## 3 Results and Discussion
The significantly lowest content of lactose was observed in yoghurt with the addition of casein-iron chelate compared to other variants (4.11% vs. 4.52%; 4.11% vs. 4.48%; _p_< 0.05). The chemical composition of yoghurt fortified with iron in different chemical forms was also analyzed by [PERSON] et al. [36]. The researchers found the significant differences between the samples for ash and protein content, depending on the storage time. It was also noted that addition of iron to yoghurt did not affect the fat content, which was also confirmed in our own research. In the study, the iron content was the parameter characterized by significant variation (_p_ < 0.05) between the analyzed samples. In yoghurt, with the introduced casein-iron chelate, the level of that element was 61.5-123 times higher than in samples with the addition of skim milk powder and casein hydrolysate. In samples not enriched with iron, its level was 0.13-0.23 mg/100 g of the product. The addition of casein-iron chelate at the level of 2% resulted in the content iron at a level of 12.3 mg per 100 g of yoghurt covering approximately the daily requirement of an adult, which is 10 mg/day for a male and 18 mg/day for an adult female. These values are elevated for pregnant women for whom the iron requirement increases to 26 mg/day, due to the coverage of the needs of the fetal tissues, placenta, and increasing hemoglobin level, especially in the second and third trimesters [37]. Iron complexes with proteins exhibit better solubility at alkaline pH and thus better digestibility. In the study conducted by [PERSON] et al. [21], authors found that iron and zinc in the form of caseinates in comparison to their inorganic salts exhibited better mineral absorption and stimulated ferritin synthesis. The reduced bioavailability of minerals in the form of salts may result from their insolubility at intestinal pH 7.0-8.0 [38]. As it was reported by [PERSON] and [PERSON] [39] iron-casein complexes retain bound iron even during their precipitation at acidic pH 2.0-4.0 in the stomach, therefore, in various food products, they can safely replace inorganic tortifying additives. In that context, the analyzed preparation may show its usefulness. Yoghurt, as a source of health beneficial probiotic bacteria, is an excellent product for iron fortification also due to its acid pH under which the protein-Fe complexes remain stable. Modulation of the composition of micronutrients in yoghurt may promote an \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multicolumn{2}{c}{**Production Variant**} & \multicolumn{1}{c}{**DM [\%]**} & \multicolumn{1}{c}{**Protein [\%]**} & \multicolumn{1}{c}{**Fat [\%]**} & \multicolumn{1}{c}{**Lactose [\%]**} & \multicolumn{1}{c}{**Fe [mg/100 g]**} \\ \hline \multicolumn{2}{c}{**Additive**} & \multicolumn{4}{c}{\(X\pm\) SD**} \\ \cline{2-6} \multirow{2}{*}{Yogurt} & Skim milk powder & 10.21 \(\pm\) 0.01 b  & 4.61 \(\pm\) 0.01 a  & 0.52 \(\pm\) 0.002 a  & 4.48 \(\pm\) 0.02 a  & 0.13 \(\pm\) 0.01 a  \\ \cline{2-6} \multicolumn{2}{c}{Casein hydrolysate} & 10.92 \(\pm\) 0.02 c  & 6.68 \(\pm\) 0.01 c  & 0.54 \(\pm\) 0.001 a  & 4.52 \(\pm\) 0.08 a  & 0.23 \(\pm\) 0.01 b  \\ \cline{2-6} \multicolumn{2}{c}{Casein-iron chelate} & 10.13 \(\pm\) 0.06 a  & 5.65 \(\pm\) 0.10 b  & 0.5 \(\pm\) 0.003 a  & 4.11 \(\pm\) 0.02 b  & 12.3 \(\pm\) 0.01 c [FONOTE:c]Footnote c: footnotemark: [ENDFOOTNOTE] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Composition parameters characteristic of yoghurts produced in various production variants. increased absorption in the human gastrointestinal tract, which could increase their health beneficial effect. In the study, the growth and viability of typical yoghurt microflora were analyzed. The analysis conducted directly after yoghurt production did not show any differences in LAB enumeration among the analyzed variants. Regardless of the additive used, the determined level of _Lactobacillus_ count was similar, and kept in a range of 7.34 to 7.43 [log10 cfu], while for _Streptococci_ this was 7.58 to 7.63.