The Effect of Ultrasound-Assisted Osmotic Dehydration Pretreatment on the Convective Drying of Apple Slices (var.Golab)

Drying is one of the widely used methods of food preservation and it is a sensitive food processing operation due to undesirable changes in the quality of dried product. In this study the effect of osmotic dyhedration and ultrasound pretreatment prior to convective drying on quality properties of apple slices was investigated. Apple slices were pretreated by osmotic dehydration in two concentration levels of sucrose solution (30, 60ºBrix) at 25 ºC for 15 and 30 minutes and were subjected to ultrasound pretreatment modulates osmotic dehydration by ultrasonic waves in a water bath at the frequency of 60 kHz in osmotic sucrose solution (30, 60ºBrix) at 25 ºC for 15 and 30 minutes. The quality of dehydrated apple was analyzed by rehydration ratio, shrinkage and color changes. The results showed that the application of ultrasound-assisted osmotic dehydration led to a decrease in rehydration ratio as compared to the control samples and observed more decrease in the samples of ultrasound-assisted osmotic than osmotic samples. Most of shrinkage belonged to the control samples and the least shrinkage was related to the samples of ultrasound-assisted osmotic. Control samples had darker color whereas the treated samples had higher lightness (L*) and lower redness (a*), yellowness (b*) and colour intensity () were represented. Based on the findings it can be concluded that the ultrasound-assisted osmotic dehydration led to improves in the color and shrinkage and obtained a decrease in rehydration ratio in the dried samples.