Drying Kinetics of Apple Tissue Treated by Pulsed Electric Field

Abstract

The aim of this work was to study the influence of pulsed electric field (PEF) on the drying kinetics of apple tissue. Therefore, mathematical models that are commonly used in the literature were applied to describe the process. PEF treatment of the samples was carried out at an intensity of E = 5–10 kV/cm and 10–50 pulse numbers. Subsequently, the apples were convectively dried at 70°C and air velocity of 2 m/s. Based on electrical conductivity measurement, the cell disintegration index Z _p was computed. Midilli et al.'s(Drying Technology, Vol. 20, pp. 1503–1513, 2001) model was evaluated as the most adequate to describe the moisture transfer in PEF-treated and intact samples. PEF pretreatment induced a reduction in drying time of up to 12% when 10 kV/cm and 50 pulses were applied. For instance, after 60 min of drying, the dimensionless moisture ratio for PEF-treated (10 kV/cm, 50 pulses) samples was 0.18 compared to 0.26 for the untreated apples. The effective moisture diffusivity, calculated on the basis of the Fick's second law, was 1.04 × 10⁻⁹ m/s for intact samples and from 1.09 × 10⁻⁹ to 1.25 × 10⁻⁹ m²/s for PEF-treated samples at 10 pulses at 5 kV/cm and 50 pulses at 10 kV/cm, respectively.

Keywords:

• Food drying
• Mathematical modeling
• Pretreatment
• Pulsed electric field

Notes

k, k _i are drying coefficients (s⁻¹); a, b are coefficients of the equations; n is an exponent; t is time (s); D _eff is the effective moisture diffusion coefficient (m²/s); and L is the half-thickness (m).

Different letters indicate significant differences at α = 0.05.