Active Polymers Containing Silver Nanoparticles Combined With Formulations Based on Essential Oils: Quality Effect on Cereals and Dairy Products

Bioactive nanocomposite diffusion films containing plant essential oils (EOs) and silver nanoparticles (AgNPs) were fabricated and tested against foodborne pathogens, spoilage organisms, and insects in packaged foods. Films were based on chitosan (CH), poly(butylene adipate-co-terephthalate) (PBAT), and polylactic acid (PLA), containing cellulose nanocrystals (CNCs), plasticizers such as glycerol (Gly) or polyethylene glycol (PEG), and three active mixtures of EOs/AgNPs (AC-1, AC-2, or AC-3). Films were characterized by their mechanical properties, water solubility (WS), water vapor permeability (WVP), in vitro antibacterial/antifungal and insecticidal properties, and release kinetics in food simulants. PBAT and PLA films displayed higher barrier properties, and no solubility compared to CH films. Bioactive CH and PBAT films showed stronger antibacterial/antifungal, and insecticidal properties against Escherichia coli O157:H7, Salmonella Typhimurium, Aspergillus niger, Penicillium chrysogenum, Mucor circinelloides, and rice weevil Sitophilus oryzae, compared to bioactive PLA film. Challenge tests were conducted on rice and yogurt inoculated with selected bacteria and fungi by applying the diffusion films. Rice was treated with bioactive CH and PBAT films, in combination with gamma (γ)-irradiation (0.75 kGy) and stored for 8 weeks. Yogurt was treated with PBAT and PLA films for 8 weeks. Results showed that bioactive films significantly reduced the growth of bacteria/fungi in both food samples. The growth of insects inoculated in rice treated with bioactive films in combination with irradiation (0.1-0.3 kGy) was controlled from the first week of storage. A combined treatment of irradiation at 3 kGy with bioactive films increased significantly the insect mortality up to 96%-100%, from Day 7 to 14 compared to treatment with bioactive films alone. PRACTICAL APPLICATIONS: Nanocomposite bioactive diffusion films developed in this study could be applied as diffusion devices of active natural compounds not only for the control of bacteria/fungi and pest insects in packaged rice (with a possible combined treatment with γ-irradiation), but also for that of bacteria/fungi in yogurt. The active formulations could be used in the food industry for controlling insect proliferation in the sector of stored cereals but also to prevent bacterial and fungal contamination in cereals and dairy products such as yogurts and their derived products.