FoodSmarTag: An innovative dynamic labeling system based on pyranoflavylium-based colorimetric films for real-time monitoring of food freshness

A colorimetric pyranoflavylium-based pH-indicator with an improved formulation was obtained and studied as an intelligent label for food freshness monitoring. Pyranoflavylium pigment at 0.2% (w/w) and glycerol at 30% (w/w) were immobilized in a cellulose acetate matrix, and a thin film was obtained by the solvent casting method. The pH-responsive properties of the film were evaluated in solutions at different pH values (pH 4 to 8) and compared with a previous formulation. Film photostability and pigment migration over time were assessed. The label's performance was evaluated using real samples (fish and meat) at controlled conditions (3 °C and modified atmosphere packaging). The results showed that increased pigment concentration visually favored its colorimetric efficacy. Regarding pigment migration and photostability, the label showed to be suitable for application in fresh meat and fish packaging. The best performance was observed for the freshness monitoring of fish samples. The indicator demonstrated high efficacy in detecting spoilage of Atlantic horse mackerel (Trachurus trachurus). After 5 days of storage, freshness parameters exceeded the limit defined by EU regulations, indicating that the fish was unfit for consumption. Simultaneously, the yellow label started to turn purple, effectively indicating the beginning of the spoilage process.