## 3 Results
### Determination of Lipid Oxidation Evolution  
The progression of lipid oxidation was evaluated by analyzing the formation of primary (PV), secondary (TBA-i), and tertiary (FR) compounds, as well as by assessing the PI. Special attention was given to comparisons between the treated and CTR batches.  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Quality Index** &
\begin{tabular}{c} **Packaging** \\ **Condition** \\ \end{tabular} & \multicolumn{4}{c}{**Refrigeration Time (Days)**} \\ \hline \hline \multirow{4}{*}{pH} & CTR & 6.25 \(\pm\) 0.02 a & 6.51 \(\pm\) 0.02 Bb & 6.58 \(\pm\) 0.15 Ab & 6.59 \(\pm\) 0.02 Bb \\ \cline{2-6}  & AF-1 & 6.25 \(\pm\) 0.02 a & 6.39 \(\pm\) 0.10 ABab & 6.40 \(\pm\) 0.16 Aab & 6.42 \(\pm\) 0.08 Ab \\ \cline{2-6}  & AF-2 & 6.25 \(\pm\) 0.02 a & 6.29 \(\pm\) 0.08 Aa & 6.44 \(\pm\) 0.11 Aab & 6.50 \(\pm\) 0.03 ABb \\ \hline \multirow{4}{*}{TMA} & CTR & 1.60 \(\pm\) 0.42 a & 1.87 \(\pm\) 0.47 Aa & 12.80 \(\pm\) 1.7 Ab & 61.50 \(\pm\) 15.7 Ac \\ \cline{2-6}  & AF-1 & 1.60 \(\pm\) 0.42 a & 2.60 \(\pm\) 0.78 Aa & 11.57 \(\pm\) 2.3 Ab & 52.67 \(\pm\) 23.6 Ac \\ \cline{2-6}  & AF-2 & 1.60 \(\pm\) 0.42 a & 2.80 \(\pm\) 0.79 Aa & 11.00 \(\pm\) 4.6 Ab & 50.20 \(\pm\) 13.1 Ac \\ \hline \end{tabular}  
* Average values \(\pm\) standard deviations (\(n\) = 3). In each row, different lowercase letters denote significant differences (\(p<0.05\)) with refrigeration time; in each column, different capital letters denote significant differences (\(p<0.05\)) as a result of the packaging conditions. ** Packaging conditions as expressed in Table 1.  
\end{table}
Table 2: Evolution of the pH and trimethylamine (TMA; mg TMA-N\(\cdot\)kg\({}^{-1}\) muscle) values * in refrigerated mackerel subjected to different packaging conditions **.  
Figure 3: Determination of the free fatty acid (FFA; g\(\cdot\)kg\({}^{-1}\) lipids) content in refrigerated mackerel subjected to different packaging conditions. Average values \(\pm\) standard deviations (\(n\) = 3). The packaging conditions are expressed in Table 1. Different lowercase letters denote significant differences (\(p<0.05\)) with chilling time; different capital letters denote significant differences (\(p<0.05\)) as a result of the packaging condition. Time 0 corresponds to initial fish.  
Peroxide formation in this study was minimal [38; 54]. Across all batches, the peroxide content ranged from 0.68 to 5.03 meq\(\cdot\)kg\({}^{-1}\) lipids throughout the study (Table 3). No significant trend with storage time was observed (\(p>0.05\)), although the highest average values were recorded at the end of the storage period in all batches. An inhibitory effect (\(p<0.05\)) on peroxide formation was noted on day 9 due to the presence of flour extract in the packaging medium; this effect was more pronounced (\(p<0.05\)) with higher concentrations of the alga extract.  
A significant increase (\(p<0.05\)) in TBARS formation was observed in all batches during the 0-6-day period (Table 3). However, by the end of the storage period, a decrease in the average value was noted in samples from batches containing the alga extract. On day 9, an inhibitory effect (\(p<0.05\)) on TBARS formation was observed in the AF-2 batch compared with the CTR batch.  
A significant increase (\(p<0.05\)) in FR values with storage time was detected in all batches (Table 3). Additionally, an inhibitory effect (\(p<0.05\)) on fluorescent compound formation was observed on day 9 due to the inclusion of alga flour extract in the packaging medium (AF-1 and AF-2 batches). This effect was more pronounced (\(p<0.05\)) with higher concentrations of the alga extract.  
A progressive decrease in the PI was detected in most cases due to refrigerated storage (Table 3). Throughout the refrigeration period, higher average values were observed in the fish samples treated with the flour extract. Significant differences (\(p<0.05\)) were found after 2 and 6 days when the high-concentration (AF-2) packaging conditions were considered.