Development of a dual-layer collagen film with insulating, antioxidant, antimicrobial, and pH-sensitive properties for the maintenance and visual monitoring of shrimp freshness

Accurate temperature control during food transportation is essential, as temperature fluctuations can accelerate bacterial proliferation and fat rancidity. Optimal packaging strategies should, therefore, minimize temperature variability in stored food whilst proactively inhibiting microbial growth, delaying fat rancidity, and enabling real-time freshness monitoring. In this study, a multifunctional bilayer collagen film (COL-OPCD) was prepared by a layer-by-layer deposition technique, consisting of an inner layer with antimicrobial, antioxidant, and pH-sensitive properties (oxidized bilberry extract/Pickering emulsion/collagen) and an outer thermally insulating layer (citric acid-diatomite, CD/collagen). The COL-OPCD film exhibited excellent thermal insulation (thermal diffusivity, 0.131 mm 2 /s; reflectivity, 64.71%), antioxidant activity (DPPH radical scavenging, 91.83%; ABTS radical scavenging, 99.73%), and antibacterial activity ( Escherichia coli inhibition rate, 90.07%; Staphylococcus aureus inhibition rate, 87.09%), and allowed real-time monitoring of freshness through visible color changes. It should be emphasized that due to the favorable protection provided by the insulated outer layer, temperature fluctuations inside the package were minimized, with a maximum temperature of 4.80 °C lower than that of the control group, preserving the antioxidant, antimicrobial, and pH-responsive properties of the inner film under high-temperature conditions. An assessment of shrimp preservation at 37 °C showed that the COL-OPCD film not only retarded temperature fluctuations in the packaging shrimp but also extended the shrimp shelf life (9 h) and monitored shrimp freshness in real-time.