Water Adsorption Isotherms of Chia (Salvia hispanica L.) Seeds

The adsorption isotherms of chia seed (CS), black chia seed (BCS), white chia seed (WCS), and chia seed flour (CSF) were determined at different temperatures (20, 35, 50, and 65 °C) using gravimetric method. Several saturated salt solutions were selected to obtain different water activities in the range of 0.07 to 0.91. Adsorption isotherms were of type II, according to Brunauer’s classification. No significant differences were found between equilibrium data of WCS, BCS, and CS samples. CSF showed lower hygroscopic characteristics than seeds. The three-parameter Guggenheim–Anderson–de Boer (GAB) model was employed to fit the experimental data in the water activity range. The goodness of the fittings, using several statistical parameters, was satisfactory. The monolayer moisture content (kg (kg d.b.)−1) calculated by the GAB model was 0.019 ± 0.004 for CS, BCS, and WCS and 0.015 ± 0.005 for CSF. The net isosteric sorption heat, calculated by means of the Clausius–Clapeyron equation, indicated that water is strongly bounded to chia at moisture content below 0.05 kg (kg d.b.)−1.