Humidity-stable carboxymethyl cellulose/anthocyanin films enabled by ovalbumin/sodium alginate nanocarriers and Al3+-mediated crosslinking for food freshness monitoring.

Owing to the film-forming property and biodegradability of polysaccharide matrices, carboxymethyl cellulose (CMC) is commonly used to fabricate bio-based pH-responsive films containing blueberry anthocyanins (BA). However, CMC inevitably absorbs moisture, readily triggering BA migration and reducing film color stability. Herein, we propose a hierarchical "framework-enhancement-confinement" strategy in which a flexible CMC-polyvinyl alcohol (PVA) framework is densified by Al3+-mediated crosslinking, while BA is confined within ovalbumin‑sodium alginate (OVA-SA) microdomains (OS) and the OS-matrix junction is concurrently stabilized to form a compact metal-polymer barrier. The resulting CMC/PVA/BA@OS/Al3+ (CP-BA@OS3-Al3+) film exhibits low moisture content (12.8 ± 0.24%), low water solubility (27.60 ± 0.74%), and moderate swelling index (70 ± 3.20%), effectively suppressing BA loss while achieving stable color evolution in 5-day pork monitoring. By establishing this multilevel structural regulation strategy, the limitation of bio-based pH-responsive films in high-humidity scenarios is overcome, expanding their practical application in intelligent packaging.