# Current Applications of Ultrasound in Fruit and Vegetables Osmotic Dehydration Processes
## 5 Properties of the Product Treated with US before or during OD  
### Physical Properties of the Product Treated with US before or during OD  
As described above, the US propagation before or during the OD causes irreversible changes in the structure of the material. Plant tissue, which was partially damaged during the pretreatment or further drying, is unable to absorb the same water content during rehydration [105]. On the other hand, porosity and material shrinkage changes during the treatments also contributed to changes in rehydration ability or texture. Furthermore, the leakage of the cellular content and activation or inactivation of various enzymes results in alteration of color of plant tissue [96; 106]. Table 1 summarizes the impact of US applied as a pretreatment or during OD on the physical properties of fruits and vegetables tissue. The effect of US on the physical properties is generally related to type of material, treatment type and parameters. [PERSON] and [PERSON] [106] studied the effect of US treatment (20%, 60% and 100% amplitude) in 61.5% sucrose solution at 30, 40 and 50 \({}^{\circ}\)C for 20, 40 and 60 min. The results show that the optimal conditions were obtained at 30 \({}^{\circ}\)C for 40 min at a 100% amplitude for obtaining good physico-chemical characteristics (mass transfer parameters, moisture content and functional properties). Moreover, sonication resulted in color changes causing a higher lightness (L*) and a lower water activity in OD samples. In addition, an increase of lightness was observed in the case of US enhanced OD of cranberries [30] and blueberries [106]. In turn, a better or unchanged color of UOD samples in comparison to OD was noted for bananas [107], kivirfuits [108] and pomerastine arils [24]. However, when the UOD material was dried, the changes were more visible [109; 110; 111]. For instance, [PERSON] et al. [110] reported a significant decrease of lightness, a*, b* and chroma parameters of UOD plum, which were explained by increased Maillard reactions. [PERSON] et al. [96] subjected carrot to OD, UOD, VOD and UVOD, and they reported a better rehydration ability (RR), lower shrinkage and hardness and higher lightness (L* value) of dried UOD samples. The authors explained that microchannel formation and higher porosity of carrot due to sonication were probably the reasons of such behavior. The applied vacuum mainly increased hardness and decreased the lightness but in combination with US (UVOD) the total color change was the lowest. Similar texture alteration was reported by [PERSON] et al. [112], who treated whole, cut and blanched cranberries with US for 30 and 60 min in osmotic solution. After the treatment the changes in the texture were observed. For all of the samples, a slight, but statistically significant, reduction in peak force was observed, whereas the work required to deform the fruit was the lowest among all the investigated samples. It was associated with the US impact on modification the plant tissue, resulting in lower cell turgor [69]. The greatest changes in mechanical properties of cranberries were observed when the combined methods were applied, including cutting or blancheding prior to sonication in the osmotic solution (C+US_30, C+US_60, BL+US_30,BL+US_60). Both the use of US and the penetration of osmotic solution inside the tissue influenced the mechanical properties of cranberries. Due to sonication, the OD was more intense, hence the loss of turgor pressure and shrinkage of the protoplast along with its separation from the cell wall [113] probably resulted in a decrease in the maximum compression force and an increase of work required to deform the sample. On the contrary, the hardness was not significantly changed in UOD pomergnate girls [24] and pomergnate seeds [100] when compared with OD. The studies carried out on kiwifruits [108] revealed that US pretreatment significantly enhanced the firmness after 120 min of OD, resulting in similar value for samples treated by 20 and 30 min of US+OD than for fresh kiwifruit.