Tailoring the properties of casein-based composite gels via regulation of the κ/ι ratio for κ2-carrageenan

Casein in processed cheese can be combined with polysaccharides such as carrageenan to form composite gels with enhanced properties. κ 2 -carrageenan is a hybrid polysaccharide that combines the strength of κ-carrageenan with the elasticity of ι-carrageenan, but the effects of varying the ratio of κ and ι units within κ 2 -carrageenan on the resulting composite gel are unknown. This study investigated how the κ/ι ratio in κ 2 -carrageenan regulates the properties of casein-based composite gels. A higher κ/ι ratio (3:1) promoted the formation of a rigid node–fibre network with high crosslinking density for enhanced gel strength (hardness: 10.73 ± 0.21 g) and thermal stability (transition temperature: 77.83 °C ± 0.19 °C). In contrast, a lower κ/ι ratio (4:3) led to a soft and spongelike architecture with superior water-holding capacity (74.79% ± 0.73%) and structural continuity. The κ/ι ratio was critical to the microstructure and macroscopic performance of the resulting composite gel owing to its effects on the sulphate group distribution and chain conformation, which steered molecular interactions via electrostatic and hydrogen bonding mechanisms. These findings provide a structure-based understanding of the functionality of κ 2 -carrageenan and establish a practical strategy for the rational design of protein–polysaccharide gels for advanced food and dairy applications. • κ/ι ratio in κ 2 -carrageenan controlled properties of casein-based composite gels. • κ 2 -1 carrageenan (κ/ι=3:1) improved gel strength of composite gels • κ 2 -2 carrageenan (κ/ι=4:3) enhanced flexibility and WHC of composite gels • Sulfate density and chain flexibility synergistically governed gel properties.