A dynamic microwave-assisted extraction (DMAE) method is established for the extraction of total ginsenosides from ginseng fibrous roots. The extraction process has been simulated and its main affection factors (liquid/solid ratio K of solvent to ginseng powders (V/m), irradiation time, irradiation temperature, extracting solution concentration, flow rate of solvent and microwave power) have been optimized by response surface methodology (RSM). The optimum conditions of extraction are the liquid/solid ratio of 270 mL/g, the extraction temperature of 75 ℃, the extraction time of 35 min, ethanol concentration of 70% (V/V), the solvent flow rate of 1.3 mL/min, and the microwave power of 500 W. The yield of ginsenosides obtained by the proposed DAME method is (15.0±0.7)%, which is well agreement with the yield predicted by the model. Compared with static microwave-assisted extraction, DMAE has a higher extraction yield and can avoid the degradation of ginsenoside.
Asian ginseng (Panax ginseng C.A. Meyer), a member of the Araliaceae plant family, is a wild plant that has been cultivated for thousands of years in many Asian countries, such as China, North Korea, South Korea, Russia and Japan. Its root is one of important Chinese herb medicines. Modern chemical and pharmacological studies indicate that many components in P. ginseng, such as flavonoid, saponins and polysaccharides, have biologic activity and pharmacological activities that include antioxidant, hypotensive, neuroprotective, antibacterial, antitumor, cognitive, sedative, analgesic and anti-stress effects. In P. ginseng, most of the bioactive ingredients are ginsenosides. These ginsenosides are of a type of triterpenoidal saponins that consist of polycyclic aglycones attached to one or more sugar side chains.
The extraction and use of ginsenosides from ginseng roots have played an important role in the pharmacy. A number of traditional extraction methods have been employed in the past years, including solvent extraction, heat reflux extraction, Soxhlet extraction, and so on. These traditional extraction processes are time-consuming and laborious.
Microwave-assisted extraction (MAE) is a relatively new method by which microwave energy is used to heat polar solvents in contact with solid samples and to partition compounds of interest between the sample and the solvent, reducing both extraction time and solvent consumption. It also produces higher extraction rates and better results with lower costs. Many biologically active compounds such as polyphenols from Myrtus communis L. leaves, anthocyanin from blueberry, ursolic acid from the leaves of eucalyptus and so on, have been extracted with application of microwave assisted extraction. The operational mode of MAE could be classified into two kinds: Static MAE (SMAE) and dynamic MAE (DMAE). In the former, the solvent and extract are kept in extraction vessel in the whole extraction process. Some compounds are easy to be decomposed at continuous high temperature. In addition, when the extraction process finished, the vessels must be cooled to room temperature before being opened to avoid losses of volatile analytes, and the extract should be filtered or centrifuged. Thus the overall extraction time is increased considerably.
DMAE is an efficient technique for avoiding the degradation of bioactive components. In DMAE, the fresh solvent is continuously injected into the extraction vessel and the target extract is rapidly moved out of the vessel. This is very important to avoid the degradation of the target extract. At present, the DMAE technique has been used for extraction of active ingredient such as caffeine, nicotine and flavonoid. Ginsenosides has weak thermal stability and main ginsenosides (Rg1, Re, Pb1, Rc and Rd) can be decomposed in the condition of prolonged heating.
In this study, a DMAE method is applied for extraction of total ginsenosides from ginseng fibrous roots to avoid the degradation of ginsenosides. And several extraction conditions are optimized and discussed using response surface methodology.
In order to avoid the degradation of ginsenosides in the extraction process at the continuous high temperature, DMAE method has been applied for the extraction of ginsenosides from the ginseng roots. Response surface methodology is used to optimize and predict the DMAE process to obtain maximum yield of total ginsenosides. The result shows that the yield of ginsenosides by DMAE method is 15% higher than that by SAME method. This work would be helpful for the further investigation for the DMAE of natural active ingredients from other herbal materials.
Zhang, Yuefei, et al. “Dynamic microwave-assisted extraction of total ginsenosides from ginseng fibrous roots.” Wuhan University Journal of Natural Sciences 20.3 (2015): 247-254.