Rebaudioside

Steviol glycosides are the chemical compounds responsible for the sweet taste of the leaves of the South American plant Stevia rebaudiana (Asteraceae), and the main ingredients (or precursors) of many sweeteners marketed under the generic name stevia and several trade names. They also occur in the related species Stevia phlebophylla (but in no other species of Stevia) and in the plant Rubus chingii (Rosaceae).

Steviol glycosides from Stevia rebaudiana have been reported to be between 30 and 320 times sweeter than sucrose, although there is some disagreement in the technical literature about these numbers. 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 sugar substitutes for diabetics and other people on carbohydrate-controlled diets. The acceptable daily intake (ADI) for steviol glycosides, expressed as steviol equivalents, has been established to be 4 mg/kg body weight/day.

These compounds are glycosides of steviol, a diterpene compound. Specifically, their molecules can be viewed as a steviol molecule, with its carboxyl hydrogen atom replaced by a glucose molecule to form an ester, and a hydroxyl hydrogen with combinations of glucose and rhamnose to form an acetal.

...
Wikipedia