Humidity-responsive polyurethane/cinnamaldehyde-HPβCD active packaging: Synergistic cinnamaldehyde release and CO2 regulation to suppress postharvest yellowing of baby kale

Postharvest yellowing significantly limits the shelf life and quality of leafy greens like baby kale ( Brassica oleracea var. alboglabra ), particularly under ambient conditions. This study developed a synergistic active packaging system to suppress postharvest yellowing of baby kale, featuring a humidity-responsive cinnamaldehyde (Cin) release mechanism coupled with selective CO 2 modulation via a polyurethane (PU) latex coating. Cin was encapsulated in hydroxypropyl-β-cyclodextrin (HPβCD) to achieve superior humidity responsiveness, with its release rate at high humidity (100% RH) exceeding the volatilization rate of free Cin while providing enhanced stability during ambient environmental exposure. The Cin/HPβCD inclusion complex was successfully incorporated into the CO 2 -regulating PU coating, achieving a high processing Cin retention rate (95.2%) and maintaining excellent optical transparency (>85%). Notably, the PU coating exhibited decoupled permeability towards moisture, gas, and Cin vapor, favoring the diffusion of water and Cin vapors while acting as a selective barrier to CO 2 . When applied to baby kale, this dual-functional packaging system provided a synergistic preservation strategy via humidity-triggered Cin release and an elevated in-package CO 2 microenvironment (up to 0.8%) that successfully retarded chlorophyll degradation and attenuated carotenoid loss, thereby suppressing leaf yellowing and better preserving the nutritional value of baby kale. It significantly extended the postharvest shelf life of baby kale from 2 to 6 days under ambient storage conditions.