Dual-functional smart indicator for direct monitoring fruit freshness

Innovative smart packaging systems that inhibit bacterial growth and monitor food quality change are urgently needed in food industry. A dual-functional polyvinyl alcohol/polyethyleneimine/methylene blue (PVA/PEI/MB) nanofiber film was prepared for inhibiting bacterial growth and monitoring freshness of fruit. The nanofibers exhibited excellent mechanical property, breathability, water resistance and biocompatibility as characterized by the tensile test, air permeability test, water contact angle and cytotoxicity experiment. In vitro antibacterial experiment showed that the nanofibers had strong antibacterial activities against Escherichia coli and Staphylococcus aureus, and the antibacterial activities were improved under light irradiation. Nanofibers showed color variation from blue to colorless under bacterial infection in a range of 101–1010 CFU/mL, which can be used to detect the freshness of fresh-cut fruit. Effectiveness of nanofibers for freshness keeping and monitoring was confirmed via fruit tests, which suggests that the dual-functional nanofibers could potentially be used in food packaging.