Abstract
Sorption isotherms of flaxseeds were determined by static gravimetric method at temperatures 40; 60; and 80 oC, over a relative moisture range of 10-95%. Six mathematical models were applied to analyze the experimental data. The modified GAB model showed the best fitting to the experimental data. The isosteric heat and differential entropy were determined by applying Clausius-Clapeyron and Gibbs-Helmholtz equations, respectively. The isosteric heat and the entropy of desorption isotherm presented similar behavior, with a sharp change in an equilibrium moisture content of 10%. The enthalpy-entropy compensation theory was applied to the isotherms, indicating that they are enthalpy-controlled.
Highlights
Flaxseed (Linum usitatissimum L.) belongs to the linseeds family and is considered a functional food because, in addition to its basic nutritional functions, it contains substances that can prevent several diseases, including degenerative and cardiovascular diseases
Where: q the net heat of sorption is given in kJ mol-1, T is st the absolute temperature in Kelvin, X is the content of the dry-base equilibrium moisture (d.b.), a is the water activity w and R is the universal gas constant (8.314 J mol-1 K-1)
Jayas, and White (1980) in their study on flax seed hygroscopicity report the best efficiency of the GAB model in describing equilibrium moisture content data compared to other models
Summary
Flaxseed (Linum usitatissimum L.) belongs to the linseeds family and is considered a functional food because, in addition to its basic nutritional functions, it contains substances that can prevent several diseases, including degenerative and cardiovascular diseases. This work was conducted to experimentally determine the moisture desorption isotherms of flaxseeds at 40, 60, and 80 oC, by selecting the mathematical model that best describes the hygroscopic behavior at those temperatures, estimating the thermodynamic properties (enthalpy and differential entropy), and assessing the applicability of the enthalpy–entropy compensation theory.
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