## 3 Results and Discussion
As far as the water gain in the rehydrated samples was concerned (Figure 1c), it can be noticed that at all considered solid-to-liquid ratios, the rehydration kinetics were similar. At the beginning of the process, water absorption was very fast, but with the increasing rehydration time, the rate of water absorption was substantially reduced, because the amount of water absorbed by the inner structure of material approached the saturation level [35]. The mass of absorbed water during the rehydration of dried red beet cubes depended on the value of the solid-to-liquid ratio. The bigger the ratio, the bigger the equilibrium value of absorbed water mass. The course of the moisture content increase during the rehydration of dried red beet cubes (Figure 1d) was dependent on the kinetics of mass gain and dry matter loss at the discussed process (Equation (2)). At the initial stage, moisture content increased faster, and then the rate of the process gradually slowed down. A similar rehydration kinetics has been observed for amaranth leaves [36], apples [19], pumpkin [11], red pepper [25], and tomatoes [23]. The value of the solid-to-liquid ratio influenced the course of the process. A higher discussed ratio caused a higher equilibrium value of moisture content. It can be, however, stated that the equilibrium values of moisture content in samples rehydrated in water in case of the solid-to-liquid ratios of 1:20 and 1:15 were close to each other. [PERSON] et al. [37] found different rehydration behaviors for freeze dried kiwi slices at the solid-to-liquid ratios of 1:25, 1:50, 1:75, 1:100, and 1:125. The lowest and the highest equilibrium moisture content values were found at the solid-to-liquid ratios of 1:25 and 1:50, respectively. It can be seen (Figure 1e) that the volume of rehydrated red beet cubes increased with the increasing rehydration time and the rate of the process was faster in the initial period of rehydration and decreased up to the saturation level. It means that at the beginning of the process water mainly filled the open void spaces of the cubes matrix and in the further stage the tissue structure was rehydrated only partially in the more external zone [38]. Such a typical rehydration behaviour has been obtained for apples [39] and potatoes [40]. The value of the solid-to-liquid ratio effected the kinetics of volume increase during rehydration. Although in the initial period the rehydration rates at all considered solid-to-liquid ratios were almost the same, cubes rehydrated in a smaller water amount obtained an equilibrium state more quickly than cubes rehydrated in a greater water amount. A high solid-to-liquid ratio caused a higher value of the equilibrium volume. It can be however noticed that the equilibrium volumes of samples rehydrated in water at solid-to-liquid ratios of 1:20, 1:15, and 1:10 were close to each other. Statistical tests of the Peleg model applied to simulate dried red beets rehydration curves are presented in Table 1. It can be noticed that all values of the coefficient of determination R\({}^{2}\) varied from 0.9731 to 0.9938 for mass gain, from 0.7081 to 0.9916 for dry matter loss, from 0.9782 to 0.9944 for water gain, from 0.9794 to 0.9935 for moisture content increase, and from 0.9507 to 0.9859 for volume increase. As far as the root mean square error (RMSE) was concerned, it can be stated that its value ranged from 0.2612 to 2.7615 g for mass gain, from 0.1276 to 0.2965 g for dry matter loss, from 0.3664 to 2.8014 g for water gain, from 0.0351 to 0.4946 d.b. for moisture content increase, and from 0.7047 to 1.9851 cm\({}^{3}\) for volume increase. Taking into account the obtained values of R\({}^{2}\) and the RMSE, it can be assumed that the Peleg model described the courses of mass gain, dry matter loss, water gain, moisture content increase, and volume increase during the rehydration of dried red beets cubes in an acceptable way at all considered values of the solid-to-liquid ratio.