Degradation of ginsenosides in American ginseng (Panax quinquefolium) extracts during microwave and conventional heating

The degradation of ginsenosides in American ginseng (Panax quinquefolium) e xtracts during microwave and water (oil) bath heating (conventional heating ) was investigated. Both the 50% ethanol-water extracts and the aqueous ext racts were boiled in a modified laboratory microwave oven and in a water (o r oil) bath, respectively. The neutral ginsenosides (Rbl, Re, Rd, and Re) a nd malonyl ginsenosides (m-Rbl, m-Rc, and m-Rd) were determined by reverse- phase high-performance liquid chromatography. The results showed that the d egradation of ginsenosides in 50% ethanol-water extracts was a first-order reaction. The malonyl ginsenosides were much less stable than the correspon ding neutral ginsenosides, with the rate constant value of the malonyl gins enosides being 3-60 times that of the neutral ginsenosides. At the same tem perature, the effect of microwave heating on the degradation of ginsenoside s was the same as that of conventional heating.