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

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 of D-th as a function of temperature followed an Arrhenius type kinetic with two diffusion regimes: (i) without thermal pretreatment (E-a approximate to 28 kJ mole(-1)) and (ii) after plasmolysis pretreatment (E-a approximate to 13 kJ mole(-1)). In the case of electrically treated samples. only one regime was observed, with an intermediate activation energy (E-a approximate to 20 kJ mole(-1)). Furthermore, it was found that an electrical pretreatment with moderate temperature elevation (10-15 degreesC) combined with a low thermal treatment, significantly enhanced the diffusion coefficient (D-el) compared with reference values. For instance, after a standard MEFP treatment (500 V cm(1), 1000 pulses, 100 mus duration) D-el was 3.9 x 10(-10) m(2) s(-1) at 20 degreesC compared with reference values of 2.5 and 4.4 x 10(10) m(2) s(1) for untreated and denatured samples, respectively, and 13.4 x 10(10) m(2) s(1) at 75 degreesC compared with 10.2 x 10(-10) m(2) s(1) for thermally,denatured samples. This indicates that an electrical treatment has a greater effect on the structure and permeability of apple tissue than thermal treatment.