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 450 times sweeter than sucrose. They are heat-stable, pH-stable, and do not ferment. Additionally, they do not induce a glycemic response when ingested, thus making them attractive as natural sweeteners for 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 acetal. 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.
While the FDA does not consider whole-leaf Stevia or crude Stevia extracts to be generally recognized as safe (GRAS) food additives, several companies have submitted notices to the FDA that they consider specific rebaudiosides to be GRAS for use as food additives, and have had these notices accepted by the FDA.
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 established an Acceptable Daily Intake (ADI) for steviol glycosides, expressed as steviol equivalents, of 4 mg/kg bodyweight/day. On 11 November 2011, the European Commission allowed the usage of steviol glycosides as a food additive, establishing maximum content levels for different types of foods and beverages.
The precursors of steviol are synthesized in plants via the non-mevalonate pathway located in plant cell plasmids, which produces isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP). IPP and DMAPP are converted to geranylgeranyl diphosphate (GGDP), which is the precursor of many diterpenoids, by GGDP synthase. GPDP is made into a cyclic compound, copalyl diphosphate (CDP), by CDP synthase, after which kaurene is produced by another cyclization catalyzed by kaurene synthase. Kaurene is then oxidized to kaurenoic acid by kaurene oxidase in a reaction that uses up oxygen and NADPH. Then steviol is produced by hydroxylation. Following several glucosylation and glycosylation reactions catalyzed by UDP-glucosyltransferases, steviol glycoside is obtained.
- 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.
- Benford, D. J.; DiNovi, M.; Schlatter, J. (2006). "Safety Evaluation of Certain Food Additives: Steviol Glycosides" (PDF). WHO Food Additives Series (World Health Organization Joint FAO/WHO Expert Committee on Food Additives (JECFA)) 54: 140.
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- Brusick DJ (2008). "A critical review of the genetic toxicity of steviol and steviol glycosides". Food Chem Toxicol 46 (7): S83–S91. doi:10.1016/j.fct.2008.05.002. PMID 18556105.
- Goyal, S. K.; Samsher; Goyal, R. K. (Feb 2010). "Stevia (Stevia rebaudiana) a bio-sweetener: a review". Int J Food Sci Nutr 61 (1): 1–10. doi:10.3109/09637480903193049. PMID 19961353.
- Ulbricht, C.; Isaac, R.; Milkin, T.; Poole, E. A.; Rusie, E. et al. (Apr 2010). "An evidence-based systematic review of stevia by the Natural Standard Research Collaboration". Cardiovasc Hematol Agents Med Chem 8 (2): 113–27. PMID 20370653.
- Joint FAO/WHO Expert Committee on food additives, Sixty-ninth Meeting. World Health Organization. 4 July 2008.
- "Is Stevia an 'FDA approved' sweetener?". fda.gov. April 4, 2012. Archived from the original on March 20, 2014. Retrieved March 20, 2014.
- "GRAS Notices". FDA GRAS notification database. FDA. March 20, 2014. Archived from the original on March 20, 2014. Retrieved March 20, 2014.
- "Commission Regulation (EU) No 1131/2011" (PDF). Official Journal of the European Union: 7. 11 November 2011. Retrieved 15 November 2011. "The CE regulation establishes steviol glycosides as food additive, and establishes maximum content levels in foodstuff and beverages."
- Brandle JE, Telmer PG. Steviol glycoside biosynthesis. Phytochemistry. 2007 Jul;68(14):1855-63. PMID: 17397883