Modelling of the sorption isotherms and determination of the isosteric heat of split pistachios, pistachio kernels and shells

Abstract

We aimed to measure the equilibrium moisture content of the Ohadi variety of pistachio shells, pistachio kernels and split pistachios using gravimetric methods at 25, 40, 55, and 70°C and saturated salt solutions with water activities ranging from 0.08 to 0.97. Then, 11 mathematical models were used to select the best model for data description. The GAB model, which had the maximum value for the correlation coefficient (R2) and minimum values for the chi-squared test (χ2) and root mean square error (RMSE), was identified as the best model for split pistachios and pistachio kernels. The Caurie model, meanwhile, was identified as the best model for pistachio shells. In this test, there was no significant hysteresis between the desorption and adsorption curves. Furthermore, the isosteric heat of adsorption and desorption were also determined using thermodynamic equations (e.g., the Clausius-Clapeyron equation).