Abstract: To achieve the real-time and non-destructive monitoring of meat freshness, a series of indicator labels with different pH values adjusted by citric acid were developed using potato oxidized hydroxypropyl starch (POHS) and high-methoxyl pectin (HMP) as the composite matrix and a Lonicera caerulea anthocyanin-Fe2+ complex as the indicator system. The color response behavior of the indicator labels under different pH conditions and their sensitivity to ammonia vapor, thermal stability, storage stability, microstructure, and molecular interactions were systematically investigated. The indicator labels were further applied to monitor the freshness of minced pork during storage at 4 ℃. The results showed that the label prepared at pH 2.5 (PPB-2.5) exhibited an obvious color change from red to purple within the pH range of 6–8. It responded rapidly and sensitively to ammonia and maintained good color stability during 30 days of storage (ΔE < 5). In addition, the indicator label showed good thermal stability and a compact microstructure, while the crosslinking effect of citric acid enhanced intermolecular interactions within the matrix. In practical application, the color change of the PPB-2.5 label was significantly correlated with the total volatile basic nitrogen (TVB-N) content, pH, and mass loss of minced pork (P < 0.05), indicating that the label could visually reflect three quality classes: fresh, semi-fresh and spoiled. This study provides a technical reference for developing highly sensitive and stable intelligent indicator materials for meat packaging.

Key words: intelligent indicator; anthocyanin-Fe2+ complex; pH optimization; freshness; minced pork