## 3 Results and Discussion
### Chemical Properties of Beetroot Samples
#### 3.3.3 Thermal Properties
The weight loss was minimal in phase I, which corresponded to the evaporation of water (range 30-90 \({}^{\circ}\)C). In phase II, the weight loss was significantly higher, and the temperature range differed from that of the earlier samples (90-380 \({}^{\circ}\)C). The molecular composition and particle structure of freeze-dried fermented yellow beetroot were analyzed using Fourier transform infrared spectroscopy (FT-IR), measuring the vibration energy between atoms in the samples [72; 73]. The FTIR spectra in Figure 4 depict samples at various salt percentages throughout the testing period. Notably, 0% (Figure 4a) and 2% (Figure 4b) salt additions are shown continuously, while the figures for 0-6% salt on the 4 th (Figure 4c) and 8 th (Figure 4d) days represent the start and end of fermentation, respectively, based on the microbiological outcomes. Similar results were observed for the other days and percentages, so we have decided to show those percentages, while 0 is the most different from other samples and 2% is the most similar to the rest of them, while 4 th and 8 th day were selected as the beginning and end of fermentation (based on the microbiological results). The graphs show the correlations between the absorbance intensity and energy expressed in wavenumbers (cm\({}^{-1}\)). Similar functional groups in the samples suggest uniform fermentation products due to the use of the same LAB variety. However, the variations in the peak heights indicate alterations in the composition and structure due to the increased fermentation time and salt addition. The distinct peaks observed in the 3800-3000 cm\({}^{-1}\) region (OH group) suggest differences due to the NaCl presence. The samples without salt had higher, less flattened peaks compared to the others, especially noticeable on the 4 th day. The minimal salt additions (1-2%) during fermentation exhibited similarities to the fresh beetroot samples in the OH group area, as observed on the 8 th day. Similar results were presented by [74] for an aqueous solution with NaCl. [PERSON] et al. [74] observed that each anion interacts with adjacent water molecules, inducing alterations in the O-H vibration bands characterized by specific peak frequencies and bandwidths in the region of 3500-2500 cm\({}^{-1}\). What is more, the stretching vibration frequencies of water molecules in an aqueous NaCl solution exhibit variations with increasing salinity at a constant temperature. The elevation in the O-H stretch frequency of water molecules as the salinity increases is attributed to the formation of larger clusters. The literature and NIST databases highlighted specific areas on the graphs. The area between 3600 and 3620 cm\({}^{-1}\) displays a strong stretching band and vibrations that correspond to the hydroxyl group present in water and phenolic compounds. The region in the range of 2925 to 2855 cm\({}^{-1}\) corresponds to the asymmetric stretching and deformations of alkyl groups like -CH, -CH\({}_{2}\), and -CH\({}_{3}\). The region between 2450 and 2300 cm\({}^{-1}\) indicates the strong stretching between the C=O groups in the carbon dioxide molecule. The region within the 1718 cm\({}^{-1}\) length range corresponds to the vibrational frequencies of the carbonyl group (C=O), while the range from 1650 to 1415 corresponds to the vibrations of nitrogen-containing groups. These vibrations may be linked to the colored compounds present in beetroot, betaxanthins, and betacyanins. The outlined bands within the 1150-900 cm\({}^{-1}\) range may involve stretching vibrations linked to the (C-O) and (C-C) groups present in saccharides, like glucose, fructose, and sucrose, among others [36; 38; 73; 75; 76]. Similar observations in beetroot samples were noted by other researchers in studies involving fermented red beetroot, including [PERSON] et al. [76] and [PERSON] et al. [77].