Mass Transfer during Osmotic Dehydration of Banana
Effects of Osmotic dehydration on water loss, solids gain, and weight reduction during osmotic dehydration were investigated in order to determine the usefulness of this technique as pre-treatment for further drying of bananas slices. Banana slices, 10 mm thick, were immersed in sucrose solutions with concentrations of 30, 40 and 50 Brix at 40, 50 and 600C for 60, 90 and 120 minutes. Water loss, weight reduction and solids gain increased with treatment time. Longer treatment time in high concentrations of sucrose resulted in a very soft product, which is difficult to handle and unsuitable for further drying. Increasing concentration at the same temperature did not cause significant increments in weight change. Higher concentrations of sucrose caused higher rates of water removal. The effective Normalized moisture content for water and Normalized solid content were determined, considering banana as slices configuration. The temperature was controlled using constant temperature stirred water bath. The ratio of the volume of slices to that of the medium was maintained at 1:4, 1:5 and 1:10 in order to ensure that the concentration of the osmotic solution did not change significantly during the experiment. The samples were withdrawn, rinsed quickly in water, blotted gently with a tissue paper in order to remove adhering water and then dried in a hot air oven at 70 0C for 18 hours. The regression analysis was done by response surface method.