## 3 Results and Discussion
### FTIR Spectra  
Typical FTIR spectra from 4000 to 650 cm\({}^{-1}\) collected from _A. platensis_ samples grown with different phosphorus concentrations are presented in Figure 5, and possible assignments of the main absorption bands are shown in Table 4. In brief, the main peaks with the highest absorbance observed for all the analyzed samples were found at 1080, 1015, 1005 (shoulder) cm\({}^{-1}\) (possibly from polysaccharides, carbohydrates, lipids and/or nucleic acids/phospholipids), at 1150 cm\({}^{-1}\) (from carbohydrates and/ or lipids), 1540 cm\({}^{-1}\) (mainly from proteins) and 1650 cm\({}^{-1}\) (mainly from proteins and/or olefinic and aromatic compounds) [45; 46; 47; 48; 49]. Figure 5: Raw FTIR spectra of A. platensis samples grown with different phosphorus concentrations: 1.5, 2, 3, 4, 89 (Control) mg-P/L. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**P-Concentration** **(mg-P/L)**} & **Glucose** & \multirow{2}{*}{\
\begin{tabular}{c} **Glucose** \\ **(Ratio to Total** \\ **Sugars, \%)** \\ \end{tabular} } & **Galactose** & \multirow{2}{*}{
\begin{tabular}{c} **Galactose** \\ **(\%DW)** \\ \end{tabular} } & **Mannose** & **(Ratio to Total** \\ **(\%DW)** & & & & & **Sugars, \%)** & **(\%DW)** & **Sugars, \%)** \\ \hline
1.5 & 53.2 \(\pm\) 0.50 & 97.3 & 0.6 \(\pm\) 0.09 & 1.1 & 0.9 \(\pm\) 0.01 & 1.6 \\
2 & 55.3 \(\pm\) 0.23 & 97.5 & 0.5 \(\pm\)0.01 & 0.9 & 0.9 \(\pm\) 0.01 & 1.6 \\
3 & 43.9 \(\pm\) 7.67 & 96.6 & 0.7 \(\pm\) 0.08 & 1.6 & 0.8 \(\pm\) 0.13 & 1.8 \\
4 & 28.9 \(\pm\) 0.38 & 94.9 & 0.9 \(\pm\) 0.1 & 3.1 & 0.6 \(\pm\) 0.07 & 2.0 \\
89 (Control) & 24.6 \(\pm\) 0.01 & 95.3 & 0.7 \(\pm\) 0.02 & 2.8 & 0.5 \(\pm\) 0.04 & 2.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Monosaccharide profile of carbohydrates of _A. platensis_ grown with different phosphorus concentrations. Results represent the average \(\pm\) SD of \(n\) = 3 replicates. Table 5 presents the performance indices for each PLS-R model built using the spectral data between the range of 1800-650 cm\({}^{-1}\), while Figure 6 presents the observed values vs. the model estimates for each studied parameter. It was observed that the indices were found to be satisfactory for all the estimated parameters except for the lipid content. In detail, after the external validation of the models (test set), the highest R\({}^{2}\) values were observed for the models built for glucose, dietary fibers, \(\beta\)-glucans, followed by carbohydrates and proteins, and finally by \(\alpha\)-glucans, while for lipids a negative R\({}^{2}\) was observed. The same decreasing order was observed in the values of RPD. According to [PERSON] et al. [50], the models for glucose, dietary fibers, \(\beta\)-glucans and carbohydrates showed high RPD values (above 3) that correspond to excellent prediction accuracy, the protein model's RPD value indicated good prediction accuracy (above 2.5), the values for the \(\alpha\)-glucans indicated poor quantitative prediction (value between 2 and 2.5), while the RPD values for lipids model were very low (0.4). Regarding the RMSE values, the lowest values were observed for \(\alpha\)- and \(\beta\)-glucans, followed by glucose, lipids and dietary fiber, and finally, by proteins and carbohydrates.