Steviol glycosides are thechemical compounds responsible for the sweet taste of the leaves of theSouth American plantStevia rebaudiana (Asteraceae) and the main ingredients (orprecursors) of manysweeteners marketed under the generic namestevia and severaltrade names. They also occur in the related speciesS. phlebophylla (but in no other species ofStevia) and in the plantRubus chingii (Rosaceae).^[1]

Steviol glycosides fromStevia rebaudiana have been reported to be between 30 and 320 times sweeter than sucrose,^[2] although there is some disagreement in the technical literature about these numbers.^[1][3] They are heat-stable,pH-stable, and do notferment.^[2]

Steviol glycosides do not induce aglycemic response when ingested, because humans cannotmetabolize stevia.^[4][5] Theacceptable daily intake (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 adverse effects of a 100 fold higher dose in a rat study.^[6]

These compounds areglycosides ofsteviol. Specifically, their molecules can be viewed as a steviol molecule, with itscarboxylhydrogenatom replaced by aglucose molecule to form anester, and ahydroxyl hydrogen with combinations of glucose andrhamnose to form anacetal.

The steviol glycosides found inS. rebaudiana leaves, and theirdry weight 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.^[2] A commercial steviol glycoside mixture extracted from the plant was found to have about 80% stevioside, 8% rebaudioside A, and 0.6% rebaudioside C.^[3]

The Chinese plantRubus chingii produces rubusoside, a steviol glycoside not found inStevia.^[1] According to the EU Stevia Regulation of 13 July 2021, however, rubusoside is one of the eleven major glycoside components ofStevia,extracted from the leaves of theStevia rebaudiana.^[7]

Stevioside and rebaudioside A were first isolated in 1931 by French chemists, Bridel and Lavielle.^[8] 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 110 to 270 times sweeter, rebaudioside C 40 to 60 times sweeter, and dulcoside A 30 times sweeter.^[2] However, a more recent evaluation found rebaudoside A to be about 240 times sweeter, and stevioside about 140 times.^[1] Rebaudioside A also had the least bitterness and aftertaste.^[2] 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.^[3]

InStevia rebaudiana, thebiosynthesis of the glucosides occurs only in green tissues. Steviol is first produced in theplastids and in theendoplasmic reticulum is glucosylated andglycosylated in thecytoplasm, catalyzed by UDP-glucosyltransferases. Rebaudioside A, in particular, is formed fromstevioside.

Though there are severalmolecules that fall into the category of steviol glycoside, synthesis follows a similar route.^[9] Synthesis of steviol glycoside begins withisoprene units created via theDXP or MEP pathway.^[10][11] Two molecules derived fromprimary metabolism,Pyruvate andGlyceraldehyde 3-Phosphate, are the initial molecules for this pathway.

Upon forming IPP andDMAPP, thediterpene GGPP is formed by via head-to-tail addition by anSn1 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 byenzymes copalyl diphosphatesynthase (CDPS) and Kuarene Synthase (KS) to form -(-)Kuarene.^[12] Severaloxidation steps then occur to form steviol.

Steviol glycosidebiosynthesis then follows several modifications from steviol that regioselectively select for sugar molecules to be placed.^[13] Once these molecules are fully glycosylated, the glycosides are then stored invacuoles.^[1]

• Glycoside
• Stevia
• Sugar substitute

• Media related toSteviol glycosides at Wikimedia Commons

• Diterpene glycosides
• Sugar substitutes
• Carboxylic acids
• E-number additives

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