Microbial transformation of geniposide in Gardeniae Fructus under the fermentation with Aspergillus niger DQWM-G11

Gardeniae Fructus, the dried fruit of Gardenia jasminoides, was fermented with Aspergillus niger DQWM-G11. The antibacterial activities of the fermented and non-fermented products were measured and the transformation of chemical constituents was detected. The results revealed that A. niger DQWM-G11 fermented Gardeniae Fructus (AFGF) possessed a stronger antibacterial effect with a minimal inhibitory concentration (MIC) value of 256 μg/mL, compared to the raw material (MIC: > 1024 μg/mL). An undescribed microbial transformation reaction was discovered, where geniposide (1) was transformed into 1β-methoxyl-4-epigardendiol (2), which was then verified. The produced component exhibited a stronger antibacterial effect (MIC: 256 μg/mL) than raw geniposide (1) (MIC: >1024 μg/mL), indicating that the increased activity of Gardeniae Fructus was due to the biotransformation. The discovery of this microbial transformation reaction will provide an important theoretical basis for further developing and applying Gardeniae Fructus and geniposide.