stevia is a genus of about 240 species of herbs and shrubs in the sunflower family (asteraceae), native to subtropical and tropical regions from western north america to south america. human use of the sweet species stevia rebaudiana bertoni is originated in south america.the species s. rebaudiana, commonly known as sweetleaf, sweet leaf, sugarleaf, or simply stevia, is widely grown for its sweet leaves. today, stevia is cultivated and used in food elsewhere in east asia, including in china (since 1984), korea, chinese taiwan, thailand, and malaysia. it can also be found in saint kitts and nevis, in parts of south america (brazil, colombia, peru, paraguay, and uruguay) and in israel. china is the world's largest exporter of stevioside and rebaudioside a.

the leaves of the stevia plant have 30–45 times the sweetness of sucrose (ordinary table sugar). the leaves can be eaten fresh, or put in teas and foods. as a sweetener and sugar substitute, stevia's taste has a slower onset and longer duration than that of sugar, although some of its extracts may have a bitter or licorice-like aftertaste at high concentrations, however its extracts of pure or high purity of rebaudioside a is of the least bitter.

with its extracts having up to 300 times the sweetness of sugar, stevia has garnered attention with the rise in demand for low-Carbohydrate, low-sugar food alternatives. medical research has also shown possible benefits of stevia in treating obesity and high blood pressure. because stevia has a negligible effect on blood glucose, it is attractive as a natural sweetener to people on carbohydrate-controlled diets. health concerns and political controversies have limited stevia's availability in many countries; for example, the united states banned it in the early 1990s unless labeled as a supplement, but in 2008 approved rebaudioside-a extract as a food additive. some countries continue to limit or ban its use until existing applications are evaluated. stevia is widely used as a sweetener in japan, south america, switzerland, australia, new zealand and parts of asia.

in 1899, the swiss botanist moisés santiago bertoni, during his research in eastern paraguay first described the plant and the sweet taste in detail. but only limited research was conducted on the topic until, in 1931, two french chemists isolated the steviol glycosides that give stevia its sweet taste. these compounds were named stevioside and rebaudioside, and are 250–300 times sweeter than sucrose, heat stable, ph stable, and non-fermentable.

steviol is the basic building block of stevia's sweet glycosides: stevioside and rebaudioside are constructed by replacing the bottom hydrogen atom with glucose and the top hydrogen atom with two or three linked glucose groups, respectively.
extraction of sweet compounds

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 a has the least bitterness of all the sweet compounds in the stevia plant. to produce rebaudioside a commercially, stevia plants are dried and subjected to a water extraction process. this crude extract contains about 50% rebaudioside a and is refined using ethanol, methanol, crystallization and separation technologies to separate the various glycoside molecules in the extract. this allows the manufacturer to isolate pure rebaudioside a.

the national research council of canada has patented a process for extracting sweet compounds from stevia by column extraction at temperatures from 0-25°c , followed by purification by nanofiltration. a microfiltration pretreatment step is used to clarify the extract. purification is by ultrafiltration followed by nanofiltration.
metabolism

based on studies conducted in the past several years, the joint fao/who expert committee on Food Additives (jecfa) has concluded that stevia Sweeteners are metabolized by a common pathway. this begins in the gut where the steviol glycosides are broken down to steviol. steviol is excreted in the urine as steviol glucuronide. the metabolized components of steviol glycosides essentially leave the body and there is no accumulation.

commercialization

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.

stevia has been grown on an experimental basis in ontario, canada since 1987 for the purpose of determining the feasibility of growing the crop commercially.

in 2007, the coca-cola company announced plans to obtain approval for their stevia-derived sweetener rebiana for use as a food additive within the united states by 2009, as well as plans to market rebiana-sweetened products in 12 countries that allow stevia's use as a food additive. in may 2008, coke and cargill announced the availability of truvia, a consumer brand stevia sweetener containing erythritol and rebiana, which the fda permitted as a food additive in december 2008. coca-cola announced intentions to release stevia-sweetened beverages in late december 2008.

shortly afterward, pepsico and pure circle announced purevia, their brand of stevia-based sweetener, but withheld release of beverages sweetened with rebaudioside a until receipt of fda confirmation. since the fda permitted truvia and purevia, both coca cola and pepsico have announced products that will contain their new sweetener.
other studies have shown stevia to improve insulin sensitivity in rats and possibly even to promote additional insulin production, helping to reverse diabetes and metabolic syndrome. preliminary human studies suggest that stevia can help reduce hypertension although another study has shown it to have no effect on hypertension. indeed, millions of japanese have been using stevia for over thirty years with no reported or known harmful effects. similarly, stevia leaves have been used for centuries in south america spanning multiple generations in ethnomedical tradition as a treatment for type ii diabetes.
the stevia leaf extract used in dietary supplements is derived from the leaves of the plant stevia rebaudiana bertoni.

benefits

• natural sweetener of no-calories
• anti-diabetic
• anti-hypertension
• anti-obesity