# Characterization and Selection of _Lactobacillus_ Strains with Potential Robotic Applications
## 3 Results and Discussion
### Resistance of Lactobacillus Strains to Simulated Upper Gastrointestinal Tract Conditions  
As already mentioned, bacterial strains, in particular _Lactobacillus_ strains, should possess several important properties to be considered as probiotic. One of the major  
Figure 2: Production of lactic acid of _Lactobacillus_ strains during cultivation at 30 \({}^{\circ}\)C (**A**)  and 37 \({}^{\circ}\)C (**B**)  for 48 h. Values are expressed as means \(\pm\) SD. Letters a–i indicate significant differences (\(p<0.05\)) between the samples, \(n=3\). criteria for effectiveness is that strains retain their viability and activity under unfavorable gastrointestinal tract conditions and during the manufacture and storage of probiotic products. Therefore, one of the first steps of the evaluation of new probiotic strains is the determination of their survival in _in vitro_ simulated upper gastrointestinal conditions [21]. The growth of the four _Lactobacillus_ strains after exposure to pH 2.5 + pepsin and pH 7.4 + pancreatin (containing lipase, protease and amylase) for 3 h is presented in Figure 3A-D. As seen from the obtained results, in all treatments and the controls, after the 5 th hour of incubation, the number of viable cells gradually began to increase, which was more pronounced in the controls and the treatments at pH 7.4 + pancreatin. In terms of OD\({}_{600\text{ nm}}\), at the end of incubation (24 th h), all treatments reached their maximum growth. In the _L. casei_ ATCC 393 and _L. casei_ RC-1 strains, the cell recovery in the treatment with pH 7.4 + pancreatin was more intensive and showed OD values close to the controls, whereas in the treatment with pH 2.5 + pepsin, the cell recovery was less pronounced. It demonstrated that these two strains were more susceptible to low pH and the presence of pepsin compared to the other two strains. In the _L. acidophilus_ RC-2 and _L. rhamn_ RC-10 strains, the cells in both treatments (pH 2.5 + pepsin and pH 7.4 + pancreatin) recovered at almost the same rate as the controls. The cell recovery, summarized in Table 1, demonstrated that all of the studied strains were resistant to the simulated upper gastrointestinal tract conditions and can be considered to have probiotic potential. Figure 3: _Cont._  
Several studies have assessed the resistance of different _Lactobacillus_ species to simulated gastrointestinal tract conditions. [PERSON] et al. [22] investigated the probiotic potential of \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Strain**} & \multirow{2}{*}{**Conditions**} & \multicolumn{2}{c}{**Cell Recovery, \%**} \\ \cline{3-4}  & & **6 h** & **24 h** \\ \hline \multirow{2}{*}{_L. casei ATCC 393_} & pH 2.5 + pepsin & 65.45 \(\pm\) 0.02 \({}^{\text{a}\text{A}}\) & 75.35 \(\pm\) 0.06 \({}^{\text{a}\text{B}}\) \\  & pH 7.4 + pancreaticin & 80.91 \(\pm\) 0.03 \({}^{\text{b}\text{A}}\) & 93.95 \(\pm\) 0.07 \({}^{\text{b}\text{B}}\) \\ \multirow{2}{*}{_L. casei_ RC-1} & pH 2.5 + pepsin & 60.25 \(\pm\) 0.01 \({}^{\text{a}\text{A}}\) & 74.24 \(\pm\) 0.03 \({}^{\text{a}\text{B}}\) \\  & pH 7.4 + pancreaticin & 86.96 \(\pm\) 0.05 \({}^{\text{b}\text{A}}\) & 96.07 \(\pm\) 0.03 \({}^{\text{b}\text{B}}\) \\ \multirow{2}{*}{_L. acidophilus_ RC-2} & pH 2.5 + pepsin & 66.67 \(\pm\) 0.01 \({}^{\text{a}\text{A}}\) & 87.50 \(\pm\) 0.15 \({}^{\text{a}\text{B}}\) \\  & pH 7.4 + pancreaticin & 87.10 \(\pm\) 0.02 \({}^{\text{b}\text{A}}\) & 98.15 \(\pm\) 0.02 \({}^{\text{b}\text{B}}\) \\ \multirow{2}{*}{_L. rhamnosus_ RC-10} & pH 2.5 + pepsin & 70.33 \(\pm\) 0.12 \({}^{\text{a}\text{A}}\) & 87.30 \(\pm\) 0.06 \({}^{\text{a}\text{B}}\) \\  & pH 7.4 + pancreaticin & 81.32 \(\pm\) 0.07 \({}^{\text{b}\text{A}}\) & 96.83 \(\pm\) 0.02 \({}^{\text{b}\text{B}}\) \\ \hline \hline \end{tabular} Values are expressed as means \(\pm\) SD. Letters a-b indicate significant differences (\(p<0.05\)) within a sample exposed to different conditions, while letters A–B denote significant differences (\(p<0.05\)) between the cultivation hours, \(n=3\).  
\end{table}