Freshness Traffic Light for Fish Products: Dual-Optode Label to Monitor Fish Spoilage in Sales Packages

Freshness and safety of fish products alongside the supply chain, from the harvest to the final consumers, represent an increasing concern due to the perishability of these foods. Therefore, there is an urgent need for low-cost, reliable, and easy-to-read devices to monitor fish products' freshness, directly implemented on sales packages. The here presented device consists of two colorimetric sensor units, in which a pH indicator, o-cresol red, is covalently bound to a plastic support, ethylene vinyl alcohol, and equilibrated at different pHs. The dual-optode label works as a freshness traffic light that turns color according to the spoilage byproducts and, thus, the real freshness. The naked-eye readout and the chemometric-assisted spoilage modeling are demonstrated and validated for a panel of fish products, simulating distribution and domestic storage conditions. The sensing performances and the versatility make this dual-optode label an interesting candidate to be implemented as smart labels in packed fish products.