# Evaluation and Characterization of Alginate Extracted from Brown Seaweed Collected in the Red Sea
## 2 Materials and Methods
### \({}^{1}\)H-NMR Spectroscopy Analysis of Sodium Alginate  
The results of the \({}^{1}\)H-NMR structure of the extracted sodium alginate from the five seaweeds showed the existence of anomeric protons of galvanonic acid and manunuronic acid, with three key signals attributed to the anomeric hydrogen of galvanonic acid between 5.1-5.2 ppm, the anomeric hydrogens of manunuronic acid, the H-5 of alternating blocks overlapping at 4.7-4.9 ppm, and the H-5 of galvanonic acid residues at 4.5-4.5 ppm. The \({}^{1}\)H NMR spectra of the extracted sodium alginates are shown in Figure 5, which are similar to the other selected seaweed alginate spectra. A high intense peak in the region of 4.7 ppm is visible, demonstrating a high content in manunuronic acid.  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Physical** & _Padina_ & _Turbinaria_ & _Homophysa_ & _Dictyota ciliolate_ & _Sargassum_ \\
**Parameters** & _boergesenii_ & _triquetra_ & _cuneiforms_ & _Dictyota ciliolate_ & _aquifolium_ \\ \hline Colour & Pale-yellow & Pale-yellow & Pale-yellow & Pale-yellow & Pale-yellow \\ pH & 9.72 \(\pm\) 0.2 & 9.62 \(\pm\) 0.1 & 9.63 \(\pm\) 0.20 & 9.8 \(\pm\) 0.1 & 9.76 \(\pm\) 0.1 \\ Moisture (\%) & 13.1 \(\pm\) 0.01 a & 12 \(\pm\) 0.2 c & 6.4 \(\pm\) 0.1 e & 9.7 \(\pm\) 0.02 d & 12.5 \(\pm\) 0.1 b \\ Viscosity (cP) * & 57.6 \(\pm\) 0.2 e & 124.4 \(\pm\) 0.1 c & 134.4 \(\pm\) 0.4 a & 108.1 \(\pm\) 0.2 d & 128.4 \(\pm\) 0.3 b \\ \hline \end{tabular}  
* Values are expressed as average \(\pm\) standard deviation. a, b, c, d, e indicate a significant difference at the level of \(p\leq\) 0.05.
* cP stands for centipoise.  
\end{table}
Table 2: Physical properties of sodium alginate extracted from the tested macroalgae.  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Functional Groups** & _P. boergesenii_ & _T. triquetra_ & _H. cuneiforms_ & _D. ciliolata_ & _S. aquifolium_ \\ \hline Hydrogen bonded O–H stretching vibration & 3217 & 3283 & 3235 & 3243 & 3261 \\ C–H stretching vibration & 2928 & 2916 & 2919 & 2920 & 2926 \\ Asymmetric stretching vibration of carboxylate O–C–O & 1602 & 1601 & 1596 & 1598 & 1597 \\ Symmetric stretching vibration of carboxylate group & 1405 & 1402 & 1403 & 1402 & 1404 \\ Guluronic units & 1082 & 1081 & 1081 & 1083 & 1084 \\ Mannuronic units & 1023 & 1026 & 1025 & 1025 & 1025 \\ C–O stretching vibration of uronic acids & 947 & 947 & 945 & 947 & 947 \\ C–H of \(\alpha\)-L guluronic acid & 904 & 903 & 901 & 903 & 903 \\ \(\beta\)-manunuronic acid residues & 870 & 874 & 873 & 872 & 872 \\ \hline \end{tabular}
\end{table}
Table 3: FTIR frequency peak (cm\({}^{-1}\)) and functional groups of the extracted sodium alginate.  
Figure 4: FTIR spectrum of sodium alginate isolated from five brown macroalgae: _P. boergesenii_ **(A)**, _T. triquetra_ **(B)**, _H. cuneiformis_ **(C)**, _D. ciliulata_ **(D)**, and _S. aquifolium_ **(E)**.  
The M/G ratios of the extracted sodium alginates were greater than 1 (Table 4), demonstrating a high dominance of mannuronic acid over guluronic acid, which was already described in the first analysis of Figure 5. Moreover, the alginate structure in these five seaweeds is mainly based in the monoblocs of mannuronic acid units with very few units of guluronic acid. Thus, the parameter \(\eta\) demonstrates a high quantity of homopolymeric blocks, in this case, of MM.  
Figure 5: \({}^{1}\)H-NMR spectra of the extracted sodium alginate from _P. boergesenii_ (**A**), _T. triquetra_ (**B**), _H. cuneiformis_ (**C**), _D. ciliolata_ (**D**), and _S. aquifolium_ (**E**).