## 3 Results and Discussion  
### Protein Extraction  
In order to determine the percentage of recovered proteins from the different sea bass side streams after applying UAE extraction, the Kjeldahl method was used. The results are shown in Table 4. It was found that the highest percentage of proteins recovered from head \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Mycotoxin**} & \multicolumn{2}{c}{**Recovery \({}^{\text{c}}\) \(\pm\) RSD \({}^{\text{d}}\) (\%)**} & \multirow{2}{*}{**SSE (\%) \({}^{\text{b}}\)**} & \multirow{2}{*}{**LOD \({}^{\text{a}}\)**} & \multirow{2}{*}{**LQ \({}^{\text{a}}\)**} \\ \cline{2-2} \cline{5-6}  & **Intraday Precision** & & & & \\ \hline AFB1 & \(78\pm 6\) & \(68\pm 8\) & 75 & 0.7 & 2.3 \\ AFB2 & \(96\pm 7\) & \(114\pm 9\) & 104 & 2.4 & 8.0 \\ AFG1 & \(90\pm 5\) & \(120\pm 10\) & 93 & 0.7 & 2.3 \\ AFG2 & \(106\pm 8\) & \(73\pm 12\) & 86 & 0.5 & 1.7 \\ ZEA & \(80\pm 6\) & \(77\pm 7\) & 65 & 0.2 & 0.7 \\ OTA & \(115\pm 9\) & \(120\pm 10\) & 72 & 5 & 17 \\ ENA & \(100\pm 7\) & \(95\pm 8\) & 85 & 0.4 & 1.3 \\ ENA1 & \(99\pm 2\) & \(100\pm 6\) & 89 & 0.2 & 0.7 \\ ENB & \(115\pm 5\) & \(105\pm 7\) & 105 & 0.05 & 0.2 \\ ENB1 & \(98\pm 7\) & \(93\pm 8\) & 75 & 0.1 & 0.3 \\ BEA & \(94\pm 8\) & \(89\pm 11\) & 99 & 0.4 & 1.3 \\ \hline \hline \end{tabular}  
* \({}^{\text{a}}\) LOD and LOQ are limits of detection and quantification. \({}^{\text{b}}\) SSE: signal suppression/enhancement. \({}^{\text{c}}\) Recoveries: analysis performed at concentrations of 10 \(\times\) LOQ. \({}^{\text{d}}\) RSD: relative standard deviation.  
\end{table} 
Table 2: Analytical parameters for method validation. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{1}{c}{**Run**} & \multicolumn{1}{c}{**Time (min)**} & \multicolumn{1}{c}{**Temperature (\({}^{\text{c}}\) C)**} & \multicolumn{1}{c}{**pH**} \\ \hline
1 & 30 & 50 & 8.5 \\
2 & 0.5 & 20 & 8.5 \\
3 & 0.5 & 35 & 7 \\
4 & 30 & 35 & 7 \\
5 & 30 & 20 & 5.5 \\
6 & 15.25 & 35 & 7 \\
7 & 30 & 20 & 8.5 \\
8 & 15.25 & 35 & 8.5 \\
9 & 15.25 & 50 & 7 \\
10 & 0.5 & 50 & 8.5 \\
11 & 0.5 & 50 & 5.5 \\
12 & 15.25 & 35 & 7 \\
13 & 15.25 & 20 & 7 \\
14 & 30 & 50 & 5.5 \\
15 & 15.25 & 35 & 5.5 \\
16 & 0.5 & 20 & 5.5 \\ \hline \hline \end{tabular}  
* \({}^{\text{a}}\) LOD and LOQ are limits of detection and quantification. \({}^{\text{b}}\) SSE: signal suppression/enhancement. \({}^{\text{c}}\) Recoveries: analysis performed at concentrations of 10 \(\times\) LOQ. \({}^{\text{d}}\) RSD: relative standard deviation.  
\end{table} 
Table 3: Dependent variable conditions for the ultrasound-assisted extraction studied. extracts (39.89%), which was observed after 15.25 min of extraction at 35 \({}^{\circ}\)C and 5.5 pH, while 31.68% of proteins were recovered from skin extracts after 30 min of extraction at 35 \({}^{\circ}\)C and pH 7. Additionally, the bone extracts yielded 75.07% of proteins after 30 min of UAE at 50 \({}^{\circ}\)C and pH of 8.5. Lastly, 30 min of ultrasound at 50 \({}^{\circ}\)C and a pH 5.5, allowed the extraction of 99.37% of proteins from the viscera extracts. Similar protein recoveries were obtained by [PERSON] et al. [31]. These authors observed protein yields that reached 62.60% when they evaluated protein recovery from tilapia fillets assisted by UAE combined with alkaline conditions. Moreover, higher protein yields were obtained by [PERSON] et al. [11] under UAE + alkaline conditions, with a recovery \(\approx\)95% of total protein from mackerel byproducts. In our study, a similar percentage of protein recovery was observed in viscera extracts (99.37%). In general, protein recovery reported in the literature by other authors varies in a range between 42% and 90%. Moreover, data available in the literature revealed that alkaline solubilization usually results in higher protein recoveries than acidic conditions [32]. In our work, proteins recovery optimal pH differed according to the side stream studied.