## 3 Results and Discussion
### Microbiological and Physicochemical Characterization of Fermented Beverages
Carbohydrate metabolism is the primary driver of product acidification, with lactic acid production being the main contributor to the observed pH decline during fermentation, imparting the distinctive sour flavor commonly associated with yogurt and other fermented beverages [10]. The fermentative capability and pH-lowering ability of all bacterial blends were confirmed during the present study (Table 2), and the results observed in the bacterial counts perfectly correlated with the measured pH values. A greater reduction of pH was observed in the samples fermented by LLV, and the fermented rice beverage had a lower pH than the fermented dairy milk. The results of the statistical analysis showed that the bacteria blend had a greater influence on the pH decline than the matrix, with the LLV combination showing superior performance. Although many countries lack specific regulations that indicate the characteristics that a yogurt or a fermented dairy product must have, Spanish legislation establishes a pH < 4.6 for this food category [27]. The dairy milk sample fermented using LLV met this criterion, whereas the sample fermented using CH culture did not, potentially due to the fermentation time established in the present research. The fermentation time was a limiting factor in this sense, but it elucidated the different fermentative capacities of both microbial combinations. On the other hand, the selected strains showed considerable potential for developing plant-based fermented derivatives by effectively reducing pH to meet safety and quality benchmarks in a short time. This fermentation process emerges as a promising approach for formulating clean-label plant-based beverages, eliminating the need for artificial acidity regulators typically employed to adjust the pH of dairy products [3]. A significant increase in TA was observed in all samples due to fermentation, although significant differences were found among samples (Table 2). Statistical analysis suggested that the matrix had a greater influence than the bacterial blend on TA. In line with pH and CFU/mL results, LLV fermented samples showed higher TA, confirming their better performance over the CH bacterial blend. All samples showed a negative correlation between pH and TA, which is consistent with the behavior of fermented foodstuffs [28]. A higher concentration of acids after fermentation, mainly organic acids such as lactic, acetic, formic, etc., leads to a higher concentration of hydrogen ions, which reduces the pH. However, other intrinsic compounds of the food matrix could play a relevant role. The presence of higher levels of proteins, lipids, and citrate in dairy milk compared to rice  
Figure 1: Results of microbiological analyses in the control and fermented samples. Different letters within the rows indicate different post hoc groupings by [PERSON]’s HSD (\(p\) < 0.05). matrix might contribute to the lower TA observed in fermented rice beverages, regardless of the bacterial blend employed for fermentation [29; 30]. Bacterial degradation of proteins into amino acids, degradation of lipids into free fatty acids (e.g., butyric acid), and the metabolism of citrate towards the production of pyruvate and lactic acid contribute to a further increase in TA in fermented dairy beverages [31]. The _Codex Alimentarius_ indicates a minimum TA of 0.6 g lactic acid/100 mL for yogurt-like products [22]. Therefore, the fermented dairy milk samples from the present study met this criterion, with values of approximately 0.6-0.7 g lactic acid/100 mL, while fermented rice beverages did not, having a TA of 0.03-0.09 g lactic acid/100 mL. These low values were in line with the results of previous research, which characterized new fermented plant-based beverages [32; 33]. TSS results also underscored the significance of the original matrix in the resulting fermented beverage. Reduction of TSS was only significantly different in the fermented dairy beverages (Table 2).