Let me present some facts on Stevia which should clarify doubts:
Stevia based sweeteners are 200 times sweeter than sugar. Stevia comes from the plant belonging to the genus Stevia. The sweetener has zero calories. This sweetener is becoming quite popular with diabetics and the obese.
Most of the Stevia based products sold in the market come from Stevia rebaudiana. The plant belongs to the Asteraceae family. It is a bush that prefers a semi-humid subtropical climate. Stevia is easy to cultivate. The plant is native to Paraguay and Brazil. Here it has been traditionally used as a sweetener in food and drink. China today, though, is the world’s largest producer and exporter of Stevia.
Stevia rebaudiana Bertoni is the sweetest of all Stevia species (Soejarto et. al. 1982; Kinghorn et al 1984) The sweetness of Stevia comes from diterpene glycosides – a group of natural sweeteners -extracted from the leaves. The leaves of Stevia plants contain stevioside, rebaudioside A, C, D, E and F, steviobioside, and dulcoside A. Stevioside is the most abundant of all the glycosides.
The plant has been also traditionally used as a natural control for Type 2 diabetes in Brazil and Paraguay. This species has been used as a sweetener by the indigenous communities in many parts of Central and South America (Melis, 1992). Steviol and stevioside have been shown to induce the pancreas to release insulin. (Jeppesen et al. 2000).
Initially, the Stevia sweetener was just a powder of Stevia leaves. This product left a bitter aftertaste in the mouth. This limited its acceptability as a sweetener. The bitter taste was attributed to the presence of stevioside present in the plant. Rebaudioside A is the sweetest and the most stable of the sweetening compounds. It is less bitter when compared to Stevioside. (Cramer and Ikan 1987).
Stevia was declared safe for use in food and beverages by the USFDA in 2008. The Food and Agriculture Organization of the United Nations and the World Health Organization (WHO) also have determined that pure stevia extract is safe for consumption when consumed within acceptable levels. The acceptable daily intake (ADI) has been put at 4 milligrams per kilogram of body weight.
More on Stevia and natural sweeteners:
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