Impact of pre-treatment methods on the drying kinetics, product quality, and energy consumption of electrohydrodynamic drying of biological materials

Electrohydrodynamic (EHD) drying is an energy-efficient drying method. This novel drying technology operates at room temperature, which makes it particularly suitable for drying biomaterials that contain heat-sensitive compounds. It has a higher drying rate than other low-temperature methods, such as solar and freeze-drying. However, its drying rate is not high enough to compete with other conventional thermal methods, such as hot-air drying. For industrial applications requiring high product throughput, the drying rate of EHD drying should be improved. One way to do this is to combine EHD with pre-treatment methods. Therefore, this study evaluated the impact of different pre-treatment methods on drying kinetics, energy consumption, and product quality attributes of apple slices dried using EHD drying. Pulsed electric fields (PEF), ultrasound, and blanching are the studied pre-treatment methods. Results show that only PEF pre-treatment could significantly decrease the EHD drying time by 39%. However, it resulted in a 26% higher browning index than the untreated EHD-dried apples, which is not appealing to consumers. The applied pre-treatment methods did not significantly affect other quality attributes, such as antioxidant activity, total phenolics, and rehydration ratio. In conclusion, using the studied pre-treatments for EHD drying increases the complexity of the process, whereas it is arguable whether the added values outweigh the energetic and quality downsides or not.