## 3 Results and Discussion  
### P. canaliculata Extracts: Total Phenolic Content and Antioxidant Activity Evaluation  
In this study, food-grade solvents (water and ethanol) were used to obtain _P. canaliculata_ extracts suitable for incorporation into edible coatings. Extraction with water and with a water:ethanol mixture (1:1) produced similar yield values (28.6 and 25.3% DW, respectively), which were approximately three times higher than the yield obtained with ethanol (9.0%). The aqueous, hydroethanolic (1:1), and ethanolic extracts of _P. canaliculata_ were evaluated for total phenolic content (TPC) and antioxidant activity using the DPPH and FRAP methods (Table 2).  
The ethanolic extract exhibited the highest TPC (203 \(\pm\) 32 \(\upmu\)g GA/mg) and the strongest activity in both the DPPH (180.7 \(\pm\) 7.4 \(\upmu\)g Trolox/mg) and FRAP (55.37 \(\pm\) 4.7 \(\upmu\)g Trolox/mg)  
\begin{table}
\begin{tabular}{l c c c} \hline _P. canaliculata_ **Extract** & **H\({}_{2}\)O** & **EtOH:H\({}_{2}\)O** & **EtOH** \\ \hline TPC (\(\upmu\)g GA/mg) & 48.7 \(\pm\) 9.1 \({}^{\mathrm{a}}\) & 55.4 \(\pm\) 3.7 \({}^{\mathrm{b}}\) & 203 \(\pm\) 32 \({}^{\mathrm{a,b}}\) \\ DPPH (\(\upmu\)g Trolox/mg) & 38.3 \(\pm\) 3.8 \({}^{\mathrm{a}}\) & 39.9 \(\pm\) 2.9 \({}^{\mathrm{b}}\) & 180.7 \(\pm\) 7.4 \({}^{\mathrm{a,b}}\) \\ FRAP (\(\upmu\)g Trolox/mg) & 15.8 \(\pm\) 2.5 \({}^{\mathrm{a}}\) & 16.2 \(\pm\) 2.1 \({}^{\mathrm{b}}\) & 55.3 \(\pm\) 4.7 \({}^{\mathrm{a,b}}\) \\ \hline \end{tabular}
\end{table}
Table 2: Total phenolic content (TPC) and antioxidant activity evaluated by the DPPH and FRAP methods of aqueous, hydroethanolic (1:1) and ethanolic extracts of _P. canaliculata_. For each method (same row), same letter means significant differences (\(p<0.05\)) between extracts.  
assays. Aqueous and hydroethanolic extracts showed similar activities, with TPC, DPPH and FRAP values clearly below those of the ethanolic extract. Moreover, a strong positive correlation was observed between TPC and antioxidant activity of all extracts, suggesting the importance of phenolic compounds as antioxidant agents. These results indicate higher efficiency of ethanol in selectively extracting antioxidant compounds. For this reason, ethanolic extract was selected for incorporation into coating solutions applied to mackerel fillets.  
The antioxidant activity of this seaweed has been reported by other authors, mostly attributed to phenolic compounds. [PERSON] et al. (2021) [26] characterized methanolic extracts from the same biomass used in this study and reported TPC, FRAP and DPPH values lower than those of the ethanolic extract but higher than those of the aqueous and hydroethanolic extracts. Similarly, [PERSON] et al. (2011) [36] reported considerably lower TPC in methanolic extracts of _P. canaliculata_ from Ireland, along with weaker antioxidant activity. On the other hand, [PERSON] et al. (2013) [37] tested several extraction conditions for _P. canaliculata_ from Ireland and described antioxidant activities consistent with the values obtained in this study, noting that cold water or 80% ethanol extractions led to better results than hot water as the extraction solvent.