Effect of Process conditions on Osmotic Dehydration of Adama Red Onion Slice Production

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Addis Ababa University


Dehydration of vegetables is a process commonly used to preserve the product. However, collapse of the structure, discoloration and beneficial compound loss are frequent quality problem. The combination of osmotic dehydration (OD) and other drying techniques is widely used process that could improve the qualities of dried products. Osmotic dehydration (OD) is one of the most promising pre-treatment techniques. It gives product of high quality and preserves reasonably good quantity of naturally occurring microelements and vitamins in fruits and vegetables. It also provides good returns in terms of less energy consumption, palatable, aesthetically acceptable and consumer preferred product. This study was undertaken to investigate the drying characteristics of Adama red onion (Allium cepa) in an oven and fludized bed dryer after treating the onion slice in osmotic solution. Osmotic dehydration (OD) conditions of onion slices were optimized using response surface methodology(RSM) with respect to osmotic solution concentration 10–20 % (w/w), soaking time (30–60 Minutes) and soaking temperature (35–55 °C) for maximum water loss (WL) and minimum solid gain (SG) as response variables. General factorial design was used as experimental design. The models developed for all responses were significant (p<0.05). The optimized conditions obtained were osmotic solution concentration 11.08%, soaking time 38.75 minutes and soaking temperature 45.8 °C in order to obtain WL of 14.7 (g/100 g of fresh weight), SG of 6.3 (g/100 g of fresh weight). The osmotically dehydrated onion slices were then dried in a fluidized bed dryer and conventional oven at drying air temperatures of 50°, 60°, and 70°C. The quality parameters, such as rehydration ratio, ascorbic acid, microbiological quality and sensory quality (color, appearance, and overall acceptability) of the dehydrated onion were determined. The highest number of acceptable quality parameters was reported for osmotic fluidized bed dried samples at 50°C (p<0.05). Key words: Osmotic dehydration, Onion, Optimization, Response surface methodology Salt solution , Fluidized bed drying ,Oven drying



Osmotic dehydration, Onion, Optimization, Response surface methodology Salt solution, Fluidized bed drying, Oven drying