## 3 Results and Discussion
### Mineral Content  
As can be observed in Figure 7, the saturation point for absorption of K, Na, and Mg in the apple flesh was reached on the 14 th day of the experimental trial. The concentration dynamics of the ions in the apple samples showed a peak on the 14 th day of the experiment,  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Salt** & **Variable** & **pH** & **Lactic Acid** & \
\begin{tabular}{c} **Reducing** \\ **Sugars** \\ \end{tabular} &
\begin{tabular}{c} **Uronic** \\ **Acid** \\ \end{tabular} \\ \hline NaCl & \multirow{3}{*}{\(\mathrm{pH}\)} & \(1\) & & & \\ \cline{2-5} KCl & & \(1\) & & & \\ \cline{2-5} MgCl\({}_{2}\) & & \(1\) & & & \\ \hline NaCl & \multirow{3}{*}{\(\mathrm{pH}\)} & \(-0.8779\) & \(1\) & & \\ \cline{2-5} KCl & & \(-0.8540\) & \(1\) & & \\ \cline{2-5} MgCl\({}_{2}\) & & \(-0.8831\) & \(1\) & & \\ \cline{2-5} NaCl & & \(0.8245\) & \(-0.6873\) & \(1\) & \\ \cline{2-5} KCl & & \(0.9549\) & \(-0.7695\) & \(1\) & \\ \cline{2-5} MgCl\({}_{2}\) & & \(0.9868\) & \(-0.8975\) & \(1\) & \\ \hline NaCl & \multirow{3}{*}{Uronic acid} & \(0.7043\) & \(-0.5335\) & \(0.9104\) & \(1\) \\ \cline{2-5} KCl & & \(0.7296\) & \(-0.3486\) & \(0.8604\) & \(1\) \\ \cline{2-5} MgCl\({}_{2}\) & & \(0.7361\) & \(-0.5618\) & \(0.8023\) & \(1\) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Pearson correlation coefficients (\(r\)) between the samples’ physicochemical characteristics.  
Figure 6: Changes in uronic acid content during apple fermentation.  
followed by a decrease on the 21 st day, and then again, a sharp increase on the 28 th day. The lowest concentration of minerals was registered on the 35 th day of the experiment.  
The concentrations of K and Na in the apple samples showed a similar trend (between 2.21 and 5.28 mg/g in the case of K and between 1.19 and 4.88 mg/g in the case of Na), and no significant difference was seen (\(p<0.05\)) between KCl and NaCl in terms of ion accumulation during the experimental trial. This can be attributed to the fact that Na and K are monovalent cations, while Mg is a divalent cation, with a higher molecular weight [10]. All of these cations use passive diffusion to be transported via ion-specific channels along their respective gradients. It has been previously highlighted that cell membrane permeability to MgCl\({}_{2}\) is six to seven times lower than cell membrane permeability to NaCl [44]. This phenomenon was also observed in our study, with significantly lower accumulation (\(p<0.01\)) of Mg cations in the flesh of the apple samples (between 0.11 and 0.68 mg/g) in the case of the MgCl\({}_{2}\) variant, compared to the NaCl variant.  
According to [PERSON] et al., on the 55 th day of fermentation of black olives with 8% NaCl, the Na concentration in the flesh of the olives was 10.08 mg/g, while in the case of olives fermented with 4% KCl and 4% CaCl\({}_{2}\), the level of K in the flesh of the olives was 4.81 mg/g [45], which is similar to the results of the present study. In another study, [PERSON] et al. recorded different values of Na in the flesh of fermented broccoli (85.22 g/kg), cucumber (81.3 g/kg), and pepper (44.5 g/kg) after 21 days of fermentation [46]. According to [PERSON] et al., the penetration of NaCl into the flesh of olives is a matter of equilibrium, which does not depend on chemical reactions at the level of the brine [11]. As a general rule, fermented vegetables contain higher levels of macro-elements such as K, Na, or Mg, compared to fresh vegetables [47].