# Current Applications of Ultrasound in Fruit and Vegetables Osmotic Dehydration Processes
## 4 Ultrasound-Assisted Osmotic Dehydration
### Comparison of Ultrasound Assisted Osmotic Dehydration to Sonication Treatment--Kinetics Aspects  
The influence of the application of US before or during OD treatment has been widely studied. The first studies concerning the utilization of US treatment (sonication) combined with (OD) assumed the application of US as a pretreatment before further OD. When US is applied as a pretreatment for the OD process, the plant tissue is usually immersed in distilled water and then subjected to the OD process in the osmotic solution. [PERSON] et al. [31; 70] studied the changes in the structure and diffusivity of melon [70] and pineapple [31] subjected to US treatment for 10, 20 and 30 min and then to osmotic solution (0, 35 and 70 \({}^{\circ}\)Brix). The changes in the structures were significant with breakdown of cells, which resulted also in a higher water loss and a higher sugar gain. Further, [PERSON] at al. [98] analyzed the influence of time of US treatment (10, 20, 30, 45 and 90 min) applied in water and in osmotic solution on water loss, sugar loss and water diffusivity during drying of papaya. They stated that sonication positively influences the effective diffusivity of water, resulting in a drying time reduction of approximately 16%. Furthermore, the results show that after 30 min of sonication papayas lost around 13.8% sugars, which can be used in production of dried fruit with a lower sugar content. Finally, the same research group investigated also the effect of the different solution concentrations (0%, 25% and 50% sucrose), times (10, 20, 30 and 45 min) and frequencies (25 and 40 kHz) of sonication applied before or during OD of strawberries, subjected further to a drying process [66]. The drying time was reduced up to 30% in comparison to untreated dried material [66]. In addition, [PERSON] et al. [32] observed that US pretreatment performed at the frequency of 25 kHz for 20 and 30 min had a positive effect on the mass exchange in the kiwifruit subjected to the OD process for a period of 30 min. Similarly, [PERSON] and [PERSON] [99] observed that pretreatment of kiwifruit with US (25 kHz, 20 min) in distilled water increased the effective moisture and solute diffusivity in samples OD treated by 300 min in 60 \({}^{\circ}\)Brix sucrose solution.  
As the use of US accelerated the dehydration process and improved some properties of the dehydrated products (described in Sections 5.1 and 5.2), the researchers started to pay more attention on the integrated process such as ultrasound-assisted OD. [PERSON] et al. [72] treated the potato cubes with static OD, OD with agitation, OD with US pretreatment and UOD. The sonication applied as a pretreatment as well as with ultrasound-assisted OD process increased water loss and solids gain. Higher water diffusivity of about 5.5-260% was observed in samples UOD treated with 30% NaCl, depending on the treatment time. However, for osmotic solution with a concentration of 70% NaCl and US pretreatment in water, diffusivity increased up to 130%. In addition, [PERSON] et al. [100] noticed higher mass transfer rate for UOD of pomeranate seeds in comparison to OD process. On the basis of surface methodology response, the optimum conditions for a higher mass transfer rate were established at 240 min, 60 \({}^{\circ}\)Brix and 41 \({}^{\circ}\)C for UOD and 240 min, 29 \({}^{\circ}\)Brix and 50 \({}^{\circ}\)C for OD process. The highest mass transfer during US-assisted OD was noted for organic cranberries, even though the assistance of US was only 30 min [39].  
Due to the fact that OD process often precedes the drying process, several studies consider obtaining products subjected to US, OD and then drying. Usually, the sonication positively impacts on shortening the drying process applied after OD. For example, [PERSON] et al. [101] noticed that the application of US with and without OD process resulted in significantly accelerated drying time of pineapple.