Drying Behaviour and Energy Requirement for Dehydration of White Onion Slices

Abstract

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.