## 3 Results and Discussion
### Functional Group Characteristics of Freeze-Dried ACM  
Several authors have reported that Attenuated Total Reflectance-Fourier transform infra-red (ATR-FTIR) spectroscopy is a good tool to determine the functional groups of bio-polymers [26,30,31]. The ATR-FTIR spectra of freeze-dried ACM showing the wavelength peaks in the range 4000-400 cm\({}^{-1}\) with the focal functional group are presented in Figure 2a. Table 1 also shows the focal functional groups in freeze-dried ACM. ATR-FTIR spectroscopy was employed in analyzing the functional groups of unprocessed ACM (Table 1 and Figure 2a). Twelve vital absorption peaks were observed from the spectrum of ACM (Table 1). The peaks at 3301 and 3080 cm\({}^{-1}\) were designated to stretching vibrations of hydroxyl groups of hydrophilic amino and defined aromatic overtone that may be due to aromatic amino acids [64,65]. The peak at 2958 cm\({}^{-1}\) could be attributed to CH\({}_{2}\), asymmetric stretch for bio-polymers such as glycoprotein or mucus [66,67]. The peak at 2924 cm\({}^{-1}\) could be attributed to the C-H symmetric and anti-symmetric stretching vibrations in CH\({}_{2}\) ascribed to pyranose rings which point to aliphatic (-CH) chains in the slime [32]. The peaks at 1634 and 1539 cm\({}^{-1}\) could be as a result of amide stretch, from 8-sheets absorption bands (Amide I bands) and aromatic C=C bending or C=C stretch in the ring (Amide II) [64,65]. The peak at 1414 cm\({}^{-1}\) represents a C-O of carboxyl group accepting zero or one H-bond or O-H (alcohols) bend while the peak at 1136 cm\({}^{-1}\) could represent anti-symmetric C-O-C glycoside bond, C-O strong bond stretch [29,68]. The peak at 1040 cm\({}^{-1}\) is ascribed to a primary amine, stretching, secondary R-carbon of amino acids for glycoprotein or mucus while the peak at 867 cm\({}^{-1}\) represents C-H out of plane bending [66; 69; 70]. In addition, the peaks at 626 cm\({}^{-1}\) are attributed to C-H vibrating bends in RC=CH sites while peaks at 524 cm\({}^{-1}\) are linked to S-S disulfide stretch in bio-polymers with proteins and collagen [69; 71; 72]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Wave Number (CM\({}^{-1}\))** & **Band Assignments** & **References** \\ \hline
3301 & Broad peak stretching vibrations of hydroxyl groups of hydrophilic & [64] \\
3080 & Defined aromatic overtone, due to aromatic amino acids & [65] \\
2958 & Mucus/glycoprotein CH\({}_{2}\) out of plane vibration & [66; 67] \\
2924 & CH\({}_{2}\) symmetric and out of plane vibration & [32] \\
1634 & Amide stretch, \(\beta\)-sheets absorption bands; Amide I & [64] \\
1539 & Aromatic C=C bending or C=C stretch in a ring; Amide II & [65] \\
1414 & C–O of carbonyl CO group accepting zero or one H-bond & [29] \\
1136 & Anti-symmetric C–O–C glycoside bond; C—O strong bond stretch; & [68] \\
1040 & Mucus/glycoprotein primary amine stretch or secondary R-carbon & [70] \\ \hline of amino acids & 867 & C–H out of plane bending & [66; 69] \\
626 & C–H bending vibration of RC=CH & [69; 71] \\
524 & S–S disulfide stretch in collagens and proteins & [72] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Functional groups of raw African catfish mucus. Figure 2: ATR-FTIR spectra of **(a)** raw freeze-dried ACM; **(b)** ACM-stabilized emulsion. The presence of amide A (N-H) stretching vibration found at around 3301 cm\({}^{-1}\), amide I at 1634 cm\({}^{-1}\) and Amide II near 1539 cm\({}^{-1}\) in ACM suggests the presence of \(\alpha\) helix with \(\beta\)- turns. The authors have. reported that although, Amide I, II, and III bands could be used to affirm protein secondary structure, FTIR investigations of amide I give better results as it is most responsive to changes in conformation and establish the presence of peptide bonds [27]. The peak of amide I occurs as a result of stretching vibration of C-O bonds and N-H bending while C-H stretching vibration is responsible for the Amide II band [27; 70].