## 3 Results and Discussion
### FTIR Characterization of Bacterial Cellulose  
ATR-FTIR spectroscopy was carried out to compare the chemical structure of the BC variants and to verify the effect of de-proteinization conditions of AW as a culture medium on the BC structure. The FTIR spectra of the BC obtained in YPM classical medium were also presented for comparison. The FTIR spectra are shown in Figure 11.  
From the spectra, it was observed that all samples had bands characteristic of BC, with slight shifts relative to one another. There were no significant differences between the spectra of BC obtained in non-proteinized whey and deproteinized whey under different conditions. At a wavenumber of about 3340 cm\({}^{-1}\), a band characteristic of O-H stretching vibrations was observed [60]. The peaks at 2894 cm\({}^{-1}\) corresponded to C-H stretching in the CH\({}_{2}\) and CH\({}_{3}\) groups [61]. The peak presented around 1640 cm\({}^{-1}\) was commonly attributed to the H-O-H bending vibrations of absorbed water [61; 62]. Peaks around 1556 cm\({}^{-1}\) and 1567 cm\({}^{-1}\) were present in all BC samples, which may indicate that their presence did not depend on the medium. Peaks around 1560-1570 cm\({}^{-1}\) were also observed by [PERSON] et al. in studies where BC was obtained in media with different carbon sources. However, this peak was described as being unknown [63]. In this study, peaks near 1410 cm\({}^{-1}\)-1425 cm\({}^{-1}\) and 1315 cm\({}^{-1}\) were observed on the spectrum, which could correspond to CH\({}_{2}\) symmetrical stretching and CH\({}_{2}\) out-of-plane wagging, respectively, as well as confirming crystalline regions in the BC structure [61; 63]. The peaks at 1335 cm  
Figure 11: ATR-FTIR spectra of the BC obtained from the culture of _K. xylinus_ K2G30 in YPM, NDAW, and deproteinized AW media.  
Figure 10: Wet and dry BC obtained in culture of _K. xylinus_ K2G30 in NDAW and deproteinized AW media.  
were attributed to C-H deformation or O-H in-plane bending. In addition, the presence of peaks at 1335 cm\({}^{-1}\), 1315 cm\({}^{-1}\), and 1280 cm\({}^{-1}\) (C-H bending) could suggest that BC was composed, to some extent, of cellulose II. However, the peaks at 3340 cm\({}^{-1}\), 1425 cm\({}^{-1}\), 1160 cm\({}^{-1}\), and 899 cm\({}^{-1}\) indicated that BC was composed mainly of cellulose I [63; 64]. Characteristic BC peaks at 1205 cm\({}^{-1}\) and 1161 cm\({}^{-1}\), attributed to symmetrical and asymmetrical stretching vibrations of C-O-C bonds, respectively, were also observed. Other BC-specific peaks were detected at 1108 cm\({}^{-1}\), 1055 cm\({}^{-1}\), and 1031 cm\({}^{-1}\) corresponding to C-O-C 1,4-\(\beta\)-glycosidic linkages or skeletal vibrations, C-O-C pyranose ring skeletal vibrations, and C-O deformation, respectively [65]. Interestingly, [PERSON] et al. [66] observed peaks in the spectra of BC obtained in whey that were characteristic of milk fat (2921 cm\({}^{-1}\) and 2851 cm\({}^{-1}\)), esters and ethers (1743 cm\({}^{-1}\) and 1163 cm\({}^{-1}\), respectively), and amine and amide groups in proteins (about 3400 cm\({}^{-1}\), 1540 cm\({}^{-1}\), and 1577 cm\({}^{-1}\)), which were not found in this study. This may indicate the relatively high purity of BC obtained in AW, regardless of whether it was deproteinized or not.