(231v) High-Yield Productino of Ginsenosides 20(S)-Rg3, Rk1, and Rg5 from Ginseng Extract By Hydrothermal Reaction
Ginseng has been widely used as an herbal medicine because it has many bioactivities such as immune system modulation, antistress activity, and antihyperglycemic activity. Moreover, its anticancer activity has been found recently. These bioactivities are generally attributed to ginsenosides which are main ingredients of ginseng. In unprocessed ginseng, intact ginsenosides such as Rg1, Re, Rf, Rb1, Rc, Rb2, and Rd are major compounds. The intact ginsenosides can be converted to transformed ginsenosides through deglycosylation and/or dehydration. Because of fewer sugar moieties, the transformed ginsenosides are more bioavailable than intact ginsenosides. Furthermore, it was revealed that the transformed ginsenosides have special bioactivities which intact ginsenosides do not have. Therefore, there have been many researches to increase the yield of the transformed ginsenosides, with three processes commonly utilized. The most typical process is steaming, which is used to make red ginseng and sun ginseng. Other processes are operated under application of acidic catalysts or microorganisms. However, these conventional methods are frequently sluggish and complex. The steaming process takes over 3 h, and biotransformation process takes longer as it includes incubation. Shorter reaction times can be achieved for the acid catalyst process, but the acid leads to corrosion of the reactor. Besides, additional step that makes the process complex is needed to separate the acid. In this study, to overcome the disadvantages of these conventional processes, hydrothermal process was introduced. The hydrothermal process consisted of two steps. First step was to extract ginseng, and second step was to carry out hydrothermal reaction of the ginseng extract. Hydrothermal reactions are either homogeneous or heterogeneous chemical reactions performed in the presence of a solvent above room temperature and atmospheric pressure in a closed system. When the solvent of a hydrothermal reaction is water, as the temperature increases to the critical temperature, the ion product of water increases, whereas the dielectric constant decreases. According to the definition of ion product, the increased ion product means higher concentrations of H+ and OH- ; hence, water with a higher ion product can be used as a good medium for acid- or base-catalyzed reactions. Moreover, with decreasing dielectric constant, water can dissolve organic materials like other organic solvents. Therefore, same effects can be achieved by hydrothermal reaction in water without using organic solvents and catalysts. Because of these properties, biomass and biowaste which traditionally needed acid catalysts or organic solvents have been hydrothermally converted to more valuable chemicals through hydrolysis and/or dehydration. As the transformation of intact ginsenosides to more valuable ginsenosides occurs through similar reaction mechanisms, we introduced the hydrothermal process to obtain transformed ginsenosides. The purpose of this study was to increase the yields of the transformed ginsenosides, such as 20(S)-Rg3, Rk1, and Rg5 and find optimized operating conditions. For comparisons, red ginseng and sun ginseng were prepared by conventional steaming. The maximum yields for the hydrothermal reaction were 2.5â??25 times higher than those for steaming. This was because that the hydrothermal reaction was a homogeneous reaction while the steaming was a heterogeneous reaction. As reactants co-exist in the same phase for a homogeneous reaction, the chemical reaction, heat transfer, and mass transfer occur more efficiently than those in a heterogeneous reaction. Additionally, the antioxidant activities were increased 1.6â??4 fold for the hydrothermal reaction. Because the increase in the antioxidant activities was not as large as that in the yields, the yields of the three transformed ginsenosides may not be the principal factor influencing the antioxidant activities. Considering yields and antioxidant activities together, the optimized operating conditions for the hydrothermal process were temperatures over 140 °C for tens of minutes.