## 4 Discussion  
Based on the obtained results and literature data, it can be concluded that the presence and amount of yeast, AAB, and LAB were characteristic of sourdough bread before and after baking [11]. In the case of baked sourdough with the addition of pure cultures of _Lacitplantiobacillus plantarum_ bacteria during preparation, environmental competition may occurred. The introduced LAB strains may have competed with the indigenous microbiota of the sourdough, leading to the domination of one group of microorganisms and the elimination of the native microbiota or that from the starter cultures. The strain showing the ability to dominate in the food system is _L. plantarum_; therefore, the addition of selected strains of this bacterial species gives great opportunities and chances to produce bread with a large population of bacteria with health-promoting properties [25]. Moreover, it was found that _L. plantarum_ strains, during heat stimulation, may secrete specific proteins with various roles in cell physiology, including chaperone activity, ribosome stability, stringent response mediation, temperature sensing, and control of ribosomal function, which have been found to play a role in the mechanisms of stress adaptation of these bacteria [26]. Due to these properties, we decided to add selected _L. plantarum_ strains of bacteria to the sourdoughs in the experiment. The tested strains were isolated from regional cheeses (Os1 and Os2) and fermented cucumbers from organic farming (O19 and O20) [16; 17; 18; 19], as well as a reference probiotic  
Figure 5: Projection of variables (discriminants) of principal component analysis (PCA) of sensory evaluation. Explanatory notes: \(\alpha\): odor; f.: flavour. strain (299v) and ATCC 8014. Despite their probiotic properties and high resistance to stress factors, breads with these strains added to them were not characterised by a high amount of LAB after baking and after a storage period. It has been observed that native microbiota of sourdough had the best survival. Bacteria natively present in various food products are adapted to the environment of these products to the greatest extent [27; 28]. The adaptation of bacteria consists of them adjusting their metabolism, enzymatic apparatus, and response to cellular stress [29]. Such a feature of bacteria can be an important factor in the production of food with added health-promoting strains of bacteria. However, it should be noted that high temperature is one of the most impactful factors in inactivating bacteria. For this reason, most methods of food preservation are based on this factor. Moreover, to have health-promoting features, food should contain an appropriate number of probiotic bacteria. According to the FAO, the dose of probiotics that causes a pro-health effect on the host body is 10\({}^{6}\) CFU, and a 100 g portion provides the appropriate dose [30]. However, it is possible that under stress conditions, a bacterial cell can entera viable but not cultivable (VBNC) state. Probiotic strains during mild heat stress or storage may lose their culturability under laboratory conditions, and probably for this reason, bacterial survival in all tested samples was low. However, it was proven that bacteria cells under a VBNC state had maintained enzyme activity, membrane integrity, and pH gradients across the cell membrane, so they could be defined as alive [31]. Several publications suggest that non-viable probiotic microorganisms, sometimes, can also provide benefits to the consumer. Recently, a new definition of postbiotic was introduced. Postbiotics are a \"preparation of inanimate microorganisms and/or their components that confers a health benefit on the host\". Effective postbiotics contain inactivated microbial cells or cell components, with or without metabolites, that contribute to observed health benefits [32]. During the baking process, probiotic bacteria are injured; some of them can enter a VBNC state, while some become inactivated, though the postbiotics may remain.