## 3 Results and Discussion
### Total Phenolic Content and Total Carotenoid Content  
As pumpkin is an excellent source of bioactive compounds including \(\beta\)-carotene [35], it is worth observing the retention of this compound after freeze-drying. Figure 3a presents the total phenolic content (_TPC_) in untreated and PEF-treated freeze-dried samples. In general, better retention of _TPC_ has been observed in the samples dried at 60 \({}^{\circ}\)C than at 40 \({}^{\circ}\)C. It could be due to the shorter drying time at higher temperatures, which might have reduced the degradation of bioactive ingredients in the dried pumpkins [36]. Moreover, at higher temperatures, the enzymes responsible for the oxidation of these compounds could be denatured [37]. In the case of _TPC_, PEF treatment has not shown a positive trend in the enhancement of its retention. The only significant increase in _TPC_ content has been observed in the case of samples pretreated with PEF\({}_{2}\) and PEF\({}_{3}\) and dried at 40 \({}^{\circ}\)C. The high variability in the results may also be attributed to the presence of substances which may interfere with the phenolics' determination and which are naturally present or are formed in the pumpkin during its processing, such as the before-mentioned products of nonenzymatic browning reactions [38; 39]. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Sample** & \(L^{*}\) & \(a^{*}\) & \(b^{*}\) & \(\Delta E\) & \(BI\) \\ \hline \multicolumn{6}{c}{**Drying at 40 \({}^{\circ}\)C**} \\ \hline U—0 kJ/kg & 76.68 \(\pm\) 0.05 \({}^{\rm cd}\) & 18.82 \(\pm\) 0.15 \({}^{\rm cd}\) & 72.77 \(\pm\) 1.31 \({}^{\rm a}\) & - & 202.4 \\ PEF\({}_{1}\)—0.1 kJ/kg & 77.31 \(\pm\) 0.31 \({}^{\rm ef}\) & 18.59 \(\pm\) 0.07 \({}^{\rm cd}\) & 72.69 \(\pm\) 0.96 \({}^{\rm a}\) & 0.68 & 198.7 \\ PEF\({}_{2}\)—0.5 kJ/kg & 76.03 \(\pm\) 0.67 \({}^{\rm b}\) & 20.51 \(\pm\) 0.59 \({}^{\rm f}\) & 74.66 \(\pm\) 1.56 \({}^{\rm b}\) & 2.62 & 216.9 \\ PEF\({}_{3}\)—1 kJ/kg & 76.66 \(\pm\) 0.36 \({}^{\rm bc}\) & 19.48 \(\pm\) 0.14 \({}^{\rm e}\) & 74.15 \(\pm\) 0.90 \({}^{\rm ab}\) & 1.53 & 210.1 \\ PEF\({}_{4}\)—2 kJ/kg & 74.25 \(\pm\) 0.21 \({}^{\rm a}\) & 22.86 \(\pm\) 0.09 \({}^{\rm g}\) & 75.32 \(\pm\) 0.42 \({}^{\rm b}\) & 5.35 & 232.7 \\ \hline \multicolumn{6}{c}{**Drying at 60 \({}^{\circ}\)C**} \\ \hline U—0 kJ/kg & 77.66 \(\pm\) 0.13 \({}^{\rm ef}\) & 17.95 \(\pm\) 0.17 \({}^{\rm ab}\) & 73.76 \(\pm\) 0.70 \({}^{\rm ab}\) & - & 201.8 \\ PEF\({}_{1}\)—0.1 kJ/kg & 77.79 \(\pm\) 0.14 \({}^{\rm e}\) & 17.89 \(\pm\) 0.02 \({}^{\rm a}\) & 73.67 \(\pm\) 0.12 \({}^{\rm ab}\) & 0.17 & 200.6 \\ PEF\({}_{2}\)—0.5 kJ/kg & 77.07 \(\pm\) 0.06 \({}^{\rm de}\) & 18.86 \(\pm\) 0.12 \({}^{\rm d}\) & 74.86 \(\pm\) 0.42 \({}^{\rm b}\) & 1.55 & 211.1 \\ PEF\({}_{3}\)—1 kJ/kg & 76.57 \(\pm\) 0.41 \({}^{\rm bcd}\) & 18.38 \(\pm\) 0.39 \({}^{\rm bc}\) & 79.06 \(\pm\) 0.55 \({}^{\rm c}\) & 5.43 & 236.7 \\ PEF\({}_{4}\)—2 kJ/kg & 76.22 \(\pm\) 0.07 \({}^{\rm bc}\) & 19.43 \(\pm\) 0.19 \({}^{\rm e}\) & 78.28 \(\pm\) 1.11 \({}^{\rm c}\) & 4.97 & 235.1 \\ \hline \end{tabular} The same letters in columns indicate homogeneous groups (Tukey’s HSD, \(p<\) 0.05, \(n=\) 6).  
\end{table} 
Table 1: Color parameters (\(L^{*}\), \(a^{*}\), \(b^{*}\)), total color difference (\(\Delta E\), in comparison to untreated dried material), and browning index (\(BI\)) of freeze-dried pumpkin samples. Figure 3b shows the total carotenoid content (\(TCC\)) in untreated and PEF-treated freeze-dried pumpkin at 40 and 60 \({}^{\circ}\)C. The \(TCC\) content in the samples dried at 60 \({}^{\circ}\)C is reducing with an increase in PEF intensities, from 98.16 to 86.72 mg \(\beta\)-carotene/100 g d.m. for untreated and PEF\({}_{4}\) samples, respectively. This can be explained by the fact that PEF treatment enhances heat and mass transfer in the plant tissue. Therefore, the more the cells are open (high \(Z_{p}\), see Figure 1), due to PEF, the more exposed the bioactive compounds are to the heat.