Infrared drying of apple (Malus domestica) slices: Effect on drying and color kinetics, texture, rehydration, and microstructure

In this study, apple slices were dried using infrared (IR) and hot air techniques and comprehensively analyzed in terms of drying and product characteristics. The influence of IR power level (450-650 W) and hot air temperature (60-75 degrees C) on mass transfer, color kinetics, product texture, microstructure, and rehydration characteristics was studied. The results indicated that drying time, color change, and energy requirement were lower in IR drying than in hot air drying. Moisture diffusivity was observed to increase with IR power (3.367 x 10-9-5.579 x 10(-9) m(2)/s) and hot air temperature (1.288 x 10-9-2.387 x 10(-9) m(2)/s). The activation energies of apple slices in IR and hot air drying were 11.94 and 21.90 kJ/mol, respectively. IR-dried apple slices were more crispy, with a porous structure and higher rehydration ability. Experimental data were fitted to nine different thin-layer drying and four-color kinetic models using non-linear regression analysis. The results of regression analysis indicated that the Midilli-Kucuk model is the best model to describe the drying behavior in both techniques. The color characteristics (L, a, and b) can be best explained by the modified color model and total color change by fraction conversion model for both IR and hot air drying of apple slices. This study revealed that IR drying of apple slices results in a better quality product in less time and energy as compared to hot air drying.