Functional enhancement of calcium alginate films using by-product-derived NADES extracts for improved protection of...

Growing concern over the environmental impact of plastic packaging has driven the development of biodegradable materials with enhanced protective functions. This study focuses on the functional enhancement of calcium alginate packaging films by incorporating bioactive extracts from red onion, apple, and ginger by-products using natural deep eutectic solvents (NADES) based on glycerol, proline, xylitol, and malic acid. NADES extracts were evaluated for antioxidant, antimicrobial, and enzymatic anti-browning activities. Proline-based NADES extracts exhibited the strongest radical scavenging activity (up to 497 ± 12 μmol/g, DPPH; 305 ± 5 μmol/g, ABTS; and 40.0 ± 0.7 μmol/g, PM assay), while malic acid-based NADES showed pronounced antimicrobial effects against most common foodborne pathogens (particularly against Bacillus cereus), and significant tyrosinase inhibition (up to 97.7 ± 0.1%), indicating a combined contribution of NADES components and the extracted phytochemicals. Selected extracts were incorporated into alginate films and characterized by scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). NADES incorporation altered film morphology, color, and surface properties: proline- and xylitol-based formulations formed uniform and well-adhered films, while malic acid-based films exhibited structural heterogeneity and surface defects. The protective performance of the films was evaluated on strawberries, blueberries, and cheese. Alginate/NADES films outperformed uncoated and pure alginate controls in reducing weight loss, delaying decay, and slowing color degradation, although their protective efficacy was influenced by both film composition and food type. Among the tested systems, films enriched with red onion by-product-derived extracts exhibited the most pronounced preservation effects, especially in high-moisture fruits such as strawberries.