## 3 Results
### Analyses of the Organic Acids
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline  & & & & & \multicolumn{6}{c}{**Incubation Time**} \\ \cline{4-13}  & & & & \multicolumn{6}{c}{**12 h**} & & \multicolumn{6}{c}{**24 h**} \\ \cline{4-13}  & & & & \multicolumn{6}{c}{**Concentration (mM)**} & & \multicolumn{6}{c}{**Concentration (mM)**} \\ \cline{4-13}  & & & & **Formic** & **Lactic** & **Acetic** & **Sum** & **pH** & **Formic** & **Lactic** & **Acetic** & **Sum** \\ \hline \multirow{4}{*}{\begin{tabular}{c} **C** \\ **C** \\ **C** \\ \end{tabular} } & \multirow{4}{*}{Mc} & 6.29 & Total 1 & (\(\pm\)0.01) & (\(\pm\)0.21) & 1.1 & 4.0 & 5.3 & & 0.3 & 8.2 & 14.1 & 22.6 \\  & & & (\(\pm\)0.01) & (\(\pm\)0.21) & (\(\pm\)0.46) & (\(\pm\)0.34) & 5.48 & (\(\pm\)0.07) & (\(\pm\)1.17) & (\(\pm\)1.06) & (\(\pm\)0.47) \\ \cline{2-13}  & & & & 0.001 & 0.004 & 0.112 & 0.1 & (\(\pm\)0.03) & 0.01 & 1.59 & 2.21 & 3.8 \\  & & & \(\%\)\({}^{\circ}\)\({}^{\circ}\) & 0.50 & 0.36 & 2.80 & 2.21 & & 1.67 & 19.34 & 15.67 & 16.82 \\ \cline{2-13}  & & & & 0.2 & 3.7 & 5.2 & 9.1 & & 0.9 & 18.3 & 22.4 & 41.6 \\  & & & (\(\pm\)0.02) & (\(\pm\)0.24) & (\(\pm\)0.32) & (\(\pm\)0.53) & 5.06 & (\(\pm\)0.08) & (\(\pm\)3.09) & (\(\pm\)1.56) & (\(\pm\)4.57) \\  & & & & 0.001 & 0.017 & 0.18 & 0.2 & (\(\pm\)0.03) & 0.04 & 1.08 & 7.36 & 8.5 \\  & & & \(\%\)\({}^{\circ}\) & 0.50 & 0.46 & 3.46 & 2.18 & & 4.67 & 5.89 & 32.39 & 17.9 \\ \hline \multirow{4}{*}{\
\begin{tabular}{c} **C** \\ **C** \\ \end{tabular} } & \multirow{4}{*}{Mc} & 6.78 & Total & 0.6 & 2.5 & 5.3 & 8.4 & & 0.5 & 6.70 & 17.6 & 24.8 \\  & & & (\(\pm\)0.05) & (\(\pm\)0.25) & (\(\pm\)0.26) & (\(\pm\)0.47) & 5.54 & (\(\pm\)0.18) & (\(\pm\)1.32) & (\(\pm\)1.02) & (\(\pm\)2.48) \\  & & & 0.001 & 0.008 & 0.05 & 0.06 & (\(\pm\)0.04) & 0.01 & 0.14 & 2.45 & 2.60 \\  & & & \(\%\)\({}^{\circ}\) & 0.17 & 0.32 & 0.94 & 0.70 & & 1.6 & 2.04 & 19.32 & 10.46 \\ \cline{2-13}  & & & & 0.7 & 4.2 & 9.5 & 14.4 & & 0.9 & 16.4 & 27.5 & 44.8 \\  & & & & (\(\pm\)0.03) & (\(\pm\)0.24) & (\(\pm\)1.15) & (\(\pm\)1.36) & 5.20 & (\(\pm\)0.1) & (\(\pm\)2.4) & (\(\pm\)0.7) & (\(\pm\)2.6) \\  & & & & 0.001 & 0.02 & 0.16 & 0.25 & (\(\pm\)0.02) & 0.03 & 0.71 & 7.20 & 7.9 \\  & & & & 0.14 & 2.14 & 1.71 & 1.76 & & 3.44 & 4.33 & 26.18 & 17.73 \\ \hline \multirow{4}{*}{
\begin{tabular}{c} **C** \\ **C** \\ \end{tabular} } & \multirow{4}{*}{Mc} & 6.51 & Total & 0.7 & 4.2 & 9.5 & 14.4 & & 0.9 & 16.4 & 27.5 & 44.8 \\  & & & (\(\pm\)0.03) & (\(\pm\)0.24) & (\(\pm\)1.15) & (\(\pm\)1.36) & 5.20 & (\(\pm\)0.1) & (\(\pm\)2.4) & (\(\pm\)0.7) & (\(\pm\)2.6) \\ \cline{1-1}  & & & & 0.01 & 0.02 & 0.16 & 0.25 & (\(\pm\)0.02) & 0.03 & 0.71 & 7.20 & 7.9 \\ \cline{1-1}  & & & & 0.14 & 2.14 & 1.71 & 1.76 & & 3.44 & 4.33 & 26.18 & 17.73 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Concentration of weak organic acids—formic, lactic, and acetic (total and non-ionic state)—produced after 12 and 24 h of incubation at 22 \({}^{\circ}\)C in two reconstituted infant formulae with different acid-buffering capacity (low/high) in monoculture with _C. sakazakii_ (Mc) and in combination with the probiotic BB-12 (Cc). ture after 24 h of incubation at pH 4.07 (\(\pm\)0.02), the concentration of weak organic acids in their non-ionic form was 40.4 mM, while, in the co-culture, the pH was 3.65 (\(\pm\)0.02) and the corresponding concentration in the non-ionic form was 57.7 mM (Table 3). The pH and the concentration of the formic, lactic, and acetic acids produced by the microorganisms after 12 and 24 h of incubation at 37 \({}^{\circ}\)C in the two RIFs are shown in Table 3. Comparing the results of Tables 2 and 3, it is clear that significantly higher concentrations (mM) of the three weak organic acids were produced during the incubation at 37 \({}^{\circ}\)C compared to those produced at 22 \({}^{\circ}\)C, and, consequently, the pH values were remarkably lower in samples incubated at 37 \({}^{\circ}\)C than in those incubated at 22 \({}^{\circ}\)C.  
The trends of the results observed in the 22 \({}^{\circ}\)C incubation were confirmed in the 37 \({}^{\circ}\)C incubation.