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.