Construction of multifunctional Gel/PVA/CS/DPTF composite films based on green NADES system and its application in fruit preservation.

Postharvest fruit spoilage and plastic-packaging pollution highlight the need for green, biodegradable active packaging with balanced mechanical and preservation performance. In this study, a choline chloride-lactic acid (ChCl-LA) natural deep eutectic solvent (NADES) system was used to obtain a NADES-loaded total flavonoid extract from Dalbergia pinnata (Lour.) Prain (DPTF), which was then incorporated into gelatin/polyvinyl alcohol/chitosan (Gel/PVA/CS) composite films. The extraction yield of total flavonoids reached 29.92 ± 0.47 mg/g, providing a stable source of plant-derived active compounds. DPTF was uniformly dispersed in the ternary matrix through hydrogen-bond-mediated interactions and regulated film properties through a dual plasticizing and physical cross-linking mechanism. At low loading, DPTF promoted molecular association and local ordering. At higher loadings, it increased chain mobility and free volume, enabling continuous mechanical modulation from a high-strength brittle film to a flexible and ductile material. Tensile strength decreased from 109.35 ± 5.08 to 10.00 ± 0.15 MPa, while elongation at break increased from 2.84 ± 0.21% to 77.04 ± 9.29%. Increasing DPTF loading also enhanced UV-shielding ability, surface hydrophobicity, aqueous stability, antioxidant activity, and antibacterial performance. GPCD-4 showed inhibition rates above 98% against Staphylococcus aureus and Escherichia coli. All films exhibited favorable cytocompatibility, hemocompatibility, and soil degradability. In fruit preservation tests, GPCD-4 delayed quality deterioration of strawberries, fresh-cut apples, and grapes through physical protection, antioxidant activity, and antibacterial action. This work demonstrates the feasibility of using NADES-loaded D. pinnata flavonoids to fabricate multifunctional biodegradable packaging films with active preservation performance.