## 3 Results and Discussion
### Population of Lactobacillus acidophilus  
The number of _L. acidophilus_ in the LA-5 monoculture was, on average, 8.1 CFU/mL \(\pm\) 0.4 immediately before use. The amount of _Lactobacillus acidophilus_ was, on average, 7.1 CFU/mL \(\pm\) 0.3, while for _Bifidobacterium_, it was 6.5 CFU/mL \(\pm\) 0.3 in the original commercial kumis (OK samples) at the time of inoculation of the mare's milk. Three types of fermented mare's milk were tested for the survival of _Lactobacillus acidophilus_ (A, K, and OK). The initial _Lactobacillus acidophilus_ cell count was, on average, 7.8 log CFU/mL \(\pm\) 0.2 (Table 1; \(p\) < 0.05.) in the A samples fermented with the LA-5 monoculture. A reduction in the population of _Lactobacillus acidophilus_ was observed in all fermented milk samples during the 21 days of storage at 5 \(\pm\) 1 \({}^{\circ}\)C (Table 2). This reduction in the _Lactobacillus acidophilus_ population in the A samples of mare's milk was statistically significant (_p_ < 0.05) from day 7 of the analysis and was accompanied by a change in the pH of the samples (Table 2). The initial _Lactobacillus acidophilus_ living cell count was, on average, 7.3 log CFU/mL \(\pm\) 0.4 in the K samples (Table 2). Storing these samples for 21 days at 5 \(\pm\) 1 \({}^{\circ}\)C resulted in a decrease in the populations of the tested bacteria, which was to a lesser extent than in the A samples but to a greater extent than in the commercial kumis (OK samples). The pH of the K samples was extremely low (Table 3) compared to the acidity measured in the commercial kumis (OK samples). Despite the low pH, the observed decrease in the number of _Lactobacillus acidophilus_ in the K samples was statistically significant starting at day 7 of the analysis (_p_ < 0.05). For comparison, the population of _Lactobacillus acidophilus_ was tested in the original commercial kumis (OK samples) and evaluated for survival under the same conditions and storage period as the previously discussed samples of mare's milk (Table 2). \begin{table}
\begin{tabular}{c c c c} \hline
**Storage Day** & **A Samples** & **K Samples** & **OK Samples** \\ \hline
1 & 7.80 \(\pm\) 0.24 a* & 7.30 \(\pm\) 0.41 a & 7.30 \(\pm\) 0.21 a \\
7 & 6.40 \(\pm\) 0.32 b & 6.80 \(\pm\) 0.16 b & 7.00 \(\pm\) 0.49 a,b \\
14 & 5.30 \(\pm\) 0.28 c & 6.10 \(\pm\) 0.20 c & 6.70 \(\pm\) 0.05 b \\
21 & 4.50 \(\pm\) 0.16 d & 5.90 \(\pm\) 0.15 c & 6.30 \(\pm\) 0.19 c \\ \hline \end{tabular}  
* The same letter in the same column means that there is no statistically significant difference for \(p\) < 0.05.  
\end{table} 
Table 2: Survival of _Lactobacillus acidophilus_ (expressed as log CFU/mL) in samples of mare’s milk during storage for 21 days at 5 \(\pm\) 1 \({}^{\circ}\)C (means and standard deviations). Thus, the observed decrease in _Lactobacillus acidophilus_ in the discussed OK samples was much less pronounced than in the A and K samples but was statistically significant from 14 days of cold storage (\(p<0.05\)). No pH changes were noted in these samples (Table 3). Table 2 shows that in the original commercial kumis (OK samples), the number of LA-5 bacteria decreased from 7.3 to 6.3 log CFU/mL, while in the K samples, it decreased from 7.3 to 5.9 log CFU/mL. This decrease is considerably smaller compared to the A samples containing only the LA-5 monoculture (from 7.8 to 4.5 log CFU/mL). The level of LA-5 in the OK samples dropped by 1 log CFU but remains relatively high despite significant acidification, indicating that LA-5 is not highly sensitive to low pH values. It can be speculated that the ratio and interactions among different bacterial cultures in the original kumis (OK samples) enhance the survival chances of the LA-5 strain in the OK and K samples compared to the A samples, which contain only the LA-5 strain. This may be due to the faster consumption of substrates by LA-5 in the A samples, where no other lactobacilli are competing for the same resources. Another possible explanation is that the LA-5 strain may be sensitive to oxygen, especially at low pH values.