Effects of ultrasound treatment on the appearance characteristics of apple slices during osmotic dehydration

Osmotic dehydration (OD) is an easy method for removing water from fruit and vegetable particles. In this study, apple slices were osmotically dehydrated in different hypertonic sucrose solutions and assisted with or without ultrasound. Sucrose concentrations, sonication power, and treatment time were the factors investigated concerning colour parameters and surface area changes of the apple slices during OD. As the sonication power increased from 0W to 150W, the lightness (L*) index values of apple slices reduced from 80.01 to 74.33. Also, with increasing sucrose solution concentration from 30°Brix to 50°Brix the lightness index values of apple slices decreased from 79.23 to 75.65. The results showed that the mean of a* and b* indexes values of dehydrated apple slices increased during OD period. The highest total colour difference (∆E) index (23.4) and lowest surface area (7.98 cm2) values were for the apple slices treated by the highest ultrasound power (150W, 40 kHz) and the highest sucrose solution concentration (50°Brix). The average surface area of fresh apple slices, dehydrated samples, hot-air drying samples, and rehydrated samples were 10.00 cm2, 8.62 cm2, 5.61 cm2, and 6.99 cm2, respectively. The results illustrated that the logistic equation was the best equation to explain the ∆E index changes of untreated and treated apple slices during OD.