Characterization and evaluation of a tray dryer with change of position: kinetics and thermodynamic properties of the process, preserving the nutraceutical properties in Golden Delicious apple slices.

Abstract

The drying kinetics in apple slices between 45–55 °C was studied until reach a moisture ratio of 10±2%. 8 thin layer drying models were statistically fitted where the Midilli-Kucuk model presented the best performance, moreover its drying constant increased with the temperature, effective diffusivity was ranged from 68.16 E^-10 – 2.28 E^-08 m² s^-1, the Arrhenius factor and activation energy were 3.74 E^-02 m² s^-1 and 28.11 kJ mol^-1, the enthalpy decreased from 25.46–25.38 kJ mol^-1, the entropy was ranged between (-0.2728 – -0.2730) kJ mol^-1 K^-1, and the Gibbs free energy increased from 112.25–114.98 kJ mol^-1. The 45 °C treatment preserved the highest phenolic compounds (51.1±1.54 mg EAG 100 g^-1), while the initial activity of elimination of radicals was 766.9±91.4 and 973.3±103.4 µg mg^-1 according to the DPPH and ABTS methods, the antioxidant activity shows an inverse behavior to the drying temperature. This work will allow to establish the temperature, time, moisture ratio and energy to drying apple slices according to local weather or under controlled conditions.