Young-Min Kim

Rebaudioside M (RM), a steviol glycoside derived from Stevia rebaudiana Bertoni, has emerged as a promising next-generation zero-calorie sweetener. However, its low natural abundance and poor aqueous solubility limit its practical application in beverage formulations. To address these limitations, two novel RM analogs, RMLC1 and RMLC2, were synthesized from stevioside (ST) through a two-step biocatalytic strategy. ST was first α-glucosylated by Leuconostoc kimchii dextransucrase to generate the α-glucosylated intermediate RD2, which was subsequently β-glucosylated by UGT76G1 to produce RMLC1 and RMLC2, with more than 95% conversion of RD2. RMLC1 and RMLC2 were stable at temperatures up to 120 °C and across a pH range of 2–10. RMLC1 and RMLC2 exhibited 139- and 127-fold higher aqueous solubility than RM, respectively, due to α-glucosylation-induced changes in molecular conformation. In a commercial low-pH beverage, both analogs showed approximately 3-fold greater storage stability than RM. In vitro digestion assays demonstrated that both analogs released less than half the glucose generated from enzymatically modified stevia. Electronic tongue analysis suggested that RMLC1 exhibited a balanced, blend-friendly taste profile, while RMLC2 displayed a sweetness-forward profile with minimal bitterness.

In this study, the optimization and modeling of microwave-assisted extraction (MAE) of water-soluble curcuminoids prepared using novel steviol glycosides (SGs) was carried out using four independent process variables at varying levels—X₁: microwave power (50–200 W), X₂: stevioside concentration (50–200 mg/mL), X₃: curcumin concentration (20–200 mg/mL), and X₄: time (1–10 min)—in response surface methodology configuration. Moreover, the effects of stevioside, as the most cost-effective natural solubilizer, were also evaluated. The water solubility of curcuminoids increased from 11 to 1320 mg/L with the addition of stevioside as a natural solubilizer. Moreover, microwave heating synergistically with stevioside addition significantly (p < 0.05) increased the solubility up to 5400 mg/L. Based on the results, the optimum conditions providing the maximum solubilization of 16,700 mg/L were 189 W microwave power, 195 g/L stevioside concentration, 183 g/L curcuminoid concentration, and 9 min of incubation time. Moreover, MAE of curcuminoids using SGs might render a significant advantage for its wide-scale application to solubilizing the multitude of insoluble functional flavonoids in fruits, plants, and food materials.