## 3 Results
### Biochemical Profiling
#### 3.1.5. Alginate Content  
The sodium alginate yield of the samples is presented in Table 6 and shows significant differences among the samples. The highest value was found in the residual pulp extracted at 60 \({}^{\circ}\)C (51.04 \(\pm\) 0.75% dw) and _S. polyschides_ extracted at 80 \({}^{\circ}\)C, while the lowest value was found in _L. ochroleuca_ extracted at 25 \({}^{\circ}\)C (7.33 \(\pm\) 0.29% dw). Microscopic examination indicated that the cell wall architecture of _M. pyrifera_ (Figure 2A) remained relatively intact and well-organized, in contrast to the residual pulp biomass (Figure 2B), which exhibited significant structural disruption. Figure 3 shows the FTIR spectra obtained from the analysis of alignates extracted from different samples. The presence of water in alginate samples is related to their hygroscopicity, which means that they tend to absorb moisture from their surroundings. The broad bands at 1600-1610 cm\({}^{-1}\) have been suggested to be the asymmetric stretching of the carboxylate (O-C-O). The peak between 1400 and 1454 cm\({}^{-1}\) is attributed to the C-OH deformation vibration [42]. The sharp peak between 1020 and 1040 cm\({}^{-1}\) can be attributed to the elongation of the C-O groups [43]. At 1200 cm\({}^{-1}\), there are slight peaks that may be related to the vibration of the sulphate group (SO\({}_{3}\)) present in sulphated polysaccharides [9]. Between 848 and 880 cm\({}^{-1}\), the peak corresponds to the deformation vibration of the bond between carbon 1 and hydrogen (C1-H) of the mannuronic acid residues, while at 940 cm\({}^{-1}\), the peak is associated with the C-O stretching of the guluronic acid residues [42]. Our results also show that there are some differences in the peaks between the extracted \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & _L. ochroleuca_ & _S. polyschides_ & _M. pyrifera_ & **Residual Pulp** \\ \hline
25 \({}^{\circ}\)C & 7.33 \(\pm\) 0.29 d & 22.67 \(\pm\) 0.74 b & 13.34 \(\pm\) 0.66 c & 41.37 \(\pm\) 0.50 a \\
60 \({}^{\circ}\)C & 13.61 \(\pm\) 0.71 d & 33.32 \(\pm\) 0.73 b & 28.32 \(\pm\) 1.05 c & 51.04 \(\pm\) 0.75 a \\
80 \({}^{\circ}\)C & 29.91 \(\pm\) 0.75 c & 46.71 \(\pm\) 1.02 a & 31.63 \(\pm\) 0.93 c & 38.85 \(\pm\) 0.43 b \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Alginate extraction yields as % of dry matter (dw) from the three seaweeds and the residual kelp pulp after alkaline extraction at different temperatures. Values are presented in % of dry matter, as mean \(\pm\) standard deviation (\(n\) = 3). Different superscript lowercase letters (a, b, c, d) indicate statistically significant differences between samples for a _p_-value < 0.05. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & _L. ochroleuca_ & _S. polyschides_ & _M. pyrifera_ & **Residual Pulp** \\ \hline  & & Macroelements (mg\(\cdot\)g \({}^{-1}\)) & & \\ \hline Phosphorus (P) & 1.18 \(\pm\) 0.05 b, c & 0.83 \(\pm\) 0.02 c & 5.29 \(\pm\) 0.03 a & 4.05 \(\pm\) 0.26 a, b \\ Sulphur (S) & 8.40 \(\pm\) 0.18 a & 7.50 \(\pm\) 0.15 a, b & 0.59 \(\pm\) 0.08 c & 2.55 \(\pm\) 0.13 b, c \\ Chlorine (Cl) & 24.84 \(\pm\) 0.86 b & 22.67 \(\pm\) 1.95 b & 77.97 \(\pm\) 0.65 a & 39.84 \(\pm\) 0.62 a, b \\ Potassium (K) & 22.34 \(\pm\) 0.35 b, c & 6.03 \(\pm\) 0.44 c & 67.72 \(\pm\) 0.62 a & 56.07 \(\pm\) 0.70 a, b \\ Calcium (Ca) & 7.80 \(\pm\) 0.32 a, b & 11.72 \(\pm\) 0.74 a & 3.61 \(\pm\) 0.05 c & 7.18 \(\pm\) 0.11 b, c \\ \hline  & & Microelements (\(\upmu\)g\(\cdot\)g\({}^{-1}\)) & & \\ \hline Iron (Fe) & 72.67 \(\pm\) 15.1 c & 137.67 \(\pm\) 10.50 b, c & 646.33 \(\pm\) 143.79 a & 229.00 \(\pm\) 6.56 a, b \\ Zinc (Zn) & 15.67 \(\pm\) 1.15 c & 33.33 \(\pm\) 2.52 a & 24.67 \(\pm\) 0.58 a, b & 22.00 \(\pm\) 1.00 b, c \\ Copper (Cu) & 5.00 \(\pm\) 0,00 b & 3.67 \(\pm\) 0.58 b, c & 8.00 \(\pm\) 1.00 a & 3.67 \(\pm\) 0.58 c \\ Arsenic (As) & 40.00 \(\pm\) 1.73 a, b & 12.67 \(\pm\) 1.53 c & 55.67 \(\pm\) 4.16 a & 26.00 \(\pm\) 1.00 b, c \\ \hline \hline \end{tabular}
\end{table}