Research Progress on natural pigment-based pH-responsive intelligent packaging materials in food applications

Natural pigment-based pH-responsive intelligent packaging offers a promising alternative for real-time food quality monitoring. This review systematically summarizes recent progress in natural pH-sensitive indicators, focusing on anthocyanins, curcumin, betalains, and chlorophylls. We analyze their molecular color-changing mechanisms, including flavylium cation transformations, keto-enol tautomerism, and demetallation. To overcome limitations such as instability and narrow response ranges, advanced enhancement strategies are highlighted, integrating nanotechnology (e.g., quantum dots, nanocellulose), synergistic co-pigmentation, and molecularly imprinted polymers (MIPs). Furthermore, the practical applications of these intelligent films in monitoring aquatic and meat freshness are evaluated, alongside a performance comparison across various polymer matrices. Finally, current limitations concerning food-contact safety, response standardization, regulatory compliance, and practical translation are discussed, and application-oriented recommendations are proposed for future research and industrial development. By comparatively linking the molecular response mechanisms and color-response reversibility of natural pigments with functional matrix design, target food-spoilage scenarios, and practical application constraints, this review provides an integrated perspective for the rational design and selection of pH-responsive intelligent food packaging materials.