Ammonia-Responsive Gelatin/Co–MOF Composite Films Based on Gallic Acid-Derived Metal–Organic Frameworks for Intelligent Food Packaging

Ammonia-responsive gelatin-based composite films containing cobalt metal–organic frameworks (Co–MOFs) synthesized using gallic acid as an organic ligand were developed and evaluated as intelligent packaging materials. Co–MOFs were incorporated into gelatin films at concentrations of 2.5, 5.0, 7.5, and 10.0% (w/w, based on gelatin). The effects of Co–MOF incorporation on the physicochemical, structural, thermal, mechanical, and sensing properties of gelatin films were systematically investigated. Increasing Co–MOF content reduced film moisture content (from 14.47 to 13.25–13.58%) and swelling capacity (from 599.37 to 484.88–547.30%), while increasing solubility (from 39.09 to 48.88%), water vapor permeability (WVP; from 1.652 to 2.054 g·mm/m2·h·kPa), and moisture sorption behavior. Sorption isotherm analyses based on the Guggenheim–Anderson–de Boer (GAB) and Brunauer–Emmett–Teller (BET) models confirmed enhanced water adsorption capacity and increased specific surface area in the films (from 356.13 to 455.74 m2/g). Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and differential scanning calorimetry (DSC) analyses demonstrated successful incorporation of Co–MOFs into the gelatin matrix, revealing good dispersion at low and moderate concentrations and partial aggregation at higher loadings. The incorporation of Co–MOFs improved the thermal stability of the films, while only a moderate reduction in mechanical strength was observed with increasing filler content. The composite films exhibited rapid and concentration-dependent colorimetric responses toward ammonia vapor. After 120 min of exposure, the color difference (ΔE) increased from less than 1 in the control film to approximately 12, 15, 24, and 27 for G/Co–MOF2.5, G/Co–MOF5, G/Co–MOF7.5, and G/Co–MOF10 films, respectively. Films containing higher amounts of Co–MOF showed faster response kinetics and greater color differences, enabling clear visual detection of ammonia. These findings demonstrate that gelatin/Co–MOF composite films based on gallic acid-derived metal–organic frameworks are promising intelligent packaging materials for monitoring food freshness and spoilage through ammonia detection.