Enhancing interfacial adhesion of chitosan coatings on waxy fruit cuticles via a calcium-gallic acid metal-phenolic network

The inherent diversity in chemical composition and microstructure of fruit wax and cuticle layers serves as a core barrier to the universal adhesion of conventional coatings on a range of fruit surfaces ( e . g ., blueberry and grape). Herein, calcium ions were introduced into chitosan-gallic acid (CS-GA) to develop a metal-phenolic networks (MPNs) modified CS coating, which was named CS-GA-Ca. According to microstructural characterization, calcium ions, as a crosslinker, form a coordination with catechol in copolymers and further reconstruct a H-bonding network, resulting in smaller molecular chain spacing and a tighter polysaccharide network structure. Furthermore, the CS-GA-Ca films demonstrated improved vapor barrier and mechanical properties. The CS-GA-Ca coating exhibited improved adhesive capacity on the wax layer of blueberries. The molecular dynamic (MD) stimulation results revealed stronger Van der Waals forces (-64.35 kcal·mol −1 ) and electrostatic interactions binding energies (-28.84 kcal·mol −1 ) between CS-GA-Ca and epicuticular wax components compared to CS-GA (-4.21/0.01 kcal·mol −1 ). Finally, the CS-GA-Ca reduced weigh loss of blueberries and grapes by 17% and 27% compared to uncoated ones over 24 days (4℃) and 10 days (25℃), respectively. Moreover, the blueberries and grapes coated with CS-GA-Ca exhibited 2.0-fold and 1.6-fold prolonged shelf life compared to uncoated ones, respectively. Overall, this study presents a promising approach for developing bio-derived coating materials to prolong the shelf life of fruits.