Electrohydrodynamic drying of fruit slices: Effect on drying kinetics, energy consumption, and product quality

Abstract

Drying is one of the most common methods of food preservation.When a hygroscopic material is dried, two mechanisms are involved: convective evaporation from the surface and internal diffusion of moisture to the surface. Due to the moisture removal, the cellular structure will be collapsed, affecting the internal diffusion and resulting in material shrinkage (Mahiuddin et al., 2018). The thickness of the material significantly affects the drying rate and shrinkage (Mujumdar, 2015). Thermal (hot air) drying is the most commonly used drying technique in industries, because of its simple operation. However, it is highly energy intensive and adversely affects product quality (Kudra, 2004). The product quality could be significantly improved with non-thermal drying techniques. Electrohydrodynamic (EHD) drying is a promising non-thermal technology with a simple equipment design, relatively small energy consumption, and low cost of operation. EHD operates at ambient temperature, producing low-density non-thermal plasma. Being accelerated in the electric field, non-thermal plasma creates the ionic wind, which disturbs the boundary layer and enhances convective evaporation of water from the surface of food material. Surface drying establishes a concentration gradient inside the food material, which is the driving force of water diffusion to the surface (Singh et al., 2012). The non-thermal nature of EHD drying makes it highly suitable for the drying of heat-sensitive materials.A systematic review on the energy efficiency of EHD drying was given by Martynenko et al. (2021b). The specific energy consumption of, EHD drying is only 14.7-2700 kJ/kg, depending on the

The Effect of Material Thickness, Load Density, External Airflow, and Relative Humidity on the Drying Efficiency and Quality of EHD-Dried Apples

“…A lab-scale EHD dryer was modified for the study [ 32 ]. The EHD system was equipped with the pins-to-mesh electrode system, as displayed in Figure 1 .…”

“…Fresh apples (McIntosh) for the experiments were collected from a local farm and kept in refrigerated storage at 4 ± 1 °C until use. Apples were cut into square slices without peel and core as mentioned in Paul et al [ 32 ]. The slices of varying thickness (1, 2, and 3 mm) were spread uniformly at 50% and 100% load densities on the mesh.…”

“…The initial (fresh) and final (dry) area and thickness of apple slices were determined through image analysis using the procedure explained by Paul et al [ 32 ]. The area and volumetric shrinkage were calculated as: where A i and A f are the initial and final area, and V i and V f are the initial and final volume of apple slices.…”

“…Similarly, the color changes were also determined using image analysis [ 32 ]. The color change, ΔE, for each set was determined as: where L o *, a o *, and b o * are the initial color values of the apple slices and L *, a *, and b * are the final color values.…”

“…Unfortunately, research on the effects of material properties and environmental factors on product quality is very scarce. A recent study reported a considerable effect of thickness on the shrinkage, color, and browning of EHD-dried apple slices [ 32 ]. Martynenko et al [ 30 ] reported that external airflow below 1.0 m/s reduced the enzymatic browning in EHD drying of apple slices.…”