Multiscale protection of anthocyanin via zein/cinnamaldehyde/sodium alginate core-shell nanoparticles enable UV-stabilized colorimetric label for monitoring shrimp and fish freshness.

Anthocyanin-based pH-responsive indicators are promising for food freshness monitoring, but UV exposure during transportation and retail display causes chromophore degradation and fading. Herein, core-shell sodium alginate/cinnamaldehyde/zein/anthocyanin nanoparticles (SCZC) were fabricated via a multiscale protection strategy. Anthocyanins were confined in a hydrophobic zein core through hydrophobic and π-π interactions, while cinnamaldehyde-assisted interfacial densification and a sodium alginate shell provided diffusion barriers against external stresses. After incorporation into a carboxymethyl cellulose (CMC) matrix, the CMC film containing 0.4 g SCZC nanoparticles (C/SCZC-0.4) exhibited improved UV and visible-light stability, with ΔEab values of only 5.21 after 4 h of UV irradiation and 5.22 after 8 days of visible-light exposure. Compared with the free-anthocyanin CMC film (C/C), C/SCZC-0.4 reduced anthocyanin migration in water from 84.34% to 35.65%, while improving oxygen barrier performance and tensile strength to 2.32 cm3·μm·m-2·day-1·kPa-1 and 30.0 MPa. The label retained pH/ammonia responsiveness and visually distinguished seafood freshness.