Microwaves In Extraction Of Chemical Constituents From Natural Products

Microwave extraction technique has become a fast developing technique in recent years. Compared with conventional methods, microwave-assisted extraction has many advantages. Because of its fast speed, high efficiency, consuming less energy and other advantages, it is mainly applied to the fields of extracting chemical constituents from the food, medicine, environmental samples and natural products.In the thesis,according to the experimental investigation, microwaves were applied in extraction of chemical constituents from natural products.1. A new method, non-polar solvent microwave extraction (NPSME) was applied to extraction of essential oils from Rhizoma zingiberis recens,Fructui Foeniculi, Pericarpium zanthoxyli, Cumimm cymimum L., Pericarpium Citri Reticulatae and Fructus anisi stellati samples by adding the microwave absorption medium(MAM) into the extraction system. Three kinds of MAM, such as carbonyl iron powders (CIP), graphite powders (GP) and carbon black powders (CBP), were used and compared. The gas chromatography-mass spectrometry (GC-MS) was applied to analyze the extracts obtained by different extraction methods. The results show that the chemical components and their contents in essential oil obtained by NPSME is consistent with that obtained by conventional hydro-distillation (HD) and extraction time was reduced when the NPSME was applied. Compared to polar solvent microwave extraction(PSME) and combined solvent microwave extraction(CSME), the NPSME is superior to PSME and CSME in extraction yield. All the experimental results show that the NPSME is satisfactory for the extraction of essential oils from dried plant samples.2. Based on this kind of new heating pattern, non–polar solvent dynamic microwave–assisted extraction (DMAE) was established, and applied to the extraction of shikonin andβ,β'–dimethylacrylshikonin from root of Arnebia euchroma (Royle) Johnst.. Several parameters of non–polar solvent DMAE, including microwave absorption medium, extraction solvent, flow rate of extraction solvent, irradiation power and sample particle diameter were optimized separately. The extraction yields of target compounds obtained by non–polar solvent DMAE were comparable with those obtained by different extraction methods, including ultrasonic extraction (UE), soxhlet extraction (SE) and polar solvent DMAE. Compared with the other extraction methods, non–polar solvent DMAE has the more advantageous in extraction time and solvent consumption.3. Pressurized microwave-assisted extraction (PMAE), was used in extracting flavonoids and terpenoids from ginkgo leaves. the influence factors such as ethanol concentration, microwave irradiation time, pressure and ethanol volume were studied. The extraction parameters were investigated by orthogonal experiment design. The results indicate that compared with conventional methods, PMAE not only took a shorter time, but also made higher yield of the analyte.