Bougainvillea glabra extract-loaded elephant foot yam starch–polyvinyl alcohol blend films as pH-indicators for monitoring milk freshness

This study reports the development of a biodegradable, pH-responsive starch–polyvinyl alcohol blend-based film for real-time monitoring of milk freshness. The film was fabricated using dual-modified elephant foot yam starch (MEFYS) and polyvinyl alcohol (PVA), incorporated with 2 %, 4 %, and 6 % betacyanin-rich Bougainvillea glabra extract (BGE). The extract exhibited a high betacyanin content (126.83 mg/g dry weight) and strong antioxidant activity (FRAP: 124.54 μmol Fe2+/g; ABTS inhibition: 17.18 %). Among the formulations, the BGE6/MEFYS-PVA film exhibited the best performance, with a tensile strength of 16.72 MPa and an elongation at break of 21.02 %. Although it exhibited a slightly higher water vapor transmission rate (15.3 g·m−2·h−1), and its water vapor permeability decreased (1.16 × 10−10 g·m−1·s−1·Pa−1) due to dense hydrogen bonding. FE-SEM analysis revealed a compact microstructure, while XRD and FTIR analyses indicated decreased crystallinity and strong interactions between starch and phenolic compounds. Thermal stability also improved, with peak degradation at 288 °C. The MEFYS–PVA blend-based films demonstrated antimicrobial activity (inhibition zones up to 19.38 mm) and distinct colorimetric changes (∆E = 20.01) that correlated with milk spoilage, including a pH drop (6.8 to 4.0) and microbial growth (3.2 to 8.2 log10 CFU/mL). This is the first report to integrate MEFYS and BGE into a smart film matrix, resulting in a material with enhanced physical and functional properties. Overall, the developed MEFYS–PVA blend-based films provides an eco-friendly and effective approach for real-time monitoring of milk freshness in dairy products.