Mass transfer phenomena during the osmotic dehydration of apple isolated protoplasts (Malus domestica var. Fuji)

Osmotic dehydration (OD) experiments of apple isolated protoplasts at different temperatures (30, 40 and 50 °C) and different water–sucrose solutions (25%, 35% and 45% w/w) were monitored. The experiments were carried out under a light microscope (mod. DM LM, Leica Microsystems) with a heating/freezing stage and standalone temperature programmer (mod. LTS350 and mod. TMS94, Linkam Scientific Ltd.), where protoplasts were maintained at controlled temperature during dehydration experiences. Sequence images were acquired at different times with a CCD camera in order to measure volume changes and to determine trans-membrane water flux. The projected area (A) of individual protoplasts was measured with Adobe Photoshop (Adobe, v.7.0).Mass transfer kinetics was analyzed, determining the phenomenological coefficient (Lw) and the permeability (Dew/dPM) of the plasmalemma. Results were in the range of those obtained by other authors: Lw = [(30 °C) 4.5 ± 0.3; (40 °C) 6.5 ± 0.4; (50 °C) 9.9 ± 0.6] × 10−5 (mol2 J−1 m−2 s−1); Dew/dPM = [(30 °C) 3.3 ± 0.3; (40 °C) 5.0 ± 0.4; (50 °C) 7.9 ± 0.4] × 10−3 (m s−1). Temperature dependence was evaluated by fitting the results to an Arrhenius plot, and activation energy was calculated for both cases (Ea = [32.4–38.8] kJ/mol).