A novel lactic acid bacteria-based smart label for irreversible time-temperature monitoring in perishable foods: milk as a model system.

Time-temperature abuse during storage and distribution compromises the safety and quality of perishable foods, particularly pasteurised milk, by accelerating microbial spoilage and reducing shelf life. A biodegradable, low-cost lactic acid bacterium-based smart label was developed for real-time monitoring of spoilage. The label was fabricated by entrapping Lactiplantibacillus plantarum isolated from kimchi in an MRS agar matrix containing glucose and phenol red, enabling fermentation-driven acidification and irreversible colour change. The smart label showed temperature-dependent behaviour, with no colour change at - 20 °C for 28 d, complete yellowing after 7 d at 4 °C, and rapid colour change within 12 h at 25 °C. When applied to pasteurised milk under temperature abuse, it distinguished safe from spoiled products, with colour intensity strongly correlated with microbial growth (ρ = 0.88, p = 0.01). The system provides a biodegradable tool for real-time monitoring in resource-limited settings.