Steviol glycosides are responsible for the sweet taste of the leaves of the stevia plant (Stevia rebaudiana Bertoni). These compounds range in sweetness from 40 to 300 times sweeter than sucrose. They are heat-stable, pH-stable, and do not ferment. They also do not induce a glycemic response when ingested, making them attractive as natural sweeteners to diabetics and others on carbohydrate-controlled diets.
The diterpene known as steviol is the aglycone of stevia's sweet glycosides, which are constructed by replacing steviol's carboxyl hydrogen atom (at the bottom left of the figure) with glucose to form an ester, and replacing the hydroxyl hydrogen (at the top of the figure) with combinations of glucose and rhamnose to form an ether. The two primary compounds, stevioside and rebaudioside A, use only glucose: 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.
In terms of weight fraction, the four major steviol glycosides found in the stevia plant tissue are:
- 5–10% stevioside (250–300X of sugar)
- 2–4% rebaudioside A — most sweet (350–450X of sugar) and least bitter
- 1–2% rebaudioside C
- ½–1% dulcoside A.
Rebaudioside B, D, and E may also be present in minute quantities; however, it is suspected that rebaudioside B is a byproduct of the isolation technique. The two majority compounds stevioside and rebaudioside, primarily responsible for the sweet taste of stevia leaves, were first isolated by two French chemists, Bridel and Lavielle (1931).
Steviol glycosides were first commercialized as a sweetener in 1971 by the Japanese firm Morita Kagaku Kogyo Co., Ltd., a leading stevia extract producer in Japan.
- Rebiana is the trade name for a zero-calorie sweetener containing mainly rebaudioside A.
- Truvia is the consumer brand for Rebiana marketed by Cargill and developed jointly with The Coca-Cola Company.
- PureVia is PepsiCo's brand of rebaudioside A sweetener which was developed jointly with Whole Earth Sweetener Company.
- Enliten is Corn Products International's brand of rebaudioside A sweetener.
- Erylite Stevia is the trade name for Jungbunzlauer's sweetener with rebaudioside A.
Health effects 
A 1985 study reporting that steviol may be a mutagen has been criticized on procedural grounds that the data were mishandled in such a way that even distilled water would appear mutagenic. More recent studies appear to establish the safety of steviol and its glycosides. In 2006, the World Health Organization (WHO) performed a thorough evaluation of recent experimental studies of stevia extracts conducted on animals and humans, and concluded that “stevioside and rebaudioside A are not genotoxic in vitro or in vivo and that the genotoxicity of steviol and some of its oxidative derivatives in vitro is not expressed in vivo.” The report also found no evidence of carcinogenic activity. The report also suggested the possibility of health benefits, in that “stevioside has shown some evidence of pharmacological effects in patients with hypertension or with type-2 diabetes”, but concluded that further study was required to determine proper dosage.
The European Food Safety Authority evaluated the safety of steviol glycosides, extracted from the leaves of the Stevia rebaudiana Bertoni plant, as sweetener and expressed its opinion on 10 March 2010. The authority concluded an Acceptable Daily Intake (ADI) for steviol glycosides, expressed as steviol equivalents, of 4 mg/kg-bodyweight per day.
See also 
- The sweetness multiplier "300 times" comes from subjective evaluations by a panel of test subjects tasting various dilutions compared to a standard dilution of sucrose. Sources referenced in this article say steviosides have up to 250 times the sweetness of sucrose, but others, including stevioside brands such as SweetLeaf, claim 300 times. 1/3 to 1/2 teaspoon (1.6–2.5 ml) of stevioside powder is claimed to have equivalent sweetening power to 1 cup (240 ml) of sugar.
- Brandle, J. (2004-08-19). "FAQ – Stevia, Nature's natural low calorie sweetener". Agriculture and Agri-Food Canada. Retrieved 2006-11-08.
- Bridel, M.; Lavielle, R. (1931). "Sur le principe sucré des feuilles de Kaâ-hê-é (stevia rebaundiana B)". Academie des Sciences Paris Comptes Rendus (Parts 192): 1123–1125.
- "Rebiana today". Cargill. Retrieved 2008-12-22.
- "New scientific studies establish the safety of Rebiana, a sweetener from the stevia plant". FlexNews. 2008-05-15. Retrieved 2008-12-22.
- "F.D.A. Approves 2 New Sweeteners". The New York Times (Associated Press). 2008-12-17. Retrieved 2008-12-22.
- Pezzuto, J.M.; Compadre C.M., Swanson S.M., Nanayakkara D., Kinghorn A.D. (April 1985). "Metabolically activated steviol, the aglycone of stevioside, is mutagenic". Proc. Natl. Acad. Sci. USA 82 (8): 2478–82. doi:10.1073/pnas.82.8.2478. PMC 397582. PMID 3887402.
- Procinska, E.; Bridges B.A., Hanson J.R. (March 1991). "Interpretation of results with the 8-azaguanine resistance system in Salmonella typhimurium: no evidence for direct acting mutagenesis by 15-oxosteviol, a possible metabolite of steviol". Mutagenesis 6 (2): 165–7. doi:10.1093/mutage/6.2.165. PMID 2056919. – full article text is reproduced here.
- Benford, D.J.; DiNovi, M., Schlatter, J. (2006). "Safety evaluation of certain food additives: Steviol glycosides" (PDF – 18 MB). WHO Food Additives Series (World Health Organization Joint FAO/WHO Expert Committee on Food Additives (JECFA)) 54: 140.
- Official Journal of the European Union (2011-11-11). "Commission Regulation (EU) No 1131/2011" (PDF). pp. 26–27 (document) or pp. 39–40 (PDF). Retrieved 2011-11-15. "The CE regulation establishes steviol glycosides as food additive, and establishes maximum content levels in foodstuff and beverages."