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.