Structure Properties of Gallic Acid-Enhanced Alginate Hydrogels for Sustainable Food Packaging as Plastic Replacement

Abstract

Structure properties of alginate and glycerol hydrogels (93:7 v/v) functionalized with gallic acid (0.1%, 0.5%, and 0.8%) (w/v) were evaluated as plastic alternatives for food packaging. A thorough characterization of these hydrogels was performed, evaluating their physico-mechanical, optical, and functional properties, particularly for potential applications in food packaging. FTIR analysis confirmed interactions between the hydrogel matrix and gallic acid, highlighting the formation of hydrogen bonds. The BET method and high-resolution scanning electron microscopy (HRSEM) further verified the homogeneity of the hydrogel surfaces. The inclusion of gallic acid led to increased thickness, permeability, and swelling capacity. However, ultimate tensile strength and fracture toughness significantly decreased, especially in hydrogels containing the highest gallic acid concentration (0.8%). Functionalized hydrogels exhibited enhanced antioxidant activity, as demonstrated by DPPH and FRAP assays. Hydrogels with 0.5% gallic acid showed a 4.4–4.8-fold increase in antioxidant activity, while those with 0.8% gallic acid achieved a 7.0–7.3-fold enhancement. The release of gallic acid from the hydrogels followed a dose-dependent pattern, with peak release occurring within 1–2 h. These findings suggest that alginate-based hydrogels functionalized with gallic acid offer a promising approach for the controlled release of bioactive compounds, presenting potential applications in innovative packaging solutions.