Smart Indicator for Fish Freshness Monitoring: A Chitosan/Gelatin/Zinc Oxide Nanoparticle Composite Incorporating Pomegranate Flower Anthocyanin Extract Nanocapsules

Abstract

This study aimed to develop a smart film for monitoring pH changes, utilizing chitosan/gelatin/nano zinc oxide (ZnO) enhanced with nanocapsules of pomegranate flower extract (PFEN). PFEN were prepared via spray drying with a maltodextrin-Arabic gum coating. The resulting chitosan/gelatin films were modified with nano ZnO (1%) and varying PFEN concentrations (1%, 2%, and 3%). The physicochemical, mechanical, optical, barrier, structural, crystallinity, thermal stability, antioxidant, and antibacterial properties of the films were comprehensively evaluated. The colorimetric response of the smart films to pH changes, anthocyanin release, and the film's potential for indicating fish freshness were also assessed. Incorporation of PFEN significantly enhanced water vapor barrier (from 6.37 to 2.94 × 10⁻¹¹ g m/m² day), tensile strength (by ~20%), and antioxidant activity (DPPH scavenging up to 78.9%) (p < 0.05). FTIR spectroscopy confirmed the compatibility of polymers and additives. SEM imaging revealed that the addition of PFEN increased film surface roughness. Films containing PFEN exhibited a clear color response to varying pH levels. The films exhibited distinct pH-dependent color changes (ΔE), correlating with increasing TVB-N values in trout fillets stored at 4°C, indicating effective freshness monitoring. The enhanced mechanical, antioxidant, and antimicrobial properties suggest that these films are suitable for use as active packaging to extend the shelf life of meat products.