## 4 Discussion  
### Antimicrobial Activity  
The results of microbiological analyses revealed that incorporating bioactive algal extracts into gelatin packaging films inhibited the growth of all five microbial groups investigated in Atlantic mackerel stored for 9 d under refrigeration conditions. Notably, the differences in three of the five microbial parameters investigated among batches were \begin{table}
\begin{tabular}{c c c c c c} \hline \multicolumn{1}{c}{**Quality Index ***} & \multicolumn{2}{c}{**Packaging Condition**} & \multicolumn{2}{c}{**Refrigeration Time (Days)**} \\ \hline \hline  & & **0** & **2** & **6** & **9** \\ \hline \multirow{4}{*}{PV} & CTR & 0.98 \(\pm\) 0.47 a & 1.24 \(\pm\) 0.43 Aa & 3.05 \(\pm\) 1.70 Aab & 5.03 \(\pm\) 1.61 Cb \\ \cline{2-6}  & AF-1 & 0.98 \(\pm\) 0.47 a & 0.72 \(\pm\) 0.35 Aa & 2.11 \(\pm\) 1.66 Aab & 2.27 \(\pm\) 0.15 Bb \\ \cline{2-6}  & AF-2 & 0.98 \(\pm\) 0.47 ab & 1.57 \(\pm\) 0.44 Aab & 0.68 \(\pm\) 0.46 Aa & 1.60 \(\pm\) 0.33 Ab \\ \hline \multirow{4}{*}{TBA-i} & CTR & 0.42 \(\pm\) 0.12 a & 0.91 \(\pm\) 0.17 Ab & 2.86 \(\pm\) 1.07 Ac & 4.77 \(\pm\) 0.76 Bd \\ \cline{2-6}  & AF-1 & 0.42 \(\pm\) 0.12 a & 1.13 \(\pm\) 0.45 Ab & 3.25 \(\pm\) 1.39 Ac & 3.10 \(\pm\) 1.77 ABc \\ \cline{2-6}  & AF-2 & 0.42 \(\pm\) 0.12 a & 1.18 \(\pm\) 0.42 Ab & 1.84 \(\pm\) 0.42 Ab & 1.77 \(\pm\) 0.27 Ab \\ \hline \multirow{4}{*}{FR} & CTR & 3.69 \(\pm\) 1.56 a & 4.85 \(\pm\) 0.77 Aa & 6.39 \(\pm\) 0.65 Ab & 7.22 \(\pm\) 0.29 Cc \\ \cline{2-6}  & AF-1 & 3.69 \(\pm\) 1.56 a & 4.89 \(\pm\) 0.17 Aa & 5.40 \(\pm\) 0.61 Aab & 6.16 \(\pm\) 0.58 Bb \\ \cline{2-6}  & AF-2 & 3.69 \(\pm\) 1.56 a & 4.44 \(\pm\) 0.94 Aa & 5.84 \(\pm\) 1.32 Aa & 4.86 \(\pm\) 0.16 Aa \\ \hline \multirow{4}{*}{PI} & CTR & 2.27 \(\pm\) 0.16 a & 2.04 \(\pm\) 0.23 Aa & 1.97 \(\pm\) 0.21 Aa & 1.88 \(\pm\) 0.47 Aa \\ \cline{2-6}  & AF-1 & 2.27 \(\pm\) 0.16 a & 2.20 \(\pm\) 0.16 ABa & 1.98 \(\pm\) 0.10 Aa & 1.94 \(\pm\) 0.53 Aa \\ \cline{2-6}  & AF-2 & 2.27 \(\pm\) 0.16 a & 2.40 \(\pm\) 0.10 Ba & 2.25 \(\pm\) 0.02 Ba & 2.14 \(\pm\) 0.12 Aa \\ \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. *** Abbreviations and units: PV (peroxide value; miliequivalents-kg\({}^{-1}\) lipids), TBA-i (thiobarbituric acid index; mg malondialdehydedehyde-kg\({}^{-1}\) muscle), FR (fluorescence ratio) and PI (polyene index).  
\end{table} 
Table 3: Determination of lipid oxidation evolution * in refrigerated mackerel subjected to different packaging conditions **. statistically significant (\(p<0.05\)). These results provide a promising strategy for developing active films incorporating algal extracts to achieve better retention of fish quality by delaying microbial breakdown. These results agree with those of previous studies on the preservative effect of _Gelidium_ sp. flour against the most common food pathogenic and spoilage bacteria [38]. Moreover, an antimicrobial effect was reported in such a study when an aqueous extract of _Gelidium_ flour was added to the icing medium employed for the chilled storage of Atlantic mackerel (_S. scombrus_) [49]. The inhibitory effect of the current alga flour on microbial growth can be attributed to the presence of various bioactive compounds. Additionally, the combination of gelatin with bioactive compounds has been shown to better protect packaged foods and extend their shelf life [55]. This combination has been reported to enhance the mechanical properties and barrier functions of the film, which are crucial for controlling the release of bioactive components [55]. In addition, the incorporation of alga flour into gelatin films can affect the release rate of bioactive compounds, which is beneficial for maintaining the efficacy of bioactive components over time [56; 57].