Water adsorption isotherms of microcapsules with hydrolyzed pinhão (Araucaria angustifolia seeds) starch as wall material Original Research Article

Water adsorption isotherms of microcapsules that use pinhão starch as the wall material and β-carotene as the core material were evaluated. Pinhão was chosen as the raw material because it is primarily composed of starch, and in the literature there are few technological aspects with regard to this polymer. Moreover, this wall material has been previously studied and demonstrated good encapsulation properties. Moisture adsorption isotherms were determined at 10, 20 and 30 °C using the gravimetric method. The Peleg model was used to fit the experimental data. The differential enthalpy and entropy of sorption were calculated using moisture sorption data; both decreased as moisture content increased. The enthalpy–entropy compensation theory was applied to adsorption isotherms and the isokinetic temperature was calculated by plotting the differential enthalpy as a function of differential entropy. We found that the adsorption process was enthalpy-controlled, the Tβ (352.61 K) was higher than the Thm (292.77 K), and the process was spontaneous (ΔG = −470.17 J mol−1).