## 4 Discussion  
This study aimed to determine the influence of typical lactic acid bacteria cultures in the dairy industry on the quality of fermented dairy, dairy-oat, and oat beverages. The dairy-oat beverage investigated in this study represents a novel approach to hybrid beverage formulation, combining the nutritional benefits of both dairy and plant-based ingredients. While similar products are not widely available on the market, industry interest in such formulations is increasing, particularly in the context of fermented beverages that could serve as functional dairy alternatives with enhanced sensory properties. The research hypothesis postulated that the addition of selected bacterial cultures would have a significant positive impact on the quality parameters of fermented beverages. The observed changes in pH during fermentation indicate that yogurt cultures, both alone and in combination with _L. plantarum_ 299 or _L. acidophilus_ La-5, significantly affected the acidity of the beverages. Dairy and dairy-oat samples exhibited similar pH values (4.1-4.5). In contrast, adding _L. plantarum_ 299 did not cause significant pH changes, suggesting the weak fermentative ability of this culture under the applied conditions. The designated fermentation period was too short, as other researchers have successfully fermented plant-based substrates with this bacterial strain [17; 18]. The lowest pH values were observed in samples fermented with _L. plantarum_ 299 and _L. acidophilus_ La-5, indicating their high fermentative activity. The current results correlate with the literature data [19]. According to [PERSON] et al. [19], the fermentation of cow and soy milk mixtures with _L. acidophilus_ La-5 achieved a pH of 4.6, demonstrating effective acidification. Dairy and dairy-oat beverages demonstrated greater pH stability than oat-based samples, which is crucial for product quality and sensory characteristics. This corresponds with previous studies showing that dairy beverages maintain a lower pH due to lactic acid bacteria efficiently fermenting lactose into lactic acid [20; 21]. In contrast, Lactococcus lactis-fermented oat beverages showed a significant pH drop to 4.25 but with lower stability [13]. While acidity is critical for fermentation, excessive acidification may negatively impact consumer acceptance, highlighting the need for balanced acidification in plant-based alternatives. Texture analysis showed that fermentation influenced beverage consistency, with samples containing mixed bacterial cultures (probiotic and yogurt) exhibiting higher hardness. This effect likely results from interactions between bacterial cultures and the beverage matrix. The highest hardness values were observed in samples fermented with the yogurt culture and _L. plantarum_ 299v, suggesting a stabilizing effect of these bacteria. In contrast, samples fermented solely with _L. plantarum_ 299v or _L. acidophilus_ La-5 did not form a gel, preventing hardness and adhesiveness measurements. Previous studies confirm that specific bacterial blends enhance gel hardness and improve texture through acidification and fermentation processes [22; 23]. _L. acidophilus_ La-5 has been shown to contribute to firmer acid gels when added to traditional yogurt cultures [24; 25]. Adhesiveness varied depending on the fermentation conditions. The highest adhesiveness values were recorded for cow's milk fermented with the yogurt culture, while dairy-oat beverages fermented with the yogurt culture and _L. acidophilus_ La-5 showed the lowest adhesiveness, suggesting a more fluid consistency and weaker gel structure. _L. plantarum_ can enhance yogurt's rheological properties by increasing viscosity and cohesiveness [26]. Additionally, LAB strains, including _L. plantarum_, exhibit superior adhesion properties, which may influence the texture of fermented products [27; 28]. Syneresis analysis revealed that dairy and dairy-oat samples fermented with the yogurt culture had the lowest syneresis (-45-60%), indicating better structural stability. The addition of _L.