| Objective:To explore the kinetics of fresh Perilla frutescens and Atractylodes macrocephala from Jiangxi Province in the hot air drying and vacuum drying process and their volatile oil composition change law,and obtain the best process parameters under multiple goals such as drying efficiency and drying quality,and provide a scientific basis for the development of drying equipment in line with the drying characteristics of traditional Chinese medicine.Methods:1 Study on drying kinetics of Perilla frutescens and Atractylodes macrocephalaThe dry basis moisture content and drying rate curves with the change of drying time,and the drying rate curves with the change of dry basis moisture content of fresh Perilla frutescens and Atractylodes macrocephala from Jiangxi Province were studied in the hot air drying and vacuum drying process at five levels of drying air temperature in the range of30-70℃.Compare the difference between the hot air drying curve and the vacuum drying curve of Perilla frutescens and Atractylodes macrocephala at different temperatures.2 Establishment and fitting of the mathematical model of drying kinetics of Perilla frutescens and Atractylodes macrocephalaThe relationship between drying parameters moisture ratio and time of fresh Perilla frutescens and Atractylodes macrocephala from Jiangxi Province during the hot air drying and vacuum drying process at different temperatures was fitted and verified by the empirical model Midilli model,Page model,Overhults model,Modified Page model,Logaritmic model,Two terms Exponential model,Newton model,etc.3 Determination of dry physical properties of Perilla frutescens and Atractylodes macrocephalaThe static method was used to determine the hygroscopic equilibrium moisture content of Perilla frutescens and Atractylodes macrocephala after hot air drying and vacuum drying at 50℃in the range of relative humidity under the combined action of Mg Cl2·6H2O,Na Br,KI,Na Cl,KCl saturated salt solutions at set temperatures of 40,50,and 60°C.The effect of relative humidity by the formation of temperature and different saturated salt solutions on the hygroscopic equilibrium moisture content of Perilla frutescens and Atractylodes macrocephala was analyzed.Four mathematical models including Henderson model,Moidifed-Halsey model,Chung-Pfost model and Oswin model were used to fit the hygroscopic equilibrium moisture content curves of Perilla frutescens and Atractylodes macrocephala with correlation coefficient,standard deviation and mean relative error as evaluation indicators,and compared fitting accuracy of the above equilibrium moisture content model to the experimental data.According to the relationship between the moisture ratio and drying time of Perilla frutescens and Atractylodes macrocephala during hot air drying and vacuum drying at different temperatures,the effective moisture diffusion coefficient(Deff)and activation energy（Ea）value of Perilla frutescens and Atractylodes macrocephala in different drying methods were calculated.4 Determination of volatile components in different dried samples of Perilla frutescens and Atractylodes macrocephala by headspace-GC-MS（HS-GC-MS）HS-GC-MS combined technique was used to determine the changes of volatile components and contents of Perilla frutescens and Atractylodes macrocephala after hot air drying and vacuum drying at different temperatures,and the drying quality of Perilla frutescens and Atractylodes macrocephala was compared between hot air drying and vacuum drying at different temperatures.Results:1 The dry basis moisture content of Perilla frutescens and Atractylodes macrocephala is decreasing with the prolongation of drying time,the drying rate increases and the time required for drying to the end point is shorter with the hot air and vacuum temperature increases,At the same time,the drying rate will also decrease with the decrease of the dry basis moisture content.Under the same temperature conditions,the hot air drying rate is faster than the vacuum drying rate,the time it takes for drying to reach equilibrium is also shorter.2 By comparing the correlation coefficient（R2）,chi-square（χ2）and standard error（RMSE）of each model,it can be seen that the Midilli model parameter average has the highest degree of fit under different drying conditions of Perilla frutescens and Atractylodes macrocephala,and Perilla frutescens in hot air drying at different temperatures is R2=0.9994,χ2=7.22×10-5and RMSE=5.94×10-3,Atractylodes macrocephala in hot air drying at different temperatures is R2=0.9992,χ2=8.78×10-5and RMSE=8.20×10-3;Perilla frutescens in vacuum drying at different temperatures is R2=0.9988,χ2=1.40×10-4and RMSE=0.0104,Atractylodes macrocephala in vacuum drying at different temperatures is R2=0.9982,χ2=2.11×10-4and RMSE=0.0109.3 Under the action of the same temperature,the hygroscopic equilibrium moisture content of Perilla frutescens and Atractylodes macrocephala increased with the increase of the relative humidity;in the same saturated salt solution,the higher the temperature,the smaller the the hygroscopic equilibrium moisture content;By comparing the correlation coefficient（R2）,standard deviation（SD）,and average relative error（MRE）of the four models,it can be seen that the parameters of the Oswin model have the highest fitting degree for hot air drying Perilla frutescens and Atractylodes,and Perilla frutescens in hot air drying is R2=0.9937,SD=0.0040 and MRE=0.0296,Atractylodes macrocephala in hot air drying is R2=0.9889,SD=0.0064 and MRE=0.0445;and the parameters of the Moidifed-Halsey model have the highest fitting degree for vacuum drying Perilla frutescens and Atractylodes macrocephala,and Perilla frutescens in vacuum drying is R2=0.9839,SD=0.0746 and MRE=0.1190,Atractylodes macrocephala in vacuum drying is R2=0.9831,SD=0.0766 and MRE=0.1521.The Deffvalue of Perilla frutescens dried by hot air at 30-70℃is2.69×10-8-2.97×10-7m2·s-1,Eais 49.82 k J·mol-1;the Deffvalue of Atractylodes macrocephala dried by hot air at 30-70℃is 1.04×10-9-6.28×10-9m2·s-1,Eais 37.47 k J·mol-1;the Deffvalue of Perilla frutescens dried by vacuum at 30-70℃is 9.98×10-9-7.91×10-8m2·s-1,Eais 41.91k J·mol-1;the Deffvalue of Atractylodes macrocephala dried by vacuum at 30-70℃is6.09×10-10-4.20×10-9m2·s-1,Eais 40.17 k J·mol-1.4 Hot air drying and vacuum drying Perilla frutescens at different temperatures were determined by HS-GC-MS,and 35,28,28,28,21,37,30,33,30 and 28 compounds were identified respectively,which accounted for accounting for more than 93.32%of the volatile components;hot air drying and vacuum drying Atractylodes macrocephala at different temperatures were determined by HS-GC-MS,and 26,24,25,23,24,26,23,27,22 and 24compounds were identified respectively,which accounted for accounting for more than92.18%of the volatile components.Conclusions:This subject comparatively studied the drying kinetic characteristics of different drying methods of Perilla frutescens and Atractylodes macrocephala from Jiangxi Province,the mathematical model of the moisture ratio in the drying process was established,the best model that can fit the moisture loss law of Perilla frutescens and Atractylodes macrocephala and the effective moisture diffusion coefficient(Deff)and activation energy（Ea）value in different drying processes are obtained.The hygroscopic equilibrium moisture content of dried Perilla frutescens and Atractylodes macrocephala was measured and model fitted.Finally,the volatile components of different dried products of Perilla frutescens and Atractylodes macrocephala were compared by headspace-GC-MS（HS-GC-MS）,which provided new ideas and method for exploring the drying characteristics and quality of aromatic traditional Chinese medicines,and provided a scientific basis for the development of drying equipment that meets the drying characteristics of traditional Chinese medicine. |
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