Tannic Acid-Coated Cellulose Nanocrystals Reinforced Robust Antimicrobial Hydrogel Colorimetric Sensor for Monitoring Tuna Freshness

Abstract Tuna is valued for its nutritional benefits, but significant waste occurs due to inaccurate shelf life estimations. Herein, we developed a multifunctional, mechanically robust, and highly sensitive visual-sensing hydrogel tailored for real-time tuna freshness monitoring. The system is constructed from a sodium alginate/polyacrylamide matrix reinforced with tannic acid-coated cellulose nanocrystals. This structural design endows the hydrogel with exceptional stretchability, toughness, antifatigue properties, and tear resistance, successfully overcoming the mechanical fragility of traditional hydrogels. Furthermore, the catechol groups from tannic acid provide reliable multisubstrate adhesiveness, alongside intrinsic antioxidant and highly effective antimicrobial activities against Candida albicans and Staphylococcus aureus, ensuring the hygienic stability of the sensor in packaging environments. For visual freshness detection, a pH/NH3 dual-responsive thymol blue was embedded into the matrix. The hydrogel indicator successfully tracked yellowfin tuna spoilage at both 4 and 25 °C, delivering distinct visual color changes (ΔE > 50). These color transitions exhibited strong linear correlations (R2 > 0.97) with key freshness indicators, including ΔE vs pH, ΔE vs TVB-N, and TVB-N vs pH. This work presents a highly durable and accurate intelligent packaging material for visual freshness monitoring, offering a promising strategy to improve food safety and reduce waste in the seafood industry.