ULTRASOUND-ASSISTED PRODUCTION OF CHITOSAN FILMS CONTAINING POLY(LIMONENE) AND MONTMORILLONITE: ANTIOXIDANT AND FUNCTIONAL PROPERTIES

Abstract: The development of biodegradable active packaging has gained prominence due to the need to reduce food loss and waste while enhancing material functionality. Incorporating bioactive compounds into biopolymer matrices enables packaging to act as a physical barrier and protect food against spoilage. Chitosan exhibits high potential for biodegradable film formation, while poly(limonene) (PLM) can serve as a functional component. This study aimed to develop chitosan films containing PLM, with or without montmorillonite (MMT) as a reinforcing agent, subjected to ultrasonic treatment, and evaluate their properties. Four formulations were produced: chitosan (C-U), chitosan/MMT (CM-U), chitosan/PLM (CP-U), and chitosan/PLM/MMT (CPM-U). Film-forming solutions contained 1.5% (w/w) chitosan, 0.45% glycerol, and 2% acetic acid, with PLM and MMT added at 5% relative to chitosan mass. Solutions were stirred for 6 h at 50 °C, sonicated for 20 min at 20% amplitude, cast in Petri dishes, and dried for 48 h. Films were characterized for thickness, mechanical properties, color, moisture content, solubility, water vapor permeability (WVP), UV-Vis optical properties, FTIR, and antioxidant activity (ABTS and DPPH). PLM incorporation primarily altered mechanical and antioxidant properties. CP-U exhibited higher elongation at break (60.24 ± 4.48%) than C-U (39.75 ± 4.82%), while tensile strength did not differ significantly among formulations (17.20–20.71 MPa). Elastic modulus decreased from 71.63 ± 28.22 MPa (C-U) to 33.87 ± 7.52 MPa (CP-U), indicating increased film flexibility. The most significant effect occurred in antioxidant activity: ABTS radical scavenging rose from 0.00 ± 0.00% (C-U) to 31.76 ± 3.80% (CP-U) and 54.92 ± 7.06% (CPM-U). For DPPH, values increased from 2.23 ± 0.64% (C-U) to 9.50 ± 0.69% and 7.95 ± 0.30% in CP-U and CPM-U films, respectively. The higher ABTS response in CPM-U suggests a possible interaction between MMT and PLM that could increase the antioxidant potential of the films, although this effect depends on the assay. PLM also decreased L* lightness, increased a* and b* color values, and reduced UV transmittance, providing better radiation protection. WVP showed no significant differences among formulations, indicating PLM and MMT did not alter water vapor permeability under these conditions. Consequently, PLM incorporation imparted superior flexibility, antioxidant activity, and UV barrier properties to chitosan films. These results highlight the potential of PLM and MMT for developing biodegradable, multifunctional materials intended for active food packaging.

Acknowledgments: This study was financed, in part, by the São Paulo Research Foundation (FAPESP) – grant #2022/02728-0, #2024/07555-2, #2025/03776-7, #2025/16617-4, and #2026/00774-6. This study received partial financial support from the National Council for Scientific and Technological Development (CNPq), grant #301184/2025-9 and #444408/2024-0; and Coordination for the Improvement of Higher Education Personnel (CAPES): Finance code 001.