Research Progress of pH-Responsive Indicator Films for Real-Time Food Quality Monitoring

Facing global food waste and safety challenges, real-time nondestructive quality monitoring via intelligent packaging has gained substantial interest. This narrative review critically examines the progress of pH-responsive freshness indicator films, with a particular emphasis on their application to meat and meat products, and emphasizes the transition from empirical exploration toward rational design. Methodologically, we synthesize recent advances in natural pigment-based indicators, focusing on their fabrication strategies (micro/nanoencapsulation, metal-organic framework immobilization, pigment blending, and matrix engineering) and performance evaluation models integrating multivariate statistical tools (principal component analysis, cluster analysis, and discriminant analysis). The results reveal that replacing synthetic dyes with anthocyanins and betalains significantly mitigates the inherent toxicity risks, while advanced immobilization and blending strategies substantially overcome poor stability and high dye migration, achieving synergistic improvements in sensitivity, anti-interference, and mechanical durability. Furthermore, establishing a comprehensive evaluation framework linking total volatile basic nitrogen accumulation to color-change thresholds is crucial for accurate interpretation. We conclude that the field is shifting from single-function validation toward multi-signal responsiveness, digital integration, and systematic implementation. It should be noted, however, that the colorimetric response of these indicators reflects quality attributes such as TVB-N accumulation rather than the presence of pathogens or toxins; therefore, these indicators cannot independently establish food safety. Future breakthroughs require addressing environmental robustness, long-term reliability, standardized evaluation protocols, and scalable cost-effective production to facilitate the transition from laboratory research to practical supply chain deployment.