Stevia or Stevia rebaudiana, is a sweet herb native to Paraguay; approximately 200 – 300 times sweeter than sugar. But where does the sweetness in the stevia plant come from, or to be specific what makes the leaves of this herb sweet?
Let’s take a look at the BTS (Behind the sweetness).
Chemical compounds present in the stevia leaf called steviol glycosides are responsible for the signature sweet taste obtained from the plant. These glycosides are extracted from the leaf via numerous methods, filtered, and processed with other ingredients to be sold as liquid stevia or in powdered form.
More than 40 of these sweet compounds have been identified and approved by the FDA; to date. All steviol glycosides share a similarity in their molecular structure. The steviol molecule is attached to glucose entities by glycosidic bonds. The number of glucose entities and the position at which glucose is attached determines the unique taste profile and sweetness intensity for different glycosides.
The following lines describe some of these sweet compounds.
The most common and most abundant of all the glycosides. Stevioside is a white crystalline powder that makes up for 9.1% of the leaf component and is almost 140 times sweeter than sucrose. It has a prominent lingering and striking bitter profile with a licorice-like aftertaste, thus restricting the usage in higher doses.
Besides the sweetening property, it has also been linked to several health benefits. Stevioside is a storehouse of vitamins, antioxidants, minerals, anti-inflammatory and antimicrobial properties, factors responsible for the potential health benefits.
Reb-A (Rebaudiana A):
Most commonly used in food and beverages, Reb-A is the second most abundant compound, about 240 times sweeter than table sugar. It has a white to off-white, granular appearance and makes up for 3.8% of the leaf. Of the rebaudioside A, B, C, and E, A is the sweetest and most stable. It has a much less bitter profile and lesser aftertaste. Rebaudioside E is comparable to Reb- A in sweetness, whereas stevioside B and C are much less sweet than stevioside.
Reb-D and Reb-M:
Reb-D and Reb-M are two of the minor components present in extremely low concentrations (trace levels) in the leaf. These are sweeter than other steviol glycosides, almost 300 times sweeter than sucrose with a taste profile closer to it, and lack any unwanted aftertaste. The sucrose-like taste function makes it easier to use these glycosides as a sugar substitute in food and beverages.
However, due to the low concentration of these compounds in Stevia, it is hard to extract a commercially valuable quantity via the conventional extraction process. Hence, techniques like fermentation are used to synthetically manufacture these compounds.