The transformation of ginsenoside Rb1 into a specific minor ginsenoside using Aspergillus niger KCCM 11239, as well as the identification of the transformed products and the pathway via thin layer chromatography and high performance liquid chromatography were evaluated to develop a new biologically active material. The conversion of ginsenoside Rb1 generated Rd, Rg3, Rh2, and compound K although the reaction rates were low due to the low concentration. In enzymatic conversion, all of the ginsenoside Rb1 was converted to ginsenoside Rd and ginsenoside Rg3 after 24 h of incubation. The crude enzyme (β-glucosidase) from A. niger KCCM 11239 hydrolyzed the β-(1→6)-glucosidic linkage at the C-20 of ginsenoside Rb1 to generate ginsenoside Rd and ginsenoside Rg3. Our experimental demonstration showing that A. niger KCCM 11239 produces the ginsenoside-hydrolyzing β-glucosidase reflects the feasibility of developing a specific bioconversion process to obtain active minor ginsenosides.

Rb1-hydrolyzing β-glucosidase from Aspergillus niger KCCM 11239 was studied to develop a bioconversion process for minor ginsenosides. The specific activity of the purified enzyme was 46.5 times greater than that of the crude enzyme. The molecular weight of the native enzyme was estimated to be approximately 123 kDa. The optimal pH of the purified enzyme was pH 4.0, and the enzyme proved highly stable over a pH range of 5.0–10.0. The optimal temperature was 70 °C, and the enzyme became unstable at temperatures above 60 °C. The enzyme was inhibited by Cu2+, Mg2+, Co2+, and acetic acid (10 mM). In the specificity tests, the enzyme was found to be active against ginsenoside Rb1, but showed very low levels of activity against Rb2, Rc, Rd, Re, and Rg1. The enzyme hydrolyzed the 20-C,β-(1→6)-glucoside of ginsenoside Rb1 to generate ginsenoside Rd and Rg3, and hydrolyzed 3-C,β-(1→2)-glucoside to generate F2. The properties of the enzyme indicate that it could be a useful tool in biotransformation applications in the ginseng industry, as well as in the development of novel drug compounds.

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