Biobased ternary films of thermoplastic starch, bacterial nanocellulose and gallic acid for active food packaging

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The use of active packaging technologies and biopolymeric materials are among the emerging trends for implementation of sustainability in the food packaging industry. Thus, herein, bioactive transparent nanocomposite films of thermoplastic starch (TPS) reinforced with bacterial nanocellulose (BNC) (1%, 5% and 10% w/w, relative to starch) and enriched with gallic acid (GA) (1 and 1.5% w/w, relative to starch) were prepared by the solvent casting method. The addition of BNC (≥5% w/w) and GA (1 and 1.5% w/w) enhanced both the mechanical properties (Young's Modulus: 1.2–2.0 GPa vs. 1.0 GPa in TPS; tensile strength: 23–39 MPa vs. 20 MPa in TPS) and the water resistance (moisture absorption and solubility in water) of the nanocomposites. All films are thermally stable up to 125 °C. It was also found that the addition of GA imparted the hydrocolloid TPS-BNC nanocomposites with UV-blocking properties and antioxidant activity (DPPH scavenging activity above 80%). In addition, the film with 10% w/w of BNC nanofibers and 1% w/w of GA had good oxygen barrier properties with a coefficient of permeability of 0.91 ± 0.12 cm3μm m−2 d−1 kPa−1 and antibacterial activity against the gram-positive Staphylococcus aureus (reduction of about 4.5 log10 colony forming units (CFU) mL−1 after 48 h). This is the first time that antibacterial activity is reported for TPS-BNC nanocomposites. The film with 10% w/w of BNC nanofibers and 1% w/w of GA was further demonstrated to have the ability of delaying the browning and weight loss of packaged fresh cut apples stored at +4 °C for 7 days. All these outcomes are of great relevance for the packaging sector, thus attesting the potential of the developed TPS-BNC-GA nanocomposites as sustainable and eco-friendly film materials for active food packaging.

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