E960
   HOME

TheInfoList



OR:

Steviol glycosides are the chemical compounds responsible for the sweet taste of the leaves of the South American plant '' Stevia rebaudiana'' ( Asteraceae) and the main ingredients (or
precursors Precursor or Precursors may refer to: * Precursor (religion), a forerunner, predecessor ** The Precursor, John the Baptist Science and technology * Precursor (bird), a hypothesized genus of fossil birds that was composed of fossilized parts of un ...
) of many sweeteners marketed under the generic name
stevia Stevia () is a natural sweetener and sugar substitute derived from the leaves of the plant species ''Stevia rebaudiana'', native to Paraguay and Brazil. The active compounds are steviol glycosides (mainly stevioside and rebaudioside), which h ...
and several trade names. They also occur in the related species '' S. phlebophylla'' (but in no other species of ''
Stevia Stevia () is a natural sweetener and sugar substitute derived from the leaves of the plant species ''Stevia rebaudiana'', native to Paraguay and Brazil. The active compounds are steviol glycosides (mainly stevioside and rebaudioside), which h ...
'') and in the plant ''
Rubus chingii ''Rubus'' is a large and diverse genus of flowering plants in the rose family, Rosaceae, subfamily Rosoideae, with over 1,350 species. Raspberries, blackberries, and dewberries are common, widely distributed members of the genus. Most of these ...
'' (
Rosaceae Rosaceae (), the rose family, is a medium-sized family of flowering plants that includes 4,828 known species in 91 genera. The name is derived from the type genus ''Rosa''. Among the most species-rich genera are ''Alchemilla'' (270), ''Sorbus ...
). Steviol glycosides from ''Stevia rebaudiana'' have been reported to be between 30 and 320 times sweeter than sucrose, although there is some disagreement in the technical literature about these numbers. They are heat-stable, pH-stable, and do not
ferment Fermentation is a metabolism, metabolic process that produces chemical changes in organic Substrate (chemistry), substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in ...
. Steviol glycosides do not induce a glycemic response when ingested, because humans cannot
metabolize Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...
stevia. The
acceptable daily intake Acceptable daily intake or ADI is a measure of the amount of a specific substance (originally applied for a food additive, later also for a residue of a veterinary drug or pesticide) in food or drinking water that can be ingested (orally) daily ove ...
(ADI) for steviol glycosides, expressed as steviol equivalents, has been established to be 4 mg/kg body weight/day, and is based on no observed effects of a 100 fold higher dose in a rat study.


Structure

These compounds are glycosides of
steviol Steviol is a diterpene first isolated from the plant ''Stevia rebaudiana'' in 1931. Its chemical structure was not fully elucidated until 1960. Steviol occurs in the plant as steviol glycosides, sweet compounds that have found widespread use as ...
. Specifically, their molecules can be viewed as a steviol molecule, with its carboxyl hydrogen atom replaced by a glucose molecule to form an ester, and a hydroxyl hydrogen with combinations of glucose and
rhamnose Rhamnose (Rha, Rham) is a naturally occurring deoxy sugar. It can be classified as either a methyl-pentose or a 6-deoxy-hexose. Rhamnose predominantly occurs in nature in its L-form as L-rhamnose (6-deoxy-L-mannose). This is unusual, since most o ...
to form an acetal. The steviol glycosides found in ''S. rebaudiana'' leaves, and their
dry weight Vehicle weight is a measurement of wheeled motor vehicles; either an actual measured weight of the vehicle under defined conditions or a gross weight rating for its weight carrying capacity. Curb or kerb weight Curb weight (U.S. English) or kerb ...
percentage, include: * Stevioside (5–10%) * Dulcoside A (0.5–1%) * Rebaudioside A (2–4%) * Rebaudioside B * Rebaudioside C (1–2%) * Rebaudioside D * Rebaudioside E * Rebaudioside F * Rubusoside * Steviolbioside The last three are present only in minute quantities, and rebaudioside B has been claimed to be a byproduct of the isolation technique. A commercial steviol glycoside mixture extracted from the plant was found to have about 80% stevioside, 8% rebaudioside A, and 0.6% rebaudioside C. The Chinese plant ''Rubus chingii'' produces rubusoside, a steviol glycoside not found in ''Stevia''. According to the EU Stevia Regulation of 13 July 2021, however, rubusoside is one of the eleven major glycoside components of
Stevia Stevia () is a natural sweetener and sugar substitute derived from the leaves of the plant species ''Stevia rebaudiana'', native to Paraguay and Brazil. The active compounds are steviol glycosides (mainly stevioside and rebaudioside), which h ...
, extracted from the leaves of the ''Stevia rebaudiana''.''COMMISSION REGULATION (EU) 2021/1156 of 13 July 2021''
/ref> Stevioside and rebaudioside A were first isolated in 1931 by French chemists, Bridel and Lavielle. Both compounds have only glucose subgroups: stevioside has two linked glucose molecules at the hydroxyl site, whereas rebaudioside A has three, with the middle glucose of the triplet connected to the central steviol structure. Early sensory tests led to claims that rebaudioside A was 150 to 320 times sweeter than sucrose, stevioside was 10 to 270 times sweeter, rebaudioside C 40 to 60 times sweeter, and dulcoside A 30 times sweeter. However, a more recent evaluation found rebaudoside A to be about 240 times sweeter, and stevioside about 140 times. Rebaudioside A also had the least bitterness and aftertaste. The relative sweetness seems to vary with concentration: a mix of steviol glycosides in the natural proportions was found to be 150 times sweeter than sucrose when matching a 3% sucrose solution, but only 100 times sweeter when matching a 10% sucrose solution.


Biosynthesis

In '' Stevia rebaudiana'', the
biosynthesis Biosynthesis is a multi-step, enzyme-catalyzed process where substrates are converted into more complex products in living organisms. In biosynthesis, simple compounds are modified, converted into other compounds, or joined to form macromolecules. ...
of the glucosides occurs only in green tissues. Steviol is first produced in the
plastid The plastid (Greek: πλαστός; plastós: formed, molded – plural plastids) is a membrane-bound organelle found in the Cell (biology), cells of plants, algae, and some other eukaryotic organisms. They are considered to be intracellular endosy ...
s and in the
endoplasmic reticulum The endoplasmic reticulum (ER) is, in essence, the transportation system of the eukaryotic cell, and has many other important functions such as protein folding. It is a type of organelle made up of two subunits – rough endoplasmic reticulum ( ...
is glucosylated and glycosylated in the cytoplasm, catalyzed by UDP-
glucosyltransferases Glucosyltransferases are a type of glycosyltransferase that enable the transfer of glucose. Examples include: * glycogen synthase * glycogen phosphorylase Glycogen phosphorylase is one of the phosphorylase enzymes (). Glycogen phosphorylase cat ...
. Rebaudioside A, in particular, is formed from stevioside. Though there are several molecules that fall into the category of steviol glycoside, synthesis follows a similar route. Synthesis of steviol glycoside begins with
isoprene Isoprene, or 2-methyl-1,3-butadiene, is a common volatile organic compound with the formula CH2=C(CH3)−CH=CH2. In its pure form it is a colorless volatile liquid. Isoprene is an unsaturated hydrocarbon. It is produced by many plants and animals ...
units created via the DXP or MEP pathway. Two molecules derived from
primary metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...
,
Pyruvate Pyruvic acid (CH3COCOOH) is the simplest of the alpha-keto acids, with a carboxylic acid and a ketone functional group. Pyruvate, the conjugate base, CH3COCOO−, is an intermediate in several metabolic pathways throughout the cell. Pyruvic aci ...
and Glyceraldehyde 3-Phosphate, are the initial molecules for this pathway. Upon forming IPP and
DMAPP Dimethylallyl pyrophosphate (DMAPP; or alternatively, dimethylallyl diphosphate (DMADP); also isoprenyl pyrophosphate) is an isoprenoid precursor. It is a product of both the mevalonate pathway and the MEP pathway of isoprenoid precursor biosynt ...
, the diterpene GGPP is formed by via head-to-tail addition by an
Sn1 The SN1 reaction is a substitution reaction in organic chemistry, the name of which refers to the Hughes-Ingold symbol of the mechanism. "SN" stands for "nucleophilic substitution", and the "1" says that the rate-determining step is unimolecular. ...
mechanism. Elongation begins when IPP and DMAPP form Geranyl Pyrophosphate (GPP). GPP elongates through the same Sn1 mechanism to create Farnesyl Pyrophosphate (FPP), and FPP elongates to form GGPP. With the formation of GGPP cyclization occurs by enzymes copalyl diphosphate
synthase In biochemistry, a synthase is an enzyme that catalyses a synthesis process. Note that, originally, biochemical nomenclature distinguished synthetases and synthases. Under the original definition, synthases do not use energy from nucleoside tripho ...
(CDPS) and Kuarene Synthase (KS) to form -(-)Kuarene. Several oxidation steps then occur to form steviol. Steviol glycoside
biosynthesis Biosynthesis is a multi-step, enzyme-catalyzed process where substrates are converted into more complex products in living organisms. In biosynthesis, simple compounds are modified, converted into other compounds, or joined to form macromolecules. ...
then follows several modifications from steviol that regioselectively select for sugar molecules to be placed.Richman, A., Swanson, A., Humphrey, T., Chapman, R., McGarvey, B., Pocs, R., Brandle, J., 2005
Functional genomics uncovers threeglucosyltransferases involved in the synthesis of the major sweetglucosides of Stevia rebaudiana
Plant J. 41, 56–67
Once these molecules are fully glycosylated, the glycosides are then stored in vacuoles.


See also

* Glycoside *
Stevia Stevia () is a natural sweetener and sugar substitute derived from the leaves of the plant species ''Stevia rebaudiana'', native to Paraguay and Brazil. The active compounds are steviol glycosides (mainly stevioside and rebaudioside), which h ...
*
Sugar substitute A sugar substitute is a food additive that provides a sweetness like that of sugar while containing significantly less food energy than sugar-based sweeteners, making it a zero-calorie () or low-calorie sweetener. Artificial sweeteners may be d ...


References


External links

* {{Transient receptor potential channel modulators Diterpene glycosides Sugar substitutes Carboxylic acids E-number additives