## 3 Results and Discussion
### Lactic Acid Purification and Characterization  
An analysis of the purification conditions was carried out, since the use of temperatures in the purification process under normal conditions and without pressure is inefficient when recovering lactic acid from a fermentation broth; therefore, the optimal temperature and time were determined in order to concentrate the lactic acid. Table 5 shows how the use of these temperatures influenced the purification performance of the lactic acid as well as the characteristics of the lactic acid obtained (color and density). Among the samples that were purified, the one with the highest yield (16.92%) belonged to ESI_P2 (_Enterococcus faecalis_ in suspension and with the lactic acid concentrated at 40 \({}^{\circ}\)C for 1 h in a rotary evaporator). This was followed by KI1_P1 (immobilized _Kluyveromyces lactis_ and with the lactic acid concentrated at 40 \({}^{\circ}\)C for 5 h in a rotary evaporator) with a yield of 8.44%. The third place corresponded to EI_P2 (immobilized _Enterococcus faecalis_ treated at 45 \({}^{\circ}\)C for 5 h to concentrate the lactic acid) with an 8.33% yield. Likewise, a difference in color was observed, obtaining whitish and yellowish colors, and this also occurred in lactic acid obtained by homofermentative strains and purified by a microfiltration process [20]. However, it has been mentioned that when using nanofil  
Figure 8: Lactic acid yield (g/L) of _Kluyveromyces lactis_ and its lactose consumption during the cheese whey fermentation. tration, a lighter color is obtained, and when using reverse osmosis, a transparent color is obtained. In addition to this, a higher concentration of lactic acid is obtained [1]. Likewise, using _Lactobacillus casei_ at 40.2 \({}^{\circ}\)C without any nutritional additives and after 3 days of fermentation, it produced a yellowish lactic acid with a density of 1.10 g/mL [5]. Therefore, it is confirmed how the fermentation conditions, strains used in the fermentation, and mode of use (suspended and encapsulated strains) generate variation in the yield of the lactic acid obtained as well as in its color and density. Likewise, these differences were also observed in the chemical characteristics of the FTIR spectra that were obtained for the purified lactic acid samples that are shown in Figures 9 and 10 and belong to those obtained using _Enterococcus faecalis_ and _Kluyveromyces lactis_, respectively. Figure 9 shows the results for the ESI_P1 and ESI_P2 samples using the deproteinized cheese whey with _Enterococcus faecalis_ in suspension at the purification conditions depicted in Table 5. It is observed that the thick band in both spectral regions between 3000 and 3500 cm\({}^{-1}\) corresponded to OH, while the sharp peak at 1637.63 cm\({}^{-1}\) indicated the presence of C=O, characteristic functional groups of lactic acid. Furthermore, by varying the purification conditions, the signal was accentuated, and a peak corresponding to the C-H group (1416.38 cm\({}^{-1}\)) appeared slightly. This variation in and value of the carboxyl group allowed us to presume that both corresponded to L-lactic acid, and in this research, there was also the presence of a peak corresponding to C=O at around 1651.07 cm\({}^{-1}\)[21], but this variation in the peaks, unlike with pure lactic acid, indicates that there were probably some impurities. Also, Figure 9 shows the spectra of the EI1_P1 and EI1_P2 samples, which corresponded to the lactic acid obtained from the deproteinized cheese whey with immobilized _Enterococcus faecalis_. A characteristic OH peak was also obtained at 3351.17 cm\({}^{-1}\) (EI1_P2) and at 3378.25 cm\({}^{-1}\) (EI1_P1), and that of the C=O group was also obtained at 1703.59 cm\({}^{-1}\) and 1640.81 cm\({}^{-1}\) (EI1_P1) and at 1638.39 cm\({}^{-1}\) (EI1_P2). The EI1_P1 sample had a peak at 1268.98 cm\({}^{-1}\) that corresponded to the C-O-C group, and this same group was present in EI1_P2 sample but at a lower intensity (1277.22 cm\({}^{-1}\)).