Quality Management and Sustainability in the Design of Active Biocomposites: Evaluation of Double-Layer Protein–Polysaccharide Complexes Enriched with Plant Extracts

Despite promising results, biocomposite research still requires elaboration, particularly with regard to functional properties and applications. In this study, multilayer biocomposites based on gelatin, κ-carrageenan and carboxymethylcellulose were enriched with sage or blackberry extracts. The films were characterized based on their physicochemical traits and bioactivity for application as active packaging and environmental biodegradation. FTIR confirmed extract integration and strong matrix interactions, while UV-VIS analysis showed efficient UV blocking. Water properties remained acceptable (WVTR ≈ 550 g/m² × d); solubility decreased for BB (41.73% vs. 53.45% control). Mechanical testing indicated a plasticizing effect: elongation increased (20.00% control; 35.35% BB; 39.29% SAGE), while tensile strength and Young's modulus decreased. Antioxidant capacity rose (FRAP: 0.38 control, 1.97 BB, 4.48 SAGE µTrolox/mg; DPPH: 6.38% control, 85.68% BB, 78.25% SAGE; MCA: none). During refrigerated storage, antimicrobial effects were most evident on days 6-9. Lipid oxidation peaked for BB (0.92 mg MDA/kg, day 9), while pH was more stable with SAGE. Biodegradation and phytotoxicity confirmed environmental safety and compostability, with increased humic acid carbon in vermicompost. Overall, the results confirm the relevance of modifying biopolymers using green chemistry and highlight their importance for quality management, food safety and sustainable circular economy strategies.