## 3 Results and Discussion
### Characterization of AW Media
It should be noted that in the deproteinized media, the lactic acid content before cultivation was different and during the deproteinization process its level of concentration decreased while the pH level increased. Most probably, this was due the formation of the complexes of lactates with calcium, phosphates, and proteins; therefore, there were fewer unbound lactates [49]. The highest lactic acid content after culturing was observed for the medium D5 and the lowest one for the medium D7, with the values of 207 \(\pm\) 3.674 mg\(\cdot\)100 mL\({}^{-1}\) and 40.5 \(\pm\) 7.348 mg\(\cdot\)100 mL\({}^{-1}\), respectively. For all deproteinized whey media, the difference between the lactic acid contents before and after the cultivation of acetic bacteria was similar and ranged from 61.5 mg to 69 mg for medium D7 and D6, respectively. This may indicate a comparable ability to grow and use nutrients on the part of acetic bacteria in the deproteinized whey media. In the NDAW medium, the difference in lactic acid content before and after cultivation was 174 mg. The almost three times higher (compared with other media) use of lactic acid by _K. xylimus_ K2G30 bacteria with the production of the largest BC mass at the same time could suggest that lactic acid had a positive impact on the increased efficiency of BC biosynthesis. The literature confirms that the addition of 0.4-1.25% lactic acid improves the efficiency of BC production. This is caused by the lactic acid acting as a promoter of the Krebs cycle, positively affecting  
Figure 7: The content of non-protein nitrogen in NDAW and deproteinized AW media during culture of _K. xylimus_ K2G30. * significant difference in the medium component before and after culture, _p_-value 0.05. * non-significant difference. the growth of the biomass of acetic bacteria and, consequently, the efficiency of the BC production [53; 56]. The calcium content in AW could be about 0.0699%, while the content of magnesium amounts to about 0.0068% [57]. This study determined the content of Ca\({}^{2+}\) and Mg\({}^{2+}\) ions in the media both before and after culturing, in order to assess the impact of these macroelements on BC production by the _K. xylinus K2G30_ strain. The calcium and magnesium contents in the NDAW and deproteinized whey media are presented in Figure 8.  
The results indicate that the amount of calcium and magnesium in the media before cultivation depended on the conditions of whey deproteinization, and decreased as the pH rose during the process. The content of calcium ranged from 0.0349% to 0.0664% in media D7 and D5, respectively. The content of magnesium ranged from 0.0037% to 0.0071% in media D7 and D5, respectively. In NDAW, the content of Ca\({}^{2+}\) and Mg\({}^{2+}\) ions before cultivation amounted to 0.0551% and 0.0059%, respectively. After culturing, no significant changes in the calcium and magnesium content in any of the tested media were observed,  
Figure 8: The content of calcium (**A**) and magnesium (**B**) in NDAW medium and deproteinized AW media during culture of _K. xylinus_ K2G30. \({}^{\mathrm{ns}}\) non-significant difference. \begin{table}
\begin{tabular}{l l c c} \hline \hline  & **Medium** & **pH** & **Lactic Acid [mg:100 mL\({}^{-1}\)]** \\ \hline NDAW & before & 5.0 & 295.5 \(\pm\) 6.185 \\  & after & 6.38 \(\pm\) 0.065 & 120.85 \(\pm\) 79.092 \\ \hline D5 & before & 5.0 & 271.5 \(\pm\) 42.585 \\  & after & 5.79 \(\pm\) 0.037 & 207 \(\pm\) 3.674 \\ \hline D6 & before & 5.0 & 216 \(\pm\) 3.674 \\  & after & 6.0 \(\pm\) 0.053 & 147 \(\pm\) 4.242 \\ \hline D7 & before & 5.0 & 102 \(\pm\) 2.121 \\  & after & 7.33 \(\pm\) 0.421 & 91.5 \(\pm\) 2.121 \\ \hline D7.5 & before & 5.0 & 91.5 \(\pm\) 2.121 \\  & after & 7.33 \(\pm\) 0.161 & 22.5 \(\pm\) 3.674 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Total acidity and lactic acid content in the NDAW medium and deproteinized AW media. which could indicate that these minerals were not used by bacterial cells in order to produce BC. This is interesting because, according to [PERSON] et al.