Stevia is the name given to extracts from leaves of the plant Stevia rebaudiana used as sweeteners or sugar substitutes. The two main compounds responsible for the sweetness of stevia are stevioside and rebaudioside A, both of which are derivatives of the diterpene, steviol.
- Stevioside is 250-300 times sweeter than sugar, but possesses a bitter aftertaste.
- Rebaudioside A is 350-450 times sweeter than sugar and is less bitter than stevioside, making it a popular option for use in sweetener preparations.
Research has suggested that the methylene double bond linking C16 and C17 is essential for the sweetness of both molecules.
Various methods have been developed for analysis of steviol glycosides in different matrices, including stevia leaves, beverages, foods and sweetener preparations. Their extraction from stevia leaves can be achieved using novel cellulose acetate phthalate-polyacrylonitrile blend ultrafiltration membranes. Analytical techniques include a reverse-phase HPLC method for high purity sweetener preparations, a liquid chromatography electrospray tandem mass spectrometry (LC-ESI/MS/MS) procedure which can discriminate between stevia plants from different geographical origins and an HPLC-UV method for sugar confectionery.
Stevia rebaudiana leaves have been used as sweeteners in Brazil and Paraguay for hundreds of years, and in Japan since the seventies. The leaves and extracts have been available as dietary supplements in the US since 1995, but steviol glycosides have only been permitted for use as food additives by the European Union since 2011.
A range of commercial products containing stevia, usually in combination with other ingredients, now exist. For example:
- Truvia, developed jointly by Cargill and Coca-Cola as both a food ingredient and a tabletop sweetener, contains the stevia-derived sweetener, rebiana, the sugar alcohol, erythritol and natural flavours
- PureVia developed by PepsiCo is a blend of rebaudioside A, cellulose, dextrose and natural flavours
- Light at Heart by Tate & Lyle is a cane sugar-stevia blend that can be used in home baking
Several studies have tested the impact of stevia extracts on the physicochemical, sensory and health promoting properties of foods, including kimchi, oatmeal cookies and yoghurt.
In recent years, sugar substitutes have become increasingly popular among consumers; one study estimated that intake by children of beverages containing low calorie sweeteners has doubled in the US over the last decade. Health concerns associated with some artificial sweeteners, such as aspartame and saccharin, have led to increased demand for stevia, because it is perceived as a natural product and is, therefore, considered by many to be safer.
One of the concerns associated with non-nutritive sweeteners in general is that, rather than helping individuals in their fight against obesity, they may actually cause weight gain, as was the case in a study involving intake of aspartame and saccharin in rats. It has been suggested that low calorie sweeteners interact with taste receptor cells in a similar manner to sucrose, initiating a series of metabolic steps aimed at responding to sucrose; when the sucrose does not arrive, hunger is not satisfied and food intake increases.
However, another study showed that neither stevia nor aspartame preloads before lunch or dinner caused human participants to eat more at either meal than they did after a higher calorie sucrose meal. In the same piece of research, stevia was also shown to significantly reduce postprandial glucose levels in comparison to sucrose and postprandial insulin levels, in comparison to both sucrose and aspartame.
Stevia has also demonstrated antihypertensive, antidiabetic, anti-inflammatory and anticariogenic activity in some studies, suggesting that it may exert generally positive effects on health. However, in one study, stevia glycosides were found to exert a negative impact on growth of probiotic bacteria, which may limit their use in certain functional foods.
Concerns have also been raised in the past about potential hormonal effects and mutagenicity of stevia compounds, but these are thought to be non-existent at the low levels used to provide sweetness.
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