## 3 Results and Discussion
### Experimental Analysis  
Figure 4 shows the results obtained in terms of bacterial growth and lactic acid fermentation without and under pH control. In particular, the curves are represented on a semilogarithmic scale for a more appropriate interpretation of the results.  
The rice flour fermentation of LpCBAL74 was characterized by a starting bacterial load at \"zero\" time of about 2.64\(\cdot\)10\({}^{6}\)\(\pm\) 1.50\(\cdot\)10\({}^{6}\) CFU/mL in non-controlled pH conditions, and of about 2.51\(\cdot\)10\({}^{6}\)\(\pm\) 6.96\(\cdot\)10\({}^{5}\) CFU/mL with pH control. From Figure 4a,b it can be observed that during the first 4 h of fermentation the bacterial load is almost constant, regardless of the pH conditions. In fact, during this first part of the fermentation process, the pH remains almost constant, with a very small fluctuation, even in the control absence. The same can be seen for the final part of the fermentation process, after 18 h, for which the bacterial growth in both scenarios has reached the stationary condition at an average microbial concentration of 2.66\(\cdot\)10\({}^{8}\)\(\pm\) 5.23\(\cdot\)10\({}^{7}\) CFU/mL and 2.49\(\cdot\)10\({}^{8}\)\(\pm\) 1.72\(\cdot\)10\({}^{7}\) CFU/mL for the controlled and uncontrolled process, respectively, up to the final 24 h concentration of 2.26\(\cdot\)10\({}^{8}\)\(\pm\) 9.35\(\cdot\)10\({}^{7}\) CFU/mL and 3.43\(\cdot\)10\({}^{8}\)\(\pm\) 3.26\(\cdot\)10\({}^{7}\) CFU/mL, respectively. From Figure 4a,b the different phases of microbial growth for both conditions (under and without pH control) can be clearly identified: the lag, the exponential and the stationary phases lasted, respectively, from 0 h to 4 h, from 4 h to 14 h and from 14 h to 24 h without the pH control; while, in the other scenario, these phases lasted, respectively, from 0 h to 6/8 h, from 6/8 h to 18 h and from 18 h to 24 h. It is worth noting that due to the variability of the results, highlighted by the error bars, the exponential phase cannot be properly identified between 6 and 8 h. For both cases, however, it is not possible to define the beginning of the death phase, which is associated with a marked reduction in the number of bacterial cells. Therefore, the exponential growth is more pronounced under pH-controlled conditions. This result can be attributed to the fact that cell proliferation, in general, is promoted at pH values close to neutral one.  
To further monitor the fermentation process, also the production of lactic acid was evaluated (Figure 4c,d). Lactic acid was produced during fermentation in both tested conditions between 8 h and 14 h and up to 24 h at the end of the fermentation process. Specifically, a more accentuated production is highlighted in the case of pH-controlled condition with a lactic acid concentration of 1.277 \(\pm\) 0.160 mg/L against 0.626 \(\pm\) 0.038 mg/L without the control, up to a maximum concentration of 5.400 \(\pm\) 163 mg/L and 1.987 \(\pm\) 90 mg/L after 24 h of fermentation. In fact, it is recognized that, as the pH decreases, there is a reduction in lactic acid, the production of which, for strains of the lactobacilli type, is optimized for  
Figure 4: Bacterial growth curves on a semi-logarithmic scale (**a**) without pH control and (**b**) under pH control; lactic acid production during the rice flour fermentation (**c**) without pH control and (**d**) under pH control.  
pH values between 5 and 6 and for the most part at pH equal to 5.8 [25], value set to the controller in this study.  
It is therefore evident how the pH control, even if it delays the exponential phase beginning, and consequently the achievement of the maximum bacterial growth and the establishment of the stationary phase, guarantees a bacterial growth which is comparable to the one occurring without pH control. Moreover, it allows obtaining a lactic acid concentration around 2.72 times higher after 24 h of fermentation and already almost double after only 14 h.