## 3 Results and Discussion
### Lactic Acid Purification and Characterization
Neither of the peaks appeared in the lactic acid obtained with the strains in suspension. Between these two samples, the EI1_P1 sample was selected, which had a peak at 1703.59 cm\({}^{-1}\), since this peak is characteristic of the C=O group of lactic acid, so it probably had a higher purity of 85% lactic acid. This was due to the characteristic peaks at 1723 cm\({}^{-1}\) (C=O) and 1120 cm\({}^{-1}\) of the C-O group [22]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Code** & **Strain** &
\begin{tabular}{c} **Culture** \\ **Medium** \\ \end{tabular} & **LA Purification Conditions** & & \multicolumn{2}{c}{**Characteristics**} \\  & & & **T** [\({}^{\circ}\)**C] & **t [h]** & **Yield [\%]** & **Density** [g/mL]** & **Colour** \\ \hline ESI\_P1 & _E. faecalis_ & DCW 1 & 60 & 45 min & 6.15 & 0.72 & Yellowish \\ ESI\_P2 & _E. faecalis_ & DCW & 40 & 1 h & 16.92 & 0.77 & Yellowish \\ KS\_P1 & _K. lactis_ & CW 2 & 40 & 5 h & 3.89 & 0.97 & Whitish \\ KS\_P2 & _K. lactis_ & CW & 45 & 5 h & 2.5 & 1.21 & Whitish \\ EI1\_P1 & _E. faecalis_ & DCW & 40 & 5 h & 5.13 & 0.81 & Whitish \\ EI1\_P2 & _E. faecalis_ & DCW & 45 & 5 h & 8.33 & 0.69 & Yellowish \\ KI1\_P1 & _K. lactis_ & DCW & 40 & 5 h & 8.44 & 0.71 & Yellowish \\ KI1\_P2 & _K. lactis_ & DCW & 45 & 5 h & 3.26 & 0.98 & Whitish \\ \hline \hline \end{tabular} Note: 1 DCW: deproteinized cheese whey and 2 CW: cheese whey.  
\end{table} 
Table 5: Lactic acid characteristics obtained from _Enterococcus faecalis_ and _Kluyveromyces lactis_. Figure 10 shows the results of the lactic acid using _Kluyceromyces lactis_, and, as with the previous strain, there was a difference when fermenting with the suspended and immobilized strains [23], with more peaks appearing when using the immobilized strains. In all cases, the presence of the characteristic peak of the OH group was observed in the range from 3000 to 3500 cm\({}^{-1}\) and at 1702.10 cm\({}^{-1}\) and 1703.26 cm\({}^{-1}\), which corresponded to C=O for KI1_P2 and KI1_P1, respectively. However, for both cases, a peak was observed at around 1638 cm\({}^{-1}\) that corresponded to C=O, which indicates that there were impurities in the lactic acid. In terms of the C=O peaks, these last peaks probably corresponded to the DL-lactic acid monomer, since the peaks are like those indicated by [PERSON] et al. [24]. Among both samples, the KI1_P2 sample could be considered the one with the highest purity, since it tended to have a sharper peak at 1702.10 cm\({}^{-1}\) and had a higher yield. Regarding the KS2_P1 and KS2_P1 samples, the peaks that belonged to OH were 3349.68 (KS2_P1) and 3339.66 (KS2_P2). There was a difference between them in the range from 1700 to 650 cm\({}^{-1}\), where there were peaks for the KS2_P1 sample that belonged to C=O at 1638.94 cm\({}^{-1}\), C-O at 1053.58, and 982.70 cm\({}^{-1}\), while for the KS2_P2 sample, there were only two peaks at 1638.03 cm\({}^{-1}\) (C=O group) and at 1039.81 cm\({}^{-1}\) (C-O group). It is important to mention that in the present work, what was indicated by [PERSON] [20] was also observed, who stated that the purification step of lactic acid in proteinized cheese whey samples is more difficult due to the lack of deproteinization and prior filtration, which was also observed in the purification stage. Additionally, not using encapsulated strains makes the filtration stage slower than when using immobilized strains. Therefore, the use of deproteinized or non-deproteinized cheese whey, as well as using suspended or immobilized strains, favors the case in which the purification of lactic acid is delayed and lactic acid is generated with different physical and chemical characteristics. Figure 9: FTIR spectra of lactic acid obtained by _Enterococcus faecalis_ in suspension (ES) and immobilized (EI).