Naked-Eye Food Freshness Detection: Innovative Polymeric Optode for High-Protein Food Spoilage Monitoring

An innovative smart label for naked-eye protein food freshness evaluation, based on polymeric sensing films, is presented. The proposed device consists of six miniaturized sensors, obtained by covalently binding six pH indicators, namely, mcresol purple (1), o-cresol red (2), bromothymol blue (3), thymol blue (4), chlorophenol red (5), and bromophenol blue (6), to an ethylene vinyl alcohol (EVOH) copolymer. All of the synthetic procedures for the functionalized polymers and their application as smart labels are thoroughly described and discussed. The innovative sensors are characterized using several instrumental techniques (DSC, FT-IR, EDX, SEM, and UV−vis). The application of the array of sensors to poultry meat and cod fillet spoilage monitoring by naked-eye evaluation and modeling by PCA is presented. Eventually, the composition of the food and the food’s headspace in the selling tray is investigated and qualitatively characterized to validate the attributes of the array of sensors. The polymeric devices seem to be very promising for industrial scale-up, with the starting EVOH copolymer being extrudable and already employed in food packaging, as well as for large-scale application, being clear, efficient, and easy to read, even by untrained people.