# Hake Fish Preservation Using Plant-Based Impregnated Polylactic Acid Food Films as Active Packaging
## 4 Conclusions  
Active packaging has been proposed as a non-thermal preservation strategy for fresh foods, offering a less intrusive alternative to methods such as high hydrostatic pressure, pulsed electric fields, or ultrasound, which act directly on the food. While active packaging is unlikely to achieve the same drastic reductions in microbial populations, its bacteriostatic effect through the temporary release of active substances offers a subtler approach. However, limitations exist, as the concentration of active compounds in the polymer must be carefully balanced to maintain the sensory and safety attributes of the food. Thus, the key challenge lies in optimizing the migration kinetics of bioactive compounds, preserving the sensory qualities, assessing the gastrointestinal viability, and achieving a demonstrable bacteriostatic effect to ensure the success of active packaging technologies. This study demonstrated the practical potential of biodegradable polylactic acid films impregnated with olive leaf extract as an eco-friendly alternative for fish preservation. The supercritical fluid impregnation process provided excellent results in the functionalization of films. This technology generated PLA-based films with antioxidant activity and demonstrated differential extract release in food simulants, suggesting tailored applications for various food types. The migration tests pointed to the aptitude of this film for their action in food with a certain fatty content such as white fish. The proposed active packaging effectively reduced the microbial growth and minimized drip loss while maintaining the pH stability in fresh hake fillets over 12 days of storage at 4 \({}^{\circ}\)C. The bactericidal effect of the olive leaf extract was evident during days 2 and 5, maintaining the mesophilic bacteria concentration on the hake fillets, which could have an impact on the marketability of the fish. In contrast, the control samples showed a more pronounced loss of freshness as evidenced by both the sensory and analytical results. Although the packaging caused a yellowish hue in the hake fillets, it did not alter the distinctive fish odor profile, demonstrating the sensory neutrality of the olive leaf extract. Despite the impregnated films having a strong green color, this did not result in any green coloration of the fish. All in all, these findings highlight the potential of supercritical CO\({}_{2}\) impregnation as an efficient technology for developing bioactive films with natural extracts. This technology shows great promise for application in highly perishable products, such as seafood, offering an innovative and sustainable solution for food preservation. Conceptualization, F.S.-G., N.D.M., C.C.-B. and L.C.-C.; Methodology, F.S.-G., M.T.-F., L.C.-C. and C.C.-B. ; Formal analysis, F.S.-G., N.D.M. and C.C.-B. ; Investigation, F.S.-G., M.T.-F. and L.C.-C.; Writing--original draft preparation, F.S.-G., N.D.M. and C.C.-B. ; Writing--review and editing, A.M.R. and L.C.-C.; Supervision, F.S.-G., C.C.-B., A.M.R. and L.C.-C.; Project administration, C.M.-S., L.C.-C. and C.C.-B. ; Funding acquisition, C.M.-S. and L.C.-C. All authors have read and agreed to the published version of the manuscript. **Funding:** This work was framed within Project \"TED2021-131822B-I00\", financed by MCIN/AEI/10.13039/501100011033 and the European Union NextGenerationEU/PRTR. These results are also part of PROYEXCEL_00920 (2021 Call), supported by the Program of Aid For Research Projects of Excellence, on a Competitive Concurrence Basis, aimed at Entities Qualified as Agents of The Andalusian Knowledge System, within the scope of The Andalusian Plan for Research, Development, and Innovation (PAIDI 2020), Department of University, Research, and Innovation of the Regional Government of Andalusia. **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** The original contributions presented in this study are included in the article.