3.2.2. ATR–FTIR Analysis for EPSRT7

In addition, ATR–FTIR spectra (Figure 3b) obtained from EPSRT7 produced with *B. amyloliquefaciens* RT7 showed peaks between 4000 and 400 cm−1, a characteristic of carbohydrates. A band at 3283 cm−<sup>1</sup> was attributed to the hydroxyl stretching vibration of the polysaccharide [68], whereas the band at 2902 cm−<sup>1</sup> was ascribed to C–H stretching vibration [69]. The peaks at 1664 and 1442 cm−<sup>1</sup> were attributed to the stretching vibration of C=O, which is characteristic of a carboxyl group [70,71]. The peak at 1530 cm−<sup>1</sup> was ascribed to C–O vibration [72]. The region at 950–1250 cm−<sup>1</sup> corresponded to CO and C–O– C stretching vibrations in carbohydrates. The absorption at 1224 cm−<sup>1</sup> could have been the pyranose ring of monosaccharides in EPSRT7. The strong peak at 1048 cm−<sup>1</sup> was attributed to the C–O–C glycosidic bond vibration, which indicated the pyranose configuration [73]. The band at 851 cm−<sup>1</sup> suggested that the EPSRT7 contained the α and ß configurations of the glucose unit [74].

The spectrum confirmed typical characteristics of a polysaccharide. The vibrational peaks resembled the peaks observed for the EPSs of other strains. In the case of EPS from *B. amyloliquefaciens* RK3, the polymer contained mannose and galactose [75]. These differences revealed that the exopolysaccharides of the different strains of *B. amyloliquefaciens* had a very varied composition of monosaccharides. This heterogeneity may have been due to both nutritional and environmental factors.
