Optimising humidity-triggered spontaneous SO ₂ releasing devices for intelligent packaging of table grapes during cold storage

With rising concerns about environmental sustainability and food safety, the demand for self-activating intelligent packaging has increased. This study optimises humidity-triggered spontaneous sulphur dioxide (SO2) releasing devices for intelligent packaging, exploring the effects of device configurations (packet or piece), gas release channel areas, material thicknesses, preservative types, and coating patterns on the grapes' preservation. In packet devices, a paper-plastic composite material forms a cavity to encapsulate the active ingredients, creating a sealed packet. In piece devices, the active ingredients are fixed between layers of composite materials to form a flat piece. Furthermore, in piece devices, dry-coating papers hold powdered active ingredients, while wet-coating papers fix the active ingredients in solution form between the composite materials. Packet devices gradually released SO2, peaking (≥ 10 ppm) within 20 days and stabilising, while piece devices rapidly reached a higher peak (≥ 20 ppm) in 5 days before declining to a lower stable level (≤ 10 ppm). Enhancing channel area or reducing material thickness accelerated SO2 release from packet devices. Powdered preservatives and high-content adjuvants expedited the release of SO2, lowering its stable concentrations. Dry-coating paper exhibited an ideal pattern of SO2 release, offering superior preservation of grapes over 65 days with the lowest bleaching rate (9.8%). It also significantly reduced abscission (64.3%), decay (80.0%), and browning (3 degrees), while showing improvements in total soluble solids (4.4%), sensory grades (7 points), and marketable fruit rate (63.9%) compared to the control. This study advances intelligent and secure packaging for table grapes, addressing food safety challenges.