Simple modelling of air drying curves of fresh and osmotically pre-dehydrated apple cubes

Air drying curves simulation of fresh and pre-osmosed apple cubes was carried out through a diffusional mass transfer model solved by the separation of variables method. The influence of an osmotic pre-treatment of apple samples on air drying curves was evaluated. Drying curves of fresh apple cubes showed case-hardening when the air drying temperature was higher than 60 degrees C, and the drying curves simulation was rendered inaccurate (%var=92.9%). The effective diffusivity coefficient in the air drying process was considerably affected by the previous application of osmotic drying (70 degrees Brix sucrose at 50 degrees C) between 30 and 180 min(D-eff decreased 38-64%). However the duration of this treatment did not show nit important influence on this diffusivity. Simulation of the air drying curves of osmotically pre-dried samples was carried out satisfactorily when neglecting sample shrinkage in the proposed model (%var = 98.4%). (C) 1997 Elsevier Science Limited.