## 2 Materials and Methods
### Lactic Acid Purification and Characterization  
Lactic acid purification was carried out on the samples that had the highest LA yield, i.e., ES1, KS2, EI1, and KI1, but each of them went through two different lactic acid purification processes (P1: purification process number 1 and P2: purification process number 2), as shown in Table 2.  
After the fermentation process was finished, 15 mL was taken into Falcon tubes to be centrifugated at 4500 RPM for 20 min. Later, the supernatant was vacuum-filtered using a Whatman 42 filter paper and passed through a vacuum microfiltration process using a 47 mm membrane filter. The filtered sample was taken to a rotary evaporator at 95 RPM  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Code** & **Strain** & **Strain** & \multicolumn{2}{c}{**Culture Medium**} \\  & & **Disposition** & **DCW 1** & **CW 2** \\ \hline ES1 & _E. faecalis_ & Suspended & X & \\ ES2 & _E. faecalis_ & Suspended & & X \\ KS1 & _K. lactis_ & Suspended & X & \\ KS2 & _K. lactis_ & Suspended & & X \\ EI1 & _E. faecalis_ & Immobilized & X & \\ EI2 & _E. faecalis_ & Immobilized & & X \\ KI1 & _K. lactis_ & Immobilized & X & \\ KI2 & _K. lactis_ & Immobilized & & X \\ \hline \hline \end{tabular} Note: 1 DCW: deproteinized cheese whey and 2 CW: cheese whey.  
\end{table}
Table 1: Coding of the proposed fermentation systems to obtain lactic acid.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Code** & **Strain** & \multicolumn{2}{c}{**Strain**} & \multicolumn{2}{c}{**Culture Medium**} \\  & & **Disposition** & **Medium** & **Temperature [\({}^{\circ}\)C]** & **Time [h]** \\ \hline ES1\_P1\({}^{1}\) & _E. faecalis_ & Suspended & DCW 3 & 60 & 45 min \\ ES1\_P2\({}^{2}\) & _E. faecalis_ & Suspended & DCW & 40 & 1 h \\ KS2\_P1 & _K. lactis_ & Suspended & CW 4 & 40 & 5 h \\ KS2\_P2 & _K. lactis_ & Suspended & CW & 45 & 5 h \\ EI1\_P1 & _E. faecalis_ & Immobilized & DCW & 40 & 5 h \\ EI1\_P2 & _E. faecalis_ & Immobilized & DCW & 45 & 5 h \\ KI1\_P1 & _K. lactis_ & Immobilized & DCW & 40 & 5 h \\ KI1\_P2 & _K. lactis_ & Immobilized & DCW & 45 & 5 h \\ \hline \hline \end{tabular} Note: 1 PD: purification process number 1; 2 P2: purification process number 2; 3 DCW: deproteinized cheese whey; and 4 CW: cheese whey.  
\end{table}
Table 2: Coding of the proposed fermentation systems and purification conditions for obtaining lactic acid.  
with the temperature and time shown in Table 2 with the aim of concentrating the lactic acid. Then, to extract the lactic acid, a known volume of sample and solvent (diethyl ether) in a 1:1 ratio were added into a 500 mL separating funnel. Later, it was shaken vigorously and left to rest until the two phases differentiated. These two phases were separated; the clearest and most transparent one was taken to a rotary evaporator at atmospheric pressure and at 40 \({}^{\circ}\)C to evaporate the diethyl ether and thus concentrate and purify the lactic acid. Table 2 depicts the coding of the samples according to the fermentation and purification conditions to obtain lactic acid.  
These samples were analyzed in the Chemistry Laboratory of the National University of San Agustin (Arequipa, Peru) by infrared spectroscopy (FTIR) analysis according to the ASTM E1252-98 [16] \"Standard Practice for General Techniques for Obtaining Infrared Spectra for Qualitative Analysis\", with the wave number range from 650 cm\({}^{-1}\) to 4000 cm\({}^{-1}\).