# Characterization and Selection of _Lactobacillus_ Strains with Potential Robotic Applications
## 3 Results and Discussion
### Resistance of Lactobacillus Strains to Simulated Upper Gastrointestinal Tract Conditions

Table 1: Percentage of cell recovery of _Lactobacillus_ strains after exposure to pH 2.5 + pepsin and pH 7.4 + pancreaticin for 3 h.  
Figure 3: Cell recovery of _L. casei_ ATCC 393 (**A**), _L. casei_ RC-1 (**B**), _L. acidophilus_ RC-2 (**C**), _L. rhamnosus_ RC-10 (**D**) in MRS broth after exposure to pH 2.5 + pepsin and pH 7.4 + pancreaticin for 3 h during cultivation at 37 \({}^{\circ}\)C for 24 h. Values are expressed as means \(\pm\) SD. Letters a–c indicate significant differences (\(p<0.05\)) between the samples, \(n=3\). three _L. casei_ strains (SB71, SB73 and SB93) and stated that the cell viability of the strain SB71 in gastric juice reduced significantly after 3 h of exposure, while intestinal juice reduced its viability between 3 and 24 h. A similar decreasing trend was observed for strain SB73. The viability of the strain SB93 was unaffected by the gastric juice but significantly reduced by the intestinal juice (between 6 and 24 h). The percentage survival of the strain SB93 after incubation in intestinal juice for 24 h was significantly higher than the other two isolates studied. Research conducted by [PERSON] et al. [23] showed that the percentage of cell recovery of four studied strains from the _L. casei_ group isolated from Kazakh dairy foods ranged between 35% and 63% after 1 h of exposure under simulated gastric conditions. Various technological approaches can be applied to improve the viability of _Lactobacillus_ species in the gastrointestinal tract and during the manufacture of fermented products. In this regard, [PERSON] et al. [24; 25] evaluated the survival of spray-dried microencapsulated and alginate-encapsulated cells of _L. casei_ ATCC 393 under simulated gastrointestinal conditions and during the production and storage of fermented milk, finding that these methods significantly improved survival rate and retained a significantly higher number of viable cells during fermented milk production. The members of _L. acidophilus_ group are normal inhabitants of the gastrointestinal tract of healthy humans and are widely documented as LAB with probiotic potential. [PERSON] et al. [26] assessed the probiotic features of three _L. acidophilus_ strains, namely WFA1 (KU877440), WFA2 (KU877441) and WFA3 (KU877442) isolated from Pakistan Dahi yogurt. The authors reported that simulated gastric conditions had a more severe impact on their survival compared to the effect of simulated intestinal conditions. The survival rates of the studied strains under gastric conditions ranged between 43.12% and 50.45%, while those under intestinal conditions varied between 57.45% and 71.36% after 24 h of incubation, which was lower in comparison with our results for _L. acidophilus_ RC-2 strain at the same time of incubation. [PERSON] et al. [27] compared the probiotic properties of various LAB and reported that survival rates of the strain _L. acidophilus_ AD1 in simulated gastric juice (pH 3.0) were 91.21%, 88.48% and 83.41% at the 1 st, 2 nd and 3 rd h, whereas the survival rates in simulated intestinal juice (pH 8.0) were 99.15%, 96.90% and 84.67% at the 2 nd, 4 th and 8 th h of incubation, respectively. Similar to _L. casei_, the various encapsulation methods (ionic gelation, extrusion, emulsification and spray drying) are also considered effective means for improving the survival and viability of _L. acidophilus_ cells in harsh environments during the digestion process or manufacture of different products [28]. _L. rhamn_ GG is a strain known for its high tolerance to adverse gastrointestinal tract conditions. [PERSON] et al. [29] established that the survival rates of the strains _L. rhamn_ X253 and _L. rhamn_ GG after incubation in artificial gastric fluid (pH 3.0) for 3 h remained above 90%. The survivability of _L. rhamn_ GG after exposure to artificial intestinal fluid (pH 8.0) for 5 h was 80%, whereas the survival rate of _L. rhamn_ X253 declined markedly to 55%. [PERSON] et al. [30] stated that the strain _L.