Effect of moderate electric field pulses on the diffusion coefficient of soluble substances from apple slices

Abstract

The effects of a moderate electric field pulse (MEFP) on the diffusion coefficient of soluble substances from apple slices have been investigated. The apparent diffusion coefficient,D, was studied for both thermally and electrically treated samples. For thermally treated samples, the variation ofDthas a function of temperature followed an Arrhenius type kinetic with two diffusion regimes: (i) without thermal pretreatment (Ea ≈ 28 kJ mole–1) and (ii) after plasmolysis pretreatment (Ea ≈ 13 kJ mole–1). In the case of electrically treated samples, only one regime was observed, with an intermediate activation energy (Ea ≈ 20 kJ mole–1). Furthermore, it was found that an electrical pretreatment with moderate temperature elevation (10–15 °C) combined with a low thermal treatment, significantly enhanced the diffusion coefficient (Del) compared with reference values. For instance, after a standard MEFP treatment (500 V cm–1, 1000 pulses, 100 μs duration)Delwas 3.9 × 10–10 m2 s–1at 20 °C compared with reference values of 2.5 and 4.4 × 10–10 m2 s–1for untreated and denatured samples, respectively, and 13.4 × 10–10m2 s–1at 75 °C compared with 10.2 × 10–10 m2 s–1for thermally denatured samples. This indicates that an electrical treatment has a greater effect on the structure and permeability of apple tissue than thermal treatment.