Novel Anti-cariogenic Characteristics of Rubusoside and Synthesis of Its Fructosides

Abstract

Rubusoside (Ru, 13-O-β-glucosyl-19-O-β-D-glucosyl-steviol) is the main component of Rubus suavissmimus S. Lee (Roasaceae), which is known as Chinese sweet leaf. In this study, Ru was characterized as anti-cariogenic materials. Ru was produced from stevioside (Ste) using β-galactosidase from Thermus thermophilus, which was expressed in E. coli BL21 (DE3) pLysS through lactose induction. The enzyme was purified by heat-treatment at 70℃ for 15 min. The 73.3% of mesophilic proteins was eliminated and it showed 85.3% activity yield. Enzyme reaction was carried out with immobilized β-galactosidase and Ru was purified with medium performance liquid chromatography (MPLC) equipped with ESLD detector. Ru at 50 mM showed 97.1 ± 0.2% inhibition activity against 0.1 U/mL mutanscrase from Streptococcus mutans. It was shown competitive inhibition activity with IC50 of 2.3 mM and Ki value of 1.1 ± 0.2 mM. MIC and MBC of Ru against S. mutans growth were 7 mM and 10 mM, respectively. MBC was higher than MIC, that is, Ru inhibits S. mutans as a bacteriostatic agent. Additionally, fructosyl-rubusoside (Ru-Frcs) was synthesized using levansucrase from Leuconostoc mesenteroides to improve the taste of rubusoside. Optimal condition for synthesizing Ru-Frcs was 217.8 mM Ru, 723.2 mM sucrose and 22.8 U/mL levanuscrase with 33.5% conversion. Purified Ru-Frc was prepared with high-performance liquid chromatography (HPLC) equipped with NH2 column at flow rate of 4 mL/min. The structure of Ru-Frc 1 and Ru- Frc 2 were confirmed with nuclear magnetic resonance (NMR) Spectrometer 850 MHz as 13-O-[β-fructofuranosyl-(2→6)-β-D-glucosyl]-19-O-β-D-glucosyl-steviol), 13-O-β-D-glucosyl-19-O-[β-fructofuranosyl-(2→6)-β-D-glucosyl]-steviol, respectively.