Study on the hydroxyl radical scavenging activity changes of ginseng and ginsenoside-Rb2 by heat processing

The free radical scavenging activities of Panax ginseng C.A. MEYER are known to increase by heat processing. Phenolic acids and Maillard reaction products (MRPs) have been suggested as active free radical scavenging components from our previous research, but heat processing-induced chemical and activity changes of ginsenosides considering the Maillard reaction have not yet been fully elucidated. In this study, we investigated the hydroxyl radical (OH) scavenging activity changes of ginsengs and ginsenoside-Rb-2 (Rb-2) by heat processing using an electron spin resonance spectrometer. Especially, Rb-2 was heat processed with the same amount of glycine, a frequently used amino acid in the Maillard reaction model system. As a result, the center dot OH scavenging activities and brown compound levels of ginseng and glycine-Rb-2 mixture were increased by heat processing. However, the increase in center dot OH scavenging activities were not in accordance with the extents of browning. On the other hand, less-polar ginsenosides such as Rg(3), Rg(5), and Rk(1) were generated from the glycine-Rb-2 mixture by heat processing. The sugar moieties at carbon-20 of Rb-2 were separated by the steaming process, less-polar ginsenosides were produced, and then the separated sugar moieties were thought to form MRPs with glycine. From the center dot OH scavenging activity tests of Rb-2, glycine, less-polar ginsenosides, and maltol, the increase in -OH scavenging activity was thought to be more closely related to the generation of center dot OH scavenging ginsenosides such as 20(S)-Rg(3) and Rg(5) by heat processing than MRPs.