A pH indicator film based on dragon fruit peel pectin/cassava starch and cyanidin/alizarin for monitoring the freshness of pork

To detect the freshness of pork in real-time without damaging the testing sample, visual pH-sensing films were created containing cyanidin and alizarin as indicator labels. The film-forming matrices were made from dragon fruit peel pectin and cassava starch, with Fourier infrared spectroscopy analysis confirming successful immobilization of the natural dyes. Adding different concentrations of natural pigments did not noticeably affect the film's moisture content and solubility, water vapor permeability, or oxygen barrier properties. The colorimetric film responded sensitively to both ammonia (pH=11) and acidic (pH=2.4) environments, and was applied to pork stored at 4 ℃ based on the volatile salt nitrogen released from the meat. As the pork deteriorated, the color of colorimetric film varied from red to blue-black, allowing for accurate monitoring of freshness without opening the package and avoiding direct contact between indicator film and pork. Therefore, this colorimetric film has fantastic prospective as a perceptive packaging material for real-time non-destructive monitoring of meat product freshness.