Kinetics investigation of thin layer plums drying simultaneously pretreated with ultrasound and osmotic dehydration

Ultrasound is one of the emerging technologies that its application in drying foodstuffs aimed at reducing the time needed to process and improve the quality characteristics of dried product is growing day by day. In this study, the simultaneous effect of ultrasound and osmotic dehydration pretreatments on thin-layer drying kinetics of plums during drying at 80°C temperature and 1.4 m/s air velocity was examined. The pretreatments applied included ultrasound waves at two levels (10 and 30 minutes), osmotic solution concentrations at two levels (50 and 70 Brix) and osmotic dehydration time at four levels (60, 120, 180 and 240 min). The results showed that increasing ultrasound time, osmotic solution concentration and osmotic process time led to a decrease in drying time and an increase in effective moisture diffusion coefficient compared to control sample. Furthermore, in order to correctly predict the drying process, the data from the experiments were fitted with some empirical models as well as some new proposed models in this study. Then, one of the proposed models was selected as the best model (based on Coefficient of Determination, Root Mean Square Error and Sum of Square Error) to describe the drying process of plums under the selected experimental conditions. Through multiple regression analysis, the relations between the coefficients of the models with the variables used were obtained.