Development and characterization of CMCS/gelatin based humidity-responsive hydrogel pads with thyme essential oil release for blueberry preservation.

Blueberries are highly perishable and humidity-sensitive, with humidity promoting microbial growth and accelerating quality deterioration during storage. To address this, we developed a humidity-responsive hydrogel pad to modulate the local microenvironment and enable controlled thyme essential oil (TEO) release, improving antimicrobial efficacy and extending blueberry shelf life. The novel pad was synthesized via solution casting, using carboxymethyl chitosan (CMCS) and gelatin as the matrix, genipin as the cross-linker, and TEO as the active component. The 2C3G pad (CMCS:gelatin = 2:3, w/w) exhibited optimal performance, achieving the highest TEO loading rate (60.02 ± 2.16 %). In vitro release experiments and kinetic modeling confirmed humidity effectively modulates TEO release: cumulative release rates were 10.01 ± 0.27 % at 30 % RH, 32.65 ± 2.10 % at 60 % RH, and 55.59 ± 0.77 % at 90 % RH. Higher gelatin content reduced TEO release under identical RH. Control blueberries showed mold growth after 5 days, whereas 2C3G-treated samples remained mold-free for 20 days, extending shelf life by over 15 days. Thus, the humidity-responsive hydrogel pad significantly improved blueberry quality and shelf life. This study provides a practical technique for designing durable antimicrobial hydrogel pads with excellent properties for food packaging.