Construction dual-temperature responsive hydrogel of hydroxypropyl methylcellulose and κ-carrageenan via formation of dynamic semi-interpenetrating physical structure

Traditional thermally irreversible or unidirectionally reversible hydrogels often lack the adaptable thermal response required for processing, storage, and sensory performance in solid fat replacers. To address this issue, a reversible dual-temperature-responsive hydrogel was created based on a semi-interpenetrating network (semi-IPN) formed by combining κ-carrageenan (κC, upper critical solution temperature) and hydroxypropyl methylcellulose (HPMC, lower critical solution temperature). Rheological analysis revealed reversible gel-sol-gel transitions, with the hydrogel exhibiting strong gel strength at 4 °C (G' > 500 Pa, tanδ≈0.1) and 80 °C (G' > 1000 Pa, tanδ≈0.1), while softening at a consumption temperature of 37 °C (G' < 1 Pa, tanδ>10). The onset melting temperature of the blends ranged between 29.1 °C and 45.5 °C, depending on κC content, covering the oral melting range of solid fats. Microstructural and spectroscopic analyses (SEM, XRD, FTIR, and ¹H NMR) confirmed physical interactions and continuous networks at 4 and 80 °C, whereas more porous networks were observed at 37 °C during cooling. Molecular dynamics simulations showed that heating dissociates κC helices prior to HPMC hydrophobic association, whereas cooling proceeds via HPMC rehydration followed by κC helix re-formation. Our results provide valuable insights into the development of smart hydrogels for application in future foods, offering a fully physical strategy for designing temperature-adaptive solid fat replacers.