Green Synthesis of a Novel Gelatin Crosslinked Oxidized Pullulan-Lignin biocomposite film for active food packaging

Biopolymer-based plastics, made from plants and microbes, are gaining popularity in food packaging due to their eco-friendliness, but degrade upon contact with water, thus requiring the addition of water-resistant materials. Lignin was extracted from cotton stalk using the acid-alkali method and was characterized through FTIR and 2D HSQC NMR to evaluate its structure and purity. Pullulan dialdehyde, gelatin, and lignin were blended using a green process to make water-stable PGL hydrogel film. Incorporation of Lignin into PDA/Gelatin blend, having imine bonds, increased network strength and solvent-resistance by extensive physical interactions like H-bonding and electrostatic interactions, which were confirmed through FTIR and XPS analysis. These films were cured at 60{degrees}C, making the process energy efficient. PGL film exhibited water stability, high mechanical strength, moisture barrier, and bioactive properties ideal for fruit preservation. Lignin improved hydrophobicity, hydrogel strength, biodegradability, and non-flammability relative to the control. The films effectiveness for food packaging was assessed by analyzing the impact on the preservation and shelf life of kinnow oranges. Physical properties, such as weight loss, firmness, and chemical properties, including pH, titratable acidity, lipid oxidation, sucrose content, antioxidant activity, and ethylene concentration of oranges before and after packaging, were monitored. PGL film showed high stability in hot and ambient water, with a water swelling index of 303%, impressive tensile strength of 8.5 MPa, and elongation at break exceeding 72%. PGL-packed oranges produced 0.034{+/-}0.0032 ppm/g of ethylene after seven days, which is 4.2-fold lower than unpacked oranges, signifying the fruit preservation ability of PGL films.