## 3 Results and Discussion
### Effect of the Pre-Treatment on the Drying Process of Carrot Tissue  
The pre-treatments in ethanol with and without ultrasound assistance, regardless of the type of processing, virtually did not affect the kinetics of the convective drying of carrot tissue, as shown in Figure 3. The drying of raw carrot slices, not subjected to any pre-treatment, to a relative water content (MR) of 0.02, took around 101 min (Table 3). In the case of EtOH treatment, the shortest processing time (5 s) caused reduction of the drying time only by 1.5%. On the other hand, the extension of the processing time (15-180 s) resulted in slightly longer drying (by 3.5-6.0%). Furthermore, the EtOH+US processing led to both a slight reduction (by 2.5% in the case of 15 s) and a slight prolongation (by 3.5-6.5% for 5, 60 and 180 s) of the drying time in relation to the tissue not subjected to the treatment. It can be summed up that despite the statistical differences, the immersion in ethanol practically did not affect the drying time (changes around 6 min are marginal from the industrial point of view), due to the increase of shrinkage of the tissue in comparison to untreated dried sample (Table 4). However, other researchers observed a reduction in drying time, when ethanol treatment was used. A shorter drying time about 48-50% [18] and about 34-53% [17] was reported during convective drying of pumpkin and apple, respectively, but for longer pre-treatment time (15-30 min), with or without ultrasound. A similar effect was noticed by [PERSON] et al. [11] for carrot subjected to 30 min ethanol pre-treatment, with and without US assistance, where the drying time was shortened (in comparison to control) of around 51 and 50%, respectively. While ethanol treatment lasted from 5 to 180 s for apples, the reduction of drying time from 4.9 to 18.3% was noted [9]. This phenomenon can be explained by ethanol entering the surface of the tissue, which caused the reduction  
Figure 2: The carotenoid content in raw carrot tissue pre-treated with and without ultrasound; a, b, etc.—different letters indicate different homogeneous groups (\(\alpha\) = 0.05), the results of two-way ANOVA indicate the significance (*) or insignificance (-) of the influence of the type and time of treatment (\(\alpha\) = 0.05). In table—the increase in carotenoid content in relation to the untreated sample. of the water content at the beginning of drying. Furthermore, ultrasound facilitates the process [11]. Moreover, [PERSON] et at. [16], who subjected potato to ethanol pre-treatment with and without US followed by infrared drying, mentioned that the creation of the microchannels might positively influence the drying time. Nonetheless, in the present study, both the treatment in ethanol alone and with ultrasound assistance resulted in an increase in the density of dried material (Table 4) and reduction of the volume, which is discussed below. This means that the treatment in ethanol causes such changes in the structure of carrots, which, contrary to the hypothesis concerning the acceleration of drying with ethanol, limits the possibility of faster evaporation of water during drying. It is also possible that US intensified the changes in the plant structure, therefore, the drying time was even longer, with some exceptions. Figure 3: The drying kinetics of carrot tissue pre-treated (**a**) without and (**b**) with ultrasound, a, b, etc.—different letters indicate different homogeneous groups (\(\alpha\) = 0.05). The shelf life of dried products depends on the obtained water activity level and the storage conditions (ambient humidity, type of packaging). Water activity affects the course of biological processes, in particular the development and ability to divide microorganisms. It is assumed that microbiologically safe dried products have a water activity not exceeding 0.6 [48]. In all cases, the water activity of dried samples was below the limit (0.250-0.274; Table 3).