Optimization of combined pre-process (osmosis-ultrasound) and additional drying with hot air of Pommelo fruit

Effect of osmosis dehydration, ultrasonic and edible coating as the pretreatment before drying has been studied in order to improve the flavor of the product, reduce thermal damages, decrease interstitial water and ease of transferring mass. The response surface method was used to optimize the drying conditions of Pommelo slices by osmosis-hot air. The concentration of edible coating (0-2% w/v) and the time of applying ultrasound (0-30 min) and the concentration of sucrose (40-80% w/w) were evaluated as independent variables on the amount of moisture content, absorption of solids, weight loss and productivity coefficient of Pommelo slices as dependent variables. All process variables were linearly significant for all responses (P<0.01). The comparison of the optimization results of coated and uncoated Pommelo osmotic dehydration showed that at the optimal point, the maximum amount of carboxymethyl cellulose coating and the osmotic dehydration time and the concentration of the osmotic solution in the coated sample were calculated as 2%, 21.86 minutes and 57.75%, respectively. The highest values of water reduction, weight loss and efficiency coefficient were 0.09172 (g/100g of solid matter), 0.091% and 19.478 respectively in the coated sample, and the highest absorption of solids with a value of 0.0089 (g/100g of solids) was reported in the uncoated sample. The results showed that the use of coating reduces the absorption of solid.