## 3 Results and Discussion
### Color Changes after Pretreatments and Drying
Similarly, soaking for longer than 10 min resulted in a statistically significant decrease in the a* value, which could be related to a significant leaching of betalain pigments due to betalains being water-soluble pigments [50]. In the case of ultrasound-treated tissue, the changes in the a* parameter were not statistically significant. Figure 3: Color parameters: L*—brightness (**a**), a*—red color (**c**), and b*—yellow color (**e**) of untreated, blanched, soaked, and ultrasound-treated raw beetroot and subjected to various types of pretreatments, and L*—brightness (**b**), a*—red color (**d**), and b*—yellow color (**f**) of untreated, blanched, soaked, and ultrasound-treated after drying with infrared–hot air method; total color change (\(\Delta\)E) in comparison to raw beetroot after pretreatments (**g**) and after pretreatments and drying (**h**); a–f—homogeneous groups are presented above column; different letters indicate statistical significance (\(p<0.05\)). After the drying process, the value of the a* parameter increased to 20.3 \(\pm\) 3.1 (Figure 3d). It was observed that, regardless of the method used, pretreatment significantly reduced the value of the a* parameter in relation to the sample subjected only to drying. In addition, when soaking and US treatment were applied, the value of the a* parameter decreased after drying, compared to pretreated samples before drying. The decrease in the proportion of the red color in the material may be related to the leaching of dyes during pretreatment or their increased oxidation during the drying process. Changes in the value of the parameter b*, describing the yellow (+) and blue (-) color, are shown in Figure 3e (after pretreatment). The value of parameter b* for raw beetroot tissue was 2.5 \(\pm\) 0.3. After pretreatment, the b* parameter changed statistically significantly only after soaking for 20 or 30 min and US treatment at 35 kHz for 20 min. The drying process reduced the value of the b* parameter to 2.2 \(\pm\) 1.1 (Figure 3f). Both blenching and soaking for 10 min resulted in a statistically significant decrease in the value of the b* parameter. As [PERSON] and [PERSON] [50] stated, the red pigment of betalains converts to yellow during thermal treatment due to thermochemical reactions. The values of the b* parameter for the other samples in our study were not statistically significantly different from those for the dried sample without pretreatment. In particular, there was no significant effect of the applied frequency or duration of ultrasound on the values of parameter b*. The total color difference (\(\Delta\)E) takes into account all the above-mentioned color parameters and represents the color difference between the pretreated samples with the raw material (Figure 3g) and between the pretreated and dried samples with the dried material without pretreatments (Figure 3h). All pretreated samples had a total color difference value above 4, indicating a clear difference between those samples and the raw beetroot. The largest value of \(\Delta\)E was recorded for blanched beetroot and was 8.8 \(\pm\) 1.4. Also, after drying, all pretreated samples differed from the only dried sample (\(\Delta\)E above 5). In turn, after drying, the blanched sample showed the smallest \(\Delta\)E among all samples, and it amounted to 5.3 \(\pm\) 1.4. The materials subjected to US and drying showed a total color difference ranging from 9.8 \(\pm\) 2.1 to 12.9 \(\pm\) 1.9, whereas the soaked and dried samples, from 10.3 \(\pm\) 1.0 to 11.1 \(\pm\) 2.0. High values of \(\Delta\)E after soaking and  
Figure 4: Macroscopic photographs of untreated, blanched, soaked, and ultrasound-treated beetroot dried with infrared–hot air method. US pretreatments may arise from the higher values of lightness and lower values of parameter a* that illustrates the redness of samples. [PERSON] et al.