Highly efficient synthesis of mono-ß-1,6-Glucosylated Rebaudioside A derivative catalyzed by glycosyltransferase YjiC.

Steviol glycosides have attracted great interest because of their high levels of sweetness and safety, and absence of calories. Improvement of their sensory qualities via glycosylation modification by glycosyltransferase is a research hotspot. In this study, YjiC, a uridine diphosphate-dependent glycosyltransferase from Bacillus subtilis 168, was found with the ability to glycosylate rebaudioside A (Reb A) to produce a novel mono ß-1, 6-glycosylated Reb A derivative rebaudioside L2 (Reb L2). It has an improved sweetness compared with Reb A. Next, a cascade reaction was established by combining YjiC with sucrose synthase AtSuSy from Arabidopsis thaliana for scale-up preparation of Reb L2. It shows that Reb L2 (30.94 mg/mL) could be efficiently synthesized with an excellent yield of 91.34% within 12 h. Therefore, this study provides a potential approach for the production and application of new steviol glycoside Reb L2, expanding the scope of steviol glycosides.

Efficient synthesis of rebaudioside D2 through UGT94D1-catalyzed regio-selective glycosylation.

Steviol glycosides have been widely applied as new sweeteners in food, beverages, health care, and daily chemical industry owing to the properties of high-intensity sweetness, low calorie, and good physiological characteristics. However, most of steviol glycosides have a bitter taste. Their organoleptic properties can be effectively improved by modifying the linked glycosyl units. In this study, UGT94D1, a uridine diphosphate-dependent glycosyltransferase from Sesamum indicum, was reported to selectively glycosylate rebaudioside A (Reb A) for the synthesis of rebaudioside D2 (Reb D2). Furthermore, a cascade reaction system was constructed to synthesize Reb D2 with 94.66% yield by coupling UGT94D1 with sucrose synthase AtSuSy from Arabidopsis thaliana. Thus, our study not only introduced a practical method for the synthesis of steviol glycosides but also provided the possibility for further exploration of Reb D2.