Bilayer pH-responsive film based on pineapple stem starch and anthocyanin extracts with improved stability for intelligent freshness monitoring of meat products

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A biodegradable bilayer hydrocolloid film was developed from pineapple stem starch (PSS) and anthocyanin extracts from agricultural waste for intelligent freshness monitoring of meat products. The bilayer comprised an anthocyanin-rich indicator layer and a moisture-resistant PSS barrier, improving color stability under high-humidity conditions commonly encountered in food packaging. Interactions between anthocyanins and PSS hydroxyl groups, together with the protective PSS barrier layer, contributed to improved moisture resistance, reducing color release after 30 min of immersion from approximately 89% in the single-layer film to approximately 29–31% in bilayer films. The bilayer films also exhibited comparable thermal stability, with ΔE values remaining below 2.2 after storage at 60 °C for 24 h. The system exhibited rapid and distinct color changes across a wide pH range (2−12) and responded to ammonia vapor within 5 min, closely reflecting spoilage-related biochemical changes. Application studies in pork packaging demonstrated distinct visual color transitions that were consistent with freshness deterioration. In addition to its sensing capability, the film exhibited antioxidant and antimicrobial activities, supporting its role as an active packaging material. These findings highlight the potential of the developed bilayer film as a sustainable and practical intelligent packaging system for freshness monitoring of meat products.