Stevia Glycosides: Chemical and Enzymatic Modifications of Their Carbohydrate Moieties to Improve the Sweet-Tasting Quality

Stevia glycosides, extracted from the leaves of the plant Stevia rebaudiana Bertoni, display an amazing high degree of sweetness. As processed plant products, they are considered as excellent bio-alternatives for sucrose and artificial sweeteners. Being noncaloric and having beneficial properties for human health, they are the subject of an increasing number of studies for applications in food and pharmacy. However, one of the main obstacles for the successful commercialization of Stevia sweeteners, especially in food, is their slight bitter aftertaste and astringency. These undesirable properties may be reduced or eliminated by modifying the carbohydrate moieties of the steviol glycosides. A promising procedure is to subject steviol glycosides to enzymatic glycosylation, thereby introducing additional monosaccharide residues into the molecules. Depending on the number and positions of the monosaccharide units, the taste quality and sweetness potency of the compounds will vary. Many studies have been performed already, and this review summarizes the structures of native steviol glycosides and the recent data of modifications of the carbohydrate moieties that have been published to provide an overview of the current progress.