The objective of the research study was to assess the survival of selected Lactobacillus bacteria strains isolated from oscypek and korycin cheese under the in vitro conditions of a gastrointestinal tract model and depending on the food additives used. The scope of the research study included the assessment of bacterial survival after 2 and 5 h incubation in a model system that simulated the gastrointestinal tract and depending on the protective additive used: UHT milk (3.2 % of fat), cream (36 % of fat), 10 % solutions of inulin and oligofructose. It was shown that the strains tested were resistant to the gastric juice with a pH value of 2.5, whereas the gastric juice model with pH of 2.0 caused the viability of those bacteria to decrease by ca. 5 logarithmic units on average after 2 h incubation in the gastric juice. The UHT milk showed a slight protective effect on the survival of bacterial cells, which could be compared to the effect of inulin and oligofructose in a low pH environment, with the applied research method. In contrast, a significant protective effect was reported on the survival of bacterial cells of the tested strains in the case of using 36 % cream; this is most likely related to a higher fat content compared to its content in the milk. Test strains, Lb. plantarum (Kor1 and Os1) isolated from food, were characterised by the properties similar to  those of the reference Lb. plantarum 299v strain; this may indicate potential probiotic properties in this area. The conducted studies indicate the validity of further studies to confirm the probiotic properties of bacteria isolated from fermented foods and their potential use as probiotics.