The effect of different pre-treatments (i.e. osmotic dehydration in 10, 15 and 20°Brix NaCl solution and drying air temperature of 50, 60 and 70°C) on drying behaviour of onion slices were investigated. The onion slices were dried in a laboratory model tray dryer. Drying of onion slices occurred in falling rate period. Five thin-layer drying models (Exponential, Page, Henderson and Pabis, Logarithmic and Power law) were fitted to the moisture ratio data. Among the drying models investigated, the Page model satisfactorily described the drying behaviour of onion slices. The effective moisture diffusivity of pre-treated samples was higher than that of non-treated samples

White onions were dried using an osmo-convective drying technique. Osmotic dehydration was done by dipping the onion slices in 10, 15 and 20 brix NaCl solution at ambient temperature for one hour. The increase in the concentration of NaCl increased the water loss, solid gain and weight reduction in onion slices. The drying times of pre-osmosed onions slices at drying air temperature of 50, 60 and 70°C were 6.75, 6.00 and 5.25 h respectively. The moisture diffusivity increased with increase in air temperature and ranged between 0.83 and 0.91x10-10 m2/s. Quality of dried product in respect to flavour strength and color was superior. A lowest specific energy consumption of about 1.98 kWh/kg was found in the air drying of onions pre-treated with 20 brix NaCl solution and at air temperature of 70°C.