Degradation of Ginsenosides in American Ginseng (Panax quinquefolium) Extracts during Microwave and Conventional Heating

The degradation of ginsenosides in American ginseng (Panax quinquefolium) extracts during microwave and water (oil) bath heating (conventional heating) was investigated. Both the 50% ethanol-water extracts and the aqueous extracts were boiled in a modified laboratory microwave oven and in a water (or oil) bath, respectively. The neutral ginsenosides (Rb(1), Rc, Rd, and Re) and malonyl ginsenosides (m-Rb(1), m-Rc, and m-Rd) were determined by reverse-phase high-performance liquid chromatography. The results showed that the degradation of ginsenosides in 50% ethanol-water extracts was a first-order reaction. The malonyl ginsenosides were much less stable than the corresponding neutral ginsenosides, with the rate constant value of the malonyl ginsenosides being 3-60 times that of the neutral ginsenosides. At the same temperature, the effect of microwave heating on the degradation of ginsenosides was the same as that of conventional heating.