The construction of hierarchically structural cotton staple fiber/chitosan cryogel label loaded with anthocyanin for monitoring fish freshness.

There is a growing need for environmentally friendly freshness indicator packaging made from bio-based materials. Herein, a new kind of freshness indicator label with hierarchical structures was developed using cotton staple fiber (CF) as the skeleton, chitosan (CS) as the polymeric matrix and binder, and mulberry anthocyanin (MA) as the pH-sensitive pigment, via simple solution casting and freeze-drying methods. The contents of CF and CS significantly influenced the structures and physicochemical properties of the CF/CS cryogel labels, such as thickness, density, porosity, mechanical strength, colorimetric response, MA release, and color stability. The optimal 1.0CF/1.0CS cryogel label, which exhibits excellent flexibility, high porosity (97.80%), good sensitivity to ammonia, low anthocyanin migration (53.8%), and color stability (ΔE < 5), was used to monitor the freshness of channel catfish at 4 °C. The color changed as follows: red (fresh: TVB-N < 10 mg/100 g) → dark red (sub-fresh) → gray-black (spoiled: TVC > 7 log CFU/g or TVB-N > 20 mg/100 g). The strong correlation between the ΔE of the cryogel label and the TVC (R2 = 0.9402) and TVB-N (R2 = 0.9575) of channel catfish verified its great potential for real-time monitoring of aquatic product freshness. Compared with conventional dense film-based indicators or synthetic dye systems, this cryogel label offers superior sensitivity due to its interconnected macroporous structure and ensures enhanced food safety by utilizing fully bio-based, non-toxic components. This work provides a cost-effective and reliable strategy for the structural design of intelligent packaging.