Optimization of recombinant SgUGT94CG1 glycosyltransferase enables efficient bioconversion of bitter mogrosides into sweet mogrosides from immature Siraitia grosvenorii.

BACKGROUND

Mogrosides, natural sweeteners derived from Siraitia grosvenorii (monk fruit), are low-calorie, high-potency, safe, and non-toxic alternatives to sucrose, making them particularly suitable for obese individuals and diabetic patients. However, the content of sweet mogrosides in naturally ripened monk fruit is limited. The glycosyltransferase SgUGT94CG1 addresses this limitation by catalyzing the in vitro conversion of bitter, low-glycosylated mogrosides into sweet, highly glycosylated mogrosides through regiospecific glycosylation.

RESULTS

The SgUGT94CG1 gene was expressed in E. coli Rosetta (DE3). Optimal conditions determined by single-factor and response surface methodology were: reaction (26.04% extract, 7.82 mM MgCl₂, 40.1 °C), induction (17.3 °C, 10.5 h, 0.47 mM IPTG), and fermentation (12.44 g/L sucrose, tryptone/yeast extract powder 6:4, 1.5 g/L CaCl₂, 1.52% inoculum). Enzyme activity increased 1.41- to 1.67-fold after optimization, and HPLC confirmed efficient conversion of bitter mogrosides to sweet mogrosides. This study provides a basis for future scale-up studies on utilizing discarded immature monk fruit.