Effect of ultrasonic pretreatments and process condition on mass transfer rate during osmotic dehydration of orange slices

The intensity and application time of ultrasound treatment before the osmotic dehydration process and the use of osmotic solutions of different concentrations can result in different dehydration intensities and sucrose gain in the orange slices and also can influence important qualitative parameters. In this research, the effect of ultrasound pretreatments (three levels of ultrasound intensity and at three different times) and the sucrose solution concentration (20, 30, and 40%) on the weight loss percentage, the solid gain percentage, the amount of removed moisture and the rehydration percentage of orange slices during osmotic dehydration process was investigated. By increasing the concentration of sucrose solution from 20 to 40%, the solid gain percentage of dehydrated orange slices increased from 7.94% to 16.29% (P<0.05); But with increase in the sonication power from zero to 150 W, the value of this parameter decreased. By increasing the sucrose solution concentration from 20 to 40%, due to the increase in the osmotic pressure of the solution, the amount of weight reduction and the moisture loss percentage of orange slices increased from 5.17% to 10.58% and from 13.11% to 27.14%, respectively. With increasing the ultrasound treatment time, the amount of removed moisture from the samples increased (P<0.05). With increasing ultrasound power, the rehydration of dried samples increased from 169.9% to 186.2%, but the ultrasound time had the opposite influence, and with increasing the ultrasound treatment time, the rehydration amount of samples decreased from 181.5% to 168.9%. In general, applying 5 min of ultrasound with a power of 150 W, due to the reduction of solid gain and increase in rehydration percentage, is recommended before the osmotic dehydration process of orange slices with a solution containing 40% sucrose.