Steviol is a diterpene molecule first isolated from the Stevia rebaudiana plant in 1931. It forms the structural backbone of the sweet compounds, known as steviol glycosides, prized for their intense sweetness without calories. Steviol is the core component that remains after these glycosides are broken down. Its discovery paved the way for modern stevia-based sweeteners.
From Plant to Product
The sweeteners on grocery store shelves are not pure steviol but are composed of various steviol glycosides from the leaves of the Stevia rebaudiana plant. The most abundant of these are Stevioside and Rebaudioside A, although over 60 different steviol glycosides exist. Each glycoside consists of the same steviol core, but with different sugar units attached to its structure.
The production process begins with harvesting and drying the stevia leaves, which are then steeped in hot water to draw out the sweet glycosides. This liquid extract is then subjected to a multi-step filtration and purification process to separate the desired glycosides from other plant materials.
This purification often involves using food-grade alcohol or ion-exchange resins to capture the steviol glycoside molecules. The result is a highly purified extract of at least 95% steviol glycosides, the form approved for food products. Newer production methods, like bioconversion and fermentation, can also produce specific glycosides like Rebaudioside M (Reb M).
Metabolism in the Human Body
When a person consumes a product with steviol glycosides, the large molecules are not broken down or absorbed in the upper gastrointestinal tract. They pass through the stomach and small intestine intact. Upon reaching the colon, the steviol glycosides encounter resident gut bacteria. These microbes possess the enzymes to break the glycosides down.
The bacteria cleave off the attached glucose units, a process that liberates the steviol backbone. Once freed from its sugar attachments, the steviol molecule is absorbed from the colon into the bloodstream and travels to the liver, where it is metabolized.
The liver modifies steviol into steviol glucuronide, a water-soluble form the body can easily eliminate. This final compound is then excreted, primarily through the urine, with no accumulation of steviol or its byproducts in the body.
Safety and Regulation
The use of high-purity steviol glycosides as a sweetener is supported by major regulatory agencies around the world. In the United States, the Food and Drug Administration (FDA) has designated them as “Generally Recognized as Safe” (GRAS). This designation applies specifically to purified extracts containing 95% or more steviol glycosides, not to whole stevia leaves or crude extracts.
Similarly, the European Food Safety Authority (EFSA) approved steviol glycosides as a food additive in 2011. Global bodies like the Joint FAO/WHO Expert Committee on Food Additives (JECFA) have also reviewed the safety data and reached similar conclusions.
To provide a guideline for safe consumption, these organizations established an Acceptable Daily Intake (ADI). The ADI is set at 4 milligrams of steviol equivalents per kilogram of body weight per day. This figure incorporates a 100-fold safety margin, meaning it is one-hundredth of the amount found to cause no adverse effects in animal studies. For a 150-pound (68 kg) person, this ADI is far more than would be used in a day.
Chemical Properties and Sweetness
Steviol and its associated glycosides are valued for their intense sweetness. Depending on the specific glycoside and its concentration, these compounds can be anywhere from 30 to over 400 times sweeter than table sugar (sucrose). This high intensity means that only a small quantity is needed to sweeten foods and beverages.
This sweetness is also stable, as steviol glycosides are resistant to breakdown from heat and changes in pH, making them suitable for cooking and baking. Unlike sugar, they are non-fermentable, which means they do not contribute to dental caries. The structural differences between the glycosides are responsible for variations in their taste profiles.
Some steviol glycosides, particularly Stevioside and Rebaudioside A (Reb A) at high concentrations, have a slightly bitter or licorice-like aftertaste for some individuals. Other glycosides, such as Rebaudioside D and M, are noted for having a cleaner, more sugar-like taste. This has led food manufacturers to use specific blends of glycosides to achieve an optimal taste profile.