Effect of Pulsed Electric Field on the Osmotic Dehydration and Mass Transfer Kinetics of Apple Tissue

Abstract

The osmotic dehydration (OD) of food plant tissue constitutes an alternative step for drying. As OD is relatively slow, pulsed electric field (PEF) can be used to accelerate this process. The application of PEF induces a cell membrane permeabilisation with formation of pores accelerating the solute and water transport through the cell membrane. In this study, apple samples were subjected to a PEF pre-treatment, followed by an immersion in an osmotic solution at 25°C containing 44.5 w/w of sucrose. The impact of pre-treatment conditions (electric field intensity, pulse number) on the concentration of osmotic solution (°Brix), the water removal and the solid content in apple samples were studied. Compared to untreated apples, the application of the PEF pre-treatment resulted in decrease of sugar concentration in the osmotic solution and higher solid content in apple samples. The variation of electric field conditions showed that the optimum PEF parameters were 0.90 kV/cm and 750 pulses with a pulse duration of 100 µs, which corresponds to an energy input of 13.5 kJ/kg. A continuous method was developed to follow the evolution of OD kinetics on the apple tissue. Experiments were fitted by a two-exponential model describing the kinetics of water and solute transfer during the OD. This enables the determination of mass transfer coefficients demonstrating that PEF increased both the convection and diffusion rates.

Keywords:

• Pulsed electric field
• Osmotic dehydration
• Apple tissue
• Concentration of osmotic solution
• Water loss
• Solid gain
• Continuous method
• Kinetic model