Highly selective microbial transformation of major ginsenoside Rb₁ to gypenoside LXXV by Esteya vermicola CNU120806.

摘要

Aims. This study examined the biotransformation pathway of ginsenoside Rb₁ by the fungus Esteya vermicola CNU 120806. Methods and Results. Ginsenosides Rb₁ and Rd were extracted from the root of Panax ginseng. Liquid fermentation and purified enzyme hydrolysis were employed to investigate the biotransformation of ginsenoside Rb₁. The metabolites were identified and confirmed using NMR analysis as gypenoside XVII and gypenoside LXXV. A mole yield of 95.4% gypenoside LXXV was obtained by enzymatic conversion (pH 5.0, temperature 50 degrees C). Ginsenoside Rd was used to verify the transformation pathway under the same reaction condition. The product Compound K (mole yield 49.6%) proved a consecutive hydrolyses occurred at the C-3 position of ginsenoside Rb₁. Conclusions. Strain CNU 120806 showed a high degree of specific beta-glucosidase activity to convert ginsenosides Rb₁ and Rd to gypenoside LXXV and Compound K, respectively. The maximal activity of the purified glucosidase for ginsenosides transformation occurred at 50 degrees C and pH 5.0. Compared with its activity against pNPG (100%), the beta-glucosidase exhibited quite lower level of activity against other aryl-glycosides. Enzymatic hydrolysate, gypenoside LXXV and Compound K were produced by consecutive hydrolyses of the terminal and inner glucopyranosyl moieties at the C-3 carbon of ginsenoside Rb₁ and Rd, giving the pathway: ginsenoside Rb₁ rightwards-arrow gypenoside XVII rightwards-arrow gypenoside LXXV; ginsenoside Rd rightwards-arrow F₂ rightwards-arrow Compound K, but did not hydrolyse the 20-C, beta-(1-6)-glucoside of ginsenoside Rb₁ and Rd. Significance and Impact of the Study. The results showed an important practical application on the preparation of gypenoside LXXV. Additionally, this study for the first time provided a high efficient preparation method for gypenoside LXXV without further conversion, which also gives rise to a potential commercial enzyme application