Stevioside is a naturally occurring, high-intensity compound extracted from the leaves of the Stevia rebaudiana shrub. It functions as a popular, calorie-free sugar alternative in food and beverages. Its use reflects a growing consumer interest in natural-source ingredients for reducing calorie intake.
Origin and Chemical Identity
Stevioside is naturally sourced from the leaves of the Stevia rebaudiana plant, a shrub native to South America, particularly Paraguay and Brazil. The compound is a type of steviol glycoside, which is the family of molecules responsible for the plant’s characteristic sweetness. Stevioside is typically the most abundant steviol glycoside found in the Stevia leaf, often making up between 5% and 10% of the dry leaf weight.
Commercial production involves a multi-step process to extract and purify the compound from the dried leaves. The initial step involves steeping the leaves in water, followed by filtration to remove solid particles. Further purification steps, such as ion exchange and treatment with activated carbon, isolate the steviol glycosides, yielding a high-purity sweetener product. Chemically, stevioside is a diterpene glycoside, where the steviol backbone is attached to three glucose molecules.
Sensory Profile and Sweetness Mechanism
Stevioside is classified as a high-intensity sweetener because its sweetening power is far greater than that of sucrose (table sugar). It is estimated to be approximately 150 to 300 times sweeter than sucrose, meaning only a tiny amount is needed to achieve the desired level of sweetness.
The sweet taste sensation begins when stevioside binds to the T1R2/T1R3 receptor heterodimer, a protein complex located on the taste buds of the tongue. Unlike sugar, which binds to multiple sites on the receptor, steviol glycosides are believed to bind to specific sites on both the T1R2 and T1R3 subunits. This binding triggers the signal cascade that the brain interprets as sweet.
Despite its intense sweetness, stevioside presents a distinct sensory profile compared to sugar, which can include a delayed onset of sweetness. The perception of sweetness tends to linger on the palate for a longer duration, contributing to a prolonged aftertaste. Furthermore, stevioside is frequently associated with subtle off-notes, such as a slight licorice or bitter flavor, which differentiates it from the clean taste of sucrose.
Metabolic Processing and Caloric Value
Stevioside contributes negligible calories due to its unique metabolic pathway. It is not absorbed in the upper gastrointestinal tract, passing through the stomach and small intestine fully intact because humans lack the necessary enzymes to break its glycosidic bonds. Since it is not absorbed into the bloodstream, it cannot be used by the body for energy, thus providing no calories.
The intact stevioside molecule eventually reaches the colon, where it encounters the resident gut microbiota. Certain bacteria within the colon, particularly species from the Bacteroides group, possess enzymes capable of hydrolyzing the stevioside. These microbial enzymes cleave the glucose units from the stevioside structure, leaving behind the non-sweet core molecule, known as steviol.
The resulting steviol is then absorbed through the colon wall into the bloodstream. Once absorbed, the liver rapidly modifies the steviol by attaching a molecule of glucuronic acid, a process called glucuronidation. This modification creates steviol glucuronide, a water-soluble compound the body cannot utilize for energy. The steviol glucuronide is then quickly excreted via the urine, preventing significant accumulation and ensuring the compound has no caloric impact.
Global Regulatory Status and Safety
Major international bodies have conducted extensive reviews to determine the safety of stevioside and other steviol glycosides for human consumption. The Joint FAO/WHO Expert Committee on Food Additives (JECFA) and the European Food Safety Authority (EFSA) have approved steviol glycosides as safe food additives. The U.S. Food and Drug Administration (FDA) has granted high-purity steviol glycosides, including stevioside, Generally Recognized As Safe (GRAS) status.
These regulatory approvals are based on comprehensive safety assessments, including toxicology and long-term consumption studies. A primary outcome of these evaluations is the establishment of an Acceptable Daily Intake (ADI) for steviol glycosides, expressed as steviol equivalents. The ADI is set at 4 milligrams per kilogram of body weight per day. This level represents the daily intake that can be consumed over a lifetime without posing an appreciable health risk.