Water adsorption and desorption isotherms of chestnut and wheat flours

Adsorption and desorption isotherms of chestnut and wheat flour at different temperatures (20, 35, 50 and 65 °C) were determined over a range of water activity of 0.09–0.91 using a static gravimetric method. According to BET classification the obtained isotherms for both flours were of type II. Taking into account IUPAC classification the hysteresis loops were of type H3. Experimental data were fitted by means of GAB and Chung–Pfost models. GAB model gave the best results for both flours, but both models can be considered adequate by the analysis of some statistical parameters such as the mean relative percentage deviation modulus, root mean square error and coefficient of determination. The net isosteric heats of sorption, estimated by the Clausius–Clapeyron equation, decreased in both flours when moisture content of samples increased. Heats of desorption were higher than the heats of adsorption at each moisture content and temperature in both flours, but in the case of wheat flour strong differences at low moisture contents were found.