Abstract:Objective: To study on isothermal moisture absorption law and hygroscopic heat of Chinese medicine extract powders,and inspect on water and energy changes during moisture adsorption process. Method: A static gravimetric method was adopted to obtain isothermal moisture absorption data of Rhei Radix et Rhizoma,Angelicae Sinensis Radix,Astragali Radix and Chrysanthemi Flos extract powder under different temperatures.Six kinds of moisture models (GAB,BET,Henderson,Smith,Oswin and Halsey) were fitted with nonlinear quadratic regression analysis to evaluate fitness of models,isothermal moisture absorption heat were calculated by Clausius-Clapeyron equation.Phenol-sulfuric acid method was adopted to determine contents of polysaccharides and oligosaccharides,which was taken as material basis for analysis of moisture adsorption behavior. Result: In these 6 kinds of models,fitness of GAB model was the highest with R2≥0.999 4,and the monolayer moisture content increased with increasing of oligosaccharides content.Under different temperatures,when water activity was smaller than a critical value,equilibrium moisture content declined with increasing of temperature,when arrived at a certain water activity,there was a crossing point,then equilibrium moisture content increased with increasing of temperature anomaly,corresponding water activities in crossing points of four extract powders were 0.75,0.65,0.68 and 0.62,respectively.Hygroscopic heat and moisture content of each extract powder was closely related,and showed a downward trend with increasing of moisture content. Conclusion: By investigating isothermal moisture absorption law of Chinese medicine extract powder,it can not only quantified adsorption ability of the powder but also describe moisture adsorption process of powder's physical condition.Compared with traditional method of critical relative humidity,this way is more innovative and has theoretical guidance meaning for production and storage problems of Chinese medicine.
