Fabrication and characterization of edible composite films derived from xylanase-enzymatic flaxseed gum and citric acid-modified soybean protein isolate: Intermolecular interactions and functional efficacy

Polysaccharide based edible films often exhibit high brittleness and poor extensibility, limiting their widespread application in food preservation. To address these limitations, plasticizer-free polysaccharide-protein composite films were fabricated from xylanase hydrolyzed flaxseed gum (EFG) and citric acid modified soybean protein isolate (ASPI). This approach aimed to concurrently enhance the flexibility, structural stability, and preservation performance of the target films. Structural characterization using FTIR and SEM confirmed the formation of a compact three-dimensional network driven by changed intermolecular hydrogen bonding, evidenced by a shift of the OH stretching band to 3430 cm^-1. The FSF matrices exhibited notable bioactivity, showing strong antioxidant capacity with hydroxyl and ABTS radical scavenging rates of 97.24% ± 5.96% and 36.64% ± 0.72%, respectively, at 2 mg/mL. The films also demonstrated effective antibacterial activity against Escherichia coli and Staphylococcus aureus. Fuzzy comprehensive evaluation identified FSF-4 as the optimal formulation (membership score: 0.698), achieving a balanced combination of mechanical strength and barrier performance. FSF-4 displayed a tensile strength of 2.87 ± 0.22 MPa, elongation at break of 85.44% ± 1.45%, and water vapor permeability of 1095.73 ± 22.01 g/(m²·24 h). Application tests showed that FSF-4 effectively preserved blueberry quality during 21 days of storage, maintaining higher firmness and weight retention than the uncoated control. Although FSF-1 exhibited greater tensile strength, FSF-4 provided superior overall performance by integrating flexibility, barrier properties, and bioactivity. These films achieved high functionality without external plasticizers, relying on the intrinsic plasticizing effect of ASPI, highlighting their potential as environmentally sustainable food-packaging materials.