Litchi polyphenols and carboxylated cellulose nanofiber synergistically improve the gel properties of κ-carrageenan gels: Insight from rheology, morphology and interaction computational simulation

κ-Carrageenan (KC), a naturally abundant hydrocolloid, has excellent biocompatibility and degradability. However, the weak strength of single KC gel limits its further application in strong food gels. With the view that nanocellulose and plant polyphenols have been shown effective in improving the quality of food gels, carboxylated cellulose nanofiber (CCN) and polyphenol-rich litchi pericarp extract (LPE) were used in combination in this study to enhance the KC gels. The experimental results showed that CCN and LPE could synergistically improve the textural and rheological properties of KC gels to an extent positively correlated with LPE concentration. KC-CCN-LPE1.50% (the KC gel with 0.5% CCN and 1.5% LPE) had the highest hardness of 1881.3 g, which was 12-fold higher than the pure KC gel, and also the highest viscosity, dynamic modulus, structural resilience, and melting temperature. The incorporation of CCN and LPE also increased the thermal stability of KC gels. Infrared spectroscopy and microstructure analysis suggested that CCN and LPE enhanced the hydrogen bonding in the gels, to form more dense and ordered network structures. Molecular dynamics simulation further verified that hydrogen bonding and van der Waals forces played a major role in the formation of KC-CCN-LPE composite gels. Therefore, the combined action of CCN and LPE can effectively overcome the weak KC gel properties, offering a novel and feasible formulation of strong food gels. The KC-CCN-LPE ternary hydrogel is promising for further development and application for wound dressings, facial masks, 3D food printing, nutrient delivery and other fields.