# Hake Fish Preservation Using Plant-Based Impregnated Polylactic Acid Food Films as Active Packaging
## 1 Introduction
Polylactic acid (PLA), a biodegradable polymer derived from renewable resources like corn has garnered significant attention in the packaging industry. It offers several advantages including high transparency, low permeability to water and gases, recyclability, and a short degradation period, making it a viable alternative to conventional plastics like polystyrene (PS), low-density polyethylene (LDPE), and PET [18; 19; 20]. Recent studies have highlighted promising results in food preservation. For example, PLA films loaded with rice straw extracts demonstrated antioxidant and antimicrobial properties, successfully preserving pork meat by inhibiting microbial growth, oxidation, discoloration, and weight loss. The extracts were incorporated into PLA using melt blending and compression molding [21]. Another study evaluated bilayer films composed of a PLA-tilapia fish gelatin-sodium alginate loaded with \(\beta\)-cyclodextrinrin inclusion complexes of cinnamaldehyde and thymol. These active bilayer films extended the shelf life of Japanese sea bass (_Lateolabrax japonicus_) by at least 3 days. As can be noted, these active films were prepared by the coating method [22]. One innovative method for incorporating active compounds into biodegradable polymers is supercritical CO\({}_{2}\) (scCO\({}_{2}\)) impregnation. The scCO\({}_{2}\) is a state reached above the critical temperature (T\({}_{\rm C}\) = 31.1 \({}^{\circ}\)C) and pressure (P\({}_{\rm C}\) = 73.8 bar) where the characteristics of the liquid and gas phases become nearly indistinguishable. The main advantage of this solvent is the ability to adjust the diffusivity, viscosity, and density in front of small changes in the pressure and temperature parameters [23]. During supercritical impregnation, CO\({}_{2}\) is pressurized and heated above its critical point, allowing it to dissolve the active compounds and then impregnate them into the polymeric material. Once the pressure is released, the CO\({}_{2}\) evaporates, leaving the active substances embedded within the material. This method is efficient, non-toxic, and environmentally friendly [24]. The scCO\({}_{2}\) impregnation of PLA films intended for food active packaging has been explored using carvone [25; 26], and thymol [27], and extracts such as thyme [28] and clove [29]. However, the performance of these types of packaging in real food matrices has been scarcely evaluated. Given this context, the main objective of this work was to produce active packaging for hake fillets using a natural extract as a source of bioactive compounds impregnated in a commercial biodegradable polymer employing supercritical technologies. For this purpose, a commercial PLA-based film was impregnated with olive leaf extract using the scCO\({}_{2}\) technique. The resulting films were assessed for their bioactivity, and extract migration properties. Their effectiveness in preserving minimally processed hake fillets was evaluated over a 12-day storage period. The impact of the impregnated films on the shelf life of the hake fillets was determined through comprehensive analyses of the physicochemical, microbiological, and sensory parameters, offering insights into their potential for enhancing food preservation.