Storage Conditions and Adsorption Thermodynamic Properties for Purple Corn

Adsorption isotherms provide insight into the thermodynamic properties governed by food storage conditions. Adsorption isotherms of purple corn of the Canterio variety were evaluated at 18, 25, and 30 degrees C, for the equilibrium relative humidity (ERH) range between 0.065 and 0.95. The equilibrium moisture (X-e) was determined by the continuous weight-change method. Seven mathematical models of isotherms were modeled, using the coefficient of determination R-2, mean absolute error (MAE), and estimated standard error (ESE) as the convergence criterion. Thermodynamic parameters such as isosteric heat (q(st)), Gibbs Free Energy (Delta G), differential entropy (Delta S), activation energy (E-a), and compliance with the isokinetic law were evaluated. It was observed that the adsorption isotherms presented cross-linking around 75% ERH and 17% X-e suggesting adequate storage conditions at these values. The GAB and Halsey models reported better fit (R-2 > 97%, MAE < 10%, ESE < 0.014 and random residual dispersion). The reduction of X-e from 17 to 7%, increases q(st), from 7.7022 to 0.0165 kJ/g, while Delta G decreases considerably with the increase in X-e presenting non-spontaneous endergonic behavior, and linear relationship with Delta(S), evidencing compliance with the isokinetic theory, governed by q(st). E-a showed that more energy is required to remove water molecules from the upper layers bound to the monolayer, evaluated using C-GAB. The models predicted the storage conditions, and the thermodynamic parameters show the structural stability of the purple corn grains of the Canteno variety during storage.

Automated summary

Adsorption isotherms provide insight into the thermodynamic properties of food storage. The adsorption isotherms of purple corn grains of the Canteno variety were evaluated, showing suitable storage conditions at around 75% ERH and 17% X-e. The GAB and Halsey models provided a better fit. The thermodynamic parameters indicated the structural stability of the purple corn grains during storage.