an "illegal undeclared sweetener".[24] The ban does not apply to the use of manufactured miraculin in
dietary supplements.[25][26] Miraculin has a
novel food status in the
European Union.[27] It is approved in
Japan as a safe
food additive, according to the List of Existing Food Additives published by the Ministry of Health and Welfare (published by the
Japan External Trade Organization).
^PDB:
3IIR; Gahloth D, Selvakumar P, Shee C, Kumar P, Sharma AK (February 2010). "Cloning, sequence analysis and crystal structure determination of a miraculin-like protein from Murraya koenigii". Archives of Biochemistry and Biophysics. 494 (1): 15–22.
doi:
10.1016/j.abb.2009.11.008.
PMID19914199.
^Swamy KB, Hadi SA, Sekaran M, Pichika MR (November 2014). "The clinical effects of Synsepalum dulcificum: a review". Journal of Medicinal Food. 17 (11): 1165–9.
doi:
10.1089/jmf.2013.3084.
PMID25314134.
^Giroux EL, Henkin RI (1974). "Purification and some properties of miraculin, a glycoprotein from Synsepalum dulcificum which provokes sweetness and blocks sourness". Journal of Agricultural and Food Chemistry. 22 (4): 595–601.
doi:
10.1021/jf60194a033.
PMID4840911.
^
abKurihara Y (1992). "Characteristics of antisweet substances, sweet proteins, and sweetness-inducing proteins". Critical Reviews in Food Science and Nutrition. 32 (3): 231–52.
doi:
10.1080/10408399209527598.
PMID1418601.
^Igeta H, Tamura Y, Nakaya K, Nakamura Y, Kurihara Y (September 1991). "Determination of disulfide array and subunit structure of taste-modifying protein, miraculin". Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology. 1079 (3): 303–7.
doi:
10.1016/0167-4838(91)90073-9.
PMID1911854.
^Ito K, Asakura T, Morita Y, Nakajima K, Koizumi A, Shimizu-Ibuka A, Masuda K, Ishiguro M, Terada T, Maruyama J, Kitamoto K, Misaka T, Abe K (August 2007). "Microbial production of sensory-active miraculin". Biochemical and Biophysical Research Communications. 360 (2): 407–11.
doi:
10.1016/j.bbrc.2007.06.064.
PMID17592723.
^Matsuyama T, Satoh M, Nakata R, Aoyama T, Inoue H (April 2009). "Functional expression of miraculin, a taste-modifying protein in Escherichia coli". Journal of Biochemistry. 145 (4): 445–50.
doi:
10.1093/jb/mvn184.
PMID19122203.
^Kato K, Yoshida R, Kikuzaki A, Hirai T, Kuroda H, Hiwasa-Tanase K, Takane K, Ezura H, Mizoguchi T (September 2010). "Molecular breeding of tomato lines for mass production of miraculin in a plant factory". Journal of Agricultural and Food Chemistry. 58 (17): 9505–10.
doi:
10.1021/jf101874b.
PMID20695489.
^Gollner AL (31 March 2009). The Fruit Hunters: A Story of Nature, Adventure, Commerce and Obsession.
Anchor Canada.
ISBN978-0385662680.