Drying Kinetics, Effective Moisture Diffusivity, and Thermodynamic Analysis of Banana Slices Under Potassium Metabisulfite (KMS) Pretreatment

Abstract

The present study investigates the effect of drying temperature and potassium metabisulfite (KMS) pretreatment on the drying kinetics, effective moisture diffusivity, activation energy, thermodynamic properties, and thin-layer drying-model performance of green banana slices. Banana slices (4 ± 0.5 mm thickness) were subjected to KMS pretreatments at concentrations of 0 (control), 0.5%, 1.0%, and 1.5%, followed by drying in a convective tray dryer at 40, 50, 60, and 70 °C. The drying process exhibited a predominantly falling-rate period. Effective moisture diffusivity ranged from 2.04 × 10−10 to 4.35 × 10−10 m2/s and increased with drying temperature. Apparent activation energy decreased from 16.19 kJ/mol for the untreated control to 13.46 kJ/mol at 1.5% KMS. Thermodynamic analysis gave enthalpy values of 10.61–13.59 kJ/mol, entropy values of −209.15 to −219.72 J/mol·K, and Gibbs free energy values of 76.35–87.73 kJ/mol. The positive ΔG values indicate that moisture removal was non-spontaneous under the investigated conditions and required external thermal-energy input. Ten thin-layer models were evaluated using R2, RMSE, and χ2; the Midilli–Kucuk model gave the best overall fit within the investigated temperature and KMS ranges. Because endpoint moisture contents differed among treatments, drying-time comparisons were additionally standardised to an interpolated moisture content of 10% d.b.