Research On The Degradation And Optimization In The Drying Process Of Some Common Chinese Herbs

Chinese herb is an important kind of medicine which is recognized more and more recently having more effectiveness in curing suspicious or chronic illness and less side-effects than synthesized medicine, with the concept of "returning to nature" and "plant herb" prevailing all over the world. More attention has been paid to the research and development of Chinese herb than ever before. However, the degradation of biochemical active mass especially curative compositions, during the traditional processing of Chinese herb, has become an increasingly serious problem while the development and utilization of Chinese herb becomes more comprehensive. Emphasis should be focused on the study of the mechanism of degradation in order to control the loss of curative compositions during the processing of Chinese herb, in which drying is the most important.The required drying conditions for different herb materials vary with their nature and the curative effects. During the drying process, the degradation rate of curative compositions changes with the temperature and moisture content and is generally considered to follow the law of chemistry kinetics. In order to evaluate curative composition contents under any instantaneous temperature and moisture content in the drying process and to find out the relationship between curative composition contents and drying operation parameters, the degradation mechanism of curative compositions of Chinese herb was analyzed, and the degradation kinetics model was established and optimized by experiment and verified by comparing simulated values with experimental data.Curative compositions in Chinese herb, such as Catolpol in Rehmannia glutinosa and Flavone in Ophiopogon japonicus, were measured by High Performance Liquid Chromatography during the drying process; Reaction orders of Rehmannia and Ophiopogon were determined by water bath experiment in the condition of static constant temperature and moisture content; With parameters of the prospective degradation control model determined by the regression of experiment data in different drying conditions, the model and its availability were verified and analyzed.The desorption equilibrium moisture contents of Rehmannia and Ophiopogon during the drying process were measured respectively by static method under different temperature and moisture content; On the basis of thermodynamics principle, the convection coefficient, effective heat transfer coefficient and effective moisture diffusion coefficient were measured by single- and multi-layer thin layer drying methods; the shrink coefficient, interstitial increment and specific heat capacity Rehmannia and Ophiopogon were also measured, the relationship between the physical properties of Rehmannia and Ophiopogon, and the temperature and moisture content was analyzed and simulated by the least square method.Based on the Pick's second law and the theory of moisture moving in the direction of temperature gradient, the heat and mass balance differential equations of common herb materials during the drying process were established and evaluated by the finite element method and finite difference method; With the heat and mass balance equations and the degradation model, a C1"1" software was developed to simulate the change and the distribution of temperature, moisture content and curative composition contents of herb materials during the drying process, and was verified by thin layer drying experiment.Taking the heated air temperatures in the first and the last stages, the moisture content at which the air temperature changes and the tempering time between the two stages as 4 factors, and with the drying rate, curative composition contents and specific energy consumption as 3 optimization targets, the drying process of Rehmannia and Ophiopogon were simulated with various temperature and tempering drying parameters; Optimized parameters were obtained by simulation and optimization of the drying process.