Minimum Integrated Functional Concentration (MIFC), unifying photocatalytic and antimicrobial modes in a...

The global problem of postharvest spoilage of fresh fruit is a significant issue, with the postharvest spoilage of perishable fruit due to microbial decay resulting in as much as 40% of total losses in developing parts of the world. One potential solution to this issue is active packaging; however, to date, a single-component integrated system with simultaneous visible light photocatalytic self-cleaning and dark-phase antimicrobial protection design has not been developed and independently tested in real-world applications. This study presents the first report of the Minimum Integrated Functional Concentration (MIFC) in LDPE/ZnO:Cu,Si nanocomposites exhibiting dual-mode functionality. The functional performance of Cu/Si-co-doped ZnO nanoparticles incorporated into LDPE via melt-blending was evaluated against CuO and Fe₂O₃ benchmarked test materials. The 5 wt% formulation of ZnO demonstrated superior performance to CuO (78.24%) and Fe₂O₃ (73.96%) by exhibiting 94.76% degradation of methylene blue exposed to 90 min of visible light compared to their results (p < 0.05). The reaction followed pseudo-first-order kinetics (R² = 0.992) and resulted in an apparent rate constant of 0.0179 min⁻¹, which is 2.7 times greater than that of the 1 wt% ZnO material. At the same time, the material resulted in ≥ 83% microbial reduction in the dark after 90 min of exposure, with differential percent microbial reductions exhibited against the three different test microorganisms tested: S. aureus (88.1%) > E. coli (83.3%) > Penicillium spp. (66.7%). The 5 wt% LDPE/ZnO:Cu,Si nanocomposite was successfully applied to naturally contaminated citrus stored at 25 ± 2°C for the purpose of extending their shelf-life from 16 to 32 days (100% increase) and suppressing Penicillium fungal growth by 92.2% on day 20 post-application. By analysing the mechanism, it was determined that •OH was the primary reactive species (58% contribution). The activation energy was found to be 18.2 kJ·mol⁻¹, supporting the use of this material at ambient temperatures. As such, the results demonstrate that 5 wt% ZnO:Cu, Si may be used for GRAS-compliant, scalable production of active food packaging that is effective and has regulatory approval.