Influence of Drying Temperature and Osmotic Pretreatment on Heat and Mass Transfer, Drying Kinetics and Quality of Dried Sweet Potato
The study investigated the effects of osmotic pretreatment and drying temperature on drying kinetics, heat and mass transfer and quality attributes of sweet potato slices. Mature sweet potato were sliced into 2, 4 and 6 mm thicknesses and subjected to osmotic pretreatment using NaCl, CaCl2 and C6H8O6 solutions at concentration of 5, 10 and 15% (w/v) for 4, 6, and 8 hours. Drying experiments were conducted in a hot air oven dryer at 50, 60 and 70°C. The results showed that moisture reduction during osmotic pretreatment significantly increased (p<0.005) with increasing solution concentration, soaking time, and drying temperature, ranging from 12.84 ± 0.31% in the control sample to 43.54 ± 0.67% in treated samples, whereas thinner slices recorded faster moisture migration. Samples pretreated with 15% NaCl recorded the highest moisture loss (27.48 ± 0.41% to 44.73 ± 0.66 %) and fastest drying rate, whereas untreated samples showed slower moisture reduction. Effective moisture diffusivity ranged from (1.12 ± 0.05) × 10 − 8 to (4.21 ± 0.14) × 10 − 8 m2/s in NaCl-treated samples at 70°C and increased with temperature and pretreatment intensity. The Midilli et al. model best described the drying behavior, producing the highest coefficient of determination (R2= 0.997) and lowest root mean square error (RMSE= 0.008). Drying at 60°C provided an optimal balance between drying efficiency, energy utilization, and sweet potato quality.