Abstract:

Hygroscopic property is one of the important parameters to study the drying and storage of Zanthoxylum
bungeanum seeds. In this work, the adsorption isotherms of Zanthoxylum bungeanum seeds were determined at 20, 30 and
40 ℃ over a water activity range of 0.005–0.982 using the static gravimetric method. These isotherms showed that the
moisture adsorption isotherm of Zanthoxylum bungeanum seeds belonged to type III isotherm, suggesting that at a certain
temperature, the equilibrium moisture content increases with increasing water activity. Among 8 classical mathematical
models, Oswin model was the best model to describe the isothermal moisture adsorption process with coefficient of
determination (R2) of 0.999 and average relative error (E) of 4.11%–8.13%, followed by GAB model. Based on these models,
the relatively safe and the absolutely safe moisture content in Zanthoxylum bungeanum seeds were 0.06 and 0.045 kg/kg,
respectively. The thermodynamic properties showed that Zanthoxylum bungeanum seeds had capillary porosity. The binding
energy of water to the seeds with a moisture content of more than 0.08 kg/kg and the net isosteric heat of adsorption were
low so that the water was easy to remove. The average capacity per unit mass of the seeds ranged from 13 to 18 mol/J, and
the most suitable pretreatment method and drying method could be achieved according to this parameter.

Key words: Zanthoxylum bungeanum Maxim, adsorption isotherm, model fitting, thermodynamic properties