Abstract
The present work aimed to study the water sorption behavior of quinoa seeds analyzing the hysteresis phenomenon and determining thermodynamic properties. Static gravimetric technique was used to obtain the equilibrium moisture content of quinoa seeds in different temperature conditions (15, 25, 35 e 50 °C) and relative humidity (between 11 and 96%). Equilibrium moisture content data were adjusted by eight mathematical models and the Modified Halsey model was the best one to describe the water sorption phenomena of quinoa seeds. Hygroscopic equilibrium moisture content of quinoa seeds is directly proportional to the water activity and decreases with increasing temperature. The hysteresis phenomena were observed throughout the range of water activity, showing more evident at low temperatures. Integral isosteric heat and differential entropy decreased with the increase of equilibrium moisture content. Gibbs free energy decreased with the increase of temperature and equilibrium moisture content. Compensation enthalpy-entropy theory was confirmed and the sorption mechanism is controlled by enthalpy.
Highlights
Quinoa (Chenopodium quinoa Willd.) is a pseudocereal cultivated in the Andean region for more than 7.000 years (Vega-Gálvez et al, 2010) and explored for food and feed
The present research had as main objective to study the mathematical modeling of water sorption isotherms of quinoa seeds in different conditions of temperature and relative humidity; investigate the alterations in thermodynamic properties of sorption processes; and analyze the hysteresis phenomenon, aiming to provide information that allows planning of storage systems that guarantee the quality of the product stock
The values of the parameters of the different hygroscopic equilibrium models fitted to the experimental data are shown in Tables 2 and 3
Summary
Quinoa (Chenopodium quinoa Willd.) is a pseudocereal cultivated in the Andean region for more than 7.000 years (Vega-Gálvez et al, 2010) and explored for food and feed. The physical-chemical stability of its starch gives functional properties (James, 2009) and greater storage potential than oilseeds These seeds have a considerable porosity in the outer layer, providing moisture loss or gain (Spehar, 2007). The present research had as main objective to study the mathematical modeling of water sorption isotherms of quinoa seeds in different conditions of temperature and relative humidity; investigate the alterations in thermodynamic properties (integral isosteric heat of sorption, differential entropy, Gibbs free energy, and enthalpy-entropy compensation theory) of sorption processes; and analyze the hysteresis phenomenon, aiming to provide information that allows planning of storage systems that guarantee the quality of the product stock.
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