The Chemical and 1,1-Diphenyl-2-Picrylhydrazyl Radical Scavenging Activity Changes of Ginsenosides Rb1and Rg1by Maillard Reaction

Abstract

The chemical and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity changes of ginsenoside <TEX>$Rb_1$</TEX>-glycine and ginsenoside <TEX>$Rg_1$</TEX>-glycine mixtures by Maillard reaction were investigated to identify the role of Maillard reaction in the increased antioxidant activity of ginseng by heat-processing. The DPPH radical scavenging activity of <TEX>$Rg_1$</TEX>-glycine mixture was more strongly increased by heat-processing than that of <TEX>$Rb_1$</TEX>-glycine mixture. From the analyses of ginsenosides, <TEX>$Rb_1$</TEX> was gradually changed into 20(S)-<TEX>$Rg_3$</TEX>, 20(R)-<TEX>$Rg_3$</TEX>, <TEX>$Rk_1$</TEX> and <TEX>$Rg_5$</TEX> by heat-processing. <TEX>$Rg_1$</TEX> was gradually changed into 20(S)-<TEX>$Rh_1$</TEX>, 20(R)-<TEX>$Rh_1$</TEX>, <TEX>$Rk_3$</TEX> and <TEX>$Rh_4$</TEX> by heat-processing. However, the generation of these less-polar ginsenosides was not related to the increased DPPH radical scavenging activity of <TEX>$Rb_1$</TEX>-glycine and <TEX>$Rg_1$</TEX>-glycine mixtures because their DPPH radical scavenging activities were already significantly increased when dried at <TEX>$50^{\circ}C$</TEX>, which temperature induce no structural changes of ginsenosides. In the comparison of browning compound levels of <TEX>$Rg_1$</TEX>-glycine and <TEX>$Rb_1$</TEX>-glycine mixtures, the extents of Maillard reaction were positively correlated with their increased free radical scavenging activities. Based on the chemical and DPPH radical scavenging activity changes of <TEX>$Rg_1$</TEX>-glycine and <TEX>$Rb_1$</TEX>-glycine mixtures by heat-processing, we clearly identified that the increased free radical scavenging activity of ginsenoside is mediated by the Maillard reaction between sugar moiety of ginsenoside and amino acid.