Abstract: Water desorption isotherm of glutinous rice flour is necessary for understanding water transfer from it to environment. On the other hand, the isotherm data can be used to explore pore characteristics a solid matrix, which will allow a deeper understanding of water adsorption mechanism. Equilibrium water contents of glutinous rice flour were determined after conditioning to 10 different water activity levels at 10, 20 and 30 ℃ using a static gravimetric method. The obtained desorption data were fitted with four selected isotherm models, and were further mined to estimate pore properties of glutinous rice flour. Glutinous rice flour exhibited a typical type-Ⅱ adsorption isotherm. The Lewicki model performed best in predicting water desorption of glutinous rice flour at a constant temperature, while the GDW model could predict the moisture content as a function of water activity and temperature. The pores in glutinous rice flour included micropore and mesopore. Pore size distribution posed a single peak located in micropore zone whose value increased with the decrease in temperature. Consequently, micropore volume also increased as temperature decreased. The pore surface in glutinous rice flour was fractal in nature. The more porous surface structure and the larger specific surface area at lower temperature contributed to the increased adsorption capacity.

Key words: glutinous rice flour, desorption, pore size, pore size distribution, specific surface area, micropore volume, fractal dimension