Enhancement of Composite Film Properties by Sweeping-Frequency Ultrasound Modified Xanthan Gum and Nano ZnO: Structural and Functional Characterization

Xanthan gum (XG) with different structures was prepared by being subjected to sweeping-frequency ultrasound (SFU) modification, and then incorporated with nano ZnO to fabricate composite films for active food packaging applications. Effects of SFU power density (0,6.25,25, 100 W & sdot;L- 1) on the molecular weight, monosaccharide composition, and structure of XG were systematically investigated. XG/ZnO composite films were prepared using the solution casting method. Physical properties of composite films were characterized by mechanical properties, color, UV absorption, thermal stability, and gas transmission rate. The interaction between XG and nano ZnO was elucidated through rheological properties and microscopic morphology. Furthermore, the antioxidant and antibacterial activities of composite films were evaluated. Results indicated that SFU effectively reduced the molecular weight of XG, with the weight-average molecular weight (Mw) decreasing to 7.92 x 104 Da after 25 W & sdot;L- 1 SFU treatment. Side-chain glycosidic bonds were disrupted, leading to a 31.58 % reduction in glucuronic acid (GluA) content. By loading 10 % nano ZnO (relative to XG dry weight), the composite film exhibited enhanced tensile strength (TS) of 32.43 MPa, excellent UV shielding properties, reduced gas transmission rate, and improved thermal stability. Rheological and microstructure analysis revealed strong interfacial bonding between SFU modified XG and ZnO nanoparticles. Consequently, composite films exhibited significant antioxidant and antibacterial activities, inhibiting E. coli by 85.90 % and S. aureus by 88.16 %. It was demonstrated that SFU modified XG/ZnO composite films can be promising for functional food packaging.