Extraction of steviol glycosides from Stevia leaves and their biotransformation with the aim to improve its taste and other biological activities

Abstract

Stevia is a natural source of sweetness, that peo ple prefer over other types of sugar and artific ial sweeteners as it is a better alternative, composed of various sweetening compounds of diterpene g lycosides (steviol g lycosides) in which the major constituents are stev iosides (along with bitterness) and rebaudioside A. But the main bottleneck in its bulk use is Stevia's bitter aftertaste. The current study was conducted to reso lve the taste-related problem of Stevia natura lly through biotransformation. The research began by isolating naturally occurring sweet compounds (steviol g lycosides) from the dried leaves of Stevia using diffe rent so lvents i.e., water, methanol, chloroform, and l-butano l. Furthermore, the extracted sweet compounds were biotransfonned by selected bacteri a l stra ins in modified M9 media (5% g lucose) to reduce the bitterness assoc iated with the steviol g lycosides and enhance their biological activities. The present study has shown better transformation of steviol glycosides with Bacillus stercoris at 40°C among the selected bacteri al strains. The thin-layer chromatographic separation technique was developed to quantify the extracted and biotransformed compounds on the silica plate with different combinations of so lvents in a mob ile phase. For maximum compou nd s separation, the optimized mobil e phase was acetone/ethy l acetate/water in a specified ratio of 50:40: I 0 vivo In addition, the chemical changes in the compounds were determined by FTTR analysis in the range of 400-4000 cm I indicating bond breaking and compounds formation. These biotransform ed compounds had improved biological activ iti es such that the anti oxidant activity which was increased to 58% compared to the control extract with 46% activity before biotransformation. This highlighted the va lue of biotransfonned stev iol g lycosides in the food and pharmaceutica l industries due to the prom inent health benefits over other sugars. However, further confirmation of steviol g lycosides after biotransformation can be obtained by performing high-pressure liquid chromatography (HPLC).