Dual pH/Humidity-Responsive HKUST-1/Chitosan/Polyvinyl Alcohol Films for Controlled Cinnamaldehyde Release and Extended Blueberry Preservation

Highly perishable fruit suffers postharvest losses from respiration, microbes, and microenvironmental shifts, which conventional packaging cannot dynamically address. This study developed dual-responsive active films via in situ hydrothermal synthesis of HKUST-1 within a chitosan (CS)/polyvinyl alcohol (PVA) matrix co-loaded with cinnamaldehyde (Cin). pH-responsiveness stems from CS amino protonation, while humidity sensitivity involves water-induced disruption of HKUST-1 carboxylate-Cu coordination. Structural properties (morphology, crystallinity, and bonding), mechanical strength, barrier function, and pH/humidity-responsive release kinetics were meticulously characterized. The acidic, high-humidity microenvironment generated during postharvest storage triggered the pH/humidity-dependent release of Cin, conferring potent antibacterial activity against Staphylococcus aureus ( S. aureus ). Preservation tests with Chilean blueberries demonstrated that the films prolonged shelf life by reducing decay, suppressing weight loss, and inhibiting microbial growth. This study establishes a novel strategy for microenvironment-responsive active packaging. The dual-release mechanism synchronizes preservative delivery with fruit spoilage signals, advancing intelligent preservation technologies for perishable foods.