## 3 Results and Discussion
### Microbiological Quality and Biological Activity of Fermented OBB
Figure 5: Total number of LAB in oat beverages with the addition of chokeberry extract and lyophilisate. Averages with different small letters (a–d) are significantly different at \(p<0.05\) (comparison within a group of samples with the addition of extract and lyophilisate separately). Averages with different capital letters (A–E) are significantly different at \(p<0.05\) (comparison between groups of samples with the addition of extract and lyophilisate). Figure 6: Total number of LAB in oat beverages with the addition of hawthorn extract and lyophilisate. Averages with different small letters (a–b) are significantly different at \(p<0.05\) (comparison within a group of samples with the addition of extract and lyophilisate separately). Averages with different capital letters (A–C) are significantly different at \(p<0.05\) (comparison between groups of samples with the addition of extract and lyophilisate). Literature data indicate that different LAB species may be successfully used as starter cultures for the preparation of cereal fermented beverages [82]. In the presented study, _L. plantarum_ was used due to the dynamics of its growth and reached a high cell number in the matrix created on the basis of oat flakes. Among LAB species, _L. plantarum_ is part of the natural microbiota occurring in spontaneously fermented cereals; however, it should be underlined that the technological properties are strongly dependent on the strain [83]. [PERSON] et al. [84] prepared a fermented oat beverage based on oat flakes with different strains of _L. plantarum_ and obtained a beverage with good nutritional and sensory properties with one of the tested strains, _L. plantarum_ LP09. The fermentation process decreased the pH to 4.2, similar to the presented work, and increased antioxidant activity, while in this study, a decrease in antioxidant activity was observed. After the fermentation, the LAB cell number was at a level of 6.5 \(\times\) 10\({}^{8}\) CFU/mL, even as the process was shorter than in the presented work, and took 12 h. Similar results concerning LAB cell numbers were obtained in the presented work. However, some authors obtained even higher results. In the work of [PERSON] et al. [85], a whole-grain oat substrate was fermented with LAB for 8 h to obtain a drink, with the probiotic culture and the oat prebiotic beta-glucan. The LAB cell number was about 7.5 \(\times\) 10\({}^{10}\) CFU/mL. In their study, the addition of some sweeteners did not influence the dynamics of the fermentation process and viability of bacteria. [PERSON] et al. [86] obtained an oat fermented drink using oat flour and _L. plantarum_ as a starter culture, indicating that oat and sugar content had the greatest impact on the growth of bacterial strains. The fermentation was carried out at 37 \({}^{\circ}\)C for 8 h, achieving 10.4 log CFU/mL. In turn, [PERSON] et al. [84] prepared a beverage from oat flakes milled into flour and conducted fermentation with _L. plantarum_, _L. casei_, and _L. paracasei_ strains. Similar results were also presented by [PERSON] et al. [87], who studied fermented drinks based on oat sprout flour. The authors showed that after 4 h of fermentation with _L. plantarum_ WCFS1, the number of LAB in the beverages was approximately 9 log CFU/mL, while the number of fungi, _E. coli_, total coliforms, and _B. cereus_ was below 1 log CFU/mL. They also did not note the presence of pathogens such as _L. monocytogenes_ or _Salmonella_ spp. in the prepared beverages. It is worth underlining that a high number of LAB, observed also in this study, guarantees the appropriate properties of the beverages because, during their development, bacteria lower the pH and produce metabolites that inhibit the growth of undesirable microorganisms. In the case of the beverages tested in the presented work, an additional factor influencing the microbiological quality was the addition of extracts and lyophilates, demonstrating antibacterial properties.