## 3 Results and Discussion
### The Influence of US or PEF Pretreatment on the Physical Properties (Color, Texture)
As depicted in Figure 1c, strawberries treated with US and PEF prior to osmotic dehydration had higher solid gain than the untreated samples. This means that more sugar had penetrated them during the dehydration process. The structure of strawberries damaged by the action of US and PEF probably exhibited higher permeability to sugar absorbed from the solution. The intensive absorption of sugar by US- and PEF-treated materials could partially constitute a barrier to the leaching of some substances from the strawberries, and this is why the treated samples showed a higher TPC retention than the untreated samples [71]. Moreover, the determination of TPC using the Folin-Ciocalteu method is linked to the risk of overestimating the content of these compounds in the analyzed material. This overestimation can occur due to the presence of reducing sugars, such as fructose, glucose, or maltose, as well as ascorbic acid [72]. The application of non-thermal preliminary treatments, both ultrasound and PEF, led (in most analyzed cases) to obtaining osmo-dehydrated strawberries with a significantly lower TAC compared to the untreated osmo-dehydrated samples (Figure 6b). The content of anthocyanins in the SA_US1_2 sample did not differ statistically from the content of these chemical compounds in the reference sample (SA_2), but this difference was relatively big (31.3%). Anthocyanins are chemical compounds characterized by relatively high solubility in water, so their reduced retention may stem from the leaching process occurring during osmotic dehydration [73]. Both non-thermal preliminary treatments cause structural changes in the treated tissue. The microscopic channels (US) created in it as well as irreversible or reversible pores (PEF) enhance the diffusion of water [67], and thus probably also the leaching of some soluble solids. Vitamin C contents in both the untreated and the US-pretreated osmotically dehydrated strawberries were similar. On the other hand, the PEF-pretreated and osmo-dehydrated samples exhibited significantly lower vitamin C content than the untreated osmo-dehydrated ones (Figure 6c). It is worth mentioning that no statistically significant differences in the ascorbic acid content have been observed between sample SA_PEF2_2 and both US-treated samples. Vitamin C dissolves very well in water, which facilitates its leaching from the material during osmotic dehydration [73]. As mentioned above, cavitation could cause the disruption of covalent bonds and, as a result, the release of, e.g., ascorbic acid [69; 70]. This might explain both the similar content of vitamin C in the samples untreated and treated with US, as well as the higher content of this bioactive compound in the US-treated samples compared to the PEF-treated samples. Permeabilizedcells, as a result of the PEF treatment, could cause higher and faster leakage of vitamin C from the strawberries into the osmotic solution [68]. Strawberries osmotically dehydrated with PEF pretreatment displayed the lowest antioxidant activity, estimated on the basis of DPPH and ABTS assays (Figure 6d). This is probably related to the increased cell permeability resulting from electroporation (facilitating the leakage of chemicals with water) [69]. Although the US pretreatment enhanced the  
Figure 6: Total polyphenols content (TPC) (**a**), total anthocyanin content (TAC) (**b**), Vitamin C content (**c**), and antioxidant activity (**d**) during osmotic dehydration of strawberries in 50% sucrose solution at 30 °C using US and PEF treatments; SA: osmotic dehydrated strawberries in 50% sucrose solution; SA_PEF1 and SA_PEF2: pulsed electric field-treated strawberries with the energy of 1 or 2.5 kJ/kg and subjected to osmotic dehydration; SA_US1 and SA_US2: ultrasound-treated strawberries for 30 and 90 s and subjected to osmotic dehydration.