## 3 Results and Discussion
### Total Phenolic and Profile of Phenolic Compounds
#### 3.1.2 Phenolic Acids Profile  
The polyphenols were identified by the economical, simple and reliable HPLC [32]. The method was validated as shown in Table 3 and Table S1, with an example chromatogram shown in Figure 1. Among ten polyphenols, the content of four polyphenic acids was determined [Table 4]. The most abundant polyphenic acid was gallic acid (beetroot, red cabbage, red pepper) and chlorogenic acid (green pepper, kale). The content of these acids after the technological processes was statistically significantly higher, especially after the SV 80 \({}^{\circ}\)C and SV 85 \({}^{\circ}\)C processes, compared to the raw vegetables. The other polyphenic acids identified were caffe acid and rosmarinic acid, the content of which depended on the process used. For most vegetables (beetroot, red cabbage, red pepper), the content of these acids increased after technological processes, especially in red pepper. Green peppers and kale are characterised by very diverse changes in the content of these two polyphenic acids under the influence of thermal processing. The increased temperature or sealing off the product in a tight bag used in sous-vide contributed to the loss of these two polyphenic acids. For example, raw green pepper contained 43.9 mg/100 g of rosmarinic acid, increasing two-fold (91.3 mg/100 g) after the SV 80 \({}^{\circ}\)C but decreasing to 8.06 mg/100 g after the SV 85 \({}^{\circ}\)C process. This suggests the influence of elevated temperature on the decomposition of bioactive substances. On the other side, the beetroot turned out to be a vegetable in which the presence of rosmarinic acid could not be determined. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Technological Processes** & **Beetroot** & **Red Cabbage** & **Red Pepper** & **Green Pepper** & **Kale** \\ \hline Raw & 526 \(\pm\) 2.88 a & 109 \(\pm\) 0.33 e & 597 \(\pm\) 8.52 a & 91.9 \(\pm\) 1.84 e & 555 \(\pm\) 5.23 c \\ SV 80 \({}^{\circ}\)C & 361 \(\pm\) 3.66 d & 217 \(\pm\) 1.37 c & 422 \(\pm\) 12.3 c & 596 \(\pm\) 15.9 c & 402 \(\pm\) 5.17 e \\ SV 85 \({}^{\circ}\)C & 476 \(\pm\) 13.4 b & 600 \(\pm\) 2.11 a & 439 \(\pm\) 9.40 b & 737 \(\pm\) 1.38 a & 613 \(\pm\) 6.33 a \\ SV 90 \({}^{\circ}\)C & 444 \(\pm\) 7.98 c & 576 \(\pm\) 6.33 b & 434 \(\pm\) 2.32 b,c & 142 \(\pm\) 0.28 d & 600 \(\pm\) 10.8 b \\ Steaming & 293 \(\pm\) 1.60 e & 187 \(\pm\) 1.91 d & 303 \(\pm\) 5.49 d & 718 \(\pm\) 11.5 b & 461 \(\pm\) 1.28 d \\ \hline \hline \end{tabular}  
* The values are presented as the mean \(\pm\) SD (\(n\) = 3). Values followed by the same letter are not significantly different at \(p\leq\) 0.05 according to [PERSON]’s multiple range test. The \({}^{\circ\circ\circ}\)\({}^{\circ}\) of the alphabet represents the highest values, and the \({}^{\mathrm{``b$}}\), \({}^{\mathrm{c}}\), d, e\({}^{\circ\circ}\)\({}^{\circ}\) stands for the statistically significant decreasing values.  
\end{table} 
Table 2: TPC (mg GAE/100 g freeze-dried vegetable \(\pm\) SD) in the tested vegetables before and after different technological processes. In contrast, red pepper was characterised by a higher rosmarinic acid content after technological processes vs. raw vegetable, which may mean that phytochemicals were preserved in an unoxidised form [9]. For example, the content of chlorogenic acid was the highest after steaming vs. other technological processes, indicating that high temperature did not always contribute to the decomposition of polyphenols, but to the loosening of the cell structure and their easier extraction. Regarding the total polyphenolic acid content [Table 4], the most beneficial technological process for vegetables such as beetroot and kale was sous-vide at 85 \({}^{\circ}\)C, red cabbage and green pepper were sous-vide at 80 \({}^{\circ}\)C, but red pepper was steamed. The differential effects of thermal processes on the polyphenolic acid content were confirmed by other authors. [PERSON] et al. [33] examined different varieties of pumpkin, proving that it is the result of several, even opposite, mechanisms.