## 3 Results and Discussion
### Antioxidant Capacity and Degree of Hydrolysis  
In vitro ABTS and FRAP assays determined antioxidant capacity. ABTS assay can determine hydrophilic and lipophilic hydrogenated radicals [44]. The low antioxidant capacity of the effluents before ultrasonic pulses is related to their low solubility in water and the low availability of antioxidant molecules. However, after applying the ultrasonic pulses, an increase of more than 50% in antioxidant activity against the radical ABTS can be observed, possibly due to protein cleavage, the availability of low-molecular-weight peptides, and the presence of antioxidant AAs (such as Ala and Phe) [45]. An excessive degree of hydrolysis and a poor degree of hydrolysis cause incomplete removal of the \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Emulsifying Capacity (\%)**} & \multicolumn{2}{c}{**Foaming Capacity (\%)**} & \multicolumn{2}{c}{**ABTS (\%)**} & \multicolumn{2}{c}{**FRAP (\%)**} \\ \hline \multirow{3}{*}{Stickwater} & C & 65.4 \(\pm\) 3.2 \({}^{\text{b}}\) & 62.9 \(\pm\) 5 \({}^{\text{a}}\) & 45.2 \(\pm\) 2.2 \({}^{\text{b}}\) & 70.4 \(\pm\) 2.2 \({}^{\text{c}}\) \\  & UP & 88.3 \(\pm\) 5.8 \({}^{\text{c}}\) & 98.4 \(\pm\) 2 \({}^{\text{c}}\) & 73.8 \(\pm\) 4.3 \({}^{\text{c}}\) & 90.5 \(\pm\) 4.0 \({}^{\text{d}}\) \\ \hline \multirow{3}{*}{Sarcoplasmic protein} & C & 44.7 \(\pm\) 4.8 \({}^{\text{a}}\) & 85.8 \(\pm\) 1 \({}^{\text{b}}\) & 39.1 \(\pm\) 3.5 \({}^{\text{ab}}\) & 24.8 \(\pm\) 2.5 \({}^{\text{b}}\) \\  & UP & 86.8 \(\pm\) 4.1 \({}^{\text{c}}\) & 98.3 \(\pm\) 4 \({}^{\text{c}}\) & 83.7 \(\pm\) 4.4 \({}^{\text{c}}\) & 91.8 \(\pm\) 3.2 \({}^{\text{d}}\) \\ \hline \multirow{3}{*}{Myofibrillar protein} & C & 35.2 \(\pm\) 2.8 \({}^{\text{a}}\) & 69.7 \(\pm\) 5 \({}^{\text{a}}\) & 32.8 \(\pm\) 3.6 \({}^{\text{a}}\) & 14.4 \(\pm\) 2.1 \({}^{\text{a}}\) \\  & UP & 76.6 \(\pm\) 7.8 \({}^{\text{bc}}\) & 99.5 \(\pm\) 3 \({}^{\text{c}}\) & 73.8 \(\pm\) 5.6 \({}^{\text{c}}\) & 97.7 \(\pm\) 3.3 \({}^{\text{d}}\) \\ \hline \multirow{3}{*}{Stromal protein} & C & 34.1\(\pm\) 5.2 \({}^{\text{a}}\) & 67.3\(\pm\) 3 \({}^{\text{a}}\) & 46.7 \(\pm\) 1.7 \({}^{\text{b}}\) & 33.5 \(\pm\) 4.5 \({}^{\text{b}}\) \\  & UP & 87.5 \(\pm\) 2.8 \({}^{\text{c}}\) & 98.2 \(\pm\) 2 \({}^{\text{c}}\) & 98.2 \(\pm\) 1.8 \({}^{\text{d}}\) & 98.6 \(\pm\) 0.9 \({}^{\text{d}}\) \\ \hline \hline \end{tabular}  
* The results are expressed as the average of four determinations. Control (C), Ultrasound pulsed (UP). \({}^{\text{a,b,c}}\) Different letters indicate significant differences between rows.  
\end{table} 
Table 2: Functional properties of stickwater (SW). ABTS radical. The degree of hydrolysis of the samples when using ultrasonic pulses was 10%, which directly influenced the size of the peptides present in the hydrolysate. Similar results were found in the SW of _Clupeonella_ sp. [46] and Pacific thread herring (_Oplistonema Libertate_) [47]. High activity of ABTS in fish wastewater has been associated with hydrophobic amino acids (Val, Ala, and Leu) at the amino terminus position [42]. With their amino-acid composition, peptide sequences such as Leu-Leu-Pro -His-His, His-Pro-Val, or Pro-His-His are considered antioxidants. Likewise, peptides that contain His in their structure can act as metal chelators and reactive-oxygen-species scavengers [47,48]. Treatment of the sample with HCl performed by the company allows for maintenance of the iron-reducing activity (FRAP) (it indicates whether a compound can donate electrons to a free radical to neutralize it) of the wastewater before treatment with ultrasonic pulses. However, antioxidant activity was increased when ultrasonic pulses were used, compared to raw sewage. Similar results have been obtained for the wastewater of Pacific thread herring (_Oplistonema Libertate_) [49], tuna (_Thumus toggool_) [50], cuttlefish (_Sepiida_) [51], and shrimp (_Peneus_ spp.) [52].