Gallic acid-grafted chitosan and pullulan as a hydrogen bonding assembled, multifunctional coating for fruit preservation

The development of eco-friendly and multifunctional edible coatings is crucial for mitigating postharvest losses of perishable fruits. Hence, a novel composite coating was engineered based on chitosan (CS) and pullulan (PUL) matrix, enhanced by a gallic acid-grafted chitosan (GS) conjugate synthesized through free radical grafting. The GS conjugate served as a multifunctional crosslinker, establishing a dense intermolecular network within the CS-PUL matrix primarily (CP) through hydrogen bonding, as confirmed by structural characterization. This molecular-level interaction significantly improved the mechanical strength (Tensile stress = 4.95 MPa, Elongation at break =121.21%) and barrier properties of the resulting coating. The chitosan/pullulan-gallic acid grafted chitosan (CP-GS) coating, applicable by spraying or dipping, exhibited remarkable antioxidant activity, achieving 97.8% DPPH radical scavenging (25 °C, 50% RH), the CP-GS coating significantly reduced weight loss, delayed the decline in titratable acidity, and effectively suppressed microbial growth, thereby extending the shelf life by 7 to 9 days compared to the uncoated samples. This study highlights the effectiveness of molecular grafting in designing advanced bio-based coatings and presents a promising strategy for fruit preservation using biological macromolecules.