Biotransformation of Ginsenoside Rb1 to Ginsenoside CK by Strain XD101: a Safe Bioconversion Strategy

Ginsenoside Rb1 is the main predominant component in Panax species. In this study, an eco-friendly and convenient preparation method for ginsenoside CK has been established, and five strains of β-glucosidase-producing microorganisms were screened out from the soil of a Panax notoginseng planting field using Esculin-R2A agar. Aspergillus niger XD101 showed that it has excellent biocatalytic activity for ginsenosides; one of the isolates can convert ginsenoside Rb1 to CK using extracellular enzyme from the mycelium. Mycelia of A. niger were cultivated in wheat bran media at 30 °C for 11 days. By the removal of mycelia from cultured broth, enzyme salt fractionation by ammonium sulfate (70%, v/v) precipitation, and dialysis, sequentially, crude enzyme preparations from fermentation liquid supernatant were obtained. The enzymatic transformed Rb1 as the following pathways: Rb1→Rd→F2→CK. The optimized reaction conditions are at reaction time of 72 h, in the range of pH 4–5, and temperature of 50–60 °C. Active minor ginsenosides can be obtained by a specific bioconversion via A. niger XD101 producing the ginsenoside-hydrolyzing β-glucosidase. In addition, the crude enzyme can be resulted in producing ginsenoside CK via conversion of ginsenoside Rb1 at high conversion yield (94.4%). FDA generally regarded, A.niger as safe microorganism. Therefore, these results indicate that A. niger XD10 may provide an alternative method to prepare ginsenoside CK without food safety issues in the pharmaceutical industry.