Enhancement of low molecular weight ginsenosides from low-quality ginseng through ultra-high-pressure and fermentation processes

Abstract

This study aimed to analyze the conversion pattern of high to low molecular weight ginsenosides in low-quality ginseng during lactic acid fermentation associated with an ultra-high-pressure process. It was found that the relative quantities of various low molecular weight ginsenosides were increased by 20 min of pressure treatment at 500 MPa following fermentation with Bifidobacterium longum. Specifically, after ultra-high-pressure extraction, the triol-type, low molecular weight Rg2 was the most abundant ginsenoside, at 1.213 mg/g. However, when low-quality ginseng was fermented, the concentrations of diol-type, low molecular weight ginsenosides (e.g., Compound-K (CK), Rh2, and Rg3) largely increased to 1.52, 1.241, and 0.947 mg/g, respectively. These data indicate that high molecular weight ginsenosides in ginseng could be broken down by two different hydrolysis mechanisms. In the fermentation process, the β-1,2 and β-1,4 glycosidic bonds in high molecular weight ginsenosides such as Re, Rc, and Rb1 were hydrolyzed to diol-type, low molecular weight ginsenosides by the β-glucosidase enzyme of the lactic acid bacterium. Meanwhile, the physical energy of the ultra-high-pressure process specifically hydrolyzed relatively weak bonds of the sugars in high molecular weight ginsenosides such as Re to form the low molecular weight ginsenoside Rg2. Rg2, Rg3, Rh2, and CK increased to 2.043, 1.742, 1.834, and 2.415 mg/g, respectively, possibly due to a synergistic effect of combining both processes. Therefore, low molecular weight ginsenosides with higher biological activities than high molecular weight ginsenosides can be selectively obtained from low-quality ginseng using both fermentation and ultra-high-pressure processes.