A novel curcumin-based bilayer indicator film for freshness evaluation of shrimp with excellent mechanical properties and moisture resistance

Curcumin-based smart films have gained widespread attention in the packaging field due to their convenience, ease of use, and environmental sustainability. However, its poor pH response, unsatisfactory mechanical properties , and limited moisture resistance severely restrict its applications. In this study, we prepared a curcumin-based bilayer indicator film with a protective layer consisting of gelatin, carboxymethyl cellulose , and hexadecyl trimethoxy silane to provide mechanical protection and moisture resistance, and an indicator layer consisting of gelatin, curcumin, and malvidin to improve the pH sensitivity of the curcumin-based film and broaden the range of color indication. Owing to the hydrophobic effect of the protective layer and cross-linking between the bilayers, the curcumin-based bilayer film exhibited excellent mechanical properties with a stress of 15.3 MPa, a strain of 101.6 %, and a Young's modulus of 38.9 MPa. The moisture resistance of the film was also improved, with a water vapor permeability as low as 1.11 ± 0.15 × 10 −10  g m m −2  Pa −1  s −1 . In addition, with the addition of malvidin, the curcumin-based bilayer film showed greater sensitivity to pH and more pronounced color changes compared to the gelatin/curcumin film for practical applications in monitoring shrimp freshness. Overall, this study demonstrated the applicability of the prepared curcumin-based bilayer indicator film for monitoring shrimp freshness and also broadened the prospects of curcumin-based films in the field of smart packaging.