## 3 Results and Discussion
### Effect of the Pre-Treatment on the Properties of Dried Material
The a* value of the untreated dried material was 17.6 \(\pm\) 2.9 and for all dried materials subjected to pre-treatments in ethanol, with and without sonication, no statistical changes in red colour were noted. Similarly, [PERSON] and [PERSON] [2] did not find a significant difference in the a* and b* value between the dried untreated carrot and the dried one subjected to US for 10-30 min. On the other hand, in our research, in the case of b* value and hue angle (h*), a significant decrease was observed for almost all dried samples subjected to both EtOH and EtOH+US pre-treatments, in comparison to control (dried, untreated). It is worth noting that for both treatments the obtained values for hue angle did not exceed 90\({}^{\circ}\) (ranged from 51.9 to 56.2), which means that the dried carrot slices were still characterized by a red-orange colour. The pre-treatment, regardless of the variant and its duration, significantly decreased the hue angle, which was probably related to immersion of the material in ethanol. Figure 4: Kinetics of the water vapour adsorption (hygroscopic properties) of dried carrot tissue pre-treated in ethanol without (**a**) and with ultrasound (**b**). The above changes in all colour parameters of dried carrots were calculated in comparison to the raw carrots and presented as the total colour difference (\(\Delta\)E). In the case of processing in ethyl alcohol (EtOH), a significant colour change was demonstrated in relation to the untreated dried material, except for the longest processing time. The total colour difference ranged from 9.7 to 13.8. It is worth noting that in the case of US-assisted treatment, \(\Delta\)E ranged from 16.1 to 18.1 and was statistically identical to the control dried sample. These results indicate a colour change (\(\Delta\)E > 5) noticeable by the eye of an inexperienced observer, which can be due to different reflection of light source from fresh and dried material. Similar results were obtained by [PERSON] et al. [26] for infrared-convective dried scallion slices when the water and ethanol, with and without sonication assistance, were used before drying. Treatment in ethanol of scallion slices without US resulted in lower \(\Delta\)E value in comparison to control (soak in distilled water) and sonicated sample in ethanol. Convective drying is usually conducted at high temperatures [29; 50], which can lead to the degradation of many biologically active ingredients in food [11; 51; 52]. Carotenoids are such ingredients in carrots [53]. The carotenoid content in dried carrot tissue pre-treated in ethanol without (EtOH) and with the ultrasound of 21 kHz (EtOH+US 21) are presented in Figure 5. The carotenoid content decreased after drying in comparison to fresh samples (Figure 2). Dried carrots not subjected to pre-treatments were characterized by the content of carotenoids of 21.00 \(\pm\) 0.28 mg/100 g d.m. Compared to raw carrots, the retention of these compounds after drying of untreated sample was 39%. [PERSON] et al. [54] reported 28% retention of carotenoids after convective drying of carrots. The degradation of carotenoid content during the processing of food products depends on the composition of the product and the parameters of the drying process itself. Carotenoids are sensitive to the action of oxygen, light, heating and enzymes, hence their losses during processing can be significant [53; 54]. However, in properly processed products, changes in carotenoid content can be limited [55]. For example, when a carrot was dried at 40 \({}^{\circ}\)C the retention of carotenoid content was 92% [56]. However, when the higher temperatures of 60, 70, 80 and 90 \({}^{\circ}\)C were used the retention was 17, 27, 30 and 36%, respectively [52].