pH-responsive colorimetric indicator films based on plasma-modified starch/PVA incorporating ovalbumin-sodium alginate-coated γ-cyclodextrin-MOF nanocomposites for salmon freshness monitoring.

Carbohydrate-polymer-based colorimetric films offer a sustainable platform for food freshness monitoring, but natural indicators often suffer from poor stability and premature migration. Here, a pH-responsive colorimetric indicator film was developed by loading anthocyanins (ACNs) into γ-cyclodextrin metal-organic frameworks (γ-CD-MOFs), coating them with an ovalbumin-sodium alginate (OVA-SA) shell, and embedding the nanocomposites in a plasma-modified corn starch/polyvinyl alcohol (PCS-PVA) matrix. The γ-CD-MOFs served as porous hosts for ACN confinement, while the OVA-SA shell helped regulate pigment release and access of alkaline volatiles. Molecular modeling and pore analysis suggested that ACNs could be accommodated within γ-CD-MOF cavities through size matching and noncovalent interactions. The resulting film showed 74.8% DPPH radical-scavenging activity, reduced ACN release, biodegradability, cytocompatibility, and clear pH/ammonia responsiveness. During salmon storage, film color evolution correlated strongly with total volatile basic nitrogen. EfficientNet-B0 achieved 96.7% classification accuracy under controlled laboratory conditions, and its generalizability to real-world applications remains to be externally validated. The structure-property results indicated that the carbohydrate-derived host framework and polysaccharide-containing shell jointly improved pigment confinement, interfacial compatibility, and colorimetric sensing performance. This work provides a carbohydrate-polymer strategy for stabilizing natural pigments and constructing freshness indicator films.