Study Of The Experiments And Mass-transfer Mechanism On Microwave-assisted Extraction Of Medicinal Plants

In order to discuss mass transfer mechanism on microwave enhancing medicinal materials extraction,choosing representative medicinal plants of astragalus and angelica as matrix, water as solvent, considering microwave special heating characteristics, complex micro structure and the extract components of Chinese medicine, this paper studied the molecule weight distribution characters of water extract, and also further analysed nano and micro dimention fluid flow and mass transfer principles within botanical materials.The main work and results are as follows:1. By compared the distribution characteristics of the molecule weight of astragalus extract by microwave assisted extraction (MAE) with that by traditional refluxing technique, it can be shown that materials with molecule weight 2000～50000 Da by MAE for 10 min is 16.6 times of that traditional reflux technique for 30 min. Materials with molecule weight bigger than 50000 Da is only 2.87 % of total extract by MAE for 10 min, but it is 7.96 % of that by traditional reflux technique for 30 min. Results indicate that MAE technique is more beneficial to the extraction of target component with bigger molecule weight and avoiding the extraction of invalid materials. MAE is also advantaged to shorten extraction time to a large extent and improve the extract ratio, and it has significant meanings to the research and development of Chinese traditional medicine modernization.2. Concerning with medicinal plant angelica, MAE is also superior to the traditional flux technique. By compared with traditional refluxing technique, it can be shown that materials with molecule weight smaller than 2000 Da by MAE for 15 min is 2.33 times of that by tradition reflux technique for 30 min, and materials with molecule weight smaller than 100000 Da by MAE for 15 min is 4.91 times of that by tradition reflux technique for 30 min.3. Further studies indicate that microwave power should be less than 400 W during MAE of astragalus, while too high power could make medicinal materials coagulated with heat, which is not good for the extraction of target components. Microwave irradiation also could make the degradation of astragalus amylase, and result in the smaller granules diameter of target components and its more concentrative distribution. The granules diameter distribution of target components extracted by MAE is between 3.8500 nm～4.3640 nm, but that extracted by traditional refluxing extraction is between 4.3230 nm～14.8118 nm. Moreover, the penetration depth of microwave should be considered in MAE, and microwave drying technique is also a kind of reasonable choose in the dehydration operation of water extract.