20(S)-Ginsenoside-Rg3

The limited natural abundance and poor extractability of rare ginsenosides have hindered their industrial use, highlighting the need for safe and efficient biotransformation strategies. In recent years, lactic acid bacteria (LAB) have emerged as promising microorganisms for producing rare ginsenosides with enhanced bioactivity. This study explored the fermentation performance and ginsenoside-conversion characteristics of two food-grade LAB strains: Lactiplantibacillus plantarum SP055 and Limosilactobacillus fermentum LB-9, in ginseng juice. We employed single-factor experiments combined with Box-Behnken response-surface methodology to optimize the fermentation conditions. The optimal parameters were 32.5 h, 3.1% (v/v) inoculum, and initial pH 6.1 for SP055, and initial pH 6.2, 35 °C, and 3.2% (v/v) inoculum for LB-9. Under these conditions, both strains significantly increased the concentration of the rare ginsenoside Rg₃ by approximately 4 to 5 times. Dynamic monitoring of the fermentation's physicochemical attributes revealed that pH, total sugars, and reducing sugars decreased, while total phenolics, total flavonoids, and antioxidant capacity increased significantly. We established an HPLC-UV method to quantify six major ginsenosides, showing that Rb₁ and Rc continuously declined, Rd experienced a transient increase, and Rg₃ and CK accumulated during fermentation. Correlation analysis indicated distinct biotransformation pathways: SP055 primarily followed the pathway Rb₁/Rc → Rd → Rg₃, while LB-9 followed the pathways Rc → Rd and Rg₃ → CK. Overall, both strains enhanced the nutritional and functional value of ginseng juice through effective biotransformation and metabolic regulation, supporting their potential for developing functional fermented ginseng beverages and the food-grade production of rare ginsenosides.