Development of pH-responsive starch/CMC–anthocyanin film for non-contact monitoring of salmon

Real-time monitoring of food freshness is crucial for effective quality control and consumer safety, significantly enhanced through the development of intelligent films. This study incorporated butterfly pea flower anthocyanins (ATH) as a pH-sensitive indicator dye within a carboxymethylcellulose (CMC) and native corn starch (NS) matrix as an eco-friendly indicator. This study intended to explore the adjustment of film-forming solution pH to enhance film sensitivity. Addition of 10 g/hg CMC significantly improved films tensile strength. FTIR confirmed successful integration of CMC and ATH with starch, while SEM images showed a uniform structure. ΔE values remained within 4–5 when stored in transparent containers at room temperature for 15 months, confirming the film’s long-term color stability and suitability for industrial storage before application. Ammonia sensitivity tests showed that 3 g/hg ATH addition to film enabled clear detection of freshness-related pH changes, while acidic pH adjustment (C10S3A(A)) further extended the detection range. During salmon storage, C10S3A(N) exhibited a blue-to-teal shift indicating fresh to spoiled states, whereas C10S3A(A) showed gradual color transitions from pink to purple then navy, reflecting intermediate spoilage stages. These results suggest that the developed film offers a promising tool for real-time freshness monitoring and quality control across food supply chains. • CMC improved starch film strength and provided an eco-friendly matrix. • Butterfly pea flower anthocyanin enabled pH-responsive color changes to composite film. • Color stability for 15 months at room temp ensure industrial storage stability. • pH changes of the film forming solution enhanced responsiveness and color transition. • Film color variation correlated with TVB-N, indicating fish freshness.