## 3 Results
### FTIR-ATR Spectral Profiling
The bands occurring at 920 and 865 cm\({}^{-1}\) are assigned to skeletal C-C stretching vibrations of monosaccharide's carbon backbone, for glucose and fructose, respectively, while the bands peaking at 818 and 776 cm\({}^{-1}\) correspond to the deformation C-C-H vibrations of fructose [40]. Sucrose C-C stretchings also contribute to the signal observed at 920 cm\({}^{-1}\). Vibrations related to the protein structure are also observable in this spectral region and overlap with some of the above mentioned sugar-specific signals; the band at 665 cm  
Figure 2: Comparative spectral features of bee pollen (FTIR-ATR spectra of unifloral bee pollen containing the highest vs. the lowest content of particular organic compound) with accentuated spectral regions indicative for the content of: proteins (**a**), sugars (**b**), sucrose (**c**), and lipids (**d**). corresponds to O=C-N bending (amide IV), and the signal at 776 cm\({}^{-1}\) to out-of-plane N-H bending (amide V) [(39; 40)]. Comparative spectral features with regard to spectral regions indicative for the detection of higher amounts of particular organic compounds (proteins, sugars, lipids) are presented in Figure 2. As presented in Figure 2a showing a comparative overview of IR spectra of _A. hippocampus_ bee pollen containing the highest vs. _T. officinal_ bee pollen with the lowest protein content, it is obvious that spectral features indicative for the protein fraction are represented with a series of absorption bands occurring in the spectral region between 1480 and 950 cm\({}^{-1}\) (integral absorption intensities are higher in the spectrum of _A. hippocampus_ bee pollen). However, within this wide region, spectral range 1480-1185 cm\({}^{-1}\) can be identified as highly specific for proteins (due to series of amide III bands) while the spectral range from 1185 to 950 cm\({}^{-1}\) may also reflect signals due to strong sugar absorptions (primarily glucose, fructose and sucrose; Figure 2b,c) appearing along with protein-related absorptions. The overlapping effects of sugar and protein signals in 1185-950 cm\({}^{-1}\) spectral region does not allow clear distinguishing of predominant compounds when both are represented in high amounts (the same goes for the spectral range from 3600 to 3000 cm\({}^{-1}\)). Figure 2b represents this combination: the spectrum of _Quercus_ spp. bee pollen containing a high sugar content (52.58%) shows spectral differences that are not particularly pronounced compared to _A. hippocampus_ bee pollen, which contains only 26.2% of sugar, but also a significant amount of proteins (27.26%) whose bands overlap in these region. Still, mentioned spectral differences becomes more prominent (in terms of lower absorption intensities) as the protein content decreases, such as in the case of _M. sativa_ bee pollen that contains less of both sugars and proteins (41.61% and 23.56%, respectively) compared to _Quercus_ spp. bee pollen. Furthermore, Figure 2c shows _P. spinosa_ bee pollen with the highest amount of sucrose (18.68%) vs. _M. sativa_ bee pollen with underrepresented sucrose content (3%). The results presented in this figure have revealed that the intensities of bands occurring at 993 and 920 cm\({}^{-1}\), are notably higher in the spectrum of _P. spinosa_ bee pollen, which indicate that these bands are sucrose-specific (the proportion of other constituents is similar in these two bee pollen samples). Moreover, the vibration at 993 cm\({}^{-1}\) transforms into a shoulder form in case when sucrose in underrepresented. As shown in Figure 2d representing FTIR spectra of _T. officinal_ bee pollen containing the highest vs. _F. vulgaris_ bee pollen with the lowest lipid content, spectral features indicative for lipids are observable in the spectral region between 1760 and 1500 cm\({}^{-1}\) comprising four lipid-related absorptions at 1740, 1645, 1545 and 1515 cm\({}^{-1}\).