Pulsed Electric Fields as an Infrared–Convective Drying Pretreatment: Effect on Drying Course, Color, and Chemical Properties of Apple Tissue

In this research, the impact of the pulsed electric fields (PEF) pretreatment on the infrared–convective drying (IR-CD) of apples and selected quality indicators (antioxidant capacity, color, and total phenolic content) of dried apples was evaluated. PEF pretreatment was carried out at the following parameters: electric field strength of 1 kV/cm, specific energy inputs of 1, 3.5, and 6 kJ/kg. Moreover, variable IR-CD process parameters were also assessed (peak wavelength of 1.2 µm, distance between the infrared lamps and the apple slices of 10, 20, and 30 cm). PEF pretreatment, by disintegrating apple cells, reduced the drying time of that fruit by 11–20%. The IR-CD of apples was the most effective at the shortest distance (10 cm) between the infrared source and the apple slices; it was associated with the intense heating of its surface. PEF-pretreated samples exhibited lower retention of antioxidants and were darker and redder than untreated ones. PEF could increase the activity of enzymes responsible for oxidizing phenolic compounds to brown pigments. The use of a medium distance (20 cm) during IR-CD promoted the highest retention of antioxidant compounds (relatively prompt drying with moderate heating of the sample surface).