# The Effect of Hybrid Drying Methods on the Quality of Dried Carrot
## 4 Discussion  
The state of water in the material is described by the water activity parameter (a\({}_{\text{w}}\)). It ranges from 1 for clean water to 0 for the environment in which no water was found [30]. The value of water activity present in food products is a parameter that determines the stability of food by directly influencing the development of microflora. Literature data indicate that water activity must be below the value of 0.6 to call the material safe, and is assigned to food groups with low water content [31; 32]. Based on the presented results, it can be concluded that the water activity of the tested dried carrot for all drying methods was below the value of 0.4, which means that the dried product was safe. The drying process caused the water to evaporate, thanks to which its activity significantly decreased in all samples, regardless of the drying method (0.176-0.390) compared to raw carrots, where the activity was 0.964. The lowest value was characteristic of freeze-dried carrots (0.176). [PERSON] et al. [18], examining the influence of drying methods on the quality of dried material, obtained a similar value of a\({}_{\text{w}}\) for freeze-dried pumpkin. Such a low value of this parameter for dried material is caused by a complicated process including a freezing step and drying under a vacuum. The higher water activity value of samples dried by microwave and convection-drying can be connected with less water removal from the sample, as the material is often baked as a result of microwave and convection-drying. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Sample** & **Average \(\Delta\)E** & **1** & **2** & **3** & **4** & **5** \\ \hline M-F & 15.55500 & & & *** & \\ F-K & 16.63000 & & & *** & \\ K-F & 18.51000 & *** & & & \\ F-M & 18.56000 & *** & & & \\ K & 19.16000 & *** & *** & & \\ F & 19.78000 & & *** & & \\ M & 26.77000 & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 7: The results of the analysis of the Tukey test of the absolute difference in color [\(\Delta\)E] for dried carrots depend on the drying method. Statistical significant differences at \(p\) < 0.05. Designations in Table 1. The asterisks in the same columns and rows indicate no statistically significant differences between the samples. Figure 8: The impact of the type of drying method on the absolute difference in color [\(\Delta\)E] of dried carrots. The same letters (a-e) in individual columns indicate the absence of a statistically significant difference between the samples (significance level 0.05). Designations in Table 1.  
This happens when the process parameters are not properly selected. Caking the surface of the material prevents the removal of water from the inner layer of the material, which results in a higher water activity compared to other drying methods. For samples dried by hybrid (combined) methods an intermediate \(\mathrm{a_{w}}\) value was obtained; however, when it comes to the differences in the duration of the process between freeze-drying-convection and freeze-drying-microwave, freeze-drying with microwave is a more effective method, because its duration was 6 h and 2.5 h, respectively (Table 1). The use of the freeze-drying process as the first stage of drying in hybrid (combined) methods resulted in obtaining the dried carrot that was the closest in terms of water activity to freeze-dried. Relatively, the low water activity of these dried samples results from the fact that in the combined methods of drying, freeze-drying was applied, preceding the actual drying process, or drying to specific water content. The low water activity is because the material subjected to the drying process was previously frozen. The combination of freeze-drying and convection-drying of carrots allowed us to obtain a material with a lower water activity compared to convective-dried. The duration of the process is longer, but not as long as in the case of the freeze-drying itself.