Delaying walnut oxidation using a compostable film comprising poly(ε-caprolactone), thermoplastic gliadins, and green tea extract

A new active packaging composed of poly(e-caprolactone) (PCL) and thermoplastic gliadin proteins incorporating green tea extract (GTE) was developed through compounding and film-extrusion process. Firstly, commercial green tea extract was analyzed, revealing that GTE primarily comprised epigallocatechin gallate (EGCG), which conferred potent antioxidant activity determined by the DPPH assay, along with moderate antibacterial activity. The incorporation of 5 wt% of GTE in the extruded films increased thermal stability and Young’s Modulus, and reduced oxygen and water vapor permeability with respect to control PCL/TPG film. Migration studies showed that the release of GTE depended on the type of food simulant, with higher levels observed in an oil-in-water emulsion simulant compared to a non-acidic aqueous food simulant, while no migration of GTE components was detected in dry foodstuffs simulant. Consequently, the antioxidant capacity derived from migrated GTE components were considerably higher in 50 % ethanol than in 10 % ethanol. Furthermore, PCL/TPG-GTE film exhibited antibacterial activity against Gram negative E. coli and Gram positive S. aureus in vitro when tested following the JIS Z2801 standard. The GTE addition also improved walnuts stability, resulting in a reduction and delay of fat peroxidation. Hence, the novel active system developed in this work can constitute a sustainable alternative to improve quality and safety of packaged products.