## 2 Materials and Methods
### Color Changes  
One of the prominent parameters in the quality of the dried agricultural products is color. Based on Table 2, the influence of the independent parameters of the \(MP\) and \(ST\), as well as the quadratic effect of the thickness, were significant (\(p<0.0001\)) on the color changes of the carrot slices. For blanched samples, the interaction effect of the \(MP\)-\(ST\) was also significant (\(p<0.0001\)) on the color changes of the samples. Figure 8 presents the interaction effects of the \(MP\) and \(ST\) on the color changes during the process of the carrot sample drying. Accordingly, the color variation range of the untreated samples was 19.29-28.68 which altered to 13.69-21.22 and 15.59-25.94 in the samples pretreated by ultrasound waves and blanching, respectively. The lowest color change (13.69) was observed in the ultrasonicated samples with a thickness of 4 mm dried at the \(MP\) of 100 W, whereas the controls with thickness of 6 mm dried at the \(MP\) of 300 W experienced the highest color changes. At constant thickness, an increase in the \(MP\) increased the difference between the color of the dried and fresh samples in all pretreatments. This observation can be assigned to oxidation, non-enzymatic browning reactions, and changes in the surface structure of the carrot samples during the drying process [18]. In drying red bell pepper [61] and okra pods [62], researchers found similar trends in which the increasing in the \(MP\) enhanced the color difference. As shown in Figure 8, the color change declined by increasing the \(ST\) from 2 to 4 mm in the untreated and sonicated samples, whereas an increase in the \(ST\) from 4 to 6 mm led to an ascending trend in the color change. In the case of the blanching pretreatment, a rise in the \(ST\) from 2 to 6 mm increased the color changes which was in line with the findings of other researchers who dried pumpkin [7] and potato [63]. For all the samples, big color changes were observed in the thickness of 6 mm as these samples required a longer time for drying. Therefore, they were exposed to oxidation and thermal degradation for a longer period of time, which enhanced the color changes in the final product [7]. After the ultrasonication and blanching pretreatments, the range of the color changes was maintained at an acceptable level. In other words, the application of the pretreatments better preserved the color features of the samples, suggesting that these pretreatments managed to prevent the browning of the carrot slices. High-temperature blanching also deactivates the enzymes such as polyphenol oxidase and peroxidase, hence decrementing the enzymic browning reactions during the drying process [32; 64]. On the other hand, ultrasonication decreased the oxygen content of the carrot samples, hence inhibiting the \begin{table}
\begin{tabular}{l l l l l l} \hline
**Pretreatment** & **Power Plant—Type of Fuel** & **Equation for CO2** & **Equation for NOx** & \(p\)**-Value** \\ \hline \multirow{4}{*}{BL **\({}^{**}\)**} & SP-NG & 10,762.27 + 2613.9A \(-\) 1921.75B & 50.09 + 12.17A \(-\) 8.94B & \textless{}0.0001 \\ \cline{2-5}  & SP-HO & 17,344.85 + 4212.66A \(-\) 3097.16B & 42.64 + 10.36A \(-\) 7.61B & \textless{}0.0001 \\ \cline{2-5}  & GT-NG & 13,232.85 + 3213.95A \(-\) 2362.91B & 32.32 + 7.85A \(-\) 5.77B & \textless{}0.0001 \\ \cline{2-5}  & GT-GO & 17,734.05 + 4307.19A \(-\) 3166.66B & 97.98 + 23.80A \(-\) 17.50B & \textless{}0.0001 \\ \cline{2-5}  & CC-NG & 7614.81 + 1849.46A \(-\) 1359.73B & 49.92 + 12.12A \(-\) 8.91B & \textless{}0.0001 \\ \cline{2-5}  & CC-TGO & 10,525.36 + 255.636A \(-\) 1879.45B & 63.96 + 15.54A \(-\) 11.42B & \textless{}0.0001 \\ \hline \end{tabular}  
* A: Thicknesses (mm), B: Microwave power (W), R\({}^{2}\): determination coefficient and CV: coefficient of variation.
* US = ultrasonication; *
* BL = blanching.  
\end{table} 
Table 3: _Cont._browning reaction [47]. This is why the least color changes occurred in the samples pretreated by ultrasound waves.