Synthesis of rebaudioside-A by enzymatic transglycosylation of stevioside present in the leaves of Stevia rebaudiana Bertoni

•Enzyme mediated transglycosylation of stevioside to rebaudioside-A.•The glucosyl moiety transglycosylated stereospecifically to get 13-O-β-stevioside.•The rebaudioside-A content in the pre-treated stevia leaves increased from 4% to 66%.•95% pure rebaudioside-A was obtained by multiple column chromatography. Rebaudioside-A is the second most abundant sweet diterpene glycoside (1–3%) present in the leaves of Stevia rebaudiana Bertoni, and is now being considered as a possible sucrose substitute due to its pleasant organoleptic properties and associated health benefits. In the present study, a novel in situ enzymatic transglycosylation of stevioside has been developed by pre-treating the stevia leaves with cellulase and adding soluble starch as the glucosyl donor. The results confirm that the transglycosylation of stevioside led to an enrichment in the rebaudioside-A content from 4% to 66%. This was further purified by multiple column chromatography to obtain 95% pure rebaudioside-A. The isolated rebaudioside-A showed concentration-dependent α-glucosidase inhibitory activity with IC50=35.01μg/ml. Thus the study highlights the biotransformation of stevioside present in stevia leaves to rebaudioside-A by a simple, inexpensive and eco-friendly process that has commercial potential.