## 3 Results and Discussion
### FTIR Spectra  
The FTIR spectra shown in Figure 3 were measured to observe the changes in chemical structure of the freeze-dried kiwiberry foam mats. The broad band found in the region of wave number 3600-3000 cm\({}^{-1}\) is characteristic of the stretching vibrations of the -OH hydroxyl group of water molecules, phenolic compounds, carbohydrates and organic acids [35; 55] as well as the N-H stretching bond of free amino acids [56]. In the analyzed region, a medium peak with a wave number around 3260 cm\({}^{-1}\) is associated with the -OH stretching vibrations of proteins [57] added during the foaming of egg ovalbumin. The bands in the region of 2950-2855 cm\({}^{-1}\) correspond to the asymmetric and symmetric stretching vibrations of C-H bonds (alkyl and aromatic) in -CH\({}_{2}\) and -CH\({}_{3}\) aliphatic groups [58; 59], assigned to cellulose [60], carbohydrates [35] as well as carboxylic acids [14; 35]. The next band in the region of the wave number around 1718 cm\({}^{-1}\) is associated with the stretching vibrations of the C=O carbonyl group, assigned to pectin with esters [60]. The amide I peak observed in the region of the wave number around 1645 cm\({}^{-1}\) results from the C=O bond stretching vibrations, while the amide II detected in the region of the wave number around 1550 cm\({}^{-1}\) results from the C-N stretching and N-H bending bond vibrations, assigned to proteins [58] added during the foaming of egg ovalbumin. The band in the region of the wave number around 1650 cm\({}^{-1}\) predominantly belongs to the C=C bond vibrations of phenolic and aromatic ingredients [61] and the -OH hydroxyl group's deformation vibrations in water molecules [56]. The variation in the fingerprint region between 1470 and 650 cm\({}^{-1}\) is related to the stretching vibrations of the C-O, C-C and C-H bonds, and the bending vibrations of the C-H bond present in the chemical structure of carbohydrates. In some cases, these bands may also originate from organic acids and carotenes [35; 56].  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Drying Temperature (\({}^{\circ}\)C)** & **Water Solubility Index (\%)** & **Water Absorption Index (-)** \\ \hline
10 & 62.68 \(\pm\) 1.05 a \({}^{1}\) & 1.53 \(\pm\) 0.03 a \\
25 & 64.31 \(\pm\) 0.67 ab & 1.55 \(\pm\) 0.06 a \\
40 & 67.55 \(\pm\) 3.38 b & 1.73 \(\pm\) 0.10 b \\ \hline \hline \end{tabular} \({}^{\dagger}\) Different letters within columns indicate the statistical difference (Tukey’s HSD, \(p\) < 0.05).  
\end{table}
Table 3: Water solubility index (WSI) and water absorption index (WAI) of freeze-dried foam-mat kiwiberry pulp.  
The vibrations in the region of the wave number around 1420 cm\({}^{-1}\) are due to the O-CH and C-C-H group deformation vibrations in carbohydrate structures [35]. In the region 1400-1170 cm\({}^{-1}\), weak bands of C-O stretching vibrations of different aromatic esters [14] and polyphenols and antioxidative components [35] from kiwiberry fruits are visible. Moreover, a strong peak of C-O and C-C bond stretching vibrations in the range from 900 to 1150 cm\({}^{-1}\) is observed, which contribute to different carbohydrate groups, such as glucose, fructose and sucrose [62]. In turn, the vibrations observed at around 1240 cm\({}^{-1}\) may be attributed to C-N stretching in proteins [60]. The region below 900 cm\({}^{-1}\) indicates the conformational changes in material and is characteristic of the numeric region vibrations in carbohydrates or C-H and C-C bonds' deformation [14; 56]. The highest discrepancies are visible for the foamed kiwiberry pulp dried at 40 \({}^{\circ}\)C probably due to the heat treatment and water content in the tested samples.