Study on osmotic dehydration of mushroom (Pleurotus sajor-caju) slices was carried out for partial removal of moisture prior to the further hybrid microwave drying. The effect of various process parameters on mass transfer kinetics was studied. Sodium chloride concentration (10–20%), solution temperature (30–60° C) immersion time (15–240 min) and solution to fruit ratio (4:1 to 8:1) were taken as independent process variables. Optimization was carried out for the osmotic study. The optimum operating conditions were found to be: solution temperature – 45o C, immersion time – 53.54 min, salt concentration – 14.09% and solution to fruit ratio 6.08:1. Correspond to these optimum values, water loss, solute gain and weight reduction was 38.13, 2.1 and 36.02 (g/100 g initial mass) respectively. An analytical solution for unsteady-state mass transfer based on Fick’s second law of diffusion was carried out to mathematically describe water loss and solute gain. Under these experimental conditions, effective water diffusivity was in the range of 2.58 - 1.13 x 10-9 m2/s, whereas solute diffusivity values were between 9.9 - 3.92 x 10-10 m2/s. Mathematical modeling of mass transfer was performed. Based on statistical results, the Power model gave the best goodness of fit on the experimental data under the above working conditions.

Keywords: Osmotic dehydration; Mushrooms; Mass transfer kinetics; Diffusion; Modeling