Facile in situ synthesis of ZnO-infused caseinate/carboxymethyl cellulose films with antibacterial properties for cheddar cheese packaging

• In situ synthesis of ZnO in NaCas-CMC matrix using thymol was developed. • Enhanced UV-blocking, water resistance, and antimicrobial properties were achieved. • Significant inhibition of L. monocytogenes on cheddar cheese by the Zn-infused film. • ZnO-infused film extended cheese shelf-life up to 20 days under refrigerated storage. • Green, surfactant-free method for sustainable active packaging holds promising applications in food safety. This study presents a green, one-step approach for the in situ synthesis of zinc oxide (ZnO) particles within a sodium caseinate (NaCas) and carboxymethyl cellulose (CMC) matrix, with functionality enhanced by thymol essential oil. Acting as a natural reducing agent, thymol facilitated ZnO synthesis within the NaCas-CMC matrix. The film prepared with 300 mg zinc nitrate and 100 mg thymol essential oil had a low swelling rate due to in situ ZnO formation, which regulated the microstructure and enhanced hydrophobicity. The ZnO-infused NaCas-CMC biocomposite films exhibited enhanced UV shielding and water resistance, attributed to the uniform dispersion of ZnO particles and their synergistic interaction with thymol. Antibacterial assays demonstrated strong inhibitory effects against key foodborne pathogens, including Listeria monocytogenes ( L. monocytogenes ) and Escherichia coli K-12 ( E. coli K-12). When applied to cheddar cheese, the films significantly suppressed microbial growth and effectively prevented external contamination, maintaining product safety over 20 days of refrigerated storage. Overall, this research highlights the potential of a green synthesis approach to develop multifunctional packaging films that enhance food safety while supporting sustainable practices, offering a promising alternative to conventional food packaging materials. Notably, this is the first report to describe the in situ synthesis of ZnO within a self-assembled caseinate film containing thymol essential oil, employing a surfactant-free and environmentally friendly processing method.