Microbial Conversion of Rare Ginsenoside Rf to 20(S)-Protopanaxatriol by Aspergillus niger

In this study, rare ginsenoside Rf was transformed into 20(<I>S</I>)-protopanaxatriol (PPT(<I>S</I>)) by glycosidase from <I>Aspergillus niger</I>. By investing the reaction conditions, the optimal conditions were obtained, as follows: pH 5.0, temperature 55 °C, and substrate concentration 1.25 mmol/l. Under optimal conditions, PPT(<I>S</I>) (1.13 μmol) prepared from 1.25 μmol Rf showed a higher yield (90.4%). The enzymatic reaction was analyzed by reversed-phase HPLC, suggesting the transformation pathway: Rf→Rh1(<I>S</I>)→PPT(<I>S</I>).