Influence of annealing and crosslinking on release properties of gallic acid from polyvinyl alcohol-based films for packaging applications

Polyvinyl alcohol (PVA) coatings are a sustainable and eco-friendly solution that offers excellent oxygen barrier properties and is safe for food contact packaging materials and can be formulated to actively protect food. To improve film performances of PVA-based films, gallic acid can be incorporated as an antioxidant and antimicrobial agent. However, PVA is sensitive to water that alters most of functional properties that could be mitigated using crosslinking with natural food grade acids combined with annealing. This study aimed to investigate the effects of crosslinking and annealing on the antioxidant properties and release behaviour of gallic acid. Films based on PVA, cross-linker and gallic acid as antioxidant were obtained from casting the film-forming solution and dried, prior being annealed. ATR-FTIR spectra were analysed to confirm chemical structure changes such as the crosslinking. Mechanical and oxygen-barrier properties were determined as functional and applicative properties of PVA films for food packaging. Crosslinking has been demonstrated to enhance the mechanical properties of the films whilst concomitantly reducing the water sensitivity of oxygen transfers. Kinetics of release of gallic acid were conducted in food simulant mimicking aqueous-lipidic foods. From the experimental kinetics, the apparent diffusion coefficient of the antioxidant has been modelled. Almost 100 % of gallic acid is released from the non-crosslinked films whereas diffusion coefficient drops by 100 times after crosslinking. However, the annealing does not significantly modify kinetics.