Abstract
Stevia rebaudiana is widely recognized as a natural, zero-calorie sweetener. However, recent evidence suggests that microbial fermentation can profoundly transform its biochemical profile, unlocking health benefits that extend far beyond sweetness. This review systematically compares unfermented versus fermented stevia extract based on biochemistry, health consequences, technology, and safety. It aims to critically evaluate the evidence demonstrating how fermentation enhances the bioavailability, bioefficacy, and functional characteristics of stevia, thereby facilitating its transition from a simple sweetener to a multifunctional food ingredient. The investigation shows that the phytochemical composition of stevia is dramatically changed by fermentation. Microbial agents such as yeast and lactic acid bacteria facilitate fermentation, which changes steviol glycosides, produces new bioactive metabolites (such as terpenoids), and increases the amount of healthy chemicals. Consequently, fermented stevia extract exhibits improved antioxidant, antibacterial, antidiabetic, and anticancer activity in vitro and in animal models. A key differentiator is its potent ability to modulate gut microbiota, effectively alleviating dysbiosis and reducing associated inflammatory markers. Furthermore, fermentation improves the sensory profile of stevia extract and facilitates its seamless incorporation into diverse food matrices, such as dairy products and beverages, without compromising sensory quality. Beyond its inherent sweetening function, fermentation transforms stevia extract and unleashes health advantages, as the evidence clearly shows. Because of its higher bioactivity and capacity to alter gut flora, fermented stevia extract is a viable functional ingredient for the food and nutraceutical industries. Future research must, however, close the existing knowledge gaps in order to realize its full potential. These gaps include the need for more elucidation of the mechanisms of action, standardization of production processes, and longer-term human clinical trials to confirm safety and efficacy. Addressing these challenges will firmly establish fermented stevia extract as a key component in the next generation of health-focused products. KEY POINTS: ∙ Fermentation increases the bioactivity of stevia extract and its gut health advantages. ∙ It turns stevia extract into a sensory-enhanced, multipurpose culinary component. ∙Mechanism studies, process standardization, and human testing are all future needs.