Zein–Curcumin Composite Edible Films for Intelligent Packaging: A Natural pH-Sensing Indicator to Monitor Sea Bream Freshness
Burcu Demirtas, Beyza Keser, Serpil Tural, Latife Betül Gül, Ilay Yilmaz, Mahmut Ekrem Parlak, Ayşe Neslihan Dündar, Maria D’Elia, Luca Rastrelli, Furkan Türker Sarıcaoğlu
Abstract
This study developed and characterized zein-based edible films enriched with curcumin as natural pH-sensitive indicators for monitoring fish freshness. Colorimetric films were prepared with different curcumin concentrations (1–7% wt) and evaluated for physicochemical, mechanical, optical, and antioxidant properties. Increasing curcumin content reduced water vapor permeability (0.085–0.110 g·mm/m2·h·kPa), lowered water contact angles (<90°), and enhanced hydrophilicity. Films exhibited high brightness, with decreased a* and increased b* values, while light transmission decreased, improving UV barrier properties. Colorimetric response (ΔE*) across pH 3–10 was more pronounced at higher curcumin levels, confirming pH-sensitivity. Antioxidant activity significantly increased with curcumin loading (up to 24.18 µmol Trolox/g). Mechanical analysis revealed decreased tensile strength but improved elongation at break, bursting strength, and deformation, supported by SEM images showing more homogeneous, micro-porous structures at 7% curcumin. Zein films containing 7% (wt) curcumin (Z/CR7) were applied to gilthead sea bream (Sparus aurata) fillets stored at 4 °C for 13 days. Results showed lower TBARS and TVB-N values in Z/CR7 compared to the control, indicating delayed lipid oxidation and spoilage. Colorimetric changes in the films corresponded with fish freshness deterioration, providing a clear visual indicator. Microbiological results supported chemical findings, though antimicrobial effects were limited. Curcumin-enriched zein films demonstrated strong potential as intelligent, biodegradable packaging for real-time monitoring of seafood quality.