An integrated “extraction-film formation” strategy using natural deep eutectic solvents for fabricating active films in fruit preservation

To achieve formulation simplification and green fabrication, this study proposes an integrated “extraction–film formation” strategy based on Natural Deep Eutectic Solvents (NADES). Choline chloride and urea were used as the NADES system combined with ultrasound to extract flavonoids from Dalbergia pinnata (Lour.) Prain (DPF), which are directly incorporated into a Gelatin/Chitosan (Gel/CS) matrix to prepare deep eutectic composite films (GCD1–4) by solution casting. This extract simultaneously serves as a homologous plasticizer and functional agent. It avoids the repeated addition of plasticizers, antibacterial, and antioxidant agents, which are commonly required in conventional film preparation. The results show that with increasing DPF content, the films transformed from “rigid and brittle” to “flexible”, the surface wettability shifted from hydrophilic to hydrophobic, water solubility significantly decreased, and UV shielding ability was enhanced. The GCD-2 film show antibacterial efficiencies of 73.37 ± 4.94 % and 96.78 ± 0.2 % against Staphylococcus aureus and Escherichia coli , respectively. Its DPPH and ABTS radical scavenging rates were 69.74 ± 0.67 % and 99.08 ± 0.9 %, respectively, demonstrated good antibacterial and antioxidant activities. Cell viability was close to 100 %, and the hemolysis rate was below 5 %, indicates good biocompatibility of the films. Furthermore, the GCD series of films demonstrated good biodegradability, indicates their strong environmental friendliness. In application tests, the GCD-2 film significantly reduced weight loss, browning, and decay in strawberries and apple slices, effectively inhibiting decay, and shows the best preservation effect. In conclusion, the Gel/CS/DPF composite films achieved synergistic “plasticization-antibacterial-antioxidation” effects through the green extract, demonstrating great potential as biodegradable active packaging materials for fruit preservation.