The transformation
of major ginsenosides to minor ginsenosides
by microorganisms was considered to be an environmentally friendly
method. Compared with GRAS (generally recognized as safe) strains,
non-food-grade microorganisms could transform polar ginsenosides to
various minor ginsenosides. In this study,
Talaromyces flavus
screened from the
P. notoginseng
rhizosphere was
capable of transforming PPD-type and PPT-type ginsenosides in the
underground parts of
P. notoginseng
to 18 minor ginsenosides.
The transformation reactions invovled deglycosylation, epimerization,
and dehydration. To the best of our knowledge, this transformation
characteristic of
T. flavus
was first reported in
fungi. Its crude enzyme can efficiently hydrolyze the outer glucose
linked to C-20 and C-3 in major ginsenosides Rb
1
, Rb
2
, Rb
3
, Rc, Rd, and 20(
S
)-Rg
3
within 48 h. The transformation of major ginsenosides to
minor ginsenosides by
T. flavus
will help raise the
functional and economic value of
P. notoginseng
.
Panax notoginseng flowers have the highest content of saponins compared to the other parts of Panax notoginseng, but minor ginsenosides have higher pharmacological activity than the main natural ginsenosides. Therefore, this study focused on the transformation of the main ginsenosides in Panax notoginseng flowers to minor ginsenosides using the fungus of Cladosporium xylophilum isolated from soil. The main ginsenosides Rb1, Rb2, Rb3, and Rc and the notoginsenoside Fa in Panax notoginseng flowers were transformed into the ginsenosides F2 and Rd2, the notoginsenosides Fd and Fe, and the ginsenoside R7; the conversion rates were 100, 100, 100, 88.5, and 100%, respectively. The transformation products were studied by TLC, HPLC, and MS analyses, and the biotransformation pathways of the major ginsenosides were proposed. In addition, the purified enzyme of the fungus was prepared with the molecular weight of 66.4 kDa. The transformation of the monomer ginsenosides by the crude enzyme is consistent with that by the fungus. Additionally, three saponins were isolated from the transformation products and identified as the ginsenoside Rd2 and the notoginsenosides Fe and Fd by NMR and MS analyses. This study provided a unique and powerful microbial strain for efficiently transformating major ginsenosides in P. notoginseng flowers to minor ginsenosides, which will help raise the functional and economic value of the P. notoginseng flower.
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