Schiff base crosslinked gelatin-Spirulina platensis protein concentrate films with enhanced antioxidant activity

The aim of this work is to produce bioactive films suitable for aerobic packaging applications by combining the bioactivity of Spirulina platensis protein concentrate (PC; 1% and 2% w/w), the sustainable nature of bovine gelatin (Ge), and sodium alginate dialdehyde (ADA, 5% w/w) as Schiff base crosslinking agent. PC was obtained by an optimized acid-base extraction process and characterized. PC showed a dose-dependent radical scavenging activity (RSA; IC₅₀  = 24.3 mg/L) related to its high content of C-phycocyanin and total phenolic compounds (32.44 ± 1.37 mg gallic acid equivalents per gram of PC). As a general trend, crosslinking decreased the water solubility, improved mechanical properties, and helped improve RSA of Ge-ADA-PC films. Ge-5ADA-2PC film recorded best compromise between solubility (only 33.6%), high UV barrier (0.134% transmittance at 400 nm), reasonable extensibility (217.00 ± 2.34%), tensile strength (3.50 ± 0.43 MPa), water vapor permeability (2.00 ± 0.17 × 10^-12  kg·m/m² ·Pa·s), and RSA (44.70 ± 2.19%). Wrapping hake fillets in this filmdelayed lipid oxidation during storage under refrigerated conditions for 11 days, maintaining the thiobarbituric acid index below 0.5 mg malonaldehyde/kg muscle. Results suggest that Ge-ADA-PC films have potential as aerobic packaging materials for oxidation-sensitive food. PRACTICAL APPLICATION: The combination of gelatin, alginate dialdehyde and Spirulina platensis protein concentrate gave rise to fully biobased films with reduced water solubility and enhanced antioxidant activity, which were able to delay the secondary lipid oxidation of refrigerated seafood. This study also shows the potential of cyanobacteria as renewable resources of high-value ingredients for the design of active and intelligent aerobic packaging solutions.