## 3 Results and Discussion
### Determination of Antioxidant Capacity
Similar trends were also observed for skin, where only the extraction time had a significant positive impact on the antioxidant activity (\(p\) = 0.0012). On the other hand, concerning the bone and viscera side streams, the pH did not have any significant impact (\(p\) > 0.05). For the bone, the antioxidant activity was enhanced as extraction time increased and temperature decreased (\(p\) = 0.008 and \(p\) = 0.0016, respectively). As for the viscera, the antioxidant activity was strongly affected by the temperature. The increase of temperature and extraction time resulted in higher antioxidant activity (\(p\) = 0.0000 and \(p\) = 0.0008, respectively). The optimal conditions for ORAC assay and their theoretical response are shown in Table 8. \begin{table}
\begin{tabular}{c c c c c} \hline
**Side Stream** & **Extraction Time (min)** & **Temperature (\({}^{\circ}\)C)** & **pH** & **Antioxidant Capacity (ABTS, \(\mu\)M TE)** \\ \hline Head & 30 & 20 & 8.5 & 128.13 \\ Skin & 30 & 20 & 5.5 & 278.37 \\ Bone & 23 & 20 & 5.5 & 318.65 \\ Viscera & 21 & 50 & 8.5 & 535.70 \\ \hline \end{tabular}
\end{table} 
Table 6: Optimal conditions for ABTS optimal values. \begin{table}
\begin{tabular}{c c c c c c c} \hline  & **Extraction Time (min)** & **Temperature (\({}^{\circ}\)C)** & **pH** & \multicolumn{4}{c}{**Antioxidant Capacity**} \\  & **Time (min)** & **(\({}^{\circ}\)C)** & **pH** & \multicolumn{4}{c}{**(ORAC, \(\mu\)M TE)**} \\ \hline  & & & **Head** & **Skin** & **Bone** & **Viscera** \\ \hline
1 & 30 & 50 & 8.5 & 350.97 & 287.72 & 241.43 & 5794.64 \\
2 & 0.5 & 20 & 8.5 & 173.65 & 139.78 & 299.97 & 2124.46 \\
3 & 0.5 & 35 & 7 & 123.73 & 140.18 & 218.42 & 2813.98 \\
4 & 30 & 35 & 7 & 215.63 & 302.99 & 263.67 & 4684.92 \\
5 & 30 & 20 & 5.5 & 248.82 & 401.45 & 617.38 & 2611.02 \\
6 & 15.25 & 35 & 7 & 262.12 & 339.24 & 264.31 & 4042.80 \\
7 & 30 & 20 & 8.5 & 316.29 & 248.48 & 698.98 & 2410.56 \\
8 & 15.25 & 35 & 8.5 & 209.32 & 303.58 & 265.13 & 3991.56 \\
9 & 15.25 & 50 & 7 & 259.20 & 264.72 & 366.77 & 5206.57 \\
10 & 0.5 & 50 & 8.5 & 325.43 & 168.56 & 223.92 & 3538.50 \\
11 & 0.5 & 50 & 5.5 & 158.86 & 156.91 & 167.65 & 3914.67 \\
12 & 15.25 & 35 & 7 & 234.45 & 303.83 & 228.42 & 4394.47 \\
13 & 15.25 & 20 & 7 & 247.48 & 226.70 & 581.28 & 3493.03 \\
14 & 30 & 50 & 5.5 & 399.12 & 331.85 & 173.95 & 5355.38 \\
15 & 15.25 & 35 & 5.5 & 145.52 & 289.52 & 334.22 & 3648.70 \\
16 & 0.5 & 20 & 5.5 & 155.49 & 239.81 & 208.39 & 2082.74 \\ \hline \end{tabular}
\end{table} 
Table 7: Antioxidant capacity values obtained by oxygen radical absorbance capacity (ORAC) assay (\(\mu\)M TE) from fish side streams extracts at different UAE (ultrasound-assisted extraction) times (min), temperatures (\({}^{\circ}\)C), and pH. Figure 4: Plots shown in (**A**,**C**,**E**,**G**) indicate the response surface plots for the percentage of antioxidant capacity as a function of the extraction time (min) and temperature (\({}^{\circ}\)C) at a constant pH. The plots in (**B**,**D**,**F**,**H**) represent the plot of the influence of the different studied parameters on the antioxidant capacity values determined as \(\upmu\)M TE (Trolox equivalent) using the ORAC assay. The results obtained showed that sea bass side streams extracts are a great source of compounds with antioxidant potential. Regarding the information in the available literature about the antioxidant capacity of fish side streams, [PERSON] et al. [33] studied the application of aqueous and hydroethanolic mixtures assisted by pulsed electric fields (PEF) to recover antioxidants of sea bream and sea bass residues (gills, bones, and head). These authors found the highest antioxidant values after PEF-assisted extraction in aqueous media. They also observed that among the different side streams studied, gill extracts showed the highest antioxidant capacity, obtaining DPPH values in sea bass gills ranging from 105.93 to 313.87 ug Trolox/g sample.