A pH-indicating smart tag based on porous hydrogel as food freshness sensors

The pH-indicating smart packaging and tags are identified within the general research and pH colorimetric smart tags are effective, non-invasive methods for indicating food freshness on a real-time basis, but their sensitivity is limited.In Herin, we developed a porous hydrogel with high sensitivity, water content, modulus, and safety. Hydrogels were prepared with gellan gum, starch, and anthocyanin. The phase separations provide an adjustable porous structure, which can enhance the capture and transformation of gas from food spoilage, hence improving the sensitivity. Hydrogel is physically crosslinked by the entanglement of chains through freeze-thawing cycles, and porosity can be adjusted by the addition of starch, so avoiding the use of toxicity crosslinkers and porogen.Our study demonstrates that the gel undergoes an obvious color shift during the spoilage of milk and shrimp, revealing its potential application as a smart tag signaling food freshness.