Pullulan-based multifunctional coating incorporating tea polyphenols with excellent storage stability and spreading for Citrus reticulata Blanco preservation.

Citrus fruits are the world's largest fruit crop, but they suffer significant losses during postharvest due to quality deterioration and pathogen infection. This study fabricated a biopolymer-based bioactive coating to improve postharvest preservation by constructing a three-dimensional pullulan (PUL)/ curdlan (CUD) network (PCW-T) loaded with whey protein (WP) and incorporating the functional molecule tea polyphenols (TP). Confocal laser microscopy, atomic force microscopy, infrared spectroscopy, etc., revealed that the WP aggregates were uniformly dispersed like a "star-island" structure in the PUL/CUD (PC) matrix formed by linear molecules-triple-helical micelle entanglements, mainly through hydrogen bonding interactions. TP was bound to each component and achieved the optimal microstructure and performance in PCW0.75-T. The PCW-T films indicated a continuous and dense microstructure, in which PCW0.75-T had the lowest surface roughness, an outstanding elongation at break of 168.49%, and the highest water contact angle of 80.8°. WP and TP significantly improved the H2O and O2 barrier of PCW-T films and nearly completely blocked UV. Notably, the PCW0.75-T film exhibited excellent DPPH radical scavenging activity of 97.32% and an antibacterial rate of 99% against Staphylococcus aureus. The highest TP residual rate of 66.31% and the best spreading ability indicated the practical feasibility of PCW0.75-T coating for citrus preservation. The PCW0.75-T coating significantly delayed the appearance deterioration, weight loss, and firmness decline of Citrus reticulata Blanco, maintained the total solids and ascorbic acid, and inhibited the respiration intensity. This work provides new insights into the development of TP-incorporated biopolymer coatings and benefits citrus postharvest preservation.