Rheological properties and microstructure of rennet-induced casein micelle/κ-carrageenan composite gels

This study aimed to investigate effects of kappa-carrageenan (κ-carrageenan) concentration and storage temperature on the rheological and texture properties of casein micelle/κ-carrageenan composite gels. The particle size, zeta potential, Fourier transform infrared spectroscopy of the mixture, and microstructure of the composite gels were measured. The movement of κ-carrageenan characteristic bond showed that the casein micelle and κ-carrageenan formed a complex with larger particle size through electrostatic adsorption. The electrostatic repulsion between molecules increased with the increase of κ-carrageenan concentration, which stabilized the mixed system. It was found that both κ-carrageenan concentration and storage conditions affected the gel's rheological properties and microstructure. As the concentration of κ-carrageenan increased, the storage modulus (G′) of the composite gels increased, the rennet coagulation time (RCT) decreased, and the water holding capacity (WHC) increased at 25 °C. Microstructure results showed that a more uniform and denser gel network structure with smaller pore sizes was formed after the addition of κ-carrageenan compared with the control. G′ and RCT were reduced and microscopic phase separation occurred after storage at 4 °C, resulting in a porous structure with large pore sizes. Thus, the addition of κ-carrageenan could enrich the diversity of food gel structure to obtain an ideal gel.