Microbial transformation of ginsenoside Rg3 to ginsenoside Rh2 by <Emphasis Type="Italic">Esteya vermicola</Emphasis> CNU 120806

In the present investigation, we successfully employed a cell-free extract of Esteya vermicola CNU 120806 to convert ginsenoside Rg3 to Rh2. Three important factors including pH, temperature and substrate concentration were optimized for the preparation of Rh₂. The optimal condition was obtained as follows: 50°C, pH 5.0 and substrate concentration of 3 mg ml⁻¹. The yield of conversion was up to 90.7%. In order to identify the specificity of the β-glucosidase activity of Esteya vermicola CNU 120806, ginsenoside Re (protopanaxatriol saponins) was treated under the same reaction system. Interestingly, no new metabolite was generated, which elucidated that the enzymatic process only occurred by hydrolysis of the terminal glucopyranosyl moieties at the C-3 carbon of ginsenoside Rg₃. The crude enzyme extract can be used for commercial ginsenoside Rh₂ preparation.