Pomegranate arils osmotic dehydration: effect of pre-drying on mass transfer

In this work, the effect of ambient drying prior to osmotic dehydration (OD) of Tunisian pomegranate arils has been investigated. The whole fruit was pre-dried under ambient climate conditions, 20 °C and a climate humidity of 66%, until obtaining hard peels. Fresh and pre-dried pomegranate arils were dehydrated in sucrose osmotic solution at optimized conditions (50 °Brix, 40 °C, 440 rpm, foodstuff to solution weight ratio of 1:4 and 420 min). Water and solute transfer during OD where monitored. Mass transfer kinetics were modeled according to Peleg equation. This model showed a relatively good fitting of experimental data of both fresh and pre-dried samples. The pre-drying prior to OD of pomegranate arils gave lower solid gain. The sucrose uptake was about 0.403, 0.173, 0.116 g/g of dry matter for 81%, 70%, 59% initial moisture content, respectively. The highest water loss to solid gain ratio was obtained for dehydrated pomegranate arils of 70% initial moisture content. Effective diffusion coefficients were determined using the analytical solution of Fick's second law. The effective diffusion coefficients decrease with decreasing arils moisture contents. The average effective diffusion coefficients were 8.3 × 10^-9 and 4.6 × 10^-9 m² s^-1 for water loss and solid gain, respectively.