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-Rb2 (Rb2)) by heat processing using an electron spin resonance spectrometer. Especially, Rb2 was heat processed with the same amount of glycine, a frequently used amino acid in the Maillard reaction model system. As a result, the .OH scavenging activities and brown compound levels of ginseng and glycine-Rb2 mixture were increased by heat processing. However, the increase in .OH scavenging activities were not in accordance with the extents of browning. On the other hand, less-polar ginsenosides such as Rg3, Rg5, and Rk1 were generated from the glycine-Rb2 mixture by heat processing. The sugar moieties at carbon-20 of Rb2 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 .OH scavenging activity tests of Rb2, glycine, less-polar ginsenosides, and maltol, the increase in .OH scavenging activity was thought to be more closely related to the generation of .OH scavenging ginsenosides such as 20(S)-Rg3 and Rg5 by heat processing than MRPs.