## 3 Results and Discussion  
### Bioactive Compounds Composition  
The phenolic content was affected by the addition of the impregnating solution before drying (Table 1). Samples subjected to VD were characterized by an average of 3% lower total phenolic (TP) content compared to the FD samples; however, these differences were not statistically significant. The lowest TP content was determined in samples dried without the addition of the impregnating solution before drying. In vacuum-dried samples, a decrease in TP concentration by 18.1% was observed, whereas, in VD samples, it was 21.3% lower than that of the fresh sample. The addition of NaCl had a protective effect on dried sweet potato slices. It probably acted as a protective coating to protect polyphenic compounds from oxidation. The samples with the addition of vegetable juices were characterized by the significantly highest total phenolics content (mean of 1.37 mg GAE/g DM for onion, mean of 1.26 mg GAE/g DM for kale, and mean of 1.33 mg GAE/g DM for onion with kale juice), as compared to the dried sweet potato without juice addition, which had the lowest value (0.76 mg GAE/g DM). Several studies have shown that sweet potato is a good source of phenolic com-pounds. The TP content found in some of these studies was higher compared to the pre-sent data, while, in others, the results were similar. [PERSON] et al. [30] found that different sweet potato genotypes contained 2.78-39.92 mg GAE/g DM. [PERSON], [PERSON], and [PERSON] [31] determined that the TP content in five sweet potato varieties was in the range of 4.15 to 16.79 mg GAE/g DM. In their studies on two contrasting cultivars of sweet potato, [PERSON], [PERSON], [PERSON], [PERSON], and [PERSON] [32] found that TP concentration varies in the range of 1.49-1.58 mg GAE/g, which is in accordance with our results. These differences may be affected by genetic factors, growth conditions, variety, soil properties, harvesting time, or geographical variations of sweet potato plants. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**(mg/g DM)** & **Total Phenolics** & **Total Carotenoids** & **Total Chlorophylls** \\ \hline F & 0.94 \(\pm\) 0.0 b  & 107.09 \(\pm\) 2.1 c  & 38.29 \(\pm\) 0.8 a  \\ FD & 0.77 \(\pm\) 0.0 a  & 92.12 \(\pm\) 1.6 b  & 37.03 \(\pm\) 0.5 a  \\ VD & 0.74 \(\pm\) 0.0 a  & 80.96 \(\pm\) 1.2 a  & 35.18 \(\pm\) 0.9 a  \\ N-FD & 0.94 \(\pm\) 0.0 b  & 105.74 \(\pm\) 2.5 c [FONOTE:c]Footnote a: footnotemark: [ENDFOOTNOTE] & 36.87 \(\pm\) 0.7 a  \\ N-VD & 0.93 \(\pm\) 0.0 b  & 78.93 \(\pm\) 2.0 a  & 35.05 \(\pm\) 0.9 a  \\ O-FD & 1.39 \(\pm\) 0.1 d  & 152.84 \(\pm\) 3.1 f  & 72.57 \(\pm\) 1.2 d  \\ O-VD & 1.35 \(\pm\) 0.1 d  & 118.10 \(\pm\) 1.7 d  & 45.17 \(\pm\) 1.0 b  \\ K-FD & 1.26 \(\pm\) 0.0 c  & 131.62 \(\pm\) 2.3 e  & 121.76 \(\pm\) 2.0 f  \\ K-VD & 1.26 \(\pm\) 0.1 c  & 109.79 \(\pm\) 1.6 c  & 119.09 \(\pm\) 1.9 f  \\ OK-FD & 1.37 \(\pm\) 0.1 d  & 174.29 \(\pm\) 2.8 g  & 92.13 \(\pm\) 1.4 e  \\ OK-VD & 1.28 \(\pm\) 0.1 c  & 173.29 \(\pm\) 1.9 g [FONOTE:d]Footnote d: footnotemark: [ENDFOOTNOTE] & 57.75 \(\pm\) 0.6 c  \\ \hline \hline \end{tabular} Note: Mean followed by different letters (a–g) in the column differs significantly (\(p<0.05\)).  
\end{table} 
Table 1: Bioactive compound content (mg/g of dry matter) of sweet potatoes dried by freeze drying (FD) and vacuum drying (VD) when fresh (F) and impregnated in sodium chloride (N), onion juice (O), kale juice (K), or onion–kale juice (OK). Mean followed by different letters in the column differs significantly (\(p<0.05\)). The addition of onion and kale juices affected the increase in TP concentration as compared to the fresh sample. This may be due to both the protective effect of the juice layer on the surface of the dried sweet potato slices and the enrichment of the samples with polyphenols from these raw materials. Both onions and kale are considered valuable sources of polyphenols. [PERSON] et al.