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

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