Modified GAB model of sorption on banana: spreading pressure and Gibbs free energy

This study aims to determine the modelling of the sorption phenomenon, which is influenced by temperature and relative humidity in Barlin bananas. Modification of GAB to obtain new equations for determining spreading pressure and Gibbs free energy values was evaluated in this study. In addition, the characteristics of bananas (surface topography, functional groups, and crystal phase) were identified. Treatment incubation temperatures were 5–25 °C using the static gravimetric method. Equilibrium moisture content was directly proportional to the temperature and water activity increased with water content of 11.52–51.36%db (adsorption) and 25.59–97.01%db (desorption). Based on the BET classification, the sorption curve of Barlin banana pieces forms a type II. Then, the Peleg model became the best model for predicting desorption and adsorption phenomena in Barlin bananas with values of R² > 0.9900, P < 0.05, and RMSE < 0.01. The process of identifying the new equation from the modified GAB equation indicates that the values of spreading pressure and Gibbs free energy are 0.93–1.68 J/m² and 0.12–52.49 J/mol, respectively. FE-SEM determination shows swelling on the material’s surface, allowing surface desorption and adsorption. Meanwhile, FTIR analysis results show the valley point at 3273.16, indicated as an OH bond, and 2926.59, indicated as a C–H bond. Then, XRD shows that the crystallinity level was 39.48%, and the peak point is 2θ = 17.08º, which generally occurs in starch.