Preparation and characterisation of pH‐responsive indicator ink for pork freshness monitoring

This study developed an intelligent indicator ink based on purple potato anthocyanin to detect the freshness of pork. The ink was composed of waterborne acrylic resin as a binder, with added additives such as dimethyl silicone oil, sodium polyacrylate and ethanol to improve its performance. Testing was conducted on the initial drying, viscosity, fineness, fluidity and stability of the ink, and all performance criteria met the requirements. Gradient solutions with pH 2–12 were dropped onto the ink to test their discoloration ability, which exhibited significant changes in colour with the difference in pH solutions. The indicator ink was applied to monitor the freshness of pork. After 7 days of storage at 4°C, the total volatile basic nitrogen content of the pork was higher than 25 mg/100 g, and the total number of bacteria was >9 log(CFU/g), indicating that the pork had gone rotten. The colour of the indicator ink shifted from purple to purplish blue and ultimately became deep blue. The results showed that the indicator ink provided an effective colour response in the process of pork deterioration, allowing for visual detection of its freshness.