## 3 Results and Discussion  
### Microbial Populations and Fermentation Monitoring  
A control and a fortified (5% Cava lees) sourdough were prepared to assess the effect of Cava lees on the fermenting microbiota of sourdough. Figure 1 shows the growth kinetics of lactic acid bacteria (LAB) and pH during the 8 days of sourdough propagation. Both types of sourdough (control without lees--SDC; with 5% lees--SD+L) were spontaneously fermented. Although the promoting effect of 5% (\(w/w\)) Cava lees on LAB growth has been reported in vitro [6] and up to a 2% (\(w/w\)) Cava lees in wheat and rye sourdoughs [15], it can be observed that the addition of Cava lees to sourdough formulation did not stimulate LAB growth in this particular food matrix.  
The initial pH of sourdoughs with 5% Cava lees (\(w/w\)) was significantly lower (\(p<0.05\)). In particular, SDC started the sourdough fermentation with a pH of 5.80 \(\pm\) 0.01, while SD+L begun with a pH of 5.06 \(\pm\) 0.07 due to the inherent acidity of Cava lees [8]. During the fermentation and propagation process of sourdough, pH decreased during the first steps of fermentation and then stabilized, obtaining values of 3.60 \(\pm\) 0.04 (SDC) and  
Figure 1: Growth of LAB (**a**) and pH (**b**) in sourdough without lees (SDC) and sourdough with 5% lees (SD+L).  
3.70 \(\pm\) 0.02 (SD+L), similar to those reported in other studies [19; 20; 21] and in accordance with the pH range of traditional sourdoughs (pH 3.5-4.5) [13]. However, there were no statistically significant differences between sourdoughs. Once sourdoughs were mature (8 days), breads were prepared (Table 2) and baked.  
Figure 2 presents the cell density of both LAB and yeast at the end of bread fermentation. When Cava lees were used in the formulation of bread (both fermented with and without sourdough) there was a higher cell count for both yeasts and bacteria. In fact, bread fermented without sourdough presented a difference of 0.7 log10 CFU/mL between the ones with Cava lees (B+L) and the controls (BC). Also, there was a higher cell density in SB+L (5.1 \(\pm\) 0.2 log10 CFU/mL) in comparison to SBC (4.1 \(\pm\) 0.1 log10 CFU/mL). Regarding yeasts, the addition of lees to formulation had the same tendency.  
Sourdough bread usually presents a pH ranging between 5.0 and 5.5 [22], which was in accordance with the results obtained in this study (Table 3). The addition of Cava lees to both sourdough bread (SB+L) and leavened bread (B+L) resulted in lower pH at the beginning of dough fermentation, and, consequently, also at the end. As previously stated, the difference in pH values between samples with and without lees was probably due to the inherent acidity of Cava lees [8]. In fact, B+L obtained the lowest pH values of all formulated doughs. Actually, the addition of Cava lees to bread formulation (B+L) resulted in the greatest drop of pH during fermentation, which could be related to the higher plate counts of both LAB and yeast (Figure 2).  
\begin{table}
\begin{tabular}{c c c c} \hline
**pH** & **SBC** & **SB+L** & **BC** & **B+L** \\ \hline t = 0 h & 5.48 \(\pm\) 0.03 a  & 5.00 \(\pm\) 0.01 b  & 5.76 \(\pm\) 0.03 c  & 4.97 \(\pm\) 0.03 b  \\ t = 2 h & 5.14 \(\pm\) 0.02 a  & 4.75 \(\pm\) 0.04 b  & 5.45 \(\pm\) 0.02 c  & 4.37 \(\pm\) 0.03 d  \\ \hline \end{tabular}
\end{table}
Table 3: pH values at the beginning (t = 0 h) and end (t = 2 h) of bread fermentation.  
Figure 2: Microbial cell density at the end of bread fermentation. Different letters denote statistically significant differences (\(p<0.05\)) between different formulations of bread. SBC: control sourdough bread; SB+L: sourdough with 5% Cava lees; BC: control bread; B+L: bread with 5% Cava lees.