Increase in the hydroxyl radical-scavenging activity of Panax ginseng and ginsenosides by heat-processing

Panax ginseng C.A. Meyer (Araliaceae), mainly cultivated in Korea and Northeast China, is processed before use based on its long history of ethnopharmacological evidence. Ginsenosides have been regarded as the main active components responsible for the pharmacological activities of ginseng. Although the Maillard reaction is known as a major source of compounds related to enhanced antioxidant activity by heat treatment in various crude drugs or foods, the chemical and free radical-scavenging activity changes of ginsenosides brought about by the Maillard reaction have not yet been elucidated. This paper gives a review of our recent findings, with emphasis on the hydroxyl radical (•OH)-scavenging activity changes of ginsengs and ginsenosides by heat-processing using an electron spin resonance spectrometer. 20(S)- Rg3 showed the strongest activity, and the next was in the decreasing order of Rb1, Rg1, Rc, Rb2, and Rd. The •OH-scavenging activities of ginsenosides were related to the ferrous metal ion-chelating activities of their aglycone, 20(S)-protopanaxadiol. In addition, the ferrous metal ion-chelating activities of ginsenosides were thought to be influenced by their types of hydrophilic sugar moieties. Moreover, Rb1 was changed into 20(S)-Rg3, 20(R)-Rg3, Rk1, and Rg5 by heat-processing, and the sugar moieties at carbon-20 were separated. The generated amount of 20(S)-Rg3 was higher than when Rb1 was heat-processed without amino acids, and a significant increase in Maillard reaction products was noted. Based upon chemical and •OH-scavenging activity tests using Maillard reaction model experiments, the scientific evidence underlying the increase in free radical-scavenging activity of ginseng induced by heat-processing was elucidated.