Drying kinetics and thermodynamic properties of Uzun pistachios dried by convective drying

The purpose of this research was to determine the drying characteristics of Uzun variety pistachios in a convectional dryer with air velocity of 1 m/s at 50, 55, 60, and 65°C. Through the end of drying, moisture transfer from in-hull, and in-shell pistachio samples was defined by using the diffusion model of Fick. The Arrhenius-type relationship was used to establish the temperature dependence of the effective moisture diffusivity. The activation energy of in-hull and in-shell pistachios was determined to be 56.04 and 34.18 kJ/mol, respectively. Five well-known models, that is, the logarithmic, page, two-term, Midilli et al., and approximation of diffusion models were fit to data of moisture ratio. The Midilli et al., and the two-term models were chosen to accurately describe the hot-air drying behavior of in-hull and shell pistachio samples. As shelf-life criteria, the water activity (aw) values of fresh and dried pistachios were determined at different ambient air temperatures. The enthalpy (ΔH) and entropy (ΔS) values of the pistachio samples decreased with increasing the air temperature, while Gibbs-free energy (ΔG) increased as the air temperature increased. Novelty impact statement Pistachio kernel has rich nutritional significance for the human diet due to its 50%–60% fat content and unsaturated fatty acid and, the drying is the most important post-harvest process in the pistachio industry. Pistachio kernels must be dried below aw of 0.82 and 0.70 for short- and long-term storage and to avoid fungal development, respectively. This work evaluates the drying conditions and presents a mathematical model for hot-air drying of pistachio nuts and, the results show that drying of pistachio can be carried out in industrial convective dryers.