κ-Carrageenan–Gelatin Physical Hydrogels for Sustained Non-Contact Essential Oil Release: Network Properties and Ant-Repellent Performance

Abstract Physical polysaccharide–protein hydrogels can load and release volatile actives, but how these additives affect the network structure, mechanics, and transport remains unclear. Noncontact active packaging also requires controlled, sustained release. κ-Carrageenan/gelatin (κ-cg/gel) hydrogels incorporating essential oils (EOs) were prepared by cooling-induced physical gelation to investigate how the oils influence network properties and volatile release. FTIR and 1H NMR data are compatible with intermolecular association (hydrogen bonding and electrostatic interactions) between the biopolymers, and FESEM of freeze-dried samples showed more open microstructures in EO-loaded gels. EO loading increased the storage modulus, compressive resistance, elastic recovery, and water retention, which is interpreted as EO-induced network reinforcement. The apparent mesh size estimated from the storage modulus decreased from about 21 to 15 nm. The hydrogels provided sustained oil release for up to 168 h (7 days), with diffusion-controlled, non-Fickian transport that fit the Higuchi and Korsmeyer–Peppas models. The κ-cg/gel-(3:1) formulation with coffee EO performed best, yielding >90% repellency of the pharaoh ant (Monomorium pharaonis, a model pest) at 24 h while retaining structural integrity under cyclic loading. Antimicrobial and antioxidant activity, surface wettability, vapor-barrier properties, and food-storage performance were not evaluated; the system is therefore presented as a promising noncontact EO reservoir that warrants further testing toward bioactive food packaging.