Grain sorption equilibria of quinoa grains Original Research Article

Quinoa has been identified as a promising source of food. Reports in the literature have focused mainly on agronomic potential, composition, nature of the starch and protein quality. Other aspects related with drying and storing of quinoa seed have received less attention. Moisture sorption isotherms constitute an essential part of the theory of drying and in the study of storage of dehydrated foods. Vapour water sorption of quinoa grains was determined at 20, 30 and 40 °C in the range of 0.089–0.851 water activity (aw) by means of the gravimetric method. Experimental curves were fitted to one three-parameter equation (Guggenheim–Anderson–de Boer, GAB equation). The equilibrium values and temperature shifts were modelled with a three-parameter equation in the approximate moisture content range of 0.02–0.18 (g water/g dry matter). An analytical expression to calculate the isosteric heat of sorption and its moisture content dependence was used and the results were compared with the isosteric heat calculated from the experimental equilibrium data by means of the Clausius–Clapeyron equation. The GAB model describe the sorption isotherms of quinoa grains at different temperatures in the range of aw investigated, the sorption areas obtained from the GAB equation were comparable with other sorption areas reported in the literature for various cereal grains and the effect of temperature on water sorption isotherms is adequately describes by an equation based on the enthalpy-entropy compensation.